The aim of this work is to investigate the effects of molecular weight distribution on some conventional flow properties of polyolefins like melt flow index, melt flow ratio, and power law index. The study is designed in two steps. First, the statistical correlation analysis was carried out for proper choice of input variables for each output property and to find the most relevant mathematical forms of the considered parameters for the modeling section. Then the considered property was correlated to the entire molecular weight distribution using spline functions. The best fit was achieved by variation of the number of spline nodes and their values. The proposed methodology is able to be coupled with a polymerization model to correlate the polymerization conditions to the final properties of the product and design a polymerization control loop.

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In the previous paper (Zahedi et al., 1 J Appl Polym Sci, to appear) the optimal conditions of a new modeling procedure for correlating a scalar response to an input spectrum were established. In this article the developed model is applied to correlate the stress-strain behavior of several commercial high density polyethylene samples to the spectrums of microstructure and morphology. Molecular weight and lamellar thickness distributions were considered as the input spectrums and Young modulus, stress and strain at the yield and break points were considered as the objective responses. The shape of the kernel functions over molecular weight and lamellar thickness distribution spectrums for each mechanical property gives an explanation of how different regions of the spectrums contribute to create the considered property. The simplicity of the procedure facilitates the interpretation of the complex influences and interactions of different structures and morphologies in various aspects of the mechanical performance of the samples. The proposed model can be used in designed experiments with samples of controlled microstructure and morphology to provide detailed information about the structure-property relationships.