Styrene butadiene-based blends containing waste rubber powder: Physico-mechanical effects of mechanochemical devulcanization and gamma irradiation

Radiation and Radical Grafting Compatibilization of Polymers for Improved Bituminous Binders-A Review

This review scrutinizes current research on new methods for enhancing bituminous binder performance through radiation and radical grafting of polymer modifiers of bitumen. It investigates innovative methods, including using waste polymers as modifiers and applying radiation for polymer grafting, to overcome challenges like high costs, low aging resistance, and storage stability issues, of which separation of phases polymer/bitumen is the most significant obstacle. These advanced modification techniques promise sustainability through the decrease of the carbon footprint of transportation systems by improving the properties and durability of binders. Additionally, this review discusses the parameters and mechanistic aspects from a scientific perspective, shedding light on the underlying processes that contribute to the improved performance of modified bituminous binders.

Short nylon tire cord and gamma irradiation impact on SBR/ultrasonic and mechanochemical devulcanized rubber blends

Devulcanization of discarded tire rubber (WR) has remained of prior attention to numerous researchers, aiming for unlimited commercial profits upon modification, especially to serve as a substituent for virgin rubber. In this concern, composites of styrene butadiene rubber (SBR) and devulcanized waste rubber, developed via two techniques: mechanochemical (DRm) and ultrasonic (DRus), and reinforced with short nylon tire cord (SNF), namely at a filling ratio of 3 and 5 phr were fabricated. All prepared specimens were exposed to various gamma radiation doses, namely 50, 100, and 150 kGy. The post-radiation characterization was investigated by FTIR and SEM techniques. Radiation-induced crosslinking density of the polymer composites was calculated and correlated with the different mechanical features. Furthermore, the TGA technique and activation energy measurement were implemented in studying the thermal behavior of the products. Incorporation of 5 phr SNF set out the thermal stability order: SBR/DRm/5 SNF > SBR/DRus/5 SNF > SBR/5 SNF. Ionizing irradiation of all composite–SNF formulations derived to a marked improvement in TS data as a result of creating further crosslinking within the polymeric matrix, reaching a maximum by the integral dose 150 kGy. The results were appreciably compared to a recently published study that applied reinforced tire fiber with polyester, as another cord utilized in the manufacture of tires. It is found that TS data observed by irradiation with 150 kGy of SBR/3 SNF, SBR/DRm/3 SNF, and SBR/DRus/3 SNF are respectively as follows: 3.7, 2.5, and 2.4 MPa, whereas the corresponding reported values for PTC reinforced counterpart blends were: 2, 1.7 and 1.8 MPa. Similarly, the TS respective values of SBR/5 SNF, SBR/DRm/5 SNF and SBR/DRus are 2.5, 1.9, and 2.2 MPa, whereas their counterparts reinforced with 5 phr PTC recorded 1.6, 1.8, and 1.2 MPa. SNF-reinforced SBR, SBR/DRm, and SBR/DRus were superior in their properties to PTC-reinforced counterpart specimens.

Waste tire rubber devulcanization technologies: State-of-the-art, limitations and future perspectives

Waste tires management is a serious and global environmental problem. Therefore, searching for low-cost and industrial-scale applicable tire recycling methods is gaining more and more attention. Waste tire rubber is valuable source of secondary raw materialsforthecircular economy and current trends indicate that application of waste rubbers during manufacturing value-added productsshould increase in near future. Sustainable development of rubber devulcanization technologies and appropriate design of cradle-to-cradle loops for rubber goods are the most promising strategies for achieving a higher level of rubber recycling. This work presents the state-of-the-art in the patented waste tire rubber devulcanization technologies including dynamic desulfurization, reactive extrusion, microwave treatment, and also other less popular methods. Special attention was focused on the used components, rubber treatment conditions and static mechanical properties of reclaimed rubbers. Moreover, environmental aspects and limitations related to rubber devulcanization technologies implementation are also discussed. Our findings showed that reclaimed rubbers described in patents are characterized by higher tensile strength and elongation break (depending on devulcanization technology median: 16.6-19.0 MPa and 321-443%, respectively) compared to the literature data (median: 10.3 MPa and 309%) or commercial products (median: 6.8 MPa and 250%). The significant differences observed in performance properties of reclaimed rubbers resulted mainly from devulcanization efficiency related to waste tires composition or source and rubber treatment conditions. Considering environmental and economic aspects, reactive extrusion is the most promising method further development rubber devulcanization technologies.

Low-Temperature Mechano-Chemical Rubber Reclamation Using Terpinene as a Swelling Agent to Enhance Bond-Breaking Selectivity

Common swelling agents used in the mechano-chemical rubber devulcanization process usually require high temperatures to achieve satisfactory swelling effects, which results in severe production of pollutants and reduces the selectivity of bond scissions. This work presents an environmentally friendly swelling agent, terpinene, which can swell the rubber crosslink structures at low temperatures. Both a rubber swelling experiment and a rubber reclaiming experiment with a mechano-chemical devulcanization method are conducted to explore the swelling effects of terpinene. After soaking in terpinene at 60 °C for 90 min, the length elongation of the rubber sample reaches 1.55, which is much higher than that in naphthenic oil and is comparable to that in toluene. When adding 3 phr of terpinene for every 100 phr of waste rubber during the reclaiming process, the bond scissions exhibit high selectivity. After revulcanization, the reclaimed rubbers have a tensile strength of 17 MPa and a breaking elongation of 400%. Consequently, the application of terpinene as the swelling agent in the LTMD method can greatly improve the properties of reclaimed rubbers, thereby enhancing the dual value for the economy and environment.

