Surface Polymerisation of Retreaded

Transcription

1 Case study Surface Polymerisation of Retreaded Tyres This case study describes re-treading and operational trials for truck and earthmover s using rubber compound with a 40% and 50% recycled content. The high recyclate inclusion has been achieved by the use of a surface polymerisation technique.

2 Surface Polymerisation of Re-treaded Tyres 2 Key facts Note: In the context of this case study the term truck relates to all s, for wheel diameters 17½ inches and above, for use on trucks or buses for road use. UK manufacturers retread on average 950,000 truck s and 5,000 earthmover s per year. Inclusion rates of up to 50% of recycled rubber powder may be achieved by use of surface polymerisation in the retread compound. Truck s can be retreaded with compound including up to 40% recycled rubber with no loss of - and in some cases improvement in - performance. The curing process is speeded up by as much as 20%, saving process time and energy, and decreasing carbon emissions. A 5% lower fuel consumption and increased life expectancy are additional benefits which can be achieved by high recycled inclusions in truck s. As well as generating a demand for recycled rubber for retreading of earthmover s, the market for truck retreads in the UK would require, at 40% inclusion rates, rubber powder from approximately 6,650 tonnes of s.

3 Surface Polymerisation of Re-treaded Tyres 3 Overview of truck retreading Most commercial vehicle s can be re-used at least once after they have been initially worn. If the is in adequate condition and damage free, it can be re-treaded. The rubber compound used in recycled manufacturing is, for most commercial re-treading, 100% virgin material. Some commercial re-treaders have recently incorporated up to 5% recycled rubber in their rubber compound, but since untreated recycled rubber does not react with the virgin rubber it is not possible to mix in a larger recycled portion. The surface polymerisation technique introduced in the UK by Rubber Recovery Ltd has the advantage of reactivating the recycled rubber and making it bond with the surrounding virgin and recycled material in a rubber compound. Surface polymerisation is already used in other markets such as the US and in Australia and has been successful there in enabling virgin materials to be replaced with recyclate. This case study reviews the retreading and road-test trials carried out in the UK by Rubber Recovery Ltd and its subcontractors Tun Abdul Razak Research Centre (TARRC), the research arm of the Malaysian Rubber Board, and re-treader OTR. The main purpose of the project has been to ascertain how recycled contents of 40% and 50% in re-treaded lorry and earthmover s perform under UK road conditions. In the UK, heavy goods vehicles generally travel shorter distances on narrower and less straight and level roads than do vehicles in the US and Australia. The wear is expected to be higher in the UK and this case study will review the project findings so far.

4 Surface Polymerisation of Re-treaded Tyres 4 Operational trials: the background Waste and Resources Action Programme (WRAP) commissioned a range of R&D, operational and demonstration projects to investigate specific issues related to the recycling of rubber from used s and the development of alternative end uses for the material. A Barnsley based business, Rubber Recovery Ltd, were successful in proposing the use of a technology that recycles rubber from used s to produce a compound of recycled rubber and virgin materials with which to retread truck and earthmover s. To date, other recycling technologies used in the manufacture of rubber compound have only achieved inclusion of small percentages (up to 5%) of recycled rubber. Rubber Recovery Ltd s technology uses a process which has been proved successful in Australia and in the US with inclusions of high as 25% recycled rubber. This case study is a description of trials with inclusions of 40% and 50% and how the high recycled re-treads perform under UK road conditions. The project has utilised the technology to provide a compound with an element of recycled rubber and has manufactured retreaded s for laboratory- and road-wear trials on truck and large earthmover s. The trials of truck and earthmover s have been operated by two organisations. Truck trials have been subcontracted to the Tun Abdul Razak Research Centre (TARRC) where they have been manufactured and tested in a laboratory and on the road. Earthmover s have been retreaded by OTR Tyres Ltd of Alfreton, and are currently fitted on dumptrucks for trials on a gasworks remediation site. Results from the truck trials are presented in this case study and results from the earthmover trials will be published by WRAP shortly. The current results and possible future results show that the technology has a commercial feasibility and is ready to be commercialised on a wider scale.

5 Surface Polymerisation of Re-treaded Tyres 5 Technical information Description Material source Material category Process Particle size Quality Units Truck or car s Rubber powder Ambient grinding 30 mesh (0.59mm) No contamination allowed

6 Surface Polymerisation of Re-treaded Tyres 6 Case study Technology Used (Surface Polymerisation) This surface polymerisation technology concerns an innovative and specially formulated polymer system that can be deposited onto milled rubber surface particles to create a new compounding tool. This new compounding tool offers many technical and physical advantages that are not currently available to the commercial rubber compounders and the manufacturing industry in general. The polymerisation system is a unique method that allows previously vulcanised rubber to become reactivated into a new master batch blend. This forms a new composite and alternative feedstock material, which is comprised of in part uncured virgin rubber and in part vulcanised. The surface polymerisation process is easily integrated with the rubber compounding process and uses standard industry equipment. The three diagrams below show schematically how the technology works. Surface Polymerisation: A three-step process Diagram 1: (1) is the previously vulcanised ground rubber particle. (2) is the ground particle surface coated with a low molecular polymer treatment. (3) is the virgin uncured rubber compound.

