Meaning
Thermally initiated cleavage of unstable oxygen-oxygen bonds represents the primary chemical reaction used to generate free radicals in polymer melts. This process, referred to as organic peroxide decomposition, acts as the initiator for polypropylene chain scission during compounding. Processors utilize this reaction to increase the melt flow rate of high-viscosity resins.
Thermal Dissociation
Temperature-controlled activation in the extruder barrel determines the rate at which the peroxide decomposes. This reaction exhibits a strong temperature dependency, with the rate doubling for every small temperature increase.
Chain Scission
Radicals generated by organic peroxide decomposition extract tertiary hydrogen atoms from the polymer backbone. This chemical interaction results in the cleavage of the polymer chain, which reduces both the average molecular weight and the melt viscosity. Compounders rely on this reaction to narrow the molecular weight distribution of the polypropylene.
This degradation process must be completed before the melt exits the extruder die to avoid mould corrosion or odour issues in the finished parts.
Byproduct Removal
Volatile organic residues are generated as secondary products during this chemical process. Vacuum degassing systems on the extruder are required to extract these volatile molecules before pelletization. Failing to remove these byproducts can result in plastic parts that fail emission tests.
