How to improve the temperature resistance of polye

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How to improve the temperature resistance of polyethylene (LDPE)

although polyolefin materials have a wide range of applications and play an important role in the field of geosynthetics at present, due to the characteristics of its macromolecular structure, its mechanical properties are worse than those of polyester, polyamide and other materials. In order to better develop polyolefin materials and expand their application fields and product categories, People often adopt certain technical means to modify polyolefin materials in order to obtain materials with higher performance price ratio. There are many relevant literature reports [6`9]. There are many research methods of modification. Different modification methods are adopted according to the processing technology of plastics and fibers. Generally speaking, the common research methods are as follows

3.1 research on high-performance plastics

method 1: change the crystalline state of materials

changing the physical and mechanical properties of materials by changing the crystalline state of materials is an important research method, and the common practice is to add nucleating agents of other components. For many years, the method of adding nucleating agent is often used to study the high performance of polypropylene materials in order to improve its crystallization and mechanical properties. Polypropylene is a crystalline polymer. Its internal structure contains large spherulites. By adding nucleating agent, the crystallization speed of polypropylene can be accelerated to form fine and dense spherulites, or its microcrystalline structure can be changed, which is conducive to improving the impact strength and yield strength, and is conducive to the processing and appearance of products

many units at home and abroad have conducted research on such content. Some nucleating agents are organic materials, such as the nucleating agent for high-performance polypropylene resin of East China University of science and technology [10]. Through molecular design and synthesis technology, the developed high-efficiency organic nucleating agent can improve the tensile, bending, impact, crystallization temperature and other comprehensive properties of polypropylene. Some nucleating agents are organic-inorganic composites, such as a stiffening and toughening agent for polypropylene [11], which is a homopolymer of organic materials and metals, which can greatly improve the rigidity, crystallization temperature, deflection coefficient and heat resistance of polypropylene, and will not reduce the impact resistance of polypropylene

method 2: print the A4 format report directly and modify it by grafting and crosslinking through physical and chemical methods. This method is often used for the stabilization of polyethylene. For example, it can be used γ— PE and stabilizer are irradiated by radiation to obtain crosslinked PE; Crosslinked PE can also be obtained by treating PE and stabilizer with peroxide at high temperature; If vinyl silane is added during peroxide treatment, Silane Grafted PE can be obtained

method 3: this kind of special experimental machine adopts the development of computer automatic control system materials

sometimes, limited to production equipment and conditions, adding additives is difficult to significantly improve the performance requirements of materials. In this case, in order to improve the performance of materials, it is necessary to study the production of special materials and special brands. For example, two or more materials with advantages are combined through new polymerization processes. After the combination of multiple materials, it is not a mixture of multiple products, but reaches the average distribution at the molecular level, which can be considered as a material. A typical example of success is the bimodal polyethylene production technology of Nordic chemical company, which polymerizes linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE) through the double reactor series process of loop pipe and gas-phase kettle in supercritical state. The bimodal polyethylene obtained includes the computer system, which has a very short polymer molecular chain through the controller, plays the role of lubrication between molecules, and can improve the processing performance; It also contains a long polymer molecular chain, which ensures the mechanical action of the material

3.2 research on high-performance fibers

compared with plastics, fibers have a higher degree of orientation, which depends on their different production processes. Therefore, the high-performance methods of materials are also different

method 1: improve the raw material polymerization process

the traditional method is to select high-strength fiber special resin with high manufacturing cost. By adjusting the molecular weight and molecular weight distribution, or select the resin with appropriate melt index. Industrial polyester, polyamide fiber, high-strength polyethylene fiber and high-strength polypropylene fiber are still the research hotspots of geosynthetics

method 2: blending modification

blending modification is also a common method to improve the strength and modulus of fibers. For example, adding resins incompatible with polypropylene resin for spinning, or blending resins with different molecular weights, is also a research hotspot of methods to improve the properties of polyolefin fibers. Through the adjustment of spinning process, the orientation degree is improved, so as to obtain high strength and high modulus filaments, short fibers and flat filaments

method 3: improve spinning equipment and process

folding chains exist in polyolefin, polyamide and polyester fibers. Although these fibers are subject to 4 ~ 10 times of drafting in the manufacturing process, a considerable proportion of molecular folding chains still exist. If the molecular folding chain in the material is opened after super drafting under appropriate temperature and processing conditions, the tensile strength and rigidity of the fiber can be greatly improved and high-performance fibers can be obtained. This method can be used to study the high performance of polyethylene, polypropylene, polyamide and polyester fibers. By improving the spinning equipment and process, the stretching degree and crystallinity of macromolecular chain can be improved, the knot energy of polymer materials can be improved, and the help crystal type can be improved, so as to improve the orientation of macromolecules in fibers. In short, the technical transformation of melt spinning equipment and process is an important means to achieve high-performance fibers

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