Morphological and Thermochemical Changes upon Autohydrolysis and Microemulsion Treatments of Coir and Empty Fruit Bunch Residual Biomass to Isolate Lignin-Rich Micro- and Nanofibrillar Cellulose

Autohydrolysis and microemulsion treatments followed by microfluidization are employed to isolate micro- and nanofibrillar cellulose (MNFC) from coir fibers and palm tree empty fruit bunches (EFB) with residual lignin content of ∼24 and ∼31 wt %, respectively. The fibers and associated MNFC are characterized in each treatment for their chemical, structural, and thermal properties. The most significant findings include the fact that two MNFC populations are produced, with distinctive structural differences and characteristic lateral dimensions of 20-70 nm and 1-3 μm. The lignin distribution after possible recondensation occurred in the form of nanodroplets. Finally, a correlation between thermal degradation of MNFC with spatial arrangement of lignin is hypothesized and a defibrillation mechanism is proposed. The detailed structural and thermochemical analyses presented here are expected to facilitate further interest in the development of new materials from MNFC isolated from coir and EFB, two abundant bioresources that are most suitable for their valorization.