Cellulose from Hardwoods Acid Pulping Studies‘ GEORGE A. RICHTER2 Brown Company, Berlin, N. H.
and dried under prescribed condiITH suitable adjustThe four most plentiful hardwoods in the tions and then tested for burstments in cooking connortheastern states are white birch, yellow ing strength and tear resistance as ditions t h e n o r t h e r n outlined in the earlier account. birch, beech, and maple. Each of these The cooks were made with bihardwoods can be pulped satisspecies can be converted into pulps by the sulfite liquors that contained 5 per factorily by all present-day cent free sulfur dioxide and 1 per acid sulfite process. Data are cited to show pulping processes. I n some cent combined sulfur dioxide. instances they respond more how these denser woods compare with the (The combined sulfur dioxide is that part which can be considered easily than do the softwoods. better known softwoods when coolcs are as combined to the base as a I n other cases, special care is remade by standard procedures. Results neutral salt. The free sulfur diquired to produce hardwood oxide includes that portion that with the hardwoods can be improved markproducts of acceptable quality. demands alkali to convert from a edly by adopting a procedure that gives bisulfite to a neutral sulfite as well I n general, the alkaline cook as that which is present as sulprocedures, as well as the neutral better opportunity for early penetration furous acid.) Sodium was used as or slightly alkaline sulfite pulpof the combined sulfite constituent of the a base. In all cases the liquor ing process, will operate more volume was such that 6 per cent acid cooking liquor. combined sulfur dioxide, based on easily with the hardwoods than Various cooks were made with large wood bone-dry wood content, was preswith most softwoods. On the ent. The wood chips were prechips to emphasize the importance of chip other hand, t h eacid sulfite procpared in a rotary knife chipper and ess is not so easily applied to dimensions. Throughout the series there were of normal moisture content. In this set of cooks substantially the hardwoods as to the spruce is consistent evidence that the ease of green wood was used. The cooks and fir. As will be noted, the pulping the several species is in the followwere made under a maximum pulp yields from birch, beech, and pressure of 75 pounds per square ing order, the first mentioned responding maple are fully as high as with inch gage and with a temperature best: spruce and fir, the birches, maple curve that allowed 5 hours to reach the spruce when such woods are 140’ C. (284’ F.). The charge cooked by the kraft process, and beech. was held at that maximum temwhereas the acid cooks favor the The calcium-base cooking liquors are perature for 3 hours. spruce yields in most cases. Bleachability of pulps was determuch less suitable than are the sodiummined by a simple laboratory The physical strength of paper base acids, and this advantage of the soprocedure that comprises two made from the softwood pulps treatments: (a) The raw pulp is dium base is exaggerated in the case of the is regularly greater than that treated in z per cent chlorine based made from corresponding type less pervious rock maple and the beech. on pulp in 4 per cent stock suspension a t 20” C. (68’ F.) for 1 hour. of hardwood pulp, although a When properly processed, these hard( 6 ) The washed fiber from the white birch pulp of kraft origin woods yield a pulp that possesses value in chlorination step is then bleached can be produced with higher with sodium hypochlorite in the the paper industry. physical strength than that presence of 0.5 per cent sodium hydroxide. To attain desired of “many softwood sulfite prodbrightness, y per cent bleach is used. Bleaching is carried out ucts. Differences in the length of fiber, in the pentosan conat 30” C., 8 per cent stock, 6 hours. Total chlorine requirement tents, and in the manner in which the cooking liquor attacks is actually the chlorine equivalent used in both steps. the cellulose during the pulping process go a long way toward explaining the data.
