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The research and developments of the renewable resources become more important for a sustainable developments and tackling issues due to the goal of the creation of a bio-based economy is challenging to agriculture, forestry, chemistry and industry. Currently, biomass palys an important role in the development of sustainable energy die to the abundance availability of this and all the biomass are behave as renewable resources. On the other hand, there natural polymer has been also attracted significant attraction. Celluloses are well known as the naturally occurring, readily available biodegradable natural polymer, most abundant plant resource on the earth and the most abundant renewable material in natural with consist many unique characteristic, such as renewability, non-toxicity, biocompatibility, biodegradability, and derived properties. It is showed that the hydrogels were prepared through natural polymers, for example, alginate, chitosan, gelatine, starch, cellulose and collagen have also attracted as much intrinsic advantages like biodegradability, biocompatibility, and also behave as natural abundance. Furthermore, these hydrogel can also be used to deliver a number of therapeutics like enzymes, antibacterial, antibodies, vaccines, contraceptives and hormones. Recently, new solvents, such as N-methylmorpholine-N-oxide (NMMO), ionic liquids (ILs), and alkali/urea (or thiourea) aqueous systems have been developed to dissolve cellulose, providing great opportunities for the preparation of cellulose hydrogels. Cellulose-based hydrogels have many favorable properties such as hydrophilicity, biodegradability, biocompatibility, transparency, low cost, and non-toxicity. Moreover, cellulose is environmental friendly and low-cost hydrogels, which will form a viable substitute for petroleum-based materials in near future.
Bio-based polymers which are made up from various type of agricultural commodities and/ or food products wastes has been develop and apply conducted in considerable research in the recent 50 years (Luo & Zhang 2010). The research and developments of the renewable resources become more important for a sustainable developments and tackling issues due to the goal of the creation of a bio-based economy is challenging to agriculture, forestry, chemistry and industry (Kumar et al., 2008; Luo & Zhang 2010). Furthermore, due to the effects of environmental pollution of synthetic polymers and the limited oil resources which are one of the most concern global issues, the natural polymers have attracted much attention in recently.
On the other hand, there natural polymer has been also attracted significant attraction. It is showed that the hydrogels were prepared through natural polymers, for example, alginate, chitosan, gelatine, starch, cellulose and collagen have also attracted as much intrinsic advantages like biodegradability, biocompatibility, and also behave as natural abundance. Furthermore, these hydrogel can also be used to deliver a number of therapeutics like enzymes, antibacterial, antibodies, vaccines, contraceptives and hormones (Chang et al. 2011).
Nowadays, there much concern and attraction is paid to the "white pollution" due to the non-biodegradable properties of the synthetic polymers, thus, it was resulted in worldwide concern about the biodegradable package films and also the plastic products which are made up by renewable agricultural resources (Sun et al. 2007). Biodegradable materials based on natural polymers represent two of the most attracting field of materials science, in which the chemical, medical and environmental scientists are contribute to human health care, thus improving quality of life, protecting environment and also can decreasing dependence to fossil fuel usage. In addition, there are various type of composite materials based on renewable resource and also variety number of natural polymer, such as polysaccharides, lipid, protein have be developed as potential biomaterials and biodegradable packaging materials due to their excellent characteristic, such as various compositions, special structures that can cover multiple application (Luo & Zhang 2010).
Recently, solid waste generation is a natural phenomenon and the quantity of waste generated is directly proportional to the population. The uncontrolled exploitation of different kinds of naturals resources and finally caused the generation of huge amount of complexes solid waste is the most concern issues in the last few decades due to the rapid urbanization and industrialization. Furthermore, the solid waste will be critical issues as long as human have been living in settled communities and the modern societies will also generates more solid waste rather than the early humans ever did. So that, it is advisable that these waste products should be investigated with an objective to be used as raw materials by industry to get desired products under these condition (Singh et al. 2011).
Biomass can be defined as modern plant matter gradually develops through photosynthetic capture of solar energy and strored as chemical energy (Gunaseelan 1997). The employed of the biomass usually is the by-products of food, beverage, or pharmaceutical production and maybe a viable alternative for the development of inexpensive biosorption process (Reddad et al. 2002 a; Yun et al., 2001). The adsorption capability of biomass usually depends on the different type of functional groups on the biomass surface such as carboxylate, hydroxyl, sulphate, phosphate, amide, and amino groups (Sag 2001; Gulati et al., 2002).
Commonly, biomass is defined as the energy source that comes from biological materials such as trees, plants, animal dung which has applied as wastes (Chiew et al. 2011). Biomass, in terms of energy industry refers to biological life and the new life that can be used as power generation for industrial production. Biomass conversion arrangement system is organized and systematic, which can be large and generate electricity and heat for an apparatus or small wood or wood furnaces with biomass (Sumathi et al 2007).
Generation of solid waste is a natural phenomenon and the amount of waste generated is directly proportional to the population. Rapid urbanization and industrialization has resulted in various kinds of exploitation of natural resources and ultimately uncontrollable generate large amount of a large complex of solid waste in the past few decades. Solid waste has become an issue that is often discussed as long as humans have lived in a settled society and modern society would generate more solid waste than early humans ever did. Sustainable biomass management practices are necessary to ensure cleanliness of the environment. In this situation is considered that residual waste by an industry should be investigated and examined with the objective to generate the biomass for other uses to get the desired product (Singh et al.2011).
Application of biomass agriculture industry has been applied in other industries in particular way show that this idea has provided an alternative substrate and on the other hands, it also can solve the environmental pollution problems, where as this waste disposal can caused other pollution problems happen (Sun et al. 2004). Typically, this function of biomass usually is by-products of food, beverage or pharmaceutical production and it can be a good alternative way for the development of a cheap biosorption process (Deng et al. 2005).
Currently, biomass palys an important role in the development of sustainable energy die to the abundance availability of this and all the biomass are behave as renewable resources. In recent years, some research has studied about the production of bio-oil from palm oil and palm oil empty fruit bunch fibres, especially in Malaysia (Fan et al. 2010).
As one of the largest exporte of palm oil and palm oil products, the pail oil industry in Malaysia has generated a huge amount of the biomass in the form of empty fruit bunch fibers (EFB), oil palm shell (OPS), and also oil palm fiber (OPF) (Shamsudi et al. 2011).
