PVC, PET, LDPE, HDPE in one article
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There are many varieties of plastic films, which can be used in agriculture, daily necessities, medicine, construction, water treatment, solar power generation, battery separators, bulletproof glass and many other fields according to their respective characteristics.
1，There are many methods for forming plastic films, among which cast film, extrusion and blow molding are the most common:
Cast film: a non-stretched, non-directional flat extruded film is produced through a melt slobbering quenching process. The film produced by this process does not have an obvious oriented structure.
Extrusion method: Common methods include uniaxial stretching and biaxial stretching. The basic principle of biaxial stretching: the polymer raw material is first heated and melted by an extruder to be extruded into a thick sheet, and then stretched by a certain multiple in the longitudinal and transverse directions in a proper temperature range by a stretching machine, so that the molecular chains are arranged in an orderly manner on a plane parallel to the film, and then heat-set under tension, and finally cooled and processed to form a film.
Blow molding: usually manufactured by extrusion blow molding, the material is plasticized and extruded to form a tube billet, which is then cooled, pulled and rolled up. Blown film is oriented. Blow molding is a simple process and is the most commonly used film forming process.
2,PVC, PET, LDPE, HDPE Film properties:
HDPE
High-density polyethylene (HDPE) is a white powder or granular product. It is non-toxic, odorless, with a crystallinity of 80% to 90%, a softening point of 125 to 135°C, and an operating temperature of up to 100°C; its hardness, tensile strength and creep properties are better than those of low-density polyethylene.
HDPE membrane is called geomembrane or anti-seepage membrane. Its melting point is about 110℃~130℃, and its relative density is 0.918-0.965kg/cm3. It is a highly crystalline, non-polar thermoplastic resin. The appearance of the original HDPE is milky white, and it is translucent to a certain extent in the thin cross section. It has good high and low temperature resistance and impact resistance, even at a low temperature of -40. Its chemical stability, rigidity, toughness, mechanical strength, and tear resistance are all excellent, and with the increase of density, the mechanical properties, barrier properties, tensile strength and heat resistance will increase accordingly, and it can resist corrosion from acids, alkalis, organic solvents, etc.
LDPE
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Low-density polyethylene (LDPE), also known as high-pressure polyethylene, is a plastic material that is suitable for various molding processes in thermoplastic molding.
LDPE film has low density, softness, low temperature resistance, good impact resistance and chemical stability. It is generally resistant to acid (except strong oxidizing acids), alkali and salt corrosion, and has good electrical insulation. LDPE is mostly used in plastic bags, and its products are mostly used in civil engineering and agricultural fields, such as LDPE geomembranes, agricultural films (shed films, mulch films, mulching films, green storage films, etc.). Its recycled materials and scraps can be made into elastic plastic products such as trash cans, tool boxes, bicycle mats, and garbage carts.
HDPE tarpaulin fabric is mainly used for shading in agriculture, forestry, animal husbandry and tourism. Weaving process: HDPE ingredients → film blowing → strip cutting and stretching into flat yarn → weaving → shaping → packaging. Weaving principle: HDPE is blown into film sheets, the film sheets are cut into uniform strips, heated and stretched into flat yarns, and woven on a coarse gauge warp knitting machine. The flat yarn has a large surface area and a large shading area to achieve a shading effect. LDPE needs to be coated on both sides for waterproofing.
PET
Polyethylene terephthalate is the most important type of thermoplastic polyester, commonly known as polyester resin. It is made by ester exchange of dimethyl terephthalate and ethylene glycol or esterification of terephthalic acid and ethylene glycol to synthesize dihydroxyethyl terephthalate, and then polycondensation reaction.
Polyester film (PET) is a thermoplastic engineering plastic. It is made into a thick sheet by extrusion and then made into a film material by biaxial stretching. The characteristics of polyester film are excellent mechanical properties, high rigidity, hardness and toughness, puncture resistance, friction resistance, high and low temperature resistance, chemical resistance, oil resistance, good air tightness and fragrance retention. It is one of the commonly used barrier composite film substrates, but the corona resistance is poor and the price is high. The film thickness is generally 0.12mm, and it is often used as the outer material of food packaging for packaging, and has good printing properties.
PVC
Polyvinyl chloride plastic is polymerized from vinyl chloride monomer and is one of the commonly used thermoplastic plastics. Its trade name is abbreviated as "chlorine plastic", and its English abbreviation is PVC. Pure polyvinyl chloride resin is a hard thermoplastic substance, its decomposition temperature is very close to the plasticizing temperature, and its mechanical strength is poor. Therefore, it is impossible to use polyvinyl chloride resin to mold products. Plasticizers, stabilizers, fillers, etc. must be added to improve the performance to make polyvinyl chloride plastics, and then processed into various products.