A novel non-aqueous sol–gel route for the in situ synthesis of high loaded silica–rubber nanocomposites

Abstract

Silica-natural rubber nanocomposites were obtained through a novel non-aqueous in situ sol-gel synthesis, producing the amount of water necessary to induce the hydrolysis and condensation of a tetraethoxysilane precursor by esterification of formic acid with ethanol. The method allows the synthesis of low hydrophilic silica nanoparticles with ethoxy groups linked to the silica surface which enable the filler to be more dispersible in the hydrophobic rubber. Thus, high loaded silica composites (75 phr, parts per hundred rubber) were obtained without using any coupling agent. Transmission Electron Microscopy (TEM) showed that the silica nanoparticles are surrounded by rubber layers, which lower the direct interparticle contact in the filler-filler interaction. At the lowest silica loading (up to 30 phr) silica particles are isolated in rubber and only at a large amount of filler (>60 phr) the interparticle distances decrease and a continuous percolative network, connected by thin polymer films, forms throughout the matrix. The dynamic-mechanical properties confirm that the strong reinforcement of the rubber composites is related to the network formation at high loading. Both the improvement of the particle dispersion and the enhancement of the silica loading are peculiar to the non-aqueous synthesis approach, making the method potentially interesting for the production of high-loaded silica-polymer nanocomposites.

Compatibilization of natural rubber/nitrile rubber blends by sol–gel nano-silica generated by in situ method

“…It is evident that r 50% , r 100% and r 200% of the composites become higher upon silica incorporation as expected. Furthermore, there is consistent and steady rise of the moduli as silica content increases in the composites (2)(3)(4)(5). This is in accordance with decreased equilibrium swelling ratio values in the series (Table 3).…”

“…One interesting point is noted here regarding peak height reduction [36,37]. The tan d peak height decreases consistently in NR phase as silica content increases for the filled composites (2)(3)(4)(5), while that in NBR phase shows inconsistent variation within small range. Thus, for these composites, in situ silica reinforces the former phase of the blend more strongly.…”

“…Then, all the crosslinking ingredients (ZnO, stearic acid, MBTS and sulfur) were added stepwise and mixed for 10 min to obtain homogenous rubber mixture. This process was followed for all the in situ silica-filled composites (2)(3)(4)(5)(6)(7). Unfilled sample (1) was prepared by dissolving 12 g of NR and 18 g of NBR in toluene and set to stirring for homogenous mixing.…”

“…There are many reports on in situ silicafilled elastomer composites where mostly single rubber system such as natural rubber (NR) [1][2][3][4][5][6][7], styrene butadiene rubber (SBR) [8][9][10][11], butadiene rubber (BR) [12], chloroprene rubber (CR) [13,14] and nitrile rubber (NBR) [15][16][17][18][19][20][21] is focused. Studies on the rubber blends, filled with in situ silica, are rather scanty in literature.…”

The filler–rubber interface in styrene butadiene nanocomposites with anisotropic silica particles: morphology and dynamic properties

“…The nanocomposites were used as models to study the influence of the particle shape on the formation of nanoscale immobilized rubber at the silica-rubber interface and its effect on the dynamic-mechanical behavior. [15][16][17][18][19] According to this model, the interaction between filler NPs is provided by the overlap of the rigid rubber layers. Spherical filler showed small contact zones between neighboring particles contacting thin rubber layers, while anisotropic particles (AR >2) formed domains of rods preferentially aligned along the main axis.…”