Nov., 1916
T H E J O C R N A L OF I,VDUSTRIAL A N D ENGISEERING CHEJIISTRY
A METHOD FOR DETERMINING THE STRENGTB OF PAPER WHEN WET By
E.
0. REED
Recei\ied July 15, 1916
Ordinarily t h e strength of wet paper is not a matter of importance. Most kinds of paper when wet are very weak and break or tear with t h e greatest ease. Certain kinds of paper, however, must be handled while wet, and it is essential, therefore, t h a t they have a sufficient wet strength t o withstand this service. This is true of photographic paper, especially of blue and brown print paper, of bag and wrapping, of paper textiles and t o a less extent of filter paper, and paper which is t o be printed while wet. While papers may comply with t h e specified physical requirements under t h e usual conditions of temperature and humidity, they may prove entirely unsatisfactory for handling when wet. I t is a well-established fact t h a t t h e moisture content of t h e paper has a great effect on paper making a n d testing, and considerable work has been done t o determine t h e properties of paper under different temperatures and atmospheric moisture conditions. The strength of paper when, wet, however, has received little attention. Beadle and Stevens' present a n article on "The Dry and 'Wet Strengths of Paper." The exact method of carrying out t h e wet-strength test is not clearly stated and only t h e wet strength of papers used in t h e manufacture of paper yarns is dealt with. Perhaps one of t h e most severe conditions t o which paper is subjected when wet is in commercial blue and brown print developing. I n this work sometimes paper 4 2 in. wide and I O or 1 2 ft. long is handled while thoroughly wet. Much of t h e so-called blueprint paper will not withstand t h e necessary wetting without injury even though its other physical qualities may be entirely satisfactory. The determination of t h e tensile strength of t h e met paper has proved t o he t h e most satisfactory test for indicating t h e strength required t o withstand t h e washing necessary t o insure permanent prints. The wet strength is determined by breaking a strip of paper of a definite width, after it has been immersed in water a t a constant temperature for a definite period of time. A Schopper tensile strength machine, calibrated t o read from I t o 1000 g., is used. The jaws of t h e clamps should open in front, so t h e ends of t h e wet strips may be inserted without injury, and are set I O cm. apart, as a short strip of wet paper can be handled more easily. The test strips are cut 1 5 mm. wide a n d sufficiently long t o allow for clamping in t h e machine. Tests are made in both the longitudinal a n d transverse directions. The strips are placed separately in a water bath a t 70' F. for 20 min. After t h e specified time they are removed one a t a time and tested immediately. To obtain accurate results extreme care must be exercised in handling and clamping t h e wet strips t o prevent injury t o them. The wet strength in t h e transverse direction of I
Chem. Xewa, 109 (1914), No. 2843, 242.
I 003
blue and brown print papers upon which most of this work has been done and also of Kraft and rope wrapping is less t h a n j o o g. I n the longitudinal direction 1000 g. is a n exceptionally high wet strength. OF TEMPERATURE OF WATERON THE WET STREKCTH (GRAXS)OF PAPER. PAPERS \\'ET FOR 20 MINCTES Direction Temperature of Water Bath--OF L&P of 50 65 70 75 100 No. KIND OF PAPER Strip G G G. G G 31470 Blue-print paper 610 563 346 679 536 Long. 282 285 219 346 288 Trans. 988+ 943 31642 Blue-print paper 73 1 lOOO+ 997 Long. 632 634 414 Trans. 564 744 28517 Blue-print paper 1000+ 1000+ 1000+ 1000+ 1000 Long. 738 695 598 Trans. 776 776 12956 BOND: 62 1 604 585 492 Before sizing 63 1 Long. 258 258 222 Trans. 271 300 12957 After animal 754 754 578 sizing 824 918 Long. 364 370 293 Trans 412 484 12914 PARCHMENT BOND. 536 464 474 398 Before sizing Long. 600 251 224 228 187 Trans. 270 12915 After animal 674 495 sizing Long. 773 704 850 309 240 309 406 329 Trans.
TABLEI-EFFECT
+
+
Table I shows t h e effect of t h e temperature of t h e water on t h e strength. The length of time of wetting was 2 0 min. in all cases. From these results it is evident t h a t in order t o obtain concordant values t h e water in which t h e strips are wet must be maintained a t a constant temperature. It will be noted t h a t wide differences exist between results obtained on a paper wet a t 50' F. and a t 100' F. There is a progressive decrease in strength with rise of temperature of t h e water in which t h e papers are wet, a n d a difference of j o F. in t h e temperature of t h e water makes a significant difference in the wet strength in t h e longitudinal direction, though t h e differences in t h e transverse direction are usually small: 70' F. has been adopted as t h e most suitable temperature a t which t o maintain the water bath. Table I1 shows t h e effect of t h e length of time of wetting on t h e wet strength. TABLE 11-EFFECT OF TIXEOF IMMERSION IS WATER ON THE WETSTRENGTH (GRAMS)OF PAPER. TEMPERATURE OF WATERBATH70' F.
