Kinetic study of the synthesis of expandable polystyrene via “multi-stage initiator dosing” method

Abstract

Expandable polystyrene (EPS) produces by free radical suspension polymerization method. In conventional method of the production of this polymer, two different initiators with two different levels of temperature are used and both initiators enter the reactor completely at the very first stage of the batch. The long duration of this process and its difficult control have led to create a new technology called ‘initiator dosing polymerization’ through which the initiator of the first stage enters reactor in several shots and at higher temperatures compared to the conventional method. The result of such an operation is to reduce the process time, reduce the amount of the consumed initiator and increase the absorption of pentane in polymer without any changes in molecular characteristics of the produced EPS. Moreover control of the system in the first stage of the polymerization is much easier. In the present study by the use of kinetic relations, the optimum dosing intervals, dosing temperatures and the amount of the initiator in the “initiator dosing polymerization” method have been identified so that the required conversion at the end of the first stage of the polymerization was achieved. There was a good adjustment of experimental and theoretical data. By the use of the calculated optimal condition in the “initiator dosing method”, there was 5 h reduction in the total time of the polymerization process and 25 % reduction in the amount of the initiator without any effect on the quality of the produced EPS.