Materials
aspect, and involves evaluating the potential hazards of working with these materials, and devising suitable risk management strategies. It is led by the UK’s Institute of Occupational Medicine.
Production boost
The first step in the project is to take production of the materials up to something approaching industrialisation – but, being such specialised materials, these volumes are not exactly astronomical. At the outset, the team was capable of making 10g batches, but later raised this to 250g – with remarkable success. This was a crucial breakthrough: as with many nano-particles, the aim is to ensure as little ‘agglomeration’ as possible, because particle size is the key property. In the case of graphene, the particles are take the form of carbon ‘sheets’ just one molecule thick. The better these sheets remain separate, the greater the effect. (The process of separating nano-particles is called exfoliation.) Production is now hovering at the 1kg scale, and will soon be upgraded to 5kg. The eventual target is to raise this to 25kg.
“Right now we can achieve
Fig. 2. Graphene is produced under highly specialised conditions. Picture courtesy: National University of Singapore.
90 per cent yields in around 24 hours,” says Hargreaves. Nano particles are notoriously difficult to mix with plastics. For this reason, the project will attempt to develop a range of pre-mixed graphene compounds (known as masterbatches). This ensures that a traditionally difficult step of the process – incorporating the graphene into the plastic matrix – has already been done. The graphene-enhanced
plastics are made into pellets and processed in the
conventional way, to produce plastic components. Nanomaster will look at two commonly used processes – injection moulding and compression moulding. The project will focus on lab-scale compounding of
graphite-polypropylene (PP) compounds. The specifics of how the compounds are made will be key to their eventual success, says Hargreaves. One important factor is shear – they physical force that acts on the materials as they are compounded together. “Because shear is important, and affects how the
graphene is ultimately distributed in the plastic, we’re doing some compounding techniques that are effectively ‘zero shear’,” he says. There will also be computer simulation work, to
Fig. 3. (Nanomaster graphite pellets) The project aims to produce graphene masterbatches that will enhance the properties of thermoplastics.
www.engineerlive.com 23
allow effective scale-up of the process from lab scale to pilot scale production. In addition to taking the pre-made graphene and
dispersing it within a masterbatch, another aim of the project is to determine whether an expanded or partially exfoliated graphite can be further exfoliated during the compounding process.
Additive manufacturing
As well as targeting conventional plastics processes, Nanomaster will attempt to develop materials for use in additive manufacturing. Additive manufacturing – also known as 3D printing – relies on building up components in a ‘layer by layer’ fashion, to create products that would be impossible to make in conventional ways. These kinds of techniques – such as selective laser sintering (SLS) and fused deposition modelling (FDM) – were originally used to make ‘rapid prototyping’ models. More recently, they have been used to make limited-run finished products. The mechanical properties of these components
are not generally very high. So more robust materials – such as those being developed by Nanomaster – could expand the scope of additive manufacturing. Materials must be specially adapted for processing in
this way. This is something the project intends to study. “One method is to make standard SLS grades and
blend them with graphene,” says Hargreaves. “But, you would have free graphene flying around and that’s not ideal.”
Alternatively, the graphene could be embedded
into the surface of the material, and then be fully encapsulated (and safe for use). This could be achieved using techniques such as spray drying or cryo-milling, he says. The team has already had some success compounding nylon 12 with expanded graphite, and creating an ABS grade for FDM processing. “One thing we need to do is refine the
manufacturing process for these additive manufacturing grades,” says Hargreaves. “Graphene could help us move this technique further towards rapid manufacturing.” ●
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52