Hydrophobized MFC as Reinforcing Additive in Industrial Silica/SBR Tire Tread Compound.

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.

Solvents drive self-assembly mechanisms and inherent properties of Kraft lignin nanoparticles (<50 nm).

HYPOTHESIS: Strikingly, Kraft lignin nanoparticles (KLNPs) can substitute polluting nanoparticles in diverse applications. An attractive method for synthesizing KLNPs is Solvent shifting. We hypothesized that by a detailed understanding of the solvent properties and influence of the process parameters, one could derive new fundamental and technical information about the lignin nanoparticle formation process. EXPERIMENTS: DMSO and THF were chosen best solvents based on the Hansen solubility parameter of lignin. The four synthesis parameters such as lignin concentration, (anti-solvent) water volume, temperature, and stirring speed were used to investigate the size, polydispersity index (PDI), morphology as well as the thermal, mechanical and optical properties of KLNPsDMSO & KLNPsTHF. FINDINGS: KLNPsTHF follows the well-known nucleation and growth (NG) mechanism, resulting in spherical KLNPs (43 ± 12 nm: 0.20 PDI). Surprisingly, KLNPsDMSO follows a unique mechanism resembling spinodal decomposition (SD), which generates rare bicontinuous-to-spherical KLNPs (17 ± 8 nm: 0.20 PDI). Remarkably, we show that the difference in the KLNPs mechanism modulates their intrinsic properties, such as glass transition temperature (Tg), specific surface area (SSA), elastic modulus (EM) and optical properties. Beyond the new mechanism, our synthesis resulted in reproducible ultra-small KLNPs with an excellent % yield. Such findings have vast implications in high-performance nanocomposites.

Dual-Silane Premodified Silica Nanoparticles-Synthesis and Interplay between Chemical, Mechanical, and Curing Properties of Silica-Rubber Nanocomposites: Application to Tire Tread Compounds.

In silica-rubber based nanocomposites, a single organo-silicon is often used to compatibilize and covalently link silica to rubber. In this work, we have investigated the impact, at micro- and macroscales, of the decoupling of the hydrophobization and the coupling activity of silane by pretreating silica with two different silane chemistries. The first one, a mercaptosilane, is the coupling agent that promotes a covalent link between silica and rubber during the sulfur-mediated vulcanization reaction. The second one, an alkylsilane, aims to improve the silica dispersion. For both kind of silanes, we have varied the chain length and studied at macroscale the dynamic mechanical properties through the key indicators that are E'' as loss modulus, E' as storage modulus, and their respective ratio tan δ. The shorter silanes combination yielded an improvement in terms of wet grip indicators with tan δ at 0 °C increasing from 0.205 to 0.237 while maintaining rolling resistance indicators at the same level. We have evaluated the impact of the silane chemistry onto the cross-linking reactivity within the fabricated rubber-based nanocomposites by using moving-dye rheometer measurements (MDR). By purposely using atomic force microscopy (AFM), we have studied the silica dispersion in the matrix and the rubber/silica interface and provided the rationale explanation of the mechanical properties observed at the macroscale. AFM observation pointed out the existence of a soft interface around silica fillers when long alkylsilanes were used. We infer that this interface impacts the polymer-filler dynamic and subsequently affects the mechanical properties of the composite material.

Original Basic Activation for Enhancing Silica Particle Reactivity: Characterization by Liquid Phase Silanization and Silica-Rubber Nanocomposite Properties.

Silica fillers are used in various nanocomposites in combination with silanes as a reinforcing filler. In tire technology, silica is generally functionalized before (pre-treated) or during mixing (in-situ silanization or post-treated). In both cases, a soft base catalyst (e.g., triethylamine or diphenyl guanidine, DPG) is typically used to accelerate and increase the yield of the silane/silica coupling reaction. In this study, we investigated how pre-treatments of silica particles with either strong amine or hydride bases impact the silanization of silica prior to or during SBR mixing for silica-rubber nanocomposite fabrication. Our findings are supported by molecular characterization (solid state 29Si NMR, 1H NMR and TGA), and scanning electron microscopy. In addition, the impact of these silica pre-treatments on a nanocomposite's mechanical properties was evaluated using dynamic mechanical analysis (DMA).

Hybrid Silica-Based Fillers in Nanocomposites: Influence of Isotropic/Isotropic and Isotropic/Anisotropic Fillers on Mechanical Properties of Styrene-Butadiene (SBR)-Based Rubber.

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.

Comprehensive Analytical Modelling of an Absolute pH Sensor.

In this work, we present a comprehensive analytical model and results for an absolute pH sensor. Our work aims to address critical scientific issues such as: (1) the impact of the oxide degradation (sensing interface deterioration) on the sensor's performance and (2) how to achieve a measurement of the absolute ion activity. The methods described here are based on analytical equations which we have derived and implemented in MATLAB code to execute the numerical experiments. The main results of our work show that the depletion width of the sensors is strongly influenced by the pH and the variations of the same depletion width as a function of the pH is significantly smaller for hafnium dioxide in comparison to silicon dioxide. We propose a method to determine the absolute pH using a dual capacitance system, which can be mapped to unequivocally determine the acidity. We compare the impact of degradation in two materials: SiO2 and HfO2, and we illustrate the acidity determination with the functioning of a dual device with SiO2.

