Abstract
Thermo-oxidation of blown low density polyethylene (LDPE) ®lms modi®ed with di€erent combination of biodegradable ®ller, prooxidant and photosensitizers was conducted in oven at 60 and 100C for a period of 14 days. Volatile and semivolatile degra- dation products were extracted by solid phase micro extraction (SPME) technique and identi®ed utilizing gas chromatography± mass spectrometry (GC±MS). Chemical and morphological changes were monitored and these are given as carbonyl index, crys- tallinity and melting behavior, molecular weight and molecular weight distribution. The samples containing solely prooxidant showed the highest susceptibility to thermal degradation during the test period. The second most degradable samples were LDPE modi®ed with 20% masterbatch (containing starch and a prooxidant). LDPE containing only starch did not show any degradation during the test period. The major degradation products were homologous series of carboxylic acids, ketones, hydrocarbons and lactones. 4-Oxopentanoic acid, 5-oxohexanoic acid and benzoic acid were identi®ed only in LDPE containing prooxidant (LDPE-
PO) and LDPE modi®ed with 20% masterbatch (LDPE-MB). A small number of aldehydes (3-methyl pentanal, benzaldehyd and
2-propyl 5-oxohexanal) were identi®ed solely in LDPE-MB. Esters could be identi®ed only from LDPE-Starch and pure-LDPE samples. The crystallinity of all the samples increased after aging at 60C except for LDPE-Starch which showed no signi®cant change in crystallinity. The melting thermograms of LDPE-PO and LDPE-MB (®rst heating) exhibited low temperature shoulders around 75C (after treatment at 60C) and appears to move downward with increasing exposure temperature (treatment at 100C).
The shoulders near 115C (second heating) increase with increasing exposure temperature which is due to a preferential scission at the tertiary carbon atom as observed by increased crystalline melting point. ATR and transmission FTIR show that