TECHNICAL FIELD OF THE INVENTION

The present invention relates to a paint composition capable of removing arsenic from ground water when coated on substrates suitable for containing water. More particularly, a chitosan modified epoxy based paint composition capable of removing arsenic from ground water when coated on substrates suitable for containing water such as water storage tank, swimming pool, reservoir etc.

BACKGROUND OF THE INVENTION
The chronic arsenic poisoning dissolved in groundwater is a worldwide public health issue. Particularly, lower Gangetic basin in India and similar part in Bangladesh. In most of the cases, arsenic exposure occurs from consumption of underground water as drinking water. Human skin is very sensitive to arsenic like skin lesions and other chronic effects of arsenic exposure via drinking water are neurological, hypertension, cardio vascular disease, respiratory disease and malignancies like skin, lung, liver and kidney. The conventional methods for the removal of arsenic from ground water are adsorption, co-precipitation, ion exchange and membrane separation. However, the major limitations of these processes are low efficiency and applicability/appropriateness of technologies – because of low arsenic concentration and differences in source water composition. In recent research trend, techniques like adsorption, ion exchange and chelation by polymer, especially different biopolymers are being extensively used for metal ion recovery because of their advantages over conventional techniques.

Chitin is a natural polymer reported 200 years ago and it is the second abundant polysaccharide on Earth after cellulose. Chitosan is obtained from chitin by partial deacetylation in alkaline medium. Chitin/chitosan is a white, hard, inelastic, nitrogenous polysaccharide found in the exoskeleton as well as in the internal structure of invertebrates. The structure of chitin is composed of ß (1,4) – linked 2 – acetamido-2-deoxy-ß-D-glucose (N-acetylglucosamine) and chitosan is a linear copolymer of a (1,4) – linked 2 – amino-2-deoxy – ß-D-glucopyranose and ß (1,4) – linked 2 – acetamido-2-deoxy-ß-D-glucose (N-acetylglucosamine).

Chemical structure of Chitin and Chitosan

Due to the presence of amine (-NH2) and hydroxyl (-OH) functional groups in the structure of chitosan, it has the ability to form complexes with the metals [Wang, X., Liu, Y. Zheng, J., Environ Sci Pollut Res. DOI 10.1007/s11356-016-6602-8]. The ability of chitosan to adsorb metal ions involves electrostatic interaction, metal chelation and ion pair formation.

Chitosan can be modified in different physical forms like nanoparticles, gel beads, membranes and fibers, chitosan flakes, molybdate-impregnated chitosan beads, chitosan immobilized sodium silicate, iron coated chitosan flakes, chitosan beads impregnated with iron, zero valent iron encapsulated chitosan nano spheres, iron crosslinked chitosan, chitosan coated sand and iron chitosan coated sand, chitosan coated bentonite, chitosan coated kaolinite have been reported for the adsorptive removal of arsenic from water [Gang, D.D., Deng, B.L., Lin, L.S., (2010) As (III) removal using an iron impregnated chitosan sorbent. J. Hazard Mater 182; 156 – 161; Gupta, A., Chauhan, V.S., Sankararamakrishnan, N., (2009) Preparation and evaluation of iron-chitosan composites for removal of As (III) and As(V) from arsenic contaminated real life groundwater. Water Res 43; 3862-3870; Gupta, A., Yunus, M,, V.S., Sankararamakrishnan, N., (2012). Zerovalent iron encapsulated chitosan nanospheres – a novel adsorbent for the removal of total inorganic arsenic from aqueous system. Chemosphere 86; 150 – 155; Gerente, C., Andres, Y., Mc Kay, G., Le Cloirec, P. (2010) Removal of Arsenic (V) onto chitosan: From sorption mechanism explanation to dynamic water treatment process. Chem.Eng. J. 158, 593 – 598; and Dambies, L., Guibal, E., Roze, A., (2000) Arsenic (V) sorption on molybdate-impregnated chitosan beads. (2000) Colloids surf. Physicochem. Eng. 170, 19 -31]. After modification of chitosan, the adsorption efficiency is increased in view of increased porosity, surface area and surface charge. In 2008, Boddu et. al. reported chitosan in combination with alumina, the adsorption efficiency of As (V) increases due to strong electrostatic force of attraction [Baddu, V.M.; Abburi, K; Talbott, J.L; Smith, E. D; Hassch, R. Removal of arsenic (III) and arsenic (V) from aqueous medium using chitosan coated biosorbent. Water Res. 2008,42,633 - 642]. The positively charged Al3+ at the surface of chitosan, adsorb negatively charged HAsO4-/H2AsO42- by electrostatic attraction. In 2012, Saha and Sarkar also reported the adsorption capacity of chitosan enhanced by using alumina nanoparticles in the combination of both chitosan-g-poly acryl amide and alumina [Saha, S., Sarkar, P., (2002) Arsenic remediation from drinking water by synthesized nano-alumina dispersed in chitosan-grafted polyacrylamide. J. Hazard Mater 227-228; 68-78]. Titanium di oxide loading onto chitosan can increase the adsorption efficiency under UV light mainly due to the ability of conversion of As (III) to As (V) [Miller, S.M., Zimmerman , J.B., (2010) Novel, bio-based, photoactive arsenic sorbent: TiO2 –impregnated chitosan bead. Water Res. 44, 5722-5729]. There are numerous scientific reports for arsenic removal from water using different chitosan composite material as adsorbent [Wang, X., Liu, Y.,Zheng, J., Environ Sci Pollut Res. DOI 10.1007/s11356-016-6602-8].

