Viscosity, of cellulose esters

Standardized test methods for analyzing the chemical composition, viscosity, and physical properties of cellulose esters have been adopted by the ASTM and are described in substantial detail (110). 

Thermal Properties. The thermal stabiUty of cellulose esters is deterrnined by heating a known amount of ester in a test tube at a specific temperature a specified length of time, after which the sample is dissolved in a given amount of solvent and its intrinsic viscosity and solution color are deterrnined. Solution color is deterrnined spectroscopically and is compared to platinum—cobalt standards. Differential thermal analysis (dta) has also been reported as a method for determining the relative heat stabiUty of cellulose esters (127). 

It has been demonstrated that wood cellulose can also be employed for the commercial manufacture of cellulose esters. Several descriptions of suitable purification processes have appeared in the technical literature. - The material has now attained large industrial use and when properly purified approaches the quality of cotton cellulose. Important considerations in the preparation of wood pulp for acetylation are the proper removal of impurities to yield a product of high alpha cellulose content without severe loss of viscosity, and with retention of uniform reactivity of the cellulose toward acetylation. Color and haze in the acetylated product are difficult to eliminate to the degree possible with cotton linters. 

Qualification of different cellulose sources for the various end use applications is determined on the basis of purity, molecular size, and a-cellulose content, a-cellulose refers to the portion of cellulose insoluble in 18% aqueous sodium hydroxide. Whereas the content of noncellulosic polysaccharides has proven to be a hindrance to the clarity of cellulose esters (determined as haze in otherwise clear films), a-cellulose content is important for the spinnability of cellulose solutions into regenerated fibers, and for viscosity characteristics of cellulose ethers. Molecular weights play an important role in various cellulose ethers. 

Viscosity Blending. As shown in Table I, a wide range of cellulose esters are commercially available. Each type may be identified by acetyl content alone, as in the case of cellulose acetate, or, for mixed esters, by the weight percent of the ester contributed by butyryl or propionyl groups following acylation. Further... 

Tanaka and co-workers [158] have used the high-temperature turbidimetric titration procedure originally described by Morey and Tamblyn [153] for determining the MWD of cellulose esters. This method has been applied to the measurement of the MWD of PP. They found that the type of MWD of this polymer is a log-normal distribution function in a range of I M) (cumulative wt%) between 5 and 90%. The effect of heterogeneity in the MWD of PP on the viscosity-molecular weight equation was examined experimentally - the results agreed with those calculated from theory. Strict temperature control ( 0.15 °C) is necessary in these determinations [159]. 

The use of a soluble metal-chelating agent such as tetrasodium ethylenediamine tetraacetate effectively stabilizes an anaerobic formulation against small amounts of metal contamination [173]. The wide variety of appUcations of anaerobic adhesives and sealants is made possible by the modifications which make the viscosity appropriate to the application. An application which requires penetration into close fitting parts should have very low viscosity while a product used with large, loose fitting parts should have a high viscosity. Polymethacrylates, cellulose esters, butadiene-styrene copolymers, acrylonitrile-butadiene-styrene copolymers, polyfvinyl chloride), copolymers of vinyl chloride and vinyl acetate, polyfvinyl acetate), cellulose ethers, polyesters, polyurethanes, and other thermoplastic resins have been used to control the flow characteristics of anaerobic sealants [174]. 

Several cellulose esters (qv) are prepared commercially. Cellulose xanthate [9032-37-5] is made by reaction of cellulose swollen in 8.5—12% sodium hydroxide solution (alkaU cellulose [9081-58-7J) with carbon disulfide and is soluble in the alkaline solution in which it is made. When such a solution, termed viscose, is introduced into an acid bath, the cellulose xanthate decomposes to regenerate cellulose as rayon fibers or cellophane sheets (see Fibers, REGENERATED CELLULOSICS). 

Both the sulfite and alkaline (kraft) methods can be modified to produce high purity chemical ceUulose. These pulps, usuaUy in the form of "dissolving pulps," are not only mosdy free of lignin and hemiceUulose, but the molecular weight of the ceUulose is degraded. This increases solubUity in alkah and provides desired viscosity levels in solution. These dissolving pulps are used to make derivatives such as sodium ceUulose xanthate [9051 -13-2] via alkah ceUulose, and various esters and ethers (see Cellulose esters Cellulose ethers). 

Higher butyryl esters, formulated with acryUc polymers, provide coatings with excellent weather resistance, good colorfastness and dispersibiUty, and good flow properties (154). Formulations for a typical automotive refinishing lacquer and a wood furniture lacquer are given in Tables 12 and 13, respectively. Low viscosity, high butyryl cellulose esters tolerate substantial amounts of alcohol solvent without appreciable increase in solution viscosity. 

