Tailoring the properties of natural fibre biocomposite using chitosan and silk fibroin coatings for eco-friendly packaging

Biocomposite sheets were created by blending taro pulp with rice straw, pineapple fibre, guar gum, and corn starch. The optimal composition, comprising 90 % taro pulp and 10 % corn starch, demonstrated impressive mechanical properties, including a tensile strength of 61.42 MPa, bursting strength of 13.19 kg/cm2, a contact angle of 63.4 degrees, and water uptake of 82.33 %. To understand whether these qualities can be improved by coating with chitosan, silk fibroin, or combinations of both, coated samples were also studied. Chitosan coating displayed a tensile strength of 26.79 MPa, while fibroin coating further reduced it to 15.87 MPa. Notably, a 50:50 chitosanfibroin blend increased the contact angle to 117.8 degrees, reducing water uptake to 49.67 % and water vapor transmission rate to 4.73 %, compared to 46.15 % and 3.96 % for pure fibroin coating. Analysis revealed similar spectra among coatings, indicating analogous functional groups. XRD showed a crystalline cellulose I structure with crystallinity indices of 71.96-74.18 %. DSC displayed transitions near 190-240 degrees C, while TGA showed two- stage degradation with T5 at 130-180 degrees C, T10 at 244-264 degrees C, and T50 at 325-336 degrees C. SEM confirmed surface modifications induced by coatings. Combinations with higher fibroin content exhibited reduced water uptake and water vapor transmission rates compared to pure chitosan due to differences in chemical composition. While chitosan enhanced tensile strength, fibroin had a mitigating effect. Although not fully biodegradable, the coated sheets showed varying degrees of biodegradability under soil burial conditions for 60 days. These findings highlight the tunable properties of biocomposite sheets through composition and coatings, promising for packaging applications.