(289b) Modeling and Control of Interpenetrating Polymer Network Process

Interpenetrating polymer network, IPN, is a broad class of polymer composites which is defined as a combination of two polymers in a network form, with at least one of them synthesized and/or cross-linked in the immediate presence of the other [1]. IPNs have been utilized in widespread commercial applications in many areas, and are considered promising in novel material development due to numerous possible technological applications [2]. The properties of IPNs are found to be closely related with their network structure and joint molecular weight distribution. While a specific polymer structure is desired for various applications, poor control of the process conditions can prevent the formation of the preferred structure, so as to affect the ultimate properties. It is our goal to develop a systematic approach to understand the control of such processes, and provide insights for the material design. Since polyethylene is currently an important commodity polymer product, IPN modification of polyethylene is of particular interest. A polyethylene/polystyrene IPN process is chosen as a case study in this work, and presented in detail.

A comprehensive kinetic model is developed, which involves simultaneous crosslinking, grafting and degradation, to predict IPN gel fraction and molecular weight distribution up to full conversion. Computational expense has been reduced considerably through a new component-decomposition strategy. Continuous variable approximation is applied for monomer polymerization and grafting reactions. Discrete population balance approach is introduced for simulation of the crosslinking reaction as well as simultaneous chain transfer and chain scission. The inter-polymer formulation is reconstructed through a statistical approach. In conjunction with pilot plant experimental studies, uncertain parameters were estimated and validated. Model prediction presents consistent agreement with gel fraction, joint molecular weight distribution and polymer composition experiments. Dynamic optimization approach is further applied to design a new operation policy. The new optimal strategy satisfies product specifications while improving the productivity. This modeling framework suggests a promising approach for IPNs IN industrial practice as well as for the study of complex polymer composites processing.

[1] L. H. Sperling, Interpenetrating Polymer Networks and Related Materials, Plenum Press, New York, 1981.

[2] D. Klempner, K. Frisch, Advances in Interpenetrating Polymer Networks, Technomic Publishing AG,Basle, 1994.