Search

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. [ABSTRACT FROM AUTHOR]

The additive manufacturing (AM) of elastomeric parts based on high-viscosity reinforced rubbers has increasingly become a topic of scientific research in recent years. In addition to the viscosity, which is several decades higher during processing than the viscosities of thermoplastics, the flowability of the compound after the printing process and the necessary chemical crosslinking of the printed component play a decisive role in producing an elastic, high-quality, and geometrically stable part. After the first technological achievements using the so-called additive manufacturing of elastomers (AME) process, the knowledge gained has to be transferred first to concrete industrial parts. Therefore, in this study, the cure kinetics of a conventional rubber compound are tailored to match the specific requirements for scorch safety in the additive manufacturing of an industrial 2-component rod seal based on an acrylonitrile butadiene rubber O-ring in combination with a thermoplastic polyurethane as the base body. Experimental tests on a test rig for rod seals demonstrate the functionality of this additively manufactured 2-component rod seal. [ABSTRACT FROM AUTHOR]

Elastomer composites with low hysteresis are of great importance for sustainable development, as they find application in billions of tires. For these composites, a filler such as silica, able to establish a chemical bond with the elastomer chains, is used, in spite of its technical drawbacks. In this work, a furnace carbon black (CB) functionalized with polar groups was used in replacement of silica, obtaining lower hysteresis. CBN326 was functionalized with 2-(2,5-dimethyl-1H-pyrrol-1-yl)-1,3-propanediol (serinol pyrrole, SP), and samples of CB/SP adducts were prepared with different SP content, ranging from four to seven parts per hundred carbon (phc). The entire process, from the synthesis of SP to the preparation of the CB/SP adduct, was characterized by a yield close to 80%. The functionalization did not alter the bulk structure of CB. Composites were prepared, based on diene rubbers—poly(1,4-cis-isoprene) from Hevea Brasiliensis and poly(1,4-cis-butadiene) in a first study and synthetic poly(1,4-cis-isoprene) in a second study—and were crosslinked with a sulfur-based system. A CB/silica hybrid filler system (30/35 parts) was used and the partial replacement (66% by volume) of silica with CB/SP was performed. The composites with CB/SP exhibited more efficient crosslinking, a lower Payne effect and higher dynamic rigidity, for all the SP content, with the effect of the functionalized CB consistently increasing the amount of SP. Lower hysteresis was obtained for the composites with CB/SP. A CB/SP adduct with approximately 6 phc of SP, used in place of silica, resulted in a reduction in ΔG′/G′ of more than 10% and an increase in E' at 70 °C and in σ300 in tensile measurements of about 35% and 30%, respectively. The results of this work increase the degrees of freedom for preparing elastomer composites with low hysteresis, allowing for the use of either silica or CB as filler, with a potentially great impact on an industrial scale. [ABSTRACT FROM AUTHOR]

Modern rubber materials face high demands in terms of oxidation stability as well as thermal resistance and, in some cases, enhanced oil resistance. At the same time, their mechanical properties have to maintain a high level. Highperformance synthetic rubbers with highly sophisticated properties – like nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR) and peroxide-crosslinked ethylene – propylene – diene rubber (EPDM) – are thus becoming more and more important. Nevertheless, irreversible aging processes limit lifetime and result in the failure of these elastomer materials. Knowledge about chemical aging mechanisms, kinetics and the weak elements in the polymer chain and in the chemical network are fundamental to understanding and predicting lifetime as well as in arriving at appropriate measures for stabilizing the polymer matrix. Alongside the polymer’s microstructure, other determining parameters are temperature, exposure to oxygen, and its diffusion into the bulk in competition to reaction speed, which is responsible for the spatial changing of the material from the surface inward. Investigations by means of selected methods like nanoindentation, FT-IR spectroscopy, chemiluminescence, and physical testing in combination with artificial aging are used to describe quantitatively the mechanistic role of the polymer’s microstructure and of crosslinking during thermal-oxidative aging. [ABSTRACT FROM AUTHOR]

For investigations on a two‐stage multicomponent injection molding process adhesion‐modified polyamide 6 and EPDM with sulfur‐curing system are used. The influence of different process temperatures is investigated on the basis of a DoE test plan with 15 factor level combinations. Within the scope of additional, more in‐depth investigations, special focus was given to the preheating temperature of the thermoplastic insert. In addition to the experimental work, results from simulations are used to assess the influencing factors. This approach allows a more precise description of the influence of temperature equilibration processes on the crosslinking reaction, especially near the interface between the two components. It is shown that the preheating temperature of the hard component (thermoplastic) in particular has a significant influence on the time course of the crosslinking reaction and ultimately on adhesion to the thermoplastic substrate. [ABSTRACT FROM AUTHOR]

ABSTRACT In this study, a new approach to reduce the environmental effects of end of life and waste rubber and, at the same time, to minimize the ZnO levels in rubber compounds is presented. The use of tire crumb as activator for sulfur vulcanization is investigated. To give an insight into the reaction mechanism, the approach is tested using model compound vulcanization (MCV) with squalene as a model molecule. The results showed that the use of the new recipe does not alter the kinetics of the vulcanization and that the cross-link degree achieved is nearly equivalent to using ZnO. However, in real rubber mixtures [natural rubber (NR), butadiene rubber (BR), and styrene-butadiene rubber (SBR)], there is not a correlation between the promising characteristics seen in MCV and the actual performance of tire crumb. The extent of cross-linking is significantly lower and the mechanical properties are worst in most of the cases. In spite of that, the results found in MCV suggest that further research should be carried out in order to take advantage of the features observed by improving or facilitating the interaction between the chemicals present in the tire crumb and the ingredients added to the rubber matrix. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2809-2820, 2013 [ABSTRACT FROM AUTHOR]

Nanofillers play as reinforcing agents of the polymer matrix. The reinforcement and dynamic mechanical properties of nanocomposites based on filled epoxidized‐poly(styrene‐co‐butadiene) rubber are investigated. The modification of the polymer matrix allows improvement in polymer–filler interaction, and thus the mechanical properties of the vulcanizates. Here, the rubber was modified by introducing the epoxy functional groups in the matrix. The quantification for epoxidation rate was analyzed by means of NMR and ~8.8% epoxidation was optimized. The nanocomposites were prepared by melt‐mixing technique. The influence of rubber epoxidation in enhancing dynamic mechanical and thermal properties was demonstrated. Stable filler networking using exfoliated graphene nanoplatelets (xg C750) and carbon black (CB‐N234) in epoxidized rubber is described through multihysteresis measurements. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47802. [ABSTRACT FROM AUTHOR]