CN113861642B - PLA/PBF/POE-g-GMA/ZnO composite material for antibacterial food packaging and preparation thereof - Google Patents

Abstract

The invention relates to the fields of polymer composite materials and food packaging materials, in particular to an antibacterial food packaging composite material, a preparation method and an application thereof. The method includes the following steps: (1) modifying nano zinc oxide with a silane coupling agent; (2) mixing the modified nano zinc oxide with PLA to obtain a master batch through a master batch method; (3) using a melt blending method PLA, PBF, POE‑g‑GMA and masterbatch were uniformly mixed to prepare PLA/PBF/POE‑g‑GMA/ZnO composites. At the same time, the PLA/PBF/POE-g-GMA/ZnO composite material prepared by the present invention can be pressed into a film with a vacuum laminator and used for antibacterial food packaging. The composite material prepared by the invention has excellent mechanical properties, and the composite film prepared by it has excellent antibacterial effect, especially can play an excellent fresh-keeping effect when packing broccoli, and is expected to become a low-cost, simple to prepare, Biodegradable food packaging material with good performance.

Description

PLA/PBF/POE-g-GMA/ZnO composites for antibacterial food packaging and their preparation

technical field

The invention belongs to the field of polymer composite materials and food packaging materials, and in particular relates to a PLA/PBF/POE-g-GMA/ZnO composite material for antibacterial food packaging, a preparation method and an application thereof.

Background technique

The plastics produced by the domestic prior art are all made of petrochemical products such as polyethylene, polyvinyl chloride, polypropylene and polyvinyl alcohol as raw materials. Due to the non-degradation of the product, "white pollution" is caused. And with the shortage of oil, the price of oil has risen again and again, and the price of plastics produced by petrochemicals has also risen again and again. Polylactic acid (PLA) is polymerized from lactic acid obtained by fermentation of starch extracted from corn and other plants. It is a bio-based source and can be completely biodegradable bioplastics. The macromolecular skeleton structure of discarded polylactic acid materials will be hydrolyzed or enzymatically decomposed into small chain segments by microorganisms, and finally degraded into water and carbon dioxide. The energy consumption of polylactic acid materials in the production process is only 20% to 50% of that of petroleum-based products, and the _CO2 generated after degradation is only half of the latter. Therefore, it has received extensive attention from all walks of life, especially in packaging materials, clothing, Automotive industry or electrical appliances and other fields. From the performance point of view, polylactic acid has three main defects that limit its industrial development: poor toughness; slow crystallization rate, low crystallinity; low melt strength. Therefore, modification of polylactic acid is a necessary means to improve its performance.

In the field of food packaging, most food packaging materials have limited antibacterial properties and are difficult to degrade. Landfilling in the soil seriously damages the sustainable use of land resources, and dumping in the ocean destroys the ecological balance of the ocean. As contemporary people's awareness of protecting the environment and saving resources is gradually increasing, expanding the application range of biodegradable plastics such as polylactic acid in daily life is an urgent task to be solved.

Contents of the invention

Aiming at the problems and deficiencies in the prior art, the object of the present invention is to provide a PLA/PBF/POE-g-GMA/ZnO composite material and a preparation method for antibacterial food packaging.

For realizing the purpose of the invention, the technical scheme adopted in the present invention is as follows:

The first aspect of the present invention provides a kind of preparation method of the PLA/PBF/POE-g-GMA/ZnO composite material that is used for antibacterial food packaging, comprises the following steps:

(1) modifying nano-zinc oxide with a silane coupling agent to obtain modified nano-zinc oxide;

(2) adopt PLA and the modified nano-zinc oxide that step (1) obtains to prepare PLA/ZnO film, the PLA/ZnO film that will obtain is pulverized, standby;

(3) Melt blending PLA, PBF, POE-g-GMA and the PLA/ZnO film prepared in step (2) to obtain PLA/PBF/POE-g-GMA/ZnO composite material.

More preferably, the PLA, PBF and POE-g-GMA have all been dried.

Preferably, the added amount of the PBF is 5%-30% of the mass of the PLA/PBF/POE-g-GMA/ZnO composite material.

Preferably, the silane coupling agent is hexadecyltrimethoxysilane.

Preferably, the added amount of the cetyltrimethoxysilane is 2.5%-10% of the mass of the modified nano zinc oxide.

Preferably, the added amount of the modified nano zinc oxide in the step (2) is 0.5%-2% of the mass of the PLA/PBF/POE-g-GMA/ZnO composite material.

Preferably, the preparation method of PLA/ZnO film in described step (2) is:

1) adding the dried PLA to a solvent for dissolution to obtain a PLA solution;

2) adding the modified nano-zinc oxide obtained in step (1) into the PLA solution, and dispersing evenly to obtain a PLA/ZnO mixed solution;

3) Transfer the PLA/ZnO mixture to a polytetrafluoroethylene mold, and dry it after the solvent evaporates to obtain a PLA/ZnO film.

Preferably, the melt blending temperature in the step (3) is 180°C.

More preferably, in the step (3), a torque rheometer is used to melt and blend the materials, and the temperature of the three sections of the torque rheometer is set to be 180°C, and the rotating speed is 60rpm; the time for machine preheating is 10min .

More preferably, the drying temperatures are both 80°C.