Malaysia produces energy supply through pamlampress fibers and empty fruit bunches fibers which are regarded as waste materials and it was not yer utilized satisfactorily. The fresh empty fruit bunch palm oil contains about 21% of oil palm, 6-7% of palm kernel, 14-15% of fiber, 6-7% of hard shell and 23 % of empty bunchs (Hamzah et al. 2010). Empty fruit bunch fibers can be obtained through the stripping process of fresh fruit bunches palm oil. Around 7.3 million metric tons of empty fruit bunch fibers will be produced annually due to the empty fruit bunch palm oil are available in huge amount and it contain a relatively high content of cellulose with average 50% contents (Umikalsom et al. 1997). In addition, empty fruit bunch also characterize with combustion properties, thermability, and dielectric properties, it show that this biomass is an important criterion for the use of microwave pyrolysis as an energy sources (Omar et al. 2011).
On the other hands, biomass palm oil can also defined as one of the largest biomass that can be develop where else the biomass palm oil contributed around 669 million of energy every year (Sumathi et al. 2007). Due to the abundance quantity of palm oil empty fruit bunch fibers, it was promoted as utaman fuel for power generation in combined heat and power plants (CHP). Many researchers have studied the potential of palm oil waster as renewable energy and assess the feasibility of biomass power plants in terms of technology availability and economic feasibility (Chiew et al. 2011).
Palm oil, which is the family of Arecaceae with binomial name, Elaeis guineensis, is one of the most important industrial plantation and crops in Malaysia (Shuit et al. 2009). Palm oil plantation is the highest yielding edible oil crop in the world with cultivated in 42 countries with the quantity in 11 million ha worldwide (Khalil et al. 2008 b). The major palm oil cultivating countries are West Africa, Southeast Asian countries like Malaysia and Indonesia, Latin American countries and also India (Shinoj et al. 2011).
In the past of the couple of decades, the Malaysia economy has gain a remarkable growth and the production of palm oil play an important part in economy growths. On the other hands, as the one of the world largest palm oil production countries, Malaysia has been occupying more than one-third of the total cultivated area which is around 3.79 million ha and also 11 % of the total land area in year 2003 (Yusoff & Hansen, 2007). There are around 45% of total palm oil production in the world is controlled by Malaysia according to the statistic obtains according to Malaysia Palm oil Board. In whatever way, the palm oil industries in Malaysia also contribute the significant pollution load into the rivers throughout the country (Singh et al. 2011).
At the present time, Malaysia has been regard as the world's largest palm oil exporter (Haslenda & Jamaludin 2011) and produces with the productivity approximately 40-60% of the world total palm oil production over the 25 years ago (Chew & Bhatia, 2008; Fan et al. 2011).
There are averages of 19.2 tonnes of palm oil Fresh Fruit Bunches (EFB) per hectare in Malaysia according to MPOB in 2010. In 2009, the total palm oil planted area increased by 4.5 $ to 4.69 million hectares (Wahid 2009). Malaysia also contributes 39 % of world palm oil production and 44% of worldwide exports (MPOC, 2009). Besides that, these small holders also contribute 40% of the total plantation ownership, with many being allocated by the Government for settlement plots (Basiron 2007; Teoh, 2010). Since the 1960s, Malaysia has been actively commercially in palm oil plantation. Therefore, a great deal of research and development has been carried out on oil palms in relations to increased yield, management, cloning technology, planting materials, specific fertilizers, disease protection and detection, processing, benefits, and mores (Hazir et al. 2012).
Palm oil plantations are the world's largest exporter plantation in Malaysia with more than 46900 km2 has been explored. The palm oil plantation in Malaysia generated large quantities of biomass in the form of oil palm empty fruit bunch (EFB), oil palm shell (OPS) and oil palm fibres (OPF) due to this biomass is one of the biggest exporter and production plantation. Therefore this biomass is yet to be exploited (Shamsudin et al. 2011).
Palm oil is composed of two species of Arecaceae or palm family that used for commercial agriculture in the production of palm oil. The mature tress shall have a single trunk and grow up to 20 meters in height. The leaves are compound leaves which the sub leaves are arranged leaves on both sides of the mid seem feathers and reach 3-5 meters in length. Besides that, the flowers are produced in dense clusters with each individual flower are small. Unlike coconut, the oil palm does not produce offshoots and the palm tree breeding is to sow seeds. The fruits need take 5-6 months to reach maturity period, it consist of a fleshy outer layer and behave oily with a single seed which are also rich in oil.
Palm oil plantation most often applied as production of palm oil in commercial agriculture industry. Since the palms are tropical palm trees which can easily be grown in Malaysia. Palm trees in Malaysia usually is derived from West Africa where elsi it is grows in the wild area and developed into agricultural grain crops in later. Figure 2.3 shows the palm trees and accessories of this plant. Palm tree and oil palm fruit bunches are shown in Figure 2.3 a and 2.3 b, where else 2.3c and also 2.3d are the palm oil biomass and grain palm oil waste (POME) (Shinoj et al. 2010).
Figure 2.3 (a) Palm tree Figure 2.3 (b) Oil palm fruit bunches
Figure 2.3 (c) Palm oil biomass Figure 2.3 (d) grain palm oil waste (POME)
Figure 2.3 (a) Palm tree, (b) Oil palm fruit bunches, (c) Palm oil biomass (d) grain palm oil waste (POME)
Sumber: (Shinoj et al. 2010).
Palm oil is defined as edible plant oil production with the highest production in the world. 1 hectare of palm oil plantation will be produce about 55 tons of dry biomass with the form of fibers, where else the production of oil just 5.5 tons only at the same period (Shinoj et al. 2010; Hasamudin and Soom, 2002).
There has more than 46,900 km2 palm oil plantation cultivated in Malaysia, which are regard as the world's largest palm oil exportation in contrast with the past (Shamsuddin et al. 2011). Furthermore, the palm oil industry is the biggest plantation cultivated with more than 2 fold rather than rubber plantation in the vast farming sector. It also refers as the fastest developing major plantation commodities and important cereal crops industry in Malaysia. At the present time, Malaysia also regard as the largest palm oil cultivation exporter and producer in the world with a production of about 40-60% of the total world palm oil production over the next 25 years (Fan et al. 2010). Besides that, smallholders have contributed 40% of the ownership of the old farm that has been allocated by the government for the plot solutions. Therefore, much research has been conducted on palm products associated with increased relationship management, such cloning technology, planting material, specific fertilizer, disease protection, tracing, processing and other benefits (Hazir 2012).
