Unburned Sugarcane Bagasse: Bio-based Phenolic Thermoset Composites as an Alternative for the Management of this Agrowaste

Brazil has played a leading role in the global cultivation of sugarcane, used in the production of sugar and ethanol, which results in sugarcane bagasse as agrowaste. This agroresidue generates electricity and second-generation ethanol, but the colossal amount available allows for alternative applications. Currently, mechanized harvesting/unburn predominates over manual harvesting/burn. The present study was conducted in this scenario and investigated the use of fibers from unburned sugarcane bagasse (SBU) in bio-based composites. Phenolic thermoset was chosen as a matrix due to its excellent properties. The mechanization/unburn method allows the use of variable length fibers (this study: 1/3/5 cm, 30 wt%). SBU was characterized in detail, highlighting the characterization via inverse gas chromatography (IGC, which provides information regarding the polarity of the groups present on the surface of the fibers). Briefly, the composition of SBU shows no significant differences compared to burnt bagasse (SBB), and IGC showed that SBU has more polar groups on the surface than SBB, which favors intermolecular interactions and then adhesion with the phenolic matrix. Composites reinforced with 3- and 5-cm fibers presented a storage modulus higher than that of the unreinforced thermoset, and the impact strength of all composites was higher than that of the thermoset (up to 45%). This set of results points to applications such as rigid packaging, non-structural parts of buildings and automotive vehicles, which increases the applications of the investigated agrowaste within the circular bioeconomy.