Синтез и характеризация некоторых производных крахмала растворимых в воде

Synthesis and characterization of some water-soluble starch derivatives

[Ž. Stojanović]

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Hemija i hemijska tehnologija - hemija i inzenjerstvo polimera / Chemistry and chemical engineering Polymer Chemistry and Polymer Engineering

Predmet istraživanja ove doktorske disertacije bila su dva tipa derivata skroba: anjonski i katjonski skrob. Za sintezu anjonskog skroba (karboksimetil-skrob) korišćena je monohlorsirćetna kiselina (ili njena natrijumova so), a za sintezu katjonskog skroba korišćen je 3-hlor-2-hidroksipropil-trimetilamonijum hlorid. U prvom delu rada ispitivan je uticaj reakcionih uslova i količine reagenasa na stepen supstitucije i granični viskozitetni broj karboksimetil-skroba. Na osnovu dobijenih rezultata određeni su optimalni uslovi pod kojima je sintetisano šest uzoraka karboksimetil-skroba – tri uzorka su pripremljena od skroba iz krompira, a tri od skroba iz kukuruza. Stepen supstitucije sintetisanih uzoraka je iznosio od 0.40 do 1.10. Uzorcima karboksimetil-skroba ispitivana su svojstva u razblaženim rastvorima upotrebom viskozimetrije, statičkog i dinamičkog rasipanja svetlosti. Kao rastvarač korišćeni su voda i rastvori natrijum hlorida u vodi. Za svaki uzorak određene su vrednosti molarne mase po masenoj zastupljenosti, MW, poluprečnika rotacije, Rg, hidrodinamičkog poluprečnika, Rh, i graničnog viskozitetnog broja, [η]. Utvrđeno je da u rastvorima soli poreklo skroba i stepen supstitucije (u ispitivanom opsegu) ne utiču na oblik i unutrašnju strukturu makromolekula. Svojstva u razblaženim rastvorima natrijum-hlorida zavise samo od jonske jačine rastvarača. Ispitivanje termičke stabilnosti sintetisanih uzoraka karboksimetil-skroba termogravimetrijskom analizom pokazalo je da porast temperature ima specifičan uticaj na osobine karboksimetil-skroba zavisno da li se on nalazi u kiselom obliku ili u obliku soli. Temperature na kojima dolazi do gubitka 5 i 50 mas.% su nezavisne od stepena supstitucije kod uzoraka karboksimetil-skroba u obliku soli, dok kod uzoraka karboksimetil-skroba u kiselom obliku postoji linearna zavisnost ovih temperatura od stepena supstitucije. Uzorcima su određene i energije aktivacije termičke degradacije i pokazalo se da je energija aktivacije termičke degradacije uzoraka karboksimetil-skroba u obliku soli niža, a energija aktivacije termičke degradacije uzoraka karboksimetil-skroba u kiselom obliku viša od energije aktivacije termičke degradacije nemodifikovanog skroba. Katjonski derivat je pripremljen modifikacijom skroba iz kukuruza. Sintetisan je jedan uzorak katjonskog skroba od koga su kontrolisanom ultrazvučnom degradacijom pripremljena još četiri uzorka. Vrednosti molarne mase po masenoj zastupljenosti, MW, poluprečnika rotacije, Rg, hidrodinamičkog poluprečnika, Rh, i raspodele molarnih masa uzoraka, su određene upotrebom gel-propusne hromatografije, statičkog i dinamičkog rasipanja svetlosti. Utvrđeno je da se sa povećanjem vremena ultrazvučne degradacije smanjuje molarna masa uzoraka uz istovremeno suženje raspodele molarnih masa. Ultrazvučnom degradacijom dobijeni su makromolekuli čiji oblik i unutrašnja struktura nisu međusobno slični. Na osnovu podataka dobijenih metodom statičkog rasipanja svetlosti utvrđeno je da nedegradirani katjonski skrob ima kompaktniju strukturu i u vodi i u rastvorima soli od odgovarajućih uzoraka karboksimetil-skroba. Takođe, na osnovu ispitivanja zavisnosti viskoznosti od brzine smicanja koncentrovanih rastvora katjonskog skroba, kao i karboksimetil-skroba u vodi kao rastvaraču utvrđeno je da katjonski skrob ima nižu viskoznost od uzorka.

The investigation of two type of starch derivates - anionic and cationic starch – is described in this thesis. Mono-chlor-acetic acid (or its sodium salt) was used for synthesis of anionic starch while its cationic derivate was synthesized by the use of 3-chlor-2-hidroxypropyl-N,N,N-trimethylamonium chloride. The experiments focused on the influence of reaction conditions and the amount of reagents on the degree of substitution and limiting viscosity number of carboxymethyl starch are presented in the first part of the thesis. According to the obtained results the optimal conditions for the starch carboximetilation were defined. Six samples of carboxymethyl starch differing in the degree of substitution (ranging from 0.4 to 1.1) were synthesized under previously defined optimal conditions – corn or potato starch were used as starting material for the synthesis of carboxymethyl starch. The properties of carboxymethyl starch were further examined in diluted solutions by means of viscometry, static and dynamic light scattering. Water and sodium chloride dissolved in water were used as solvent. Weight-average molecular weight, MW, radius gyration, Rg, hydrodynamic radius, Rh, i limiting vicosity number, [η] were determined for each sample. It was shown that starch origin and degree of substitution (within the investigated range) did not affect the shape and the internal structure of macromolecules in salt solution. Properties of macromolecules in diluted solutions depended only on the solvent ionic strength. The influence of temperature on acidic and salt form of carboxymethyl-starch was also analyzed. Thermogravimetric analysis showed that there are some differences in the behavior of these carboxymethyl starch forms. In salt form, temperatures needed for 5 or 50 mas.% weight loss were independent on degree of substitution in analyzed caboximethylstarch samples while a linear dependence of temperature on degree of substitution were recorded for samples of carboxymethyl-starch in acid form. Comparing to unmodified starch, activation energy of thermal degradation for salt form of carboxymetyl starch was lower while it was higher for carboximethyl-strach acidic form. Finally, cationic derivate was prepared by modification of corn-originated starch. One sample of cationic starch was synthesized and four additional samples were prepared by its controlled ultrasonic degradation. Diluted solutions of cationic starch samples were investigated by gel-permeability chromatography, static and dynamic light scattering. Weight-average molecular weight, MW, radius gyration, Rg, hydrodynamic radius, Rh, and molar mass distribution were determined for each sample. It was shown that: 1) duration of ultrasonic degradation inversely correlated to sample molar mass; 2) increase in duration of ultrasonic degradation resulted in narrowing of the molar mass distribution. Changes in the internal structure of macromolecules that depended on duration of ultrasonic degradation were also observed. Comparison of synthesized cationic starch with samples of carboxymethyl starch showed that in both water and salt solutions cationic starch has more compact structure. It was also shown that viscosity of concentrated cationic starch solution was lower than viscosity of solution of carboxymetyl starch having similar molar mass. However, concentrated cationic starch solution showed more pronounced pseudoplastic behavior.

karboksimetil skrob, katjonski skrob, staticko i dinamicko rasipanje svetlosti, termogravimetrijska analiza

carboxymethyl starch, cationic starch, static and dynamic light scattering, thermogravimetric analysis

547.917(043.3)

Skrob

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