Structural And Performance Characterization Of Lcpu/Engineering Plastic (Molecular Composite) 3D Printed Materials

In this paper,two types of liquid crystal polyurethane(LCPU)were synthesized by molecular structure design.Due to the structural characteristics of the two kinds of LCPU,they have certain compatibility with the corresponding engineering plastics polycarbonate(PC)and nylon(PA6).Thanks to LCPU has the rheological characteristics of easy to orient,LCPU and engineering plastics are used to make molecular composites by melt thermal blending.PC-type LCPU system: The effect of the combination of PCDL and BDO on the liquid crystallinity and thermal transition temperature of PU is discussed when the bisphenol A group and the diphenylmethyl group form a rigid crystal-forming unit system.The results show that when the ratio of PCDL to BDO is 0.54:1,the liquid crystal of the product is the best.It is a nematic thermotropic liquid crystal with a melting point of 134.4? and a clearing point of 220.3?.The liquid crystal temperature range is 85.9?.It does not degrade before 250?,and can be molecularly compounded with PC as the PC-type LCPU.PA-type LCPU system: The phenylene crystal-containing diol obtained by the transesterification reaction while in the polycondensation reaction,when the ratio of TDI to MDI is 2:1,the product PU liquid crystal properties are better.It is a nematic thermotropic liquid crystal with a melting point of 160.9? and a clearing point of 210.2?.The liquid crystal temperature range is 49.3?.It does not degrade before 250?,and can be molecularly compounded with PA as the PA-type LCPU.In the molecular composite system,the LCPU liquid crystal microfibers have a diameter of 200 nm?300 nm,the length and diameter ratio of the microfibers are long,and the distribution is uniform.The tensile strength of LCPU/PC is increased from 60.4 MPa of PC to 67.47 MPa,with the increase of 11.6%;and the tensile strength of LCPU/PA is increased from 48.87 MPa of PA to 73.64 MPa,with the increase of 50.69%.In terms of rheology,the addition of LCPU significantly improved the processing properties of PC and PA.The fixed shear rate,the shear viscosity,shear stress and inlet pressure drop of the composite decreased with the increase of the mass percentage of LCPU.The nonNewtonian index of the composite is also increased.The reduction of shear viscosity enables the composite to be 3D printed by FDM molding technology,and the molding process will become relatively easy.The lowviscosity of the consumables will be more conducive to ensuring the appearance of the surface of the 3D printed product.In addition,the LCPU in the composite materials can make the enhancement by microfibers which is continuous,resulting in a substantial increase in the mechanical properties of the material.This breakthrough is expected to overcome the adverse effects of the point-additive material process on the mechanical strength of the polymer material in 3D printing process.