Degradation of polyethylene during extrusion. II. Degradation of low‐density polyethylene, linear low‐density polyethylene, and high‐density polyethylene in film extrusion

Citations Over TimeTop 24% of 2003 papers

Abstract

Abstract The degradation of different polyethylenes—low‐density polyethylene (LDPE), linear low‐density polyethylene (LLDPE), and high‐density polyethylene (HDPE)—with and without antioxidants and at different oxygen concentrations in the polymer granulates, have been studied in extrusion coating processing. The degradation was followed by online rheometry, size exclusion chromatography, surface oxidation index measurements, and gas chromatography–mass spectrometry. The degradations start in the extruder where primary radicals are formed, which are subject to the auto‐oxidation when oxygen is present. In the extruder, crosslinking or chain scissions reactions are dominating at low and high melt temperatures, respectively, for LDPE, and chain scission is overall dominating for the more linear LLDPE and HDPE resins. Additives such as antioxidants react with primary radicals formed in the melt. Degradation taking place in the film between the die orifice, and the quenching point is mainly related to the exposure time to air oxygen. Melt temperatures above 280°C give a dominating surface oxidation, which increases with the exposure time to air between die orifice and quenching too. A number of degradation products were identified—for example, aldehydes and organic acids—which were present in homologous series. The total amount of aldehydes and acids for each number of chain carbon atoms were appeared in the order of C5>C4>C6>C7≫C2 for LDPE, C5>C6>C4>C7≫C2 for LLDPE, and C5>C6>C7>C4≫C2 for HDPE. The total amounts of oxidized compounds presented in the films were related to the processing conditions. Polymer melts exposed to oxygen at the highest temperatures and longest times showed the presence dialdehydes, in addition to the aldehydes and acids. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1525–1537, 2004

Related Papers

• → Determination of the Composition of LDPE/LLDPE Blends via 13C NMR(2020)6 cited
• → Calorimetric study of blends of low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) temperature rising elution fractionation (TREF) fractions(1995)37 cited
• → Effects of the processing conditions and blending with linear low‐density polyethylene on the properties of low‐density polyethylene films(1991)29 cited
• → Effect of oxidation and space charge on high-field phenomena of low-density polyethylene prepared by metallocene catalyst(2002)1 cited