Innovative Application of Modified Waste Plastics in Plastic Pipes

Innovative Application of Modified Waste Plastics in Plastic Pipelines 

Source: Jung abstract

This paper briefly introduces the recovery of waste plastics, all of which are the development and production of modified special materials for large diameter buried pipes and toughening masterbatch for HDPE recovery. The relevant technical level has reached the advanced level at home and abroad, hoping to provide some reference for relevant enterprises and professionals. Barrel statement 1. Sources of Recycled Plastics The extensive use of plastic products has become an indispensable part of people's daily work and life in modern civilized society. While we produce a large number of new plastic products every day, a large number of waste plastics are also constantly produced in people's work and life. At present, China's waste plastics are mainly plastic films, plastic filaments and woven products, foam plastics, plastic packing cases and containers, daily plastic products, plastic bags and agricultural plastic films. It is understood that in 2010, the recycling of waste plastics in China exceeded 10 million tons, and in 2014, the domestic production of plastic products was 73.8778 million tons, the domestic usage was 67.8537 million tons, and the domestic recycling of plastic was about 20 million tons. According to the World Wide Web, the recovery rate of waste plastics is extremely low at present. Only 10% of the 7 billion tons of waste plastics are recovered. About 3,400 plastic bottles are discarded every second. The annual plastic waste is about 260-300 million tons, of which 8 million tons flow into the sea every year. According to statistics, in 2015 alone, more than 300 million tons of plastic products will be produced and 500 million tons of plastic will be used in 2016. It is estimated that plastic consumption will grow at an annual rate of 8% and reach more than 700 million tons in 2030. Once so much plastic is discarded, if it is not properly stored, transported, processed, applied and post-treated, it will certainly destroy the environment and endanger people's health. At the same time, as a kind of renewable resources, it is also an important part of circular economy. 2. Significance of Recycling Waste Plastics The recycling of renewable resources is an inevitable choice for the development of circular economy. Its strategic goal is to establish an environment-friendly economy and a resource-saving society. Circular economy is exploring the road of sustainable development of human beings, environment and resources from the proposing of concepts, the establishment of theories to the development of practice, that is, to establish an environment-friendly and resource-saving economy and advocate an environment-friendly and resource-saving society. Moreover, the realization of this goal will be carried out in all aspects and links of production and life in modern society. Plastic recycling is a major strategic issue for the country to solve the shortage of resources. There is a big gap in the consumption of petroleum resources in our country, and the situation that plastic raw materials rely heavily on imports has not been fundamentally changed. Recycling recycled plastic has become one of the shortcuts to solve the shortage of raw materials, with a wide range of sources and low cost. At present, on the basis of recycling 6 million tons of domestic recycled plastics every year, China has become a country with a large import volume of waste plastics by importing and digesting about 5 million tons of waste plastics. Plastic recycling is not only conducive to regional economic growth, especially provides an important way to solve the surplus labor force in rural areas, and provides an ideal channel for urban and rural residents to increase their income and employment, but also makes great contributions to the country's resource recycling and environmental protection. It has become one of the environmental protection industries that cannot be ignored in the sustainable development of the national economy. After the rapid development in recent years, some apparent characteristics of the plastic recycling industry have changed: recycled plastic is playing an increasingly prominent role in the raw material market and has obvious competitive advantages in the market. The sustained high price of raw materials is the driving force behind the strong development of the recycling industry. For example, China adds more than 3 million tons of waste plastics every year. If it is recycled, it can generate profits of more than 1.5 billion yuan. 3. Brief Introduction of New Achievements in Waste Plastic Recycling Technology The recycling of waste plastics includes three steps: collection, separation and recycling. The effective separation of waste plastics is the key to realize high-quality recycling. At present, simple recycling of waste plastics has been widely used: for example, the development of waste masterbatch produced in factory production process 1. Brief introduction Buried polyethylene hollow winding structural wall drain pipe and buried polyethylene double-wall corrugated drain pipe, commonly known as large-diameter buried pipes, have been identified by the Ministry of Construction of the People's Republic of China as a scientific and technological achievements promotion project in 2004, replacing cast iron pipes and cement pipes in an all-round way. Cement pipes and cast iron pipes are 30-40 times heavier than plastic pipes respectively, and their pressure resistance is much lower than that of plastic pipes. They are much inferior to low-pressure polyethylene sewage pipes in terms of economy and quality and safety service life. Therefore, cast iron pipes and cement pipes have been determined to restrict and stop production of products. Low-pressure polyethylene buried pipes have been identified as relatively good large-diameter sewage pipe products. This product has shown a geometric multiple growth in recent years, one of the important reasons is the policy and national conditions. Since the reform and opening up in our country, more than 3,000 county-level cities and development zones have developed vigorously. However, the sewage system owes too much. Most of the development zones and newly-built urban areas use cement pipes with a diameter of less than one meter as the main sewage pipe. Some still use septic tanks as sewage disposal methods in communities. When rainfall is heavy, low-lying parts of the city are flooded and factories shut down, causing great losses. Many provinces and cities use sewage