NICHOLAS M. TRIVISONNO, LIENG HUANG LEE, and SELBY M. SKINNER Case Institute of Technology, Cleveland 6, Ohio
Adhesion of Polyester Resin to Treated Glass Surfaces
T H E effect of glass finishing agents on the bonding strength between polyester resin and glass has been in question. I t is generally believed that these agents affect the adhesive bond strength between resin and glass (3, 5-7, 70, 79, 20), which in turn affects strength of reinforced plastics. Other opinion holds that adhesion changes little (77), or that the adhesive bond strength is not a primary factor in determining the strength of reinforced plastic (73). Glass surfaces were treated with some 60 finishing agents or combinations of agents, chosen for their ability to form a primary chemical bond between the glass and unsaturated polyester resin, or good adhesion to glass and plastics (72). A simultaneous study was made of the electrostatic phenomena that occur in adhesion (8, 9, 74-78) and account for a portion of the adhesive forces.
Effects of Glass Finishing Agents on Bonding Strength
Cross-Lapped Glass Adhesion Specimens. Adhesion specimens for testing
Figure 1, Cross-lapped adhesion specimens, with cementing iig and holder used with Baldwin Tate-Emery testing machine
9 12
the effect of glass surface treatments were made from cross-lapped glass blocks I1/a x 1 x '/z inch (Figure 1). Initial adhesion tests were made on glass blocks that had been subjected to a detergent wash, soaking in 18% nitric acid a t 50" C. for 24 hours, distilled water wash, soaking in acetone for 24 hours, and drying at 100' C. for 1 hour. Previously existing finishes (Table I) were applied in accordance with procedures given in the literature. Where necessary, as with silane-containing finishes and Volan, a distilled water wash was used after application of the finish. Otherwise the materials were applied so as to assure proper cure or reaction conditions. The finishing agents for the initial tests were for the most part applied from 3% solutions in suitable solvents (Table 11). A specially prepared polyester resin, used for these preliminary tests, was composed of 5, 5., and 11 moles of maleic anhydride, phthalic anhydride, and diethylene glycol, respectively, and 0.0037, of p-tert-butyl catechol. Styrene was added to the esterified product to a final composition of 30% by weight. The resulting solution had an acid number of 28 and a viscosity at 25' C. of 500 to 1000 cp. Catalysis was with 0.17% of 6% cobalt naphthenate, and 0.5% of 60% methyl ethyl ketone peroxide, resulting in an 8-minute gel time at room temperature (23' C.). After cementing, the specimens were allowed to cure for 1 week a t 27' C. in a nitrogen atmosphere before testing. Fifteen finishing agents which gave a wide distribution of bond strengths were chosen, and final adhesion tests were made on specimens that had been treated and cured as much as possible like the glass cloth laminates. The glass blocks were subjected to the same cleaning schedule as the glass cloth-Le., a detergent wash, distilled water rinse, ace-
INDUSTRIAL AND ENGINEERING CHEMISTRY
tone rinse, and heat cleaning at 345' C. for 8 hours. The finishes were applied from lY0 instead of 37, solutions. Paraplex P-43 polyester resin (Rohm & Haas) catalyzed with 2% of a mixture of 50% benzoyl peroxide in tricresyl phosphate was used to cement the blocks together, and they were cured for 1 hour at 71' C., followed by 0.5 hour at 116' C. The specimens were tested for adhesion following conditioning for 2 weeks at 23" C. and 50% relative humidity. Glass Cloth Laminates. Laminates were made from the group of 15 selected finishes. A single roll of 181 style heatcleaned glass cloth was used. Each laminate was formed from 12 layers of glass cloth, 9 X 5l/2 inches, laid face to back. Prior to treatment with the finish, the cloth was rinsed with acetone and heat-cleaned at 345' C. for 8 hours. The finish was applied in the same manner as with the glass blocks. The
Figure 2. Laminates were prepared in a vacuum impregnation apparatus