Experimental Cooks .TableI illustratestypical pulpvalues that canbe obtained when the several species of wood under consideration are cooked by the bisulfite process: The cooks were made in rocking chrome steel digesters that hold a charge of about 3 pounds of wood chips. The ratio of weight of li uor to weight of chips was much the same as is regaarly used commercially. The temperature and pressure curves were controlled by a relief valve and by the application of external heat. At the end of the cook the charge was washed, screened, and then subjected to a laboratory ball-mill beating (1). The beaten stock was sheeted 1 The
first paper in this series appeared in January (9). Present address, Eastman Kodak Company, Rochester,
TABLE I. ACIDSULFITE COOKS~ Wood species Yield % Screehingsb, % Lignin Pentoians % Ether-sol..’ 9% Physical te&C Bursting strength Tear resistance Chlorine requirement, %
Spruce
Fir
White Birch
Yellow Birch
Rock Maple
Beech
47.5 2.5 1.2 4.5 1.1
47.0 2.6
45.0 2.1 1.5 9.3 2.6
44.8 1.9 1.2 8.9 1.4
44.9 1.8 0.9 7.2 0.3
43.5 3.4
116
90 115
90
145 160 5
1.1 4.1 1.3
136
LS0 a
5138
J
io0
a
1.3 6.8 0.45 78 1p05
a Acid contained 5% free SO%,1% oombined SO2 (sodium base); maximum cookinq temperature, 140° C.; cooking curve, a hours t o reach 1403 C., held there 3 hours; maximum pressure, 76 pounds gage. b Screenings represent unpulped wood product t h a t remains b y allowing the pulp fibers t o pass through rapidly vibrating slotted screen plates. c Determined o n hand sheets made from,stock t h a t ,was beaten in a ball mill for 50 minutes in accordance with t h e method prewously described ( I ) .
,
N.Y.
532
April, 1941
I N D U S T R I A L A N D E N G I N E E R I ~ GC H E M I S T R Y
533
Spruce White birch Beech EDGES OF UNBEATEN PULPSHEETS TO SHOW FIBER LENGTH (X61/~) FIGURE 1. TORN In some instances the lignin value or a raw stock stain test was used to estimate the chlorine requirement. All values in the tables are expressed in terms of a bleached pulp brightness of 90.
Influence of Wood Seasoning on Ether-Soluble Resins in Pulp
A marked reduction in the ether-soluble content in the birch pulps can be obtained when a seasoned wood is cooked. Table I1 contains a typical set of values to illustrate the improvement. I n this series of experiments the fresh wood was characterized, and in each case pulps were produced soon after the wood was cut. Portions of the same wood were seasoned in log form for a 2-year period and again subjected to test and pulped. All cooks were made under substantially the conditions adopted for cooks in Table I. The results in Table I1 are significant. Other data confirm the findings. Seasoning periods as short as 8 months will yield similar results if the aging occurs during the warmer seasons and under conditions that favor the contact of sunlight and air. It does not appear practical to extend the seasoning of wood beyond the 2-year period, and no information is a t hand to show whether further exposure of wood will enable the operator to produce an unbleached white birch sulfite pulp of appreciably less than one per cent ethersoluble content.
Table I shows: 1. The softwood pulp yields are higher. 2. Of the hardwoods, the beech gives slightly lower yield. This has been found to be almost always the case and is probably related to the higher density of the wood which is less readily penetrated by the combined sulfur dioxide of the liquor, and consequently undergoes some additional hydrolysis. The lower pentosan values found in the beech pulps lend strength to this explanation. It will be shown later that the lower yield with the beech is less marked when very long low-temperature cook periods are adopted. I n such instances the penetration of reagent takes place more completely below the temperature where a deficiency of combined sulfur dioxide leads to severe hydrolysis of pentosans and cellulose. 3. The physical tests of paper made from the spruce and fir pulps are definitely superior both in respect to bursting strength and tear resistance. 4. Of the hardwoods, the birches (particularly the white Effect of Chip Dimensions birch) produce sulfite pulp that has greater papermaking All species of wood produce a pulp with higher yield and strength than the maples and the beech. This observation improved quality if the chip units are more carefully designed is largely explained by fiber length measurements (Figure 1). than is ordinarily realized with the high-speed rotary knife 5. The pentosans are higher in the hardwoods and highchippers. The improvement in pulp quality is both physical est of all in white birch. The loss of original wood pentosan and chemical, as evidenced by the test values in Table 111. during cooking is somewhat greater with the hardwood, In all cases the more perfect chips yielded pulps that are which indicates greater susceptibility to hydrolysis than is the case with the softwood Dentosan. 6. The ether-soluble matter is surprisingly high in the white birch pulp and reflects the OF WOODSEASONING ON EXTRACTABLES IN PULPPROTABLE11. EFFECT higher oleoresins (2) in the green wood. Yellow DUCED BY ACID SULFITE PROCESSQ birch pulp is less resinous and the maples White Birch Yellow Birch Rock Maple Wood Pulp Wood Pulp Wood Pulp and beech are least. This order of ethersoluble content is regularly found when the Green Wood several species are subjected to the acid pulping Ether-sol. 7% 3.04 4.34 0.90 0.83 0.55 0.30 Acid-alcodol-sol., 7% 2.43 1.52 0.23 2.57 0.15 procedures, even though the cooking conditions .. 0.59 1.11 .. 0.96 .. 0.98 Hot-water-sol., 7% are modified rather widely. After 2-Year Seasoning 7. With pulps of approximately the same 0.21 0.63 0.20 Ether-sol.. 1.15 1.40 lignin content, the bleach requirement necesAcid-alcohoFso1.. 7% 2.45 0.63 1.55 0.37 0.32 0.45 Hot-water-sol., % .. 0.58 .. 0.52 sary to attain a desired degree of brightness is T h e log was sawed across 4 I n this series the wood chips were prepared i n the laboratory. roughly the same, although the beech pulp the rain into desired s/,-inoh lengths, a n d t h e plaques were t h e n split t o & chip thickness of 'f[iinch. frequently demands a slightly higher chlorine equivalent.
