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 th at of a corresponding polymer. One-step preparation of composites also lead s to essential energy savings since polymer fusion and melt mixing are elim inated. Structure and properties of poly(6-caprolactam) matrix polymerized with the initiator/activator systems sodium dihydridobis(2-methoxyethoxo)al uminate/cyclic trimer of phenyl isocyanate are affected by rising concentra tion of (gamma-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 r eactions. Incorporated short glass fibers (SGF) (up to 13.2 vol.-%) do not markedly affect the matrix properties. As expected, SGF decrease the compli ance (increase the moduli) of composites, but do not affect the time depend ence of the creep. Increasing the fraction of SGF also decreases the yield strength of composites, which indicates poor interfacial adhesion; the latt er is only slightly improved by fiber sizing. Impact strength decreases wit h the fraction of as-received SGF, while a moderate opposite trend can be s een for the composites containing silane treated fibers.