Polymers

22 pages, 4386 KiB

Open AccessArticle

Synthesis, Characterization, and Evaluation of the Adsorption Behavior of Cellulose-Graft-Poly(Acrylonitrile-co-Acrylic Acid) and Cellulose-Graft-Poly(Acrylonitrile-co-Styrene) towards Ni(II) and Cu(II) Heavy Metals

by Amany S. El-Khouly and Yoshiaki Takahashi

Polymers 2024, 16(3), 445; https://doi.org/10.3390/polym16030445 - 5 Feb 2024

Cited by 2 | Viewed by 979

Abstract

In this study, the synthesis and characterization of grafted cellulose fiber with binary monomers mixture obtained using a KMnO₄/citric acid redox initiator were investigated. Acrylonitrile (AN) was graft copolymerized with acrylic acid (AA) and styrene (Sty) at different monomer ratios with [...] Read more.

In this study, the synthesis and characterization of grafted cellulose fiber with binary monomers mixture obtained using a KMnO₄/citric acid redox initiator were investigated. Acrylonitrile (AN) was graft copolymerized with acrylic acid (AA) and styrene (Sty) at different monomer ratios with evaluating percent graft yield (GY%). Cell-g-P(AN-co-AA) and Cell-g-P(AN-co-Sty) were characterized by SEM, FT-IR, ¹³C CP MAS NMR, TGA, and XRD. An AN monomer was used as principle-acceptor monomer, and GY% increases with AN ratio up to 60% of total monomers mixture volume. The adsorption behaviors of Cell-g-P(AN-co-AA) and Cell-g-P(AN-co-Sty) were studied for the adsorption of Ni(II) and Cu(II) metal ions from aqueous solution. Optimal adsorption conditions were determined, including 8 h contact time, temperature of 30 °C, and pH 5.5. Cell-g-P(AN-co-AA) showed maximum adsorption capacity of 435.07 mg/g and 375.48 mg/g for Ni(II) and Cu(II), respectively, whereas Cell-g-P(AN-co-Sty) showed a maximum adsorption capacity of 379.2 mg/g and 349.68 mg/g for Ni(II) and Cu(II), respectively. Additionally, adsorption equilibrium isotherms were studied, and the results were consistent with the Langmuir model. The Langmuir model’s high determinant coefficient (R²) predicted monolayer sorption of metal ions. Consequently, Cell-g-P(AN-co-AA) and Cell-g-P(AN-co-Sty) prepared by a KMnO₄/citric acid initiator were found to be efficient adsorbents for heavy metals from wastewater as an affordable and adequate alternative. Full article

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17 pages, 7043 KiB

Open AccessArticle

The Influence of the Flexibility of a Polymeric Adhesive Layer on the Mechanical Response of a Composite Reinforced Concrete Slab and a Reinforced Concrete Beam Girder

by Paweł Szeptyński, Jan Grzegorz Pochopień, Dorota Jasińska and Arkadiusz Kwiecień

Polymers 2024, 16(3), 444; https://doi.org/10.3390/polym16030444 - 5 Feb 2024

Cited by 1 | Viewed by 1215

Abstract

This study addresses the challenges of modeling flexible connections in composite structures employing a polymeric adhesive layer. These types of connections provide a more uniform stress distribution compared to conventional rigid connectors. However, they lack standardized design rules and still require much research [...] Read more.

This study addresses the challenges of modeling flexible connections in composite structures employing a polymeric adhesive layer. These types of connections provide a more uniform stress distribution compared to conventional rigid connectors. However, they lack standardized design rules and still require much research to sufficiently comprehend their properties. The novelty of this research lies in proposing an analytical solution to address these issues. Its aim is to investigate the influence of the stiffness of the polymer adhesive on the girder’s deflection and on the maximum stresses in both the adhesive and concrete. The analyzed composite structure consists of a reinforced concrete (RC) slab and an RC beam connected with a layer of flexible polyurethane (FPU) adhesive. Analytical and numerical approaches for the description of the mechanical response of a composite bridge girder are presented. Another objective is to validate the analytical design formulas using 3D nonlinear numerical analysis, both in the case of uncracked and cracked concrete. Seven types of FPUs are tested in the uniaxial tension test, each examined at five strain rates. The obtained data is used to predict the mechanical response of the considered girder using finite element analysis (FEA) as well as with a simplified one-dimensional composite beam theory. Fair agreement is found between the FEA results and theoretical predictions. A comparison of the results obtained for these two models is performed, and the similarities and discrepancies are highlighted and discussed. Full article

(This article belongs to the Special Issue Polymer Composites for Structural Strengthening)

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34 pages, 2277 KiB

Open AccessReview

Wastewater Treatment Using Membrane Bioreactor Technologies: Removal of Phenolic Contaminants from Oil and Coal Refineries and Pharmaceutical Industries

by Mohd Jahir Khan, Agung Wibowo, Zoheb Karim, Pattaraporn Posoknistakul, Babasaheb M. Matsagar, Kevin C.-W. Wu and Chularat Sakdaronnarong

Polymers 2024, 16(3), 443; https://doi.org/10.3390/polym16030443 - 5 Feb 2024

Cited by 3 | Viewed by 3100

Abstract

Huge amounts of noxious chemicals from coal and petrochemical refineries and pharmaceutical industries are released into water bodies. These chemicals are highly toxic and cause adverse effects on both aquatic and terrestrial life. The removal of hazardous contaminants from industrial effluents is expensive [...] Read more.

Huge amounts of noxious chemicals from coal and petrochemical refineries and pharmaceutical industries are released into water bodies. These chemicals are highly toxic and cause adverse effects on both aquatic and terrestrial life. The removal of hazardous contaminants from industrial effluents is expensive and environmentally driven. The majority of the technologies applied nowadays for the removal of phenols and other contaminants are based on physio-chemical processes such as solvent extraction, chemical precipitation, and adsorption. The removal efficiency of toxic chemicals, especially phenols, is low with these technologies when the concentrations are very low. Furthermore, the major drawbacks of these technologies are the high operation costs and inadequate selectivity. To overcome these limitations, researchers are applying biological and membrane technologies together, which are gaining more attention because of their ease of use, high selectivity, and effectiveness. In the present review, the microbial degradation of phenolics in combination with intensified membrane bioreactors (MBRs) has been discussed. Important factors, including the origin and mode of phenols’ biodegradation as well as the characteristics of the membrane bioreactors for the optimal removal of phenolic contaminants from industrial effluents are considered. The modifications of MBRs for the removal of phenols from various wastewater sources have also been addressed in this review article. The economic analysis on the cost and benefits of MBR technology compared with conventional wastewater treatments is discussed extensively. Full article

(This article belongs to the Section Biomacromolecules, Biobased and Biodegradable Polymers)

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18 pages, 5223 KiB

Open AccessReview

Rheology of Highly Filled Polymer Compositions—Limits of Filling, Structure, and Transport Phenomena

by Alexander Ya. Malkin, Valery G. Kulichikhin, Svetlana Yu. Khashirova, Igor D. Simonov-Emelyanov and Anton V. Mityukov

Polymers 2024, 16(3), 442; https://doi.org/10.3390/polym16030442 - 5 Feb 2024

Cited by 5 | Viewed by 1239

Abstract

The current state of the rheology of various polymeric and other materials containing a high concentration of spherical solid filler is considered. The physics of the critical points on the concentration scale are discussed in detail. These points determine the features of the [...] Read more.

The current state of the rheology of various polymeric and other materials containing a high concentration of spherical solid filler is considered. The physics of the critical points on the concentration scale are discussed in detail. These points determine the features of the rheological behavior of the highly filled materials corresponding to transitions from a liquid to a yielding medium, elastic–plastic state, and finally to an elastic solid-like state of suspensions. Theoretical and experimental data are summarized, showing the limits of the most dense packing of solid particles, which is of key importance for applications and obtaining high-quality products. The results of model and fine structural studies of physical phenomena that occur when approaching the point of filling the volume, including the occurrence of instabilities, are considered. The occurrence of heterogeneity in the form of individual clusters is also described. These heterogeneous objects begin to move as a whole that leads to the appearance of discontinuities in the suspension volume or wall slip. Understanding these phenomena is a key for particle technology and multiphase processing. Full article

(This article belongs to the Section Polymer Composites and Nanocomposites)

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16 pages, 8385 KiB

Open AccessArticle

Kinetic Study of the Diels–Alder Reaction between Maleimide and Furan-Containing Polystyrene Using Infrared Spectroscopy

by Tongtong Wang, Dali Gao, Hua Yin, Jiawei Zhao, Xingguo Wang and Hui Niu

Polymers 2024, 16(3), 441; https://doi.org/10.3390/polym16030441 - 5 Feb 2024

Viewed by 1546

Abstract

The Diels–Alder (D–A) reaction between furan and maleimide is a thermally reversible reaction that has become a vital chemical technique for designing polymer structures and functions. The kinetics of this reaction, particularly in polymer bulk states, have significant practical implications. In this study, [...] Read more.

