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uv-cooi tt-n STATUS REPORT NEW ENTERPRISES ASBESTOS REINFORCED RESINS Authors: C. W. McGary P. L. Smith L. C. Shriver Doto: Pro|oct No.! Filo No.: October 7, 1963 161W21 1342 SUMMARY Chrysotile asbestos and aqueous acids react in two ways: the acid is neutralized by a magnesium hydroxyl group and is retained in the asbestos; the acid is neutralized, and the mag nesium salt is dissolved or precipitated in the water layer. Very weak acids, such as magnesium dihydrogen diphosphate, give the first effect. Intermediate acids, such as acetic acid, give both effects and incomplete reaction. Strong acids, such as hydrochloric acid, give the second effect which is stoichiametrically complete. Dibasic and tribasic acids, which have a wide spread in ionization constants, have been used as cross-linking agents for asbestos. These materials, however, disrupt the asbestos structure by extracting magnesium prior to cross-linking through the weaker acid, groups. The effect on resin properties of partially neutrali zing these acids before mixing with asbestos will be investigated. Since water is required in these reactions, more satisfactory techni ques for molding and curing must be sought. STRUCTURE OF ASBESTOS In the last report the re-occurring formula unit of asbestos was 'given as Mgg(OH)gSi^Og. The magnesium-hydroxyl attack points on the molecule were considered to be six ($Si-OMgOH) groups per re-occurring asbestos unit. In view of more enlightened information since obtained from Sterling Forest and elsewhere on the structure of asbestos, this assumption is not strictly true. Originally it was supposed that the siloxane bulwark of the molecule was a chain of connected duodecagons of the structure shown in Figure I. This configuration leaves six unsatis-_ fied silicon bonds to carry the six (OMgOH) groups. Actually, how ever, the siloxane nucleus is not a chain polymer as shown but a "sheet" polymer of interlocking duodecagons, as indicated in Figure II. It can be seen with this configuration only one valence of each silicon is unsatisfied, or four bonds per re-occurring formula unit are available to hold 6-Mg's, 5 extra 0's, and 2 extra OH's. (8-6). It is obvious then that conventional full valence bonding cannot be applied here and apparently the coordinate bonding of magnesium is involved. It also appears that magnesium atoms,-holding Research and Development Department Chemicals Division Union Carbide Corporation of acid per'formula weight of asbestos Mf^(OH) gS^Og is present, this reaction will continue until all the magnesium has been removed and only a siloxane residue remains. If less than 12 ^equivalents of acid per formula weight are present, however, the reaction will continue until (1) all the acid is neutralized, (2) the atoms of magnesium solubilized will be one-half the equivalents of acid reacted and (3) the remaining magnesium atoms and their accompanying hydroxyl groups will be left in the asbestos molecule-untouched. In short, the reaction of "strong" acids with asbestos can be considered as their essentially instantaneous action of 2H+ ions to remove a magnesium atom from the molecule. This group includes, in addition to the totally ionized acids, other polybasic acids whose "first hydrogens" are relatively strong such as maleic (1.4 x 10"2) and phosphoric acid (7.5 x 10~3). Data obtained using maleic acid are shown in Table IV and V and for phosphoric acid in Table III.. 2. Acids in the 10~5 Range of Dissociation Constant The conventional straight chain organic acids (acetic, butyric, adipic, succinic, etc.) are included in this group. Their chemical action on asbestos departs markedly from that of the strong acids and (based chiefly on the behavior of acetic acid) may be characterized as follows: (1) Their