Ethers, starch

When a 30-40% starch suspension is reacted with ethylene oxide or propylene oxide in the presence of hydroxides of alkali and/or alkali earth met- 

These products swell instantly, even in cold water and in ethanol. Dispersions of 1-3% carboxymethyl starch have an ointment-like (pomade) consistency, whereas 3 % dispersions provide a gel-like consistency. These products are of interest as thickeners and gelforming agents. 

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In industrial production of acid-modified starches, a 40% slurry of normal com starch or waxy maize starch is acidified with hydrochloric or sulfuric acid at 25—55°C. Reaction time is controlled by measuring loss of viscosity and may vary from 6 to 24 hs. For product reproducibiUty, it is necessary to strictly control the type of starch, its concentration, the type of acid and its concentration, the temperature, and time of reaction. Viscosity is plotted versus time, and when the desired amount of thinning is attained the mixture is neutralized with soda ash or dilute sodium hydroxide. The acid-modified starch is then filtered and dried. If the starch is washed with a nonaqueous solvent (89), gelling time is reduced, but such drying is seldom used. Acid treatment may be used in conjunction with preparation of starch ethers (90), cationic starches, or cross-linked starches. Acid treatment of 34 different rice starches has been reported (91), as well as acidic hydrolysis of wheat and com starches followed by hydroxypropylation for the purpose of preparing thin-hoiling and nongelling adhesives (92). 

Hydroxylall l Starch Ethers. Starch hydroxyethyl ethers with a degree of substitution (DS) of 0.05—0.10 ate produced in various ways, but usually their preparation begins at the end of the wet-milling process, utilizing a high soHds-starch suspension. The ether modification of ungelatinized starch is filterable and can be produced economically in a pure form. 

Cationic Starches. The two general categories of commercial cationic starches are tertiary and quaternary aminoalkyl ethers. Tertiary aminoalkyl ethers are prepared by treating an alkaline starch dispersion with a tertiary amine containing a P-halogenated alkyl, 3-chloto-2-hydtoxyptopyl radical, or a 2,3-epoxypropyl group. Under these reaction conditions, starch ethers are formed that contain tertiary amine free bases. Treatment with acid easily produces the cationic form. Amines used in this reaction include 2-dimethylaminoethyl chloride, 2-diethylaminoethyl chloride, and A/-(2,3-epoxypropyl) diethylamine. Commercial preparation of low DS derivatives employ reaction times of 6—12 h at 40—45°C for complete reaction. The final product is filtered, washed, and dried. 

Etherification. Carbohydrates are involved in ether formation, both intramoleculady and intermoleculady (1,13). The cycHc ether, 1,4-sorbitan, an 1,4-anhydroalditol, has already been mentioned. 3,6-Anhydro-a-D-galactopyranosyl units are principal monomer units of the carrageenans. Methyl, ethyl, carboxymethyl, hydroxyethyl, and hydroxypropyl ethers of cellulose (qv) are all commercial materials. The principal starch ethers are the hydroxyethyl and hydroxypropylethers (see Cellulose ethers Starch). 

Starch Ethers. A large number of starch ethers have been prepared and patented only a few are manufactured and used commercially. Commercially available starch ethers are the hydroxyalkyl ethers, hydroxyethylstarch [9005-27-0] and hydroxypropylstarch [9049-76-7] and cationic starches. 

Starch Esters. As with the starch ethers, a large number of starch esters have been prepared and patented, but only a few are manufactured and used commercially. Both inorganic and organic acid esters can, and have been, made. The latter are prepared by the same general procedure used to make starch ethers. 

Cationic Starches. Commercial cationic starches are starch ethers that contain a tertiary amino or quaternary ammonium group, eg, the diethylaminoethyl ether of starch or the 2-hydroxy-3-(trimethylammonio)propyl ether of starch [9063-45-0], sold as its chloride salt [56780-58-6]. 

Etherification. A mixture of ethylene chlorohydrin ia 30% aqueous NaOH may be added to phenol at 100—110°C to give 2-phenoxyethanol [122-99-6] ia 98% yield (39). A cationic starch ether is made by reaction of a chlorohydfin-quaternary ammonium compound such as... 

