Structures and Properties of Biaxially Oriented Polypropylene Films after Annealing Treatments
Biaxially oriented polypropylene(BOPP)films with excellent optical and mechanical properties play an important role in the packaging field.However,in the southern weather with high temperature,BOPP films tend to shrink,resulting in fold defects and product deformations.The post-shrinkage of BOPP films strongly affects the gas emission,beauty,cost and the sales.The evolutions of structures and properties of BOPP films during the annealing at 40-80 ℃ were systematically investigated by differential scanning calorimetry,wide-angle X-ray diffraction,gloss meter,tribometer,haze meter,tensile testing machine,heat sealer,and thickness gauge.The results show that the longer the annealing time and the higher the annealing temperature,the larger the shrinkage rate of BOPP films,the higher the crystallinity and crystal orientation after annealing.Meanwhile,the thickness,haze,friction coefficient,gloss,and heat seal strength change little,while the shrinkage rate decreases and tensile strength increases.This study provides theoretical guidance for improving the post-shrinkage of BOPP films.