reaction with asbestos is never complete even when very high excess concentrations of acid and temperatures of 100-108C are employed. Reaction of 40-50% of the magnesium is easily and quickly obtained at concentrations of 6-24 mols of acid per formula weight of asbestos. As concentration of acid is ' increased the maximum reaction point rises slowly until at 60 mols acid concentration 70-75% reaction of magnesium is obtained. Data for these various concentrations of acetic are given in Table VI.. (2) While substantial magnesium cleavage does occur in reactions with these acids, it approaches stoichiometric quantities only when large excesses of acid are employed and is relatively low when less than theoretical concentrations are employed. For example with acetic acid, when 6.0 mols of acid per formula weight of asbestos is used, only 14% of the magnesium reacted is cleaved from the asbestos molecule. These data for acetic acid are summarized in Table VII. These data, together with other fragmentary data obtained at lower temperatures, suggest that, with the proper selection of acid concentration, time and temperature, considerable pendant group attachment might be accomplished with a minimum of magnesium cleavage. More data will be obtained on this important point. From these data for the action of acetic acid, a wide difference in reactivity of magnesium atoms (or probably more correctly their attached hydroxyls) is indicated, since roughly 40-50% of the magnesium is attacked rather readily, but approximately 25% can probably not be attacked at all. It is also evident that 4 the cleaving reaction by the "second" mol of acid lags considerably behind the reaction of the "first" mol which simply couples by neutralization. 3. Acids in the 10~7 to 10~8 Range of Dissociation Constant When the dissociation constants of acid groups are in the low range of lO-? to 10-8, reaction will occur with the more re active asbestos hydroxyl without any discernible magnesium cleavage. This conclusion is based on data collected for the action of the ,, "second" H+ ions of maleic (8,6 x lO-?) and phosphoric (6.2 x 10"a) acids in the cross-linking of asbestos. A more detailed discussion will appear later in the report. (See Tables III, IV, and V.) NONAQUEOUS ACID REACTIONS* Limited investigation of the reaction of maleic acid with asbestos in refluxing ketones (80-140C.) as solvents indicates very low reaction rates and maximum reactions of only 15-20%. In addition, magnesium is cleaved in stoichiometric quantities. This approach, therefore, is not promising. Data obtained in methyl ethyl ketone is shown in Table VIII and in cyclohexanone in Table IX. CROSS-LINKING OF ASBESTOS From the foregoing discussion of the WITH DIBASIC ACIDS action of "strong" acids on asbestos it is evident that in the- cross-linking of asbestos with either maleic or phosphoric acids, the "first" H* ions can only cleave magnesium from the molecule. It follows then that the cross-linking must be accomplished by the "second" H+ ions of the acid salts formed by the cleavage reaction. With maleic acid, the acid salt would be magnesium dihydrogen dimaleate, Mg (OOCCH=CHCOOH)2 and for phosphoric acid, magnesium tetrahydrogen diphosphate Mgfl^PO^^* Chemical analyses made during actual cross-linking experiments with the two acids confirmed this con clusion. This consideration lead to the attempted preparation and isolation of the two salts for their subsequent use as cross- linking agents. Although the Hg(H2PO^)2 was not isolated, a hydrated form of the maleic salt was obtained and employed in several cross-linking experiments. This cross-linking method has the advantage over the use of the acid and asbestos directly, of bringing the more reactive hydroxyls into play in the cross- linking reaction. Otherwise these reactive