Grafting of itaconic acid onto LDPE by the reactive extrusion: Effect of neutralizing agents

Grafting of itaconic acid (IA) onto low-density polyethylene (LDPE) was performed by reactive extrusion where the initiator was dicumyl peroxide, and the neutralizing agents (NAs) were zinc oxides and hydroxides as well as magnesium oxides and hydroxides. The carboxyl groups were neutralized in molten LDPE directly in the course of acid grafting, and in prefabricated functionalized polyethylene (LDPE-g-IA). It was found that neutralizing agents introduced into the initial reaction mixture increase the yield of LDPE-g-IA while the carboxyl groups were neutralized partially or totally through chemical reactions. The physical structure of LDPE-g-IA did not in fact suffer any substantial changes. From the standpoint of neutralization activity, the NAs studied could be arranged as follows: Zn(OH)(2) > ZnO > Mg(OH)(2) > MgO. NA, added into the initial reaction mixture improved the grafting efficiency of IA onto LDPE. In case of the one-step process (neutralization simultaneously with grafting), the neutralizing effect appears stronger than that in the two-step process (neutralization of prepared LDPE-g-IA). This means that neutralization of carboxyl groups in IA was less effective when NA was introduced into LDPE-g-IA than for the case of the initial reactive mixture. Chemical neutralization of grafted IA results in products of improved resistance to thermal oxidation and thermal stability of melt. This result is of practical importance to the opportunities for widening the application range for PE modified by grafting IA, while preparing polymer blends to be compounded, processed, and used at elevated temperatures. (C) 2003 Wiley Periodicals, Inc.