FIGURE1. COMPARTMENT FOR STORING AND TRAYS FOR EXPOSURE OF PAPERS TO S U N
Relative Permanence of Papers Exposed to Sunlight GEORGEA. RICHTER, Brown Company, Berlin, N. H. HEN exposed t o air, The work to date has comprised This article deals with the first division of exm a n y organic coms e v e r a l s e r i e s of e x p o s u r e s perimental work on the relative permanence of pounds oxidize more over intervals of several weeks papers when exposed to sunlight. A large numreadily in the presence of sunand a t different times of the ber of commercial and specially prepared papers light. The wave lengths most year. This was done with the were exposed under various conditions, and a prer e s p o n s i b 1e in promoting the object of measuring discrepanchemical oxidation usually decies in d e g r a d a t i o n that can liminary attempt was made to correlate physical pend upon the nature of the maoccur because of differences in degradation with chemical oxidation. The study terial and the character of the light intensity a t different times included a search f o r means to relard the spoilchange that takes place. There of t h e y e a r . C o n c l u s i o n s age of paper exposed to light by prociding suitable is some indication, as will be eviand c o m p a r i s o n s of test data protection. Additions of chemicals and special denced in the experimental data, are mostly confined to respective that different types of cellulose, groups of samples e x p o s e d a t sizing agents, as well as physical protection by for instance, are peculiarly sensithe same time. As will be evicoverage, were attempted. tive to different regions of the dent, however, many additional sun’s spectrum. In some cases d e d u c t i o n s a p p e a r justified the visible and the longer ultraviolet rays are very destructive, in view of the similarity of results in the respective groups of whereas other usually more resistant celluloses are little samples exposed during different seasons. affected by the longer rays but suffer profound changes when Figures 1 and 2 illustrate the apparatus used in making the exposed to the short ultraviolet regions. For example, or- exposures. Provision was made for a storage compartment dinary newsprint depreciates rapidly in sunlight even when into which the trays that held the papers could be rolled durprotected by relatively thick layers of glass which absorb the ing periods of darkness and rain. The compartment was short ultra\-iolet rays of the sun completely, whereas a highly painted black inside. It was dust-proof and practically moispurified cellulose undergoes much less decomposition when ture-proof. Except for special experiments the sheets were protected similarly by glass. fastened to reenforced Celotex trays and exposed to the sun’s Since direct or diffused sunlight is ordinarily more respon- rays for a specified period. The sheets were then turned and sible for the spoilage of paper than is artificial light, it was again exposed so that the action of the light was applied on considered preferable to base conclusions mostly upon results both sides of the sheet. Daily hours of exposure and a tabuobtained by exposure of papers to the sun’s rays. A large lation of daily temperatures were recorded but are not fully number of supplementary studies were also made with the given here. As will be noted, the exposures were made durmercury type of light. This work with the artificial light ing all seasons of the year. may ultimately suggest a procedure that will permit a standSince the ultimate purpose of this investigation was to esardization of conditions of exposure as well as a more conven- tablish data and information that could be of value to the ient method for continuing the investigation in the labora- paper maker, it was considered important that the changes tory. in physical properties of the paper constitute an important Although the identification of samples and the actual meas- part of the study. Prior work has demonstrated that the soure of changes that take place were made in the research called folding endurance of paper is the physical test most laboratories of this company at Berlin, N. H., the exposures seriously affected by any of the common weathering agents; t o sunlight were carried out in Florida at the township of and although, as will be shown, the changes in pop test and Shawano, in the Everglade region west of Palm Beach. This tear values were determined in some of the sunlight series, it location proved to be convenient, and, in so far as it is favored was again found that the folding endurance is most sensitive by relatively long hours of continuous sunlight, it offers an and most indicative of physical degradation of papers. opportunity of conducting such tests within reasonable time Whenever possible, chemical changes were also recorded. periods, This was done in the case of so-called unsized waterleaf papers 177
178
INDUSTRIAL AND ENGINEERING
Sample No. Type of paper
1
CHEMISTRY
Vol. 21, No. 2
TABLEI. EFFECT OF SUNLIGHT ON SUEDPAPERS OF SERIES I
Basis weight Siaing agents
punfied wood fiber bond 43.1 Rosin
9a 100% purlfied wood fiber bond 45.0 Rosin and glue
10 100% purified wood fiber bond 42.0 Rosin
70 120
419 622
490 470
166 135
722 584
480 469
477 465
1 2 2
35 91 12
58 21 7
11 18 12
57 102 15
66 23 9
41 22 7
5 25% rag bond
100%
rag bond
4 100% rag bond
sulfite
7 100% sulfite
46.4 Rosin and due
29.6 Rosin and due
45.2 Rosin and glue
44.8 Rosin and starch
44.2 Rosin and starch
31 38
85 71
1
3 1 2
3 100%
rag bond
2 100% rag bond
43.5 Rosin and glue
44.2 Rosin and due
100%
Original fold: 1055 410 717 971 With 1214 428 982 904 Across Exposed fold: With 45 33 85 37 Across 64 41 77 58 Fold retention (av.), % 5 9 8 6 a Samples 8 and 9 are same base stock; 9 was glue-sized.
