PHYSICAL TESTING OF GLUE COMPOSITIONS Sorbitol and Glycerol in Printers Rollers W. C. GRIFFIN AND E. G. ALMY Atlas Powder Company, Tamaqua, Pa.
S
EVERAL years ago the operating characteristics of various glue formulations were improved by using as a plasticizer a mixture of glycerol and commercial sorbitol solution. I n order to establish rules for formulation, the physical properties of glue composition were studied. Formulations chosen for the work embraced printers roller compositions and extended into flexible glues and to hectograph compositions on either side. Of primary importance in the manufacture of softened glue rollers is the relation between viscosity, temperature, and composition of the mass. This relation was investigated in some detail. The performance characteristics of a roller comuosition may be divided into two classes: those influencing the length of the operating life of the roller, such as toughness and heat resistance; and those affecting the quality of the printing, such as surface tack and resilience. Tensile and gel strengths of the roller composition were found to correlate reasonably well with operating life in the field. By measuring gel strength a t two temperatures, SECTlON A-A same idea was obtained of the resistI ance of the roller to softening due to heat. During field trials with formulas devised to obtain the above correlations, the indications were that the tack and resiliency characteristics of sorbitol-glycerol roller composition were satisfactory. Laboratory evaluation of these properties was not undertaken. The physical properties of a roller composition depend upon the water MOLD ACTUAL SIZE content which, under operating conditions, is a function of the hygroscopicity of the composition (4) and the atmospheric conditions. This paper describes the methods and apparatus used t o determine the viscosities of gel, and tensile strengths of glue composition plasticized with sorbitol, with glycerol, and with mixtures of the two over a considerable range of water contents. The ratios of softener to glue studied varied from 1 : l to 5:1, which covers the range of formulations commonly employed in the printers roller industry and inTENSILOMETER FILLING DEVICE cludes formulas employed in the flexible glue, hectograph, and adFigure 1. Tensilometer and Accessories
Viscosity, tensile strength, and gel strength data on a wide range of glue compositions are presented. A comparison of glycerol and sorbitol as softeners is presented, along with data on combinations of the two. Physical properties deteriorate rapidly with an increase in water content. Generally speaking, sorbitol gives a stronger compositioni.e., higher viscosity and tensile and gel strengths; these physical properties are very sensitive to water content of the composition. In general, compositions softened with sorbitol show higher viscosity, higher gel strength, and higher tensile strength than those softened with glycerol.
-
I
948
INDUSTRIAL AND ENGINEERING CHEMISTRY
October, 1945 hesive industries. Formulations containing tanning or i n solu bilizing agents are not included in thisstudy. Standard methods of testing glue were adopted by the National Assoc i a t i o n of G l u e Manufacturers in 1934 (1,3),utilizing the Bloom gelometer and a pipet-type viscometer. However, little has been published concerning the testing of plasticized glue compositions a t low water contents. It was therefore necessary t o devise s ~ b ablemethodsoftesb ing. The dependence of these properties on water content is so great that i t was necessary to know accurately the moisture content of each composition under test. The rapid titrimetric method for determining water (8)developed in this laboratory made possible the requisite control analyses.
500,000 2o4000 WOO0 %000 2qOO0 I0,Ooo -0
TESTING
%OOO
5.0
4000 4.0
gw
2,000 I.000
;C
3.0
d
50 0
j 5000
200
s 2.0
IO0
:% E 54000 J
3
g
i. $
5.0
24000 lop00
hO
7
3.0
''i
smo 2
9
~
,P00
5
500
5
2,000
4
1,000
200
:%E
5.0
so,0oo
Z
W
10,000
0
aooo
~ 4.0
5000 2,000 1.00p
.?so 200
1,000 6 00
150
500
IO0
400
300
50
J
% N;
METHODS OF
6.0
1,0~000
949
200
* 200
too
\
i! g
I50
DETERMINATION P t OB VISCOSITY. A ; i too Hoeppler fallings ball viscometer (6, 50 6 ) w y used for the roller compositions. 0 Viscosities were de200 termined at 75" C. (167' F.) which is in the range of castIS 0 ing temperature for printers roller comIO0 positions. The li quid density was aa50 sumed t o be 1.3 grams per cc. in all Weigh1 Persentage of W o I I # tests. Maximum Figures 2 to 5. Physical Properties of Softened deviation from this Glue Compositions: 2, Viscosity2 3, Tensile value would be 0.1 Strength; 4, Gel Strength at 25 C.; 5, Gel gram per cc., which Strength at 40" C. A. Arlex as softener) variations with weisht percents e water would introduce an eontent; una of coumtant softener-glue ratio *%own. error of less than B. Glyoerol M softener) variations with weight percent e water contents linea of aonstant softener-glue ray0 2%. This is within shown. C. Arlex-gl oerol as *oftener; variations with peraentye of the reproducibility h l e x fn softener finem of eonatant softener corn of the compositions. dotted una are A-Arlex or d-gly-1 softener E%:!
