Monitoring polyolefin modification along the axis of a twin-screw extruder. II. Maleic anhydride grafting

The physico-chemical phenomena developing along the screw axis of a twin-sc rew extruder during the grafting of maleic anhydride (MA) onto polyolefins [polyethylene (PE), ethylene-propylene rubber (EPM), and polypropylene (PP) ] were investigated. For this purpose, sampling devices located along the e xtruder barrel were used to collect polymer samples that were subsequently characterized to follow the degrees of grafting and crosslinking or degrada tion. A similar evolution of MA grafting was observed regardless of the pol yolefin type or MA and peroxide concentration when grafting was performed u nder identical conditions, that is, the same peroxide type and set temperat ure. A correlation between the MA grafting and the calculated peroxide deco mposition was established. Chemical reactions occurred along the extruder a xis until the peroxide was fully converted. More detailed quantitative meas urements of the peroxide decomposition and MA grafting would allow the deve lopment of accurate process models. The final MA content depended on the po lyolefin composition (PE > EPM much greater than PP). As expected for PE, c rosslinking occurred in addition to grafting, but after a certain residence time, the PE network degraded. The PP viscosity reduction after MA graftin g was due to the conversion of tertiary PP radicals into primary PP radical s after grafting. (C) 2000 John Wiley & Sons, Inc.