Study On Preparation And Performance Of 4D Printing Shape Memory Polymer For Buildings Thermal Management

To meet the intelligent control of solar radiation in building thermal management by coupling of deformation and thermal performance of dynamic thermal management devices,the shape memory polymers(SMPs)composites are employed to achieve heat flow controlling and efficient building thermal management by shifting anisotropic thermal conductivity coupling with change of shape in response to stimulus.The main results are shown as following:Polylactic acid(PLA)composites with different 2D fillers were prepared and characterized by XRD,SEM and FTIR.The filler orientation,morphology and chemical composition of the fillers in the matrix are investigated.The results show that BNNS-OH originated from chemical modification of h-BN improve the compatibility of the fillers with the matrix.Compared with casting and tape-casting methods,4D printing shows a better orientation of 2D fillers.The composites with 25wt% BNNS-OH/PLA prepared by 4D printing has demonstrated a significant anisotropic thermal conductivity with in-plane and cross-plane thermal conductivity of 3.27 W/m K and 0.85 W/m K,respectively.The composite thick films in form of BNNS-OH/PLA,PEEK-p/BNNS-OH/PLA and PEEK-f/BNNS-OH/PLA were prepared to investigate their shape memory properties.The results show that the incorporation of PEEK-p(powder)and PEEK-f(fiber)could increase the shape memory properties of the composites,and shape memory properties were correlated with the alignment direction,distribution and deformation of PEEK-f.The relationship between the surface temperature of SMPs composite and the grayness of flake graphite filler under sunlight conditions was investigated.folding hexahedral structures and switchable window arrays were designed and fabricated.The results show that the 4Dprinted structures are more sensitive to light compared to other methods,and the printed structures have better shape recovery performance while the PEEK fibers is aligned along the direction of deformation.The unfolding process of hexahedral structure with different grayscale hinges under light demonstrates that the grayscale could be used as a control condition for programmable deformation,and further demonstrates programmable switch of windows arrays under light.4D printed shape memory composite structures with programmable thermal conductivity directions has demonstrated that anisotropic thermal conductivity of the composites could be achieved by orientation of 2D fillers in matrix.The programmable deformation of 4D printed structures has been modulated by the photo-thermal behavior of SMPs with different grayness,synchronously,heat flow direction and size could be controlled by the change of anisotropic thermal conductivity coupled with deformation.Devices based on shape-performance coupling demonstrated potential applications in intelligent building thermal management.