Microscopic Air Entrapment Mechanics in Textured Mold Surfaces
Microscopic air entrapment in textured molds stems from rapid melt front advancement trapping gas in surface valleys, manageable via controlled fill rates and porous micro-venting.
Thermalscission
Meaning
Chemical degradation involves the breaking of covalent bonds in a polymer backbone due to excessive heat. While exposure to high temperatures occurs in most processing steps, thermalscission leads to a permanent reduction in molecular weight. This process alters the fundamental properties of the resin by shortening the chain lengths.
Molecular Weight
Chain length determines the toughness and impact resistance of a finished component. When thermalscission occurs, the material becomes brittle and loses its ability to withstand mechanical loads. This degradation is often irreversible.
Viscosity Shift
Molten polymer flows more easily when its molecules are smaller. Excessive heat in the barrel causes a sudden drop in melt viscosity, which often results in flash or inconsistent part weights. Monitoring the melt flow index of regrind helps identify if thermalscission has compromised the material during previous heat cycles.
Economic Consequence
Reclaiming scrap material requires careful attention to the number of times a resin passes through an extruder. Each trip subjects the polymer to heat that can trigger thermalscission and lower the value of the stock. High performance polymers often have lower tolerances for this degradation than commodity grades.
If the molecular weight drops below a critical threshold, the material can no longer meet the original specifications for the part. This loss of properties makes the material unsuitable for high stress applications.