Although these methods are simple, relatively efficient and safe but the disadvantages associated with these methods are slow metal precipitation, aggregation of metal precipitates which need further treatment before disposal to environment as well as higher cost of regeneration. One of such major achievement was accomplished by using combination of nano matal oxides and chitosan as new adsorbent for water treatment in view of abundant site on surface for uptake of arsenic [Cumbal, L., Sengupta, A.K., (2005) Arsenic removal using polymer supported hydrated iron (III) oxide nanoparticles: Role of Donnan membrane effect, Environmental Science Technology, 39, 6508-6515]. In case of chitosan supported nano metal oxides, chitosan serves to stabilize the nano metal oxides to prevent aggregation and stabilization of nano materials but the major limitations are high operating cost of nano metal oxides as well as regeneration of the process. Hence, there is an imperative need to novel approaches for purifying water at low cost, using less energy and above all minimize the impact on the environment.

Interestingly, most of the research attention has been paid to adsorption technique for the removal of arsenic from water. Chitosan, having large number of amine groups in its structure is most suitable for use as support for adsorption of arsenic as well as different heavy metals and also it is biocompatible, nontoxic and biodegradable. There are numerous scientific reports on the adsorption capacities of crosslinked chitosan, chitosan nanofibers, chitosan nanoparticles, chitosan composites, modified/pure chitosan and porous chitosan [Zia, Q., Tabassum, M., Gong, H., Li, J., (2019) A Review on Chitosan for Removal of Heavy Metal Ions. J. Fiber Bioengineering and Informatics 12.3, 103-128]. Of late, hydrogel of biopolymers like cellulose, sodium alginate, chitosan, dextrin are widely used for heavy metal adsorption and the overall process is more economical and sustainable [Pathan, S., Bose, S., (2018) Aresenic Removal using green renewable feedstock – based hydrogel; current and future perspectives. 3, 5910 – 5917; Khan, M., Lo, I. M., (2016) A holistic review of hydrogel applications in the adsorptive removal of aqueous pollutants: recent progress, challenges and perspectives, Water Res.106, 259-271]. Min et.al. developed iron functionalized chitosan electro spun nanofiber for removal of trace arsenate from water [Min L. L., Zhong, L. B., Zheng, Y. M., Liu, O., Yuan, Z. H., Yang, L. M., (2016) Functionalized chitosan electrospun nanofiber for effective removal of trace arsenate from water DOI 10.1038/sep32480]. The chitosan nano fiber was fabricated by electrospinning a mixture of chitosan, polyethylene oxide and Fe3+ followed by cross linking with ammonia vapor. Such fabricated nano fiber is highly effective for As (V) adsorption at neutral pH but high operating cost and more complex operation are the major limitations associated with such techniques. However, the use of chitosan bio composite with other polymeric and/or activated inorganic materials via impregnation, encapsulation, coating and /or polymerization techniques are most effective for removal of arsenic from water [Rahim, M., Haris, M.R.H.M., (2005) Journal of Radiation Research and Applied Sciences, 8, 255-263].

