Filler Matrix Interface Characteristics and Mechanical Reinforcement in Elastomeric Nanocomposites

Carbon black and silica are fundamental components of elastomeric composite materials [1].  Over the last years, layered silicates have been actively investigated [2] and they are already applied for the production of rubbery goods, including tyres. We studied clay layering in hydrocarbon elastomers, reporting the preparation of tailor made nanostructures [3].

This contribution investigates the characteristics of the filler matrix interface and the dynamic-mechanical properties of elastomeric nanocomposites based either on precipitated silica or on a layered silicate. Interface was investigated through EPR spin labelling [4] and Solid State NMR [5], whereas raw and sulphur cured compounds were characterized through dynamic–mechanical measurements [6].

Spin labelled precipitated silicas zeosil 1165 (160-170 m²/g) bearing surface anchored nitroxyl probes of different length were synthesized and experimentally tested by EPR in SBR-SiO₂ blends. The chain mobility was found to be enhanced with increasing the label length as a consequence of the increase of the distance from the SiO₂ surface. The EPR dynamics study was extended to flurohectorite silicate (Somasif 100) by anchoring 2,2,6,6 tetramethyl piperidinyl nitroxyl labels to the silicates lamellae by ion exchange. Results are reported arising from EPR measurements performed as a function of the temperature (up to 400 K).

The organic-inorganic heterogeneous layered silicate / rubber interface was addressed by ¹H-²⁹Si and ¹H-¹³C 2D Heterocorrelated MAS NMR spectra at high spinning speed (15kHz) with Lee-Goldburg homonuclear decoupling [5]. The NMR experiments allowed us to detect, separately, carbon, silicon and hydrogen under magnetic communication with one another and provide direct proof of the intimate relationships between polymer and filler components; this is a remarkable example of direct detection of hybrid interfaces by 2D NMR.

Compounds were prepared based on isoprene rubber and a Montmorillonite modified with an ammonium salt, in the absence or in the presence of carbon black. Master curves of the dynamic storage modulus, G', as a function of frequency were determined for the unvulcanized samples. For each system the master curve was obtained in a wide range of frequency by adopting a frequency-temperature superposition scheme. A wider rubbery plateau was observed in the presence of the nanofiller.

The reinforcement of sulphur cured compounds brought about by organoclays is discussed.

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[2] Maiti M., Bhattacharya M., Bhowmick A.K. Rubber Chemistry and Technology 2008, 81, 384.

[3] (a) Galimberti M., Lostritto A., Spatola A., Guerra G., Chem. Mater. 2007, 19, 2495–2499 (b) Galimberti M., Senatore S., Conzatti L., Costa G., Giuliano G., Guerra G., Polym. Adv. Technol. 2009, 20 135

[4] Buttafava A., Ghisoni G.M., Faucitano A., Negroni G., Priola A., Peditto F., Turturro A., Castellano M., Res. Chem. Intermed. 2002, 28 N.2,3, 191

[5] Bracco S., Valsesia P., Ferretti L., Sozzani P., Mauri M., Comotti A., Microporous and Mesoporous Materials 2008, 107,102.

[6] Ramorino R., Bignotti F., Pandini S., Riccò T. Composites Science and Technology 2009, 69, 1206