Tailoring surface energy of cellulose nanocrystals (CNCs) via low-pressure plasma polymerization to control the interfacial properties in polycaprolactone (PCL)/CNC nanocomposite

Interfacial properties of nanomaterials and polymer matrix in nanocomposites strongly affect not only the dispersion of nanomaterials within the matrix, but also the mechanical properties and performance of nanocomposite. This work is aimed at providing a facile and single-step method for tailoring surface energy of cellulose nanocrystals (CNCs) to control the interfacial properties of polycaprolactone (PCL)/CNC nanocomposite. 1H,1H,2H,2H-perfluorodecyl acrylate (PFDA) monomers were polymerized on the surface of CNCs using low-pressure plasma polymerization. The success of polymerization process was verified by a variety of analytical techniques. As a direct consequence of dominance of polymerization or ablation processes, CNCs with various surface energies ranging between 8.0 and 42.4 mJ/m² were successfully obtained by changing plasma power and duration in both continuous and pulse modes, and pulse-off time in pulse mode. The unmodified and modified CNCs with known surface energies were added to the PCL-based solution to make PCL/CNC nanocomposites with different interfacial properties through dry casting. Using DMTA and tensile measurement experiments, it was demonstrated that the compatibility of surface energies between two components of a nanocomposite, i.e., nanoparticle and matrix, is of paramount importance to enhance the dispersion of nanomaterials within the matrix as well as controlling the interfacial properties to reach the desired mechanical properties. Using modified CNCs with tailored surface energies, T_g, Young’s modulus and tensile strength of the PCL/CNC nanocomposite were increased by approximately 13.4%, 23.6% and 14.8%, respectively, with respect to the neat PCL film. These values for unmodified CNCs were about 11.1%, 17.9% and 0%, respectively.