More preferably, the preparation method of modified nano zinc oxide in the step (1) is:

(a) uniformly disperse the nano-zinc oxide in the solvent, reflux at 40°C for 1 hour, and then ultrasonically disperse for 20 minutes;

(b) adding water and adjusting the pH of the solution to 2, adding a silane coupling agent after reflux for 1 hour, stirring and reflux at 40° C. for 1 hour, adjusting the pH to 10 and then reflux for 2 hours to obtain a reflux product;

(c) Centrifuging the reflux product after taking it out, removing the supernatant, taking the centrifuged product and placing it in a polytetrafluoroethylene mold, drying at 80° C. overnight to obtain the modified nano-zinc oxide.

More preferably, the solvent in the step (a) is absolute ethanol.

Preferably, the solvent in the step 1) is trichloromethane, the dissolution method is heating and dissolving, and the heating temperature is 40-60°C; the dispersion method in the step 2) is stirring and ultrasonic treatment, and the stirring time is 15-30min. The ultrasonic treatment time is 10-15 minutes; the drying time in the step 3) is 12-24 hours.

The second aspect of the present invention provides a PLA/PBF/POE-g-GMA/ZnO composite material prepared by the preparation method.

The third aspect of the present invention provides an application of the PLA/PBF/POE-g-GMA/ZnO composite material in antibacterial food packaging.

Preferably, the specific operation of using the PLA/PBF/POE-g-GMA/ZnO composite material for antibacterial food packaging is: vacuum pressing the prepared PLA/PBF/POE-g-GMA/ZnO composite material , to obtain PLA/PBF/POE-g-GMA/ZnO composite film.

More preferably, the specific operation of the vacuum lamination treatment is: laying the prepared PLA/PBF/POE-g-GMA/ZnO composite material between two layers of polytetrafluoroethylene films, and placing the two layers of polytetrafluoroethylene The film and its inner composite material are transferred to a vacuum lamination machine for lamination. After lamination, the upper and lower layers of polytetrafluoroethylene film are removed to obtain a PLA/PBF/POE-g-GMA/ZnO composite film.

Preferably, the thickness of the PLA/PBF/POE-g-GMA/ZnO composite film is 70 μm.

Compared with the prior art, the beneficial effects of the present invention are as follows:

(1) The main components PLA and furyl polyester (polybutylene 2,5-furandicarboxylate, PBF) in the PLA/PBF/POE-g-GMA/ZnO composite material prepared by the present invention belong to biodegradable Degradable materials, and PBF belongs to the "strong and tough" material type. Adding PBF to PLA can make the composite material have a higher elongation at break, while the decrease in tensile strength and elastic modulus is small, and then exhibit excellent mechanical properties. When the amount of modified zinc oxide (m-ZnO) in the composite material is 0.5wt%, the elongation at break of the composite material reaches 132.1%, which is about 5 times that of PLA, and the tensile strength is 77.4MPa, Young's The modulus is 1167.1MPa, the mechanical properties are good, and the balance between rigidity and toughness is achieved.

(2) The present invention finally selects silane coupling agent hexadecyltrimethoxysilane (HDTMS) to modify nano-zinc oxide by comparing two kinds of silane coupling agents, and the modified nano-zinc oxide obtained has good Hydrophobic and lipophilic, and can achieve nano-level dispersion effect in organic solvents, and then combine the masterbatch method to obtain good dispersion of modified nano-zinc oxide in composite materials. At the same time, the crystallinity of the PLA/PBF/POE-g-GMA/ZnO composite material prepared by the invention is significantly increased, the number of spherulites is increased compared with the PLA material, and the gas barrier performance is significantly enhanced.

(3) The PLA/PBF/POE-g-GMA/ZnO composite film prepared by the present invention has remarkable antibacterial effect. When the amount of modified nano-zinc oxide was 1wt%, the antibacterial rates of PLA/PBF/POE-g-GMA/ZnO composite films against Staphylococcus aureus and Bacillus subtilis reached 99.9% and 99.5%, respectively, and Escherichia coli had a lower survival rate. When the amount of modified nano-zinc oxide was 1.5wt%, the antibacterial rates of PLA/PBF/POE-g-GMA/ZnO composite films against these three bacteria reached 99.2%, 100% and 99.9%, respectively.

(4) The PLA/PBF/POE-g-GMA/ZnO composite film prepared by the present invention can be used for food packaging. After adding nano-zinc oxide, the sensory quality evaluation of broccoli packaged in PLA/PBF/POE-g-GMA/ZnO composite film is better, the mass loss rate is lower, and the relative conductivity and chlorophyll content change are smaller, which can reach the western blue flower. Fresh-keeping effect of blue flowers.

Description of drawings

Fig. 1 is the comparison diagram of the suspension sedimentation of nano-zinc oxide before and after modification, wherein, a is the m-ZnO suspension of 5wt% HDTMS, and b is the un-ZnO suspension;

Fig. 2 is the agar plate diagram of the PLA/PBF/POE-g-GMA/ZnO composite film prepared by different contents of nano-zinc oxide on Escherichia coli inhibitory effect;

Fig. 3 is a curve diagram of the preservation effect of broccoli stored for 0 to 5 days, wherein a is a curve diagram of sensory quality change, b is a curve diagram of mass loss rate change, c is a curve diagram of relative electrical conductivity change, and d is a curve diagram of chlorophyll content change .

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail through the following embodiments in conjunction with the accompanying drawings. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

It should be noted that, in the case of no conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and embodiments.

