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INDUSTRIAL AND E N G I N E E R I N G C H E M I S T R Y
3 = refers t o exit from upper salt bed of reactor Subscripts 0 through 3 are also used to refer t o the level of conversion a t these points Superscripts
’ = refers to pseudo-bed of catalyst of size required to account for catalytic plus all homogeneous reactions REFERENCES
(1) de Simo, M., U. S. Patent 2,187,393 (Jan. 16, 1940). (2) Fisher, R. A., Ph.D. thesis in chemical engineering, Purdue
University, February 1950.
(3) Fisher, R. A., and Smith, J. M., IND.ENG.CHEM.,42, 704-9
(1950).
*
1281
(4) Folkins, H. O., Miller, E., and Hennig, H., Ibid., 42, 2202-7
(1950). (5) Forney, R. C., Ph.D. thesis in chemical engineering, Purdue University, August 1950. (6) Forney, R. C., and Smith, J. M., IND. ENG.CHEM.,43, 1841-8 (1951). (7) Hougen, 0. A., and Watson, K. M., “Chemical Process Principles,” Part 111, “Kinetics and Catalysis,” Chap. 19, pp. 902-72, New York, John Wiley & Sons, 1947. (8) Jackson, E. G., M.S. thesis in chemical engineering, Purdue University, August 1951. (9) Preuner, G., and Schupp, W., Z. physik. Chem., 68, 129-58 (1909). (IO) Thacker, C. M., and Miller, E., IND.ENQ. CHEM.,36, 182-4 (1944). (11) West, J. R., Ibid., 42,713 (1950). ACCEPTEDMarch 14. 1953. RECEIVED for review November 24, 1952.
(End of Symposium) Reprints of this symposium may be purchased for 75 cents each from the Reprint Departmlt, American Chemical Society, 1155 Sixteenth St., N.W., Washington 6, D. C.
Finishes for Glass Fabrics for
Reinforcing Polyester Plastics L. P. BIEFELD AND T. E. PHILIPPS Owens-Corning Fiberglas Corp., Newark, Ohio
L
AMINATES of fibrous glass fabrics and heat-convertible, unsaturated polyester plastics are used extensively in the aircraft industry. They have high strength] low weight, and dimensional stability. They resist water, corrosion, and weather (1, 16, 91). Figure 1 illustrates a glass-polyester frame part for a helicopter. Figure 2 shows a comparison of tensile yield strength for glass-polyester combinations, structural aluminum, and steel. Continuous-filament glass fabrics as they come from the loom do not give laminates with these desirable properties. The fabrics contain a n oily, starch size which prevents fast, complete wetting out by the plastic during impregnation, and prevents good adhesion of the plastic to the fibrous glass in the cured laminate (5). I n order to obtain laminates with good properties, the original size must be removed from the fabric and a glass-topolyester coupling or finishing agent must be applied. The desizing and finishing processes convert the fabric from a poor t o an excellent reinforcing agent for the polyester plastics. During the past few years, several finishes for fibrous glass fabrics for reinforcing heabconvertible polyester plastics have been developed and some are being used commercially (1, 7, 16, 17, .94]27, $8, 94). Several of these finishes are considered here with respect to the general requirements of a good finish, the types of finishing agents employed, the desizing and finishing processes used, and the laboratory evaluation of the finished fabrics. FINISHING REQUIREMENTS
FABRICWEWINO BY POLYESTER. Glass fabric-polyester laminates are made up by impregnating a succession of layers of cloth with a n unsaturated] heat-convertible polyester (9.9). The finished fabric should be wet out rapidly and completely during impregnation to eliminate the formation of small air bubbles on the fiber which separate it from the plastic, and to obtain good adhesion between the plastic and the fibrous glass during the curing process. To give good reinforcement, a fibrous glass
filament should be supported a t least every five diameters along its entire length (24). Figure 3 illustrates the effect of fabric finish on the rate and completeness of wetting by a typical, unsaturated polyester laminating plastic. A drop of the polyester was placed on each swatch and photographed after a n interval of 20 seconds. A is a swatch from a desized fabric. B is from a fabric which was desized and finished with methacrylatochromic chloride, a good glass-to-polyester coupling agent. C and D are from desized fabrics t h a t were finished with laurato and stearatochromic chlorides, respectively; they are poor coupling agents. The sizes of the spots show t h a t A and B wet out much better than C and D. FABRIC ADHESIONTO CUREDPOLYESTER. The finished glass fabric should adhere strongly to the cured plastic matrix; the adhesion must not be weakened by the presence of moisture. Because bare glass does not adhere well to heatrcomerted polyesters, especially in the presence of moisture, the finishing agent must be or contain a coupling agent which bonds to the fibrous glass surface and t o the plastic matrix. Thus, even though a desized fabric is well wet out by the polyester, as shown by A in Figure 3, a good laminate is not obtained with this fabric because the cured polyester is not well bonded to the bare fibrous glass. Adhesion between the fabric and the plastic is very important. Without it, the combination is weak; if high external forces are applied, delamination will occur. The stresses must be transferred from fiber to fiber through the plastic matrix to avoid high stress concentrations. Good adhesion is necessary to prevent buckling of the fibers under compression and t o allow the fibers to go into tension if the laminate is put into tension or flexure (34). REMOVAL OF ORIGINAL SIZE. All glass fibers t h a t are to be twisted into yarns and woven into fabrics must have a protective, lubricating size (3, I S , 26). The ingredients of a commonly used
