Research on Biodegradable Packaging Plastic Technology

With the extensive use of packaging materials, the disposal of some waste packaging materials is currently a problem that needs to be solved. There are three methods for disposal of waste packaging materials: landfill, incineration, and recycling. The landfill method not only causes pollution to the land, but also wastes a large amount of land. The incineration method releases a large amount of toxic gases and pollutes the atmosphere. The recycling and collection method is troublesome to collect and sort, and it is difficult to apply. Therefore, it is very necessary to develop suitable packaging materials.

Biodegradation is a new method for solving waste packaging materials. It has the characteristics of convenient storage and transportation, and a wide range of applications. Among biodegradable packaging materials, biodegradable packaging plastics is a common packaging material.

1 Biodegradable plastics and their classification

Biodegradable plastics are plastics that can be degraded by microorganisms in the presence of water and nutrients. Biodegradable plastics are divided into two categories, complete biodegradation and biodegradable degradation, based on their mechanisms and forms of destruction.

1. 1 completely biodegradable plastic

Fully biodegradable plastics are plastic materials whose molecular structure can be completely decomposed by microorganisms or enzymes into simple compounds. At present, such materials mainly include natural macromolecule type, synthetic type, microbial synthesis type and plant transgenic type materials.

1.2 Biodegradable Biodegradable Plastics

Biodegradable degradable plastics are mainly degradable plastics composed of natural polymers and synthetic polymers. At present, the composite method that is expected to be applied in the packaging field is still based on blending, and its preferred substrate is also starch and cellulose.

2 Biodegradable packaging material degradation mechanism

2. 1 complete biodegradation mechanism

The mechanism of complete biodegradation is that biodegradable materials can be completely decomposed into low-molecular compounds such as CO2, H2O, or ammonia under the action of microorganisms in the natural world such as bacteria, mold, and algae. It has the characteristics of convenient storage and transportation, a wide range of applications. There are roughly three modes of action in the degradation process.

1) The physical effects of the organisms cause the mechanical destruction of the material due to the growth of biological cells;

2) the biological effects of microorganisms on the polymer to produce new quality;

3) Direct action of enzymes Microbial erosion results in partial material splitting or oxidative lysis.

2. 2 Bio-destructive degradation mechanism

Refers to the use of natural polymers (starch, cellulose, etc.) microbial degradability, using synthetic plastics modification (copolymerization), overcome the shortcomings of poor natural polymer strength, get biodegradable plastic.

3 Biodegradable Packaging Plastics Research

Biodegradable packaging plastics can be biodegradable packaging plastics that can be decomposed under natural environmental conditions in a short period of time. It is a new method that replaces the current conventional plastics and solves “white pollution”, and is also a research hotspot at home and abroad.

Research on biodegradable materials has been reported both at home and abroad. Biodegradable packaging plastics include starch-based biodegradable plastics, microbial fermentative synthetic biodegradable materials, cellulose-based biodegradable plastics, light/biodegradable plastics, and synthetic biodegradable materials.

3.1 starch-based biodegradable plastics

Starch-based biodegradable plastics have been reported. Teng Lijun et al. used starch-polyethylene biodegradable film and general plastic films of polyethylene (PE) and polypropylene (CPP) as materials, and studied the physical and mechanical properties. The research shows that the degradation rate of the degraded materials used in the test is greater than 20% within 20-30 days; the water absorption and permeability are higher than those of the general-purpose films PP and CPP; the mechanical properties can meet the requirements. At the same time, the application prospect of biodegradable films in the packaging field was analyzed. Starch plastics generally refer to plastics whose composition contains starch or its derivatives. Plastics with natural starch as the filler and natural starch or its derivative blend system as the main component 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 of raw starch with general-purpose plastics such as PE and styrene (PS), it is often necessary to introduce ethylene vinyl acetate and other compatibilizers to prepare blends. In foreign countries, especially in Italy, the United States, and Japan, the research on starch-based polyvinyl alcohol plastics is in the ascendant. Each has its own technical features and has reached a certain height. The production of its products has formed a certain scale and influence. Modified to produce a biodegradable plastic with a high starch content (90% or more), which is an opaque gray resin, has a melting point of about 175 to 200°C, is extruded at 130°C using a twin-screw extruder, and is granulated with water. Plasticizer molding processing, its injection product performance and PS similar, but the tensile strength is better than PS, aerobic and anaerobic conditions are easily biodegradable, suitable for fast food packaging materials. Foreign countries have already mass-produced blended starch-based plastics, but also developed and produced degradable plastics using gelatinized starch and PVA blends. In recent years, a new kind of starch composite material has been developed abroad. Since it does not contain non-degradable macromolecules or small molecule components, it can be completely biodegraded in the environment and can be used for disposable plastic products.

