PS is an amorphous resin, has no obvious melting point, and has a wide melting temperature range, and can be melted into a melt between 120 and 180 °C.
The thermal stability of PS is good, and the decomposition temperature is above 300 °C. Although the thermal stability of PS in an inert gas is good, in the heated state, thermal oxygen causes its degradation reaction, so it is necessary to add an antioxidant such as primary antioxidant 1010 and secondary antioxidant 168.
PS has a higher thermal conductivity and a faster heating and cooling rate.
PS melt belongs to non-Newtonian fluid, and the viscosity of the melt is moderate; the viscosity is strongly dependent on the change of shear rate, but the influence of temperature is also obvious. PS is very fluid and is a plastic that is easy to process.
The water absorption rate of PS is relatively low, and generally does not require drying before processing; if there is special need (such as requiring high transparency) to dry, the specific drying temperature is 70-80 ° C, 1.5 hours.
PS is prone to internal stress during processing. In addition to selecting the correct process conditions, improving product design and reasonable mold structure, the product should be heat treated. The heat treatment conditions are: treatment in a hot air circulating drying oven or hot water at 65 to 85 ° C for 1 to 3 hours.
The molecular chain of PS is relatively rigid, and it is best not to add metal inserts to prevent stress cracking.
2. Processing method of polystyrene PS:
(1) Injection molding: the ordinary injection molding machine can be selected. When the thickness of the product is in the range of 2.3 to 3 mm, the limit flow length and thickness ratio are 200:1, the draft angle is not less than 1°, and the depth of the exhaust hole of the exhaust hole is less than 0.03. Mm, the temperature difference between the two mold temperatures is less than 3 ~ 6 °C. The specific injection molding process conditions are: molding temperature of 180 to 215 ° C, injection pressure of 30 to 150 MPa, and mold temperature of less than 70 ° C.
(2) Extrusion: PS can be processed on a common extruder, and the extruded products include pipes, bars, sheets, films, fibers, and the like. The strength is low and the brittleness is not stretched after molding, and the transparency, gloss, strength and toughness are obviously improved after stretching. The extrusion temperature of the PS is between 150 and 200 °C.
(3) Foam molding: GPPS is used as raw material, and the foaming agent is divided into chemical foaming agent and physical foaming agent. The one-step extrusion is used, and the foaming agent is directly mixed with the PS or the physical foaming agent is injected into the PS melt in the extrusion melting section, and the foaming and cooling are performed by extrusion. The foam made of GPPS has the advantages of fine cells and high strength. The main products of high foaming materials are blister packaging materials such as fast food lunch boxes, art decorative plates and foam nets, and low foaming materials are imitation wood profiles, sheets, plates and the like.
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