Solution viscosity starch

Figure 8. Solution viscosity as a function of calcium chloride concentration for hydrolyzed poly(starch-g- (2 propenamide)) terpolymer.

Not all modified starches are suitable for removal by aqueous dissolution alone. Such modifications of natural starches are carried out to reduce solution viscosity, to improve adhesion and ostensibly to enhance aqueous solubility. Commercial brands vary [169], however, from readily soluble types to those of limited solubility. Indeed, some may be as difficult to dissolve as potato starch if they have been overdried. It is thus very important to be sure of the properties of any modified starch present. If there are any doubts about aqueous dissolution, desizing should be carried out by enzymatic or oxidative treatment. Even if the size polymer is sufficiently soluble, it is important to ensure that the washing-off range is adequate. Whilst the above comments relate to modified starches, other size polymers such as poly(vinyl acetate/alcohol) and acrylic acid copolymers vary from brand to brand with regard to ease of dissolution. 

The other important function of the binder is its effect upon the rheological properties of the coating mix. Starch, which is widely used, is unsuitable for use in its unmodified form because its solution viscosity is generally too high and also because of the problem of retrogradation. It is usually modified by reducing its molecular weight by either oxidative or hydrolytic (sometimes enzymatic) procedures. 

Oxidized Starches. Alkaline hypochlorite treatment introduces carboxyl and carbonyl groups, effects some depolymerization, and produces whiter (bleached) products that produce softer, clearer gels. Ammonium persulfate is used in some paper mills with continuous thermal cookers to prepare in situ bigb solids, low viscosity dispersions. Most of the hypochlorite-oxidized starch and all the ammonium persulfate-oxidized starch is used in the paper industry. The low solution viscosity and good binding and adhesive properties of these products make them especially effective in high solids, pigmented... 

Lyophilic sols are true solutions of large molecules in a solvent, Solutions of starch, proteins, or polyvinyl alcohol in water are representative of numerous examples. Properties of these solutions at equilibrium (for example, density and viscosity) are regular functions of concentration and temperature, independent of the method of preparation. The solvent-macromolecule compound system may consist uf more than one phase, each phase in general containing both components. Thus, if a solid polymer is added to a solvent in an amount exceeding the solubility limit, the system will consist of a liquid phase (solvent with dissolved polymer) and a solid phase (polymer swollen with solvent, i.e., a polymer with dissolved solvent). 

There are several practical applications involving interactions between starch and saccharides. For example, starch-derived sugars are used as plasticizers for starch.956 Thus, the addition of potato starch to sugar syrup increases the solution viscosity to a level where it retains gas bubbles and is suitable for producing froths.957 Agaran, starch, and swollen Sephadex G-200 form a mixed support for zone electrophoresis.958 A plywood of improved strength resulted from the blending of an aqueous solution of... 

Osmotic pressure measurements for the determination of MW were used in 1900 to characterize starch. Twenty years later, the solution viscosity measurements were introduced by Staudinger for this purpose. However, it was Mark and his collaborators who developed the concept of the intrinsic viscosity ([r ]) and demonstrated that it provides information on the volume of individual colloidal particles, thus on MW. For the freely rotating chains the dependence (today known as Mark-Houwink-Sakurada equation) was obtained [Guth and Mark, 1934] ... 

FIG. 32. Viscosity as a function of shear rate for three starch solutions (Race, 1993). A, starch solution A B, starch solution B C, starch solution C. (a) Measured at 70°C in the high pressure cell, (b) Measured at 130°C in the high pressure cell. Note that in (a) the viscosity was measured at 70°C, the starch solution A behaves similar to B but significantly smaller than starch solution C in (b) the viscosity was measured at 130°C, the viscosity starch solution A was significantly greater than that of solution B and C, while solution B and C behaves in a similar way. 

The method of cooking has an impact on the starch solution viscosity. The more energy put into the cook, be it thermal energy or mechanical, the greater will be the disentanglement of the starch molecules and hence the lower the solution viscosity. This lower viscosity is due to better dispersion and not to any degradation of the starch molecules. 

Starches are altered in several ways. Derivatized starches have greater water solubility and changed rheological characteristics. Crosslinked starches increase viscosity and promote granule stability in solution. Depolymeiized starches create solutions with lower viscosity. Combinations of crosslinkages, depolymerizations, and derivatizations are common. Dextiins, a special class of modified starches, constitute a variety of industrially important starches. Modified and derivatized starches are used in numerous industries as adhesives, thickeners, stabilizers, and emulsifiers. 

Solutions of starch-acrylamide, graft copolymers, were prepared by J. J. Meister and the solution viscosity was researched with the goal to prepare highly viscous solutions He was able to prove, that graft copolymers also age. However, the data have another feature not found in the viscosities of the PAAm-solutions. That is, that graft-copolymer solution viscosity increases between 24 and 48 hours. After this a typical viscosity decrease can be observed as was mentioned earlier. 

---