INDUSTRIAL A Y D ENGINEERING CHEMISTRY
May, 1928
Table IX-Effect
491
of Adding Accelerator t o Aged Uncured Rubber COMPOUND A
WHEN CURED
Tensile strength
Elong.
Min. 60 100 110 130 60 100 110 130
Lbs./sq. i n .
%
2940 3020 2715 2725 2130 2300 2520 2385
60 100 110 130
Of
c :u ;;
Directly after mixing
After 67 months’ storage uncured
After 67 months’ storage uncured with the addition of 0.16% hexa calculated on rubber (1/1 original amount added)
After 67 months’ storage uncured with the addition of 0.32% hexa calculated on rubber
After 67 months’ storage uncured with the addition of 0.65% hexa calculated on rubber
COMPOUND C Load at 300% elonp..
-
Time of cure at 40 Ibs.
Tensile Load a t strength E l o w . 300% elonn.
% Lbs./sp. i n .
640 630 585 575 560 530 550 535
Lbs./sq. in. 615 730 815 S65 655 890 910 930
Min. 50 90 100 120 50 90 100 120
Lbs./sq. in. 2155 3400 3165 3135 1440 2440 2500 2620
805 730 735 685 885 775 745 715
140 220 269 300 115 150 160 230
2020 2520 2495 2350
555 545 535 515
660 970 1000 1100
50 90 100 120
1820 2680 2890 3140
890 760 735 730
80 195 240 245
60 100 110 130
2460 2620 2610 2500
600 560 555 525
660 945 970 1085
50 90 100 120
2100 2700 3160 2560
815 655 680 620
115 275 310 370
60 100 110 130
2545 2880 2880 2710
585 550 535 515
755 1045 1140 1230
50 90 100 120
2230 2640 3240 2320
805 655 665 595
155 280 340 420
and rubber, and the large amount of work done by the paint chemist should be studied by the rubber technologist. PART111-The effect of aging unvulcanized compounded rubber is to retard the cure greatly and to lower the re&nforcing properties slightly. Unvulcanized compounded rubber that has lain around in holland cloth for several years is sticky and has to be milled on cold rolls, but after adding accelerator and vulcanizing a good product is obtained. The retardation, in this program, is not due to adsorption of accelerator by the pigment since some of these stocks are practically “pure gum” stocks.
If this program on “normal aging” were being started today, all of these nine compounds would not have been chosen; other formulas would have been used containing antioxidants that mere unknown six years ago; certain new accelerators would have been used; and hygroscopic6reclaim stocks would have been added. Acknowledgment The writers wish to acknowledge the assistance of Howard Hock, who drew the curves shown in this article and helped in making the tests.
Recent Work on the Oxidation of Cellulose’ A Review Covering Two Years J o h n L. Parsons HAMMERMILL PAPERCOMPANY, ERIE, PA.
R
ECENT progress towards the interpretation of the nature of oxidized cellulose (oxycellulose) and a satisfactory means for its estimation has been commensurate with the advance in the chemistry of the parent substance, cellulose. The chemistry of cellulose degradation products is necessarily intimately related to that of cellulose itself. While our knowledge of the latter has been developed chiefly from the viewpoint of pure organic chemistry, it is gratifying to note that greater cognizance is being taken of the fact that cellulose is a product of the plant world and fundamentally different in its physical and chemical properties from most synthetic organic compounds. Recently Sponsler and Dore’,* have postulated a theory of cellulose structure which takes into account the physical and chemical nature of the fiber. Unfortunately, relatively little is known with certainty concerning the chemical processes involved in plant synthesis; in fact our knowledge of the simpler saccharides is far from complete. Owing to the complex character of the problem relating to the study of oxidized cellulose, progress has been slow. 1 Presented as a report of the Oxycellulose Committee before the Division of Cellulose Chemistry at the 74th Meeting of the American Chemical Society, Detroit, Mich., September 5 to 10, 1927. Numbers in text refer to bibliography at end of article.