Although Malaysia is the largest exporter of palm oil in international market, but, it has one significant problems in the processing of oil palm fruit bunch, like the management of the wastewater generated after processing of the plants. Normally, the palm oil mills can produces amount around 4.3 million tons of shell annually in Malaysia. The biomass will be burned in the furnace by the palm oil mill in generally. In whatever way, this phenomenon has given rise to the problems of environmental pollution in the immediate area and will also offer limited value to the industry (Tan et al. 2007 c).
Empty fruit bunches fibers (EFB) are the main by-products producing in palm oil industry with quantity around 0.22 ton of EFB fiber will be produce thought every ton of fresh bunch fibers and it can annually produce around 2.96 x 106 ton of EFB fibers (Ahmadzadeh & Zakaria, 2007). After the separating the palm oil fruit from fresh fruit bunch (FFB) sterilized mechanism in the condition steam treatment at 294kPa for 1 hour, it will left fibrous mass behind, namely, empty fruit bunch fibres. It can possible to yield up to 73% of fibres and thus it is more attractive in term of availability and cost (Rozman et al. 2004; Shinoj et al. 2011). There are consists of 66.97 % of holoocellulose (44.2% cellulose and 33.5% hemicelluloses( Hamzah et al. 2010)) and 24.45 % of lignin in palm oil EFB (Rodriguez et al. 2008). There around 17 million tons of EFB fiber will be produced annually after process extraction of palm oil in Malaysia palm oil industry every year (Rahman et al. 2006). Besides that, there are EFb fiber has been utilize throughout several approach to utilize different type of product, such as paper pulp, composite board (Khalid et al. 2008), thermoset polymer (Chai et al. 2009) and active carbon (Alam et al. 2009). On the other way, biomass become an important part in the sustainable energy research and developemetn due to its interesting characteristic as it behave an abundant viability and completely renewable resources (Fan et al. 2011).
During the oil extraction processing from EFB fibers, it will produce several by-products like fibres (30%), shell (6%), decanter cake (3%) and also empty fruit bunch (EFB) (28.5%) (Pleanjai et al. 2004). In 2004, the productivity of solid biomass and POME which generated from 381 palm oil mill has been estimated reach around 26.7 million and 30 million respectively (Yacob et al. 2005). It is a big issues concerning about deal this enormous amount of waste from palm oil miss and it may lead to the environment deterioration issues due to this biomass are rich in organic substances (Singh et al. 2011).
The primary solid wastes palm oil from palm oil processing are empty fruit bunches, fibers and shells with productivity 23% EFBs, 14% fibers and 7% shells per ton of fresh fruit bunch (FFB) annually. In palm oil plantations, the EFB contributs around 19.5 million tons and these were returned to the plantation for mulching at 60 tons per hectare in 2008. In latest development, palm oil mills reuse mainly pressed fibers and shells as fuel to generate the steam and energy for the requirement of their mill with a surplus energy left over (Omar et al. 2011).
EFB fibers commonly is known as abunda amount fiber which can easily obtain in the form of waster fron the processing of palm oil fresh fruit bunch in the palm oil mill. In particular way, the empty fruit bunch fibers is waste material after oil filtration procedures from palm oil fruit bunch (Tan et al. 2010). Based on this statement, it was shown that empty fruit bunch fibers is a great potential biomass and it is appropriate to carry out in this studies due to it is cheap and readily available.
Figure 2.42 Empty fruit bunch fibres.
Source : (Shinoj et al. 2010).
Rajah 2.43 Oil palm fruit
Source: Shinoj et al.2010.
Celluloses are well known as the naturally occurring (Gupta et al. 2011), readily available biodegradable natural polymer (Kim et al. 2010), most abundant plant resource on the earth and the most abundant renewable material in natural (Dogan & Hilmioglu, 2009) with consist many unique characteristic, such as renewability, non-toxicity, biocompatibility, biodegradability, and derived properties (Gavillon & Budtova 2007; Pei et al. 2013). Furthermore, cellulose also known as one of the important industrial raw materials due to is has potential to substitute for some petrochemical (Mascal & Nikitin 2008; Nogi& Yano, 2008; Pei et al. 2013). Cellulose also one of the most promising raw material for application of biodegradable plastic due to its behave as versatile biopolymer with immense potential and low price for use in the non-food industries among various types of candidates of biodegradable polymer (Almeida et al. 2010).
With the 7.5 x 1010 tons annual production of cellulose, thus it is widely applied as a raw material in industrial application like manufacture of paper, textiles and pharmaceutical component (Gupta et al. 2011). Cellulose also attracts attention as possible gel substrate while the only known native cellulose gel form is bacterial cellulose, it can be dissolved and regenerated to give highly swollen gels forms, which is utilized as food, nata de coco (Kim et al. 2010).
Cellulose is the most abundant organic matter on the earth and it perhaps is the most studied polymer since discovered more than 150 year ago. Lignocellulosic biomass is classified as an attractive renewable source of holocellulose that consist of straw, perennial grasses, plant stalks and woody biomass. Lignocellulosics are mainly comprises of cellulose, hemicelluloses and lignin which are bonded together by covalent bonding, van der Waals forces and various type of intermolecular bridge to form a complex structure , hence make it behave resistant to enzymatic hydrolysis and insoluble in water. Cellulose also is an unbranced chain anhydroglucose nd basis of the plant cell structure due to it is a major component of plant fiber that serve as a structural component of plants (C6H10C5) (Wu et al. 2009) in which it structure are linked head to tail by b-glycosidic linkages. Due to its behave high degree of intra-and intermolecular hydrogen bonding , the b-linkage in cellulose will form linear chain that are highly stable and resistant to chemical attact (Kumar et al. 2010).
