Comparative effects of cobalt carboxylates on the thermo‐oxidative degradation of LDPE films

Abstract

This article reports the effect of three cobalt carboxylates-cobalt stearate (CoSt 3 ), cobalt palmitate (CoPal 3 ), and cobalt laurate (CoLau 3 )-on the thermo-oxidative degradation of low-density polyethylene (LDPE) films prepared by sheeting process. The carboxylates were blended with LDPE in the concentration range of 0.05-0.2% (w/w). The degradation was monitored by techniques such as FTIR spectroscopy, change in the mechanical properties (tensile strength and elongation at break), viscometry, surface electron microscopy, melt flow index measurements, and apparent density measurements. Studies indicate that films containing these additives are highly susceptible to thermooxidative degradation. Oxygen containing functionalities such as carbonyl and vinyl species are generated on the surface of polyethylene because of thermo-oxidation, as indicated by FTIR studies. This oxidative process is accelerated in the presence of cobalt carboxylates. The degradation of LDPE was found to increase proportionally with concentration as well as with increasing chain length of the cobalt carboxylate, and follow the order CoSt 3 > CoPal 3 > CoLau 3 .

Investigating the role of metal oxidation state on the degradation behaviour of LDPE

“…The increase in crystallinity also contributes to the embrittlement of the films as well as other factors like reduced molecular weight and/or photo crosslinking of the polyethylene chains. The cracks formed as a result of the embrittlement can be observed in the SEM micrographs and such observations have been reported in our previous papers [7][8][9].…”

“…It is well known that transition metals can exhibit variable oxidation states and it is this characteristic property that is responsible for their pro-oxidant nature. Although there have been several studies on the degradation behaviour of polyethylene films containing transition metal stearates [5][6][7][8], literature on the activity of a transition metal in its common oxidation state is scarce. The central metal responsible for the prooxidative ability usually belongs to the first transition series like manganese, iron and cobalt as stearates, all of which have the capability to exist in both þ2 and þ3 oxidation states.…”

Europium Stearate Additives Delay Oxidation of UHMWPE for Orthopaedic Applications: A Pilot Study

“…The samples also were placed at an angle with respect to the plane perpendicular to the incident ray to diffract the light incident on the surface. Spectra were normalized at the 2020 wave-number CH 2 twisting peak, which has been shown to remain relatively unaffected by the changes in the polymer structure induced by thermal, high-energy, or mechanical treatments [5,8,31].…”

“…Some joint implants consist of a metal or ceramic component articulating against UHMWPE [18,20]. Degradation of this polymer leading to implant failures related to fatigue, wear, and others [20,26,42] can be accelerated or exacerbated as a result of oxidation of the polymer during storage and service [4,11,18,[31][32][33][34][35][36][37].…”

Prediction of processing parameters of secondary polyethylene with iron carboxylates in the preparation of prooxidants’ additives

“…Известно [5], что широко применяемые методы контроля технологических свойств тер-мопластичных материалов, например, измере-ние ПТР, не могут достаточно точно описать поведения перерабатываемых полимерных композиций в экструзионном оборудовании.…”