Advanced Characterization of Recycled Rubber From End-of-Life Tires

Abstract

There are currently many well-established applications for recycled rubber from end-of-life tires (ELT), but it is essential to investigate and seek new approaches to enhance the value of these products. Recent developments in new technologies and innovative recycling and devulcanization processes have opened up new perspectives for ELT crumb rubber. To promote the use of these products in newly added value applications, it is essential to develop and optimize methods that allow the characterization of parameters related to the ultimate properties of potential final applications. In this respect, a novel characterization methodology based on advanced 1H double-quantum (DQ) nuclear magnetic resonance experiments has been applied for the first time to quantify the key parameters that characterize the structure of ELT crumb rubber after diverse recycling processes: from simple mechanical grinding to complex devulcanization methods. This experimental approach enables the quantification of parameters that define the network structure of rubber, such as the nonelastic network defects (sol fraction, dangling chain ends, loops), the cross-link density, and the heterogeneity of the network, directly from rubber granulate and powder (without any additional sample preparation steps), overcoming most of the drawbacks and uncertainties that limit the application of traditional rubber characterization methods (e.g., equilibrium swelling experiments). By applying this experimental approach, it is possible to identify and quantify the actual technical limits for a complete selective devulcanization process of ELT crumb rubber.

Micromechanical modeling of devulcanized ground tyre rubber, graphene platelets, and carbon black in recycled natural rubber blends

“…It is worth highlighting that Flory-Rehner has some limitations for filled materials and different vulcanizates, and that other techniques are now considered to give a better correlation with crosslink index, such as double quantum nuclear magnetic resonance (DQ-NMR). 63 However, Flory-Rehner remains a widely used and simple technique that can help draw comparisons between similar rubbers. 64,65…”

Dynamic Permittivity Measurement of Ground-Tire Rubber (GTR) during Microwave-Assisted Devulcanization

“…Time-domain NMR experiments were applied to GTR samples to evaluate the evolution of the rubber network structure according to the applied microwave-assisted devulcanization protocol following the procedure and data analysis explained elsewhere [35]. Solid-state 1 H double-quantum (DQ) NMR experiments were carried out in a Bruker minispec mq20 spectrometer (Billerica, MA, USA) operating at 0.5 T with 90 • pulses of 3.1 µs length and a dead time of 12 µs at a temperature of 80 • C. The recycle delay time was fixed to 0.5 s for filtering the liquid-like NMR signal from processing oils and other small molecules (e.g., accelerators, waxes, and antioxidants) but ensuring the complete magnetization of rubber protons, with a characteristic longitudinal relaxation time of T 1(rubber) ~60 ms [35].…”

Mats Made from Recycled Tyre Rubber and Polyurethane for Improving Growth Performance in Buffalo Farms

“…When it comes to tyres, their rubber composition consists of high-value polymers with persistent chemical and physical properties that withstand alteration even during recycling phases [50,51]. While this makes tyres highly non-degradable, requiring special disposal methods, it also encourages industry stakeholders to develop strategies that exploit the vast potential of resources that can be recovered from this waste, particularly rubber [52][53][54][55]. For the disposal of ELTs, currently two major disposal pathways are adopted [50,56]: (i) recycling, which results in the recovery of specific materials; (ii) energy recovery in specialised facilities, mainly cement plants.…”

“…Granules have a grain size of between 10 and 2 mm, and are usually involved in the manufacturing of various products, such as: floor tiles, roofing materials, floor and wall sound insulation products, road signs, safety surfaces, asphalts, road curbs and barriers, impact dampers, and playground surfaces [61]. Finally, rubber powder has a grain size of less than 2 mm and it is usually reused to produce paints, sprays, electrical cables, automotive parts, sealants, coatings, and flooring [52].…”