The Diels–Alder (D–A) reaction between furan and maleimide is a thermally reversible reaction that has become a vital chemical technique for designing polymer structures and functions. The kinetics of this reaction, particularly in polymer bulk states, have significant practical implications. In this study, we investigated the feasibility of utilizing infrared spectroscopy to measure the D–A reaction kinetics in bulk-state polymer. Specifically, we synthesized furan-functionalized polystyrene and added a maleimide small-molecule compound to form a D–A adduct. The intensity of the characteristic absorption peak of the D–A adduct was quantitatively measured by infrared spectroscopy, and the dependence of conversion of the D–A reaction on time was obtained at different temperatures. Subsequently, the D–A reaction apparent kinetic coefficient k_app and the Arrhenius activation energy E_a,D–A were calculated. These results were compared with those determined from ¹H-NMR in the polymer solution states. Full article

(This article belongs to the Section Polymer Analysis and Characterization)

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32 pages, 7045 KiB

Open AccessReview

Recent Developments in Polyurea Research for Enhanced Impact Penetration Resistance and Blast Mitigation

by Yifan Wang, Lailong Ding, Jiayu Lin, Xishun Qiu, Chao Wu, Changhao Liu, Yicheng Tian, Rui Zhang, Weibo Huang and Mingliang Ma

Polymers 2024, 16(3), 440; https://doi.org/10.3390/polym16030440 - 5 Feb 2024

Cited by 2 | Viewed by 2509

Abstract

Polyurea has gained significant attention in recent years as a functional polymer material, specifically regarding blast and impact protection. The molecular structure of polyurea is characterized by the rapid reaction between isocyanate and the terminal amine component, and forms an elastomeric copolymer that [...] Read more.

Polyurea has gained significant attention in recent years as a functional polymer material, specifically regarding blast and impact protection. The molecular structure of polyurea is characterized by the rapid reaction between isocyanate and the terminal amine component, and forms an elastomeric copolymer that enhances substrate protection against blast impact and fragmentation penetration. At the nanoscale, a phase-separated microstructure emerges, with dispersed hard segment microregions within a continuous matrix of soft segments. This unique microstructure contributes to the remarkable mechanical properties of polyurea. To maximize these properties, it is crucial to analyze the molecular structure and explore methods like formulation optimization and the incorporation of reinforcing materials or fibers. Current research efforts in polyurea applications for protective purposes primarily concentrate on construction, infrastructure, military, transportation and industrial products and facilities. Future research directions should encompass deliberate formulation design and modification, systematic exploration of factors influencing protective performance across various applications and the integration of numerical simulations and experiments to reveal the protective mechanisms of polyurea. This paper provides an extensive literature review that specifically examines the utilization of polyurea for blast and impact protection. It encompasses discussions on material optimization, protective mechanisms and its applications in blast and impact protection. Full article

(This article belongs to the Section Polymer Applications)

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17 pages, 4313 KiB

Open AccessArticle

Catalysis of Silver and Bismuth in Various Epoxy Resins

by Hayun Jeong and Keon-Soo Jang

Polymers 2024, 16(3), 439; https://doi.org/10.3390/polym16030439 - 5 Feb 2024

Viewed by 1254

Abstract

Epoxy resins find extensive utility across diverse applications owing to their exceptional adhesion capabilities and robust mechanical and thermal characteristics. However, the demanding reaction conditions, including extended reaction times and elevated reaction temperature requirements, pose significant challenges when using epoxy resins, particularly in [...] Read more.

Epoxy resins find extensive utility across diverse applications owing to their exceptional adhesion capabilities and robust mechanical and thermal characteristics. However, the demanding reaction conditions, including extended reaction times and elevated reaction temperature requirements, pose significant challenges when using epoxy resins, particularly in advanced applications seeking superior material properties. To surmount these limitations, the conventional approach involves incorporating organic catalysts. Within the ambit of this investigation, we explored the catalytic potential of metallic powders, specifically bismuth (Bi) and silver (Ag), in epoxy resins laden with various curing agents, such as diacids, anhydrides, and amines. Metallic powders exhibited efficacious catalytic activity in epoxy–diacid and epoxy–anhydride systems. In contrast, their influence on epoxy–amine systems was rendered negligible, attributed to the absence of requisite carboxylate functional groups. Additionally, the catalytic performance of Bi and Ag are different, with Bi displaying superior efficiency owing to the presence of inherent metal oxide layers on its powder surfaces. Remarkably, the thermal and mechanical properties of uncatalyzed, fully cured epoxy resins closely paralleled those of their catalyzed counterparts. These findings accentuate the potential of Bi and Ag metal catalysts, particularly in epoxy–diacid and epoxy–anhydride systems, spanning a spectrum of epoxy-based applications. In summary, this investigation elucidates the catalytic capabilities of Bi and Ag metal powders, underscoring their ability to enhance the curing rate of epoxy resin systems involving diacids and anhydrides but not amines. This research points toward a promising trajectory for multifarious epoxy-related applications. Full article

(This article belongs to the Special Issue Advanced Epoxy-Based Materials IV)

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15 pages, 10959 KiB

Open AccessArticle

MD-DFT Calculations on Dissociative Absorption Configurations of FOX-7 on (001)- and (101)-Oriented Crystalline Parylene Protective Membranes

by Weihui Luo, Liang Bian, Faqin Dong, Jianan Nie and Jingjie Yang

Polymers 2024, 16(3), 438; https://doi.org/10.3390/polym16030438 - 5 Feb 2024

Viewed by 951

Abstract

Crystalline poly-para-xylylene (parylene) has the potential for use as a protective membrane to delay the nucleation of explosives by separating the explosives and their decomposition products to decrease the explosive sensitivity. Here, molecular dynamics (MD) and density functional theory (DFT) techniques were used [...] Read more.

Crystalline poly-para-xylylene (parylene) has the potential for use as a protective membrane to delay the nucleation of explosives by separating the explosives and their decomposition products to decrease the explosive sensitivity. Here, molecular dynamics (MD) and density functional theory (DFT) techniques were used to calculate the dissociative adsorption configurations of 1,1-diamino-2,2-dinitroethylene (FOX-7) on (001)- and (101)-oriented crystalline parylene membranes. Based on the results of the calculations, this work demonstrates that the -NO₂–π electrostatic interactions are the dominant passivation mechanism of FOX-7 on these oriented surfaces. FOX-7 can dissociatively adsorb on oriented parylene membranes due to the interactions between the LUMO of the toluene (or methyl) groups on parylene and the HOMO of the -NO₂ (or -NH₂) groups on FOX-7. The formation of a new intermolecular H-bond with the ONO group leads to FOX-7 decomposition via intramolecular C-NO₂ bond fission and nitro-to-nitrite rearrangement. The most likely adsorption configurations are described in terms of the decomposition products, surface active groups of parylene, binding behaviors, and N charge transfer. Importantly, the (001)-oriented parylene AF8 membrane is promising for use as a protective membrane to passivate the high-energy -NO₂ bonds during the dissociative adsorption of FOX-7. This study offers a new perspective on the development of protective membranes for explosives. Full article

(This article belongs to the Section Polymer Physics and Theory)

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12 pages, 2179 KiB

Open AccessArticle

Machine Learning Backpropagation Prediction and Analysis of the Thermal Degradation of Poly (Vinyl Alcohol)

by Abdulrazak Jinadu Otaru, Zaid Abdulhamid Alhulaybi and Ibrahim Dubdub

Polymers 2024, 16(3), 437; https://doi.org/10.3390/polym16030437 - 5 Feb 2024

Cited by 2 | Viewed by 1834

Abstract

Thermogravimetric analysis (TGA) is crucial for describing polymer materials’ thermal behavior as a result of temperature changes. While available TGA data substantiated in the literature significantly focus attention on TGA performed at higher heating rates, this study focuses on the machine learning backpropagation [...] Read more.

Thermogravimetric analysis (TGA) is crucial for describing polymer materials’ thermal behavior as a result of temperature changes. While available TGA data substantiated in the literature significantly focus attention on TGA performed at higher heating rates, this study focuses on the machine learning backpropagation analysis of the thermal degradation of poly (vinyl alcohol), or PVA, at low heating rates, typically 2, 5 and 10 K/min, at temperatures between 25 and 600 °C. Initial TGA analysis showed that a consistent increase in heating rate resulted in an increase in degradation temperature as the resulting thermograms shifted toward a temperature maxima. At degradation temperatures between 205 and 405 °C, significant depths in the characterization of weight losses were reached, which may be attributed to the decomposition and loss of material content. Artificial neural network backpropagation of machine learning algorithms were used for developing mathematical descriptions of the percentage weight loss (output) by these PVA materials as a function of the heating rate (input 1) and degradation temperature (input 2) used in TGA analysis. For all low heating rates, modelling predictions were observably correlated with experiments with a 99.2% correlation coefficient and were used to interpolate TGA data at 3.5 and 7.5 K/min, indicating trends strongly supported by experimental TGA data as well as literature research. Thus, this approach could provide a useful tool for predicting the thermograms of PVA materials at low heating rates and contribute to the development of more advanced PVA/polymer materials for home and industrial applications. Full article

(This article belongs to the Collection Thermal Characterization of Polymers and Polymer Composites)

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15 pages, 3906 KiB

Open AccessArticle

Effect of Prestrain on Payne Effect and Hysteresis Loss of Carbon-Black-Filled Rubber Vulcanizates: Measurements and Modeling

by Boyuan Yin, Xinyue Jiao, Haibo Wen, Yan Li and Ming Li

Polymers 2024, 16(3), 436; https://doi.org/10.3390/polym16030436 - 4 Feb 2024

Cited by 1 | Viewed by 1087

Abstract

The performance of a viscoelastic damper is governed by the mechanical properties of the viscoelastic material, which are sensitive to prestrain. Among viscoelastic materials, carbon black (CB)-filled rubber vulcanizate is commonly used in structural applications. In this paper, the prestrain-dependent Payne effect and [...] Read more.

