Three-ply composite laminates prepared from E-glass or N-glass chopped strand mats (CSMs) and jute (J) fabrics as reinforcing agents and amine-cured epoxy resin as the matrix material were subjected to dynamic mechanical thermal analysis at a fixed frequency of 1 Hz over a temperature range of 30-180ЊC. The volume fraction of fibers ranged between 0.21 and 0.25. The reinforcing effect for the three fibers is in the order E-glass ú N-glass ӷ jute. Glass-reinforced composites show a higher storage modulus (E) than that of jute-reinforced composites. The E values of glass-jute hybrid composites lie between those of glass-reinforced and jute-reinforced composites. Odd trends in temperature variability of the loss modulus ( EЉ) and the damping parameter, tan d, and in the glass transition temperature ( T g ) for the three different unitary and four different hybrid composites are interpreted and understood on the basis of odd differences in (1) the chemical nature and physical properties of the three different fibers (E-glass, N-glass, and jute), (2) the void content and distribution, (3) the thermal expansion coefficients of the main phases in the composites, (4) the degree of matrix stiffening at or near the fiber-matrix interface, and (5) the extents of matrix softening in the zone next to the interface.
SYNOPSISGraft copolymerization of acrylamide on cotton (dialdelyde cellulose, DAC) fibers and fabrics was studied in a limited aqueous system using K,Sz08 as the initiator. Grafting parameters under different sets of conditions were determined and the mechanism of graft copolymerization discussed. Optimum conditions for grafting were established and the effect of polyacrylamide grafting on tenacity, modulus, breaking elongation, and stiffness of the cotton (DAC) fabrics and on their dyeability and moisture regain properties were also studied; 9-10% grafting of polyacrylamide on (DAC) fabric at pH 7-10 imparts an improved balance in its mechanical and other properties. 0 1995 John Wiley & Sons, Inc.
I NTRO D U CTl ONReports on graft copolymerization of acrylic monomer such as acrylonitrile, methyl acrylate, and methyl methacrylate are widely available in the literature.'+ Grafting in such cases renders cellulose fibers and fabrics somewhat less hygroscopic or hydrophilic in view of the hydrophobic nature of the relevant grafted-on acrylic polymers. Acrylamide monomer giving a hydrophilic polymer has drawn limited attention for studies in graft copolymerization on cellulose. Likewise, vinyl grafting on oxycellulose has also been studied5-' scantily. It is in this background that studies of graft copolymerization of acrylamide on cotton cellulose fibers and fabrics of a controlled, low degree of oxidation were undertaken and relevant results are reported in this paper.
EXPERIMENTAL
Materials
Cotton CelluloseMill cleaned S-4 quality cotton fiber and a plain weave cotton (poplin) fabric (having an average of * To whom correspondence should be addressed.
Monomer and Other ChemicalsAR-grade acrylamide ( AAm) (monomer), potassium persulfate (initiator), and sodium metaperiodate ( reagent for oxidation of cotton cellulose)were obtained from E. Merck.
A simple
and efficient tert-butyl hydroperoxide-mediated
direct trifluoromethylation of indazoles using sodium trifluoromethanesulfinate
has been developed under metal-free conditions. A library of trifluoromethylated
products with broad functionalities has been synthesized with moderate
to good yields. A radical mechanistic pathway has been proposed for
the present protocol.
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