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Analysis Of Advantages And Disadvantages Of Several Composite Material Recycling Technologies In My Country

Aug 28, 2020

According to incomplete statistics, there are more than 10,000 registered composite materials-related companies in my country. According to the output statistics of enterprises above designated size in the composite materials industry, the historical data provided by the China Composites Industry Association (formerly China Fiberglass Industry Association) shows that as of 2018, the number of composite materials in my country has exceeded 34 million tons.

According to the statistics of China Unsaturated Polyester Resin Supply Branch, Marketing and Epoxy Resin Association, and according to the consumption statistics of unsaturated polyester resin in the fiber reinforced field, the output of China's composite materials in 2017 and 2018 was close to 5 million tons. According to this calculation, China's current composite material products exceed 50 million tons, and continue to grow at an annual rate of 10%.

According to calculations, the efficiency of corner waste (including scrap) in the composite production process is about 6%. On this basis, it can be concluded that China already has more than 2 million tons of composite finished products, and the general service life of the finished products is about For 20-30 years.

In the mid-1990s, China's composite material industry entered an explosive period. At that time, the technical threshold of the composite material industry was low, materials and technology were relatively backward, and product life quality was difficult to guarantee. In the process of explosive growth of composite materials, enterprises are dominated by sales, and the market is highly competitive and destructive, which makes it difficult to guarantee the quality and durability of products, such as composite sand pipes, composite cooling towers, composite cable protection pipes, In the SMC septic tank, serious quality problems appeared in the initial stage of relatively primitive market competition, which made it difficult to guarantee the durability of the supplied products. In addition, composite products have a wide range of applications and different application environments. The application environment will also affect the natural aging and product fatigue in certain areas (such as outdoor products or load-bearing products). As a result, the durability of composite materials is difficult to meet the theoretical life requirements in practice, which accelerates the production of composite products. At the same time, because of the slow development of recycling technology, most of the solid waste of composite materials is buried, so it is difficult to obtain accurate statistics.

my country has been studying and exploring composite material recycling technology. The research direction of recycling technology of various enterprises, universities and research institutions is cooperation in recycling, incineration energy collection methods, cement kiln treatment, mechanical crushing and the use of additives, pyrolysis, and chemistry. Dissolution (directional depolymerization), degradable materials, etc. Each method has its originality and advantages, but also has its disadvantages.

1. Energy gain-burning

The method of obtaining energy is a relatively straightforward process. Energy is obtained by burning part of the polymer resin material that can be used for power generation and heat supply. However, due to the low resin content of the composite material, despite the high calorific value, the total calorific value is limited; due to the high content of glass fiber in the composite material, Therefore, during the combustion process, if a large amount of glass fiber is melted into glass, it will easily adhere to the furnace body or grate, resulting in potential safety hazards. Therefore, industrialization is impossible. In fact, waste treatment plants and power generation The factory is not willing to recycle FRP products.

2. Co-processing of cement kiln

The collaborative process of cement kilns in the United Kingdom and Germany is relatively mature. For a long time, people have conducted many experiments on the composition and quantity of alkali-free glass fibers in cement kilns to ensure that the quality of cement will not be affected after adding. However, my country has no mature experiments. Data and mature application experience. At present, some companies are working in this field. Perhaps this treatment method will be adopted in the near future. However, in a sense, cement kiln joint treatment is only the treatment of waste that cannot be reused. No need to talk about high value.

3. Chemical dissolution (directed depolymerization)

Through the solvent, temperature and pressure, the polymer is opened at a certain key position to form a long-chain monomer or resin raw material, which is a good way to make a circular economy a reality. At present, many universities in China are conducting various researches (mainly plastics and rubber) based on polymer materials. The matrix resin degradation process of thermoset composites is also very active, but it has not yet been industrialized. Most of the research results are in the laboratory state, the equipment investment is relatively large, and the economics need to be further evaluated.

4. Biodegradation

At present, many universities have carried out the development of biodegradable bio-based and biodegradable materials (mainly plastics and rubber), but there are few studies on thermosetting resin bio-based and biodegradable materials. Currently, only polylactic acid and Due to the difference in performance and the high cost of degradable materials, some materials are still in the research stage, making it difficult to achieve industrial applications.