CP can also be prepared by the reaction of cellulose with phosphoms oxychloride in pyridine (37) or ether in the presence of sodium hydroxide (38). For the most part these methods yield insoluble, cross-linked, CP with a low DS. A newer method based on reaction of cellulose with molten urea—H PO is claimed to give water soluble CP (39). The action of H PO and P2 5 cellulose in an alcohol diluent gives a stable, water-soluble CP with a high DS (>5% P) (40). These esters are dame resistant and have viscosities up to 6000 mPa-s(=cP) in 5 wt % solution. Cellulose dissolved in mixtures of DMF—N2O4 can be treated with PCl to give cellulose phosphite [37264-91-8] (41) containing 11.5% P and only 0.8% Cl. Cellulose phosphinate [67357-37-5] and cellulose phosphonate [37264-91 -8] h.a.ve been prepared (42). 

All of the eommereial alkyl eyanoaerylate monomers are low-viseosity liquids, and for some applications this can be an advantage. However, there are instances where a viseous liquid or a gel adhesive would be preferred, sueh as for application to a vertical surface or on porous substrates. A variety of viscosity control agents, depending upon the desired properties, have been added to increase the viscosity of instant adhesives [21]. The materials, which have been utilized, include polymethyl methacrylate, hydrophobic silica, hydrophobic alumina, treated quartz, polyethyl cyanoacrylate, cellulose esters, polycarbonates, and carbon black. For example, the addition of 5-10% of amorphous, non-crystalline, fumed silica to ethyl cyanoacrylate changes the monomer viscosity from a 2-cps liquid to a gelled material [22]. Because of the sensitivity of cyanoacrylate esters to basic materials, some additives require treatment with an acid to prevent premature gelation of the product. 

The viscosity of polymer solutions has been considered theoretically by Flory,130 but although this theory has been applied to cellulose esters,131 no applications have yet been made in the case of the starch components. Theoretical predictions of the effect, on [17], of branching in a polymer molecule have been made,132 and this may be of importance with regard to the viscometric behavior of amylopectin. 

Uses and Physiological Properties of Carbon Disulphide.—Besides its employment as a solvent (see p. 260), carbon disulphide is used extensively in the manufacture of viscose silk. Viscose is a solution of the sodium salt of the cellulose ester of thiolthioncarbonic acid (p. 268) in water or dilute aqueous sodium hydroxide, or it may be described as an aqueous solution of the sodium salt of cellulose xanthic acid. For its production cellulose is steeped in concentrated sodium hydroxide solution and then pressed, the product being called alkali-cellulose and the formula CeH10O5.NaOH assigned to it. This is converted into viscose by treatment with carbon disulphide, when the colour changes to golden yellow ... 

The cellulose esters that result from the process described are chemical raw materials and are used by many branches of the chemical industry. They are generally characterized by acyl content in weight percent and viscosity in seconds, the viscosity being obtained by timing the fall of a steel ball through a solution of the cellulose ester in accordance with ASTM Method D 134 . Low-viscosity esters are generally used in solution processes high-viscosity esters are used in the production of plastics. 

The ADMET polymerization of sugar-based monomers is much less explored than the ROMP approach, and only a few examples have been reported to date. Bui and Hudlicky prepared a,oo-dienes derived from a biocatalytically synthesized diene diol, from which chiral polymers (up to 20 kDa) with D-c/uro-inositol units were prepared via ADMET in the presence of 1 mol% of C4 [169]. Furthermore, several ot,co-dienes containing D-mannitol, D-ribose, D-isomannide, and D-isosorbide have been synthesized by Enholm and Mondal [170]. Also in this study, C4 was used to catalyze the ADMET polymerizations at 1 mol% catalyst loading. As pointed out by the authors, the viscosity increased as the reactions progressed and vacuum had to be applied to efficiently remove the released ethylene. Unfortunately, the polymers obtained were not further analyzed. As already mentioned above, Fokou and Meier have also reported the ADMET polymerization of a fatty acid-/D-isosorbide-based a,co-diene [126]. Furthermore, Krausz et al. have synthesized plastic films with good mechanical properties by cross-linking fatty esters of cellulose in the presence of C3 [171-173]. 

More recently, Rogovin and his associates, in their study of the stability of Viscose relative to other cellulose esters, reacted methyl chloro-... 

This suggestion is in agreement with the well-known fact that the equilibrium rigidity of cellulose ether and ester molecules changes greatly with solvent composition and is also confirmed by the stroi n ative temperature dependence of the statistical size of their chains. The latter property is manifested in a decrease of the intrinsic viscosity, translational friction - and the flow birefringence ) with increasing temperature (Fig. 32) ... 

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