Preparation and Characterization of Functionalized Chitosan Derivatives from Prawn Waste for Cellulose Fibre Modification to Enhance Textile Properties

The prawn processing industry has been rapidly growing in all the costal countries. In these industries, prawns are processed to headless or peeled or both, while head and shell portions are considered as wastes. Therefore, a huge amount of bio-waste is generated throughout the world and it is estimated about 6-8 million tons annually [1]. It’s a serious environmental concern to dispose such an enormous amount of waste. Although these wastes are biodegradable in nature but produce obnoxious smell, attract pathogenic insects and thus create an unhygienic atmosphere.


Introduction
The prawn processing industry has been rapidly growing in all the costal countries. In these industries, prawns are processed to headless or peeled or both, while head and shell portions are considered as wastes. Therefore, a huge amount of bio-waste is generated throughout the world and it is estimated about 6-8 million tons annually [1]. It's a serious environmental concern to dispose such an enormous amount of waste. Although these wastes are biodegradable in nature but produce obnoxious smell, attract pathogenic insects and thus create an unhygienic atmosphere.
This problem can be solved by immediate recycling of the prawn shell generated and extraction of commercially valuable products to be further used in other applications [2]. We know that crustaceans shell contains 15-40% chitin, 25-40% proteins and 30-50% minerals [3]. Among them chitin is considered the second most abundant natural biopolymer after cellulose. Chemically chitin is poly-β-(1-4)-N-acetyl-D-glucosamine, whereas chitosan, a deacetylated form of chitin, is polyβ-(1-4)-D-glucosamine. As a natural bio-material, chitosan has versatile properties such as nontoxicity, biocompatibility, biological activity and biodegradability [4,5] that widen its applications in many fields such as drug delivery [6,7], waste water treatment [8,9], cosmetics [10,11], C industry [12][13][14][15], textile etc. But in all these cases, chitosan is only applicable for acidic condition due to its poor solubility in neutral and basic medium. So, it is necessary to enhance the solubility of chitosan in water over a wide range of pH.
The solubility of chitosan can be improved by introducing

