Analysis of the oxypropylation process of a lignocellulosic material, almond shell, using the response surface methodology (RSM)

Developing polyols from abundant and renewable biomass resources is an important topic for polymer synthesis. In this work, the Response Surface Methodology (RSM) was applied to a novel oxypropylation case study, almond shell (AS), an agroindustry lignocellulosic by-product. Mathematical models were developed to determine responses maximizing the reaction efficiency to yield polyols with specific technical requirements (polyols suitable for rigid polyurethane foams; hydroxyl index between 300 and 800 mgKOH/g, and viscosity below 300 Pa*s). In a general way, the properties of the obtained polyols were within the range of the ones currently used commercially, reinforcing the interest to exploit lignocellulosic bio-residues for polyol synthesis. For simultaneous minimization of homopolymer content and unreacted biomass, values of 14.0% and 14.1% were achieved, respectively. This was attained using a formulation with an AS/PO ratio of 20.1/79.9 g/ml and a catalyst content of 3.14%, giving rise to a polyol with an hydroxyl index of 392.1 KOH/g and a viscosity of 107.4 Pa*s. Overall, the advantages of using RSM to better understand complex reactive systems and the interest to use these statistical approaches as decision-making tools was demonstrated.