A PULP-PRODUCING CENTER
Relative Permanence of Papers Exposed to Sunlight. I1
GEORGE A. RICHTER Brown Company, Berlin,
OW
N. H.
HEN paper is exposed to sunlight, oxidation occurs in no uncertain manner. The paper loses physical strength, and definite cal groups, although a comparison of interrelated groups is quite permissible, since the exposures were all made over the chemical changes take place as evidenced by an increase in same general time period. The exposures extended from copper number of the cellulose, a drop in alpha-cellulose November 1, 1932, until February 20, 1933, and were made content, and a marked decrease in the viscosity of the fiber when dissolved in cuprammonium solutions. The extent of a t Shawano, Fla. The usual precautions for protecting the paper samples adequately during periods of nonexposure were the changes that result depends largely upon the character observed ( 3 ) . As in previous work, full weather data are of the fiber comprising the paper and upon the presence of secondary ingredients such as rosin, alum, etc. Many data have already This article is a continuation of the general experimental study been reported in a previous article (3). of the stability of paper when exposed to natural sunlight. Various In view of certain omissions and a few inconsistencies that appear in the means of retarding the usual rapid degradation of paper when report Of the previous series of exposed to sunlight were attempted. The study also includes the exposures, a much more comprehensive use of accelerants to promote oxidation of cellulose in the presprogram was inaugurated. Inasmuch ence of light rays. The experimental findings available at this as the schedule comprises a relatively time are summarized and various suggestions are offered for future large number of items and attempts t o cover several phases of the general probinvestigations. lem, the data will be presented in logi432
APRIL, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
'
available although such detailed information is not attempted in this review. Daily maximum temperatures ranged from 70" to 90' F. (21' to 32' C.) with most days averaging a maximum of about 80" F. (27' '2.). As in the case of previous studies of the permanence of papers that have been made in the Brown Company laboraTABLEI. EFFECTOF SUNL~GHT EXPOSURE ON PAPERS Puri- Purified fied SUI- Sul- Wood Wood Rag Rag Rag fite fite Fiber Fiber Bond Bond Bond Bond Bond Bond Bond No. 1" No. 2a No. 3" No. l b No. 2b No. la No. 2' Mullen pop test: Original Exposed Retention, %
119 107 90
117 108 92
127 116 91
60 59 98
86 84 98
133 113 85
128 135C
AY. tear, grams: Original Exposed Retention, %
83 72 87
82 78 95
86 86 100
58 86
50
43 41 95
97 90 93
98 93 95
Tensile strength (with machine)d Original 19.3 Expqsed 18.1 Retention. % 94
19.5 17.6 90
19.3 18.8 98
12.8 12.6 98
19.9 19.1 96
18.4 16.9 92
17.9 16.4 92
Stretch (with machine), %: Original Exposed Retention, %
3.53 2.98 84
3.35 3.45 103
1.32 1.27 96
1.69 1.79 105
6.24 4.81 77
6.15 5.88 96
25 9
38 1
30 0.8
44 3
3.5 0.2
4.5 0.7
Ink penetration: Original Exposed
3.32 3.42 103 120f 2
...
All rag and purified wood fiber papers were rosin-sized in the beater and were then glue-sized and air-dried. bThe sulfite papers were rosin-sized in the beater and starch-sized in the machine tub. C Apparent increase. d In pounds necessary t o break a strip of the paper 0.5 inch wide
433
that usually attends the application of a surface sizing with glue. Some types of paper increase tremendously in fold values when they are heavily glue-sized. It is generally believed that this fold improvement is of a more or less temporary nature and that the gain in fold value is sacrificed quite readily when the paper is aged for periods of time. It is conceivable that, although the sacrifice in fold value will be more marked in the case of a glue-sized paper, the ultimate fold value after exposure may, nevertheless, still exceed the fold value of a similarly exposed and corresponding paper that has not been glue-sized. It was intended that a comparison should be made between two sets of papers that had enhanced in fold value to widely different degrees by the application of surface glue. Final results revealed that the two sets of paper were not widely different in character. As shown in Table 11,the slight differences in fold retention are, however, in the right order, and these differences add testimony to the belief that the folding strength developed by means of the cellulose gel itself and because of the knitting of the fibers in the base sheet is most important.
Group I11 In series 111, Table N of the previous article (3), there is preliminary evidence that a purified wood fiber paper suffers less loss in folding endurance by sunlight exposure when it is protected by uncoated Cellophane and also by glass. Inasmuch as direct sunlight can play a major part in the degradation of paper, it was deemed advisable to obtain confirming data on this subject of adequate protection by glass. In this set of experiments three types of paper were included: (a)
Waterleaf paper made from purified wood fiber.
