Composites of alkaline poly(6-hexanelactam) with solid lubricants: one-step synthesis, structure, and mechanical properties

One-step preparation of composites of alkaline poly(6-hexanelactam) (PCL) w ith solid lubricants (SL), such as graphite and molybdenum disulfide, is an energy-saving process as additional polymer fusion and melt mixing are not necessary. The initiator/activator system used were: (i) sodium dihydridob is(2-methoxyethoxo) aluminate (SYN)/cyclic trimer of phenyl isocyanate (PIC ); (ii) sodium/hexamethylene-1,6-diisocyanate (HMDIC); (iii) SYN/HMDIC. The se systems have been found suitable for the composite synthesis since they are relatively insensitive to tracts of humidity and other low-molar-mass c ompounds which may be adsorbed on lubricant surfaces. Incorporated graphite (up to 20 wt.-%) and MoS2 (up to 40 wt.-%) do not perceptibly affect glass transition temperature, melting temperature and crystallization temperatur e while polymer yield, polymerization degree and rate decrease. The crystal linity assessed by DSC passes through a maximum at 20% of MoS2 in contrast to that detected by X-ray diffraction (XR) measurements. As expected, the m ean spherulite diameter drops profoundly. Both SL affect mechanical propert ies of produced composites: (i) increase the modulus; (ii) decrease the com pliance, the time dependence of which remains close to that observed for th e matrix; (iii) reduce the yield strength; (iv) slightly lower the impact s trength of composites. A tentative hybrid composite containing 15 wt.-% of graphite, 5 wt.-% of MoS2, and 5 wt.-% of mineral oil (as a liquid lubrican t) shows a modulus high enough and its propensity to creep is not enhanced. The observed changes in mechanical properties of PCL caused by the incorpo ration of SL do not preclude applications analogous to those of unfilled PC L. Friction properties of the composites were beyond the scope of this work .