Particle size distribution effects on physical properties of injection molded HA/PLA composites

Effects of particle size distribution on physical properties such as viscosity, heat and mechanical properties of injection-molded hydroxyapatite (HA)/poly lactic acid (PLA) were investigated. The melting temperature of PLA was shifted to a lower temperature because of the dispersion of HA particles. However, the cold crystallization temperature shifted to a lower temperature at high HA composition, suggesting that HA particles acted as a nuclear agent. x(c,PLA) of the composites with bimodal particle size distribution showed the lowest of all three composites, suggesting that mobility of PLA polymer chain was reduced by bimodal particle size distribution, which means the increase of restriction at interface between polymer matrix and particle. Melt flow rate (MFR) increased because of dispersed HA particle. The reason was thought that hydrolysis degradation of PLA occurred during melt-mixing process is accelerated by HAp particle dispersion. The MFR of composites increased concomitantly with increased particle size. Mechanical properties such as flexural strength and the modulus of bimodal-HA/PLA composite with both 5 and 1m of representative size were higher than those of monomodal-HA/PLA composites with 5 or 1m of representative size within the range of the results of this paper. Fracture surfaces were affected by the particle size distribution. It was suggested for the reasons to relate the interparticle distance and restriction of the interface between the matrix and particles.