Sustainable composites of surface-modified cellulose with low-melting point polyamide

The present study proposed a series of sustainable polyamide/cellulose composites with up to 60% bio-based content to address environmental issues arising from using fossil-based polymers. Furthermore, it addressed one of the most challenging cellulose/polymer composites' issues, filler/matrix compatibility. Accordingly, the microcrystalline cellulose (MCC) surface was treated through the grafting of n-octadecyl isocyanate (ODI) molecules. The elemental analysis confirmed the substitution of approximately 9 ODI molecules per 100 anhydroglucose units, resulting in superhydrophobic MCC formation with a water contact angle of 130°. The surface-modified MCC was melt blended with a bio-based low–melting point polyamide, developed through copolymerization of 11-aminoundecanoic acid and 12-aminolauric acid. Scanning electron microscopy images confirmed no evidence of surface-modified MCC agglomeration, even at a high loading of 30 wt%, suggesting a uniform dispersion of the filler particles and excellent compatibility between two phases. Consequently, the storage modulus, tensile modulus, and yield stress were enhanced by 40%, 100%, and 50%, respectively, in the composite sample with 30 wt% of MCC, proving excellent stress transformation from the matrix to particles arose from good adhesion between cellulose particles and polyamide chains. Furthermore, all samples revealed suitable melt flowability and viscoelastic performances, suggesting their excellent processability, a critical property for engineered thermoplastics. On top of that, the presence of the surface-modified particles considerably decreased water uptake capacity and water vapor transmission of the polymer matrix, making it interesting for specific applications like packaging films.