Chapter: 1. Introduction

Transcription

1 Chapter: 1 Introduction

2 1.1 Guar gum an engineering biopolymer: Guar gum is a high molecular weight galactomannan obtained directly from the Cyamopsis tetragonoloba (Family leguminous) seed pericarp. The biopolymer presents a very ordered structure of β, 1-4-linked linear mannose chain interposed with α, 1-6-linked galactose substituent at almost every second residue points. (Fig.1). 1 The ratio of mannose to galactose unit (M/G) in native guar gum ranges from 1.8:1.0 to 2.0:1.0. The biopolymer chemical characteristic is often assigned due to seed geographic variations. The guar gum powder from the seeds often associates oligomers, soluble amines and salts which necessitate adopting different processing techniques to meet specification criterions for applications. The crude gum is a yellowish white to near white free flowing powder with a very bland taste and no odor. It is often argued that the domesticated guar plant C. tetragonoloba was brought up in India during the 10 th and 13 th century AD by the Arab traders as horse fodder. The origin of the plant was later traced in the drought tolerant wild African species C. senegalensis. 2 The guar plant is grown in the aired regions since long as a food for both human and the cattle. Currently guar gum is sourced for different industrial purposes almost exclusively from the C. tetragonoloba, grown in India and Pakistan. Guar gum industry was however developed in the United States during the late 1940s. During the World War I supply of locust been gum used in paper making was very irregular and that gave space for examining guar as a substitute. Commercial steps for production of guar polymer were thoroughly worked in the University of Arizona, the University of Purdue and in the Institute of Paper Chemistry, Wisconsin USA. The C. tetragonoloba, seed powder was finally adjudged as an improved substitute for paper making, textile sizing and printing. Guar gum soon found use as additive in dynamite for 1

3 blocking water access. Subsequently the biopolymer is used almost exclusively as a primary gelling agent in water based slurry type explosives. Guar gum derivatives are developed much later to meet more specific needs in different industries. Carboxymethyl guar gum was perhaps the first major derivative that was used extensively for industrial application. Development of newer guar gum derivatives and their applications in petroleum oil and shell gas recovery have resulted in rapid increase in guar gum consumption. Currently guar gum is one of the highly consumed sustainable raw materials and the volume consumption is second only to that of cellulose. 3, Guar gum chemistry in water environment is intriguing and the biopolymer presents unique rheology modifying properties. The biopolymer is currently applied across a broad spectrum of industries including oil well drilling, textiles, cement, cosmetics, explosives preservations, packaged food, paper, paints and pharmaceuticals. 4 Guar gum derivatives application potentials are also explored in more challenging areas like medical devices and bio-imaging areas. 5,6 Functional properties of the biopolymer depend upon individual chemical structure, mannose to galactose ratio, molecular weight and nature of branching. Different types of guar gum and derivatives were developed so as to suite as better emulsifier, water builder, stabilizer, thickener and charge carrier flocculent applications. 7 The native guar water thickening potential by mass is 5-8 times higher than that of the starch. Non-ionic nature, stability over a wide ph range (5-7) and compatibility with different salts has extended aqueous guar solution applications in different areas. Processed guar gum solutions demonstrate non Newtonian, thixotropic, pseudoplastic and shear thinning behavior. 2

4 Fig.1. Guar gum structure Guar gum is often structurally modified to meet different industrial needs. Different techniques known for guar gum modifications can be broadly classified into four categories; bio-genetic, physical, chemical and enzymatic. Bio-genetic seed variations were worked to attain cultivation yield, adopting the plant in harsher soil conditions and polymer viscosity enhancement in water solutions. The product enzymatic variations appeared costlier and that technique produced much less adoptable polymer characteristics. Enzymatic hydrolysis of galactose units for example has resulted in mannose chain only compound but the biopolymer property stability was low in salt and acid environment. 8 Physical variations depend much on powder size grading, salt and hydration effects. The biopolymer covalent modifications but have resulted in different compounds for application adaptation. One cationic derivative for example is widely used as high quality hair conditioner in shampooing. 9 There exist enormous scope for guar biopolymer structural modifications such that different new generation sustainable materials requirements can be addressed. One abridged list of engineered guar gum derivatives for varied applications across different industries is presented in Table 1. 3

5 Table 1: A perspective on industry wide applications of engineered guar gum Sr. Division of Type of Purpose Engineered No Industry Applications Specified Guar Gum 1 Oil and gas: Drilling mud Fuel loss controlling Hydroxypropyl guar, Fracturing and and hydraulic agent, popping and carboxymethyl drilling fracturing gelling agent for hydroxypropyl guar, enhanced oil recovery; carboxymethyl guar and water retention, polyoxyalkylene lubricant turbulence and grafted guar. 10,11,12 cooling of drill bits; material suspension and mobility, viscosity shale inhibitor and formation of permeable agent. 2 Mining and Concentration Flocculating and Grafted hydroxypropyl recovery of of mining ore, settling agent, filter aid. guar, guar grafted materials filtration, polystyrene and other coagulation and cationic or anionic flocculation 13, 14 guar. 3 Metallurgy and Frothing buster Flocculants and Polyacrylamide grafted minerals and bonding depressant for solid carboxymethyl guar and recovery agent for valuable minerals cationic guar. 15,16 4

