P
0.131220
U. S . Department of Agriculture, Forest Servic e
FOREST PRODUCTS LABORATOR Y
In cooperation with the University of Wisconsi n
MADISON, WISCONSIN
COMPARISON OF WOOD CELLULOS E
AND COTTON CELLULOSE
By S . A . MAHOOD
Chemis t
an d
D . E. CABLE
Assistant Chemis t
}
1
Published i n
JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTR Y
August, 1922
COMPARISON ' OP WOOD CELLULOSE AND COTTON CELLULOSE 1
By S . A. MAHOOD, Chemis t
and
D. E . CABLE, Assistant Chemis t
Summary
Data recorded in this paper show that the wood cellulose mos t
nearly corresponding to cotton, taking purified linters as a standard ,
is obtained by recooking "easy bleaching" sulfite pulp with soda an d
bleaching with 2 percent bleach . The significant differences are foun d
in the amounts of furfural-yielding constituents present and in th e
gamma-cellulose contained in this pulp, but which is not found in th e
linters . This sample, however, represents the lowest yield on the basi s
of the original wood .
The recooked, raw cooked sulfite pulp (232 LR) bleached wit h
3 percent bleach does not differ so markedly from the above sample an d
represents a 6 percent higher yield on the basis of the original wood .
Esterification tests might show this to be a suitable form of ra w
material, assuming that similarity to cotton cellulose is a prerequisit e
for wood cellulose for this purpose .
Since the data show that bleaching is a very efficient metho d
of removing the nonce' .lulose material, it is probable that the yield of
cellulose suitable foA the manufacture of esters co ul d be materially
increased by giving a light or raw cooked stock a bleac'-tin ; treatmen t
prior to recooking with soda .
Alkaline cooking produces a larger amount of beta-cellulos e
than acid cooking, the amount increasing w4 .th the severity of the cooking conditions . From a chemical standpoint ; pulps produced by alkal i
are less similar to cotton than those produced by acid cooking or b y
acid and alkaline cooking . On this basis the former appears to be les s
suitable for esterification .
On the basis of the data given, cellulose from wood and cellulose from cotton do not represent identical chemical aggregates, and th e
-Presented at the Cellulose Symposium of the Division of Industrial &
Engineering Chemistry at the 60th Meeting of the .American Chemical
Society, Chicago, Ill ., Sept . 6-10, 1920 .
R1036
same is true of wood celluloses obtained by acid cooking and b y
alkaline cooking . The practice of checking wood cellulose accordin g
to the specifications for cotton is, therefore, a questionable procedure .
Introductory
It is customary in determining the suitability of woo d
cellulose, to be employed as a substitute for cotton cellulose in th e
manufacture of cellulose esters, to refer the former to specification s
ordinarily applied to cotton . This practice is perhaps due more t o
lack of data regarding the celluloses than to lack of appreciation o f
the possible differences in the nature of these chemical aggregates .
It is, of course, possible to obtain a cellulose from wood by suitabl e
means of degradation that approximates cotton cellulose, but availabl e
information indicates that cellulose from wood can not be made identical with cellulose from cotton . To obtain a product that even approximates cotton cellulose entails a loss so great that it renders th e
process uneconomical .
In connection with a study of the preparation of wood cellulose suitable for the manufacture of cellulose esters comparisons wer e
made of wood and cotton celluloses varying in purity from the origina l
raw materials to severely cooked and highly bleached samples, for th e
purpose . (1) of following the chemical changes which occur in wood pulps
on successive cooking and bleaching treatments in order to dete .cnin a
whether the conditions in these treatments could be changed so ac t o
increase the yield of suitably purified cellulose and (2) to determin e
so far as possible the points of similarity or difference of cellulos e
from wood and that from cotton . Data of this nature should be o f
value not only in the manufacture of cellulose esters, but alio in al l
allied industries involving the chemical utilization of cellu :' .oso and
also in the pulp and paper industry .
