Cure kinetics, microheterogeneity, and mechanical properties of the high‐temperature cure of vinyl ester resins

Abstract

A kinetic model has been developed that is based on the irreversible thermodynamic fluctuation theory, in which the conversion of comonomers is a function of the curing relaxation time, reaction time, and reaction temperature. This modified model permits a better prediction of the course of the high-temperature cure reaction of vinyl ester (VE) resins under isothermal conditions. The microheterogeneity in cured resins was investigated through the measurement of the residual heat of isothermally cured samples with differential scanning calorimetry and through the observation of the fracture surfaces of samples under different cure conditions with scanning electron microscopy (SEM). The SEM photographs demonstrated the existence of clusters of microgels of about 20 m in samples isothermally cured at 80°C for 3 h. The results of the dynamic mechanical thermal analysis of postcured samples verified the microheterogeneity in the cured samples and showed that the glasstransition temperatures were not affected by the curing conditions. The effect of postcuring on the conversions of VE and styrene varied with the different cure schedules. The postcure for a sample isothermally cured at 80°C increased the tensile strength and flexural strength. On the contrary, the postcure for samples isothermally cured at 120°C reduced the tensile strength and flexural strength.

Optimization of Thermal and Mechanical Properties of Unsaturated Polyester Resin as a Binder in Polymer Concrete for Manufacturing Precision Tool Machine Bases

“…Research literature suggests that varying the resin curing rate via curing temperature [29] or initiation mechanism or post-curing heat treatment of the resin affect UPE resin damping properties. Li et al [30] studied the effect of high temperature curing and post-curing heat treatment on the microheterogeneity of UPE and its effect on its mechanical properties. Kim et al [31] used UV initiation curing of UPE and found that the type and the amount of photo initiator affect the level of improvement in mechanical properties.…”

Influence of tribological test on the global conversion of natural composites

“…Due to this fewer C=C bonds these resins have a lower crosslinking density compared with the unsaturated polyester resins, and as these bonds are in the extremes of the chain, they are easier to be accessed, which may lead to an almost complete conversion in the curing [8,22] .…”

“…This potential affection is based on that the curing process is a heterogeneous, highly exothermic free radical copolymerization [15,22] where three reactions occur at the same time: vinyl ester homo-polymerization, styrene (or any other unsaturated vinyl monomer as mentioned before) homo-polymerization and vinyl ester-styrene copolymerization [3,8,13,17] . 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.…”

“…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.…”