6
2 4
only, inasmuch as the sizing reagents present in commercial papers interfere with the accuracy of such determinations. In general, changes in alpha-cellulose, in viscosity, and in copper number appear to parallel the changes that take place in folding endurance, although there are a few inconsistencies which deserve further attention. The physical tests were made a t 45 per cent relative humidity. Methods of chemical analysis and physical tests are discussed in previous publications.‘ The usual procedure was to make tests of the unexposed and exposed papers at the same time. The unexposed papers were kept carefully stored in a cool, dry, dark compartment until the time when the exposed samples had been returned for examination and test. Fold determinations were made on several standard strips that had been cut both in the “with” and the “across” direction of the sheet, and averages were calculated therefrom. The tests determined up to and including Table I11 have a nomenclature as follows: “With” is the line of rupture in the machine direction of the sheet; “across” is the line of fold across the machine direction. From Table IV on, the nomenclature was reversed : “With” becomes the line of fold a t right angles to the machine direc-
Sa
100%
11 100%
purified wood fiber bond 61.0 Rosin
12
loo./,
purified wood fiber bond 64.7 Rosin and glue
13 100%
i,“f-
wood fiber bond 43.4 Rosin and glue
of the sample sheets. As is evident from the tabulated results, this treatment proved far too drastic and caused serious injury to all papers exposed. The relative changes in physical tests are, however, interesting and offer further testimony that the most resistant papers include those made from highgrade rag and from purified wood fibers. TABLE11. EFFECTOF SUNLIGHT ON WATERLEAF PAPERSO F SERIESI WITH No SIZEOR COLOR Sample No. Type of paper
14 Rag
Basis weight Orininal DH . Original fold: With Across Exposed fold: With Across Fold retention, % Copper No.: Original Exposed
34.7 5.2
15 Purified wood fiber 29.0 4.8
16 Sulfite 43.0 4.6
17 Purified wood fiber 42.0 4.8
21 27
9 3
184 110
761 1457
6 10 33
2
3 0 1
206 463 30
0.88 4.22
0
17
1.01 6.38
3.11 9.54
.. ..
The exposure test commenced January 27,1931. On March 25 the first 200-hour exposure had been completed, and the papers were turned and subjected to an additional 200 hours of sunlight on the reverse side. The second exposure was c o m p l e t e d May 22, 1931. The treated s h e e t s w e r e carefully wrapped, packed, and forwarded to New Hampshire f o r i n s p e c t i o n and tests. Inasmuch as the exposures continued during clear weather only, the records include entire days when the sheets remained in the protecting compartment and also many days when only 2 to 6 hours of exposure were possible. Atmospheric temperature during the active days ranged from 10” to 30” C. Heat units, which aim to measure sunshine intensity, were furnished daily by the Miami Sun Ray Research Division of the J. H. Adams Foundation. One heat unit, expressed metrically, will raise the temperature of water 1” C. for 1.41 cm. of water’s depth. The quantity of heat corresponds to 1.41 calories per sq. cm. These figures were obtained through 0. J. Sieplein of the University of Miami, and are availTRAYS a b l e a l t h o u g h n o t i n c l u d e d i n t h i s arFIGURE2. PAPERSLAID OUT ON EX~OSURE ticle. . ~ . ~ ~ ~ The samples included in series I were commercial papers tion; “across” becomes the line of fold in the machine direction. Inasmuch as fold retentions are calculated on a basis and waterleaf papers that contained no size, alum, color, and of total fold, this change in method of reporting fold endur- the like. Table I summarizes typical results obtained with the commercial papers. Table I1 includes similar data ance does not affect the results. on waterleaf papers. SERIESI Among the glue-sized rag bonds were included portions of I n the absence of prior knowledge, the first experimental several of the best known brands. The papers of purified program in Florida specified a 200-hour exposure on each side wood fiber origin were manufactured on a commercial machine and were glue-sized in the usual manner by subjecting 1 IND. EN^. CHIM.,28, 131, 266, 371 (1931).
February, 1935
INDUSTRIAL AND ENGINEERING
CHEMISTKY
179
TABLE111. RESULTS OF EXPOSURE ON PAPERS OF SERIESI1 Sample No. Type of paper
1 Rag bond
2 Rag bond
3 Rag bond
Sizing
Rosin and glue 46.8
Rosin and glue 41.6
Rosin and glue 44.4
4.8 4.8 4.8
5.0 4.8 4.8
5.4 5.2 5.2
Basis weight pH: Original After 100 hr. After 200 hr.
4 Purified wood fiber bond Rosin
6 Purified wood fiber bond Rosin
32.6
54.7
7 Purlfied wood fiber bond Rosin and glue 52.7
5.0 4.8 4.8
5.0 4.6 4.6
5.0 4.8 4.8
90 Purified wood fiber
14 Kraft paper
16 Sulfite
10 Sulfite bond
11 Sulfite bond
12 Sulfite bond
15 Kraft paper
Newaprint
Waterleaf
Waterleaf
Water- Waterleaf leaf 26.1
46.1
Rosin and starch 43.7
Rosin
49.6
Rosin and starch 42.6
Rosin
47.4
Rosin and starch 45.8
4.8 4.6 4.4
4.8 4.6 4.4
... ... ...
4.6 4.4 4.2
4.6 4.4 4.2
5.0 4.8 4.8
4.2 4.0 4.0
8G
Rag
43.6
18)
31.0 4.4 2.2 2.2
...
