Cellulose Reprecipitated

This solution will dissolve cellulose which can be reprecipitated by acidification, a fact used in one of the processes for producing rayon. 

Figure 2. Hypothetical view of a fibre surface showing cellulose fibrils (C), lignin (L), hemicellulose (H) and reprecipitated xylan (RX).

Seven primary cellulose triacetate fractions were Isolated by this method. The first primary fraction rich in hemlcellulose was redissolved and reprecipitated into three subfractions in the same way as described above. The refractionation of the first fraction was necessary to isolate the hemlcellulose material for subsequent analysis and characterisation. 

Cellulose is sometimes used in its original or native form as fibers for textile and paper, but is often modified through dissolving and reprecipitation or through chemical reaction. The xanthate viscose process, which is used for the production of rayon and cellophane, is the most widely used regeneration process. The cellulose obtained by the removal of lignin from wood pulp is converted to alkali cellulose. The addition of carbon disulfide to the latter produces cellulose xanthate. 

Materials. Cellulose Triacetate. Celanese cellulose triacetate was purified by dissolution in reagent grade methylene chloride, followed by filtration and reprecipitation into an excess of reagent grade 2-propanol. The polymer was collected on a Buchner funnel, washed with 2-propanol, and dried. Clear films of 5-mil thickness were cast from methylene chloride solution and used for the photolytic studies. 

Estimation of Selenium in Sulphide Minerals.s—In various sulphite-cellulose manufactories difficulties have occurred which have been traced to the presence of selenium in the pyrites used for burning. Part of the selenium remains in the burnt pyrites and part volatilises with the sulphur dioxide. 20 to 30 grams of pyrites are dissolved in hydrochloric acid (dens.=1-19) and potassium chlorate. Zinc is added to reduce the iron to the ferrous condition more hydrochloric acid is then added, the solution boiled and stannous chloride added to precipitate selenium. Since the selenium may contain arsenic, it is collected on an asbestos filter, dissolved in potassium cyanide and reprecipitated using hydrogen chloride and sulphur dioxide. The element may then be estimated by the iodometric method described below. In order to determine the relative proportion of volatile to non-volatile selenium, the pyrites may be roasted in a current of oxygen. After this treatment the contents of the tube are dissolved in warm potassium cyanide and the selenium reprecipitated and estimated in the ordinary way. 

An interesting observation has been made while attempting to purify nitrocotton by dissolving it in acetone followed by predpitation with water. Guncotton (sample 1) was fairly well purified and stabilized by this method, but collodion cotton (sample 4) retained almost the whole amount of add present in it before purification and it was just as unstable as before, because the sulphuric esters were dissolved and reprecipitated with the nitrocellulose. Inddentally this is convincing chemical evidence confirming the existence of sulphuric acid cellulose esters in lower nitrated cellulose. 

In order to make the separation of unreacted cellulose from the apparent graft easier it was acetylated under nondegradative conditions in acetic anhydride-pyridine mixtures. The apparent graft copolymer was first soaked in methanol, methanol was replaced by water and then acetylated with a 1 2 acetic anhydride-pyridine mixture for 36 hr at 100 °C. After the reaction, the product was precipitated with n-hexane. The precipitate was redissolved in chloroform-methanol and reprecipitated with methanol. The reprecipitation was repeated and finally a purified acetylated product was obtained. When pure cellulose was used for the acetylation it was confirmed that by this procedure cellulose is converted almost totally (98.5 to 99,6%) to triacetate. 

Such investigations performed by the authors concerned nitration of cellulose-PS graft copolymer, PS isolated from this product and PS obtained by suspension homopolymerization of styrene. The grafted PS was isolated so as to preserve its molecular mass, chemical composition and supramolecular structure104 the homopolymer was reprecipitated from benzene into methanol. The molecular mass of grafted chains was 8 x 105—106 and that of the homopolystyrene 5 x 10s. 

A solution of the adenosine derivative (2 mmol) in 1,0-1.6 M aq chloroacetaldchyde (20 mL) at pH 4.0 4.5 was stirred at 24-37 C for 12-72 h until no starting material was detectable by TLC (on Easterman chromatogram cellulose sheets using i-PrCOjH/NH OH/HjO, 71 1 24, v/v/v) and until the peak ratios 265/275 run became constant in the UV absorption spectra. The etheno product was decolorized with charcoal and evaporated to dryness in vacuo, Recrystallization of the residue by dissolving in a minimum amount of HjO, followed by addition of EtOH and EtjO to the cloud point or reprecipitation from aq EtOH followed by an EtOH wash yielded pure product (yield 90-95%). 

