Summary
This article briefly introduces the recycling of waste plastics, all of which are for the development and production of large-diameter buried pipe-refining special materials for recycling HDPE, and the development and production of reinforced and toughened master batches. The relevant technical level has reached the advanced level at home and abroad, and hopes to be able to Professionals provide some references.
Description
1, the source of recycled plastic
Extensive use of plastic products has become an indispensable part of daily life in modern civilized society. While we produce a large number of new plastic products every day, a large amount of waste plastics are constantly produced in people’s working lives. At present, China’s waste plastics Mainly plastic film, plastic wire and woven products, foam plastic, plastic packing boxes and containers, daily plastic products, plastic bags and agricultural plastic film.
It is understood that in 2010, the domestic recycling of waste plastics exceeded 10 million tons. In 2014, the output of China's domestic plastic products was 73.7778 million tons, domestic use was 67.8353 million tons, and domestic plastic recycling volume was about 20 million tons.
According to Global Sources, the recycling rate of waste plastics around the world is extremely low. Only 70% of the 7 billion tons of waste plastics are recycled. About 3,400 plastic bottles are discarded every second. The annual amount of plastic waste is about 2.6-3. Billion tons, of which 8 million tons flow into the ocean every year. According to statistics, in 2015 alone, the global production of plastic products exceeded 300 million tons. In 2016, the amount of plastics used globally reached 500 million tons. It is expected that global plastic consumption will With an annual growth rate of 8%, the annual consumption of plastics in 2030 will reach more than 700 million tons. Once so many plastics are discarded, their storage, transportation, processing, application and post-processing are bound to damage the environment. People's health. At the same time, as a renewable resource, it is also an important part of the recycling economy.
2, the significance of recycling waste plastics
The use of recycled and renewable resources is an inevitable choice for the development of circular economy. The strategic goal is to establish an environment-friendly economy and a resource-saving society. The concept of circular economy, the establishment of theory, and the development of practice are all exploring. People and the environment, the road to sustainable development of resources, is to establish an environment-friendly, resource-saving economy and advocate an environment-friendly, resource-saving society; and, to realize the realization of this goal to the modern Social production, all aspects of life and all aspects.
Recycling of plastics is a major strategic issue for the country to resolve resource shortages. China's oil resources consumption gap is very large, and the situation where plastic raw materials are heavily dependent on imports has not been fundamentally changed. Recycling recycled plastics has become one of the shortest ways to solve the shortage of raw materials, and sources Extensive and low cost. At present, on the basis of recycling and recycling of 6 million tons of domestic recycled plastics every year, China imports about 5 million tons of waste plastics through imports, becoming the world's largest importer of waste plastics.
Recycling and recycling of plastics is not only conducive to regional economic growth, especially providing an important way to solve surplus labor in rural areas. It provides an ideal channel for rural and urban residents to increase their income and employment. It also provides resources recycling and environmental protection for the country. Great contribution has become one of the environmental industries that cannot be ignored in the sustainable development of the national economy.
After rapid development in recent years, some apparent characteristics of the plastic recycling industry have changed: The status and role of recycled plastics in the raw material market has become increasingly prominent, and the market has obvious competitive advantages. Raw material prices continue to remain high, and the recycling and recycling materials industry is developing strongly. The driving force is for example. In China, more than 3 million tons of waste plastics are added every year. If they are recycled, they can generate profits of more than 1.5 billion yuan.
3, introduction of the latest achievements of 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 achieving high-quality recycling. Currently, simple recycling of waste plastics has been widely used: The waste generated in the production process (legs, scraps, wastes, etc.) can be easily reused because it is relatively clean and of a single type; some plastics that facilitate manual sorting (such as plastic shells in waste household appliances, beverage bottles, etc.) First, it is classified by manual classification and then recycled. However, some difficult-to-treat metal-plastic composite materials (such as aluminum-plastic composite ointment tubes, aluminum-plastic plaster boards, etc.) have not yet been effectively utilized.