..
Fold, original: 32806 272 1149 1403 165 144 481 222 297 160 67 1345 1864 1244 With 2000 111 1537 643 277 177 189 115 865 1520 717 1062 915 1100 865 Across 1437 Fold after 100 hr.: 71 46 21 13 152 97 132 64 34 634 335 71 487 569 With 681 25 370 18 4 8 268 188 200 529 384 117 308 274 7 Across 408 Fold after 200 hr.: With 232 26 165 210 99 40 19 8 12 7 5 22 9 Across 205 39 93 116 220 65 38 1 4 2 2 59 5 Fold retention, %: 100 hr. 32 34 31 19 36 36 64 68 15 10 12 9 12 18 2 200 hr. 13 8 16 7 12 14 39 25 4 2 4 3 4 4 3 Samples 8 and 9 are handmade sheets from semi-beaten stocks. 6 Sample 18 was folded with much reduced tension in the machine because of low physical tests; other samples were tested with the usual 1000-gram tension.
the papers to a secondary bath of glue, after which they were air-dried. The sulfite papers were nationally known products. All papers suffered severely by the prolonged exposure to sunlight. The waterleaf papers were more resistant. The rag waterleaf sheet, manufactured for esterification purposes, happened to possess a rather high pH value and stood up relatively well, as did one of the purified wood fiber papers. The sulfite waterleaf sample was rendered practically strengthless.
I
S
4
5
6
7
PH Before fxposure
8
Miami were recorded, although no endeavor was made to correlate these values with the degradation of the various samples. Table I11 summarizes the important findings of the second series of exposures. Under the conditions of treatment the better grade rag bonds and the glue-sized bonds that were made of a purified wood fiber base approximated 33 per cent in fold retention a t the end of 100 hours of sunlight (50 hours on each side). Fold retention is expressed in terms of the per cent of the original fold value retained after the paper has been aged. All tests unless otherwise specified were made a t 45 per cent relative humidity. These same papers retained only about 15 per cent of their original folds when exposed for 100 hours on each side. The fold endurances of these papers after exposure are all in the same order of magnitude. The unsized waterleaf rag and the purified wood fiber papers were both prepared on a hand mold instead of on a continuous Fourdrinier machine. The rag stock was produced from new white shirt cuttings. The purified wood fiber was refined to
9
FIGURE 3. EFFECTOF PH ON COPPERN ~ E R
All of the above papers were discolored by the sun’s rays. I n the case of the sulfite papers both the waterleaf and the sized samples took on a decided tan hue. The waterleaf rag and purified wood fiber papers were only slightly yellowed. On the other hand, the sized high-grade papers were appreciably discolored. Rosin and dyestuffs ordinarily used in the manufacture of such bonds are largely responsible for this change in color.
SERIESI1 The excessive degradation experienced in the first series suggested a second program in which the exposure t o the sun was reduced to 100 and to 50 hours on each side. These exposure tests were started August 20, 1931, and ended October 25, 1931. The recorded temperatures were somewhat higher than were found in the first series. This is readily explained by the season in question. During many of the days temperatures exceeded 32’ C., and on a few occasions 38’ C. was reached. Again sunshine intensity units as available a t
PH Before €xposure FIGURE 4. EFFECTOF PH ON FOLDRETENTION
contain about 94 per cent alpha-cellulose. The results show conclusively that a beaten waterleaf fiber sheet that contains none of the usual sizine; reagents and alum residues is definitely more resistant to the oxidation effect of the sun’s rays. Fold retentions of approximately 65 per cent a t the end of the 6rst 100-hour exposure (50 hours on each side) are to be compared with the corresponding values of 33 per cent in the case of the sized papers.
1NDUSTRIAL AND ENGINEERING
180
h
3
4
M
CHEMISTRY
Vol. 27, No. 2
The commercial sulfite wood pulp papers were markedly inferior in permanence to the purified wood fiber and the rag papers. Fold retention values of approximately 12 and 4 per cent were obtained after the 100- and the 200-hour sunlight e x p o s u r e s , respectively. The waterleaf sulfite sheet appears no more resistant than do the sized sulfite papers. Possibly this can be attributed to the inherent low relative stability of the sulfite fiber itself. It is interesting that a typical commercial-sized kraft paper proved only slightly superior in stability to a sulfite bond and quite inferior t o a rag or purified wood fiber bond sheet. The results of a machine-made waterleaf kraft paper are also included, although unfortunately there is strong probability that this paper was produced with circulating water that contained some alum residues. Later work substantiates the abnormality of this single result. A single newsprint sample of g r o u n d w o o d origin failed miserably in resisting the sun's rays, even after the first 100-hour period. Copper numbers of the original and the exposed samples of waterleaf paper are included as preliminary evidence that oxidation occurs in no uncertain manner. The papers used in this series experienced changes in color similar to those of series I; that is, the unsized rag and purified mood fiber papers showed minor d i s c o l o r a t i o n , whereas all of the sulfite sheets became deeply colored. The h i g h - g r a d e glue-sized papers were slightly affected.
