DESC:FIELD OF THE INVENTION
The present invention relates to novel Xylan-xanthan biopolymers, alternative to conventional thermoplastic. The invention also relates to the process of synthesis/ preparation of biodegradable green composite polymers from xanthan polymer, a microbial exopolysaccharide and xylan polymer. The invention also relates to the synthesis of xylan polysaccharide from hemicellulosic-hydrolysate produced from agro-residues rich in hemicelluloses such as rice straw, wheat straw, sugarcane bagasse, corn cobs, etc. More particularly, the present invention also provides for the production of Xylan-xanthan biopolymers in a very cost-effective and convenient method from the agro-residues rich in hemicellulose.

BACKGROUND OF THE INVENTION
Plastics have overwhelmed the market as the lead material for most applications including packaging, support matrices, cutlery etc. This phenomenon is not desirable since traditional plastics offer imperviousness to degradation by water, chemicals, daylight, and microorganisms and hence tend to persist in the environment long after their utility has been served. Furthermore, after production, the same properties that make conventional plastics attractive for commercial applications also produce further environmental costs by preventing biodegradation which increases the demand and size of landfills to facilitate the increasing amounts of plastic entering the municipal solid waste stream. One solution to these problems is plastic recycling which can reduce the dumping of used plastic into the environment; however, this process is inherently energy intensive and is often accompanied by the dangerous leaching of chemicals into the environment. Consequently, conventional plastics are no longer a sustainable solution. Therefore, it would be advantageous if a material with plastic-like properties and negligible environmental impact is produced. The production of biopolymers from various biological substrates (both plant and microbial based) has been explored in an effort to enable biodegradable functional polymers/ bioplastics. However, advanced materials and processes are needed for commercial viability to be established.

US 2013/0344550 A1 (Charles Miller et al., 2013) describe a method for producing bio-plastics from algae, where the glycerol produced by algae is then fermented to polyhydroxy alkanoates (PHB). However, the yields of the products are not encouraging for its economic viability.

US 2006/0105439 A1 (James P Nakas et al., 2006) describe the bioconversion of xylan into biodegradable polyesters through microbial fermentation process. However, the process is critical with lesser yields. It has also been reported that xanthan and chitosan can be used for making polyelectrolyte gels that can be used for encapsulation and controlled release of cells, enzymes or therapeutic agents (Sanem Argin-Soysal et al., 2009).

US8299172B2 (Schilling Christopher et al., 2008) describes a method for producing biodegradable plastic from natural materials containing polysaccharides by treating the polysaccharide-containing materials with a basic aqueous solution, subsequently treating the mixture with a modifying material that converts pendant hydroxyl groups at any carbon atom of the anhydrous glucose units of the saccharide to create polysaccharide carboxylate, and then reacting the product with proteins to produce a biodegradable copolymer with electrostatic chemical bonds between protein and polysaccharide carboxylate molecules. The process provides relatively inexpensive methods for preparing biodegradable plastics that are useful for manufacturing various articles.

WO2013096891A1 (Solazyme Inc., 2012) describes biomass-based materials and valuable uses of microalgal biomass including: (i) acetylation of microalgal biomass to produce a material useful in the production of thermoplastics; (ii) use of triglyceride containing microalgal biomass for production of thermoplastics; (iii) combination of microalgal biomass and at least one type of plant polymer to produce a material useful in the production of thermoplastics; (iv) anionization of microalgal biomass to form a water absorbant material; (v) cationization of microalgal biomass, and optional flocculation, to form a water absorbant material; (vi) crosslinking of anionized microalgal biomass; (vii) carbonization of microalgal biomass; and (viii) use of microalgal biomass in the making of paper.

WO2010107402A1 (Bakir Ufuk., 2009) describes hemicellulose based film and/or coating material composition and the production stages for making the film and/or coating material used in the packaging of fruits and vegetables in which the film and/or coating material is produced from agricultural wastes such as cotton stalk, sunflower stalk, corn cob, stalks and brans of various cereals such as wheat, oat, barley, hazelnut shell or forestry wastes such as saw dust wherein said film and/or coating material is anti-microbial, anti-fogging and capable of removing undesired gases.

WO2007012142A1(Changping Chen., 2005) describes a method of preparing a biodegradable polymer composition, said method comprising melt mixing a first polysaccharide, a first biodegradable polyester and a compatibiliser, wherein said compatibiliser has been formed separately by reacting a second polysaccharide and a second biodegradable polyester in the presence of a trans-esterification catalyst.

