*N. Sai Prasanna
In recent times, packaging sector is gaining much interest among scientists, food researchers and consumers as well. Food packaging plays a key role in addressing key challenges in sustainable food consumption for minimizing the environmental pollution. Packaging helps food industry in food quality preservation during storage by controlling gas and vapour exchanges with the external atmosphere, preventing food safety issues i.e., food-borne diseases and food chemical contamination and extending shelf-life of packed foods¹. Though modern packaging provides more safer, reliable, shelf-stable and clean food; but on the worst side, these packages are designed for single use, non-biodegradable and not recyclable. Thus food and food packaging materials make up almost half of all municipal solid waste disposal (as per US Environmental Protection Agency). Thereby, these food packages (especially petroleum-based plastics) are thrown away as solid waste in landfills and waterways, thus emerged as indomitable sources of environmental pollution causing severe threat to humanity and aquatic life including to our air and soil. Therefore, packaging industry is yet to resolve these challenges to replace plastic with biodegradable or green packaging technology for contributing to sustainability and environmental safety. In particular, there is also strong need for more research and development aiming at producing innovative and sustainable packaging materials with wider awareness, alternative products at economic prices. The research should also address the long-term crucial issues like persistent plastic waste accumulation, incremental usage of petroleum-based plastics in food packaging, non-biodegradability and environmental damage.
Biodegradable packaging involves the use of biopolymers, which includes naturally available polysaccharides, proteins, lipids and polyesters either alone or in combination for the film production for packing of various foods. Though these protein and polysaccharide-based films provide suitable oxygen barrier properties and relatively acceptable mechanical strength, but have poor moisture and water vapour barrier ability². To enhance the film functionality in terms of strength, elongation, barrier property, optical property, or even the biological safety point of view, these biopolymer matrices are being reinforced with various nanofillers which can improve mechanical, optical, antimicrobial, and barrier properties. At present times, a lot of research has already been focused on various nanofillers from different sources, and further research is going on to find nanofiller reinforced biocomposites that can effectively be utilized for food packaging applications³. The nanofillers (dimensions of < 100 nm) can be classified into organic or inorganic clays (Montmorillonite), natural celluloses (nanocrystals, nanofibrils, bacterial nanocellulose), natural biopolymers (chitosan), natural antimicrobial agents (nisin), metal (silver, copper, zinc), and metal oxides (e.g. TiO₂, ZnO, Ag₂O). These nanofillers for food packaging applications are based on their morphology and are classified as nanoparticles, nanofibrils, nanorods, and nanotubes⁴. The utilization of biodegradable polymers and nanofillers for bionanocomposite films and packaging has opened new pathways for both academia and food industry to make sustainable packaging materials that could replace conventional plastic materials causing environmental pollution. One such nanofillers were cellulose nanocrystals (CNCs), emerged as strong, renewable, unique and economic nanomaterials of near future.
These CNCs are derived from renewable and broadly available nature resources (i.e., plant, animal, bacterial, and algal biomass). Rich cellulosic sources subjected to controlled hydrolysis with strong acids (like sulfuric or hydrochloric acid) which selectively degrades the amorphous regions of cellulose and produces more crystalline regions. Thus in cellulose hydrolysis, hierarchical structure of cellulose will be disintegrated resulting in the formation of cellulose nanocrystals, while the cellulose nanofibers are formed in the mechanical disintegration processes. The dimensions, morphology, and crystallinity of the resulting CNCs depends on the cellulosic source – a pre-treatment process and hydrolysis condition such as acid concentration, acid to cellulose ratio, reaction temperature and time. Bacterial nanocelluloses produced through certain enzymes which will degrade cellulose and also other accompanying polymers (such as pectin, hemicellulose and lignin)⁵. These CNCs have drawn the attention of researchers in the recent times, due to its unique properties like high surface area to volume ratio, light in weight, and excellent mechanical properties. These nanofillers can be derived from the celluloses, which are available widely as bio-waste from the outer skin or peels, pulp, seeds, etc., of fruits and vegetables; and from husks, hulls, shells and straws of agro-crops like paddy, soya, wheat, pistachio, etc., during their harvesting, consumption, storage and agro-waste such as sugarcane waste, mango pulp waste, cotton seeds waste, during industrial processing. These biowastes can be properly utilized for the engineering applications like production of CNCs, which later is identified as suitable nanofillers to develop biocomposites of sustainable packaging solutions for the food industry applications.
