Thermoplastic-recycled rubber

Michael, H., Scholz, H., and Mennig, G., Blends from recycled rubber and thermoplastics, Kautsch. Gummi Kunst., 52, 510, 1999. 

Ismail, H. and Suryadiansyah, S., Thermoplastic elastomers based on polypropylene/natural rubber and polypropylene/recycle rubber blends. Polymer Test., 21, 389, 2002. 

Mixing of natural rubber with polyolefin is one of the methods used to prepare thermoplastic natural rubber (TPNR). TPNR behaves like vulcanized rubbers at ambient conditions, but at elevated temperatures they melt and flow like a thermoplastic material. Thus TPNR could be processed using conventional thermoplastic processing machinery without requiring vulcanization, and these materials could be reprocessed. Thus there is low level of wastage, as scrap too can be recycled. 

Another application of the injection system consists of recycling old and waste rubber. The reactive mixing of crumb rubber with a melted polymer represents an innovative way of recycling these waste rubbers [6]. Some thermoplastic elastomer may contain up to 60% recycled rubber derived from used vehicle tires, and thus through the reactive injection system the rubber scrap is revulcanized [7]. 

On the other hand, the mechanical properties of thermoplastic vulcanizates containing ground tire rubber have been investigated with the aim of increasing use of recycled rubber. The compositions tested included passenger car combined with EPDM, SBR rubber, isoprene rubber, and butadiene rubber. It was found that the particle size of the ground tire rubber had small effect on mechanical properties, but that the choice of the sulfur accelerator was significant [26]. 

A number of methods [11,13-17] have been applied in an attempt to solve the problem and to find more effective ways of tire rubber recycling and waste rubber utilization. These methods include retreading, reclaiming, grinding, pulverization, microwave and ultrasonic processes, pyrolysis, and incineration. Processes for utilization of recycled rubber are also being developed, including the use of reclaimed rubber to manufacture rubber products and thermoplastic-rubber blends and the use of GRT to modify asphalt and cement. 

Thermoplastic elastomer (TPE) blends have been broadly studied as a new class of materials. TPEs offer various advantages and require no state-of-the-art processing machinery, while scrap and rejects are recyclable. Blends can be homogeneous, phase separated or both. TPEs are multi-phase polymer systems consisting of hard and soft domains that can be copolymers or mechanical blends. This phase separation leads to materials having unique and viable commercial physical properties. TPEs exhibit the thermoplastic characteristics of the hard thermoplastic phase, and resilience as a result of the rubbery domains. TPEs based on natural rubber (NR) and thermoplastic blends are known as thermoplastic natural rubber (TPNR) blends. There are two types of TPNR, namely thermoplastic polyolefin (TPO) and thermoplastic vulcanizate (TPV).3... 

Kuriakose et al. mentioned that the reduction of the molecular weight of NR by mastigation" improved the processability of NR/PP thermoplastic blends. It was also observed that quinoline imparts better ageing resistance than imidazole when used as antioxidants in the blend. Another study observed that the highest thermal stability is attained with the addition of ethylene-propylene diene rubber to the NR/PP blend." TPEs can also be developed from recycled rubber (PP/RR) and Ismail and Suryadiasnsyah observed that its thermal stability was higher than that of PP/NR." " ... 

Murphy and co-workers [3] have looked into the effect on physical properties of blending ultrafine rubber particles into thermoplastics. A large range of blends were produced using a munber of recycled thermoplastics and recycled rubbers in a batch process. The influence that the particle size of the rubber, the total amount of recycled rubber, and the degree of compatibilisation had on the physical properties was determined and reported. 

Jacob C, De P.P., Bhowmick A.K., and De S.K. Recycling of EPDM waste. II. Replacement of virgin rubber by ground EPDM vulcanizates in EPDM/PP thermoplastic elastomeric composition, J. Appl. 

When a thermoplastic polyurethane elastomer is heated above the melting point of its hard blocks, the chains can flow and the polymer can be molded to a new shape. When the polymer cools, new hard blocks form, recreating the physical crosslinks. We take advantage of these properties to mold elastomeric items that do not need to be cured like conventional rubbers. Scrap moldings, sprues, etc. can be recycled directly back to the extruder, which increases the efficiency of this process. In contrast, chemically crosslinked elastomers, which are thermosetting polymers, cannot be reprocessed after they have been cured. 

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