One-step synthesis of hybrid composites of poly(6-hexanelactam) combining solid tribological additives and reinforcing components

Four types of composites of polyamide 6 with hybrid tribological additives were synthesized via anionic adiabatic "in situ" polymerization of 6-hexanelactam (ε-caprolactam) initiated with metallic sodium and activated with cyclic trimer of phenyl isocyanate or diphenylmethane 4,4′-diisocyanate. The optimization of the initiator/activator systems in the range of 0.3 to 1.2 mol-% and of the initial polymerization temperatures from 125 to 150 °C preceded the composite preparation. Combinations of fillers and their maximum applied concentrations (in wt.-%) were the following: MoS2/graphite/oil (5/16/9), carbon fibers/graphite/oil (5/20/10), copper phthalocyanine (7), and B2O3 (11). Analysis of selected composites encompassed water extraction, DSC, and DMTA measurements. All tested fillers decreased the polymerization rate, polymer yield, melting temperature and crystalline fraction. Polymerization rate constants of the neat polyamide 6 obtained for various initial temperatures obeyed the Arrhenius plot giving an average activation energy value of 78.6 kJ · mol-1.