General Background The search for efficient bio-based materials is the main challenge of the next decade
The search for efficient bio-based materials is the main challenge of the next decade. If such materials can be found, they could provide a solution to international issues such as the petroleum shortage, global warming, and geopolitical conflicts that are linked to minerals or metals and incineration waste residues (Lavoine et al., 2012). There is general interest in the sustainable production of chemicals or materials from biomass, which may play a major role in producing systems traditionally produced from petroleum. Biodegradable plastics and biocompatible composites generated from renewable biomass feedstock are regarded as promising materials that could replace petrochemical based polymer in order to reduce global dependence on fossil fuel sources and provide simplified end-of-life disposal (Brinchi et al., 2013).
With the emergence and development of nanotechnology, cellulose, the most ancient and important natural polymer on Earth revives and attracts more attention in the new form of “nanocellulose” to be used as novel and advance material. In general, cellulose is a fibrous, tough, water-insoluble substance which plays an essential role in maintaining the structure of plant cell walls.
Cellulose is the product of biosynthesis from plants, animals, or bacteria, while the general term “nanocellulose” refers to cellulosic extracts or processed materials, having defined nano-scale structural dimensions (Abitbol et al., 2016). For plants, cellulose is found in a composite form composed of polymers, lignin and hemicelluloses. They are physically and chemically bound together. Lignin is theoretically considered as adhesive, holding cellulose and hemicelluloses. Cellulose is considered as the main part of a plant structure, whereas hemicellulose, or sometimes called medium phase, acted as media in plant structures in order to connect both lignin and cellulose. In general, there is pectin in this plant structure, but the amount of pectin is too small compared to the other three compositions (Ummartyotin & Manuspiya, 2015).
Generally, the family of nanocellulose can be divided in three types; 1) cellulose nanocrystals (CNC), with other designations such as nanocrystalline cellulose, cellulose (nano)whiskers, rod-like cellulose microcrystals; 2) cellulose nanofibril (CNF), with the synonyms of nanofibrillated cellulose (NFC), microfibrillated cellulose (MFC), cellulose nanofibres; and bacterial cellulose (BC) (Lin & Dufresne, 2014).
Potentials and advantages in the use of CNCs are related not only to their useful, unsurpassed, physical and chemical properties, but also their biodegradability, renewability, sustainability, abundance and high biocompatibility. In fact its dimension, in the nanometer scale, opens a wide range of possible fascinating properties to be discovered.
Self-assembly of cellulose nanocrystals is a powerful method for fabrication of biosourced photonic films with a chiral optical response. While various techniques have been exploited to tune the optical properties of such systems, the presence of external fields has yet to be reported to significantly modify their optical properties. By using a small commercial magnets, the orientation of the cholesteric domains is enabled to tune in suspension as they assembled into films (Frka-Petesic et al., 2017).
Isolation of CNCs from cellulose source materials occurs in two stages. The first one is a pre-treatment of the source material. For wood and plants, the complete or partial removal of matrix material (hemicelluloses, lignin and pectin) is required generally. The second one is a controlled chemical reagent, generally hydrolysis which is to remove the amorphous regions in the cellulose matrix. Different cellulose sources give different characteristics and also different aspect ratios of cellulose. The aspect ratio is a measure of length and width of the cellulose, the crystals or fibres. The higher the aspect ratio, the higher is the reinforcement capacity when incorporated in composite materials.
CNCs are obtained by breaking down the cellulose fibres and isolating the crystalline regions. Chemical treatments using strong acid (sulphuric acid, nitric acid, and hydrochloric acid), to hydrolyse cellulose fibres and often used to produce CNCs. One of the drawbacks of using sulphuric acid is the presence of the sulphate groups on the cellulose nanocrystals, assist the degradation of cellulose, mainly at a higher temperature, hence interfering its thermal stability and affect the performance of CNCs in bionanocomposites (Adel et al., 2018).
Recently, chemical treatment using ammonium persulphate (APS) for CNCs extraction has attracted attention owing to its resultant properties on CNCs. This green oxidant is highly water soluble, inexpensive and commercially available. Moreover, versatile procedure can process a diverse range of cellulosic materials without the need for pre-treatments to remove non-cellulosic plant contents such as lignin and hemicellulose. The use of APS results in the formation of highly carboxylated CNCs, as opposite to sulphated CNCs produced using sulphuric acid, respectively (Leung et al., 2011).
1.2 Problem Statement
Due to environmental crisis and limited non-renewable petroleum based materials, research efforts focussing on bio-based polymers from natural resources have increased tremendously in recent years (Orue et al., 2017; Orue et al., 2016; Eceiza & Arbelaiz, 2014; Mondragon et al., 2014). Cellulose is the most abundant renewable macromolecule, available in large quantities on Earth and are therefore easily accessible and inexpensive sources, which is crucial in the production of nanocellulose at low cost (Ng et al, 2015). However, a research on nanodiameter cellulose has not been realized until a few years ago in which an extensive collection of information has become available (Habibi et al., 2010).
In general, the cellulose nanocrystals has been prepared mainly by acid hydrolysis. One of the main reason of using sulphuric acid as a hydrolysing agent is the grafting of anionic sulphate ester groups on the surface of CNCs (Dufresne, 2013). To produce colloidally stable CNCs by sulphuric acid hydrolysis, the conditions regarding temperature, acid concentration, reaction time and ratio of acid to cellulose sources must be carefully controlled (Peponi et al., 2014). The geometrical dimensions of CNCs depends on the origin of the cellulose substrate and hydrolysis conditions (Dufresne, 2017). However, acid hydrolysis treatment usually involves complicated and lengthy processes and poisonous chemicals by products.
Significance of Study
Ammonium persulfate oxidation for nanocellulose extraction attracts attention because this green oxidant is highly water soluble, inexpensive and commercially available. Due to APS exceptionally low long-term toxicity, it can be safely used on a large amount. This versatile method can be applied on a wide range of cellulosic materials without requiring any pre-treatments to remove the amorphous layer (Adel et al., 2018).
Recently, Nanocellulose penetrates medical and life sciences markets with an estimation of 97 billion. It was reported by ” Future Market Inc.” in The Global Market for nanocellulose to 2017, published in October 2012 (Lin & Dufresne, 2014). Nanocellulose is used as essential materials in various applications such as packaging, biomedical and pharmaceutical products, water treatments, energy, electronics and biosensor due to their unique and exceptional features (Jonoobi et al., 2015; Oun & Rhim., 2017).