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The aminoxyl radical (N-O•) combines with free radicals in polymers: N-O• + R• → N-O-R Although they are traditionally considered as light stabilizers, they can also stabilize thermal degradation. Even though HALS are extremely effective in polyolefins, polyethylene and polyurethane, they are ineffective in polyvinyl chloride (PVC). It ...
Octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate is significantly less volatile than simpler phenolic antioxidants such as butylhydroxytoluene (BHT). This makes it more suitable to stabilising plastics, as it is not driven out by the high temperatures experienced during plastic extrusion and moulding, [2] when they are heated to 150-320 °C (300–600 °F). [3]
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Hindered amine light stabilizers (HALS) are chemical compounds containing an amine functional group that are used as stabilizers in plastics and polymers. [1] These compounds are typically derivatives of tetramethylpiperidine and are primarily used to protect the polymers from the effects of photo-oxidation; as opposed to other forms of polymer degradation such as ozonolysis.
Polymerization in which polymer is formed in monomer, or monomer-solvent droplets in a continuous phase that is a nonsolvent for both the monomer and the formed polymer. Note 1: In suspension polymerization, the initiator is located mainly in the monomer phase. Note 2: Monomer or monomer-solvent droplets in suspension polymerization have
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After polymerization, the acidic catalyst must be deactivated and the polymer stabilized by melt or solution hydrolysis to remove unstable end groups. Stable polymer is melt-compounded, adding thermal and oxidative stabilizers and optionally lubricants and miscellaneous fillers.
The thermal-oxidative degradation of a polymer starts at lower temperatures than the merely thermal degradation. Both types of degradation proceed via a radical mechanism. [8] Aromatics offer a good protection against both types of degradation, because free radicals can be delocalized through the π-system of the aromatic and stabilized. In ...