7 Surface Polymerisation of Re-treaded Tyres 7 Diagram 2: During curing the surface polymer interacts with the virgin compound and combines both the virgin and already vulcanised rubber into the polymer matrix. Diagram 3: The end result is a fully cured crosslinked compound containing both virgin and surface-treated components to be repolymerised and become an advanced reactivated rubber compounding tool and material. Re-treading of Truck and Earthmover Tyres The recycled rubber compound produced by using the surface polymerisation technique was split between re-treading truck and earthmover s. The re-treading operations were carried out by TARRC for truck s and OTR for the earthmovers. The retreading process is described in more detail below. TARRC re-treading The recycled rubber compound used for re-treading was imported from Rubber Recovery Ltd s American supplier and delivered to TARRC s research facility. TARRC have a process which replicates that of large commercial re-treaders on a small scale. TARRC was contracted to build s both with recycled content and without ( control s), in order to minimise trial error.

8 Surface Polymerisation of Re-treaded Tyres 8 Two compound mixes of 40% and 50% recycled rubber were made at TARRC s research site and applied to carcasses using a mould-cure re-treading method. The control re-tread was made in the same way but with only virgin rubber compound. The new compound, control or recycled, was added to both the tread and sidewalls of the carcasses, after which the s were cured in a mould in way similar to the manufacture of a new. Since the newly moulded tread needed vulcanising, the s were processed under pressure at a specified temperature: this creates a chemical bond between the old carcass and the new tread regardless of the recycled content. Initial comments from TARRC s builders were that the visual appearance of the recycled compound looked grainy due to the small rubber particles in the material. The recycled compound did however perform well during the actual re-treading and moulding process. Vulcanisation is a very energy intensive part of the production process and it is important to keep the heat and pressurised curing process short to reduce costs and environmental impact. The cure time for the recycled re-treads was actually cut by 20% compared to the control s from 10 minutes to 8 minutes. The visual appearance of the recycled was indistinguishable from the control after the process. The shorter cure time will be of positive financial benefit for commercial re-treaders, as well as decreasing carbon emissions by as much as 20%. OTR tests The task given to OTR was to re-tread a number of earthmover s by using compounds with 40% and 50% recycled content. OTR also re-treaded the control s used in the later field trials to avoid trial error.

9 Surface Polymerisation of Re-treaded Tyres 9 Earthmover s in different stages of re-treading The re-treading of earthmover s proved to be more problematic than initially anticipated. This first trial of compound with a 50% recycled content showed that, whilst the rubber would extrude and spread on the stripped carcass, it did not have the required tack. The re-tread strip s tack is the processed compound s ability to stick layer on layer during the re-treading process. The strip must adhere for a short time whilst the rubber is built up to the required thickness before being moulded. Without sufficient tack a can not be re-treaded. This was an unfortunate characteristic of the recycled compound but it did not affect the chemical nature of the curing since low tack is merely a process issue and does not affect the final re-

10 Surface Polymerisation of Re-treaded Tyres 10 tread. The problem was overcome by experiments with additives carried out by TARRC which managed to provide the additional required tack to the recycled compound. The additives have not had any significant impact on the economics of re-treading. The shorter curing time of the recycled compound will, in a commercial application, have large positive benefits for earthmover s since they normally need to be in a mould approximately four hours. A 20% time reduction would imply a 45-50min time saving resulting in a lower cost and reduced emissions. Earthmover being cured in a mould TARRC s successful completion to increase the tack of the compound got the project back on track after only a few months delay. TARRC achieved the improved tack by adding 2.5% additional natural rubber and 6% of tackifier Escorez 1102b. Since TARRC s milling capacity was insufficient for the milling required to blend in the different additives, the milling operation was transferred to Avon Rubber plc s production facility in Yarnbrook. As stated, these extrusion trials delayed progress and the manufacturing process had to be extended. However it was completed in early 2007, mainly due to the commitment and expertise showed by TARRC and OTR. The delay has

11 Surface Polymerisation of Re-treaded Tyres 11 unfortunately knocked-on to delay the earthmover field trials which are not complete at time of writing. Field Trials of Truck Tyres The truck s built by TARRC were fitted to dual drive axled tipper lorries that experienced mixed road conditions, mainly onhighway. The vehicles chosen for the field trials had four axles: two steering axles with two s per axle at the front of the vehicle and two drive axles with four s per axle at the rear. Dual drive axles tipper lorry fitted with re-treaded s The re-treaded test s were fitted to both drive axles, called axles 3 and 4. The two different axles impart different wear on the s with the 4 th axle being generally described as high severity wear and the 3 rd as medium severity. This difference arises from the amount of scrubbing experienced during vehicle manoeuvres. Tyres on axle 3 tend to roll more whilst those on axle 4 suffer more sideways scrubbing.