6 precipitation separation. 4 Coal industry Coal suspension and shock impregnation Improve flowability as friction reducing suspending agent. Hydroxypropyl guar Medical, Colon target Carrier and protection Ionic or covalent cross- Biomedical and drug delivery of drug molecules from linked guar and pharmaceuticals the acidic digestive hydrophilic juice. derivatives. 18,19 Organ target Targeted drug delivery Guar gum nanoparticles drug delivery carrier scaffold. and its functionalized derivatives. 20 Tablet Controlled release, Guar gum acetate, formulation and sustained release, carboxymethylated coating forming free filming guar, guar grafted with agent. poly(acrylamide), poly(acrylic acid) and poly(nisopropylacrylamide). 21, 22, 23, 24, 25 Suspension Emulsifier and Carboxymethyl guar. 26 stabilizer. 5

7 Diluents and binder Bulking and adjuvant agent for formation of granules in tableting. Borax cross-linked Carboxymethyl guar. 27 Laxatives and body weight loss aids Bulk laxative or bulk occupied for appetite depressant. Partial hydrolyzed of guar, carboxymethyl-ohydroxypropyl guar. 28, 8 Diabetic treatment Reduction of urinary glucose loss. Guar gum hydrolysate and partially hydrolysed guar, composites, depolymerized guar. 29, 30,31,32 Hyperlipidemia Interference in fat absorption, lipid reducing agent. Partially hydrolysed guar gum, guar gum hydrolysate and depolymerized guar. 33 Wound healing application Antimicrobial, ROS controller, moisture retainer. Cationic guar gum with metal nanocomposite. 34 Antibacterial film Bactericidal. Guar gum alkylaminesilver nanocomposite. 35 6

8 Treat dry eye Lubricating agent Hydroxypropyl guar. 36 Cancer chemopreventive and antiinflammatory Modulate the macrophage functions, carcinogen metabolism and antioxidant capacity Guar gum c- glycosylated and guar sulphated derivative Cosmetics Excipient in ointments, creams, lotions, pastes and jellies Thickening, binders, emulsion stabilizers, and film formers agents in aqueous medium. Hydroxypropyl guar, guar hydroxypropyltrimoniu m chloride, carboxymethyl guar and nonionic guar 38,39,40,41 Hair conditioners and skin conditioners Thickener, emulsifier, moisture protective, colloid uniform film forming agent. Hydroxyalkyl hydroxypropyl guar, guar hydroxypropyltrimoniu m chloride, hydroxypropyl guar hydroxypropyltrimoniu 42, 43, 44 m chloride. Hair wave set Waving or straightening agent. Quaternized guar gum, 45, 46 cationic guar. 7

9 7 Biomedical In vivo imaging Imaging agent. Radioactive or florescence tag guar gum and guar nanoparticles. 47, 5 Sensor Biomedical sensing agent. Guar gum-metal nanocomposite Packaging Bio-plastic Moisture and air barrier self stand film, light protective or transparent Guar gum-aryl derivatives, blends and 49, 50, 51, 52, composites. packing material. Increase flexibility, mechanibility and sealability. Coating Increase durability, porosity modifier, interpenetrating network forming agent. Guar gum caproyl ester and composites Bioremediation Coagulant Coagulating and flocculating agent. Hydroxypropyl guar, guar gum nanoparticles and nanocmposites. 54,55,56 8

10 Adsorbent Adsorbing agent, flocculating agent. Carboxymethyl guar, cross linked guar, hydrogel, derivative and composites. 57,58,59,60 Antimicrobial Killing, inhibition of microbes. Quaternary guar gum derivatives and 61, 35 nanocomposites. Filter and membrane Filter bed, semi permeable bed, interpenetrating networks former. Electro-spinning guar gum fibers, cross linked guar and hydrophobic 61, 62, 63, 64 derivative. 10 Food Frozen foods Viscosity modifier, water retention, retards ice crystal growth, stabilizer. Hydrophilic guar derivatives, centroid mixture and 65, 66 composites. Prepared cheese Emulsifier, increased curd solids yield, improved softness. Modified or partially hydrolyzed guar gum. 7 Baked foods Dough improvement, greater moisture retention, prolonged 67, 68 Guar composites. 9

11 shelf life. Dairy products Texture after sterilization, improves texture, maintains uniform viscosity and color. Partially hydrolyzed guar. 69 Dressings and sauces Cold water dispersible, acid resistant, stabilizer of emulsion inhibits moisture loss. Blend of guar and xanthan gums and guar derivatives. 70 Canned foods Reduces splash while filling viscosity control prevention of fat migration. Guar derivatives. 71 Beverages Acid resistant thickening and suspending agent. Medium viscosity modified guar Paint Water soluble or insoluble painting Solubilizer of dye, thicker and disperser of dye solution, durability improver. Hydrophilic guar derivatives

