Determination of Silicones in Textile Materials GERALD M. PETTY Arkansas Co, Inc., Newark,
N. J.
An estimation of the amount of silicone in textile materials is required for the control of this process for the durable waterproofing of textile materials. In a method which requires no unusual or specialized equipment, the textile material, treated with silicone, is wet-ashed, using concentrated sulfuric and nitric acids and, eventually, concentrated perchloric acid. The silica is determined by conventional methods. Attempts to extract cured silicones from textile materials by solvents gave unsatisfactory results.
SOLVENT EXTRACTION O F SILICONES
Before the silicone has been cured, solvent extraction with petroleum ether (boiling point, 30' t o 60" C,), isopropyl alcohol (about 99.8%), benzene, or solvent naphtha usually recovered 95% or more of the silicone. After curing, prolonged extraction with benzene or solvent naphtha in a Soxhlet apparatus gave nonreproducible recoveries which were generally in the range of 30 t o 60%. QUANTITATIVE DETERMINATION O F SILICONES
Reagents. Sulfuric acid, 9570, reagent grade. Fitric acid, 70%, reagent grade. Perchloric acid, 60%) reagent grade. Hydrofluoric acid, 48%, reagent grade. Hydrochloric acid, 3775, reagent grade.
S
ILICOSE oils, also known as lon- molecular weight polysiloxanes, are extensively used in processing textile materials in order t o impart a water-repellent finish which is resistant both to washing and t o dry cleaning. The silicone oil is dispersed in water with an emulsifying agent or dissolved in a suitable solvent, and is mixed with a catalyst which promotes polymerization. The catalyst is usually an organometallic compound. It is then applied t o the textile material in equipment which is found in most textile mills. The silicone oil thus deposited, is then cured (polymerized) by heating the impregnated textile material briefly a t a high temperature. For instance, heating a t 160" C. for 5 t o 8 minutes is recommended for silicone oils on cotton
Apparatus. Borosilicate glass beakers, watch glasses, and funnels, and platinum crucibles were used throughout. Sampling. Sampling in a textile finishing plant is usually limited to the ends of runs. As samples so taken are less representative of the entire run than samples taken a t regular intervals through the run, larger samples are needed for analysis than in the latter case. As the peroxide bomb procedure is limited t o samples generally less than 1 gram, the gravimetric procedure described below is preferred. Procedure. For the quantitative determination of silicones in textile fabrics, weigh 5 to 10 grams of the material to 0.01 gram. Place the sample in a 600-ml. borosilicate glass beaker which is covered with a borosilicate watch glass, add 30 ml. of concentrated sulfuric acid, and, in small portions, add about 35 ml. of concentrated nitric acid. Heat moderately ("medium" heat on an electric heater) for 20 minutes to 2 hours. Use a medicine dropper to add 1 t o 5 ml. of concentrated perchloric acid, and heat the sample vigorously. The earlier addition of perchloric acid may be hazardous. If the liquid remains opaque, cool it slightly, add 5 t o 10 ml. of concentrated nitric acid and, after further moderate heating, add 1 to 5 ml. of concentrated perchloric acid, followed by vigorous heating. Continue this cycle until the liquid is clear. It is usually water-white or only slightly tinted. Heat the sample vigorously until the volume of liquid is reduced to about 20 to 25 ml. Cool to room temperature, dilute cautiously with 100 to 150 ml. of distilled m-ater, and add 1 to 2 ml. of concentrated hydrochloric acid. Boil and filter the solution while hot, on a Whatman No. 40 filter paper or its equivalent. Police the beaker vigorously, as the silica is a verv adherent precipitate. Wash the precipitate several times with hot water, and then ash in a platinum crucible. Weigh the crucible and contents t o 0.0001 gram. iZdd a few drops of concentrated sulfuric acid and 2 to 15 ml. hydrofluoric acid, and volatilize t h e acids, together with the silica, a t a temperature low enough so t h a t there is no spattering. Heat the crucible strongly, cool, and weigh again. The difference in the two weights is silica (SiOe). Si02 X 1.00 = methyl hydrogen silicone; SiO, X 1.23 = dimethyl silicone.