SERIES111
h
The results of series I1 demonstrated that even the best papers retained only a small percentage of their original folding endurance when exposed t o Florida sunlight for a total of 200 hours. It was deemed best to standardize on a 100-hour total exposure (50 hours on each side) both for convenience and to insure a reasonable degree of residual strength in the exposed papers. Series I11 was planned as a more ambitious program. As is apparent from Tables IV, V, and VI, efforts were made to extend our knowledge by a study of sunlight effects on waterleaf papers in which there had been deliberately added a secondary ingredient that would serve either as a preservative or as a deteriorant. An attempt was also made to determine whether an increased density of the base sheet would result in improved stability because of reduced availability of circulating air to cellulose. Treatments of paper with mercerizing and vulcanizing agents prior to the sunlight exposure were also made. Preliminary studies of the beneficial results of protection of paper by regenerated cellulose films and by regenerated cellulose as a sizing agent are of interest, as are the first figures on glass protection of the various types of cellulose. The actual exposure was made from May 2 to 18, 1932. Noonday temperatures ranged from 25" to 30" C. The same general details of exposure were observed as in previous cases. For convenience the data are segregated into logical groups to emphasize better the tendencies that exist. Table IV is a summary of a set of papers pre-
February, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
pared for the purpose of studying possible means of protection against sunlight. The base sheet was a normal waterleaf purified wood fiber paper that had been produced on a Fourdrinier machine from a fairly well-hydrated stock. In its manufacture distilled water was obviously out of the question, and consequently the p H value is slightly lower (4.6) than would be specified for best stability.
181
magnitude. The fold retentions improved definitely as the p H value of the treated papers increased. The borax-treated papers experienced less increase in copper number by sunlight exposure. Figures 3 and 4 illustrate the copper number and fold changes graphically. It would prove of interest to investigate the effect on sunlight permanence in those cases where the acid and alkaline salts are added during the beating process. Similar work with sized papers is also in order. TABLEV. EFFECTOF ~IERCERIZATION O R VKLCAX~ZATIOX ox Marked increase in initial folding endurance can be imPAPERS OF SERIES I11 parted by certain sizing agents and plasticizers, as is witnessed Sample N o . 21 23 24 25 by samples 22-4, 14, and 15. A combination of glue and History of paper Waterleaf 22 mercerized 22 vulcanized 22 treated glycerol is particularly effective in this respect. On exposure purified a o o d in sheet form in sheet form successively fiber (proa i t h 18% a i t h 70' BB. as in 23 and to sunlight the glycerolated and the viscose-treated papers duced on NaOH soin. ZnCh soln. then as were outstanding in percentage retention of fold, and in the machine) a t 20' C . , (at 50' C . ) , in 24 washed a n d washed free of case of the viscose-treated papers the actual retained folding dried chemical, and dried endurance after exposure was more than double the correBasis weight 30.9 42.1 30.6 44.0 sponding figure of the original waterleaf papers. In the pH:" majority of cases also the copper number increase varied Original 4 5 4.2 5.2 5.2 Final 4.2 4.2 5.2 5.4 inversely as the stability of the papers, as measured by fold Original fold: retention. There is one exception which may possibly be With 522 4735 6912 12178 238 2791 Aorosa 2264 10541 explained by the difficulty of obtaining accurate copper numExposed iold: ber determinations on a paper that has been treated with both With 452 2070 1189 6065 Across 149 730 850 3710 glue and glycerol. The glass-protected paper (20a) illusFold retention, % 79 37 22 43 trates this correlation in a striking manner. The samples Co per No.: 8rigi nal 1.26 2.0 1.47 2.16 treated with glue and with glue plus glycerol were vastly Exposed 3.9 4.3 4.56 4.38 improved in initial folding endurance, but the calculated perViscosity: Original 4.2 Treated papers would not respond t o centage fold retentions were quite low, indicating an imperExposed 0.45 the viscosity procedure manence of the added folding strength. The study of perThe p H values of treated papers are quite independent of chemical manence of sized papers that are characterized by the prestreatment, since the aashing steps that follow cause substantially complete removal of the chemicals used. This explains the slight differences in origience of plasticizer and by a relatively high pH value (6 to 8) nal p H values of the various papers in this series. may prove of value. Table V shows that, when a purified wood fiber paper is Sample 26 was made by passing the original Purified wood mercerized or vulcanized, the folding endurance is enhanced fiber Paper (sample 7 ) through a calender stack to increase in tremendous proportions, but that these treated papers are its density. This increased compactness improved the initial peculiarly sensitive to sunlight. Notn-ithstanding this great fold test. After the 100-hour sunlight test, the calendered difference in relative