Performance of PP
1: Physical properties: Polypropylene is a non-toxic, odorless, milky white, highly crystalline polymer with a density of only 0.90~0.9lg/cm3. It is one of the lightest varieties of all plastics. It is particularly stable to water, with a water absorption rate of only 0.01% in water for 24 hours, a molecular weight of about 80,000-150,000, and good formability. However, due to the large shrinkage rate (1-2.5%), thick-walled products are easy to sink, and for some parts with high dimensional accuracy, it is difficult to meet the requirements. The surface gloss of the product is good and easy to color.
2: Mechanical properties: Polypropylene has high crystallinity and regular structure, so it has excellent mechanical properties. Its yield, tensile, compressive strength, hardness, and elasticity are higher than HDPE, but at room temperature and low temperature, due to its own molecular structure regularity, the impact strength is poor. When the molecular weight increases, the impact strength also increases, but the molding and processing performance deteriorates. Polypropylene has outstanding resistance to bending fatigue.
Degree, such as PP injection molding integrated movable hinge, can withstand 70 million times of opening and closing folding and bending without damage.
3: Thermal performance: Polypropylene has good heat resistance, its melting point is 164-170℃, the product can be sterilized at a temperature above 100℃, and it will not deform at 150℃ when not subjected to external force. It has good stress relaxation resistance at 90℃, and its brittle temperature will crack at a temperature of -35℃. Its cold resistance is not as good as polyethylene. If it is reinforced with asbestos fiber and glass fiber, it has a higher heat deformation temperature, dimensional stability, and low-temperature impact performance.
4: Chemical stability: Polypropylene has good chemical stability. In addition to being corroded by concentrated sulfuric acid and concentrated nitric acid, it is relatively stable to various other chemical reagents, but low molecular weight aliphatic hydrocarbons, aromatic hydrocarbons and chlorinated hydrocarbons can soften and swell polypropylene. At the same time, its chemical stability increases with the increase of crystallinity. Therefore, it is suitable for various chemical pipelines and accessories, and has good anti-corrosion effect.
Performance of HDPE
1: HDPE is a milky white, translucent waxy solid. Compared with LDPE and LLDP, HDPE has the smallest degree of branching, and the molecules can be tightly stacked, so the density is the highest.
(0.9410.965g/cm2), high crystallinity, HDPE has higher rigidity and toughness, good mechanical properties and higher operating temperature. Compared with LDPE, it has higher moisture resistance, oil resistance, steam permeability resistance and environmental stress cracking resistance, electrical insulation, impact resistance and cold resistance are all very good; HDPE is better than LDPE in strength and stiffness, better than PVC and PP in toughness, better than PVC in processing characteristics, better low temperature resistance and anti-aging performance than PP, and higher working temperature than PVC and LDPE. HDPE has low water absorption, is non-toxic, has excellent chemical stability, and the film has low permeability to water vapor and air.
2: Main uses of HDPE
High-density polyethylene is suitable for injection molding, extrusion, blow molding, hollow molding, spraying, rotational molding, coating, foaming, thermoforming, hot melt welding and other molding processes.
