The Surface Modification of Cellulose Fibers for Design of Bio-Based Flame Retardant Composites

Environmental pollution caused by the widespread use of petroleum-based plastics has become a serious problem worldwide. To overcome this problem, many research studies have been conducted to find sustainable and eco-friendly alternatives such as cellulose which is abundantly existing in nature and can be extracted from wood, bacteria, and tunicate. Among them, tunicate cellulose shows great promise due to the high crystalline fiber with lightweight, tensile strength, biocompatibility, biodegradability, straightness, and excellent mechanical properties. However, cellulose has low thermal stability which limits its processability compared to commercial polymers such as polyimide and polytetrafluoroethylene. Therefore, it is necessary to improve the thermal properties of cellulose for partial or complete replacement of commonly used polymers with green alternatives. The thermal stability of cellulose can be modulated by changing the surface functional group with halogen group elements. However, these elements generate toxic gases such as halogen and dioxin during combustion. Modifying the surface group of cellulose with phosphorylation creates a protective layer on cellulose by generating char which reduces oxygen permeability and hence retarding the spread of fire. Since it is a non-toxic flame retardant, we proposed to substitute the surface functional group of cellulose from hydroxyl group to phosphorus group. Different composites can be designed by utilizing these phosphorylated cellulose fibers. Morphology and surface properties of the resultant product were evaluated using scanning electron microscopy and atomic force microscopy. The composition and crystallinity of the composite were analyzed through Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). Thermal and mechanical properties were investigated using thermogravimetric analysis (TGA), limiting oxygen index tester (LOI tester), and tensile tester. Phosphorylated cellulose can be utilized in a wide range of fields from flame retardant fabrics to mechanical reinforcement materials and biomedical applications such as catalysts and adsorbents.