Polymers

16 pages, 2576 KiB

Open AccessArticle

Effect of Chitin Whiskers on the Molecular Dynamics of Carrageenan-Based Nanocomposites

by Marta Carsi, Maria J. Sanchis, Clara M. Gómez, Sol Rodriguez and Fernando G. Torres

Polymers 2019, 11(6), 1083; https://doi.org/10.3390/polym11061083 - 25 Jun 2019

Cited by 16 | Viewed by 3708

Films of carrageenan (KC) and glycerol (g) with different contents of chitin nanowhiskers (CHW) were prepared by a solution casting process. The molecular dynamics of pure carrageenan (KC), carrageenan/glycerol (KCg) and KCg with different quantities of CHWs as a filler was studied using [...] Read more.

Films of carrageenan (KC) and glycerol (g) with different contents of chitin nanowhiskers (CHW) were prepared by a solution casting process. The molecular dynamics of pure carrageenan (KC), carrageenan/glycerol (KCg) and KCg with different quantities of CHWs as a filler was studied using dielectric relaxation spectroscopy. The analysis of the CHW effect on the molecular mobility at the glass transition, T_g, indicates that non-attractive intermolecular interactions between KCg and CHW occur. The fragility index increased upon CHW incorporation, due to a reduction in the polymer chains mobility produced by the CHW confinement of the KCg network. The apparent activation energy associated with the relaxation dynamics of the chains at T_g slightly increased with the CHW content. The filler nature effect, CHW or montmorillonite (MMT), on the dynamic mobility of the composites was analyzed by comparing the dynamic behavior of both carrageenan-based composites (KCg/xCHW, KCg/xMMT). Full article

(This article belongs to the Special Issue Polymeric Thin Films and Membranes)

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Full article ">Figure 1
Temperature dependence of the dielectric permittivity, ε′ (left) and the dielectric loss, ε″, (right) for the samples studied, at several frequencies in Hz (1: 4.9 10−2, 2: 1.2 100, 3: 8.7⋅100, 4: 9.5 101, 5: 1.0 102, 6: 1.1 104, 7: 1.2 105, 8: 9.1 105). Full article ">Figure 2
Temperature dependence of (a) the dielectric permittivity (ε′) and (b) the dielectric loss (ε″) at 102 Hz for the samples studied. Full article ">Figure 3
Frequency (a) and temperature (b) dependence of the loss modulus (M″) at 293 K and 102 Hz, respectively. KC (circle), KCg (square) and KCg/xCHW nanocomposites with x = 5 (up triangle), 10 (down triangle) and 15 (diamond). Full article ">Figure 4
Temperature dependence of the relaxation times for analyzed samples. KC (circle), KCg (square) and KCg/xCHW nanocomposites with x = 5 (up triangle), 10 (down triangle) and 15 (diamond). Lines are the best fitting to the experimental data. Full article ">Figure 5
Filler content dependence of the glass transition temperature Tg (full symbols) and fragility index m (open symbols) for both KCg/xMMT (square) and KCg/xCHW (cicle) nanocomposites (x = 0, 5, 10 and 15). Stars correspond to the sample without g (KC). The lines only represent the trend behavior. Inset: FTIR spectra of KCg matrix and KCg/15MMT and KCg/15CHW nanocomposites. Full article ">Figure 6
Filler content dependence of the relative free volume at the glass temperature, ϕg/B (full symbols) and the value of the expansion coefficient of the free volume, αf (open symbols) for both KCg/xMMT (square) and KCg/xCHW (cicle) nanocomposites (x = 0, 5, 10 and 15). Stars correspond to the sample without glycerol (KC). Full article ">Figure 7
Filler content dependence of the apparent activation energy associated with the relaxation dynamics of the chains at Tg, Ea (Tg), for both KCg/xMMT (square) and KCg/xCHW (circle) nanocomposites (x = 0, 5, 10 and 15). Stars correspond to the sample without g (KC). Full article ">

23 pages, 5509 KiB

Open AccessArticle

Submicron-Sized Nanocomposite Magnetic-Sensitive Carriers: Controllable Organ Distribution and Biological Effects

by Marina V. Novoselova, Sergey V. German, Olga A. Sindeeva, Oleg A. Kulikov, Olga V. Minaeva, Ekaterina P. Brodovskaya, Valentin P. Ageev, Mikhail N. Zharkov, Nikolay A. Pyataev, Gleb B. Sukhorukov and Dmitry A. Gorin

Polymers 2019, 11(6), 1082; https://doi.org/10.3390/polym11061082 - 25 Jun 2019

Cited by 24 | Viewed by 4564

Abstract

Although new drug delivery systems have been intensely developed in the past decade, no significant increase in the efficiency of drug delivery by nanostructure carriers has been achieved. The reasons are the lack of information about acute toxicity, the influence of the submicron [...] Read more.

Although new drug delivery systems have been intensely developed in the past decade, no significant increase in the efficiency of drug delivery by nanostructure carriers has been achieved. The reasons are the lack of information about acute toxicity, the influence of the submicron size of the carrier and difficulties with the study of biodistribution in vivo. Here we propose, for the first time in vivo, new nanocomposite submicron carriers made of bovine serum albumin (BSA) and tannic acid (TA) and containing magnetite nanoparticles with sufficient content for navigation in a magnetic field gradient on mice. We examined the efficacy of these submicron carriers as a delivery vehicle in combination with magnetite nanoparticles which were systemically administered intravenously. In addition, the systemic toxicity of this carrier for intravenous administration was explicitly studied. The results showed that (BSA/TA) carriers in the given doses were hemocompatible and didn’t cause any adverse effect on the respiratory system, kidney or liver functions. A combination of gradient-magnetic-field controllable biodistribution of submicron carriers with fluorescence tomography/MRI imaging in vivo provides a new opportunity to improve drug delivery efficiency. Full article

(This article belongs to the Special Issue Engineering and Material Advances in Polymer-Based Drug Delivery Systems)

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15 pages, 3704 KiB

Open AccessArticle

Identification of Some New Triply Periodic Mesophases from Molten Block Copolymers

by Junhan Cho

Polymers 2019, 11(6), 1081; https://doi.org/10.3390/polym11061081 - 25 Jun 2019

Cited by 4 | Viewed by 2995

Abstract

Using field-theoretic simulations based on a self-consistent field theory (SCFT) with or without finite compressibility, nanoscale mesophase formation in molten linear AB and ABC block copolymers is investigated in search of candidates for new and useful nanomaterials. At selected compositions and segregation strengths, [...] Read more.

Using field-theoretic simulations based on a self-consistent field theory (SCFT) with or without finite compressibility, nanoscale mesophase formation in molten linear AB and ABC block copolymers is investigated in search of candidates for new and useful nanomaterials. At selected compositions and segregation strengths, the copolymers are shown to evolve into some new nanostructures with either unusual crystal symmetry or a peculiar morphology. There exists a holey layered morphology with Im3 symmetry, which lacks one mirror reflection compared with Im3m symmetry. Also, a peculiar cubic bicontinuous morphology, whose channels are connected with tetrapod units, is found to have Pn3m symmetry. It is shown that there is another network morphology with tripod connections, which reveals P432 symmetry. The optimized free energies of these new mesophases and their relative stability are discussed in comparison with those of double gyroids and double diamonds. Full article

(This article belongs to the Special Issue Self-assembly of Block Copolymers)

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16 pages, 3504 KiB

Open AccessArticle

Synthesis and Characterization of a Lignin-Styrene-Butyl Acrylate Based Composite

by Daniel López Serna, Perla Elizondo Martínez, Miguel Ángel Reyes González, Antonio Alberto Zaldívar Cadena, Erasto Armando Zaragoza Contreras and María Guadalupe Sánchez Anguiano

Polymers 2019, 11(6), 1080; https://doi.org/10.3390/polym11061080 - 25 Jun 2019

Cited by 5 | Viewed by 4573

Abstract

In recent years, the pursuit of new polymer materials based on renewable raw materials has been intensified with the aim of reusing waste materials in sustainable processes. The synthesis of a lignin, styrene, and butyl acrylate based composite was carried out by a [...] Read more.

