THE JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
Oct., 1922
933
The Chemistry of Wood’1z IV-The
Analysis of the Wood of Eucalyptus globulus and Pinus monticola By S. A. Mahood and D.E. Cable FOREST PRODUCTS LABORATORY, DEPARTMENT OF AGRICULTURE, MADISON, WISCONSIN
I
N THIS article, which is the fourth of a series by the Forest Products Laboratory on the chemistry of wood, the analysis of two new species is reported. The method of analysis employed in the earlier work has been followed closely, except for a modification of the method of preparing a sample for analysis and the inclusion in the analysis of methods for determining lignin and alpha-, beta-, and gammacellulose, which progress in the subject seems to justify. Recent investigations in wood chemistry have been made by Johnson and HoveyS and Dore4 in this country and Schwalbe and Beekerb and Konig and Beckere in Europe. A proximate summative analysis of some California woods has been made by Dore. The values obtained, however, are not strictly comparable with ours, on account of differences in the methods employed. It is desirable to determine as many well-defined splitting products of wood as possible, but until further progress is made in that direction the summation of the values obtained in an analysis appears to be of secondary importance. To merge the well-defined methoxy and acetyl groups into the ill-defined “proximate constituents,” lignin and cellulose, would seem to reverse the order of progress, unless these “proximate constituents” are further analyzed, as in the more recent work of Dore.’ SAMPLING
The difficulties encountered in obtaining wood in a form suitable for analysis have been pointed out in a previous paper.* It is believed that the 80- to 100-mesh ground sawdust, the preparation of which is described there, fulfils the requirements: (1) of being a sufficiently representative sample, and (2) of affording material which will be uniformly attacked by reagents and which can be manipulated with facility in the course of the analysis.
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For the purpose of determining the variations in results that might be occasioned by this change in the material analyzed, comparable runs were made on samples of Eucalyptus globulus in each form. The results, exclusive of the cellulose determinations which are fully considered in the paper already referred to, are given in Table 1.. It will be noted that the significant differences between the results in the two series are found in those determinations where surface contact and hence the size of particle comes into play, i. e., the solubility determinations, while the determinations involving partial or complete decomposition of the wood give concordant results. The variations in the values for pentosan and methyl pentosan are probably due to variations in the extraction of the latter. The somewhat greater solubility in hot and cold water of the material which seemed in the main the coarser of the two led us to sift the 40-mesh sawdust and determine the solubility of the different fractions. The results are given in Table 11. TABLE 11-EFFECT OF SIZE
ON COLD WATER-SOLUBLE DETERMINATION Soluble in Weight X Per Weight of Cold cent WaterFraction Sample Water Soluble Mesh Grams Per cent Content 40-60 16.40 5.47 89.9 60-80 14.60 5.78 84.5 80-100 2.55 5.97 15.2 100-120 3.55 5.83 20.7 120 6.59 8.05 53.1 TOTAL 43.69 263.4 263.4 Welghted average solubility 43. 6Q= 6.03 per cent
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The increase in solubility shown may be due: (1) to decrease in size of particle, or (2) to concentration of the more soluble portions of the wood in the finer material, or both. Since the analytical data, excluding the solubility values, in Table I show the two samples to be uniform in composition,
TABLE I-EFFECT O F SIZE OF WOOD PARTICLE ON RBSULTSOF ANALYSIS (Values given are in per cent of the oven-dry (105’ C.) weight of the wood) MATERIAL Ground sawdust passing an 80- but retained on a 100-mesh wire Sawdust passing a 40-mesh sieve
Determination Number
1 2 Mean 1 2 Mean
Ash 0.26 0.27 0.27 0.21 0.1s 0.20
Cold Water 5.30 5.33 5.32 6.47 6.52
6.60
To overcome possible objections to Schorger’s procedure in using one sample for the celluIose determinations and another sample for obtaining the remaining values in the analysis, material in the same form, namely, 80- to 100- mesh ground sawdust, has been employed for all determinations. 1 Presented before the Section of Cellulose Chemistry at the 63rd Meeting of the American Chemical Society, Birmingham, Ala.. April 3 to 7, 1922. Published with permission of the Department of Agricultute. 9 The earlier papers of this series were published in THIS JOURNAL, 9 (1917). 556, 624, 748, by Dr. A. W. Schorger, whose work the present authors have continued. a Paper, 21, No. 23 (1917), 36. 4 THISJOURNAL, 11 (1919). 556; 12 (1920). 264. 6 2. angew Chem., 82 ( I s l e ) , 229. e Ibid., 32 (1919), 155. THIS JOURNAL, 12 (1920). 473,476. 8 Ibid.. 12 (1920), 873.
