Analysis of the concept and practice of green plastics (IV)
overview of the development of degradable plastics abroad
in the late 1960s, some foreign scholars, inspired by the aging phenomenon of polymer materials, began to study degradable plastics, trying to solve the increasingly serious problem of plastic waste pollution. In the early stage, the degradable plastics studied abroad were mainly photodegradable plastics, and then thermooxidative degradable plastics were gradually added. However, both photodegradable plastics and thermooxidative degradable plastics require certain environmental conditions for their degradation. After plastic waste is discarded, it is either placed in a closed waste treatment system (incineration, landfill, composting, etc.) or exposed to the natural environment with uncertain conditions, which is difficult to ensure the fixed conditions required for photodegradable plastics and thermooxidative degradable plastics. Therefore, in most cases, these degradable plastics researched and developed in the early stage cannot be completely degraded, whether in the waste treatment system or in the natural environment, due to the limitations of conditions. Since the 1980s, biodegradable plastics have been developed abroad. Biodegradable plastics are a kind of plastics that can be degraded by microorganisms into carbon dioxide (CO2) or methane (CH2), water (H2O), mineralized inorganic salts of contained elements and new biomass under aerobic or anoxic conditions. These microorganisms are abundant and common in nature or composted waste treatment systems. Therefore, biodegradable plastics are easy to be completely degraded in nature or composted waste treatment systems. In addition, due to the low release energy of biodegradable plastics during combustion, even in the incineration waste treatment system, biodegradable plastics also have the advantages of environmental friendliness that non biodegradable plastics cannot match. By the end of 9O, some developed countries such as the United States, Japan, Belgium, Italy, Germany and other countries had achieved large-scale production and application of biodegradable plastics. In addition, South Korea 1 The jaw was not put in place when clamping, and the development and application of biodegradable plastics began to be comprehensively promoted in 2001. When biodegradable plastics are discarded after they have no use value, the main treatment method chosen is composting or anaerobic digestion. In the United States and Germany, the Biodegradable Plastics Association simply refers to biodegradable materials as Compostable Plastics, and certifies and marks them
development overview of degradable plastics in China
from the late 1970s, China began to develop degradable plastics, but mainly focused on photodegradable plastics. In the early 1990s, the research and development of degradable plastics mainly focused on additive degradable plastics. Starch was mainly added or blended with polyolefin polymers. By the mid-1990s, this type of degradable plastic reached its peak. The reason is that some enterprises do not have a deep understanding of degradable plastics, but feel that it is also an investment "opportunity" related to environmental protection. They have not done in-depth city 12. Limit protection: it has two levels of program-controlled and mechanical protection; According to the field survey, without tracking the dynamics of foreign countries, it went online blindly, resulting in hundreds of extrusion lines of starch filling type alone within a few years. In most cases, these additive degradable plastics can not be completely degraded, either in the waste treatment system or in the natural environment, because of the restrictions of conditions. Therefore, as people have a deeper understanding of degradable plastics, the market of this kind of degradable plastics has gradually shrunk since the mid-1990s. So far, only a few degradable masterbatch production enterprises are in normal production
from the mid-1990s, China began to develop biodegradable plastics, and the Ministry of science and technology has also provided financial support to many scientific research institutions or enterprises producing biodegradable materials. At present, the distribution of biodegradable materials in China can be shown in Figure 2. As shown in Figure 2, the main types of biodegradable plastics that can be produced on a large scale are PHBV (hyd roxybuty rate co hyd roxyvale rate), Polyhydroxybutyric acid/valerate), PPC (CA rbon dioxidepolymer, carbon dioxide polymer), PVA (polyvinyl alcohol), PEG (polyethylene glycol), PHA (polyhydroxy roxyaikanoic or polyhydroxy roxyaikanoates); PLA (p0iyiactic acid o r poiyiactide, polylactic acid), PCL (polycap rolactone, polycaprolactone), ppdo (expand the utilization of aluminum in new energy vehicles, special vehicles, transportation vehicles and other fields), PBS (P o I y b u t h y i e n e s u c i n a t e, polybutylene succinate), P H B [poiyhy clear and strict product identification requirements D roxybuty ric acid o r poiyhyd roxybuty rate; chitosan (polysaccharide), tannin polyurethane, polyester amide, etc.
(to be continued)