Introduction to the characteristics of composite bags: Customized chemical and physical properties of composite bags: It is a semi-crystalline material. It is harder than PE and has a higher melting point. Since the homopolymer type is very brittle when the temperature is higher than 0°C, many commercial PP materials are random copolymers with 1 to 4% ethylene or clamp copolymers with higher ethylene content.

Copolymer PP material has lower thermal distortion temperature (100℃), low transparency, low gloss, low rigidity, but has stronger impact strength. The strength of the composite bag increases with the increase of ethylene content. The Vicat softening temperature of the composite bag is 150°C.

Due to the high crystallinity, the surface rigidity and scratch resistance of this material are very good. There is no environmental stress cracking problem in food composite bags. Usually, the Dongguan composite bag factory is modified by adding glass fiber, metal additives or thermoplastic rubber. The flow rate MFR of composite bags is in the range of 1-40. PP materials with low MFR have better impact resistance but lower elongation strength. For materials with the same MFR, the strength of the copolymer type is higher than that of the homopolymer type. Due to crystallization, the shrinkage rate of the composite bag is quite high, generally 1.8~2.5%. And the direction uniformity of shrinkage is much better than that of PE-HD and other materials.

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Adding 30% of glass additives can reduce the shrinkage to 0.7%. Both homopolymer and copolymer PP materials have excellent moisture absorption, acid and alkali corrosion resistance, and solubility resistance. However, it has no resistance to aromatic hydrocarbons (such as benzene) solvents, chlorinated hydrocarbons (carbon tetrachloride) solvents, etc. The composite bag does not have oxidation resistance at high temperature like PE.

Polypropylene (PP) is the lighter type of common plastics. It has excellent electrical properties and can be used as a high-frequency insulation material resistant to humidity and heat. The composite bag is a crystalline polymer. When the melt is condensed, due to the large change in specific volume and high degree of molecular orientation, it shows a large shrinkage rate (1.0%-1.5%). In the molten state, heating up to reduce its viscosity has little effect. Therefore, in the molding process, the injection pressure and shear rate should be increased mainly to improve the molding quality of the product.