Surfactant-Modified Carboxymethyl Bacterial Cellulose with Tunable Hydrophobic and Thermal–Mechanical Properties

Bacterial cellulose (BC) is a biodegradable, renewable material with exceptional mechanical properties, but its hydrophilicity and rigidity after dehydration limit its broader application in biobased materials including sustainable packaging and related flexible film and coating products. In this work, we report a two-step surface modification strategy to enhance the hydrophobic and thermal–mechanical performance of BC. First, carboxymethylation was performed using chloroacetic acid to introduce anionic carboxyl groups on the BC fibril surface. These negatively charged sites were then modified with cationic surfactants n-decylamine (C10), lauric arginate (LAE), or octadecylamine (C18). The resulting materials were characterized by using contact angle measurements, Fourier transform infrared spectroscopy (FTIR), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Among the surfactants tested, MC18-modified BC showed an increased surface hydrophobicity (contact angle ∼95 vs 32° for unmodified BC), reduced storage modulus (0.5 from 4.8 GPa for unmodified BC) indicating enhanced flexibility, and improved Tmax (314.5 vs 296 °C for unmodified BC). Surfactant-modified BC has the potential to be a more sustainable material that could be used as a substitute for high-density polyethylene (HDPE) films due to its comparable storage and loss moduli (0.8 and 0.8 GPa for storage modulus; 100 and 100 MPa for modified BC and HDPE, respectively).