Silicane Modified Graphene Oxide Toughening Epoxy Resin And Its Slow Dynamics Induced By Reaction

Epoxy resins and their nanocomposites are one of the widest used thermosets.There are still problems of them at both fundamental and application aspects.From the view point of applications,the study of epoxy resins is focused on the balance of the mechanical properties and the flame retardancy.It's still the hot spot of this study for preparing the practical and secure epoxy resins.In other hand,from the view point of fundamental research,the recent understanding of the curing process of epoxy system is based on the description with state transformation diagram.There are some remarkable results of the gelation and the formation of network inside the system.However,the understanding of the post curing stage,particularly accompanying the glass transition,is still phenomenological.Mostly,the glass transition is only represented with a glass transition temperature which is ill-defined.Thus,the curing process was studied with the combination of phenomenological curing kinetics and time-resolved viscoelastic spectrum.The following is the outline of this work and conclusions.1.Short PDMS chains were grafted to GO surface by one-step synthesis to prepare a novel type of GO ramification,PDMS-GO.PDMS-GO exhibited remarkable toughening and synergistic flame retardant effects in the matrix of epoxy resin,and improved the water resistance of the cured epoxy nanocomposites.Small addition of 0.29 wt%of PDMS-GO with 0.3 wt%of P made the cured epoxy nanocomposites reach the UL94 V-0 level with LOI value of 29.2,T_5wt%of 339?,and char yield of 21.4 wt%.At the same time,the flexible strength was significantly increased to 101.2 MPa,comparing to 67.9 MPa for the epoxy containing 0.3 wt%of P only due to the good dispersion of PDMS-GO in the epoxy matrix.Therefore,the DGEBA epoxy containing 0.3 wt%of P and 0.29 wt%of PDMS-GO is the optimal formula with the balanced performance in flame-retardant,mechanical toughness,and water resistance and is expected to satisfy electronic applications.2.Analyzing the results of DSC measurement of the curing of G0.29,there were two complex points:the first one was the apparent activated energy increasing remarkably during the curing process,and the other one was about the differential reaction model function f???,which couldn't be fit by a single reaction model,but two.Then,the kinetic differential equation of rate was developed to quantitatively describe both the isothermal curing process and non-isothermal curing process successfully.In addition,the discussion about the parameters of the kinetic equation of rate showed the diffusion arrested effect in the late stage of curing,reflecting the dynamics of the curing system frozen to slow down during the curing reaction,which may be universal.3.With Multiwave techniques,the time-resolved viscoelastic spectra of the curing process at different temperature were obtained.As for the reaction at T_cur=150?,the related spectrum showed both TCS and TAS,reflecting the separation of the relaxation times of the relaxable elements with different scales,when the system gradually frozen into the dynamics arrested state during curing process.As for higher temperatures,there was no enough time to detect the whole process of the formation of the permanent modulus plataus in measurable time window anymore.Thus,two complex relaxation behaviors would be seen.Firstly,this coupling of gelation and?-relaxation changed the behavior near liquid-solid transition from gelation to the glass-like type transition,and broke the TCS of the spectra.Secondly,with the comparison of the TAS behavior of the curing process at different temperatures,both the master curves and the shift factors,the separation of?-relaxation and glass transition was noticed.This illuminateed the difference of the relaxation units of?-relaxation and glass transition.