BIOMAT
Development of Thermoplastic Biocomposites
Project Manager: Robert West, QinetiQ Ltd.
Project Duration: 1 December 2002 to 31 July 2007
Collaborators: QinetiQ, The BioComposites Centre (University of Wales), BioFibre Ltd, Hemcore Ltd, AEI Compounds Ltd, Engenuity Ltd, Premier Engineering Solutions Ltd, Birkby’s Plastics Ltd, Fibre Developments Ltd.
Government Sponsors: DEFRA (Department for Environment, Food and Rural affairs)
BBSRC (Biotechnology and Biological Sciences Research Council)
Background
Natural fibres offer many attractive technical and environmental qualities when used as reinforcements in polymer composites. They provide high specific strength and stiffness, processability, and low raw material and manufacturing energy costs to a range of thermoplastic and thermosetting composite materials, for exploitation in a wide range of industrial applications.
These benefits mean that the potential market for natural fibre reinforcement is very large. The automotive industry, in particular, is keen to exploit their cost, weight and environmental benefits in thermoplastic injection moulded products. However, there remain barriers to realising the full potential of these materials for many industrial applications.
Aim
The aim of the Biomat project was to address the outstanding issues that are currently preventing the use of natural fibres in cost acceptable, sustainable, injection mouldable, industrial composite materials. The project addressed technical barriers in the following key areas: fibre extraction and treatment; material compounding and injection moulding; mould and component design, and; manufacture of components.
Summary of Main Research Outcomes:
Fibre extraction and treatment
In fibre composite materials, the aspect ratio of the fibre controls, to a large extent, the efficacy of reinforcement. The initial stage of the project therefore explored fibre extraction treatments capable of separating technical (i.e. bundles of) fibres into high aspect ratio individual fibres or ‘ultimates’. Technical flax, hemp and Coppice willow fibre types were treated using various physical and chemical processes, both singly and in combination. Fibres which have been assessed included those from the following treatments: hot water refluxing; HCL refluxing; ultrasound; hydrogen peroxide/acetic acid maceration. Many of these treatments released fibres with high aspect ratio reinforcement capability and valuable environmental durability.
Effective fibre reinforcement requires optimum bonding, or coupling, of the fibre to the matrix of the composite material. To this aim, a range of chemical applications were evaluated, namely organo-silanes, QinetiQ’s novel end-group chemistries, and maleic anhydride grafted polypropylene (MAPP). By applying various macro-mechanical tests, electron microscopy and contact angle measurements, MAPP conclusively showed significant improvements to the physical properties of natural fibre-polypropylene compounds.
Material compounding and injection moulding
Moulding compounds of the fibre and polypropylene were produced using the twin-screw compounding method. The compounding process risks fibre length reduction and structural damage, as high melt processing temperatures and high shear mixing actions are used to disperse the fibre. However, by process optimisation, the project produced materials with mechanical properties comparable to commercial glass-filled polypropylene. The project also identified overarching, fundamental issues related to the feeding of low bulk density fibre into compounding equipment, which were addressed sufficiently to move the project forward.
QinetiQ investigated a wide range of flax and hemp fibre systems for their ability to compound into polypropylene in order to achieve our objectives for physical performance and injection mouldability in compounds which could be scaled to industrial practices. The following aspects were considered: quantitative characterisation of thermal and fibre length reduction; composite micromechanics theory; and semi-empirical predictions of tensile strength and stiffness characteristics. The project achieved a key milestone when Hemcore hemp fibre-based moulding compounds, produced in the laboratory, not only produced comparable properties to the glass fibre-PP benchmarks, but also significant environmental stability, as required for automotive interior applications. These materials were subjected to tests for odour release, flammability and fogging of windscreens by condensing material volatiles, with all tests giving satisfactory results.
Mould and component design
To understand the effects of injection moulding on the microstructures and the physical properties of the mouldings, systematic assessments of the injection parameters and the flow rheology (including its linkages to the ‘skin-core’ microstructures in the mouldings) were undertaken. Flow was quantified under representative injection moulding conditions, using a specially developed ‘in-situ’ capillary rheometer. The examinations confirmed the applicability of conventional tool design and processing practices to the production of the Biomat demonstrator components.