The performance of a viscoelastic damper is governed by the mechanical properties of the viscoelastic material, which are sensitive to prestrain. Among viscoelastic materials, carbon black (CB)-filled rubber vulcanizate is commonly used in structural applications. In this paper, the prestrain-dependent Payne effect and hysteresis loss of CB-filled rubber vulcanizates are investigated through experimental and theoretical analysis. Based on the experimental results, the classic quantitative models proposed by Kraus, Huber–Vilgis, and Maier–Göritz are used to describe the Payne effect. The results show that the Maier–Göritz model is most suitable to describe the Payne effect, especially for the loss modulus. After calculating the area of the hysteresis loops, hysteresis loss curves at various dynamic strain amplitudes are parallel to each other. Through application of the time–strain superposition principle, the hysteresis loss at any arbitrary prestrain can be predicted. Thus, the aim of this paper is to provide guidance for researchers in choosing an accurate model for future investigations of the prestrain-dependent Payne effect. An accelerated characterization method is useful for the prediction of the hysteresis loss of rubber products using small amounts of experimental data, which can provide manufacturers with more attractive and lower cost opportunities for testing the mechanical properties of rubber products. Full article

(This article belongs to the Special Issue Time-Dependent Mechanical Behavior of Polymers and Polymer Composites)

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18 pages, 2438 KiB

Open AccessArticle

On Cyclic-Fatigue Crack Growth in Carbon-Fibre-Reinforced Epoxy–Polymer Composites

by Silvain Michel, Neal Murphy, Anthony J. Kinloch and Rhys Jones

Polymers 2024, 16(3), 435; https://doi.org/10.3390/polym16030435 - 4 Feb 2024

Cited by 3 | Viewed by 991

Abstract

The growth of cracks between plies, i.e., delamination, in continuous fibre polymer matrix composites under cyclic-fatigue loading in operational aircraft structures has always been a very important factor, which has the potential to significantly decrease the service life of such structures. Whilst current [...] Read more.

The growth of cracks between plies, i.e., delamination, in continuous fibre polymer matrix composites under cyclic-fatigue loading in operational aircraft structures has always been a very important factor, which has the potential to significantly decrease the service life of such structures. Whilst current designs are based on a ‘no growth’ design philosophy, delamination growth can nevertheless arise in operational aircraft and compromise structural integrity. To this end, the present paper outlines experimental and data reduction procedures for continuous fibre polymer matrix composites, based on a linear elastic fracture mechanics approach, which are capable of (a) determining and computing the fatigue crack growth (FCG) rate, da/dN, curve; (b) providing two different methods for determining the mandated worst-case FCG rate curve; and (c) calculating the fatigue threshold limit, below which no significant FCG occurs. Two data reduction procedures are proposed, which are based upon the Hartman-Schijve approach and a novel simple-scaling approach. These two different methodologies provide similar worst-case curves, and both provide an upper bound for all the experimental data. The calculated FCG threshold values as determined from both methodologies are also in very good agreement. Full article

(This article belongs to the Special Issue Research Progress on Mechanical Behavior of Polymers)

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Sketch of the double cantilever beam (DCB) continuous carbon-fibre epoxy polymer matrix composite test specimen. Showing the initial, starter-crack, delamination of length, ao, in the DCB specimen, which was introduced to a pre-crack length of ap before measurements were taken for the cyclic-fatigue test. Full article ">Figure 2
Values of logarithmic da/dN versus logarithmic <math display="inline"><semantics> <mrow> <mo>∆</mo> <msqrt> <mi>G</mi> </msqrt> </mrow> </semantics></math> from the tests performed at Empa for the carbon-fibre epoxy polymer composite. Values are given in the legend for the pre-crack extension length, ap-ao, prior to the start of measurements from the DCB fatigue test. (Also shown are the computed relationships from using Equation (2) with the values of <math display="inline"><semantics> <mrow> <mo>∆</mo> <msqrt> <msub> <mrow> <mi>G</mi> </mrow> <mrow> <mi>t</mi> <mi>h</mi> <mi>r</mi> </mrow> </msub> </msqrt> </mrow> </semantics></math> and A as determined from fitting the experimental results to give the Hartman-Schijve linear, master relationship, as shown later in <a href="#polymers-16-00435-f005" class="html-fig">Figure 5</a>). Full article ">Figure 3
Values of logarithmic da/dN versus logarithmic <math display="inline"><semantics> <mrow> <mo>∆</mo> <msqrt> <mi>G</mi> </msqrt> </mrow> </semantics></math> from the tests performed at UCD for the carbon-fibre epoxy polymer composite. Values are given in the legend for the pre-crack extension length, ap-ao, prior to the start of measurements from the DCB fatigue test. (Also shown are the computed relationships from using Equation (2) with the values of <math display="inline"><semantics> <mrow> <mo>∆</mo> <msqrt> <msub> <mrow> <mi>G</mi> </mrow> <mrow> <mi>t</mi> <mi>h</mi> <mi>r</mi> </mrow> </msub> </msqrt> </mrow> </semantics></math> and A as determined from fitting the experimental results to give the Hartman-Schijve linear, master relationship, as shown later in <a href="#polymers-16-00435-f005" class="html-fig">Figure 5</a>). Full article ">Figure 4
Values of logarithmic da/dN versus logarithmic <math display="inline"><semantics> <mrow> <mo>∆</mo> <msqrt> <mi>G</mi> </msqrt> </mrow> </semantics></math> from the tests performed at Empa compared to those performed at UCD for the carbon-fibre epoxy polymer composite. Values are given in the legend for the pre-crack extension length, ap-ao, prior to the start of measurements from the DCB fatigue test. Full article ">Figure 5
The linear, master relationship obtained for all the Empa and UCD tests for the carbon-fibre epoxy polymer composite as calculated using the Hartman-Schijve (H-S) methodology, i.e., Equation (2). Full article ">Figure 6
Values of logarithmic da/dN versus logarithmic <math display="inline"><semantics> <mrow> <mo>∆</mo> <msqrt> <mi>G</mi> </msqrt> </mrow> </semantics></math> from the tests performed at Empa and UCD for the carbon-fibre epoxy polymer composite. Values are given in the legend for the pre-crack extension length, ap-ao, prior to the start of measurements from the DCB fatigue test. The worst-case, upper-bound curve for the FCG rate calculated from the Hartman–Schijve methodology (see Equation (2)) is shown in blue, which uses the ‘mean-3σ’ values for <math display="inline"><semantics> <mrow> <mo>∆</mo> <msqrt> <msub> <mrow> <mi>G</mi> </mrow> <mrow> <mi>t</mi> <mi>h</mi> <mi>r</mi> </mrow> </msub> </msqrt> </mrow> </semantics></math> and A (= <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>G</mi> </mrow> <mrow> <mi>c</mi> <mi>o</mi> </mrow> </msub> </mrow> </semantics></math>) (see <a href="#polymers-16-00435-t001" class="html-table">Table 1</a>). The data points from the simple-scaling methodology (see Equation (5)) are also shown with a best-fit line drawn through them. (See text for explanation of ‘Curve AB’, shown as black dots). Full article ">Figure 7
The logarithmic da/dN versus logarithmic <math display="inline"><semantics> <mrow> <mo>∆</mo> <msqrt> <mi>G</mi> </msqrt> <mo>/</mo> <mo>∆</mo> <msqrt> <msub> <mrow> <mi>G</mi> </mrow> <mrow> <mi>d</mi> <mi>a</mi> <mo>/</mo> <mi>d</mi> <mi>N</mi> </mrow> </msub> </msqrt> <mo> </mo> </mrow> </semantics></math>normalised curves for the Empa and UCD test data. The values of <math display="inline"><semantics> <mrow> <mo>∆</mo> <msqrt> <msub> <mrow> <mi>G</mi> </mrow> <mrow> <mi>d</mi> <mi>a</mi> <mo>/</mo> <mi>d</mi> <mi>N</mi> </mrow> </msub> </msqrt> </mrow> </semantics></math> used for each test are the values of <math display="inline"><semantics> <mrow> <mo>∆</mo> <msqrt> <mi>G</mi> </msqrt> </mrow> </semantics></math> corresponding to a FCG rate of da/dN = 10−8 m/cycle as determined from <a href="#polymers-16-00435-f002" class="html-fig">Figure 2</a> and <a href="#polymers-16-00435-f003" class="html-fig">Figure 3</a> for the Empa and UCD experimental data, respectively. (Values are given in the legend for the pre-crack extension length, ap-ao, prior to the start of measurements from the DCB fatigue test). Full article ">

19 pages, 4735 KiB

Open AccessArticle

Preparation of PLGA Microspheres Using the Non-Toxic Glycofurol as Polymer Solvent by a Modified Phase Inversion Methodology

by Douglas Sobel, Barath Ramasubramanian, Puja Sawhney and Keerat Parmar

Polymers 2024, 16(3), 434; https://doi.org/10.3390/polym16030434 - 4 Feb 2024

Viewed by 1017

Abstract

Poly(D,L-lactide-co-glycolide is a biodegradable copolymer that can release pharmaceuticals. These pharmaceuticals can provide local therapy and also avert the clinical issues that occur when a drug must be given continuously and/or automatically. However, the drawbacks of using poly(D,L-lactide-co-glycolide include the kinetics and duration [...] Read more.

