Do you really understand what is degradable plastic?Knowledge Science(Part I)

How does non-degradable plastic products affect our daily life
2020-06-30
Are biodegradable materials completely degraded in different environments? Is it harmful to the environment?Knowledge Science(Part II)
2020-07-20

Do you really understand what is degradable plastic?Knowledge Science(Part I)

  • What is degradable plastic?
  • Degradable plastics is a big concept, it is under specified environmental conditions, after a period of time and contains one or more steps, resulting in a significant change in the chemical structure of the material and loss of certain properties (such as integrity, molecular mass, structure or machinery Strength) and/or broken plastic. Among them, photodegradable plastics and thermal oxygen degradable plastics are ruptured plastics, and should not be attributed to biodegradable plastics. Degradable plastics should be tested using standard test methods that reflect changes in performance, and their categories should be determined according to the degradation method and service life. Without combining the types of degradable plastics and their degrading environmental conditions, degrading plastics in general does not mean that such plastics can be completely degraded into environmentally friendly substances.

 

  • What is a biodegradable material?
  • 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 plastics refer to the degradation caused by the action of microorganisms existing in nature under natural conditions such as soil and/or sandy soil, and/or specific conditions such as composting conditions or anaerobic digestion conditions or aqueous culture medium. Eventually it is completely degraded into carbon dioxide (CO2) or/and methane (CH4), water (H2O) and mineralized inorganic salts of the elements and new biomass (such as microbial dead bodies).

    It should be noted that every biodegradable material includes paper, etc., and its degradation requires certain environmental conditions. If it does not have degradation conditions, especially microbial living conditions, its degradation will be very slow; at the same time, not every biological Degradable materials can degrade rapidly under any environmental conditions. Therefore, the treatment of biodegradable materials should be based on their environmental conditions, combined with the structure of the material itself to analyze and determine whether it is a biodegradable material. How to judge whether a material is biodegradable, a series of detection method standards have been issued internationally and China, which is answered in the standard question.

 

  • What are the types of biodegradable plastics?
  • 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. Currently on the market, biodegradable plastics produced using natural polymers mainly include thermoplastic starch, biocellulose, and polysaccharides Modified with polyamino acids and their blended and chemically modified products; The second category is polymers obtained by microbial fermentation and chemical synthesis, such as polylactic acid (PLA), etc.; The third category is polymerization directly synthesized by microorganisms Substances, such as polyhydroxyalkanoate (PHA), etc.; The fourth category is biodegradable plastics obtained by blending and processing these materials or blending and processing these materials with other chemically synthesized biodegradable plastics.

    Petrochemical-based biodegradable plastics refer to plastics obtained by polymerizing petrochemical monomers by chemical synthesis methods, such as polybutylene terephthalate-adipate (PBAT) and polybutylene succinate (PBS), carbon dioxide copolymer (PPC), polyglycolic acid (PGA), etc.

 

  • What is compostable biodegradable plastic?
  • Composting is an aerobic treatment method for composting. Compostable refers to the ability of materials to be biodegraded during the composting process. A material includes paper, plastic, etc. If it claims to be compostable, 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 clearly 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, rural farming manure, urban domestic waste, kitchen waste, municipal sludge, food industry waste, etc. Composting as a treatment method that produces compost, is a biochemical process that uses microorganisms that are widespread in nature to promote the conversion of 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 oxygen is given. Aerobic composting is the process of decomposition of organic matter in the presence of oxygen. 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 microorganisms degrading solid and semi-solid organic substances under aerobic medium 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 use of household food waste or garden waste for aerobic composting, which is used to produce compost for home use. Household composting takes longer than industrial composting, but it generally does not exceed one year.

    Whether it is industrial composting and household composting, the organic waste it handles should have the following characteristics:

    a) Biodegradability (ie the original biodegradability of the material)

    b) Disintegration performance during composting;

    c) Will not adversely affect the biological decomposition process;

    d) Adversely affect the final compost quality, such as excessive harmful elements.