Air bubbles were removed by using an ultrasonic treatment for 10 min(Unique, USC-1400, Brazil).The obtained film solution was placed in polystyrene Petridishes (0.113 g/cm2) and dried in an air circulating oven (DeLeo,B5AFD, Brazil) at 35◦C for 14 h. The films were stored prior to the analyses for a minimum of 48 h, in desiccators with controlled rel-ative humidity, containing a saturated sodium bromide solution(58% RH, 25◦C)