CA 2034943 A1 (Walter Denzinger et al., 1991) describes the preparation and use of Graft copolymers of monosaccharides, oligosaccharides, polysaccharides and modified polysaccharides.

US5639865 (Wolff Walsrode Aktiengesellschaft., 1995) relates to novel thermoplastic, biodegradable polysaccharide ether esters, such as for example cellulose ether esters or starch ether esters, and to the production of such graft copolymers from polysaccharides, epoxides and dicarboxylic acid anhydrides and to the use thereof, for example as moldings, films or coatings.

The article “Bioplastics from Biomass - Acetylation of Xylans with Green Chemistry. Agnes Stepan, publications.lib.chalmers.se/publication/185639” describes the acetylation of Xylan and formation of thermal and water resistant properties of Xylan film after acetylation. This work is a contribution to the designing of novel xylan based materials and their feasible and environmentally friendly production. Acetylated arabinoxylans have a potential to replace many of the oil based plastics and become a future bioplastics.

The article “Solubilization of hemicellulose and lignin from wheat straw through microwave-assisted alkali treatment. Janker-Obermeier, V.Sieber, M. Faulstich, D. Schieder, Industrial Crops and Products, Volume 39, September 2012, Pages 198-203” describes the saccharide and lignin-releasing potential of microwave assisted alkali pre-treatment on wheat straw. More than 80% of the hemicellulose and 90% of the lignin could be removed from the solid wheat straw matter without excessive saccharide degradation or solubilizing high amounts of cellulose. This makes microwave-assisted alkali pretreatment an effective method for the pre-treatment of wheat straw.
Therefore there is a need to produce cost-effective biodegradable plastics or bio-polymers or biopolymer composite with better stability and from a simplified process resulting in high yield.

OBJECTIVES OF THE INVENTION
The main objective of the present invention is to provide a biocomposite material made from natural sources in cost effective manner. The natural sources are xylan derived from -lignocellulosic biomass and xanthan obtained from microbial fermentations.

Another objective of the present invention is the production of a biocomposite material made from natural sources. The natural sources are xylan derived from lignocellulosic biomass and xanthan obtained from microbial fermentations.

Yet another objective of the invention is synthesis of the xylan polysaccharide from hydrolysate produced by thermochemical pretreatment of agro-residues rich in hemicelluloses such as rice straw, wheat straw, sugarcane bagasse, corn cobs, etc.

Yet another objective of the present invention is to provide a general method of preparation of novel xanthan-xylan derived biopolymers which can be used as biodegradable alternative to conventional thermoplastic.

SUMMARY OF THE INVENTION
In an aspect the invention discloses a biopolymer comprising
(i) a xanthan;
(ii) a xylan or its salt or its derivatives thereof; and
(iii) a di-aldehyde cross-linking plasticizer.

In another aspect, the biopolymer includes xanthan in the range of 1-5% w/w.

In yet another aspect, the biopolymer includes the xylan or its salt or its derivatives in the range of 1-5% w/w.

In the preferred aspect, the biopolymer includes xylan obtained by the thermochemical pretreatment of agro-residues rich in hemicelluloses.

In another preferred aspect, the biopolymer includes xylan obtained from the agro-residues rich in hemicellulose selected from the group consisting of rice straw, wheat straw, sugarcane bagasse and corn cobs.

In yet another preferred aspect, the biopolymer includes xanthan characterised by the degree of polymerisation in the range of 1000-2000g/mol.

In preferred aspect, the biopolymer includes the cross linking plasticizer selected from PEG-200, Glycolic acid, Glycerine, and polyvinyl alcohol.

As disclosed herein a process of producing biopolymer comprising,
(i) adding the xanthan to the xylan or its derivatives;
(ii) adding a di-aldehyde cross-linking plasticizer to step(i); and
(iii) mixing at 300rpm, at 50°C for about 2-3 h to obtain the composite.

As further disclosed herein, a process of producing biopolymer comprising,
(i) treating 10% by wt. xanthan in water with dilute sulphuric acid;
(ii) mixing the xanthan solution obtained in step (i) to the xylan or its derivatives;
(iii) adding a di-aldehyde cross-linking plasticizer to step(ii); and
(iii) mixing at 300rpm, at 50°C for about 2-3 h to obtain the composite.

