Sulphur Copolymers with Pyrrole Compounds as Crosslinking Agents of Elastomer Composites for High-Performance Tyres.

Driving a car at extreme speeds, road holding, and sustainability do not go together well. Formula 1 racing is exciting but is not an example of sustainability. The aim of this work was to use materials, suitable for the treads of high-performance racing tyres, that can favour both high performance and sustainability. In particular, the objective was to achieve high dynamic rigidity at high temperatures (>100 °C) and a stable crosslinking network. A copolymer from an industrial waste such as sulphur and a comonomer from a circular biosourced material were used as the crosslinking agent of an elastomer composite based on poly(styrene-co-butadiene) from solution anionic polymerization and a carbon black with a high surface area. The biosourced circular material was 1,6-bis(2,5-dimethyl-1H-pyrrol-1-yl)hexane (HMDP), the di-pyrrole derivative of hexamethylenediamine. Two poly(S-co-HMDP) copolymers, with different S/HMDP ratios (6 and 8.9, Copolymer 1 and Copolymer 2) were carefully characterized by means of 1H-, 13C-, 2D1H-1H-COSY and 2D 1H-13C HSQC NMR. The comparison of the spectra highlighted the substitution with sulphur of the ß-position of the pyrrole ring: mono-substitution largely prevailed in Copolymer 1 and also bi-substitution in Copolymer 2. The copolymers were used as additives in the vulcanization system. Compared with a reference composite, they allowed us to achieve more efficient vulcanization, a higher density of the crosslinking network, higher dynamic rigidity, better ultimate tensile properties, and better stability of the crosslinking network at high temperatures. Compared with a traditional oil-based crosslinking agent for elastomer composites with high rigidity and a stable structure at high temperatures, such as the perthiocarbamate 6-((dibenzylcarbamothioyl)disulfaneyl)hexyl 1,3-diphenylpropane-2-sulfinodithioate, the poly(S-co-HMDP) copolymers led to higher dynamic rigidity and better ultimate tensile properties. These improvements occurring simultaneously are definitely unusual. This work paves the way for the upcycling of circular materials in a large-scale application such as in tyres.

Application of Plasticizer Glycerol in Lignosulfonate-Filled Rubber Compounds Based on SBR and NBR.

The work deals with the application of biopolymer fillers in rubber formulations. Calcium lignosulfonate was incorporated into styrene-butadiene rubber and acrylonitrile-butadiene rubber in a constant amount of 30 phr. Glycerol in a concentration scale ranging from 5 to 20 phr was used as a plasticizer for rubber formulations. For the cross-linking of the compounds, a sulfur-based curing system was used. The study was focused on the investigation of glycerol in the curing process; the viscosity of rubber compounds; and the cross-link density, morphology, physical-mechanical, and dynamic mechanical properties of vulcanizates. The study revealed that the application of glycerol as a plasticizer resulted in a reduction in the rubber compounds' viscosity and contributed to the better dispersion and distribution of the filler within the rubber matrices. The mutual adhesion and compatibility between the filler and the rubber matrices were improved, which resulted in the significant enhancement of tensile characteristics. The main output of the work is the knowledge that the improvement of the physical-mechanical properties of biopolymer-filled vulcanizates can be easily obtained via the simple addition of a very cheap and environmentally friendly plasticizer into rubber compounds during their processing without additional treatments or procedures. The enhancement of the physical-mechanical properties of rubber compounds filled with biopolymers might contribute to the broadening of their potential applications. Moreover, the price of the final rubber articles could be reduced, and more pronounced ecological aspects could also be emphasized.

Hexagonal Boron Nitride as Filler for Silica-Based Elastomer Nanocomposites.

