Abstract
In this work we have characterized one particular type of halogen-free flame retardant polymeric composition, used as sheath of electrical wires and cables. The five pure powders used were Surlyn™9320 (ionic thermoplastic), Elvax™265 (thermoplastic - vinyl acetate and ethylene copolymer - EVA), Martinal™OL104 (Al(OH)3 - halogen-free flame retardant), Cloisite™20A (organoclay) and Irganox™1010 (phenolic antioxidant). Nine premixes were also formulated using these pure components by a design of experiments known as CCRD (Central Composite Rotational Design). In all premixes prepared, the mass ratio of Cloisite™ 20A to Irganox™1010 was constant. Commercial Elvax™265 and Surlyn™9320 pellets were previously cryogenically fragmented with dry ice in a cutting mill. The flow properties of pure powders and premixes were determined using the rotational shear cell accessory of the FT-4 powder rheometer at four different consolidation conditions. The following decreasing order of cohesion for pure powders was established: Martinal™OL104 ~ Cloisite™20A > Elvax™265 > Surlyn™9320 > Irganox™1010. All premixes planned were classified as cohesive powders. The flow properties average values of the premixes such as cohesion, unconfined yield strength and internal friction among particulates as well as the compressibility percentage were dependent on mass ratio of Al(OH)3 to polymeric total fraction in certain consolidation stress. All flow properties were also dependent on consolidation stress, except the angle of effective internal friction (EAIF). The flow function (FF) average values of ELVAX™ 265 presented anomalous variations regarding the levels of applied consolidation stress. The variability of the flow properties was associated to stick-slip and relaxation phenomena mainly due to sticky and elastic characteristics of the EVA particles. The Al(OH)3 particles (Martinal™OL104) have actuated as anti-tack of Elvax™265. Consequently, the anomalous variability of the flow function average values disappeared for the nine premixes.