Experimental?
Since even "normal" or cotton cellulose is still an uncertai n
chemical entity the method of attack in making these comparisons ccnsistea in etermining the constants usually stipulated in specification s
for cotto
and also certain constants which have been employed in th e
analysis of the ligno-celluloses .t The determinations made will b e
?Acknowledgment is made to Messrs . M. W. Bray and J . A . Staidl fo r
assistance in securing the data given in this paper .
.Weaver "Military Explosives" (1912) 188 ; Marshall "Explosives"
696 ; Paper (1919) V .23, No .23 .
Jour . of Ind. & Engin . Chem .
9 (1917) 556 ; Cross and Bevan "Paper-ma k
ing" (1916) 93 .
R103.6
(1917 )
-2-
*iefly outlined and the experimental data given after which the result s
will be discussed and such comments made on methods as seems necessary .
Moisture was determined by drying at 1050 C . ; waxes, fats ,
and resins were found by extraction with ether for 4 or 5 hours ; solubilities in 1 percent aTkpii and in hot and cold water were obtained b y
treatment with those reagents for 1, 3, and 4e hours, respectively .
Pentosans and methyl pentosans were determined by distilling the materia l
under investigation with 12 percent hydrochloric acid (Sp•gr+ 1 .06) ,
treating the furfural contained in the distillate with phloroglucinol,
weighing the resulting mixed phloroglucides, and weighing again afte r
the extraction of methyl furfural phloroglucide by means of alcohol .
Cellulose determinations were made by a modification of the method o f
Cross and Bevan and involve alternate treatment with chlorine gas an d
a 2 percent solution of sodium sulphite to a point whore no colo r
results with the sulphite solution after treatment with chlorine .
Acetic acid by hydrolysis was found by boiling for 3 hours with 2 . 5
percent sulphuric acid, distilling the acid extract under a pressur e
of 4+o to 50 mm. and titrating the resulting distillate with standar d
alkali . Methoxy groups were determined by di_$t9 .lling with erioci c
acid according to the Zeisel method .
Lignin or the noncellulose conte t was obtain d by a modification of the method of Ost and Wilksening employed in the hydrolysi s
of cellulose . Four grams of the pulp was extracted with ether an d
treated with 10 times its weight of 72 percent sulphuric acid and the
hydrolysis allowed to proceed for 16 hours at room temperature . The
solution was then diluted to 3 percent and boiled under a reflux condenser for 2 hours . This caused a coagulation of the suspended materia l
and the residue was then filtered on an alundum crucible and dried and
weighed .
ee
.
Solubility in 7 .14 percent sodium hydroxide (or 10 percen t
KOH), which is regarded as a measure of the degree of bleaching, was
determined by treatment of two grams of oven dry pulp with 100 cc . o f
alkali at 10 00 C. A flask provided with a reflex condenser and containing the mixture was heated in a salt bath for exactly 3 hours . The
mixture was then acidified with acetic acid and the residue filtere d
off, dried and weighed .
The "copper number " 6 is also regarded as a measure of th e
degree of bleaching . This value was obtained by treating 2 grams o f
'.Cross and Bevan "Researches on Cellulose," III (1905-10) 39.
6Schwalbe, "Chemie der Cellulose" (1911) 625 .
3-
Pehling solution and boiling under a reflex conpulp with 50 cc .
dea=,er on a hot plate for exactly 15 minutes . The residue was the n
f on
lundum crucible and washed free from alkali . The
ssolved in nitric acid (10.7 percent) and the amoun t
need by titration with thiosulphate solution under
tions .
the chlorination meth o
th causti c
se •., treatmen . .
