Effect Of Different Dimensional Inorganic Materials On The Curing Kinetics Of Epoxy Resin

Epoxy（EP） is an important thermosets being widely applied as matrixresin in fabricating insulating materials, paints, adhesives. In addition, due toits excellent mechanical property, chemical stability, processability, and lowcosts, epoxy resin was widely used as matrix resin of many compositematerials. However, there are also some disadvantages for the epoxy resinbecause of its highly crosslinking structure, such as poor impact-resistanceand strong internal stress.Inorganic materials are of great potential in modification of epoxy resins.It is known that the influences of inorganic materials on the properties ofepoxy resin composites are depending on the curing process. The differentdimensional inorganic materials shall have different influences on the curingkinetics. However, the comparison is not mentioned in the literatures.In this work, we chose three kinds of inorganic materials as modifier toinvestigate the influences of filler shape and concentration on the curingkinetics of epoxy resin. Differential scanning calorimeter（DSC）was usedduring the study. Analysis on the isothermal and non-isothermal curingkinetics was conducted. The three inorganic materials are silicon nitride（Si₃N₄） nano-whisker of one dimension, layered double hydroxides （LDHs） oftwo dimensions and tetra-needle like ZnO whisker （T-ZnOw） of threedimensions.In a typical process, the fillers were first treated with3-Triethoxysilyl-propylamine （APTES）, and then being dispersed in the epoxy resin with aid ofsonication and stirring. Parts of the mixtures were used in DSC analysis, andthe others were cured under proper temperature for a period of time tofabricate epoxy resin composites. The cured samples were used to investigatethe thermal stability.The temperatures in the isothermal analysis were set to be140,160and180C respectively. The experimental data can be well fitted into the Kamelmodel, or the self-accelerating model. It was found that the reaction rateconstant k2of the E51/DDM/Si₃N₄composites was higher than that of thepristine epoxy resin under the same temperature. The k2value increased first, but dropped later as the Si₃N₄whisk concentration increasing. The k2values ofthe E51/DDM/LDH composites was all lower than that of the pristine epoxyresin. With the LDHs concentration increasing, the k2values increasedgradually. For the E51/DDM/T-ZnOw composites, the k2values were allhigher than that of the pristine epoxy resin and increased with the T-ZnOwconcentrations. In general, the activation energy of the composites in theinitial stage （E,1） was lower than that of th e epoxy resin. However, theactivation energy in the middle and final stages（E,2）was significantly lowerthan the initial stage of the activation energy.In the non-isothermal analysis, the heating rates were set to be1,2,5and8C/min respectively. The Kissinger method, the integration method ofFlynn-Wall-Ozawa and the differentiation method of Friedman were applied.Among them, the Friedman method was used to verify the results obtainedfrom Flynn-Wall-Ozawa method. The results showed that, the shape of thefillers was the major factor influencing the curing reactions of epoxy resin. Allthe three inorganic materials could effectively lower the reaction energy ofepoxy resin. For the E51/DDM/Si₃N₄composites, the initial curing activationenergy of the samples with low whisker concentrations （1-2.5wt%） was almostthe same as that of the pristine epoxy resin. However, it dropped remarkablyas the whisker concentration increased to5wt%. In the final stage, theactivation energy of all the E51/DDM/Si₃N₄composites was lower than that ofthe pristine epoxy resin, indicating the good acceleration effect of Si₃N₄whiskers. For the E51/DDM/LDHs composites, the activation energy of thecomposites with lower LDHs concentrations （1-2.5wt%） decreasedcontinuously with the LDHs concentration, and it increased in the final stage.For the E51/DDM/T-ZnOw composites, the activation energy was lowereddown with addition of T-ZnOw, but the lowering effect was weaken as theT-ZnOw concentration increasing.The results obtained from thermo-gravity analysis showed that, theresidual weight of the composites increased. That is, the Si₃N₄whiskers, theLDHs and the T-ZnOw were all able to improve the thermal stability of epoxyresin.