534
INDUSTRIAL AND ENGINEERING CHEMISTRY Type A chips, unsorted
Type B chips,
inch with grain,
inch thick
Type E chips
Type D chips FIGURE 2.
3/4
Vol. 33, No. 4
VARIOUSTYPESOF WOODCHIPS( X4/6)
characterized by higher bursting strength, tear value, and pentosans, and by lower ether-soluble and lignin contents. Yield is regularly higher with the laboratory chips, and screenings are correspondingly lower. These differences can be largely attributed to the irregularity of chip size in the case of the rotary knife product as well as to the presence of the thicker wood units (Figure 2 ) . This effect is further demonstrated by other data that follow.
Control of Hydrolysis in Cooking Both papermaking strength and yield of sulfite hardwood pulps can be preserved more successfully by a change in cooking practice so designed as to repress hydrolysis of the cellulose and the pentosan groups. The beneficial effect is more pronounced with the less uniform mill-made chips than with the carefully prepared labora-
tory chips. This is to be expected when one considers that special means to assure uniform and complete penetration would have a greater influence on the less perfect chips. This modification in cooking procedure need not necessarily have an adverse effect on the bleachability of the pulps so produced. Of the several possible methods designed t o improve cooking, three are mentioned to illustrate the point. The adoption of a modified cooking practice depends largely upon a net balance of savings in yield and quality as contrasted to somewhat higher chemical costs and, in the one case, to the added inves&nent of apparatus. If we reduce the maximum cooking temperature and extend the total time of cook from a normal period of 10 hours to 16 or 18 hours, then because the combined sulfur dioxide has a better opportunity to penetrate the hardwood more completely before those temperatures are reached where more
INDUSTRIAL AND ENGINEERING CHEMISTRY
April, 1941
535 ~~
~
TABLE111. EFFECTOF CHIP DESIGNON PULPCHARACTERISTICS Wood s ecies" Wood atips typeb Yield, ,% Screenings 70 Freedom from wood shives Pentosans % Physical tksts ( 1 ) Bursting strength Tear resistance Ether-sol, % Lignin, %
White Birch A
B
44.4 1.8 Fair
46. 0.2 Good
Yellow Birch A B 44.4 45 1.6 0.8 Fair Good
8.3
9.3
7.8
8.2
117 130 1.5 1.4
125 140 1.1 1.3
92 0.6 '18 1.2
113 148 0.45 0.9
Rock Maple B 43.4 44. 0.8 0.4 Good Excellent 7.2 7.6
White Maple B 43.2 44 0.6 0.4 Good Excellent 5.4 5.5
A
B
41.9 2.5 Poor
42. 1.6 Fair
6.6
6.8
96
65 75 0.30 0.7
78 105 0.45 1.3
110 0.4 1.0
A
99 106 0.25 0.7
98
0.28 , 0.8 5 All seasoned wood the cooking conditions were the same as those shown in Table I b Chi s A made in k commercial rotary kpife chipper about a/4 inch long and l/s i o 8/4 inch Yength, and the plaques were then split t o a chip thickness of 1/s inch.
l/d
inch thick.
