Study On Shape Memory Effect Of BACE/PBEP Copolymers And Their Composites

Shape memory polymer(SMP)is a new kind of smart polymer materials,which can sense the environment stimulation and make certain response to stimuli by changing its mechanical parameters(such as shape,position or strain)to its original state.It is this unique feature that makes the shape memory polymers rapidly developed and widely applied in the intelligent textiles,biomedical engineering,smart structures and aerospace,etc.In recent years,the research on shape memory polymers had mainly concentrated on the shape memory polymers with single polymer structure and low glass transition temperature(Tg).It is difficult to adjust the structure and the glass transition temperature of shape memory polymers.To solve this problem,this work tries to prepare a novel kind of shape memory polymers based on the bisphenol A type cyanate ester(BACE)and polybutadiene epoxy(PBEP).This new shape memory polymer,which consisted of two components,can adjust its structure and glass transition temperature.Firstly,BACE possesses good thermal property and easy processability and its glass transition temperature is about250 o C;Secondly,PBEP has long flexible aliphatic carbon chain,which can be used as a reversible phase,and cyanate ester triazine ring can be acted as irreversible phase,which provides a structural basis for the preparation of shape memory polymer.Based on shape memory BACE/PBEP polymer,the fiber-reinforced and electroactive shape memory composites were fabricated.Fundamental trends were established between the structure,filler content and the shape memory properties.The main contents and conclusions are listed as follows:First,the curing systems of BACE and PBEP with different molecular weight were prepared,the cross-link density,the chain flexibility and the structure of the shape memory polymers were investigated.The gel time showed that without any additional catalyst,the curing of BACE could be catalyzed by PBEP.After the curing process of100 o C/3 h + 120 o C/2 h + 150 o C/40 min + 180 o C/40 min,the reaction between the functional groups had completely carried out.The bending strength decreased with increasing molecular weight of PBEP.The cross-link density,the storage modulus and Tg decreased as the molecular weight of PBEP increased.The highest and lowest glass transition temperatures were 173 o C and 99 o C,respectively,which had met therequirement of adjusted Tg.A similar trend in the water absorption rate was observed with increasing molecular weight of PBEP.The highest water absorption rate was1.2%.It demonstrated that the curing system possessed good heat and humidity resistance.Shape memory test results revealed that all the curing system showed excellent shape memory effect except A-2500(The molar ratio of BACE and PBEP is9:0.5.).In addition,the shape memory recovery time shortened with increasing molecular weight of PBEP at the same temperature.With increasing cycles,the shape recovery ratio reduced slightly.However,it was still more than 98%.It demonstrated that the BACE/PBEP curing system showed excellent shape memory performance.Then,keeping the molecular weight of PBEP unchanged,the BACE/PBEP with different molar ratio curing systems were prepared and the influence of the structure changes on the properties of curing systems were investigated.It was indicated that the gel time shortened with increasing content of PBEP and temperature.The bending strength of the curing system showed a similar trend.The flexible structure ratio increased with increasing content of PBEP.Therefore,the cross-link density,the storage modulus and Tg of the curing system decreased.The highest and lowest glass transition temperatures were 167 o C and 135 o C,respectively.The water absorption results showed that the highest water absorption rate was 6% and it demonstrated that the curing system possessed good heat and humidity resistance.Shape memory test results showed that the shape memory recovery time shortened with increasing content of PBEP under the same temperature.Second,in order to improve the mechanical properties of shape memory BACE/PBEP polymer,fiber-reinforced shape memory BACE/PBEP composites were fabricated and the influence of the reinforcing filler on the properties of shape memory materials was studied.The study on the glass fiber(GF)reinforced BACE/PBEP composites showed that bending strength was improved by adding the glass fiber to the matrix.The bending strength of the composites with glass fiber content of 0.6 wt% was 102 MPa,increasing by 23%.The storage modulus and Tg increased with increasing content of GF.Shape recovery time shortened as the temperatures rose and the glass fiber content reduced.Under the same temperature,shape recovery time increased with the increase content of glass fiber.With increasing shape recovery cycles,shape recovery ratio declined slightly.And then,calcium sulfate whisker(CSW)reinforced shape memory composites based on BACE/PBEP curing systems were fabricated.The tests revealed that bending strength was improved by adding the CSW to the matrix.The bending strength of the composites with CSW content of 5 wt % was 107 MPa,which increased by 29%.The Tg and storage modulus increased with the increase content of CSW.SEM photos showed that when the content of CSW exceeded 10 wt%,clusters was easily formed and the interface performance between CSW and polymer matrix became poor,resulting in reduction of mechanical properties.Shape recovery time shortened as the temperature rose and the CSW content reduced.Under the same temperature,shape recovery time increased with the increase content of CSW.With increasing shape recovery cycles,shape recovery ratio reduced slightly.Furthermore,with the BACE/PBEP curing system as the matrix,the electroactive shape memory BACE/PBEP composites were prepared by adding the conductive carbon black(CB)into the matrix.The electric properties,mechanical properties,dynamic mechanical analysis and the electroactive shape memory effect were systematically studied.The results showed that carbon black particles acted as the role of physical cross-link point in the composites,which effectively improved the mechanical properties of the composites.Since the high modulus of CB,the storage modulus of composites increased with increasing content of CB.The volume resistivity of the composites dropped rapidly when the carbon black content increased from 5 wt% to 8 wt%.This revealed that the conductive ingredient network was gradually formed.The BACE/PBEP/CB composites showed good thermal-induced shape memory effect and the shape recovery time shortened with the increase of the temperature.Electroactive shape memory effect could be observed with a few seconds with the carbon black content of 5 wt% and the applied voltage of 60 V.The eletroactive shape recovery time shortened with the increase content of carbon black and the applied voltage.Besides,after four shape recovery cycles,shape recovery ratio decreased gradually,but it was still greater than 80%.It indicated that the BACE/PBEP/CB composites showed good electroactive shape memory effect.The infrared thermometer revealed that the temperature rose above glass transition temperature faster with the increase of voltage and the decrease of resistance.Finally,keeping the amount of carbon black at 3 wt%,another electroacitve shape memory BACE/PBEP composites were fabricated by adding carbon fiber into the BACE/PBEP/CB composites and the electric properties,the dynamic mechanical analysis and the eletroactive shape memory effect were studied.Due to the synergy effect of CB and CF,a sharp transition of the volume resistivity occurred when adding a small amount of carbon fiber.Because of carbon black particles and carbon fiber with high modulus,the storage modulus and Tg increased with increasing content of carbon black.With the applied voltage of 60 V,the carbon black content of 3 wt% and the carbon fiber content of 0.3 wt%,the BACE/PBEP/CB/CF composites began to show excellent electroactive shape memory properties.The deformation recovery time shortened with increasing content of carbon fiber and applied voltage and the shape memory recovery ratio increased with the increase content of carbon fiber and applied voltage.The infrared thermometer revealed that the temperature rose above glass transition temperature faster with the increase of voltage and the decrease of resistance.