As the most abundant renewable resource on the earth, cellulose will become as the main chemical resource in future (Schurz, 1999). Therefore, due to the high demand for environmental friendly and biocompatible products (Klemm, Heublein, Fink, & Bohn, 2005; Chang et al. 2010)., there numerous of new functional materials forms through cellulose are being developed over a broad range of application (Klemm, Heublein, Fink, & Bohn, 2005). Cellulose is a renewable resource that many of the planet. It has some interesting features. For example, bio-compatibility and can terbiodegrasikan and thus is a great interest for developing environmentally friendly materials and bio-compatibility (Wu et al.2009). Cellulose can be applied to prepared hydrogels easily with fascinating structure and properties cause it having abundant hydroxyl groups in its structure. So that, it is necessary to studied cellulose-based hydrogels in both industrial application and fundamental research (Chang & Zhang et al. 2011).
Due to its behave as the most abundant polysaccharide available worldwide, cellulose is considered as an almost inexhaustible raw material and it can been formed into in several type like fibers, films, gels, micro- and nano-particle for different purpose and practical use (Cai et al., 2007; Klemm, Heublein, Fink, & Bohn, 2005; Luo, Liu, Zhou, & Zhang, 2009; Zhou, Chang, Zhang, & Zhang, 2007) ( Wang & Chen 2011).Due to the cellulose consist of many excellent properties, such as abundance, renewability and useful mechanical properties, it has been attracted much interest for material usage (Klemm, Heublein, Fink, & Bohn, 2005; Isobe et al. 2012).
Due to the unique properties of cellulose such as non-toxicity, stability under temperature and variation pH, variety type of new material have been manufactures from these natural compounds. It is a renewable resource and additional benefits in cellulose derivatives as a raw material that will not exhaust, in which it can reproduce naturally (Wanrosli et al. 2010).
Cellulose is the main component that makes up the cell walls of plants and may be a polysaccharide that has the greatest molecular weight (Whistler & Smart 1953). Table 2.1 below shows the chemical composition of several cellulose resources:
Table 2.1 Chemical composition of several cellulose resources
Source: Heinze & Liebert 2001
Cellulose is one of the most polysaccharides resistant to chemicals and microorganisms. The molecules of cellulose are tends to be extend, bututs structure can usually be twisted and turned. Cellulose can be dissolved only in the certain circumstances due to its behave large and its strong bonding between moklecule. Therefore, cellulose have been the most important industrial ram caused it is one type of natural polymer that is easily available (Whistler & Smart 1953).
Cellulose known as the environmentally friendly material can be widely used to producea variety of useful products. That is because, cellulose is not only is a lot of resource and can be easily renewable, butit also has special features such as biodegradability, hydrophilic nature and morphology of the fiber forming ability verdatile semi-crystalline (Mao et al. 2008).In whatever way, the handling and formation of cellulose is difficult. Rigidity of cellulose chain and the amount of hydrogen bondingnetwork connecting will causing it difficult dissolve in organicor inorganic solvent in generally (Yang et al. 2011b). Thus, the difficulty of dissolving cellulose wil be one of the major limitations in the application of cellullose.
Cellulose consist of a linear chain of Î²-D-unit glucopiranosa in which connected by bonds (1-4) glikosik at the molecular scale. The hydroxyl group of cellulose molecules tend to form intramolecular hydrogen bonding between cellulose molecules of the same. While the intermolecular hydrogen bonds formed between adjacent chains. Hydrogen bonds between the molecules are arranged in orderly cause cellulose is crystalline (Landry et al. 2010)
Figure 2.1 cellulose molecular structure
Source: Kumar et al. 2010
Depending on the origin of the cellulose, the average number of units anhidroglukosa (Aug) in the cellulose molecule can vary from 3, 000 to 10, 000. XRD findings and microscopic imaging has shown that each of the crystalline cellulose molecule consists of at least 120 Aug, giving the minimum chain length of 60 nm micellar cellulose (Landry et al. 2010). Cellulose polymer chain length depends on the number of constituent Aug (degree of polymerization, DP) and varies according to the origin and treatment of raw materials cellulose (O'Connell et al. 2008).
Regenerated cellulose has been act an important artificial polymeric material in various forms. Through Nmethymorpholine oxide (NMMO) solvent, it can form several major commercial products like viscose rayon, cuprammonium rayon and "Lyocell" fibers. The general properties of regenerated cellulose are crystallinity, mechanical properties and swelling properties have been reported extensively. Besides that, the orientation of the lattice plane of cellulose II on the solid surface is one of the important characteristic of regenerated cellulose. This is because all the hydroxyl group are arranged nearly perpendicular to the plane, thus it make this plan behave as highly hydrophilic, so that, exposure of this plane on the surface make the regenerated cellulose become as high wettabililty materials (Isobe et al. 2011).
From old days, there much effort has been focused on the research on regenerated natural cellulose and it's primarily structure formation has also been investigated. The generation of cellulose by molecular dynamics (MD), reproducing hypothesized formation of sheet-like structure was simulated by Miyamoto in recently. But they were either deduced these formations from the resulting structure or based on computer simulation, while these studies gave a continuing picture of the primary structures formation of regeneration cellulose. There are no in situ observation have been given for the molecular process in cellulose regeneration from solution even though there several research and development about the hydrophobically stacked monomolecular sheet at the early stage of washing mechanism during mercerization has been done by Nishiyama, Kuga & Okano at 2000 (Isobe et al. 2011).
Regenerated cellulose (RC) membrane has been widely applied to membrane separation technologies such as dialysis, ultra filtration and fractionation of polymer mixtures , and is keeping its importance because of the chemical stability, biological compatibility, high tenacity in the wet state, enabling the preparation of thin membranes, and better balance of material permeability and water ultra filtration rate . Now RC membrane prepared from viscose process still occupied an important position, although the process has been met with the increasing environmental problem. The development of non-polluting process based on organic and aqueous solvents of cellulose is of great scientific and practical interest (Zhou et al. 2002).
Cellulose, the most abundant resource in nature, has been chosen as a good candidate for fabricating hydrogels owing to its hydrophilicity, biodegradability, and safety. Cellulose, which are known as the most abundance resource in nature, has been chosen as a good candidate for the fabricating hydrogels due to it's consist of much excellent characteristic, such as hydrophilicity, biodegradability and safety (Chang et al.2011).