1282
INDUSTRIAL AND ENGINEERING CHEMISTRY
glass size, vc.hich is applied to the filaments as they are formed, are dextrinized starch gum, hydrogenated vegetable oil, nonionic emulsifying agent, cationic glass lubricant, gelatin, and polyvinyl alcohol. These ingredients must be removed or chemically altered before or during the finishing process. The oily and incompatible ingredients prevent good fiber wetting during impregnation and fiber adhesion to the cured polyester in the
Figure 1. Helicopter Frame Element Constructed of Glass Fabric-Polyester Laminate
laminate, The presence of the water-sensitive starch, gelatin, polyvinyl alcohol, and emulsifying agent results in very poor reinforcement of the plastic in the presence of moisture. The capillary action of the fibers sized with this mixture is great. The moisture absorption of laminates containing these fibers will be high, and the fabric-to-plastic adhesion nil1 be poor. Figure 4 illustrates the capillary action of original, desized, and finished fabrics. The fabric strips mere suspended for 6 hours in water colored with a red dye. Numbers 1, 2, 3, and 4 are from finished fabrics, 5 is from a desiaed fabric, and 6 is from the original, sized fabric. Finished fabric 2 shows a relatively high capillary rise. Laminates containing this fabric have lower wet strengths than laminates reinforced with the other finished fabrics. Laminates made with the original, sized fabric and the desized fabric have very poor wet strengths. The preferred method is to desize the fabric rather than alter the size chemically before or during finishing. The size can be removed from the fabric by heat cleaning or by washing. Both desizing processes cause a deterioration in the strength of the fabric, Heat cleaning is preferred because no traces of detergent, soap, or organic matter are left on the fabric. Unless great care is taken during scouring, the fabric is tenderized as it works in the aqueous bath. It is important t o remove all the organic matter completely with as little injury to the fabric as possible. If any harmful inorganic substances are present on the fabric, they must be removed by rinsing in water during either the desizing or the finishing processes. APPLICATION OB FINISHISG AGENT. The finishing agent is applied to the desized, clean glass fabric. This material is essentially a coupling agent which bonds securely to the fibrous glass surface. The unreacted portion of the coupling agent is of such a nature that it can bond to the laminating polyester during
Vol. 45, No. 6
polymerization. Thus, the fiber surface which is originally incompatible and inert to the polyester is changed to one which is compatible and reactive with it. The finishing agent is the chemical intermediate which joins the fiber surface to the plastic matrix by mmhanicai and chemical bonding. The bonds betiveen the glass surface and the coupling agent, and between the coupling agent and the plastic matrix, must be of such a nature that they are not appreciably weakened by internal mechanical stresses. The chemical action of the environment to which the laminate is exposed should not neaken or break these bonds. The process by which the finishing agent is applied shopld not injure the fabric nor should it contaminate the fabric surface. Care should be taken during the operations because desized fabrics are easily injured when wet, owing to the sensitivity of a wet, bare glass fiber surface to abrasion. High concentrations of acid and alkali must be avoided in the desizing and finishing processes. They are destructive to the fine fibers and equipment. Acids, bases, and salts left on the fibers, even in low concentration, will affect the properties of the laminate, especially in the presence of moisture. The finishing agent should be applied with commonly used textile finishing equipment. Water is the preferred medium of application because of the availability of suitable equipment, economics of finishing, and absence of toxicity, corrosion, and flammability. Certain finishing agents have been recommended which require organic solvents or application from the vapor phase (6, 7 , 15, 17, 86). To date, these have not received wide commercial acceptance because of the disadvantages inherent in the finishing processes required. QUALITY COKTROL FOR FINISH. The finish should be of such a nature that a rapid, reasonably accurate quality control test can be set up t o determine if the finished fabric is satisfactory. This is very important, as the amount of finishing agent applied to the fabric is usually very low and the appearance and handle of the fabric are not changed. The difference betiveen a satisfactory and a n unsatisfactory finish cannot be detected by visual or manual inspection.