L&P No. 31470
31471 30857 31632 28542
Direction Time of Wetting-Minutes of 10 20 30 45 60 KIND OF PAPER StriD G. G. G. G. G. 591 557 Blue-print paper 662 534 495 Long. 277 277 Trans. 312 274 262 446 434 Blue-print paper 487 438 420 Long. 236 226 Trans. 257 222 456 498 Bond paper 539 453 Long. Trans. 258 238 270 213 Blue-print paper l000+ 908 850 Long. 793 562 Trans. 489 464 414 Blue-print paper 935 842 847 Long. 800 649 Trans. 592 5 64 549 537
.
The figures show t h a t i t is necessary t o immerse t h e paper for a definite time t o obtain valuable a n d uniform results. The results obtained on paper immersed only I O min. indicate, in most cases, t h a t t h e water has not penetrated uniformly a n d t h e individual results are much more erratic "than when t h e paper is immersed for longer periods. After 2 0 min. immersion, which has been adopted as a suitable period for wetting, t h e individual results are more concordant though minimum results are not obtained in t h a t time. T h e transverse strength is but little affected by even longer periods of immersion. I n commercial practice blue and brown print papers are seldom in the water b a t h more t h a n 20 min. Table I11 shows t h e concordance of averages of j tests in each direction on t h e same paper made on
T I 1E J O C R iV A L 0 F I N D U S T RI A L A S D E N G I N E E R I - V G C H E M I S T R Y
1004
different days under t h e adopted constant conditions of wetting for 20 min. a t 70' F. Since t h e wetstrength tests are registered in grams and difficulty is experienced in handling and clamping t h e strips 'f ABLE 111-DUPLICATE AVERAGESOF WET STRENGTII MADE UNDER THE SAME CONDITIONS Papers wet a t 70' F. for 20 min. FIRST AVERAGEOF FIVE SECOND AVERAGE OF FIVE Long. L Rr P Trans. Long. Trans NO.
28541.. . . . . . 31632 . . . . . . . 28540.. . . . . . 314iO.. ..... 314il . . . . . . .
G. 812 810 690 563 416
G.
6. 521 408 376 282 224
829 800 690 59 1 426
G. 531 433 395 277 221
of wet paper in t h e tester, these averages are considered very close. It is necessary t o discard results on strips which have not been properly clamped. Care must also be taken not t o put a strain on t h e strip while clamping. Wet strength is apparently controlled by the kind of stock, length of fiber, character of beating, kind and quality of sizing and b y t h e formation of t h e sheet. Table IITshows t h a t i n every case t h e wet strenght was considerably increased by animal sizing. TABLE: IV-EFFECT
ANIXAI,SIZING O N THE WET STRENGTH O F PAPER PaDers wet at 70' F for 20 min Per WET S T R E N G T H cent Increase LRrP Long. Trans. Due t o Sizing No. K i m OF PAPER FIKISH G. G. Long. Trans. Bond Unsized 604 258 ........ Animal sized i57 364 25.3 41.1 Bond Unsized 826 432 ........ Animal sized 981 575 18.8 33.1 464 224 Parchment Bond Unsized ........ Animal sized 704 309 51.7 37.9 668 323 Parchment Bond Unsized ........ Animal sized 873 463 30.7 43.3 749 370 Parchment Bond Unsized . . . . . . . . Animal sized 983+ 483 31.2 30.5 Bond Uncalendered unsized 270 162 ........ 12989 Unsized 293 158 12991 Animal sized 649 lii.5 1 4 i : S 12993 Bond Unsized 295 12988 hnimal sized 730 OF
T'ol. 8 , NO.
