Grafting of polyethylenes by reactive extrusion. I. Influence on the molecular structure

Abstract

ABSTRACT:Grafting of polyethylenes is an important method used in the modification of polyolefins with functional groups. Lately, the use of extruders as polymerization reactors has increased considerably. However, knowledge of the details of the reaction in the extruder is still limited. In this investigation, the grafting of various commercial polyethylenes, high-density polyethylenes (HDPEs), and linear low-density polyethylenes (LLDPEs) with diethyl maleate (DEM) was carried out in two corotating twinscrew extruders with different screw configurations and extrusion conditions. Two initiators at different concentrations were used. It was found that when the initiator level was raised in the LLDPEs the grafting degree increased and the molecular weight distribution of the grafted LLDPE2 did not show appreciable differences when they were compared to the virgin resin. On the other hand, the terminal vinyl group concentrations decreased at the expense of increasing the trans unsaturation concentrations. This last result is consistent with the formation of long-chain branching. Additionally, the weight-average molecular weight of grafted high-density polyethylene (HDPE1-g-DEM) decreased. The grafting efficiencies were consistent with the attained residence times and also with the kinetics of the decomposition of the peroxides.

FTIR analysis of silane grafted high density polyethylene

“…The peak intensities at 1092 and 1192 cm 21 start to increase, this corresponds to an increase in the quantity of Si-O-C bonds because more VTMOS is present. The peaks at 1092 and 1192 cm 21 were also used to measure the relative amount of silane grafting R. 11,16,20 This was determined by measuring the area of the absorption peaks of the Si-O-CH 3 groups and calculating the ratio of these peaks with respect to the absorbance peak at 719 cm 21 due to (2CH 2 -) n that is chosen to be the internal reference of the polyethylene (remains unchanged during the grafting reactions).…”

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

“…Because PE1 and PE2 had the same structure, the significant difference in the grafting content should have been related to the lower molecular weight (lower viscosity) of PE2. In fact, according to Rosales et al, 14 high-viscosity materials yield lower degrees of functionalization.…”

“…Free-radical initiators such as peroxides have been used to initiate the reaction. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] The grafting process is usually performed in the melt in an extruder, that is, via reactive extrusion (REX). 1,2 It is carried out at elevated temperatures with highly viscous and probably heterogeneous systems.…”

Maleic anhydride‐grafted linear low‐density polyethylene with low gel content

“…Among these unsaturated monomers, maleic anhydride (MAH) is widely used. However, the grafting polymerization of MAH onto PE is often accompanied with side reactions, such as crosslinking, which leads to the high content gels [4][5][6]. Many efforts have been made to enhance the grafting degree (GD) and reduce the gel content (GC).…”