cloth was impregnated with Paraplex P-43 polyester resin (catalyzed with 270 of a mixture of 50% benzoyl peroxide in tricresyl phosphate) a t 60-mm. pressure (70) a t about 45' C. for 30 to 40 minutes. The resin and cloth were first deaerated for 15 minutes under these conditions, and then the cloth was lowered into the resin (Figure 2 ) . The impregnated cloth was heatsealed in poly(viny1 alcohol) envelopes, and air bubbles were removed by hand smoothing. The cloth was cured between open plates separated by stops 0.120 inch thick; the cure cycle was 1 hour at 71" C. and 100 p.s.i,, followed by 0.5 hour at 116" C. and 100 p.s.i. Four laminates were made with each finish. Each laminate was cut into eight flexural specimens 4 inches long and 1 inch wide, four samples parallel to the wrap and four perpendicular. The finished specimen was conditioned under ASTM conditions (2 weeks a t 23" C. and 50% relative humidity) before flexure testing (7). Half of the samples were tested dry and half after a 2-hour boil in water (Table 111). Results, Flexural strength results for the laminates were subjected to statistical analysis. The finishes were divided into groups showing significant differences in mean flexural strength values at the 99% confidence level as shown by the Tukey test (4,for both the dry and the 2-hour water boil tests (Table 111). Wet strength retention was calculated for each finish (Table IV). Mean dry flexural strength in the warp direction for the laminates was plotted against bonding strength as obtained in the final adhesion tests with Paraplex P-43 resin (Figure 3). Discussion. The glass finishes tested can be classified into three general types: chemically bonding, polymeric, and combinations of chemically bonding and polymeric. The chemically bonding types contain functional groups capable of reacting with the glass surface, the unsaturated polyester resin, or both. Bonding of the polymeric finishes has been attributed to dipolar or van der Waals-type forces, hydrogen bonding, or electrostatic forces. When a combination of a chemically bonding material and a polymer is used, it is often possible to obtain a chemical bond network which ties together the glass surface, the polymeric finishing agent, and the polyester resin. The chemically bonding materials are represented by vinyltrichlorosilane, vinyltriethoxysilane, methacrylato chromic chloride, and tolylene diisocyanate, which react as shown a t bottom of page
915. Adhesion tests show that both the chemical bonding and polymeric types of finish improve the bonding strength between unsaturated polyester resin and
Table 1. Trade Name Acryloid A-10 Bostik 7026 Butarez 25 Butvar 76 C-802 Cycleweld C-3 Cycleweld H-2-D Cycleweld 55-9 Epon 1007 Fuller's adhesive J-1151 M-3C Metagrip 3799 No. 385 NOL-24 NOL-28 P-360 Phenolic P-97 R-108 R-313 Silastic S-5302 Tygobond 30 Volan X-31 571 833-8 2021
Composition and Source of Commercial Products
Composition Acrylic ester resin Poly(viny1 butyral) Liquid polybutadiene Poly(vinylbutyra1) Not specified Phenolic-neoprene Phenolic-Buna N Phenolic-poly(viny1 butyral) Epoxy resin Poly(viny1 acetate) emulsion Epoxy resin Phenolic-neoprene Not specified Epoxy resin Allyltrichlorosilaneresorcinol Vinyltrichlorosilaneresorcinol Epoxy resin Phenolic resin 2,4,6-Trimethylolphenyl allyl ether Epoxy resin Silicone rubber Vinyl resin-synthetic rubber Methacrylatochromic chloride Poly(viny1 siloxane) Neoprene latex Synthetic resin-synthetic rubber Phenolic-Buna N
glass. Vinyltrichlorosilane, or vinyltriethoxysilane is much more effective than methyltrichlorosilane, supporting the contention that the vinyl group polymerizes with the styrene-unsaturated polyester resin. Tolylene diisocyanate also proved effective as a finishing agent. I n this case the isocyanate groups are potentially capable of reacting with the hydroxyl groups of the glass surface, and excess hydroxyl or carboxyl groups on the polyester. Adsorbed water on the glass surface can also react to form long-chain molecules. Bonding strengths equal those obtained with vinyltrichlorosilane. An attempt was made to introduce an unsaturated group into the tolylene
Table
II.