0
600
9 500 4 f
s
400
300
P :
:
900
I5
100
600 500
400
3oo 200
'O0 Wight Pwc-nlop. of Woler
INDUSTRIAL A N D ENGINEERING CHEMISTRY
950
300
iY)QOOO
to0,ooo 200
M.OOO
2qooo 100 l0,OOO
*ooo 0 2.000
lpoo 500
200
*ooo
woo zoo0
p
l,OOO
v)
N
Ratio of Softener to Glue (as Is)
I 8
Figures 6 to 9. Variation of Physical Properties of Softened Glue Compositions with Softener-Glue Ratio (as Is)
g
0 a000
f
m c
A, Arlex as aoftener; B , glycerol M aoftener. Linea show momstant water content (analysad).
2,000
woo
D~ERMINATION OR TENSILE STRENGTH. Measurements were made on a sample of the composition cast in a separable dumbbell mold that freed a 0.25-inch-diameter test section, held in metal at both ends. The test pieces were pulled until rupture occurred, and the load a t rupture was calculated to pounds per squase inch. The sample was loaded automatically on a machine developed specifically for the purpose. The design of the machine and the molds is illustrated in Figure l. Rate of loading of the samples was 215 grams per second. Tensile atrengths were determined a t 25' C. DETERMINATION OF GEL STRENGTH. The instrument employed wm based on the principle of the Bloom gelometer (I). The instrument measures the weight required to press a cylindrical plunger of 1 sq. cm. Gross section into the surface of the b p l e of composition to a depth of 4 mm. Conditions adopted by the National Association of Glue Manufacturers for the testing of gluea produce a gel that has much less compression redietonce than that of a printers roller. Therefore, our instrument was designed to provide a faster rate of loading (76 grams p r second) and a higher total capacity than the Bloom gelometar. Tests were made a t 25' and at 40' C. The firmness at room temperature was thus determined, together with the softening effect of rising temperature, which gives an indication of heat resistance. DETERMINATION OF WATER CONTENT. The Fischer volumetric method was modified as described in an earlier paper (9). Briefly, the method involved weighing the sample (0.5 to 1.0 gram) into a glass-stoppered flask, adding 5 ml. of glacial acetic
0 50 0
400
300
zoo
d
3 400
L
m
3 c7
300 200
100 0
Ratio of sortenor to M a l
Vol. 3'1, No. 10
INDUSTRIAL A y D ENGINEERING CHEMISTRY
oclab.r,1945
~ TABLE I. A N A L YOB~ m Glue
No.
loftener
Softener: Glue Ratio (a8 Is)
Ad.&
B
8 R0-R Vboimit
d,
COMPOSITIONS
36 300
l0:WO 77,400
143 11s 100
2100 1805 2486
878 200 376
17.1 21.0 16.0
42 WO 14:SW 26,700
185 131 160
1990 1606 2120
210 119 408
19.3 21.6
11 160 5:WO
122 93
2016 1760
237 117
ibi
380 0,480 064 290 75.000 44,800 23 100 9:2M 0,970 4,SM 3,780 2 610 2:lM 2,480 1046 d428 88,400
34 88 63
1.76:l 1.76:l 1.76:l
14.8 18.7 14.9
1.75:l 1.7S:l 1.75:l 1.76:l 1.7b:l
a.2s:i
3.26:l 3.26:l 3.S:l 3.S:l 4.0:l 4.0:l 4.0:l 6.0:l 5.0:l 6.O:l 1:l 1:l 1:l 1.76:l 1.7S:l 1.76:l 2.6:l 2.6:l 2.6:l 3.26:l
u
'C.
57 37 15s
398 OOO 177'000 Sl:Mn, 82.700 37 wo d200 79 700 30:raO 10.350 10 100 20:4W 11,0W 3 670 11:aao 1.wo 10,Ooo
::E! 1.76:l
19.9 a2.9 2S.8 17.0 19.8 22.4 14.0 10.7 22.1 10.7 15.2 17.0 21.7 10.0 23.2 16.0 24.9 80.7 14.8 23.1 28.6 17.6 18.6 20.2 10.7 17.9 20.1 14.8 15.9 10.6 13.2 14.8 W.6 12.1
1:l 1:l 1:l 1.76:l 1.76:l 1.7S:l 2.6:l 2.6:l 2.6:l 3.0:l
nith,
ToMII~
at 750 at 260 c., Centipotw Lb./Sq. In.