Solubility in Sodium Hydroxide 1 Per cent 17.91 17.90 17.90 18.09 18.10 18.10
Hot Water 8.36 8.16 8.26 9.78 9.69 9.74
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Ether 0.62 0.58 0.60 0.79 0.77 0.78
Acetic Methoxy Acid by Groups Methyl Hydrolysis (CHaO) Pentosan Pentosan 1.56 17.80 2.89 1.48 6:67 18.00 2.59 1.52 6.87 17.90 2.74 1.56 6.64 17.27 3.06 1.34 7.07 17.52 3.00 1.45 6.83 17.39 3.03
it is assumed that the increase in solubility shown in Table I1 is due largely to the effect of the size of particle. The data show that either form of material will give results that are essentially comparable, but since the 80to 100-mesh material has been shown to be most suitable for the cellulose determination, this material has been used through the present investigation. LIGNIN When the cellulose in wood is removed by hydrolyzing it to soluble forms, a residue is left which is fairly constant, even through the hydrolytic agent and the conditions of hydrolysis are varied somewhat.6 The residue retains a surprising similarity to the lignin of the original wood, considering the rather drastic treatment necessary for the
934
THE JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
hydrolysis of the cellulose. For example, the residue obtained by treating the wood of E. globulus with 72 per cent sulfuric acid gave the characteristic color for lignin when treated with chlorine and sodium sulfite. The changes which occur are apparently superficial and may involve the loss to a greater or less extent of methoxy and acetyl groups and furfural-yielding constituents. The values obtained, however, appear to be sufficiently constant to warrant their determination in an analysis of wood. Preliminary experiments showed 72 per cent sulfuric acid, employed by Ost and Wilkeningg in the hydrolysis of cellulose, to be a more efficient hydrolytic agent and more convenient to handle than hydrochloric acid. There is considerable difficulty in filtering the lignin residues, owing to the more or less colloidal nature of the solution. This can be largely overcome by boiling the solution after dilution. In order to adopt a method of procedure, it was necessary to determine (1) the time of exposure to the acid necessary to effect complete hydrolysis, and (2) the effect of boiling the solution. By varying the time of exposure to sulfuric acid it was found that a period of 16 to 24 hrs. is sufficient for complete hydrolysis. The values obtained for western white pine, Pinus monticola, calculated on the basis of the ovendry wood, follow:
Vol. 14, No. 10
hrs. The lignin is then filtered on a tared alundum crucible (previously treated with acid), washed free from acid with hot water, dried a t 105” C., and weighed. CELLULOSE The cellulose values obtained in the analysis of wood are quite constant for conifers on the one hand and broadleafed trees on the other. The celluloses from these two groups are differentiated by the amounts of pentosan they contains1 Future work will probably show other differences, not only between the celluloses from these two groups but also between that from individual species of each group, It seemed desirable, therefore, to introduce into the analysis the mercerization testlo as a possible means of further differentiating the celluloses isolated by chlorination. RESULTS The results of the analysis of four representative samples each of western white pine and eucalyptus are given in Table V. The pine was grown in Bonner County, Idaho, and the eucalyptus in Santa Clara County, California.
