Controlled growth of in situ silica in a NR/CR blend by a solution sol–gel method and the studies of its composite properties

Abstract

Silica is grown in situ into a natural rubber (NR)/chloroprene rubber (CR) blend (at 40/60 ratio), by a solution sol-gel method, where the silica content in rubber blend is increased in a controlled manner exceeding the limit found for the same blend ratio in the soaking sol-gel method. Reaction conditions have been optimized to get adequate conversion of tetraethoxysilane (TEOS, a silica precursor) to silica. Rheological, thermal, mechanical and viscoelastic properties of all the composites are compared with those of the unfilled rubber blend at similar conditions. Thermal and mechanical properties of the composites are found to improve consistently as silica content in the composite increases owing to increased rubber-filler interaction as revealed in dynamical mechanical analysis (DMA). Further improvement in the properties is observed for a particular composite where a silane coupling agent ((g-aminopropyl)trimethoxysilane, g-APS) is used in the reactive sol-gel system during in situ generation of silica. This is attributed to the uniform distribution of silica in the rubber matrix and strong rubber-filler interaction, caused by bifunctionality of silane, as revealed by morphology and DMA studies respectively. The reinforcement effect of silica is evaluated by comparing the experimental results with theoretical values obtained from the Guth-Gold model and the modified Guth model. The present study supplements the in situ silica generation in NR/CR blend of 40/60 ratio, following the solution sol-gel method, to the earlier study involving the soaking sol-gel method where the maximum reinforcement was found for this composition.

Reinforced chloroprene rubber by in situ generated silica particles: Evidence of bound rubber on the silica surface

“…The glass transition temperature ( T g ) of the silica filled composites, as observed in the tan δ vs. temperature plot [Figure (c–d)], remains almost unaltered with respect to that of unfilled composite. Such findings are reported for reinforced CR and styrene‐butadiene‐rubber (SBR) where T g of the composites are found to remain unaffected by the presence of silane coupled silica particles. However, for the composite with γ‐APS integrated in situ silica, maximum reduction in tan δ peak height is observed.…”

“…Also, there are few reports on the improvement of properties of silica filled rubber like NR and EPDM by addition of a small amount of CR owing to strong CR–silica interaction that improves the silica dispersion and mechanical properties of the composites . In this context, role of sol–gel derived nanosilica, generated in situ in the CR matrix, in improving the silica dispersion and mechanical properties of the CR composites appears to be very promising …”

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

“…Studies on the rubber blends, filled with in situ silica, are rather scanty in literature. Of late, we have reported several interesting results on in situ silica generation in rubber blends comprised of nonpolar (NR) and polar (CR or NBR) rubber [22][23][24]. Our studies revealed that in situ silica could significantly enhance the compatibility of the heterogeneous immiscible rubber blend in addition to its appreciable reinforcement effect.…”

“…These results are well supported by the increased crosslinking density values along the series which are derived from Flory-Rehner equation of vulcanized composites (Eq. 3; Table 3) that is generally followed in many reported work [15,23,24,35]. We have also determined equilibrium swelling ratio of the rubber phase Q r considering Krause equation, that is applicable for highly reinforcing filler system (Eq.…”

Development and characterization of graphitic carbon nitride as nonblack filler in natural rubber composites

“…Given this most scientific efforts are devoted to developing novel sustainable filler materials to enhance the mechanical strength of rubber products . These fillers are primarily classified into two categories (1) black fillers, for example, carbon black, carbon nanotubes and (2) nonblack fillers such as nanostructure silica, clay, and alumina . Although fillers tend to improve the mechanical properties of the rubber matrix, the filler reinforcement mechanism is still complicated and remains in debate.…”