hydroxyls are wasted in making the magnesium salt by cleavage before cross-linking occurs. In one instance a highly cross-linked product (97.7% of carboxyl reacted) was prepared in the form of a patty by this method. The ratio of carboyl/unit formula of asbestos was 1.33 or 4.5 hydrols to each carboxyl. This product was extremely hard and had fair water resistance. Other attempts using the same ratios but different curing conditions were not as successful, although one sample, prepared in the form of a cylinder (68% of carboxyls reacted) showed 1900 lbs/sq.in. compressive strength. The rate of temperature rise (with the resulting removal of water) versus the rate of cure is optimum within narrow limits for this reaction, due to the limited solubility of the salt in water (approximately 5% 5 at 25C and' probably 25% at 80C.)- The large amount of water which must eventually be removed from the cured specimens '50-65%) makes it difficult to maintain formed"shapes during curing. This dis advantage, because of the lower water content, is not so pronounced in the phosphoric acid reaction and further work is planned with this acid employing an acid salt prepared and left in solution. In summarizing acid cross-linking, it might be pointed out that the products prepared from either maleic or phosphoric acids are rock like in character and have considerable breaking strength-. This'was par ticularly'true of the sample prepared'from"maleic.salt which was almost completely cross-linked. This sample required repeated heavy hammer blows * break it. Lack of.water resistance is a major problem with these products. Samples vary from fa.st disintegration in cold water in one hour, to slow surface disintegration after overnight soaking. At present the lack of equipment here to form definite shapes (as cylinders for compression testing), which do not contain numerous voids, is a definite handicap in completely evaluating the cross-linked products. CONCLUSIONS The rate of reaction of an aqueous acid with asbestos varies directly with temperature, concentration, time, and acid ionization constant. Only strong acids (ionization con stants of 10"3 or higher) react appreciably at 25C. and stoichiometrically in boiling aqueous solutions. Strong acids serve only to cleave magnesium from asbestos. Only weak acids (ionization con stants of 10"5 or lower, and preferably about 10"7) are useful for attacking pendant groups and cross-linking. Even weaker aicds (e.g., phenols) may be capable of reaction. The minimum strength required for reaction is not yet known. Although acids will react in the absence of water, re action is appreciably facilitated by the presence of water. The mechanism of cross-linking with dibasic acids having one strong and one weak acid group (e.g., maleic and phosphoric acids) involves 1) cleavage of magnesium to form a dibasic mag nesium salt (e.g., Mg(00CCH-CHC00H)2) and 2) neutralization of the acid groups of this salt by reaction with the remaining - MgOH groups of the asbestos. In order to prevent magnesium cleavage, it is advantageous to prepare the dibasic magnesium salt from magnesium hydroxide. As a result of this study, several possible routes are suggested to the preparation of asbestos-containing compositions for use as pipe, formica-type laminates, building panels, printed circuits, and auto body patch kits. These reactions, which would cross-link the asbestos, are outlined via the following list of reactants: 1. Polybasic acids (e.g., dimer acid, etc.). magnesium dimaleate, 6 2.' Styrene + unsaturated acids (e.g. , magnesium dimaleate. acrylic acid and u carboxyl-capped polyester) 3. PolyphenoIs. 4. Diepoxides + polybasic acids. 5. Diepoxides (e.g., EP-206 with ammonium fluoborate catalyst). 6. Styrene + neutral esters of unsaturated acids (e.g., acrylic, methacrylic, and maleic). 