Example 1

A preparation method for a PLA/PBF/POE-g-GMA/ZnO composite film for antibacterial food packaging, comprising the following steps:

1. Preparation of modified nano zinc oxide

(a) Evenly disperse 10 g of nano-zinc oxide in 100 mL of absolute ethanol solvent, ultrasonically oscillate for about 15 min, reflux at 40° C. for 1 h, and then ultrasonically disperse for 20 min.

(b) Add appropriate amount of water, then use 0.1mol/L HCl solution to adjust pH=2, then reflux at 40°C for 1 hour, then add hexadecyltrimethoxysilane (HDTMS) dropwise into the flask, stir and reflux at 40°C After about 1 hour, the pH was adjusted to 10 with NaOH, and the product was refluxed at 40° C. for 2 hours to obtain the refluxed product.

(c) Centrifuge the reflux product for 5 minutes after taking it out, remove the supernatant, take the centrifuged product and place it in a polytetrafluoroethylene mold, and dry it in an oven at 80°C overnight to obtain the modified nano-zinc oxide (m-ZnO) . In the modified nano zinc oxide, the content of HDTMS is 5wt%.

2. Preparation of PLA/ZnO thin film

1) Dry the PLA at 80°C, take 10g of the dried PLA and dissolve it in 100mL of chloroform, heat and stir at 40°C until all the PLA is dissolved to obtain a PLA solution.

2) Add 0.4 g of the modified nano-zinc oxide prepared in step 1 into the PLA solution, stir for 15 min, cool to room temperature after the solution turns uniform white, and disperse ultrasonically for 15 min to obtain a PLA/ZnO mixture.

3) The PLA/ZnO mixture was transferred to a polytetrafluoroethylene mold, volatilized in a fume hood overnight, and then dried in an oven at 80° C. for 12 hours to obtain a PLA/ZnO film.

3. Preparation of PLA/PBF/POE-g-GMA/ZnO composites

(I) Turn on the torque rheometer (model: CTR-300), set the temperature of the three stages of the torque rheometer to 180°C, and the rotation speed to 60 rpm; the machine warm-up time is 10 minutes. After the torque rheometer is preheated and the rotation speed is stable, 22g PLA, 8gPBF (manufacturer: Ningbo Jisu New Material Technology Co., Ltd.), 2g POE-g-GMA (methacrylic acid shrink Glyceride grafted polyolefin elastomer (manufacturer: Jiayirong Polymer Shanghai Co., Ltd.) was added to the feed port of the torque rheometer.

(II) After the rotational speed of the torque rheometer is stable, chop the PLA/ZnO film prepared in step 2 and add it to the feed port of the torque rheometer.

(Ⅲ) After the torque is balanced, the material obtained by blending in the torque rheometer is taken out and shredded to obtain a PLA/PBF/POE-g-GMA/ZnO composite material, which is a composite particle.

4. Preparation of PLA/PBF/POE-g-GMA/ZnO composite film

Take the composite material prepared in step 3 and spread it between two layers of polytetrafluoroethylene film, and place the two layers of polytetrafluoroethylene film and the composite material inside the two layers of iron plates directly without using a mold. Put it into the vacuum laminator to press the film. After lamination, the two layers of polytetrafluoroethylene films were removed to obtain a 70 μm PLA/PBF/POE-g-GMA/ZnO composite film.

Example 2

A preparation method of PLA/PBF/POE-g-GMA/ZnO composite film for antibacterial food packaging is basically the same as in Example 1, except that in the modified nano-zinc oxide obtained in step 1, The content of HDTMS is 2.5 wt%.

Example 3

A preparation method of PLA/PBF/POE-g-GMA/ZnO composite film for antibacterial food packaging is basically the same as in Example 1, except that in the modified nano-zinc oxide obtained in step 1, The content of HDTMS was 7.5 wt%.

Example 4

A preparation method of PLA/PBF/POE-g-GMA/ZnO composite film for antibacterial food packaging is basically the same as in Example 1, except that in the modified nano-zinc oxide obtained in step 1, The content of HDTMS was 10 wt%.

Example 5

A kind of preparation method content of the PLA/PBF/POE-g-GMA/ZnO composite film that is used for antibacterial food packaging is basically the same as that of Example 1, and its difference is: step 2) in the modified nano zinc oxide addition 0.2g.

Example 6

A kind of preparation method content of the PLA/PBF/POE-g-GMA/ZnO composite film that is used for antibacterial food packaging is basically the same as that of Example 1, and its difference is: step 2) in the modified nano zinc oxide addition 0.6g.

Example 7

A kind of preparation method content of the PLA/PBF/POE-g-GMA/ZnO composite film that is used for antibacterial food packaging is basically the same as that of Example 1, and its difference is: step 2) in the modified nano zinc oxide addition 0.8g.

Example 8

A preparation method of PLA/PBF/POE-g-GMA/ZnO composite film for antibacterial food packaging is basically the same as in Example 1, except that the heating temperature is 50°C in step 1); The stirring time in 2) is 20 minutes, and the ultrasonic time is 12 minutes; the drying in step 3) is 18 hours.

Example 9

A preparation method of PLA/PBF/POE-g-GMA/ZnO composite film for antibacterial food packaging is basically the same as in Example 1, except that the heating temperature is 60°C in step 1); In 2), the stirring time is 30 min, and the ultrasonic time is 10 min; in step 3), the drying time is 24 h.

