Effect of Blending and Conjugation of Carboxymethyl Cellulose and Zein in Bioplastic Materials

Carboxymethyl cellulose (CMC) can be extracted from agricultural waste and better employed in the formulation of bioplastics to promote sustainability. Zein, a hydrophobic prolamin protein that can be obtained from industrial wastes of the corn industry. It may be combined with hydrophilic CMC, resulting in composite materials where both functionalities are synergistically enhanced. In the zein/CMC systems studied in the present work, CMC was added directly in the mixing stage. Physical interactions take place as blends are formed, and the effect of the CMC concentration was studied from 5–30%. At the highest CMC concentration, those blend systems were compared to conjugated systems, where prior chemical conjugation of both biopolymers was carried out at 60°C for 48 h. The physical and chemical interactions between the biopolymers certainly affected the viscoelastic properties of the eventually obtained injection-moulded bioplastics. Thus, samples softened after the addition of CMC, independent of the procedure followed. Thus, the addition of CMC always resulted in a reduction in the viscoelastic moduli (i.e., E’ decreased from approximately 900 MPa in the absence of CMC to 265 MPa in the presence of 30% CMC, either blended or conjugated). Conversely, the samples presented much higher water uptake capacity (WUC) values when conjugation was carried out. Therefore, the WUC of zein bioplastics (approximately 200%) increased to 950% for 30% conjugated CMC, which is almost twice the value obtained when the same amount of CMC was added in the mixing stage. Biodegradable biocomposite materials obtained through conjugation could be of great interest for developing hydrophilic green materials.