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biodegradable
Degradable Plastics Popular Science Knowledge Series
25
May
May
What are biodegradable materials?
Biodegradable materials include biodegradable natural polymer materials such as cellulose, starch, paper, etc., as well as biodegradable plastics obtained by biosynthesis or chemical synthesis.
Biodegradable plastic refers to degradation caused by the action of microorganisms in nature under natural conditions such as soil and/or sand, and/or specific conditions such as composting conditions or anaerobic digestion conditions or in aqueous culture fluids. Eventually, it will be completely degraded into carbon dioxide (CO2) or/and methane (CH4), water (H2O) and mineralized inorganic salts of the elements contained therein, as well as new biomass (such as microbial dead bodies, etc.).
It should be noted that every kind of biodegradable material, including paper, requires certain environmental conditions for its degradation. If the degradation conditions are not available, especially the living conditions of microorganisms, its degradation will be very slow; at the same time, not every kind of organism Degradable materials can quickly degrade under any environmental conditions. Therefore, when dealing with biodegradable materials, we should start from its environmental conditions and analyze the structure of the material itself to determine whether it is a biodegradable material. How to judge whether a material is biodegradable, internationally and China have issued a series of testing method standards, which are answered in the standard question.
What types of biodegradable plastics are there?
According to the raw material source of biodegradable plastics, it can be divided into two types: bio-based biodegradable plastics and petrochemical-based biodegradable plastics.
Bio-based biodegradable plastics can be divided into four categories: The first category is plastics directly processed from natural materials. At present, the biodegradable plastics produced by natural polymers on the market mainly include thermoplastic starch, biocellulose, and polysaccharides. And polyamino acids and their blending modification and chemical modification products; the second category is the polymer obtained by microbial fermentation and chemical synthesis, such as polylactic acid (PLA), etc.; the third category is the polymerization directly synthesized by microorganisms Materials, such as polyhydroxyalkanoate (PHA), etc.; the fourth category is biodegradable plastics obtained by blending these materials or blending these materials with other chemically synthesized biodegradable plastics.
Petrochemical-based biodegradable plastics refer to plastics obtained by polymerizing petrochemical monomers by chemical synthesis, such as polybutylene terephthalate (PBAT), polybutylene succinate (PBS) ), carbon dioxide copolymer (PPC), polyglycolic acid (PGA), etc.
What is compostable biodegradable plastic? Composting is an aerobic treatment method to produce compost. Compostable refers to the ability of materials to be biodegraded during the composting process. A material including paper, plastic, etc., if it is declared to have compost ability, it must be stated that the material is biodegradable and disintegrable in the composting system (as shown in the standard test method), and is completely biodegradable in the final use of the compost . Compost must meet relevant quality standards. Quality standards such as low heavy metal content, no biological toxicity, and no obvious distinguishable residues.
What is the difference between industrial composting and household composting? Fertilizer is an organic soil conditioner obtained by biological decomposition of the mixture. The mixture is mainly composed of plant residues, and sometimes also contains some organic materials and certain inorganic substances. The raw materials for composting can be organic solid wastes in urban and rural areas, such as agricultural crop stalks, farming manure in rural areas, urban household waste, kitchen waste, municipal sludge, and food industry waste residues. Composting, a treatment method to produce compost, is to use microorganisms that are widely present in nature to controllably promote the biochemical process of transforming degradable organic matter in solid waste into stable humus. Composting can be divided into aerobic composting and anaerobic composting according to the process of microbial growth and whether it is oxygenated. Aerobic composting is the process of decomposing organic matter in the presence of oxygen, and the final products are CO2, H2O, and heat. And humus, anaerobic composting is under anaerobic conditions, anaerobic microorganisms degrade organic matter into CH4, CO2, H2O, heat and humus. Generally speaking, composting refers to aerobic composting.
Industrialized composting refers to the process of aerobic degradation of solid and semi-solid organic matter by microorganisms at moderate temperature or high temperature under controlled conditions to produce stable humus. The general cycle is 180 days, but with the changes in aerobic composting technology, the shortest time is 30 days or even shorter.
Household composting refers to the aerobic composting process that mainly uses household kitchen waste or garden waste to produce compost for home use. Household composting takes longer than industrial composting, but generally the longest is no more than one year.
Whether it is industrialized composting or household composting, the organic waste handled should have the following characteristics:
a) Biodegradability (that is, the original biodegradability of the material);
b) Disintegration performance during composting;
c) Will not adversely affect the biological decomposition process;
d) Have an adverse effect on the quality of the final compost, such as excessive amounts of harmful elements.
