Synthesis And Microwave Actuation Properties Of Nano Carbon/epoxy Shape-memory Polymer Composites

Shape memory polymers(SMPs)can keep their temporary shapes,and return to initial shapes under outer stimulus,which have the advantages of low density,low cost,large deformation,and good bio-compatibility.Thus SMPs have excited the scientists in the field of smart materials recently.Compared with the other SMPs,epoxy-based SMPs(ESMP)show relatively higher mechanical strength,better environmental durability,and lower cost,making them great candidates in many fields including aeronautics and astronautics.However,the mechanical strength,thermal stability,and actuation method of pristine ESMP hinder its practical applications in aeronautics and astronautics.In order to enhance the mechanical strength,improve the thermal stability,and expand the actuation route of ESMP,several carbon nanomaterials with different structures are chosen as reinforcing phases or functional fillers for fabricating ESMP nanocomposites.The micro-structures,mechanical properties,and shape memory properties of the nanocomposites are investigated.This paper may provide a valuable reference for the practical applications of ESMP-based materials.In this paper,thermally reduced graphite oxide(Tr GO)was produced by exfoliating graphite oxide(GO).ESMP reinforced with 1wt% Tr GO was fabricated by solution blending and three-roll mill(TRM)mixing,respectively.The micro-structures,mechanical properties,thermal stability,and thermo-actuated shape memory properties of the Tr GO/ESMP nanocomposites synthesized by the two different methods were compared systematically.The effect of Tr GO content(1~3wt%)on the structures and properties of the Tr GO/ESMP nanocomposites fabricated by TRM mixing were investigated.Tensile and three-point bending tests were conducted to characterize the mechanical properties of the Tr GO/ESMP nanocomposites.Dynamic mechanical analysis(DMA)was used to characterize the thermomechanical properties.The thermal stability of the nanocomposites were characterized by thermogravimetric analysis(TGA).Thermo-actuated shape recovery tests were carried out to measure the influence of Tr GO on the shape memory properties of ESMP.The growth temperature of carbon nanotubes(CNTs)array was optimized by investigating the effect of growth temperature on the height and alignment of CNTs array during chemical vapor deposition(CVD).CNTs array/ESMP nanocomposite was fabricated by impregnating shape memory epoxy resin into the CNTs array through solution infiltration followed by thermal polymerization.The alignment of CNTs in this composite was characterized by scanning electronic microscopy(SEM),and compared with the random CNTs/ESMP composite fabricated by mechanical stirring.Nanoindentation tests were carried out to characterize the moduli and hardnesses of pristine ESMP,random CNTs/ESMP composite,and CNTs array/ESMP composite.The microwave heating properties of the three materials were measured by recording the rates of temperature rise in microwave radiation.The effect of random CNTs or CNTs array on the microwave-actuated shape memory properties of ESMP was investigated by microwave-triggered shape recovery tests.The results revealed that the CNTs array/ESMP nanocomposite showed a shorter shape recovery time than pristine ESMP and the random CNTs/ESMP composite.Microwave-responsive nanocomposites consisting of ESMP and different dimensional carbon nanomaterials(0D carbon black(CB),1D multi-walled carbon nanotubes(MWCNTs),2D graphene nanoplatelets(GNPs),and 3D functionalized graphene sheets(FGSs))were fabricated by TRM mixing.The dispersion states of the carbon nanomaterials in ESMP and the interfaces between filler and matrix were characterized by scanning electronic microscopy(SEM).The reinforcement effects of the four carbon nanomaterials on the mechanical properties of ESMP were compared using tensile and three-point bending tests.The microwave heating properties of the materials were compared by recording the temperature changes in microwave radiation.Among them,the FGSs/ESMP nanocomposite had the fastest rate of temperature rise.The microwave-actuated shape memory properties of the materials were compared using microwave-triggered shape recovery tests.Possible mechanisms of the microwave propagation and absorption in the nanocomposites were proposed based on the structures and dispersion states of the four carbon nanomaterials in ESMP matrix.