Robustness Study of a Tensile Modulus Prediction Model for Semicrystalline Polymers

This work presents a robustness study of a previously developed empirical model that links Young's modulus to two key parameters of crystalline structure; crystallinity and lamellae thickness. The reliability of this modulus prediction model was tested by using different calorimeters and different polypropylene grades as well. Small samples were fabricated from injection-molded bars from different locations of the specimens in order to check the effect of structural inhomogeneity originated by the dynamic processing conditions. In addition, the standard deviation and consequently the accuracy of the prediction was tested by repeated calorimetric measurements. The crystalline structure and melting characteristics were measured by differential scanning calorimetry (DSC). The tensile properties of studied specimens were evaluated by standardized tensile tests. Although, the accuracy and reliability of the prediction model is dependent on the instrument used for thermal analysis, reasonably good agreement was found between the predicted and measured values in most cases. However, we may note that only well-calibrated calorimeters are suitable for reliable prediction of the modulus.