The Process of Gel Fiber Formation
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THE PROCESS OF GEL FIBER FORMATION N.TANEDA, T.KAWAGUCHI, D.ARAI, AND K.MATSUZAKI Asahi Glass Company Ltd., Advanced Glass R&D Center, Kanagawa-ku, Yokohama-shi, 221 Japan
Hazawa-cho,
ABSTRACT The gel fiber formation was studied for the spinnable silica sols prepared from a mixture of TEOS, H2 0, EtOH and HNO 3 ( 1 : 2 : 2 : 0.01, in mole ratio). The effect of polysiloxane molecular size in the spinning sol on spinnability indicated that the tough skeleton of gel, which is preferable for fabrication of high-strength fiber without breakage, was formed by the selective connection of large size polymers (about 106 in M.W.) during the spinning. It was also found that the smaller size polymers in gel fiber continued to react with water in the atmosphere after the spinning, and attached to the skeleton to strengthen the fiber. INTRODUCTION It is well known that the sol from TEOS solution prepared under the condition that H2 0/TEOS ratio is less than 2 with acid catalysis is spinnable. Several authors have studied the spinnability as functions of starting compositions, rheological behavior of the sol, and polymer structure [1-6]. However,the details have not been reported so far. In this article we studied the effect of molecular size of polysiloxane in the sol on spinnability by Size Exclusion Chromatography (SEC)[7], stretch factor, and the strength of gel fiber. EXPERIMENTAL Tetraethylorthosilicate ( TEOS ) was used as a starting material. The mixture of TEOS, EtOH, H2 0, and HNO 3 in the mole ratio of 1: 2 : 2 : 0.01 was stirred vigorously at room temperature, and then the solution was kept at about 79'C under EtOH reflux. The gelation point was determined when EtOH did not reflux. The gelation time(tg) was about 70hrs. The spinning sols were prepared by cooling down the solutions after certain refluxing. Since in the previous work[8] the sols with viscosity at 25"C above 50 poise were found to be suitable for the dry-spinning, in this study the viscosity was adjusted to be 50 to 80 poise by extracting some extent of the solvent from each solution. The lower the average molecular weight of sol, the more its solvent should be extracted to adjust the viscosity. The sols were turned into gel fiber by the dry-spinning method as reported in reference[9]. The molecular weight (M.W.) of spinning sols and gel fibers were analyzed by SEC with a differential refractometer (Waters Associates Model R401). THF 3was made to flow through 4 columns (ULTRASTYRAGEL 500A, 10 A, 10 4 A, 10 5 A, made by Waters Associates) at the rate of 1.0 ml/min. Samples were diluted to lwt% in the solid content in tetrahydrafuron (THF) and filtered
Mat. Res. Soc. Symp. Proc. Vol. 180. 01990 Materials Research Society
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by disk filter of 0.7,am in pore size Molecular weight(M.W.) was represented The tensile strength of gel fiber length was measured with a strain rate stron model 1122.
before the measurement. by polystyrene standard. mono-filament of 25mm in of 0.5mm/min. by an In-
RESULTS AND DISCUSSION Polymerization of the sols Figure 1 show
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