Meaning
Chemical processes that link individual polymer chains into a three-dimensional network define the transition from a liquid resin to a rigid structural matrix. During cure, matrix crosslinking occurs as reactive groups on the monomer molecules form covalent bonds with each other. This process increases the molecular weight of the system and transforms the fluid into an infusible polymer.
Monitoring this reaction is critical for determining when a manufactured part can be safely demolded without causing permanent distortion.
Network Formation
Interconnected structures are built as chemical reactions progress from isolated chains to a fully gelled network. The extent of matrix crosslinking determines the glass transition temperature of the polymer, which rises as the density of the covalent bonds increases. If the reaction is terminated too early, the material remains brittle and will fail under operating loads.
Thermal Activation
Heat must be supplied to the mold to overcome the activation energy barrier of the crosslinking reaction. When matrix crosslinking is initiated, the rate of bond formation increases with temperature until the mobility of the reacting species is restricted by the gelation of the polymer. To achieve a complete cure, the tool temperature must be held above the glass transition temperature of the fully cured matrix.
If this thermal limit is not maintained, the reaction will cease prematurely, a state known as under-cure, which reduces the thermal resistance of the composite part.
Mechanical Property Development
Cohesive strength and shear modulus of the composite depend directly on the density of the formed chemical bonds. As matrix crosslinking reaches its target level, the polymer develops the stiffness required to support the structural fibers. This development ensures that the material can resist environmental stresses and moisture absorption during its service life.