(a) Waterleaf paper made from sulfite pulp.
tories, all physical tests were conducted a t 45 per cent relative humidity. The chemical tests were made according to procedures described in a previous article (1).
Group I Earlier work had given evidence that the tear test, the tensile strength, and the pop test are affected much less than are the fold figures when papers are artificially aged in circulating air a t 100" C. (9). The same relationship between physical tests of stability exists when papers are subjected t o sunlight exposures. This is well illustrated by Table I. Several commercial papers were selected for the purpose, and sunlight exposures were made for 50 hours on each side. I n those cases where an increase in test is recorded, it is reasonably safe to assume some inaccuracy in the test. It is fully demonstrated that papers of the types in question suffer relatively little decrease in tear values or in tensile and pop tests when exposed to the sun. Ink resistance is profoundly affected as in the earlier work. It is of interest to note that the rosin- and starch-sized papers are as sensitive to changes in writing quality as are the glue-sized sheets. Whether other sizing agents are less affected by exposure to light rays remains to be determined. It is quite conceivable that a special post-treatment of a glue-sized paper with formaldehyde vapors or with chromic salt solution would result in improved retention of writing qualities when such paper is exposed to the sun's rays. The use of the various artificial resins as sizing agents may reveal outstanding stability in the case of one or more of them.
Group I1 Although the full purpose of the experiment that involved the second group of papers was not quite realized, the results are sufficiently interesting to report. The program called for a study of the permanence of the fold endurance increment
(c) Unused newsprint that contained about 85 per cent groundwood.
The protected sheets were supported on each side by plates of ordinary window glass of 2.5 mm. thickness. Two exposures were made, one for 50 hours on each side, the second for 100 hours on each side. As shown in Table I11 and graphically in Figure 1, the sunlight exposure caused definite deterioration of all three papers, even when covered with window glass. The glass did protect the purified wood fiber TABLE11. EFFECT OF GLUE-SIZING ON DEGRADATIOX BY FLORIDA SUNLIGHT Sample
(All papers exposed 50 hours on each side) 10610 1061-Gb 10SSC
1088-Gd
Mullen pop test: Original Exposed Retention, %
117 111 95
133 113 85
116 109 94
128 135.
Av. tear, grams: Original Exposed Retention, %
119 105 88
99 90 91
123 111 90
98 93 95
15.2 14.4 95
18.4 16.8 91
15.6 15.0 96
17.9 16.4
1421 694
1653 776
1444 628
1653 1152
l--"" lxn
1059 612 69
104s 542
1081 746 65
Tensile strength (with machine) : Original Exposed Retention, 70 Fold endurance: Original: With Scross Exposed : With .. ..._ Acroas Fold retention, 70
603 82
77
...
...
A machine-made paper from a furnish of purified wood fiber and purified leaf fiber (beater-sized 1 . 0 7 rosin, and 0.7% glue). b Same as 1061 after dub-si& with glue; glue content inoreaaed to 2.26%. Similar to No. 1061, except rosin = 1%; glue = 0.5870. d Post-treated as in 1061-G; final glue content 2.44%. 6 Apparent increase. a
-
VOL. 27, NO. 4
INDUSTRIAL AND ENGINEERING CHEMISTRY
434
carbon dioxide tubes were additionally protected against water and oxygen by enclosing in them fresh sodium. After these tubes were sealed, they were heated at 90’ C. for 2 hours. The oxygen tube was kept dry by meam of activated alumina held in a wire container. During the exposure the tubes were rotated every 2 hours in order to distribute the light rays properly. Total time of exposure was 100 hours. Folds were made in the machine direction only because of the limited amount of sample. Table IV includes the important data. The hydrogen protected the purified wood fiber paper perfectly but did not prevent some loss in fold in case of the sulfite sheet. The visible spectrum that passes through the glass appears active and causes changes in the sulfite sheet even in the absence of oxygen. The fact that the copper number did not change appreciably, even though the sulfite paper suffered loss in folding endurance, may signify