}
I*o,o 00
- t 9
n
lO0,OOO
li
p’
80,000
’
4Q,000
_I
2
20,000
W
$
0
W. VOLUME
STEEL
Figure 2. Tensile Yield Strengths of ,Fibrous GlassPolyester Plastic Combinations, Aluminum, and Steel
LIFE OF FISISH.Another requirement of a satisfactory finish is that it shall not become ineffective before the fabric is used. The finished fabric should be as satisfactory for use after a year or two as it was immediatelv after finishing. This means that the coupling agent on the fabric should not be appreciably affected on long exposure to air a t room temperature. TYPES OF FINISHING AGENTS
A number of organosilicon compounds are ORGANOSILICON. good finishing agents. The class of compounds in which the organic radical is bonded directly to a silicon atom is better than the organosilicates in which the organic groups are bonded to the
June 1953
'INDUSTRIAL AND ENGINEERING CHEMISTRY
silicon by an ester linkage. The former linkage is stronger and not so susceptible to hydrolysis or thermal decomposition (23). All the good organosilicon finishing agents have two common properties. The organic groups contain short, unsaturated chains which are capable of reacting or polymerizing with the reactive, unsaturated bonds in the heat-convertible polyester. T h e inorganic or polar groups, actually or potentially present, are capable of reacting with the fibrous glass surface. These compounds have dual chemical functionality. They act as chemical bonding, coupling, or bridging agents to react with both the fibrous glass surface and the unsaturated polyester. Some of the organosilicon materials which are used as finishing agents are diallyldiethoxysilane ( S I ) , vinyltrichlorosilane (6, 7 , 36), the soluble salts of the vinyl- and allylsiloxanols (1, 8, 14, 19), and vinylsiloxane (16, 17). The allyl or vinyl groups in these materials react with the active, unsaturated bonds of the polyester during polymerization. I n the case of the first two types of materials, the presence of moisture and use of heat in the fixation process hydrolyze and condense the monomers on the fibers to form siloxanes which are very probably bonded to the silicon in the glass surface by siloxane linkages. The siloxanols and siloxanol salts probably condense further and react with the glass surface in a similar fashion. The high heats used for the siloxanes presumably cause linkage to the glass surface by the same types of bonds. Table I shows these groups and the temperature range required for the reaction or fixation of these materials on the fibrous glass surface.
1283
heat treatment volatilizes off the oils and converts the other sizing ingredients to a more water-insoluble material which adheres fairly well t o the fibrous glass surface (24, 35). However, the wet strengths of polyester laminates made with this type of finished fabric are poor. A
c Figure 3.
B
D
Effect of Finish on Glass Fabric Wetting by Polyester Laminating Solution
TABLE I. VARIATION OF FIXATION TEMPERATURE WITH GLASS-REACTIVE GROUPS
Compound Vin ltrichlorosilane Didyldiethoxysilane Siloxanol salts Vinylsiloxane
x
*
Glass-Reactive Group -Sicla =Si(OCzHs)n 5 Si-OM - Si-0-Si 2 =
Fixation Range,
c.
