Understanding the Reinforcement Effect of Fumed Silica on Silicone Rubber: Bound Rubber and Its Entanglement Network

Abstract

In this work, fumed silica was compounded with silicone rubber and processed under two different extraction conditions to quantitatively analyze bound rubber for studying filler−rubber interaction. When nanocomposites were treated with toluene at 90 °C under ultrasonic (US) irradiation, physisorbed polymer chains were more substantially removed when compared to the traditional room temperature (RT) extraction method. The bound rubber fraction of silicone rubber filled with 40 phr of silica was 32.85% by RT treatment, while the US-treated one was reduced to 6.20%. A thin layer of tightly bound rubber adsorbed on the silica surface could be obtained by US treatment as observed by scanning electron microscopy and transmission electron microscopy. Low-field 1 H NMR results confirmed that the obtained tightly bound rubber chains were strongly constrained. The attenuated total reflectance-infrared spectra showed that the formation of tightly bound rubber caused redshift of the Si−O−Si characteristic peaks of silica, and the obtained tightly bound rubber has lower total surface energy than the rubber matrix, indicating the formation of a more stable structure. The reagglomeration potential energy of silica during the curing process was significantly reduced due to the presence of the bound rubber layer. In addition, the amount of tightly bound rubber is mainly related to the surface physical and chemical properties of silica and is less affected by the concentration. Fumed silica tends to form nanofiller networks in rubber that are woven of multiple fillers entangled with bound rubber chains to reinforce the rubber. Therefore, fillers with higher bound rubber content and a better-dispersed aggregate structure in the rubber could more significantly enhance the physical properties of nanocomposites.

Performance Enhancement of Silicone Rubber Using Superhydrophobic Silica Aerogel with Robust Nanonetwork Structure and Outstanding Interfacial Effect

“…The uncured fumed silica-PVMQ compounds left a large number of macro-pores due to the extraction of free polymer and exposed a porous filler–rubber network structure, which was woven by a large number of branched fumed silica aggregates and bound polymer chains. According to our previous studies and reports from other researchers, the silicone rubber and silica mainly form a tightly bound rubber (TBR) layer by hydrogen bonding (between the oxygen atoms on the silicone rubber and the hydroxyl groups on the silica) and loosely bound rubber (LBR) by physical winding (or van der Waals force). ,− Moreover, when the interspace between nanoparticles is narrow enough, the bound rubber chains will be anchored on multiple nanoparticles at the same time, thus forming a huge polymer reinforced-filler network structure (mainly indirect bridging of nanoparticles by TBR-LBR and TBR-TBR interwinding and direct bridging by TBR winding, respectively) (Figure g).…”

“…The entanglement network of silica aerogels-PVMQ is extraordinarily different from fumed silica-PVMQ; it exhibits a strong ability not only to bind polymer chains but also to develop a more extremely dense and solid filler−rubber entanglement network, as illustrated in Figure 5e. In contrast, fumed silica is distributed in the rubber in dendritic aggregates of smaller size, 16,41 and even at very high filler loadings (60 phr), there are still large gaps between the fumed silica clusters that were not favorable for the adsorption of polymer, and therefore the tendency of the aggregates to bridge each other through the polymer chains may be extremely poor, as illustrated in Figure 5f. To accurately quantify the filler−rubber entanglement network structure, the N 2 adsorption−desorption isotherms and Barret−Joyner−Halenda (BJH) aperture distribution of the RT-extracted composites were compared (Figure 6a,b).…”

Integration of experimental methods and molecular dynamics simulations for a comprehensive understanding of enhancement mechanisms in graphene oxide (GO)/rubber composites

“…In order to further con rm the interaction between GO and the three different types of rubber, the bound rubber content (BdR%) of the GO/NR, GO/SBR, and GO/XNBR nanocomposites were determined. BdR% refers to a type of rubber that cannot be extracted with a suitable solvent, as it is the result of a strong interaction between rubber and ller [31] . As shown in Fig.…”

Interaction of silica with polystyrene: mechanical properties, polymer/filler adhesion and failure behavior

“…Fortunately, the surface chemistry of silica is much more clearly defined than that of many other types of filler. Hence the polymer-filler interactions and their influence on the reinforcement properties of the material can be much more easily studied with silica as a filler [42,43]. Silica can be classified, according to its nature, as natural and synthetic.…”