Meaning
Covalent bonding between polymer chains creates a three dimensional network that restricts molecular movement. This crosslinking process prevents the material from melting upon heating and imparts permanent structural stability to the cured object. Rubber goods and thermoset resins rely upon this internal architecture to maintain mechanical integrity under extreme thermal stress.
Thermoplastics lack this network and remain fusible unless additive modification forces the formation of these linkages.
Molecular Architecture
The density of these bridges dictates the modulus and solvent resistance of the finished part. High bridge frequency leads to increased rigidity and brittleness while a lower frequency allows for greater elasticity and elongation. Moulders monitor the state of cure through rheological measurements since incomplete reaction leads to premature failure of the molded component.
A stable network prevents the material from creeping under static load.
Processing Control
Thermal energy or chemical agents initiate the reaction during the final stage of cycle time within the heated tool. Operators adjust the dwell time and the melt temperature to ensure the reaction proceeds to the required degree of conversion before ejection occurs. Excessive residence time causes the material to degrade while short cycles produce undercured parts with high tackiness and insufficient hardness.
Economic Consequence
Virgin resin prices often rise when manufacturing requires specialized curative additives that shorten shelf life during storage. Regrind materials containing these cured particles do not reprocess effectively because the existing network prevents the chain flow necessary for injection molding. Scrap rates escalate when the cure window shifts away from the set process parameters and creates parts with inconsistent internal density.
Defective parts with uneven crosslinking lack the uniform shrink rates required for precision components.
