We report the preparation and structural and mechanical characterization of a tough supramolecular hydrogel, based exclusively on hydrophobic association. The system consists of a multiblock, ...segmented copolymer of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic dimer fatty acid (DFA) building blocks. A series of copolymers containing 2K, 4K, and 8K PEG were prepared. Upon swelling in water, a network is formed by self-assembly of hydrophobic DFA units in micellar domains, which act as stable physical cross-link points. The resulting hydrogels are noneroding and contain 75–92 wt % of water at swelling equilibrium. Small-angle neutron scattering (SANS) measurements showed that the aggregation number of micelles ranges from 2 × 102 to 6 × 102 DFA units, increasing with PEG molecular weight. Mechanical characterization indicated that the hydrogel containing PEG 2000 is mechanically very stable and tough, possessing a tensile toughness of 4.12 MJ/m3. The high toughness, processability, and ease of preparation make these hydrogels very attractive for applications where mechanical stability and load bearing features of soft materials are required.
Silica is used as reinforcing filler in the tire industry. Owing to the intensive process of silica production and its high density, substitution with lightweight bio-based micro fibrillated ...cellulose (MFC) is expected to provide lightweight, sustainable, and highly reinforced tire composite. MFC was modified with oleoyl chloride, and the degree of substitution (DS) was maintained between 0.2 and 0.9. Subsequently, the morphology and crystallinity of the modified MFC were studied and found to be significantly dependent on the DS. The advantages associated with the use of the modified MFC in synergy with silica for the reinforcement of styrene butadiene rubber (SBR) nanocomposite was investigated in comparison with silica/SBR compound. The structural changes occasioned by the DS values influenced the processability, curing kinetics, modulus-rolling resistance tradeoff, and tensile properties of the resultant rubber compounds. We found that the compound made with modified MFC at a DS of 0.67 (MFC16) resulted to the highest reinforcement, with a 350% increase in storage modulus, 180% increase in Young`s modulus, and 15% increase in tensile strength compared to the referenced silica-filled compounds. Our studies show that MFC in combination with silica can be used to reinforce SBR compound for tire tread applications.
The improvement of mechanical properties of polymer-based nanocomposites is usually obtained through a strong polymer-silica interaction. Most often, precipitated silica nanoparticles are used as ...filler. In this work, we study the synergetic effect occurring between dual silica-based fillers in a styrene-butadiene rubber (SBR)/polybutadiene (PBD) rubber matrix. Precipitated Highly Dispersed Silica (HDS) nanoparticles (10 nm) have been associated with spherical Stöber silica nanoparticles (250 nm) and anisotropic nano-Sepiolite. By imaging filler at nano scale through Scanning Transmission Electron Microscopy, we have shown that anisotropic fillers align only in presence of a critical amount of HDS. The dynamic mechanical analysis of rubber compounds confirms that this alignment leads to a stiffer nanocomposite when compared to Sepiolite alone. On the contrary, spherical 250 nm nanoparticles inhibit percolation network and reduce the nanocomposite stiffness.
We present a structural and dynamic study on the simplest supramolecular hetero-association, recently investigated by the authors to prepare architectural homogeneous structures in the melt state, ...based on the bio-inspired hydrogen-bonding of thymine/diaminotriazine (thy-DAT) base-pairs. In the combination with an amorphous low T
poly(butylene oxide) (PBO), no micellar structures are formed, which is expected for nonpolar polymers because of noncompatibility with the highly polar supramolecular groups. Instead, a clear polymer-like transient architecture is retrieved. This makes the heterocomplementary thy-DAT association an ideal candidate for further exploitation of the hydrogen-bonding ability in the bulk for self-healing purposes, damage management in rubbers or even the development of easily processable branched polymers with built-in plasticizer. In the present work, we investigate the temperature range from T
+ 20 °C to T
+ 150 °C of an oligomeric PBO using small-angle X-ray scattering (SAXS) and linear rheology on the pure thy and pure DAT monofunctionals and on an equimolar mixture of thy/DAT oligomers. The linear rheology performed at low temperature is found to correspond to fully closed-state dimeric configurations. At intermediate temperatures, SAXS probes the equilibrium between open and closed states of the thy-DAT mixtures. The temperature-dependent association constant in the full range between open and closed H-bonds and an enhancement of the monomeric friction coefficient due to the groups is obtained. The thy-DAT association in the melt is more stable than the DAT-DAT, whereas the thy-thy association seems to involve additional long-lived interactions.
