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Material processing of PVC

- Jan 08, 2018 -

PVC form of different, different, processing methods are also diverse, can be suppressed, extrusion, injection, coating and so on. The particle size of polyvinyl chloride resin, fish eye, pine density, purity, foreign impurities and porosity have all influence on the processability, and the viscosity and gelling properties of the paste resin should be considered.

Polyvinyl chloride is amorphous polymer with small shrinkage rate. Before the powder processing should preheat to remove moisture, enhance plasticizing effect, prevent bubble. And PVC is very easy to decompose, especially at high temperature with steel, copper contact easier decomposition (decomposition temperature 200 degrees). Forming temperature range is small, the material temperature must be strictly controlled. The use of screw injection machine and through the nozzle, the aperture should be large to prevent dead end of the material. Mold pouring system should be coarse, gate section should be large, mold should be cooled, mold temperature 30-60 degrees, material temperature 160-190.

Under the glassy temperature (Tg,80℃), polyvinyl chloride is a glassy state, and the tg→ viscous flow temperature (Tf, about 160 ℃) is highly elastic rubber-like, plasticity, and in tf→ thermal decomposition temperature (Td) is viscous flow, the higher the temperature, the easier the flow. When the temperature exceeds TD,PVC to decompose a large amount of hydrogen chloride (HCl), the material loses chemical stability and physical properties, so TD is the upper limit temperature for processing. Because of the large intermolecular force of polyethylene, the TF is very high, and even close to the decomposition temperature, it is necessary to add plasticizers to reduce TF. On the other hand also need to add stabilizer, so as to improve the PVC TD, in order to process molding.


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