Analysis of Biodegradable Polymers (2)

Natural polymer biodegradable plastic

If the biodegradable polyesters prepared with hydroxycarboxylic acids can meet specific commercial properties, then the problem to be solved after adding plastics such as starch, cellulose, chitosan, or protein fillers is to properly process the filler components in the composite materials. Than the relationship, ensure the degradation system, so that the material has a good physical-mechanical performance and reasonable prices. Starch is widely used as a natural compound in biodegradable packaging materials. Water-soluble films containing starch and pectin can be broken down by bacteria after adding plasticizers (such as glycerol, polyglycol). It should be noted that as the starch content increases, the brittleness of the film also increases. Composite materials containing natural starch, amylose, and a small amount of weak acids can be produced by extrusion molding of boards and packaging products. When processing composites containing high amylose starch and natural starch, glycerol, urea, and polyethylene glycol with a molecular weight of more than 3,000 are added as plasticizers and then extruded on a twin screw to pelletize. The extruded pellets can produce hoses with an expansion ratio of 30, a shrinkage rate of 14%, and a strength of 10 MPa, and can also produce agricultural and packaging degradable films. To reduce the cost of living biodegradable materials (such as packaging materials, agricultural film, plastic film, garbage bags), it is recommended to use crude starch blended with polyvinyl alcohol, talcum powder and other fillers. The use of fine starches and the addition of water-soluble polyvinyl alcohol to produce foamed plates, disposable tableware. The degradation materials produced by adding 10% to 30% polyvinyl alcohol have better strength, flexibility and water resistance. The study of the permeability of the material in soil revealed that the ingredients in the material were rapidly degraded within one week. It has been proposed to produce biodegradable blister packaging materials using starch and hydroxycarboxylic acid polyesters. As we can see, although starch itself will degrade, in order to accelerate the rate of degradation to produce products with specific properties, polyester polymers are added to the composites in addition to starch. The starch- and polylactide-containing films were degraded in a compost at 40C for 7 days.

At present, some companies have turned the research and application of starch biodegradable materials into actual use of these materials. Biotec GmbH uses starch to produce compostable plastic that can be used in different fields:

- Production of disposable plastics from biodegradable pellets by injection molding - Foaming materials for food packaging - Compostable blown film from pellets - Bioflex

Environmentally friendly materials with good degradation properties can be degraded in compost at 30°C for 2 months and can produce substances that are conducive to plant decomposition. The use of this material with good degradation properties in life has broad prospects. In a plan to protect the surrounding environment, the Czech company Fatra started a compostable Ecofol film together with a starch producer and a polymer research institute. Ecofol is a biodegradable polyolefin film with added starch. Since the raw materials are cheap, the price of the film is only 70 kroons/kg. This thin film compost can be degraded in 3 to 4 months. The polymers produced by the blending of cellulose with epoxy compounds and dicarboxylic acid anhydrides are completely degraded within 4 weeks. This polymer can produce bottles, disposable containers and plastic films. The multilayer packaging film produced by mixing cellulose with pregelatinized starch has good resistance to high temperature and low temperature and is resistant to oil stains, and is suitable for the packaging of microwave ovens and electric oven baking products. In the production of biodegradable plastics, not only cellulose but also other products from the plant kingdom are used, in particular lignin, and lignin-containing substances are mixed with proteins and other fillers. Japanese research scholars have used processed pulp with polyester-vinyl ester and base oil to produce agricultural biodegradable materials.

In recent years, researchers have paid particular attention to the use of chitosan and cellulose composites for the production of degradable materials. When the content of chitosan in the composite material is 10% to 20%, the degradation film has good strength and water resistance. The density of the film is 01~0.3g/cm3, and it completely degrades and disappears in the soil within 2 months. The films of chitosan, microfiber and gelatin blended organisms have high strength and can be degraded by microorganisms when they are buried in the ground. They can be used as packaging films and mulch films, and can also be formed into pallets by molding the blends. The translucent film had a dry strength of 133 N/mm 2 and a wet strength of 21 N/mm 2 . Chitin is the main component of shells and fungi cell walls of crustaceans and insects such as shrimps and crabs. Yield is second only to cellulose. Chitosan is pulverized, hydrolyzed, and deacetylated into polysaccharides, and an acetic acid solution is prepared in a certain proportion, heated, cast into a film, and the film degrades in soil or sea water within a few months. The biodegradability of the film is related to the chitosan processing method. The chitosan films produced by the deacetylation contain NH2 groups, which degrade much faster than cellophane or polycarboxybutyrate films in aerobic compost. Degraded chitosan can accelerate the degradation and use this feature to produce a polyethylene film containing 10% chitosan. The results of the study show that this film can be completely degraded in 28 days. Researchers are also interested in natural proteins or steroids. People have produced films containing corn glutinous-hydrophobic proteins to package foods with high moisture content or used as food bags.

