Acetate starch ester

This group (sometimes called water-soluble resins) includes such chemically treated natural polymers as carboxymcthylcclluosc, mcthylccllulosc, and other cellulose esters, as well as various kinds of modified starches (esters and acetates). 

Starch esters are thermoplastic materials with properties that are somewhat similar to that of cellulose esters. In particular, starch acetate (DS < 0.2) is used as a coating agent for paper and as a food or detergent additive. 

Starch acetates are the most easUy prepared of the starch esters. They have served frequently for the characterization of starch fractions, for investigations of starch structure and as intermediates - in the preparation of methylated starch. Although most acetylation work has been done on white potato starch, considerable attention has been given to the acetylation of other starches such as those from com, - - - waxy com, wheat, - - - canna, rice, " horse chestnut and banana. ... 

Starches have been chemically modified to improve their solution and gelling characteristics for food applications. Common modifications involve the cross linking of the starch chains, formation of esters and ethers, and partial depolymerization. Chemical modifications that have been approved in the United States for food use, involve esterification with acetic anhydride, succinic anhydride, mixed acid anhydrides of acetic and adipic acids, and 1-octenylsuccinic anhydride to give low degrees of substitution (d.s.), such as 0.09 [31]. Phosphate starch esters have been prepared by reaction with phosphorus oxychloride, sodium trimetaphosphate, and sodium tripolyphosphate the maximum phosphate d.s. permitted in the US is 0.002. Starch ethers, approved for food use, have been prepared by reaction with propylene oxide to give hydroxypropyl derivatives [31]. 

Common starch esters include the acetates. High d.s. starch acetates have been formed by using acetic anhydride with either sodium acetate or pyridine catalysts at 90-100 °C [158,159,160]. The major use of starch acetates have been in the study of the stmctures of amylose and amylopectin after acid hydrolysis. Acetylation of granular starch in aqueous suspension by acetic anhydride at pH 10-11 is used to produce low d.s. starch acetates that are primarily used for the stabilization of their viscosity and for their water-soluble clarity. The acetylation decreases the hydrophilic character and increases the hydrophobic character of starch. The major uses of starch acetates is in the paper industry for surface sizing to give improved print quality, uniform porosity, surface strength, and resistance to various solvents [161]. 

Various anhydrides show significant differences in reactivity. For instance, acetic anhydride reacted with starch in the presence of formamide, whereas phthalic anhydride required pyridine to react. This property was utilized in preparation of starch esters carrying two different acyl groups simultaneously.19181919 Mixed starch esters may also be prepared by using a mixture of various anhydrides in... 

In other reactions of starch esters, for example, 2,3-di-O-acetylamylose reacted with A-iodosuccinimide in the presence of triphenylphosphine to give 2,3-di-0-acetyl-6-deoxy-6-iodoamylose.2019 The ester bonds are fairly stable to acid-catalyzed hydrolysis. Starch esterified with acetylsalicylic acid administered to dogs did not increase the acetylsalicylic acid level to any significant extent in the animal s blood serum.2020 The slow release of herbicides from their esters with starch was analyzed.2021,2022 Alkaline hydrolysis of starch esters is easier than acid hydrolysis.2023 The enthalpy of starch acetate formation was 143.5kJ/mole, and acetylation decreased the susceptibility of the starch backbone to enzymatic hydrolysis and iodine uptake.2024 The hydrolysis of starch and starch acetate in alkaline solutions obeys second-order kinetics.1988... 

Miladinov et al. reported the preparation of starch-fatty acid esters by reactive extrusion of plasticized starch and acid anhydrides (acetic, propionic, heptanoic and palmitic anhydrides) in the presence of sodium hydroxide as a catalyst [87]. Starch esters have been prepared by REX using maleic anhydride (MA) as a cyclic dibasic acid anhydride in the presence of 20 wt% glycerol as plasticizer. This material was melt-blended with biodegradable polyester. 

The performance of the TPS/MMT nanocomposities using different kinds of starch have been studied. Nejad et al. [251] developed nanocomposites through the melt intercalation of nanoclays and starch esters from high amylose starch. Starch acetates (SAs) and starch propionates (SPs) were tested in combination with glycerol triacetate (triacetm) as a plasticizer for concentrations up to 30 and 20 wt %, respectively, with different types of organomodified and unmodified... 

Waxy starch, hydroxypropyl ether Waxy starch, carboxymethyl ether Waxy starch acetic acid ester... 

Appropriately formulated starch esters with plasticizers and other additives provide resin compositions that can be used to make injection molded products and for direct lamination onto Kraft paper. Starch acetates up to ds=2.S undergo complete and rapid biodegradation. In the case of starch triacetates, 70% of the carbon is converted to CO2 at 58°C in 45 days (25). 

Starch esters represent an important class of starch derivates and have been recently reviewed by Tessler and Billmers [63]. Starch esters can be produced by an aqueous process, at low alkalinity, under controlled pH, and low temperature reactions usually reaching a fairly low degree of substitution (DS<0,2) [64]. Starch acetates with a DS of 2.4 or higher are not biodegradable, like cellulose, while intermediate DS acetate would be easily biodegradable [63,31,32]. Most commercially used starch derivates have a DS less than 0.2 [60]. Pure amylose starch is considered the most desirable precursor for starch-ester based thermoplastics since amylopectin has an adverse impact on mechanical and physical properties of these derivatives [64]. 

Starch can react with organic anhydride in water to yield starch esters, such as starch acetate that have been produced commercially by this process. Esters have also been prepared by aqueous reaction with vinyl esters, the byproduct acetaldehyde can be used to cross-link the starch by lowering the pH once esterification has been completed. 

---