(1).
In order t o develop a water-repellent finish which has good durability t o laundering and t o dry cleaning, it is usually necessary t o have 0.75 t o 1.25% of silicone present in the fabric, depending on the type of fiber and the construction of the fabric. Accordingly, the analysis of fabrics treated n-ith silicone assumes considerable importance in connection with this specified silicone content. The silicone oils which have been most extensively used for
i"
this purpose are methyl hydrogen silicone. -Si-0-
dimethylsilicone,
(
TIT3 -Si-0-
\
,
, and
where the siloxane unit is re-
peated several times per molecule ( n varies from about 12 to about 7 0 ; n = 20 may be considered representative). McHard, Servais, and Clark ( 2 ) have proposed colorimetric, volumetric, and gravimetric methods for determining the silicon content of organosilicon compounds. I n each case, the organosilicon compound is converted by peroxide bomb or by wet oxidation with various acids t o sodium silicate or t o silicic acid. After the destruction of the organosilicon molecule, further treatment depends on the method selected for the final determination of silicon.
ANALYTICAL RESULTS
Some strips of acetate-viscose fabric, approximately 9 X 60 inches, which weighed about 65 grams, were treated with methyl hydrogen silicone emulsions of various concentrations on a Butterworth laboratory padder. Two sets of analyses were made, one on samples taken from the middle of each strip, the other on samples taken from the trailing end of the strip. The results were:
QUALITATIVE T E S T FOR SILICONES
When silicone oils, alone or in mixtures, are burned in a crucible, the smoke contains white flakes of silica, and a white collar of silica forms inside the crucible a t the rim. This test holds for silicone oils in textile materials, prior t o the heat treatment during which the silicone oils are polymerized. However, after polymerization this qualitative test usually fails.
Number B264-9 B264-10 B264-11 B264-12
250
Middle Sample (MeHSiO),,,
End Sample (MeHSiO)n,
Decrease,
0.42 0.65 1.00 1.66
0.34 0.53 0.81 1.34
19 18 19 19
%
%
%
'
251
V O L U M E 28, NO, 2, F E B R U A R Y 1 9 5 6 Only insignificant differences have been found in samples taken from mill runs. I n small scale laboratory runs, however, in order to obtain significant results, samples for analysis must be taken from the same position on each piece of fabric. DISCUSSION
Analyses made by this method agreed within 0.02% with those made in another laboratory by a colorimetric method in which the sodium silicate from the peroxide bomb is made t o react with ammonium molybdate, and the intensity of the resulting blue color is measured a t 715 mM. The agreement was very poor with analyses made in still another laboratory by dry oxidation in crucibles, as would be expected from the partial volatility of silicone oils a t high temperatures. The average difference between duplicate samples is 0.007%. Silica is a normal constituent of soil. If the textile fabric is not clean, or if silicon-containing compositions such as clay, talc, or colloidal silica have been used in processing, all the silicon present will be reported as silicone when determined by this method. The usual silica content of textile materials finished without the use of silicon-containing baths, and subsequently protected from
soil, is 0.00 t o 0.01%; occasionally amounts up t o 0.03% are found. The silicon content of textile materials which have been processed with silicon-containing compositions will be much higher than where silicon compounds are accidentally present. I n any case, it is always well t o run an analysis for silica on a sample of the fabric before it has been treated with a silicone waterrepellent, if such untreated material is available. ACKNOWLEDGMENT
The author wishes to express his appreciation for the substantial encouragement and advice given by Alton A . Cook, technical director of The Arkansas Co., Inc. LITERATURE CITED
(1) Cook, A. A, and Shane, N. C., Teztile Research J . 25, 105-10 (1955). (2) hIcHard, J. A . , Servais, P. C., and Clark, H. A., ANAL.CHEW
20, 3 2 5 8 (1948). RECEIVED for review April 8, 1955. Accepted November 5, 1955. Presented in part before the Analytical Group, North Jersey Section, ACS, Meeting-hMiniature, January 1955, Newark, N. J.