5. Pyrolysis

Pyrolysis is a method of opening the polymer chains of organic components by extracting energy to form multi-component small gases or liquids and separating fibers and fillers. This method can be made of light-weight gases and liquids through condensation, catalysis and distillation. Manufactured from fuel oil. Large-scale pyrolysis of the product does not require segmentation to more effectively recycle carbon fiber products. Currently, Shanghai Jiaotong University and Shanghai Yeshi Technology Co., Ltd. are conducting pilot trials. The Shanghai humus pyrolysis process requires separation and grinding of carbon fiber products before pyrolysis. The recycled carbon fiber is short fiber, and it is difficult to control its length gradient. In addition, there are no standard requirements for the length and shape of short carbon fibers. The main direction of recycling carbon fiber is to produce thin felt or fabric. The traditional cutting felt technology and equipment is to cut the unbroken fiber into a certain length and then evenly disperse it into shredded felt. There is no research on technology and equipment. In addition, how to ensure the uniformity and good dispersion of the short fiber length needs further research. The manufacturing process of carbon fiber mat also needs to remove static electricity and anti-explosive properties, which requires relatively high equipment. Reuse of carbon/glass hybrid fiber.

In order to pyrolyze the glass fiber composite material, it is necessary to accurately calculate its efficiency from an economic point of view and prove the feasibility of its industrialization approach. The required energy and the amount of pyrolysis oil will affect the various production processes of glass fiber composite materials. Resin content. Pyrolysis has been greatly improved. The pyrolysis energy is upgraded from electricity, natural gas, coal, microwave, etc. to pyrolysis gas and pyrolysis oil directly produced by compound pyrolysis, which greatly reduces the cost of the pyrolysis process and the consumption of natural energy, but if gas is used to provide pyrolysis energy Can pyrolysis and pyrolysis oil fully meet the energy demand of pyrolysis? Can more valuable light oil be produced? For this, more experimental data is needed. If the energy produced by pyrolysis cannot meet the energy required for pyrolysis, the promotion of the industrialization of pyrolytic glass fiber composites is questionable.

6. Reprocessing

For composite products, after their service life expires or is scrapped, their functions can be directly transferred or processed to change the direction of use, so that they can be reused. For example, the blades can be used in pipelines, water storage tanks, plateau water shortage areas, and septic tanks. Etc.; blade webs can be processed into walls, insulation boards, etc., to obtain higher reuse value, but because the number of recovered blades is relatively small, further research on reuse products and their directions of use is needed .

7. Mechanical crushing and adding

At present, this method is the lowest operating cost and the easiest industrial recycling technology, but currently, cement products such as composite products (SMC/BMC), building boards, non-load-bearing manhole covers, paving slabs and Malacca have been applied. Most recycling companies or local governments move, collect or decompose recycled materials for temporary disposal; if they are crushed and processed, the environmental and safety risks will be greater because they can easily induce dust and combustion, and rainwater will be more serious The ground pollutes the ground.

The use of traditional cement products or concrete, due to the alkali harvest reaction of glass fiber and cement, has caused the construction industry to dare not use it, but this problem can be solved by using processed glass fiber shortcuts in crack-resistant mortar. The function and reaction mechanism of glass fiber in mortar have been studied to replace the existing PP fiber, lignin fiber and alkaline glass fiber. Technological progress includes the recovery and dissociation equipment of constant temperature composite materials and various additives. This equipment can ensure Glass fiber and resin and maintain a certain length gradient, these additives hinder the aggregation reaction between glass fiber and cement, ensure the uniformity of fiber dispersion, and provide better crack resistance and impermeability. After a third-party comparison test, various properties are better than traditional PP fiber. Compared with PP fiber, processing glass fiber has greater advantages. Today, this technology has been used in many projects.

In summary, combined with the current development of composite material recycling technology, it is feasible to apply glass fiber waste to anti-tank mortar through the crushing method. The pyrolysis technology can realize the recycling of carbon fiber, but further business models and recycling facilities are required. Research and discussion. After the experimental data is completed, the pyrolysis of the glass fiber reinforced composite material must be determined after the performance calculation. The directional depolymerization technology must also study the separation technology of the glass fiber, the depolymerization efficiency and key equipment. It is expected that the industry will realize it quickly, and will recognize high matrix resin utilization and recycling effects. To solve the problem of matrix resin recycling in composite materials from the source, the test of degradable matrix materials is the ultimate direction, but at the same time, glass fiber recycling should be considered under process conditions.

From the perspective of the overall technology of recycling and industrial development, the application of recycling technology should be based on the current status of recycling technology to realize the industrialization of recycling complexes; the industrialization of various recycling methods must focus on recycling glass fibers The method of reuse. The goal of popularizing and applying all recycling technologies is industrialization, high efficiency, low cost and high value. Based on the analysis of the current technical status, the steps to realize composite material recycling are as follows: 1. Reuse; 2. Mechanical crushing and adding reuse; 3. Thermal Solution method; 4. Energy recovery; 5. Directional depolymerization method; 6. Biodegradation method.

The development of the thermosetting composite solid waste recycling industry has a long way to go. It is hoped that enterprises, research institutions and universities in the industry will continue to work hard on research and exploration.