Solubility of additives: Grafting of itaconic acid onto LDPE by reactive extrusion. II. Effect of stabilizers

Abstract

Static and dynamic mixers set on the Brabender plastograph were used to investigate the grafting of itaconic acid (IA) onto low-density polyethylene (LDPE) by the reactive extrusion. The initiators of free-radical reactions were monoperoxide 2,5-dimethyl-2-hydroxy-5-tert-butylperoxy-3-hexyne and diperoxide 2,5-dimethyl-2,5-di(tert-butyl peroxy)-hexane. The reaction mix contained stabilizers of phenolic type as follows: 2,6-ditertbutyl-4-methyl phenol; ester of 3,5-ditert-butyl-4-hydroxyphenyl-propanoic acid and pentaerythritol; 4-alkoxy-2-hydroxy-benzophenone; and 1,4-dihydroxybenzene. The effect of stabilizers, which follow the radical mechanism on the grafting of IA and on the crosslinking, depends on their solubility in the polymer and the monomer. The stabilizers (e.g., 1,4-dihydroxybenzene) with increased affinity toward the monomer reduce the grafting yield and inhibit crosslinking. At 0.3-0.5 wt % of the stabilizer insoluble in the monomer, the grafting yield can be increased, while inhibiting the LDPE-g-IA crosslinking, irrespective of the peroxide used. Hence, classical stabilizers can initiate grafting reactions at raised concentrations, temperatures, and application of the shearing stresses. They also help to obtain a high-grafting yield and a reduced crosslinking degree. A stabilizer, having a close affinity toward LDPE, influences the LDPE-g-IA structure. The stabilizer content of 0.5 wt % transforms the topological structure of LDPE-g-IA into uniblock. Its molecular weight distribution (MWD) may be narrow (M n /M w Ͻ 2) or broad (M n /M w Ͼ 2), depending on the concentration of the initiator used.

Mechanism and Kinetics

“…Pesetskii et al investigated the grafting of itaconic acid onto PE and found that initiator solubility effects were more important than k d values [37] . Furthermore, free -radical inhibitors soluble in polyethylene but insoluble in itaconic acid inhibited crosslinking but did not signifi cantly affect grafting [38] .…”

Functionalization of polyolefin melts containing carbon nanotubes and the properties of their blends with polyamide 6

“…The course of the main as well as the secondary processes depends much on the nature of the radical reaction's initiator and the reaction system's composition, as a whole. In particular, mutual dissolution of reactants in the polymer melt plays an important role in ensuring the grafted product output and in concurrent reactions, which include oligomerization of the monomer being grafted [10,11]. It may be expected that the adsorption of the initiator prepared with an active filler, or some other carrier, added to the reaction system will noticeably affect the course of the main and concurrent processes of PO functionalization.…”

Structure and properties of polyamide 6 blends with low‐density polyethylene grafted by itaconic acid and with neutralized carboxyl groups

“…In recent years, a number of investigations have been made in the field of chemical engineering and structural analysis of low-density polyethylene (LDPE), modified by grafting of itaconic acid (LDPEg-IA) in the course of reactive extrusion [7][8][9][10][11] as well as with carboxyl groups, which were neutralized by oxides or hydroxides of metals (LDPE-g-IA…”