A dual-curing process is defined as a combination of two curing reactions taking place simultaneously or sequentially. It is a method to combine two otherwise distinct polymer networks. The resulting interpenetrating polymer network exhibits superior properties compared to its individual parts [1]. In this study, a combination of two simultaneous and sequential photopolymerization processes was investigated. Photoinitiated polymerization have the advantages of rapid cure, low energy consumption, high efficiency, low volatile organic compound emission, and the large number of applications in not only conventional areas such as coatings, inks, and adhesives, but also in high-tech domains, such as microelectronics, optoelectronics, laser imaging, stereolithography, and nanotechnology [2]. The replacement of petroleum-based materials by materials derived from renewable resources in such technologies would give the ecological and economic benefits.
In this work, two processes of free radical and cationic photocross-linking of biobased monomers carried out simultaneously and sequentially were investigated by the real-time photorheometry. This method provides the wide range information on typical rheological properties such as viscosity and storage modulus G', loss modulus G'', loss factor tan$\delta$, and complex viscosity $\eta$* while a material is irradiated with UV/VIS light. It enables to track the occurrence of structural phenomena, such as gelation and vitrification, indicating the moment, when the structural changes have started [3].
The dual photocuring of various acrylated and epoxidized vanillin and glycerol-based monomers was investigated in this study. Several free radical and cationic photoinitiators were used. The influence of the initial reaction mixture composition to the photocuring kinetics, rheological properties, rigidity and shrinkage of the resulting cross-linked polymers was investigated.
It was determined that the highest values of storage modulus G' and thus the highest rigidity were achieved using sequential dual photocuring process. The gel point of the most dual photo-curing systems was higher than that of pure acrylates but lower than that of pure diglycidyl ethers. The shrinkage of the samples of the most dual photocuring systems was lower than that of the pure acrylates but higher than that of pure diglycidyl ether samples.