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

Abstract

Controlled growth of in situ silica, into natural rubber (NR)/nitrile rubber (NBR) blend (40/60 composition by weight) following solution sol-gel method, results in a coherent blend morphology with enhanced composite properties. Similar composites, i.e., in situ silica-filled NR/ NBR blend (40/60 by weight), showed better mechanical properties than any other composition that were prepared by soaking sol-gel method in earlier study. However, silica content in the rubber blend was limited to 20 phr (parts per hundred parts of rubber) and could not be increased under experimental condition following soaking sol-gel method. In the present work, silica content is increased (up to 30 phr) beyond that limit for the same blend composition. Accordingly, mechanical properties of the NR/NBR composites are improved. Use of a silane coupling agent, viz., bis-(3-triethoxysilylpropyl)-tetra sulfide, in the reactive sol-gel system during in situ silica generation brings in remarkable effect in silica distribution, rubber-filler interaction and mechanical properties of the composites. TEM micrographs of the selected composites reveal that silica is mostly grown at the interfacial region, when silane is used in particular. This results in further enhancement in mechanical properties and compatibility of the blend at the same silica content as evident from stress-strain and dynamic mechanical analysis studies. The reinforcement of effect in situ silica is assessed by Guth-Gold equation and modified form of Guth equation (with shape factor f = 2.53). The results are supported by the detailed studies on rheological, morphological, mechanical and viscoelastic properties of the composites. Graphical AbstractKeywords Rubber blend Á Sol-gel method Á In situ silica Á Rubber-filler interaction Á Silane treatment Á Reinforcement

Curing characteristics, swelling, and mechanical properties of natural rubber/nitrile butadiene rubber blends with and without compatibilizer

“…The NR/NBR vulcanizates without MBS showed typical rubber phase separation (Figure 7b) due to poor interfacial adhesion between the NR and NBR phase resulting from dissimilar polarity (Angnanon et al, 2011). Two distinct phases, NR (black) and NBR (gray), indicate the immiscibility of the components in the blends (Bansod et al, 2016). The rubber blends with MBS show that there is no phase separation identified on the tensile fracture surface of the NR/NBR blends (Figures 7(c)-(h)).…”

Promoting the dispersibility of silica and interfacial strength of rubber/silica composites prepared by latex compounding

“…Firstly, it is of significance to modify silica to improve its dispersibility in the rubber matrix, and many related studies have been conducted. [15][16][17][18][19][20] For example, silica modified by silane coupling agents, [21][22][23][24][25][26] surfactant, [27][28][29][30] both silane coupling agents and surfactant, [31] grafting polymer, [32,33] adding other fillers, [34][35][36] ionic liquid. [37] What's more, mechanical force can also improve the dispersibility of silica, but it has little effect on the enhancement of interface strength due to the bad compatibility of silica and rubber.…”

“…Among them, silica modified by silane coupling agents was a more extensive approach in which some hydroxyl groups on the surface of silica are grafted by the organic group of silane coupling agent. [21][22][23][24][25] This kind of partially organic structure can not only help the dispersibility of silica, but also enhance the interface adhesion between silica and rubber. But silane coupling agent is usually mixed with silica and rubber through the mechanical blending method, which is inefficient and need high temperature condition.…”

“…[40] The sol-gel co-precipitation method referred to adding a silica-forming precursor to NRL, followed by a series of conversions to directly form silica/NR composites. [25] By the above method, the silica particles were uniformly dispersed in composites, but the process was complex and unsuitable for large-scale production, so its practical application was limited to a certain degree. [41] Attentively, the latex compounding method was mixing NRL and silica dispersions in water together and the rubber compounds were obtained by precipitation with a solution such as formic or calcium chloride.…”

Comparative behavior of in situ silica generation in saturated rubbers: EPDM and hydrogenated natural rubber

“…This indicated that the small amount of in situ silica could slightly reinforce the blends and reduced the flexibility of the rubber chains. This phenomenon was also observed for the reinforced NR, NR/nitrile rubber (NBR) blend and SBR modified by grafting with vinyltriethoxysilane (VTES) . To compare with rubber blends reinforced by using ex situ commercial silica at similar silica content, the Si‐EPDM/NR and Si‐HNR/NR vulcanizates showed slightly lower both TS and EB values than the in‐situ silica‐reinforced samples.…”