Application of Biodegradable Polymer in Cushion Packaging Materials (I)

[ABSTRACT] Foam plastics have excellent performance and occupy an important position in the buffer packaging materials, but the waste after use brings serious environmental pollution. Some biodegradable polymers can meet the requirements of environmental protection and have great development and utilization value. This article outlines the application of biodegradable polymers in buffer foaming materials.

[Key words] foam plastic; buffer packaging material; biodegradable polymer; starch

Buffer packaging materials have a wide range of applications in the packaging field and are an important part of packaging materials. During the process of loading and unloading goods, the goods are subjected to impact and vibration under the action of external forces, and they are prone to damage. Buffer packaging can play a role in protecting the goods and is an essential part in the circulation environment. At present, the main application of buffer packaging materials are foam plastic, pulp mold, air cushion film and so on. Among them, foam occupies a dominant position, its products have a good ability to absorb shock and vibration, low density, low water absorption, good corrosion resistance, low thermal conductivity, good electrical insulation, and can use different formulations and processing Process to produce materials of different densities and morphologies. Foam plastics can be used for household electrical appliances, precision instruments and meters, mechanical parts, valuables, fragile items, and various types of handicrafts, etc. as cushioning cushioning materials, and can also be made into various shapes of packaging products, such as: turnover boxes, each Food packaging cushions, trays, etc. Especially for large-scale electronic products, mechanical parts, precision instruments, valuables, etc., other buffer packaging materials are difficult to meet the requirements in terms of process and performance, and foam plastics play an indispensable role. However, current foams mainly consist of polystyrene, polyethylene, polyvinyl chloride and polyurethane, all of which belong to organic polymer materials and are derived from petroleum resources. With the continuous development of commodity logistics and electronic information industry, the amount of foam packaging products is rapidly increasing, which accelerates the consumption of petroleum, a non-renewable resource, and faces the increasingly exhausted predicament. On the other hand, the wastes after the use of foam packaging products have brought serious negative impact on the environment, exacerbating white pollution. Therefore, starting from the source and vigorously developing and promoting environmentally-degradable foam plastics is the most fundamental solution, and it is in line with the trend of green packaging in the plastic packaging industry.

In recent years, the research and development of environmentally degradable foams at home and abroad have attached great importance and have made some progress. The application of some biodegradable polymer materials can meet the requirements of environmental protection, and has important research value and practical significance for the preparation of degradable foam materials. This article gives an overview of the research status, existing problems and development prospects of biodegradable polymer materials in foams.

Research status

Biodegradable polymer materials can be divided into natural polymer materials, chemical synthetic polymer materials and microbial synthetic polymer materials. Starch, plant fiber, chitosan and other natural polymers are rich in natural resources and are cheap. They can be decomposed into glucose by the action of microorganisms in the natural environment, and are finally metabolized into water and carbon dioxide. They are inexhaustible renewable resources. It is widely used in biodegradable foaming materials. Starch, in particular, has many apparent and potential functional groups on its molecular chain segments, and has a very broad value for development and utilization. There are many reports at home and abroad, and it has become the core and main body of research. In addition, chemically synthesized polymer materials such as polyvinyl alcohol (PVA) and ethylene-vinyl alcohol copolymer (EVOH) can be decomposed by the physical, chemical, and direct action of microorganisms in a natural environment and have biodegradability. There are also many researches and applications in degradable foaming materials.

(1) Application of modified starch

Starch is a kind of strong polar crystalline material, with strong hydrogen bonds between molecules and molecules, poor thermoplasticity, and difficult processing. At the same time, starch is a hydrophilic material. Not only is the foam prepared from pure starch not suitable It is used in environments with high water or humidity, and climate change also has a greater impact on the performance of the product. Therefore, starch should be modified to meet the requirements of production and application. The swelling of starch in water is related to the gelatinization of starch, and the gelatinization of starch ultimately determines the foaming performance of starch. Therefore, all the modification methods related to gelation can be used for the modification of starch in foam plastics. . Starch modification methods mainly include esterification, etherification and cross-linking.

Esterified starch is generally used to increase the water resistance of starch and to alleviate the water absorption and brittleness of starch-based materials. RLShogren et al. use high amylose corn starch, acetic anhydride and sodium hydroxide aqueous solution to prepare acetate starch. The results showed that water is a highly efficient plasticizer for acetate starch. When a large amount of water is present, the glass transition temperature decreases from 165 to 185°C in dry starch to 95 to 35°C. This is mainly due to the substitution of acetyl groups for the starch hydroxyl groups, which weakens the Intermolecular hydrogen bonding makes the starch molecular chain easy to move in the dry state. Acetate starch with a degree of substitution of 2.5 is extruded at a water content of 15% and extruded at 150°C to obtain an expanded, water-resistant, smooth-surfaced foam with higher density and compressive strength than polystyrene foam but less elastic than polystyrene. In foam, the acetate starch degrades during extrusion. C. Fringant et al. used acetylated starch to prepare foam plastics. The results showed that the contact angle of the foamed plastic did not change significantly after being immersed in water. The foam prepared from pure starch began to deform within 1 hour after being immersed in water and then became a jelly. Whereas foams made from acetylated starch with a 50% substitution of 2.8 and 50% of the original starch remained intact after 24 hours, but became soft and flexible.

Naozumi Teramoto et al. introduced a semidry method for the preparation of starch ethers. This method uses 1-bromopropane in the presence of sodium hydroxide, prepared in the reaction of DMSO. Studies have shown that when the degree of substitution is 1.9, the starch is thermoplastic, providing conditions for the foaming process. Lacourse et al. invented a process for producing foamed plastics with high amylose modified (mainly hydroxypropyl starch) at a humidity of 10-21% and a temperature of 150-250°C.

Huang Yujie and other applications of glyoxal cross-linked starch to prepare foam products, the experimental results show that the cross-linked starch water resistance is good, 2.5 times the unmodified starch, and through orthogonal experiments to obtain the best reaction conditions. Billmers and others invented water-resistant foam products, in which starch is R1STR2Yx structure, ST is starch, R1 is dimethylene or vinyl, R2 is a hydrocarbon group containing 10 to 16 carbon atoms, Y is a metal atom, and X is an atom Count to keep the charge balanced. Its degree of substitution is 0.03 to 0.12.

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