Biodegradable plastic

The study of biodegradation began in the United States during the Second World War, when it was limited to the study of the biodegradation of PVC, cellulose derivatives, and natural rubber. In the early 20th century, Titus and later Burgess and Darby put forth strong opinions about biodegradable plastics around plastics, and developed studies on the degradation of plastics by fungi and bacteria. Later, Zanova and Evans further improved plastics. The study of biodegradability.
Biodegradation in the natural world depends on special materials and special organisms, such as paper, plastic, and chemical substances, and their organisms such as fungi and bacteria. According to the ASTMO-1924-63 standard, the United States Environmental Protection Agency (EPA) uses plastics (including PE, PS, PET, etc.) for the biodegradation test of Aspergillus and Penicillium. This test involves the aliphatic ester chain attached to the main chain of the polymer, and the photosensitivity characteristics of the polymer, etc., for accelerated biodegradation tests. Various stabilizers, plasticizers, lubricants, antioxidants, and various fillers and starches (polysaccharide molecules, protein molecules) and various metabolic active agents (ammonia, acid, biopolymers) are added to plastic resins. , polar and non-polar solvents, etc.). It has been confirmed by experiments that this will promote the growth and reproduction of microorganisms and accelerate the biodegradation effect of plastics.
Biodegradable plastics need to maintain the characteristics of plastics, namely, stability in use, various applications, ease of handling, and economics; use of biological systems in the degradation of the main components of the molecular chain of plastics breaks. (ie, use light, biological, or chemical effects, and the use of additives to promote degradation).
The use of PE plastic packaging containers, PET bottles and other various plastic packaging containers in foreign recycled plastic products. However, plastic diapers, feminine hygiene products, and medical products (such as surgical folds, drapes, wraps, and face masks) are no longer used for regeneration. Some baby diapers belonging to wood pulp products are themselves degradable materials, but because the inner lining is made of PP, the outer surface is also made of PP. If it is used for regeneration, separation technology and cleaning are needed, which is not economical in cost accounting.
First, the main degradation of the polymer:
1. Starch-degrading polymers break down the starch chains in the PE polymer chains with bacterial enzymes, breaking the polymer chains into small units, which in turn causes the entire mechanical strength of the PE to decrease and rapidly degrade.
2. Microbial degradation produced by bacteria The polymer is fermented by bacterial saccharification enzymes, and the linear polyester product (PHBV polymer) is degraded, and the plastics are degraded by bacteria in the soil and sludge ponds.
Dr. Lawrence Swanson of the American KE Association, New Jersey Institute of Technology, and Dr. Suny Byookhaven of New York State explored and developed techniques for adding starch and additives to PP and PE to degrade waste plastics in soft mud and seawater.
Germany has introduced PP and PE plastics that are biodegradable in water and liquids from Belland, South America.
Foreign experts generally believe that in an environment rich in oxygen and humidity, it can promote rapid biodegradation of plastics, such as degradation by anaerobic bacteria, but will produce methane gas.
Second, the current foreign production of biodegradable plastic products Overview A large number of garbage bags in the process of filling the land, can achieve rapid biodegradation. In the PE, PP film to add organic metal composite multi-layer plastic agricultural film, you can get rapid degradation.
ICI uses natural bacteria to produce biodegradable plastic bottles that package shampoos. The bacteria can convert a large amount of glucose into shampoo bottles. Under conditions of aerobic bacteria, they can contact with water, carbon dioxide, and decayed soil. Through natural bacteria and fungi, they can Plastic bottles and plastic films are biodegraded. The company claims that this type of biodegradable plastic is PHBV, which is durable, stable and resistant to water before it is biodegraded.
A large number of modern biodegradable plastics were developed by the Warner-Lambert company, which uses potato starch, rice starch, and wheat starch, and Morris Plains NJ Pharmaceutical Co., Ltd. uses pressure to humidify, heat, and compress starch to form a tough matrix, along with plastics. Take molded and extruded plastic products.
The commercial biodegradable plastics currently available on the market use glucoamylase in potato or cheese, which is composed of lactic acid, which is a biodegradable plastic structure. This structure is different from cereal starch alone in that it is degraded by using its plasmodium. plastic.
