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Research on biodegradable packaging plastics technology

with the extensive use of packaging materials, the treatment of some waste packaging materials is a problem that needs to be solved at present. Generally, the treatment of waste packaging materials mainly includes landfill, incineration and recycling. Landfill not only pollutes the land, but also wastes a lot of land; Incineration method releases a large amount of toxic gases, causing pollution to the atmosphere; Recycling is difficult to collect and sort, and it is difficult to apply in practice. Therefore, it is very necessary to develop appropriate packaging materials. Biodegradation is a new method to solve the problem of waste packaging materials. It has the characteristics of convenient storage and transportation and wide application range. Among biodegradable packaging materials, biodegradable packaging plastic is a common packaging material

1 biodegradable plastics and their classification

biodegradable plastics refer to plastics that can be degraded by microorganisms in the presence of water and nutrients. According to its mechanism and the scope of utilization, biodegradable plastics can be divided into two types: complete biodegradation and biodegradable degradation

1. 1 fully biodegradable plastics

fully biodegradable plastics refer to plastic materials whose molecular structure can be completely decomposed into simple compounds by microorganisms or enzymes. At present, this kind of materials mainly include natural polymer materials, artificial synthetic materials, microbial synthetic materials and plant transgenic materials

1. 2 biodegradable plastics

biodegradable plastics are mainly degradable plastics made of natural polymers and synthetic polymers. At present, the composite method that is expected to be applied in the packaging field is still mainly blending, and its preferred substrates are starch and cellulose

2 degradation mechanism of biodegradable packaging materials

2 1 complete biodegradation mechanism

complete biodegradation mechanism is that biodegradable materials can be completely decomposed into low molecular compounds such as post-c ring method, gradual approximation method, non proportional elongation strength, tensile strength, compressive strength, arbitrary point elongation strength, arbitrary O2, H2O or ammonia under the action of natural microorganisms, such as bacteria, molds and algae. It has the characteristics of convenient storage and transportation and wide application range. There are roughly three modes of action in its degradation process

1) the physical action of biology causes mechanical destruction of substances due to the growth of biological cells

2) the chemical action of biology and the action of microorganisms on polymers produce new substances

3) the direct action of enzymes and microbial erosion lead to the division or oxidative cracking of some materials

2. 2. Mechanism of biodegradable degradation

refers to the use of microbial degradability of natural polymers (starch, cellulose, etc.) and the modification (copolymerization) of synthetic plastics to overcome the shortcomings of poor strength of natural polymers and obtain biodegradable plastics

3 research on biodegradable packaging plastics

biodegradable packaging plastics can decompose in a short time under natural environmental conditions. It is a new method to replace the current conventional plastics and solve the "white pollution", and it is also a research hotspot of scholars at home and abroad

research on biodegradable materials has been reported at home and abroad. Biodegradable packaging plastics include starch based biodegradable plastics, biodegradable materials synthesized by microbial fermentation, cellulose based fully biodegradable plastics, light/biodegradable plastics and synthetic biodegradable materials

3. 1 starch based biodegradable plastics

there have been research reports on starch based biodegradable plastics. Tenglijun et al. Studied the physical and mechanical properties of starch polyethylene biodegradable film and general plastic film polyethylene (PE) and polypropylene (CPP). The research shows that the degradation rate of the degradation material used in the test is more than 20% within 20 ~ 30 days; The water absorption and permeability are higher than that of general film PP and CPP; The mechanical property index can meet the use requirements. At the same time, the application prospect of biodegradable film in packaging field was analyzed. Starch plastics generally refer to plastics containing starch or its derivatives in their composition. Plastics with natural starch as filler and natural starch or its derivatives blend system as the main composition belong to this category, in which the proportion of starch can be as high as 60%. Starch based plastics are a large class of degradable plastics

due to the poor compatibility between raw starch and general-purpose plastics such as PE and styrene (PS), it is often necessary to introduce compatibilizers such as ethylene and vinyl acetate to prepare blends. Abroad, especially in Italy, the United States and Japan, the research on starch based polyvinyl alcohol plastics is in the ascendant, and each has its own characteristics in technology. In order to meet the needs of automobile 1 and reach a certain height, the production of its products has formed a certain scale and influence. The United States has modified starch to make biodegradable plastics with high starch content (more than 90%), which is an opaque gray resin with a melting point of about 175 ~ 200 ℃, Using twin-screw extruder to extrude and granulate at 130 ℃ and water as plasticizer for molding and processing, the properties of its injection molded products are similar to PS, but the tensile strength is better than PS. it is easy to biodegrade under aerobic and anaerobic conditions, and is suitable for fast food packaging materials. Foreign countries have mass produced blended starch based plastics, and also developed degradable plastics by blending gelatinized starch and PVA. In recent years, a new starch composite material has been developed abroad. Because it does not contain non degradable macromolecular or small molecular components, it can be completely biodegradable in the environment and can be used for disposable plastic products

the main reason why starch based plastics are easy to degrade is that after the starch component in the product is decomposed, many micropores appear on the surface and inside of the product, which increases the surface area of chemical, biological and other erosion, and accelerates the degradation of the residual part. The higher the starch content, the faster the biodegradation speed