Supplier Rohm & Haas B and B Chemical Co Phillips Petroleum Monsanto American Resinous Prod. Cycleweld Cement Products Cycleweld Cement Products Cycleweld Cement Products Shell Chemical H. B. Fuller Co. Armstrong Cork Co. Narmco Products Adhesive Products Corp. Carl H. Biggs Co. Prepared in lab. after Naval Ord. Lab. recipe Wilross Products Co. Monsanto General Electric Carl H. Biggs Co. Dow-Corning U. S. Stoneware Co. Du Pont Linde Air Products Dow Magic Chemical Co. Narmco Products
diisocyanate molecule by reaction with acrylic acid. The resulting product gave good results, but not so good as the tolylene diisocyanate alone. Similarly, a mixture of vinyltrichlorosilane and tolylene diisocyanate did not improve the bonding strength above that obtained with either component alone. Methacrylate chromic chloride, which has a double bond attached to a polar grouping like that introduced into the tolylene diisocyanate, gave little improvement over the untreated glass surface. Methyltrichlorosilane, which cannot react with the polyester resin, gave comparable results, indicating that degree of chemical bonding obtained with methacrylatochromic chloride was not high.
Composition of Glass Finishing Agents
Finish
No. 1 2
3 4 5 6 6A-1 6A-2 6A-3 6A-4 6A-5 6B 6C
C~rnpn.~ MTS Butadiene-AA copolymer AA-vinyl acetate copolymer AA-vinyl acetate-VTS polymer R-108 R-108 VTS R-108 VTS R-108 VTS R-108 VTS R-108 VTS R-108 VTS R-108 MTS R-108 VTS Acryloid A-10
(Continued on
% 2 3 3 3 3 3 4 3 0.9 3 1.8 3
Solventa T D D
Bond Strength, P.S.I. AV. Max.
D D
133 104 81 126 153 573
177 133 85 140 165 775
D
363
472
D
477
515
D
534
713
D
416
486
D
603
810
D
230
250
D
485
665
D
6
3 8
1 3 3 4 3 4 1 page 914)
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Table II.
No. 6D 6E 6F 6G
7 8 8A 8B 9 10 11 12 12A 13 14 15 16 17 18 19 20 21 22 22A 23 23A 24 24A 26 27 28 29 31 32
33 34 34A 35 35A 35B 35c 35D 35E 36 36A 36B 36C
Composition of Glass Finishing Agents (Continued)
Finish Compn.a R-108 VTS Butvar 76 R-108 VTS Epon 1007 R-108 VTS Phenolic P-97 R-108 VTS Phenolic P-97 Butvar 76 VTS Tygobond 30 VTS Tygobond 30 VTS R-108 Tygobond 30 None 833-8 Volan Butarez 25 VTS Butarez 25 Bostik 7026 NOL 28 NOL 24 Hydrolyzed vinyltriethoxy silane (VTES) X-3 1 Fuller’s adhesive Hydrolyzed VTES 571 571 Hydrolyzed VTES Silastic 5-5302 Cycleweld C-3 Cycleweld C-3 VTS Cycleweld 55-9 Cycleweld 55-9 VTS Cycleweld H-2-D Cycleweld H-2-D VTS R-313 No. 385 Fuller’s adhesive J-1151 2021 M-3 C P-360 Hydroabietyl maleate (HAM) HAM VTS Tolylene diisocyanate (TDI) TDI VTS TDI R-108 TDI R-108 VTS TDI AA TDI AA VTS Butvar 76 Butvar 76 Tygobond 30 Butvar 76 TDI Butvar 76 HAM
70
Solvent4
Bond RtrPnath. P.P.T. AV. Max.
3 4 1 3 4 1
D
514
759
D
547
1000
3
D
44 1
548
D
2 74
500
T T
3 70 720
480 902
1.5 3 3
D
721
920
3 0
T
3 2
A W T
469 99.5 530 132 318
546 125 687 181 439
T D T T W
185 123 360 332 286
215 170 447 408 303
T W
175 264
218 2 74
w w
200 269
256 290
T D D
50.0 237 511
58.8 265 550
D D
170 307
212 495
D D
278 317
335 413
T-MIBK T-MIBK W T T T T D D
226 92 178 203 265 460 173 123 293
226 108 200 217 289 493 258 162 364
T T
3 73 374
471 483
T-MIBK
238
258
T-MIBK
427
514
T
305
353
T
332
405
D D
23 1 248
341 346
D
140
180
D
302
357
4 1
3 4 1 1 3 3 1
3
1 3 3 3
3 3 3 1.5 1.5 3 1.5 1.5 3 3
3 1 3 3 1 3 3
...