25-75 125-175 200-250 250-300
The variation in required temperature correlates with the reactivity of these groups. For similarly treated glass surfaces, variation of contact angles and static friction with heat treatment substantiates these data. Additional evidence for the reactivity of these agents with the fibrous glass surface is that after proper fixation by heat they cannot be removed by washing in solvents or by heat unless the temperatures are above the fixation temperature or the decomposition temperature of the material (26). The one organochromium material which ORGANOCHROMIUM. has found extended use as a finishing agent is the Werner complex, methacrylatochromic chloride (10, 30, 34). A number of others have been tried, b u t none of these is a s good as this one. As in the case of the organosilicon finishing agents, the material has active, unsaturated groups which react with the unsaturated polyester. I n the presence of water, the compound probably forms a hydrated, complex cation which upon dilution, raising the pH, or mild heating hydrolyzes to form a basic complex. I n the presence of heat or increase in pH, the cationic complex condenses through dehydration and formation of chromium-oxygenchromium linkages to give an insoluble positive coating which attaches to the negative glass surface (34). This attachment is probably through the formation of silicon-oxygen-chromium bonds by reaction with the silanol groups in the glass surface. MISCELLANEOUS.Other classes of compounds containing short-chain unsaturated groups can be used as chemical finishing agents. The silicate derivatives have been investigated to some extent (29). The unsaturated nitrogen containing compounds such as amines, amides, and imidazolines and the cationic amino polymers have been evaluated, but are not so effective as the organosilicon or organochromium compounds (32). Heat treatment of the glass fabric containing the original oily, starch size has been used commercially as a finish. The
Other finishing methods have been investigated, but are not used extensively. One is the use of acids or alkalies a s etching or leaching agents. Dilute acids can be used t o dissolve or leach out part of the basic constituents in the fibrous glass. An active surface containing voids originally occupied by these constituents is formed. This type of glass surface is very adherent to materials such as dyes and plastics (4, 20). Caustic and acid washes have been used to roughen the surface (11,12, 33). Fabrics have been finished by sandblasting the surface ( 2 ) . As in the case of caustic washing, the roughened fibrous glass surface is more adherent to plastics than the original smooth fiber surfaces. The principal objection to all these finishes is that the glassplastic bonds are mostly mechanical in nature and are weakened by the presence of moisture. Wet strengths of the laminates are poor. DESIZING AND FINISHING PROCESSES
HEATCLEANING. Prior to the application of the present finishes, glass fabrics must be desiaed. This is accomplished best by heat, although scouring has been used. Both methods cause a loss in tensile strength of the fabric. Figure 5 shows the effect of heat on tensile strength of a glass fabric. For comparison, a curve is given showing the effect of heat on the tensile strength of a single fiber. Desizing by heating, commonly called heat cleaning, can be performed either in a continuous or a batch process. The conditions will vary depending upon the type of fabric. I n a continuous operation, fabric is passed through a gas-fired heating chamber a t a temperature of about 650" C. and a t a rate of 10 to 20 feet per minute. In a batch operation, glass cloth is rolled onto a perforated sheet steel mandrel and placed in a gas-fired oven. Heat is applied in two cycles, first a t approximately 250" C. until most of the volatiles are removed, and secondly a t about 350" C. until all the organic matter is burned off the fibers, Color, tensile strengt>h, and ignition loss a t 650" C. are used a s quality control tests. To be considered completely heat cleaned, a fabric must be white and have a maximum ignition loss of 0.1 %. This loss is due to moisture adsorbed by the fibers
i284
INDUSTRIAL AND ENGINEERING CHEMISTRY
a t storage conditions. The tensile strength of the desized fabric should be at least 50% of the strength of the original fabric. HEAT-TREATING PROCESS.Although this treatment has been supplanted by the newer finishes, there is still some use for "heattreated" fabric. Fabrics with this treatment are dark brown to t a n in color. The volatile, oily matter in the size is driven off by heat and the starch is caramelized by the heat-treating operation (35). This process is accomplished by running fabric over two large, gas-fired, heated steel rolls. The temperature and speeds of the rolls are dependent upon the weight of fabric. The temperatures range from 27.5' to 326' C. and speeds vary from 6 to 12 feet per minute.
