Cellulose nanofibrils versus cellulose nanocrystals: Comparison of performance in flexible multilayer films for packaging applications

Cellulose nanomaterials (CNMs) are a unique type of nanomaterial that are produced via several routes including chemical and mechanical, including the most researched cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs). CNM films exhibit excellent oxygen barrier properties in medium to low relative humidity conditions. The oxygen barrier characteristics are desirable for CNM film proposed use in food packaging applications where both performance and biodegradability are of concern. However, the oxygen barrier property of CNM films is reduced if films are exposed to high relative humidity (RH) because of moisture-induced plasticizing and swelling. In this research, CNM films were laminated with polypropylene (PP) film using a polyurethane (PU) adhesive tie layer to form flexible multilayer film packaging. The physical properties of the CNM films indicated that CNC films were denser (similar to 1.4 g/cm(3)) than CNF films (1.1-1.3 g/cm(3)). Casting weight affected the densities of the CNM films and this effect was material type dependent. Optical property evaluation showed that the CNC films were clearer than the CNF films. Laminating CNF films with PU improved the transparency of the CNF films. Mechanical test results showed that CNC and CNF laminates containing thicker CNM films had similar maximum tensile strength as the control PP/PU laminates. Laminating CNM films with PP and PU significantly improved the barrier properties of the CNM films. For example, the water vapor transmission rate of CNC film dropped from 516 to 1.0 g/(m(2).day). The oxygen transmission rate of CNC film at 80 % RH decreased from 126 to 6.1 cm(3)/(m(2).day).