According to the international standard classification, polypropylene (PP) is divided into homopolymer polypropylene (PP-H), block copolymer polypropylene (PP-B) and the random copolymer polypropylene (PP-R)
Common
PP homopolymer and copolymers have a very low water vapor permeability (0.5 g / cc / 100 square inches / 24 hours).
Homopolymer and copolymer PP materials have excellent resistance to moisture absorption, resistance to acid corrosion, anti-solubility. However, it aromatic hydrocarbons (such as benzene) solvents, chlorinated hydrocarbons (carbon tetrachloride) solvents is not resistance. PP did not like PE at elevated temperatures has antioxidant activity.
difference
Since the type of PP homopolymer is higher than the temperature above 0 ℃ very brittle so many commercial PP material is added 1-4% ethylene random copolymer or a higher ratio of clamp-stage ethylene content copolymer.
Copolymer PP materials have a lower heat distortion temperature (100 ℃), low transparency, low gloss, low rigidity, but have a stronger impact strength. Strength of PP increased with increasing ethylene content increasing. PP Vicat softening temperature of 150 ℃. Due to the high degree of crystallinity, surface rigidity and scratch resistance properties of this material is very good. PP environmental stress cracking problem does not exist.
A total propylene copolymer is modified PP, which has a synthetic rubber component, a fire is burning flat wire pull, pull Debu long. The homo PP changed to Hou Sila was burned long, silk circular.
Generally, the ratio of random copolymer PP PP homopolymer good flexibility and low rigidity. Them when the temperature dropped to 32 ° F, but also to maintain a moderate impact strength, and when the temperature dropped to -4 ° F, the usefulness will be limited. Flexural modulus (1% secant modulus of strain) of the copolymer in the range of 483 ~ 1034MPa, and the homopolymer in the range of 1034 ~ 1379MPa. Effect of molecular weight PP copolymer material is not as rigid PP homopolymer large. Izod notched impact strength is generally in the 0.8 to 1.4 foot-pounds / inch.
Chemical resistance
PP random copolymer acid. Alkalis, alcohols, low-boiling hydrocarbon solvents and many organic chemicals have a strong resistance. At room temperature, PP copolymers are essentially insoluble in most organic solvents. Moreover, when exposed to soap, lye soap. Aqueous reagent and alcohols, they do not like many other polymers that would occur environmental stress cracking damage. When in contact with certain chemicals, especially liquid hydrocarbons. Chlorinated organics and strong oxidizing agents, can cause surface cracks or swelling. Non-polar compounds are generally easier than the polar compounds absorbed polypropylene.
Barrier properties
PP homopolymer and copolymers have a very low water vapor permeability (0.5 g / cc / 100 square inches / 24 hours). These properties can be improved by orientation. Stretch blow molded polypropylene bottles Yiba resistance to water vapor permeation performance improvement to 0.3, the oxygen permeability of 2500.
Electrical Properties
Generally, polypropylene has good electrical properties, including: high dielectric strength, low dielectric constant and low dissipation factor; however, power applications usually selected homopolymer.