discharge as a municipal assessment index to promote the improvement of the sewage discharge system, but the project is expensive and the municipal finance is unable to lay the sewage discharge project, so many cities still cannot meet the standards. In order to change the above situation, after many years of pilot projects, the National Development and Reform Commission (NDRC) will follow. Provinces and cities can use private enterprises and fund-raising channels to carry out sewage disposal projects. Sewage charges will be deducted from tap water fees and the sewage disposal projects will be returned to the municipal government 15 years later. In this way, the sewage disposal project will become a win-win project with no compensation, and investors will flock to it. However, the municipal government can not only solve the pollution problem without spending a penny, but also bring benefits of employment and bidding management from the pollution discharge project. Therefore, the municipal government is very active. It is estimated that the demand for large-diameter buried pipes will exceed 1.2 million tons within three years, becoming one of the bulk products of plastic products second only to LDPE films and PVC pipes. To sum up, because plastic pipes have greater advantages than traditional pipes such as cast iron pipes, steel pipes and cement pipes, with the popularization and application of plastic buried pipes, large-diameter plastic buried pipes represented by HDPE large-diameter double-wall corrugated pipes have become the mainstream of drainage systems. However, in the process of popularization and application of HDPE large-diameter double-wall corrugated pipe, the ring rigidity of plastic pipe cannot reach S2 grade with the increase of diameter. The definition formula of pipe ring stiffness is as follows: Where SR is the ring stiffness, MPa; E is the elastic modulus of the pipe material, MPa; I is the moment of inertia of the pipe wall per unit length, m3, for solid wall pipes, I=e3/12; Dm tube average diameter, m. From the above formula, it can be seen that the ring stiffness decreases sharply with the reciprocal of the third power of the pipe diameter when the pipe diameter increases. In order to increase the ring stiffness to S2, the moment of inertia I can be increased by improving the shape of the pipe. Or increasing the elastic modulus E of the material. 2. Development and research HDPE large diameter buried pipe is made of HDPE plastic. In principle, recycled materials and fillers are not added during use. This is because most of the recycled materials made in China are added with fillers. At the same time, the sources of recycled materials are not uniform, and the melting index ranges from 0.1 to 20. Therefore, the technology cannot adapt to the situation. When the recycled materials are used due to quality problems after addition, large-area surface collapse will be caused, causing great harm. How to modify and recycle recycled materials so that they can be applied to large diameter buried pipes? According to the existing conditions, we have developed and produced the stiffening and reinforcing masterbatch for large-diameter buried pipes, which not only improves the elastic modulus and reduces the cost, but also makes other properties basically unchanged or improved. The masterbatch can be applied to large-diameter buried pipes produced entirely from recycled materials, with satisfactory results. The process route adopts the existing twin-screw extruder granulation method and has the advantages of convenient processing, good production effect, easy management and no generation of three wastes. Under the guidance of plastic multi-component composite blending modification theory, we carefully configured and screened the components of the masterbatch. Selection of inorganic powder: inorganic powder added to plastic must improve ring stiffness and reduce cost. After the test comparison, it was found that the effect of using calcium carbonate to improve the ring stiffness was not significant. After that, we chose an inorganic powder which can improve the ring stiffness and reduce the cost. Selection of carrier: the carrier must have good compatibility, molding processability, chemical stability and dispersibility with the pipe resin, as well as high carrying capacity, to carry inorganic powder and various additives to the maximum extent to ensure smooth appearance and uniform internal quality of the masterbatch itself. After that, we chose a multi-component composite carrier, carrying 90% of inorganic powder and processing aids with a mass fraction of 10%. Selection of processing aids: The purpose of adding various processing aids is to comprehensively balance various properties of the master batch. The addition amount of each processing aid has a certain range in the master batch. The main reason is that after the master batch is added, certain properties of the pipe are excellent, other properties remain unchanged, and normal production is ensured. The main processing aids include: composite coupling agent, dispersant, internal and external lubricant, reinforcing agent, compatilizer, etc. Effect: With the support of Hangzhou Unicom Pipe Factory in Zhejiang Province, we added our inorganic powder reinforced and toughened masterbatch to all recycled HDPE plastics and achieved success. At the same time, the silicon whisker reinforced and toughened masterbatch produced by a factory in Sichuan and a factory in Jiangsu were added to the same HDPE recycled material in the same proportion for comparative tests. The results show that the performance is similar, but obviously the cost performance is much better. This is a breakthrough because the strengthening and toughening effects of ordinary inorganic powder and whisker silicon are not on the same order of magnitude. 3. Discussion From the main performance table, it can be seen that the ring stiffness of large-diameter buried pipes produced by adding reinforcement masterbatch to all HDPE recycled materials can reach S2 grade; When a thin-wall die is used, the measured technical performance index is basically the same as that of silicon masterbatch with whiskers. This is a breakthrough. The actual production operation is simple and convenient, and the original production process conditions do not need to be changed; The production efficiency is improved, and the production cost is reduced; Under the conditions of the same performance and the same addition ratio, the test that the meter weight of the pipeline is close to or lower than that of the pipeline added with whisker silicon masterbatch is currently in progress.