Poly(D,L-lactide-co-glycolide is a biodegradable copolymer that can release pharmaceuticals. These pharmaceuticals can provide local therapy and also avert the clinical issues that occur when a drug must be given continuously and/or automatically. However, the drawbacks of using poly(D,L-lactide-co-glycolide include the kinetics and duration of time of poly(D,L-lactide-co-glycolide drug release, the denaturing of the drug loaded drug, and the potential clinical side effects. These drawbacks are mainly caused by the volatile organic solvents needed to prepare poly(D,L-lactide-co-glycolide spheres. Using the non-toxic solvent glycofurol solvent instead of volatile organic solvents to construct poly(D,L-lactide-co-glycolide microspheres may deter the issues of using volatile organic solvents. Up to now, preparation of such glycofurol spheres has previously met with limited success. We constructed dexamethasone laden poly(D,L-lactide-co-glycolide microspheres utilizing glycofurol as the solvent within a modified phase inversion methodology. These prepared microspheres have a higher drug load and a lower rate of water diffusion. This prolongs drug release compared to dichloromethane constructed spheres. The glycofurol-generated spheres are also not toxic to target cells as is the case for dichloromethane-constructed spheres. Further, glycofurol-constructed spheres do not denature the dexamethasone molecule and have kinetics of drug release that are more clinically advantageous, including a lower drug burst and a prolonged drug release. Full article

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12 pages, 3665 KiB

Open AccessArticle

Water-Based Generators with Cellulose Acetate: Uncovering the Mechanisms of Power Generation

by Seung-Hwan Lee, Hyun-Woo Lee, So Hyun Baek, Jeungjai Yun, Yongbum Kwon, Yoseb Song, Bum Sung Kim, Yong-Ho Choa and Da-Woon Jeong

Polymers 2024, 16(3), 433; https://doi.org/10.3390/polym16030433 - 4 Feb 2024

Cited by 3 | Viewed by 1542

Abstract

Power generation technologies based on water movement and evaporation use water, which covers more than 70% of the Earth’s surface and can also generate power from moisture in the air. Studies are conducted to diversify materials to increase power generation performance and validate [...] Read more.

Power generation technologies based on water movement and evaporation use water, which covers more than 70% of the Earth’s surface and can also generate power from moisture in the air. Studies are conducted to diversify materials to increase power generation performance and validate energy generation mechanisms. In this study, a water-based generator was fabricated by coating cellulose acetate with carbon black. To optimize the generator, Fourier-transform infrared spectroscopy, specific surface area, zeta potential, particle size, and electrical performance analyses were conducted. The developed generator is a cylindrical generator with a diameter of 7.5 mm and length of 20 mm, which can generate a voltage of 0.15 V and current of 82 μA. Additionally, we analyzed the power generation performance using three factors (physical properties, cation effect, and evaporation environment) and proposed an energy generation mechanism. Furthermore, we developed an eco-friendly and low-cost generator using natural fibers with a simple manufacturing process. The proposed generator can contribute to the identification of energy generation mechanisms and is expected to be used as an alternative energy source in the future. Full article

(This article belongs to the Special Issue Advances in Natural Fiber Polymer Composites)

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Process sequence real images of rare cellulose acetate column (CAC) sampling: coating solution preparation, coating method, and drying process. Full article ">Figure 2
Experimental setup for measuring cellulose acetate column generator (CACG) performance in a temperature- and humidity-controlled acrylic box. Full article ">Figure 3
(a) Chemical structure of cellulose acetate and (b) cetyltrimethylammonium bromide. (c) Fourier-transform infrared spectra of CAC, carbon black (BC), and CACG. (d) N2 adsorption isotherms of the CAC, CACG, and CB. (e) Zeta potential results of coating solution. (f) Intensity distribution results of coating solution. Full article ">Figure 4
(a) SEM image of cellulose acetate column generator. (b) EDS mapping for each element (C, O, Br, and N) of the cellulose acetate column generator. (c) SEM images of the cellulose acetate column generator by location (left, middle 1, 2, right). Full article ">Figure 5
Schematic of the energy generation mechanism of water-powered generator. (Yellow arrow, Direction of electron movement). Full article ">Figure 6
CACG performances (Voc, Isc) and resistance based on physical properties. (a) Same length: 20 mm; diameter: 5 and 7.5 mm. (b) Same diameter: 7.5 mm; length: 10, 20, 30, 40, and 50 mm. Full article ">Figure 7
CACG performance (Voc, Isc) based on cation effect (length: 20 mm; diameter: 7.5 mm). (a) Injection solutions consist of DI water and NaCl; (b) performance depending on the amount of NaCl in the injection solution. Full article ">Figure 8
CACG performance (Voc, Isc) based on cation effect (length: 20 mm, diameter: 7.5 mm). (a) Measurement of performance changes due to relative humidity (30%, 50%, and 80%). (b) Series and parallel connections of the CACG. Full article ">

19 pages, 3552 KiB

Open AccessArticle

Thermally Conductive and Electrically Insulating Polymer-Based Composites Heat Sinks Fabricated by Fusion Deposition Modeling

by Simone Bagatella, Annacarla Cereti, Francesco Manarini, Marco Cavallaro, Raffaella Suriano and Marinella Levi

Polymers 2024, 16(3), 432; https://doi.org/10.3390/polym16030432 - 4 Feb 2024

Cited by 1 | Viewed by 1283

Abstract

This study explores the potential of novel boron nitride (BN) microplatelet composites with combined thermal conduction and electrical insulation properties. These composites are manufactured through Fusion Deposition Modeling (FDM), and their application for thermal management in electronic devices is demonstrated. The primary focus [...] Read more.

This study explores the potential of novel boron nitride (BN) microplatelet composites with combined thermal conduction and electrical insulation properties. These composites are manufactured through Fusion Deposition Modeling (FDM), and their application for thermal management in electronic devices is demonstrated. The primary focus of this work is, therefore, the investigation of the thermoplastic composite properties to show the 3D printing of lightweight polymeric heat sinks with remarkable thermal performance. By comparing various microfillers, including BN and MgO particles, their effects on material properties and alignment within the polymer matrix during filament fabrication and FDM processing are analyzed. The characterization includes the evaluation of morphology, thermal conductivity, and mechanical and electrical properties. Particularly, a composite with 32 wt% of BN microplatelets shows an in-plane thermal conductivity of 1.97 W m⁻¹ K⁻¹, offering electrical insulation and excellent printability. To assess practical applications, lightweight pin fin heat sinks using these composites are designed and 3D printed. Their thermal performance is evaluated via thermography under different heating conditions. The findings are very promising for an efficient and cost-effective fabrication of thermal devices, which can be obtained through extrusion-based Additive Manufacturing (AM), such as FDM, and exploited as enhanced thermal management solutions in electronic devices. Full article

(This article belongs to the Special Issue Polymer Materials and Design Processes for Additively Manufactured Products)

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Full article ">Figure 1
Diffractograms of 3D-printed PA–32BN (a) and PA–32BN–MgO (b) highlighting the peaks associated with the crystalline planes of BN and MgO. Full article ">Figure 2
Cross-section images by Scanning Electron Microscopy of 3D-printed PA–32BN at magnification 150× (a) and 2500× (c); PA–32BN–MgO at magnification 75× (b) and 1500× (d). Modified images with colors to highlight fillers in PA–32BN (e) and PA–32BN–MgO (f). Full article ">Figure 3
Thermal properties of PA–32BN and PA–32BN–MgO analyzed through TGA (a,b) and DSC (c,d). Full article ">Figure 4
Schematic illustration of the dog-bone-shaped specimens for tensile tests, fabricated by FDM with three different raster orientations to the applied force: oblique (±45°), vertical, and horizontal (from left to right). Full article ">Figure 5
Technical drawing of the pin fin heat sink (a), 3D CAD model (b), and the 3D-printed FDM-manufactured version (c,d). Full article ">Figure 6
(a) Thermograms of PA–32BN pin fin heat sink heated by a conductive system after 5 s, 105 s, and 605 s. (b) Temperature profiles as a function of the pin height of pin fin heat sinks heated by a conductive system, comparing plain polymer, PA–32BN, and PA–32BN–MgO at various times. (c) Temperature profiles as a function of time at 16mm height on pin fin heat sinks heated by a conductive system, comparing plain polymer, PA–32BN, and PA–32BN–MgO. Full article ">Figure 7
Thermograms from both top (a) and frontal (b) viewpoints of PA–32BN pin fin heat sink heated by an irradiation system, showing highlighted temperature profile curves. (c) Temperature profiles along the diameter of the heat sinks made of plain polymer, PA–32BN, and PA–32BN–MgO at 600 s, extrapolated from the top viewpoint. (d) Temperature profiles along the pin height of pin fin heat sinks heated by an irradiation system, comparing plain polymer, PA–32BN, and PA–32BN–MgO at various times, extrapolated from the frontal viewpoint. Full article ">

18 pages, 7018 KiB

Open AccessArticle

Comprehensive Analysis of Rheological, Mechanical, and Thermal Properties in Poly(lactic acid)/Oxidized Graphite Composites: Exploring the Effect of Heat Treatment on Elastic Modulus

by Mónica Elvira Mendoza-Duarte and Alejandro Vega-Rios

Polymers 2024, 16(3), 431; https://doi.org/10.3390/polym16030431 - 4 Feb 2024

Cited by 2 | Viewed by 1087

Abstract

This study is focused on investigating the rheological and mechanical properties of highly oxidized graphite (GrO) incorporated into a poly (lactic acid) (PLA) matrix composite. Furthermore, the samples were annealed at 110 °C for 30 min to study whether GrO concentration has an [...] Read more.