Although cellulose is the renewable organic resource with abundance quantity in which its can be converted into several cellulose derivatives and regenerated maetrials, but, its poor solubility properties in common solvent limited its application (Cai et al 2007; Kimura et al. 2011).In fact, the mechanism of cellulose dissolution is difficult to complete without the chemical modification or derivatization due to it's behave as rigid long-chain and strongly inter-molecular and intra-molecular hydrogen-bonded structure in cellulose (Fink et al. 2001; Zhang et al. 2010). Therefore, cellulose require to be "activated" or made it "accessible" to be dissolved, even though these notions are not clearly defined in generally. traditional method of the regenerated cellulose fibres and films production has been largely based on the viscose or the cuprammonium technologies in generally, in which it can caused the hazardous environmental pollution problems happens (Zhang et al. 2010).
Therefore, in fact to solve these environmental pollution problems, there are some identifying new solvent systems for cellulose processing has been found, such as cuoxam, cuen andcadoxen which are commonly known as lithium chloride/N, N-dimethylacetamide (Li/DMAc) (Chang & Zhang 2011) contain metal complexes, N-methylmorpholinr-N-oxide monohydrater (NMMO) (Zhao et al. 2007), and ionic liquids (Castro et al. 2007) are limited to laboratory scale application due to its volatility toxicity, high cost properties (Zhang et al. 2010) and not environmental benign (Gupta et al. 2011), Therefore, there is a critical need to develop alternative solvents to dissolve cellulose for its widespread utilization (Gupta et al. 2011).
The NMMO/H2O system is the most powerful in attaining exceedingly high concerntration solutions and it has been commercialized to manucfacture Tencel or Lyocell fiber among various type of cellulose solvent that has been developed. In whatever way, this cellulose solvent systems also consist drawback, such as, it required occur in the condition of high temperature for dissolution and antioxidants to avoid the side reaction of the solvent, hence causing degradation of cellulose and high costs. Thus, NMMO/H2O system is not suitable for the purpose of complete replacement of the viscose technology (Zhang et al. 2010).
Therefore, there are some approach about the cellulose solvent have been develop and studied, such as thesolubility of microcrystalline cellulose and steam-exploded cellulose in the aqueous NaOH systems in which the native cellulose pulp the produces are act as limited solubility properties (Zhang et al. 2010), due to the.
Currently, Cai and Zhang, has been developed a new class of cellulose solvent based on aqueoustic caustic alkali and urea. This new class of cellulose solvent has been constituted as a potential alternative for viscose process (Cai & Zhang et al. 2005). In addition, this new solvent has been deserving to be noticed as a potential to giving highly transparent of hydrogel on regeneration mechanism consider with the economic and environmental conditions (Cai et al. 2008). Composed of nanometric cellulose fibrils and its offer much possibility as separation material and substrate for composites, this type of hydrogel has nanoporous network properties (Mao et al. 2006; Isobe et al. 2011).
Recently, Zhang et al has been found a novel solvent of the cellulose dissolution in the percooled condition of -12 °C with the composition of solvent 7 wt% NaOH/ 12 wt% urea aqueous solutions. In addition, there are several studies has been reported by Chang et al. 2011 showed that this cellulose dissolution is characterize as a "green process" in this solvent systems. NaOH/urea aqueous solution is a good homogenous derivation systems that can be obtain throughout "green" process, and the cellulose in this systems act as an excellent material for the application as smart materials due to it consists of abundance of OH group in this function. So that, it can gain much attention in the fabricating cellulose-based hydrogels by occupying two cellulose derivatives to exploit new ways for preparing smart hydrogels by chemical cross-linking (Chang et al. 2011).
Recently, there has new approach about the new class of cellulose solvent has been successfully developed by Zhang's group with applied the aqueous NaOH solution systems with either urea or thiourea for the cotton linter dissolution. In this composition, it has found that the optimal parameter of the solvent is either 7/12/81 NaOH/urea/H2O or 9.5/4.5/86 NaOH/thioure/H2O. Although the precise structure of the solvent complex involved is still not clearly understood, but, both the solvent systems were inexpensive and less toxic. In addition, Zhang's group also successfully developed a new complex aqueous cellulose dissolution that contain of NaOH, urea and thiourea , it was able to dissolve the cellulose at a short time under the mechanism conditions in which pre-cooled to temperature between -8 and -12 °C (Jin et al. 2007; Zhang et al. 2010).
Furthermore, in NaOH/urea aqueous solution, it can successfully dissolved the native cellulose, thus, it can also fabricated high quality cellulose fiber, films, hydrogels and microspheres (Cai et al. 2007; Liu et al. 2009; Luo & Zhang et al. 2010; Pei et al. 2013). In addition, there are some biopolymer composites like cellulose/casein films, cellulose/corn protein films, as well as cellulose/ alginate hydrogel with behaving good mechanical properties has been made through NaOH/urea aqueous solution ( Chang et a. 2009, Yang et al. 2009; Pei et al. 2013).
A cellulose solvent system with act as the excellent characteristics like non-toxic and inexpensive based on cold aqueous caustic alkali and urea/thiourea solution was approach in recently. Because of the minimal shrinkage of the cellulose solution on coagulation by non-solvent, therefore this class of solvent is especially suitable for the preparation of cellulose gel. The resulting gels formed through this system are characterized as transparency, and it can be converted to aerogels with low density and nanoporous structures. Cellulose can also be utilized for chemical modification and introduction of various functionalities, in which it consist of abundance hydroxyl group in its structure (Kim et al. 2010).
Alkali/urea aqueous solution
A series of cellulose soluble solvents had been developed to applied as pretreatment methos to disrupt packing arrangement of cellulose fibrils in the crystalline domains, such as LiOH/urea system (Liu & Zhang et al. 2009) in recently development. The dissolution of cellulose will disrupt the hydrogen bonding networks in cellulose by forming new H-bonds between the solvent and cellulose as a low energy require and environmentally friendly process. The original cellulose fibres architecture is mostly lost after the cellulose regeneration mechanism du e to the crystal structure transformation (Wang et al. 2011).
Zhang's laboratory has been successfully develop new solvent, such as NaOH/urea, NaOH/thiourea and LiOH/urea aqueous systems, in which the mechanism conditions are pre-cooled from -12 to -5 °C in recently research (Cai et al. 2007; Cai et al. 2008; Luo & Zhang et al. 2010).
