Gas Chromatography Peak Deconvolution Algorithms in Post Consumer Polyolefins
Mathematical peak deconvolution separates coeluting volatile degradation products from polyolefin oligomer baselines, enabling accurate resin qualification.
Oligomer Degradation
Meaning
Chemical breakdown involves the scission of polymer chains into shorter segments due to thermal or oxidative stress during processing. This process of oligomer degradation reduces the molecular weight of the resin and results in the migration of low molecular weight fractions to the surface of a moulded part. Such migration creates surface bloom, alters the optical clarity of clear parts, and weakens the mechanical bonds of adhesives applied to the component.
Thermal Stability
The degree of resistance to heat during injection moulding dictates how rapidly this material decay occurs within the barrel. High temperatures combined with long residence times accelerate the cleavage of bonds within the molecular structure. Resin suppliers define the thermal processing window on a datasheet to prevent this phenomenon from compromising the bulk properties of the plastic.
Moulders must monitor actual melt temperatures against these specifications to ensure the material retains its designed performance characteristics throughout the production run.
Economic Impact
Regrind material contains a higher concentration of chain fragments than virgin resin because the plastic has experienced multiple heat cycles. Excessive usage of recycled content increases the susceptibility of the melt to further degradation when subjected to the shear forces of the screw. A lower viscosity resulting from shorter chain lengths requires adjustments to packing pressure and cooling times to maintain part dimensions.
These modifications introduce hidden costs in cycle time inefficiency and higher scrap rates caused by visible defects on the surface of the finished goods.
Component Specification
Parts intended for automotive interiors or optical devices often carry strict requirements regarding extractable low molecular weight content to prevent fogging. Engineers set these limits on the final product to account for the migration of degraded material from the core to the surface under environmental heat exposure. A part specification restricts the total allowance for these volatile components while the material specification for the raw resin focuses on the stability of the polymer chain during the conversion process itself.
The variance in melt flow rate between initial material qualification and end of run samples identifies the degree of chemical breakdown experienced by the polymer during high volume production.