CN105199541A discloses a preparation method for an aqueous anticorrosion coating, relates to a preparation method for a coating, and concretely relates to a preparation method for a chitosan/nanometer zinc oxide composite material filled aqueous epoxy resin. The chitosan/nanometer zinc oxide composite material is prepared by performing blending modification on nanometer zinc oxide and chitosan. Nanometer zinc oxide possesses obvious anti-ageing performance and anti-ultraviolet characteristic, the agglomeration problem of nanometer zinc oxide is solved by preparing the composite material from nanometer zinc oxide and chitosan, and also the amino at the chitosan monomer molecule is capable of reacting with epoxy resin, and the filling material can be tightly combined with epoxy resin. The method helps to improve the outdoor weatherability of aqueous epoxy resin, the aqueous epoxy resin is safe, environment-friendly and non-toxic, electrochemical corrosion is alleviated, anticorrosion period is prolonged, the crosslinking density of the aqueous epoxy resin is enhanced, and the anticorrosion performance of the aqueous epoxy resin is effectively improved.

Therefore, there is a need to design a chitosan modified epoxy resin-based paint which can be applied as coating inside of water storage tank for removal of arsenic from ground water. This scientific study is unique, very simple and cost effective for removal of arsenic from water by adsorption on coating surface.

OBJECT OF THE INVENTION
It is first object of the present invention to provide a chitosan modified epoxy resin-based paint composition to remove arsenic from ground water when coated on substrates suitable for containing water such as water storage tank, swimming pool, reservoir etc.

It is a second object of the present invention to provide a chitosan modified epoxy resin-based paint composition to remove arsenic from ground water when coated on substrates suitable for containing water which is not only simple and economical but effective.

It is a third object of the present invention to provide a method for preparation of a chitosan modified epoxy resin-based paint composition to remove arsenic from ground water when coated on substrates.

It is a fourth object of the present invention to provide a method for removal of arsenic from ground water stored in water storage tank, swimming pool, reservoir and the like by applying a chitosan modified epoxy resin-based paint composition.

SUMMARY OF THE INVENTION
The following disclosure presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

One aspect of present invention relates to a paint composition to remove arsenic from ground water stored in a storage system, comprising:

a. a pigmented base comprising
a binding component in a range of 25 – 50 wt% of total paint composition;
an arsenic adsorbent in a range of 1 – 5 wt% of total paint composition;
other paint ingredients in a range of 45 – 75 wt% of total paint composition;
b. a curing agent; such that said pigmented base and said curing agent is mixed in a ratio of 1.5 – 5: 1;
wherein the binding component is amine modified epoxy resin and the arsenic adsorbent is chitosan uniformly dispersed within the epoxy resin binder.

Another aspect of present invention is a process of preparation of a paint composition to remove arsenic from ground water stored in a storage system, comprising:
a. preparing a pigmented base comprising
a binding component in a range of 25 – 50 wt% of total paint composition;
an arsenic adsorbent in a range of 1 – 5 wt% of total paint composition; and
other paint ingredients in a range of 45 – 75 wt% of total paint composition;
b. mixing the pigmented base with a curing agent in a ratio of 1.5 – 5: 1;
wherein the binding component is amine modified epoxy resin and the arsenic adsorbent is chitosan uniformly dispersed within the epoxy resin binder.

Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The above and other aspects, features and advantages of the embodiments of the present disclosure will be more apparent in the following description taken in conjunction with the accompanying drawings, in which:

Figure 1 illustrates schematic presentation for preparation of chitosan modified epoxy paint as disclosed in one of the embodiments.

Figure 2 illustrates FTIR absorption spectra of unmodified epoxy resin (A), amine modified epoxy resin (B), chitosan in 1% acetic acid solution (C) and hybrid resin of amine modified epoxy resin and modified chitosan (D)

Figure 3 illustrates DSC heat flow versus temperature curve of different chitosan loaded epoxy coating as disclosed in one of the embodiments. A – Epoxy coating without chitosan loading, B – 1% Chitosan loaded epoxy coating, C - 2% Chitosan loaded epoxy coating, D - 3% Chitosan loaded epoxy coating.

Figure 4 illustrates percentage removal of arsenic from ground water sample at different time
(A - 1 % chitosan loaded epoxy coating, B – 2 % chitosan loaded epoxy coating and C- 3 % chitosan loaded epoxy coating).

Figure 5 illustrates effect of Chitosan loading in epoxy coating on removal of arsenic from natural ground water sample (A – 230 µg/lit. arsenic contaminated ground water, B - 1030 µg/lit. arsenic contaminated ground water)

Figure 6 illustrates DSC curves at different time of underwater exposure in 2% chitosan loaded epoxy coating. (1 – DSC curve before underwater exposure, 2 – DSC curve after 48 hrs. of underwater exposure, 3 – DSC curve after 144 hrs. of underwater exposure, 4 – DSC curve after 240 hrs. of underwater exposure, 5 – DSC curve after 360 hrs. of underwater exposure).

Figure 7 illustrates variation of Tg of the coating at different time of underwater exposure.

Figure 8 illustrates schematic diagrams for removal of arsenic by the application of chitosan modified epoxy coating.

Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may not have been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION OF THE PRESENT INVENTION
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure as defined by the claims and their equivalents. It includes various specific details to assist in that understanding, but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.

All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which various embodiments belong. Further, the meaning of terms or words used in the specification and the claims should not be limited to the literal or commonly employed sense but should be construed in accordance with the spirit of the disclosure to most properly describe the present disclosure.

The terminology used herein is for the purpose of describing particular various embodiments only and is not intended to be limiting of various embodiments. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising" used herein specify the presence of stated features, integers, steps, operations, members, components, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, members, components, and/or groups thereof.

The present disclosure will now be described more fully with reference to the accompanying drawings, in which various embodiments of the present disclosure are shown.

In one embodiment present invention relates to a paint composition to remove arsenic from ground water stored in a storage system, comprising:
a. a pigmented base comprising
a binding component in a range of 25 – 50 wt% of total paint composition;
an arsenic adsorbent in a range of 1 – 5 wt% of total paint composition; and
other paint ingredients in a range of 45 – 75 wt% of total paint composition; and
b. a curing agent; such that said pigmented base and said curing agent is mixed in a ratio of 1.5 – 5 : 1;
wherein the binding component is amine modified epoxy resin and the arsenic adsorbent is chitosan uniformly dispersed within the epoxy resin binder.

According to one implementation of present invention, the other paint ingredients are selected from dispersing agents, defoamers, thixotropic agents, bentone, rutile, barytes, talc and combinations thereof.

In a preferred embodiment, the curing agents are selected from phenalkamine, modified polyamine and combinations thereof.

In one of the preferred embodiments, said dispersing agents are selected from modified polysiloxane, block acrylic copolymers in a range of 0.2 – 1.2 wt% of total paint composition.

In another implementation, said defoamers are selected from silicone derivative, mixture of hydrocarbon, metallic soap and non ionic surfactant in the range of 0.05 – 0.3 wt % of total paint composition

In another embodiment, said thixotropic agents are selected from hydrophilic fumed silica, natural clay in the range of 0.04 – 1.0 % of total paint composition

In another preferred embodiment, the composition also comprises bentone in the composition in a range of 0.1 – 0.5 %, rutile in a range of 5 – 15 %, and extenders like barytes, talc, silica in a range of 10 – 22 %.