This study is focused on investigating the rheological and mechanical properties of highly oxidized graphite (GrO) incorporated into a poly (lactic acid) (PLA) matrix composite. Furthermore, the samples were annealed at 110 °C for 30 min to study whether GrO concentration has an effect on the elastic modulus (E’) after treatment. The incorporation of GrO into PLA was carried out by employing an internal mixing chamber at 190 °C. Six formulations were prepared with GrO concentrations of 0, 0.1, 0.5, 1, 1.5, and 3 wt%. The thermal stability, thermomechanical behavior, and crystallinity of the composites were evaluated utilizing thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and differential scanning calorimetry DSC, respectively. The thermal stability (according to T_max) of the PLA/GrO composites did not change substantially compared with PLA. According to DSC, the crystallinity increased until the GrO concentration reached 1 wt% and afterward decreased. Regarding the heat treatment of the PLA/GrO composites, the E’ increased (by two orders of magnitude) at 80 °C with the maximum value achieved at 1 wt% GrO compared with the non-heat-treated composites. Full article

(This article belongs to the Special Issue Study of the Mechanical and Rheological Behavior of Polymer Materials)

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14 pages, 4495 KiB

Open AccessArticle

Polybenzoxazine-Based Nitrogen-Containing Porous Carbon and Their Composites with NiCo Bimetallic Oxides for Supercapacitor Applications

by Thirukumaran Periyasamy, Shakila Parveen Asrafali, Seong-Cheol Kim, Deivasigamani Ranjith Kumar and Jaewoong Lee

Polymers 2024, 16(3), 430; https://doi.org/10.3390/polym16030430 - 3 Feb 2024

Cited by 1 | Viewed by 1019

Abstract

Supercapacitors (SCs) are considered as emerging energy storage devices that bridge the gap between electrolytic capacitors and rechargeable batteries. However, due to their low energy density, their real-time usage is restricted. Hence, to enhance the energy density of SCs, we prepared hetero-atom-doped carbon [...] Read more.

Supercapacitors (SCs) are considered as emerging energy storage devices that bridge the gap between electrolytic capacitors and rechargeable batteries. However, due to their low energy density, their real-time usage is restricted. Hence, to enhance the energy density of SCs, we prepared hetero-atom-doped carbon along with bimetallic oxides at different calcination temperatures, viz., HC/NiCo@600, HC/NiCo@700, HC/NiCo@800 and HC/NiCo@900. The material produced at 800 °C (HC/NiCo@800) exhibits a hierarchical 3D flower-like morphology. The electrochemical measurement of the prepared materials was performed in a three-electrode system showing an enhanced specific capacitance for HC/NiCo@600 (Cs = 1515 F g⁻¹) in 1 M KOH, at a current density of 1 A g⁻¹, among others. An asymmetric SC device was also fabricated using HC/NiCo@800 as anode and HC as cathode (HC/NiCo@600//HC). The fabricated device had the ability to operate at a high voltage window (~1.6 V), exhibiting a specific capacitance of 142 F g⁻¹ at a current density of 1 A g⁻¹; power density of 743.11 W kg⁻¹ and energy density of 49.93 Wh kg⁻¹. Altogether, a simple strategy of hetero-atom doping and bimetallic inclusion into the carbon framework enhances the energy density of SCs. Full article

(This article belongs to the Special Issue Electrochemistry of Conducting Polymers)

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SEM images of (a) HC; (b–e) HC/NiCo at different calcination temperatures (600–900 °C); and (f) EDX spectrum of HC/NiCo@800. Full article ">Figure 2
(a,b) HR-TEM images of HC/NiCo@800 along with (c) SAED pattern and (d–i) elemental mapping. Full article ">Figure 3
CV graphs of (a) HC/NiCo@600; (b) HC/NiCo@700; (c) HC/NiCo@800 and (d) HC/NiCo@900. Full article ">Figure 4
(a) CV graphs of HC/NiCo; (b) GCD graphs of HC/NiCo; (c) specific capacity of HC/NiCo; and (d) EIS spectra of HC/NiCo. Full article ">Figure 5
(a) GCD; (b) specific capacitance; (c) cyclic stability; and (d) EIS spectra of HC/NiCo@800. Full article ">Figure 6
(a) CV; (b) GCD; (c) specific capacity; (d) cyclic stability; (e) EIS spectra; and (f) Ragone plot of HC/NiCo@800//HC. Full article ">Scheme 1
Schematic diagram of the preparation of HC/NiCo at different temperatures. Full article ">

19 pages, 5987 KiB

Open AccessArticle

Exploring Functional Polymers in the Synthesis of Luminescent ZnO Quantum Dots for the Detection of Cr⁶⁺, Fe²⁺, and Cu²⁺

by Leire San José, Nastasiya Yuriychuk, Olga García, Mar López-González and Isabel Quijada-Garrido

Polymers 2024, 16(3), 429; https://doi.org/10.3390/polym16030429 - 3 Feb 2024

Viewed by 1282

Abstract

The main aim of this work is to demonstrate that well-defined methacrylate-based copolymers with oligoethylene glycol side chains and functional groups such as thiol and glycidyl, obtained by photo-initiated reversible addition-fragmentation chain transfer (RAFT) in ethanol, are highly suitable as templates in the [...] Read more.

The main aim of this work is to demonstrate that well-defined methacrylate-based copolymers with oligoethylene glycol side chains and functional groups such as thiol and glycidyl, obtained by photo-initiated reversible addition-fragmentation chain transfer (RAFT) in ethanol, are highly suitable as templates in the synthesis and protection of ZnO quantum dots (ZnO QDs) with remarkable photoluminescent properties. While the affinity of thiol groups to metallic surfaces is well established, their interaction with metal oxides has received less scrutiny. Furthermore, under basic conditions, glycidyl groups could react with hydroxyl groups on the surface of ZnO, representing another strategy for hybrid synthesis. The size and crystalline morphology of the resulting hybrids were assessed using DLS, TEM, and XRD, indicating that both polymers, even with a low proportion of functional groups (5% mol) are appropriate as templates and ligands for ZnO QDs synthesis. Notably, thiol-containing polymers yield hybrids with ZnO featuring excellent quantum yield (up to 52%), while polymers with glycidyl groups require combination with the organosilane aminopropyl triethoxysilane (APTES) to achieve optimal results. In both cases, these hybrids exhibited robust stability in both ethanol and aqueous environments. Beyond fundamental research, due to the remarkable photoluminescent properties and affordability, these hybrid ZnO QDs are expected to have potential applications in biotechnology and green science; in particular, in this study, we examined their use in the detection of environmental contaminants like Fe²⁺, Cr⁶⁺, and Cu²⁺. Specifically, the limit of detection achieved at 1.13 µM for the highly toxic Cr⁶⁺ underscores the significant sensing capabilities of the hybrids. Full article

(This article belongs to the Special Issue Advances in Hybrid Polymers)

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13 pages, 4925 KiB

Open AccessArticle

Reinforcement of Cement Nanocomposites through Optimization of Mixing Ratio between Carbon Nanotube and Polymer Dispersing Agent

by Seok Hwan An, Ki Yun Kim and Jea Uk Lee

Polymers 2024, 16(3), 428; https://doi.org/10.3390/polym16030428 - 3 Feb 2024

Cited by 1 | Viewed by 997

Abstract

Carbon nanotubes (CNTs), known for their exceptional mechanical, thermal, and electrical properties, are being explored as cement nanofillers in the construction field. However, due to the limited water dispersion of CNTs, polymer dispersing agents like polycarboxylate ether (PCE) and sulfonated naphthalene formaldehyde (SNF) [...] Read more.

Carbon nanotubes (CNTs), known for their exceptional mechanical, thermal, and electrical properties, are being explored as cement nanofillers in the construction field. However, due to the limited water dispersion of CNTs, polymer dispersing agents like polycarboxylate ether (PCE) and sulfonated naphthalene formaldehyde (SNF) are essential for uniform dispersion. In a previous study, PCE and SNF, common cement superplasticizers, effectively dispersed CNTs in cement nanocomposites. However, uncertainties remained regarding the extent to which all dispersing agents interacted efficiently with CNTs. Therefore, this research quantitatively assessed CNT interaction with dispersing agents through dispersion and centrifugation. Approximately 37% of PCE and 50% of SNF persisted compared to CNT after centrifugation. The resulting cement nanocomposites, with optimized mixing ratios, exhibited enhanced compressive strength of about 14% for CNT/PCE (78.13 MPa) and 12.3% for CNT/SNF (76.97 MPa) compared to plain cement (68.52 MPa). XRD results linked strength reinforcement to increased cement hydrate from optimized CNT dispersion. FE-SEM analysis revealed that CNTs were positioned within the pores of the cement. These optimized cement nanocomposites hold promise for improved safety in the construction industry. Full article

(This article belongs to the Special Issue Functional Hybrid Polymeric Composites)

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18 pages, 14694 KiB

Open AccessArticle

Nanostructured Poly-l-lactide and Polyglycerol Adipate Carriers for the Encapsulation of Usnic Acid: A Promising Approach for Hepatoprotection

by Benedetta Brugnoli, Greta Perna, Sara Alfano, Antonella Piozzi, Luciano Galantini, Eleni Axioti, Vincenzo Taresco, Alessia Mariano, Anna Scotto d’Abusco, Stefano Vecchio Ciprioti and Iolanda Francolini

Polymers 2024, 16(3), 427; https://doi.org/10.3390/polym16030427 - 3 Feb 2024

Cited by 1 | Viewed by 1295

Abstract

The present study investigates the utilization of nanoparticles based on poly-l-lactide (PLLA) and polyglycerol adipate (PGA), alone and blended, for the encapsulation of usnic acid (UA), a potent natural compound with various therapeutic properties including antimicrobial and anticancer activities. The development of these [...] Read more.

