Effect of Drying Methods on the Morphological and Functional Properties of Cellulose Ester Films

This study presents the synthesis and characterisation of cellulose long chain fatty acid ester films using a novel distillable ionic liquid (IL), 5-methyl-1,5,7-triaza-bicyclo-[4.3.0] non-6-enium acetate [mTBNH][OAc] in combination with DMSO as a cosolvent. The cellulose esters cellulose diacetate (CDA), cellulose laurate (CL), and cellulose palmitate (CP) were fabricated through an evaporation-induced phase separation method (EIPS) and dried under two conditions: conventional oven drying (RO) and vacuum oven drying (VO). The influence of drying conditions on the structural, thermal, and surface properties of the films was evaluated using XRD, TGA, SEM, AFM, and contact angle measurement techniques. XRD confirmed an amorphous structure in all films, with no significant effect on the drying conditions. TGA revealed consistent thermal degradation profiles across all samples, with ester group decomposition accruing between 140 and 250 °C and main cellulose backbone degradation near 350 °C. The SEM cross-section showed a uniform film, devoid of cavities and layered structures. AFM analysis demonstrated that VO-dried films had smoother surfaces compared to RO-dried films, correlating with increased contact angles and enhanced hydrophobicity. A strong inverse relationship between surface roughness and hydrophobicity was observed, particularly in VO-dried samples, although this was not statistically significant due to data variability. Overall, the drying method had minimal impact on the internal structure and thermal stability; it significantly influenced surface morphology and wettability.