Enzymatic Recycling of High-Value Phosphor Flame-Retardant Pigment and Glucose from Rayon Fibers

Viscose (also known as Rayon) filaments are obtained from regenerated cellulose and are used in many different sectors mainly as reinforcement material in tires and other cord applications and in the clothing industry. The incorporation of a phosphor containing pigment imparts flame-retardancy properties to these fibers, which then can be used as part of personal protection textiles delivering wear comfort. There are no recycling strategies for these materials being brought to landfills or chemically degraded since incineration is difficult because of their flame retardancy. In this study, an enzyme-based strategy for the recovery of glucose and of the phosphor pigment without altering their chemical structures was developed as a circular economy solution. Rayon fibers were completely hydrolyzed by a cellulase preparation while 98% of the glucose (reducing sugar assay and HPLC analysis) and more than 99% of the flame-retardant pigment present in the fibers was recovered. The recovered pigment was analyzed via H-1, C-13, and P-31 NMR, and the purity >95% was comparable to that of the commercially available pigment. The recovered glucose was successfully used as carbon source for ethanol production by Saccharomyces cerevisiae while the recycled phosphor pigment was reused in viscose filament production leading to similar mechanical properties like those measured for virgin fibers. This work presents an environmentally friendly recycling strategy of functional rayon fibers for the recovery of the two major components, namely, glucose and the pigment.