Zhejiang Crushing Equipment Co., Ltd. has devoted itself to the research of special crushing equipment for many years. Based on the existing technologies at home and abroad, it has initially developed a special crushing technology for the treatment of waste aluminum-plastic composite materials with a capacity of 500 Kg/h and processing 200 Kg/h. The high-pressure electrostatic separation technology has been made into a segmented prototype and is currently preparing to enter the pilot test. This technology uses mechanical crushing and dissociation, and electrostatic separation to treat waste aluminum-plastic composite materials. The main process flow is as follows:
Waste aluminum plastic composites → slice → crushing and dissociation → high-voltage electrostatic separation → plastic granulation → finished products
Its processing features are:
(1) Pulverization: This technology changes the aluminum originally attached to the plastic surface into a separated state by crushing, and becomes a mixed powder of aluminum and plastic. The main working principle is as follows: The material passes through a multi-layer combined turbine rotor with high-speed rotation and The stator applies repeated impacts to the pellets, rubbing and shearing to crush it, and disassociates the aluminum from the plastic. The technology is equipped with a built-in grading rod and a reflux device to automatically return undecomposed powder to the machine. Continue smashing until it meets the requirements; dissipated good material is discharged through the discharge port.
(2) High-voltage electrostatic separation technology for the recycling of waste aluminum-plastic composite materials
Using the difference in the electrical conductivity of aluminum and plastic, the mixed powder is separated by high-voltage electrostatic separation technology for aluminum and plastic. The working principle is as follows: When the powder passes through the rotating drum and the corona field generated by the high-voltage corona electrode, The space is electrically charged, and the charge obtained by the aluminum is immediately transferred by the grounded roller and falls under the force of the centrifugal force and gravitational force generated by the roller, and is then collected by the conveyor and sent; the plastic cannot be charged Pass away and adsorb on the surface of the drum, and then it is brought to the rear. After being brushed off, it is brushed out and sent through the conveyor to collect and collect. The middle part of the material is the unqualified separation product. After being conveyed by the conveyor, it is bucket type. The hoist is sent to the hopper and then continues to separate.
Schematic diagram of working principle of high-voltage electrostatic separation technology for recycling aluminum scrap composites
The innovation of this technology lies in the adoption of advanced physical recycling technology: waste aluminum-plastic composite materials → slicing → comminution and dissociation → high-voltage electrostatic separation → plastic granulation, and the process design of cyclic separation of aluminum and plastics. Domestic blank. The technology recovery effect can make the purity of recycled aluminum 97%, and the recovery rate of aluminum 98%. The purity of recycled plastic is up to 95%. It should be pointed out that this technology can also be crushed and separated by proper adjustment. Multi-layer coextrusion composite plastic waste.
Modified HDPE Recycled Material to Produce Large Diameter Buried Pipes
1, briefly
In modern society, pipeline transportation is one of the infrastructures that guarantee normal social production, life, and economic prosperity. Because plastic pipes have more advantages than traditional pipes such as cast iron pipes, steel pipes, and cement pipes, they are Our country has achieved rapid development. According to incomplete statistics, the output of plastic pipe in our country has grown from less than 200,000 tons in 1990 to nearly 800,000 tons in 2000, and it has grown by as much as 300% in the last decade of the last century. After entering the new century, it will continue. With rapid growth, the total output of plastic pipes in China was nearly 1.7 million tons in 2004. According to statistics from China's pipeline industry groups, China's plastic pipe production climbed to 12.1 million tons last year. Among them, with the promotion and application of plastic buried pipes, Diameter double wall corrugated pipe, winding pipe has become the mainstream of large-diameter plastic buried pipe drainage system.
The production of large-diameter double-wall corrugated pipes is mainly made of high-density polyethylene. Now, with the explosive rise of oil prices worldwide, the price of plastics as a synthetic polymer material for cracking petroleum also rises to an unprecedented height. In order to reduce costs and increase competitiveness, recycled plastics have been added to many plastic products. However, it is well known that the performance of ordinary recycled plastics is difficult to achieve the performance of new materials of the same material. In the promotion of environmental protection, economizing on the road of circular economy In today's society, how to use plastics modification to modify the waste plastic recycling material, the performance indicators of various aspects are close to or reach the level of new materials, thus lowering the cost of the premise of ensuring quality is a major issue before us.
To use regrind as a new material, you need to solve the following problems:
◆ The physical and mechanical properties (such as tensile strength, impact strength, etc.) of recycled materials have generally declined;
◆ Recycled material is heated several times, causing degradation of some polymer materials in plastics, aging, and increase of melt flow rate, although most plastics contain anti-aging agents;
◆ The color and surface gloss of each batch of recycled material are not the same, the degradation degree of aging is not the same, and the degree of surface cleanness is not the same. Both the appearance and the intrinsic quality, each batch is different;
◆ The modified high-density polyethylene recycled material must be lower than the price of the new material of the same type of 1000-2000 yuan per ton, will have commercial value.
In view of the above difficulties, we applied the multiple compound blending modification theory and technology, repeatedly trial-produced, overcame various difficulties to produce special materials for HDPE large-diameter double-wall corrugated pipe, winding pipe modified and recycled high-density polyethylene.
