Composite Resin Matrix Light Curing Performance Study

With the advantages of their high stiffness-to-weight and strength-to-weigthratios, resin matrix composite materials have been widely used in automobile,construction, and weigh-sensitive aeronautical and astronautical industries.However, resin matrix composite have disadvantages during thermal-curingprocess, such as low curing rate, the volatilization of solvents, ineffective energy,low stability storage, especially for profile products, it is difficult to operate andcostly to design moulds. By the virtue of UV-curing technology, which wascharacterized by the intensive works in the field of practical use ofphotochemical polymerization, all the problems above can be solved. The maininterest of using UV-light to induce the polymerization reaction to producecomposite material lies in the high polymerization rates, which can be reachedunder intense illumination, together with the advantage of a solvent-freeformulation curable at ambient temperature.The prepolymer selected for this study is acrylic epoxy resin(CEP), whichis typically used in UV-curable resins for its excellent light activity andproperties of UV-cured products. In this study, epoxy and acrylate were mixed tosynthesize CEP resin, using triethylamine as catalyst, hydroquinone aspolymerization inhibitor and controlling the reacting temperature at90-95℃.Testifyed by Fourier transform infrared spectrometry(FTIR), the CEP resin wassuccessfully synthesized.As the designing ratio, the CEP resin, photoinitiators and active diluentwere homogeneously mixed together. Then the mixture was coated on a piece ofglass, controlled the thickness between1to1.5mm. Exposing it to the UV-light,we characterized its curable degree with gel fraction. The main works focusedon the effects of curable parameters including four kinds of pyrolyticphotoinitiators, active diluents A and B, inhibitor hydroquinone, coupling agentTBT, radiation distance on CEP’s UV-curable properties.Irgacure184and Darocur1173areα-hydroxyl alkyl benzene photoinitiator,which induce CEP resin polymerize steadily. Especially as the concentration is 4%, it has higher induction activity. The system usingα-amine alkyl benzeneketone TPO cure with light photo-oxidative degradation. However, Irgacure907has slower initiating rate and occurs serious photo-oxidative degradation. Whenusing compound photoinitiators, Irgacure184/BP、Darocur1173/ITX double thecuring rate, compared with single photoinitiator, while Irgacure907/ITX haveweaker initiating effect, comparing with the curable system only usingIrgacure907, even if after10min, it is still in uncurable state. According to theresult, we find it is the best option to choose α-hydroxyl alkyl benzene or itscompound system as photoinitiator and control the concentration at4%.Also the kinds of reactive diluent, the additives and radiation distance havegreat effects to the curing rate. Using multifunctional reactive diluents, thesystem has faster curable rate. However, the internal stress of cured film isserious, and it is easy to warp. At the starting stage, hydroquinone slow thecurable rate. Gradually, the reaction rate increase. Gradually speaking, it can’taffect the total curable time. Using TBT as coupling agent, it is bad forUV-curable composite materials to shape. Decreasing the radiation distance is abetter way to enhance UV-light efficiency and increase cross-link rate. However,the temperature on the sample surface was higher. In order to decrease thethermal effect, we designed15cm as the best radiation distance.According to weight loss test in different solvent, cured products usingIrgacure184(4%) have good solvent-resistance property. FTIR andthermogravimetry(TG) technology were used respectively to monitor the finalconversion rate of UV-curing product and observe its thermal property. The datashow that the double bonds conversion reach73.41%. The thermaldecomposition temperature is300℃.Considering the importance of mechanical features of resin base incomposite materials, rigidity, strike resistance, attaching strength and flexibilitywere tested following the different state standards respectively. Cured productsusing Irgacure184(4%) has better mechanical features. To further understand itsmicrostructure and effect in different curing conditions, scanningelectromicroscope(SEM) images of fracture and surface of CEP samples were presented. Most of the samples present brittle fracture under external force. Onlyone using Irgacure184(4%) images slight ductile fracture and impact resistance.So Irgacure184(4%) can be the preferred photoinitiator for CEP UV curing.