In recent years, the pursuit of new polymer materials based on renewable raw materials has been intensified with the aim of reusing waste materials in sustainable processes. The synthesis of a lignin, styrene, and butyl acrylate based composite was carried out by a mass polymerization process. A series of four composites were prepared by varying the amount of lignin in 5, 10, 15, and 20 wt.% keeping the content of butyl acrylate constant (14 wt.%). FTIR and SEM revealed that the –OH functional groups of lignin reacted with styrene, which was observed by the incorporation of lignin in the copolymer. Additionally, DSC analysis showed that the increment in lignin loading in the composite had a positive influence on thermal stability. Likewise, Shore D hardness assays exhibited an increase from 25 to 69 when 5 and 20 wt.% lignin was used respectively. In this same sense, the contact angle (water) measurement showed that the LEBA15 and LEBA20 composites presented hydrophobic properties (whit contact angle above 90°) despite having the highest amount of lignin, demonstrating that the interaction of the polymer chains with the –OH groups of lignin was the main mechanism in the composites interaction. Full article

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13 pages, 6141 KiB

Open AccessArticle

Synthesis of Poly(N-vinylpyrrolidone)-Based Polymer Bottlebrushes by ATRPA and RAFT Polymerization: Toward Drug Delivery Application

by Yi-Shen Huang, Jem-Kun Chen, Shiao-Wei Kuo, Ya-An Hsieh, Shota Yamamoto, Jun Nakanishi and Chih-Feng Huang

Polymers 2019, 11(6), 1079; https://doi.org/10.3390/polym11061079 - 22 Jun 2019

Cited by 19 | Viewed by 6445

Abstract

Atom transfer radical polyaddition (ATRPA) was utilized herein to synthesize a specific functional polyester. We conducted ATRPA of 4-vinylbenzyl 2-bromo-2-phenylacetate (VBBPA) inimer and successfully obtained a linear type poly(VBBPA) (PVBBPA) polyester with benzylic bromides along the backbone. To obtain a novel amphiphilic polymer [...] Read more.

Atom transfer radical polyaddition (ATRPA) was utilized herein to synthesize a specific functional polyester. We conducted ATRPA of 4-vinylbenzyl 2-bromo-2-phenylacetate (VBBPA) inimer and successfully obtained a linear type poly(VBBPA) (PVBBPA) polyester with benzylic bromides along the backbone. To obtain a novel amphiphilic polymer bottlebrush, however, the lateral ATRP chain extension of PVBBPA with N-vinyl pyrrolidone (NVP) met the problem of quantitative dimerization. By replacing the bromides to xanthate moieties efficiently, we thus observed a pseudo linear first order reversible addition–fragmentation chain transfer (RAFT) polymerization to obtain novel poly(4-vinylbenzyl-2-phenylacetate)-g-poly(NVP) (PVBPA-g-PNVP) amphiphilic polymer bottlebrushes. The critical micelle concentration (CMC) and particle size of the amphiphilic polymer bottlebrushes were characterized by fluorescence spectroscopy, dynamic light scattering (DLS), and scanning electron microscopy (SEM) (CMCs < 0.5 mg/mL; particle sizes = ca. 100 nm). Toward drug delivery application, we examined release profiles using a model drug of Nile red at different pH environments (3, 5, and 7). Eventually, low cytotoxicity and well cell uptake of the Madin-Darby Canine Kidney Epithelial (MDCK) for the polymer bottlebrush micelles were demonstrated. Full article

(This article belongs to the Special Issue Reversible-Deactivation Radical Polymerization)

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12 pages, 1359 KiB

Open AccessArticle

Nonisothermal Crystallization Kinetics of Acetylated Bamboo Fiber-Reinforced Polypropylene Composites

by Yu-Shan Jhu, Teng-Chun Yang, Ke-Chang Hung, Jin-Wei Xu, Tung-Lin Wu and Jyh-Horng Wu

Polymers 2019, 11(6), 1078; https://doi.org/10.3390/polym11061078 - 22 Jun 2019

Cited by 22 | Viewed by 3913

Abstract

The crystallization behavior of bamboo fiber (BF) reinforced polypropylene (PP) composites (BPCs) was investigated using a differential scanning calorimeter (DSC). The results showed that unmodified BF as a nucleation agent accelerated the crystallization rate of the PP matrix during cooling whereas there is [...] Read more.

The crystallization behavior of bamboo fiber (BF) reinforced polypropylene (PP) composites (BPCs) was investigated using a differential scanning calorimeter (DSC). The results showed that unmodified BF as a nucleation agent accelerated the crystallization rate of the PP matrix during cooling whereas there is no significant effect on the improved crystallization rate in BPCs with acetylated BFs. Based on the Avrami method, Avrami–Ozawa method, and Friedman method, the corresponding crystallization kinetics of PP reinforced with different acetylation levels of BFs were further analyzed. The results demonstrated that the crystal growth mechanism of the PP matrix for BPCs with unmodified and various acetylated BFs exhibited tabular crystal growth with heterogeneous nucleation. A higher cooling rate is required to achieve a certain relative crystallinity degree at the unit crystallization time for BPCs with a higher weight percent gain (WPG) of acetylated BFs (WPG >13%). Furthermore, based on the Friedman method, the lowest crystallization activation energy was observed for the BPCs with 19% WPG of acetylated BFs. Full article

(This article belongs to the Special Issue Wood Plastic Composites)

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12 pages, 5169 KiB

Open AccessArticle

Nonisothermal Crystallization of Surface-Treated Alumina and Aluminum Nitride-Filled Polylactic Acid Hybrid Composites

by Zelalem Lule and Jooheon Kim

Polymers 2019, 11(6), 1077; https://doi.org/10.3390/polym11061077 - 21 Jun 2019

Cited by 9 | Viewed by 4189

Abstract

This work investigates the nonisothermal crystallization and melting behavior of polylactic acid (PLA), filled with treated and untreated alumina and nano-aluminum nitride hybrid composites. Analysis by attenuated total reflectance Fourier transform infrared spectroscopy revealed that the treated fillers and the PLA matrix developed [...] Read more.

This work investigates the nonisothermal crystallization and melting behavior of polylactic acid (PLA), filled with treated and untreated alumina and nano-aluminum nitride hybrid composites. Analysis by attenuated total reflectance Fourier transform infrared spectroscopy revealed that the treated fillers and the PLA matrix developed a good interaction. The crystallization and melting behaviors of the PLA hybrid composites were investigated using differential scanning calorimetry showed that the degree of crystallinity increased with the addition of hybrid fillers. Unlike the untreated PLA composites, the complete crystallization of the treated PLA hybrid composites hindered cold crystallization during the second heating cycle. The crystallization kinetics studied using the Avrami model indicated that the crystallization rate of PLA was affected by the inclusion of filler particles. X-ray diffraction analysis confirmed crystal formation with the incorporation of filler particles. The inclusion of nano-aluminum nitride (AlN) and the increase in the crystallinity led to an improvement of the storage modulus. Full article

(This article belongs to the Special Issue Thermal Analysis of Polymer Materials)

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Full article ">Figure 1
(a) FTIR spectra of the raw and treated alumina; (b) Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) of the polylactic acid (PLA) composites. Full article ">Figure 2
Crystallization thermographs of neat and hybrid composites: the effects of filler loading at cooling rates of (a) 5 °C/min, (b) 10 °C/min, and (c) 20 °C/min and the effects of filler treatment at cooling rates of (d) 5 °C/min, (e) 10 °C/min, and (f) 20 °C/min. Full article ">Figure 3
Relative crystallinity curve as a function of temperature: (a) neat PLA and (b) T-PLA50. Full article ">Figure 4
Cold crystallization and melting thermographs of neat and hybrid composites: effect of filler loading at heating rates of (a) 5 °C/min, (b) 10 °C/min, and (c) 20 °C/min; effect of filler treatment at heating rates of (d) 5 °C/min, (e) 10 °C/min, and (f) 20 °C/min. Full article ">Figure 5
Avrami curves for (a) neat PLA; (b) PLA40; and (c) T-PLA40. Full article ">Figure 6
XRD patterns of the alumina and the PLA composites. Full article ">Figure 7
Storage modulus as a function of temperature at different frequencies. Full article ">

23 pages, 5735 KiB

Open AccessArticle

Computer Simulation of Anisotropic Polymeric Materials Using Polymerization-Induced Phase Separation under Combined Temperature and Concentration Gradients

by Shima Ghaffari, Philip K. Chan and Mehrab Mehrvar

Polymers 2019, 11(6), 1076; https://doi.org/10.3390/polym11061076 - 21 Jun 2019

Cited by 10 | Viewed by 3865

Abstract

In this study, the self-condensation polymerization of a tri-functional monomer in a monomer-solvent mixture and the phase separation of the system were simultaneously modeled and simulated. Nonlinear Cahn–Hilliard and Flory–Huggins free energy theories incorporated with the kinetics of the polymerization reaction were utilized [...] Read more.