2, Development and Development
Based on the existing conditions, we have developed and produced two kinds of modified high-density polyethylene recycled materials: One is a pure modified high-density polyethylene recycled material, and it is necessary to add and increase rigidity when it is used, to strengthen (toughen) the masterbatch. The second is to increase the elastic modulus of large-diameter buried pipe reinforced, reinforced (toughened) modified high-density polyethylene recycling special materials.
(1) The process route adopts the existing twin screw extruder granulation method, which has the advantages of convenient processing, good production effect, easy management, and no waste generation.
(2) Under the guidance of plastic multiple-composite blend modification theory, we carefully configure and filter the various components of modified recycled materials:
The choice of recycled materials: As a recyclable material that can be modified (such as high-density polyethylene), the recycled material must be clean and of good purity, ie containing less impurities in other waste plastics, and the difference between each batch should be as small as possible. Ample sources and low prices are also some of the factors that must be considered. In the end, we chose two kinds of disposable high-density polyethylene recycled materials, which are used for the production of modified high-density polyethylene recycled materials for pipe production. The effect is very good. it is good.
The choice of modifiers: The basic requirement for modifiers is that the addition of plastics must improve various physical and mechanical properties and at the same time improve the anti-aging properties. After tests and comparisons, it is found that the addition of an additive has no significant effect on performance. Finally, we have selected three types of composite additives that can both improve performance and reduce costs. We can use synergies to improve overall performance and meet usage requirements.
The selection of processing aids: The purpose of adding various processing aids is to comprehensively balance the various properties of the modified recycled materials. The amount of each processing aid added has a certain range in the modified recycled materials, which makes the properties stable. , And can guarantee normal production. The main processing aids are: anti-aging agents, dispersants, internal and external lubricants, colorants and so on.
(3) Main performance
3, application effect
With the assistance of Zhuhai Bay Plastics Co., Ltd., the trials were conducted by several of its partners and the results were satisfactory. With the first modified high-density polyethylene recycled material produced by us, 30 to 60% of large-diameter buried ground produced by adding masterbatch was added. The coiled tubing meets the quality requirements and has a cost advantage. The second large-diameter reinforced-reinforced (high-toughness) modified high-density polyethylene reclaimed material that we produced to increase the elastic modulus of the large-diameter buried pipe produced large diameter The buried double-wall corrugated pipe passed the small test and was in the pilot test.
4, discuss
(1) As can be seen from the main performance table, the index of the modified high-density polyethylene recycled material is higher than that of the new material; the indexes of the modified recycled high-density polyethylene special material except for the elongation at break decrease slightly, and the others are all high In the new material; shows that its modification is successful.
(2) It is easy to operate in actual production, without changing the original production process conditions.
(3) Production efficiency is increased, production costs are reduced, and the actual cost per ton product can be reduced by about 1,000 to 2,000 yuan.
100% increase in size, reinforced (toughened) masterbatch for large-diameter buried pipes for recycled materials
1, briefly
Buried polyethylene hollow-wound structural wall drainage pipes and buried polyethylene double-wall corrugated drainage pipes are commonly known as large-diameter buried pipes. In 2004, the Ministry of Construction of the People's Republic of China was established as a scientific and technological achievements promotion project, which completely replaced cast iron pipes and Cement pipe. Cement pipe and cast iron pipe are 30-40 times the weight of plastic pipe, and the pressure resistance is much lower than that of plastic pipe. They are inferior to low-pressure polyethylene sewer pipe in terms of economy, quality and safety, etc., so the cast iron pipe And cement pipe has been set as a restriction and stop production.
Low-pressure polyethylene buried pipe has been identified as a relatively large-caliber sewage pipe product. The product has grown geometrically in recent years, an important reason is caused by policies and national conditions. China has since reform and opening up more than 3000 County-level cities and development zones are flourishing, but there are too many sewerage systems. Most cement development zones and newly built urban areas use cement pipes with a diameter of less than one meter as the main pollutant discharge pipeline. Some communities still use septic tanks as a means of sewage disposal. , When the rainfall was high, the city was flooded and the factory was suspended, causing great losses. Many provinces and municipalities used the sewage as a municipal assessment indicator to promote the improvement of the sewerage system. However, the project was costly and the city’s finance was unable to lay the sewage. Therefore, many cities are still unable to meet the targets. The Central Government has changed the above conditions. After many years of experimentation, the National Development and Reform Commission will follow. The provinces and cities can pass sewage treatment projects through private enterprises and fund-raising channels. The sewage charges are deducted from the water fees. After 15 years, sewage projects Returned to the municipal government. The sewage project turned into a win-win project that only made no compensation. The investors flocked. The city government did not spend a penny. To solve the pollution problem, the sewage project can also bring benefits of employment and bid management. 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, making it second only to LDPE film in plastic products. One of the major products of PVC pipe.