stability, the end products in the Paper Possessed a fold ~ m h a n c esomewhat higher than did of the treated papers possessed a greater residual fold than did the corresponding uncalendered paper, although the Percent- the untreated paper. Also, the original purified wood fiber age fold retention is somewhat less. If this result can be con- paper of this series possessed a particularly high fold retenfirmed by suPPlelnentaV tests, it may Possibly be accounted tion. This may be explained by the fact that in this series for by the increased penetration Of sun's rays into the sheet all folds made with joo-gram rather than the usual 1000that had been rendered thinner by the calender stack. gram tension, The results are, therefore, not to be comBoth Cellophane and glass afforded appreciable protection pared directly with other series of tests. to the uncalendered DaDer from the action of sunlight. although the Cellophane is known to transmit some ultra$olet VI. EFFECTOF TREATMENT ON FOURDRINIER MACH~TE light which glass absorba. Moisture-proof Cellophane, so- TABLL ON PAPERS OF SERIES I11 called, was much less effective. Its protective effect may be Sample No. 15-0 2a 2c 2d offset partly by a decomposition of the water-resistant coating of paper Waterleaf 15-0 treated u i t h soin sulfite made used in its manufacture. Resins and nitrocellulose are usufrom holcontaining 8 % ally present in the waterproof coating. landerglue and beaten fiber 0 570 formalWhen a n unwaterproofed commercial Cellophane which and on dehyde based contained about 7 per cent glycerol was exposed to sunlight Fourdrinier weight increase In on glue: machine weight of increase in for 100 total hours, it retained about 70 per cent of its original paper, 11.3% weight, 13.4% 44.2 48.7 50.5 47.0 fold strength. The relative imperviousness of the film as Basis weight : well as the glycerol present may well account for the rela- p HOriginal 4.5 4.7 5.4 4.8 Final 4.2 4.3 5.0 4.6 tively high physical permanence. Similar experiments should Original fold: be made in the absence of glycerol. With 240 464 1259 297 292 427 Across 217 998 The changes in copper numbers of the paper in question are Exposed fold: consistent with the retention in folds. With 31 152 53 12 Across 60 96 120 71 Samples 9, 8A, 8, 7, 10, and 11 constitute a series in which retention, % 19,9 32.8 7.7 11.5 purified wood fiber papers were rendered alkaline or acid by Fold No.: dipping the waterleaf sheets into salt solutions of prescribed Copper Original 3.84 3.75 Exposed 6.00 5.26 strength, followed by drying without an intermediate washing. The treatments altered the initial fold considerably. Increased alkalinity by use of borax and increased acidity Table VI is in certain respects comparable with the by use of alum caused a reduction of fold strength amounting corresponding typical treatments included in Table IV. I n to approximately 50 per cent of that of the untreated paper. this set a normal waterleaf sulfite paper was produced on a With the exception of the most acid paper, the resulting folds Fourdrinier machine and used as a base on which certain after the sunlight exposure were all in the same order of secondary materials-namely, glue and glycerol-were de-
182
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 27, No. 2
TABLE VII. EFFECTOF PROTECTIOX ON PAPERS OF SERIES IV (Exposed September to November, 1933) Sample No. History of paper
1 Purified wood fiber waterleaf 52.0
2 1, glassprotecteda
3 4 1, Cellophane- 1, protected protectedb with waterproof Cellophane0 51.0 51.0
5 Unused goodgrade newsprintd
6 5 glassp;otected'
7 5, Cellophaneprotectedb
Basis weight 51.3 32.0 32.6 30.0 pH: Original 4.6 4.6 4.6 4.6 3.8 3.8 3.8 4.2 4.5 Exposed 4.3 4.4 1.6 1.8 1.6 Copper No.: Original 1.78 1.78 1.78 1.78 4.44 4.44 4.44 4.8 Exposed 3.54 3.94 4.08 22.0 20.6 23.0 Original fold : With 687 687 687 687 388 388 388 Across 174 174 174 174 324 324 324 Exposed fold: With 287 520 407 361 63 52 65 Across 141 190 121 136 24 61 27 Fold retention, % 50.0 82.8 61.3 57.7 12 16 13 Viacosity : Original 0.85 0.85 ... ... ... ... Exposed 0.35 0.45 ... ... ... ... a Glass protection with standard window glass of uniform thickness of 0.08 inch. b Nonmoiature-proof Cellophane; contained 10% glycerol and was 0.0088 inch thick (No. 300 in the trade). C Moisture-proof Cellophane of same thickness as in b. d In order to obtain a reasonable degree of accuracy, all folds on newsprint were made with a reduced tension of 350 grama.
8
5, protected
with moisCure-proof Cellophanec
30.4 3.8 1.4 4.44 22.6 388 324 20 20 5.0
..
posited. The original paper after the 100-hour exposure in sunlight retained 19.9 per cent of its fold. By the addition of 7.5 per cent glycerol by weight this retention was improved to 32.8 per cent. The copper 'number change was quite as expected. By addition of glue or glue and glycerol to the base sheet, the initial fold was increased materially, although after sunlight exposure the retained fold was not markedly higher than in the case of the untreated sulfite sheets. Here again
FIGURE5. PROTECTION OF SUNLIGHT-EXPOSED PAPERSBY CELLOPHANE AND GLASS
the initial enhancement of fold by glue and glue mixtures appears to be impermanent. However, this failure of protection by glue may not necessarily follow with a rosin-sized paper, which is in itself much less stable than the corresponding waterleaf sheet.
