Comparative study of the tribological properties of polyamide 6 filled with molybdenum disulfide and liquid crystalline additives

Abstract

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.

Friction and multiple scratch behavior of polymer+monomer liquid crystal systems

“…Pin-on-disk tests for PS and SAN show that 1 wt% of a MLC improves the wear resistance of these polymers [12,15]. Similar results for PA6 [13] reveal a similar or even superior antiwear property compared to the well known solid lubricant MoS 2 .…”

“…We have previously reported [13,15] tribological properties of PS and SAN with LC1 additions in pin-on-disk tests against AISI 52100 steel under variable load, speed and sliding distance. We have found that addition of 1 wt% LC1 produces a dynamic friction reduction with respect to pure PS between 10 and 14%, depending upon test variables.…”

“…After milling the polymers with the corresponding proportion of MLC, PS and SAN samples were obtained by pressing the powders at 22 MPa while heating them at 150 8C in a Buehler metallographic press as previously described [13]. PA6 and PA6CMLC systems were injection molded at 250 8C also as described in [13].…”

“…The present work represents a continuation of work on external lubricants conducted in Cartagena [11][12][13]15,16], work on friction [17], scratching and wear [18,19] at the University of North Texas (UNT), and also joint work of both groups [20,21]. Thus, the Cartagena group has demonstrated that monomer liquid crystals (MLCs) in base oils lower wear rates in steelCsteel and steelC aluminum contacts [11].…”

“…Thus, the Cartagena group has demonstrated that monomer liquid crystals (MLCs) in base oils lower wear rates in steelCsteel and steelC aluminum contacts [11]. Similarly, tribological properties of polystyrene (PS) and styrene/acrylonitrile (SAN) copolymer [12,15] as well as polyamide 6 (PA6) [13] have been modified using MLCs as lubricants. Ye and coworkers [14] reported fairly low friction values obtained using a ball-ondisk technique for metal pairs in the presence of fluorinated alkylimidazole borates, which are MLCs.…”