GTR/Thermoplastics Blends: How Do Interfacial Interactions Govern Processing and Physico-Mechanical Properties?

Mohammad Reza Saeb,Krzysztof Formela,Łukasz Zedler,Xavier Colom,Agnieszka Susik,Javier Cañavate,Paulina Wiśniewska,Agnieszka Tercjak,Henri Vahabi

doi:10.3390/ma15030841

Abstract

In this work, GTR/thermoplastics blends (in ratio 50/50 and 75/25 wt.%) were prepared by melt-compounding in an internal mixer. During research, trans-polyoctenamer rubber (TOR), ethylene-vinyl acetate copolymer (EVA), ethylene-octene copolymer (EOC), and linear low-density polyethylene (LLDPE), were used in their thermoplastic phase. Microstructure and processing-performance property interrelationships of the studied materials were investigated by: atomic force microscopy (AFM), scanning electron microscopy (SEM), rubber process analyzer (RPA), Mooney viscometer, plastometer, gas chromatography with mass spectrometry, differential scanning calorimetry (DSC), tensile tests and swelling behavior. In blends of thermoplastics with a high content of GTR (50 and 75 wt.%), the thermoplastic modifier type had a significant impact on the processing behavior and microstructure of blends. In terms of the physico-mechanical properties, the GTR/thermoplastics ratio affected elongation at break, hardness, and density, while its effect on tensile strength was negligible. DSC analysis showed that thermoplastics, as modifiers of GTR, should be considered as binders and not plasticizers, as reflected in the almost constant glass-transition temperature of the blends. RPA measurements indicated higher values of G* and η* for GTR-rich blends. SEM showed a rubber-like interfacial break, while AFM confirmed interfacial contact between GTR and thermoplastics.

Highlights

Literature data have confirmed that melt-blending of thermoplastics and ground tire rubber (GTR) allows production of thermoplastics elastomers or thermoplastics/GTR blends [1–3], which have huge potential to be used at an industrial scale
In terms of the measurements, the Mooney viscosity, mass-flow rate (MFR)/melt volume-flow rate (MVR), and rubber process analyzer (RPA) tests conducted on the blend samples were performed at 100 ◦ C and 190 ◦ C, respectively, such that GTR blends with thermoplastics could be compared from a processability point of view with neat rubbers/thermoplastic elastomers (Mooney viscosity) and thermoplastics/thermoplastic elastomers (MFR/MVR)
The results showed that the presence of thermoplastics with softening and melting temperatures close to 100 ◦ C (EOC, linear low-density polyethylene (LLDPE)) affects the rubber-like character and elasticity of modified GTR, which resulted in overloading of the torque during Mooney viscosity measurements

Summary

Introduction

Melt-compounding is a solvent-free, low-cost and high-efficiency method for the preparation of novel polymeric materials with desired performance properties. This processing technique is a very promising approach to rubber recycling, especially in the utilization of waste tires. The basic parameter to evaluate the differences between thermoplastics and thermoplastic elastomers is the elongation at break, which for thermoplastic elastomers should reach at least 100% at break [4]. Another parameter for consideration is the compression set, which for thermoplastic elastomers should be lower than 50% [5]

Methods

Results

Conclusion