According to the distribution of ethylene monomer in the molecular chain, * * * PP can be divided into random * * * polymer (PPR) and block * * * polymer (PPB). PPH has good rigidity but poor impact resistance, especially low-temperature impact resistance and creep resistance. PPB has good impact resistance, but its creep resistance is as poor as PPH. PPR has good impact resistance and creep resistance.
Homopolymer pp: The homopolymer of polypropylene PP is abbreviated as PPH, which is a polymer of single propylene monomer. Polypropylene (PP), as a thermoplastic polymer, began commercial production on 1957, and is the first stereoregular polymer. Its historical significance is more reflected in that it has been the fastest-growing major thermoplastic, with the total national output reaching 3 million tons in 2004. It is widely used in the field of thermoplastics, especially in fiber and filament, film extrusion, injection molding and so on.
* * * Similarities
The water vapor permeability of PP*** polymer and homopolymer is very low (0.5g/ml/ 100 square inch /24h).
Both homopolymer and polymer PP materials have excellent moisture absorption resistance, acid and alkali corrosion resistance and solubility resistance. But it is not resistant to aromatic hydrocarbon (such as benzene) solvents and chlorinated hydrocarbon (carbon tetrachloride) solvents. The oxidation resistance of PP at high temperature is not as good as that of PE.
discrepancy
Because homopolymer PP is very brittle when the temperature is higher than 0℃, many commercial PP materials are random * * * polymers, containing 1-4% ethylene, or sandwich * * polymers with higher ethylene content.
* * * Polymer-based PP material has low thermal deformation temperature (100℃), low transparency, low gloss and low rigidity, but strong impact strength. The strength of polypropylene increases with the increase of ethylene content. The Vicat softening temperature of polypropylene is 65438 050℃. Because of its high crystallinity, this material has good surface hardness and scratch resistance There is no environmental stress cracking problem in PP.
* * * C is * * * poly modified PP, which contains synthetic rubber components. When it burns, the wire is flat and cannot be stretched for a long time. However, after homopolymerization changed to PP, the silk was drawn long and round.
tangible property
Generally speaking, random PP*** polymer has better flexibility and lower rigidity than PP homopolymer. When the temperature drops to 32°F, they can still maintain moderate impact strength, while when the temperature drops to-4 F, their use is limited. * * The bending modulus of polymer (secant modulus at 1% strain) is in the range of 483 ~ 1034 MPa, while that of homopolymer is in the range of 1034 ~ 1379 MPa. The molecular weight of PP * * polymer material has less influence on rigidity than PP homopolymer. The impact strength of notched cantilever beam is generally in the range of 0.8 ~ 1.4 ft lb/inch.
chemical resistance
Random polypropylene * * * polymer pair acid. Strong resistance to alkali, alcohol, low-boiling hydrocarbon solvents and many organic chemicals. At room temperature, PP*** polymer is basically insoluble in most organic solvents. In addition, when exposed to soap, soap lye. In water-based reagents and alcohol, they are not damaged by environmental stress cracking like many other polymers. When in contact with certain chemicals, especially liquid hydrocarbons. Chlorinated organic compounds and strong oxidants can cause surface cracking or swelling. Nonpolar compounds are usually more easily absorbed by polypropylene than polar compounds.