other major chemical changes than those ordinarily caused by oxygen. The purified wood fiber paper, on the other hand, is less sensitive to the visible light when oxygen is not mesent. It would REWINDERSI N THE MACHINEROOMOF A PAPERMIL,L prove of interest and valie t o d e t e r m i n e whether the ultraviolet rays would attack the highly purified cellulose in the absence of oxygen. Such an exmaterially and the sulfite sheets to a lesser extent, but proved periment could be conducted by means of transparent quartz of no protection whatsoever in the case of the newsprint. The yisihle part of the spectrum is evidently responsible for the tubes. action of light on newsprint. Whether the small percentage of repins present in the newsprint sheet can account for any TABLE Iv. E X P O S OF ~ EPAPER TO SUNLIQHT IN GLASS TUBES IN PRESENCE OF VARIOUS GASES of this vast difference in behavior is questionable. The Waterleaf Purified Waterleaf Sulfite changes in folding endurance, the increase in copper number, Gas Wood Fiber Paper Paper and the decrease in viscosity are quite consistent. in Fold re- Copper Original Fold re- Copper Original Tube tention No. copper No. tention No. copper No. Past experience h a < indicated that oxygen is necessary for % % degradation of cellulose when exposed to light. T o check HZ 98 1.86 1.78 66 3.7 3.7 this further, the investigation was extended to include expoCOZ 90 2.10 .... 47 4.0 ... Air 90 3.1 .... 58 4.7 ... sures of two types of paper in glass tubes which had been preDry 0, . . . . . .... 42 4.2 ... Moist 0, .... 38 6 . 0 . .. 78 3 . 1 pared to contain various gases and vapors: A purified wood fiber waterleaf paper and a waterleaf sulfite Both papers suffered more damage in the presence of carbon sheet, in both cases similar to those used for the glass plate experiments, mere chosen for these trials. The samples were so dioxide. Whether this is the result of a n oxidation by the cut that, when slipped inside of the 32-mm. glass tube, the single carbon dioxide or of traces of gaseous impurities should be strip of paper just covered the surface. The tube was of ordinary determined by additional experiments. laboratory soft glass with walls about 2 mm. in thickness. The results in the case of the wet oxygen were as expected. The gases were taken from commercial cylinders. Replacement of air was quite thorough. The gas was led to the bottom Both fold endurance and copper number were seriously afof the large tube by means of a smaller one, and waste gases fected, showing that the visible rays can catalyze oxidation were led from the opposite end. After suitable time the flow under favorable conditions. Dry oxygen was somewhat less of gas was cut off and the tube was evacuated by means of a pump. severe although definitely reactive. The paper samples conThis cycle was repeated several times. The hydrogen and the VALUEOF WINDOW GLASS TABLE 111. PROTECTIVE
Time ezposure (each side), hr. Basis weight, lb.” pH: Original Expoeed
Waterleaf Purified Wood Fiber UnproGlass tected protected 50 50 100 52 4.6 4.4
..
..
4:4
4:3
Co per No.:
Waterleaf-
4.4
..
1.78 Briginal 130 . 90 Exposed 4.3 3:3 4:1 Viscosity: 1.05 0.75 Original 0:45 0:iO 0.55 Exposed 0.35 Fold. Original: 234 With 1094 Across 209 170 Ex osed: 42 623 594 719 tith 162 202 182 67 Across Fold retention, % 58 80 70 27 ounda of 480 sheets of paper, each 24 X 36 inches. 0 “Basis weight” is weight in b All of the folds in the case ofnewsprint in this series were made with reduced tension
.. ..
I
--Sulfite Unprotected 50 83
.. ..
Glass
protected 50 100
...
..
,.. 4.1
4:0
-NewsprintUnprotected 50 31 3.6
..
Glass protected 50 100
..
..
i:s
i:4
7:2
4.5 19.0
1i:o
23:o
b:i
0:45
....
....
.. ..
... ...
..
596, 412
.. ..
....
6:9
79 124 55
I
.
69 66 33
in the folding machine.
52 58 11
91 49 14
32 30 6
APRIL, 1935
INDUSTRIAJ, AND ENGINEEIUNG CHEMISTRY
435
tained in tubes that were filled with air ranked about with those that were maintained in an atmosphere of carbon dioxide, and suggest again that the carbon dioxide may have contained some acidic impurity. Similar experiments with sized papers are necessary to determine whether in the presence of rosin and glue even the highly purified fibers would deteriorate rapidly in air when exposed to the visible spectrum alone.