Cellulose solution has been prepared form the NaOH/urea aqueous systems and it was applied to manufacture cellulose membrane novel fibre, films and gels by Zhang's laboratory. They found that the cellulose can exhibits as good mechanical characteristic in hydrogel matrix rather than traditional water-soluble natural polymer. Sodium alginate (SA) is defined as an acidic polysaccharide which are made or formed from linear block copolymer of 1-4 linked b-D-mannuronic acid and a-Lguluronic acid. It is readily convert into hydrogel component while the metallic divalent cations such as Ca2+ are added into SA solution. Although there are several type of material based on alginated have been presented throughout mechanism of blending, grafting and cross-linking, but there are never published any reported about the preparation of hydrogel from cellulose and SA in NaOH/urea aqueous systems. In addition, cellulose exist as a wormlike chain structure in the cellulose systems of NaOH/urea aqueous solution. According to Chang et al. 2009, cellulose and SA were dissolved in NaOH/urea aqueous solution to form the macroporous structure of hydrogel throughout chemical cross-linking mechanism. Besides that, the hydrogels were formed through the mixture of the both of the solution with different feed ratiosn to differentiate the different role between cellulose and SA (Chang et al. 2009).
Proposed mechanism for cross-linking reaction of cellulose and SA in alkali aqueous solution with ECH
Source: Chang et al. 2009
NaOH /urea solution
Recently, a milestone work in this field has been established by Zhang and coworkers, who successfully developed a series of nontoxic and recyclable cellulose aqueous solutions based on NaOH/urea and NaOH/thiourea (Zhang, Cai, & Zhou, 2005). These solvent systems can effectively dissolve cellulose over a large concentration range at low temperature through forming new hydrogen bonding and inclusion complex (IC) structure (Cai et al., 2008). Cellulose membranes have been prepared from the aforementioned cellulose solution via solution casting method. The membranes obtained usually suffered from low mechanical strength at a highly hydrated state due to its loose mesh-like structure (Mao et al., 2006; Ruan et al., 2004; Yang et al., 2007). This disadvantage greatly limited the application of regenerated cellulose products in some fields especially those need high-strength cellulose at hydrated state (Wu et al. 2010).
There were a series of novel solutions systems of cold alkaline/urea or thiorurea aqueous, in which consists of NaOH/urea, LiOH/urea, NaOH/ thiourea, etc has been studied as cellulose solution systems in latest development. There has a channel inclusion complex hosted by urea or thiorurea encaged the cellulose macromolecular in the aqueous solution at the condition of low temperatures. Resulting in the dissolution of cellulose, it can provide a rationable on the formation of a good dispersion of cellulose. 7 %NaOH/ 12% urea aqueous solution are defined as the most attractive and interesting of one of its convenient avaibility and low cost among all type of the alkali aqueous solutions. As compared of many organic solvent and the recent reported ionic liquids (ILs), the dissolution of cellulose at a low temperature can be considered as an environmentally friendly mechanism due to its consist some unique characteristic, such as avoidance of evaporation of the chemical agents. Furthermore, this cellulose solvent also known as a promising media for the ether homogeneous synthesis due to its behave abasicity properties. There has variety type of cellulose derivatives has been successfully synthesis under this homogeneous conditions, for example, there are methylcellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxylmethy cellulose, cyanoethy cellulose, quaternized cellulose and also cellulose polyelectrolytes (Li et al. 2011).
There are several research effort have been made on the elaboration of cellulose film forming solution with using cheap and non-polluting direct solvent such as alkaline, in addition to liquid ionic solvent recently (Cao et al. 2009). The dissolution of cellulose by NaOH /urea aqueous solvent and the 13CNMR spectra suggested the complete dissolution of the biopolymer and also the intra-molecular hydrogen bonds have been destroyed in this solution according to Zhang et al. 2005. In addition, the NaOH /urea alkaline dissolution will created a significant ion-pair interaction favouring new intermolecular interaction between urea and cellulose. Therefore, the chemical shifts gained were a non-derivatizing cellulose solvent, as same as those gained from the cellulose solvent of LiCl /DMAc. After the mechanism with an optimal coagulant H2SO4 5% wt / Na2SO4 5% wt aqueous solution, it can obtained a excellent properties of the cellulose films.The cellulose dissolution based on NaOH aqueous solutions, in which consist of thiourea can easily dissolved the cellulose rather than NaOH/ urea aqueous solutions. Besides that, NaOH/ thiourea also can appeared as direct cellulose solvent rather than derivative aqueous solution systems. In whatever way, the bioresourced products based on cellulose showed that it still reveal some defect if compared to common thermoplastics. NaOH urea alkaline system are allowing to preserve the biodegradability as one of the effective technologied, which is used to develop the biocomposites by the association of the cellulose with other biopolymers exhibiting film forming properties and derived from the renewable resource (Almeida et al. 2010).
In NaOH /urea aqueous systems, the NaOH and urea are behaved as non-toxic and inexpensive material. So that, it is worth nothing is there is no evaporation process of any chemical agents during the mechanism of dissolution of cellulose at low temperature, hence, it can preserve clean air in the environment even though production on large scale is held. Furthermore, during the processing of the mechanism of cellulose dissolution, it can easily separate and recycled the by-products to be reutilized. Na2SO4 and urea are the commonly by-products in the coagulation bath, which can be separated easily by using flash evaporation and then crystallization, that is because it contain a large difference solubility between Na2SO4 and urea. Because this process is the non-polluting and easily to recycle, so that is usually known as "green technology" pathway (Luo & Zhang 2010).
Hydrogel are generally defined as three dimensional (Samchenko et al. 2011), hydrophilic, polymeric network, with the chemical or physical cross-linked, capable to absorb large amount of water of biological liquids within their porous structure (Chang & Zhang et al. 2011; Samchenko et al. 2011).the hydrogel water holding capacity occur mainly cuased by the presence of hydrophilic groups like amido, amino, carboxyl, hydroxyl groups etc in polymer chains. The water content of hydrogel may varied from 10 % to thousands of times of the dry polymer network's weight (Samchenko et al. 2011; Hoffman 2012). Besides that, hydrogel also behave as sensitivity to environment, tissue-like water content and elacticity that provided the potential for the application in biomedical field (Opera et al.2012). According to definitions of hydrogels types, it can be divided into those formed form natural polymers and those formed through synthetic polymer according to the source applied(Samchenko et al. 2011). Besides that, hydrogels can also be divided into chemical gels and physical gels on the basis of the cross-linking method (Samchenko et al. 2011). Physical gels are usually can formed through molecular self-assemblu through ionic or hydrogen bonds; where else the chemical gels are fored by covalent bonds (Schermen & Merten, 2009). It is worth nothing that the hydrogel have widely application in various field such as food, biomaterials, agriculture, water purification, etc (Chang & Zhang et al. 2011).