12 Surface Polymerisation of Re-treaded Tyres 12 The position of s on test vehicles Schematic picture of test vehicle Axles 1&2: Steering axles. NB: Re-treaded s are traditionally NOT used on steering axles in the UK. Axles 3&4: Drive axles. On the test lorry, where the control and recycled re-treads were fitted for the trials. Typical re-treaded s

13 Surface Polymerisation of Re-treaded Tyres 13 Results Rolling resistance To establish the rolling resistance (the resistance between the road and the ) of the recycled re-treads, a well established ISO method was used by Rubber Recovery Ltd. This implies measuring the difference in resistance between an ISO prescribed load and a load of less then 20kg. The difference between the results is defined as the rolling resistance. Four separate readings were carried out. The average results from the last three readings are reported in Table 1. A low result indicates a low rolling resistance and consequently good fuel economy. Table 1: Rolling resistance of truck s Control 40% recycled 50% recycled Value kgf Rating (vs. control) The results from this trial are a reduction in the order of 20% of the rolling resistance for the recycled rubber compared to the virgin rubber control. According to TARRC, this would equate to a 5% reduction in fuel consumption. Service and wear trials The wear on the two rear axles was measured monthly on all vehicles involved in the trial. TARRC calculated predicted mileage from 14mm tread available for wear (2mm left on when replaced): results are shown in the tables below. The large difference in service life between the 40% and 50% test is,

14 Surface Polymerisation of Re-treaded Tyres 14 according to TARRC, due to different service conditions of the test vehicles: variations such as these are not uncommon. The re-treaded s with 40% recycled rubber exceeded the performance of the control s on axle 3, but not on axle 4, where the results are almost the opposite: Table 2: Trials of 40% recycled treads Axle 3 Service life, km Control Inner Control Outer 40% recycled Inner 40% recycled Outer 39,400 45,700 51,200 54,400 Rating 108% 120% Axle 4 Service life, km Inner Outer Inner Outer 36,900 41,800 27,800 31,800 Rating 75% 76% *This figure is based on the first 4mm of wear of the control due to a casing failure of the. Estimates based on normal wear and the performance of the other control s gives a service life of 47-49,000 km. Hence the 108% rating. Replacement of 50% virgin compound with recycled material was not successful. The life of the recycled s was only half of the control s:

15 Surface Polymerisation of Re-treaded Tyres 15 Table 3: Trials of 50% recycled treads Axle 3 Service life, km Control Inner Control Outer 50% recycled Inner 50% recycled Outer 93,500 76,000 51,900 49,800 Rating 56% 66% Axle 4 Service life, km Inner Outer Inner Outer 49,800 55,400 22,900 27,300 Rating 46% 49% Conclusion: Truck Tyres Recycled rubber compound can be used to replace a large proportion of virgin rubber in re-treads. The material can match, and in some instances exceed, the performance of virgin compound. The s performed well and actually outperformed the control s, with a 40% recycled mix giving less wear on the 3 rd (drive) axle. On the 4 th axle the with 40% recycled content wore 25% faster than the control s. Tyres with a 50% recycled content were not successful, as they only had a half the life of the control s.

16 Surface Polymerisation of Re-treaded Tyres 16 Field Trials of Earthmover Tyres The trial of the earthmover s was, as mentioned earlier, delayed because of the complications in the re-treading process. No measured wear results had been reported back at the time of writing. The s are run on an old gasworks site which is currently being cleaned up and remediated by the VHE group which owns Rubber Recovery Ltd. The site conditions are of several different soil environments including crushed concrete. The only indications of the s current status are a number of visual inspections carried out on site. According to these, the recycled re-treads are performing well and are not experiencing a high wear rate. Rubber Recovery Ltd expect to make the first wear measures in the end of March Earthmover ready for field trial

17 Surface Polymerisation of Re-treaded Tyres 17 Technical Benefits The trials of the re-treaded truck s with recycled content showed a divergent picture. Tyres with a 40% recycled content on the third axles of the trial lorry showed both decreased wear rate and decreased rolling resistance. This is a very good result since it implies an increased life expectancy of the and a fuel saving in the order of 5%. The same on the fourth axles showed a similar decrease in rolling resistance but a 25% decrease in life expectancy due to the high degree of sideways skidding ( scrubbing ) on that axle. This implies the same decrease in fuel consumption but as stated a shorter life. The results from the trials points at truck s with a 40% recycled content being well suited for applications with a relatively low skid. The trials of a 50% recycled content in the re-treading rubber compound showed increased wear rates of as much as 50% compared to the control s. A 50% recycled blend must therefore be said to lack technical benefits. The re-tread manufacturing process will, on a commercial scale, benefit from a recycled content in the rubber compound due to a 20% saving in curing time. This is particularly important for the large earthmover s which, when re-treaded with virgin compound, need approximately four hours in a mould to cure.