H
Weighe d
r:t NaO
e
` ea t
th a
'r
the cellumes th .
minutes
L:c-m t pera
b
equivalen4
hen
d with
filter on a • al
um
on the . "~
le
washe d
igheip
acid
ater bath s
u
-et
t e cottrn samp s examir4 cons
bout 20 percent of hulls0 (2) n
on, (3) munition lintels pre
raw linter s
oncentratio
n
their weight o f
raw
linters
ent, and (4) pulped linte
_a Ume-soda-ash liquor contain approximately 8 . g pounds o f
Saustic Soda to 100 pounds of raw linters :
--
40e wood cdIllulose samples analyzed were prepared by Messrs .
. P. Edwardes of the Section of Pulp and Paper of the
,
s- t4c to Whit e
=
(Picea can
y
;.
n .
the cooks .
subjecting
ed in the tables .
380 C .
solution. A
the ble
of bleached and °bleached •
Fis given in Table 1 .
1. D. W„aado,
Sab•-_- .tory by va
T
_,
.
.
Themical society, 34 (1912) 422 .
--Cross and Be , °R .
Bevan, "Pape
fail)
41036
637 •
es on Cellulose,' III (1905-10) 23 ; Cross and
1916)_97 : Sehwalbe, "Chemie der Cellulose "
The analytical data obtained on these samples are given i n
Table 2 . In the case of the sulphite pulps the letters "L» and " W I i , :
indicate light or raw cooked and well or normal cooked pulps ,
respectively . "It" indicates the pulp has been recooked with a weak
(1 percent) caustic soda liquor. In the soda and sulphate runs "L "
indicates a light or normal cooked pulp while "Wu indicates a well o r
Severely cocked pulp .
The sam=ples were air dried in the form of paper and the
material, prepared for analysis by running it throlf a shredder whic h
gave a fluffy product with the individual fibers more or i ass separated :
Discussion of Result s
Moisture
i
basisr
ao -5uir
lh
where
. ___
:e v
to
the purposa~i% g a
the other determinations .
the
be
air
dried at 68° F. in a n
kJ ng eno
to
of
aptoximately
25 percent .
thidity
'a
awes
om
ed by slid cooking is more bygroscopkO
line
~t alt ;>>'.r
the reverse has bee n
The "
eached sulphite pulps ar e
s and absorbent cotton while the
ed sulphate are less hygrog the
ecreases the hygroscopicity of the sulphite pulps ,
ffinity for water of those pulps that have been sub atment .
Ash
All celluloses retain a certain amount of the mineral constituents contained in the original raw material irrespective of th e
method employed in their iso tion . Schorger_
4 found cellulose from
spruce weed to conta
age of 0 .30 percent ash . Purifisd
cotton yields an a .,..
from 0 .10 to 0.50 percent while raw
cotton contains 1 percent or more of mineral constituents .12 The ash
values in the wood celluloses examined, while fairly uniform for eac h
series, are high compared to spruce wood on the one hand_ and to purifie d
cotton on the other . The high values are undoubtedly due to insufficien t
washing of the pulps and to the tendency of cellulose to adsorb mineral
salts .
~Schwalbe "Chemie der Cellulose" (191* '
lO
Schwalbe "Chemie der Cellulos
1 1
4.
R1036
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Water-Soluble Conten t
Cellulose is generally regarded as insoluble in water .!
While
ater soluble content of the samples analyzed may be accounte d
by soluble salts retained from previous treatments many o f
for in
the sampi' show appreciable amounts of water soluble material whic h
can not b
ted for in this way . The wood celluloses isolate d
appear to cain more water soluble material than the treated cotto n
cellulose .
e sulphite pulps are more soluble in hot than in Q .
water under the conditions of these experiments while the rever ,
of the pulps from alkaline treatment . Bleaching increasers
ty of the sulphite pulps, but tends to decrease the sol .ity
*diphate pulps . Cross and Bevan? have recentll show n
cellulose is changed both qualitatively and quantitativel y
with water.
