Meaning
Polymer degradation measurement expresses the number of covalent backbone bond fractures occurring within a specific mass or volume of polymer resin during thermal processing or environmental exposure. Calculating chain scission density provides a quantitative measure of degradation in virgin or recycled resins. The metric governs degradation kinetics under thermal shear during compounding and UV aging in outdoor service.
It applies specifically to linear or branched thermoplastic backbones and ceases to apply once crosslinking mechanisms dominate resin aging.
Viscosity Shift
Shear stress during extrusion breaks high molecular weight polymer chains into shorter segments. Increases in chain scission density lower melt viscosity rapidly, causing severe drop in melt strength during film blowing or profile extrusion. Moulding operations suffer from flash and barrel drool when resin experiences uncontrolled thermal cleavage inside the injection cylinder.
Mechanical Degradation
Tensile strength and impact resistance decline predictably as polymer backbones fracture under repeated heat cycles. Measuring chain scission density allows compounders to track degradation in regrind streams containing post-consumer polyolefins. High scission levels embrittle structural parts and reduce environmental stress crack resistance significantly.
Stabilizer Efficiency
Antioxidants and phosphite stabilizers slow down bond cleavage by scavenging free radicals formed during high shear processing. Processing trials track chain scission density across multiple extrusion passes to verify additive package effectiveness. When stabilizer loads are inadequate, scission accelerates exponentially after the initial pass.
