Effects of temperature on cure kinetics and mechanical properties of vinyl-ester resins

Abstract

The relationships among cure temperature, chemical kinetics, microstructure, and mechanical performance have been investigated for vinyl–ester resins. Fourier transform infrared spectroscopy was used to follow the reactions of vinyl–ester and styrene during isothermal curing of Dow Derakane 411‐C‐50 at 30 and 90°C. Reactivity ratios of vinyl–ester and styrene vinyl groups were evaluated using the copolymer composition equation. The results indicate that the ratio of vinyl–ester to styrene double bonds incorporated into the network is greater for 30 than for 90°C cure. Mechanical properties were obtained for systems subjected to isothermal cures at 30 and 90°C and postcured above ultimate Tg. The results show that the initial cure temperature significantly affects the mechanical behavior of vinyl–ester resin systems. In particular, values of strength and fracture toughness for postcured samples initially cured isothermally at 30°C are significantly higher than those obtained for samples cured isothermally at 90°C. Examination of fracture surfaces using atomic force microscopy revealed the existence of a nodular microstructure possessing characteristic nodule dimensions that are affected by the temperature of cure. Such features suggest the existence of phase separation during cure. A binary interaction model in conjunction with chemical kinetic data and estimated solubility parameters was used to evaluate enthalpic interactions between the growing polymer network and monomers of the vinyl–ester system. The results indicate that the interaction energy becomes increasingly endothermic as cure progresses and that this energy is affected by the temperature of cure through differences in copolymerization behavior. Hence, in addition to entropic factors, the changes in enthalpic contribution to the Gibbs free energy suggest that the probability of phase separation increases with extent of cure and that its onset is potentially affected by cure temperature. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 725–744, 1999

Influence of tribological test on the global conversion of natural composites

“…FTIR technique helps to evaluate global conversion of monomers or reactive groups that participate during curing reaction, such as the case of styrene and vinyl ester double bonds [5] . In this case, global conversion before and after tribological test of these groups are evaluated for both neat and Musaceae fiber bundles composites.…”

“…Additionally, these authors mentioned the formation of microgel or nanogel of VE that suggest the presence of multiple phases at the molecular level during the cure process. The results obtained in this work suggest that the tribological test affects this molecular distribution and potentially affects the mechanical or physical behavior [5] . The formation of these microgels are documented by other author such as Dua et al [43] and Rodriguez et al [27] when studied the curing of these resins at different isothermal curing.…”

“…Polymers such as unsaturated polyester resins, epoxy resins and vinyl ester resins have been used as matrix for composite materials in an uncountable amount of technical applications [1][2][3][4][5][6][7][8][9][10][11] . The most popular of them due to the low cost, reasonable good properties and simplicity for processing are the unsaturated polyester resins, but when better mechanical or chemical resistance properties are required, the epoxy resins are preferred.…”

“…The crosslinking reaction undergoes in differential form because the vinyl ester double bonds at the beginning of the reaction, reacts faster than the ones of the styrene, but in the final part is the opposite. This differential in the crosslinking forms microgels which grows and coagulate and then adding between them, which brings to the final nodular form [5,13,22,27] . The reaction rate of the vinyl ester and the monomer may be divided in two parts, a faster one, where the maximum rate of reaction is located may be due to the easier diffusion of the components.…”

“…Also are used diacylperoxides, peresteres, diaryl peroxides, dialkyl peroxides, hydroperoxydes such as cumene hydroperoxyde [3] cumyl hydroperoxyde [5] , for high temperature curing the most common initiator is benzoyl peroxyde (BPO) [1,12,15,19] , but t-butyl proxy-benzoate [22] is used as well sometimes. An activator does the decomposition in free radicals of the initiators.…”