Vol. 45, No. 6
excess finishing agent and harmful soluble, inorganic salts. This is followed by another pass through the drying equipment. Limits of 0.03% minimum to 0.06% maximum pickup based on elemental chromium give optimum properties. The chromium in the fabric is measured colorinietrically by removal from the fabric and oxidation to dichromate ion. APPLICATIONOF SOLUBLE SALTSOF VISYL OR ALLYLSILOXAKOLS. A finishing bath is prepared containing 0.75% solution of soluble salts of vinyl or allyl silosanols in water. If alkali metal salts are used, the solution is adjusted to a pH of 4 by the addition of hydrochloric acid. If ammonia reaction products are used, a p H of about 7 is preferred. These solutions or dispersions may be simply obtained hy the addition of the vinylor allylchlorosilane to n-ater containing the desired alkali metal hydroxide or ammonia. Conditions such as concentration, rate of addition, agitation, and temperature of solution must be properly regulated. Heat-cleaned glass fabric is passed through a dip tank containing the finishing bath and dried over a standard slasher, through a tower or through a horizontal drying oven. Depending upon the type of fabric, temperatures may range from 105' to 200' C. and speeds may vary from 6 to 20 feet per minute. In order t o remove soluble inorganic salts, the fabric is washed with water and redried. Determination of the amount of unsaturation present on the finished fabric is used as a control test. This test is the same a s used for fabrics finished with the diallyldiethoxysilane. Tests are also run to maintain residual inorganic matter a t a minimum. FINISH EVALUATION
Figure 4.
Capillary Action of Original, Desized, and Finished Fibrous Glass Fabrics
-4properly heat-treated fabric has a total residue of 0.5 to 1.0% as determined by igniting a t a temperature of 650" C. in a muffle furnace. A maximum acetone-extractable content is 0.05%. APPLICATION O F DIALLYLDIETHOXYSILANE. Diallyldiethoxysilane is applied to heat-cleaned glass cloth by passing the fabric through a dip tank containing a 0.5% solution of the silane in an organic solvent such as xylene. 4 s this silane hydrolyzes and polymerizes rather slowly in water a t room temperature, a dilute, \vel1 agitated aqueous dispersion can be used in place of the organic solution. I n fact, a better finish is obtained by this type of application. Removing solvent or dispersing medium, and setting the finish on the glass are accomplished by the use of a vertical tower or other appropriate forced drying equipment, a t temperatures of 125' to 175' C. The speed varies according to type and weave of fabric being run. The amount of active unsaturated groups on the fabric surface is determined by a bromination method ( I @ , modified for use on finished glass fabrics. APPLICATIONO F hfETETACRYLATOCHROl\IIC C H L O R I D E . RIethacrylatochromic chloride is applied t o glass cloth from a water solution containing 0.4% of the active material. This solution is prepared by diluting the commodity n-ith water and neutralizing with aqueous ammonia. Heat-cleaned fabric is passed through a dip tank containing this solution and dried in a vertical tower, horizontal oven, or standard five-drum slasher. Temperatures of 150" to 175" C. are employed in drying in towers or ovens. A temperature of 126' C. is maintained on slasher drums; in order to ensure complete dryness, infrared lamps are used a t the end of the slasher, adjusted so that the temperature of the fabric does not exceed 156' C. The throughput speed depends on the type of fabric and the kind of drying equipment used. The treated fabric is then given a water rinse to remove the
I n order to obtain comparable PREPARATION OF LAMINATES. data for laminates reinforced by the finished fabrics discussed in this paper, all samples were prepared under identical conditions. They were made by the same technician in the same press by the follon4ng procedure. The fabric is designated a3 ECC 181; this fabric is widely employed for reinforcing plastics. The cloth is cut into twelve 12.5 x 12.5 inch squares. Approximately 600 grams of a typical laminating, unsaturated, styrene-polyester copolymer is applied in equal portions to each ply of fabric. The layup is made on a large sheet of cellophane over a smooth surface. Resin is poured in the center of the cloth and spread out with a spatula. The construction of all the panels is parallel-Le., warps in all plies of fabric are parallel. The cellophane is then folded over the Iayup and a smooth, flat plate is laid on top. Herculite glass plates serve well for both top and bottom surfaces. The resin is then alloTved to soak into the fabric for 2 hours, so that the slower wetting fabrics are thoroughly impregnated. a f t e r the soaking period, the top plate is removed and the excess resin and entrapped air are worked out by wiping carefully with a spatula over the cellophane surface. The panel is then turned over and this operation is repeated on the other side. Care must be exercised to prevent air from re-entering the panel. The laminate is then cured betvieen smooth, stainless steel plates in a hydraulic press equipped with steam-heated platens. The layup is placed in the press and a pressure of 15 pounds per square inch is applied. Steam is then turned on and :he platen temperature is raised from room temperature to 121 C. in 10 minutes, After 30 minutes a t this temperature, cooling water is run through the platens and the laminate is cooled while remaining under pressure. The panel is then removed from the press and the cellophane is stripped from the surface.
