Research on Recycling and Utilization of Plastics (II)

three. Chemical reduction

Researchers began to try to extract the chemical composition of plastics for reuse. The process used is to cut the long chains of polymers and restore their original properties. The cracked materials can be used to make new plastics. Some methods promote the chemical cracking of bonded carbon atoms by adding chemical elements, or add energy to promote thermal cracking.

German company Bayer developed a hydrolytic chemical reduction method to crack the PUC sponge pad. Tests have shown that the chemical reduction method is technically feasible, but it can only be used to handle clean plastics, such as corner powders and other plastic wastes produced in the manufacturing process. Plastics that have been used in the home and are contaminated with other contaminants are difficult to dispose of using chemical decomposition. The application of this reduction method, until the 21st century will not be a large number of use of hydrolysis to deal with waste. Some new chemical decomposition methods are still in the process of research, the United States Ford Motor Company is currently using esterification method to deal with automotive plastic parts.

The American Institute of Technology in Ransom developed a solution that can break down plastic waste, heating this patented solution together with six different types of plastic that are mixed together. At different temperatures, six polymers can be extracted separately. In the experiment, the polystyrene plastic chips and related solutions were mixed at room temperature into a dissolved state, which was sent to a sealed container for heating, and then sent to a lower pressure “flashing chamber” where the solution quickly evaporated. Recycling, and the rest is pure polystyrene that can be reused.

It was alleged that the purification device used in the research could purify 1 kg of polymer per hour. New York State Government and Niagara. Mohawk Power is planning to join forces to build a small pilot plant. Investors claim that after the plant is completed, 4 tons of polymer material can be recovered per hour. Its cost is only 30% of the raw materials for production and it has very obvious commercial value.

four. Hydrolysis method

Many experts believe that hydrogenation can be used to process mixed plastic products. The mixed plastic chips are placed in a hydrogen reactor and subjected to a specific temperature and pressure to produce raw materials such as synthetic crude oil and gas. This treatment can be used to treat PVC waste, which has the advantage of not producing toxic dioxins and chlorine. Using this method to process mixed plastic articles, according to different plastic components, 60%-80% of them can be refined into synthetic crude oil. Three chemical companies in Germany and other countries, BASF, pointed out in their common research report that hydrogenation is the best method for thermal cracking, and the synthetic crude oil obtained from the analysis has good quality and can be used for oil refining.

The University of Kentucky in Lexington, United States, invented a process for converting waste plastic into high-quality plastic fuel oil. The fuel produced in this way is very much like crude oil, even lighter than crude oil, and more easily extracted into high-octane fuel oil. This kind of fuel oil produced from waste plastics does not contain sulfur and has very few impurities. A similar method is used to liquefy the plastic with coal. Can also produce high quality fuel oil.

Researchers mixed various plastics with zeolite catalysts, tetralin, etc. in a shower and put it into a reactor called a “pipe bomb”. They pressurize and heat with hydrogen to promote macromolecule plastics. Decomposes into smaller molecular weight compounds. This process is similar to that in crude oil processing. After this waste plastic processing, the oil production rate is very high, and the polyethylene plastic bottle's oil output rate can reach 88%. When waste plastic and coal are mixed and liquefied in a roughly 1:1 ratio, better quality fuel oil can be obtained. After the economic benefits of this process are evaluated, it is expected that the use of waste plastics to produce fuel oil will be transformed into a blast furnace benefit within 5-10 years. At present, Germany has begun to establish a reactor with the hope of producing 200 tons of plastic fuel in Botepo.

Fives. Subtractive design method

Research and development departments taking into account the need for recycling and dismantling when designing products, and materials that are suitable for recycling in the United States, do not focus on which type of plastic should be used to make individual parts, but consider the materials that can be widely used. This is a revolutionary change in conception.

In order to facilitate recycling, designers began to avoid using multiple plastics when designing products. The US company BMW plans to reduce its plastics category by 40% in its new vehicle design, with the aim of facilitating the recycling of waste plastics. The reason why the automotive industry has reduced the use of plastics and considered the additional nature in the design is mainly to expect to win an excellent image that respects environmental protection and is appreciated by consumers. At present, this design concept is gradually infecting the entire plastics processing industry.

However, every effort has not been made to eliminate any of the 20 types of plastics in the market. After all, the diversity of the products has led to the ever-changing categories of plastics, such as the plastics used in the production of computers and the plastics used in the production of automobiles.

To this end, experts recommend the establishment of relevant recycling standards, which stipulate that special industries can only use specified materials, otherwise they cannot control effective recycling. The electronics and automotive industries have already started to establish such standards.