Group IV
It was thought that, if the papers could be adequately protected from light, air, and oxygen by means of an oil film, less deterioration would take place. A refined, medicinal petroleum oil was used for the purpose. Tbe types of papers recorded in the experiments of Table I11 were used. In all cases the sheets were well saturated with oil. After the sunlight exposure (50 hours on each side), the papers were extracted free of oil and compared with corresponding samples that had not been oil-soaked. Theresults are not recorded in tabular form, but in all cases there was no evidence of any protec-
CORNEROF
A
I'ULP-TESTING LABORATORY
paper, aiid urioaed newsprint were immersed in glycerol, and after complete penetration were ridof excess liquid by squeeze rolls a i d then exposed to the sun's rays for 50 hours on each side. Corresponding base papers that contained no glycerol were exposed simultaneously. The severc drop in initial folding endurance by the addition of the glycerol as well as a partial loss of glycerol from the sheets so treated (evaporation and seepage to supporting trays) makes it impossible to judge the degree of preservation in terms of folding endurance, but the copper number increase as determined on the original arid on the exposed papers shows that oxidation was retarded by the film of glycerol that coated the fibers. In all cases the glycerolated papers were extracted free of glycerol before determining copper number. Such water extraction may have removed small quantities of soluble reducing suhstances, but it does not seem prohable that the markedly lower copper number values of the sunlight-exposed glycerolated papers can he wholly explained by such removal of __...__~
TABLEV. EFFECTOF GLYCBROL ON PROTECTION OF PAPER FROM SUXL~GIIT DETERIORATION waterleaf Purified Wood Fiber
FIGURE 1. P n m ~ c m v sVALUEOF Wx~noru G U S S AGAINST SUNLIGHT
tiun by the oil. Both the fold losses and the increase in copper numbers were very little different from those in the case of the unoiled samples. Further work should he initiated with a pur$)ose of ascertaining whether other types of oil may offer better protection. The addition of a suitable alkali such as borax or ammonium carbonate in the base sheet or in the surface film may exclude the possibility of an acid state and may, therefore, prove beneficial. Such experimerits should he made with both waterleaf and with sized papers.
Group V It was thought that a neutral glycerol might prevent ready access of oxygen to the cellulose in paper. Therefore, samples of waterleaf puriiied wood fiber paper, waterleaf sul6te
Baais i ' 3 i C I i t . lb.: Untiented phper
Glyaerolated papers. usexyosad Glyceralated p8pcm emosed
GI ecral. %:
fr, unerpoaed p*peis In exposed pwem
Conper No.: Untreatd ~ n p e i a unexposed , Untreated papers, emosed
Glyeeroiatcd nspere, unexposed Glyaeiolatrd p81~eis.exposed
Wateilesi
Unused
Papor
Paper
print
Sulfits
52
43
66 59
52
2s 11
19
1.8 1.6
4.8
2.7
49
13
3.9
10.0 3.9 6.4
News31 3s 34
26 10 4.5
19.0 4.6 11.0
soluble m a t e d . TableVincludes theimportant data. blare work shoiild he done with sized papers in order to deterinme whether the glycerol will retard the accelerated deterioration that usually occurs in the presence of rosin. , A slight degree of alkalinity may prove particularly beneficial in the case of glycerol protection because of the tendency for glycerol to form acidic products when oxidized.
INDUSTRIAL AND ENGINEERING CHEMISTRY
436
TABLE VI.
PROTECTlON BY
A BtEse Paper 52.5
REGENERATED CELLULOSE, STARCHES, WAXES, C
5% Rosin Soln. 55.2 7.3
lv
D
Stearic Ac!d Soln. 53.2 0.69
E
1% Carnauba Wax Soln. 54.6 1.76
Basis weight, lb. Increase in weight, % . .. Fold endurance: Original: 951 541 714 722 With 1026 265 188 172 250 Across 215 After exposure: 366 444 495 132 With 537 198 63 143 180 Across 194 57.6 65.0 55.5 26.8 Fold retention, % 58.8 Copper No.: 2.2 1.9 2.0 Original 1.8 1.9 7.3 3.7 4.2 Exposed 4.3 4.3 These samples were extracted free of starch before making the copper number determination.
.
a
B Water Dip 52.7
Group VI The search for materials that would exert a protecting influence on papers when exposed to the sun's rays was continued. The base paper and the secondary reagents and method of application included the following: (A The base paper was waterleaf of purified wood fiber origin and irom the same lot that was used for the previous group of experiments. (B) , The original sheet was dipped in distilled water and airdried in order to serve as a blank for comparison with the other solution dips. (C) Waterleaf pa ers were immersed in a 5 per cent solution of rosin in alcohol anfthen dried. (D) The base paper was saturated with a 1 per cent stearic acid solution in alcohol and then dried. (E) The base paper was treated as in experiment D, except that carnauba wax was used. (F) The base paper was immersed in a 3 per cent solution of hydrolyzed starch No. 1. (G) The base paper was treated with a 3 per cent solution of hydrolyzed starch No. 2. (H) The base paper was treated with a 5 per cent viscose solution and cellulose was regenerated as described later. (J) The base paper was treated as in experiment H, except that a 2 per cent viscose solution was used.
