Introduction to the hottest biodegradable plastics

2022-08-25
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Introduction to biodegradable plastics

the research on biodegradation began in the United States in World War II 3, beam [yoke]. At that time, it was limited to the biodegradation of PVC, cellulose derivatives, and natural rubber. Titus in the early 20th century and Burgess and darby in the late 20th century put forward strong opinions on biodegradable plastics around the sensitivity of plastics to biology, and carried out research on the degradation of plastics by fungi and bacteria. Later, zanova and Evans further improved the research on the biodegradability of plastics

biodegradation in nature depends on special materials and special organisms, such as paper, plastic, chemical substances, and organisms such as fungi and bacteria. According to astmo standard, the United States Environmental Protection Agency (EPA) conducts biodegradation test of plastics (including PE, PS, pet, etc.) mixed with Aspergillus and Penicillium. The test involves the aliphatic ester chain attached to the main chain of the polymer, as well as the photosensitive properties of the polymer, for accelerated biodegradation test. Add various stabilizers, plasticizers, lubricants, antioxidants, fillers and starch (polysaccharide molecules, protein molecules), as well as various metabolic active agents (ammonia, acids, biopolymers, polar and non-polar solvents, etc.) to the plastic resin according to different use conditions and requirements. Experiments have proved that this will promote the growth and reproduction of microorganisms and accelerate the biodegradation effect of plastics

biodegradable plastics need to maintain plastic properties, namely, stability in use, various applications, ease of treatment, and economy; In terms of degradation, biological systems are used to break the main components of plastic molecular chains. (i.e. the use of light, biological, or chemical effects, as well as the use of additives to promote degradation)

PE milk packaging containers, PET bottles and other plastic packaging containers are widely used in recycled plastic products abroad. However, plastic diapers, women's hygiene products, medical supplies (such as drapery for surgery, wrapping products, masks and other products) are no longer used for recycling. Although some baby diapers belonging to wood pulp products are degradable materials, because the lining adopts P, the outer surface also uses PP according to the needs of customers. If recycled, separation technology and cleaning are required, which is uneconomical in cost accounting

I. main degradation of polymers:

1 The starch degraded polymer

decomposes the starch chain in the PE polymer chain with bacterial enzymes, breaking the polymer chain into small units, thus promoting the rapid degradation of the whole mechanical strength of PE

2. Microbial degradable polymers produced by bacteria

linear polyester products (PHBV polymers) are degraded by bacterial saccharifying enzyme fermentation, and plastic products are degraded by bacteria in soil and sludge pond

Dr. Lawrence Swanson of the K.E. Association of the United States, New Jersey Institute of technology, and Dr. sunny byookhavan of New York explored, studied and developed the technology of adding starch and additives to PP and PE, which can degrade waste plastics in soft mud and seawater

Germany introduced PP and PE plastics that can be biodegradable in water and liquid from South American company belland

foreign experts generally believe that in an environment rich in oxygen and humidity, it can promote the rapid biodegradation of plastics, such as by anaerobic bacteria, but it will produce methane gas

II. Overview of biodegradable plastic products produced abroad at present

a large number of garbage bags can achieve rapid biodegradation in the process of filling land. Adding organic metal compound multilayer plastic agricultural film to PE and PP film can obtain rapid degradation effect

ICI uses natural bacteria to produce biodegradable plastic bottles for packaging shampoo. The bacteria can convert a large amount of glucose into shampoo bottles. Under the condition of aerobic bacteria, they can contact with water, carbon dioxide and rotten soil. Through natural bacteria and fungi, they can biodegrade plastic bottles and plastic films. The company calls this kind of degradable plastic PHBV, which has durability, stability, water resistance and other properties before biodegradation

a large number of modern biodegradable plastics are developed by Warner Lambert company, which are made of potato starch, rice starch and wheat starch. Morris Plains NJ pharmaceutical company adopts pressure humidification, heating and pressing starch to form a ductile matrix, and molds and extrudes various plastic products together with plastics

at present, the commercial biodegradable plastic on the market uses the bacterial lactic acid formed by the glucose enzyme in potatoes or cheese as the biodegradable plastic structure. This structure is different from the simple use of cereal starch, which uses its medium to degrade plastic

