Rheology, extrudability and mechanical properties of ceramizable silicone composites
Dariusz M. Bieliński, Rafał Anyszka, Marcin Masłowski, Tomasz Pingot, Zbigniew Pędzich
Quarterly No. 3, 2011 pages 252-257
DOI:
keywords: cables, ceramizable silicone composites, rheological characteristic, extrudability, mechanical properties
abstract Ceramizable silicone composites of various origin, designated as A, B and C, which can be used for insulation jackets of electrical cables, were the subject of investigations. The rheology and processing studies of the materials were carried out with a one-screw laboratory Brabender Measuring Extruder 19/10 DW (Germany), operating with a screw rotational speed from 10 to 200 rpm. For evaluation of the rheological characteristics of the mixes, ƞ = f(ɣR) an oval capillary die head was used, whereas a Garvey’s head was mounted to the machine for determination of the extrusion rate, linear shrinkage and swelling of the extrudate (Barrus’ effect). Extrudability studies of the mixes were carried out according to ASTM D 2230-83. The vulcametric characteristics of the materials contained 2,4 (di)chloro benzoyl peroxide, as a curing agent, were evaluated with a Monsanto 100 (USA) vulcameter, according to ISO 3417. The mechanical properties - tensile strength (TS) and tear strength (TES) of the crosslinked composites were determined with a universal mechanical testing machine Zwick 1435 (Germany) according to ISO 37 and ISO 34 standards respectively. Despite similar rheological characteristics, mix A exhibits the best extrudability. It manifests itself by the highest extrusion rate, minimum linear shrinkage and the lowest expansion of the extrudate among the materials studied. All the mixes studied can be extruded with a wide range of screw rotational speed. The higher the rotational speed, the better the efficiency of extrusion, which meets industrial expectations. Edge defects appear on the surface of the extrudates when the rotational speed is low (below 60÷90 rpm). The mechanical properties of the composites studied meet the requirements of the cable industry: TS = 7÷9 MPa, TES = 12÷15 kN/m and EB ≈ 300%. The composition of the mineral phase, in a glaze and silicone rubber matrix, is responsible for the differences in the extrudability of the composites studied. Composites containing small particles of milled quartz and wollastonite dominate over the one based on large particles of mica and zinc oxide, regarding the processing parameters.