Optimization of thick layers photopolymerization systems applying experimental and analytical approach

Abstract

PurposeOver the last several years, the range of applications of photopolymerization process has been steadily increasing, especially in areas such as rapid prototyping, UV inks, UV coats and orthodontic applications. In spite of this, there are still several challenges to be overcome when the application concerns materials with thick layers. In this context, the main goal of this work is to outline a scheme to optimize the process of photopolymerizarion for thick layers, identifying its differences in relation to those applicable for thin layers.Design/methodology/approachFor this research, the authors have applied multivariable analysis methods which allow the identification of principal conclusions, based on analytical and experimental results. For analytical analysis, the authors applied numerical optimization for multivariables, while experimental analysis was done based on design of experiments. Both the analyses were based on methyl methacrylate as monomer and Omnirad 2500 as photoinitiator, with the adjustable variables being initiator concentration; power of light source; light wave length; and thickness of layer. The range of values chosen for initiator concentration was between 1 and 10 per cent, while for light power, the range was 5‐9 W. For light wave length, the authors selected 325 and 400 nm as limits for their study and 0.12 and 4 mm as the range for thickness of layers. For the analytical approach of their study, it was possible to identify optimum conditions for curing thick layers, besides looking at optimum condition at each step along the varying thickness. On the other hand, in the experimental approach, the authors just considered the initiator concentration and thickness as variables, applying gravimetric and photometric analysis to determine the conversion curve of material.FindingsIn conclusion based on these studies, it was possible to identify the influence of thickness and initiator concentration as function of penetration depth, polymerization rate and homogeneity of material, in addition to determining the effect of light power and light wave length over the process. As a result of these studies, it was possible to identify situations wherein the material will possibly undergo a high degree shrinkage in addition to showing consequences of high quantity of initiator. On the other hand, low concentration of initiator is shown to provide more homogeneous solution besides being more suitable for deep layers. It was also possible to compare analytical and experimental results, making it possible to predict the behaviour of material for other conditions.Originality/valueThe main value of this work is to show the possibility of optimizing photopolymerizable systems through an analytical approach. In addition, it emphasized the viability of the application of UV curable material for producing moulded parts.