Kinetics of Controlled Cure System Triggered by Release of Encapsulated Catalyst

• Published in: Thermochimica acta Vol. 699; p. 178884
• Main Authors: Li, Jun, Zhao, Min, Dan, Florin, Matteucci, Scott, Bloxom, Stephanie, Banks, Andrew, Katz, Joshua S., Chen, Liang, Hasso, Doug, Young, Owen, Powell, Terri, Yu, Xindi
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.05.2021
• Subjects: Activation energy; Autocatalytic kinetic model; Encapsulated catalyst; Non-isotherm kinetics; Polyurethane catalyzed trimerization; Polyurethane catalyzed trimerization; Non-isotherm kinetics; Autocatalytic kinetic model; Activation energy; Encapsulated catalyst
• ISSN: 0040-6031; 1872-762X
• DOI: 10.1016/j.tca.2021.178884

This Figure illustrates the fraction of catalyst release (red symbols) and the progress of PU cure (green symbols) with time at 70 °C. Temperature favors the release of trimerization catalyst, which when reaching a critical concentration triggers the prepolymer cure. [Display omitted] •Encapsulated trimerization catalyst enhances formulations pot-life under the storage conditions and enables on-demand curing of urethane prepolymer.•Melting behavior of carrier wax is tunable by temperature and governs how curing process triggers.•In-vitro modeling of catalyst release and trimerization kinetics from non-isothermal data allows process modeling in any temperature mode.•Under isothermal conditions, the delayed release of the encapsulated catalyst is manifested as and induction time, which was correlated to the apparent diffusion coefficient of the catalyst from the melted encapsulation material. Controlled cure is desired in many industrial processes to control open time, stress build-up, morphology and structure of cured materials. Curing strategies that include triggered release of an encapsulated active (e.g. catalyst, hardener) enable one-part curing systems - a mixture of encapsulated active and reactive prepolymer. The dynamic nature of cure triggered by release of encapsulated active, however, complicates the curing process. The catalyzed trimerization of a urethane prepolymer model system was studied to elucidate the polyisocyanurate (PIR) dynamic curing. Curing kinetic parameters of trimerization catalyzed by the neat and encapsulated catalyst were obtained with three kinetic methods by non-isothermal DSC. There was not much difference in total heat of reaction -ΔHrxn but the polymerization onset, Tonset, and the peak temperature, Tp, were shifted towards higher temperatures, by 20 to 30 °C, with the encapsulated catalyst. In addition, the activation energy, E, the preexponential factor, lnA, and the overall order of reaction m + n were enhanced. Simulations show that the delay in the cure onset temperature is manifested as a lag time under isothermal conditions. This lag time was correlated to the apparent diffusion coefficient, Da, using Fick’s second law of diffusion, which allowed modeling the temperature effect on the encapsulated catalyst release into the model prepolymer.