Chemical Science Review and Letters ISSN 2278-6783 Review Article Polyaspartic Acid - A Versatile Green Chemical Ajay Kumar Galgotias University, Greater Noida, Budha Distt. Gautam Nagar, UP Abstract and its hydrogels. Applications of polyaspartate It is one of the most common scale inhibitor. and its hydrogels of are described. The polyacrylate is nontoxic and Biodegradability with respect to methods of environmentally benign, but it is not preparation and variation in molecular weight of biodegradable. Polyaspartate a biodegradeable the polyaspartate is reviewed. polymer possess similar properties to the polyacrylates and is used as an antiscalant, *Correspondence adispersant and superabsorber. In this article we Ajay Kumar review, methods of synthesis of polyaspartate [email protected] Keywords: Polyacrylate, polyaspartic acid, hydrogels, antiscalants, biodegradability Introduction environmental problem from a landfill perspective. When polyacrylate is used as an antiscalant or a When water is heated in a boiler, soluble salt present in dispersant, it becomes part of waste water. The the water are precipitated out and start forming the scale. polyacrylate is nonvolatile and not biodegradable, so the Various antiscalants have been developed for the only way to remove it from the water is to precipitate it prevention of the scale. Antiscalants prevent scale as an insoluble sludge. The sludge must then be land formation entirely or permit the scale to be deposited in filled. Thus polyacrylate leaves its carbon foot print[1,2]. such a way that it is easily removed by the fluid flowing along the pipe or heat transfer surface. Antiscalants Therefore there was need to develop chemical complex with the cations present in water to prevent agents which possesses properties of polyacrylate and formation of the insoluble inorganic solids. The are biodegradable. Polyaspartate has similar properties polyacrylate is one of the most common scale inhibitors. to the polyacrylates and so it can be used as a dispersant, The polyacrylate is a polyanion. Polyelectrolytes are or an antiscalant, or a superabsorber. Polyaspartate is polymers with bound positive or negative charges ,are biodegradeable. The polyaspartate increases the also called macroions or polyions , can be polyanions or nutrient level in plants by keeping fertilizer available for polycations, are generally water soluble polymers if their an extended period of time [3]. In this article we structure is linear. Polymeric antiscalants are generally review the methods of synthesis , applications and low molecular weight polymers. Polymeric dispersants biodegradability of polyaspartate and its hydrogel. consist of higher molecular weight fractions. Dispersants do not stop the formation of scale, but instead are able to Synthesis keep the scale particles suspended in the bulk fluid by imparting a negative charge to the particles. The Poly(aspartate)s are condensation polymers of aspartic polyacrylate comprises 5% of many laundry detergent acid. They are synthetic poly(amide)s that are structural formulations because of its dispersant properties. A and functional analogues of biomineralization crosslinked form of the sodium salt of polyacrylic acid is controlling proteins. Their synthesis has been reviewed used as a super absorbant material in diapers and other in several articles [4-6]. The three main methods for the personal hygiene products. Crosslinked polyacrylate has industrial production of poly(aspartic acid) are [5-9] , a great affinity for water, but is unable to dissolve and thermal condensation of aspartic acid, catalyzed swell in aqueous solution. Because of the presence of the polymerization of aspartic acid, and thermal charged groups on the polymer chain of a polymerization of maleic acid and ammonium polyelectrolyte, the polymer will be highly expanded in hydroxide. In the thermal condensation process, the aqueous solution.The polyacrylate is nontoxic and aspartic acid is first converted to poly(succinimide) by environmentally benign, but it is not biodegradable. It heating the acid to a temperature above 180oC. Then is widely used for many applications and it poses an poly(succinimide) is transformed into poly(aspartic acid) Che Sci Rev Lett 2012, 1(3), 162-167 Article CS29204210 162 Chemical Science Review and Letters ISSN 2278-6783 by alkaline hydrolysis. The yield is high, nearing been reported [41]. A water insoluble polyamino acid complete conversion. Use of a catalyst lowers the cross linked gels have been prepared with the absorbing condensation temperature and enables shorter reaction capacity of 20 times the weight of 1% NaCl solution times. An alternative way to produce poly(succinimide) [42] . Gamma –irradiation to prepare the biodegradable