A self-healing sulfur vulcanized natural rubber (NR) is here reported using the common ingredients in a traditional NR formulation. The dynamic character of the di- and polysulfide bonds naturally present in covalently cross-linked rubbers was found to be responsible for the healing ability and the full recovery of mechanical properties at moderate temperatures provided the material was employed in a nonfully cured starting state. Results show that a compromise between mechanical performance and healing capability can be reached by tailoring the amount of sulfur, the cross-linking density, and the disulfide/polysulfide ratio. The healing efficiency was found to depend on the postcuring storage time, the time between damage creation and re-establishment of mechanical contact, and the actual healing time. Furthermore, a dedicated electron spin resonance (ESR) test allowed establishing the underlying healing principle based on temperature-induced free sulfur radicals. The main observations presented here can serve as the basis for the design and preparation of other self-healing polymers with long-term durability based on di-/polysulfide bridges and other reversible moieties

The rapid utilization of carbon fibre reinforced composite (CFRC) and glass fibre reinforced composite (GFRC) in main sectors, such as automobile, aerospace, wind turbines, boats and sport parts, has gained much attention because of its high strength, light weight and impressive mechanical properties. Currently, the increasing amount and handling of composite waste at their end-of-life (EoL) has a negative impact on resources conservation and the environment. Pyrolysis, a two-step process, appeared as most viable process to recover not only valuable materials but also produce fuel and chemicals. However, the testing facilities and optimized operation of composite waste in pyrolysis processes to produce materials with low energy consumption and acceptable mechanical properties are still under development and discussion before commercialization. The aim of this article is to review the studies on CFRC/GFRC recycling via pyrolysis processes and highlight their technical challenges and re-use possibilities in high performance composites. The forthcoming commercialization challenges and respective market potential to recyclates using the pyrolysis process will be addressed. This study will also introduce the strong connection between recycling and re-usability of fibres which would help to explain the concept of circular economy and cradle-to-cradle approach. Finally, based on updated studies and critical analysis, research gaps in the recycling treatments of fibrous composite waste using pyrolysis processes are discussed with recommendations.

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The dump temperature and mixing interval between rubber, silica and silane coupling agent for silica-filled natural rubber (NR) tire tread compounds using bis-triethoxysilylpropyl tetrasulfide (TESPT) as silane were optimized. The dump temperature turns out to be the key parameter governing the properties of the silica-filled NR compounds. The increase in

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For both environmental and economic reasons, there is broad interest in recycling rubber and in the continued development of recycling technologies. The use of postindustrial materials is a fairly well-established and documented business. Much effort over the past decade has been put into dealing with of end-of-life tires from landfills and vacant fields. It is only in the last few years that more business opportunities for recycled rubber have come to the forefront. Reclaiming rubber has gained increasing interest, more so in Europe than in North America. In those areas, much work has been done to refine the processes used. The major form of recycled rubber is still ground rubber. This is produced either by cryogenic, ambient, or wet grinding. The material is then used neat with sulfur/curatives, binders, or cements. The binders are normally moisture curable urethanes, liquid polybutadienes, or latex to produce items such as mats, floor tiles, and carpet undercushion. Recycled rubber is still used as tire derived fuel, but less so than 10 years ago. Another outlet is as an additive to asphalt. Recycled rubber can be used in the plastics industry, for which much development is being done. Large particle size ground rubber or chips are used in civil engineering applications, landscaping, or artificial turf. In terms of applications, most use is outside of the conventional rubber industry. Cost factors are still addressed in the tire industry. As of 2012, approximately 8–10% recycled material is used in tires. The biggest obstacles to further adaption are safety factors and property loss. Better methods are needed for treating or modifying the rubber surface and for regenerating the rubber through devulcanization. Devulcanization gives the highest quality recycled material in terms of processing and properties. However, shortcomings to devulcanization are reduced process safety and odorous chemicals that are required at present.

It is generally believed that only intermolecular, elastically-effective crosslinks influence elastomer properties. The role of the intramolecular modifications of the polymer chains is marginalized. The aim of our study was the characterization of the structural parameters of cured elastomers, and determination of their influence on the behavior of the polymer network. For this purpose, styrene-butadiene rubbers (SBR), cured with various curatives, such as DCP, TMTD, TBzTD, Vulcuren®, DPG/S8, CBS/S8, MBTS/S8 and ZDT/S8, were investigated. In every series of samples a broad range of crosslink density was obtained, in addition to diverse crosslink structures, as determined by equilibrium swelling and thiol-amine analysis. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were used to study the glass transition process, and positron annihilation lifetime spectroscopy (PALS) to investigate the size of the free volumes. For all samples, the values of the glass transition temperature (Tg) increased with a rise in crosslink density. At the same time, the free volume size proportionally decreased. The changes in Tg and free volume size show significant differences between the series crosslinked with various curatives. These variations are explained on the basis of the curatives’ structure effect. Furthermore, basic structure-property relationships are provided. They enable the prediction of the effect of curatives on the structural parameters of the network, and some of the resulting properties. It is proved that the applied techniques—DSC, DMA, and PALS—can serve to provide information about the modifications to the polymer chains. Moreover, on the basis of the obtained results and considering the diversified curatives available nowadays, the usability of “part per hundred rubber” (phr) unit is questioned.

Silane coupling agents containing different specific functionalities are studied to gain understanding of their roles in silica‐filled natural rubber (NR) compounds. Five different silane coupling agents, that is bis‐(triethoxysilylpropyl) tetrasulfide (TESPT), bis‐(triethoxysilylpropyl) disulfide (TESPD), octyltriethoxysilane, vinyltrimethoxysilane, and bis‐(trimethyl‐silylmethyl) tetrasulfide (TMSMT), are comparatively investigated, by taking the most commonly used TESPT as a reference. The results reveal that alkoxy‐based silanes can effectively reduce the filler–filler interaction and lower compound viscosity owing to the effect of silane‐to‐silica hydrophobation which contributes to better compatibility between silica and NR. The alkoxy‐silanes with a sulfur moiety, that is TESPT and TESPD, show more pronounced improvement in overall properties as a result of filler–rubber interactions. The use of TMSMT which has no alkoxy groups but contains only a sulfur moiety elucidates that there are three reaction mechanisms involved in systems with sulfur‐alkoxy‐based silane. These are as follows: (1) the silane‐to‐silica or silanization/hydrophobation reaction; (2) the silane‐to‐rubber or coupling reaction; and (3) rubber–rubber crosslinking originating from active sulfur released by the polysulfide‐based silane TESPT. These simultaneous reactions are temperature dependent, and show an optimum level at a dump temperature of approximately 140–150°C, as depicted by filler–filler and filler–rubber interactions, as well as mechanical properties of such compounds. POLYM. ENG. SCI., 55:836–842, 2015. © 2014 Society of Plastics Engineers