Copper-CNT interfacing with Cu-doped polydopamine in CNT carpet: copper nucleation and resistance decrease upon soft annealing.

In recent years, Cu-CNT composites have attracted much attention due to their remarkable properties, in comparison to pure copper, such as higher ampacity and a lower thermal coefficient of resistance. However, the fabrication of an efficient Cu-CNT composite is still challenging, mainly due to the high cuprophobicity of CNTs. To strengthen the chemical interactions between Cu and CNTs, we propose using a Cu-doped polydopamine coating as an interface between CNTs and metallic copper. This work reports on the nucleation of copper particles on the surface of MWCNTs that are coated with Cu-doped polydopamine after annealing in an inert atmosphere at 573, 673 and 773 K. We show, for the first time to the best of our knowledge, that the polydopamine coating oxidizes during annealing and efficiently reduces Cu ions into metallic Cu. Interestingly, the sheet resistance of coated CNT carpets can be reduced by 33 and 37.6% after annealing at 573 and 773 K, respectively. Furthermore, the sheet resistance decrease does not depend on the size of copper particles (diameter ranging from 13 to 27 nm) or their surface density (from 2.27 × 1010 to 5.7 × 108 particles per cm2). This sheet resistance drop is mainly attributed to the appearance of pyridinic nitrogen in the Cu-doped polydopamine structure after annealing at 673 K and above. Finally, we measure a negative temperature coefficient of resistance for all of the CNT carpets.

Decoupling the Contributions of ZnO and Silica in the Characterization of Industrially-Mixed Filled Rubbers by Combining Small Angle Neutron and X-Ray Scattering.

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.

Tuneable interplay between atomistic defects morphology and electrical properties of transparent p-type highly conductive off-stoichiometric Cu-Cr-O delafossite thin films.

Off-stoichiometric copper chromium delafossites demonstrate the highest values of electric conductivity among the p-type transparent conducting oxides. Morphological and structural changes in Cu0.66Cr1.33O2 upon annealing processes are investigated. Chained copper vacancies were previously suggested as source of the high levels of doping in this material. High resolution Helium Ion Microscopy, Secondary Ion Mass Spectrometry and Transmission Electron Microscopy reveal a significant rearrangement of copper and chromium after the thermal treatments. Furthermore, Positron Annihilation Spectroscopy evidences the presence of vacancy defects within the delafossite layers which can be assigned to the Cu vacancy chains whose concentration decreases during the thermal process. These findings further confirm these chained vacancies as source of the p-type doping and suggest that the changes in electrical conductivities within the off-stoichiometric copper based delafossites are triggered by elemental rearrangements.

Mesoporous TiO2 anatase films for enhanced photocatalytic activity under UV and visible light.

Mesoporous TiO2 films with enhanced photocatalytic activity in both UV and visible wavelength ranges were developed through a non-conventional atomic layer deposition (ALD) process at room temperature. Deposition at such a low temperature promotes the accumulation of by-products in the amorphous TiO2 films, caused by the incomplete hydrolysis of the TiCl4 precursor. The additional thermal annealing induces the fast recrystallisation of amorphous films, as well as an in situ acidic treatment of TiO2. The interplay between the deposition parameters, such as purge time, the amount of structural defects introduced and the enhancement of the photocatalytic properties from different mesoporous films clearly shows that our easily upscalable non-conventional ALD process is of great industrial interest for environmental remediation and other photocatalytic applications, such as hydrogen production.

Crystal Growth Mechanisms of BiFeO3 Nanoparticles.

A wet-chemical synthesis process was designed to obtain reproducible single-phase multiferroic BiFeO3 nanoparticles. The phase purity, single crystallinity, and size of the nanoparticles are confirmed through the analysis of X-ray diffraction patterns, Raman spectroscopy, and high resolution transmission electron microscopy experiments. Crystal nucleation happens within the amorphous-rich area in multiple seeds, leading to the formation of single crystalline nanoparticles with no preferential faceting. Crystallization mechanisms of BiFeO3 nanoparticles were investigated following the Kissinger-Akahira-Sunose approach, indicating that two crystallization steps are responsible of the complete BiFeO3 nanoparticle formation. The first crystallization step involves a maximum of 70% of the final crystal volume, arising from nanocrystal nucleation and growth. The second step occurs above this threshold crystal volume fraction, and it is related to the nanocrystallite coalescence process. Analysis of the thermodynamic process of the crystallization of BiFeO3 nanoparticles following Ostwald rules suggests a relatively low energy barrier for crystal nucleation, highlighting that phase pure, single crystalline BiFeO3 nanoparticles are obtained using the present optimized wet-chemical synthesis process, with temperatures as low as 450 °C.