Experimental Studies on Mechanical Properties and Thermal Behavior of Polyoxymethylene/CaCO3 NanoComposites

Nanocomposites based on polyoxymethylene (POM)، containing 1. 5 to 9 wt% of CaCO3 nanoparticles، were prepared by melt compounding، using a co-rotating twin screw extruder، followed by injection molding process. The thermal behavior، mechanical properties as well as morphology were characterized. The inclusion of CaCO3 nanoparticles into POM slightly affected the melt flow index. The differential scanning calorimetry (DSC) results indicated that the incorporation of CaCO3 nanoparticles has nucleating effect and can raise the temperature and the degree of crystallinity. The results of shrinkage assessments revealed that crystal nucleation and filling effects of CaCO3 nanoparticles have counter effects on thermal contractions. Incorporation of the CaCO3 nanoparticles into POM improved tensile and flexural properties as well as the impact resistance at the same time. The maximum tensile strength، tensile modulus، flexural strength، flexural modulus and impact strength were achieved in the order given by applying 1. 5، 6، 3، 6، 3 wt% of CaCO3 nanoparticles، which corresponded to 13، 40، 33، 15 and 20% higher than those of pure POM. The notable improvements of tensile، flexural and impact properties as a result of incorporating 3 wt% of CaCO3 nanoparticles were attributed to the nucleation and crystallinity enhancements as well as relatively uniform dispersion of CaCO3 nanoparticles in POM matrix. The morphology studies indicated that CaCO3 nanoparticles inclusion can alter the fracture mechanism from brittle-to-ductile-brittle، a sharp transition from ductile-to-brittle fracture observed in POM/CaCO3 nanocomposite.