In this study, the self-condensation polymerization of a tri-functional monomer in a monomer-solvent mixture and the phase separation of the system were simultaneously modeled and simulated. Nonlinear Cahn–Hilliard and Flory–Huggins free energy theories incorporated with the kinetics of the polymerization reaction were utilized to develop the model. Linear temperature and concentration gradients singly and in combination were applied to the system. Eight cases which faced different ranges of initial concentration and/or temperature gradients in different directions, were studied. Various anisotropic structural morphologies were achieved. The numerical results were in good agreement with published data. The size analysis and structural characterization of the phase-separated system were also carried out using digital imaging software. The results showed that the phase separation occurred earlier in the section with a higher initial concentration and/or temperature, and, at a given time, the average equivalent diameter of the droplets <d_ave> was larger in this region. While smaller droplets formed later in the lower concentration/temperature regions, at the higher concentration/temperature side, the droplets went through phase separation longer, allowing them to reach the late stage of the phase separation where particles coarsened. In the intermediate stage of phase separation, <d_ave> was found proportional to

t^{* α}

, where

α

was in the range between

\frac{1}{3}

and

\frac{1}{2}

for the cases studied and was consistent with published results. Full article

(This article belongs to the Special Issue Thermodynamics of Polymer/Solvent Systems)

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13 pages, 4222 KiB

Open AccessArticle

Tensile and Interfacial Loading Characteristics of Boron Nitride-Carbon Nanosheet Reinforced Polymer Nanocomposites

by Venkatesh Vijayaraghavan and Liangchi Zhang

Polymers 2019, 11(6), 1075; https://doi.org/10.3390/polym11061075 - 21 Jun 2019

Cited by 15 | Viewed by 4326

Abstract

The discovery of hybrid boron nitride–carbon (BN–C) nanostructures has triggered enormous research interest in the design and fabrication of new generation nanocomposites. The robust design of these nanocomposites for target applications requires their mechanical strength to be characterized with a wide range of [...] Read more.

The discovery of hybrid boron nitride–carbon (BN–C) nanostructures has triggered enormous research interest in the design and fabrication of new generation nanocomposites. The robust design of these nanocomposites for target applications requires their mechanical strength to be characterized with a wide range of factors. This article presents a comprehensive study, with the aid of molecular dynamics analysis, of the tensile loading mechanics of BN–C nanosheet reinforced polyethylene (PE) nanocomposites. It is observed that the geometry and lattice arrangement of the BN–C nanosheet influences the tensile loading characteristics of the nanocomposites. Furthermore, defects in the nanosheet can severely impact the tensile loading resistance, the extent of which is determined by the defect’s location. This study also found that the tensile loading resistance of nanocomposites tends to weaken at elevated temperatures. The interfacial mechanics of the BN–C nanocomposites are also investigated. This analysis revealed a strong dependency with the carbon concentration in the BN–C nanosheet. Full article

(This article belongs to the Special Issue Synthesis–Processing–Structure–Property Interrelationship of Multifunctional Polymer Nanocomposites)

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20 pages, 4275 KiB

Open AccessArticle

Radial Basis Function Neural Network-Based Modeling of the Dynamic Thermo-Mechanical Response and Damping Behavior of Thermoplastic Elastomer Systems

by Ivan Kopal, Marta Harničárová, Jan Valíček, Jan Krmela and Ondrej Lukáč

Polymers 2019, 11(6), 1074; https://doi.org/10.3390/polym11061074 - 21 Jun 2019

Cited by 34 | Viewed by 4297

Abstract

The presented work deals with the creation of a new radial basis function artificial neural network-based model of dynamic thermo-mechanical response and damping behavior of thermoplastic elastomers in the whole temperature interval of their entire lifetime and a wide frequency range of dynamic [...] Read more.

The presented work deals with the creation of a new radial basis function artificial neural network-based model of dynamic thermo-mechanical response and damping behavior of thermoplastic elastomers in the whole temperature interval of their entire lifetime and a wide frequency range of dynamic mechanical loading. The created model is based on experimental results of dynamic mechanical analysis of the widely used thermoplastic polyurethane, which is one of the typical representatives of thermoplastic elastomers. Verification and testing of the well-trained radial basis function neural network for temperature and frequency dependence of dynamic storage modulus, loss modulus, as well as loss tangent prediction showed excellent correspondence between experimental and modeled data, including all relaxation events observed in the polymeric material under study throughout the monitored temperature and frequency interval. The radial basis function artificial neural network has been confirmed to be an exceptionally high-performance artificial intelligence tool of soft computing for the effective predicting of short-term viscoelastic behavior of thermoplastic elastomer systems based on experimental results of dynamic mechanical analysis. Full article

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

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Diagram of the RBF-ANN structure for DMA multi-frequency spectrum prediction. Full article ">Figure 2
Temperature-frequency dependences of average storage modulus, loss modulus and loss tangent of TPU over the temperature range from 146 K to 527 K at constant strain rate of 0.1 Hz and frequencies of 0.5 Hz, 1 Hz, 2 Hz, 5 Hz and 10 Hz. Full article ">Figure 3
Performance plot of training RBF-ANN. Full article ">Figure 4
(a) Linear regression plot for training data; (b) Linear regression plot for validation data; (c) Linear regression plot for testing data. Full article ">Figure 5
(a) Comparison of the training target with simulated training outputs for E′(T, f); (b) Comparison of the training target with simulated training outputs for E″(T, f); (c) Comparison of the training target with simulated training outputs for tanδ(T, f). Full article ">Figure 5 Cont.
(a) Comparison of the training target with simulated training outputs for E′(T, f); (b) Comparison of the training target with simulated training outputs for E″(T, f); (c) Comparison of the training target with simulated training outputs for tanδ(T, f). Full article ">Figure 6
(a) Comparison of the validation targets with validation outputs for E′(T, f); (b) Comparison of the validation targets with validation outputs for E″(T, f); (c) Comparison of the validation targets with validation outputs for tanδ(T, f). Full article ">Figure 6 Cont.
(a) Comparison of the validation targets with validation outputs for E′(T, f); (b) Comparison of the validation targets with validation outputs for E″(T, f); (c) Comparison of the validation targets with validation outputs for tanδ(T, f). Full article ">Figure 7
(a) Comparison of the testing targets with testing outputs for E′(T, f); (b) Comparison of the testing targets with testing outputs for E″(T, f); (c) Comparison of the testing targets with testing outputs for tanδ(T, f). Full article ">Figure 7 Cont.
(a) Comparison of the testing targets with testing outputs for E′(T, f); (b) Comparison of the testing targets with testing outputs for E″(T, f); (c) Comparison of the testing targets with testing outputs for tanδ(T, f). Full article ">Figure 8
(a) Error plot for training data; (b) Error plot for validation data; (c) Error plot for testing data. Full article ">

15 pages, 1575 KiB

Open AccessEditor’s ChoiceArticle

Thermal Conductivity and Electrical Resistivity of Melt-Mixed Polypropylene Composites Containing Mixtures of Carbon-Based Fillers

by Beate Krause, Piotr Rzeczkowski and Petra Pötschke

Polymers 2019, 11(6), 1073; https://doi.org/10.3390/polym11061073 - 21 Jun 2019

Cited by 49 | Viewed by 7020

Abstract

Melt-mixed composites based on polypropylene (PP) with various carbon-based fillers were investigated with regard to their thermal conductivity and electrical resistivity. The composites were filled with up to three fillers by selecting combinations of graphite nanoplatelets (GNP), carbon fibers (CF), carbon nanotubes (CNT), [...] Read more.

Melt-mixed composites based on polypropylene (PP) with various carbon-based fillers were investigated with regard to their thermal conductivity and electrical resistivity. The composites were filled with up to three fillers by selecting combinations of graphite nanoplatelets (GNP), carbon fibers (CF), carbon nanotubes (CNT), carbon black (CB), and graphite (G) at a constant filler content of 7.5 vol%. The thermal conductivity of PP (0.26 W/(m·K)) improved most using graphite nanoplatelets, whereas electrical resistivity was the lowest when using multiwalled CNT. Synergistic effects could be observed for different filler combinations. The PP composite, which contains a mixture of GNP, CNT, and highly structured CB, simultaneously had high thermal conductivity (0.5 W/(m·K)) and the lowest electrical volume resistivity (4 Ohm·cm). Full article

(This article belongs to the Special Issue Synthesis–Processing–Structure–Property Interrelationship of Multifunctional Polymer Nanocomposites)

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12 pages, 1882 KiB

Open AccessArticle

Anisotropy of Thin Foils Obtained from Microwave-Irradiated Poly(Vinyl Alcohol) Aqueous Solutions

by Cristina-Delia Nechifor, Magdalena Aflori and Dana-Ortansa Dorohoi

Polymers 2019, 11(6), 1072; https://doi.org/10.3390/polym11061072 - 21 Jun 2019

Cited by 6 | Viewed by 3022

Abstract

In this paper, poly(vinyl alcohol) (PVA) foils of comparable thickness were obtained by using 10 wt % PVA aqueous solutions exposed to microwave (MW) radiations for different times. The main goal of this paper is to identify the effects of MW irradiation on [...] Read more.