12 12 Textile printing Cotton fabric, Reduces dusting film Carboxymethyl guar, and dyeing lather, rayon forming thickening for hydroxypropyl guar and silk, wool sizing printing dye, reduces 74, 75, 76 cross linked gel. and carpet warp breakage, printing durability modifier. 13 Paper Photographic paper wrapping paper, kraft and filter paper Improved erasing and writing, better breaking, mullen and folding strengths, improved adhesion, replaces hemi-cellulose, increase binding strength, fold, pick, pulp hydration, retention of fines, decreases porosity, denser surface. 2-hydroxy- 3- propyl ether guar, (trimethylammonio)- carboxymethyl-2- hydroxypropyl ether guar, amino ethyl guar and guar gum-graft- poly(acrylamide-co- diallyldimethylammoni 77, 78, 79 um chloride). 14 Tobacco Reconstitution of fragmented tobacco Binding agent, strengthening agent. Cationic guar Explosives Stick explosives and blasting slurries Cross linking, water proofing, gelling agent. Sulphonated guar, cross-linkable guar, guar gum ether and 11

13 cyanoethyl ether of 81, 82, 83, 84 guar. 16 Fire fighting Water control for fighting fires Friction reducing, dispersion and direction control. Hydroxyethyl and hydroxypropyl guar ether Ceramics Enamels and electroceramics Fixing, binding, thickening agent. Anionic guar derivatives and composites Photography Emulsions and gelatine stabilizer solutions Gelling, emulsifying, hardening agent. Borate cross-linked guar and hydroxypropyl 87, 88 guar. 19 Synthetic resins Polymerisation, suspension and collagen dispersion Viscosity modifying, binding agent. Guar gum nitrilotriacetic acid, cross-linked guar with cyanuric chloride or epichlorhydrin and guar gum 4-hydroxybenzoic acid. 89, 90, Agriculture Erosion control Maintaining moisture Hydroxyalkyl guars. 92, Hydroseeding around the seeds

14 Guar gum was first introduced as cattle feed; however, the industrially processed guar and derivatives have found more applications later in non-food areas. The native guar gum however expresses very acceptable mouth-feeling quality and blends well with the milk proteins. The biopolymer yields no energy in metabolism and propagates directly up to the colonic region. Such interesting property mix has enhanced many intellectual property protections for the native guar, processed guar and derivatives in food and non-food areas. A patents overview on engineered guar gum as applied in different industry applications is presented in Table 2. Examining across multifarious applications of guar plant biopolymer and derivatives indicate structural robustness and adoptive capacity of the biopolymer even in very harsh application environment. The biopolymer is economic because of consistent agriculture yield, low cost cultivation and easier seed processing techniques. In one consolidation, the guar biopolymer is very advantageous for sustainable materials applications because of (i) ready availability, (ii) ease in chemical modifications, (iii) intricate biopolymer water chemistry, (iv) robustness in chemical environment and (v) more appropriate material properties like molecular film formations and rheology characteristics. Table 2: A Patent review on engineered guar gum. Application Patent No. Year Patent Description/ Title Area Gas and oil well drilling US A Slurry concentrate and associated methods of use. 94 WO A Aqueous guar compositions for use in oil 13

15 field and slickwater applications. 95 EP B Oxidized guar for oilfield servicing fluids. 96 EP A Methods for oil or gas well drilling, washing and/or fracturing. 97 US A Drilling fluid, drilling fluid additive, methods of making and using, such fluid and additive, methods of operating a well. 10 WO/2011/ Drilling fluid additive comprising oil and multiple guar compounds. 98 US A Biodegradable foam compositions for oil field operations. 99 US B Method of forming temporary blocking gel containing guar derivative. 100 WO A Oil-well cement fluid loss additive composition. 101 US B Stabilizing crosslinked polymer guars and modified guar derivatives. 102 WO A Grafting polymerization of guar and other polysaccharides by electron beams. 103 WO A Environmentally acceptable fluid polymer suspension for oil field services

16 US A 1997 Particle transport fluids thickened with acetylate free xanthan heteropolysaccharide biopolymer plus guar gum. 105 US A 1996 Method of gelling a guar or derivatized guarpolymer solution utilized to perform a hydraulic fracturing operation. 106 US A 1994 Method for killing a gas blowout of a well. 107 EP Carboxymethyl guar based drilling fluids. 108 EP High temperature guar-based fracturing fluid. 109 US A 1987 Enzymatically-treated guar gums. 110 US A 1978 Thickening compositions containing xanthan gum, guar gum and starch. 111 Pharmaceut -ical US A Pharmaceutical soft gelatin capsule dosage form with modified guar gum. 112 EP A Carboxylated polysaccharides phosphated or bisphosphonated derivatives, optionally cross-linked, and their preparation and biomedical uses

17 EP A Cosmetic and/or pharmaceutical compositions containing alkyl or alkenyl glycosides, fatty acids partial glycerides, esterquats and hydroxyalkylated guar as thickener. 114 US A Topical delivery system for cosmetic and pharmaceutical agents. 43 Cosmetics WO A Cosmetic and household care compositions. 115 US A Guar hydroxypropyltrimethylammonium chloride and uses thereof in hair treatment compositions. 116 US B Procedure for the preparation of purified cationic guar. 117 US B Liquid cosmetic cleansing-agent composition. 118 US A Control of fluid migration in wet-wipes. 71 EP A Solid cosmetic composition for topical use. 119 US A Aminoalkyl-containing guar derivatives. 120 EP A Cation-modified galactomannan 16