Abstract
The purpose of this research was to develop water soluble textile modifiers based on biopolymer having improved textile properties including tensile strength, moisture absorption, wash resistance, dye-ability and colour fastness properties. Two fibre reactive chitosan derivatives such as N-(2-hydroxy) propyl-3-trimethylammonium chitosan chloride (HTAChC) and N-methylolacrylamide-N-(2-hydroxy) propyl-3-trimethylammonium chitosan chloride (NMA-HTAChC) were synthesized from chitosan through dispersion of chitosan with glycidyltrimethylammonium chloride (GTMAC) in aqueous medium and dissolution of HTAChC in aqueous N-methylolacrylamide (NMA) solution in presence of NH4Cl and 4-methoxyphenol, respectively. The physicochemical properties of prepared derivatives were studied and the degree of quaternization (DQ) of HTAChC was 0.94, double bond content of the NMA-HTAChC was 0.926 mmol/g and moisture content of HTAChC and NMA-HTAChC were 22.06% and 18.78%, respectively. The FTIR spectra of HTAChC showed prominent peak at 1480 cm -1 (C-H bending), 1650 cm-1 (C=O group) and that of NMA-HTAChC showed the peaks at 1670 cm -1 (C=O stretch) and 1545 cm -1 (N-H bending) which confirms the synthesized derivatives. The prepared derivatives were further used for modification of cotton and jute fibres Graft yield percent of HTAChC and NMA-HTAChC on cellulose fibre surfaces were 10.69% and 14.74% for jute and 14.56% and 18.86% for cotton, respectively. Grafting was investigated by FTIR, SEM, TGA, DTA and DTG analyses. The surface of modified fibre was investigated by SEM and the surface was smoother than unmodified fibre. The modified fibre showed decreased thermal stability, improved moisture absorption, wash resistances and tensile strength compared to unmodified fibres. It was also observed that textile modifying properties of NMA-HTAChC is better than HTAChC due to higher fibre affinity of NMA-HTAChC to cellulose fibres. Dyeing of modified and unmodified cotton and jute fibres with reactive and direct dyes revealed that dye exhaustions were increased up to 10% due to modification. hydrophilic groups on chitosan backbone such as carboxymethyl, dihydroxyethyl, sulfate, phosphate, hydroxyalkylamino, or by grafting a water soluble polymer [16][17][18] and quaternization of amine group of chitosan [19]. Among these, due to permanent positive charge on nitrogen atom, the quaternary chitosan derivatives show higher affinity for cellulose fibre surface and H-bonding potential, which can improve the tensile strength of the modified cellulose fibres [20]. Hence, it is assumed epoxide of glycidyltrimethylammonium chloride (GTMAC) reacts with the primary amino groups of chitosan following a nucleophilic addition pathway to synthesize quaternary derivative N-(2-hydroxy) propyl-3-trimethylammonium chitosan chloride (HTAChC). Again, HTAChC is treated with N-Methylolacrylamide (NMA) to obtain N-methylolacrylamide-N-(2-hydroxy) propyl-3trimethylammonium chitosan chloride (NMA-HTAChC) for higher functionality with excellent textile finishing properties, because NMA has two reactive groups, a N-methylol group and a double bond conjugated with a carbonyl group.
The demands of natural cellulose jute and cotton fibres in apparel industry is increasing day by day throughout the world due to several unique properties such as biodegradability, agricultural renewability, softness, moisture absorbency, comfort ability in wear etc. Beside these, cellulose fibres possess some inherent limitations such as high dimensional stability, shrinkage, susceptibility towards sunlight (UV), microbial degradation, lower dye uptake etc. which limit the direct use of these fibres in textile. To minimize the unfavorable properties and to achieve the quality textile fibre, surface modification is necessary. Many workers have modified the cellulose fibres with numerous chemicals prior to dyeing and achieved better results in many cases [21]. But the environmental issue was not considered because the modifiers were synthetic, toxic in nature, non-biodegradable as well as non-hygienic for human health. An ideal textile modifier needs to be safe, nontoxic, environmental friendly and durable to wash, so textile researchers prefer to apply eco-friendly modifiers on cellulose fibres. This paper deals with the preparation of water soluble quaternary ammonium chitosan derivatives such as HTAChC and NMA-HTAChC from prawn shell waste and modifications of cellulose jute and cotton fibres with these prepared bio-materials to functionalize the fibre backbone which in turn will enhance the dyeability. Considering chemical characteristics and modification properties, these derivatives would play significant role in textile areas mainly as a modifier for cellulose fibres instead of petroleum based chemical modifier and at the same time would help to manage the environmental pollutions around the prawn processing industrial areas.

Deacetylation of chitin to chitosan from prawn shell waste
The collected prawn shell was first washed with water and dried at 105°C for 72 h, then the size was reduced to 40-60 mesh using hammer mill. The ground prawn shell was treated with 1 N HCl and 1 N NaOH maintaining shell to extractant ratio of 1:16 (w/v) at 105°C for 4 h for demineralization and deproteinization [22]. The process was carried out second and third time for pure chitin extraction [2,22]. The conversion of chitin to chitosan was achieved by the treatment of chitin with 40% NaOH (w/v) at 105°C for 3 h to remove the acetyl groups with a solid to solvent ratio of 1:20 (w/w). After this process solid separated from the alkali layer were extensively washed with distilled water to neutral and dried in a vacuum oven at 50°C for 24 h. The process was repeated out second and third time for pure chitosan extraction [2,23]. The reaction of chitin into chitosan is given below (Figure 1).

Preparation of HTAChC
Chitosan (1 g) was dispersed in 20 mL of distilled water maintaining at 85ºC by a hot plate with magnetic stirrer. As chitosan was completely dispersed, GTMAC was added three times with constant stirring at a 2 h interval. After a total 10 h reaction, the clear and yellowish reaction solution was poured in 200 mL cold acetone while stirring and kept in the refrigerator overnight. The next day, acetone was decanted and the remaining gel-like product was dissolved in 100 mL methanol. The solution was precipitated in a 250 mL acetone and ethanol (4:1) mixture. The filtrated crude HTAChC was purified by washing with hot ethanol using a soxhlet extractor for 24 h. The final product was collected and dried at 60°C overnight. The obtained product was HTAChC. The reaction of chitosan and GTMAC to obtain HTAChC is shown in Figure 2.