In this paper, poly(vinyl alcohol) (PVA) foils of comparable thickness were obtained by using 10 wt % PVA aqueous solutions exposed to microwave (MW) radiations for different times. The main goal of this paper is to identify the effects of MW irradiation on the induced optical birefringence of PVA stretched foils, since it is known that the changes in the chemical and physical properties of polymers induced by radiations can influence the asymmetry of their molecular structures from which the birefringence of polymers derives. The efficiency of the MW oven was estimated, and the contribution of sensible and latent heat and heat loss to the absorbed energy was discussed. The effects of MW irradiation, in terms of absorbed energy, were evidenced by using FTIR spectra analysis, contact angle measurements, scanning electron microscopy (SEM) images, and induced optical birefringence. The dehydration (cross-linking) of PVA in aqueous solution and the dependence of the anisotropy on the absorbed MW energy, stretching ratio, and the type of hydrogen bonds formed are discussed in this study. Full article

(This article belongs to the Special Issue Radiation Polymers)

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16 pages, 5004 KiB

Open AccessArticle

Integration of Polypyrrole Electrode into Piezoelectric PVDF Energy Harvester with Improved Adhesion and Over-Oxidation Resistance

by Kyungha Baik, Sohyun Park, Changsang Yun and Chung Hee Park

Polymers 2019, 11(6), 1071; https://doi.org/10.3390/polym11061071 - 21 Jun 2019

Cited by 8 | Viewed by 4831

Abstract

Smart textiles for wearable devices require flexibility and a lightweight, so in this study, a soft polypyrrole (PPy) electrode system was integrated into a piezoelectric polyvinylidenefluoride (PVDF) energy harvester. The PVDF energy harvester integrated with a PPy electrode had the piezoelectric output voltage [...] Read more.

Smart textiles for wearable devices require flexibility and a lightweight, so in this study, a soft polypyrrole (PPy) electrode system was integrated into a piezoelectric polyvinylidenefluoride (PVDF) energy harvester. The PVDF energy harvester integrated with a PPy electrode had the piezoelectric output voltage of 4.24–4.56 V, while the PVDF energy harvester with an additional aluminum-foil electrode exhibited 2.57 V. Alkaline treatment and chemical vapor deposition with n-dodecyltrimethoxysilane (DTMS) were employed to improve the adhesion between the PVDF and PPy and the resistance to over-oxidation in aqueous solutions. The PVDF film modified by an alkaline treatment could have the improved adhesion via the introduction of polar functional groups to its surface, which was confirmed by the ultrasonication. The surface hydrophobicity of the PPy electrode was enhanced by the DTMS coating, resulting in the improvement of the resistance to over-oxidation with a water contact angle of 111°. Even with the hydrophobic coating, the electrodes remained electroconductive and continued to transfer an electric charge, maintaining the piezoelectricity of the PVDF film. The developed electrode-integrated energy harvester is expected to be applied to smart textiles because it offers the advantages of efficient piezoelectric generation, flexibility, and durability. Full article

(This article belongs to the Special Issue Innovative Functional Textiles)

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12 pages, 2701 KiB

Open AccessArticle

Ionic Porous Organic Polymers Based on Functionalized Tetraarylborates

by Patryk Tomaszewski, Marcin Wiszniewski, Krzysztof Gontarczyk, Piotr Wieciński, Krzysztof Durka and Sergiusz Luliński

Polymers 2019, 11(6), 1070; https://doi.org/10.3390/polym11061070 - 21 Jun 2019

Cited by 4 | Viewed by 4383

Abstract

Lithium tetrakis(4-boronatoaryl)borates were subjected to polycondensation reactions with selected polyhydroxyl monomers such as 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and 2,3,6,7-tetrahydroxy-9,10-dimethylanthracene (THDMA). Obtained boronate-type ionic porous polymers TAB1–4 were characterized by PXRD, ⁶Li and ¹¹B magic-angle spinning nuclear magnetic resonance (MAS NMR), FT-IR, SEM, and [...] Read more.

Lithium tetrakis(4-boronatoaryl)borates were subjected to polycondensation reactions with selected polyhydroxyl monomers such as 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and 2,3,6,7-tetrahydroxy-9,10-dimethylanthracene (THDMA). Obtained boronate-type ionic porous polymers TAB1–4 were characterized by PXRD, ⁶Li and ¹¹B magic-angle spinning nuclear magnetic resonance (MAS NMR), FT-IR, SEM, and TGA. They exhibit relatively good sorption of H₂ (up to 75 cm³/g STP), whereas N₂ uptake at 77 K for lower pressure range is relatively poor (up to 50 cm³/g STP below P/P₀ = 0.8). In addition, the effect of elongation of aryl arms in the tetraarylborate core on the materials’ properties was studied. Thus, it was found that replacement of the 4-boronatophenyl with 4-boronatobiphenylyl group has a negative impact on the sorption characteristics. Full article

(This article belongs to the Special Issue Covalent Organic Frameworks (COFs) and Related Porous Organic Materials)

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Full article ">Figure 1
SEM images of TAB1–4. Full article ">Figure 2
6Li (a) and 11B (b) magic-angle spinning nuclear magnetic resonance (MAS NMR) spectra of TAB1. Full article ">Figure 3
N2 (a) and H2 (b) sorption isotherms @77 K for materials TAB1–4. Full article ">Figure 4
Pore size distribution (NLDFT model) for TAB1–4 based on N2@77K sorption data. Full article ">Figure 5
CO2 (a) and CH4 (b) sorption isotherms @273 K for materials TAB1–4. Full article ">Scheme 1
Structures of polyhydroxyl precursors. Full article ">Scheme 2
Synthesis of tetraarylborate precursors 1 and 2. Full article ">Scheme 3
Basic structural motifs of materials TAB1–4. Full article ">

14 pages, 4378 KiB

Open AccessArticle

Poly(furfuryl alcohol)-Polycaprolactone Blends

by Gabriele Nanni, José A. Heredia-Guerrero, Uttam C. Paul, Silvia Dante, Gianvito Caputo, Claudio Canale, Athanassia Athanassiou, Despina Fragouli and Ilker S. Bayer

Polymers 2019, 11(6), 1069; https://doi.org/10.3390/polym11061069 - 20 Jun 2019

Cited by 26 | Viewed by 8178

Abstract

Poly(furfuryl alcohol) (PFA) is a bioresin synthesized from furfuryl alcohol (FA) that is derived from renewable saccharide-rich biomass. In this study, we compounded this bioresin with polycaprolactone (PCL) for the first time, introducing new functional polymer blends. Although PCL is biodegradable, its production [...] Read more.

Poly(furfuryl alcohol) (PFA) is a bioresin synthesized from furfuryl alcohol (FA) that is derived from renewable saccharide-rich biomass. In this study, we compounded this bioresin with polycaprolactone (PCL) for the first time, introducing new functional polymer blends. Although PCL is biodegradable, its production relies on petroleum precursors such as cyclohexanone oils. With the method proposed herein, this dependence on petroleum-derived precursors/monomers is reduced by using PFA without significantly modifying some important properties of the PCL. Polymer blend films were produced by simple solvent casting. The blends were characterized in terms of surface topography by atomic force microscopy (AFM), chemical interactions between PCL and PFA by attenuated total reflection-Fourier transform infrared (ATR-FTIR), crystallinity by XRD, thermal properties by differential scanning calorimetry (DSC), and mechanical properties by tensile tests and biocompatibility by direct and indirect toxicity tests. PFA was found to improve the gas barrier properties of PCL without compromising its mechanical properties, and it demonstrated sustained antioxidant effect with excellent biocompatibility. Our results indicate that these new blends can be potentially used in diverse applications ranging from food packing to biomedical devices. Full article

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(a) Photographs of polymer solutions of polycaprolactone (PCL) and poly(furfuryl alcohol) (PFA) resin dissolved in dichloromethane (DCM) containing different PFA concentrations; (b) photographs of the blend films obtained after casting the solutions and drying. The films have a thickness of approximately 100 μm and a diameter of 3 cm. Atomic force microscopy (AFM) images and 3D rendering of (c) a PCL film and (d) a 50/50 blend film. The AFM images are 10 μm × 10 μm in size. Full article ">Figure 2
Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectra of pure PCL and PFA resin as well as blend films. The band assignments of PCL (black) and PFA (red) as well as the chemical structures of both substances are included. Full article ">Figure 3
(a) Melting temperature and percent crystallinity for PCL and different PCL/PFA blends measured by DSC and XRD, respectively. Mass loss curves (b) and derivatives of each curve (c) for PFA, PCL and different PCL/PFA blends measured by TGA. Full article ">Figure 4
Representative stress-strain curves (a), elastic modulus (b), and elongation at break (c) of neat PCL and blends at different PCL/PFA proportions. Full article ">Figure 5
Confocal images of CHO cells growing on 50/50 PCL/PFA (a) and 70/30 PCL/PFA (b). Nuclei are labeled with DAPI (4′,6-Diamidino-2-phenylindole dihydrochloride, blue) and cytoskeleton is labeled with Alexa-Fluor Phalloidin (green). The cells morphology is healthy. The real-time proliferation curves are displayed in panel (c). On PCL/PFA, cells reached confluence after 48 h. The growth rate decreased compared to control, where cells built multilayers (see <a href="#app1-polymers-11-01069" class="html-app">Figure S2</a>), as the multistep curve indicates. Full article ">Figure 6
(a) Change in the absorption spectra upon reaction of 2,2-diphenyl-1-picrylhydrazyl (DPPH•) with a 70/30 sample. (b) Loss of the characteristic deep violet color of the DPPH• solution after being in contact with different samples for 24 h. (c) Radical scavenging activity of PCL and PCL/PFA blends tested against DPPH• in a spectrophotometric assay. Full article ">Figure 7
Oxygen transmission rate of neat PCL and PCL/PFA blends in 95/5, 90/10, 70/30 and 50/50 proportions. Full article ">Scheme 1
Thermal degradation mechanisms of PCL (top panel). Reproduced with permission from American Chemical Society [<a href="#B36-polymers-11-01069" class="html-bibr">36</a>]. Thermal degradation mechanisms of PFA (bottom panel). Reproduced with permission from Elsevier [<a href="#B35-polymers-11-01069" class="html-bibr">35</a>]. Full article ">

11 pages, 2989 KiB

Open AccessArticle

Extended 2,2′-Bipyrroles: New Monomers for Conjugated Polymers with Tailored Processability

by Robert Texidó, Gonzalo Anguera, Sergi Colominas, Salvador Borrós and David Sánchez-García

Polymers 2019, 11(6), 1068; https://doi.org/10.3390/polym11061068 - 20 Jun 2019

Cited by 8 | Viewed by 3514

Abstract

The synthesis of 2,2′-bipyrroles substituted at positions 5,5′ with pyrrolyl, N-methyl-pyrrolyl and thienyl groups and their application in the preparation of conducting polymers is reported herein. The preparation of these monomers consisted of two synthetic steps from a functionalized 2,2′-bipyrrole: Bromination of [...] Read more.