Since CNCs possesses modifiable properties due to abundant hydroxyl groups presence which resulted in better biodegradability and biocompatibility, thus enable to protect environment from non- conventional plastic damage. Thereby, such nanocrystals when reinforced as nanofillers in bio-composites films, delivers effective food packaging materials. Besides food packaging applications, the unique characteristics like good mechanical and optical properties, high aspect ratio, better tensile strength, low thermal expansion coefficient, make CNCs applications in various fields like biocomposites, food packaging materials, as stabilizers in oil-water emulsion, paper making, coating additives, thermo-reversible and tenable hydrogels making optically transparent films and biopharmaceutical applications such as drug delivery and fabricating temporary implants like sutures, stents etc. In recent decades, the combination of cellulose nanotechnology with green solvent (alkaline/urea, ionic liquid, etc.) technology made researchers expand cellulose applications in biomedical, energy storage, optical fields too.
Recently, IIT Kharagpur researchers have developed cellulose nanomaterials (CNCs), i.e., from cucumber peels for producing eco-friendly commercial-grade food packaging materials. Researchers Dr. Jayeeta Mitra, Assistant Professor and N. Sai Prasanna, research scholar at Dept. of Agricultural and Food Engineering have developed unique nanocrystals from the cellulose content of raw cucumber waste which can improve mechanical, and barrier properties of biopolymers. In India cucumber is a native crop frequently used in salads or pickles, cooked vegetables or consumed raw, thus making its cellulose content available in large volume and at low prices. After processing, cucumbers generated about 12% residual wastes either in the form of peels or whole slices. Research scholar N. Sai Prasanna reported that cucumber peels possessed greater cellulose content (18.22%) than other peels waste. The cucumber peels were collected from local hostels, dried and powdered, which later acid (HCl) treated, alkali (NaOH) treated and bleached (NaOCl) to remove hemicelluloses, pectins, lignin, waxes, phenols, etc., in order to isolate chemically purified celluloses. This purified cellulose was acid hydrolysed with H₂SO₄ (60 wt%)to prepare CNCs. The properties of cellulose nanocrystals (CNCs) were characterized by employing various techniques like morphological studies done through microscopies (Scanning Electron, Tramission Electro, & Atomic force), colloidal properties (Dynamic light scattering), crystallinity (X-ray Diffractometry), thermal properties (Thermogravimetric analyser).The crystallinity percentage of these CNCs were as high as 74.1% along with thermal stability of more than 200 °C, negative zeta potential values (< -30 mV), and acid hydrolysis yield of 65.55%, resulted as strong nano-filler reinforcement in bio-nanocomposites. This study provided better insights into their crystalline, thermal and colloidal properties of CNCs from cucumber cellulose.
The researchers further made a note for “packaging industry players in India for substantial investments to improve packaging material properties for better sustainability, disposal and decomposition issues, thereby focussing on sustainable packaging and plastic free world”. The Active packaging technology in food and beverage industry has demand for minimally processed and preservative free foods. In active packaging, nanocrystals incorporated into polymeric films, which can prevent microbial food contamination. The ability to impart very low oxygen permeability made the nanocellulosic materials highly desirable in food packaging business. All these demands for biodegradable packaging will surely shoot up nanocellulose market in coming future.
Thus cellulose being, the most ancient and important natural polymer available on the earth, has been seen drawing the attention in the form of a novel and advanced biomaterials of CNCs due to its renewability, biodegradability, abundance, and low cost nature. On reinforcing CNCs as nanofillers in biopolymers, its nanoscale dimensions can form a nanoporous entangled network, strong filler-matrix interactions, homogenous structure formed with adequate dispersion of the CNCs in biopolymer matrix, excellent barrier properties and mechanical properties. All these features made the scientists, food researchers and technologists for efficient application of CNCs as sustainable food packaging materials. A lot of residual waste obtained in the by-product form of peels, seeds or skin, pulp, hulls, etc., agro-processing industries, contains a valuable content of celluloses. Thereby utilization of such celluloses for production of CNCs will help the problems of bio-wastage disposal and environmental pollution to be controlled through some extent and their application for biodegradable packaging will boost the modern packaging sector towards a sustainable development and plastic free world. Though cellulose nanomaterials have the potential to replace non-renewable materials with more sustainable environmental friendly resources, but there is a lack in its commercialization. The key challenges and barriers are related to its production and processing methods, need for proper characterization and standards, the need for better understanding of potential impact on environmental, health, and safety issues, the need for market-pull and technical readiness, need to be more focused and researched for its industrial commercialization.
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- Prasanna, N. S., & Mitra, J. (2020). Isolation and characterization of cellulose nanocrystals from Cucumis sativus peels. Carbohydrate Polymers, 247, 116706.
Contact DetailsResearch Student,
Indian Institute of Technology Kharagpur,
Kharagpur, West Bengal, India, 721302.