Two-dimensional hexagonal boron nitride (hBN) has attracted tremendous attention over the last few years, thanks to its stable structure and its outstanding properties, such as mechanical strength, thermal conductivity, electrical insulation, and lubricant behavior. This work demonstrates that hBN can also improve the rheological and mechanical properties of elastomer composites when used to partially replace silica. In this work, commercially available pristine hBN (hBN-p) was exfoliated and ball-mill treated in air for different durations (2.5, 5, and 10 h milling). Functionalization occurred with the -NH and -OH groups (hBN-OH). The functional groups were detected using Fourier-Transform Infrared pectroscopy (FT-IR) and were estimated to be up to about 7% through thermogravimetric analysis. The presence of an increased amount of oxygen in hBN-OH was confirmed using Scanning Electron Microscopy coupled with Energy-Dispersive X-ray Spectroscopy. (SEM-EDS). The number of stacked layers, estimated using WAXD analysis, decreased to 8-9 in hBN-OH (10 h milling) from about 130 in hBN-p. High-resolution transmission electron microscopy (HR-TEM) and SEM-EDS revealed the increase in disorder in hBN-OH. hBN-p and hBN-OH were used to partially replace silica by 15% and 30%, respectively, by volume, in elastomer composites based on poly(styrene-co-butadiene) from solution anionic polymerization (S-SBR) and poly(1,4-cis-isoprene) from Hevea Brasiliensis (natural rubber, NR) as the elastomers (volume (mm3) of composites released by the instrument). The use of both hBNs in substitution of 30% of silica led to a lower Payne effect, a higher dynamic rigidity, and an increase in E' of up to about 15% at 70 °C, with similar/lower hysteresis. Indeed, the composites with hBN-OH revealed a better balance of tan delta (higher at low temperatures and lower at high temperatures) and better ultimate properties. The functional groups reasonably promote the interaction of hBN with silica and with the silica's coupling agent, sulfur-based silane, and thus promoted the interaction with the elastomer chains. The volume of the composite, measured using a high-pressure capillary viscometer, increased by about 500% and 400% after one week of storage in the presence of hBN-p and hBN-OH. Hence, both hBNs improved the processability and the shelf life of the composites. Composites obtained using hBN-OH had even filler dispersion without the detachments of the filler from the elastomer matrix, as shown through TEM micrographs. These results pave the way for substantial improvements in the important properties of silica-based composites for tire compounds, used to reduce rolling resistance and thus the improve environmental impacts.

Application of Sulfur and Peroxide Curing Systems for Cross-Linking of Rubber Composites Filled with Calcium Lignosulfonate.

Calcium lignosulfonate in different loadings was applied to the rubber matrix based on EPDM. A sulfur curing system, organic peroxide, and a combination of organic peroxide with two coagent types were used for cross-linking of rubber compounds. The work was focused on the investigation of filler content and curing system composition in the curing process, cross-link density, morphology, and physical-mechanical properties of composites. The achieved results demonstrated that the curing parameters of rubber compounds cured with the sulfur system were significantly different from those cured with peroxide systems. There was also an observed different influence of curing systems composition on cross link density, though in all cases, the degree of cross-linking showed a decreasing trend with increasing content of lignosulfonate. The tensile strength of the composites cured with sulfur system and organic peroxide was comparable, regardless of lignosulfonate loading. This points to the application of both curing systems in cross-linking of rubber compounds with biopolymer filler. However, the introduction of coagents in peroxide vulcanization led to the improvement of adhesion and compatibility between the rubber and the filler on the filler-rubber interface. This subsequently resulted in the improvement of the tensile characteristics of composites. The introduction of organic peroxide in combination with coagent seems to be a very simple and efficient way for the preparation of biopolymer-filled composites with applicable physical-mechanical properties.

Towards the Development of a Strategy to Characterize and Model the Rheological Behavior of Filled, Uncured Rubber Compounds.

In this paper, an experimental strategy is presented to characterize the rheological behavior of filled, uncured rubber compounds. Oscillatory shear experiments on a regular plate-plate rheometer are combined with a phenomenological thixotropy model to obtain model parameters that can be used to describe the steady shear behavior. We compare rate- and stress-controlled kinetic equations for a structure parameter that determines the deformation history-dependent spectrum and, thus, the dynamic thixotropic behavior of the material. We keep the models as simple as possible and the characterization straightforward to maximize applicability. The model can be implemented in a finite element framework as a tool to simulate realistic rubber processing. This will be the topic of another work, currently under preparation. In shaping processes, such as rubber- and polymer extrusion, with realistic processing conditions, the range of shear rates is far outside the range obtained during rheological characterization. Based on some motivated choices, we will present an approach to extend this range.

Multipurpose Processing Additives for Silica/Rubber Composites: Synthesis, Characterization, and Application.

Processing additives are a special group of chemicals included in rubber formulations to facilitate the flowability of the resultant compounds. Their addition generally affects the cured properties of the subsequent rubber composites, and fine-tuning of the compound formulation is therefore required. In this work, an attempt has been made to address this issue through the preparation of new bio-based processing additives capable of promoting the mixing of the rubber compound while at the same time enhancing mechanical properties following curing. A significant decrease in the mixing energy at the first stage of mixing (~10%) has been observed by substituting only a small percentage of the conventional petroleum-derived process oil with aminated epoxidized soybean oil. Concomitantly, it is found that this aminated epoxidized soybean oil promotes rubber curing and increases the tensile strength of the final composite by ~20% compared to the control.

