Unveiling the Role of Ultrasonication Variables on Lignin-Containing Cellulose Nanocrystal Dispersion in Poly(ethylene oxide)-Based Suspension and Resulting Morphology and Mechanical Properties

The biodegradability, abundant availability, and outstanding intrinsic properties of cellulose nanocrystals (CNCs) make them suitable candidates for functionalizing polymer materials. Lignin is another abundant material in nature and is a remarkable UV-blocking agent. Hence, their combination can produce a material with multifunctional properties. However, the self-assembling ability of CNCs can make it challenging to develop their well-dispersed suspension in polymer-based aqueous solutions. However, it is essential to identify the effective ultrasonication parameters to obtain the desired particle sizes and morphology. This study investigated the role of ultrasonication treatment in dispersing lignin-containing CNCs (L-CNCs) within the water-soluble poly(ethylene oxide) (PEO). The aqueous suspensions were prepared by dispersing L-CNC in 1 wt % of PEO solution, where varying ultrasonication times (3, 6, and 9 min) and different amplitudes (50 and 100%) were employed. The morphology, particle size, and dispersion of L-CNCs were analyzed by using zeta potential analysis, and scanning electron microscopy. Mechanical and physical properties were also assessed through dynamic mechanical analysis, differential scanning calorimetry and fourier transform infrared spectroscopy. The results indicated that an increase in sonication time and amplitude could significantly influence the dispersion of L-CNCs within the PEO polymer matrix, as evidenced by the increase in the zeta potential. Increased sonication time and amplitude improved dispersion and reduced the size and number of agglomerations. Ultrasonication at 100% amplitude for 9 min resulted in a 400% and more increase in the storage modulus of composite films. The comprehensive results obtained from this study aim to enhance our understanding of optimal ultrasonication parameters, contributing to an improved L-CNC dispersion and enhanced composite material performance.