Effect of γ-irradiation and antimicrobial agent on properties of poly(L-lactide) active films

Data on irradiation of poly(L-lactide) (PLLA) based active packaging is still limited. Therefore, effect of gamma-irradiation on neat PLLA and active packaging with oligohexamethylene guanidine hydrochloride (OHMG<middle dot>HCl) has been studied. Combined use of irradiation and active packaging technology is promising approach to maintain food safety and prolong shelf life. It has been found that regardless of the OHMG<middle dot>HCl content PLLA undergoes chain scission during irradiation and this process becomes less pronounced at doses higher than 50 kGy. Slight racemization of PLLA during exposure has been observed using polarimetry and C-13 NMR spectroscopy. Mechanical properties of films have been examined. Biocide addition led to a 30% decrease in films elongation at break. Irradiation either caused elongation decrease. Dose of 50 kGy and higher made PLLA active films brittle. Multiple melting behavior of irradiated PLLA has been analyzed by differential scanning calorimetry. Fraction of crystals with higher melting temperature rose with dose. Possible reason for this phenomenon is formation of alpha ' form with less ordered chain packaging that recrystallizes during heating. The biocide addition has not affected this process. Furthermore, in vitro antimicrobial test has shown efficacy of films with 2 wt.% of OHMG<middle dot>HCl against gram-negative, gram-positive bacteria and fungi.