Adding the carboxymethyl group makes the starch less prone to damage by heat and bacteria. Carboxymethyl starch is used as an additive in oil drilling mud. It is also used in the goo that makes ultrasound examinations so messy. Carboxymethyl starch is also called a starch ether. 

Starch ethers, 4 720 Starch graft copolymers, 4 722 Starch-granule morphology, 26 273 Starch hydrolysates, hydrogenated, 12 39 Starch industry, enzyme use in, 10 252-253... 

Commercially available cationic starches for wet end application are quaternary and tertiary products. These products have been available since about the mid 1950 s and no new basic chemistry has been developed since that time. The development in the late 1940 s and early 1950 s of starch ethers and esters made in the original granule form led to a torrent of starch derivatives for industrial use. Very few of these became commercial. This is possibly because the functions that were required by the industrial and food markets were far... 

The reaction proceeded through nucleophilic displacement of chloride and a starch ether was formed. The ether derivative was quaternized and made cationic by addition of a mineral acid. Teriary amino starches so made are used predominantly at acidic pH where the charge remains maximum. As neutral pH is approached, the charge is diminished until at weakly alkaline pH the charge is lost. 

Quaternary ammonium starch ethers are prepared by reacting the chlorohydrin form of... 

Wilke, O., Mischnick, P. (1997). Determination of the substitution pattern of cationic starch ethers. Starch, 49, 453 58. 

Non-ionic starch ethers are used in the food industry to avoid water release from frozen food and in the paper industry as a coating agent. 

Cationic starch ethers are used in the paper industry to increase the cohesion and rigidity of cellulose fibres and as a flocculant for the selective separation of negatively charged particles. 

The TEMPO - sodium hypochlorite - sodium bromide system has been applied to starch ether derivatives, particularly hydroxyethyl starch, which has a primary hydroxyl group on the hydroxyethyl ether group that can also be oxidized to a carboxyl group and carboxymethyl starch. The apparent goal was improved sequestering agents via higher carboxyl content and the proper multidentate conformations... 

Figure 18.2 Relationship between solids content and viscosity for a series of commercial starch ethers.

Corn starch for use in an enzymic conversion process should not contain more than 0.4% protein. In some cases modified starches, such as starch ethers, are used as feedstock. Higher product cost is balanced by the substantial reduction of retrograda-tion in products thus obtained. The feedstock has to be buffered in order to reach the required pH level for optimum enzyme activity in the process water of the paper mill. Additional adjustments may be required at the mill site when filtered surface water, which varies with the seasons, is used. Calcium salts for improved heat stability of the enzyme are added by the starch supplier or the paper mill. Further addition of sodium chloride will promote enzyme activity, and urea will broaden the critical pH range. Starch preservatives have to be added after the enzyme has been inactivated. 

Etherification with Oxidation (Oxidized Starch Ethers)... 

Tapioca Starch ether Hydroxypropylated and thinned starch Gums... 

SYNS ESSEX 1360 ESSEX GUM 1360 ETHYLEX GUM 2020 HAS (GERMAN) HES HESPANDER HESPANDER INJECTION HYDROXYATHYLSTARKE (GERMAN) o-(HYDROXYETHYL)STARCH 2-HYDROXYETHYL STARCH o-(2-HYDROXYETHYL)-STARCH 2-HYDROXYETHYL STARCH ETHER PENFORD 260 PENFORD 280 PENFORD 290 PENFORD P 208 PLYSMASTERIL STARCH HYDROXYETHYL ETHER TAPIOCA STARCH HYDROXYETHYL ETHER... 

HYDROXYETHYL STARCH ETHER see HLB400 4 -(2-HYDROXYETHYI ULFONYL)ACETANILIDEsee HLB500... 

SEQUAPEL ND provides excellent spray ratings--even when applied with high levels of handbuilders such as polyvinyl acetate, polyvinyl alcohols, or starch ether. SEQUAPEL ND can also be used with thermosetting resins. 

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