SERIESI V The preliminary trials with glass- and Cellophane-protected papers that were used in series I11 prompted a second
and somewhat more extended experiment. Two papers were used-a waterleaf p u r s e d wood fiber sheet and an unprinted, good grade of groundwood newsprint. Exposures were made to the direct sunlight and also with superimposed glass and Cellophane protection. Glass of good clarity and uniformity was chosen. The glass plates were used in frames with the paper samples enclosed between two plates. The Cellophane protection was arranged by inserting the papers in envelopes constructed of the film material. Fifty hours of sunlight exposure on each side of the sheet were specified in all cases. Table VI1 summarizes the results. Some of the data are shown graphically in Figure 5. The unprotected purified wood fiber paper shows a retention of about 50 per cent in fold value. The moisture-proof Cellophane offers some protection but the plain Cellophane is somewhat more effective. The glass is outstanding in protection value. The copper number and viscosity changes in the case of the unprotected and the glass-covered sheets are significant. The pH values of the exposed samples appear progressively higher as the degrading effect of the sun has been lessened. Neither glass nor Cellophane offers protection to newsprint exposed to the sun's rays. I n all cases the copper number increase is pronounced and the p H values are materially lower than in the original unexposed paper. These results are significant and have a direct bearing on the question of relative activity of the various wave lengths in sunlight on paper. Ordinary glass transmits the longer ultraviolet rays. The atmosphere filters from the sunlight most of the rays of shorter wave length than 290 millimicrons. The somewhat superior protection by means of glass when compared with Cellophane denotes the probability that the shorter ultraviolet rays that pass through Cellophane may be responsible for some of the deterioration of high-grade papers when exposed to sunlight. There is some evidence, however, that the long ultraviolet regions and the visible rays have also a marked destructive action. The results with the glass-protected newsprint demonstrate that this very unstable paper is affected by sun's rays in the visible region. Data in subsequent series of sunlight exposure add testimony to the foregoing. There was no appreciable difference in the marked browning of the newsprint in the unprotected and the glassor film-protected cases.
SERIESV It was thought sufficiently important to establish three points on a sunlight aging curve in order to estimate the rate
February, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
a t which commercial papers would depreciate when so exposed. In this series the first set comprised three samples: A. A paper made from equal parts of a purified wood fiber and a purified manila fiber. This sheet was sized with 1 per cent rosin in the beater, then tub-sized with a solution of 6 per cent glue and 1 per cent formaldehyde based on glue, and finally airdried. B. A paper representing the same base sheet as sample A but tub-sized with a solution of 6 per cent glue that contained 2 per cent alum based on glue. C. A well-known commercial glue-sized rag bond.
183
extended to include similar surveillance tests under ultraviolet light and also by means of the better known hot-air test a t 100" C. The apparatus and details of the ultraviolet light treatment will be described in a future article dealing more particularly with the deterioration of paper by means of ultraviolet light. I n general, the apparatus consists of a slowly revolving open cylinder, on the inner face of which are attached the papers under test. A stationary ultraviolet light
These samples were exposed to Florida sunlight during the months of December, 1932, to March, 1933, inclusive, for 36, 72, and 96 hours on each side. The set was exposed only during periods from 2 hours after sunrise to 2 hours before sunset, so as to favor the action of the more active ultraviolet rays. The results are tabulated in Table VI11 and shown graphically in Figure 6. There appears to be a steady diminution in folding strength as the exposure continues, and, although the experimental data deserve a further check, there is a suggestion that formaldehyde when used as a hardening agent for glue will render papers less sensitive to the destructive action of sunlight. Color changes were progressively more marked in all cases as the exposure continued. TABLE VIII. PROGRESSIVE DEGRADAT~OK OF PAPER OF SERIES V EXPOSED TO SUNL~GHT Paper Basis weight pH: Original 36 36 hr. exposure 72 72 hr. exposure 96 96 hr. exposure Fold endurance: Original : With Across 36 36 hr. exposure: With Across 72+72 hr. exposure: With Across 96 96 hr. exposure: With Across Fold retention, yo: 36 36 hr. exposure 72 72 hr. exposure 96 96 hr. exposure Ink penetration, min.: Original 36 36 hr. exposure 72 72 hr. expoeure 96 96 hr. exposure
+ ++
+
+
+ ++ + + +
A 52.6
B 52.4
C 41.0
4.7 4.5 4.3 4.3
4.4 4.3 4.4 4.4
0
24
48
72
2203 2255
2114 1996
1570 1576
1812 1728
1734 1053
1126 815
1545 1568
1537 1310
637 558
1495 1291
1385 1144
432 474
83 73 66.5
69.3 61.5
28.8
35 1.2 0.5
722 0.9 0.1 0.1
55 0.6 0.5 0.3
0.1
80
61.7 58.0
Previous work had exhibited marked sacrifice in writing quality of sized papers when exposed to light. Inasmuch as this set of experiments offered a splendid opportunity of determining the extent of these changes in ink resistance, ink penetration tests were made on all of the original and exposed papers. In making this test, specimens of paper were floated on the surface of the ink (Carter's Ryto ink was used as the standard) and were kept continuously under observation until transudation of ink was detected on the upper side. Results are expressed as the time interval of the staining through of the ink, approximately 90 per cent penetration being taken as the end point. The rapid and extraordinary degree to which writing qualities were dissipated is striking. PRELIMINARY COMPARISON OF SEVERITY OF ULTRAVIOLET WITH SUNLIGHT
The nature of the aging curves of the previous set of papers stimulated further interest, and three additional papers were chosen for similar tests. I n order that the degrading effect of the sunlight might be compared directly with the progressive destruction of papers by other agencies, the program was
120
/#4
- fitdHours.
