INFLUENCE OF REACTOR CONDITIONS, ANTIOXIDANT, AND PROCESSING ON THE DEGRADATION OF LDPE

The extrusion of LDPE was simulated under well‐defined conditions by using a Brabender Plasti‐Corder. The grades tested according to gel formation were synthesized in a modified autoclave reactor. With the basic synthesis conditions the same two different reactor pressures were used and at both pressures, two melt index levels were maintained. The two grades with the lower reactor pressure were synthesized under two‐phase conditions. With the Brabender Plasti‐Corder the influence of melt temperature, mixing efficiency, mixing time, as well as BHT content was investigated. By studying the torque, the gel content, and the change in molecular weight distribution, the following results were obtained. LDPE synthesized under two‐phase conditions is sensitive to gel formation, and this can be more easily seen when the melt index is low. Gel formation was also found to increase with increasing melt temperature and increasing mixing time. The effect of mixing efficiency was minor. When the polymer contained BHT, there was a decrease in torque drop as well as gel content. The Brabender curves had peaks indicating molecular enlargement; and when using more BHT, these peaks developed at a later moment. From the GPC data it can be seen that combination of secondary radicals is typical for the two‐phase grades, whereas stripping of LCB predominates for the single‐phase grades. Copyright © 1979 John Wiley & Sons, Inc.