Preparation of NMA-HTAChC
Acrylamidomethylation of HTAChC is carried out by dissolving HTAChC to an aqueous NMA solution in presence of NH 4 Cl. The HTAChC (1 g) was dissolved in 5 mL of 48 wt. % aqueous NMA solution with a small amount of 4-methoxyphenol (0.2% w/v) which was added as a polymerization inhibitor at room temperature. To the solution, NH 4 Cl (0.5 g) was added and dissolved to maintain the acidic medium for acrylamidomethylation reaction. The reaction solution was reacted at 140°C for 8-20 min using an oil bath. After reaction, 15 mL of methanol was added to the reaction solution and it was stirred for 10 min. The product was precipitated in 100 mL acetone and kept overnight for decant. The decanted product obtained is crude NMA-HTAChC. Crude NMA-HTAChC was washed thoroughly with a mixture of acetone and ethanol (1:1) for several times and finally with ether. The white reaction product was dried at 40°C under vacuum for 2 days. The synthesis reaction of NMA-HTAChC is shown in Figure 3.

Preparation of jute fibre
Jute fibre (30 cm) was taken from middle portion for the present investigations. The raw jute fibre was scoured with a mixture of 6.50 g detergent and 3.50 g soda in one litre water at 75°C for 30 min in a beaker in the ratio of 1: 50 (w/w) [24]. This scoured jute fibre was bleached with a 5 g/L sodium chlorite solution of pH 4 at 85-90°C, for

Preparation of cotton fibre
At first, the cotton fibres were washed with 0.2% Na 2 CO 3 solution at 75°C for 30 min in a beaker in the fibre to liquor ratio of 1:50. The fibres were then washed thoroughly with distilled water and dried in the open air. After that the fibres were dried in an oven at 60°C and then stored in a desiccator [24,26].

Grafting of cellulose fibres with HTAChC and NMA-HTAChC
Required amount of HTAChC or NMA-HTAChC was dissolved in distilled water. Then the washed fibre sample was dipped into the liquor with maintaining fibre to liquor ratio of 1:50 at 70-75°C and allowed to stand for 1h. MgCl 2 .6H 2 O (1.2% of liquor) was added to the liquor as catalyst along with Triton X-100 (0.1% of liquor) as a penetrating agent and sodium lauryl sulfate (0.1% of liquor) as softening agent. The treated fibres were washed in distilled water to remove unfixed HTAChCor NMA-HTAChC. The fibre was dried at 60ºC to a constant weight. The grafting reaction of cellulose with HTAChC and NMA-HTAChC are shown in Figure 4.

Exhaust dyeing of modified jute and cotton fibres
Dyeing was carried out using 0.3% reactive dye (on the weight of fibre) in a dyeing machine (DYSIN, Taiwan, China) at 65°C for 1.5 h using a plastic stoppered conical flasks. The exhaustion of dye was determined colorimetrically (Type-S104, No-221, Spectrophotometer, WPA Linton Cambridge, UK) by using the following equation: Where, Do and De are the initial and exhausted dye bath concentration, respectively.

Determination of degree of deacetylation of chitosan
The degree of deacetylation (DD) of chitosan was determined by the potentiometric titration method. 0.5 g of chitosan was dissolved in 25 mL of 0.1 M standard aqueous HCl solution and calculated amount of KCl was added to adjust the ionic strength. The titrant was a solution of 0.05 M NaOH. pH of the solution during titration was measured using pH meter under continuous stirring [27]. The standard NaOH was then added stepwise and the conductivity of the solution were recorded by a Professional Benchtop Conductivity Meter (BC-3020, Singapore) and a curve with two inflection points is observed in Figure 5. The difference between the volumes of these two inflection points corresponded to the acid consumption for the salification of amine groups of chitosan and permitted the determination of degree of acetylation, through the following Equation: Where, V 1 are the base volumes referred to first inflection points in mL, V 2 are the base volumes referred to second inflection points in mL, M b is the base molarity in g/mol, and W is the original weight of the polymer in gram.

