ABSTRACT:The effect of adding a 1 wt % proportion of thermotropic liquid crystals 4,4Ј-dibutylazobenzene (LC1) and 4-octyl, 4Ј-cyanobiphenyl (LC2) on the tribological properties of polyamide 6 (PA 6) is compared with that of the addition of MoS 2 in different concentrations (1 and 5 wt %). Friction and wear are determined in a pin-ondisk tribometer by using injection-molded additivated nylon disks against steel or aluminum pins, below (25°C) and above (80°C) glass transition temperature. Polymeric blends are characterized by differential scanning calorimetry and by optical and scanning electron microscopy and microanalysis. Concentration of liquid crystalline additives is higher at the surface than in the bulk of PA 6 disks. Crystallinity degree of PA-6 is not significantly changed by the presence of additives. Addition of 1 wt % LC1 improves processibility of PA 6 by increasing its melt flow rate. Cyanoderivative liquid crystal (LC2) shows the best wear-reducing ability for PA 6/steel contacts at all temperatures.

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In the present study, an epoxy resin coating containing a uniformly dispersed 9 wt% of the ionic liquid 1-octyl-3-methylimidazolium tetrafluoroborate (EP+9%[OMIM]BF 4 ) has been applied by spin coating on a neat epoxy substrate, and its abrasion resistance under multiple scratch has been compared with that of neat epoxy coating. EP+9%[OMIM]BF 4 presents the lowest surface damage after 15 successive scratches. The ionic liquid-modified coating reduces instantaneous penetration depth in a 13% and residual depth in a 22% with respect to EP, and increases viscoelastic recovery (after 30 seconds) in a 7.6%. The lubricating effect of the ionic liquid reduces the coefficient of friction up to the tenth scratch number. EP and EP+9%[OMIM]BF 4 have also been obtained in the form of spin-coated films with similar visual transparency. Dynamic-mechanical characterization of the films under a tensile configuration confirms that the addition of the ionic liquid increases the ductility and reduces the glass transition temperature of the epoxy resin.