Green Plastics Concept and Practice Analysis (4)

Foreign Development of Degradable Plastics

In the late 1960s, some foreign scholars were inspired by the aging phenomenon of polymer materials and began to study biodegradable plastics in an attempt to solve the problem of increasingly serious plastic waste pollution. In the earlier period, the degradable plastics studied abroad were mainly photodegradable plastics, and later gradually increased in thermal oxygen-degrading plastics. However, both the photodegradable plastics and the hot oxygen degradable plastics require certain environmental conditions for their degradation. After the plastic waste is discarded, they are either placed in a closed waste disposal system (incineration, landfill, composting, etc.) , Or it is exposed to a natural environment with unfixed conditions, and it is difficult to ensure the fixed conditions required for light and thermo-oxidative degradation of plastics. Therefore, these early-stage researched and developed degradable plastics cannot be completely degraded in most cases due to conditions, both in the waste disposal system and in the natural environment. From the 1980s, research and development of biodegradable plastics began abroad. Biodegradable plastics are those that can be degraded by microorganisms into a class of mineralized inorganic salts of carbon dioxide (CO2) or methane (CH2), water (H2O), contained elements, and new biomass under aerobic or anoxic conditions. plastic. It is also common for these microorganisms to exist in large quantities in the natural or composting waste treatment systems. Therefore, biodegradable plastics are easily degradable in nature or in composting waste treatment systems. In addition, since biodegradable plastics have low release energy when they are burned, biodegradable plastics have environmentally friendly advantages that non-biodegradable plastics cannot match, even in incineration waste disposal systems. By the end of 1990, some developed countries such as the United States, Japan, Belgium, Italy, and Germany had achieved large-scale production and application of biodegradable plastics. In addition, South Korea began to promote the development and application of biodegradable plastics 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 signs them.

Domestic Development of Degradable Plastics

From the late 1970s, domestic research and development of degradable plastics began, but mainly concentrated on photodegradable plastics. In the early 1990s, research and development of degradable plastics mainly focused on additive-based degradable plastics. Mainly for the addition or blending of starch to polyolefin polymers, by the mid-1990s, this type of degradable plastic reached its peak. The reason is that some companies do not know much about degradable plastics, but they think that it is also an “opportunity” for environmental protection investment. Without deep market research and tracking of foreign dynamics, they blindly go online, resulting in several years of Within that, there are hundreds of starch-filled extrusion lines. Since these added degradable plastics are, in most cases, subject to conditions, they cannot be completely degraded either in the waste disposal system or in the natural environment. Therefore, as people have a deeper understanding of degradable plastics, the market for such degradable plastics gradually narrowed after the mid-1990s. At present, only a few degradable master batch manufacturers are in normal production.

From the mid-1990s, China began to develop biodegradable plastics, and the Ministry of Science and Technology also provided financial support for a number of scientific research units or companies that produce biodegradable materials. At present, the distribution of biodegradable materials in China can be represented by Figure 2. As shown in FIG. 2 , the types of biodegradable plastics that can be produced in large scale are mainly PHBV (hydoxybuty rate-CO-hYdRoxyVale rate), polyhydroxybutyrate/valerate), and PPC (CaRbOn diOXide copolymer). Carbon dioxide polymer), PVA (polyvinyl alcohol), PEG (polyethylene glycol), PHA (poIyhyd roxyaIkanoic or poIyhydroxyIkanoates, polyhydroxyalkanoate); PLA (POIyIactiC acid O r POIyIactide, PLA) , PCL (POlYCaP rOlactone, polycaprolactone), PPDO (polydioxanone), PBS (POIYbUthYI enesuccinate, polybutylene succinate), PHB [POIyhYd roxYbUtY riC acid O r POIyhYd rOXYbUtY rate; chitosan, tannin polyurethane, polyesteramide, etc.

(to be continued)