TESTIXG PROCEDURES. The glass fabrics mere evaluated for use in reinforcing polyester plastics by measuring several physical properties of the carefully prepared laminates. Samples for evaluating each type of fabric were taken from three different foot-square laminates. A random sampling and testing procedure was employed. The test methods used to measure physical properties were: compressive strength, Method 1021; flexural strength, RIethod 1031; specific gravity, Method 5011 ; water absorption, Method 7031; and impact strength, Method 1071 (9). Two important modifications were made in the impact test method. The
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6.
i l
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INDUSTRIAL AND ENGINEERING CHEMISTRY
thickness of the sample was the thickness of the laminate. The samples were not notched; thus the total width under impact was 0.5 inch. The measurements of glass content by volume and the organic content by weight of the laminates were carried out according to the Owens-Corning Fiberglas Corp. test method L-517L. A suitable sized sample of laminate is placed in a muffle furnace a t about 550" C. and ignited to constant weight, The organic content by weight is calculated from this loss on ignition. The size or finish coating on the fibers is a small fraction of the total organic matter; the organic content by weight is essentially the plastic content of the laminate. The glass content by volume is calculated from the loss on ignition and the specific gravity of the sample and of the glass fibers. The specific gravity of the glass fibers is 2.52 and the average specific gravity of each set of laminates is 1.9. ,Calculations showed t h a t all laminates contained less than 1% voids. Table I1 gives the average flexural LAMINATE PROPERTIES. strengths and moduli of elasticity in flexure for the various types of laminates tested. The flexural strengths are expressed in units of 1000 pounds per square inch and the moduli in units of 1,000,000pounds per square inch.
the organosilicon finish. The organochromium finish is a good commercial finish applied from a water solution. Table I11 shows the average compressive strengths in units of 1000 pounds per square inch and average, unnotched, edge impact strengths in foot-pounds. The wet compressive strengths are obtained with samples tested wet after 2-hour immersion in boiling water.
TABLE111. COMPRESSIVE A N D IMPACT STRENGTHS OF GLASS FABRIC-POLYESTER LAMINATES Compression,
Wet Compressiona, 103 Lb./ Sq. Inch
Edge Impact, .Ft. Lb.
46
41
25
Drv
Fabric Finish Original Heat cleaned Organoohromium Siloxanolate Vinyltrichlorosilane (modified) 4
103/~b. Sq. Inch 16 25 35 34
Tested wet after immersion in boiling water for 2 hours.
As in the case of flexural strengths, the compressive strengths of laminates reinforced with finished fabrics are superior to those containing sized or desized fabrics. The best finish is modified TABLE 11. FLEXURAL STRENGTHS OF GLASSFABRIC-POLYESTER vinyltrichlorosilane applied from organic solvents. The comLAMINATES mercial finishes, methacrylatochromic chloride and sodium Wet Dry Wet siloxanolates applied from water, give compressive strengths Flex, Dry Flexa, Modulus, ModulusQ, 103 103 106 108 which are very good but are not equivalent to the experimental, Lb./Sq. Lb./Sq. Lb./Sq. Lb./Sq. solvent-type finish. Fabric Finish Inch Inch Inch Inch Original 37 22 Heat cleaned 52 20 Organochromium 73 57 Vinylsiloxanolate so 69 Vinyltrichlorosilane (modified) so 77 Tested wet after immersion in boiling water for 2 Q
*.
2.7 3.2 3.4 3.7
2.4 2.5 3.1 3.6
3.8
3.7
hours.
