The thermal expansion coefficient of polypropylene and related composites /

The variability of thermal expansion coefficients during the molding of plastics causes the development of frozen thermal stresses in the molded parts. Also, the distribution of thermal expansion coefficients of the material in the molded part plays an important role in controlling shrinkage and warpage. In turn, the distribution of linear thermal expansion coefficients (LTECs) depends on the distributions of crystallinity and orientation in the part. In the case of fibre reinforced polymers, the distributions of fibre concentration and orientation are also important.In this project, a model has been proposed for estimating the LTEC of fibre reinforced plastics as a function of crystallinity, matrix orientation, and fibre concentration and orientation. Also, extensive data have been obtained regarding the LTEC of polypropylene with and without fibre reinforcement. Extruded pellets and injection molded parts were considered. Model predictions have been compared with experimental data