*
Preparation of Oxidized Cellulose According to Karrer,2oxycellulose presents a greater enigma than the formation of hydrocellulose because of the fact that the first is applied to cellulose when attacked under any condition by any kind of oxidant. There’are probably as many methods of preparing oxidized cellulose as there are oxidizing agents available, and these may act on the cellulose fiber in any combination of five ways: (1) depolymerization of the cellulose; (2) hydrolysis, with tendency to hydrocellulose formation; (3) oxidation; (4) swelling of the fiber; and (5) esterification. Knecht and Mueller3 observed that mercerized yarn is more easily oxidized by acid permanganate than by hypochlorites, whereas in an earlier study Knecht and Egan4reported that ordinary cotton yarn is more readily attacked by bleaching liquor and hypochlorous acid than by acid permanganate. I n the first example no difference was noted whether the yarn was mercerized with sodium hydroxide or nitric acid. When the oxidation experiments were carried out in a vacuum there was noticeably less variation in the copper number by means of which the degree of oxidation was measured. According to Clibbens and Ridge,smercerized cotton is attacked much more rapidly by hypochlorite solutions than unmercerized cotton, while unmercerized cotton
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I N D U S T R I A L A N D ENGINEERING CHEMISTRY
is rapidly oxidized by hypocMorite solutions containing alkali of mercerizing strength. I n a study of metallic alkali-cellulose compounds Heuser6 noted that the copper compound of the formula (CeHloO&.Cu(OH)*.(NaOHh changes color from blue to green on standing. In the presence of alkali the cupric hydroxide decomposes into oxygen and cuprous oxide. The oxygen attacks the cellulose, changing i t into oxidized cellulose and at the same time effecting a depolymerization of the unchanged cellulose. Properties
Oxidized cellulose preparations are distinguished from other cellulose degradation products by their slight acidity and the evolution of carbon dioxide and furfural in the presence of boiling hydrochloric acid solution. The quantities of these substances produced appear to depend greatly on the kind and amount of oxidant employed. Oxidized cellulose also attracts basic and not acid dyestuffs, although this statement must be modified in the light of recent researches from the Shirley Institute (England).' When treated with calcium hydroxide, isosaccharinic acid is formed, which compound is presumably related to the presence of the reducing group in cellulose degradation products, for cellulose is not amenable to this treatment. Recently, however, Karrer and Lieser* prepared a hydrocellulose by the action of phosphoric acid which possessed a very low copper number, was completely soluble in, 10 per cent sodium hydroxide solution, and did not yield isosaccharinic acid with calcium hydroxide. Constitution
Ordinary oxidized cellulose may be divided into three fractions: (1) the alkali-insoluble portion, which is similar to if not identical with the unchanged cellulose; (2) the alkalisoluble portion which is precipitated when the solution is acidified; and (3) the alkali-soluble fraction not precipitated by acids. The lowest degraded and acid-forming substances are assumed t o be present in this third fraction. Karrer and Lieser state that alkali solubility is not affected when the aldehyde group in the degradation products is reduced by means of sodium amalgam. Hibbert and Parsonsg show that solubility of oxidized cellulose preparations in alkali varies with both the volume of alkali solution and the concentration of the solution. A colloidal solution of oxidized cellulose has been prepared2 by dialyzing an alkaline solution of the material in a parchment or collodion sac until free from alkali. A stiff jelly is left which is partly soluble in distilled water. Such solutions are faintly turbid and readily pass through filter paper. Colloidal particles are visible, however, through the ultra-microscope. Salts and acids precipitate the oxidized cellulose from solution. Transference experiments indicate that the particles migrate to the anode. According to Heuser and Niethammer,lQ alkali absorption by cellulose and its degradation products is a measure of the degree of depolymerization. Using the direct method of Gladstone, they obtained the following values in per cent sodium hydroxide retained: purified cellulose, 11.75; Girard's hydrocellulose, 17.25; Cellulose regenerated from cuprammonium solution, 17.98; oxidized cellulose (by hydrogen peroxide), 21.7; oxidized cellulose (by potassium permanganate), 24.12; and Knoevenagel and Busch's alkali-soluble hydrocellulose, 25, Further evidence for the depolymerization of the cellulose structure has been given by Herzogl' as a result of his x-ray analysis of cellulose preparations. The position and probably the size of the crystallites in oxi-
Vol. 20, No. 5
