INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 23, No. 3
Preparation of Synthetic Resins from Alkali Lignin' Max Phillips and Herman D. Weihe COLOR AXD
A
FARV XT'ASTE DIVISIOV,B U R E A U
OF C H E M I S T R Y AND SOILS,
WASHINGTON, D C.
LTHOUGH the probSynthetic resins have been prepared by condensing were heated for 1 hour. The lem of the utilization lignin with furfural and with the following aromatic resin obtained was b l a c k , of lignin has for Some amines : aniline, o-toluidine, p-toluidine, cymidine, brittle, and lustrous. time engaged the attention of 0-nitraniline, p-nitraniline, dimethylaniline, m-toluCYM I D I N E ( ~ - M E T H Y G ~ a great many investigators, ylenediamine, benzidine, tolidine, cu-naphthylamine, A M I N O ~ - ~ S O P R OBENPYL and P-naphthylamine. A study of the optimum coni t is still largely u n s o l v e d . ZENE)-TO equal parts lignin Katurally most of the workditions for preparing these resins has been made. and cymidine 1 part conceners have concentrated on deSome of the more important properties and possible trated hydrochloric acid was veloping uses for the lignin in uses for these resins are given. added, and the mixture was the waste liquors from the heated for 1 hour a t 150" C. wood-pulp mills, as this constitutes the principal industrial A hard, brittle resin was obtained. source of lignin (1). O-~ITRANILINE-EqUa~ parts of lignin and o-nitraniline During the past three years investigations have been under were heated for 1 hour a t 150" C. A very tough, black, way in this bureau on the chemistry of lignin, particularly lustrous resin was obtained. that isolated from annual crop plants ( 2 t o 5 ) . As a result p-SITRANILIh-E-EqUa1 parts of lignin and p-nitraniline of that work the possibility of utilizing lignin in the prepara- were heated for 1 hour a t 150" C. A bluish black, very tough tion of synthetic resins suggested itself. Accordingly, the resin was obtained investigation recorded in this paper was undertaken and DIhlETHYLANILIXE-The dimethylaniline resin may be carried out. prepared either by heating 2 parts of lignin and 1 part dimethylaniline a t 170" C. for i hour, o r b y heating3 parts Experimental Procedure lignin and 2 parts dimethylaniline a t 150" C. for 1 hour. The lignin used in the various experiments described in In either case a very tough, black resin is obtained. The this paper was isolated from corncobs by the alkali method, resin contracts on cooling and does not stick to glass, so that it can be readily molded in glass tubes. as described in a previous communication (4). m-TOLUYLENEDIAMIXE-EqUa1 parts of lignin and mI n order to determine the optimum conditions for the preparation of each resin, it was necessary to determine ex- toluylenediamine were heated for 1 hour a t 150" C. A black, perimentally the following three factors: (1) optimum tem- hard, brittle, lustrous resin was obtained. BENZIDINE-Equal parts of lignin and benzidine were perature, ( 2 ) optimum ratio of lignin to the second component heated a t 200' C. for 1 hour. il dark brown, lustrous resin (concentration), and (3) optimum time of heating. Several preliminary experiments were first conducted for was obtained. TOLIDINE-one part of lignin and 2 parts tolidine were the purpose of determining the temperature a t which lignin would react with the organic compound selected, to yield a heated a t 170" C. for 1 hour and a black, hard, lustrous and resinous condensation product. Keeping the preliminary tough resin was produced. a-NAPHTHYLAMINE-TWO parts lignin and 1 part a-naphtemperature thus determined constant and temporarily adopting one hour as the time of heating, experiments were con- thylamine were heated a t 150" C. for 1 hour, and a hard, ducted in which the concentration of the aromatic amine or black, and rather brittle resin was obtained. P-NAPHTHYLAMINE-EqUd parts lignin and P-naphthylfurfural with respect to the lignin was the sole variable. Having thus determined the optimum concentration, ex- amine when heated a t 150' C. produced a black resin having periments were then conducted in which the concentration properties similar to that obtained from a-naphthylamine. and temperature were kept constant