Photo-oxidative weathering of biodegradable nanocomposite films containing halloysite

This study reports the results of photo-degradation experiments performed on biodegradable nanocomposite blown films based on a commercial grade of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/ poly (butylene adipate-co-terephthalate) (PBAT) blend added with different amounts (3, 5 and 10wt%) of tubular halloysite nanoclays, natural and organomodified. The films, subjected to photo-oxidative weathering in a climatic chamber under UV exposure, were systematically analysed in order to check the chemical-physical changes induced by the aging protocol, taking the as-produced films as the reference materials. In particular, the samples were characterized using several techniques (colorimetry, water contact angle tests, UV-Vis and ATR-FTIR spectrophotometry, X-ray diffraction, oxygen permeability and mechanical tests). The experiments demonstrated that all nanocomposite films, compared to the unfilled one, show higher changes in the total color difference ?E* and higher reduction in the average transparency, due to the changes in the molecular structure of the polymer (hydrolysis of the ester linkage, multiple chain scissions and crosslinking), as it came out from ATR-FTIR analysis. The phenomenon, which basically involves the amorphous phase, tends to increase with the nanofiller percentage in the films and is more relevant in the presence of the organomodified halloysite. As a consequence of the photodegradation of the amorphous polymer chains that increase their molecular mobility, the oxygen permeability worsens, even in presence of the nanofillers. Instead, in terms of mechanical response, the addition of pure and organomodified halloysite to polymer matrix had positive effects on tensile properties both before and after photo-oxydation.