DiBenedetto Glass Transition Modeling in Diffusion Controlled Resins
DiBenedetto modeling governs vitrification prediction, preventing unreacted resin pockets and internal residual stress during structural composite cure cycles.
Rabinowitch Diffusion Factor
Meaning
Polymerisation rates in highly cured thermosetting resins become restricted as the growing molecular network limits the movement of remaining reactive species. Rabinowitch diffusion factor is a mathematical parameter used to adjust the reaction rate constant to account for this diffusion-controlled regime. It reduces the predicted reaction rate once the curing system begins to transition from a liquid to a glass.
Implementing this calculation allows engineers to model the end of the cure cycle with high accuracy.
Rate Adjustment
Kinetic models that do not account for diffusion control will overestimate the reaction rate in the late stages of cure. The Rabinowitch diffusion factor modifies the effective rate constant based on the local glass transition temperature and cure temperature. When the cure temperature falls below the transition temperature, the reaction slows down dramatically.
Including this factor in process models ensures the calculated cure time is long enough to achieve the desired degree of conversion.
Demoulding Confidence
Premature part removal from the tooling can cause deformation if the matrix has not achieved the required cure state. Because the Rabinowitch diffusion factor improves the accuracy of the cure model, manufacturers can trust the simulated conversion values to decide when to demould. This confidence allows companies to run shorter cycles without risking part damage.
Reducing cycle times directly increases the output of the production facility.
Kinetic Measurement
Fitting cure kinetics models to experimental heat flow data requires specialized software that can extract the diffusion parameters. This fitting process yields the necessary constants to define the diffusion factor for a specific resin.