Cellulose esters weights

Fig. 11.2 Spherulite growth rate of poly(3-hydroxybutyrate) as a function temperature in blends with two different cellulose acetate butyrates. Numbers on curves cellulose ester weight percent. (From Pizzoli et al. (2))...

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). 

Experimental studies of the adsorption of polyelectrolyte have been reported by several authors Pefferkom, Dejardin, and Varoqui (3) measured the hydrodynamic thickness of an alternating copolymer of maleic acid and ethyl vinyl ether adsorbed on the pore walls in cellulose ester filter as a function of the molecular weight and the concentration of NaCl. Robb et al. (4) studied the adsorption of carboxy methyl cellulose and poly (acrylic acid) onto surfaces of insoluble inorganic salts. However, their studies are limited to the measurements of adsorbance and the fraction of adsorbed segments. 

Heat-setting resins cannot be plasticized by low molecular weight plasticizers. Polyvinyl acetals have been claimed for these products. American Cyanamid Co. has suggested polyvinyl acetals or butyrals in an amount of 10 to 25% of the resin for urea and melamine resins. For varnishes and adhesives, combinations of phenolic resins and polyvinyl formal are recommended. Polyvinyl acetals with higher alkyl radicals are suitable for cellulose esters and improve elasticity as well as resistance against water. 

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 tin content of the tributylstannylcarboxymethyl cellulose ester is practically unchanged on boiling in water for one hour. When subjected to hydrolysis with 0.1 Af solutions of HCl and NaOH for 1 h at 20 C, the tributylstannyl residues of this ester are completely split off. Thus, polymeric acylates ctf trialkyltin, like low-molecular-weight or-ganotin compounds of this type, are unstable to the action of aqueous solutions of acids and alkalis. 

No systematic studies of the principles governing the synthesis of cellulose esters by the trans-esterification reaction had been available in the literature until the present authom published work permitting one to ascertain the relation between the reactivity cf low-mol ular-weight esters and their structure, and the direction trf the reactions involved. 

Fig. 5. Sedimentation coefficient (s] vs. molecular weight M for cellulose esters 1 cellulose carbanilate in ethyl acetate 2 cellulose butyrate in methyl ethyl ketone ) 3 cellulose mono-phenylacetate in benzene 4 cellulose diphenyl phosphonocarbamate in dioxane ) 5 cellulose benzoate in dioxane ...

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. 

The two primary categories of cellulose derivatives, cellulose esters and cellulose ethers, which dominate the markets for cellulose derivatives (O Table 8), have somewhat different raw material requirements. Whereas both types of modification technologies prefer to start with chemical cellulose of high a-cellulose content, ethers give preference to molecular weight considerations while esters are sensitive to impurities. This is a consequence of the predom-... 

The structure of cellulose has only relatively recently been tackled through the examination of its trinitrate, that is. nitrocellulose of ca, 14% N. Trinitrate of cellulose was chosen as a readily available cellulose ester, soluble in polar solvents, of an almost unique unbranched polymer chain structure having a broad range of molecular weights manifested by the degree of polymerization 250-9000. 

Of the methods of synthesis of cellulose esters, the one that has been most thoroughly studied is the reaction of trans-esterification, and this method is widely used for the synthesis of low-molecular-weight esters. The alcoholysis of a low-molecular-weight ester (methyl- and n -propyl-borate) with hydroxyl groups of cellulose was first used (37) for die preparation of cellulose borate. This was followed by the trans-esterification, with cellulose, of the esters of phosphorous acids (see above), i.e. mono-, di- and trimethylphosphites (71, 72, 75), esters of phosphonic acids (76), and also phenyl-/ -chloroethyl- and / -fluoroethylphosphites (77, 78). Of considerable interest is the reaction of alcoholysis, with cellulose, of the esters of aryl- and naphthalenesulphonic add, which results in the formation of cellulose ethers, rather than esters (79-81). 

Polymer chemists have found the fully acetylated product, called a trlester, to be of limited value in the plastics and coatings industries. Some free hydroxyl groups along the polymer chain are necessary to effect solubility, flexibility, compatibility, toughness, etc. Acylation to a predetermined degree less than the triester is not feasible if a uniform, soluble product is desired. Therefore, the cellulose is fully acylated and then hydrolyzed back to the desired hydroxyl level. The hydrolysis reaction is relatively slow and may be controlled and terminated as required. Commercial cellulose esters may contain up to 5% by weight of hydroxyl obtained in this manner. 

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