PP (polypropylene)

plastic-raw-materials

PP (polypropylene)



Typical Applications:

Automotive industry (made mainly from PP enhanced with metal additives: fenders, ventilation pipes, fans, bumper and wheel housing covers, dashboards, steering wheels, handles, battery housing, etc.), consumer goods (hangers, chairs, stools, buckets, basins, toys, stationery, office supplies, furniture, turnover boxes, TV set cases, electric fan blades, dishwasher door liner, refrigerator door liner, dryers, pipes, washing machine frames and covers, lawn mowers and sprinklers, building boards, etc.), packaging films (for food, medicine, cigarettes, etc.), fiber (ropes, fishing nets, tents, water proof cloth, carpets, blankets, clothing materials, mosquito nets, artificial lawn, artificial wool, diapers, filter cloth, non-woven cloth, curtains, etc.)

 

Injection Molding Process Conditions:

Drying treatment: not required if stored properly.

Melting temperature: 220 ~ 275, not to exceed 275.

Mold temperature: 40~80(50is recommended). Crystallization degree is mainly determined by mold temperature.

Injection pressure: maximum 1800 bar.

Injection speed: High-speed injection molding can usually reduce the internal pressure to the minimum. Low speed injection molding at higher temperatures should be used if defects occur on the surface of the product.

Runner and pouring gate: For cold runner, the typical runner diameter range is 4~7mm. It is recommended that only circular injection port and flow channels be used in the whole mold body. All types of pouring gates are available. Typical gate diameters range from 1 to 1.5mm, but gates as small as 0.7mm can be used. For the edge pouring gate, the minimum gate depth shall be half of the wall thickness; the minimum gate width shall be at least twice the wall thickness. PP materials can suit hot runner system completely.

 

Chemical and Physical Properties:

PP is a semi-crystalline material. It is harder than PE and has a higher melting point. Because the PP of homopolymer type is very fragile when temperature is above 0 above , many PP materials for commercial use are mixed with 1 ~ 4% of random copolymer of ethylene or even higher ratio of block copolymer of ethylene. PP of copolymer type has low heat distortion temperature (100), low transparency and gloss, low rigidity, but high impact resistance. The strength of PP increases with the increase of ethylene content. PP Vicat softening temperature is 150. Due to its high crystallinity, the material has excellent surface stiffness and scratch resistance. There is no environmental stress cracking problem for PP. PP is usually modified by adding in glass fiber, metal additives or thermoplastic rubber. PP’s flow rate MFR ranges from 1 to 40. PP with low MFR has higher impact resistance but lower tensile strength. For materials with the same MFR, the strength of copolymer type is higher than that of homopolymer type. Due to crystallization, PP has a very high shrinkage rate, generally between 1.8 and 2.5%. And the direction uniformity of shrinkage rate is much better than that of PE-HD and other materials. A 30% glass additives will lead to the shrinkage of PP to 0.7%. PP materials of homopolymer type and copolymer type have excellent moisture absorption resistance, acid and alkali corrosion resistance and solubility resistance. However, it is not resistant to aromatic hydrocarbon (such as benzene) solvents, chlorinated hydrocarbon (carbon tetrachloride) solvents and so on. PP is not as resistant to oxidation as PE at high temperatures.


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