Polypropylene (PP) and PP/halloysite nanotube nanocomposite parts of 0.7 mm thickness (-PP and -PP/HNT) were molded via micro-injection molding (MIM)

and PP part of 3.5 mm thickness (m-PP) was molded via conventional injection molding (CIM).The relationship between mechanical properties and crystal structures and the influence of HNT on mechanical properties and thermal stability of the molded parts were investigated.Compared with the m-PP part

the tensile strength and storage modulus (40 ℃) of -PP part were increased by 67% and 48%

respectively

due to its significantly higher crystallinity (76.7%) and shear layer thickness percentage (57.8%).The addition of a low content (2 phr) of HNT further increased the tensile strength

storage modulus and thermal stability of -PP parts.This was mainly ascribed to the good dispersion of HNT in PP matrix.Although the contents of crystal in both -PP and -PP/HNT parts (20% and 26.3%) were significantly higher than those of m-PP part

the elongations at break of the former two parts were obviously lower than those of the latter one.This indicated that the effect of toughness decrease caused by molecular orientation was stronger than the toughening effect of the crystal for both -PP and -PP/HNT parts.