Meaning
Polymer mass transfer analysis defines the crank diffusion model through mathematical prediction of penetrant migration inside semi-crystalline thermoplastics. Fickian concentration gradients govern this framework during high-temperature injection molding and subsequent cooling phases. The boundary condition stops applying when molecular relaxation rates exceed molecular diffusion rates within amorphous domains.
Moisture absorption kinetics and residual solvent outgassing in engineering resins rely entirely on this governing relationship.
Penetrant Penetration
Concentration profiles shift according to polymer chain packing density and free volume fraction within the molded matrix. High crystallinity restricts molecular mobility, which forces diffusing species to travel along tortuous amorphous pathways. Temperature variations alter the diffusion coefficient exponentially through Arrhenius activation energy relationships.
Ambient humidity levels dictate surface concentration spikes during the initial exposure period.
Resin Degradation
Hydrolytic cleavage accelerates when migrating moisture molecules react with susceptible ester linkages inside polybutylene terephthalate melts. Molecular weight reduction manifests as melt flow rate elevation and mechanical property loss during processing. Virgin polymer pellets exhibit predictable absorption curves, whereas regrind batches contain altered morphology that increases penetrant uptake velocity.
Datasheet values assume isotropic structure, but anisotropic shear orientation in molded parts creates directional concentration imbalances.
Processing Defect
Dimensional distortion and surface blistering originate from localized vapor pressure accumulation driven by inadequate drying protocols. Processing technicians adjust barrel residence time and hopper dehumidification dew points to suppress gas entrapment defects. Moulders hold tighter moisture tolerances across production runs than raw material specifications mandate for standard pellets.
Elevated scrap rates emerge when diffusional flux exceeds venting capacity during the mold filling stage.
