Virgin Resin Specification Gaps and Undeclared Regrind Content
Undeclared regrind in virgin polymer collapses oxidation stability and broadens viscosity bands, increasing landed cost per good part despite initial pellet discounts.
Optical Gels
Meaning
Localized polymeric inclusions with altered refractive index create visible defects in transparent extruded film and moulded components. Unmelted high molecular weight species or crosslinked polymer networks appear as optical gels during optical inspection of clear products. These inclusions impair light transmission and generate stress concentration points that reduce mechanical toughness.
Scope of measurement covers optical clarity metrics, halting where opaque fillers obscure internal phase boundaries.
Formation Pathway
Excessive residence time in stagnant extrusion regions initiates crosslinking and degradation of the polymer matrix. Material adhering to barrel walls or die lips undergoes thermal branching over extended runs. High temperature spikes accelerate this chemical transformation, producing hard gel structures that resist melting.
Shearing forces detach these degraded particles into the main melt stream, carrying them into the final product geometry.
Defect Detection
Online laser inspection systems scan continuous film webs to identify refractive discontinuities down to micron dimensions. Digital camera sensors capture light distortion caused by inclusion boundaries, categorizing defect frequency per unit surface area. Exceeding gel counts triggers material rejection or line adjustments.
Purging Response
Eliminating crosslinked inclusions requires mechanical cleaning or high-viscosity purging compounds to strip dead zones inside the extruder. Processors adjust screw speed profiles to clear stagnant pockets before thermal degradation advances. Regrind containing elevated gel concentrations introduces particulate contamination into virgin production feeds.