and the time of heating Resins from Lignin and Furfural varied. Adopting a similar mode of procedure, the optimum temperature was determined. HYDROCHLORIC ACIDAS CATALYSVThree parts of lignin, The optimum methods for preparing the various resins, as well as their most important physical properties, are given 5 parts furfural, and 1 part concentrated hydrochloric acid below. All reactions were carried out under ordinary at- when heated a t 80" C. for 1 hour produced a hard, black, mospheric pressure unless otherwise indicated. The quan- lustrous and tough resin. This product differed entirely in tities of materials used are all expressed as parts by weight. its physical properties from the resin obtained by heating furfural with hydrochloric acid. The reaction product did not contain uncombined lignin. Condensation with Aromatic Amines SODIUM CARBONATE AS CiTALYsT-Ten parts lignin, 5 parts ANILINE-TWO parts lignin and 1 part aniline were heated furfural, and 0.5 part dry sodium carbonate were heated in a t 150' C. for 1 hour. A dark brown, hard and brittle resin a sealed glass tube a t 150" C. for 1 hour. A black, hard, was obtained. When hydrochloric acid was added to the lustrous, and somewhat brittle resin was obtained. reaction mixture or, what amounts to the same thing, when PYRIDINE AS CATALYSYTen parts lignin, 5 parts furfural, aniline hydrochloride was used in place of the aniline, no and 1 part pyridine were heated in a sealed tube a t 150" C . improvement in the resin obtained could be observed. for 1 hour. The resin was black and plastic. O-TOLUIDINE-TWO parts lignin and 1 part o-toluidine were CALCIUMOSIDE AS CATALYST-Ten parts lignin, 5 parts heated at 170" C. for 1 hour. A black, hard resin having a furfural, and 1 part calcium oxide were heated in a sealed rather glassy surface was obtained. tube a t 150" C. for 2 hours. The resin was similar to that p-ToLuIDINE-Three parts lignin and 2 parts p-toluidine obtained when sodium carbonate was used as the catalyst except that it was somewhat softer. 1 Received December 3, 1930.
March, 1931
INDUSTRIAL A N D ENGINEERING CHEMISTRY Solubility of Resins
iill the resins prepared from lignin and aromatic amines are fusible and readily soluble in mixtures of organic solvents, such as a mixture of furfural, benzene, and 95 per cent ethanol (1:l:l by volume); or ethanol and benzene (1:l by volume); and acetone and benzene (1:l by volume). They are less soluble in the pure solvents themselves and in mixtures of 95 per cent ethanol and p-cymene, or methanol and p-cymene (1 :1 by volume), All the resins are readily soluble in furfural. The resins prepared from lignin and furfural, in the preparation of which basic catalysts were used, were all soluble in the above-mentioned solvents. On the other hand, the furfurallignin resin which was prepared using the hydrochloric acid catalyst was of the insoluble and infusible type. Applications
The soluble resins described above were each dissolved in 1:1 ethanol (95 per cent)-benzene solution, sufficient resin
being used to make approximately 10 per cent solutions, and applied with a brush on white oak. After the first coat was entirely dry, a second coat was similarly applied. The a p pearance of the coats of varnish on the wood is shown in Table I. A number of experiments were also carried out with the view of determining the feasibility of using the resins as binders in the preparation of compressed boards from ptiper. The general method consisted in making up solutions of the resins in 1:1:1 ethanol-benzene-furfural solution and impregnating large sheets (6 X 18 inches) of filter paper. These sheets were allowed to dry, then cut into &inch squares and placed
