Application of degradable plastics

The development of the plastics industry began during World War II. Due to the unique and outstanding properties of plastics, military engineers and researchers paid attention and interest. After World War II, the application of plastics went from military to civilian and entered a period of rapid development. Scientific and technological progress has developed the plastics industry. So far the plastics industry has covered all areas of industry, agriculture, and people's daily lives, so plastics have made tremendous contributions to humanity!

According to different uses and environments of plastic products, different requirements are imposed on plastic properties, such as plastic agricultural films, shopping bags, food bags, and industrial packaging materials. At the same time they are widely used, they also bring about some negative effects. Commonly referred to as "white pollution." In order to solve the "white pollution" problem, various solutions and voices have been proposed: Some people advocate a complete ban on the use of the system, but so far it has been banned, it shows that it has the vitality of continuing to live; Some advocate the use of substitutes - fiber molding Products, degradable plastics, and even the restoration of paper packaging. Therefore, at the beginning of the 1990s, the climax of China's degradable plastics research and development began to set off. There are about forty or fifty research and production units throughout the country.

By cutting off plastic macromolecular chains into small molecules by light or microbes, they eventually turn into water and carbon dioxide and disappear into the natural world. This process is called the plastic degradation process. Currently, degradable plastics produced by industrial production are induced by the addition of a third auxiliary agent. The effect of photodegradation or biodegradation of ordinary plastics is referred to as blended degradable plastics. For example, a certain amount of photosensitizer is added to PE (usually a metamorphic element—Fe, Co, Ni, Ce, etc.), of which the most commonly used is iron, a cheap and low-toxicity metal organic compound, such as iron stearate, and ergocene. After being blended with iron and its derivatives, etc.), it can be processed and molded. Starch-based plastics are the most common biodegradable plastics at home and abroad. They provide nutrients for the survival and reproduction of microorganisms by starch, and the microorganisms use plastic starch granules as a breakthrough point to make plastics. Degradation of the product caused by the degradation of the mechanical properties of the product. The Institute of Land Research of the Chinese Academy of Sciences has studied the effects of photolysis of agricultural plastic film residue on crop root development. The conclusion that 4cm2 fragments have no effect on the development of crop roots. In the early 1990s, we performed soil tests on starch-based PE membranes in gravel soil. It was found that after six months, the membranes turned into havoc, the mechanical properties decreased significantly, the weight became lighter, and the roots of the plants penetrated the membrane. The phenomenon of growth shows that the starch-based PE film has biodegradability.

Plastic degradation process requires certain objective conditions, photodegradation can not leave the light, and under a certain humidity environment; biodegradation must have the presence of microorganisms, degradation rate and microbial species, quantity, and microbial survival and reproduction conditions - Temperature, humidity related, this process takes some time. For example, natural cotton fabrics in the ground, after a period of time, become rotten, and gradually disappear, this process is actually a biodegradation process, but we are used to rot.

Degradable plastic quality evaluation and performance testing, so far there is no fast and easy and reliable method. Although photodegradation has been a reliable laboratory testing method, it is more expensive. For the biodegradation test method, because it involves the use of bacteria, environmental factors and other reasons, which brings a lot of inconvenience, the production companies, quality supervision departments can not timely determine the quality of the product and guard against shoddy products. In the previous period, many biodegradable products were not up to standard. Although starch was added to plastics, there was no significant degradation effect. (Agricultural experts in the United States proposed in the 1960s as starch in plastic products.) Additives below 6% are not degradable plastics!); also for blended photodegradable plastics, based on practical experience, the amount of photosensitizer added is different in HDPE and LDPE, and the amount used in HDPE is large, even in the same In the PE products of different varieties, the thickness of the products is different, and the added amount is also different. If it does not cause the manufacturer to pay enough attention, it will cause differences in degradation performance, which may bring about some negative effects. Due to insufficient management and quality control of degradable plastics, individual people started from purely commercial interests, and the amount of photosensitizer or starch was not in place. This caused confusion and confusion and brought about some negative effects.

The use of degradable plastics is very broad. The packaging materials in the foreign trade area are very eye-catching. Foreign traders often specify that they use degraded packaging materials in international trade. As far as I know, some manufacturers in Japan, South Korea and Taiwan have ordered biodegradable plastics from China. In addition, there are special departments that need to degrade plastics. Therefore, the appearance and development of degradable plastic materials is not only to solve the "white pollution" problem of plastics, but also in many respects it has its own needs and values. The development of its application areas also needs our attention.

Shanghai Institute of Chemical Industry Senior Engineer Wu Chao