Polyolefins are high molecular weight hydrocarbons. They include Low-Density and High Density Polyethylene and Polypropylene. All are break-resistant, nontoxic, and non-contaminating. These are the only plastics lighter that water. They easily withstand exposure to nearly all chemicals at room temperature for up to 24 hours. Strong oxidizing agents eventually cause embitterment. All polyolefins can be damaged by long exposure to ultraviolet light.
Polyethylene- the polymerization of ethylene results in an essentially straight chain, high molecular weight hydrocarbon. Polyethylenes are classified according to the relative degree of branching (side chain formation) in their molecular structures, which can be controlled with selective catalysts.
Like other polyolefins, the polyethlyenes are chemically inert. Strong oxidizing agents will eventually cause oxidation and embitterment. They have no known solvent at room temperature. Aggressive solvents will cause softening or swelling, but these effects are normally reversible.
Low Density Polyethylene - (LDPE) has more extensive branching, resulting in a less compact molecular structure.
High Density Polyethylene – (HDPE) has minimal branching, which makes it more rigid and less permeable.
Polypropylene – (PP) is similar to polyethylene, but each unit of the chain has a methyl pendant group attached. It is translucent, autoclavable, and has no known solvent at room temperature. It is slightly more susceptible than polyethylene to strong oxidizing agents. It offers the best stress-crack resistance of the polyolefins. Products made of polypropylene are brittle at ambient temperatures and may crack or break if dropped from bench top height.
Polypropylene Copolymer – (PPCO) is an essentially linear copolymer with repeated sequences of ethylene and propylene. It combines some of the advantages of both polymers. PPCO is autoclavable, and offers much of the high temperature performance of polypropylene. It also provides some of the low-temperature strength and flexibility of polyethylene.
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