1. Poor impact resistance at low temperatures;
2, the difficulty is painted or adhered by the adhesive;
3. The molding surface reinforced with glass fiber is not smooth;
Polypropylene provides a balance of properties and price points that most thermoplastics cannot achieve.
Polypropylene is easy to form and has good chemical and mechanical properties.
Glass fiber reinforced polypropylene improves dimensional stability, warpage resistance, rigidity and strength. The heat distortion temperature of 40% glass fiber reinforced polypropylene at 264 psi can be increased to 149 °C. The thermal expansion coefficient of polypropylene reinforced with 40% glass fiber is reduced to half.
When a chemical coupling agent is added, the glass fiber reinforced polypropylene can meaningfully improve its tensile strength and flexural strength beyond the general glass fiber reinforced polypropylene.
The tensile strength of polypropylene reinforced with 30% chemically coupled glass fibers is improved by 180% compared to unreinforced polypropylene, and is 50% better than conventional glass fiber reinforced polypropylene.
In general, chemically coupled polypropylene improves strength properties without altering its modulus, heat resistance, electrical properties, or hardness.
The talc-filled polypropylene improves the rigidity, hardness, and heat resistance of the polypropylene.
The Tg of PP is low. After demolding, the product shrinks after occurrence, and the amount of shrinkage increases as the thickness of the product increases. About 90% is completed in 6h after demolding, and 10% will be completed in ten days. Specific measures to reduce shrinkage are: shortening the injection time, extending the dwell time, increasing the material temperature and mold temperature. When molding, increasing the injection pressure, prolonging the injection and holding time, and lowering the mold temperature can reduce the post-shrinkage. The use of copolymerized PP or modified PP is beneficial to reduce shrinkage. For products with high dimensional stability requirements, heat treatment should be carried out at a heat treatment temperature of 80 to 100 ° C for a period of 1 to 2 hours.
It is worth noting that the post-contraction of PP products is more serious. Therefore, the product should be aged. PP products exhibit brittleness at low temperatures and are sensitive to gaps.
PP Polypropylene Chemical and Physical Properties PP is a semi-crystalline material. It is harder and has a higher melting point than PE. Since the PP temperature of the homopolymer type is very brittle when it is higher than 0 ° C, many commercial PP materials are random copolymers of 1 to 4% ethylene or a clamp copolymer of a higher ratio of ethylene. The copolymer type PP material has a low heat distortion temperature (100 ° C), low transparency, low gloss, low rigidity, but has a stronger impact strength. The strength of PP increases as the ethylene content increases. The Vicat softening temperature of PP is 150 °C. Due to the high degree of crystallinity, this material has excellent surface stiffness and scratch resistance.
There is no environmental stress cracking problem in PP. Typically, PP is modified by the addition of glass fibers, metal additives or thermoplastic rubber. The flow rate of PP has a MFR ranging from 1 to 40. Low MFR PP materials have better impact resistance but lower elongation. For materials of the same MFR, the strength of the copolymer type is higher than that of the homopolymer type. Due to crystallization, the shrinkage rate of PP is quite high, generally 1.8 to 2.5%. And the direction uniformity of shrinkage is much better than materials such as PE-HD. The addition of 30% glass additive can reduce the shrinkage to 0.7%. Both the homopolymer type and the copolymer type PP materials have excellent moisture absorption resistance, acid and alkali corrosion resistance, and solubility resistance. However, it is not resistant to aromatic hydrocarbons such as benzene solvents, chlorinated hydrocarbons (carbon tetrachloride) solvents, and the like.
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