Determination of degree of quaternization of HTAChC
The degree of quaternization (DQ) of GTMAC on chitosan was measured by conductometric titration of Clwith aqueous silver nitrate (AgNO 3 ) solution [28]. Dried HTAChC (0.1 g) was dissolved in 100 mL of distilled water and conductometrically titrated with aqueous 0.017 N AgNO 3 aqueous solution. Conductivity of the solution was observed with a Professional Benchtop Conductivity Meter (BC-3020, Singapore). A curve with one inflection point was obtained by plotting

Degree of deacetylation of chitosan
The content of free amino groups in the polysaccharide can be determined by degree of deacetylation (DD) which differentiates between chitin and chitosan. This deacetylation process involves the substitution of acetyl groups from the molecular chain of chitin with complete amino group (-NH 2 ) and the end use of chitosan depends mainly on this high degree chemically reactive amino groups. Since the degree of deacetylation depends mainly on the method of purification and reaction conditions [29], it is therefore essential to determine its degree of deacetylation prior to its end usages. From Figure 7, it is    This was due to the fact that when fibres were washed at room temperature, only some extra deposition of compounds on fibre surfaces was removed. In case of high washing temperature, loosely bonded substances and impurities deposited on the fibre surface were removed finally resulting some weight loss and decreased the grafting percentage. Loss in grafting percentage in case of NMA-HTAChC modified jute and cotton fibres were comparatively greater than that of HTAChC modified jute and cotton fibres. This is due to the higher solubility of NMA-HTAChC modifiers in water and detergent solution. Also, loss in grafting is slightly higher in case of detergent wash compare to distilled water wash due to the more surface activity of detergent solution.

FTIR Spectroscopy
FTIR spectroscopy of the chitosan, HTAChC and NMA-HTAChC shows the evidence of the conversion of chitosan to HTAChC and NMA-HTAChC. Chitin and chitosan can be differentiated by FTIR peak analysis. Chitin shows two strong absorption peaks at 1660 cm -1 and 1557 cm -1 for C=O stretching and the N-H bending of the secondary amide respectively. In the case of chitosan, peak at 1600 cm -1 indicates that most of the secondary amide has been changed to primary amine by the alkaline deacetylation (Figure 10b).
In Figure 10c, two absorption peaks at 1480 cm -1 and 1650 cm -1 corresponding to the C-H bending of trimethylammonium group and C=O stretch of the secondary amide, respectively in the spectra of HTAChC. It can be mentioned that the H atom of primary amine is successfully replaced by CH 2 CH(OH)CH 2 N + (CH 3 ) 3 Clgroup [30] and Degree of quaternization (DQ) of HTAChC obtained was 0.94 ( Table 2).
The IR spectra of the NMA-HTAChC, as shown in Figure  10d, it can be observed that the peaks at 1670 cm -1 and 1545 cm -1 corresponding to the C=O stretch and N-H bending of the secondary amide in the acrylamidomethyl group, respectively. The double bond content of prepared NMA-HTAChC was calculated as 0.926 (mmol/g NMA-HTAChC).
seen that the degree of deacetylation (DDA) value of chitin was 85% at temperature 80 o C, 50% alkaline solution, solid to liquor ratio of 1:50 (w/v) for 4 h refluxing in presence of ethanol.

Moisture content
Moisture content of chitosan, HTAChC and NMA-HTAChC were 10.3%, 22.4% and 18.7% respectively. Moisture absorption capacity of HTAChC is much higher than chitosan because of its high affinity to moisture due to the presence of quaternary amino group and secondary alcoholic group. Moisture absorption capacity of NMA-HTAChC is also higher than chitosan but slightly lower than HTAChC because primary hydroxyl group of chitosan backbone of HTAChC is occupied by NMA in NMA-HTAChC. Moisture content of prepared compounds is shown graphically in Figure 8.
In the present investigation it is observed from Figure 8 that HTAChC and NMA-HTAChC modified fibre showed higher moisture content compared to unmodified fibres. Because HTAChC and NMA-HTAChC provide more hydrophilic group on cellulose fibre backbone which in turn increases the moisture content of modified jute and cotton fibres.