Titrimetric Determination of Zirconium in Magnesium Alloys PHILIP J. ELVING University
of Michigan,
Ann Arbor, M i c h .
EDWARD C. OLSON The Upjohn Co., Kalamazoo, Mich.
The addition of zirconium to magnesium alloys intended for use at high temperatures requires rapid methods for determining zirconium in such alloys. The titrimetric measurement of zirconium by standard cupferron solution, employing amperometric detection of the equivalence point, has been applied to the direct determination of zirconium in commercial magnesium alloys following acid dissolution. The method is rapid, simple, and accurate, and should supplement the colorimetric alizarin S and gravimetric p-halomandelic acid procedures.
zirconium occurs in both acid-soluble and acid-insoluble forms; the amount of the latter is usually small in comparison with t h e acid-soluble zirconium, and in currently available alloys is usually kept to within 0.02 t o 0.05%, since large percentages may be harmful. The dissolution procedures used in the present study are based on those proposed by Wengert ( 6 ) , which separate acidsoluble and acid-insoluble zirconium by treating the sample with dilute ( 1 to 4)hydrochloric acid; the insoluble fraction is changed to a soluble form by fusion with potassium hydrogen sulfate. Essentially the same dissolution procedure was used by Papucci and Klingenberg (4). EXPERIMENTAL
T
HE need for accurate and rapid methods for the determina-
tion of small amounts of zirconium in magnesium and magnesium alloys was cited by Wengert ( 5 ) in describing the colorimetric determination of zirconium in magnesium alloys by the alizarin red S method, and Papucci and Iclingenberg (4)in describing a similar gravimetric procedure using p-bromo- or pchloroniandelic acid. The addition of zirconium t o such alloys improves the operating temperatures and grain structure without adversely affecting the machinability and creep resistance when used for high temperature purposes as in jet engines. As zirconium can be rapidly and accurately determined gravimetrically and titrimetrically, employing cupferron as precipitant in 10% (ca. 2M) sulfuric acid solution ( S ) , it seemed that the titrimetric method employing amperometric equivalence-point detection might be advantageous as a supplement t o the colorimetric ( 5 )and gravimetric ( 4 ) methods. The present study describes the application of a titrimetric zirconium procedure to two magnesium alloys which were being used in a cooperative evaluation of the colorimetric alizarin red S procedure. Commercial magnesium alloys containing zirconium fall into two groups; one contains up to 6% of zinc and 0.8% zirconium; the other about 3y0 of rare earths and 0.4% of zirconium. The
Reagent grade sulfuric acid (specific gravity 1.84) was diluted 1 to 10 by volume with distilled water. Cupferron was purified and stored as previously described ( 3 ) ; an approximately 0.01 to 0.02X standard solution was prepared daily by dissolving a carefully weighed portion in air-free water. Commercial waterpumped nitrogen was used for deoxygenating without further purification; other chemicals used were of reagent or C.P. grade, Titration was performed in a 150-ml. beaker fitted with a fourhole rubber stopper to accommodate the electrodes, buret (5or 10-ml. capacity, graduated t o 0.02 or 0.05 ml.) and nitrogen inlet; the beaker lip served as gas outlet. A Sargent M o d e l X X I polarograph or Fisher Electropode was used in conjunction with a dropping mercury electrode and a reference saturated calomel electrode (S.C.E.). PROCEDURES
Dissolution (Soluble and Insoluble Zirconium). Weigh 3.0 grams (0.370 Zr) or 2.0 grams (0.6y0Zr) of sample into a 400-ml. beaker. Cover with a watch-glass, cool in an ice bath, then add 1 ) hydrochloric acid. After discautiously 150 ml. of cold ( I solution is complete as indicated by the cessation of gas bubbles, filter through KO.42 Whatman paper into a 250-ml. volumetric flask, wash the beaker and residue with hot water which is transferred to the flask via the filter paper, transfer the residue to the filter paper, and dilute the flask contents to volume; this solution contains the acid-soluble zirconium.
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