40'0. 8600 678 3040 278 2890 as0 2000 350 1500 240 114 1140 1890 323 1400 236 1120 117 908 140 187 142 700 75 792 84s 988 070 480 LicQugid 020 400 Liquid 390 Li uid 2945 610 2850 4ao 2.340 234 1883 297 1620 244 1480 113 1190 211 117s 159 108s 104 97s 171 860 110 110 820 628 2620
water
968
193 171 173 149
is5
140 100 84
137 108 88 91 75 98
so 7
161 174 168 118 97 94
&a
68 07
06
wid, allowing the sample to stand overnight at room temperature to &ect solution, adding an excess of modified Fischer reagent, and titrating with water-alcohol solution. The acetic acid introduces water for which a correction muat be made. On occasion, samples very low in water, or tanned t o an insoluble state, were found which would not disperse completely with this treatment. In such caae the sample was heated gently after standing overnight in acid. No compositions have been encountered that would resist this combined treatment. GLUE COMPOSITIONS
Several series of compositions were prepared, tested, and anCLlYBd: (a) aU*orbitol, (a) all-gIYwrO1, and ( 0 ) Soribtol-glY* softened compositions. The b ' e d e n b me fisted with specifications:
A graae of hide glue contsining approximatsly 16 water m d y d 15.3qr); 410 to 415 gel strength (8loom) h-millipoise vurcosity, ground to 24-26 mesh, PfI 5.9 in &% Solution (PHOf PlmtiC1d glue mixture was found t o be 6.0 * 0.2). GLYCEROL.DMamite made. 1%water. SORBITOL. Coinmerci~solution-(hlex)containing 16% water. The ratio of softener to glue was varied between the limits of 1:1 and 5: 1. Each basic composition waa prepared at three different water contents so that the effect of varying water content on the properties under consideration could be determined. A t one softener-glueratio (1.76: l), thecomposition of the softener waa varied from 100% h l e x to 100% glycerol in 25% steps to study the effects of this progressive substitution. The liquid ingredients, including any added water, were weighed into a tared round-bottom flask. The amount chosen was one third t o one half of the volume of the h k . The mixture was ,warmed t o 65-76' C. (with 8 steam or hot water jacket), and the proper quantity of glue was added.
%
951
A tared altpninum stirrer, anchor type, WBB inserted, and the glue waa mixed with the liquid by swirling and brief hand stirring until all of the glue waa wetted by the liquid medium. The neck of the flask waa covered with an inverted one-hole rubber stopper, fitting loosely about the stirrer ahaft. The stirrer waa then driven at a speed of approximately 100 r.p.m. Heating waa continued in the water bath (at 75' C.) until there were no detectable swollen undispersed glue particles. A uniform cooking time could not be established since the dispersion and degradation of the glue at the cooking temperature are a function of time, water content, and softener-glue ratio. Thus, in a highratio or high-water-content composition the glue is dispersed in appreciably less time than in a low-ratio or low-water-content formula; if t h e two are heated the same length of time, the higher rate of degradation for the former cornposition would result in too great a change in physical properties. One and a half hours were sufficient for complete cooking of a majority of the compositions. Thirty minutes and 4 hours represent extremes in time of cooking. Good agreement of data were obtained on duplicate preparations. PHYSICAL PROPERTIES
The data are summarized in Table I. It must be kept in mind that softener-glue ratios and softener percentage compositions are based on the ingredienta as commercially available. The water contents (column 4) are, on the other hand, analyzed values and include the moisture of the ingredients as well aa the added water. In computing the formulas, it was necessary to allow for the water of the ingredients in order to bring the analyzed water values within thedesiredrange. The physical properties given in Table I are plotted as a function of water content (at constant softener-glue ratios) in Figures 2 to 6. A satisfactory graph for viscosity vu. water content, e& sentially linear throughout the working range, waa obtained by 1), where cp. r e p plotting the empirical function log-log (cp. resents the Hoeppler viscosity in centipoises. Besides being considered from the standpoint of varying water content, the data may be expressed aa a function of the softenerglue ratios (at constant water contents) in Figures 6 to 9. I n plotting viscosity uu. softener-glue ratio (Figure S), linear curves were obtained if logarithmic scales were used for both ordinate and abscissa. For the other properties no true linear relations were found. However, the use of the logarithm of softener-glue ratio in these curves was found t o be advantageous.
+
TABIJ~ 11. COMPARISON OF ~ O P E R L YCOOKED rn O ~ R C O O X E D SORBITOI~SOBTENED COMPOSITIONS No,
Softener: Glue (as Ratio Ia)
%
An- Visoosit st dater aed 7b0C..6entipoises 81
Tensile a t
Lb.,Elq. 7S0 C..In.
