Assessment of UV exposure and aerobic biodegradation of poly(butylene adipate-co-terephthalate)/starch blend films coated with radiation-curable print inks containing degradation-promoting additives

Biodegradable poly(butylene adipate-co-terephthalate) (PBAT) and thermoplastic starch (TPS) blend films were printed with white, yellow, red, blue, and black inks based on epoxy acrylate resin. Clear PBAT/TPS films were used as the control. Ink formulations were also modified with (1% w/w) and without the degradation-promoting additives cobalt stearate (CoSt) or cerium stearate (CeSt). Printed PBAT/TPS films were cured under ultraviolet light emitted by a medium-pressure mercury lamp at 10.3 kW m−2, and then further aged in a accelerated weathering chamber at a total irradiance of 0.89 W m−2 continuously for 250 h at 50 ± 3 °C. Subsequently, samples were exposed to an aerobic composting biodegradation process at 58 °C and 55% relative humidity for 60 d. Color (L*, a* and b*), gloss and hardness indexes, as well as FTIR spectra, were obtained. Thermal properties and molecular structure were monitored before and after UV exposure and biodegradation tests. The addition of CoSt affected the color, gloss and hardness of the samples exposed to UV aging. The degradation of the PBAT/TPS + CoSt films depended on the nature of the ink pigment and on their capacity to absorb UV photons. UV exposure of PBAT/TPCS samples resulted in a larger reduction of weight average molecular weight (M¯w) and the evolution of CO2. The incorporation of the degradation-promoting additives increased the sensitivity of the films to UV degradation, and CoSt had a large impact in the final M¯w of the samples.