Key properties towards citrus nanostructured cellulose processing:A rigorous DoE study of the Hy-MASS concept

A detailed design of experiment (DoE) study to investigate cause-effect interaction of three process variables: temperature (120-200 °C), holding time (0-30 min) and concentration (1.4-5.0 wt.%), on processing of citrus cellulosic matter using acid-free microwave-assisted selective scissoring (Hy-MASS) is reported. Analysis of variance (ANOVA) showed that post microwave processing, yield of cellulosic matter (25-72 %), decomposition temperature (345-373 °C) and crystallinity index (34-67%) were strongly affected by temperature. SEM and TEM analyses showed that the isolated cellulosic matter was heterogeneous comprising a mixture of micro- and nano-fibres more akin to microfibrillated cellulose (MFC) at low processing temperatures and tending towards aggregated cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC) at higher temperatures. The water holding capacity of the processed cellulosic matter (15-27 g H2O·g-1) was higher than the original feedstock or previously reported values. The average molecular weight of the cellulosic matter (113.6-1095.9 kg·mol-1) decreased significantly by a factor of 10 above 180 °C, invoking significant scissoring of the cellulosic chains. The process energy input and costs varied between 0.142-0.624 kWh and 13-373 €/kg, respectively, and were found to be strongly dependent of the reaction time.