4
y e•
pext
cent sodium hydroxide is i n
'nee the alkaline solution is t
ing . This almost invariably results in the
j,~grobably analogous to beta-cellulose )
remain in solution . Notwithstanding this differ=tlkli
a d
e values for solubiJ .it- . in 1 percen aa
ca lly all cases . nalk
~gener a
ability
r'
ableachingj•
ble exception :, t_
7
•o ed (221L series s • `~
light o
ained in
ght cooked series where no inc r
are due to two compensating changes whic h
occuc oc rs o~M
=
4dicated by the lignin values, bleaching removes th e
al, which is more or less soluble in alkali, on th e
as alkali soluble constituents from the residual
'bther . The effect is a practically constant percentage
e material with 7 .14 percent sodium hydroxide . With 1
~,do not compensate so closely, bu t
quite Ipparent .
e
recooked samples which have been lightly
e soda pulps and the well cooke d
•ters and absorbent cotton in thei r
general, however, the wood cellulese s
egree
sy in
se which has been subjected to
are more sol•NJ
ban co
"
'l-JITMM%
corresponding treatment . I •
*literal of t
tog er with
o
R
chwalbe "Chemie der Cellulose" (1911) 19 .
Cellulose" (191 g) 311 0
X1036
The solubility in 7 .14 percent sodium hydroxide is apparentl y
due to the presence of lignin, furAural--yielding constituents an d
gamma-cellulose in the pulp and also to the conversion of some of the
more resistant celluloses into soluble form during the 3 hours boiling
with the alkali in the test . Evidence for this is given in Table 3
where the solubility in alkali on the one hand is compared with th e
beta- and gamma-cellulose and loss on chlorination on the other . I n
the alkaline pulps the conversion of insoluble to soluble cellulos e
has apparently reached its limit in the original cook .
Table 3 .
Sample
number
: 7 .14 percent NaOH
soluble
Percent
221L
223L
224L
•
°
26 .46
26 .93
26 .36
Loss o n
: Beta- and gamma- :
n
cellulose*
:
chlorinatio
:
:
Percent
:
Percent
°
°
17e1$
13 .97
15 .61
17 .1 8
12 .87
6 .7 2
°
5 .05
3 .67
2 .99
4 .1 1
221W
2231
224W
225W
'
'
°
1
23 .70
32 .76
11 .78
11 .31
12 .49
16 .o6
231WR
232WR
233WR
231WR
235YTR
°
'
I
°
°
3 .63
5 .31
12 .81
20 .02
36 .87
9.85
1. g l
6 .57
9.00
214 .09
°
°
1 .87
1 .90
1 .93
2 .32
4 83 9
2 .5$
.
.6 $
13 .36
18 .95
1 .9~4
17 .68
°
6 . g3
4.80
5 . x+4
3 .83
19 .89
19.59
Munition linters . :
3.
201L•.Soda
201N-Soda
211L-Sulphate
21].W Sulphate
5 .93
5 .89
8 .61
5 .51
'
:
'
°
°
°
°
°
°
*Calculated on the basis of the original pulp .
If time and temperature of treatment and strength of alkal i
were the same in the alkali soluluility determination and in the determination of alpha-, beta-, and gamma-cellulose the sum of columns 2 and 3
would more nearly approximate column 1 . That the 7 .14 percent solubility
figures are in the main greater than this sum in the case of the sulphit e
pulps, especially those which have not been redigested, indicates tha t
x1036
this solubility test is too severe a test for these pulps as consider able of what is determined as alpha-cellulose is dissolved during th e
test .
Acetic Acidby Rydrolysi s
Spruce wood yields on hydrolysis with dilute sulphuric aci d
1 .59 percent of fatty acids consisting almost entirely of acetic acid .
The data show the acetyl groups producing this acid to be removed bot h
by acid and alkaline cooking . Acetic acid residues, if present in th e
wood, are not resolved by subsequent cooking or bleaching into a condi tion in which they yield acetic acid on further hydrolysis with dilut e
sulphuric acid . The recooked sulphite pulps and also the soda an d
sulphate pulps correspond with cotton in yielding practically n o
acetic acid by hydrolysis .