Comparative example 1

A kind of preparation method content of the PLA/PBF/POE-g-GMA/ZnO composite film that is used for antibacterial food packaging is basically the same as that of Example 1, and its difference is: do not carry out the preparation of step 1 and step 2; The addition amount of PLA in (I) is 38g, the addition amount of PBF is 2g, and the preparation of step (II) is not carried out.

Comparative example 2

A kind of preparation method content of the PLA/PBF/POE-g-GMA/ZnO composite film that is used for antibacterial food packaging is basically the same as that of Example 1, and its difference is: do not carry out the preparation of step 1 and step 2; In (I), the addition amount of PLA is 36g, the addition amount of PBF is 4g, and the preparation of step (II) is not carried out.

Comparative example 3

A kind of preparation method content of the PLA/PBF/POE-g-GMA/ZnO composite film that is used for antibacterial food packaging is basically the same as that of Example 1, and its difference is: do not carry out the preparation of step 1 and step 2; The addition amount of PLA in (I) is 32g, the addition amount of PBF is 8g, and the preparation of step (II) is not carried out.

Comparative example 4

A kind of preparation method content of the PLA/PBF/POE-g-GMA/ZnO composite film that is used for antibacterial food packaging is basically the same as that of Example 1, and its difference is: do not carry out the preparation of step 1 and step 2; The addition amount of PLA in (I) is 28g, the addition amount of PBF is 12g, and the preparation of step (II) is not carried out.

Comparative example 5

A preparation method of PLA/PBF/POE-g-GMA/ZnO composite film for antibacterial food packaging is basically the same as in Example 1, except that no silane coupling agent is used in step (b) , that is, modify without adding a silane coupling agent; obtain unmodified nano zinc oxide (un-ZnO) in step (c); use unmodified nano zinc oxide in step 2) to prepare PLA/ZnO film.

Comparative example 6

A kind of preparation method content of the PLA/PBF/POE-g-GMA/ZnO composite film that is used for antibacterial food packaging is basically the same as that of Example 1, and its difference is: the silane coupling agent used in step (b) It is gamma-aminopropyltriethoxysilane (KH-550), and the content of the silane coupling agent in the modified nano-zinc oxide is 5 wt%.

Comparative example 7

A kind of preparation method content of the PLA/PBF/POE-g-GMA/ZnO composite film that is used for antibacterial food packaging is basically the same as that of Example 1, and its difference is: the silane coupling agent used in step (b) It is KH-550; in the modified nanometer zinc oxide, the content of silane coupling agent is 7.5wt%.

Comparative example 8

A kind of preparation method content of the PLA/PBF/POE-g-GMA/ZnO composite film that is used for antibacterial food packaging is basically the same as that of Example 1, and its difference is: do not carry out the preparation of step 1 and step 2; The addition amount of PLA in 3 is 32g, does not carry out the preparation of step (II).

Comparative example 9

A kind of preparation method content of the PLA/PBF/POE-g-GMA/ZnO composite film that is used for antibacterial food packaging is basically the same as that of Example 1, and its difference is: do not carry out the preparation of step 1 and step 2; In (I), no PBF and POE-g-GMA were added, and the amount of PLA was 40 g, and the preparation of step (II) was not carried out.

(1) Discussion on the dosage of PBF

In order to explore the influence of PBF content on the mechanical properties of composite materials, the inventors used the PLA/PBF/POE-g-GMA/ZnO composite materials prepared in Comparative Examples 1 to 4 as test samples, and the corresponding PBF contents were 5wt%, 5wt%, 10wt%, 20wt%, 30wt%, did the following tensile and impact tests: the test sample was pressed into a dumbbell-shaped sample with a vacuum laminator (tensile sample, the specification is 2 * 35 * 0.5mm) and a rectangular sample Strips (impact splines, specification 75×20×1mm) were subjected to a tensile test on a universal tensile testing machine. The test program was plastic-film stretching, and the tensile speed was 5mm/min. Each spline was selected to measure the thickness at 3 places and the average value was taken, and 5 parallel experiments were performed for each group. Grind a 4mm-deep 45° V-shaped notch on one side of the impact bar with a notch prototyping machine, and measure its impact strength on a cantilever beam pendulum impact measuring instrument. The results are shown in Table 1. The experimental results show that Comparative Example 3 has the best mechanical properties, and it is preferable to select the PBF addition amount of 20wt% for the subsequent preparation of the composite material.

Table 1 Effect of PBF content on mechanical properties of composites

(2) Selection of silane coupling agent

In order to investigate the impact of the type and amount of silane coupling agent on the hydrophilicity and lipophilicity of nano-zinc oxide, the contriver adopts Example 1, Example 2, Example 3, Comparative Example 5, Comparative Example 6, and Comparative Example 7 to prepare The modified nano zinc oxide is the test sample, and the corresponding silane coupling agent types and contents are HDTMS 5wt%, HDTMS 2.5wt%, HDTMS7.5wt%, 0wt%, KH-5505wt%, KH-5507.5wt%, The following experiments were done: the water-air contact angle was measured by a static contact angle tester to reflect the hydrophilicity and hydrophobicity of the sample surface; the lipophilicity of the sample was tested by the lipophilicity test. The results are shown in Table 2.