1
3 3 3 3
3 3 3 3 3
3 3 3 3
3 3 3 3
3 3 3 3 3 3 3
3
3 3 3 3 3
a T = toluene; D = dioxane; W = water; A = acetone; MTS = methyltrichlorosilane; AA = acrylic acid; VTS = vinyltrichlorosilane.
9 14
INDUSTRIAL AND ENGINEERING CHEMISTRY
High polymer films also improved bond strength in several cases. In fact, finishes composed of combinations of the phenolic-neoprene or vinyl resin-synthetic rubber types improved adhesion of polyester resin to glass more than any of the chemically bonding finishes. The improved performance of a polymeric finish may be attributed to its acting as a flexible layer between the rigid polyester and the rigid glass. Stresses set up at the interface by the shrinkage of the polyester during cure thus can be relieved by the finish. This viewpoint is supported by the fact that the best polymeric finishes contained some type of elastomer. Combinations of chemically bonding and polymeric types of finish were tried in an effort to take advantage of the good properties of each. Table I V shows that the wet strength retention obtained with lhe chemically bonding type or finish i s much better than that obtained with a nonchemically bonding type. When water penetrates to the adhesive interface, it can mask electrical forces between the adherends because of its high dielectric constant. When covalent bonds can form. however, this effect is less significant or absent because of the very close approach of the bonding substances. A proper combination of the two types of finish would thus give the flexibility of the polymeric type combined with the covalent bonding of the Chemically bonding type. Finishes of this type are 6, 8, 12, 18, and 20 (Table 11). Finishes 18, 20, and 12-representing poly(viny1 acetate)-vinyltriethoxysilane, neoprene latex-vinyltriethoxysilane!and liquid polybutadiene-vinvltrichlorosilane-have no sites on the polymer molecule capable of reacting with the chemically bonding component; the bond strength is intermediate between that obtained with either component alone. Finishes 6 and 8-2,4,6-trimethoxyphenyl allyl ethervinyltrichlorosilane, and vinyl resin [probably poly(viny1 butyral) ]-synthetic rubber-contain sites on the polymer molecule capable of reacting with the vinvltrichlorosilane. In this case the bonding strengths are higher than those obtained with either component alone, and the wet strength retentions are the highest obtained rvith any of the finishes. It appears that a higher average bonding strength was obtained with finish 8, than with finish 6 because it gives a more flexible coating. The polymercontaining finishes, however, tend to seal together the fine filaments of the glass cloth, making it difficult for the polyester resin to penetrate and wet out the cloth thoroughly. Thus finish G is better than 8 as a finish for glass cloth because it is originally of much lower molecular weight, and does not cause as much sealing together of the filments. This is further illustrated in Figure 4 ;
A D V A N C E S IN A D H E S I V E S
Table 111.
the relative transparencies of the laminates show that with finish 6, the polyester resin has wet out the glass much better. If the finish could be applied to the filaments at the furnace bushing as they are drawn, this difficulty could be overcome. When bond strengths greater than those conferred by vinyltrichlorosilane were obtained, the specimen invariably broke within the glass and bond strength was too low. In Figure 3, therefore, the high bonding strength points should be extended some distance to the right, further flattening the curve. The strength of the laminate is strongly dependent on the bonding strength between the polyester resin and glass initially, but once a certain value of adhesion is reached and exceeded, laminate strength remains fairly constant. The critical value of adhesion depends on the strength and modulus of elasticity of the resin and glass used, and also on the arrangement, size, and length of the glass fibers. I n this case increasing the bond strength above that obtained with vinyltrichlorosilane results in only a small increase of laminate strength, although this increase is statistically significant (Table 111). Microscopic examination of the broken laminate edges after flexural testing clearly points out the effect of bonding between the resin and fiber. Figure 5 illustrates a laminate treated with vinyltrichlorosilane, in which the bond strength is high and the fiber bundle has remained fairly coherent, with only short fiber ends pulling loose. Inter-
Grouping of Finishes
(Groups show significant differences a t 99% confidence level according to Tukey test) Dry Wet Flexural Flexural Finish strength, strength, Finish No. p.s.i. p.s.i. No. 6 75,000 6 67,400
7 15
71,600 71,200
7 15 12
12 8 16 11 14
68,000 65,300 64,000 62,200 57,600 57,000 53,600 52.700 49,400 48,600 45,700 19,600
a
63,200 63,000 62,000 61,000
16 14 11 20 18 17 10 9 1? 21
57,400 54,000 46,200 45,600 44,300 36,800 32,500 32,000 31,700 16,100
10 9 20
17
ia
19 21
Table IV. W e t Refention at 95% Finish
No. 8
6 14 12
ia 15 16 7
Strength Retention Limits, %
82.6-100 82.6-97.6 79.5-100 79.2-99.0 77.3-100 78.0-99.0 74.2-100 67.1-100
Flexural Strength Confidence Level
No. 20 21 11 19 17 9
Strengtli Retention Limits, % 66.1-100 64.4-98.6 58.8-90.4 47.4-91.6 43.3-96.2 45.8-76. o
10
41.2-74.8
Finish
Reaction of Chlorosilanes with the Glass S u r f a c e
_-I___I-
__1___1_
-Si- 0 - SI- 0 I
Qeoction
'F
0
100
ZOO 300 400 Bonding Slrenpih- Ib /sq in.