The reason why starch-based plastics are easily degraded is mainly due to the decomposition of starch components in the products, and many micropores appear on the surface of the products up to the inside, which increases the surface area for chemical, biological, and other erosion and accelerates the degradation of the remaining parts. The higher the starch content, the faster the biodegradation rate.

3.2 Biofermentation of Synthetic Biodegradable Plastics

Biodegradable packaging materials made from honey and oil are both thermoplastic and fully biodegradable. Its main products are the "Biopol" copolyesters of 3-hydroxybutyl and 3-hydroxypentyl esters (0% to 30%) from British ICI, and the polyhydroxybutyrate (PHB) developed by the Institute of Resources Research, Tokyo Institute of Technology, Japan. ) and aliphatic copolyesters developed by the Massachusetts Institute of Technology (MTI). One of the major advances was Biopol, which was developed in the United Kingdom by ICI in 1976, using microbial starch fermentation. It began industrialization in 1990. The product has a thermal decomposition temperature of 200°C and can be completely decomposed in the compost site for 1 year without secondary pollution. In addition, PHB is a substance that stores raw materials in the bacteria to cope with food stress and can be activated by many bacteria, leading to rapid degradation. Research in this area has great development prospects.

3. 3 synthetic biodegradable plastics

The use of chemical synthesis to manufacture biodegradable packaging materials has greater flexibility than microbial synthesis methods and the products are easy to control. The research and development work is to synthesize a substance having a structure similar to a natural polymer or a polymer containing a readily biodegradable functional group. The current main products are polylactic acid (PLA) and polycaprolactone (PCL). PLA is a kind of polyhydroxy acid. As a kind of biological raw material, it has good biodegradability and has good biological compatibility. And bioabsorbability [11] does not leave any environmental problems after degradation. Its manufacturers mainly include Shimadzu Corporation and Mitsui East Asia Chemical Corporation in Japan, Cargill Corporation and Ecochem Corporation in the United States. In 1998, Germany's Danone and Cargill Dow collaborated to develop a rapidly degradable DANONE yogurt cup using polylactic acid as raw material. Japan Bell Spinning Fiber Co., Ltd. uses polylactic acid extracted from corn as a raw material to produce a biodegradable foamed plastic. Some of the physical and chemical properties of this material are the same as those of polystyrene, so existing plastic foaming equipment can still process it. PCL is formed by the open chain polymerization of E-caprolactone under the action of a catalyst. The soil slowly decomposes and it can decompose to 95% in a year.

Degradable plastics is one of the effective ways to solve the environmental pollution problems of disposable plastic packaging products. It can be described as green plastic packaging materials. In recent years, the industrialization process has been rapid. According to reports, the application of degradable polymer materials in the United States in 2000 can reach 1 million tons; in Europe, it also increases at an annual rate of 400,000 to 500,000 tons; the development and production of degradable plastics in China have also become hot spots. Some varieties have entered the market and the outlook is in the ascendant.

At present, the industrialized degradable plastics include photodegradation, photobiodegradation, biodegradation, biodegradation, and the like. Although the photodegradation technology is relatively mature, the environmental impact factors of its degradation behavior are very complicated, which limits its application in the packaging field.

3.4 Cellulosic Based Biodegradable Plastics

Natural polymer cellulose, like starch, is non-thermoplastic and cannot be processed by conventional processing methods. The use of blending or chemical modification methods to destroy the hydrogen bonds of cellulose, to react the hydroxyl groups on cellulose molecules, to obtain cellulose derivatives, and then blended with unmodified cellulose or raw starch, etc. Degradable plastics with different properties are processed into various products or membranes with good mechanical properties, low production costs, and fast degradation rates. Some studies have found that 30% to 85% of degradable cellulose derivatives are blended with 30% to 70% of unmodified cellulose or raw starch, and can be made into a variety of molding methods such as injection molding and casting. Products or membrane materials, their performance, degradation rate, production costs have the potential to promote the application of packaging, can be used for food, daily necessities packaging.

3. 5 light/biodegradable plastics

In biodegradable plastics, the degradation behavior of the material must be performed in a biologically active environmental medium. Adding a proper amount of photosensitizer can make the plastic have both photo and biological degradation properties. Under certain conditions, the controllability of degradation rate is obviously improved. Therefore, the development of photobiodegradable plastics has received widespread attention at home and abroad. Has become an important research and development direction of degradable plastics. In recent years, extensive studies have been conducted on the degradation rate, degradation control, completeness of degradation, environmental safety of degradation products, and evaluation methods for degradable materials, and have achieved certain breakthroughs. Applications of these materials in the field of packaging will Has a broad development prospects.

Reprinted from: China Packaging Machinery Network