The synthesis of 2,2′-bipyrroles substituted at positions 5,5′ with pyrrolyl, N-methyl-pyrrolyl and thienyl groups and their application in the preparation of conducting polymers is reported herein. The preparation of these monomers consisted of two synthetic steps from a functionalized 2,2′-bipyrrole: Bromination of the corresponding 2,2′-bipyrrole followed by Suzuki or Stille couplings. These monomers display low oxidation potential compared to pyrrole because of the extended length of their conjugation pathway. The resulting monomers can be polymerized through oxidative/electropolymerization. Electrical conductivity and electrochromic properties of the electrodeposited polymeric films were evaluated using 4-point probe measurements and cyclic voltammetry to evaluate their applicability in electronics. Full article

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Structures of 2,2′-bipyrroles 1a–c. Full article ">Figure 2
Synthesis of 2,2′-bipyrroles 1a–c (G = 2-pyrrolyl, 2-(N-methylpyrrolyl) and 2-thienyl, R = Et). Full article ">Figure 3
Cyclic voltammograms of 2,2′–bipyrrole monomers in THF (10 mM) + 0.1 M TBAP. The voltammograms correspond to 1b (a), 1c (b), and 1a (c). Working electrode during quaterpyrrole electropolymerization (d) (R = Et). Full article ">Figure 4
2,2′-Bipyrrole oligomers in the cyclic voltammetry media after 100 cycles shown by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) spectrometry: 1c (a) and quaterpyrroles 1a and 1b (b,c) (R = Et). Full article ">Figure 5
FE-SEM images of 1c (a,c) and 1b (b,d). Full article ">Figure 6
Monomer free voltammograms of 1b (a) and 1c (b). Electrochromic behavior of the films observed during the cyclic voltammetry of 1b (c) and 1c (d) (R = Et). Full article ">

8 pages, 1674 KiB

Open AccessArticle

Preparation of Zirconia Nanofibers by Electrospinning and Calcination with Zirconium Acetylacetonate as Precursor

by Vyacheslav V. Rodaev, Svetlana S. Razlivalova, Andrey O. Zhigachev, Vladimir M. Vasyukov and Yuri I. Golovin

Polymers 2019, 11(6), 1067; https://doi.org/10.3390/polym11061067 - 20 Jun 2019

Cited by 21 | Viewed by 4639

Abstract

For the first time, zirconia nanofibers with an average diameter of about 75 nm have been fabricated by calcination of electrospun zirconium acetylacetonate/polyacrylonitrile fibers in the range of 500–1100 °C. Composite and ceramic filaments have been characterized by scanning electron microscopy, thermogravimetric analysis, [...] Read more.

For the first time, zirconia nanofibers with an average diameter of about 75 nm have been fabricated by calcination of electrospun zirconium acetylacetonate/polyacrylonitrile fibers in the range of 500–1100 °C. Composite and ceramic filaments have been characterized by scanning electron microscopy, thermogravimetric analysis, nitrogen adsorption analysis, energy-dispersive X-ray spectroscopy, and X-ray diffractometry. The stages of the transition of zirconium acetylacetonate to zirconia have been revealed. It has been found out that a rise in calcination temperature from 500 to 1100 °C induces transformation of mesoporous tetragonal zirconia nanofibers with a high specific surface area (102.3 m²/g) to non-porous monoclinic zirconia nanofibers of almost the same diameter with a low value of specific surface area (8.3 m²/g). The tetragonal zirconia nanofibers with high specific surface area prepared at 500 °C can be considered, for instance, as promising supports for heterogeneous catalysts, enhancing their activity. Full article

(This article belongs to the Special Issue Electrospun Nanofibers: Theory and Its Applications)

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18 pages, 1681 KiB

Open AccessEditor’s ChoiceReview

Microbial Degradation of Synthetic Biopolymers Waste

by Valentina Siracusa

Polymers 2019, 11(6), 1066; https://doi.org/10.3390/polym11061066 - 20 Jun 2019

Cited by 177 | Viewed by 15943

Abstract

Over the last ten years, the demand of biodegradable polymers has grown at an annual rate of 20–30%. However, the market share is about less than 0.1% of the total plastic production due to their lower performances, higher price and limited legislative attention [...] Read more.

Over the last ten years, the demand of biodegradable polymers has grown at an annual rate of 20–30%. However, the market share is about less than 0.1% of the total plastic production due to their lower performances, higher price and limited legislative attention in respect to the standard materials. The biodegradability as a functional added property is often not completely perceived from the final consumers. However, the opportunity to use renewable resources and to reduce the dependency from petroleum resources could become an incentive to accelerate their future growth. Renewable raw materials, coming from industrial wastes such as oilseed crops, starch from cereals and potatoes, cellulose from straw and wood, etc., can be converted into chemical intermediates and polymers, in order to substitute fossil fuel feedstock. The introduction of these new products could represent a significant contribution to sustainable development. However, the use of renewable resources and the production of the bioplastics are no longer a guarantee for a minimal environmental impact. The production process as well as their technical performances and their ultimate disposal has to be carefully considered. Bioplastics are generally biodegradable, but the diffusion of the composting technology is a prerequisite for their development. Efforts are required at industry level in order to develop less expensive and high performance products, with minimal environmental impact technologies. Full article

(This article belongs to the Special Issue Biopolymer Modifications and Characterization)

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17 pages, 4710 KiB

Open AccessArticle

Piezoelectric Response in Hybrid Micropillar Arrays of Poly(Vinylidene Fluoride) and Reduced Graphene Oxide

by Igor O. Pariy, Anna A. Ivanova, Vladimir V. Shvartsman, Doru C. Lupascu, Gleb B. Sukhorukov, Tim Ludwig, Ausrine Bartasyte, Sanjay Mathur, Maria A. Surmeneva and Roman A. Surmenev

Polymers 2019, 11(6), 1065; https://doi.org/10.3390/polym11061065 - 20 Jun 2019

Cited by 32 | Viewed by 4995

Abstract

This study was dedicated to the investigation of poly(vinylidene fluoride) (PVDF) micropillar arrays obtained by soft lithography followed by phase inversion at a low temperature. Reduced graphene oxide (rGO) was incorporated into the PVDF as a nucleating filler. The piezoelectric properties of the [...] Read more.

This study was dedicated to the investigation of poly(vinylidene fluoride) (PVDF) micropillar arrays obtained by soft lithography followed by phase inversion at a low temperature. Reduced graphene oxide (rGO) was incorporated into the PVDF as a nucleating filler. The piezoelectric properties of the PVDF-rGO composite micropillars were explored via piezo-response force microscopy (PFM). Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) showed that α, β, and γ phases co-existed in all studied samples, with a predominance of the γ phase. The piezoresponse force microscopy (PFM) data provided the local piezoelectric response of the PVDF micropillars, which exhibited a temperature-induced downward dipole orientation in the pristine PVDF micropillars. The addition of rGO into the PVDF matrix resulted in a change in the preferred polarization direction, and the piezo-response phase angle changed from −120° to 20°–40°. The pristine PVDF and PVDF loaded with 0.1 wt % of rGO after low-temperature quenching were found to possess a piezoelectric response of 86 and 87 pm/V respectively, which are significantly higher than the |d₃₃^eff| in the case of imprinted PVDF 64 pm/V. Thus, the addition of rGO significantly affected the domain orientation (polarization) while quenching increased the piezoelectric response. Full article

(This article belongs to the Special Issue Micro- and Nano-Fabrication Approaches for Polymers)

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14 pages, 1965 KiB

Open AccessArticle

Carbon Nanotube versus Graphene Nanoribbon: Impact of Nanofiller Geometry on Electromagnetic Interference Shielding of Polyvinylidene Fluoride Nanocomposites

by Mohammad Arjmand, Soheil Sadeghi, Ivonne Otero Navas, Yalda Zamani Keteklahijani, Sara Dordanihaghighi and Uttandaraman Sundararaj

Polymers 2019, 11(6), 1064; https://doi.org/10.3390/polym11061064 - 20 Jun 2019

Cited by 32 | Viewed by 5162

Abstract

The similar molecular structure but different geometries of the carbon nanotube (CNT) and graphene nanoribbon (GNR) create a genuine opportunity to assess the impact of nanofiller geometry (tube vs. ribbon) on the electromagnetic interference (EMI) shielding of polymer nanocomposites. In this regard, GNR [...] Read more.