500
Figure 3. Variation in flexural strength with adhesive bond strength for different finishes
mediate adhesion with longer loose fiber ends is obtained with untreated glass and Figure 6 illustrates the poor adhesion obtained with a silicone rubber finish, and the long fiber ends which have pulled out of the polyester resin. The degree of wetting of the fibers and the adhesion between polyester resin and fiber glass are indicated by the relative transparencies of the laminates (Figure 4). I n general, the better the adhesion, the more transparent the
of Methacryloto Chromic Chloride with the Glass Surfoce H2 C =C-CH
__I__
- SI - 0 - Si - 0 - SiI -
I I I R e a c t i o n of Chlorosilanes with Resorcinol
Reactions of Tolylenc Oiisocyonote FH3
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915
Figure 4. Relative transparencies of laminates with various finishing agents
Figure 5. Broken laminate edge, high bond strength
Figure 6. Broken laminate edge, low bond strength
laminate. Examination of these laminates explains why finishes 8 and 10 had lower laminate strengths than expected from their bond strength values. The relative opacity of their laminates suggests incomplete wetting of the fibers by polyester resins and consequent scattering of light. This accounts qualitatively for the points in Figure 3 which lie far off of the curve. Conclusions. Application of a surface treating agent to a glass surface has a definite effect on the adhesive bond strength obtained with an unsaturated polyester resin-styrene combination. Agents that are capable of reacting with both the unsaturated polyester-styrene resin and the glass surface, such as methacrylatochromic chloride, vinyltrichlorosilane, and tolylene diisocyanate, improve the bond strength. Certain types of polymeric materials, such as poly(vinyl butyral)-neoprene or phenolicneoprene, also improve the adhesive bond, probably in part because of the formation of a flexible layer which takes up stresses between the glass and polyester resin caused by shrinkage of the polyester-styrene mixture during polymerization. Finishes from combinations of chemically bonding materials and polymers with which they are capable of reacting possess the advantages of both types. Thus a flexible finish is obtained which increases the bonding strength above that obtained with either material alone, and exhibits excellent wet strength retention. Examples of such finishes are 2,4,6-trimethylolphenyl allyl ether-vinyltrichlorosilane,and poly(vin) 1 butyral)-synthetic rubber-vinyltrichlorosilane. Finishes that improve bond strength also improve the flexural strength of reinforced plastics fabricated from a n unsaturated polyester-styrene resin and treated glass cloth. When the bond strength is greater than that obtained with vinyltrichlorosilane, the improvement is not as marked as at lower bond strengths, however. Finishes that incorporate a chemically bonding agent give wet strength retentions superior to those obtained with nonchemically bonding finishes. Relation of Electrical Effects to Adhesion
Figure 7. men
Cylindrical adhesion speci-
Brass stock is j/, inch in diameter, % inch long, drilled and tapped '/z inch deep for a %.lo thread
9 16
Measurements of the electrical charge transfer accompanying the adhesive bond were not satisfactory with the crosslapped specimens because of the thickness of high resistance dielectric and the difficulty of interpreting results with the geometry of the specimens and holders. New specimens were made in which a thin slip of glass, 0.15 mm. thick, was cemented to a brass cylinder with a n epoxy resin. Two of these were then cemented together with polyester resin to form a n adhesion specimen (Figure 7 ) . One of the glass slips was treated with
INDUSTRIAL AND ENGINEERING CHEMISTRY
