Experimental results have been presented that indicate that the diene reaction adduct of hevachlorocyclopentadiene with maleic acid may be utilized as a major constituent in the synthesis of polyester resins that are unusually flame resistant, particularly in the presence of a small proportion of antimony oxide. A number of new difunctional derivatives of hexachlorocyclopentadiene have been disclosed that are suitable for the synthesis of polyester resins of similar but modified properties. A comparison with essentially equivalent resins made from phthalic anhydride and tetrachlorophthalic anhydride illustrates the superior flame resistance and heat resistance of the new compositions disclosed in this paper.
LITERATURE CITED
(1) Fruhwirth, O., Ber., 74B, 1700-1 (1941). (2) Herafeld, S. H., Lidov, R. E., and Bluestone, H. (to Velsicol Corp.), U. 8. Patent 2,606,910 (Aug. 12, 1952). (3) &Bee, E. T., Purdue Research Foundation, private communication. (4) McBee, E. T., and Baranauckas, C. F. (to Purdue Research Foundation), U. S . Patent 2,509,160 (hlay 23, 1950).
( 5 ) McBee, E. T., and Devaney, L. W. (to Purdue Research Foundation), U. 9. Patent 2.473,162 (June 14,1949). (6) Norton, J. A , Chem. Rez., 31, 319-523 (1942). (7) Prill, E. 4., J . Am. Chem. SOC.,69, 62-3 (1947). (8) Straus, F., Kollek, L., and Heyn, K., Ber., 63B, 1865-85 (1930). RECEIVED for review Dccember 1, 1Q53.
ACCEPTEDMarch 26, 1'351.
Polyester ResinGlass Fiber Laminates JOHAN BJORKSTEN, L. L. YAEGER, AKD J. E. HENNING Bjorksten Research Laboratories, Inc., 323 W. Gorham S t . , 'Madison 3, Wis. Glass fiber reinforced polyester laminates are considered with respect to the bond between the two components. The effect of moisture and several mechanical and chemical treatments on this bond are briefly discussed. One silane bonding agent is treated in detail, and experimental evidence substantiates an existing theory that explains how? this compound aids adhesion between glass fibers and a polyester resin.
T
HIS paper summarizes several existing theories on adhesion between glass and polyester resins and present,s new dat,a illustrative of variables in adhesion between glass surfaces and polyester resins.
if temperatures above 220" F. are used in curing (36, 36'). An increase in humidity from 5 to 50% causes a drop of 15 to 20% in the flexural strengths of laminates fabricated a t 220" F. and a 25 to 407, losq for laminates made with a 250' F. cure.
PRESENT CON SIDERATION S
ilWHESION CHARACTERISTICS
The two constituents of a reinforced laminate with whicht, his experimental work is concerned are glass fabric and polyest,er resins. The adhesion between these two substances occurs a t the interface; the t\vo primary variables are the structure of the polyester resin and the surface present'ed by the glass. Polyester resins, for the most part,, are prepared from glycols and one or more dicarboxylic acids, one of which may be unsaturated. These compounds are react,ed to form a polymer, which is then dispersed in a monomer, usually styrene. The most widely used reactants are maleic and fumaric acids and ethylene and propylene glycols. The glass surface has hydroxyl groups directly attached t o it and also has a film of water, possibly 100 molecules thick (23). The glass fabric was heat cleaned to remove all weaving sizes before any additional treatment. These then, are the two substances that, must adhere t o each other in a laminate. All dat'a in the paper were obtained on one resin and one glass fabric throughout, thus standardizing these variables.