dized cellulose are slightly changed from normal cellulose. Using the Debye and Sherrer method of crystal analysis and a tube with a copper target, Ott12 observed, however, that the reflection angles for cellulose (precipitated from a phosphoric acid solution), hydrocellulose, and oxidized cellulose are identical. The evidence of Heuser and Stockigt that there is present in oxidized cellulose a glucuronic acid group has been confirmed by a number of recent investigators. Schwalbe and Feldtmann'a actually succeeded in isolating d-glucuronic acid salt from bleached straw pulp. M a r c u ~ s o nfound ~~ glucuronic acid in healthy, slightly decayed, and rotten pine wood to the extent of 4.4, 10.3, and 12.5 per cent, respectively. The lignin constituent does not participate in these reactions. I n his theory of coal formation he believes that cellulose during decay is converted to oxidized cellulose and pectin substances. The glucuronic acid constituent of the former is then changed to humic acid, which in turn is transformed into coal. The derivatives of oxidized cellulose have apparently received the attention of few investigators during the last two years. Among the researches of Atsuki16 the relation between the copper number of oxidized cellulose and its nitrate is shown to vary inversely with the yield, the nitrogen content, and the viscosity of the latter. Atsuki states that if the copper number of the oxidized cellulose (prepared with bleaching powder) is in excess of 10 the nitrogen content sharply decreases and other properties of the ester are affected. Sodium hydroxide saponifies both the normal and the oxidized cellulose nitrates, but sodium sulfite exerts a. selective solvent action only on the highly oxidized cellulose nitrates. Acetylation tests9 indicate that the number of hydroxyl groups in oxidized cellulose decreases from three to nearly two for cotton cellulose oxidized by neutral barium permanganate (copper number, 10). The foregoing experimental results furnish additional evidence for the contention of Hibbert and Parsons9 that oxidized cellulose is a mixture of a comparatively large amount of unattacked and possibly depolymerized cellulose with small quantities of complex aldehydic and acidic oxidation products. According to Hess,16it is chiefly a mixture of cellulose and cellulose A with small amounts of other substances. Karrerz considers that the mixture is an adsorption system, similar to hydrocellulose, of the unchanged and slightly changed cellulose and its degradation products. No evidence is yet available to indicate what reactions occur in the stages immediately preceding and following the breakdown of fibrous structure. Sponsler and Dore1 have attempted to reconcile their concept of cellulose structure with the physical properties of the fiber. They are of the belief that the cellulose fiber is stabilized longitudinally by primary valence forces which unite the glucose units alternately in the 1-1 and 4-4 linkages. The structure is stabilized laterally by secondary valence forces of oxygen atoms. Breakdown of fibrous structure begins with the separation of the longitudinal chains, as a result of which the possibilities for rearrangement are almost unlimited, Oxidation implies the conversion of certain chains of glucose units to xylose units by the removal of the carboxyl group from the glucuronic acid complex, according to the scheme: COH
I
(CH0H)r
I
CHzOH
COH 0
1
COH 0
1
+ (CHOH)4 + (CH0H)r I I CHzOH COOH
These altered chains would thus become xylan, according to Sponsler and Dore.
INDUSTRIAL Ah’D ENGINEERING CHEMISTRY
May, 1928
The Copper Number Test
Although the determination of the Schwalbe copper number of oxidized cellulose has been employed as a measure of the degree of attack, the method has recently been subjected to considerable criticism on account of its empirical nature.” Hydrocellulose also possesses the property of reducing Fehling’s solution. These cellulose degradation substances can not be differentiated by either the copper number test or the alkali solubility determination. Ristenpart18 discovered that the determination of copper numbers of dyed cotton is complicated by the fact that most dyestuffs fix a certain amount of copper. To correct for this retention of copper a blank test must be made on cotton free from oxidized cellulose but dyed to match the colored sample. Apparently, Ristenpart has overlooked the possibility of using the SchwalbeHagglund copper number procedure in which only the copper in the cuprous state is determined. The volumetric method of Schwalbe and Becker for estimating the acidity of oxidized cellulose has been investigated by Karrer and LieserI8who found that all such preparations, when titrated with phenolphthalein as the indicator, consume small amounts of alkali. The figures obtained do not parallel the copper number, which is to be expected. Acidity is expressed in the form of the “acid number,” which is the number of cubic centimeters of normal solution required to titrate 1 gram of oxidized cellulose using the above indicator. A recently developed procedure which is claimed to be superior to the Schwalbe copper number is based on the reaction of a sodium