finishing agent 6; the polyester resin adhered tightly to this surface and broke cleanly from the other surface. A Baldwin Tate-Emery tensile test machine was used to break the specimens, with the stress applied accurately perpendicular to the plane of the interface; leads from the adherends were connected directly to the oscilloscope (76) with no potential source in the circuit other than the adherends. After break, the separated surfaces were dusted with a mixture of charged fluorescent powders to obtain a pattern of the electrical charge distribution. Results. A typical electrical charge pattern obtained immediately after break is shown in Figure 8. Figure 9 shows a typical oscilloscope trace for a specimen broken in air at atmospheric pressure, 23' C., and 50% relative humidity. The vertical voltage scale is 25 volts per major scale division, and the horizontal time scale is 100 microseconds per major division. The peak voltage is therefore about 80 volts, and the total time of the trace about 1 millisecond. These traces were nearly reproducible from sample to sample. Oscilloscope Traces. The voltage us. time trace obtained when an oscilloscope is connected across the specimen during break indicates that, at the interface there was a transfer of charge prior to the break (74, 78) (essentially a double layer). Adhesive break is a nonequilibrium rapid separation of the two halves of the double layer, and from the trace-for example, from the area or curvature-the magnitude of the charge originally separated can be found. The indicated original charge separation can be used to calculate the electrostatic component of adhesion. Integration of the area under the trace shows that the charge distribution in these cases is equal to or more than the 8 e.s.u. per sq. cm. necessary for discharge in air (an electrical field of about 30,000 volts per cm.), indicating that the original charge transfer was greater than the amount obtained from integration. The determination of these charge values, and their values in relation to the experimental parameters will be treated elsewhere. The theoretical considerations involved in this transfer of charge have been pursued exhaustively (74, 75, 77, 78). Charge Distribution and Electrical Discharge during Break. Both freshly separated surfaces are insulating and therefore the charge remains on these surfaces for appreciable lengths of time (27). The charge flow through the external circuit brings an inductively neutralizing charge to the metal on the other side of the dielectric. However, the charged fluorescent powder is blown into direct contact with the charged surface, and positively and negatively charged powder particles deposit selec-
ADVANCES IN ADHESIVES tively on oppositely charged portions of the surface. Because under ultraviolet illumination, the two differently charged types of powder fluoresce in different colors, the color distribution permits mapping of the charge distribution on the specimen immediately after break. From the charge patterns it is evident that electrical discharge has occurred during the break. The charge pattern pictured in Figure 8 can be explained as follows. As the charged sample halves separate, there is a Kelvin condenser type of rise in electrical potential between the&. Initially there is essentially zero atmospheric pressure between the separating disks. As the sample halves separate, the pressure differential between the atmospheric pressure surrounding the sample and the near zero pressure in the interior causes flow of air from the rim toward the center of the separating halves. As the air effuses in toward the center, a region is formed where the product of the air pressure and distance of separation of the surfaces is suitably related to the voltage between the surfaces (Paschen’s law), so that a n electrical discharge occurs. This discharge lowers the charge density around the rim of the sample, and therefore the electrical potential between the two halves in the vicinity of the rim. A potential difference is set u p between the center of the specimen and the rim, and a surface discharge now occurs parallel to the original interface, and along the insulating glass or polyester; this is responsible for the Lichtenberg-figure-like pattern in the center portion of the pattern. This surface discharge tends to equalize charge distribution over the surface of the glass or polyester. As the halves of the specimen separate further, this charge is again responsible for increase of potential, and a second discharge takes place between halves of the sample, accounting for the thin line surrounding the Lichtenberg figure. Relation