Stabilizer cellulose derivatives

In explosives, diphenylamine stabilizes cellulose nitrate by reacting with nitrogen oxides (see Explosives and propellants). The products formed include /V-nitrosodiphenylamine and mono andpolynitro derivatives. 

Weathering. This generally occurs as a result of the combined effect of water absorption and exposure to ultra-violet radiation (u-v). Absorption of water can have a plasticizing action on plastics which increases flexibility but ultimately (on elimination of the water) results in embrittlement, while u-v causes breakdown of the bonds in the polymer chain. The result is general deterioration of physical properties. A loss of colour or clarity (or both) may also occur. Absorption of water reduces dimensional stability of moulded articles. Most thermoplastics, in particular cellulose derivatives, are affected, and also polyethylene, PVC, and nylons. 

In this study, adsorption behavior of water soluble polymers and their effect on colloid stability have been studied using polystyrene latices plus cellulose derivatives. As the aqueous solution of hydroxy propyl cellulose(HPC) has a lower critical solution temperature(LCST), near 50 °C(6 ), an increased adsorption and strong protection can be expected by treating the latices with HPC at the LCST. 

These stabilizers are added to the formulation in order to stabilize the emulsion formed during particle preparation. These stabilizers, however, can also influence the properties of the particles formed. The type and concentration of the stabilizer selected may affect the particle size. Being present at the boundary layer between the water phase and the organic phase during particle formation, the stabilizer can also be incorporated on the particle surface, modifying particle properties such as particle zeta potential and mucoadhesion (203). Other polymers have also been evaluated as stabilizers in earlier studies such as cellulosic derivatives methylcellu-lose (MC), hydroxyethylcellulose ( ), hydroxypropylcellulose (HPC), and hydroxypropylmethylcellulose (HPMC), as well as gelatin type A and B, carbomer and poloxamer (203). 

The present Section is mainly concerned with differences of stability between the two classes of derivatives and any variations within each class. Their stability toward hydrolytic agents has frequently been examined, and, for the thiocarbonates, the thermal stability has also received attention. These studies have, in general, been neither exhaustive nor quantitative, and comparative data are directly available for certain cellulose derivatives only. The progressive replacement of the oxygen atoms in a neutral carbonic ester by sulfur appears to lead to a decrease in the sensitivity to alkali and an increase in the sensitivity toward acids, water, and heat. As expected, the acid esters are less stable than their neutral analogs toward the last-named agents. 

Among the various types of cellulose derivatives, it is the cellulose esters that find the widest practical application and complete succesfully in a number of branches of the industry with synthetic polymers. The complete or partial esterification of the hydroxyl groups of cdlulose can yield cellulosic materials having such technically valuable properties as thermoplasticity, hydrophobicity, resistance to heat and light, stability to the action of putrefying microorganisms, bactericidal action, etc. 

Test strips were prepared by oxidation of cellulose with KIO4 to a polyaldehyde, followed by condensation with 1-naphthylamine to a poly-Schiff base and reduction with NaBH4 to an immobilized naphthylamine cellulose derivative, which is mechanically stabilized on a polypropylene sheet. PAA can be detected on addition of nitrite to the test solution and contacting with the strip, where azo dyes are formed. Quantitative analysis can be carried out by diffuse reflectance spectroscopy. The method was applied to pharmaceutical preparations with RSD better than 30%246. 

This class of cellulose derivatives has attracted the attention of investigators because of their specific properties, primarily their increased hydrophobicity. There is, however, a serious drawback, typical of most silicon-containing cellulose esters prepared by the action of trialkyl-chlorosilanes, namely, the low stability of the C-O-Si bond to hydrolysis. One way of overcoming this difficulty is to increase the length of the organosilicon radical. 

Water-soluble cellulose derivatives themselves adsorb onto solid particles and may for instance affect the suspension properties of these insolubles. The mechanisms involved are quite complex and depend on the polymer concentration. At low concentrations macromolecules influence the electrophoretic mobility and the flocculation of the particles. At higher concentrations, surface coverage by the adsorbed polymer is sufficient to prevent particle-particle interaction and thus to stabilize the suspension sterically. As an example, the effect of NaCMC (among other polymers) on the zeta potential, flocculation and sedimentation properties of sulfadimidine has been investigated by Kellaway and Najib [115,116],... 

The adsorption of nonionic cellulose derivatives (HPMC 2910, HEC, and HPC) and their stabilizing effect on suspensions of polystyrene latices and of the antirheumatismal ibuprofen have been examined by Law and Kayes [117, 118]. Adsorption isotherms (see Fig. 20 for HPMC and ibuprofen) are of a sigmoidal type rapid initial adsorption, then a plateau corresponding to monolayer adsorption and finally a further increase in adsorption. At the same time, a gradual reduction in the sedimentation volume (decreased flocculation) is observable, while the redispersibility tends to be optimum (minimum number of revolutions necessary) at values of HPMC corresponding to a monolayer surface coverage. 

Palladium nanoparticies can be easily prepared by displacement of the dba ligands by CO from Pd(dba)2. An intermediate unstable carbonyl complex forms, which collapses into clusters. By this method, palladium nanoparticies of sizes in the range 2-5 nm could be obtained using PVP or cellulose derivatives as stabilizers. Such particles were recently used to probe the mechanism of the Heck reaction. A correlation between the initial reaction rate and the particle sizes was established. The small particles proved more active in agreement with the presence of more surface palladium atoms with low metal-metal coordination number. ... 

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