Table 2 The effect of the type and amount of silane coupling agent on the hydrophilicity and lipophilicity of nano-zinc oxide

serial number Contact angle (°) Lipophilicity (%) Embodiment 1 (5wt% HDTMS) 145 58.5 Example 2 (2.5wt% HDTMS) 85 39.0 Embodiment 3 (7.5wt%HDTMS) 147 60.9 Comparative example 5 (without silane coupling agent) 25.5 0 Comparative example 6 (5wt% KH-550) 39 19.3 Comparative Example 7 (7.5wt% KH-550) 41 23.0

The general formula of silane coupling agent is RSiX ₃ , where R represents an active functional group that has the ability to react or has affinity with polymer molecules. During the research process, we found that the silane coupling agent can act as a "molecular bridge" in the material: after the silane group is hydrolyzed, the hydroxyl group can react with the functional group on the surface of the powder; at the same time, another part of the group can interact with the organic The polymer undergoes physical entanglement or chemical reaction, and the inorganic powder filler is connected with the polymer to achieve coupling. During coupling, X is first hydrolyzed to form silanol, and then reacts with hydroxyl groups on the surface of inorganic powder particles to form hydrogen bonds and condense into Si—M covalent bonds (M represents the surface of inorganic powder particles). At the same time, the silanol in each molecule of silane associates with each other and oligomerizes to form a film of network structure covering the surface of the powder particles, making the surface of the inorganic powder organic.

It can be seen from Table 2 that because the surface of un-ZnO is rich in hydroxyl groups, it has strong hydrophilicity and a contact angle of 25.5°, which is not conducive to uniform dispersion in polymers and has poor compatibility. When the silane coupling agent is HDTMS, the contact angle and lipophilicity of nano-zinc oxide tend to increase first and then remain unchanged with the increase of HDTMS content, and reach equilibrium when the HDTMS addition is 5%, which means that at this time The number of silane coupling agents on the powder surface has reached saturation. This is because the hydroxyl groups on the surface of nano-zinc oxide cannot completely associate with the silane coupling agent due to steric hindrance, and will first form a monomolecular layer of physical adsorption on the surface of zinc oxide, and then form surface micelles. However, the modification effect of KH-550 is significantly lower than that of HDTMS. Compared with un-ZnO, the contact angle of m-ZnO modified by KH-550 has little change, because HDTMS is a hexadecane carbon chain, and contains two Compared with the KH-550 of alkanes, the hydrophobicity is stronger. Therefore, when HDTMS is used to modify nano-zinc oxide, and the dosage is 5wt%, a good lipophilic and hydrophobic effect can be achieved.

(3) Discussion on the amount of silane coupling agent

In order to investigate the impact of the amount of silane coupling agent on the dispersion effect of nano-zinc oxide, the inventors did the following experiments respectively:

The modified nano-zinc oxide prepared in Example 1, Example 2, Example 3, Example 4, and Comparative Example 5 is respectively used as a test sample, and its corresponding silane coupling agent content is respectively 5wt%, 2.5wt%, 7.5wt%, 10wt%, 0wt%; respectively take 0.1g nano-zinc oxide sample, add appropriate amount of ethanol dispersion, place in a four-way cuvette, ultrasonically oscillate for about 15min, until the particles are evenly dispersed and the dispersion is translucent , and then use a laser particle size analyzer to test the particle size of nano-zinc oxide. The results are shown in Table 3.

The modified nano-zinc oxide prepared in Example 1 and Comparative Example 5 were respectively used as test samples, and the suspension sedimentation and transmission electron microscopy were used to carry out appearance tests, and the results are shown in FIG. 1 . When using a transmission electron microscope for appearance testing, take a small amount of nano-zinc oxide sample in a transparent sample bottle, add ethanol and ultrasonically disperse it for 10 minutes, use a micro-syringe to pipette 2 μL of the suspension on the copper grid, and then use a transmission electron microscope to observe and record Microscopic topography.

The impact of the dosage of table 3 silane coupling agent on the average particle size of nanometer zinc oxide

serial number Average particle size (nm) Embodiment 1 (5wt%) 90.47 Embodiment 2 (2.5wt%) 122.97 Embodiment 3 (7.5wt%) 111.01 Embodiment 4 (10wt%) 136.21 Comparative example 5 (without silane coupling agent) 205.02

Due to the small size effect and surface effect of nano zinc oxide, it has a large specific surface area and surface potential energy, and the particles are easy to agglomerate to increase the size. Before modification, the nano-zinc oxide particle size is mainly distributed between 90-460nm, and the number of particles with a particle size of about 200nm is the largest (for example, the average particle size of un-ZnO in Table 2 is 205.02nm). It can be seen from Table 3 that as the content of HDTMS increases, the particle size of m-ZnO first decreases and then increases, and the number of particles with a particle size of about 100nm is the largest. Among them, the particle size of 5% HDTMS is distributed in a smaller size area, which can be calculated by software, and its average particle size is 90.47nm, which meets the requirement that the size of nanoparticles is between 1 and 100nm. This is because the silane coupling agent is coated on the surface of zinc oxide to reduce mutual agglomeration. With the increase of the amount of coupling agent added, the layer-by-layer coating of coupling agent makes the particle size increase instead.