to Oscilloscope Pattern. I n the oscilloscope pattern of Figure 9, it would seem that the major discharge effects occur at the initial high peak, and on the downward slope. Because individual discharges take place in the order of 10-7 second, they are smoothed out on the time scale of the trace, and it is impossible to pick out small discharge detail. During the initial portion of the curve, field emission may occur, a t least from points or other regions of sharp curvature. The secondary peak a t 180 microseconds is apparently due to the continued separation of the residual charges after the first (rim) discharge, while the small transient a t 260 microseconds is caused by a mechanical displacement of the charged surfaces due to the arrival of a reflected
shock wave initiating in the initial break. Conclusions. A charge transfer occurs at an adhesive interface between an unsaturated polyester-styrene resin and glass. T h e value of the charge transfer accompanying the adhesive contact between the two substances exceeds that necessary to produce atmospheric discharge. The atmospheric discharge occurs between the two halves of the bonded specimen in accordance with physical principles governing electrical discharge, and accounts for the crackling and blue light sometimes observed when adhesive specimens are broken in the dark. As the discharge occurs, the remaining charge which can contribute to the electrostatic component of adhesion is decreased, so that the value of this component decreases progressively during the early stages of break. On insulating-such as polymericsurfaces, there remain charge distributions after break which, together with the oscilloscope trace during break, permit description of the electrical effects occurring during the actual break. literature Cited
(1) Am. SOC. Testing Materials, Philadelphia, Pa., “ASTM Standards,” pt. 6, p. 165, Tentative Method of Test D 790-491’, 1955. (2) Zbid., D 1344-54T, Pt. 7, p. 1219, 1955. (3) Bacon, C. E., Modern Plastics 29, 126 (July 1952). (4) Bennett, C. k, Franklin, N. L., “Statistical Analysis in Chemistry and the Chemical Industry,” Wiley, New York, 1954. (5) Biefield, L. P., Philipps, T. E., IND. END.CHEM.45,1281 (1953). (6) Bjorksten, J., Yaeger, L. L., Modern Plastics 29, 124 (July 1952). (7) Bjorksten, J., Yaeger, L. L., Henning, J. E., IND.END. CHEM.46, 1632 (1954). (8) Deryagin, B. V., Krotova, N. A., Doklady Akad. Nauk S.S.S.R. 61, 849 (1948). (9)1Deryagin, B. V., Krotova, N. A.? Kirillova, Y. M., Ibid., 97, 475 (1954). (10) Erickson, P. W., Silver, I., Perry, H. A., Division of Paint, Plastics, and Printing Ink Chemistry, 125th Meeting, ACS, Preprint, 14, 19 (1954).
Figure 8. Typical electrical charge pattern on freshly separated surfaces Positive and negative charged regions shown b y arrows
are
(11) Hecht, 0. F., Coles, H. W., Keeler, M. M., in Clark, F., Rutzler, J. E., Savage, R. L., “Adhesion and Adhesives Fundamentals and Practice,” pp. 60-4, Wiley, New York, 1954. (12) Moser, F., Division of Paint, Plastics, and Printing Ink Chemistry, 127th Meeting, ACS Preprint, 15, 83-92 (1955). (13) Outwater, J. O., Jr., Modern Plasttcs 33, 156 (March 1956). (14) Skinner, S. M., J.Appl. Phys. 26, 498 (1955). (15) Skinner, S. M., Gaynor, J., Plasttcs Technol. 1, 626-32 (1955). (16) Skinner, S. M., Gaynor, J., Sohl, G., Modern Plastics, 33, 127-36, 264 (February 1956). (17) Skinner, S. M., Savage, R. L., Rutzler, J. E., Jr., J. Apple Phys. 24, 438 (1953). (18) Zbid., 25, 1055-6 (1954). (19) Slayter, G., others, Modern Plasttcs 21, 100 (May 1944). (20) Steinman, R., Zbid., 29, 116 (November 1951). (21) Woodland, P. C., Ziegler, E. E., Modern Plastzcs 28, 95 (May 1951). RECEIVED for review October 4, 1957 ACCEPTED December 20, 1957 Division of Paint, Plastics, and Printing Ink Chemistry, Symposium on Recent Advances in Adhesives, 132nd Meeting, ACS, New York, N. Y . , September 1957. Work on effects of glass finishing agents performed under an Industry Preparedness Measure contract with the Military Medical Supply Agency (formerly Armed Services Medical Procurement Agency). Work on electrical effects supported by Office of Ordnance Research, U. S. Army.
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