The present study investigates the utilization of nanoparticles based on poly-l-lactide (PLLA) and polyglycerol adipate (PGA), alone and blended, for the encapsulation of usnic acid (UA), a potent natural compound with various therapeutic properties including antimicrobial and anticancer activities. The development of these carriers offers an innovative approach to overcome the challenges associated with usnic acid’s limited aqueous solubility, bioavailability, and hepatotoxicity. The nanosystems were characterized according to their physicochemical properties (among others, size, zeta potential, thermal properties), apparent aqueous solubility, and in vitro cytotoxicity. Interestingly, the nanocarrier obtained with the PLLA-PGA 50/50 weight ratio blend showed both the lowest size and the highest UA apparent solubility as well as the ability to decrease UA cytotoxicity towards human hepatocytes (HepG2 cells). This research opens new avenues for the effective utilization of these highly degradable and biocompatible PLLA-PGA blends as nanocarriers for reducing the cytotoxicity of usnic acid. Full article

(This article belongs to the Special Issue Polymeric Materials for Drug Delivery II)

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21 pages, 4881 KiB

Open AccessArticle

A Theoretical Investigation of the Polyaddition of an AB₂+A₂+B₄ Monomer Mixture

by Sergei V. Karpov, Artem Iakunkov, Dmitry A. Chernyaev, Vladimir G. Kurbatov, Georgiy V. Malkov and Elmira R. Badamshina

Polymers 2024, 16(3), 426; https://doi.org/10.3390/polym16030426 - 3 Feb 2024

Viewed by 808

Abstract

Hyperbranched polymers (HBPs) are widely applied nowadays as functional materials for biomedicine needs, nonlinear optics, organic semiconductors, etc. One of the effective and promising ways to synthesize HBPs is a polyaddition of AB₂+A₂+B₄ monomers that is generated in [...] Read more.

Hyperbranched polymers (HBPs) are widely applied nowadays as functional materials for biomedicine needs, nonlinear optics, organic semiconductors, etc. One of the effective and promising ways to synthesize HBPs is a polyaddition of AB₂+A₂+B₄ monomers that is generated in the A₂+CB₂, AA′+B₃, A₂+B′B₂, and A₂+C₂+B₃ systems or using other approaches. It is clear that all the foundational features of HBPs that are manufactured by a polyaddition reaction are defined by the component composition of the monomer mixture. For this reason, we have designed a structural kinetic model of AB₂+A₂+B₄ monomer mixture polyaddition which makes it possible to predict the impact of the monomer mixture’s composition on the molecular weight characteristics of hyperbranched polymers (number average (DP_n) and weight average (DP_w) degree of polymerization), as well as the degree of branching (DB) and gel point (p_g). The suggested model also considers the possibility of a positive or negative substitution effect during polyaddition. The change in the macromolecule parameters of HBPs formed by polyaddition of AB₂+A₂+B₄ monomers is described as an infinite system of kinetic equations. The solution for the equation system was found using the method of generating functions. The impact of both the component’s composition and the substitution effect during the polyaddition of AB₂+A₂+B₄ monomers on structural and molecular weight HBP characteristics was investigated. The suggested model is fairly versatile; it makes it possible to describe every possible case of polyaddition with various monomer combinations, such as A₂+AB₂, AB₂+B₄, AB₂, or A₂+B₄. The influence of each monomer type on the main characteristics of hyperbranched polymers that are obtained by the polyaddition of AB₂+A₂+B₄ monomers has been investigated. Based on the results obtained, an empirical formula was proposed to estimate the p_g = p_A during the polyaddition of an AB₂+A₂+B₄ monomer mixture: p_g = p_A = (−0.53([B]₀/[A]₀)^1/2 + 0.78)υAB₂ + (1/3)^1/2([B]₀/[A]₀)^1/2, where (1/3)^1/2([B]₀/[A]₀)^1/2 is the Flory equation for the A₂+B₄ polyaddition, [A]₀ and [B]₀ are the A and B group concentration from A₂ and B₄, respectively, and υAB₂ is the mole fraction of the AB₂ monomer in the mixture. The equation obtained allows us to accurately predict the p_g value, with an AB₂ monomer content of up to 80%. Full article

(This article belongs to the Special Issue Computational and Experimental Approaches in Polymeric Materials)

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0 pages, 11234 KiB

Open AccessArticle

Analysis of the Rotation Bending Test Method and Characterization of Unidirectional Carbon Fiber-Reinforced Polycarbonate Tapes at Processing Temperatures

by Daniel Laresser, Matei-Constantin Miron, Milan Kracalik, Felix Baudach and Zoltán Major

Polymers 2024, 16(3), 425; https://doi.org/10.3390/polym16030425 - 2 Feb 2024

Cited by 1 | Viewed by 919

Abstract

Bending is one of the dominant material deformation mechanisms that occurs during the forming process of unidirectional (UD) thermoplastic tapes. Experimental characterization of the bending behavior at processing temperatures is crucial to obtaining close-to-reality data sets for process analysis or material modeling for [...] Read more.

Bending is one of the dominant material deformation mechanisms that occurs during the forming process of unidirectional (UD) thermoplastic tapes. Experimental characterization of the bending behavior at processing temperatures is crucial to obtaining close-to-reality data sets for process analysis or material modeling for process simulation. The main purpose of this study is to characterize to a high degree of accuracy the temperature-dependent bending behavior of single and multi-ply specimens of carbon fiber-reinforced polycarbonate (PC/CF) UD tapes at processing temperatures, which implies a molten state of the thermoplastic matrix. The application of the rotation bending test using a customized fixture may come with systematic deviations in the measured moment that result from a pivot offset or an effective clearance that is unknown under realistic test conditions. The present research analyzes these effects with analytical methods, experimental investigations, and simulations using a finite element model. In this context, a compensation method for the toe-in effect is evaluated. With this approach, we were able to obtain reliable data and characterize the bending resistance within the desired processing window. The data reveal a major drop in bending resistance between 200 °C and 250 °C and a less significant decrease between 250 °C and 300 °C. Analysis of the thickness-normalized bending resistances indicates a non-linear relationship between specimen thickness and measured moment but an increasing shear-dominated characteristic at higher temperatures. Full article

(This article belongs to the Section Polymer Analysis and Characterization)

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15 pages, 4566 KiB

Open AccessArticle

Expansion Injection Molding Process Using Clamping Force for Melt Compression

by Joon Hyoung Park and Sun Kyoung Kim

Polymers 2024, 16(3), 424; https://doi.org/10.3390/polym16030424 - 2 Feb 2024

Viewed by 1220

Abstract

Melt expansion followed by compression has been utilized for high-speed filling. In general, this technology was developed for a machine level. Recently, mold-level technology has been tried. In this study, an expansion injection molding process was examined, which included compressing a polymer melt [...] Read more.

Melt expansion followed by compression has been utilized for high-speed filling. In general, this technology was developed for a machine level. Recently, mold-level technology has been tried. In this study, an expansion injection molding process was examined, which included compressing a polymer melt through cylinder action facilitated by the movement of the platen, followed by the expansion of the polymer melt into a mold cavity. A mold system including temperature control and valve actions, similar to hot runner systems, was designed and built. The test results show good filling when the injection pressure was high. Simulations were also carried out, highlighting consistent pressure and filling trends, while revealing limitations tied to the characteristics of the state model. This research indicates promise for expansion injection molding through platen compression but emphasizes the need for the seamless integration of valve action with the injection molding machine for large-scale production. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

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28 pages, 3612 KiB

Open AccessReview

Nanocellulose Composite Films in Food Packaging Materials: A Review

by Yanting Xu, Zhenzeng Wu, Ao Li, Nairong Chen, Jiuping Rao and Qinzhi Zeng

Polymers 2024, 16(3), 423; https://doi.org/10.3390/polym16030423 - 2 Feb 2024

Cited by 7 | Viewed by 4518

Abstract

Owing to the environmental pollution caused by petroleum-based packaging materials, there is an imminent need to develop novel food packaging materials. Nanocellulose, which is a one-dimensional structure, has excellent physical and chemical properties, such as renewability, degradability, sound mechanical properties, and good biocompatibility, [...] Read more.