adding 15% cereal starch polymer to plastics can also degrade plastics. This method uses bacteria to devour cereal starch while swallowing plastic residues. However, although the plastic breaks into tiny particles, it can still resist degradation for many years. The cereal starch additive produced by ADM company can quickly biodegradable plastic film bags and various plastic bags. The biodegradation is characterized by breaking the polymer long chain into small pieces and filling the land. ADM company has been committed to developing new degradable plastics in recent years

it is reported that the proportion of biodegradable plastics used abroad has increased from 40% to more than 60%

the commonly biodegradable cereal starch groups are 50 ~ 52 μ Oval potato starch of M, 36.4 μ M of wheat starch, 25 μ M taro starch and lotus root starch, 14.2 corn starch, 5 ~ 5.6 μ M rice starch, cassava starch, etc

the mixture of adding starch to the polymer is called SPE material for short. The specific gravity of thermoplastics is generally 0.924 ~ 1.450, while the specific gravity of starch is generally 1.5. When at 50 μ Mixing 30% rice starch into m-thick PE film can promote microbial invasion under a certain ambient temperature. Mix 60% starch or 50% starch into LDPE plastic, and it needs to be stirred for 4min. Since LDPE film blowing is very sensitive to starch mixture, it is generally 20% mixture. If it is used for a short time, 50% starch can also be added. For LDPE molding bottle blowing, 50% starch can be mixed, while LDPE woven tape can be mixed with 10% starch, if it is used φ 120mm large screw extruder, its die temperature is ℃, the compression ratio is 4:1, the cylinder temperature is 190 ℃, and at the same time, it adopts cold air flow for cooling, 50 μ 30% of LDPE film blowing mixed starch, 30% of LDPE molded products mixed with corn starch, and 30% of LDPE pressed plate mixed starch

pp polymers can generally be mixed with 50% starch, PP belts with 15% starch (about 6:1), polyurethane elastomers with 40% starch, PP woven belts, and molded products with rice starch (its extrusion temperature is 230 ℃)

confirmed foreign reports: if plastic plates are buried in compost (the depth is 10cm, 60cm, 100cm, the depth is selected according to the specific situation, and the angle is 45 °), they can be degraded by fungi and bacteria after 7 months; If composting is cleaned, the surface layer of 10cm plate can be degraded by fungi and bacteria in six weeks when the temperature is below 52 ℃. If the plastic plate is buried in the soil (buried depth of 40cm), it can be degraded by fungi and bacteria for 4 months. 1mm thick polyurethane elastic plate mixed with 40% starch is buried in the outdoor garden soil (buried depth of 5 ~ 10cm). It takes two weeks to cluster fungi and bacteria on the plate, which will degrade rapidly after four-star period

adding 0.5% concentration of glucose mixture can make the plastic box appear discoloration, pores, embrittlement, and be degraded by black spores. Adding 0.1 ~ 0.5% glucose mixture can decolorize and soften PVC plastic products and be degraded by melanospores. When PE film waste is buried in black soil, it will be degraded by anaerobic work, but anaerobic bacteria will produce hydrogen sulfide (H2S) pollution source. PE waste plastic bottles are buried in the soil at a depth of 4.6m. If anaerobic bacteria are used for degradation, it will take 4-7 years. If the buried waste plastic film is degraded by aerobic bacteria, it will take 3-5 years

for example, the use of active agents and esters with oxygen absorption and metabolism can change the properties of plastics, make plastics weightless and accelerate biodegradation

in addition, adding additives to plastics will further accelerate biodegradation

III. there are generally five types of biodegradable plastic films in foreign countries: 1) natural polymer additive film; 2) The polymer produced by microorganisms is added into the membrane; 3) Biopolymer addition membrane; 4) Adding biodegradable substances to make membrane; 5) Adopt the membrane made of degradable substances produced by microorganisms in the soil and the membrane that can be biodegradable by bacteria in the soil. Experts believe that biodegradable membranes developed by contemporary countries belong to this category

(compiled by Zhang Jianping)

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