Preparation of bio-based polyurethane hydroponic foams using 100% bio-polyol derived from Miscanthus through organosolv fractionation

Abstract

A novel bio-based polyurethane (BPU) hydroponic foam was developed by substituting up to 100% of petroleum-derived polyol with bio-polyol derived from cost-effective organosolv fractionation of Miscanthus in an acetic acid-water (9/1, v/v) mixed solvent. The optimal operating conditions for organosolv fractionation were determined to be 100 °C for 120 min with 10% H2SO4 (based on dry biomass), yielding ~38% bio-polyol and ~56% crude cellulose. The obtained bio-polyol contains a significant amount of active hydroxyl groups as determined by FTIR and 1H NMR spectra analyzes, with a hydroxyl number of 157 mg KOH/g and a low weight-average molecular weight (Mw = 1900 g/mol). All BPU foam samples were evaluated for their foaming, physical, mechanical, and morphology properties. When compared to a reference foam, all BPU foams had a high open cell content of 70–80% and a maximum water absorption capacity of ~1180%. At 10% deformation, all BPU foams had comparable compressive strengths ranging from 27 kPa to 38 kPa. SEM analysis revealed that all BPU foams, especially the 100% BPU-4 foam sample, had an average cell size of 176 µm, which was comparable to that of a reference foam (172 µm). TGA analysis indicated that these foam samples were thermally stable at temperatures up to 200 °C. This research work demonstrated that the BPU foams containing up to 100% bio-polyols, with their high open cell content and high water absorption capacity, as well as relatively low mechanical strength and good cell uniformity and thermal stability, would find hydroponic application as horticultural growing media.