18 polysaccharide and cosmetic composition containing the same. 121 US B Shampoo containing a cationic guar derivative. 122 US B Detergent cosmetic compositions for haircare application and use thereof. 123 US A Cosmetic compositions comprising a cationic polymer/anionic surfactant mixture and use of said mixture as conditioning agent. 124 WO A A cationic polymer composition and its use in conditioning applications. 125 US B Washing and conditioning compositions based on silicon and hydrophobic guar gum. 126 US B Make-up removing composition. 127 WO A Keratin treating cosmetic compositions containing high ds cationic guar gum derivatives. 128 US B Hair straightening/smoothing composition. 45 US B Detergent compositions containing an hydroxylalkyl ether surfactant and a 17

19 cationic guar gum. 129 US B Cosmetic composition based on nonionic guar gum and on non-crosslinked anionic polymer. 41 US A 2000 Cosmetic composition based on guar gum and silicones. 130 US A 2000 Alkaline hair conditioning compositions containing cationic guar. 131 EP B Cosmetic composition containing nonionicguar gum and a non-cross linked anionic polymer. 132 US A 1995 Combined personal cleansing and moisturizing compositions. 39 US A 1992 Conditioning shampoo comprising a surfactant, a non-volatile silicone oil and guarhydroxypropyltrimonium chloride as a cationic conditioning polymer. 44 US A 1986 Skin lubricating cosmetic composition. 133 US A 1984 Shampoo compositions containing hydroxypropyl guar gum. 42 US A 1981 Hair care compositions

20 US A 1977 Conditioning shampoo composition containing a cationic derivative of a natural gum (such as guar) as the active conditioning ingredient. 134 Water treatment CA A Water treatment composition and method of using same. 135 US A Non-destructive method for algae contaminated water treatment and algae harvest or removal. 136 WO A Water treatment compositions and methods of use. 56 US A Absorbent product comprising a cationic modified guar gum. 137 US B Waste water treatment method. 138 US A 1998 Derivatized guar gum composition including nonionic and cationic groups which demonstrate excellent solution clarity properties. 139 Textiles US A Protection of the color of textile fibers by means of cationic polysaccharides. 140 EP A Composition for the treatment of textile materials

21 US B Formula and process for crosslinking antimicrobials to textiles. 142 WO A Textile printing paste. 143 WO A Thickener for textile printing paste. 144 US A 1997 Carboxymethylated guar galactomannan as a sizing agent. 145 US A 1995 Removal of printing paste thickener and excess dye after textile printing. 146 EP B Oxidized polygalactomannan for improved textile washing. 147 US A 1991 Oxidized polygalactomannan for improved textile washing of pad-dyed carpet. 148 EP A Composition and method for rheology controlled printing of fabric and carpet. 149 EP A Textile conditioning compositions with low content of cationic guar gum. 150 US A 1978 Process for recycling textile warp yarn size. 151 US A 1977 Polygalactomannan gum formate esters. 64 Paper US A 1998 Paper coatings containing guar or reduced molecular weight guar

22 US A 1997 Enhancement of paper dry strength by anionic and cationic guar combination. 153 US A 1981 Novel blend of algin, TKP, and guar gum. 154 US A 1977 Polygalactomannan gum formate esters. 64 Explosives US A Fast hydrating guar powder, method of preparation, and methods of use. 155 US A 1988 Explosive compositions. 156 US A 1980 Explosive compositions containing sulphonated guar gum derivatives. 81 US A 1978 Thickened aqueous slurry explosive compositions. 157 US A 1975 Explosive compositions containing guar gum derivative. 82 US A 1974 Gelled chromium acetate cross-linked aqueous slurry type salt explosives, and manufacture. 158 US A 1973 Cyanoethyl ether of galactomannan gum. 83 US A 1973 Explosive composition containing a glycol and guar gum ether. 84 US A 1973 Aqueous gel for slurry explosives composition and method of preparing said 21

23 gel. 159 Dietary fiber US B Dietary fiber formulation and method of administration. 160 WO/2009/ Gummy candies based on dietary fibre. 161 WO A Dietary supplement composition. 162 US A Dietary fiber composition. 163 US A 1999 Compositions of dietary fiber rich and low viscosity beverages. 164 EP B Nutritionally complete feeding composition containing hydrolysed soluble fiber. 165 US A Enteral nutrition and medical foods having soluble fiber. 166 US A 1990 Cholesterol-lowering combination compositions of guar gum and niacin. 167 Food EP A Biscuit comprising guar gum in a rod-like form. 168 US A 1999 Glaze composition with vegetable gums. 169 US A 1998 Bulking agents and processes for preparing them from food gums. 170 EP Reduced calorie fruit spreads comprising a high-intensity sweetener and a gum blend 22