The world's electronic and electrical markets have paid attention to the recycling of waste plastics. International Business Machines Corporation (IBM) has begun to code plastic parts for computers and business machines, and is developing reusable plastic electronic components and simplifying disassembly equipment. The product structure, while also considering the elimination of surface coloration of components, the reduction of the amount of external adhesives used to control plastic additives is reduced to the use of recycled process components and additional components.

The recycling of discarded auto parts has also made great progress. Many countries are based on the premise that recyclable and easy recycling can be used as raw material for automotive plastic parts selection and product design. Some countries have already formulated effective recycling numbers and recycling plans for plastic parts for automobiles, and are considering the development of a unified marking system that will help dismantle and sort automotive plastics. Countries such as Europe and the United States are still studying chemical depolymerization to recover automotive plastics.

six. Biodegradation

While actively developing technologies for recycling plastics, research and development of biodegradation has become a research hotspot in the plastic processing industry in various countries in the world. The researchers hope to develop a plastic that can degrade in a microbial environment to deal with the pollution of farmland, forests, and oceans by a large number of disposable plastics, especially plastic film and multi-pack waste. The research goal is to develop a plastic that can guarantee its use performance during use, and once it is used up, it can be decomposed by the microorganisms in the environment and it can completely enter the ecological cycle. At the same time, the production cost of this plastic is relatively low and it has a corresponding economy. If it is such a biodegradable plastic, it can be composted with ordinary biological waste after use, without having to pay a great deal of money for collection, classification and regeneration. Moreover, the decomposition products enter the ecological cycle and no waste of resources occurs.

In the research and development of biodegradable plastics, all countries in the world have invested a lot of financial resources and manpower, and spent a lot of energy on research. The plastics processing industry generally believes that biodegradable plastics are the new technological issues in the 21st century.

At the end of the 1980s, in order to solve the problem of degradation of garbage bags, under the impetus of American corn merchants, polyethylene bags with added starch were popularized as biodegradable plastics in Europe and America. However, due to the fact that polyethylene cannot be degraded, its application has been greatly reduced. Just because of the rich source of raw materials for starch, and the cheaper prices, there are still many researchers engaged in research in this area, hoping to achieve breakthroughs in degradability through various formulation technologies.

The currently developed technical routes include microbial fermentation synthesis and chemical synthesis using natural polymers (cellulose, lignin, and chitin) synthesis methods. Some water-soluble resins of biodegradable plastics have been developed, but the total In fact, its production costs have not reached the requirements of industrial mass production.

After several years of research, experts from Germany's Bayer Research Fiber Products have made a plastic that can be completely decomposed into humus. The packaging film made of this plastic can be rapidly decomposed in the soil and “differentiated and disintegrated” and can return to nature within 10 days. According to the identification of environmental organizations, such plastics and their decomposed neutralized substances are safe and reliable to the environment and humans. The new plastic developed by the company is made by mixing hard and non-extendable cellulose with polyurethane. After burying this new type of plastic in soil, it can become a delicious food for microorganisms in the soil. The rapidly multiplying microorganisms can quickly digest this material into humus hair. A household cling film made from this material can be completely powdered after 14 days and lose 80% of its weight after 8 weeks. Using this material to make nutrients for the culture, it was homogenized into humus several weeks after implantation in the soil, and it acted as a compost. Due to the high production cost of this new technology. It is several times that of ordinary plastics, so it is difficult to achieve commercial production at present.

In the application of experiments, after years of efforts, China has achieved initial success in biodegradable polyethylene film research projects, developed biodegradable plastic film samples, and conducted a small-scale trial, from the perspective of its technical maturity , has not yet reached the level of application of large-scale promotion. China has not set foot in the field of additive photodegradable plastics. In the United States, photodegradable plastics have been used for the lifting of bottled beverages for many years. Israel and Canada have trials of photodegradable plastic films, but no large area applications have been reported.

It is predicted that if the industrialization study of biodegradable plastics is counted as 100, the current development and research is only at the relative stage of 30, and it is expected that industrialization will be achieved after 2000. At present, the United States is leading the development of this technology, ranking third in Europe and third in Japan.

In general, there are still many problems to be overcome in the research and development of biodegradable plastics. First of all, there is no unified understanding of the definition of plastic degradation. What does biological decomposition actually mean? In other words, how long is the decomposition time of biodegradable plastic determined? In addition, what should be the decomposition product? Is the final product carbon dioxide and water, or is it any form of residue that is harmless to practical use?

Second, there is no universally accepted method for evaluating biodegradable plastics. At present, the American Materials Testing Association, the Japan Industrial Standards Association, and the International Organization for Standardization are actively conducting this work. Although the United States has officially issued a number of results, ASTM cannot fully apply to the actual processing of plastic waste.

Source: Waterborne Coatings Network