The wet flexural strengths were obtained by testing samples which were immersed in boiling water for 2 hours. The wet samples were broken immediately after removal from the water. The results obtained for samples conditioned in this manner are about the same a s for samples immersed for 30 days in water a t room temperature. These data show the superiority of finished fabrics over the original fabric containing the oily, starch size and the fabric desized by heat cleaning. The average dry flexural strength and modulus for laminates containing the original fabric are low. This is the result of the oily size on the fibers, which prevents good wetting by the polyester laminating solution and prevents good fiber-to-plastic adhesion in the cured laminate. The desized fabric gives better dry flexural strength and modulus to laminates than the original fabric because of better wetting and physical bonding of the plastic to the fibers. The wet flexural strength and modulus are poor because of the effect of the moisture on the mechanical bonding between the plastic and the fibers. The data show that the best finishing agent to obtain good dry and wet flexural strengths is vinyltrichlorosilane modified with ~-chloroallyl alcohol. However, this finish has not been used commercially because it must be applied from organic solution and corrosive hydrochloric acid is liberated during the finishing process (6, 7 , 5 6 ) . The soluble salts of vinylsiloxanols are very good finishing agents. The fabric used in the laminates tested was finished with the sodium salts. The advantage of this type of finishing agent is that it is applied from a water solution. The laminates containing fabric finished with methacrylatochromic chloride gave good flexural strengths and moduli; however, the results are not quite so good as those obtained with
T E MPE R ATU RE OC, Figure 5. Effect of 2-Hour Heat Treatments on Tensile Strength of Glass Fabric and Single Filament of Glass
The high Izod, unnotched, edge impact strength for the laminate containing the original, sized fabric is characteristic of fabrics sized or finished with oily materials. A good example of this effect is a laminate containing fabric finished with polytetrafluoroethylene aqueous suspensoid. Upon impact, the poor fiber-to-plastic adhesion allows fiber slippage, high strain distribution, and fabric-plastic delamination over a wide area. High results are obtained, as these changes absorb considerable impact energy,
TABLE IV.
WATERABSORPTION A N D COMPOSITION OF GLASS FABRIC-POLYESTER LAMINATES
Fabric Finish Original Heat cleaned Organochromium Siloxanolate Vinyltrichlorosilane (modified)
Water Absorption,
%
Organic, Wt. %
Glass, VOl. %
0.54 1.00 0.14 0.17
33 31 34 30
48
0.10
30
53
49 52
53
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Table IV shows the average percentage of water absorption by the laminates after 24 hours’ immersion, the average percentage by weight of organic material, and the average percentage by volume of fibrous glass in the various types of laminates tested. The water absorptions by the laminates containing finished fabrics are much lower than by laminates containing sized or desized fabrics. T.hese data correlate n-ith the wet-strength data for the laminates. The glass content must be considered when comparing strengths of laminates. For example, the tensile strength increases with increasing glass content and maximum compressive strength is obtained a t a plastic content of 45 to 50% by weight. The differences in average glass contents shown in Table I V are not great enough to cause significant differences in strengths. The higher organic content in the laminates containing the original sized and organochromium finished fabrics is due to less plastic squeezing out of the mold during the molding process. From the summary of data given in Tables 11, 111, and IV, it can be concluded that very good laminate properties are obtained by the use of fabrics finished with the commercial finishing agents, methacrylatochromic chloride and sodium salts of vinylsiloxanols. Also, it is evident that fabrics finished with the experimental finishing agent, vinyltrichlorosilane modified with p-chloroallyl alcohol, give laminates with the best properties. CONCLUSIONS