G e l ~ ~ ~ ~ ~ t h
260
40a
..,
Properly Cooked ~-17 A-18 A-20 A41
4.0:r 4.0:l 5.0:l 6.0:l
;:$::: i:gi: g:gi:
24.9 30.7 23.1 28.5
g;i I;:;
968
00
804 298
63
380
34
7
070 480 460 390
80
Liquid Liquid Liquid
Overoooked 414 129 318 169
7 7 7 7
260 160 270
240
Liquid Liquid Liquid Liquid
INDUSTRIAL AND ENGINEERING CHEMISTRY
952
Vol. 37, No. 10
Compositions corresponding to formulas A-17, -18, -20, and -21 of Table I were prepared, and heating was continued for approximately 4 hours aftkr the glue had been dispersed. Table I1 lists the properties of the overcooked compositions and those prepared in the standard manner. The difference in results is most noticeable in the gel strength determinations. The degradation of the glue in this fashion, a t a constant pH, is apparently a function of time, temperature, and concentration of glue. Thus, certain of the 1: 1 compositions were cooked for a long time without noticeable degradation, but high-softener or high-water-content glue formulas seem to be greatly aff ccted by such trcatment. The discrepancies noted in the 25” C. gel strength (Figure 4A) are probably traceable to this trouble. Apparently, for the same reason the 25’ C. gel strengths for sorbitol-glycerol cornpositions were too erratic to plot. The present data are based on glue having a gel strength of 415 grams and are therefore strictly applicable to the preparation of formulas from such a glue. However, they have been used for comparative purposes with some success for glues with gel strength ranging from 200 to 465 grams.
50.000
20,000 10.000 5,000
CONCLUSIONS
Ratio of Softener t o Glue
Figure 10. Variation of Physical Properties of Glue Compositions with Composition of Softener at 20% Water Content and 1.75-1 Softener-Glue Ratio
Figure 10 illustrates the variation of physical properties with changing composition of softener (at constant softener-glue ratio and at constant water content). It is generally conceded that, with prolonged heating, glue compositions undergo deterioration. I n the present work i t was not feasible to standardize on a single heating time for all compositions since the time required for complete dkpersions of the glue was much shorter at high softener-high water contents than when the glue content was high. Furthermore, it was evident that the degradation was more severe when the water content was high so that the practice throughout this study was to pour each batch as soon as there were no detectable particles of swollen glue in it. Serious degradation by overcooking is illustrated in the following experiments.
The curves show that the replacement of glycerol by sorbitol in glue compositions increases the viscosity, tensile strength, and gel strength. I n most applications, these are desirable treAds. Thus, in printers rollers, higher tensile and gel strengths, particularly a t elevated temperatures, permit higher press speeds and operating temperature. The higher viscosity of sorbitolcontaining compositions may necessitate modification of operating procedure and formulation. I n printers roller formulas, particularly, it is undesirable to increase the fluidity for ease in casting by increasing the water content since this would increase the risk of roller shrinkage. The proper modification is to raise the casting temperature or to increase the softener-glue ratio (or a combination of the two). It was not feasible to include in this study all of the properties pertaining to the quality of a roller. Thus, resiliency, tack, etc., are important factors. I n general, it has been found in plant tests that a roller of excellent wearing properties combined with good printing characteristics is obtained when approximately equal quantities of glycerol and sorbitol are used. LITERATURE CITED
(1) Alexander, Jerome, ‘ G l u e and Gelatin”, A.C.S. Monograph 11, 1st ed., p. 227, New York, Chemical Catalog Co., 1923; Allen’s “Commercial Organic Analysis”, 5th ed., Vol. 10, Chapter on Scleroproteins, 1933. (2) Almy, Griffin, and Wilcox, IND.ENQ.CKEM.,ANAL.ED., 12, 392-6 (1940). (3) Government Printing Office, Tech. Bull. 24 (1942).
(4) Griffin, IND. ENG.CHEM.,to be published. (5) Hoeppler, F., Chem.-Ztg., 57, 62-3 (1933). (6) Hopppler, F., 2. tech. Physik, 14, 165 9 (1933).
Correlating Vapor Compositions and Related Properties of Solutions-Correction A mistake in this paper which appeared in the September, 1944, issue has been called to my attention. I n the discussion under “Partial Heats of Solution” on page 860, the second sentence reads: “The heat required to vaporize one mole of one component ( L ) from a solution is equal to the latent heat of the pure com-
ponent ( L ” ) ,plus its partial heat of solution ( H ) , etc.” This sign should be minus rather than plus, as well as those in the corresponding formulas of Table I, the second line for pi. This line should read as follows:
D. F. OTHMER
