Opinion
Although a lot of research has been carried out on cellulose nanofibers, there are certain areas associated with their manufacturing, processing, postprocessing, and application that are yet to be explored to their full potential.
15.4.1 Environment and Human Safety
Although CNFs and BCNFs degrade in nature by the activity of bacteria and enzymes, there is a need to build infrastructure to enhance their biodegradation. Also, the effect of CNFs that are directly or indirectly liberated into the environment and knowingly or unknowingly inhaled by humans is yet to be examined. It is already found that inhalation of certain nanofibers induces irritation or inflammation in the respiratory pathway, which may damage the lungs. A study on the effect of CNFs on rats has shown that CNFs persisted for a long time in a rat’s lungs and provoked respiratory symptoms. Hence, proper safety measures should be followed for the employees working in the cellulosic nanofiber-based composite manufacturing units.
15.4.2 New Opportunities for Agro-Based Industries
The cellulosic fibers obtained from agricultural wastes like grasses, weeds, straws, stalks, hulls, and wood can contribute toward the non-food-agricultural-based economy. These agro-based fibers can replace the inorganic or mineral-based reinforcing fibers in nanocomposites. There is a dire need to explore the use of agro- based fibers for different applications as this will help to manage the disposal of agro waste.
On similar grounds, forests provide the raw materials for CNF production and increased use of CNFs can help in reviving the forest industry.
15.4.3 Cellulose-Based Implants
Due to their high purity, BCNFs are preferred for tissue engineering and scaffold application. For wider application, new techniques need to be developed to produce oriented fibers in different shapes and sizes. Different chemical treatments are needed to explore and improve the interaction of BCNFs with the human body.
Cellulose degrades slowly inside the human body. It is found that oxidized cellulose has the potential to be used as an implant material as the time frame of its degradation can be controlled. Hence, more such efforts are required to improve the applicability of CNFs/BCNFs for biomedical implants and scaffolds in the near future.
Summary
The economic and environmental issues produced by petroleum- based polymers can be tackled by exploring easily available, cheaper, and biodegradable natural polymers as an alternative to synthetic plastics. The current review discusses the multiple sources of natural cellulose, the structural aspects and properties of CNFs, and the mechanical production of CNFs, along with the challenges, and finally justifies the CNFs as a source of renewable polymer nanocomposites.
It is observed that the characteristic properties of CNFs eventually vaiy with the origin, location, and age of the CNFs; the part of the plant they are extracted from; and the extraction technique used. The complex structure of lignocellulose presents the main difficulty in the separation of CNFs. Energy-efficient and economic separation of CNFs can be done by choosing a suitable plant source along with effective pretreatment. Chemical or enzymatic pretreatments, separation techniques, surface modification, and drying are found to affect the final mechanical characteristics of CNFs. CNFs obtained from the plant cell wall and the BCNFs obtained from bacteria are the source of multitude nanocomposites applicable in coatings, food packaging, advanced textiles, biomedical devices, tissue engineering scaffolds, and electronic devices.
The concerns regarding the disposal of synthetic polymers, their recycling cost, and the harm caused by them to the aquatic, aerial, and terrestrial life have prompted government authorities and environmentalists to think about the easily available, biodegradable, and green sources of polymers. CNFs and BCNFs have the potential to relieve many of those concerns. Systematic research on the natural polymers to be used in nanocomposites, the exploration of alternative applications, and designing of cost- and energy-efficient production techniques for the synthesis of bionanocomposites are surely the solution of the current times.