One of the implementations of present invention, referring Fig. 1, relates to a process of preparation of a paint composition to remove arsenic from ground water stored in a storage system, comprising:
c. preparing a pigmented base comprising
a binding component in a range of 25 – 50 wt% of total paint composition;
an arsenic adsorbent in a range of 1 – 5 wt% of total paint composition; and
other paint ingredients in a range of 45 – 75 wt% of total paint composition;
d. mixing the pigmented base with a curing agent in a ratio of 1.5 – 5: 1;
wherein the binding component is amine modified epoxy resin and the arsenic adsorbent is chitosan uniformly dispersed within the epoxy resin binder.

In another implementation of present invention, the process step of preparing a pigmented base may further comprise the steps of
i. preparing amine modified epoxy resin solution from poly epoxide resin solution and mixing with other paint ingredients (solution A); and
ii. preparing aqueous solution of chitosan (solution B) by mixing 1 - 5 gm chitosan in 1 gm acetic acid in 100 gm water;
iii. mixing said solution A and B to obtain chitosan-epoxy hybrid resin system as the pigmented base.

In a preferred embodiment, the curing agents are selected from phenalkamine, modified polyamine and combinations thereof.

According to one implementation of present invention, the other paint ingredients are selected from dispersing agents, defoamers, thixotropic agents, bentone, rutile, barytes, talc and combinations thereof.

In one of the preferred embodiments, said dispersing agents are selected from modified polysiloxane, block acrylic copolymers in a range of 0.2 – 1.2 wt% of total paint composition.

In another implementation, said defoamers are selected from silicone derivative, mixture of hydrocarbon, metallic soap and non ionic surfactant in the range of 0.05 – 0.3 % of total paint composition.

In another embodiment, said thixotropic agents are selected from hydrophilic fumed silica, natural clay in the range of 0.04 – 1.0 % of total paint composition

In another preferred embodiment, the composition also comprises bentone in the composition in a range of 0.1 – 0.5 %, rutile in a range of 5 – 15 %, and extenders like barytes, talc, silica in a range of 10 – 22 %.

In one of the implementations, the preparation step of amine modified epoxy resin adduct from poly epoxide resin solution comprises the steps of preparing a 50% w/w solution of epoxy resin in 2 Methoxy ethanol solvent and followed by mixing of Di ethanol amine in molar ratio 0.5 – 2.5 per mole of epoxy resin under stirring at a temperature of 65 - 750C for 1 - 2 hr.

Different embodiments of present invention could be better understood with the help of few examples provided below:

EXAMPLE 1

Epoxy Paint Composition and Characterization
A solution of poly epoxide resin (Epoxy equivalent weight, 176 – 180) (50% w/w) in 2 Methoxy ethanol solvent was prepared. 85.72 gm of this epoxy solution was taken in a round bottom flask and 14.28 gm of Di ethanol amine was added slowly under stirring at a temperature of 65 - 700C for 1 hr. After addition, 70 - 750C temperature was maintained for 2 hrs. to form epoxy amine adduct.

An aqueous solution of chitosan was prepared in 1 % aqueous acetic acid solution separately.

The chitosan modified epoxy paint is two component water dilutable system. The pigmented base was prepared by mixing amine modified epoxy resin and other paint ingredients under high speed disperser (HSD) with dispersion speed of around 600 to 700 rpm for 50 - 60 min. and finally the chitosan in 1 % aqueous acetic acid solution was added and mixed for 10 min at 100 -130 rpm. The chitosan-epoxy hybrid resin system was formed, after mixing the solution of amine modified epoxy resin and chitosan. A composition of chitosan modified epoxy base is presented in Table 1.

Table 1 Composition for pigmented base
Ingredients Quantity in wt %
Modified Epoxy Resin 41.30
Chitosan 1.50
1% Acetic acid in water 31.80
Dispersing agent 0.70
Defoamer 0.13
Thixotropic agent 0.10
Bentone 0.17
Rutile 8.30
Extenders 16.00

Before application of paint, the pigmented base and epoxy curing agent mixed in a ratio of 2: 1 by weight.

