Question

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8. Describe one method for fiber surface treatment for glass fibers (hint: include the any chemical process in the narrative).

Answer 1

"MATERIALS & METHOD: Measurements were carried out with an Intersmat IGC 12 gas chromatograph fitted with a katharometer detector. Column tem' perature was maintained at 294 + ldegreeK throughout the measurements by adapting a secondary forced-air convector to the original system. Short glass fibers (rock melts of Danish origin) from ""Rockwool International"" were used for column packing. They present the particularity of forming, on sieving, spherical agglomerates of about 1 mm diameter well suited for the filling of the columns. The fibers had mean diameters of 6 #m and a specific surface area of 0.25 m 2 g-1. Their bulk composition was: SiO2 = 46%, CaO = 16%, A1203 = 17%, Fe203 = 9%, and MgO = 12%. In a typical run, retention volumes were obtained with a 1.0-m-long steel column of 6.35-mm external diameter fitted with 7.747 g of glass fiber agglomerates having a mean diameter in the range of 0.5-1.0 mm. The carrier gas was helium, with a flow rate of about 20 cm 3. min -1 as determined at the column outlet with a soap bubble flowmeter. Corrections were allowed for saturated vapor pressure of water, pressure drop across the column (0.03 MPa), and the difference in temperature between column and flowmeter. Column conditioning was attained by heating to 120degreeC during 24 hours under helium flow. Retention volumes, defined on a unit weight basis, were finally brought to standard conditions at 273degreeK, allowance being made for column gas hold up using the air-peak method. A 1-#1 Hamilton syringe was used to inject small amounts of solute consistent with the highest-sensitivity range of the katharometer. Comparative measurements were also cartied out with a column packed with commercial-grade powdered PTFE known to interact only through London dispersion forces. About 17 g of PTFE were required to fill a column having the same dimensions as before. The solute probes were reagent analytical grade from Fluka and were used without further purification. The product used for surface modification of the glass fibers were -aminopropyltriethoxysilane (A 1100 from Union Carbide) and isopropyl tri(dodecylbenzenesulfonyl) titanate (TTBS-9 S from Kenrich Petrochemicals). Surface modification was carried out in situ on two identical columns packed with glass fibers, by injecting a large excess of the coupling agents at the column inlet. The silane was used as a 2% aqueous solution and the titanate was also dissolved in isopropyl alcohol as a 2% solution. About 5 cm 3 of each solution were used to make sure that the whole column content underwent contact with the treating solutions. The columns were then heated to 120degreeC for 24 hours under high helium flow so as to remove the excess products and leave homogeneously treated substrates. Specific surface area remained practically constant after surface modification. (This procedure does not alter the morphology of the chromatographic supports.) If sufficient time was allowed between successive injections, there was no evidence of some of the probe ramaining on the glass and producing changing surface: after that time peaks were reproducible and no programmed heating desorption peak could be detected up to -110degreeC."