acetate solution of silver nitrate with the aldehydic groups in the cellulose product.lQ The amount of silver separated on the fibers is quantitatively determined by dissolving the metal in nitric acid and titrating the resulting solution with 0.01 N ammonium thiocyanate solution. A second treatment is necessary on the same fibers to determine the silver retained by adsorption. I n their published researches on the chemical analysis of cotton, Birtwell, Clibbens, and GeakeZ0announce that the rise of the copper number relative to the fall of viscosity of hydrocellulose preparations conforms to a simple equation, NcuVz = 2.6, where NcU is the copper number and V is the log of the relative viscosity of the cuprammonium solution. By this means i t is possible to differentiate sharply between hydrocellulose and oxidized cellulose. Improved methods for the analysis of cotton materials, developed a t the Shirley Institute, England, consist chiefly of the SchwalbeBraidy copper number test, viscosity in cuprammonium solution, and methylene blue absorption from buffered solutions. Using these methods the rates of consumption of oxygen by cotton cellulose and changes of its properties were
493
investigated. Within the range of hydrogen-ion concentration p H 5-10, characteristic of commercial hypochlorite bleach liquors, the maximum rate of attack on the cellulose occurs a t the neutral points6 Slightly acid hypochlorite solutions are less rapid in their action than neutral solutions. In a strongly alkaline solut,ion hypobromite is a more rapid oxidizing agent. For a constant oxygen consumption alkaline hypochlorite solutions produce the lowest copper numbers and highest methylene blue absorptions; acid solutions produce the highest copper numbers and lowest absorptions; the neutral solutions are intermediate in both respects. For a constant time of t,reatment the neutral solution yields higher copper numbers and methylene blue absorptions than either slightly acid or alkaline liquors.’ The most common cause of overbleaching in industrial practice is evidently the excessiye use of hypochlorite solutions in the vicinity of the neutral point. Conclusion ‘ In agreement with Cross and DorBeI2’a review of the literature on cellulose degradation products leads to the critical and inevitable conclusion that there are no lines of demarcation or differentiation justifying the term “oxycellulose” as applied to a chemical individual. To prevent ambiguity the term “oxidized cellulose” is much to be preferred to denote suc,h a mixture of reactions which evidently are involved in the oxidation of cellulose. Bibliography 1-Weiser, Colloid Symposium Monograph, Vol. IV, p. 174 (1926). 2-Karrer, “Polymere Kohlenhydrate,” p. 198 (1925). 3-Knecht and Mueller, J . SOC.Dyers Colouristr, 42, 46 (1926); PapierFabr., 24, 476 (1926). 4-Knecht and Egan, J. Soc. Dyers Colourisfs,39, 67 (1923). 5-Clibbens and Ridge, J. Textile I n s f . , 18, 135T (1927). 6-Heuser, Papier-Fabr., 25, 241 (1927). 7-Birtwell, Clibbens, and Ridge, J . Textile Insf., 16, 13T (1925). 8-Karrer and Lieser, Cellulosechemie, 6, 2 (1926). 9-Hibbert and Parsons, J. Soc. Chem. Ind.,44, 473T (1925). 10-Heuser and Niethammer, Cellulosefhemie,6, 13 (1925). 11-Herzog, Papier-Fabr., 23, 121 (1925). 12--0tt, Helu. Chim. Acto, 9, 31 (1926). 13-Schwalbe and Feldtmann, Ber.. 58, 1534 (1925). l4-Marcusson, 2. angew. Chem., 99, 898 (1926). I F A t s u k i , J. Faculty Eng. Tokyo I m p . Uniu., 15, 55 (1924); C. .A , 19, 727 (1925). 16-Hess, Papier-Pabr., 23, 122, 164 (1925). 17-Clibbens and Geake, J . Textile Inst., 16, 27T (1924); Papier-Fabr., 25, 401 (1927); Staud and Gray, IND.ENG. CHBM.,17, 741 (1925); 19, 854 (1927); Schwalbe, Papiev-Fabr., 25, 157 (1927). 18-Ristenpart, Melliands’ Texlilber., 6, 830 (1925). Ig-Anon, 2. angew. Chem., 39, 343 (1926); Papiev-Fabr., 24, 492 (1926). 20-Birtwel1, Clibbens, and Geake, J . Textile Inst., 17, 145T (1926). 21-Cross and Doree, “Researches on Cellulose,” Vol. IV (1922).
Purification of Alcohol for Preparation of Alcoholic Potassium Hydroxide1 Sol Kiczales 1956 CROTONA P A R K W A BRONX, Y, New YORK,N. Y.
P R E P A R E a solution of lead acetate containing 2.5 to 3 grams of lead acetate in 5 ml. of distilled water for each liter of alcohol. Add the solution to the alcohol in a glassstoppered bottle and thoroughly mix. Dissolve 5 grams of KOH in 25 ml. of warm alcohol (for each liter of alcohol), cool the solution somewhat and pour it slowly, without stirring, into the alcoholic solution of lead acetate. After one 1
Received F e b r u a r y IO, 1928
hour, shake thoroughly. Let the mixture stand overnight or until most of the precipitate has settled, filter and distil. The precipitate formed is evidently an addition product of lead oxide and the aldehyde, formed by a reaction similar to that between silver oxide and aldehyde. This method is better than the silver oxide method, not only because of its economy, but also because the lead oxide-aldehyde product is more insoluble than the silver oxide-aldehyde product, and therefore the removal is more complete.