24 (locust bean/guar/carboxymethyl cellulose/pectin or carrageenan). 171 WO/1994/ Chewing gum containing guar gum hydrolyzate. 172 CA A Extensively depolymerized guar as a bulking agent for foods. 173 US A 1978 Thickening compositions containing xanthan gum, guar gum and starch. 111 US A 1965 Food mixes with lower alkyl derivatives of guar gum incorporated therein. 174 Agriculture US A Method for preventing soil erosion. 175 WO A Agrochemical formulations with improved drift control. 176 US A Spray drift adjuvant formulation and method of use. 177 WO A Growth enhancement of plant. 178 CA A Method for preventing soil erosion. 179 US B Low use rate agricultural compositions and methods for use. 180 US A Agricultural spray solution compositions and methods

25 US A Seed coatings, coating compositions and methods for use. 182 WO A Process for preparing diluted agrochemical spray formulations with improved drift control. 183 US B Agricultural promoters/active ingredients. 184 US B Manufacture and use of an deposition aid. 185 US B Free-flowing fertilizer compositions. 186 US A 1998 Guar as a deposition and bioefficacy aid. 187 US A 1996 Guar gum as drift control agent. 188 US A 1995 Hydraulic binder composition and its uses. 92 US A 1991 Agricultural gel-forming compositions.189 US A 1974 Method of making mulch composition. 93 Rheology modifier EP B Rheology modifying admixture. 190 US A Method of achieving improved product rheology, cosmetic consumer acceptance and deposition. 191 US B Rheology modifier comprising a 24

26 tetrakis(hydroxyalkyl) phosphonium salt for polymer fluids. 192 US A Rheology modifier for cement slurries. 193 WO A Rheology modifier for ceramic glazes. 86 US B Guar gum based flowing gel play composition. 194 WO A Rheology modified compositions and processes thereof. 195 US A 1996 Fracturing fluid treatment design to optimize fluid rheology and proppant pack conductivity. 196 US A 1987 Coal suspension flowability improvers. 17 US A 1978 Thickening compositions containing xanthan gum, guar gum and starch. 111 Building Additives US B Building additives based on purified hydrophobically modified hydroxyalkyl guar. 197 WO A Additives based on methyl guar for use inbuilding compositions. 198 US A Building additives based on purified hydroxyalkyl guar. 199 Fire US A 1981 Chemical retardants for forest fires

27 Control Biomedical EP A Polysaccharides cross-linked by ether bonds, their preparation and biomedical applications. 200 EP A Carboxylated polysaccharides phosphated or bisphosphonated derivatives, optionally cross-linked, and their preparation andbiomedical uses. 113 WO A Materials for medical implants and occlusive devices. 201 US A 1996 Solid multipurpose ultrasonic biomedical couplant gel in sheet form and method. 202 EP B Hydrophilic, pressure sensitive biomedical adhesive composition. 203 Imaging US A 1995 Stable artifact-free imaging contrast suspension agent. 6 US A 1971 Ferromagnetic contrast media and method of use. 204 Adhesive CA C 2007 Polymers as detackification agents for adhesives contained in secondary fiber. 205 EP B Denture adhesive composition. 206 Bioefficacy aid US B Carboxyvinyl polymer-containing nanoparticle suspensions

28 US A 1998 Guar as a deposition and bio-efficacy aid. 208 Paint CN A 2014 Elastic latex paint. 209 CN A 2014 Antimicrobial anticorrosive latex paint. 210 CN A 2014 Environment-friendly latex paint. 211 WO A Paint formulations. 212 WO A Hydroxypropyl guar. 213 WO/2007/ Paint removers containing hydroxypropyl guar. 214 WO A Multicoloured paint composition. 215 US A 1999 Biostable water-borne paints. 216 US A 1993 Coating composition containing as thickeners polygalactomannans modified with hydrophilic and hydrophobic groups. 217 US A 1979 Thickener for reactive dyes. 218 The biopolymer is currently one highly focused area in different material chemistry applications. Most articles published are concerned with covalent and non-covalent modifications on guar gum in order to reap benefits in multifarious areas. Guar gum processing and physicochemical aspects per se cover a large interest in scientific community. A select number of publications are also concerned with newer guar 27

29 biopolymer derivatives synthesis for applications in health care and environment. Guar biopolymer and derivatives are currently explored relentlessly in newer fields like bioremediation, medical devices, nanoparticles stabilization, drilling property enhancements and others. 1.2 Chemical conversions in guar gum: Covalent modifications in polysaccharides are fascinating and that often extend an edge in different applications. Guar gum is uniquely branched galactomannan containing a number of surface hydroxyl groups. Guar gum hydrates well due to intermolecular hydrogen bond formations and easy penetration of water molecules. Different salts like potassium, iron, boron or aluminium diffuse well in the guar gum matrix and hydrogels. They are also known to provide rheology modifications and property enhancement in specific applications. Guar gum is very adoptive in chemical environment but the effective property is often constrained due to lack of surface functional groups. Chemical conversations in guar gum can change properties in ionic and water deficient medium. More reactive surface hydroxyl groups of guar gum permit structural design. Various functional groups were introduced in guar gum backbone in order to i) increase not only the water solubility of guar gum, ii) modify rheology properties, iii) alter biopolymer film surface characteristics and similar others. Newer self assembly structures were also controlled in derivatives. Guar gum surface OH groups can be converted in displacement reactions for typical property enhancements of macromolecule. The chemical modification of guar gum is thus a powerful tool for controlling interaction of the polymer with drug molecules, enhance loading capability, tailor release profile and similar others. 28