VOL. 21, NO. 4
ETC., .4GAINST
G
SUNLIGHT H
J 2% Viscose Soln. 60.9 8.4
1082 566
1317 1127
1307 765
552 256 49.2
1129 1000 87.3
1009 485 72.2
2.1 3.7
1.9 3.9
F 3% Starch No. 1 55.6 5.7
3% Starch No. 2 56.0 7.7
1038 226 542 209 59.4 1.7n 3.4'
1.7" 3.3"
5% Viscose Soh 64.9 16.3
viscose-treated papers were striking. Fold retentions were increased from 58 per cent in the case of the untreated sheets to 87 and 72 per cent, respectively, in the sheets that contained regenerated cellulose. It is also noteworthy that the initial folds and the folding endurance of the exposed papers were also vastly improved. The copper number changes were in the expected order. The addition of rosin resulted in a marked sacrifice in stability. The increase in copper number was also of high order. As consistently found, the color of this rosin-containing sheet assumed a dark tan shade when exposed to light. A supplementary extraction with ether improved the color materially, indicating that most of the coloration is caused by changes in the rosin itself. Stearic acid and carnauba wax when present in relatively small amounts appeared to have no effect on the stability of the paper when so exposed. The physical state of the residual wax or fatty acid is probably of some importance. In new work some of the treated sheets should be subjected to the searing effect of a hot calender process, to approach more nearly the condition of a continuous film than can be realized by a simple deposit of wax from a solution. Then again a slightly alkaline condition may be necessary to make certain that the beneficial effect of film protection is not offset by the formation of acids during sunlight oxidation. No protection was experienced in the case of the two soluble starches. Table V I summarizes t h e r e s u l t s of this series, and Figure 2 illustrates the changes in physical tests graphically.
In the case of the rosin, stearic acid, and carnauba wax the sheets were thoroughly soaked, pressed free of liquor, and dried, The soluble starches were used similarly. In the case of the viscose treatments the sheets were immersed, p r e s s e d free of excess liquor, and then passed through a solution of saturated ammonium s u l f i t e , a n d c e l l u l o s e was finally regenerated by means of cold 1 per cent sulfuric acid solution. The regenerated c e l l u l o s e was then desulfurized by means of a 1 per cent sodium sulfide solution and thoroughly washed. The sheets w e r e substantially white in color. The original and the treated samples were all exposed to sunlight for 50 hours on each side as usual. T h e results obFIGURE 2. PROTECTIVE VALUE OF SIZE,STARCH,WAX, ETC., AGAINST SUNLIGHT tained with the
Group VI1 M o r e knowledge p e r t a i n i n g to the accelerated effect of sunlight on the deterioration of paper may suggest precautions that are necessary to obtain maximum life of manuscripts. With this as an object, two sets of samples were prepared and exposed to Florida sunlight for 50 hours on each side. Here again the same type of base waterleaf paper was chosen, and various s e c o n d a r y reagents were added
INDUSTRIAL AND ENGINEERING CHEMISTRY
APRIL, 1935
by a process of sheet saturation in dilute solutions of the materials in question. Most of the samples so treated were tested immediately after the treatment and also again after they had been stored in the absence of sunlight during the period that sunlight exposures were under way. This was done in order to determine more accurately the actual increased rate of decomposition of papers in sunlight. I n the case of the ferrous and ferric oxalate solutions, part of the sheets were immersed in a secondary solution of 0.5 per cent ammonia and then dried. The presence of the chemicals did not cause appreciable increase in copper number in those samples that were stored for the 5-month period in the abSence of sunlight, although the folds decreased somewhat in all cases. This small drop in fold test may be due in part to actual aging or, more probably, to an adjustment in the fold testers during that period. The fold retentions were calculated on a basis of tests of exposed papers us. stored papers, and, inasmuch as all of these tests were made on alternate strips of the papers in question and during the same testing days, the results are comparable. The sodium molybdate exerted a serious destructive effect, both in loss of fold and in rise of copper number. On the other hand, the sodium stannate appeared to have a real protective effect. The lesser acidity as measured by pH value may have been partly responsible for this protective effect. More work should be done with this chemical. The papers treated with magnesium hydroxide indicated improved stability, and such types of paper deserve further attention. ~ ~ _ _ _ _ _ _
TABLEVII.
~~~
437
exposures. In the case of the experiments listed in Table VI11 only the stored samples were considered in calculating the percentage fold retention of the sunlight-exposed papers.
