Degradation of agar films in a humid tropical climate: Thermal, mechanical, morphological and structural changes

Agar films were subjected to natural weathering exposure in a humid tropical climate for 90 days to determine their biodegradation behavior and functionality. Exposed samples were taken at 15, 30, 45, 60 and 90 days. Mechanical, thermal, structural and morphological properties were determined using tensile test, differential scanning calorimetry (DSC), attenuated reflectance infrared spectroscopy (ATR-FTIR), X-ray diffraction and environmental scanning electron microscopy (ESEM). The photodegradation process and temperature-relative humidity fluctuations promoted a decrease in agar mechanical properties in early exposure stages (30-45 days) caused by a reduction in agar molecular size and a decrease in the number of sulfate groups. These changes alter agar crystallinity, causing contraction that leads to formation of micro-fractures and embrittlement, and promote microbial attack. Accelerated weathering exposure of agar films showed that outdoor climate parameters play an important role in their degradation. These results will aid in further research to determine the potential use of agar as an environmentally friendly solution to the problem of biodegradable composites disposal.