The Effect of Injection Speed on Morphology and Mechanical Properties of Polyoxymethylene/Poly(Lactic Acid) Blends

Abstract

Polyoxymethylene (POM)/Poly(lactic acid)(PLA) blends were injection molded at three different injection speeds as 50mm/s, 100mm/s and 300mm/s for investigation the effect of injection speed on morphology and mechanical properties of this blends. The tensile test was carried out for examination of mechanical properties. Morphology was observed by polarized optical microscope and polarizing micrographs that was supported by Raman spectra. At injection speed of 50mm/s, mechanical properties of POM/PLA blends increased with decreasing POM content but when 20%wt of POM was added into PLA, the results dropped obviously due to a poor distribution of both POM and PLA phases. That can be confirmed by polarizing micrographs and Raman spectra. It was found that the POM-rich phase mostly combined in the core area. The dispersion of POM-rich phase expanded to a wide area when the injection speed increased to 100mm/s and 300mm/s, respectively. The improvement of distribution of POM-rich phase has an influence on the enhancement of mechanical properties. Tensile modulus of POM 20wt.% increased from 2.8GPa to 3.0GPa while its tensile strength increased from 50.5MPa to 55MPa. Thus, the high injection speed can enhanced the phase distribution and mechanical properties at low POM content but has not a significant effect when POM content over 40%wt.