Meaning
A specific reactive functionality consisting of an acidic oxygen atom linked to a terminal carbon atom defines the carboxylic end group. Molecular chains in thermoplastic polyesters possess this site as a primary location for degradation or chain extension reactions during thermal processing. The concentration of these units determines the hydrolytic stability of the polymer matrix under high temperature and humidity conditions.
Polymer Stability
Chemical susceptibility increases when the count of these functional sites rises within a resin batch. Each carboxylic end group facilitates acid-catalyzed chain cleavage during subsequent melt cycles. Excessive moisture exposure in the hopper accelerates this reaction through proton donation, which reduces the molecular weight and mechanical integrity of the final moulded part.
Resin Specification
Datasheet values report this concentration in units of microequivalents per gram to allow for direct comparison between virgin resin grades. Moulding houses verify these numbers to determine the drying duration required before injection to reach an acceptable moisture floor.
Economics Variance
Regrind materials frequently display higher values than virgin counterparts because thermal history creates new chain scissions that terminate in active acid sites. Purchasing departments track this variable because high acid numbers necessitate longer cycle times to manage secondary reactions and limit viscosity drift in complex geometries. Higher concentrations indicate lower material shelf life and poorer structural outcomes in demanding industrial applications.
