Preparation And Functionalization Of Polydopamine/Epoxy Shape Memory Composites

Smart material is a kind of intelligent material that can perceive the changes of external stimuli,analyze,process and judge them,and take corresponding measures to make appropriate response.Shape memory epoxy(SMEP)as a kind of smart material can perceive the stimulating change of the external environment,making the temporary shape recover to its initial shape,because of its high mechanical strength,low curing shrinkage rate,excellent adhesive performance and shape memory performance,it has high potential application in aerospace,construction engineering and biomedicine and other fields,however,the single shape memory driving mode,low elongation at break,hard to reshaping,and lack self-healing ability have hindered its wide application to some extent.With the development of science and technology and the continuous improvement of living standards,people's requirement for green safety and intelligence of materials have been constantly improved.Water-borne epoxy(WEP)is an environmentally friendly material that utilize water as dispersion medium,which has the advantage of solvent-based epoxy resin performance.However,it has disadvantage of single shape memory driving mode,low elongation at break,and lack of self-healing ability also exist,and the molding process needs to be performed with the help of mold.Due to the single function,the application scope of WEP is greatly limited.Therefore,this paper focuses on the functionalization of WEP in the following three aspects(1)In order to endow WEP light-driven function,polydopamine(PDA)nanoparticles with excellent photothermal conversion performance were used as filler to prepare PDA/WEP composites by freeze-drying and hot-pressing.the effect of PDA on the property of the composites was studied.The results showed that the tensile strength of the composites increased with the increasing of the fraction of PDA,compared with pristine WEP,the tensile strength of 0.5wt%PDA/WEP composite was improved by 72%.The composites had excellent shape memory performance,the shape fixity ratio(Rf)and shape recovery ratio(Rr)of the composites were up to 99%.moreover,when the PDA content was 1wt%,the temperature of the composite risen from 25? to 215? within 18 s under near-infrared(NIR)light irradiation,and the light-driven shape recovery was completed within 6 s.(2)In order to broaden the application range of WEP,and create complex shapes that are difficult to achieve in the mold forming process,based on the work of(1),PDA/WEP(PW)/WEP composites were prepared by post-treatment with PW coating modification.The effects of crosslinking density on the mechanical property and shape memory property of WEP were systematically studied,and the light-driven property and shape transition property of PW/WEP composites were explored.The results showed that the elongation at break of WEP increased with the decreasing of the crosslink density,and the highest can reach 215%.WEP had excellent shape memory performance,the Rf and Rr were all up to 92%.The shape recovery of WEP completed within 10 s under 808 nm NIR light,and the shape transformation of the pre-strain composites from two-dimensional flat to three-dimensional space was successfully realized by using the temperature gradient induced by NIR light.(3)In order to endow WEP with self-healing function,starting from the design of the polymer molecular structure,the reversible dynamic disulfide bond was introduced into WEP molecular structure to obtain a self-healing disulfide bond waterborne epoxy resin(sWEP),the PDA nanoparticles were introduced into this matrix,and PDA/sWEP composites were prepared by melt blending and hot pressing.The mechanical property,shape memory property and self-healing property of the PDA/sWEP composites were studied.The results showed that the introduction of lwt%PDA nanoparticles significantly improved the mechanical property of the PDA/sWEP composites,and the tensile strength increased from 36.1 MPa to 50.3 MPa.The PDA/sWEP composites also had shape memory property,the Rf and Rr were 98.7%and 71.6%,respectively.In addition,PDA/sWEP composites had excellent self-healing property,at 160? and 3 MPa,the self-healing efficiency can reach 84%after 30 min of hot pressing,moreover,the self-healing efficiency reached 64%after exposed to 120 mW/cm2 NIR light for 30 min.