Thermal Oxidation and Structural Changes of Degraded Polyethylene in an Oxygen Atmosphere

Abstract

High-temperature bulk thermolysis of high density polyethylene was performed to obtain degraded polyethylene, which was then left in an oxygen atmosphere for oxidation reaction at 160 • C at different oxidation times, yielding a series of polyethylene degradation-oxidation products. Using infrared spectroscopy, chemical titration, gel chromatography, and differential scanning calorimetry, the structural changes of the polyethylene degradation-oxidation products were investigated. Hydroxyl, carboxyl, ester, and other functional groups were introduced into the molecular chains of oxidation products, and the number of carboxyl groups sharply increased with increasing oxidation time. The breaking of molecular chains as well as combination reactions, such as esterfication, during the oxidation process lead to decrease of number-average molecular weight (M n ) and increase of both weight-average molecular weight (M w ) and molecular weight distribution, and an initial increase and leveling off of the carboxyl number per molecular chain. It is noteworthy that oxidation occurred primarily near weak bonds, mainly terminal vinyl unsaturations. Thus, compared with degraded polyethylene, the oxidation products showed little changes in the melting and crystallization behaviors; even when the oxidation time was up to 4 hr, the drop in the melting and crystallization temperature was less than 3 • C. These results might lay a foundation for exploring tailored low molecular weight polymers to be used just as they are or after chemical modifications of olefinic functions.

Degradation of Conventional and Oxodegradable High Density Polyethylene in Tropical Aqueous and Outdoor Environments

“…The degradation of each material caused the appearance of bands between 1800 and 1600 cm -1 , which can be assigned to ketones. This results agrees with those published by other researchs (Chiellini et al 2006, Huang et al 2011, Krehula et al 2014, de la Orden et al 2015. Figure 7 shows the average results of measurements of the absorbance of the carbonyl index during the experiment.…”

Rotational Rheology of Wood Flour Composites Based on Recycled Polyethylene

“…Generally, in presence of oxygen and high temperatures, the oxidation process of polyethylene starts from weak bonds close to terminal vinyl groups and generates oxygen-containing groups, such as alcohol, ketone, acid, and so on [ 43 ]. In the samples treated at 220 °C compared to pristine r-PE, it can be noted: (i) the formation of a shoulder in correspondence of 1713 cm −1 (close to the peak at 1720 cm −1 , typical of carbonyl groups), which can be correlated to the presence of ketones; (ii) the reduction in the peak at 1650 cm −1 , which can be linked to a decrease in double bonds [ 41 ]; (iii) a small increment in intensity at 1377 cm −1 , which can be due to the occurrence of branching.…”

On the influence of morphology and chemical defects on charge transport dynamics in polyethylene: thermal ageing and concentration gradient

“…Anandakumaran and Stonkus [45] also reported comparable behavior, in the case of XLPE and ethylene/propylene rubber samples aged for periods of up to 24 000 h at temperatures ranging from 115 °C to 140 °C; this work reported that the induction time was reduced by approximately 50% on increasing the ageing temperature by 10 °C. Indeed, Huang et al [46] reported an induction time of just 2 h when a temperature of 160 °C was employed to age HDPE. As such, the effect of thermal ageing on carbonyl concentration seen at the oxidised surface in figure 3 is consistent with published data.…”