A
70 80
0.25 0.6
Beech
80
Chips B made in laboratory: the logs were sawed t o
TABLE IV. SINGLE-STAGE BISULFITE COOKS Wood species
White Birch
Mixed H a r d w o o s
A A B B A A A intense hvdrolvtic action occurs, less damage Wood chip typeto cellulose takes place and more of the ori& Ce&:o;D& Combined%80%.% 5 5 5 4 5 5 5 nal pentosans are retained in the pulp. The 1 2 2 3 1 2 1 Na Na '/zCa-1/aNaC N a Na Na Na combined sulfur dioxide once in place Serves as Eyzbined soz based on dry 6 12 12 15 6 12 6 a buffer against excess hydrolysis without interMax wood temp,equivalent, c, Yo 140 -140 140 135 140 140 118 fering with delignification. When the maximum Time of cook hr. 8 8 8 10 8 8 14 4 4 4 3 4 4 2 temperature is reduced to approximately 125" C. ~;$$,O~~.$~~;, gage 75 75 75 75 75 75 65 45 49.6 49. 52. 44 49 46.8 (257' F.), that temperature should be reached &i;i:~~%~ % 0.2 0.2 0.3 1.0 1.2 0 . 8 0.8 in not less than 6 hours and the cook should Pentosans'$ 9.2 12.4 12.0 13.0 7.2 10.80 9.0 continue for a total period of about 12 hours p%f$$$:rength 122 155 143 152 98 133 106 125 120 116 130 122 136 123 or more, depending upon the species of wood cT l ;g[;;% 5 5 5 6 5 5 5 and the pulp bleachability that is sought. a See Table 111. Higher yields and superior pulpmaking propComprised about equal percentages of white birch yellow birch, rock maple, and beech. The combined SOz is present in equal amounts as the sodium and the calclum salt. erties can also be realized without extending the time of cook if other provisions are made to preserve the pentosan by repression of exWhite birch was converted into type B chips. The chips cess hydrolysis. We can, for instance, hasten the penewere submerged in a 10 Per cent sodium sulfite solution at 100" tration of acid salt and simultaneously ensure the presence of C. (212" F.) and with an applied ressure of 100 pounds er square a sufficient quantity of the bisulfite to Serve as a inch gage for 4 hours. The free Yiquor was then drainex from the buffer material if its concentration in the cook liquor is treated wood, which at this stage contained about 5 per cent of combined sulfur dioxide, based upon dry wood. Cold, 5 per increased beyond the usual percentage. When this is done, cent, free sulfur dioxide solution was added to cover the wood, we can adopt maximum temperatureof 1350 to 1400 and the temperature was raised to 135' C. (275" F.) in 2 hours (275" to 284" F.). and held there 4 hours. Under such conditions pulping occurs A third alternative that may be adopted for improved readily, and there was a yield of approximately 50 per cent. The pentosan value of the p u b was 11 per cent, and the physical yields rests upon the general principle of positive placement strength compared favorably with that which can be obtained of a calculated and necessary amount of sulfite salt within in a single-stage cook and with an acid that contains 2 per cent the Wood chip before the free Sulfurous acid itself iS added combined sulfur' dioxide. The bleachability of the presoak to the charge. I n such a sequence the chips are first Precook product is equal to that of the single-stage cooks that were made with the Same type of wood. soaked under pressure with alkali sulfite, bisulfite, or with a suitable base which will form bisulfite when it is later brought Use of Calcium-Base Acids in contact with the sulfurous acid. The concentration of the Inasmuch as the cost of manufacture of sulfite pulp is in presoak liquor is so adjusted that subsequent drainage of part dependent upon the cost of the base that is used in the liquor will leave within the chip from 3 to 6 per cent of compreparation of the bisulfite solution, it is natural that the bined sulfur dioxide equivalent, based on dry wood. The pulpmaker use the less expensive calcium salt whenever poschemical-containing drained wood chips are then covered sible. Unfortunately, the calcium-base liquors possess some with a 3 to 6 per cent sulfurous acid solution. The temdisadvantages that frequently result in secondary losses which perature can be raised to a normal level as rapidly as pracmore than offset the initial savings. This is particularly true tical, inasmuch as the combined sulfur dioxide is already of Bardwood and can be attributed to the lesser rate of penein place and no destructive hydrolysis can take place. By tration of the calcium salts and to the unavoidable presence this two-step sequence the entire procedure need require no of calcium sulfate. With the denser woods the difference in more than a total of 10 hours to complete the pulping. This behavior of the calcium bisulfite and the more costly sodium presoak cook process can be applied advantageously to both and ammonium bisulfite is marked, and that difference is softwood and hardwood (Figure 3). exaggerated whenever the wood chips are thicker across the Table IV illustrates the advantages that can be gained by grain than inch. The heaviest woods, such as the beech adoption of the modified single-stage cooks described above. and rock maple, which sometimes reach a density of 45 pounds I n all cases the higher yield is accompanied by a higher of dry wood per cubic foot wet wood, offer a greater problem pentosan content in the pulp and a higher level of bursting than do some of the faster growing birches that have a corstrength. The tear values are slightly lower, as is to be exresponding density figure in the neighborhood of 35 pounds. pected whenever the acid sulfite process is so carried out that It is well known that the rate of penetration of the sulfite more of the original pentosans are retained by the pulp. salt can be hastened by raising the free sulfur dioxide conA single example of the presoak sequence will show the centration beyond the conventional 5 per cent, and expericonditions under which such a cook can be carried out sucmental cooks were made to demonstrate that the cooking cessfully : ~
c.