Group VI11 The chemical changes that take place in the base cellulose fiber itself when exposed in air in the presence of sunlight are obviously of importance in the study of the general problem of permanence of various types of cellulose. Two samples were prepared in loose fiber form. The purified wood fiber was thoroughly disintegrated by means of a hammer mill in the dry state and air-floated t o form a loose mat about 8 mm. thick. A sample of absorbent cotton was prepared by drawing out the fiber in the form of a loose pack having substantially the same thickness. A third sample comprising raw cotton was likewise prepared. Each sample was enclosed between a coarse-mesh galvanized screen and exposed to Florida sunlight for 100 hours on each side. Changes that occurred in chemical tests are listed in Table E. -411 values show distinct evidence that oxidation has taken place by sunlight exposure. The alpha-cellulose value in the case of the purified wood fiber is considerably lower than was expected and may be attributed t o the fact that the determination was made on the mechanically ruptured product. It is well known that mechanical abrasion and the exposure of new surfaces results in a lower alpha-cellulose test when the usual procedure of this test is applied. The purified wood fiber remained uncolored
~
k2CELERATlNG
EFFECTOF VARIOUSCHEMICALS ox DEGRADATION OF WATERLEAF PAPEREXPOSED TO SUNLIGHT
-
0.001 7 0
0.2% 0.001% 0.001% 0.001-0.5% Ferric Ferrous Ferrlc Oxalate Sodium Molybdate-OxalateOxalateSoln., Followed --No ReagentSoh. Soh Soh. Soh. by Ammonia OrigiEX- OrigiEx- OrigiEx- OrigiEx- OrigiEx- OrigiEXnal Stored posed nal Stored posed nal Stored posed nal Stored posed nal Stored poaed nal Stored poaed 1668 1528 799 1789 1483 399 1735 1504 724 1698 1416 700 1526 1286 680 Total folds, with and across 1446 1303 756 Fold retention %: .. 52 .. 27 .. .. 48 .. . 49 53 Based on stired sample 58 91 48 83 22 87 42 83 41 84 44 . 90 52 Based on original sample 1.9 1.9 4.3 2.0 2.0 7 . 0 1.9 2 . 0 4.35 1.9 1.9 3.8 Coppe,r No. 1.84 1.78 4 . 3 1.9 1.8 4.2 Viscosity .. .. 0.85 0.35 .. 0.8 0.35 .. PH .. 4 : s 414 .. 4 : 4 412 .. 6 . 2 4 . 8 .. 4:7 4:6 4.6 4.4 .. 415 4:3
{Kite--
7
. ..
.. ..
..
7
.. ..
..
..
..
.
.. ..
..
::
EXPOSURES OF PAPERS TREATED WITH VARIOUS CHEMICALS TABLEVIII. SUNLIGHT 0.5%
No Treatment Total folds, with and across Fold retention, Yo
Stored 1303
i:s
4.6
ExDosed 756 5s
4.3 4.4
Ammonium Carbonate Water Dip Soln. EXExStored Dosed Stored posed 1216 675 1068 628 55 59 i:g 4.3 i:9 4.6 4.7 4.6 4.4 4.2
The iron salts were definitely catalysts of fold degradation. The very low concentrations of iron solutions used make it likely that this catalytic effect is more marked than in the case of the molybdate solution, where much higher concentrations were employed. The ferrous and the ferric salts showed no marked difference in their behavior. Future work should include experiments in which the iron salts are studied from a standpoint of promoting degradation of cellulose in the presence of rosin. It is also important t o establish a relationship between the percentage of inorganic accelerants present and the rate of degradation of papers of different types, when exposed to oxidation. The more durable papers will probably prove less sensitive to the presence of iron residues than will the sulfite and the groundwood products. It is also probable that ferric impurities will greatly hasten the oxidation of cellulose in the presence of rosin. Tables VI1 and VI11 summarize the important results of this group of
0.5%
Ammonium Acetate , Soln. ExStored Dosed 1130 716 63 i:s 4 . 6 4.8 4.4
0.5%
Zinc Acetate Soln.
ExStored 969 i:g 6.7
Posed 511 53 3.7 6.0
Sstd.
Magnesium Hydroxide Soln. ExStored Dosed 1211 776 64 i:9 3.7 7.7 6.0
0.2% Sodium Tungstate Soln. ExStored Dosed 1288 638 50 i:s 3 . 7 5.0 4.6
and illustrated again that degradation of cellulose can take place without a corresponding change in color. The cotton samples became slightly more yellow on exposure.
Group IX Indirectly related to the deterioration of cellulose when exposed to sunlight and air is the question of changes that occur when wood substance itself is so oxidized. Only a preliminary experiment was conducted, but the results are of sufficient interest to include in this article. An additional host of experiments suggest themselves. In this first trial thin slabs of wood were prepared. The general surface ran parallel with the grain and the sections were planed to a thickness of approximately inch. These veneer-like pieces comprised white birch, spruce, and poplar woods. They were exposed for 100 hours on each side in the usual manner. The exposed strips were scraped only to a depth of about l/lw inch,
438
TABLE IX. CHEM~CAL CHANGES IN LOOSE FIBERMATSDURING SUNLIGHT EXPOSURE Absorbent Purified Wood Cotton Fiber Stored Exposed Stored Exposed
Raw Cotton Stored Exposed e-Cellulose, % Decrease &Celldone, % Copper No. 7.14% aoda-sol., Increase Viscosity Color
VOL. 27, NO. 4
INDUSTRIAL AND ENGINEERING CHEMISTRY
98.7
..0.5..