The similar molecular structure but different geometries of the carbon nanotube (CNT) and graphene nanoribbon (GNR) create a genuine opportunity to assess the impact of nanofiller geometry (tube vs. ribbon) on the electromagnetic interference (EMI) shielding of polymer nanocomposites. In this regard, GNR and its parent CNT were melt mixed with a polyvinylidene fluoride (PVDF) matrix using a miniature melt mixer at various nanofiller loadings, i.e., 0.3, 0.5, 1.0 and 2.0 wt%, and then compression molded. Molecular simulations showed that CNT would have a better interaction with the PVDF matrix in any configuration. Rheological results validated that CNTs feature a far stronger network (mechanical interlocking) than GNRs. Despite lower powder conductivity and a comparable dispersion state, it was interestingly observed that CNT nanocomposites indicated a highly superior electrical conductivity and EMI shielding at higher nanofiller loadings. For instance, at 2.0 wt%, CNT/PVDF nanocomposites showed an electrical conductivity of 0.77 S·m⁻¹ and an EMI shielding effectiveness of 11.60 dB, which are eight orders of magnitude and twofold higher than their GNR counterparts, respectively. This observation was attributed to their superior conductive network formation and the interlocking ability of the tubular nanostructure to the ribbon-like nanostructure, verified by molecular simulations and rheological assays. Full article

(This article belongs to the Special Issue Synthesis–Processing–Structure–Property Interrelationship of Multifunctional Polymer Nanocomposites)

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Full article ">Figure 1
Optimized geometries of (a) β- polyvinylidene fluoride (PVDF), (b) α-PVDF, (c) graphene nanoribbon (GNR), and (d) carbon nanotube (CNT). Initial and optimized structures of (e–h) GNR/PVDF (left side) and (i–l) CNT/PVDF (right side). The atoms in black, blue and orange correspond to carbon, hydrogen, and fluorine, respectively. Full article ">Figure 2
(a) Frequency dependence of the absolute magnitude of complex viscosity, (b) normalized out-of-phase component of complex viscosity <math display="inline"><semantics> <mrow> <mfrac> <mrow> <msup> <mi>η</mi> <mo>″</mo> </msup> </mrow> <mrow> <msub> <mi>η</mi> <mn>0</mn> </msub> </mrow> </mfrac> </mrow> </semantics></math> plotted as a function of reduced frequency <math display="inline"><semantics> <mrow> <msub> <mi>λ</mi> <mn>0</mn> </msub> <mi>ω</mi> </mrow> </semantics></math> for GNR/PVDF nanocomposites and (c) frequency dependence of the absolute magnitude of complex viscosity and (d) normalized out-of-phase component of complex viscosity <math display="inline"><semantics> <mrow> <mfrac> <mrow> <msup> <mi>η</mi> <mo>″</mo> </msup> </mrow> <mrow> <msub> <mi>η</mi> <mn>0</mn> </msub> </mrow> </mfrac> </mrow> </semantics></math> plotted as a function of reduced frequency <math display="inline"><semantics> <mrow> <msub> <mi>λ</mi> <mn>0</mn> </msub> <mi>ω</mi> </mrow> </semantics></math> for CNT/PVDF nanocomposites. All measurements were performed at a strain amplitude of <math display="inline"><semantics> <mrow> <msub> <mi>γ</mi> <mn>0</mn> </msub> <mo>=</mo> </mrow> </semantics></math> 0.1% and <math display="inline"><semantics> <mrow> <mi>T</mi> <mo>=</mo> </mrow> </semantics></math> 240 °C. Solid lines in (a,c) are best fits obtained using a modified 5-parameter Carreau model (see text for details). Full article ">Figure 3
Stress dissipation upon application of a finite strain of γ = 10% for (a) CNT/PVDF and (b) GNR/PVDF nanocomposite samples at different concentrations at 240 °C. The stepper motor response time is 0.1 s. Full article ">Figure 4
(a) Electrical conductivity, (b) electromagnetic interference (EMI SE) and (c) imaginary permittivity over the X-band (8.2–12.4 GHz) of parent CNT and GNR nanocomposites. Full article ">Figure 5
Comparison of (a) shielding by reflection, (b) shielding by absorption and (c) total EMI SE of CNT/PVDF and GNR/PVDF nanocomposites. Full article ">

16 pages, 3326 KiB

Open AccessArticle

Dimensional Stability and Process Capability of an Industrial Component Injected with Recycled Polypropylene

by José Eduardo Galve, Daniel Elduque, Carmelo Pina, Isabel Clavería, Raquel Acero, Ángel Fernández and Carlos Javierre

Polymers 2019, 11(6), 1063; https://doi.org/10.3390/polym11061063 - 20 Jun 2019

Cited by 14 | Viewed by 4181

Abstract

The usage of recycled polymers for industrial purposes arises as one of the most promising methods of reducing environmental impact and costs associated with scrapping parts. This paper presents a systematic study of the dimensional stability of a raw and 100% recycled polypropylene [...] Read more.

The usage of recycled polymers for industrial purposes arises as one of the most promising methods of reducing environmental impact and costs associated with scrapping parts. This paper presents a systematic study of the dimensional stability of a raw and 100% recycled polypropylene subjected to realistic environmental conditions occurring along its working life. The component studied is an internal part of an induction hob assembly. Industrial samples manufactured with both materials, in the same mold, and in the same injection machine, are subjected to ejection conditions, storage conditions (50 °C), and extreme performance conditions (80 °C). Induced dimensional changes are registered and analyzed using a coordinate measuring machine, and a tactile sensing probe. To verify the process capability of the samples manufacturing, C_p and C_pk values are calculated to evaluate the suitability of the recycled material as an alternative. Results conclude that, although the use of recycled material implies slight differences in terms of dimensional stability due to the changes induced in the polymer structure, these differences are not significant enough to affect the injection process capability. Therefore, recycling arises as one effective method to reduce both overruns associated with the consumption of raw polypropylene material and its environmental impact. Full article

(This article belongs to the Special Issue Recycling of Polymers and Multiphase Polymer-Based Systems)

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17 pages, 7395 KiB

Open AccessEditor’s ChoiceArticle

Synthesis of a Novel Phosphorous-Nitrogen Based Charring Agent and Its Application in Flame-retardant HDPE/IFR Composites

by Junlei Chen, Jihui Wang, Aiqing Ni, Hongda Chen and Penglong Shen

Polymers 2019, 11(6), 1062; https://doi.org/10.3390/polym11061062 - 19 Jun 2019

Cited by 29 | Viewed by 4868

Abstract

In this work, a novel phosphorous–nitrogen based charring agent named poly(1,3-diaminopropane-1,3,5-triazine-o-bicyclic pentaerythritol phosphate) (PDTBP) was synthesized and used to improve the flame retardancy of high-density polyethylene (HDPE) together with ammonium polyphosphate (APP). The results of Fourier transform infrared spectroscopy (FTIR) and ¹³C [...] Read more.

In this work, a novel phosphorous–nitrogen based charring agent named poly(1,3-diaminopropane-1,3,5-triazine-o-bicyclic pentaerythritol phosphate) (PDTBP) was synthesized and used to improve the flame retardancy of high-density polyethylene (HDPE) together with ammonium polyphosphate (APP). The results of Fourier transform infrared spectroscopy (FTIR) and ¹³C solid-state nuclear magnetic resonance (NMR) showed that PDTBP was successfully synthesized. Compared with the traditional intumescent flame retardant (IFR) system contained APP and pentaerythritol (PER), the novel IFR system (APP/PDTBP, weight ratio of 2:1) could significantly promote the flame retardancy, water resistance, and thermal stability of HDPE. The HDPE/APP/PDTBP composites (PE3) could achieve a UL-94 V-0 rating with LOI value of 30.8%, and had a lower migration percentage (2.2%). However, the HDPE/APP/PER composites (PE5) had the highest migration percentage (4.7%), lower LOI value of 23.9%, and could only achieve a UL-94 V-1 rating. Besides, the peak of heat release rate (PHRR), total heat release (THR), and fire hazard value of PE3 were markedly decreased compared to PE5. PE3 had higher tensile strength and flexural strength of 16.27 ± 0.42 MPa and 32.03 ± 0.59 MPa, respectively. Furthermore, the possible flame-retardant mechanism of the APP/PDTBP IFR system indicated that compact and continuous intumescent char layer would be formed during burning, thus inhibiting the degradation of substrate material and improving the thermal stability of HDPE. Full article

(This article belongs to the Special Issue Thermal Insulating and Fire-Resistant Polymer Composites)

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21 pages, 3079 KiB

Open AccessEditor’s ChoiceReview

Selectively Biodegradable Polyesters: Nature-Inspired Construction Materials for Future Biomedical Applications

by Tomáš Urbánek, Eliézer Jäger, Alessandro Jäger and Martin Hrubý

Polymers 2019, 11(6), 1061; https://doi.org/10.3390/polym11061061 - 19 Jun 2019

Cited by 46 | Viewed by 6657

Abstract

In the last half-century, the development of biodegradable polyesters for biomedical applications has advanced significantly. Biodegradable polyester materials containing external stimuli-sensitive linkages are favored in the development of therapeutic devices for pharmacological applications such as delivery vehicles for controlled/sustained drug release. These selectively [...] Read more.