In the preferred aspect, the process of producing biopolymer composition includes xylan obtained by thermochemical pretreatment of agro-residues rich in hemicelluloses.

DESCRIPTION OF THE INVENTION
This invention relates to biodegradable green composite/ Green plastic/ biopolymer/ bio composite/ biopolymer composition derived from natural, biodegradable polymers: Xylan or its salt or its derivatives and Xanthan.

As used herein, “Green plastic” refers to a plastic whose components are derived from renewable raw materials. The green plastic is typically biodegradable, and can be shaped inter alia, by being formed, molded or extruded into a desired shape.

As used herein, “biopolymer” refers to a polymer derived from natural source such as plant or an animal. A biopolymer may also be a combination of such polymers, such as in a mixture or as a copolymer.

In the preferred embodiment of the present invention, the biodegradable green composite polymer composition comprises the xanthan polymer, a microbial exopolysaccharide and the xylan polymer, second major constituent of plant cell wall polysaccharides. These raw materials are renewable and sustainable.

There are several reports on biodegradation of xanthan (Hashimoto et al., 1998; Nankai et al., 1999; Muchova et al., 2009) and xylan (Varma et al., 2017; Zhang et al., 2018). The products of degradation of xanthan may include D-glucuronic acid, D-mannose, pyruvylated mannose, 6-O-acetyl D-mannose etc., while the products of xylan degradation includes majorly xylose, arabinose, mannose, acetates, galactose etc.

In an embodiment, the invention relates to the synthesis of xylan from hydrolysate produced by the thermochemical treatment of agro-residues rich in hemicelluloses such as rice straw, wheat straw, sugarcane bagasse, corn cobs, etc.
The production of the xylan cellulose in a very cost-effective and convenient as the raw materials include a renewable agriculture resource like rice straw, wheat straw, sugarcane bagasse, cobs etc.

In the preferred embodiment, the xylan component is extracted form lignocellulosic biomass such as rice straw, wheat, sugarcane bagasse etc. by a process of thermochemical pretreatment. Briefly, 100 g of the biomass is taken in 1000 ml water and heated at 170 – 200C for 15 – 30 minutes in a closed batch reactor (Parr Instruments, USA). The liquid hydrolysate generated is then treated with chilled absolute ethanol in a ratio of 1:2 (v/v), which leads to the precipitation of the xylan fraction.

The invention relates to the production of biopolymer composition made of raw materials, derived from natural sources; the xylan is derived from lignocellulosic biomass while xanthan is a product of microbial fermentations. As both substrates are readily degradable and essentially harmless, they can be used for food, medical, pharmaceutical applications.

The xanthan-xylan derived biopolymer can be used as biodegradable alternative to conventional thermoplastics.
The esterified biopolymers can be a potential platform for functionalizing various bioactive polymers, surfactants, hydrocolloids, coating materials etc.
They can be used as an environmentally benign grafting polymer supports for microbial screening of environmental samples and also for cell culture applications.
The biopolymers described here exist as thin membranes and hence, have great potential in cosmetic applications such as peel-off (or) wash off masks.

Xanthan is secreted by the bacteria. Compositionally, xanthan is composed of pentasaccharide repeat units, comprising glucose, mannose, and glucuronic acid; Xanthan plays an important role in industrial applications as thickener, emulsion stabilizer and it has been added to water-based drilling fluids due to its pseudoplastic behavior and thermal stability.
Source of Biomaterial: Xanthan was procured form local sources.

Xylan is obtained by thermochemical separation from plant biomass. Xylan is composed of mainly pentose sugars (mainly xylose and arabinose). Xylan is considered to be a green polymer that may play an essential role in the renewability of waste products due to its biodegradable and biocompatible nature. Derivatives of Xylan like xylan acetate/ xylan propionate/ xylan butyrate/ long chain fatty acid xylan ethers etc. can be used herein.
However, xylan has a disadvantage as it lacks elastic properties and acid stability.
Source of Biomaterial: Xylan was extracted from agricultural biomass (rice straw, wheat straw, bagasse etc.) grown locally near Bangalore, India and was also procured form local sources.

The biopolymer composition obtained by blending xanthan and xylan via cross linking plasticizer has surprisingly showed acid stability, thermal stability and uv light stability as shown in Example 3.