536
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE V.
Vol. 33, No. 4
PERFORMANCE OF SODIUM AND CALCIUM BISULFITE LIQUORS WHENUSEDTO PULPSEVERAL WOODSPECIESOF DIFFERENT DIMENSIONAL FORM" Sodium-Base Acid 7 Spruce: Original Log, 11.6 Inches in Diameter, 90 Annual Rings
7
Chips Length, in. Width, in Yield, Screenings % Freedom fr'om wood shives Pentosans, Yo Physical tests Bursting strength Tear resistance CI requirement, R
vc
Calcium-Base Acid
3/4
1/4
'/a
I/a
45
Trace Good 5.2 159 155 6.0
163 181 6.5
150 188 7.0
188 186 6.5
155 174 6.0
146 146
6.0
161 147 6.5
157 152 6.5
138 212 7.0
164 145 6.5
2 l/E
43.3 2.5 Good 4.8
44.0
145 168 6.5
136 143 6.8
'/a
2
1.4
Fair 4.5
Fir: Original Log, 8.8 Inches in Diameter, 65 Annual Rings Chips Length, in. Width, in. Yield, % ' Screenings % Freedom from wood shives Physical tests Bursting strength Tear resistance C1 requirement, 70
3/4
'/a
47.1 Trace Excellent 168 220 6 0
a/4
l/4
2
3/4 1/2
48.4 0.6 Good
42.0 5.5 Poor
49.3 0.9 Good
48.4 None Good
168 221
163
169 197
156 198 6.6
209 6.5
6.5
6.5
a/a
'/a
]/a 50.0 0.8 Good
42.8 8.0 Fair
153
169 187 7.0
166 204 7.0
49.9 None Excellent 192 6.0
i2.8 20.0
Very poor 167 172 7.5
1/2
>/a
'/4
'/S
46.6 3.2 Fair
52.9 0.6 Fair
49.8 0.8 Good
157 201 7.0
7.0
164 172
147 189 7.0
White Birch: Original Log, 11.5 Inches in Diameter, 106 Annual Rings Chips Length, in. Width, in Yield % Screehings, % Freedom from wood shives Physical tests Bursting strength Tear resistance C1 requirement, ' 70
3/4 1/8
47.6
Trace Good
47.2 1.0 Fair
122 157
115 167
4.0
4.0
40.6
5,s
Very poor 100 156 5.0
Beech: Chips Length,,in. Width, in. Yield % Screehings 7 Freedom f;om wood shives
44.7
Physical tests Bursting strength Tear resistance C1 requirement, %
3/4
3/a
'/a
'/a
47.2
Trace Good 113 168 4.5
47.4
2
'/a
'/a
1/8
48.2
Trace Trace Excellent Excellent 124 168 4.0
113 142 4.0
46.9
40.8
i'l.9
l/a
47.7
0.8 Good
46.8 0.3 Good
5.0
129 161
103 135 5.0
L/a
2
2.1
7.5
Poor
Very poor
42.6 5.0 Poor
129 168 5.5
107 153 6.0
110 161 6.5
96 157 5.0
Poor
14.2
2
'/2 1/4
'/4
l/a
Original Log, 11.2 Inches in Diameter, 107 Annual Rings
0.3 Fair
38.1 7.7 Poor
Bir 32.9 19.4 Very poor
90 140 5.0
86 130 6.5
83 137 6.0
'/Z
1/4
i/4
'/a 43.4
40.1 5.1
Poor
129 5.5
1.0 Fair
88 134
5.0
2 '/a 45.1 0.6 Fair
kt.5 11.0 Poor
83 115 5.0
98 142 6.0
=/a
3/4 1/4
3/4
'12
I/ 2 '/4
l/a
'/a
41.4
22.7 28.9 Very poor
14.8 41.3 Very poor
25.4 24.2
13.0
5.0
84 126 6.0
57 91 6.5
81 120 6.0
89 128 5.6
78 111 6.0
Poor
32.4
Poor
Poor
Rock Maple: Original Log, 8.35 Inches in Diameter, 104 Annual Rings Chips Length, in. Width, in. Yield % Screehings % Freedom fr'om wood shives
48.0 0.2 Good
l/&
3/4
7.0
Poor
19.3 Very poor
Physical tests Bursting strength Tear resistance C1 requirement, %
104 121 4.0
96 123 4.5
80 171
1/2
S/4
'/a
41.3
iG.2
5.0
it.3 2.5
'/a >/a
2
a/a
311
Good
k$.l Trece Good
42.8
Poor
47.4 0.2
104 116 4.5