T\vo types of adhesion are possible bet'vreen the resin and the glass, mechanical and chemical. Mechanical Adhesion. Several processes for increasing laminat,e st'rengths that depend on mechanical treatment, surface etching, or cleaning have been described. These use acid washes (3, ai?), caustic and acid washes ( I S , 14, Sb), and sandblasting (2). All bonds of this nature are subject' to att'ack by moisture;
MOISTURE AND WATER ABSORPTION
The amount of water or moisture vapor present during the various stages of processing and laminating is important in determining the physical characteristics of the final laminate, and therefore, t~othe degree that adhesion exists between the glass and resin. An investigation of the effects of humidity during the fabrication of a laminate revealed that higher humidity conditions reduce the strength of a laminate, especially
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FINISH-
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Figure 1. RIechanical Adhesion in Laminates
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46, No. 8
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Figure 2. Adhesion of Chlorosilane Derivative to Glass
Polyesters-
pounds promote an excellent bond between the glass and resin, presumably through a reaction involving the silicone part of the molecule with the glass surface and the organic part of the compound with the resin. The reactivity of the organosilicon compounds with the glass surface depends on the compound used. Published results indicate that the organic chlorosilane derivatives, as shown by the temperature required for fixation, are the most reactive toward the glass surface. These silanes require lower temperatures for good bonding than diallyldiethoxysilane, siloxanol salts, or vinyl siloxane (4). In addition, their resultant moisture sensitivity is less, and their ultimate flexural strength is highest. The decrease in moisture absorption in a finished laminate, which, in turn, affects the wet flexural strength values of the bond and laminate has been shown ( 3 , 62, 33-36, 38). The wet flexural strength of a laminate is its flexural strength after immersion in boiling distilled water for 2 hours. The moisture absorption of a laminate made from heat cleaned glass was reduced from 1 to 0.1% by the application of a modified vinyltrichlorosilane treatment, and the wet flexural strength valueslof the laminate were increased from 20,000 to 77,000 pounds per square inch (4). Application of Silanes. Unsaturated chlorosilane derivatives are usually applied to glass cloth from a xylene solution, and the concentration range is 2.5 to 5%. If vinyltrichlorosilane is used, it is reacted with a n unsaturated alcohol in a 50% xylene solution
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therefore, all laminates made from fabric treated by any of these methods could not be used in conditions where moisture may be a factor. Further results obtained from several experiments that show the mechanical adhesion in laminates, as indicated by flexural strength data, are presented in Figure 1. The results in the first two columns are from laminates prepared with glass having no surface treatment, and the second and third are etching treatments using a hot sodium hydroxide solution; the latter two treatments differ only in immersion times in the treating solution. Although improved dry flexural strengths are obtained from the finishing treatment. the reduction of strength on immersion in water is quite pronounced, indicating that this type bond is readily degraded. Chemical Adhesion. Chemical adhesion should provide the best means for avoiding moisture absorption caused by bond degradation and for promoting high bond strengths. This type adhesion has been accomplished through the application of an intermediate compound to the glass surface, reactive toward both the glass and resin. Compounds that have improved adhesion include silicate derivatives (28, 29), amines (30,38), various organic derivatives of zirconium, aluminum, titanium, boron, and other metals (38), and starch-fixation treatments (24, 25, 34). However, the most successful compounds for increasing adhesion between glass and polyester resin have been organic derivatives of silicon and chromium. The organic chromium compound most ~ i d e l yused in industry as a glass cloth b i s h is methacrylate chromic chloride (10-12, 16, 19, 31, 33). Other chromium compounds are inferior to the methacrylate chromic chloride ( 4 ) . Organosilicon compounds are the base material for several finish treatments for glass fabric (1,6-8, 16-18, 20, 21, 26, 27, 38) and may possibly be the base for a commercial finish of which the composition has not been revealed (26, 27). These comAugust 1954
w4
2 3 SIZE OF ORGANIC GROUPS ATTAZHED (CARBON ATOMS)
DRY FLEXURAL STRENGTH
WET FLEXURAL
STRENGTH
Figure 4. Variations in Unsaturated Group on Silane Molecule
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DRY FLEXURAL STffENGTU WET FLEXURAL STRENGTH I
2 3
DIVINYL DICHLOROSILANE Er"nYL VINYL DICULOROSILANE PHENYL VINYL DICHLOROSILANE
Figure 5. Effect of Various Silanes on Flexural Strength
and then diluted to the application concentration. The solution is applied to heat cleaned glass fabric by a dip method. The treated cloth is dried, washed in water, and dried again to complete the treatment (5-7, 37, 58). ADHESION THEORIES
Various theories have been propounded to account for the
INDUSTRIAL AND ENGINEERING CHEMISTRY
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687 n e 6
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the figures for ( 2 ) , no appreciable benefits are gained b y substituting a chlorine group in the alpha position, but with thc chlorine group in the beta position, as in ( 3 j , detrimental results are noted. If t,he p-chlorovinyltrichlorosilane is reacted with 8-chlorally1 alcohol, a definite improvement over the use of the former alone is noted (4), hut these rcsults are not superior t,o those obtained from the use of vinyltrichlorosilane and p-chlorally1 alcohol ( 5 ) . The columns above (6) show the effect from shifting the chlorine group on the allylosy radical from the beta t o the gamma position, xvhich results in decrrased flesural strengths in the latter case as (tompared with the beta position.