Japan's Showa Corporation has developed a biodegradable polymer that can be used as a TV housing and a computer housing. This is a thermosetting plastic prepared by heating an amino resin and a protein. The structure has not been discussed in detail. Samples of materials provided by the company have high thermal stability, toughness and elasticity and can be decomposed by bacteria in water or soil. The use of natural polymers such as glycans and proteins to produce biodegradable films has broad prospects because raw materials can be constantly updated, and raw material resources can also be said to be endless. In-depth research on biodegradable composite materials to ensure that the material's performance enables mass production is a top priority for researchers.

Synthetic biodegradable polymer

Although the biodegradable carboxylated carboxylic acid polyesters and natural polymer composites have developed rapidly, they have given industrialized production of polyethylene, polypropylene, polyvinyl chloride, polystyrene, and polyethylene terephthalate with good degradation. Performance is still the focus of research. Since the above polymers and their products can be permanently stored in the ground, it is particularly important to make these polymers have a degrading ability. We have now actively studied the following three aspects:

- Adding functional groups capable of accelerating photodegradation to biodegradable polymer structures - Adding natural fillers that accelerate the biodegradation of the base resin in the mass production of composite materials - Comprehensive development of biodegradable plastics based on industrial development

Ethylene oxide-containing ethylene polymers are photodegradable polymers, and vinyl ketone monomers can be used as photodegradants for polyethylene and polystyrene. The addition of 2% to 5% of vinyl ketone monomer to the ethylene copolymer or styrene copolymer can produce a film that can be subjected to the performance of polyethylene or polystyrene, and the film has photodegradability under ultraviolet irradiation of 290 to 320 nm. Photoactive fillers, dithiocarbamate iron, nickel dithiocarbamate, and related peroxides can be added to the composite to produce hydrocarbon landfill membranes. Pulp, carbonyl-containing alkyl ketones, and debris are added to the agricultural polyethylene film, polypropylene, and polyethylene terephthalate to accelerate photo-biodegradation. The film can be preserved for 8 to 12 weeks before photo-biodegradation. Production of biodegradable plastics using polyester and polyester amides is a future development trend. The two large chemical companies BASF and BAYER AG are actively involved in this research project. In 1995, BASF developed Ecoflex F, a completely biodegradable film that can be used as a packaging bag, agricultural film, and sanitary napkin. Ecoflex F mechanical properties can be compared with low density polyethylene, its fracture strength, toughness, water resistance, water vapor permeability are high. The film has good adhesion and can be printed on ordinary equipment. According to the production capacity, the company uses its own raw materials to produce synthetic polyester pellets, the price is 6.5 ~ 8.0DM/kg and the product price will change with the quality. The company also produced biodegradable foams for packaging using composites containing high-viscosity copolyesters. The company also developed biodegradable plastic products based on polyester and starch.

From the second half of 1990, BAYER AG produced a new compost biodegradable plastic BAK-1095, BAK-2195, a polyester amide that is degradable under aerobic conditions. The material has strong adhesion and can be widely used in the food industry and agriculture as a moisture-proof and weatherproof packaging. The BAK-1095 compost bag can be decomposed into carbon dioxide and water in a humid environment for 10 days. BAK-2195 injection molding is easier, and materials with added cellulose, sawdust, and starch have better hardness and strength. The material has a melting point of 175°C and can be injected into flower baskets, bottles, disposable containers, and hygiene products. After the above products are buried underground, they can be quickly decomposed by bacteria, fungi, and molds. In order to reduce the cost of biodegradable esters and polyester amides, many companies adopt flexible production methods, use industrialized raw materials as much as possible, and process final products on ordinary equipment as much as possible. The polymer produced by the extrusion process is non-toxic, meets the requirements of environmental protection and can significantly reduce the price of biodegradable plastics. The most important thing is to reduce plastic waste and shorten the time for plastics to be buried. According to information provided by BASF, Western Europe's demand for compost biodegradable polyesters, copolyesters and starch biodegradable materials will reach 200,000 tons/year. North Korea Sun Kyong Ind has developed a biodegradable polyester film Skyprene with a structure similar to that of polybutylene succinate that accepts polyethylene or polypropylene. Skyprene has the characteristics of instantaneous strength and recyclability of products. It can be biodegraded to form carbon dioxide and water in fresh water, seawater or buried underground for 60 days.

In recent years, people are actively researching and developing biodegradable composite materials containing both polyester-polyester amide groups, urethane and carbonate groups, especially carboxyl-containing carboxylic acids, so that large-scale production of compost products can be achieved. Manufactured products have high physical-mechanical properties and are easily priced.

in conclusion

The research and analysis of biodegradable plastics show that we have achieved certain achievements in this field. With the increase in the demand for packaging containers and packaging materials, and the increase in disposable supplies, there will be more and more plastic waste generated, which will cause greater damage to the surrounding environment. Therefore, people hope to restrict the use of non-biodegradable plastic packaging containers and packaging materials through strict legislation, and vigorously develop biodegradable plastics with a wide range of uses, low prices and excellent performance. In the European countries, governments and large chemical manufacturers have reached consensus on biodegradable plastics and solved some thorny problems. This is obvious to all. At the same time, in order to expand the research results of existing biodegradable plastics, researchers will develop new photo-biodegradable polymers.

From: Packaging magazine Author: Sun Tongtong