In the last half-century, the development of biodegradable polyesters for biomedical applications has advanced significantly. Biodegradable polyester materials containing external stimuli-sensitive linkages are favored in the development of therapeutic devices for pharmacological applications such as delivery vehicles for controlled/sustained drug release. These selectively biodegradable polyesters degrade after particular external stimulus (e.g., pH or redox potential change or the presence of certain enzymes). This review outlines the current development of biodegradable synthetic polyesters materials able to undergo hydrolytic or enzymatic degradation for various biomedical applications, including tissue engineering, temporary implants, wound healing and drug delivery. Full article

(This article belongs to the Special Issue Condensation Polymers and their Applications)

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14 pages, 1273 KiB

Open AccessArticle

Biotechnological Preparation of Gelatines from Chicken Feet

by Pavel Mokrejš, Petr Mrázek, Robert Gál and Jana Pavlačková

Polymers 2019, 11(6), 1060; https://doi.org/10.3390/polym11061060 - 18 Jun 2019

Cited by 25 | Viewed by 5648

Abstract

In the European Union (EU), about five tons of poultry by-product tissues are produced every year. Due to their high collagen content, they represent a significant raw material source for gelatine production. The aim of the paper was the biotechnological preparation of gelatine [...] Read more.

In the European Union (EU), about five tons of poultry by-product tissues are produced every year. Due to their high collagen content, they represent a significant raw material source for gelatine production. The aim of the paper was the biotechnological preparation of gelatine from chicken feet. The influence of selected process factors on the gelatine yield, gel strength, viscosity, and ash of gelatine was observed; a two-level factor design of experiments with three variable process factors (enzyme addition, enzyme treatment time, and gelatine extraction time) was applied. After grinding and separating soluble proteins and fat, the purified raw material was treated in water at pH 7.5 with the addition of endoprotease at 23 °C and after thorough washing with water at 80 °C, gelatine was extracted. By the suitable choice of process conditions, gelatine with high gel strength (220–320 bloom), low ash content (<2.0%) and viscosity of 3.5–7.3 mPa·s can be prepared. The extraction efficiency was 18–38%. The presented technology is innovative mainly by the enzymatic processing of the source raw material, which is economically, technologically, and environmentally beneficial for manufacturers. Chicken gelatines are a suitable alternative to gelatines made from mammals or fish, and can be used in many food, pharmaceutical, and biomedical applications. Full article

(This article belongs to the Special Issue Polymer Biointerfaces)

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10 pages, 1683 KiB

Open AccessEditor’s ChoiceArticle

Design of Controlled Release System for Paracetamol Based on Modified Lignin

by Mahboubeh Pishnamazi, Hamid Hafizi, Saeed Shirazian, Mario Culebras, Gavin M. Walker and Maurice N. Collins

Polymers 2019, 11(6), 1059; https://doi.org/10.3390/polym11061059 - 18 Jun 2019

Cited by 80 | Viewed by 7855

Abstract

The influence of lignin modification on drug release and pH-dependent releasing behavior of oral solid dosage forms was investigated using three different formulations. The first formulation contains microcrystalline cellulose (MCC 101) as the excipient and paracetamol as the active pharmaceutical ingredient (API). The [...] Read more.

The influence of lignin modification on drug release and pH-dependent releasing behavior of oral solid dosage forms was investigated using three different formulations. The first formulation contains microcrystalline cellulose (MCC 101) as the excipient and paracetamol as the active pharmaceutical ingredient (API). The second formulation includes Alcell lignin and MCC 101 as the excipient and paracetamol, and the third formulation consists of carboxylated Alcell lignin, MCC 101 and paracetamol. Direct compaction was carried out in order to prepare the tablets. Lignin can be readily chemically modified due to the existence of different functional groups in its structure. The focus of this investigation is on lignin carboxylation and its influence on paracetamol control release behavior at varying pH. Results suggest that carboxylated lignin tablets had the highest drug release, which is linked to their faster disintegration and lower tablet hardness. Full article

(This article belongs to the Special Issue Polymers in Biomedical Engineering)

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11 pages, 1777 KiB

Open AccessArticle

Transparent, High Glass-Transition Temperature, Shape Memory Hybrid Polyimides Based on Polyhedral Oligomeric Silsesquioxane

by Zhongxu Lan, Xueli Chen, Xiao Zhang, Chongyu Zhu, Yanlei Yu and Jia Wei

Polymers 2019, 11(6), 1058; https://doi.org/10.3390/polym11061058 - 18 Jun 2019

Cited by 29 | Viewed by 6795

Abstract

Optically transparent polyimides with excellent thermal stability and shape memory effect have potential applications in optoelectronic devices and aerospace industries. A series of optically transparent shape memory polyimide hybrid films are synthesized from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 2,2′-bis-(trifluoromethyl)biphenyl-4,4′-diamine (TFMB) with various polyhedral oligomeric [...] Read more.

Optically transparent polyimides with excellent thermal stability and shape memory effect have potential applications in optoelectronic devices and aerospace industries. A series of optically transparent shape memory polyimide hybrid films are synthesized from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 2,2′-bis-(trifluoromethyl)biphenyl-4,4′-diamine (TFMB) with various polyhedral oligomeric silsesquioxane (POSS) contents and then subjected to thermal imidization. The hybrid films show good optical transparency (>80% at 400 nm and >95% at 500 nm) with cutoff wavelengths ranging from 318 to 336 nm. Following the incorporation of the inorganic POSS structure, the hybrid films exhibit excellent thermal stability with glass transition temperature (T_g) ranging from 351 to 372 °C. The hybrid films possess the highest T_g compared with the previously-reported shape memory polymers. These findings show that POSS is successfully utilized to develop transparent polyimides with excellent thermal stability and shape memory effect. Full article

(This article belongs to the Collection Silicon-Containing Polymeric Materials)

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(a) DMA, (b) DSC, (c) TMA, and (d) TGA curves of pure PI and PI-POSS hybrid films. Full article ">Figure 2
Photographs and transmittance of pure PI and PI-POSS hybrid films with thickness about 15 µm. Full article ">Figure 3
(a) Shape memory of flower-shaped PI-2 with thickness about 50 μm. The permanent shape was placed on a hot stage at 370 °C and bent with a certain angle, followed by cooling down to room temperature to fix the temporary shape. Then it recovered to permanent shape in 6 s when it was placed back onto the 370 °C hot stage. It can keep the temporary shape on the 270 °C hot stage. (b) Shape memory of flower-shaped PI-4 with thickness about 30 μm. The permanent shape was placed on a hot stage at 400 °C and bent with a certain angle, followed by cooling down to room temperature to fix the temporary shape. Then it recovered to permanent shape in 2 s when it was placed back into the 400 °C hot stage. It can keep the temporary shape on the 300 °C hot stage. (c) Shape memory cycle in TMA of PI-4. An external force was applied at 400 °C to deform a specimen to a certain strain. Then the specimen was cooled down (20 °C/min) to 200 °C, the stress released, and the specimen equilibrated for 5 min and then reheated (10 °C/min) to 400 °C to trigger recovery. Full article ">Scheme 1
Synthesis of PI-POSS hybrids. Full article ">

14 pages, 4029 KiB

Open AccessArticle

Thermally Healable and Recyclable Graphene-Nanoplate/Epoxy Composites Via an In-Situ Diels-Alder Reaction on the Graphene-Nanoplate Surface

by Cho-Rong Oh, Dae-Il Lee, Jun-Hong Park and Dai-Soo Lee

Polymers 2019, 11(6), 1057; https://doi.org/10.3390/polym11061057 - 18 Jun 2019

Cited by 12 | Viewed by 4044

Abstract

In this work, thermally healable graphene-nanoplate/epoxy (GNP/EP) nanocomposites were investigated. GNPs were used as reinforcement and crosslinking platforms for the diglycidyl ether of bisphenol A-based epoxy resin (DGEBA) through the Diels-Alder (DA) reaction with furfurylamine (FA). The GNPs and FA could then be [...] Read more.

