Composites of alkaline poly(6-caprolactam) and short glass fibers: one-step synthesis,structure and mechanical properties

If incorporation of short fibers precedes the polymerization process, their damage is reduced because the viscosity of a monomer is much lower than that of a corresponding polymer. One-step preparation of composites also leads to essential energy savings since polymer fusion and melt mixing are eliminated. Structure and properties of poly(6-caprolactam) matrix polymerized with the initiator/activator systems sodium dihydridobis(2-methoxyethoxo)aluminate/cyclic trimer of phenyl isocyanate are affected by rising concentration of (γ-aminopropyl)triethoxysilane sizing agent: polymerization is slower, but polymerization degree rises; yield strength and notched impact strength decrease, while crystallinity and modulus remain unaffected. When the initiation system sodium tetra(6-caprolactamo)aluminate/cyclic trimer of phenyl isocyanate is alternatively used, the polymerization is somewhat faster, but the polymer is insoluble in m-cresol due to side crosslinking reactions. Incorporated short glass fibers (SGF) (up to 13.2 vol.-%) do not markedly affect the matrix properties. As expected, SGF decrease the compliance (increase the moduli) of composites, but do not affect the time dependence of the creep. Increasing the fraction of SGF also decreases the yield strength of composites, which indicates poor interfacial adhesion; the latter is only slightly improved by fiber sizing. Impact strength decreases with the fraction of as-received SGF, while a moderate opposite trend can be seen for the composites containing silane treated fibers.