The comparison diagram of the suspension sedimentation of nano-zinc oxide before and after modification is shown in Fig. 1. In Figure 1, a is the m-ZnO suspension of 5% HDTMS. After standing for 3 hours, the m-ZnO can still be seen to be uniformly dispersed in ethanol with the naked eye, and there is a cupping phenomenon due to its good lipophilicity. The overall performance is basically no sedimentation , calculated by the formula, the dispersion degree of m-ZnO can reach more than 99%. In Figure 1, b shows the dispersion of un-ZnO in ethanol, which shows that the sedimentation speed of un-ZnO is relatively fast, the particle deposition phenomenon appears at the bottom, and the suspension at the top is translucent. The formula can be used to calculate the concentration of m-ZnO The degree of dispersion was 60%. This is because the collision and agglomeration of the particles increases the particle size of the nano-zinc oxide, which causes the particles to sink due to the increased gravity.

In order to prove the modification effect of silane coupling agent HDTMS on nano-zinc oxide from a microscopic point of view, the microscopic morphology of the sample was observed by transmission electron microscopy, and it was found that the modified nano-zinc oxide aggregated large particles were opened, and the aggregation phenomenon was obtained. Visible improvement.

In summary, when the amount of HDTMS is 5wt%, a better dispersion effect can be achieved.

(4) Performance test

1. Analysis of mechanical properties of PLA/PBF/POE-g-GMA/ZnO composites

In order to investigate the effect of the amount of nano-zinc oxide on the mechanical properties of PLA/PBF/POE-g-GMA/ZnO composites, the inventors adopted Example 1, Example 5, Example 6, Example 7, Comparative Example 5, and Comparative Example respectively. The composite materials prepared in Example 8 and Comparative Example 9 are test samples, and the corresponding nano zinc oxide dosages are m-ZnO 0.4g, m-ZnO 0.2g, m-ZnO0.6g, m-ZnO 0.8g, un- ZnO 0.4g, unused nano-zinc oxide, unused nano-zinc oxide (pure PLA material), did the following experiments: the test sample was pressed into a dumbbell-shaped spline with a vacuum laminator (stretched spline, the specification is 2× 35×0.5mm) and rectangular splines (impact splines, the specification is 75×20×1mm), the tensile test is carried out on a universal tensile testing machine, the test program is plastic-film stretching, and the tensile speed is 5mm/min . Each spline was selected to measure the thickness at 3 places and the average value was taken, and 5 parallel experiments were performed for each group. First, a 4mm-deep 45° V-shaped notch was ground on one side of the impact bar with a notch prototyping machine, and its impact strength was measured on a cantilever beam pendulum impact measuring instrument. The results are shown in Table 4.

Table 4 Effect of the amount of nano-zinc oxide on the mechanical properties of PLA/PBF/POE-g-GMA/ZnO composites

It can be seen from Table 4 that as the zinc oxide content increases, the crystallinity of the composite material increases gradually. The increase of the crystallinity of the composite will lead to the decrease of the elongation at break and the impact strength, and the material tends to change from tough to brittle. However, compared with the pure PLA material, the elongation at break and impact strength of the PLA/PBF/POE-g-GMA/ZnO composite material have been significantly improved, and the material shows the beneficial effect of "strong and tough". And when the added amount of modified nano-zinc oxide is 1wt%, the PLA/PBF/POE-g-GMA/ZnO composite material can achieve better "strong and tough" performance.

2. Analysis of antibacterial performance of PLA/PBF/POE-g-GMA/ZnO composite film

In order to investigate the impact of the amount of nano-zinc oxide on the antibacterial effect of PLA/PBF/POE-g-GMA/ZnO composite film, the inventors adopted Example 1, Example 5, Example 6, Example 7, Comparative Example 5, and Comparative Example 5 respectively. The composite film prepared in Example 9 is the test sample, and the corresponding dosages of nano zinc oxide are m-ZnO 0.4g, m-ZnO 0.2g, m-ZnO 0.6g, m-ZnO 0.8g, un-ZnO 0.4g, Nano-zinc oxide (pure PLA material) was not used, and the following experiment was done: the antibacterial rate of the composite film against Escherichia coli was calculated by using the plate counting method through the agar plate diagram of the bacteria, and all the operating steps of the experiment were carried out in a sterile environment. Among them, in this experiment, the bacterial liquid was first cultivated on the surface of the sample, and then eluted, and then the eluate was coated, cultivated, and counted on the solid medium. Among them, the composition of the solid/liquid medium is shown in Table 5 . The whole test process is divided into four days, and the specific operation steps are as follows:

The first day: according to the formula in Table 4, prepare the solid culture base in the Erlenmeyer flask, put it in the sterilization box for sterilization, and then pour it into the petri dish while it is hot, and wait for the agar to solidify slowly. Take out the Erlenmeyer flask containing the bacteria from the refrigerator, add a few drops of culture solution to the solid base, smear it evenly with a sterilized coating rod, and then place it in a 37°C incubator for 24 hours.

The next day: Prepare the liquid medium according to the formula in Table 4, put it in a sterilization box for sterilization, take it out, cool it under an ultraviolet lamp to avoid contamination by bacteria, and divide it into several petri dishes. Use a sterilized inoculation loop to scrape an appropriate amount of bacteria from the solid base prepared on the first day and transfer it to the freshly prepared liquid base. After shaking well, absorb an appropriate amount of bacterial liquid to dilute 1000 times. The same amount of diluted bacterial solution was added dropwise to the surface of the sample, and then a sterilized PE film was pasted on it, and then the sample was placed in a marked empty Petri dish and incubated in a 37°C incubator for 24 hours.