Owing to the environmental pollution caused by petroleum-based packaging materials, there is an imminent need to develop novel food packaging materials. Nanocellulose, which is a one-dimensional structure, has excellent physical and chemical properties, such as renewability, degradability, sound mechanical properties, and good biocompatibility, indicating promising applications in modern industry, particularly in food packaging. This article introduces nanocellulose, followed by its extraction methods and the preparation of relevant composite films. Meanwhile, the performances of nanocellulose composite films in improving the mechanical, barrier (oxygen, water vapor, ultraviolet) and thermal properties of food packaging materials and the development of biodegradable or edible packaging materials in the food industry are elaborated. In addition, the excellent performances of nanocellulose composites for the packaging and preservation of various food categories are outlined. This study provides a theoretical framework for the development and utilization of nanocellulose composite films in the food packaging industry. Full article

(This article belongs to the Section Polymer Membranes and Films)

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Schematic illustration of nanocellulose preparation from plants(adapted from [<a href="#B12-polymers-16-00423" class="html-bibr">12</a>].with permission of ELSEVIER). Full article ">Figure 2
Some carbon sources used as culture medium materials to prepare bacterial cellulose. Full article ">Figure 3
Usage of nanocellulose composite films in food packaging. Full article ">Figure 4
Preparation methods of nanocellulose composite films: (a) solvent casting method, (b) layer-by-layer assembly, (c) electrospinning, (d) melt process, (e) coating (adapted from [<a href="#B48-polymers-16-00423" class="html-bibr">48</a>] with permission of Talyor & Francis). Full article ">Figure 5
Schematic diagram of oxygen permeation process in films. Full article ">Figure 6
(a) Gas diffusion path of CNF; (b) gas diffusion path of CNCs through composite films (adapted from [<a href="#B73-polymers-16-00423" class="html-bibr">73</a>] with permission of ELSEVIER). Full article ">Figure 7
(a) Preparation of TOCN UV-blocking films; (b) performance changes in thermally treated TOCN films; (c) contact angles of water droplets (adapted from [<a href="#B85-polymers-16-00423" class="html-bibr">85</a>] with the permission of ELSEVIER). Full article ">Figure 8
Schematic illustration of polymer biodegradation process (adapted from [<a href="#B107-polymers-16-00423" class="html-bibr">107</a>] with the permission of ELSEVIER). Full article ">

16 pages, 5436 KiB

Open AccessArticle

Nanocomposites Based on Thermoplastic Acrylic Resin with the Addition of Chemically Modified Multi-Walled Carbon Nanotubes

by Szymon Demski, Dariusz Brząkalski, Maciej Gubernat, Kamil Dydek, Paweł Czaja, Konrad Żochowski, Paulina Kozera, Zuzanna Krawczyk, Bogna Sztorch, Robert Edward Przekop, Michał Marczak, Hermann Ehrlich and Anna Boczkowska

Polymers 2024, 16(3), 422; https://doi.org/10.3390/polym16030422 - 2 Feb 2024

Cited by 1 | Viewed by 1341

Abstract

The main goal of this work was an improvement in the mechanical and electrical properties of acrylic resin-based nanocomposites filled with chemically modified carbon nanotubes. For this purpose, the surface functionalization of multi-walled carbon nanotubes (MWCNTs) was carried out by means of aryl [...] Read more.

The main goal of this work was an improvement in the mechanical and electrical properties of acrylic resin-based nanocomposites filled with chemically modified carbon nanotubes. For this purpose, the surface functionalization of multi-walled carbon nanotubes (MWCNTs) was carried out by means of aryl groups grafting via the diazotization reaction with selected aniline derivatives, and then nanocomposites based on ELIUM^® resin were fabricated. FT-IR analysis confirmed the effectiveness of the carried-out chemical surface modification of MWCNTs as new bands on FT-IR spectra appeared in the measurements. TEM observations showed that carbon nanotube fragmentation did not occur during the modifications. According to the results from Raman spectroscopy, the least defective carbon nanotube structure was obtained for aniline modification. Transmission light microscopy analysis showed that the neat MWCNTs agglomerate strongly, while the proposed modifications improved their dispersion significantly. Viscosity tests confirmed, that as the nanofiller concentration increases, the viscosity of the mixture increases. The mixture with the highest dispersion of nanoparticles exhibited the most viscous behaviour. Finally, an enhancement in impact resistance and electrical conductivity was obtained for nanocomposites containing modified MWCNTs. Full article

(This article belongs to the Special Issue Advances in Thermal, Electrical and Mechanical Properties of Polymer Composites)

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16 pages, 10920 KiB

Open AccessArticle

Investigation of Hybrid Electrodes of Polyaniline and Reduced Graphene Oxide with Bio-Waste-Derived Activated Carbon for Supercapacitor Applications

by Imen Benchikh, Abdelrahman Osama Ezzat, Lilia Sabantina, Youcef Benmimoun and Abdelghani Benyoucef

Polymers 2024, 16(3), 421; https://doi.org/10.3390/polym16030421 - 2 Feb 2024

Cited by 5 | Viewed by 1301

Abstract

Graphene-based materials have been widely studied in the field of supercapacitors. However, their electrochemical properties and applications are still restricted by the susceptibility of graphene-based materials to curling and agglomeration during production. This study introduces a facile method for synthesizing reduced graphene oxide [...] Read more.

Graphene-based materials have been widely studied in the field of supercapacitors. However, their electrochemical properties and applications are still restricted by the susceptibility of graphene-based materials to curling and agglomeration during production. This study introduces a facile method for synthesizing reduced graphene oxide (rGO) nanosheets and activated carbon based on olive stones (OS) with polyaniline (PAni) surface decoration for the development of supercapacitors. Several advanced techniques were used to examine the structural properties of the samples. The obtained PAni@OS−rGO (1:1) electrode exhibits a high electrochemical capacity of 582.6 F·g⁻¹ at a current density of 0.1 A·g⁻¹, and an energy density of 26.82 Wh·kg⁻¹; thus, it demonstrates potential for efficacious energy storage. In addition, this electrode material exhibits remarkable cycling stability, retaining over 90.07% capacitance loss after 3000 cycles, indicating a promising long cycle life. Overall, this research highlights the potential of biomass-derived OS in the presence of PAni and rGO to advance the development of high-performance supercapacitors. Full article

(This article belongs to the Special Issue Polymer Based Electronic Devices and Sensors III)

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21 pages, 9868 KiB

Open AccessArticle

Strain Rate and Temperature Influence on Micromechanisms of Plastic Deformation of Polyethylenes Investigated by Positron Annihilation Lifetime Spectroscopy

by Cezary Makarewicz, Marta Safandowska, Rafal Idczak, Slawomir Kolodziej and Artur Rozanski

Polymers 2024, 16(3), 420; https://doi.org/10.3390/polym16030420 - 2 Feb 2024

Viewed by 1006

Abstract

Plastic deformation of low/high density polyethylene (LDPE/HDPE) was analyzed in this work using positron annihilation lifetime spectroscopy (PALS). It was shown that in undeformed LDPE, both the mean ortho-positronium lifetime (τ₃) and its dispersion (σ₃), corresponding to the average [...] Read more.

Plastic deformation of low/high density polyethylene (LDPE/HDPE) was analyzed in this work using positron annihilation lifetime spectroscopy (PALS). It was shown that in undeformed LDPE, both the mean ortho-positronium lifetime (τ₃) and its dispersion (σ₃), corresponding to the average size and size distribution of the free-volume pores of the amorphous component, respectively, were clearly higher than in HDPE. This effect was induced by a lower and less uniform molecular packing of the amorphous regions in LDPE. During the deformation of LDPE, an increase in the τ₃ value was observed within the local strains of 0–0.25. This effect was mainly stimulated by a positive relative increase in interlamellar distances due to the deformation of lamellar crystals oriented perpendicular (increased by 31.8%) and parallel (decreased by 10.1%) to the deformation directions. At the same time, the dimension of free-volume pores became more uniform, which was manifested by a decrease in the σ₃ value. No significant effect of temperature or strain rate on the τ₃ and σ₃ values was observed during LDPE deformation. In turn, in the case of HDPE, with an increase in the strain rate/or a decrease in temperature, an intensification of the cavitation phenomenon could be observed with a simultaneous decrease in the τ₃ value. This effect was caused by the lack of annihilation of ortho-positonium (o-Ps) along the longer axis of the highly anisotropic/ellipsoidal cavities. Therefore, this dimension was not detectable by the PALS technique. At the same time, the increase in the dimension of the shorter axis of the cavities was effectively limited by the thickness of amorphous layers. As the strain rate increased or the temperature decreased, the σ₃ value during HDPE deformation increased. This change was correlated with the initiation and intensification of the cavitation phenomenon. Based on the mechanical response of samples with a similar yield stress, it was also proven that the susceptibility of the amorphous regions of LDPE to the formation of cavities is lower than in the case of amorphous component of HDPE. Full article

(This article belongs to the Section Polymer Physics and Theory)

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18 pages, 3678 KiB

Open AccessArticle

Toward Producing Biopolyethylene/Babassu Fiber Biocomposites with Improved Mechanical and Thermomechanical Properties

by Eduardo da Silva Barbosa Ferreira, Fabiano Santana da Silva, Carlos Bruno Barreto Luna, Anna Raffaela de Matos Costa, Fernanda Menezes de Sousa, Laura Hecker de Carvalho, Renate Maria Ramos Wellen and Edcleide Maria Araújo

Polymers 2024, 16(3), 419; https://doi.org/10.3390/polym16030419 - 2 Feb 2024

Cited by 3 | Viewed by 1214

Abstract

The development of polymeric biocomposites containing natural fibers has grown over the years due to the properties achieved and its eco-friendly nature. Thus, biocomposites involving a polymer from a renewable source (Biopolyethylene (BioPE)) and babassu fibers (BFs), compatibilized with polyethylene grafted with maleic [...] Read more.