DISCUSSION OF RESULTS In most cases the results parallel rather closely those obtained by Schorger for conifers and broad-leafed trees, TABLE111-EFFECT OF TIMEOF EXPOSURE ON LIGNINDETERMINATION respectively. Western white pine is shown to be very similar Time of Exposure Lignin Content in composition to longleaf pine, the most notable differHours Per cent 4 27.77 ence between the two being in their relative solubility in 27.32 8 27.09 16 hot and cold water and alkali, longleaf pine being quite 27.03 24 appreciably more soluble in all three reagents. The effect of boiling is to reduce slightly the yield of nonEucalyptus does not approach the hardwoods already cellulose material, as shown by the following results, also on analyzed in this series as closely in composition as western western white pine. white pine does the conifers. Among the most notable TABLEIV-EFFECT OF T I M E OF BOILINGON LIGNINDETERMINATIONdifferences is the low-ash content of eucalyptus, which corresponds more nearly with that of the conifers. The yield Time of Boiling Lignin Content Minutes Per cent of acetic acid by hydrolysis from eucalyptus wood is much 28.89 Not boiled 27.07 less than that from the hardwoods previously analyzed. 15 26.82 45 It has been shown, however, that eucalyptus yields nearly 26.76 120 as much acetic acid by destructive distillation as the hardIt will be noted that a 15-min. boiling reduces the yield woods ordinarily distilled.ll approximately 2 per cent, and that practically no further The cellulose isolated from the two woods contains ap1oss takes place on continued boiling. proximately the same amount of alpha-cellulose. It is I n view of the above results, the following procedure interesting to note that the remaining portion of the celwas adopted for the determination of the lignin values lulose in the case of eucalyptus is almost entirely gammareported in this paper. It is possible that the conditions cellulose, while in the pine it is about equally divided beare not the optimum for hardwoods. tween beta- and gamma-cellulose. These resolution products Two grams of air-dried material are extracted for 4 of the celluloses should be studied further. hrs. with a minimum boiling-point mixture of alcohol and The lignin values are higher for pine than for eucalyptus. benzene. After removal of the solvent by suction the sample I n other words, the conifer appears to be the more highly is treated with ten times its weight of 72 per cent sulfuric lignified, a fact contrary t o the usual botanical conception acid. The sample and acid are intimately mixed with a of the relative lignification of these two groups of plants. stirring rod, causing the wood to become completely dis- It should be noted that the cellulose and lignin values for integrated after a few hours. After hydrolysis has been the individual samples compensate, higher lignin values being allowed to proceed at room temperature for 16 hrs., the acid obtained from samples with a lower cellulose content. is diluted to a concentration of 3 per cent. The solution is 10 Cross and Bevan, “Researches on Cellulose,” S (1905-IO), 23; Cross then boiled under an air-cooled reflux condenser for 2 and Bevan, “Paper-Making,” 1916, 97;Schwalbe, “Chemie der Cellulose,” 9
39.
C. F. Cross and E. J. Bevan, “Researches on Cellulose,” S (1905-IO),
1911, 637. 11 U.S. D t p t . Agr., Bull. 608.
TABLE V-COMPLETE ANALYTICAL RESULTS ON WHITEP I N E AND Euc)ALYPTUS (Results in percentage of oven-dry (105‘ C>.) sample) c Moisture -SOLUBILITY IN-Acetic MethMethyl in Air1 Per Acidby oxy Sample Dry Cold Hot cent Hyrlrol- Groups, Pento-. Pento- Cellusan lose Aloha .. No. Sample Ash Water Water Ether NaOH ysis (CHaO) san SPECIES Western White Pine 1 6 18 0 21 2 60 3 35 4 00 13 97 1 2 1 4.38 6.75 3.41 58.53 70.58 4.59 7.19 3.25 62.29 64.34 2 7:68 0:20 1:73 2:57 4:42 12:70 0:94 (Pinus rnonticola) 3 7.00 0.18 3.92 7.25 3.98 15.92 1.37 4.86 6.48 3.33 59.40 74.29 -. 4 7.15 0.19 4.40 4.78 4.63 16.51 1.09 4.41 7.46 2.90 58.61 49.27 .-61 .Mean 7.00 0.20 3.16 4.49 4.26 14.78 1.03 4.56 6.97 3.22 59.71 64 1 6.99 0.23 2.65 4.41 0.54 16.57 2.31 7.11 21.41 1.97 59.67 67.85 2 6.55 0.20 4.93 6.96 0.52 18.42 1.97 6.37 20.66 2.14 58.53 69.75 3 6.87 0.27 5.31 8.26 0.60 17.90 1.51 6.87 17.90 2.74 56.45 68.99 4 5.90 0.24 5.79 8.27 0.59 21.40 1.62 6.56 20.39 2.48 55.83 Mean 6.58 0 . 2 4 4.67 6.98 0.56 18.57 1.85 6.73 20.09 2.33 57.62 68.86 ~
...
-Methyl
IN CELLULOSE
Pentosan Lignin 1.59 27.22 2.97 24.15 1.68 27.55 1.56 26.82 1.95 26.44 3.92 24.04 2.44 25.24 2.24 25.07 21.76 1.26 26.74 0.70 31.10 20.96 2.46 25.27
PentoBeta Gamma san 18.16 11.26 4.47 5.66 10.69 24.97 9.17 16.54 5.19 27.27 23.46 5.96 16.32 19.06 6.33 2.11 31.04 20.35 0.00 31.25 21.62 0.00 31.01 zO.iO
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