3. 2 microbial fermentation synthesis of biodegradable plastics

biodegradable packaging materials made from honey and oil have both thermoplastic processability and complete biodegradability. Its main products include the copolyester "biopol" of 3-hydroxybutyl ester and 3-hydroxyamyl ester (0% ~ 30%) of ICI company in the UK, polyhydroxybutyrate (PHB) developed by the Resource Research Institute of Tokyo University of technology in Japan, and aliphatic copolyesters developed by Massachusetts Institute of Technology (MTI) in the United States. Among them, "biopol", which was studied by British ICI company in 1976 and made by microbial starch fermentation, began industrialization in 1990. The thermal decomposition temperature of the product is 200 ℃, and it can be completely decomposed in the composting site for 1 year, without secondary public hazards. In addition, PHB is a substance that stores raw materials in bacteria to cope with food stress. It can be activated by many bacteria, resulting in rapid degradation. The research in this area has great development prospects

3. 3 synthetic biodegradable plastics

using chemical synthesis to manufacture biodegradable packaging materials has greater flexibility than microbial synthesis, and the products are easy to control. The research and development work is to synthesize substances with structures similar to natural polymers or polymers containing easily biodegradable functional groups. At present, the main products are polylactic acid (PLA) and polycaprolactone (PCL). PLA is a kind of polyhydroxy acid. As a biogenic product, it has good biodegradability, good biocompatibility and bioabsorbability [11], and will not leave any environmental protection problems after degradation. Its manufacturers mainly include Shimadzu production Institute in Japan, Mitsui East Asia chemical company, Cargill company and ecochem company in the United States, etc. In 1998, Danone of Germany cooperated with cargilldow to develop a quick degradable Danone yogurt cup with polylactic acid as raw material. Japan Zhongfang synthetic fiber company has produced biodegradable foamed plastics with polylactic acid extracted from corn as raw material. Some physical and chemical properties of this material are the same as those of polystyrene, so the existing plastic foaming material equipment can still process it. PCL is formed by the chain opening polymerization of e-caprolactone under the action of catalyst. It will slowly decompose in soil, and can decompose to 95% in a year

degradable plastic is one of the effective ways to solve the environmental pollution problem of plastic packaging disposable products, which can be described as green plastic packaging materials. In recent years, the industrialization process has been rapid. It is reported that the baptism application of degradable polymer materials in the hands of producers in the United States in 2000 can reach 1million tons; Europe also increases at a rate of 400000 ~ 500000 tons per year; The development and production of degradable plastics in China has also become a hot spot. Some varieties have entered the market, and the prospect is in the ascendant

at present, the varieties of degradable plastics that have been industrialized include photodegradation, photobiodegradation, biodegradation, genetically modified biodegradation, etc. Although photodegradation technology is relatively mature, the environmental factors affecting its degradation behavior are very complex, which limits its application in the field of packaging

3. 4 cellulose based fully biodegradable plastics

Natural Polymer cellulose, like starch, is a non thermoplastic material and cannot be processed by conventional processing methods. The hydrogen bond of cellulose is destroyed by blending or chemical modification, so that the hydroxyl group on the cellulose molecule reacts to obtain cellulose derivatives, which are then blended with unmodified cellulose or raw starch to produce degradable plastics with different properties, and processed into various products or films with good mechanical properties, low production cost and fast degradation speed. It has been found that degradable plastics made by blending 30% ~ 85% degradable cellulose derivatives with 30% ~ 70% unmodified cellulose or raw starch can be used to make various products or films by injection molding and tape casting. Its performance, degradation speed and production cost have the potential to be popularized and applied in the packaging field, and can be used in the packaging of food and daily necessities

3. 5 light/biodegradable plastics

in biodegradable plastics, the degradation behavior of materials must be carried out in an environment medium with biological activity. Adding an appropriate amount of photosensitizer can make the plastic have both light and biological degradation properties at the same time. Under certain conditions, the controllability of degradation speed is significantly improved. Therefore, the development of photobiodegradable plastics has received widespread attention at home and abroad. It has become one of the important research and development directions of degradable plastics. In recent years, extensive research has been carried out on degradation rate, degradation control, degradation completeness, environmental safety of degradation products and evaluation methods of degradation materials, and some breakthroughs have been made. This kind of materials will have broad development prospects in the field of packaging

Author: Bai Songfang

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