In the FTIR spectra (Fig. 2), the presence of sharp peak at 900 cm -1 is due to the presence of epoxy moiety in epoxy resin (Fig. 2A). After reaction of amine with epoxy group secondary -OH groups are formed which indicates the formation of broad absorption spectra at 3200 - 3500 cm-1 as well as disappearance of absorption peak at 900 cm -1 (Fig. 2B) which clearly indicates the formation of amine adduct with epoxy resin. The characteristic absorption peak at 1550 – 1650 cm-1 corresponds to chitosan in acetic acid complex (Fig. 2C). The characteristic peaks of chitosan corresponds to amide at 1648 cm-1 and NH2 bending at 1540 cm-1 has merged with the broad absorption peak of – COOH functional group. The significant absorption bands i.e. at 1597, 1733 and 1855 cm-1 confirm the modification of chitosan in amine modified epoxy resin matrix (Fig. 3D).

The change of total arsenic concentration in natural ground water with time after keeping water in container coated with chitosan modified epoxy paint is presented in Table 2.

Table 2. Change of total arsenic concentration in natural ground water with time
Percentage chitosan loaded in epoxy paint after mixing the pigmented base and the epoxy curing agent in a ratio of 2: 1 by weight Under water exposure time (hrs.) of the coating Initial conc. of total arsenic i.e. As (III) and As (V) is 230 µ g / lit
Total arsenic in water at different time interval
(µg/lit)
Percentage removal of arsenic* Percentage efficiency for removal of arsenic** (µg/sq.cm/cc of water)
1 48 73 68 8.72
144 69 70 8.94
240 50 78 10.00
360 44 81 10.33

*Percentage removal of arsenic = (Initial conc. of arsenic in water – conc. of arsenic in water at different time interval) x 100/ Initial conc. of arsenic in water.

**Percentage efficiency of chitosan modified epoxy coating for removal of arsenic = (Initial conc. of arsenic in water – conc. of arsenic in water at different time interval) x 100/total adsorbed surface area x total volume of water.

EXAMPLE 2

Effect of Chitosan content on removal of arsenic from water
To investigate the effect of chitosan loading in coating composition, a pigmented base was prepared in high speed disperser (HSD), taking 3 % chitosan in epoxy base composition Table 1.

The change of total arsenic concentration in natural ground water with time after keeping water in different container coated with chitosan-based epoxy coating is presented in Table 3.

Table 3. Change of total arsenic concentration in natural ground water with time
Percentage chitosan loaded in epoxy paint after mixing the pigmented base and the epoxy curing agent in a ratio of 2: 1 by weight Under water exposure time (hrs.) of the coating Initial conc. of total arsenic i.e. As (III) and As (V) is 230 µ g / lit
Total arsenic in water at different time interval
(µg/lit)
Percentage removal of arsenic Percentage efficiency for removal of arsenic (µg/sq.cm/cc of water)
2 48 31 87 11.05
144 22 90 11.35
240 14 94 11.8
360 8 96.5 12.1

EXAMPLE 3
Effect of Chitosan content on removal of arsenic from water
To investigate the effect of chitosan loading in coating composition, a pigmented base was prepared in high speed disperser (HSD), taking 4.50 % chitosan in epoxy base composition Table 1.and keeping the other ingredients same as Table 1.

The change of total arsenic concentration in natural ground water with time after keeping water in different container coated with chitosan based epoxy coating is presented in Table 4.