7. Diisocyanates. Other potential areas of application for asbestos are: 8. As coatings, modifiers for latexes, and molding powders after reaction with either a drying oil acid or acrylic acid. 9. Acid scavengers (e.g., as an HC1 acceptor)for chemical reactions. 10. Soil conditioner for slow release of Hg into soil. 11. Fertilizer after reaction with NH4H2PO4. 12. Flame-proof foams (taking advantage of the hydroxyl functionality of asbestos rather than using as an inert) by reaction with isocyanates. EXPERIMENTAL In the study of the activity of acids in aqueous digestions, 30.0 gms. of asbestos in 700 cc of acid solution was employed. In the ketone digestions a ratio of 40 gms./ 500 cc was employed. With cross-linking experiments using phosphoric acid a recipe of asbestos 100 parts, 87% phosphoric acid 80 parts and water 25 parts, was employed. In maleic acid cross-linkings various ratios of materials were used but all within the following limits: Water 6-8 gms., maleic acid 12 jms and asbestos 16.3 to 30 gms. In the maleic salt cross-linking reactions a single recipe of water 90 gms., maleic salt 20 gms. and asbestos 51.0 gms. was used. The mixes in the cross-linking experiments; were worked by hand and formed into "patties" for curing, except in one case where cylinders were formed by packing in glass tubes. ANALYTICAL Magnesium content was determined by the method outlined in the report of April 8, which involves determining the amount of standard alkali necessary to precipitate the magnesium as hydroxide. "First" H+ ion was determined by titrating with methyl red (pH range 4.4-6.2) as indicator; and "second" H+ ion by finishing the titration with Phenolphttalein (pH range 8.3-10) as indicator. lw ATTACHMENTS: 9 Tables J TABLE I REACTION OF ASBESTOS WITH AQUEOUS HYDROCHLORIC ACID AT 102C. (500 cc acid solution^O.O gms asbestos. Equivalent data for acid given below are per formula weight of asbestos-554.) Reference Number 102LCS23-2 23-1 23-3 27 31 Reaction time, hrs 1.5 1.0 1.5 2.0 2.0 Hols HC1 Initially 2.00 4.06 8.21 7.53 12.00 Hols HC1 At Reaction Completion 0 0 0 0.08 0.326 Hols HC1 Reacted 2.00 4.06 8.21 7.45 11.67 Atoms Hg Solubilized 0.96 2.00 4.06 3.97 5.80 Mg x2 1.92 4.00 8.12 7.94 11.60 TABLE II REACTION OF ASBESTOS WITH AQUEOUS HYDROCHLORIC ACID AT AMBIENT TEMPERATURES (550 cc acid solution/40 gms. asbestos. Equivalent data for amounts of acid given below are per formula weight of asbestos-554) REF. No. 102LCS43 Reaction Time,hrs 0 17.75 45.5 89.5 100.5 Hols HC1 Unreacted 13.35 4.40 2.79 1.72 1.64 Hols HC1 Reacted 0 8.95 10.56 11.62 11.71 Atoms Hg Solubilized 0 3.52 4.93 5.69 5.75 Mg x2 0 7.04 9.86 11.38 11.50 TABLE III REACTION OF ASBESTOS WITH AQUEOUS PHOSPHORIC. ACID AT BOILING TEMPERATURE (103C.) (500 cc aqueous phosphoric acid solution/30 gms. asbestos. Acid equivalent data given below are per formula weight of asbestos-554. Initial concentration of acid-6.065 mols acid/formula weight asbestos). Reaction Time Hrs. Equivalents 1st H+ Unreacted Reacted Equivalents 2nd H+ Unreacted Reacted 0 2.75 5.25 10.75 13.75 6.065 1.76 0 0 0 0 4.30 6.065 6.065 6.065 6.065 5.42 4.02 2.83 2.71 0 .64 2.04 3.23 3.35 TABLE IV REACTION OF ASBESTOS WITH AQUEOUS MALEIC ACID AT BOILING TEMPERATURE (103-106C) (500 cc maleic acid solution/30 gms asbestos. Acid equivalent data given below are per formula weight of asbestos-554.) Reaction Time Hrs. 0 3 8 11 14 102LCS14--A. Initial Concentration-Qpi mols maleic acid Equivalents 1st in* Unreacted Reacted Equivalents 2nd H-*Unreacted Reacted Atoms Mg Solubilized 6.01 2.27 0.00 0.00 0.00 0 3.74 6.01 6.01 6.01 6.01 5.82 5.60 5.31 5.04 0 0.19 0.41 0.70 0.97 0 1.94 2.97 2.91 3.05 Mg x 2 0 3.88 5.94 5.82 6.10 102 14-B- Initial Concentration 4.25 Mols. 0 4.25 0 4.25 0 0 3 1.62 2.63 4.01 0.24 1.24 2.48 8 0.19 4.15 