Study On The Morphological Evolution And Properties Of The Fibers Fabricated In Situ Among Polymer Blends By Fused Deposition Modeling

Fused deposition modeling(FDM)is a new type of additive manufacturing technology based on extrusion.The complete FDM process from materials to final products includes the combination of twin/single screw extruder,hot roll stretching,and the extruding layer-by-layer deposition through a movable printing nozzle.Thus,it is very important to study FDM processing links and parameters.In this dissertation,polylactic acid(PLA)and thermoplastic polyurethane(TPU)blends were selected as research materials.The mechanism of hot-drawing process on the fiber formation in FDM process was systematically studied.The effects of TPU morphology on the properties of PLA/TPU blends were also studied.Finally,the influence of FDM process parameters on the surface quality and mechanical strength of different materials were investigated.The research results of this paper were as follows:(1)In the FDM processing,the drawing force field of the single-screw extrusion system could produce long-fiber TPU;the whole stretch ratio of the FDM printing process could reach 26.13,which making the TPU to be distributed in the form of short fibers in the sample.At the same time,the average length of the fibrous TPU could be adjusted from 67.24 ?m to 103.72 ?m.In contrast,TPU was distributed in spherical or ellipsoidal shape in the injection molded samples.The morphological difference of TPU could be attributed to the fact that FDM processing had a stronger stretching field and a faster cooling rate than injection molding.(2)The in-situ fiber preparation by FDM promoted the interface interaction between TPU and PLA,which blurred the interface between the fibrous TPU and the PLA matrix.The surface of the TPU fiber provided an additional heterogeneous nucleation center for PLA crystallization,accelerating the crystallization of the PLA.At the same TPU content,the glass transition temperature of PLA and TPU of the FDM sample and the crystallinity of PLA were higher than those of the injection molded sample.(3)In the FDM processing,TPU fibers could not only be oriented,but also formed mesh structure.The oriented fiber structure allowed the strength and modulus of the FDM sample to reach the injection molding level.Moreover,when,the network-like TPU printed at a raster angle of ±45° had better toughening effect,which made up for the weakening effect of printing pore on impact strength,and the impact strength of the printed sample could reach or exceed the level of the injection molded sample.(4)The effects of nozzle-bed distance(NBD)on the properties of different material sample were investigated in detail.It was found that when the NBD increased from 0.10 mm to 0.20 mm,the interlayer adhesion force of ABS resin decreases from 163.58 N to 100.64 N,with a decrease rate of 38.48%,while that of PLA was 10.14%.With the increase of NBD,the pores in the sample also increased,which resulted in a decrease in mechanical properties such as tensile,compression,bending strength and modulus of the part.Taking all the properties into consideration,the optimal NBD value was determined to be 0.10 mm.