%
0.98 3.15
.... .... .. ..
96.29 2.41 1.44 2.04 7.6 4.45
98.88
.. .
0.70 1.47 2.5
... 13.4 ...
95.5 3.38 3.76 2.30 11.9 9.4 2.4
92.0
.4.6 ...
1.08 8.1
.... 4.2 ... .
89.25 2.75 7.9 2.56 16.3 8.2 1.5 No
were then exposed to the sun’s rays for 100 hours on each side. Corresponding samples of the original pulp were stored away from sunlight and a t the end of the exposure period the stored and the exposed sheets of pulp were beaten in a laboratory beater under identical conditions. A marked change in fold endurance is apparent in Table XI. The tear value was less affected.
Group XI
There had been some indication that the cellulose samples had lost weight when exposed to the sun’s rays. This was checked by careful preparation of samples and by subsequent TABLEX. CHEMICAL CHANGES OF SUNLIGHT-EXPOSED WOOD exposure of such samples to sunlight. Exposures were made for 100 hours on each side of the respective sheets. Changes Spruce White Birch Poplar Original Exposed Original Exposed Original Exposed in weight were determined both on a bonedry basis and on a 6.2 25.2 5.2 Cppqer No. 15.7 3.5 19.5 basis of conditioned paper a t 45 per cent relative humidity. 28.14 28.20 22.80 20.20 Llgmn, % 24.56 15.85 The fibers studied included: (a) High-grade 100 per cent ra filter paper. the approximate limit of the color change. The scrapings (b) A waterleaf urified wood fber paper. were tested and compared with the unexposed wood. Table (c) Handmade sgeets of unbeaten, umized groundwood. X lists the results obtained. Color changes were very I n addition to loss in weight the groundwood sample was marked. The spruce turned yellowish brown, whereas the characterized by increased solubility in a boiling 1 per cent birch and the poplar became reddish brown. Had exposures caustic soda solution. been made so as to permit the action of rain on the surface, The results (Table XII) show a definite loss in weight in all the samples would probably have assumed the familiar cases, ranging from 1 to 2 per cent. The relative changes in weather-beaten gray appearance. Changes in copper number the case of the bone-dried and humidified samples are not were similar to those experienced with spruce groundwood absolutely consistent but of the same general order, neverthesamples that were exposed in other series. Sunlight oxidation less. It would be necessary to carry out a great many more attacked the lignin component of the wood quite definitely similar experiments before attempting to draw conclusions in the case of the poplar and the birch. This is interesting beyond the single fact that such samples appear to form gasebecause i t is well known that the lignin present in the deciduous reaction products to a measurable extent. Analysis of ous wood responds more easily to the usual alkaline pulping gases so developed would be of interest. processes than does the lignin of the coniferous wood. The exposed scrapings when put in water turned the solution a deep yellow, demonstrating the water-solubility of some of TABLEXII. Loss OF WEIGHTOB CELLWLOSIO OXIDIZEDIN SUNLIGHT the reaction products. SI;& yellcYwing
Sliaht yellowing
change
~~
ON SUBSEQUENT TABLBXI. EFFECTOF SUNLIGHT EXPOSURE BEATING PROPERTIES OF REFINED WOODFIBER
Stored Pulp a-Cellulose, % Coppef No. Viscosity Color
95.17 1.08 6.3
Exposed Pulp Sheets
92.15 2.1s 1.15
No change
After 100-Minute Beating Slowness Tear Strength, pop test Folding endurance
8.3 212 76 100
13.7 154 76 44
chemical changes in the unbeaten fiber will be reflected in the physical tests of papers that are made from the corresponding pulps. The damage so caused by overcooking or overbleaching, for instance, is well recognized by the pulp maker. The results obtained when such oxidation was induced by atmospheric exposure in the presence of sunlight confirmed the belief that the unhydrated fibers suffer profound changes and that the beating properties are likewise affected. A representative sample of unbeaten purified wood fiber was used for the purpose. It was formed into relatively thin sheets (50 pounds basis weight) and these uncompacted sheets
~~~~
Waterleaf Purified Wood Fiber $,per Paper Groundwood OrigiEx- OrigiEx- Origi- Exnal posed nal posed nal posed
Group X Although the results may be of no direct value to those who are primarily interested in the keeping qualities of paper in manuscript form, there is a certain value in the knowledge of the sacrifice that may be expected in potential strength that can be developed on beating when so-called half-stocks and pulps are subjected to aging conditions such as are typified by sunlight exposure. *Itis reasonable to expect that
~
Ra Filter
Bone-dry weight, grams Loss % WeiLht at 45% humidity, grams Loss on exposure, % Viscosity 1% soda-sol., %
249.0
246.0 1.2
263.5
259.5 196.5 194.5 1.51 .. 1.03 0.5 5.4 0.5
...