11
physical qualities under ordinary testing conditions or vice veysa. While this is true, study of t h e subject has led t o t h e opinion, however, t h a t wet strength is controlled chiefly by beating, sizing, and formation. High wet strength may be obtained with long stock beaten "wet," well matted and so sized as t o render t h e fibers water-resistant. X detailed study will be made of t h e effect of different papermaking procedures on wet strength, in order t o reach more definite conclusions as t o the factors affecting this characteristic of paper. Experience has demonstrated t h a t by means of this test it can be determined whether a blue or brown print paper will vithstand. t h e customary washing without tearing. The method promises t o be of even greater utility in predetermining the behavior of bag and wrapping paper when wet, especially of cement and lime bags. Quantities of these materials are being shipped in paper bags, many of which tear readily when damp and oEer no protection t o their contents against moisture. The method will enable users of such bags t o determine whether they will prove satisfactory in service. S L- M 3IAR Y
Owing t o t h e impracticability of obtaining samples of paper made from t h e same stock by different methods of beating or beaten for different lengths of time or sized with different amounts of rosin or glue or both, it is not possible to show here in figures t h e effect
Wet strength is a n essential property of paper for certain special uses. It is indicated by determining t h e tensile strength of wet strips, cut longitudinally and also transversely of the sheet. Strips 1 5 mm. in width and of sufficient length t o allow a breaking length of I O O mm. are immersed in water a t 70' F. for 2 0 min. and then tested in a machine calibrated to read in grams. I t is important t h a t thc paper be immersed for a definite period of time and in water of n uniform temperature, as these factors greatly influence t h e test. Care must be exercised in making tests as paper is so easily injured when wet. K e t strength is controlled by the combination of factors which influence other physical properties of
TABLBV~-RESLTTS
PHYSICAL
:;:
LRrP No. 31899 31909 31910 30857 30730 30856 30858 2854: 285 1i 31803 31249 30855 31250 31922 3 192 1
OF'
EXAMIKATION
OF T A R I O r S
Krms
Weight ThickSTOCK(Per cent) 24 X 36 ness ASH SUI- Chem. (500) 1/10000 Per PAPER Rag fite Wood Lbs. ' In: cent 73 0.2 Filter 100 Printing 21 50 1 .0 1.2 52 39 Writing 0.8 30 100 Bond 100 0.6 36 Bond 0.6 53 33 Bond 2.3 38 Bond 0.5 35 Blue-print io0 0,6 43 Blue-print 100 40 0.5 Blue-print 100 1.0 100 36 Ledger 1.2 100 40 Ledger 3.6 36 ... Ledger 0.9 50 .,. Kraft 2.8 90 ... Rope
OP P.APER-.%l.L
TESTSN A D E A T 70' F.
AKD
65 P B R
C E K T REL.4TlVE
HUMIDITY
WET
SIZ1h.G
Per cent Ros- Aniin mal 0 . 0 0.0 0 . 9 0.0 1.1 0.6 1 . 8 4.2 1.0 3.6 1.6 1.5 1.2 0.0 3.7 1 , i 3 . 8 2.3 1.8 4.8 1.0 3 . 5 2.6 4 . 4 1.5 0.0 0.7 0.0 2.9 0 . 0
of each of these factors nor t o state exactly t h e factors and procedures which may produce a satisfactory wet strength. In Table Y are given complete results, including wet strength, on samples representative of various kinds of stock papers. Examination of these results does not show a definite relationship between wet strength and any of the other characteristics of paper, ,2 paper with a high wet strength will not necessarily exhibit satisfactory
STRENGTH TENSILE STREKGTH FOLDING STRENGTH Mullen Factor Break Stretch ENDURANCI:70°F.20 min. Av. per Kg. Per cent Long. Trans. Long. Trans. STARCH Pts. Wt. Long. Trans. Long. Trans. Double Folds Gms. Gms. Trace 66 12.0 0 . 2 8 2.6 2.1 6 5 100 0.8 1.3 None 1 0 . 0 0.22 2.8 1.9 3 2 429 328 0.3 1.2 273 2.5 4.2 Present 3 5 .5 0 . 6 8 8 . 4 4.1 197 93 476 Present 249 39.5 0.99 8.0 4.4 2686 877 527 4.0 6.8 Present 1798 613 47.5 1.01 9.0 4.6 3.1 6 . 3 722 l000+ Present 33.0 0.71 6.5 3.5 400 456 2.9 4 . 6 131 738 299 None 26.0 0.54 7.6 3 " , 1 . 7 4.0 164 98 673 Present 629 3.5 7.0 42.0 0.78 6.5 5.4 1439 1308 808 66 I Present 9.2 5.3 265 2.5 4 . 9 42.5 0 . 6 9 135 1000 947 538 Present 76.0 1 . 2 3 1 3 . 8 7 . 6 3576 2666 3.9 6.6 4.6 6.6 1000+ 523 Present 62.0 1.21 10.7 5 . 8 3489 1626 512 Present 2729 1206 5,3 1.1 926 59.5 1.08 10.8 5 . 9 406 7 . 2 3.8 Present 270 58 1.3 4 . 6 749 28.5 0.60 1312 9.4 4.2 1 . 7 3.7 1000+ 639 None 4 3 . 0 0.75 540 None 114.0 1.30 1 4 . 6 5 . 8 1000+ 456 3 . 0 6 . 1 20000+ 3061
+
paper such as length of fiber, beating. kind and quality of sizing and formation of t h e sheet, yet there is no direct relationship between t h e met and dry strengths of paper. This test promises t o be of value in predetermining t h e serviceability of paper used for bags, especially for cement and lime. wrapping: photographic, paper textiles and even paper n-hich is t o he printed while wet. I,EATHERAKD PAPERLABORATORY
DEPARTMEKT O F AGRICULTVRE,
r\'.4SHISGTOX