The addition of 15% cereal starch polymer to plastics can also degrade plastics. This method uses bacteria to eat grain starch while swallowing plastic residue. However, although plastics are broken into tiny particles, they are still resistant to degradation for many years. The starch additive produced by ADM can rapidly biodegrade plastic film bags and various plastic bags. The characteristics of this biodegradation are: The strand breaks into small pieces and fills the land. In recent years, ADM has been continuously developing new degradable plastics.
It has been reported that the proportion of biodegradable plastics used abroad has increased from 40% to over 60%.
The commonly used biodegradable cereal starch groups are 50-52 μm oval potato starch, 36.4 μm wheat starch, 25 μm glutinous and stigma starch, 14.2 corn starch, 5 to 5.6 μm rice starch, and tapioca starch.
The mixture of starch in the polymer is abbreviated as SPE material. The specific gravity of thermoplastics is generally 0.924 to 1.450, while the specific gravity of starch is generally 1.5. When 30% rice starch is mixed in a 50 μm thick PE film, it can promote the invasion of microorganisms while maintaining a certain ambient temperature. In the LDOE plastic mixed with 60% starch or 50% starch, need to stir 4min, given that LDPE blown film is extremely sensitive to starch mix, so generally take 20% of the mixture, such as short-term use can also add 50% starch, LDPE Molded blow-molded bottles can be mixed with 50% starch, while LDPE braided tape can be mixed with 10% starch, such as φ120mm large screw extruder, die head temperature is 280-300°C, compression ratio is 4:1, cylinder The temperature is 190 °C, while cooling with a cold air flow, 50μm LDPE blown film blended starch is 30%, LDPE molded products mixed with 30% corn starch, LDPE pressed sheet mix 30%.
PP polymer can be generally mixed with 50% starch, PP tape mixed with 15% starch (about 6:1), polyurethane elastomer mixed with 40% starch, PP braided tape, molded product mixed rice starch (its extrusion temperature is 230°C) .
Confirmed foreign reports: If the plastic sheet is buried in compost (depth of 10cm, 60cm, 100cm, depending on the selected depth, the angle is 45 °), after 7 months can be degraded by fungi and bacteria; such as cleaning compost, The surface layer of the 10cm plate, when the temperature is below 52°C, can be degraded by fungi and bacteria for six weeks. If the plastic sheet is buried in the soil (buried at a depth of 40cm), it will be degraded by fungi and bacteria for 4 months, and 1mm thick polyurethane elastic sheet mixed with 40% starch will be buried in the outdoor garden soil (buried at a depth of 5 to 10cm). The cluster of fungi and bacteria on the plates lasted two weeks and they rapidly degraded in four weeks.
Adding a 0.5% concentration of glucose mixture can cause decolorization, small holes, and embrittlement in the plastic box and be degraded by black spores. Adding a glucose mixture with a concentration of 0.1 to 0.5% can decolorize and soften the PVC plastic products and be degraded by the black spores. PE film waste is buried in black soil and will be degraded by anaerobic work. However, anaerobic bacteria will produce hydrogen sulfide (H2S) pollution source. PE waste plastic bottle is buried in soil with a depth of 4.6m. If it is degraded by anaerobic bacteria, it will reach For 4 to 7 years, if the buried plastic film is degraded by aerobic bacteria, it will be 3 to 5 years.
For example, the use of active agents and esters with oxygen-absorbing function and metabolism can change the properties of plastics and make plastics lose weight and accelerate biodegradation.
In addition, the addition of additives to plastics will further accelerate biodegradation.
Third, the type of foreign biodegradable plastic film is generally five kinds: 1) the use of natural polymers plus film; 2) to take the polymer produced by micro-organisms plus film; 3) using bio-polymer film; 4) by adding The biodegradable substance is added to the film; 5) A film is added which is made of a degradable substance produced by microorganisms in the soil, and a biodegradable film is made using bacteria in the soil. Experts believe that biodegradable membranes developed by contemporary countries are all within this category. (Zhang Jianping compiled)