Cross linked polyethylene and ethylene vinyl acetate copolymer
DATE：2022/12/22 9:07:54 / READ： / SOURCE：This station
2.1.9 Cross linked polyethylene
Cross linked polyethylene is a method of modifying polyethylene. The commonly used cross linked polyethylene in industry includes radiation cross-linked polyethylene, peroxide cross-linked polyethylene and silane cross-linked polyethylene. Polyethylene (LDPE, HDPE, LLDPE and MDPE can all) can change its physical and mechanical properties by partially cross-linking reaction between its macromolecular chains through cross-linking. PEX is the abbreviation of cross-linked polyethylene.
Cross linked polyethylene (XLPE) is a thermosetting plastic with a network structure. After the cross-linked polyethylene products are formed, they cannot be molded again. At this time, they can also be machined.
Cross linked polyethylene is non-toxic, tasteless and non absorbent; Wear resistance, solvent resistance, stress cracking resistance, weather resistance, aging resistance and dimensional stability are very good; Low softness, good heat resistance, can be used for a long time below 140 ℃, and the softening point can reach 200 ℃; Impact strength, tensile strength, creep resistance and rigidity are better than HDPE; Good electrical insulation, low temperature resistance, chemical stability and radiation resistance; The crosslinked polyethylene film is thin, transparent and has good water vapor permeability; After being heated, expanded (stretched), cooled and shaped, cross-linked polyethylene can naturally recover to its original shape and size when it is reheated above the crystallization temperature.
The properties of silane crosslinked polyethylene are shown in Table 2-31. See Table 2-32 for properties of radiation crosslinked polyethylene film. The properties of peroxide crosslinked polyethylene are shown in Table 2-33.
Ethylene vinyl acetate copolymer (EVA or E/EVA) is also called ethylene vinyl acetate copolymer, which is made by copolymerization of ethylene (E) and vinyl acetate (VA).
2.1.10.1 Performance characteristics
EVA resin molded products have good flexibility and elasticity. They still have good flexibility in a 50 ℃ environment, good transparency and surface gloss, non-toxic, good chemical stability, strong anti-aging and ozone resistance; It is well mixed with other fillers, and has good colorability and shaping processability. The properties of EVA are closely related to the content, molecular weight and melt flow rate of vinyl acetate. When MFR is constant, with the increase of vinyl acetate content, its elasticity, flexibility, compatibility and transparency are improved, but its crystallinity decreases; If the content of vinyl acetate decreases, its performance is close to that of polyethylene, but its rigidity, abrasion resistance and electrical insulation performance are improved. If the vinyl acetate content is fixed, when MFR value increases, the softening point decreases, and the processability and surface gloss are improved, but the mechanical strength decreases; If MFR value decreases, the molecular weight increases, and the impact property and stress cracking resistance are improved.
2.1.10.2 Forming method and use
EVA resin can be molded by injection molding, extrusion, blow molding, calendering, rotational vacuum thermoforming, foaming, coating, heat sealing and welding. Film products include packaging film, heat shrinkable film, agricultural film, food packaging film, laminated film, etc. Industrial uses include household appliances accessories, window sealing materials, wire insulation sheaths, etc. Daily sundries include toys, cushions, container covers, etc. Car accessories include shock absorbers, mudguards and decorative accessories. EVA resin can be modified by mixing it into LDPE and HDPE in a certain proportion.
Cross linked polyethylene is a method of modifying polyethylene. The commonly used cross linked polyethylene in industry includes radiation cross-linked polyethylene, peroxide cross-linked polyethylene and silane cross-linked polyethylene. Polyethylene (LDPE, HDPE, LLDPE and MDPE can all) can change its physical and mechanical properties by partially cross-linking reaction between its macromolecular chains through cross-linking. PEX is the abbreviation of cross-linked polyethylene.
Cross linked polyethylene (XLPE) is a thermosetting plastic with a network structure. After the cross-linked polyethylene products are formed, they cannot be molded again. At this time, they can also be machined.
Cross linked polyethylene is non-toxic, tasteless and non absorbent; Wear resistance, solvent resistance, stress cracking resistance, weather resistance, aging resistance and dimensional stability are very good; Low softness, good heat resistance, can be used for a long time below 140 ℃, and the softening point can reach 200 ℃; Impact strength, tensile strength, creep resistance and rigidity are better than HDPE; Good electrical insulation, low temperature resistance, chemical stability and radiation resistance; The crosslinked polyethylene film is thin, transparent and has good water vapor permeability; After being heated, expanded (stretched), cooled and shaped, cross-linked polyethylene can naturally recover to its original shape and size when it is reheated above the crystallization temperature.
The properties of silane crosslinked polyethylene are shown in Table 2-31. See Table 2-32 for properties of radiation crosslinked polyethylene film. The properties of peroxide crosslinked polyethylene are shown in Table 2-33.
Cross linked polyethylene can be molded by extrusion, injection, molding and other methods. Extruder can be used to extrude and shape heat-resistant pipes, hoses, heat shrinkable films, sleeves, wires, cable coatings, etc; Inject high pressure and high frequency resistant heat insulation materials, corrosion resistant parts, containers and foamed plastics in chemical equipment with injection molding machine. For example, Sanren Brand XLPE, DJ200 and DJ210 produced by Shanghai Petrochemical Company are special materials for extruding cross-linked cables.
Ethylene vinyl acetate copolymer (EVA or E/EVA) is also called ethylene vinyl acetate copolymer, which is made by copolymerization of ethylene (E) and vinyl acetate (VA).
2.1.10.1 Performance characteristics
EVA resin molded products have good flexibility and elasticity. They still have good flexibility in a 50 ℃ environment, good transparency and surface gloss, non-toxic, good chemical stability, strong anti-aging and ozone resistance; It is well mixed with other fillers, and has good colorability and shaping processability. The properties of EVA are closely related to the content, molecular weight and melt flow rate of vinyl acetate. When MFR is constant, with the increase of vinyl acetate content, its elasticity, flexibility, compatibility and transparency are improved, but its crystallinity decreases; If the content of vinyl acetate decreases, its performance is close to that of polyethylene, but its rigidity, abrasion resistance and electrical insulation performance are improved. If the vinyl acetate content is fixed, when MFR value increases, the softening point decreases, and the processability and surface gloss are improved, but the mechanical strength decreases; If MFR value decreases, the molecular weight increases, and the impact property and stress cracking resistance are improved.
2.1.10.2 Forming method and use
EVA resin can be molded by injection molding, extrusion, blow molding, calendering, rotational vacuum thermoforming, foaming, coating, heat sealing and welding. Film products include packaging film, heat shrinkable film, agricultural film, food packaging film, laminated film, etc. Industrial uses include household appliances accessories, window sealing materials, wire insulation sheaths, etc. Daily sundries include toys, cushions, container covers, etc. Car accessories include shock absorbers, mudguards and decorative accessories. EVA resin can be modified by mixing it into LDPE and HDPE in a certain proportion.
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