The present biopolymer is prepared by cross-linking a modified microbial polymer and a plant-based biopolymer. The reaction conditions used for synthesis of this polymer are moderate and did not cause any loss of reactants or products. The plant-based polymer used for making the present biopolymer was indigenously prepared from agro-residual biomass and the recovery yield of this polymer was >80 %.

The present invention is briefly described with reference to the following representative examples, which are given by way of illustration and should not be construed to limit the scope of the present invention.

MATERIALS AND METHODS

Xanthan and Xylan polymers will be used as the starting polymer substrates/reactants for the synthesis of biodegradable polymers/ Green plastic.

The xylan polysaccharide can be prepared from hemicellulosic-hydrolysate produced by the thermochemical pretreatment of agro-residues rich in hemicellulose such as rice straw, wheat straw, sugarcane bagasse, corn cobs, etc. xylan is soluble in aqueous solutions even at 4 % (wt.) concentrations.

The xanthan polysaccharide is highly viscous in aqueous solution even at very lower concentration 0.1% (wt.) and it affects the free flowing property of biopolymer. Therefore degree of polymerization of xanthan can be reduced by using two approaches.
a) Deacetylated/ Depyruvylated xanthan (molecular weight ~2000000 g/mol, high degree of polymerization) is initially plasticized/ crosslinked with any one of the biodegradable chemical agents such as polyethylene glycol (200/400/2000/4000) or glycerol/ glycolic acid or glutaraldehyde or ethylene glycol, followed by conditioning
b) Degree of polymerization (DP) of xanthan is reduced to ~1000-2000 g/mol by subjecting it to acidolysis with various concentration of dilute sulphuric acid (0.05-0.3% v/v) leading to the formation of highly compatible/reactive oligomers of xanthan.

EXAMPLE
EXAMPLE 1: Synthesis of Xylan:
The xylan component is extracted from lignocellulosic biomass such as rice straw, wheat, sugarcane bagasse etc. by a process of thermochemical pretreatment. Briefly, 100 g of the biomass is taken in 1000 ml water and heated at 170 – 200C for 15 – 30 minutes in a closed batch reactor (Parr Instruments, USA). The liquid hydrolysate generated is then treated with chilled absolute ethanol in a ratio of 1:2 (v/v), which leads to the precipitation of the xylan fraction.

EXAMPLE 2: Biopolymer with varying concentrations direct xanthan & xylan using plasticizer
The influence of various concentrations of xanthan and xylan/ xylan derivatives (xylan acetate/ xylan propionate/ xylan butyrate/ long chain fatty acid xylan ethers etc.,) was evaluated for its ability to make a moldable biopolymer composite. These concentrations were varied from 1-5% (wt.) with respect to each polymer in the presence of a plasticizer such as glutaraldehyde and water. The ingredients were mixed in a round bottom flask at a speed of 300 rpm for 2-3 h at 50°C and the glutaraldehyde was added during mixing. Then the resulted composite material was used for casting the films.

Table 1a:
Ingredients Concentration in % wt/wt of biopolymer.
Example 1a Example 1b Example 1c Example 1d Example 1e
Xanthan 1% 2% 3% 4% 5%
Xylan derivatives:
Xylan acetate+PEG-200 1% + 0.5 % 2% + 0.5 % 3% + 0.5% 4% + 0.5% 5% + 0.5%

Table 1b:
Ingredients Concentration in % wt/wt of biopolymer.
Example 1f Example 1g Example 1h Example
1i Example
1j
Xanthan 1% 2% 3% 4% 5%
Xylan acetate+Glycolic acid 1% + 0.5 % 2% + 0.5 % 3 % + 0.5% 4 % + 0.5% 5 % + 0.5%

Table 1c:
Ingredients Concentration in % wt/wt of biopolymer.
Example 1k Example
1l Example 1m Example 1n Example 1o
Xanthan 1% 2% 3% 4% 5%
Xylan acetate+Glycerine 1% + 0.5 % 2% + 0.5 % 3 % + 0.5% 4 % + 0.5% 5 % + 0.5%

Table 1d:
Ingredients Concentration in % wt/wt of biopolymer.
Example 1p Example 1q Example 1r Example 1s Example
1t
Xanthan 1% 2% 3% 4% 5%
Xylan acetate+ PVA 1% + 0.5 % 2% + 0.5 % 3 % + 0.5% 4 % + 0.5% 5 % + 0.5%