18 Surface Polymerisation of Re-treaded Tyres 18 Cost benefits There are two components to the cost benefits of using recycled rubber with a surface polymerisation technique: raw material savings and process savings. Raw material savings: The price of virgin rubber compound is currently trading for prices in excess of 1000 per tonne. Rubber can generally be granulated to a cost of maximum 350 per tonne. This gives a minimum 650 margin for increased process cost for the surface polymerisation technique. Whilst there is potential for this product to reach the market at a cost below that of virgin compound, the principal aims are to give comparable or improved performance whilst significantly addressing environmental issues. Process savings: The 20% decreased cure time for a 40% recycled content re-tread will decrease energy costs for the re-treader substantially. (Since different moulds have different fuel consumptions, an average saving is very difficult to estimate.) Decreased cure time also implies increased through-put of this process, allowing a higher production rate at re-treaders where moulding capacity is a production bottleneck. Fuel saving for vehicle operator: According to TARRC, the 20% decrease in rolling resistance will lead to a saving of about 5% on vehicle fuel consumption.

19 Surface Polymerisation of Re-treaded Tyres 19 Environmental benefits Replacement of virgin rubber compound with recycled ground rubber will save resources in several ways: Oil substitution due to the decreased use of virgin compound: An ordinary re-treaded truck which uses only virgin re-tread compound is on average saving 57 litres of oil compared to a new. If Rubber Recovery s surface polymerisation technique is implemented and 40% recycled rubber is added, an additional 10.6 litres of oil can be saved per. This would be equivalent to about 9,750,000 litres of oil if all UK truck re-treads used a 40% recycled inclusion. It is more difficult to estimate the oil substitution for earthmover s, because of the more specialised and individual re-treading technique. There are however substantial oil savings to be made form retreading these s. Decreased fuel consumption from road transport: The 20% decrease in rolling resistance from the recycled retreads will according to TARRC give a fuel saving about 5%. A five percent saving of fuel will both have a positive financial benefit to the lorry operator and help improve carbon emission targets. Decreased energy requirements in the moulding process: The 20% decrease in cure time will decrease the energy consumption of re-treading. The moulding of s is the most energy-intensive part of the process and, according to Rubber Recovery Ltd, a time reduction will generate significant savings especially for the large earthmover s. Market creation for waste s. With a UK re-tread market of 950,000 truck s per year, replacing 1% of the virgin compound creates a demand for rubber crumb of ca.117 tonnes. This equates to ca.167 tonnes of s. Consequently a 40% inclusion of recycled rubber in all UK truck re-treads would imply a market demand of about 4,650 tonnes of rubber crumb and 6,650 tonnes of waste s per year.

20 Surface Polymerisation of Re-treaded Tyres 20 Details of parties Client Rubber Recovery Limited Engine Lane Shafton Barnsley S72 8SP Contact: Mr Mark Stevenson Tel: Fax: Web: Subcontractors TARRC Brickendonbury Hertford SG13 8NL Contact: Mr Paul Brown Tel: OTR Bluebell Close Clover Nook Industrial Park Alfreton DE55 4RD Contact: Mr Darren Flint Tel:

21 Surface Polymerisation of Re-treaded Tyres 21 This case study was developed for WRAP by: Disclaimer: WRAP and Oakdene Hollins Ltd believe the content of this report to be correct as at the date of writing. However, factors such as prices, levels of recycled content and regulatory requirements are subject to change and users of the report should check with their suppliers to confirm the current situation. In addition, care should be taken in using any of the cost information provided as it is based upon numerous project-specific assumptions (such as scale, location, tender context, etc.). The report does not claim to be exhaustive, nor does it claim to cover all relevant products and specifications available on the market. While steps have been taken to ensure accuracy, WRAP cannot accept responsibility or be held liable to any person for any loss or damage arising out of or in connection with this information being inaccurate, incomplete or misleading. It is the responsibility of the potential user of a material or product to consult with the supplier or manufacturer and ascertain whether a particular product will satisfy their specific requirements. The listing or featuring of a particular product or company does not constitute an endorsement by WRAP and WRAP cannot guarantee the performance of individual products or materials. For more detail, please refer to WRAP s Terms & Conditions on its web site: Published by Waste & Resources The Old Academy Tel: Action Programme 21 Horse Fair Fax: Banbury, Oxon info@wrap.org.uk OX16 0AH Helpline: Freephone