Day 3: Prepare a solid medium, elute the bacteria that grew on the surface of the sample the next day with normal saline, pipette an appropriate amount of eluent and drop it into the solid medium, spread it evenly with a sterilized coating rod, and put it in Incubate in a 37°C incubator for 24 hours.

Day 4: Observe the growth of bacteria on the surface of the solid medium and take pictures for records. The antibacterial rates of PLA/PBF/POE-g-GMA/ZnO composite films are shown in Table 6.

Table 5 Solid/liquid medium composition table

Reagent Liquid Medium Components Solid Media Components normal saline 100mL 100mL Sodium chloride 0.5g 0.5g Yeast Dip Powder 0.5g 0.5g Peptone 1g 1g Tween 80 Appropriate amount 0 agar 0 1.5g

Table 6 Effect of the amount of nano-zinc oxide on the antibacterial effect of PLA/PBF/POE-g-GMA/ZnO composite film

It can be seen from Table 6 that the antibacterial effect of the modified nano-zinc oxide is obviously better than that of the unmodified nano-zinc oxide, which may be because the modified nano-zinc oxide has better dispersibility and its antibacterial rate has been effectively improved. PLA/PBF/POE-g-GMA/ZnO composite film along with the increase of modified nano zinc oxide addition, its antibacterial effect has also been effectively improved, and in modified nano zinc oxide addition is 0.4g (i.e. 1wt% m-ZnO), its antibacterial effect is nearly saturated. Wherein Fig. 2 is the agar plate diagram of PLA/PBF/GPOE/ZnO composite film to Escherichia coli. Therefore, when the added amount of modified nano zinc oxide is 1wt%, the PLA/PBF/POE-g-GMA/ZnO composite film can achieve a better antibacterial effect.

3. Analysis of the preservation effect of PLA/PBF/POE-g-GMA/ZnO composite film on broccoli

In order to investigate the effect of the amount of nano-zinc oxide on the fresh-keeping effect of PLA/PBF/POE-g-GMA/ZnO composite film on broccoli, the inventor adopts embodiment 1, embodiment 5, embodiment 6, embodiment 7, and The composite films prepared in Example 5, Comparative Example 8, and Comparative Example 9 are test samples, and the corresponding nano-zinc oxide dosages are m-ZnO 0.4g, m-ZnO 0.2g, m-ZnO 0.6g, m-ZnO 0.8 g, un-ZnO 0.4g, no nano-zinc oxide, no nano-zinc oxide (pure PLA material), the following experiments were done, and the results are shown in Figure 3.

(1) Evaluation of sensory quality: According to the national agricultural standard NY/T941-2006, during the broccoli storage period (0-5 days), the paper tape is torn off every day, and the broccoli samples are taken out for observation, and according to its color, smell, etc. Scoring, taking the average of 5 people's scoring as the sensory quality evaluation score.

(2) Change in mass loss rate: Weigh the mass of broccoli with an analytical balance every day, and calculate the mass loss rate (weight loss rate) according to formula (1).

(3) Relative conductivity: first cut 1g thin slices from the sample, put it into a weighing bottle and add 20mL deionized water, shake for 5min, let stand for 3h, measure the conductivity at this time as γ ₁ ; transfer the liquid to a small In a beaker, boil in an oil bath at 140°C to kill the fruit and vegetable tissue, take it out and cool it to room temperature, and measure the conductivity γ ₂ at this time. The calculation formula of relative conductivity (γ _e ) is shown in formula (2).

(4) Chlorophyll content: measure the absorbance of the chlorophyll acetone solution extracted from broccoli with a UV spectrophotometer, wherein the maximum absorption peaks of the acetone extracts of chlorophyll a and b are at wavelengths 645nm and 663nm. Using the photometric measurement mode, pour chlorophyll into a cuvette, measure the absorbance at different wavelengths with acetone as a reference, and calculate the chlorophyll content according to formula (3) and formula (4).

ρ _T =ρ _a +ρ _b =20.29A ₆₄₅ +8.05A ₆₆₃ (3)

In formula (3): ρ _a (mg/L) and ρ _b (mg/L) represent the mass concentrations of chlorophyll a and b, respectively. A ₆₆₃ and A ₆₄₅ refer to the absorbance values of the samples at wavelengths of 663nm and 645nm. The specific operation steps are: tear off the paper tape, cut 1g from the broccoli, add it to an agate mortar, add 2mL of acetone and grind it finely until the sample is in the form of a slurry. Pour it into a beaker, add acetone to 20mL, and place it in a dark place for about 24 hours due to the light absorption of chlorophyll. Then rinse the sand core funnel with acetone, filter the filtrate into a glass sample bottle, and mark the name. Finally, measure the absorbance of the sample at wavelengths of 663 nm and 645 nm with an ultraviolet spectrophotometer, and subtract the acetone blank.

Fig. 3 is a graph showing the results of the fresh-keeping evaluation experiment in the above-mentioned 4. As shown in a and b in Figure 3, as the storage time of broccoli becomes longer, the sensory qualities such as color and smell of broccoli show a downward trend, and the decline trend is slow at first and then fast; the quality loss increases first and then remains unchanged trend. And with the increase of the content of the modified nano zinc oxide in the composite film, the sensory quality of the broccoli decreased more slowly, and the proportion of the decline was smaller; the mass loss was smaller, and the higher the content, the smaller the loss. But un-ZnO 0.4g, no nano-zinc oxide, no nano-zinc oxide (PLA material) packaged broccoli sensory quality degradation and mass loss rate are very large.