107 127 4.0
103 106 4.0
87 116 5.0
4.5 Poor
iS/4 /4
27.3 25.5 Very poor
9s
112
5.5
1/1
1/2
'/a
I/( '/4
2 1/a
18.3 39.7 Very poor
27.9 23.2 Very poor
41.4 6.1 Poor
42.2 3.2 Poor
106 132
98 75
94 120 5.0
5.0
5.5
5,O
114 110
"All cook acids contained 5% free 602, 1%combined SOz, 6% combined SOa based on dry wood content in chip charge: oooking curve, progressive increase in temperature t o 140' C. in 5 hours a n d held there 3 hours; maximum pressure, 75 pounds gage.
acid with the higher free sulfur dioxide content will improve the result that can be obtained with the calciumbase acid. Table V indicates the degree of difference in yield and quality of hardwood pulp, depending upon the selection of the sulfite base and the type of wood chips employed. Table VI shows figures obtained when laboratory-prepared thick white birch chips were cooked under several conditions with calcium-base acids. Table VI1 comprises data obtained when mill-made chips were sorted to size and cooked with both calcium- and sodium-base liquors. A close examination of Tables V, VI, and VI1 reveals the following: 1. The importance of chip dimensions is clearly demonstrated. If the chips are sufficiently thin, then length is immaterial. On the other hand, chips that are more than I/g inch thick require the dimension with the grain t o be relatively short to assure satisfactory pulping. Thinness of chips is even more important with a calcium-base acid than when sodium bisulfite solutions are used. Chips produced in a commercial rotary knife cutter are ununiform, both in regard t o length and thickness. Here also the cooking data
show that the smaller chips that are screened from the runof-the-mill product are more easily pulped, and that the large units separated in a similar fashion give poor results when cooked in the same manner separately. The evidence supports the conclusion that under the cooking conditions adopted in this series, sufficient lateral pentration of the sodium bisulfite occurs with the thinnest chips, regardless of length. Thicker chips must not exceed a length beyond which the end penetration is incomplete. 2. The calcium-acid sulfite liquors perform less favorably even with those chips which are only I/s inch in thickness, and that difficulty is exaggerated in the case of the denser beech and rock maple. 3. When the wood units are 1/4 inch thick, there is a greater difference in the behavior of the sodium- and the calcium-base acids. With chips 1/4 inch thick and "4 inch long, the sodium acids penetrate the softwoods and the birch sufficiently well in the allotted time t o assure a fairly satisfactory pulping result. Under similar conditions poor results were obtained with beech and with rock maple. Chips of the above size gave unsatisfactory yields with all species
INDUSTRIAL AND ENGINEERING CHEMISTRY
April, 1941 TABLE VI.
