Pillalamarri Srikrishnarka
Dielectica traverses through the literature on this topic – and summarizes as they appear.
Key words: Biodegradable plastic, Cellulose nanofibers, Mechanical and Thermal stability
Chennai, India: Plastics have become somewhat inseparable and part and parcel of our day-to-day life. The US flag hoisted on the moon by astronaut Neil Armstrong was made of nylon. The global plastic production has totaled 356 million tons at the end of 2018. From disposable spoons, plates all the way to IV tubes, plastics have become truly insuperable.
However, due to their non-recyclable and nonbiodegradable nature, they end up in landfills, rivers, and oceans. These then pose a grave threat to the survivability of the local ecology, which breakdowns the sustainability of the environment. To address this, there have been few laws imposed that did impact the usage of single usage plastics. However, to meet the growing demands alternatives to plastic needs to be ventured.
Before diving into the substitutes of plastics, let’s think why we are fascinated to use plastics? Plastics are of less weight and offer protection from water and rain. These are also flexible, affordable, possess good mechanical and thermal stability. Moreover cost of plastic is low as compared to many. So, the substitute that we have to find must offer these properties of plastics. Therefore it can be easily replaceable of plastics. However, mass awareness which is very important and highly appreciable to implement this.
We have plastics of various origins, natural, petrochemical and aliphatic polyesters. Petrochemical-derived plastics are albeit most durable, offer very high tensile strength and offer high thermal resistance, are the leading agents for damaging the environment due to their least biodegradability. In this regard, aliphatic polyesters offer some biodegradability but suffer from poor mechanical and thermal properties.
Cellulose is one of the most abundant natural polymers on earth which is biodegradable. Studies have shown that more than 1011 tons of cellulose can be produced every year through photosynthesis. From this cellulose, cellulose nanofibers can be extracted, that can be used as a structural material due to its unique properties of having high tensile strength comparable to that of steel and high modulus. Owing to exploit these wonderful properties of cellulose nanofibers, Guan et al., of the University of Science and Technology of China from China realized a substitute for the petrochemical-based structural material. [1]
Cellulose nanofibers have a typical diameter in the range of 5-10 nm and these fibers were crosslinked by simply spraying aqueous calcium chloride solution. The resulting hydrogel was pressed under a pressure of ~ 1 MPa for 12 h and finally dried under ~ 50 MPa at 80 oC for 1 h. The resulting product was tested for its mechanical and biodegradability studies. They observed that due to crosslinking, the modulus rose to ~ 16 GPa and flexural strength to ~ 300 MPa. The system was so versatile to process, that they could drill holes through the product without damaging the overall structure and even process it into desired complex shapes. The crosslinked product degraded within 90 days when it is placed under soil. These observations are truly inspiring, one day in the near future substitute for plastics is truly possible by modifying the naturally available polymers.
References:
[1] Q. F. Guan, H. B. Yang, Z. M. Han, Z. C. Ling, K. P. Yang, C. H. Yin, and S. H. Yu, Nano Lett. 2021, 21, 21, 8999–9004.
https://pubs.acs.org/doi/10.1021/acs.nanolett.1c02315