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

Abstract

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.

Gradient Composites of Alkaline Poly(6-hexanelactam) with Graphite: One-Step Synthesis, Structure, and Mechanical Properties

“…A load of about 20 N resulted in an average final deflection of about 4 to 4.5 mm in the center of the test pieces so that all tests were performed within the interval of the linear stress-strain relationship. As we have shown in our previous paper, [6] experimental creep curves can be fitted by the Nutting equation [17 -19] e(r,t) = K N r m N t n which separates the effects of stress r and time t on the creep deformation. The isothermal dependence of tensile compliance D (r,t) = e (r,t)/r then reads:…”

“…It is a common practice that reinforcements are mixed with molten thermoplastics at elevated temperatures, which holds also for polyamides. [1 -3] Alternatively, the incorporation of particulate fillers or short fibers may precede the polymerization process [4][5][6] (analogously to composites with a thermosetting matrix [7] ). Such a procedure usually leads to essential energy savings since additional polymer fusion and melt mixing are no longer necessary.…”

“…Anionic activated polymerization has been shown to be particularly convenient for the preparation of poly(6-hexanelactam) (poly-e-caprolactam, PCL) and its composites. [5,6] It is routinely initiated with strong bases (causing the formation of free lactam anions) and activated with N-acyllactam growth centers, e. g., isocyanates or their products with polyols, promoting the propagation of polymer chains. [5, 8 -10] The anionic polymerization of 6-hexanelactam is accompanied by side reactions which bring about decomposition of both lactam anions and growth Full Paper: In a one-step synthesis of gradient composites, molten monomer of 6-hexanelactam was mixed with graphite (5 wt.-%) and alkaline polymerization was performed under quasi-isothermal conditions at about 170 8C.…”

“…[6,12] These composites are suitable for preparation of bulky castings such as cylindrical, rectangular, sheet and tube-shaped products. However, the sheetlike products with a uniform distribution of a filler or lubricant may not be suitable enough for applications where only one side of the sheet is exposed to wear conditions, while the opposite side is expected to have properties ensuring sufficient interfacial adhesion in fixing the sliding part to a machine.…”

“…The incorporated filler underwent sedimentation due to the gravity during initial stages of the polymerization process. Initiators and activators of anionic polymerization were used which had been proved [5,6,10,12] to be rather insensitive to the presence of water and impurities adsorbed on fillers and solid lubricants.…”