537
EFFECTOF CHANQE IN CURVE WHENCOOKING THICKWHITEBIRCHCHIPSWITH CALCICM BISULFITELIQUOR^
hlax. pressure, lb. Y%Y% Screehings, % Grade Physical tests Bursting strength Tear resistance
75 29.4 18.3 Very poor 78 142
75 30.8 15.2 Poor
75 39.6 7.0 Poor
50 97
100
75 38.6 2.4 Very poor 47 84
141
42.4 1.8 Poor 96 143
75 23.5 29.6 Very poor 69 71
75 38.4 8.1 Very poor 44 79
39.6
7.1
Very poor 60 74
a Cook acid contained 5% free SO2 1% combined SO2 (all calcium base), 5% combined SOBbased on wood. log rings 57. log diameter 10.75 inches. Initial pressure(wa8 50 poGnddgage. The timperature ourve b Nitrogen pressure was applied t o the di ester contents ?t the beginning t o assist penetration. of the previous cook was fqllowed,. T h e &ester was relleved when increased temperature brought total pressure t o 75 pounds. This maximum pressure was maintained by progressive rellef as temperatures were further increased.
TABLE VII.
COMPARISON OF SODIUM AND CALCIUM ACIDSWITH MILL CHIPS"
maple chips were reduced to a 1/4-inch length. It is evident that with such thicker chips the 8 end penetration of acid salt plays an all-important 4 4 43.0 36.0 role, and that the wood structure determines the 0.6 9.0 ease of the end penetration under given condi87 80 92 82 82 82 97 80 tions. As already noted, the calcium bisulfite 118 106 118 110 120 92 121 118 solutions have a definitely lower penetration a Mixed hardwood chips containing approximately equal amount? of white birch, yellow Coefficient. birch, beech, a n d ma le were used. Chipp were made in rotary kn!fe chipper. Except as noted, cooks were mas, with acids contalning 5% free 802,1% combined 902. Cook curves 4. penetration of salt and yields specified 140° C. maximum temperature 75 pounds maximum gage pressure. b Chips A, unsorted as delivered thr&h a rotary knife chipper t o the mill chip loft, Can be favored somewhat by adopting a cookohips D , same as A b u t sorted t o contain only, those t h a t refuse t o pass through a l-inci ing procedure that promotes penetration before screen; chips E ,s+me as A b u t sorted t o contain only those t h a t pass a s/Anch screen and are held on a l/z-inch screen. the higher temperatures are reached. This can c Contained 8% free 602 and 1% combined SOz. be accomplished by a modification in the temperature curve whereby the charge is held at some intermediate temperature for a few hours before the higher temperatures are reached, or it may be done of wood when a calcium-base acid was substituted for the by application of artificial pressure during the early stages of sodium bisulfite mixture. the cook. Table VI illustrates the degree of improvement I n general, with the temperature curve adopted, lateral in results when using thick chips and a calcium-base acid. penetration of cooking reagent is insufficient to carry bisulfite to the center of the thicker chips before destructive hydrolysis occurs. Hence, with such thicker chips it becomes necessary to resort to a lesser grain dimension to assure adequate travel of the acid salt through the ends or with the grain. With the 1/4-inch-thick chip, a reduction of length to between l/* and '/4 inch results in satisfactory pulping of the rock maple and beech when sodium bisulfite acids a r e used. T h e calcium-base liquors, however, fail to give a satisfactory pulp even in those cases where the thick beech and rock Wood ohip typeb Acid base Total time, hr. Hr. t o max. temp. Yield Yo Scree.hings, % Physical tests Bursting strength Tear resistance
A
A
Na 8
Ca
A
A
D
D
E
E
Ca 1 0 6 41 0 3.5
CaC 1 0 5 43.3 1.6
Na 8 4 41.4 3.4
Ca 8 4 32.9 13.0
Na 8 4 43.7 1.0
Ca 8 4 40.0 3.5
538
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 33, No. 4
and sheeted than does the corresponding pulp obtained from the heartwood by an identical White Birch Spruce cooking procedure. No satisfactory explanation Wood specie6 Chip" aource SapHeartSapHeartSapHearthas been reached. I n some direct comparisons wood6 wood6 woodo woodo woodo wood0 the average fiber length of the sapwood pulp is Yield. yo 44.4 43.2 47.7 46.0 47.7 46.7 Screenings, yo 2.1 2.0 1.0 1.0 0.3 0.2 definitely greater than that of the heartwood Absence of shives Fair Fair Good Good Excellent Excellent product. This is not always the case, however. Ether-sol., '32 1.68 2.59 1.22 1.78 .... .... Pentosans, Yo .. .. 5.73 10.68 4.3 4.5 The fact that heartwood was once sapwood would Lienin. % .. .. 