Study On Function Of 3D Printing Biomass/Thermoplastic Polyurethane Shape Memory Composites

With the increasingly prominent environmental and energy problems,the development of new biomass/polymer composites with low-cost renewable biomass materials as reinforced fillers have been become the trend of sustainable energy development in the world.3D printing technology is an emerging process in the manufacturing industry,with unique advantages in the fabrication of personal customization and complex structural products.It provides opportunities for the high value and diversified utilization of biomass composites.To efficiently utilize biomass resources and develop functional 3D printing materials,thermoplastic polyurethane elastomer(TPU)was filled with biomass materials such as poplar wood flour and cellulose nanocrystals(CNC)to construct a series of flexible,photothermal stimulus responsive shape memory and self-healing 3D printing smart composites.In this study,the construction scheme and interface control method of biomass/TPU composites suitable for fused deposition modeling(FDM)3D printing technology were systematically discussed.The biomass material,TPU and polycaprolactone(PCL)were mixed together to prepare a 3D printed composites with excellent shape memory performance,and the mechanism of its shape memory function was studied.The forming technology and mechanism of CNC reinforced TPU/PCL shape memory polymer composites were investigated,and the photoresponsive shape memory function of TPU/PCL composites with carbon nanotubes was analyzed,which provided a new research idea and method for the preparation of high-performance functional polymer composites.The main research contents and results of this paper are as follows:(1)A low-cost flexible 3D printed biomass composite filament was prepared by melting blending and FDM process using poplar wood flour and TPU as raw materials.The interfacial compatibility of the composite with 20 wt% poplar wood flour content was modified by different modifiers.The results showed that the addition of maleic anhydride grafted ethylene propylene diene monomer(EPDM-g-MAH)significantly increased the elongation at break of the composite,which was nearly 100.14% higher than that of the unmodified composite.Compared with other modifiers,the addition of EPDM-g-MAH compensated the flexibility of the composites,and improved the storage modulus and complex viscosity of the composites.The interfacial compatibility of wood flour /TPU composites was improved.The products 3D printed through the wood flour /TPU composite filament were different from the traditional hard 3D printed products in the current market.(2)To meet the requirements of functional 3D printing materials,PCL is added to poplar wood powder /TPU blend to prepara thermal-induced shape memory composites,which enforces3 D printing with time dimension,and enables 3D printed products shape can be changed with the external environment to realize 4D printing.The shape memory properties of poplar wood flour /TPU/PCL composites with different mass ratios were tested,and the mechanism of the shape memory function was illustrated by combining the crystallization and melting properties of different composites.The results showed that the shape memory performance of the wood flour /TPU composite could be improved by adding PCL.The PCL phase in the composite can crystallize rapidly to fix the temporary shape when the temperature was below the program temperature,and during the shape recovery process the fused PCL can return gradually to the original shape with TPU.When PCL content was 30wt%,the shape fixation and shape recovery properties of the composites reached the optimal value.In addition,carbon black was used to provide poplar wood flour/TPU/PCL composites with photothermal response shape memory performance,and the thermal conductivity of the composites can be improved.The 3D printed products were obtained by FDM process,and the excellent shape memory properties of the 3D printed composites were verified.(3)To further improve the mechanical properties of TPU/PCL shape memory blends,CNC was used to enhance the TPU/PCL blend polymer.The effects of different contents of CNC on the chemical structure,mechanical properties,microstructure,thermal properties and rheological properties of the composites were studied.The reinforcement mechanism of CNC modified TPU/PCL composites was further analyzed by molecular dynamics simulation.The results showed that CNC effectively improved the interfacial bonding of TPU/PCL blends,and improved the mechanical properties and thermal stability of the composites.The dispersion of PCL in the TPU matrix can be improved by adding CNC.Molecular dynamics simulation results showed that CNC improved the interface compatibility of composite materials by generating hydrogen bond interactions with TPU and PCL.When the content of CNC was 1%,all the properties of the composites reached the optimal value.Among them,the tensile strength and elongation at break of the composites reached 31 MPa and 1600%,respectively.(4)In the view of the limitations of direct heating-induced shape memory materials in the application process,the development and modification of near infrared induced shape memory composites were studied by using multi-walled carbon nanotubes(MWCNTs)and dopamine based on CNC-reinforced TPU/PCL composites.The results showed that the composite prepared by dopamine-modified MWCNTs(PMWCNTs)enhanced the interface adhesion of the composites.When PMWCNTs content was 3%,the tensile modulus,tensile strength,crystallization properties and thermal properties of the composites were improved.The modified composites still had excellent shape memory performance after three thermal-mechanical shape memory cycle tests,and the shape fixation performance was better than that of the unmodified composites.On the premise of adding a small amount of filler,the original shape memory performance of the composites was retained,and the mechanical performance of the composite material was improved.Combined with FDM technology,3D printed products with near-infrared induced shape memory function can be obtained.(5)To solve the problems of mechanical properties and shape memory effect reduction caused by mechanical damage of shape memory polymer materials in practical application,selfhealing properties were endowed to polymer composites to carry out the research on self-healing shape memory polymer composites.A thermoreversible Diels-Alder dynamic crosslinking selfhealing shape memory composite was prepared based on TPU/PCL blend polymer,using maleic anhydride and furan methylamine modified CNC as reinforcer and crosslinker.The chemical structure,mechanical properties,thermal properties,shape memory properties and self-healing properties of the composites before and after modification were studied.The strengthening and toughening mechanism of the modified composites was systematically analyzed from the molecular point of view by molecular dynamics simulation.The modified composite had better flow capacity,mechanical properties and thermal stability.The modified composite not only retained the original shape memory performance,but also had high self-repair ability.The tensile shear test proved that the tensile shear strength of the healed composite reached 86.75% of the original composites and the elongation at break was about 91.02% of the original composites.In addition,the potential applications of the developed composites were demonstrated by designing a double-layer flexible composite structure with modified composites as the substrate and multiwalled carbon nanotubes/CNC materials as the conductive layer/UV shielding layer.