A key aim of the Biomat project was to validate the laboratory developments for industrial-scale compounding processes. This required investigation of the many outstanding issues that industry has highlighted to be problematic when dealing with natural fibre on an industrial scale. Ultimately, solutions were found by using the know-how in the plastics recycling industry, and several hundred kilos of moulding compounds were produced for the demonstrator components injection moulding trials. Cost assessments on these materials (an accrual of raw materials and industry-specific processing costs) showed the potential of these moulding compounds to be at least 10% cheaper by weight than similar glass fibre-reinforced materials.
Manufacture of components
The project consortium selected an accelerator pedal to demonstrate structural durability of the Biomat materials, while a car door interior panel was used to assess mouldability. Natural fibre-based accelerator pedals, based on a glass fibre-reinforced nylon benchmark design, were successfully produced. A pedal design for the natural fibre material was also developed by finite element modelling and showed that the natural fibre design was potentially 2.5 times structurally stiffer and 9% lighter than the existing pedal benchmark. In addition, a 3-D stereolithography model of the new design was also produced and subjected to vehicle pedal package assessments and transit van track trials. The test programme conducted on the Biomat pedals, at Birkby’s Plastics Ltd, was able to substantiate the physical performance of these parts and materials. Further tests assessed the chemical resistance of the Biomat pedals to a range of automotive fluids, producing very good results. Track trials of fitted vehicle pedal assemblies into transit vans were successfully conducted by Ford Motor Company Ltd.
Natural fibre interior door panels were moulded by Visteon, using a production tool for unfilled plastics. Complete units were produced, but the challenging aspect was to produce long material flows, at low melt temperatures, with minimum fibre damage. Some discolouration to the moulded units was noted but Visteon was confident that, with minor modifications to the tooling, this issue could be resolved. Successful further long-flow trials were based on the moulding of a dashboard cover, and the main impact of long-flow on odour release was evaluated by Ford Motor Company Ltd, with satisfactory acceptance of these parts.
Progress Towards Commercialisation
The project has addressed the major outstanding barriers to the use of natural fibre reinforced composite materials for industrial injection moulded parts. However, further work is required to commercialise these materials, not only to make these materials more economically attractive, but also to build confidence amongst the aspiring natural fibre plastics processors community. Further work is needed to address the following specific issues:
(1) The Biomat moulding compounds which demonstrated the best physical and environmental characteristics required a number of labour intensive fibre handling and compounding steps to achieve the desired properties. There is a strong need to develop appropriate compounding technologies in order to maximise the technical and economical benefits obtainable from natural fibre compounds. The technical factors which require fundamental assessments are: linkages between the fibre physical forms; fibre cohesion; control of fibre feeding into compounding equipment, and; moulding compound production quality and economics.
(2) The Biomat consortium has identified supply chain relationships that need to be better understood and developed into viable commercial concerns. Materials supply routes need to be established: this requires a number of technical and economical factors to be understood and assimilated into a supply chain that, in particular, develops the fibre supplier capabilities for the intensive end-user requirements.
Further Work
Many of the Biomat consortium partners are currently engaged in structuring a pre-commercialisation project. The follow-on project will also have industrial representations capable of addressing the materials supply chain and compounding issues.
While the commercialisation plans are driven towards automotive markets, continuing market surveys suggest much wider applicability of these materials across many different industry sectors. Our aim will be to identify a range of application areas across a range of market sectors, such as retail, civic and, construction, etc.
QinetiQ and the consortium partners are identifying compounding companies who can support the planned developments, and whom are suitably positioned in the materials supply chain to exploit the Biomat technology into commercial markets.
Further information is available from:
Robert West, QinetiQ Ltd.
Tel: 01252 394014, E-mail:
Natural fibre-reinforced polypropylene accelerator pedal assembly
Natural fibre-reinforced polypropylene car interior door panel
Natural fibre-reinforced polypropylene accelerator pedal assembled into a Ford Transit van
Some of the Biomat team members on the day of the accelerator pedal track trials at Ford Motor Company, Dunton, UK. (L to R): Nigel Fawcett, Rajinder Singh, Jonathan Alms, Andy Gent, Reinhold Kling, Lisa Jenkins, Mike Duckett, Qiuyun Liu.