The general requirements of a satisfactory, commercial finish for glass fabrics intended for reinforcing polyester plastics have been established. Several types of good finishing agents have been discovered. These agents are coupling agents which bond the glass fibers securely to the plastic. Commercial desizing and finishing processes have been developed and conditions established to obtain good, consistent results. These developments are resulting in the commercial fabrication of glass fabric laminates which have better and more uniform properties than were previously obtained. ACKNOWLEDGMENT
The authors wish to thank Irwin Aber of the Chemistry Laboratory, who prepared the laminates, and Ronald Wiley, Ross McPeek, and Ralph Hammond of the Testing Department, who obtained the laminate property data. LITERATURE CITED
(1) Bacon, C. E., M o d e r n Plastics, 29 ( l l ) ,126 (1952). ( 2 ) Belteridge, G. W. (to Rubhaglas, Ltd.), Brit. Patent 561,356 ( M a y 16,1944). (3) Biefeld, L. P. (to Owens-Corning Fiherglas Corp.), U. S. Patent 2,392,805 (Jan. 15, 1946). (4) Ibid.,2,582,919(Jan. 15, 1952). (5) Biefeld, L. P., and Philipps, T. E., Am. Dyestuf Reptr., 4 1 (171,501 (1952). (6) Bjorksten, J., Henning, J. E., Yaeger, L. L., and Roth, R . J., AF Tech. Rept. 6220,Supplement I, U. S. Air Force, Wright Air Development Center, Wright-Patterson Air Force Base, Dayton, Ohio, 1951
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(7) Bjorksten, J., and Yaeger, L. L., M o d e r n Plastics, 29 (11), 124 (1952). (8) Elliott, J. R . , and Krieble, It. H. (to General Electric Co.), U. S. Patent 2,507,200 (May 9,1950). (9) Federal Specification LP-406b, “Plastics, Organic: General Specifications, Test Methods,” Superintendent of Documents, U. S. Government Printing Office, Washington 25, D. C., Sept. 27,1951. (10) Goehel, IM. T., and Iler, R. K. (to E. I. du Pont de Nemours & Co.), U. S. Patents 2,544,666, 2,544,667, 2,544,668 (March 13,1951). (11) Grant, J. A , and Babcock, D . E . (to Owens-Corning Fiherglas Corp.),Ibid. 2,477,407 (July26, 1949). (12) Hartman, S. 9.. Brit. Patent 607,035 (1948). (13) Hyde, J. F. (to Corning Glass Works), U. S. Patent 2,390,370 (Dee. 4,1945). (14) Ibid., 2,472,799 (June 14, 1949): 2,567,110 (Sept. 4, 1951); 2,582,215 (Jan. 15, 1952). (15) Jellinek, M .H., Society of the Plastics Industry, Inc., Reinforced Plastics Division, Seventh Annual, Technical Session, Proceedings, Section 17 (1952). (16) Kline, G. M., Modern Plastics, 28 (12), 113 (1951). (17) Linde Air Products Co., New York 17, N . Y . ,Linde Data Bulletin, “Application of Linde Sizing GS-1 for Producing Moisture Resistant Polyester Laminates,” 1952. (18) Lucas, H . J., and Pressman, D . , IND. ENG.CHEX.,ANAL.E D . , 10,140 (1938). (19) JIacMullen, C. W. (to Cowles Chemical Co.), U. S. Patent 2,587,636 (March4,1952). (20) Nordberg, M. E. (to Corning Glass Works), Ibid., 2,494,259 (Jan. 10,1950). (21) Parsons, G. B., M o d e m Plastics, 29 ( 2 ) ,129 (1951). (22) Plastics Catalogue Corp., 575 Madison Ave., New York 22, K. Y., “1951 Modern Plastics Encyclopedia and Engineer’s Handbook,” pp. 394-7,1951. (23) Rochow, E . G., “Chemistry of the Silicones,” 2nd ed., Chap. 2 , Kew York, John Wiley & Sons, 1951. (24) Slayter, G., et al., M o d e r n Plastics, 21 (9), 100 (1944). (25) Spitze, L. A , , and Richards, D. O., J. A p p l . P h y s . , 18, 904 11947). Steinhock, H. (to Owens-Corning Fiherglas Corp.), U. S. Patent 2,245,620 (June 17, 1941); (vested in Alien Property Custodian) 2,371,933 (March20, 1945). Steinman, R., M o d e r n Plastics, 29 (3), 116 (1951). Steinman, R., Society of the Plastics Industry, Inc., Reinforced Plastics Division, Seventh Annual Technical Session, Proceedings, Section 16 (1952). (29) Steinman, R . (to Owens-Corning Fiherglas Corp.), U. S. Patent 2.513.268 (June 27.1950). 130) I b i d . , 2,k52,910 (May 15, 1951); 2,611,718 (Sept. 23, 1952). Ibid., 2,563,288 (Aug. 7,1951). Ibid., 2,563,289 (Aug. 7, 1951). Talet, P. A,, and Cor, P. (to SociBtB Kobe1 Francaise), Ibid., 2,572,407 (Oct. 23, 1951). (34) Torrey, J. V. P . , “Volan Product Information,” Bulletin, Grasselli Chemical Department, E. I. du Pont de Nemours & Co., Inc., Wilmington98, Del., July 10, 1952. (35) White, E., Steinman, R., and Biefeld, L. P. (to Owens-Corning Fiberglas Corp.), U. S. Patent 2,446,119 (June 27, 1948). (36) Yaeger, L. L., Henning, J. E., Marshall, S. V., and Cox, R. P., A F Tech. R e p t . 6220,U. S. Air Force, Air Materiel Command, Wright-Patterson Air Force Base, Dayton, Ohio, 1950. RECEIVED for review December 12, 1952. ACCEPTEDFebruary 4, 1953. Presented before the Division of Paint, Varnish, and Plastics Chemistry, Symposium on Resins in Textile Finishes, a t the 122nd Meeting of the AMERICANC H m r I c A L SOCIETY,Atlantic City, pi. J.