Relative conductivity and chlorophyll content can show a basic indicator of plant cell membrane permeability, that is, when the cell membrane is damaged, the cell membrane permeability increases, so that intracellular electrolytes and chlorophyll are extravasated, and the conductivity of the plant cell extract The rate increased, and the chlorophyll content in the cells decreased. When the cell dies, chlorophyll is freed from the chloroplast, and the free chloroplast is very unstable, and it will be decomposed by light, acid, alkali, oxygen, and oxidant. Therefore, the greater the relative conductivity measured in the experiment and the lower the chlorophyll content, the greater the permeability of the cell membrane and the higher the cell death rate. As shown in c in Figure 3, as the storage time of broccoli becomes longer, the relative conductivity of broccoli tends to increase, but the composite film containing nano-zinc oxide obviously slows down this trend, which shows that adding nano-zinc oxide The zinc composite film has a certain slowing effect on cell death. As shown in Figure 3 d, as the broccoli storage time becomes longer, the chlorophyll content in the broccoli gradually decreases, and with the increase of the content of the modified nano-zinc oxide in the composite film, the composite film has no effect on broccoli. The fresh-keeping effect of flowers tends to increase. In summary, the PLA/PBF/POE-g-GMA/ZnO composite film has a good effect on the preservation of broccoli.

To sum up, the present invention effectively overcomes the deficiencies in the prior art, and has high industrial application value. The purpose of the above-mentioned embodiments is to illustrate the substantive content of the present invention, but not to limit the protection scope of the present invention. Those skilled in the art should understand that the technical solution of the present invention can be modified or equivalently replaced without departing from the essence and protection scope of the technical solution of the present invention.

Claims (7)

1. a preparation method for the PLA/PBF/POE-g-GMA/ZnO composite material for antibacterial food packaging, it is characterized in that, comprises the following steps: (1) Modify nano-zinc oxide with a silane coupling agent to obtain modified nano-zinc oxide; (2) Prepare a PLA/ZnO film by using PLA and the modified nano-zinc oxide obtained in step (1), crush the obtained PLA/ZnO film, and set aside; (3) Melt blending PLA, PBF, POE-g-GMA and the PLA/ZnO film prepared in step (2) to obtain PLA/PBF/POE-g-GMA/ZnO composite material; Wherein, the silane coupling agent described in step (1) is hexadecyltrimethoxysilane; the addition amount of said hexadecyltrimethoxysilane is 2.5%～10% of the quality of modified nano-zinc oxide; The amount of modified nano zinc oxide added in step (2) is 0.5% to 2% of the mass of the PLA/PBF/POE-g-GMA/ZnO composite material; the amount of PBF added in step (3) It is 5% to 30% of the mass of PLA/PBF/POE-g-GMA/ZnO composite material; The preparation method of the modified nano-zinc oxide in step (1) is: (a) uniformly disperse the nano-zinc oxide in the solvent, reflux at 40°C for 1 hour and then ultrasonically disperse for 20 minutes; (b) add water and adjust the pH of the solution to 2 After reflux for 1 hour, add a silane coupling agent, stir and reflux at 40°C for 1 hour, adjust the pH to 10, and then reflux for 2 hours to obtain the reflux product; In a tetrafluoroethylene mold, the modified nano-zinc oxide was obtained after drying overnight at 80°C. 2. The preparation method of PLA/PBF/POE-g-GMA/ZnO composite material for antibacterial food packaging according to claim 1, characterized in that, the preparation method of PLA/ZnO film in the step (2) for: 1) Add the dried PLA into the solvent to dissolve to obtain the PLA solution; 2) Add the modified nano-zinc oxide obtained in step (1) into the PLA solution and disperse evenly to obtain a PLA/ZnO mixed solution; 3) The PLA/ZnO mixture was transferred to a polytetrafluoroethylene mold, and dried after the solvent evaporated to obtain a PLA/ZnO film. 3. The preparation method of PLA/PBF/POE-g-GMA/ZnO composite material for antibacterial food packaging according to claim 2, characterized in that the melt blending temperature in the step (3) is 180 °C . 4. the preparation method of the PLA/PBF/POE-g-GMA/ZnO composite material that is used for antibacterial food packaging according to claim 3, is characterized in that, described step 1) middle solvent is chloroform; The dispersion method in step 2) is stirring and ultrasonic treatment, the stirring time is 15-30 min, and the ultrasonic treatment time is 10-15 min; the drying time in step 3) is 12-24 h. 5. A PLA/PBF/POE-g-GMA/ZnO composite material prepared by any one of claims 1 to 4. 6. an application of the PLA/PBF/POE-g-GMA/ZnO composite material described in claim 5 in antibacterial food packaging. 7. The application of PLA/PBF/POE-g-GMA/ZnO composite material in antibacterial food packaging according to claim 6, is characterized in that, utilizes described PLA/PBF/POE-g-GMA/ZnO composite material The specific operation applied to antibacterial food packaging is as follows: the prepared PLA/PBF/POE-g-GMA/ZnO composite material is subjected to vacuum lamination treatment to obtain PLA/PBF/POE-g-GMA/ZnO composite film; the composite The film thickness is 70 μm.

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