Pseudoplastic properties

Several new exopolysaccharides such as welan and rhamsan produced by Alcaltngettes spp may supercede xanthan for some industrial applications. These are based on the same repeat tetrasaccharide backbone of glucose, glucuronic acid, glucose and rhamnose but differ in the substituents rhamsan has a disaccharide side chain and welan a monosaccharide. Both are stable at high temperature and have excellent pseudoplastic properties. 

Xanthan gum shows a good solubility in water, giving a highly viscous solution with a pseudoplastic appearence and a temperature independent viscosity. Xanthan gum is used in pharmaceuticals for its excellent emulsifying and suspending properties. The pseudoplastic properties of this gum enables tooth pastes and ointments both to hold their shape and to spread readily. 

Since n is less than unity, the apparent viscosity decreases with the deformation rate. Examples of such materials are some polymeric solutions or melts such as rubbers, cellulose acetate and napalm suspensions such as paints, mayonnaise, paper pulp, or detergent slurries and dilute suspensions of inert solids. Pseudoplastic properties of wallpaper paste account for good spreading and adhesion, and those of printing inks prevent their running at low speeds yet allow them to spread easily in high speed machines. 

If the suspension has pseudoplastic properties, the sedimentation rate is greater according to the difference between the gravitational force on the suspended par-... 

Xanthan gum ( ) is the high molecular weight natural exopolysacoharide produced by the bacterium Xanthomonas campestris. Xanthan gum owes its commercial importance to its thickening, suspending and pseudoplastic properties in aqueous systems ( ) Both industrial and food approved xanthan gum are available. 

The xanthan gum is used as stabilizer, thickener, and emulsifier that are extensively used in pharmaceutical and cosmetic industries [139]. The pseudoplastic properties of this gum enable ointtnents to hold their shape and to spread readily. It is a suitable suspending vehicle for deUvering antispasmodics topically along the length of esophagus in patients with esophageal spa. 

The viscoelastic behavioral profile of HPMC Ophthal H corresponded closely with Amvisc Plus, a hyaluronic acid product. Compared to the remaining HPMC products, a slight pseudoplastic property was recognized in this product, similar to hyaluronic acid products. These results support the conclusion that categorizing viscoelastics in substance groups does not always make evident their functional differences. 

Shark-skin occttrs when the melt index and the coefficient n are small. This may happen when a larger amount of plasticizer is used Die swell is caused by elastic deformation in flow. It resrrlts from material expansion after it leaves the die. Increase in shear rate increases die swell. Parison sagging is caused by a decrease in pseudoplastic properties (coefficient n becoming closer to unity) and decreased friction between metal and melt. 

Drift and Mist Control. The pseudoplastic properties of PEO solutions reduce mist formation during spraying of aqueous solutions that contain PEO. This property is used in metal-working fluids to lower worker exposure to mists from the cutting and grinding aids. PEO may also be used to focus the spraying area of herbicides and water-based coatings. 

Table 18.5 showed the power law index and the consistency of flow of STR5L/EPDM and STR5L/BEPDM blends. Shear flow curves of the pure rubbers and their blends illustrated the pseudoplastic property as shear thinning behaviour with a power law index napparent shear viscosity of the two sets of blends decreased as the shear rate increased as shown in Figures 18.22 and 18.23 for STR5L/EPDM blend and STR5L/BEPDM blend, respectively. 

Solutions of h. in water are compatible with other water-soluble polymers, they are less sensitive to electrolytes than MC, have pseudoplastic properties and are not very stable against enzymatic degradation. H. forms clear films, which can be plasticized by glycerol or polyglycols. They are water-soluble unless treated with dialdehydes. 

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