Ether Extrac t
This extract contains the waxes, fats ; resins, etc . not removed from the pulps by cooking . Spruce wood yields an extract o f
1.36, while subjecting this wood to said acid cooking tends to concen trate . the extractive material in the pulp as is shown in Sample 221L .
Strong bleaching, however, tends to reduce the amount of extractive s
in the sulphite pulps, but does not cause an elimination of them beyon d
a certain point as indicated in the well cooked series . The cotton s
yield smaller amounts of extractive materials than the woods . Soda
cooking is slightly more efficient in removing these materials tha n
sulphite or sulphate cooking . Subsequent bleaching of the soda an d
su.'phate pulps, in contrast with the sulphite pulps, does not remov e
any of the residual extractives . In fact, the percentage of ethe r
soluble constituents appears to be slightly increased by the action o f
bleaching powder on the alkaline pulps . The two soda cooks are neares t
the maximum specification of 0 .4 percent of extractive matter fo r
cotton, but none of the samples of pulp meet this requirement .
Pentosan, Methyl Pentosan, and Furfuroid s
The furfural and methyl furfural-yielding constituents o f
wood are usually calculated in terms of pentosan and methyl pentosa n
and this procedure was followed in tabulating the present results .
Since the extraction of methyl furfural-phloroglucide with alcohol i s
not entirely satisfactory the results are also calculated in terms o f
furfural which eliminates the effect of this extraction in the dat a
recorded under the heading of "Furfuroids" and which gives values mor e
comparable than the values under the other two headings . In general ,
however, the values in all three columns parallel each other rathe r
closely .
81036
-g-
The chief source of furfural in woods are the pentosans
although the lignin also contains furfura lwyielding constituents . In
pulps there may be hydrocellulose and oxycellulose present which als o
yields furfural . Since the yield of furfural from each series o f
pulps is constant or nearly so the indication is that very little hydro cellulose or oxycellulose is formed during bleaching . This seems t o
show that the solubility of the pulps in alkali, which increases rapidl y
with increased bleaching and which is usually attributed to the abov e
modifications, is due to some other change in the cellulose .
The pulps contain larger percentages of pentosan and methy l
pentosan than the cottons . To what extent this makes them less suit able than cotton for este i.cation has not been fully determine d
although it is commonly regarded that, in cellulose for nitration, th e
presence of lower carbohydrate bodies leads to a less stable nitratio n
product .
Methoxy Conten t
Methoxy groups are characteristic of the lignifiedcelluloses .
They are contained chiefly in the lignin and are, therefore, largel y
removed by cooking and by bleaching . The absence of methoxy groups i s
regarded as an indication of a very pure form of cellulose . The
bleached soda pulps and the recooked sulphite pulps compare very favorably with the cottons which are shown to contain very small amounts o f
methoxy . Benedikt and Bramberger2
. found no methyl groups in cotton,
but small amounts in sulphite cellulose .
Cellulose
The yields of cellulose from the pulps by the chlorinatio n
method more nearly approach those from cotton in the case of the re cuoked normal cooked sulphite pulp and the well cooked soda and sulphat e
pulps . There is, however, considerable difference in the nature o f
these celluloses when the alpha-, beta-, and gamma-celluloses an d
furfural-yielding constituents in them are considered . The gammacellulose for each series of bleached pulps is fairly constant, but i s
less than that for the unbleached pulps of the same series in the cas e
of the sulphite pulps and greater in the case of the soda and sulphat e
pulps . All the wood celluloses contain more gamma-cellulose than th e
purified cotton samples . In the manufacture of nitrocellulose gamma cellulose is said to be lost during nitratio nl) and, therefore, reduce s
the yield of nitrocellulose obtained .
2Monatshefte 11, 260-67 .
1Jour . of Industrial & Engin . Chem., 12 (1920) 3S2 .