Because hydrogel's physical properties are similar to those of human tissues and also possess excellent biocompatibility, therefore, it have attracted much attention and interest. About 50 years ago, hydrogels were first reported for biomedical application. Nowadays, it was widely applied in various fields, which consist from agriculture to controlled drug delivery systems(Opera et al.2012). The polymer blending are to be considered as a most useful method for the improvement or modification of the polymeric materials's physicochemical properties. Numerous blends between the biopolymer and synthetic polymers re of particular significant cause these polymers can be applied as biomedical and biodegradable materials. Hydrogels that are fabricated from natural polymers are consists of many unique adavantage; for example, abundant, in general, non-toxicity, biocompatible, biodegradability and aso biological function. Hence,it become promising for the application in the biomedical field, especially polysaccharides (Chang et al. 2008).
Hydrogels can also classified according to conventional and stimulus responsively ones. The conventional hydrogels usually defined as cross-linked polymer chains which can absorb water from aqueous medium without changing the equilibrium swelling under the condition of the change in pH, temperature, electric field or other external stimuli of the environments. Where else the stimulus responsive hydrogel are the polymeric network in which their equilibrium swelling changing rapidly due to the changing of the environment. Therefore, there are many physical like temperature, pressure,light, electri, magnetic andsound fiels and chemicals stimuli which consist of pH, ionic strength, ions or specific molecular recognition events which can be used to induce the different responses of the systems of smart hydrogels (Samchenko et al. 2011).
Usually, cellulose hydrogel can be fabricated through chemical crosslinking mechanism of water soluble cellulose derivative, like cellulose acetate, hydroxyethylcellulose and sodium carboxymethylcellulose (Enthceva et al. 2004). But the physically crosslinking of ellulose hydrogel can be obtained by developing intermolecularhydrogen bonds via hydroxyl groups iin cellulose molecular chains.There are steps involving in the formation of such gel systems, pregelation and regeneration. Cellulose/ poly (vinyl alcohol) hydrogel can be prepared from NaOH/urea aqueous solution by applying a pre-gelation process of freezing and thawing for 98 hours (Chang et al. 2008). Whenever the cellulose/ NaOH/thiourea aqueous solution was stored at 5, 20 and 35 ° C pre-gelation temperatures for three week to gaet dense structure cellulose physical hydrogel. Where else, cellulose NaOH aqueous solution was kept at room temperature for 15 hours for the preparation of the pre-gelated cellulose gel and afterwards the regeneration kinetics of cellulose gel as investigated with immersed in a nonsolvent bath. In spite of success to obtain a good mechanical strength gels, solute permeability and non-toxicity gels (Wu et al. 2010), these method generally consists of a time-consuming pre-gelation process, in which it is not practical for the industrial production (Wang & Chen 2011).
Cellulose has many hydrogel which can be easily form hydrogel bonding linked network, so that with through this physical cross-linking, it can be obtained from a cellulose solution. In whatever way, cause by its act as highly extended hydrogen bonded structure which make its very difficult to be dissolved in common solvent (Edgar et al. 2001), so that there a lack of appropriate solvent is a major problems for preparing cellulose hydrogel. N-methylmorpholine-N-oxide (NMMO), ionic liquids (ILs),and alkali /urea (or thiourea) aqueous system have been developed to dissolove cellulose providing great possibility for the cellulose hydrogel preparation in recently (Chang & Zhang 2011).
As reported by Cai and Zhang, cellulose solution (4 wt %) was prepared by the mixture of LiOH/urea/water with a ratio of 4.6/15/80.4%. the dry cellulose was added and stirred vigorously for 10 min after the solvent is cooling to 15 °C, hence it can obtins a transparent solution with 4 wt% concentration. After that, this solution was aubjected to centrifugation for 20 min at 3500 rpm in the condition 4°C to ensure the air bubbles in the solutionare removes. After that, the solution was cast on glass plate to form 1mm thick layer, and immersed in methanol bath for around1 hour for the regeneration purpose. Then, the regenerated cellulose gel was washed with deionized water thoroughly (Kim et al. 2010; Kimura et al. 2011; Isobe et al. 2011). Furthermore, compared with NaOH/urea system, LiOH/urea system can obtained stronger dissolution power and higher thermal stability properties of cellulose solution (Cai & Zhang 2005; Isobe et al.2012).
Properties of hydrogel
These unique properties of hydrogel like swelling and deswelling make it's become important in biological application (Bardejee et al.2008). The swelling ratios for the hydrogel will be decreased with the increasing concentration of cellulose concentration. Therefore, cross-linking degree is generally known as having great influence for the determining the water absorbency of hydrogels. Physical cross-linking if the polymer chain also play an important role in the determining of the swelling ratio of hydrogel except for the chemical crosslinking of cellulose by ECH (Chang et al. 2010). The smartness of hydrogels usually are determined by their swelling and shrinking properties, blended ability, curl and degrade in respond to external stimuli, such as pH, solvent, temperature, electric and magnetic fields (Bardejee et al. 2008).the physical cross-linking of the hydrogel is strengthened by more and more inter-molecular hydrogen bonds and chain entanglements, thus resulting in the decreasing of swelling ratios due to the increasing of concentrations of the cellulose. This viewpoint showed that the more rigid and stable of hydrogen bonding could be set up by the molecular rearrangement in cellulose during the freezing mechanism. The strong interaction and partial crystallinity which occur in hydrogel obtained by freezing process, which hinder the water molecules penetration, develop the swelling degree of hydrogels by freezing being lower rather than obtain through heating process (Chang et al. 2010).
