Liquid crystal polymers (LCP) as processing aids and reinforcing agents. A study of nylon 6/LCP blends

Liquid Crystal Polymers (LCP) as Processing Aids and Reinforcing Agents. A Study of Nylon 6 / LCP BlendsLiquid crystal polymers (LCPs) are a new class of polymeric materials that present very interesting chemical and physical ~roperties.'-~In particular, low viscosity and long range molecular orientation are their most important features.Among physical properties, the values of modulus and stiffness are very An interesting use of these polymers is to blend them with conventional thermoplastic materials in order to achieve blends easily processable and with improved mechanical properties?-"Indeed, some authors 7-9 noticed that the adding of small amount of LCPs gives rise not only to an improvement of the main mechanical properties, but also to a reduction of the viscosity and then of the energy necessary to the processing with respect to the neat polymer.In this work the effect of small amounts of a commercial thermotropic copolyesteramide, made from Celanese, on the mechanical and processing characteristics of a polyamide 6 is studied.In particular, the energy necessary to extrude these blends is considera. EXPERIMENTALThe materials used in this work were a polyamide (nylon 6) and an all-aromatic copolyesteramide.The polyamide was kindly supplied by SNIA (Italy) and is commercially known as ADS 40.The melt flow index is 4.60 following ASTM D1238 cond.R.The copolyesteramide was purchased from Celanese (U.S.A.) and is commercially known as Vectra B950.This liquid crystal polymer is synthesized from hydroxynaphtoic acid (60%), aminophenol(20%), and terephatlic acid (20%).The chemistry and the properties of these types of copolyesters have been reviewed by Calundann and Jaffe" and by Chung."Both materials were carefully dried at T = 120°C under vacuum for at least 24 h, and then blended using a laboratory single screw extruder (D = 19 mm, L/D = 25) Brabender equipped with a die assembly for ribbon.Two thermal profile were used for all the investigated materials:(a) 200, 220, 240, and 260°C; (b) 200, 240, 280, and 290OC.During extrusion the torque was continuously recorded and the flow rate determined by direct weighing.The content of Vectra in the blends, 9, was 1,2.5,3.5,5,10, and 20% wt/wt.A few tests were performed, for comparison, using glass fibers as reinforcing agents at a concentration cp of 5 and 10% wt/wt.The extrusion of these latter materials were carried out only with the lower thermal history.Strips of 0.5 cm were cut out from the ribbon in order to determine the mechanical properties.Stress-strain curves were determined using an Instron model 1122 at an elongational rate of 1.66 mix-'.All the results are average of at least seven measurements.Rheological measurements were carried out using a capillary viscometer Rheoscope lo00 (CEAST, Italy), at 260 and 290°C.The capillary was 1 mm in diameter with length to diameter ratio of 40.