Waste masks pose a serious threat to the environment, including marine plastic pollution and soil pollution risks caused by landfills since the outbreak of COVID-19. Currently, numerous effective methods regarding disposal and resource utilization of waste masks have been reported, containing physical, thermochemical, and solvent-based technologies. As for physical technologies, the mechanical properties of the mask-based materials could be enhanced and the conductivity or antibacterial activity was endowed by adding natural fibers or inorganic nanoparticles. Regarding thermochemical technologies, catalytic pyrolysis could yield considerable hydrogen, which is an eco-friendly resource, and would mitigate the energy crisis. Noticeably, the solvent-based technology, as a more convenient and efficient method, was also considered in this paper. In this way, soaking the mask directly in a specific chemical reagent changes the original structure of polypropylene and obtains multi-functional materials. The solvent-based technology is promising in the future with the researches of sustainable and universally applicable reagents. This review could provide guidance for utilizing resources of waste masks and address the issues of plastic pollution.

There is increasing attention to the production of cellulose nanocrystals (CNCs) from lignocellulosic biomass by enzymatic hydrolysis with cellulase. In this study, the feasibility of the application of a cellulase system from engineered strain Penicillium oxalicum cEES in the production of CNCs was assessed. Using commercial eucalyptus dissolving pulp (EDP) as substrate, the CNCs were successfully obtained by enzymatic hydrolysis with the cellulase cEES, and the total yields of CNCs reached 15.7% through three-step enzymatic hydrolysis of total 72 h (24 h for each step). The prepared CNCs were characterized and found that their crystallinity and thermal stability were higher than that of EDP. In the later stage of enzymatic hydrolysis, the process efficiency of enzymatic preparation of CNCs greatly decreased because of the high crystallinity of cellulosic substrate, and a simple homogenization treatment can promote the enzymatic hydrolysis, as well as produce fusiform CNCs with more uniform size and more fermentable sugar that could be further converted into fuels and bulk chemicals through fermentation. This study provides a feasible enzymatic preparation process for CNCs with engineered cellulase and commercial cellulosic materials. Graphical Abstract

Corn fiber, a by-product from the corn-processing industry, is an attractive feedstock for cellulosic ethanol because of its rich carbohydrate content (mainly residual starch, cellulose, and hemicellulose), abundant reserves, easy collection, and almost no transportation cost. However, the complex structure and components of corn fiber, especially hemicellulose, make it difficult to be effectively hydrolyzed into fermentable sugars through enzymatic hydrolysis. This study developed a simple and easy industrialized process without detoxification treatment for high-yield ethanol produced from corn fiber. Corn fiber was pretreated by dilute acid under the conditions optimized by Box-Behnken design (0.5% H2SO4 at 105°C for 43 min), and 81.8% of total sugars, including glucose, xylose, and arabinose, could be recovered, then the mixture (solid and hydrolysates) was directly used for semi-simultaneous saccharification and fermentation without detoxification, and ethanol yield reached about 81% of the theoretical yield.

Endoglucanase (EG) is a key enzyme during enzymatic preparation of cellulose nanocrystals (CNCs). Myceliophthora thermophila is a thermophilic fungus that has thermal properties and a high secretion of endoglucanases (EGs), and could serve as potential sources of EGs for the preparation of CNCs. In this work, four different GH families (GH5, GH7, GH12, and GH45) of EGs from M. thermophila were expressed and purified, and their enzymatic characteristics and feasibility of application in CNC preparation were investigated. It was shown that the MtEG5A from M. thermophila has good potential in the enzymatic preparation of CNCs using eucalyptus dissolving pulp as feedstock. It was also observed that there was a synergistic effect between the MtEG5A and other MtEGs in the preparation of CNCs, which improved the yield and properties of CNCs obtained by enzymatic hydrolysis. This study provides a reference for understanding the enzymatic characteristics of different families of EGs from M. thermophile and their potential application in nanocellulose production.