In this work, thermally healable graphene-nanoplate/epoxy (GNP/EP) nanocomposites were investigated. GNPs were used as reinforcement and crosslinking platforms for the diglycidyl ether of bisphenol A-based epoxy resin (DGEBA) through the Diels-Alder (DA) reaction with furfurylamine (FA). The GNPs and FA could then be used as a derivative of diene and dienophile in the DA reaction. It was expected that the combination of GNPs and FA in DGEBA would produce composites based on the interfacial properties of the components. We confirmed the DA reaction of GNPs and FA at the interface during curing of the GNP/EP nanocomposites. This procedure is simple and solvent-free. DA and retro DA reactions of the obtained composites were demonstrated, and the thermal healing properties were evaluated. The behavior of the GNP/EP nanocomposites in the DA reaction is similar to that of thermosetting polymers at low temperatures due to crosslinking by the DA reaction, and the nanocomposites can be recycled by a retro DA reaction at high temperatures. Full article

(This article belongs to the Special Issue Thermosets II)

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21 pages, 4259 KiB

Open AccessEditor’s ChoiceArticle

Permeation of a Range of Species through Polymer Layers under Varying Conditions of Temperature and Pressure: In Situ Measurement Methods

by Bernadette Craster and Timothy G.J. Jones

Polymers 2019, 11(6), 1056; https://doi.org/10.3390/polym11061056 - 17 Jun 2019

Cited by 22 | Viewed by 6206

Abstract

Minimising the transport of corrosive reactants such as carbon dioxide, hydrogen sulfide and chloride ions to the surfaces of carbon steel pipes by the use of polymer barrier layers is of major interest in the oil and gas sector. In these applications, there [...] Read more.

Minimising the transport of corrosive reactants such as carbon dioxide, hydrogen sulfide and chloride ions to the surfaces of carbon steel pipes by the use of polymer barrier layers is of major interest in the oil and gas sector. In these applications, there is a requirement to assess the performance of these barrier layers although it is difficult to perform long-term predictions of barrier properties from the results of short-term measurements. New methodologies have been successfully developed to study the permeability of carbon dioxide (CO₂) and hydrogen sulfide (H₂S) through polymer layers under variable conditions of elevated temperatures of 100 °C and pressures of the order of 400 barg. In situ variation of the temperature and the inlet pressure of the gas (or gas mixture) allowed the activation energy and pressure dependence of the permeability to be determined without outgassing of the specimen. These methodologies have been applied to the measurement of the permeability of moulded polyphenylene sulfide (PPS) to supercritical CO₂ in the presence of H₂S. The diffusion coefficients of sodium chloride and potassium chloride through both PPS and polyether ether ketone (PEEK) at ambient temperature and pressure have also been measured. Full article

(This article belongs to the Special Issue Gas Transport Behavior of Polymer Films)

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18 pages, 3833 KiB

Open AccessEditor’s ChoiceArticle

The Thermal and Mechanical Properties of Poly(ethylene-co-vinyl acetate) Random Copolymers (PEVA) and its Covalently Crosslinked Analogues (cPEVA)

by Ke Wang and Qibo Deng

Polymers 2019, 11(6), 1055; https://doi.org/10.3390/polym11061055 - 17 Jun 2019

Cited by 44 | Viewed by 8997

Abstract

The thermal and mechanical properties of poly(ethylene-co-vinyl acetate) random copolymers (PEVA) and its covalently crosslinked analogues (cPEVA) were controlled by the overall crystallinity of the polymer networks. The cPEVAs with different VA-content were synthesized by thermally-induced crosslinking of linear PEVA with [...] Read more.

The thermal and mechanical properties of poly(ethylene-co-vinyl acetate) random copolymers (PEVA) and its covalently crosslinked analogues (cPEVA) were controlled by the overall crystallinity of the polymer networks. The cPEVAs with different VA-content were synthesized by thermally-induced crosslinking of linear PEVA with dicumyl peroxide (DCP). This work was mainly concerned with the effect of vinyl acetate (VA) content on the crosslinking density, thermal and mechanical properties of PEVAs and cPEVAs, respectively. The chemical composition was analyzed by thermogravimetric analysis and ¹H-NMR. The thermal and mechanical properties of PEVAs and cPEVAs have been studied through a series of conventional analytical methods, including gel content determination, different scanning calorimetry, thermogravimetric analysis, dynamic mechanical thermal analysis and traditional mechanical measurements. The experimental results show that the thermal and mechanical properties of PEVAs and cPEVAs increase with decreasing the VA-content. A broad melting transition with a ΔT_m in the range from 78 °C to 95 °C was observed for all polymer networks. Full article

(This article belongs to the Special Issue Polymer Structure and Property)

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14 pages, 3214 KiB

Open AccessArticle

Hardware and Software Development for Isotonic Strain and Isometric Stress Measurements of Linear Ionic Actuators

by Madis Harjo, Tarmo Tamm, Gholamreza Anbarjafari and Rudolf Kiefer

Polymers 2019, 11(6), 1054; https://doi.org/10.3390/polym11061054 - 17 Jun 2019

Cited by 24 | Viewed by 3405

Abstract

An inseparable part of ionic actuator characterization is a set of adequate measurement devices. Due to significant limitations of available commercial systems, in-house setups are often employed. The main objective of this work was to develop a software solution for running isotonic and [...] Read more.

An inseparable part of ionic actuator characterization is a set of adequate measurement devices. Due to significant limitations of available commercial systems, in-house setups are often employed. The main objective of this work was to develop a software solution for running isotonic and isometric experiments on a hardware setup consisting of a potentiostat, a linear displacement actuator, a force sensor, and a voltmeter for measuring the force signal. A set of functions, hardware drivers, and measurement automation algorithms were developed in the National Instruments LabVIEW 2015 system. The result is a software called isotonic (displacement) and isometric (force) electro-chemo-measurement software (IIECMS), that enables the user to control isotonic and isometric experiments over a single compact graphical user interface. The linear ionic actuators chosen as sample systems included different materials with different force and displacement characteristics, namely free-standing polypyrrole films doped with dodecylbenzene sulfonate (PPy/DBS) and multiwall carbon nanotube/carbide-derived carbon (MWCNT-CDC) fibers. The developed software was thoroughly tested with numerous test samples of linear ionic actuators, meaning over 200 h of experimenting time where over 90% of the time the software handled the experiment process autonomously. The uncertainty of isotonic measurements was estimated to be 0.6 µm (0.06%). With the integrated correction algorithms, samples with as low as 0 dB signal-to-noise ratio (SNR) can be adequately described. Full article

(This article belongs to the Special Issue Functional Polymers in Sensors and Actuators: Fabrication and Analysis)

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Figure 1
a: Stress and strain measurement (linear muscle analyzer) setup [<a href="#B10-polymers-11-01054" class="html-bibr">10</a>]. (1) Linear Actuation Staging (LAS), (2) beaker with electrolyte, (3)(4)(5) electrodes of the potentiostat, (6) ionic electroactive material sample, (7) force sensor. b: Connection hierarchy of the devices used for measurement setup. Full article ">Figure 2
a: Block diagram of the automated multiple stress or strain measurement processes, and b: Layout of the graphical user interface (single force experiment) of the developed software. Full article ">Figure 3
Scanning electronic microscopy (SEM) images of a: Polypyrrole Doped with Dodecylbenzene-Sulfonate (PPy/DBS) surface (scale bar 30 µm) with inset—the cross-section (scale bar 10 µm), and b: MWCNT-CDC fiber surface (scale bar 5 µm) with inset—cross-section (scale bar 50 µm). Full article ">Figure 4
Cyclic voltammetry measurements (scan rate 5 mV s−1, 3 cycles) of PPy/DBS films in LiTFSI-PC electrolyte in voltage potential (dashed) range 0.65 to -0.6V showing in a: isometric (measured force, black line), and b: isotonic (measured displacement, black line) results against time. Full article ">Figure 5
MWCNT-CDC fiber under cyclic voltammetry (scan rate 5 mV s−1 (3 cycles), potential range 0.65 to −0.6 V) in LiTFSI-PC electrolyte. a: Near 0 dB SNR isotonic displacement measurement results (black line) and force sensor data fused with measurements data (red points) with voltage (dashed, blue). b: Fused and shifted isotonic measurements (red points) after being processed by slack correction algorithm with voltage (dashed, blue) compared to isotonic displacement (original LAS position measurements). c: Near 0 dB SNR strain measurement data correction algorithm. LAS and force sensor data (inputs) are fused via Equation (7). Then 0.5 um and 0.7 um gaps are eliminated, and resulted data is outputted. Full article ">Figure 6
Cyclovoltammetric (scan rate 5 mV s−1, 3rd cycle) isometric measurement results of MWCNT-CDC fibers in LiTFSI-PC electrolyte at potential range 0.65 to -0.6V, showing the force measurements (mg) (black line) and the uncertainty (B type) of the force measurements (mg) (red dotted). Full article ">

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Polymers, Volume 11, Issue 6 (June 2019) – 155 articles

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