3.93 0.32 1.79 3.58 11 0.00 4.25 3.56 0.69 2.01 4.02 14 0.00 4.25 3.45 0.80 1.89 3.78 . TABLE V REACTION OF ASBESTOS WITH AQUEOUS MALEIC ACID AT AMBIENT TEMPERATURE. (700 cc maleic acid solution/30 gms. asbestos. Acid equivalent data given^below are per formula weight of asbestos-554. REF. NO. 102LCS25 Initial Concentration 6.08 mols maleic acid. Reaction Time. hrs. 0 3.25 22.5 53.5 75.0 99.5 Equivalents 1st H+ Unreacted Reacted 6.08 5.32 4.25 2.93 2.19 1.36 0 0.76 1.83 3.15 3.89 4.72 Equivalents 2nd H+ Unreacted Reacted 6.08 6.03 6.07 6.05 5.70 6.08 a 0.05 0.01 0.03 0.35 -0.03 Atoms Mg Solubilized 0 0.52 0.89 1.61 2.09 2. 9 Mg x 2 0 1.04 1.78 3.22 4.18 4.58 REF. NO. 102LCS45 Initial Concentration 11.73 Mols Maleic Acid. 0 17.25 43.75 60.5 11.73 8.71 6.76 4.01 0 3.02 4.97 7.72 11.73 11.59 11.73 11.64 0 0.14 -0.20 0.09 0 1_36 2.14 3.41 2.72 4.28 6.82 TABLE VI REACTION OF ASBESTOS WITH BOILING ACETIC ACID SOLUTIONS (700 cc acetic acid solution/30 gms. asbestos) Ref. No. 102LCS51 If II 102LCS52 J.02LCS29 II If 102LCS37 II 102LCS38 102LCS39 II Reaction Time, Hours Reaction Temp. C. 2.0 4.25 7.0 10.8 100 II II II 1.67 4.25 7.08 11.00 16.00 101 16.0 5.75 10.0 Ambient 102 102 3.0 8.0 103 103 3.0 8.0 16.0 105 II If 6.0 22.0 108 II Initial Cone, of Acid MoIs/ Formula Weight Asbestos 1.09 2.95 6.03 12.0 24.0 60.0 Mols Acid Used/Formula Wt. Asbestos 0.40 0.45 0.52 0.69 0.90 1.19 1.45 1.64 1.70 0.39 3.23 3.48 4.30 4.48 5.14 6.23 6.35 7.35 8.10 Atoms Mg Solubilized Formula Wt. Asbestos --_ -- 0.13 0.14 Mg x2 ---- -- 0.26 0.28 0.19 0.33 0.33 0.35 0.36 0.38 0.66 0.66 0.70 0.72 0 0.37 0.745 0 0.74 1.49 1.80 1.95 3.60 2.90 2.55 3.14 3.20 5.10 6.28 6.40 3.68 3.85 7.36 7.70 . *- Ref. No. 102LCS51 52 29 37 38 39 TABLE VII REACTION OF AQUEOUS ACETIC ACID ~ WITH ASBESTOS AT BOILING TEMPERATURE (100-108C) (700 cc of acetic acid solution/30 gms. asbestos) Approx. Time For Reaction Maximum Hrs. Reaction Temp. C Initial Cone. Of Acid Mo Is/formula Wt. Asbestos % .Magnesium Attacked % Mg Cleaved Mg Cleaved Mg Attacked % 10.8 100 1.09 9.6 2.3 24.0 16.00 101 2.95 22.2 6.0 27.0 5.75 102 6.03 47.7 6.2 13.0 3.0 103 12.0 41.8 30.0 72.0 8.0 105 24.0 51.5 47.3 92.0 6.0 108 60.0 71.0 64.1 90.2 TABLE VIII REACTION OF MALEIC ACID IN NON-AQPEOUS MEDIUM (METHYL ETHYL KETONE) AT 80C (550 cc maleic acid solution/40 gms. asbestos. Acid equivalent data below are per formula weight of asbestos554. Initial concentration of acid on this basis-6.02 mols. Ref. No. 102LCS42.). Reaction , Time, Hrs. 0 17.25 41.75 65.75 89.75 113.75 Equivalents 1st H+ (Methyl red indicator) Unreacted Reacted- 6.02 5.68 5.33 5.08 5.07 5.07 0 0.34 0.69 0.94 0.95 0.95 Titrations with phenolphthalein compared with methyl red indicated practically no 2nd IT* reaction. Analysis of water soluble portion of residue from reaction indicated 0.34 atoms of Mg/formula weight of asbestos solubilized as magnesium salt. TABLE IX REACTION OF ASBESTOS IN NON-AQUEOUS MEDIUM (CYCLOHEXANONE) AT 140C. (700 cc. of maleic acid solution/40 gms. asbestos/ Acid equivalent data below are per formula weight of asbestos-554. Initial concentration of acid on this basis-5.77 mols.) Reaction Time, Hrs. 0 2.17 7.17 13.17 Equivalent 1st and 2nd H+ (Phenolphthalein indicator) Unreacted Reacted 5.77 4.85 4.64 4.65 0 0.82 1.03 1.02 Titrations with methyl red indicator were not sharp in this instance so that differentiation of reaction of 1st IV and 2nd H+ was not obtained. DISTRIBUTION / Dr. S. W. Tinsley, 511 Mr. W. J. Reid, NYO Information Retrieval Mr. H. L. Batleman, 511 Mr. J. W. Biddle, 511 Dr. F. Johnson, 511 Mr. G. S. Jordan, 242 Mr. C. . Metten, 511 Mr. T. F. Mooney, NYO Mr. D. H. Mullins, 511 Dr. F. A. Mumpton, 242 Mr. C. T. Patrick, 511 Dr. B. Phillips, 511 Mr. H. F. Reichard, 242 Mr. N. J. Setter, 242 Mr. A. B. Steele, NYO Dr. D. L. Stockton, 242 Authors (10)