0.80 1.13 0.47 1.37 Prysiiai tests suggest that the difference in properties of the 125 112 156 155 111 52 Bursting strength two pulps may be largely accounted for by 183 143 190 116 Tear resistance 252 187 C1 requirement, % 5 6 5 6 5 6 chemical differences that take place as the All chipa '/iinch long */# inch thick heartwood is formed and may indirectly inb Acid contained 5% iree €301, 1% bombined 80s (sodium base), 5% combined SOz fluence the hydrolytic effect on the cellulose t h a t based on wood: cooking curve, to 135' C . in 6 hours, held there 4 hours; 75 pounds maximum pressure. occurs during a cook. c Acid oontained 5% free 50s. 17' combined 801 sodium base), 6% combined SO, based on wood: cooking curve, t o 1408 C . in 4 hours, h h d there 4 houra; 75 pounds maxiBoth softwoods and hardwoods yield regularly mum pressure. a sapwood pulp that bleaches more easily than does the corresponding heartwood pulp. Table VI11 shows some of the values obtained with spruce and with white birch. The yellow birch and the 5. When cooking the heterogeneous lot of mill-prepared wood chips, an increase in free sulfur dioxide from 5 to 8 per beech behave similarly. The bleachability of these several pulps parallels the respective lignin content and it, in turn, is cent renders the calcium-base acid almost as effective as a directly related to the lignin found in the original heartwood sodium-base liquor that is made up a t the lower free sulfur and sapwood (2, Table V). dioxide level. Table VI11 also shows that where values were established, 6. Improper penetration of the combined sulfur dioxide the heartwood pulps are richer in pentosans and in etheringredient of the cook liquor during the early stages of the cook results not only in reduced yield and a high percentage soluble content. Wood analyses give no positive indication of screenings, but also causes a marked sacrifice in physical that we should expect the pentosans to be in that order but show ample evidence that the ether-soluble content should tests and in cleanliness of screened pulp. be higher in the heartwood pulp. 7. Less complete penetration of the acid salt into the larger chips is responsible for the greater demand for chlorine or its equivalent when such pulps are converted into bleached Acknowledgment products. This is clearly demonstrated with all species of The author is indebted t o C. W. Thing, M. W. Hayes, and wood investigated. The results simulate those obtained D. H. McMurtrie for their help in supervising the experiwhen an attempt is made to cook wood chips with an initial mental cooks and the analyses. liquor that is deficient in the bisulfite salt. TABLEVIII. COMPARISON OF SAPWOOD AND HEARTWOOD
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Comparison of Sapwood and Heartwood Experimental cooks have shown repeatedly that pulp made from sapwood has a higher tear resistance when hydrated
Mildew-Resistant Treatments on Fabrics KE deterioration of cotton fabrics due to the growth of mildew causes enormous loss, both industrially and in the household. Sometimes mildew merely discolors the fabric or gives it a musty odor, but more often mildew actively attacks the cellulose and causes considerable loss in fabrio strength. Certainly any method which will prevent such growth will markedly increase the durability and utility of the fabric. Thus a mildew-resistant fabric would have increased value to the consumer.
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1 Present address, Western Regional Research Laboratory, Bureau of Agricultural Chemistry and Engineering, U. 6. Department of Agriculture, Albany, Calif.
Literature Cited (1) Richter, IND.ENG.CHIM.,23, 266 (1931). (2) Ibid., 33,75 (1941).
MARGARET S. FURRY AND HELEN M. ROBINSON U. S. Bureau of Home Economics, Washington, D. C.
HARRY HUMFELD' U. S. Bureau of Plant Industry, Washington, D. C. Chemical finishes can be applied to cotton fabrics that will give adequate protection against mildew development. However, for general utility these finishes must have other desired characteristics. They must be comparatively easy to apply; they must not decrease the strength of fabrics or cause excessive shrinkage; they should withstand weathering and repeated laundering; and they should be colorless, odorless, and nontoxic to human beings. At the Bureau of Home Economics, investigations were undertaken to obtain satisfactory treatments for making cotton resistant to mildew. This paper reports an exploratory survey of finishing treatments which were considered of possible value as mildew preventives. Included in the study
