Mechanical properties of silicone vulcanizates crosslinked with polymethylhydrosiloxanes,
containing silica and calcium carbonate
Polimery 2006, No 1, 48
Silicone vulcanizates were obtained by crosslinking of poly(dimethyl-siloxane-a,w-diols) (Polastosil, Table 1) with poly[(methyl, phenyl) hydrosiloxanes] (PMHS, PMFHS) of different functionality (Table 2) in the presence of tin catalyst: dibutyltin dilaurate (DBTL). PMHS and PMFHS of linear and branched random structures: MD22DH10M, MD66DH10M, MD40(TPhM)10(TPhOH)10DH10M, MD42(TPhOH)5DH10M, MD42(TPhOH)10DH10M and MD42(TPhM)5(TPhOH)5DH10M (where: M=Me3SiO0.5, D=Me2SiO, DH=MeHSiO, TPhOH=O0.5(C6H5)Si(OH)O0.5, TPhM=O0.5(C6H5)Si(OSi Me3O0.5) were synthesized by hydrolytic polycondensation of appropriate chlorosilanes. Chemical structure and tacticity of PMHS were analyzed using NMR spectroscopy (Fig. 1-4). The content of Si-H groups was determined by iodometric titration (according to Westermark-Schowen procedure). Elastomer and rubber blends, without fillers or containing them (Zeosil 45, Sipernat 310 or precipitated calcium carbonate), were prepared by addition of stoichiometric amounts of crosslinking agent and catalyst in order to obtain 2-3 mm thick layers. Their gelation times, measured at room temperature, increased with a decrease in Si-H bonds content in crosslinking agent (Fig. 5). Tensile strength (Rr) and relative elongation at break (εr) were measured for solid (non-porous) samples (Fig. 6-10). Vulcanizates prepared of Polastosil M-2000 filled with: Sipernat 310 (for 10 wt. %: Rr=1.30-0.62 MPa, εr=170-310%), calcium carbonate (for 10-20 wt. %: Rr=0.62-0.83 MPa, εr=150-180%), and mixtures of Zeosil 45 with CaCO3 showed the best mechanical properties.
Key words: silicone rubbers, poly(dimethyl-siloxane-α,ω-diols), poly[(methyl, phenyl) hydrosiloxanes], functionality, crosslinking, gelation time, fillers, mechanical properties
M. Fejdyś, J. Chruściel, A. Miazga
Mechanical properties of silicone vulcanizates crosslinked with polymethylhydrosiloxanes, containing silica and calcium carbonate