Tire Rubber Recycling with High-Performance Ultrasound
Waste tire rubber is a toxic, non-biodegradable material making its disposal an environmental and economical problem. Ultrasonic devulcanization is a fast and efficient method to recycle waste tire rubber allowing to reuse waste tires. Ultrasonic tire rubber recycling is relatively simple process, which has been successfully tested. Linear process scalability of ultrasonic tire recycling makes it possible to treat large volumes on industrial scale at economical costs.
The Problem of Rubber Waste
Waste tire rubber causes a significant environmental problem due to their toxicity and non-degradability. Their vulcanized crosslink carbon structure and toxicity makes the disposal an environmental burden. Conventional rubber recycling techniques are uneconomical, not environmental-friendly, and the new rubber material produced with the recycled rubber shows low quality since the main polymeric chains of waste rubber are altered and weakened.
Since tires are part of the most problematic waste sources, environmental-friendly and economical methods or recycling are required. Pyrolysis and devulcanization are the most successful recycling processes for tires. The progress in waste tire recycling is essential to stop the environmental burden of tire rubber and helps to reduce dumping tires in landfills.
Ultrasonic treatment can intensify and improve both modern tire recycling processes, pyrolysis and devulcanization.
Ultrasonic system for devulcanization of waste rubber
Customized extruder block to couple sonication into hot elastomer
Ultrasonic Devulcanization of Tire Rubber
By ultrasonic devulcanization, sulfur-sulfur and sulfur-carbon chemical bonds in tires are decrosslinked, which results in a soft rubber melt. This ultrasonically generated rubber melt can be reprocessed and moulded into new rubber products, e.g. new tires. A major advantage of ultrasonic devulcanization is the significantly lower heat required. First, the waste tire parts are heated to approx. 400ºF or 200ºC, then fed with a screw feeder through an flow cell, where the waste rubber is sonicated with high-performance ultrasonics in under high pressure. During the ultrasonic devulcanization the rubber is transformed from its previous solid state to a highly viscous matter. Intense ultrasonication breaks the three-dimensional network of vulcanized elastomers quickly.The ultrasonic treatment of decrosslinking the chemical bonds takes only a few seconds. The sonicated rubber melt can be reinforced with curing agents and fillers and be moulded into new rubber products.
Ultrasonic Upgrade of Pyrolytic Residues
Pyrolytic residues can be upgraded by sonicating them in hydrochloric and hydrofluoric acids in order to obtain pyrolytic carbon black. Ultrasonic treatment can successfully upgrade pyrolytic residues from waste tires to the high value-added commercial carbon black. Ultrasonic post-pyrolysis treatment thereby improves the overall efficiency of the waste tire pyrolysis significantly.
High Performance Ultrasonicators
Hielscher Ultrasonics is your experienced partner when it comes to high-performance ultrasonic processes. Ultrasonic devulcanization requires high-power industrial ultrasonic processors, which can work under high pressure and high temperature conditions. Another prerequisite is the delivery of very high amplitudes. Amplitudes of up to 200µm can be easily continuously run in 24/7 operation. For even higher amplitudes, customized ultrasonic sonotrodes are available. Hielscher’s high-pressure/high-temperature sonotrodes are manufactured and tuned for the demanding conditions of the devulcanization process. With customised dies, the ultrasonic horn (sonotrode) is inserted into the extruder barrel. The robustness of Hielscher’s ultrasonic equipment allows for 24/7 operation at heavy duty and in demanding environments. High-performance and reliability turn Hielscher ultrasonicators into the work horse of rubber reclamation!
The table below gives you an indication of the approximate processing capacity of our ultrasonicators:
| Batch Volume | Flow Rate | Recommended Devices |
|---|---|---|
| 1 to 500mL | 10 to 200mL/min | UP100H |
| 10 to 2000mL | 20 to 400mL/min | UP200Ht, UP400St |
| 0.1 to 20L | 0.2 to 4L/min | UIP2000hdT |
| 10 to 100L | 2 to 10L/min | UIP4000hdT |
| n.a. | 10 to 100L/min | UIP16000 |
| n.a. | larger | cluster of UIP16000 |
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Literature/References
- Hong, Chang-Kook; Isayev, A.I. (2003): An Application of High-Power Ultrasound to Rubber Recycling. The Rubber Society of Korea: Elastomers and Composites Vol 38, Issue 2; 2003. 103-121.
- Walvekar, Rashmi; Mohammad. Afiq, Zulkefly; Ramarad, Suganti; Kalid, Siddiqui (2018): Devulcanization of Waste Tire Rubber Using Amine Based Solvents and Ultrasonic Energy. MATEC Web of Conferences Vol. 152, 2018.
Facts Worth Knowing
Vulcanization / Devulcanization
Vulcanization is a process to make natural rubber, which has low durability and flexibility, harder and durable. Therefore, natural rubber is heated and by adding sulphur crosslinking between the polymers is achieved. By crosslinking the polymeric rubber molecules, so-called polyisoprenes, are bonded to each other by sulfur atoms. Through vulcanization so-called vulcanized rubber is produced, which offers higher performance and durability. Vulcanized rubber can be found in tires, rubber hoses, shoe soles, toys etc.
Devulcanization is a technique where the crosslink structure, specifically the sulphur-sulphur and/or carbon-sulphur bonds are cleaved. This can be done by various methods such as mechano-chemical, chemical, biological, and using high-power ultrasonication.
Rubber
Rubber are also known as elastomers. Elastomer is an abbreviation for elastic polymer. Elastomers exhibit viscoelastic characteristics: They are sticky, very elastic polymers. The term rubber is frequently used to distinguish the group of elastomers that must be vulcanized or cured to be useful.
What are Tire Rubber Made of?
Tire rubber (American English) or tyre rubber (British English) are made of several components, including rubber, fillers and and other additives. Tire rubber can be consist in natural rubber, made from the latex sup, which is secreted from the bark of the rubber tree, or from synthetic rubber. Synthetic rubbers are made from petroleum. The most common synthetic rubber forms are styrene-butadiene rubber (SBR), polybutadiene rubber, and butyl rubber. Whilst rubber is the main ingredient of tires, fillers and additives are integrated to build a more functional tire material. Carbon black and/or silica are very common tire fillers added to reinforce the tire compound. Carbon black and silica enhance the grip, male tires more resistant against punctures and reduce the rolling resistance of the tire. Antioxidants, antiozonants and anti-ageing agents are other additives, which are improve tire quality and to prolong tire life.