Scattering techniques with neutrons and X-rays are powerful methods for the investigation of the hierarchical structure of reinforcing fillers in rubber matrices. However, when using only X-ray ...scattering, the independent determination of the filler response itself sometimes remains an issue because of a strong parasitic contribution of the ZnO catalyst and activator in the vulcanization process. Microscopic characterization of filler-rubber mixtures even with only catalytic amounts of ZnO is, therefore, inevitably complex. Here, we present a study of silica aggregates dispersed in an SBR rubber in the presence of the catalyst and show that accurate partial structure factors of both components can be determined separately from the combination of the two scattering probes, neutrons, and X-rays. A unique separation of the silica filler scattering function devoid of parasitic catalyst scattering becomes possible. From the combined analysis, the catalyst contribution is determined as well and results to be prominent in the correction scheme. The experimental nano-structure of the ZnO after the mixing process as the by-product of the scattering decomposition was found also to be affected by the presence or absence of silica in the rubber mixture, correlated with the shear forces in the mixing and milling processes during sample preparation. The presented method is well suited for studies of novel dual filler systems.
The quantification of interactions between fillers and filler with elastomers in nanocomposites relies on the combination of different microscopy techniques. Small Angle X-ray scattering is a key ...method for the identification of the filler network morphology at the nanoscale. Hybrid nanocomposites containing fillers with diverse morphology and reinforcing ability represent considerable complexity thereby justifying ongoing research in this area, as a consequence of the multiple interactions between fillers and also the filler with the elastomer. Therefore, a microscopic structural investigation of a dual-filled elastomer for tire applications is presented. Chemically modified micro-fibrillated cellulose in combination with traditional silica filler dispersed by melt processing in a styrene-butadiene (SBR) random copolymer were investigated. Small-Angle-X-ray Scattering and Scanning-transmission-electron-microscopy (STEM) revealed non-mixing of the two fillers on the silica scale and the predominant formation of individual filler clusters. Through a novel data deconvolution procedure, partial structure functions corresponding to the contribution of each filler to the scattering function were extracted. This approach offers a suitable methodology to identify the compatibility between morphologically different fillers and their mutual effect on the dispersion.
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•Dual-filler Nanocomposites.•Small Angle X-ray Scattering.•Micro fibrillated cellulose.•Highly dispersible silica.•Decoupling of scattering functions.
In this study, the evolution of the scattering function of silica-filled styrene-butadiene copolymer rubbers (SBRs) under a continuous uniaxial strain cycle is investigated in situ with a ...complementary mechanical analysis. The microscopic hierarchical arrangement of aggregating nanofiller particles in the rubber matrix is determined by ultrasmall-angle X-ray scattering (USAXS) at different strain stages up to 100%. The application of strain during the collection of the scattering images allows a unique correlation of the evolution of the microstructure with a macroscopic deformation. Industrially mixed filled rubber compounds are investigated in the absence of ZnO, typically used as a curing activator and strongly contributing to the scattering function, to relate the scattering function and its evolution to the unambiguous contribution of the silica fillers. The effect of the deformation is reflected in the two-dimensional (2D) scattering patterns as well as in the sectorially averaged intensities along the principal axes of the deformation tensor. A scattering model, based on fractal concepts, is applied to the orientation-dependent intensities, allowing a quantitative correlation between the external strain and the induced structural changes on a 10–100 nm length scale. The singular role of the initial preferential orientation of the silica clusters is investigated in this work due to a direct correlation between the initial states of the clusters and the stress–strain behavior of the rubbery system. Conclusions on the observed hysteresis could be drawn by the combination of microscopic and macroscopic observations.
