Interfacial Friction Dynamics of Erucamide Derivatives under Hot Bar Sealing
Primary erucamide melts under hot bar sealing platens, increasing viscous drag and tooling varnish; secondary amides preserve boundary slip and seal integrity.
Thermal Degradation Onset
Meaning
Polymer processing safety relies on a specific temperature threshold where chemical breakdown begins. This threshold is thermal degradation onset, which represents the temperature at which a polymer begins to lose mass or suffer chain scission under heat. It defines the upper limit of the resin’s processing window.
Chemical Degradation
Exposure to temperatures above this limit initiates a series of chemical reactions that break down the polymer chains. This causes a reduction in molecular weight, leading to loss of physical properties like impact strength and tensile elongation. Gaseous byproducts may also be generated, causing bubbling and void formation in the molten plastic.
Once the process starts, it is often autocatalytic and accelerates quickly.
Process Controls
Moulders must keep melt temperatures well below this transition point, factoring in the shear heating that occurs as the polymer flows through narrow gates. Residence time in the heated barrel must also be managed to prevent long-term thermal exposure. If the machine runs too slowly or sits idle, the resin can degrade even at normal processing temperatures.
Thermal sensors and screw design help minimize localized hot spots.
Resin Behavior
Additives and stabilizers are mixed into virgin resins to raise this thermal threshold and broaden the processing window. Regrind materials typically have a lower thermal degradation onset because they have already undergone at least one processing cycle. This prior exposure consumes some of the thermal stabilizers, leaving the material more vulnerable to heat.
Combining regrind with virgin resin can help mitigate this risk by restoring a portion of the active stabilizing additives.