/68
/92
FIGURE6. PROGRESSIVE DEGRADATION OF PAPERSEXPOSED TO
4.5 4.4 4.3 4.3
96
€xpo5ure toSun/@
SUNLIGHT
of a type that is marketed under the name of Alpine type burner D. C. by the Hanovia Company operates a t a point near the axis of the revolving cylinder. This quartz mercury light is operated electrically a t 100 to 115 volts by current generated from a motor generator set. There is a rheostat a t the lamp for control of the voltage drop and current through the lamp. Thus all samples are subjected to exactly the same number of light hours. Provision is made to avoid temperatures over 28" C. a t the paper surface. The 100" C. exposure was extended over a 21-day period, whereas the ultraviolet light exposures as well as the Florida exposures were made for 36, 72, and 96 hours on each side of the papers as in the previous set. The three supplementary papers used in these experiments were : A. A nationally known glue sized rag bond. B. A glue-sized air-dried paper of mixed furnish containing purified wood fiber and purified manila fiber. C . A waterleaf unsized sheet of machine-made paper from a purified wood fiber furnish, with an alpha-cellulose content of 95 per cent.
The Florida exposures were made from December, 1932, to March, 1933. Maximum daily temperatures approximated 28" C. Results are given in Table IX. Results of sunlight exposures and of the mercury light treatments are shown graphically in Figure 7. I n the case of sample C (Table I X ) , both the natural and artificial light rays proved to be much more severe than did the longer continued exposure to circulating air a t 100" C. The ultraviolet treatment of sample A was inadvertently omitted, but here also the sun's rays mere more destructive than was hot air. Sample B behaved peculiarly in that the sun's rays were definitely more deleterious than were the heat treatments, but for some reason the ultraviolet light was less drastic in its action. This apparent discrepancy demands further study. It is conceivable that the difference in behavior of samples B and C under the ultraviolet light may be explained by the absence of ultraviolet light rays of certain
184
Vol. 27, No. i
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLEIX. PRELIMINARY COMPARISON OF EFFECTOF LIGHTAND HEATON PAPERB OF S E R I E V~ -HEAT
EXPOSURE-
-FLORIDA
Exposure, hr. Basis weight Pop test (actual) Fold endurance: With Across Fold retention, %
0 44.2 51.2 1340 1255
..4.4
PH
72 42.6 51.1 1046 890 74.6 4.2
336 42.6 46.2
504 43.1 44.3
619 541 44.7 4.1
487 432 35.4 4.0
EXPOSURE-
SUNLIQHT
SAMPLE A
+
+
36 36 42.2
0 42.0
...
72 72 42.9
...
...
1353 1322
955 808 66.0 4.3
... 4.4
539 407 35.4 4.3
ULTRAVIOLET LIQHT
+
96 96 42.0
...
... ... ... ...
363 221 21.8 4.3
...
0 46.4 65.9 1203 1273
...
4.5
RH
72 47.1 62.0
336 46.3 59.1
504 46.7 57.0
1134 1040 87.8 4.3
68i 799 59.9 4.2
626 718 5s.3 4.2
36 4-36 46.2
0 46.2
...
t . .
1121 1238
648 679 56.4 4.4
.4. ..6
72 f 7 2 45.9
...
443 379 34.8 4.3
96 4-96 45.5 322 309 26.1 4.3
...
0 43.0 29.1 421 7s
... 4.6 1.41
Ezpper No.
72 42.8 29.6
336 42.7 25.6
504 42.6 23.5
348 67 82.7 4.5 1.62
337 72 81.6 4.4 1.84
275 60 66.8 4.3 1.98
36 -I- 36 41.8
0 42.2
...
...
480 67
281 89 67.6 4.6 4.5 1.41 3.2
...
237 47 51.9 4.5 3.8
..,
wave lengths that are normally present in sunlight and that destroy the glue which is less affected by rays of the artificial light and consequently serves more effectively as a protection against oxidation. Supplementary data will be available in a later article.
72 4- 72 41.9
+
1203 1273
1026 980 81.1
...
.
.
142 49 34.9 4.3 4.4
...
+
+
424 78
...
...
...
+
48 48 42.5 28.7
0 43.0 29.1
I
...
...
...
72 f 72 96 96 47.2 46.6 60.6 55.7 1026 1000 82.0
...
,..
96 f 96 42.0
...
48 48 47.2 62.1
SAMPLE C
Exposure, hr. Basis weight Pop test (actual) Fold endurance: With Across Fold retention, 5%
... ...
...
0 46.4 65.9
...
,.
...
SAMPLE B
Exposure, hr. Basis weight Pop test (actual) Fold endurance: With Across Fold retention, %
EXPOSURQ
916 862 71.9 . . I
+
72 72 96 96 42.5 42.5 27.4 24.6
207 43 49.8
183 39 44.3
107 27 26.7
2.5
2.7
3.4
...
...
1.4
...
hours after sunrise to 2 hours before sunset, thereby omitting those periods when the intensity of ultraviolet rays was low because of atmospheric absorption. The first two series were not limited in this way. 'Three types of paper from identical r a s t e r samples were compared : 1. A commercial glue-sized 100 per cent rag bond. 2. A sample of waterleaf sulfite paper produced commercially. 3. A sample of waterleaf paper made on a commercial machine from a purified wood fiber stock; the alpha-cellulose content of the unbeaten fiber was about 95 per cent.
TABLE
x.
COMPA4RISONOF AGIKGO F PAPER DIFFERENT SEASONS Ex-
1.
SAMPLE Glue-aized rag bond
2
3.
