Significance
Cellulose is one of the most abundant biopolymers on earth with the advantage potential to be an excellent sustainable alternative to petroleum-based plastics. As we as society becomes more environmentally conscious, we will intensify the urgent need for renewable, biodegradable materials which are unlike conventional plastics that are derived from non-renewable fossil fuels and can pollute the environment for hundreds of years while cellulose on the other hand can be broken down naturally. Despite its vast availability and obvious eco-friendly properties, cellulose has been challenging to fully utilize for industrial applications because of its complex structure of strong intra- and intermolecular hydrogen bonds that hold cellulose chains together which resists dissolution and this has been a real barrier to make raw cellulose into useful fibers, films, and composites. Scientists have tried various methods to process cellulose, such as the viscose and lyocell processes which involve the use of toxic chemicals like carbon disulfide (CS2) and N-methylmorpholine-N-oxide (NMMO), both are harmful to both the environment and human health. Moreover, these processes are energy-intensive that require high temperatures to dissolve the cellulose and by this add further environmental burdens through increased energy consumption. To over these challenges, recent study published in Nano Letters Journal and conducted by Xiaodi Liu, Yichen Tian, Li Wang, Lei Chen, Zhiping Jin, and led by Professor Qiang Zhang from the East China Normal University, the researchers developing an excellent environmentally friendly and cost-effective method to cellulose dissolution and regeneration. The starting point in their innovation was to modify cellulose with minimal carboxymethyl groups which we believe introducing that chemical modification was key because it weakened the strong intermolecular hydrogen bonds that typically resist the dissolution of cellulose. Indeed, the researchers found that the cellulose could be dissolved rapidly in aqueous NaOH without assistance from other reagent and at temperatures just above 0°C by introducing these carboxymethyl groups and such achievement can occur with low energy consumption and avoided as well traditional high-temperature methods. They tested the dissolution process with different degrees of substitution of carboxymethyl groups to determine the optimal balance between ease of dissolution and the mechanical integrity of the regenerated material. The researchers discovered that cellulose with a DS of 0.15 dissolved efficiently in NaOH which produced a clear, stable solution in less than a minute. This we believe was a major breakthrough as the dissolution occurred at a much higher temperature than traditional alkali methods which usually require subzero temperatures. Moreover, the special carboxymethyl cellulose with a low DS in the case can be obtained largely from the manufacturer of carboxymethyl cellulose with high quality and low cost. Additionally, the researchers noted that the cellulose concentration in the solution could reach up to 14 wt%, which is nearly twice the concentration typically achievable with other alkali-based processes. Once they dissolved the cellulose, it was regenerated into films using an ethanol-water coagulation bath and the resulting cellulose films were highly transparent and demonstrated excellent mechanical properties. These mechanical properties were on par with and in some cases superior to those of cellulose films produced through more traditional methods involving harmful toxic solvents. Interestingly, the mechanical strength of the regenerated films was strongly influenced by the temperature at which the NaOH solution had been pre-cooled. Films produced from solutions prepared at lower temperatures exhibited greater tensile strength and flexibility, with the highest strength observed when the NaOH was cooled to 0°C. This suggested to the authors that the precooling temperature played a critical role in optimizing the cellulose structure during the regeneration process.
The team of experts explored the effects of different raw cellulose sources including wood pulp, poplar, and bamboo and despite the variations in the raw material, the modified cellulose from all sources successfully dissolved and regenerated with the films produced from poplar and bamboo had lower mechanical strength compared to those made from wood pulp. Nonetheless, the ability of the new method to process multiple cellulose sources highlighted the versatility of their method and suggested that it could be applied broadly across various industries. The researchers also looked at the recyclability of the regenerated cellulose films and to test this, they dissolved used cellulose films in NaOH once again and regenerated them into new films. Remarkably, the recycled films retained almost the same mechanical properties as the original ones. In a another set of experiments, they examined the biodegradability of the cellulose films where the researchers buried samples of regenerated cellulose alongside films made from common synthetic polymers, such as poly(methyl methacrylate) (PMMA) and polytetrafluoroethylene (PTFE) in soil and after two weeks, the cellulose films had completely degraded, whereas the synthetic polymers remained largely intact. This finding highlighted the environmental benefits of using cellulose as a renewable, biodegradable material that would not contribute to long-term waste accumulation.
In conclusion, Professor Qiang Zhang and colleagues reported for the first time a new method that uses only aqueous alkali at moderate temperatures and requires minimal chemical modification of cellulose. We believe one of the most important implications of the research team is its potential to reduce the carbon footprint associated with the production of cellulose-based materials and in a world increasingly focused on reducing environmental impact, the new method could contribute significantly to the development of eco-friendly materials, especially in industries that rely heavily on plastics, such as packaging, textiles, and biomedical products. Another thing we like about the new method, is its versatility which opens up new possibilities for using various cellulose sources, from wood pulp to agricultural waste, thus broadening its potential impact. Additionally, because traditional cellulose-processing methods are expensive, the new method, with its lower energy requirements and reduced reliance on expensive chemicals, could make cellulose-based materials more affordable which expedite their adoption in various industries.
Reference
Liu X, Tian Y, Wang L, Chen L, Jin Z, Zhang Q. A Cost-Effective and Chemical-Recycling Approach for Facile Preparation of Regenerated Cellulose Materials. Nano Lett. 2024;24(29):9074-9081. doi: 10.1021/acs.nanolett.4c02351.