In summary, 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 plastics represented by HDPE large-diameter double-wall corrugated pipes are buried. Pipes become the mainstream of the drainage system.
However, in the process of popularizing and applying HDPE large-diameter double-wall corrugated pipe, the ring stiffness of the plastic pipe cannot reach the S2 level with the increase of the diameter. The definition of the pipe ring stiffness is as follows:
In the formula, 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 of the unit length, m3, for the solid wall pipe, I=e3/12 (the wall thickness of the real wall pipe, m);Dm tube average diameter, m.
From the above formula (1), it can be seen that ring stiffness decreases sharply as the pipe diameter increases to the third power when the pipe diameter increases. To increase the ring stiffness to S2 level, you can improve the pipe's profile to increase the moment of inertia I; or increase the material. The elastic modulus E, to be solved.
2, Development and Development
The raw material of HDPE large-diameter buried pipe is HDPE (low-pressure polyethylene) plastic. In principle, no recycled material and filler are added. This is because most of the domestic recycled and recycled materials are filled with fillers, and the source of recycled materials is not uniform. Melt index From 0.1 to 20, it can not be adapted to the process. When quality problems occur after adding it, it will cause a large area of ground surface to collapse, which is extremely harmful.
How can we modify and recycle recycled materials before we can apply them to large-diameter buried pipes? Based on the existing conditions, we have developed and produced not only to increase the elastic modulus, to reduce costs, but also to make other properties basically unchanged or improved. Large-diameter, reinforced (toughened) masterbatches for large-diameter buried pipes can be used in large-diameter buried pipes produced from recycled materials to achieve satisfactory results.
(1) Process route The advantages of the existing twin-screw extruder granulation method are convenient processing, good production effect, easy management, and no waste generation.
(2) Under the guidance of the plastic multiple compound blending modification theory, we carefully compose and screen each part of the masterbatch.
Selection of Inorganic Powders: Inorganic powders added to plastics must be able to increase the ring stiffness and at the same time reduce the cost. After a trial comparison, it has been found that the use of calcium carbonate to improve the ring stiffness has no significant effect. Finally, we have selected a Inorganic powders that increase ring stiffness and reduce costs.
The choice of carrier: The carrier must have good compatibility with the pipe resin, molding processability, chemical stability and dispersibility, and high load carrying capacity to carry the inorganic powder and all kinds of additives to the maximum extent. The material itself is smooth and clean, and the internal quality is uniform. Finally, we have selected a multiplex composite carrier to carry 90% of the inorganic powder and processing aids at a mass fraction of 10%.
The selection of processing aids: The purpose of adding various processing aids is to comprehensively balance the various properties of the masterbatch. The amount of each processing aid has a certain range in the masterbatch, mainly the addition of a masterbatch. Excellent performance, the rest of the properties remain unchanged, and to ensure normal production. The main processing aids are: compound coupling agent, dispersant, internal and external lubricants, reinforcing agents, compatibilizers, etc.
(3)Effects: With the support of Hangzhou Unicom Pipe Factory in Zhejiang Province, we added inorganic powder reinforced toughening masterbatches produced by us for recycling HDPE plastics. We succeeded. We also used a factory in Sichuan, Jiangsu. The production of whisker-silicon based reinforced matrix masterbatch was similarly added to the same HDPE regrind for comparative tests. The results showed comparable performance, but the price/performance ratio was much better. This is a breakthrough because The stiffening and toughening effects of common inorganic powders and the stiffening and toughening effects of whisker silicon are not an order of magnitude.
3 Discussion
(1) As can be seen from the main performance table, the stiffness of the pipe rings produced in the large-diameter buried pipes with the reinforced reinforcement (toughening) masterbatch added in all the HDPE back materials can reach the S2 level;
(2) When thin-walled molds are used, the actual measured technical performance index is basically the same as the performance of the added whisker-silicon masterbatch; this is a breakthrough;
(3) The actual production operation is simple and the original production process conditions do not need to be changed;
(4) The production efficiency increases, and the production cost decreases;
(5) Under the same conditions of performance and the same ratio of addition, the test that the weight of the pipe is close to or less than the weight of the pipe to which the whisker-silicon masterbatch was added is in progress.