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in an electrically heated hydraulic press which was heated to 150" C. and subjected to a pressure of 16,000 pounds per square inch (1125 kg. per sq. cm.) for about 1 hour. The resin prepared from dimethylaniline and lignin was found t o give the most proniising results. A compressed board was obtained having a polished finish and considerable strength. It appeared to be inferior, however, to a board similarly prepared in which furfural-phenol resin was used as the binding material. The other resins tested appeared to be unsuitable for this purpose. of L i g n i n Resins W h e n Applied as Varnishes t o White Oak SAADE GIVENBY 2 COATSOF RESINIX 10% 1:l ETHANOL-BENZENE RESIN SOLUTIOX Lienin-aniline Reddish brown Lignin-o-toluidine Light brown Lignin-$-toluidine Mahogany or dark brown Dark brown Lignin-cymidine Lignin-o-nitraniline Mahogany Lignin-p-nitraniline Dark brown Lignin-dimethylaniline Dark brown Light brown Lignin-n-toluylenediamine Yellowish brown Lignin benzidine Light brown Lignin-tolidine Reddish brown Lignin-a-naphthylamine Lignin-@-naphthylamine Brown Lignin-furfural NanCOs as catalyst Mahogany Lignin-furfural pyridine as catalyst Dull brown Brown Lignin-furfural CaO as catalyst
T a b l e I-Appearance
+ + +
Literature Cited (1) Johanson and Hovey, Canadian Dept. of Interior, Forestry Branch, Bull. 66 (1919). (2) Phillips, J . A m . Ckem. Soc., 49,2037 (1927). (3) Phillips, Ibid., 60, 1986 (1928). (4) Phillips, I b i d . , 61,2420 (1929). (5) Phillips, I b i d . , 52, 793 (1930).
Hard Spots in Vulcanized Rubber Compounds* J. H. Howey FIRESTONE TIRE& RUBBERCOMPANY, AKRON,OHIO
A R D K E S S , as deThe cause of local variations in the hardness of exings has been that they charfined by the l i . s. T. perimental slabs of carbon-black tread stocks at differacteristically exhibit a rather sf.standard ( ~ 3 1 4 - ent points on the same slab has been investigated. wide s p r e a d of values be29T), is that property by It has been found that areas of excessive hardness tween different readings on virtue of which the surface correspond to regions where the maximum flow or thesamesample. Anymeans and adjoining layers of the displacement occurred in the rubber when the stock of reducing this spread in was Pressed into the mold at the time of cure. A material resist indentation by values-that is, of increasing a s p h e r i c a l penetrator of knowledge of this fact is of importance in testing the the precision of the readingstandard size under a defihardness of a stock according to the A. s.T. M . standard is of great importance, since of hardness, increasing the Precision and reliability it makes it possible to rely nite pressure. Of ;ill the properties of rubber stocks of this convenient test. more on hardness tests and that are measured in order It has been shown that these variations in hardness thus take advantage of their to determine their suitability cannot be attributed to non-uniform regions in the conveniences. for specified uses, hrbrdness rubber-pigment-sulfur-accelerator mixture, and it is It had been noticed f o r can be measured most conconcluded that they must be due either to altered some time that experimental veniently and most quickly. conditions of dispersion in the regions of maximum test slabs showed a wider Hardness measurements can displacement or to a local grain effectset UP by the flow. spread in t h e i n d i v i d u a l be made on almost any type readings on a given sample of finished product without affecting the salability of the than did factory-cured tires of the same stock. Observaparticular piece on which the test is made, as well as on tions on the hardness of the tread of cured tires of a parspecial test pieces. The measuring apparatus is portable ticular carbon-black stock would lie constantly between 50 and inexpensive. The hardness of a particular test piece and 5 5 , whereas the readings on a laboratory test slab of the can be measured in less than IO minute by 21 practiced same stock would frequently lie anywhere between 45 and operator, which is of especial advantage in factory control 55. These slabs were 1.91 X 3.81 X 12.7 cm. (0.75 x 1.5 x work. The chief disadvantage in the use of hardness read- 5 inches) and the measurements were made by a Firestone penetrometer calibrated according to the A. S.T. hl. standard Received September 20, 1930. Presented before the Division of cited above* The penetrometer reading is the depth of penem Rubber Chemistry a t the dOth Meeting of the American Chemical Society, Cincinnati, Ohio, September 8 to 12, 1930. tration of the point in thousandths of an inch, so that smaller
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