30 Chemically modified guar gum improves its bulk properties for sustained release characteristics. In guar gum three hydroxyl groups are available for chemical conversion. The primary hydroxyl group at C6 position is highly susceptible to chemical conversion, but C2 and C3 positions are also moderately reacting sites. Several chemical transformations techniques may be applied to develop guar gum derivatives with variable degree of substitution (DS). The polymerisation degree (PD) is another important factor, giving an average length of the biopolymer, guar gum (expressed in number of monomer units present in a single sequence). A loss in PD during a reaction indicates that degradation of the guar gum backbone structure. Chemical conversion in guar gum was carried out earlier for commercial applications. Guar gum ethers and esters found applications in various fields including oil well drilling, constructing materials, packaging materials, binder, cosmetics, biomedical and as well as in pharmaceutical applications. It is remarkable to note that chemical modification reactions in guar gum were not often very restrictive. Guar gum ethers like methyl, carboxymethyl, hydroxyethyl, hydroxypropyl, 2-hydroxy-3-(trimethylammonio) propyl etc were reported. Some guar gum esters that were reported include formate, acetate, propionate, butyrate, benzoate, phthalate and higher fatty acid esters. Different techniques were adapted for guar gum chemical modifications. Different major guar derivatives and the reactions adapted in covalent conversions are classified systematically Guar gum ethers: Guar gum ethers are water-soluble polymeric derived from Guar gum. Generally, the ether derivatives are synthesized via Williamson ether reactions. The technique is facile and 29

31 proceeds appropriately in water medium. The surface free hydroxyl groups of guar gum that form alkoxides in presence of strong alkali are used to equilibrate with the etherifying reagents. The reaction is known to follow SN 2 mechanism. Ether reactions of guar gum are industrially important and derive biopolymers with unique properties. 219 Such derivative properties are important in a number of application areas like the construction cementing additives, flocculants, antimicrobial coating materials, ceramics and castables, water based paints additives, cosmetics products, and pharmaceuticals. For construction products, guar gum ethers act as viscosity modifier, binders, film formers and water-retention agents. They also function as foam stabilizer, suspending agents, surfactants, protective colloids, emulsifiers and lubricants. Some significant guar gum ethers that are reported so far include sulfated, methylated, carboxymethylated, hydroxyethylated, hydroxypropylated, hydroxyethyl amino hydroxypropylated, hydroxy-(trimethylammonio) propylated, carboxymethyl-hydroxypropylated and carboyxymethyl-2 hydroxy-3-trimethylammonia 220, 221, 222, 61, 223, 224, 116, 225, 73 propylated guar gum Cationic guar gum: Guar gum biopolymer is non-ionic in nature. Cationic guar gum derivatives like the quaternary ammonium or the amine functionalized guar gum are extensively used in cosmetic as substantive conditioning agent in shampoo preparation. 44, 122 Similar compounds are also used relatively recently as mining flocculating agents. Cationic guar gum derivatives are commercially available. Variations in the degree of substitution (DS) and the formulation types have resulted in multi-charge carrier filming guar derivatives useful in surfactant rich products like the shampoo. Guar hydroxypropyl 30

32 trimonium chloride for example is known to improve smoothness, hair luster, manageability and texture cosmetics of hairs. 42, 226 Cationic guar as flocculant is known to improve flocculation capacity, and thus, has wide number of industrial applications in mining, processing of ores and minerals recovery. The range of cationic guar derivatives were reported as grafting reaction products and higher DS was achieved in isopropyl alcohol/water media. Similar derivatives were reportedly useful in food processing, as 174, 227, 25 mucoadhesives and as antimicrobial coating compounds Carboxymethylated guar gum: Among the guar gum derivatives types, the carboxymethyl guar gum (CMGG) derivatives are most economical and have found widest applications across different industries. Introduction of anionic carboxymethyl groups into non-ionic guar gum improve thickening capacity, foaming ability, binding and stabilizing properties in water rich medium. Carboxymethylated guar gum is widely used in cosmetic, in pharmaceutical formulations, in cutter lubricants, in paper production and textile sizing. 26, 228,229,153,145 Carboxymethyl guar gum is also experimented successfully in colon target drugs and for per-oral drug delivery of hydrophilic macromolecules. The basic concept of etherification reactions generally adopted for carboxymethylation is polysaccharide alkali activation and subsequent covalent conversions in monochloroacetic acid or the sodium salt of monochloroacetic acid (SMCA). The reaction medium can be aqueous solutions or guar slurry in aqueous-organic solvents. The first step is alkoxide activation and the second step is SN 2 replacement with carboxymethyl groups. Alternatively, dry conversions were also conducted on native guar gum powder in presence 31

