Thermal stability, polysaccharide

In a current rheological study [296], the galactoxyloglucan from Hymenia courbaril was mixed with starch containing 66% amylose and with waxy corn starch (amylopectin). The gel mixtures showed, under static rheological conditions, an increase in paste viscosity compared to those of the polysaccharides alone. Dynamic rheometry indicated that the interactions resulted in increased thermal stability of the gel formed in comparison to that of the starch alone. 

Thermal stability is a crucial factor when polysaccharides are used as reinforcing agents because they suffer from inferior thermal properties compared to inorganic fillers. However, thermogravimetric analysis (TGA) of biocomposites suggested that the degradation temperatures of biocomposites are in close proximity with those of carbon black composites (Table-1). 

The unusual thermal stability and water uptake properties are due to the formation of a three-dimensional network in polysaccharides at high processing temperatures [12]. 

Chemical stabilizers have been used to reduce the rate of oxygen-promoted degradation of polysaccharides at T>225°F. Methanol and sodium thiosulfate are the most commonly used (86). Sodium dithio-carbamate, alkanolamines, and thiol derivatives of imidazolines, thiazolines, and other heterocyclic compounds have also been tested for this application. Calcined dolomite (B7) and Cu(l) and Cu(ll) salts (88) have been reported to increase the thermal stability of HEC. 

C. Decomposition was complete at 600°C. As shown in Figure 2, the thermal decomposition of 10 occurred gradually with 65% residual weight still observable at 600°C. The TGA curves of 9 and 10 indicated that the thermal stabilities of the present hyperbranched aminopolysaccharides were much higher than those of normal linear polysaccharides. For example, chitin showed a significant weight loss at 275 28°C. 

Silylation reactions on polysaccharides with chlorosilanes and silazanes were attempted more than 50 years ago resulting in hydrophobic silyl ethers with both increased thermal stability and solubility in organic solvents [376]. The silylation reaction for the protection of hydroxyl groups in mono- and polysaccharides exhibits many advantages, e.g. fast silylation, solubility of silylether in organic solvents suitable for subsequent derivatisation, stability of the resulting silylether under basic conditions but easy deprotection of the silyl moieties by acid hydrolysis or nucleophilic agents like fluoride and cyanide ions [377]. The partial and complete silylation of dextran was studied in detail by Ydens and Nouvel [215-217]. 

High temperatures can break native S—S bonds and form new S—S bonds that can lock the protein into a denatured configuration. Low pH, sodium dodecyl sulfate. Tween 80 , chaotropic salts, and exogenous proteins have been used to protect proteins from thermal inactivation.f Ethylene glycol at 30-50% was used as a protectant of antiviral activity of p-interferon preparations. Human serum albumin was used inrecombinant human interferon-pser-i7, which resulted in increased thermal stability. Water-soluble polysaccharides such as dextrans and amylose and point-specific (site-directed) mutagenesis have also been used to increase thermal stability of therapeutic proteins and peptides. 

Pullulan is a glucan of (1 6)-a-D-linked maltotriose residues produced by Aureobasidium pullulans from starch or sucrose feedstockJ It is well soluble in aqueous medium and forms films that possess thermal stability and are antistatic and elastic. Pullulan has adhesive properties and is directly compressible under heat with moisture. The polysaccharide is produced on an industrial scale and is used for multiple applications, including food, pharmaceuticals, and cosmetics. It has recently been classified as GRAS by the U.S. FDA. 

The extent to which starch and cellulose form volatile decomposition products in the absence of inorganic material may be seen from the results shown in Table IV for the percentage weight of polysaccharide remaining after pyrolysis under vacuum. Although differences between starch and its components are small, cellulose is relatively more stable. The general order of thermal stability appears to be amylose < starch < amylo-pectin < cellulose. 

GC—TF can at least give three types of information about a component thermal stability, the functional groups present in the molecules, and some information on the overall structure of the molecule. Fang and McGinnis [283] showed that the GC-TF is a valuable technique for the separation and identification of the complex mixture of products that resulted from the pyrolysis of bark polysaccharides from loblolly pine. 

Figure 4 Thermal stability of lysozyme-polysaccharide conjugates. O, lysozyme , lysozyme-dextran conjugate , lysozyme-galactomannan conjugate. Lysozyme-polysaccharide conjugates were prepared by dry heating at 60°C for 2 weeks. Sample solutions (0.1%) in 67 mM phosphate buffer (pH 7.4) were heated at an increasing rate of l°C/min. The resulting turbidity was measured with the absorbance at 500 nm.

Keywords Polysaccharides, green composites, graft copolymers, drug-fungicide delivery, thermal stability, biodegradation... 

Polysaccharides and their graft copolymers find extensive applications in diversified fields. Grafting is known to improve the characteristic properties of backbones. Such properties include water repellancy, thermal stability, flame resistance, dyeability and resistance towards acid-base attack and abrasion. Modification of natural cellulosics through graft copolymerization of methyl methacrylate onto Cannabis indica, rayon, jute, cotton, etc., has resulted in the improvement of their morphology and other physicochemical properties [9-23]. 

Under pressure grafting is one of the techniques for the incorporation of acid-base resistance, water repellancy, water absorbency, thermal stability and other morphological changes in the polysaccharides [42-44]. Under pressure. 

Preparations of pancreatic ribonuclease, ribonuclease from Actinomyces rimosus, and the nuclease from Serratia marcescens have been covalently bound to 4 3-hydroxyethylsulphonylanisole-, 4j3-hydroxyethylsulphonylaniline, and 3-Cl-2-hydroxypropyl derivatives of dextran and dialdehyde-dextran and to the 4-aminobenzyloxymethyl ester of dextran.The yield and thermal stability of the modified nucleases depends both on the amount and the character of the functional groups activating the polysaccharide. 

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