The stability of poly(lactic acid) packaging films as influenced by humidity and temperature

The effect of moisture sorption on stability of poly(lactic acid) (PLA) films at food-packaging conditions, obtained by different humidities (11 % to 98% RH) and temperatures (5 degrees C and 25 degrees C), was investigated by decrease in number average molecular weight (M) and loss of tensile strength. Hydrolysis of the PLA ester linkages resulted in a 75% decrease over 130 d at 25 degrees C and 98% RH. At cooling conditions the decrease amounted to 35%. An equilibrium moisture sorption isotherm could not be determined as the irreversible hydrolysis of PLA induced an ongoing moisture uptake. The rate increased when the humidity and temperature increased from 5 degrees C to 25 degrees C. After 189 d at 98% RH, moisture sorption was 7 g/100 g and 86 g/100 g at 5 degrees C and 25 degrees C, respectively. Loss of tensile strength was minor and primarily due to reversible plastization by moisture. Only at 98% RH and 25 degrees C, loss of tensile strength became pronounced (45%). Consequently, the present PLA material is in general expected to be mechanically stable when packaging foods covering the region from dry to moist food and storage conditions from chill to ambient temperatures.