Preparation, Structure And Properties Of Silicone Rubber-Based Ceramifying Composites

Silicone rubber-based ceramifying composites are some new kinds of fire-resistant materials,mostly used in fire-retardent cables. It might be some blends of silicone rubber, some filler such as minerals and fluxing agents, and crosslinking agents etc. These composites show the same flexibility and mechanical properties as common silicone rubber at room temperature. When being exposed in high-temperature environments or in fire, those composites could be transformed to self-supporting ceramics. Consequently, the flame would be blocked to spread into the interior of the composites. In this paper, the effect of firing conditions and compositions on the properties of composites was investigated, and the silicone rubber and ceramic residue were characterized by TGA, SEM, EDS and XRD analysis. The mechanism of ceramifying was also explored.Firstly, the effect of firing temperature and heating speed on the properties of composites was investigated. The results showed that the weight loss of silicone rubber increased from 48.6% to 50.2%, and the linear shrinkage increased from-1.4% to 4.0%, and flexural strength of ceramics increased from 1.0MPa to 12.5MPa with the temperature increasing from 700℃ to 1100℃. However, the heating speed only has minor effect on the properties of silicone rubber and ceramic residue.Secondly, the effect of softening point and content of glass frits on the properties of composites was investigated. With the softening point increasing from 320℃ to 850℃, thermal stability of composites was improved. When the softening point of glass frit was 480℃, the ceramics showed the highest flexural strength and impact strength with the values of 21.2MPa and 7.7J·m-1, respectively. SEM analysis showed that there were many micro pores in the cross-section of ceramics containing the frit(soften point 480℃)with the structure of connecting some fillers via some “bridges” produced by liquid phase. New melted matrix was formed and new crystal phase appeared in the ceramics. However, many cracks were found in the cross-section of ceramics containing the frits with the softening points of 320 ℃, 650 ℃ and 850 ℃ respectively. With content of the frit(soften point 480 ℃) increasing from 0phr to 30 phr, the curing speed of blends increased, and the flexural strength of ceramics increased from 2.0MPa to 13.3MPa, but the mechanical properties and thermal properties of the blends decreased. The surface of ceramics became more smoothing with less cracks and bubbles with the increasing content of frits.Lastly, the effect of silica with different variety and content on the properties of the composites was explored. The results showed that the tensile strength of composites increased by 100%, and the weight loss of the composites after firing decreased from 55.8% to 37.6% with the content of fumed silica increasing from 0phr to 40 phr. The compressive strength of ceramics increased from 0.6MPa to 5.8MPa, and the surface deficiency of ceramics decreased gradually. SEM analysis showed that more compact structure was formed and higher ceramifying strength was obtained in the ceramics containing fumed silica than that of precipitated silica.