Table 4. Change of total arsenic concentration in natural ground water with time

Percentage chitosan loaded in epoxy paint after mixing the pigmented base and the epoxy curing agent in a ratio of 2: 1 by weight Under water exposure time (hrs.) of the coating Initial conc. of total arsenic i.e. As (III) and As (V) is 230 µ g / lit
Total arsenic in water at different time interval
(µg/lit)
Percentage removal of arsenic Percentage efficiency for removal of arsenic (µg/sq.cm/cc of water)
3 48 38 83 10.66
144 36 84 10.77
240 30 86.9 10.91
360 22 90.4 11.35

The chitosan loading influences the glass transition temperature (Tg) of the coating. The increase of Tg in different chitosan-epoxy hybrid resin based paints are plotted in DSC heat flow versus temperature results (Fig. 3). The Tg of chitosan-epoxy hybrid resin based paints and after loading of 1, 2 and 3 percent chitosan are 410C, 42.40C, 48.20C and 51.80C respectively. Due to the introduction of hard nitrogenous polysaccharide, chitosan in the epoxy system, the hardness of the film as well as Tg increases.

Removal of Arsenic from Natural Ground Water by Chitosan Modified Epoxy Coating
With increase of chitosan loading in the epoxy matrix, the percentage removal of arsenic is not very significant. This is an adsorption phenomenon and adsorption process depend on surface area of the adsorbent. At low concentration of chitosan, the agglomeration is relatively less and uniformly dispersed in the epoxy matrix. However, with increase in chitosan loading, agglomeration starts, resulting poor dispersion.

The percentage removal of arsenic from a sample of natural ground water contaminated with arsenic (at the level of 230 µg/lit.) by different percentage of chitosan loaded epoxy coating with time is presented in Fig. 4.

From Fig. 4, it is clearly evident that the arsenic removal efficiency of all the chitosan loaded epoxy coating is gradually increasing with time. The decrement of adsorption capacity is not observed even after 15 days at normal temperature in high arsenic concentration of natural ground water.

The efficiency of such chitosan modified epoxy coating for removal of arsenic from high arsenic concentration of natural ground water have also been performed. The effect of chitosan loading in the epoxy coating for removal of arsenic from arsenic concentration in natural ground water in 20 days is presented in Fig. 5. The initial concentration of arsenic in the arsenic contaminated natural ground water for this study was 230 µg / lit. and 1030 µg/lit.

The uptake of metal ions on chitosan may proceed through different mechanisms like chelation of metal cations on the free electronic doublet of amine groups or ion exchange mechanism. Nitrogen atom of amino group has one loan pair whereas oxygen atom of hydroxyl group has two lone pairs of electrons, these can bind arsenic through a lone pair of electrons forming a complex. Because of high electronegativity of oxygen atom than nitrogen atom, the nitrogen atom has a greater tendency to donate the lone pair of electrons for sharing with arsenic ion to form a complex more easily than the oxygen atoms. Therefore, amine groups are responsible for the uptake of arsenic cations by a chelation mechanism as follows:

Chitosan-NH2 + H3O+ Chitosan-NH3+ + H2O
Chitosan-NH3+ + AsO3-3/AsO4-3 + H2O Chitosan Arsenic Complex + H3O+

With the formation of chelate complex between arsenic and chitosan molecule, the coating film becomes harder. This is evident with the increase of Tg in chitosan-arsenic complexed coating film. DSC curves at different time interval of underwater exposure coating films are shown in Fig. 6. The plot of variation in glass transition temperature (Tg) of the coating at different time of underwater exposure is as presented in Fig. 7.

From Fig. 7, it is clearly evident that initially the rise of Tg is very significant but after a certain time this rise is quite slow. Because with time, the void microstructures of the epoxy coating is gradually filled up by arsenic.

For bulk scale modeling of this novel technology following indigenous methodology can be adopted. These methodologies are very simple, low cost as well as commercially feasible.

An arrangement for arsenic removal could be done by putting chitosan modified epoxy coated panels inside of the water tank (Fig. 8). The main advantages of this arrangement are, these panels can be replaced, repainted and reused.

Claims:
1. A paint composition to remove arsenic from ground water stored in a storage system, comprising:
a. a pigmented base comprising
a binding component in a range of 25 – 50 wt% of total paint composition;
an arsenic adsorbent in a range of 1 – 5 wt% of total paint composition; and
other paint ingredients in a range of 45 – 75 wt% of total paint composition; and
b. a curing agent; such that said pigmented base and said curing agent is mixed in a ratio of 1.5 – 5 :1 to form said pain composition;
wherein the binding component is amine modified epoxy resin and the arsenic adsorbent is chitosan uniformly dispersed within the epoxy resin binder.