Tensile strength of cellulose fibres
As shown in Figure 9, HTAChC and NMA-HTAChC modified cellulose fibre has more breaking strength than unmodified cellulose fibres. These are due to the modification of cellulose fibres with HTAChC and NMA-HTAChC which cause reduction of crystallinity of cellulose fibre. The improvement in fibre strength of modified cellulose fibre may be attributed to the penetration of modifier particles in fibre pores and crosslinking to the adjacent fibre molecules. It is also clear that NMA-HTAChC has higher fibre strength improving properties compare to HTAChC which is due to better crosslinking activity with cellulose fibre than HTAChC.

Wash resistance of modified jute and cotton fibres
From Table 1, it is seen that, when the modified fibres were washed with distilled water and detergent solution at room temperature there was minor change in weight loss (loss in grafting) whereas when it was washed with distilled water and detergent solution at 40 o C and 60 o C temperature there were occurred a considerable decreases in weight loss. The FTIR spectra of unmodified, HTAChC modified and NMA-HTAChC modified cotton fibres are mostly similar as the adsorption peaks were obtained in the spectra of entire sample except the new additional peak in the modified cotton fibres. The FTIR spectra of modified cellulose fibres show a new peak at 1480 cm -1 for HTAChC and 1545 cm -1 for NMA-HTAChC which are the evidence of grafting of HATCC or NMA-HTAChC on cellulose cotton and jute fibre.

Scanning Electron Microscopy Analysis
Surface morphology of unmodified and HTAChC and NMA-HTAChC modified cellulose fibres were studied by scanning electron micrographs ( Figure 11). The SEM micrograph shows the fractured surfaces of the untreated cellulose fibres and the smoother surfaces of HTAChC and NMA-HTAChC modified cellulose fibres. The SEM of unmodified cellulose fibres shows the presence of large amounts of micro pores on its surface while few pores are visible on HTAChC and NMA-HTAChC modified cellulose fibre which indicates the incorporation of HTAChC and NMA-HTAChC on cellulose chain of cotton and jute fibres surface.

Thermal Analysis
The Thermo Gravimetric Analysis (TGA) describes the thermal behaviour of a sample. Figure 12 shows the thermal behavior of raw and modified jute and cotton fibres. From the thermograms, necessary thermal information of jute and cotton fibres is enlisted in Table 3. TGA thermogram shows that decomposition paths for unmodified and modified cellulose fibres have three stages of thermal degradation. There is a weight loss in first stage between 100-120°C, due to dehydration of cellulose. In second stage between 200°C and 270°C, rapid weight losses are observed for thermal degradation of the cellulose fibres. In third stage, residual char is formed through weight loss which reaches       to be a fixed weight. On the basis of initial decomposition temperature (T i ), the thermal stability of unmodified and modified cellulose fibres shows the following order: unmodified >HTAChC modified >NMA-HTAChC modified.
From DTA curve, a large exothermic peak is observed, due to oxidative decomposition of cellulose fibre samples, which involves the evolution of CO and CO 2 , and formation of carbonaceous residue [31].
In the DTG, two exothermic peaks were observed at 310-350°C and 425-470°C, respectively. The second peak is deeper and sharp than that of the first peak which reveals that weight loss in second stage is higher HTAChC and NMA-HATChC modified fibres exhibit considerably deep dye colour (Table 5). This could be due to attachment of HTAChC to the cellulose fibre backbone, which helps to increase the functionality as well as reactivity. NMA-HTAChC modified cellulose fibre exhibits comparatively higher dye absorption due to presence of secondary amino group and vinyl group in NMA-HTAChC.

Conclusion
Two water soluble functionalized chitosan derivatives (HTAChC and NMA-HTAChC) were successfully prepared from prawn shell waste via chitin and chitosan. Later prepared HTAChC and NMA-HTAChC were applied to cellulose fibres to evaluate their textile finishing properties. The incorporation of HTAChC and NMA-HTAChC on fibres backbone was confirmed by both FTIR and SEM analysis. The modified cellulose fibres showed improved tensile strength, moisture absorption, wash resistances and dyeability than that of unmodified fibres, whereas thermal stability decreases. The prepared HTAChC and NMA-HTAChC can be successfully used as textile modifier for the improved performance of jute and cotton fibres. The synthesis of HTAChC and NMA-HTAChC for value added environmentally friendly textile modifier and other applications will thus help to manage pollution from prawn shell waste in prawn processing zone.