33 of powdered sodium hydroxide and monochloroacetic acid in a small amount of aqueousorganic liquid medium. Solvent less carboxymethylation of guar gum with varibale DS was done by using monochloroacetic acid and catalytic amount of NaHCO 3 in dry state. Another approach for carboxymethylation of guar was by using acrylamide and sodium hydroxide. Different grades of carboxymethyled guar gum were developed for enhanced cold-water solubility, solution stability, solution clarity and increased viscosity. 230,231,232, Hydroxyalkylated guar gum: Hydroxypropyl guar (HPG) has good thixotropic behavior and is mostly used in petroleum oil well drilling and oil recovery processes. Hydroxypropyl guar gum (HPGG) was first commercially semi-synthesized in 1960 by the General Mills Inc USA. Originally it found applications in the paper and textile industries as sizing agent and pigment thickener in printing operations. Non lumping hydroxyalkylated guar derivative achieved higher thickening characteristics and has replaced locust bean gum used earlier in textile printing. Another similar derivative O-(2-hydroxyethyl), O-(2-hydroxypropyl), O-(2- carboxymethyl) guar gum was reported for enhanced rate of hydration, improved rheological behavior, high viscosity in water and moisture retaining characteristics. Hydroxyethyl guar (HEG) was synthesized by reacting native guar gum with ethylene oxide in the presence of an alkali catalyst. Newer route using phase transfer catalyst was also reported for hydroxypropyl guar gum synthesis. The modified guar has higher viscosity, pressure stability and can form light transparent films. A newer hydroxyethyl amino hydroxypropyl guar gum (EAHPG) derivative was prepared by reacting paratoluenesulfonate activated hydroxypropyl guar gum with ethanolamine following 32

34 nucleophilic substitution reactions. Most of all the hydroxyalkyl guar gum derivatives including the newer ones are meant to act as rheology modifiers and are used in petroleum oil drilling as fracking fluids Methylated guar gum: Methylation is of outstanding importance in polysaccharide chemistry. Methylation and other alkylation reactions onto the guar galactomannan chain are performed following catalytic substitution reactions. Denham and Woodhouse method is generally consider as standard for methylation of sugar chains by using dimethylsulfate (DMS) in alkaline condition. 235 In case of guar gum the surface hydroxyl groups are exposed and intermolecularly hydrogen bonded. The protocol objective is but to derive guar gum in any or all of the hydroxyl groups of the galactomannan backbone. The reaction between guar gum and alkyl reactant is normally conducted in presence of sodium hydroxide to form an intermediate alkoxide derivative. That in turn reacts with the DMS and methyliodide reagent in Williamson type reaction for introducing methoxyl substituents along the polysaccharid chain. 221 Microwave irradiation reportedly assists in rapid reactions for complete methylation on all exposed hudroxyl groups of guar gum. 236 Methylated guar gum effect some viscosity enhancement but the product did not find much application in industry Guar gum esters: A series of synthetic routes are introduced in order to derive polysaccharides esters for industrial applications. Native guar gum is used as an emulsifier, thickener and binder in 33

35 food industry because they are non-toxic, biodegradable and having very good emulsifying and thixotropic properties. Esterification of guar alters the physicochemical properties immensely. The guar gum palmitoyl ester was synthesized under heterogeneous conditions. Guar gum powder was reacted with palmitoyl chloride in toluene and pyridine was used as a promoter. Some of the cost effective techniques reported for preparation of different guar gum esters were reactions of anhydrous gum with acetic, succinic or octenylsuccinic anhydride under mild catalysis conditions in NaHCO 3. In another technique guar gum succinate ester was derived from succinic anhydride reactions using 4- dimethylaminopyridine in dimethyl sulfoxide as catalyst. Resultant material was structured hydrogel that exhibited excellent water absorbency and biodegradability. The hydrophobic guar gum esters were also synthesized by reacting gum with n-octenyl succinic anhydride 237, 238 (OSA) or oleic acid in presence sodium bicarbonate in ethanol Guar gum grafts and copolymers: In the last decade, various grafting reactions were experimented in order to introduce various functional groups onto the polysaccharide chain structures. This has provided a range of newer sustainable materials for applications. 239, 240, 241, 242, 243, 244 The critical grafting reactions are generally mediated through free radicals formation by radiation, thermal, electrochemical, photochemical or chemical methods so as to replace the native biopolymer primary hydroxyl groups. Grafting conversions impart significantly new or hybrid properties which are often superior in applications. Graft polymers and copolymers were used as efficient flocculating, binding, thickening, stabilizing and film forming agents. Some of that have found applications in textile printing, cosmetics, coating, 34

