Meaning
Molecular fragments emerge when polymer backbones break under thermal, mechanical, or oxidative stress. These chain scission products represent the reduced molar mass species that form as the original long-chain structure undergoes irreversible covalent bond cleavage. This transformation permanently alters the physical properties of the material, typically leading to a decrease in viscosity and a loss of mechanical integrity.
Processing Impact
Heat and high shear forces inside an injection moulding barrel drive these degradation mechanisms. When chain scission products accumulate within a melt, the material exhibits a lower melt flow rate compared to its initial virgin state. Moulders must monitor this reduction in molecular weight because it changes the shrinkage characteristics of the finished part and weakens the final structural load capacity.
Material Economics
Regrind introduces a higher concentration of these small molecular fragments into the production cycle compared to virgin feedstock. Each pass through a heated barrel increases the ratio of broken chains, which forces processors to blend the regrind with virgin pellets to maintain a stable viscosity. Relying on excessive regrind without adjustment results in brittle parts that fail to meet the ductility requirements set by the original material datasheet.
Tooling Variance
Cavity pressure sensors detect the change in rheology that follows significant molecular breakdown. Excessive amounts of these fragmented species allow the resin to flash into thin gaps of the mould or cause jetting at the gate. Precise temperature management prevents the cascade of bond breaks that otherwise renders a plastic resin unfit for high-performance applications.
