Effects of short-glass-fiber content on material and part properties of poly (butylene terephthalate) processed by selective laser sintering

With proportion of short-glass-fiber (SGF) addition (15, 30, 45, and 60 wt%) taken as a parameter, the powder properties of composite-copolymer poly(butylene terephthalate) (cPBT) powder and various properties of the cPBT-SGF specimens manufactured by selective laser sintering (SLS) were evaluated. Even in the case that SGF was added, the flowability of the powder was dramatically improved by adding silica to it. Moreover, as the proportion of added SGF was increased, the flowability was degraded. In the case proportion of SGF addition was taken as a parameter, tensile strength and flexural strength of the SLS specimen were maximized by SGF addition of 30 wt%; however, impact strength was maximized by SGF addition of 45 wt%. As the proportion of added SGF was increased, the amount of SGF "debonding" also increased, while the amount of resin that adheres to the SGFs decreased and porosity increased. In addition, the average glass-fiber length of the SLS specimens decreased with the addition of 45-wt% SGF, whereas it did not decrease with addition of 30-wt% SGF. Furthermore, in contrast to long fibers easily aligning and remaining in the direction of the roller, SGFs did not align in the direction of layer-thickness. Compared to SGF addition having an insignificant effect on mechanical properties, it significantly improved thermal properties (i.e., heat deflection temperature and linear-expansion coefficient) and reduced shrinkage. Moreover, even if SGF was added, it had little effect on the crystallization properties of the powder and SLS-formed specimen.