Dry fractionation of olive pomace as a sustainable process to produce fillers for biocomposites

Abstract

Olive pomace (OP) is the agro-industrial residue of olive oil extraction composed of residual pulp and stone. This work aims at exploring the possibility of using dry fractionation (combination of grinding and sorting processes) to produce pulp-rich and stone-rich fractions with the highest purity and yield. The physical-chemical characteristics (composition, thermal stability, color, surface free energy) of the obtained powders were discussed in relation to the applied processes. It was shown that dry fractionation could be successfully used to convert OP into valuable fractions using processes avoiding the consumption of water and the generation of effluents or co-products. Results revealed that the separation of the pulp from the stone using friction solicitations in a ball mill operating in mild conditions (2min at a frequency of 15Hz) was as efficient as wet fractionation in terms of powder characteristics, achieving a total yield of 99.4% against only 82.1% in the case of wet fractionation and without using water while a water:biomass ratio of 5:1 was required for wet fractionation. Produced powders exhibited contrasted biochemical composition (either rich in lignin or cellulose) and surface free energy, and were thermally stable up to at least 210°C. It was concluded that they could be interestingly used as raw resources for the production of fillers that will be further incorporated in polymer matrices to produce a range of biocomposites.