Effect of calcium carbonate nanoparticles on the soil burial degradation of polybutyleneadipate-co-butylenetherephthalate films

A polybutyleneadipate-co-butylenetherephthalate (PBAT) sample, commercially known as Ecoflex®, was processed via melt extrusion with calcium carbonate (CaCO3) nanoparticles (average diameter = 70 nm, specific surface area = 17 m2/g) coated with a hydrophobic coating made of a mixture of calcium stearate and calcium palmitate. Blown films (average thickness = 40 ?m) of PBAT and two composites with a filler content of 2 wt% (PBAT-2%) and 5 wt% (PBAT-5%) were prepared and degradation test in soil up to 180 days carried out. Additionally, biodegradation test according to ISO 14851 was carried out. The effect of the addition of CaCO3 nanoparticles on soil burial degradation was assessed by surface wettability and scanning electron microscopy (SEM). Weight loss measurements were used to follow biodegradation in soil. Attenuated Total Reflection-Fourier Transform Infra-Red (ATR-FTIR) and X-ray Photo electron Spectroscopy (XPS) analyses highlighted chemical modifications induced by soil degradation. CaCO3 nanoparticles decreased surface wettability and discouraged the disintegration in soil of the PBAT-2% and PBAT-5% film samples. SEM showed no significant changes on the morphology of the materials with the addition of CaCO3 nanoparticles. Interestingly, SEM imagines after soil degradation highlighted in the PBAT-2% and PBAT-5% films selective zones of disintegration. In agreement with the literature, XPS showed an increasing peak area C1s ratio of C-O to C=O with degradation time. Moreover, carbonyl index determined by ATR-FTIR for virgin PBAT was unchanged, while in nanocomposites it increased after the soil burial test. In fact, the addition of CaCO3 nanoparticles leads to a rise in the area of the carbonyl zone due to the presence of the carbonate group. Overall, the results revealed that polymer films after biodegradation in soil have a higher carbonate content than initial samples.