Table 1e:
Ingredients Concentration in % wt/wt of biopolymer.
Example 1u Example 1v Example 1w Example 1x Example 1y
Xanthan 1% 2% 3% 4% 5%
Xylan acetate+ Glutaraldehyde 1% + 0.5 % 2% + 0.5 % 3 % + 0.5% 4 % + 0.5% 5 % + 0.5%

EXAMPLE 3: Biopolymer with acid lysed xanthan & xylan derivative
10%wt. xanthan (in water) was treated with various concentrations of dilute sulfuric acid (0.05-0.3%v/v). The xanthan solution was mixed with various concentrations of xylan/ xylan derivatives (xylan acetate/ xylan propionate/ xylan butyrate/ long chain fatty acid xylan ethers etc.,) and a di-aldehyde cross-linking plasticizer such as glutaraldehyde (0.5%) at 300rpm, at 50°C for about 2 h in a round bottom flask. Then the resulted composite material was used for casting the films.

Table 2
Ingredients Concentration in % wt/wt of biopolymer.
Example 2a Example 2b Example 2c Example 2d Example 2e
Oligomeric-xanthan (or)
Deacetylated-/
Depuruvylated-Xanthan 1% 2% 3% 4% 5%
Xylan derivative:
Xylan acetate+ Glutaraldehyde 1% + 0.5 % 2% + 0.5 % 3 % + 0.5% 4 % + 0.5% 5 % + 0.5%

EXAMPLE 4: stability characteristics:
The biopolymer was tested for its stability against various physical (steam, temperature, and U.V light) and chemical agents (ethanol and dilute acid). All these stability tests were carried out with sample films (1 x 6 cm) prepared by using the synthesized xylan-xanthan biopolymer in Example 2 and 3. The stability tests were performed at 30-120 °C for the duration of 20- 120 min. Results was presented in table 3. Furthermore, the steam, U.V and ethanol treated (sterilized) specimens were also explored for sterility tests.

Table 3: Stability and sterility test for the developed novel biopolymer

Sr. NO Type of treatment Stability Sterility
1 Autoclaving (120 °C/ 15 min)- ? ?
2 Steaming at 100oC for 20 min Not stable ?
3 UV treatment ? ?
4 70 % Ethanol treatment for 50 min ? ?
5 Sulphuric acid treatment (0.1 %) ? ND
,CLAIMS:We Claim:
1. A biopolymer comprising
(i) a xanthan;
(ii) a xylan or its salt or its derivatives thereof; and
(iii) a cross-linking plasticizer.

2. The biopolymer as claimed in claim 1, wherein the xanthan is present in the range of 1-5% w/w.

3. The biopolymer as claimed in claim 1, wherein the xylan or its salt or its derivative is present in the range of 1-5% w/w.

4. The biopolymer as claimed in claim 1-3, wherein the xylan is obtained by the thermochemical treatment of agro-residues rich in hemicelluloses.

5. The biopolymer as claimed in claim 4, wherein the xylan is obtained from the agro-residues rich in hemicelluloses selected from the group consisting of rice straw, wheat straw, sugarcane bagasse and corn cobs.

6. The biopolymer as claimed in claim 1-2, wherein the xanthan is characterised by the degree of polymerisation in the range of 1000-2000g/mol.

7. The biopolymer as claimed in claim 1-6, wherein the cross linking plasticizer is selected from the group selected from glutaraldehyde, PEG-200, Glycolic acid, Glycerine, and polyvinyl alcohol.

8. A process of producing biopolymer as claimed in claim 1, the process comprising,
(i) adding the xanthan to the xylan or its salt or its derivatives;
(ii) adding a cross-linking plasticizer to step (i); and
(iii) mixing at 300rpm, at 50°C for about 2-3 h to obtain the biopolymer.

9. A process of producing biopolymer as claimed in claim 1, the process comprising,
(i) treating 10% wt xanthan in water with dilute sulphuric acid;
(ii) mixing the xanthan solution obtained in step (i) to the xylan or its salt or its derivatives;
(iii) adding a cross-linking plasticizer to step (ii); and
(iii) mixing at 300rpm, at 50°C for about 2-3 h to obtain the biopolymer.

10. The process of producing biopolymer as claimed in claim 8 or 9, wherein the xylan is obtained by the thermochemical treatment of agro-residues rich in hemicelluloses.