The development of polymeric biocomposites containing natural fibers has grown over the years due to the properties achieved and its eco-friendly nature. Thus, biocomposites involving a polymer from a renewable source (Biopolyethylene (BioPE)) and babassu fibers (BFs), compatibilized with polyethylene grafted with maleic anhydride (MA) and acrylic acid (AA) (PE-g-MA and PE-g-AA, respectively) were obtained using melt mixing and injection molded into tensile, impact, and HDT specimens. Babassu fiber was characterized with Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TGA), and scanning electron microscopy (SEM). The biocomposites were characterized using torque rheometry, TGA, tensile strength, impact strength, thermomechanical properties, Shore D hardness, and SEM. The data indicate that the torque during the processing of compatibilized biocomposites was higher than that of BioPE/BF biocomposites, which was taken as an indication of a possible reaction between the functional groups. Compatibilization led to a substantial improvement in the elastic modulus, tensile strength, HDT, and VST and a decrease in Shore D hardness. These results were justified with SEM micrographs, which showed babassu fibers better adhered to the surface of the biopolyethylene matrix, as well as an encapsulation of these fibers. The system investigated is environmentally sustainable, and the results are promising for the technology of polymeric composites. Full article

(This article belongs to the Special Issue Biopolymers and Bio-Based Polymer Composites)

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13 pages, 4497 KiB

Open AccessArticle

Fabrication of Fish Scale-Based Gelatin Methacryloyl for 3D Bioprinting Application

by Kitipong Pasanaphong, Danai Pukasamsombut, Sani Boonyagul, Sukanya Pengpanich, Tulyapruek Tawonsawatruk, Danuphat Wilairatanarporn, Kittisak Jantanasakulwong, Pornchai Rachtanapun, Ruedee Hemstapat, Sutee Wangtueai and Nuttapol Tanadchangsaeng

Polymers 2024, 16(3), 418; https://doi.org/10.3390/polym16030418 - 1 Feb 2024

Viewed by 1669

Abstract

Gelatin methacryloyl (GelMA) is an ideal bioink that is commonly used in bioprinting. GelMA is primarily acquired from mammalian sources; however, the required amount makes the market price extremely high. Since garbage overflow is currently a global issue, we hypothesized that fish scales [...] Read more.

Gelatin methacryloyl (GelMA) is an ideal bioink that is commonly used in bioprinting. GelMA is primarily acquired from mammalian sources; however, the required amount makes the market price extremely high. Since garbage overflow is currently a global issue, we hypothesized that fish scales left over from the seafood industry could be used to synthesize GelMA. Clinically, the utilization of fish products is more advantageous than those derived from mammals as they lower the possibility of disease transmission from mammals to humans and are permissible for practitioners of all major religions. In this study, we used gelatin extracted from fish scales and conventional GelMA synthesis methods to synthesize GelMA, then tested it at different concentrations in order to evaluated and compared the mechanical properties and cell responses. The fish scale GelMA had a printing accuracy of 97%, a swelling ratio of 482%, and a compressive strength of about 85 kPa at a 10% w/v GelMA concentration. Keratinocyte cells (HaCaT cells) were bioprinted with the GelMA bioink to assess cell viability and proliferation. After 72 h of culture, the number of cells increased by almost three-fold compared to 24 h, as indicated by many fluorescent cell nuclei. Based on this finding, it is possible to use fish scale GelMA bioink as a scaffold to support and enhance cell viability and proliferation. Therefore, we conclude that fish scale-based GelMA has the potential to be used as an alternative biomaterial for a wide range of biomedical applications. Full article

(This article belongs to the Special Issue 3D Printing of Polymer-Based Composite Materials)

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19 pages, 1252 KiB

Open AccessArticle

A Systematic Investigation on the Effect of Carbon Nanotubes and Carbon Black on the Mechanical and Flame Retardancy Properties of Polyolefin Blends

by Eid M. Alosime and Ahmed A. Basfar

Polymers 2024, 16(3), 417; https://doi.org/10.3390/polym16030417 - 1 Feb 2024

Cited by 2 | Viewed by 975

Abstract

Due to high filler loading, clean, commercial, thermoplastic, flame-retardant materials are mechanically unstable when insulating wires and cables. In this study, composite formulations of linear low-density polyethylene (LLDPE)/ethylene–vinyl acetate (EVA) containing a flame retardant, such as magnesium hydroxide (MH; formula: Mg(OH)₂) [...] Read more.

Due to high filler loading, clean, commercial, thermoplastic, flame-retardant materials are mechanically unstable when insulating wires and cables. In this study, composite formulations of linear low-density polyethylene (LLDPE)/ethylene–vinyl acetate (EVA) containing a flame retardant, such as magnesium hydroxide (MH; formula: Mg(OH)₂) and huntite hydromagnesite (HH; formula: Mg₃Ca(CO₃)₄, Mg₅(CO₃)₄(OH)₂·3H₂O), were prepared. The influence of carbon nanotubes (CNTs) and carbon black (CB) on the mechanical properties and flame retardancy of LLDPE/EVA was studied. Three types of CNTs were examined for their compatibility with other materials in clean thermoplastic flame-retardant compositions. The CNTs had the following diameters: 10–15 nm, 40–60 nm, and 60–80 nm. Optimum mechanical flame retardancy and electrical properties were achieved by adding CNTs with an outer diameter of 40–60 nm and a length of fewer than 20 nm. Large-sized CNTs result in poor mechanical characteristics, while smaller-sized CNTs improve the mechanical properties of the composites. CB enhances flame retardancy but deteriorates mechanical properties, particularly elongation at break, in clean, black, thermoplastic, flame-retardant compositions. Obtaining satisfactory compositions that meet both properties, especially formulations passing the V-0 of the UL 94 test with a minimum tensile strength of 9.5 MPa and an elongation at break of 125%, is challenging. When LLDPE was partially substituted with EVA, the limiting oxygen index (LOI) increased. The amount of filler in the formulations determined how it affected flammability. This study also included a reliable method for producing clean, black, thermoplastic, flame-retardant insulating material for wire and cable without sacrificing mechanical properties. Full article

(This article belongs to the Special Issue Flame Retardant and Mechanical Properties of Polymer Materials)

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14 pages, 2673 KiB

Open AccessArticle

Temperature-Responsive Separation Membrane with High Antifouling Performance for Efficient Separation

by Tong Ji, Yuan Ji, Xiangli Meng and Qi Wang

Polymers 2024, 16(3), 416; https://doi.org/10.3390/polym16030416 - 1 Feb 2024

Viewed by 1119

Abstract

Temperature-responsive separation membranes can significantly change their permeability and separation properties in response to changes in their surrounding temperature, improving efficiency and reducing membrane costs. This study focuses on the modification of polyvinylidene fluoride (PVDF) membranes with amphiphilic temperature-responsive copolymer and inorganic nanoparticles. [...] Read more.

Temperature-responsive separation membranes can significantly change their permeability and separation properties in response to changes in their surrounding temperature, improving efficiency and reducing membrane costs. This study focuses on the modification of polyvinylidene fluoride (PVDF) membranes with amphiphilic temperature-responsive copolymer and inorganic nanoparticles. We prepared an amphiphilic temperature-responsive copolymer in which the hydrophilic poly(N-isopropyl acrylamide) (PNIPAAm) was side-linked to a hydrophobic polyvinylidene fluoride (PVDF) skeleton. Subsequently, PVDF-g-PNIPAAm polymer and graphene oxide (GO) were blended with PVDF to prepare temperature-responsive separation membranes. The results showed that temperature-responsive polymers with different NIPAAm grafting ratios were successfully prepared by adjusting the material ratio of NIPAAm to PVDF. PVDF-g-PNIPAAm was blended with PVDF with different grafting ratios to obtain separate membranes with different temperature responses. GO and PVDF-g-PNIPAAm formed a relatively stable hydrogen bond network, which improved the internal structure and antifouling performance of the membrane without affecting the temperature response, thus extending the service life of the membrane. Full article

(This article belongs to the Special Issue Carbon/Polymer Composite Materials)

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Reaction mechanism, 1H NMR spectra, and TG curves of copolymer synthesis: (a) reaction mechanism; (b) the full 1H NMR spectrum of the copolymer; (c,d) the local spectrum of copolymer 1H NMR; (e) TG curves of the copolymer. Full article ">Figure 2
Comprehensive performance of PVDF/PVDF-g-PNIPAAm membranes: (a) water flux; (b) rejection rate; (c) antifouling performance FRR; (d) mechanical properties; (e) porosity; (f) water contact angle. Full article ">Figure 3
SEM photographs of the membranes: (a1–f1) the upper surfaces of pure PVDF membranes, PVDF/PVDF-g-PNIPAAm membranes, 0.25 wt%, 0.50 wt%, 0.75 wt%, 1.00 wt% GO content PVDF/PVDF-g-PNIPAAm/GO membranes; (a2–f2) the cross-section of the pure PVDF membranes, PVDF/PVDF-g-PNIPAAm membranes, 0.25 wt%, 0.50 wt%, 0.75 wt%, 1.00 wt% GO content PVDF/PVDF-g-PNIPAAm/GO membranes. Full article ">Figure 4
Porosity and hydrophilicity of PVDF/PVDF-g-PNIPAAm/GO membrane: (a) porosity; (b) hydrophilicity. Full article ">Figure 5
Comprehensive performance of PVDF/PVDF-g-PNIPAAm/GO membranes: (a) water flux; (b) rejection rate; (c) antifouling performance FRR; (d) mechanical properties. Full article ">Scheme 1
(a) Schematic diagram of PVDF/PVDF-g-PNIPAAm/GO membrane formation; (b) schematic illustration of temperature response behavior. Full article ">

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Polymers, Volume 16, Issue 3 (February-1 2024) – 141 articles

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