POSURE
BY
SUNLIGHT
AT
FOLD RETENTION AFTER EXPOS U R E ox EACX SIDEFOR:
PERIOD 36 hr. B
C
57.5 66.0 61.7
72 hr. 31.0 35.4 38.0
96 hr. 23.7 21.8 28.8
Waterleaf eulfite paper
A B C
32.8 36.2 25.8
13.3 14.5 12.9
6.6 7.2 6.4
Waterleaf purified wood fiber paper
.?,
6716 63.3
5119 45.5
3419 32.7
A
0
0
24
48
72
96
/ZO
/44
Exposure t o Li9ht - Total Hours.
/68
/92
FIGURE7. EFFECTOF EXPOSURE OF PAPERSTO SUNLIGHT AND ULTRAVIOLET LIGHT
B
C
The Mullen or pop test is progressively lowered as heat or As was to be expected, Table X shows that the sulfite sheets light treatments are continued, but these changes are much less marked than are the changes in folding values. It is degraded most rapidly. The glue-sized rag bond cannot be also obvious that in the case of the waterleaf paper (sample C) compared directly with the waterleaf paper produced from the the copper number increase is much more-rapid when degradation takes place in the presence of A -fxposedSqt.-/VoK light. I n all cases the p H values decrease in ac106 cordance with previous data. Sacrifice in color of papers was greatest in the presence of light. SERIESVI At this stage it was thought necessary to know more regarding the effect of seasonal changes of sunlight intensity, so that the results of exposures made during different periods of the year may be more intelligently compared and interpreted. This series included no exposures in midsummer. The periods were, respectively: A. September t o November, 1932. B. December, 1932, to February, 1933. C. February to March, 1933. The treatments during the period C were so prescribed that papers were exposed only from 2
s75
&
s
\u
q50
$
8?fi
0 0
48
96
/44
/92
0
$8
96
/M
192
0
48
96
/44 /9Z
Total Hours Exposure (Both &des) t o F/or/doSunhqht FIGURE8. COMPARISON OF AGINGOF PAPERBY SUNLIGHT AT DIFFERENT
SEASONS
February, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
p u r s e d wood fiber, but the direct comparison of results in case of each type of paper exposed during each of the seasonal periods is justified. The omission of the early morning and late afternoon sunlight hours in series C did not appear t o cause much difference in the general results. Figure 8 shows graphically the changes in fold endurance that occur for each paper during the different periods in question. The sunlight intensity as measured by spoilage of paper does not appear vastly different in the several seasons investigated.
CONCLUSIONS 1. Four hundred hours of exposure to Florida sunlight caused severe degradation of several typical high-grade papers. Sized papers suffered greater loss in physical strength than waterleaf papers. 2. When waterleaf papers of rag or purified wood fiber origin are exposed to Florida sunlight for 50 hours on each side (100 hours total), approximately 65 per cent retention of fold endurance can be expected. Sized papers produced from similar stock will retain only about 35 per cent of their original fold endurance. Sulfite papers and newsprint are least resistant when exposed in like manner. 3. Three points on a sunlight aging curve were established for three types of glue-sized papers. 4. Differences in fold retentions obtained when papers were exposed t o Florida sunlight for prescribed periods during different seasons of the year were not of high magnitude. 5. A preliminary study of comparative losses in physical strength that are realized on papers exposed t o natural sunlight, artificial light, and the well-known oven test was not convincing, although there was some evidence that the natural sunlight exposure produced the most drastic sacrifice in strength of papers. 6. The writing properties of sized papers were rapidly
185
and seriously impaired when such papers were exposed to sunlight. Even relatively short periods of exposure were very effective in destroying the initial high resistance to ink penetration. 7 . Ordinary window glass and unwaterproofed Cellophane were definitely effective in protecting a wood fiber paper from the devastating action of the sun's rays. Window glass appeared to offer no protection to groundwood newsprint exposed to sunlight. Slight alkalinity in the case of chemical wood fiber papers was also conducive to long life when such papers were exposed to sunlight. 8. The marked increase in folding endurance obtained when a waterleaf wood fiber paper was sized with glue in the presence of plasticizers was largely sacrificed when such papers were exposed to sunlight. Waterleaf sulfite papers behaved similarly when so treated and exposed. 9. Preliminary work indicates strongly that, when the waterleaf paper is treated with viscose, it takes on added folding strength and that this increment is relatively permanent when the treated papers are exposed to sunlight. 10. Mercerization and vulcanization (zinc chloride treatments) of waterleaf purified wood fiber papers resulted in tremendous increase in fold endurance. Fold retention on sunlight exposure was less in the case of these chemically treated papers than of the untreated papers, but actual fold strength of the sunlight-exposed, chemically treated papers exceeded that of the corresponding untreated exposed sheets.
ACKNOWLEDGMENT The writer wishes to acknowledge the assistance of E. W. Lovering who carried out the program of work in the Berlin, N. H., laboratory, and of H. P. Vannah, who supervised the sun exposures in Florida. RECEIVED October 1, 1934.
Courtew, Foster- Wkeeler
CLOSE-UPOF THREEALCOHOL CONDENSERS SERVEDBY THE STEAMJET IN UPPER RIGHTHAND CORKER. THESTEAM-JET AIR P w REPLACES THREELARGERECIPROCATING VACUUM Pws.