Schweitzer s Reagent.—Chemically it is an inert compound wholly insoluble in water, most neutral reagents and in dilute acids or alkalies under ordinary conditions. It is probable that no solvent dissolves cellulose without decomposition or hydration. The solvent most commonly used is an ammoniacal solution of copper oxide made by dissolving freshly precipitated copper hydroxide in ammonium hydroxide. This solution is known as Schweitzer s reagent. After solution in this reagent acids reprecipitate the cellulose as a hydrated cellulose. 

During the preparation of viscose rayon, cellulose is dissolved in a bath containing sodium hydroxide and later reprecipitated as rayon using a solution of sulfuric acid. Name the salt that is a by-product of this process. Rayon production is, in fact, a significant commercial source for this salt. 

Later still, methods were discovered by which cellulose could be dissolved unchanged, and then reprecipitated as fiber or film by subsequent chemical treatment. This process yields viscose rayon fiber and cellophane film from the reconstituted cellulose and is still in use. These are much more useful products than were available from the early acetate rayon. 

A polysaccharide can be conveniently degraded for purposes of structural determinations in a rather simple way. The polysaccharide to be examined is dissolved in an excess of an oxygen-free solution of a base, usually saturated lime-water, and allowed to stand at 25-37° for several months. Cations are then removed from the solution with a suitable cation-exchange resin. Residual polysaccharide may be precipitated with three volumes of ethanol, and the degradation products separated by cellulose-column chromatography, or by fractional reprecipitation of their calcium salts. ... 

Cellulase is a complex of enzymes showing various types of activities. Cellulose substrates include highly resistant crystalline forms such as cotton, various types of microcrystalline cellulose such as Avicel and hydrocellulose, sulfite pulps such as Solka Floe, as well as filter paper and cotton fabrics. More susceptible substrates include swollen or reprecipitated cellulose, cellophane, and ball-milled cellulose. Most susceptible are the soluble derivatives (of low D.S.) such as carboxymethylcellulose and cellulose sulfate. It is not surprising that there are many assay methods to detect or measure cellulase (9). These methods differ markedly in sensitivity, and in cellulase components detected, depending on the substrate used, the effect measured, and the duration and conditions of... 

In addition to the standard XAD resins, other materials such as diethylaminoethyl (DEAE)-cellulose, a weak anion exchanger, have also been developed for HS isolation. The DEAE-cellulose is particularly convenient for HS isolation from large volumes of samples. Studies have demonstrated that DEAE isolates and the main XAD fractions consist of similar organic compounds.DEAE-cellulose has several advantages over the macroporous XAD resins in that it allows a higher flow rate, it does not require preacidification of the water samples, and the absorption efficiency is relatively high. About 76% of the adsorbed HS can be recovered by elution with 0.1 M NaOH. However, if pure HS samples are required, further purified procedures such as reprecipitation and HCl/HF treatment for removal of inorganic impurities have to be carried out with both methods. ... 

Cellulose Triacetate. Cellulose triacetate (triethylcellulose) can interact stereoselectively with enantiomers of chiral drugs [48-50]. It has regions of crystallinity, which allow for enantioselective inclusion of drugs (solutes), especially those having substituent-free phenyl groups. However, it loses its enantioselectivity when solubilized and reprecipitated owing to the breakdown of the crystalline structure. 

Cellulose 11 (hydrated cellulose regenerated cellulose) Helicystis algae Dissolving and reprecipitating cellulose 1 mercerized fibers 0.792 0.908 1.034 117.0... 

The nitration of cellulose became a base for a laige number of empirical efforts to modify cellulose. Louis Menard discovered that tetranitrated cellulose could be dissolved in a mixture of diethyl ether and ethanol (3,4). He labeled the resulting thickened liquid collodion. In the mid 1860 s, John W. Hyatt mixed collodion and camphor (S) to form a hard brittle material he called celluloid. In 1875, Allied Nobel announced the development of blasting gelatin, a combination of collodion and nitrogylcerin. A development which lead to several artificial fabrics occurred when Hilaire de Chaidoimet announced spun cellulose nitrate fabric at the Paris Exhibition in 1889 (6). The material was too flammable to be practical but lead to the development of reprecipitated cellulose, rayon, and cellulose acetate, a common fiber and plastic. 

---