2. The paint composition as claimed in claim 1, wherein the curing agents are selected from phenalkamine, modified polyamine and combinations thereof.

3. The paint composition as claimed in claim 1, wherein the other paint ingredients are selected from dispersing agents, defoamers, thixotropic agents bentone, rutile, barytes, talc and combinations thereof.

4. The paint composition as claimed in claim 3, wherein said dispersing agents are selected from modified polysiloxane, block acrylic copolymers in a range of 0.2 – 1.2 wt% of total paint composition.

5. The paint composition as claimed in claim 3, wherein said defoamers are selected from silicone derivative, mixture of hydrocarbon, metallic soap and non ionic surfactant in the range of 0.05 – 0.3 % of total paint composition.

6. The paint composition as claimed in claim 3, wherein said thixotropic agents are selected from hydrophilic fumed silica, natural clay in the range of 0.04 – 1.0 % of total paint composition.

7. The paint composition as claimed in claim 3, wherein the composition comprises Bentone in the composition in a range of 0.1 – 0.5 %, rutile in a range of 5 – 15 %, and extenders like barytes, talc, silica in a range of 10 – 22 % of total paint composition.

8. A process of preparation of a paint composition to remove arsenic from ground water stored in a storage system, comprising:
a. preparing a pigmented base comprising
a binding component in a range of 25 – 50 wt% of total paint composition;
an arsenic adsorbent in a range of 1 – 5 wt% of total paint composition; and
other paint ingredients in a range of 45 – 75 wt% of total paint composition;
b. mixing the pigmented base with a curing agent in a ratio of 1.5 - 5:1;
wherein the binding component is amine modified epoxy resin and the arsenic adsorbent is chitosan uniformly dispersed within the epoxy resin binder.

9. The process as claimed in claim 8, wherein the step of preparing a pigmented base comprises the steps of
i. preparing amine modified epoxy resin solution from poly epoxide resin solution and mixing with other paint ingredients (solution A); and
ii. preparing aqueous solution of chitosan (solution B) by mixing 1 - 5 gm chitosan in 1 gm acetic acid in 100 gm water;
iii. mixing said solution A and B to obtain chitosan-epoxy hybrid resin system as the pigmented base.

10. The process as claimed in claim 8, wherein the preparation step of amine modified epoxy resin adduct from poly epoxide resin comprises the steps of preparing a 50% w/w solution of epoxy resin in 2 Methoxy ethanol solvent and followed by mixing of Di ethanol amine in molar ratio 0.5 – 2.5 per mole of epoxy resin under stirring at a temperature of 65 - 750C for 1 - 2 hr.

11. The process as claimed in claim 8, wherein the curing agents are selected from phenalkamine, modified polyamine and combinations thereof.

12. The process as claimed in claim 8, wherein the other paint ingredients are selected from dispersing agents, defoamers, thixotropic agents bentone, rutile, barytes, talc and combinations thereof.

13. The process as claimed in claim 12, wherein said dispersing agents are selected from modified polysiloxane, block acrylic copolymers in a range of 0.2 – 1.2 wt% of total paint composition.

14. The process as claimed in claim 12, wherein said defoamers are selected from silicone derivative, mixture of hydrocarbon, metallic soap and non ionic surfactant in the range of 0.05 – 0.3 % of total paint composition.

15. The process as claimed in claim 12, wherein said thixotropic agents are selected from hydrophilic fumed silica, natural clay in the range of 0.04 – 1.0 % of total paint composition.

16. The process as claimed in claim 8, wherein the composition comprises bentone in a range of 0.1 – 0.5 %, rutile in a range of 5 – 15 %, and extenders like barytes, talc, silica in a range of 10 – 22 % of total paint composition.