. ..
1.55
...
186 ...
.
...
...
183 234.2 1.6
...
... .253 ..
231 1.36 248 1.97
ii:o ii:i
If succeeding experiments confirm the finding that the groundwood loses no more weight when exposed than does cotton or other high-grade fiber, it will suggest that other major changes are more responsible for the severe loss in physical test and the increase in copper number that is consistently found when newsprint is exposed to natural sunlight. The great increase in 1 per cent soda-soluble matter reflects more clearly the great chemical changes that the groundwood has undergone.
Conclusions 1. When papers are exposed to sunlight, the sacrifice in tear strength, tensile strength, and pop test is minor compared with corresponding loss in folding endurance. 2. Rosin- and starch-sized papers when evosed to the sun appear a t least as sensitive to loss in writing qualities as are glue-sized papers. Special sizing agents are suggested for the production of papers that will withstand the action of the sun’s rays more successfully. 3. There is further evidence that, when the folding strength of paper is greatly enhanced by application of glue, the increment in fold is largely lost when such papers are exposed to the sun’s rays.
APRIL, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
SPRUCEWOODSTORAGE PILE FOR
Further study of the protection of paper from the sun’s rays by means of glass confirms previous results. The protective effect of gla5s is marked in the case of papers made from purified mood fiber. Sulfite papers are partly protected, whereas newsprint deteriorates as rapidly under glass a$ when exposed to the direct rays. Additional work is suggested. 5 , When purified wood fiber papers are exposed to sunlight in an atmosphere of hydrogen and protected by glass, there appears to be no degradation of the papers. On the other hand, the sulfite paper when similarly exposed does experience a loss in fold strength, although the copper number does not increase. When similar papers are exposed in glass tubes filled with oxygen, they retain 78 and 38 per cent of their original fold strength, respectively, and copper number changes are in the same order. When air is substituted for oxygen, the physical sacrifice is less severe, resulting in fold retentions of 90 and 58 per cent, respectively. Further work i s suggested 6. S o protection was realized from attempts made to protect paper from oxidation in sunlight by coating the sheet with a neutral mineral oil. 7 . There is further evidence that a glycerolated paper is somewhat less bellsitire to the sun’s rays than the unglycerolated sheet. Broad conclusions are not possible until more data have been accumulated. 8. Preliminary experiments indicate no improvement in sunlight stability of paper that has been surface-sized with various m-axes and starches. The presence of rosin is definitely harmful. As in previous work, a coating of regenerated cellulose prepared by means of properly applied viscose solutions proved highly advantageous, both in respect to actual fold drength and also fold retention. 9. The presence of sodium molybdate or of iron compound. in a waterleaf purified wood fiber sheet hastens deterioration of papers when exposed to sunlight. Sodium stannate appears to have a real protective effect. More work i.; nece-ary t o eGtablish whether such protective effects are
A
439
PULPMILL
obtained by virtue of antioxidant properties or whether such protection is realized because of slight alkalinity of the treated sheet. 10. It was demonstrated that unhydrated cellulose in the form of uncompacted pads will oxidize when exposed to sunlight. Alpha-cellulose, copper number, and viscosity of cuprammonium solutions reflect chemical changes that are to be expected. 11. Preliminary experiments with wood veneer strips prove that, when such surfaces are exposed to the sun, the copper number changes are very great, and in the case of poplar wood a marked delignification takes place. 12. Previous experiments demonstrated that chemical oxidation of cellulose, such as can be caused by the action of hypochlorite solutions, affects adversely the stability of papers produced from such oxidized cellulose. Sew work shows that, when unbeaten cellulose is degraded by the sun’s rays, it becomes impossible to develop the maximum physical tests in paper produced from the sunlight-exposed fiber after it has been hydrated. In other words, the cellulose fiber can lose a high percentage of its potential paper-making strength if it is allowed to degrade in sunlight prior to beating. 13. Waterleaf papers exposed to the sunlight for a 100hour period on.each side lose from 1 to 2 per cent in weight. It is conceivable that even greater losses will be experienced in the case of thinner sheets when so exposed.
Acknowledgment The author wishes to give credit to H. P. Vannah, under whose supervision the sunlight exposures were made in Florida. E. SV. Lovering prepared all samples, made all tests, and assembled all findings.
Literature Cited (1) Richter, G.A., IND. ENQ.CHEM.,23, 131 (1931). (2) Ibid., 26, 1154 (1934). (3) Ibid., 27, 177 (1935). RECEIVED November 20, 1934.
