Introduction

Increased consumerism and production of clothes, the textile industry produces a substantial amount of waste every year, and currently, most of the waste becomes part of municipal solid waste. Annually, the world produces approximately 92 million tons of textile waste. The survey shows that textile waste occupies about 5% of landfill space in the US and amounts between 3-5% of the annual local municipal solid waste. Currently, estimation of annual textile waste generation in Israel is still insufficient, mainly due to a lack of strategies and facilities for textile waste collection.

Textile waste consists of significant cotton amounts, 37% globally and 65% in Israel. Given its high cellulose content (>88%), cotton-based textile waste has a strong market viability for nanocellulose extraction.

Nanocellulose - Cellulose nanocrystal

Cellulose is a linear polymer of the six-carbon sugar glucose and is a structural component of the cell wall of nearly all plants. The unique hierarchical architecture of natural cellulose consisting of nanoscale fibrils and crystallites allows the extraction of the nano-constituents via mechanical and chemical methods.

Cellulose nanocrystals (CNC) exhibit excellent mechanical properties. The theoretical Young’s modulus of a CNC along the cellulose chain axis is estimated to be 167.5 GPa, which is similar to the modulus of Kevlar and even higher than the modulus of steel. The experimental Young’s modulus of cotton CNCs is 105 GPa and the modulus of tunicate CNCs is 143 GPa.

Nanocellulose is a potential candidate for many applications in many scientific areas given characteristics such as biodegradability, biocompatibility, chemically adaptable surface, large surface area, and high mechanical strength.

Production method and scale-up study

The CNC can be generated by the splitting of amorphous domains, as well as by the breaking of local crystalline contacts between nanofibrils and nanocrystalline, through hydrolysis with highly concentrated sulfuric acid. After hydrolysis, the CNC dispersion is diluted with water and washed using successive centrifugations. Neutralization or dialysis with distilled water is performed to remove free acid from the dispersion. The freeze drying is utilized eventually to sublime the aqueous phase and meanwhile maintain the nano-scale dimensions for materials applications.

Sulfuric acid is the largest cost item in CNC production when the process is without an effective recovery step. Nothing else is close to the sulfuric acid cost and environmental concern, thus, the acid recovery study is the priority followed by the extraction process.

The collected waste acid after reaction mostly contains glucose and caramelized acid degradation products. In order to clean up the acid; it may require centrifugation or treatment with activated charcoal to remove trace contaminants. Then reconcentrate the sulfuric acid to a certain concentration for reuse.