R1036
Jr
.-,
E
r
s_
I .J
EE
Pulps obtained by the alkaline' cooks contain a higher pertentage of beta-cellulose than those obtained by the acid cooks . Mild
bleaching has little effect, but heavy bleaching converts alpha-int o
beta-cellulose . Upon nitration beta-cellulose iMsaid to give a les s
stable product, but the evidence on this point is not conclusive .
-
•
1
Purfuroids as pointed out by Cross and Bevan appear to b e
normal constituents of cellulose isolated from wood . This differentiates wood cellulose from cotton cellulose although the data sho w
the latter to contain small amounts of furfural--yielding constituents .
The sample which is the nearest approach to the purest
.ton sample (
re) from the standpoint of the nature and
ad" cellulos
diked normal cooked sulphite pulp (232WR )
ed
bleach.
y•"
IAA!
--~
The
-to and is commonly applied
*tit portion of woo :
of ose . In this paper ligni n
t9 fined as the residia ~
e in
rcent sulphuric under the
conditions already outli
are not corrected for
e the ash content for each seali .es of samples is practically
distant .
raalrVI
r .,
A stronger concentration of !acid is 'sometimes employed in
this determination . However, we obtai"'l: higher values using 95 percent
sulphuric acid as indicated by the following figures :
OMple number g
:72 percent sulphuric acid:95 percent sulphuric aci d
.
ercent
Mean
: Percent :
Mean
p
X31
114
----• .05
:
1 .05
---:
----- : ----1 .65 ------ :
0 .96
:
1 .65
------------ -
1 .65
:
The p educe in ma
to determinations *ith 95 percen t
acid wa% #q treat the
for 5 minutes with ten times its
in cc . of acid . The reac
ture was then diluted to twenty
its volume and boiled uncle
ex condenser for l+ hours . The
aloes obtain pd are probably►, 'to a certain amount of charrin g
cellulose .l~
_ __
_~
-1
."Cellulose" (1903) g3 .
16 Ztschr ysiol
. Chem. (lgg2) a (7) 913 .
r10--
Soft wood y like spruce contain approximately 25 to 30 percen t
lignin, which as shown by the data is removed to a greater or les s
degree in the pulping process, depending upon the severity of cookin g
conditions and the nature of the process employed . The effect o f
bleaching in removing lignin from sulphite pulp is well indicated i n
each of the series of bleached samples, 'but particularly in the cas e
of the raw cooked sulphite samples (221L series) . On the other hand
the inability of bleaching to remove the lignin from alkaline cooke d
pulp is well illustrated in the soda and sulphate samples . Bleaching
appears to increase rather than decrease the amount of material in soluble in sulphuric acid . The well cooked sulphite pulps giv e
values that agree well with those for cotton, but the pulps obtaine d
by alkaline looking ttu1 rather high in lignin .
,'
'
Copper Number
-
IThe copper number was proposed by Schwalbe as a means o f
imeasuring the degree of bleaching of cellulosic materials and a
detailed method of procedure was worked out in his laboratory fo r
making the determination . The simpler method employed in this inves gation, as already outlined, gives comparable results and is les s
tedious than the original method . Blank runs on Fehling's solutio n
gave an average value of 0 .38, which was assumed to be constant and th e
values were not corrected for it .
'The values obtained increase with increasing amounts o f
bleach employed, but the unbleached samples also yield values o f
nearly the same magnitude as the mildly bleached pulps showing tha t
products other than those produced in bleaching also reduce Fehlin gi s
solution . Bancroftil concluded that the reducing action on Fehling' s
solution is probably not characteristic of oxycellulose, to which i t
is in part attributed, but to decomposition products of the cellulose .
The differences in the copper number with increased bleachin g
are not so pronounced as the corresponding differences in the alkal i
solubility . The latter constant appears, therefore, to be more suit able as a means of determining the degree of bleaching than the coppe r
number . The usual specification of a copper number not to exceed 1 .0
would exclude all of the pulps except 2311,8 .