High Shear Mixing to recycle vulcanized rubber by devulcanisation
In dealing with the vulcanised rubber waste generated
both from industrial scrap and used products, the main focus to date has been
on methods of disposal (burying in landfill sites, in the sea, in road surfaces
or as filler in other products) and of destruction (typically incineration)
rather than on true recycling, i.e. converting waste back into products that use the original material
properties. None of the above approaches
make full use of the material properties of rubber nor do they solve the environmental
problem of tyre dumps.
The
ability to fully recycle rubber so that recovered material is reused for the
same products and applications would solve a major pollution problem in Europe.
Mechanochemistry and Free Radical Chemistry theory indicates that this
is achievable by selectively cleaving and then closing off the crosslinks
found in vulcanised rubber waste and returning the material to a solubilised
state. This may be achieved through a mixing process resulting in a material
that is both soluble and elastic. Experimental
work has indicated this effect for both 2g and 2 kg samples.
To
achieve this effect a new rubber mixing technology is required which is capable
of applying very high shear stresses to the material. The patented High Shear Mixer (HSM) technology is based on the long-established
science of mechanochemistry. The HSM
subjects a viscoelastic material, typically a rubber, to very high levels
of stress at low processing temperatures, while simultaneously controlling
the alignment of the molecular structure. This action maximises the effectiveness and efficiency of routine
compounding. It also selectively ruptures
crosslink chains, thereby devulcanizing previously cured rubber and restoring
it for reuse. The principle applies
equally well to continuous as it does to batch operations.
Mixers based on
HSM technology have been built and tested at 2g and 2kg laboratory scales
for a range of materials. The next
step is the industrialisation of the technology.
This project aims to move this promising technology out of the laboratory
by applying it to industrial materials and processes at industrial scales.
Objectives
This co-operative research project plans to:
1. Extend the existing
work on establishing the process parameters for the solubilising of car (SBR)
and truck (NR) tyre rubbers for recycling to include industrial tyre waste
materials in slab, sheet, shred and crumb form.
2. Extend the programme
to include other viscoelastic polymers such as EPDMs, nitriles and neoprenes.
3. Identify the industrial
machine scale in terms of economic and process requirements
4. Design, develop,
build, test and implement industrial scale plant to fully evaluate the technology
for both tyre and General Rubber Goods waste within Europe.
5. Develop and evaluate
applications for the resultant materials, including the reuse of the recycled
materials in the original applications
The project goal is to evaluate this technology
as a means of cost-effectively eliminating the waste rubber problem within
Europe.
Description
of the Work
More specifically, the evaluation will cover:
·
The optimisation of the process for the solubilising of car (SBR) and truck
(NR) tyres considering:
·
The condition of the material introduced to the process. This is to include evaluation of the effect
on the final material condition when introducing whole tyres, rubber chips
and rubber crumb to the process
·
Process parameters to include processing time, speed, temperature, gaps
and % let-down
·
The condition of the final material to include process parameters such
as % let-down of final mix, recompounding parameters and recuring times. The final cured recycled materials are to be
fully mechanically and chemically tested against standard non-recycled materials
to identify any differences in characteristics.
·
The extension of the evaluations above to include a wider range of crosslinked
viscoelastic materials such as EPDMs, nitriles and neoprenes.
·
The process and economic factors influencing the scale of the process and
the potential output requirements of an industrial application
·
The integration of an industrial scale machine with existing rubber processing
and recovery systems, processes and installations
·
The quality of the material produced by a 20 kg machine (process time approximately
10 minutes) recovering both end of product life materials and in-house factory
scrap
·
Applications for the recovered material, including reincorporation in the
original application. The performance
of the material in the applications will also be evaluated.
Milestones,
Expected Results and Exploitation of Results
On successful evaluation of the technology (Phase I), this project would be extended
to include the scaling up and implementation of an HSM in an industrial environment
(Phase II) to establish the viability
of this technology as a means of cost effectively eliminating the waste tyre
problem and other rubber waste problems (e.g. from in-factory waste materials) within Europe.
Exploitation of the results is possible after
successful evaluation of the scaling up.
A Technology Implementation Plan will be set up. A range of industrial machines are to be developed
(outside the scope of the proposed project) based upon the mathematical relationships
validated during the proposed CRAFT-project.
Full view of the 2kg HSM showing operating
position