36 packaging, paper industry, water purification, mineral extraction and drilling industries. Grafted acrylamide copolymer on guar gum was reported. 245, 246, 247 High energy gamma radiations was used and different DS products were developed. In another technique peroxydiphosphate-metabisulphite redox pair at moderate temperature was used to develop a series acrylamide graft guar gum compounds. Overtly microwave irradiation appeared successful in guar gum grafting reactions. A graft copolymer guar g-polyacrylamide was developed under microwave irradiation conditions without application of catalysts and the product was reportedly useful as efficient flocculating agent. 248, 15 High grafting ratio (~66 %) was achieved in relatively mild reaction conditions. which is quite high as compared to grafting obtained by conventional method. Hydrophilic hydrogel O-Carboxymethyl- Ohydroxypropyl guar gum (CMHPG) developed similarly expressed have acid resistance capacity. Different DS grade products are commercially available for applications in colon targeted controlled drug delivery systems. An interesting guar based fixative Guar-graft polyacrylamide-codiallyldimethylammonium chloride was developed using, diallyldimethylammonium chloride as an initiator in hexane/ethanol solvent medium. The grafted polymer proved effective in adsorbing hydrophobic wood resin particles onto paper making fibre surfaces and is effective over a range of ph conditions. A stimuli-responsive graft polysaccharides with enhance thermal stability was reported. The Poly (N-isopropylacrylamide) chain graft onto CMHPG in aqueous solutions was developed using potassium persulfate and N,N,N,N -tetramethylethylene diamine as the initiation system. Different other guar based graft copolymers with varying DS values like the acrylated guar gum expressed better filming properties, enhanced elongation strength and transference. 249 Similar agents 35

37 are useful in acrylic emulsion paints. Cationic guar gum-g-epichlorohydrin was investigated by some researcher by reacting epichlohydrin with guar gum in the mild alkaline condition at room temperature. This grafted derivative has flocculating, thickening and conditioning characteristics. 250 An aqueous soluble photopolymerizable guar gum methacrylate hydrogel was developed by reacting glycidyl methyl methacrylate in presence of persulfate/ascorbic acid as initiator redox pair. This copolymer was experimented for fabrication of tissue engineering scaffolds and in removal of health hazard Cr ions from waste water. Poly-sodium acrylate graft guar gum was developed using ceric ammonium sulphate/dextrose as redox initiators and that material have found application as ph responsive superabsorbent bio-medical hydrogels. 251 Newer hydrophobic derivatives of guar like the polyalkoxyalkyleneamide derivative series were developed as components for hydraulic fracturing fluids A perspective on modified guar gum and biohybrids for applications: Resurgence in guar gum application research in recent times is very noteworthy. In the alone nearly 2900 research articles were published and 10 number of patents filled on modified guar gum for diverse applications. Some of the reasons for that are i) increasing demand for sustainable materials, ii) unique mannose galactose chemistry of guar, iii) water activity, iv) favorable protein polysaccharide interactions of guar gum, v) biocompatibility and biodegradability. The biopolymer derivative appeared as one excellent stabilizer for nanoparticles. Silica nanopatrticles entrapped with anionic modified guar gum were recently reported for industrial effluent water purification purposes. 253 Hybrid nanocomposites were developed and used for rapid removal of toxic dyes and 36

38 metal ions. Nanomaterials like functionalized silica can be entrapped in cross linked guar gum. Biopolymer nanocomposites were proposed as superior tools for hydrocracking. 254 Similarly tin dioxide nanoparticles graft guar gum was reported for hydrazines electrochemical detection in a multi-chemical environment. 255 Guar gum derivatives intercalating properties were also intelligently applied in bentonite clay nanocomposites design. 256 Modified guar gum nanocomposites were successfully experimented for basic ph delivery of anti-inflammatory drug ibuprofen. Guar gum-montmorillonite ordered nanocomposites structures enabled ibuprofen entrapment and super-sustained delivery in the intestinal regions. The biopolymer is one excellent film forming material. Guar gum can simultaneously entrap and stabilize a range of metal and metal oxide nanoparticles concentrates. 35, 51 Films thermal, mechanical and barrier properties were enhanced due to nanoparticles arrays in a composite structure design. This effect was used to develop active films for food and related packaging materials design. In another work continuous dispersion of micronized zerovalent iron in guar gum was successfully used for reclaiming ground water and decontamination. 257 One recent report relates to modified guar gum application as flocculant for highly polluted industrial waste water treatment. 258 The biopolymer act as one efficient water clarifies and the effects are often comperative with the common inorganic clarifiers. 259 Many polysaccharides including guar gum have gained attention as new generation tissue engineering materials. 260 Besides being biocompatible the polysaccharides display distinctive interactions in the protein and amino acid interfaces. This effect was often used in appropriate tissue engineering scaffold design. Guar gum derivatives stand alone and as 37

39 drug carrier are in advanced trial for wound healing applications. Unique galactomannan platform has enabled cell attachment, biochemical massaging and complex tissue regeneration. 241 Guar gum is one excellent choice for drug delivery applications. Several guar gum derivatives were developed for disease specific drug delivery to the colonic region. 261 Guar gum blend and hydrogels were developed as ph responsive delivery system for steroids up to the colic region. 262 Guar gum blend biogels were also proposed for site specific drug delivery. 263 The biopolymer acts as a dietary pre biotic fiber and demand for that purpose is increasing very fast. Enzyme hydrolyzed and partially depolymerized guar gums are generally applied. Structure modified guar gum is one very efficient dietary fat absorber. 264 The hydrolyzed biopolymer is often recommended as food supplement for hyperglycaemic patients. 265 The galactomannan guar gum associate interesting physico-chemical properties that appears attractive in different new generation applications. 38

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