Comparative impact of gamma radiation on reinforced nitrile rubber with graphite and agro waste activated carbons

In this article, graphite fine powder and two types of activated carbon (AC) namely based-on waste corn and sugarcane bagasse were implemented as reinforcers for the nitrile rubber (NBR). Both types of AC were prepared through a low-temperature chemical carbonization treatment. Each type of these fillers, at 5, 10, and 15 wt%, was mixed with NBR on a rubber mill and pressed under heat to develop sheets to be gamma irradiated at 100 kGy. Filler characterization using Fourier Transform Infrared spectrophotometer (FTIR) spectroscopy and scanning electron microscopy (SEM) were discussed. X-ray diffraction (XRD) proved that graphite has a crystalline structure but corn and bagasse ACs have amorphous nature. Furthermore, dynamic light scattering (DLS) analysis was used to determine the particle size of the studied fillers. In addition, mechanical properties, XRD, thermal stability, and SEM of the prepared unirradiated or irradiated NBR‒composites were investigated. The physicomechanical features of the NBR matrix could be enhanced by the presence of reinforcing fillers, even at relatively low filler loading. The composites filled with graphite showed superior mechanical parameters and also have the highest thermal stability as indicated by their high-temperature mass loss (Tm). Generally, irradiated samples expressed grander properties than unirradiated ones as a result of the radiation-induced crosslinking structures.

Devulcanization of ground tire rubber: microwave and thermomechanical approaches

We devulcanized ground tire rubber (GTR) in a laboratory microwave oven and an internal mixer, measured the soluble content and the cross-link density of the samples, and then used Horikx's analysis. The results showed that microwave treatment caused severe degradation of the polymer chains, while in the case of thermomechanical devulcanization, the selective scission of covalent cross-links is more common. Four devulcanized ground tire rubber (dGTR) samples were chosen for further study and three groups of samples were produced: dGTR samples containing vulcanizing agents and different amounts of paraffin oil (dGTR-based mixtures), natural rubber-based rubber mixtures with different dGTR contents and reference rubber mixtures with dGTR-based mixtures (increased vulcanizing agent contents). Cure characteristics showed a plasticizer-like effect of dGTR. Tensile and tear strength decreased drastically with increasing dGTR content; however, elongation at break values did not follow such a trend. Mechanical properties improved with increased vulcanizing agent contents. The examined properties of the samples improved even further with the use of thermomechanically devulcanized samples. Horikx's analysis showed that this is attributable to moderate polymer chain scission.

Preparation of Octadecyl Amine Grafted over Waste Rubber Powder (ODA-WRP) and Properties of Its Incorporation in SBS-Modified Asphalt

Through a covalent grafting reaction, octadecyl amine (ODA) was grafted on the surface of waste rubber powder (WRP) to obtain an ODA-WRP modifier, which was in turn compounded with a styrene-butadiene-styrene block copolymer (SBS) to prepare ODA-WRP/SBS-modified asphalt. The three major indicators (i.e., dynamic shear rheometer (DSR), multi-stress creep recovery (MSCR), and separation tests) showed that 1-ODA-WRP effectively improved the complex shear modulus (G*), elastic Modulus (G'), and loss modulus (G″) by 36.47%, 40.57%, and 34.77% (64 °C and 10 Hz), respectively, as compared to pristine SBS-modified asphalt. Fluorescence microscopy (FM) results concluded that the enhancement in mechanical properties was accredited to the better compatibility of various components in asphalt and establishment of network structure between ODA-WRP and SBS in ODA-WRP/SBS-modified asphalt. Fourier infrared spectroscopy (FT-IR) and scanning electron microscope (SEM) analyses confirmed the successful synthesis of ODA-WRP. This study could be of great help in synthesizing ODA-WRP asphalt modified with SBS for highways and construction applications.

Effect of Compounding Conditions on Static and Dynamic Mechanical Properties of High Density Polyethylene/Ground Tire Rubber Blends

Searching for new and cost-effective methods of waste rubber recycling is a subject of research in many scientific centers in the world. In this paper there are presented results of the research of the extrusion process of cheap and environmentally friendly thermoplastic compositions containing 50% wt. of masses of ground tire rubber (GTR). The aim of this study was to determine the relationship between the mixing conditions and properties of obtained products, which is important from a technological point of view. The mixing conditions were determined by using two variables: the screw configuration (co-rotating and counter-rotating) and the type of polyethylene. In the case of both variables, thermoplastic compositions were treated with various shear forces induced by screw speed changes. The influence of mixing conditions on the extrusion process was determined (screw torque, melt flow rate) as well as static and dynamic mechanical properties of obtained materials.