Susceptibility of starch-filled and starch-based LDPE to oxygen in water and air

Abstract

ABSTRACT:The susceptibility of starch-filled and starch-based polyethylenes to oxygen in water and air was analyzed and compared. LDPE containing 7.7% starch and a prooxidant formulation in the form of masterbatch (LDPE-MB) was compared to pure LDPE, LDPE with 7.7% starch (LDPE-starch), and a blend with 70% starch and 30% ethylene maleic anhydride (starch-EMA). Thermal ageing at 80ЊC in air and water was followed by monitoring the molecular weight changes, the formation of carbonyl groups, and degradation products by SEC, FTIR, and GC-MS. It was demonstrated that LDPE-MB was the most susceptible material to degradation in both environments, although the degradation was faster in air than in water. The slower degradation in water is explained by a deactivation or leaching out of the pro-oxidant during the aging. The degradation of pure LDPE and starch-EMA is faster in water than in air. LDPEstarch was the only material that did not degrade during 11 weeks in water at 80ЊC. The addition of starch to LDPE made this material even more stable than pure LDPE to aging in water. The molecular weight distribution of LDPE-MB narrowed during aging in air. In water, on the other hand, the MWD of LDPE-MB, LDPE, and LDPEstarch broadened. The lower oxygen concentration in water increases the probability for molecular enlargement reactions in comparison to the case in air. Mono-and dicarboxylic acids were the major products identified in both environments. Ketoacids were formed in both air and water, but ketones and hydrocarbons were only identified after aging in air. Either these products are not formed or they remain in the polymer matrix rather than migrate out into the water. Lactic acid and 2-furancarboxaldehyde were only identified in the starch-EMA material degraded in water at 80ЊC. LDPE, LDPEstarch, and starch-EMA did not form any degradation products during 11 weeks at 80ЊC in air in agreement with the neglible molecular weight changes observed.

Development of a solid-phase extraction method for simultaneous extraction of adipic acid, succinic acid and 1,4-butanediol formed during hydrolysis of poly(butylene adipate) and poly(butylene succinate)

“…We have earlier applied SPE for extraction of mono-and dicarboxylic acids, hydroxyacids, ketones, ketoacids, aldehydes, hydrocarbons, lactones and alcohols after aging of polyesters and degradable polyethylenes [4,7,8,[16][17][18]33,34]. Identification and quantification of degradation products formed during hydrolysis of aliphatic polyesters can be a tedious procedure including many extraction steps.…”

“…solid phase microextraction and GC-MS analysis of the degradation products showed oxidation-induced changes in recycled and thermo-oxidized polyamide 66 considerably earlier than tensile testing, FTIR or DSC [1,2]. The amount and type of degradation products formed was also in good correlation with the degree of degradation in the polymer matrix [2][3][4]. Among other methods used to analyze polar degradation products from polymers, HPLC in combination with atmospheric pressure chemical ionization mass spectrometry (APCI-MS) and electrospray ionization mass spectrometry (ESI-MS) can be mentioned [5].…”

Oxo‐Biodegradable Polymers: Present Status and Future Perspectives

“…Carboxylic acids tend to accumulate during prolonged exposure times since other oxygen -containing products formed in the early stages of the degradation process, such as alcohols, aldehydes, and ketones, are susceptible to further oxidation to produce carboxylic acids. In classic studies [18,19] , most of the lowmolecular -weight degradation products from both thermally -and photooxidized PE have been isolated and identifi ed by solid -phase extraction coupled with gas chromatography/mass spectrometry. Accordingly, numerous semivolatile compounds have been identifi ed [17] including alkanes, alkenes, ketones, aldehydes, alcohols, mono -and di -carboxylic acids, lactones, keto -acids, and esters.…”

“…Owing to their relative thermal stability (compared to photoinstability), ketone groups are considered as typically associated with the thermal degradation of PE. Other products, recognizable in the volatile and semivolatile fractions of PE oxidation products, such as keto -acids, have been identifi ed during low -temperature thermal degradation, whereas lactones are usually generated under extreme conditions or after extensive degradation has occurred [18,19,21] .…”

Photodegradable Polymers

“…This contrasts with the photolytic E-CO polymers where their product analysis revealed higher concentrations of vinyl and methyl ketones in support of the more important role that Norrish II process plays in these polymers [29]. The identity of more than 200 abiotic oxidation products from various classes of degradable polymers have been examined extensively using a wide range of analytical techniques with the conclusion that the most dominant class of the final degradation products is aliphatic carboxylic acids [55][56][57][58].…”