Defining the lower and upper limit of the effective modulus of CNT/polypropylene composites through integration of modeling and experiments

The focus of this study is to evaluate the effective modulus of carbon nanotube (CNT) reinforced polypropylene (PP) composites based on numerical techniques that account for CNTs non-uniform distribution, agglomeration, waviness and alignment with respect to the applied load direction. A three-dimensional (3D) finite element model with multiple CNTs embedded within the PP matrix in presence of CNT/PP interphase is built and subjected to tensile loading. The thickness and stiffness of CNT/PP interphase, dispersion and distribution of CNTs within the PP matrix, their alignment with respect to the applied load and their waviness are characterized using atomic force microscopy and scanning electron microscopy of the CNT/PP composites made by melt mixing and injection molding. The modulus predicted numerically is in good agreement with that obtained experimentally, according to ASTM D638. The proposed elaborated numerical model can provide the lower and upper limit of the modulus and guide the manufacturing of CNT/PP composites with engineered properties in a scalable and cost effective way.