Elsevier

Waste Management

Volume 29, Issue 5, May 2009, Pages 1480-1485
Waste Management

Characterization of the properties of thermoplastic elastomers containing waste rubber tire powder

https://doi.org/10.1016/j.wasman.2008.10.004Get rights and content

Abstract

The aim of this research was to recycle waste rubber tires by using powdering technology and treating the waste rubber tire powder with bitumen. It has been proven that the elongation at break, thermal stability and processing flowability of composites of polypropylene (PP), waste rubber tire powder (WRT) and bitumen composites are better than those of PP/WRT composite. A comparative study has been made to evaluate the influence of bitumen content and different compatibilizers on the properties of PP/WRT/bitumen composites, using a universal testing machine (UTM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and a capillary rheometer. The results suggested that the properties of PP/WRT/bitumen composites were dependent on the bitumen content and the kind of compatibilizer used.

Introduction

With an ever increasing number of automobiles in the world, the disposal of used rubber tires has been a significant problem in recent years. The ever increasing stockpile of waste rubber tires is a potential environmental hazard. One way of utilizing waste rubber tires is to recycle them. The recycling of waste rubber tires consists of three parts: heat utilization, processing and original utilization. The generation and utilization of waste rubber tires in Korea is shown in Table 1. From Table 1, it can be observed that the majority of waste rubber tires produced in Korea are used as fuel in cement kilns, which is ecologically unviable since it is well known that the combustion of waste rubber tires leads to emission of greenhouse gases like COx and NOx.

Our laboratory has been focusing considerable attention on the development of technologies to effectively recycle waste rubber tires (Kim and Burford, 1999, Kim and Park, 1999, Shanmugharaj et al., 2007). Recycling of waste rubber tires requires special techniques, because waste rubber tires are a thermoset material, which cannot be reprocessed like thermoplastics. Powder utilization is one of the most attractive techniques for its effective utilization. A promising way of ‘recycling’ waste rubber tire powder (WRT) is to incorporate it into thermoplastics to obtain thermoplastic elastomers (TPEs). However, the adhesion between the WRT and the polymer matrix is usually very weak due to the crosslinked structure of WRT. In order to solve the problem, some attempts were made to produce thermoplastic rubbers by adding WRT to the corresponding recipes (Lee et al., 2007, Shanmugharaj et al., 2005). It was recognized early that the WRT should be devulcanized, or at least partially devulcanized, to facilitate the molecular entanglement between the WRT and the polymer matrix. For devulcanization, various routes were attempted, such as thermomechanical and thermochemical treatments (Kim et al., 2006, Radeshkumar and Karger-Kocsis, 2002).

Following the above guidance, special attention has been focused on the effective utilization of WRT in TPEs. In the first stage of this 10-year project (2000–2002), we developed technologies to produce ultra fine powders from waste rubber tires. In the second stage (2003–2005), we developed technologies to manufacture thermoplastic elastomers from WRT. Some products, like the brake pedal and rubber wheels, have been developed and commercialized successfully. In the third stage (2006–2009), we are developing technologies for mass production based on WRT.

In order to achieve this target and produce TPEs which contain WRT and exhibit competitive properties, bitumen and compatibilizer were incorporated into polypropylene/WRT composites due to their devulcanized, plasticized and compatibilized effect on the composites. In this work, the influence of bitumen content and different compatibilizers on the properties of polypropylene/WRT/bitumen composites is discussed.

Section snippets

Materials

Polypropylene (PP, H360F), manufactured by SK Corporation in Korea, was obtained. Styrene–ethylene–butylene–styrene (SEBS, Kraton G1652) and maleic anhydride-grafted styrene–ethylene–butylene–styrene (SEBS-g-MA, Kraton FG-1901X) were obtained from Shell Chemical Co. Ltd. Maleic anhydride-grafted ethylene–propylene–diene monomer (EPDM-g-MA, KEPA1130B) was supplied by Kumho Polychem Co. Ltd in Korea. Bitumen (X-4) was obtained from Waterproofbank Company in Korea. WRT was produced by Hongbok

Influence of bitumen and compatibilizer on the tensile mechanical properties of the composites

One of the major criteria for a thermoplastic elastomer is that elongation at break is more than 100%. This is the primary reason why we focus on the tensile mechanical response of composites in this work. The influence of bitumen and compatibilizer on the tensile mechanical properties of composites is shown in Table 2. Comparing sample 1 with sample 2, it can be found that the elongation of the composite increases in the presence of bitumen, due to the devulcanizing effect of the bitumen. The

Conclusion

In this work, waste rubber tire powder was treated with bitumen. It was proven that the presence of bitumen can improve the elongation at break, thermal stability and processing flowability of PP/WRT composites due to the devulcanizing and plasticizing effects of bitumen. Moreover, the presence of compatibilizer (SEBS-g-MA) can also enhance the elongation at break and thermal stability of PP/WRT composites, whereas it decreases the processing flowability. This originates from the

Acknowledgement

The authors are grateful to the support from the BK21 program in Korea.

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