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PP physical and mechanical properties
The strength and rigidity of PP are better than that of low pressure PE. Due to the high degree of regularity of PP molecular structure, its impact resistance at set, room temperature and low temperature is poor. Its stress-strain relationship depends on strain rate, molecular weight and crystallinity. The yield value and elastic modulus of PP mainly depend on the crystallinity; the impact strength also varies with the content of the isotactic substance in the polymer. The molecular weight can affect the impact strength, that is, the molecular weight is large and the impact strength is large, but the forming processability also follows It has a greater bending fatigue life. It has a living hinge that can withstand more than 70 million fold bends without damage marks; however, its gap is particularly sensitive.
PP has excellent fiber-forming properties and has excellent tensile properties. When the temperature exceeds 80 ° C, the tensile strength drop due to temperature rise becomes less, that is, at 100 ° C, the tensile strength at normal temperature is retained. Half of it. The molecules of PP are oriented in the direction of melt flow, because its strength is also directional, that is, the tensile impact strength perpendicular to the orientation direction is 50% lower than the orientation direction, PP hardness is less than PS and ABS; but higher than PE and Excellent surface gloss with a coefficient of friction of 0.12 similar to nylon. 15 to 30 mg per 1000 abrasions.
Thermal and electrical properties of PP:
PP has good heat resistance, melting point is 164~170 °C, and it is resistant to boiling at temperatures above 100 °C. Without external force, the temperature will not be deformed even at 150 °C, and it can be used continuously at 110 °C under low load. The stress relaxation resistance at 90 ° C is good. The low temperature is -15~-20 °C, and the embrittlement temperature is related to the isotactic structure content and average molecular weight. When the content of the same isotactic structure is small, the smaller the melt index, the lower the embrittlement temperature, and the higher the isotactic structure content, the higher the embrittlement temperature.
Electrical performance:
PP is a very good electrical insulator that does not absorb water, is not affected by air humidity, and has a high breakdown voltage. It is a slow burning material. Low dielectric constant (2.2~2.6), basically unaffected by temperature; high dielectric strength in the range of 26*106 V/m, high temperature, high dielectric strength, high volume resistance, different dielectric constant, high temperature and volume The resistance drops, the volume resistivity at room temperature is 1017 Ω.cm, and the temperature drops to 1013 Ω·cm when it rises to 93 °C; at a high temperature, the leakage of current is kept to a minimum.
Chemical properties and environmental resistance of PP:
PP has good resistance to chemical attack and staining, especially for environmental stress cracking, and inorganic salts of inorganic salts, rare or concentrated solutions of alkalis, and even elevated temperatures. Chemical action, but halogen elements, fuming nitric acid, fuming sulfuric acid and other highly oxidizing agents, will erode PP plastic, there is almost no solvent to dissolve it at room temperature, only aromatic hydrocarbons, chlorinated hydrocarbons It can soften and swell, especially when the temperature rises more significantly.
Environmental resistance:
At normal temperature, PP is completely free from water erosion less than day/0.01% water absorption, and water vapor permeability is also very low; when temperature rises, the life of plastic will be shortened because the stabilizer is in contact with water. The tertiary carbon atom containing a methyl group in the long chain of the PP molecule is weak in resistance to depolymerization; it is easily oxidized and depolymerized under the action of ultraviolet rays.
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