by thermal polymerization of maleic acid and super – absorbent hydrogel (36-38) has also been applied ammonium hydroxide. The structure, chemical characteristics, and properties of a poly(aspartate) Applications: depend on the method of preparation [5]. Several other similar methods of preparation of poly(aspartate) have Several new environmentally acceptable scale-inhibitors been reported in the literature. [10-31]. compared with conventional antiscalants are known [43- 58]. Polyaspartic acid an environmentally benign agent for the dissolution of calcium salt deposits. The chelating A new original method of synthesis polyaspartic power of polyaspartic acid with calcium is investigated acid is presented by thermal polymerization of maleic by performing the potentiometric titration against acid derivatives under microwave irradiation [32]. The polyaspartic acid solutions. It is found that polyaspartic reaction required following steps: maleic anhydride is acid is fully deprotonated at pH 7. The titration curves hydrolised in water to give maleic acid (step 1), then it is are successfully modeled by assuming that four aspartyl converted into ammonium derivatives by addition of residues from an actual polyaspartic acid molecule ammonium hydroxide (step2). The stage 1 and 2 require consist of a hypothetical molecule (denoted as H4L) that temperature of 100°C. In this way, ammonium salt or/ has four distinct acid moieties (four dissociation and amide of maleic acid is obtained. The cyclic constants). The resulting dissociation constants and product, namely anhydro-poly( aspartic acid) (step3) is calcium-binding constants for polyaspartic acid at pHs formed. The temperature of polymerization is raised (10, 7, 5, and 3.5) show that polyaspartic acid replaces gradually in order to achieve high yield of interfacial water to react with calcite at high pH (≥7) and polycondensation. Water from the reaction is removed the dissolution of calcite can be described by a surface by means of distillation. Finally, linear polyaspartic acid adsorption and complexation mechanism. At low pH is obtained after hydrolysis of the cyclic form at room (≤5), surface adsorption of polyaspartic acid on calcite temperature (step 4). The hydrolysis of the anhydro- surface still plays an important role, and both acidic + n-4 poly( aspartic acid) leads to poly(aspartates) containing species attacks (H and HnL , n = 1,2,3,4, attacking 4- n-4 peptide bonds. The preparation of poly(aspartic acid) carbonate sites) and chelant attacks (L and HnL , n = from maleic anhydride and ammonia through in a two 1,2, attacking calcium sites) affect the calcite steps reaction has also been reported [33]. dissolution. The dissolution of calcite in acidic polyaspartic acid solutions represents the most In 1999, Rohm and Haas Company’s researchers complicated case [59]. reported, lightly cross-linked, high molecular weight sodium polyaspartates with superabsorbing, and Another investigates the use of sodium electrolyte-responsiveness properties [34]. They used polyaspartate, a nontoxic, biodegradable polycarboxylic ethylene glycol diglycidylether as a cross-linker. To sequestrant is for removing calcium phosphate deposit enhance the swelling capacity, several hydrophilic consisting of hydroxyapatite (HAP) and brushite or polymers such as starch, ethyl cellulose, carrageenan, β- dicalcium phosphate dihydrate (DCPD) from stainless cyclodextrin, and CMC have been incorporated into the steel surfaces. Cleaning studies show that the use of hydrogels (after or before the hydrolysis step) to attain sodium polyaspartate under alkaline conditions modified super absorbing polymer (SAP) composites significantly enhances the removal rates when compared [35-38]. For the crosslinking of polyaspartic acid , to deionized water. In acidic solutions, sodium various methods have been introduced , including polyaspartate concentrations below 300 ppm inhibit chemical and radiation processes. To prepare SAP removal of HAP/DCPD deposits whereas higher researchers have also used difunctional amine , amino concentrations increase the removal rate. Comparative acid , or their polymeric analogs as the chemical cleaning studies at alkaline pHs show that sodium crosslinker. Polyethylene glycol diglycidylether (PEG- polyaspartate cleans the surface at a rate comparable to diepoxide) with different molecular weights has also sodium citrate but slower than in been employed to synthesize biodegradable poly(aspartic ethylenediaminetetraacetic acid. Supplementary acid) hydrogels with super-swelling behaviour [39]. dissolution experiments show that sodium polyaspartate Method of producing super – absorbing polymeric enhances the HAP/DCPD dissolution rate while network of polyaspartate from crosslinked