1 Anti-aging polymer
It is not difficult to understand from the above discussion that polymer materials are always subject to aging, either fast or slow, which is a common phenomenon, manifested in the corresponding degradation of their physical properties or special functions, such as hardening, stickiness, embrittlement, and discoloration. , Reduced or lost strength, and decay, loss, etc. of the original function of the functional polymer. Virtually any polymer needs to properly prevent aging or slow down the rate of aging. Even the short-term use of plastic products such as disposable food packaging bags, there are anti-aging problems in the process of molding. The problem of ageing of permanently used polymer materials such as coatings and adhesives is even more pronounced. The use of effective anti-aging measures can often expand the application of a polymer or be used in more severe conditions, and it can also be economical due to prolonged service life. From the point of view of environmental protection, if the actual service life of a long-term, permanent-use type of plastic can be extended, the amount of waste can be reduced, thereby reducing environmental pollution or reducing the environmental load. In conclusion, the anti-aging of polymer materials is another major aspect of polymer science as the synthesis of polymers.
Aging of polymer materials includes both inherent chemical factors such as the chemical structure and physical state of the polymer itself, as well as external heat, light, electricity, high-energy radiation, mechanical stress, oxygen, ozone, water, acid, alkali and bacteria. Enzymes, etc., are all-encompassing, and vary depending on the type of polymer, the difference in products, performance requirements, and the use environment, and are complicated and there is no single standard and method for preventing aging. Aging and anti-aging are a large area. There are many monographs. It cannot be elaborated here. The general approach of anti-aging is simply summarized as follows:
1 Use a reasonable polymerization route and qualified monomers and auxiliary materials for polymer synthesis to obtain the high anti-aging properties it may have; or use targeted methods such as copolymerization, blending, and cross-linking to increase the polymer content. Anti-aging properties.
2 The use of advanced (suitable) processing and molding technology (including the addition of various additives to improve processing performance and heat, oxygen stabilizers, etc.) to prevent the aging process, to prevent or minimize the generation of new aging inducing factors.
3 According to the main aging mechanism of specific polymer materials and the practical environmental conditions of the products, add various stabilizers, such as heat, oxygen, light stabilizers, anti-mold agents and so on.
4 Use possible appropriate physical protection measures such as surface coating, surface protection film, etc. to reduce the effects of aging.
5 According to the polymer properties, avoiding serious shortcomings and choosing scientifically, and developing and promoting special plastics and their products, it is not suitable for outdoor use to avoid outdoor use, and is not suitable for high temperature use to avoid high temperature use.
2 Green polymer concept
Aging and anti-aging research, for a long time, its purpose is mainly to improve the durability of polymers. There is no doubt that this direction will continue in the future. However, with the development of the polymer industry and the expansion of the application fields, the amount of synthetic polymers to be discarded has increased year after year. Therefore, in order to prevent pollution, the demand for the natural decomposition of polymers to return to nature has become increasingly strong. In the future, the research and development of synthetic polymers will surely be based on their use to improve durability and use the end of life to develop. Therefore, in the 1990s, the human intuitionists proposed the concept of “green polymerâ€. The term comes from green chemistry and technology. It is harmless to the environment and environment-friendly in the manufacture, application, and waste disposal of polymer materials. the meaning of. How to dispose of non-polluting environment-friendly waste polymer materials without environmental pollution, how to develop and utilize environmentally degradable polymer materials are two key issues in polymer greening projects.
1 Treatment of environmental inert polymer waste
Environmentally inert polymers are polymers that do not degrade naturally in the environment. At present, there are three methods to deal with the waste of environmental inert polymers.
(1) Soil Burial Method This method is not suitable because it is difficult for the polymer to degrade, and it is often buried for tens or even hundreds of years. It occupies a large amount of land. For a country with a small number of people like ours, this method is not suitable.
(2) Incineration incineration produces a large amount of harmful toxic gases and residues, which seriously pollutes the environment and is environmentally unacceptable. Even with various advanced incinerators, it is burned under high temperature and high pressure (>1200 °C, higher than 105 to 106 Pa). Although the waste can be fully converted into the available energy, the investment is large, and there are still hidden dangers of waste gas pollution in the incineration, so this method is not perfect.
(3) Recycling and recycling of waste This law not only turns waste into treasure, saves oil resources, but also reduces environmental pollution. Therefore, it is the method that best meets the concept of green polymer. There are many successful examples. For example, waste organic glass is cracked into monomer MMA by anathermal heat; waste polyethylene terephthalate (PET) is converted into monomer by methanol alcoholysis, and then After the polycondensation reaction, PET was again obtained. The waste nylon 66 carpet was dissolved by ammonia to recover the monomer, and the recondensed nylon 66 was used as the engineering plastic for the automobile body. The recycled PE made from waste polyethylene (PE) was used in large quantities for preparation. Mail packaging bags; waste PS packaging materials, especially disposable lunch boxes, used BaO to deal with high temperature decomposition into monomers for reuse. Of course, when promoting the recycling of polymer waste, it is necessary to emphasize the promotion of the use of polymer materials and the classification and management of polymer materials. This has been a successful experience abroad.
2 Development and utilization of environmentally degradable polymer materials
The environmental degradation is mainly biodegradation, and it is divided into biodegradation type and completely biodegradable type. The former is a part of the polymer resin can be biodegradable material after processing into products, after the discarded because this part of the environment can degrade the overall morphology of the collapse, is an incomplete degradation type. For example, starch, natural minerals, aliphatic polyesters, and the like are added to a polyolefin resin, and the processed plastic is a disintegrating type of environmentally degradable material. Completely biodegradable polymer materials are biosynthetic natural polymer materials or modified natural polymer materials, or synthetic polymers of certain structures. Considering the scale and cost, the preparation of biodegradable polymer materials by chemical synthesis has the most practical significance. The biodegradable polymer materials that are currently researched and developed most are aliphatic polyesters, polyvinyl alcohols, polyamides, polyamide esters, and amino acids. Among them, the largest output and the most widely used are aliphatic polyesters, such as polylactic acid (polyhydroxypropionic acid), polyhydroxybutyric acid, polyhydroxyvaleric acid, and the like. These polyesters are easily hydrolyzed due to ester bonds, and the main chain is soft. They are easily decomposed or metabolized by microorganisms in the natural world or by enzymes in animals and plants, and eventually become CO2 and water.
The use of biotechnology to prepare biodegradable polymer materials, although the current high cost, but most consistent with the concept of green polymer. For example, natural cellulose or sugar can be fermented by bacteria to produce hydroxybutyric acid and hydroxyvaleric acid. The polymers polymerized with them have the properties similar to polypropylene, but can be completely degraded by the environment; for example, corn and sugar beet are used as raw materials and fermented. Get lactic acid, bulk polymerization into polylactic acid. It can be used to make medical surgical sutures that can be self-degraded without the use of stitches; instead of using PE as a packaging material and agricultural film, it solves the most troubling waste disposal problem in this area. From these examples, it can be seen that the use of biotechnology, from raw materials to products, from production to application, to post-disposal disposal, can produce no pollution to the environment at all, and instead of renewable non-renewable agricultural and sideline products as raw materials The oil resources, this is truly embodies the green connotation.
We believe that with the continuous advancement of human society, the concept of greening polymer materials will become the consensus of mankind that the century will be a century of green polymers.