Formulating for rigid PVC using multivariate analysis

The wide range of lubricants available for rigid PVC, and their complex interactions or synergisms, has meant that the formulator has often had to rely more on quantitative experience, however incomplete, rather than on quantitative data. Multivariate analysis offers the possibility of investigating lubricants and fillers with a relatively small number of rheological experiments and defining their role in a wide range of formulations. A computer program and associated methodology has been developed that allows up to five formulations or fusion parameters to be examined with a maximum of just thirty‐three torque rheometry experiments. The technique generates both first and second order coefficients for each parameter, coefficients that quantify all possible pair interactions, and applies statistical techniques to evaluate the significance of each coefficient. The levels of “internal” and “external” lubricants and fillers, as well as the charge volume and shear rate in the rheometer, have been correlated with fusion peak time and torque, equilibrium torque and melt temperature and other features of the fusion curve. The data are also presented in a series of graphs so that subsequent formulation can be done by interpolation, without further experimentation. The result have sometimes been unexpected and can help in understanding the role of the various additives in the extrusion of rigid PVC.