Replacing commercial carbon black by pyrolytic residue from waste tire for tire processing: Technically feasible and economically reasonable.

Decades of researches have proved that pyrolysis can not only realize the harmless disposal of waste tire, but also carry out the goal of waste resource utilization via recycling pyrolytic products (e.g. pyrolytic carbon black, CBp). The current work studied the effect of CBp obtained from the commercial scale pyrolysis of waste tire, on the properties of natural rubber and butadiene rubber. CBp was incorporated into a carbon black quality identification standard formula in combination with N234 commercial carbon black (cCB) first. After screening a better substitution ratio, the composite material of CBp and cCB was mixed with more additives, and the experiment was carried out with a real production formula. To restore the practical production situation, the experiment process adopts the most commonly used process to avoid major changes in commercial production. CBp was tested at increasing loading levels as partial or full replacement of cCB. The physico-mechanical properties of the rubber compounds were studied by tests of physical, mechanical, and vulcanization properties. With the increase in the amount of CBp added, the physical and mechanical properties of the rubber compound showed a trend of slightly increasing first and then rapidly decreasing. The addition of CBp can increase the yield strength and stiffness of the rubber, but it may also lead to a decrease in hardness. Meanwhile, the substitution ratio of CBp up to 50% has been proven to improve safety and achieve a more stable vulcanization process of rubber compounds. CBp can replace up to half of cCB without significantly reducing the quality of tire rubber. The economic value of partial replacement of cCB by CBp has also been evaluated, demonstrating that adding a small amount of CBp can directly reduce the cost of raw materials, indirectly reduce the use of fossil energy promoting carbon dioxide reduction worldwide.

Study of Carbon Black Types in SBR Rubber: Mechanical and Vibration Damping Properties.

Styrene-butadiene rubber mixtures with four types of carbon black were studied in this paper. The mechanical properties, including the ability to damp mechanical vibration, were investigated, along with dynamical mechanical analysis (DMA). It has been found that carbon black types N 110 and N 330, having the largest specific surface area and the smallest particle diameter, provide a good stiffening effect. These particles have significant interactions between the rubber, resulting in good reinforcement. On the other hand, the carbon black N 990 type has a lower reinforcing effect and improved vibration damping properties at higher excitation frequencies due to higher dissipation of mechanical energy into heat under dynamic loading. The effect of the number of loading cycles on vibration damping properties of the rubber composites was also investigated in this study. It can be concluded that the abovementioned properties of the investigated rubber composites correspond to physical-mechanical properties of the applied carbon black types.

Sensor-Based Real-Time Detection in Vulcanization Control Using Machine Learning and Pattern Clustering.

Recent paradigm shifts in manufacturing have resulted from the need for a smart manufacturing environment. In this study, we developed a model to detect anomalous signs in advance and embedded it in an existing programmable logic controller system. For this, we investigated the innovation process for smart manufacturing in the domain of synthetic rubber and its vulcanization process, as well as a real-time sensing technology. The results indicate that only analysis of the pattern of input variables can lead to significant results without the generation of target variables through manual testing of chemical properties. We have also made a practical contribution to the realization of a smart manufacturing environment by building cloud-based infrastructure and models for the pre-detection of defects.

The fabrication of microcrystalline cellulose-nanoZnO hybrid composites and their application in rubber compounds.

Microcrystalline cellulose (MCC) was first swollen and then hybridized with nano-ZnO to prepare MCC-ZnO hybrid composites using a microreactor technique. The microstructure of the ZnO particles was controlled and characterized. The results showed that the nano-ZnO particles had a Wurtzite structure and were successfully loaded on the surface of the MCC, and the ZnO morphologies could be shaped as spheres, rods or tubes by controlling the size of microreactor. The hybrid ratio of ZnO was approximately 20%. The MCC-ZnO hybrids were used in SSBR2557A/SiO2 compounds to replace portions of the silica. The results showed that MCC-ZnO compounds had improved processing and mechanical properties compared to the pure MCC sample. The dynamic mechanical analysis (DMA) indicated that MCC-ZnO compounds had higher wet-skid resistance and lower rolling resistance than the control samples. The interfacial bonding between the hybrids and rubber was also improved; the sizes of the hybrid composites decreased in situ during the rubber processing.