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•Synthesis of epoxidized soybean oil (ESO) with varying epoxy content.•Partial replacement of petroleum-based oil by ESO in silica-filled rubber compounds.•Reduction of mixing energy ...with the incorporation of ESO.•Importance of epoxy to silica-silanol ratio in controlling rubber properties.
Epoxidized vegetable oils are well-known as biobased, sustainable additives for polymers. However, relatively little work has been done to explore their effects on silica-filled rubber composites in depth. In order to address this knowledge gap, high purity epoxidized soybean (Glycine max (L.) Merr.) oils with varying levels of epoxidation were synthesized and compounded with a model silica-filled styrene-butadiene rubber formulation. The green properties, process characteristics, and cured properties (quasi-static and dynamic mechanical characteristics) of the resultant compounds were then assessed. A ∼7 % decrease in mixing energy was observed with the inclusion of ∼0.8 vol% of 100 % epoxidized soybean oil. Changes in cure kinetics and dynamic mechanical properties were observed as a function of epoxy group concentration. The changes in dynamic mechanical properties are explained in terms of changes in silica dispersion state as a consequence of epoxidized soybean oil addition.
The present work deals with the structural and dynamic characteristics of a silica filler network within an industrial elastomeric composite with time-resolved Ultra-Small-Angle-X-ray Scattering ...(USAXS), collected for the first time in-situ under periodic uniaxial deformation. The in-situ configuration allows a unique correlation between the x-ray patterns highlighting the structure of the filler and the dynamic-mechanical stress-strain response that characterizes the full composite. A scattering model is applied to quantitatively identify the filler network evolution as a function of dynamic strain. To address the Payne effect and the underlying structural modifications correlated to intra- and inter-filler-aggregate effects, all rubbers were pre-conditioned to suppress stress-softening related to the Mullins effect. Sector-averaged scattering intensities along the parallel strain direction reveal a jamming/de-jamming transition between clusters. The dynamic stress response of the full composite shows onsets of non-linear behavior with contributions assigned to both filler and rubber phase separately.
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•Scattering analysis of silica-filled SBR elastomers.•Study of the Payne effect through in-situ combination of USAXS and DMA methods.•Relationship between structural and dynamic-mechanical properties.•Identification of jamming/de-jamming transition upon oscillatory deformation.
With the advancement of additive manufacturing (AM) and the mass adoption of 3D printing technology, it is essential to shift focus to environmentally and economically sustainable materials. As the ...utilization of renewable feedstocks is quite limited in this context, the utilization of more bio-based raw materials in the ongoing development of AM represents an essential means of achieving this shift. In this work, vat photopolymerization 3D printing has been used to process vegetable oil-based (VO) resins with an ultralow concentration of 0.07 vol % nanocellulose fibrils (NFC) and crystals (NCC). The developed nanocellulose containing bio-based vat photopolymerization resin shows excellent shelf stability, enabling high-resolution printing. Compatibilization of the nanocellulose with the polymer matrix was achieved through the introduction of isocyanate or acrylate groups via reactions of acryloyl chloride (AC) and hexamethylene diisocyanate (HMDI) with cellulose surface hydroxyls. Surface functionalization results in ∼20–30% increases in interfacial adhesion and stress transfer, yielding significant improvements in mechanical performance (4× higher toughness, 2.4× higher tensile strength, and 2× higher tensile strain) in 3D-printed specimens. Fourier-transformation infrared (FTIR) spectroscopy complemented by solid-state nuclear magnetic resonance (NMR) techniques enabled a more detailed study of the chemical structure of these materials as well. Tensile performance comparison with literature data on VO-based natural fiber-reinforced resins showed that this work brought bio-based resins one step closer to competing with petroleum-based resins. The prepared VO/nanocellulose resins are promising candidates for high-performance bio-based resins derived from completely renewable feedstocks.
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