ORY FLEXURAL STRENGTH WET FLEXURAL STRENGTH
I 2 3 4 5
6
YINYL TRICHLOROSILANE d-CHLOROVINYL TRICHLOROSILANE p-CHLORO VINYL TRICHLO ROSIL ANE ~CHLOROVINYL TRICHLOROSILANEt ~ C H L O R O A L L Y L ALCOHOL YINYL TRICHLOROSILANE t P-CHLOROALLYL ALCOHOL YINYL TRICHLOROSILANE r-CHLOROALL YL ALCOHOL
+
Figure 6. Variation in Strength from \-ariation in Position and Sumber of Chlorine Croups
action of the unsaturated chlorosilane derivatives. One theory is that the reaction of the compound with t'he glass proceeds as shown in Figure 2: Step 1 takes place before the addition of the compound to the glass. Step 2 is the reaction between the silane arid t,he glass surface. of the size 'iT.ith water. Step 3 is t,he hydro1 The silane is t'hus firmly at,tached t'o the g l a s surface, and the organic part of the radical is free to react wit'li the resin. Although the reaction with the resin ha.s been postulated as t'aking place through t'he unsaturated groups, a theory, recently presented, indicated that a reaction may also take place through the hydroxyl groups. This is a better esplanation for the good results obtained when this type of finish is used x i t h epoxy resins. It is reasonably propoeed that t,he reaction between the glass mrface and the silane is followed by a hydrolysis of some secondary chlorines present on the silane b y the film o€ LvatcXr present on the glass surface. The compound formed is then free to polymerize, creating a sheat,h of silou:i!icx groups around the glass filaments, which ~ o u l drender them more water repellent and more compat,ible with ihe resin. This structure (9) voiild probably resemble that shown iu Figure 3. % . structure of this suit, ill which tlie si1 to each other and to the glass through enter into a chemical react,ion i7it.h tlie re the double bonds and/or the hydroxyl groups. I n either case, t,he groups attached to the silane should have considrrahle effect on the adhesion bet,iveen the resin and the size, and t h plnes and the size. Variation in Groupings. yltriehlorosilane is used initially nyldichlorosilane, and t'he unin place of the $-chlorally saturated groups are increased in size, the resulting adhesion is decreased as shown b y the flexural strength in Figure 4 . If cheniical bonding with polyester resins is achieved through unsat'uratcd groups on the silane molecule, a reduction in the number of these groups should result in decreasing adhesion. Figure 5 compares divinyldichlorosilane, eth>-lvinyldichlorosilane, and phenylvinyldichlorosilane. The reduction in strength is apparent r h e n one vinyl group is replaced n i t h either t,he ethyl or phenyl radical. The retention of the flexural strength by cthylviiiyldichlorosilicane and phenylvinyldichlorosilicsne after nat'er immersion indicates that some water resistance is obtained through the use of thesc compounds. Figure 6 shows the effoct the chlorine group on t,he organic radical has on the sizing compound. The columns shove the figure (1j represent the dry and wet strengths of a laminate using vinyltrichlorosilane as the sizing compound. As indicat'ed by
1634
'
DRY FLEXURAL STRENGTH, WET FLEXURd: STRENGTH I
XYLOL
2 MINERAL SPIRITS 3 CARBON TETRACHLORIDE
Figure '7. EReect of Solvents on Flexural Strength
Variations in Solvent. I X c k o n and Silver notcd that the addition of hydrogen chloride to the double bonds present in t
