I am working on my senior year project about cyanoethylation using tapioca starch and acrylonitrile in the presence of basic catalyst.
As I understood, the viscograph of the cyanoethyl starch is supposed to look like the native one with lower gelatinization temperature but what I got the profile of crosslinked starch and the granule shapes were round. I have done several experiments with the same conditions and chemicals but the results were the same. Also, when I adjusted the reaction time to 1-24 hr. the profiles of starch were quite similar except for those of 14-18 hours.
p.s. I only used ACN, NaOH and Na2SO4
At first sight your results looked quite puzzling. However, in the literature intragranular cross-linking between -OH and -CN groups in the making of cyanoethyl starch has been reported. See the book by O.B. Wurzburg: Modified starches: properties and uses, p. 188-189, CRC Press (1986) with a patent literature reference on this phenomenon (Ref. 165). The relevant section from this source and the reference are in the added file.
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