In summary, transparent hydrogels have been successfully synthesized from cellulose in NaOH/urea aqueous solutions by using ECH as cross-linker and by heating and freezing methods; it can be successfully synthesized the transparent hydrogel. The macroporous structure could be observing in the hydrogel prepared through heating method, where else the hydrogel prepared by freezing displayed fibres like structure. The light transparency and equilibrium swelling ration of hydrogel will be decreased with the increasing of the cellulose concentration, where else the reswelling water uptake and the storage modulus increased. The cellulose hydrogel obtained by heating will displayed better light transmittance, higher equilibrium swelling ratios, higher water uptakes and relatively weaker mechanical strength rather than the hydrogel post treated by freezing method. There several difference to the type and physical crosslinking extent of cellulose molecule, through the heating and freezing mechanism, as well as the chemical cross-linking (Chang et al. 2010)
There are several types of macromolecular structures might exist for physical and chemical, such as crosslinked or entangled networks of linear homopolymers, linear copolymer, and block or graft copolymer; polyion-multivalent ion, polyion-polyion or H bonded complexes; hydrophilic networks stabilized by hydrophobic domains; ans IPNs or physical blens (Hoffman 2012).
Besides that, hydrogel can also occurs as many different physical forms, such as
Solid molded forms (e.g., soft contact lenses)
Pressed powder matrices (e.g., pills or capsule for oral ingestion)
Microparticles (e.g., as bioadhesive carriers or wound treatments),
Coatings (e.g., on implants or catheters; on pills or capsules; or coatings on the inside capillary wall in capillary electrophoresis),
Membranes or sheets (e.g., as a reservoir in a transdermal drug delivery patch; or for 2D electrophoresis gels),
Encapsulated solids (e.g., in osmotic pumps), and
Liquids (e.g., that form gels on heating or cooling).
A wide and diverse range of polymer compositions have been applied to manufactured hydrogels. This polymer can be differentiate into natural polymer hydrogels, synthetic polymer hydrogels and combinations of the two classes (Hoffman 2012).
Hydrogels also can define as 'permanent' or 'chemical' when they are covalently cross-linked networks. Besides that, chemical hydrogel might also be generated through crosslinking of water soluble polymers, or by hydrophobic polymers to hydrophilic polymers plus crosslinking to form a network. Sometimes, crosslinking is not necessary in the latter case. For example, the PAN in the hydrolysis to form amide and acid groups from nitrile, they can stabilize the hydrogel by hydrophobic interactions if the nitrile groups remain in sufficient concentration and association, hence a physical hydrogels will be form. Crosslinked hydrogels reach an equilibrium swelling level in aqueous solution in which it mainly decided by the crosslink density which estimated by the MW between crosslinks, Mc in crosslinked state. The chemical hydrogels not behave like physical hydrogel as it are not homogeneous. Furthermore, they usually consist of low water swelling and high crosslink density region, which also known as 'clusters'. In sometimes, it's are desired on the solvent composition, temperature and solid concentration during gel formation, phase separation can exist and water filled 'void; or macroporous can form. Where else, the free chain ends represent gel network 'defect' which do not contribute to the elasticity of the network in the chemical gel. Where else other network defect are chain 'loops' and entanglement, which also do not contribute to the permanent network elasticity (Hoffman 2012).
Through hyaluronate, alginate, starch, gelatin, cellulose (Chang et al. 2010), chitosan and their derivatives, it can form various types of cellulose which showing it has potential application in biomaterials fields due to their excellent properties like safety, safety, hydrophilicity, biocompatibility and biodegradability (Chang & Zhang 2011).
Syhthetic polymer based hydrogel are those formed through by cross-linking poly (ethylene glycol),poly (vinyl. alcohol), poly(amide-amine), poly(N-isopropycrylamide) polyacrylamide, and poly(acrylic acid) and their copolymers (Kim, Singh, & Lyon, 2006). Besides that, synthetic hydrogel such as pEG-based hydrogel have some advantages rather than natural hydrogel, like photopomerization ability, adjustable mechanical properties, and it's are easy control of scaffold architecture and chemical composition. In whatever way, it can't provide an ideal environment to support cell adhesion and tissue formation alone which is cause by their bio-inert nature behaviour. That has a number of polysaccharides have similar properties to PEG phase of biocompatibility and low protein and cell adhesion, and they can be biodegraded to nontoxic products that are easily assimilated by the body (Shoichet 2010; Chang & Zhang 2011).
Superabsorbent hydrogels are hydrophilic cross-linked, linear or branched polymer with the ability to adsorb huge amount of water, saline or physiological solution. These resource are fabricated through water polymer by crosslinking them either using radiation or cross linker (Pourjavadi et al. 2004), with capable water absorption and swelling properties, but it can't dissolve in water. The most efficient water absorbers are polymer networks that carry dissociated, ionic functional groups which capable swell in water and hold huge quantities of water while maintaining the physical dimensions structure. These smart hydrogel have potential applied in site-specific delivery of drugs to specific of the gastrointestinal tract and it have been form for the delivery of low molecular weight protein drugs. Furthermore, the responsive or smart hydrogel have become as an important part in the medicine, pharmacy and biotechnology research and development field (Mahdavini et al. 20040; Chang & Zhnag 2011).
Composite hydrogel from cellulose and other polymer have been fabricated through blending, complex formation, and IPN technology, to combine the different cellulose and other polymer properties. Various type of composite hydrogel can be designed in wide range from macroscopic materials like membranes, fibers and bead to microscopic materials like microgels and nanogels (Chang & Zhang 2011).
Cellulose-based hydrogel also exhibit as many excellent properties like hydrophilicity, biodegradability, biocompatibility, transparency, low cost and non-toxicity. Furthermore, cellulose also exhibit as environmental friendly ans low-cost hydrogel which will form a viable substitute for petroleum-based materials in near future (Chang & Zhang 2011). Hence, cellulose based hydrogel have wide range application in tissue engineering (Peppas et al. 2006), controllable delivery system (Chang et al. 2010), blood purification, sensor, agriculture,as well as waterpurification (Zhou et al.2005) and also chromatographic supports (Xiong et al 2005;) nowadya, scientist also devoted much focus to developing novel hydrogels for wide application, for example, biodegradable materials for drug delivery, tissue engineering, sensorm contact lenses, purification, etc (Chang & Zhang 2011).