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Established Production Methods for thermoplastic composites
The processing steps for the manufacture of thermoplastic composites are much simpler than for thermoset. The thermoplastic has to be melted, intimately mixed with the fibres, and formed into the final shape. No chemical reactions, as with thermoset materials, are involved. However, the development of thermoplastic composites has been restricted due to the greater difficulty of this fibre impregnation with thermoplastic melts when compared to thermoset resins. This is due to the higher viscosities of thermoplastic melts which are between 10-100 Pa.s. as compared to 0.2-2Pa.s. for thermoset resins. Conventional thermoplastic composite manufacturing routes are two stage processes. Firstly, a precursor material is formed e.g.:
- Commingled fibres: tows of continuous fibres of glass or carbon intermingled with continuous fibres of the polymer
- Prepregs: Reinforcement fibres impregnated with a polymer matrix in the form of thin sheets
- Powder impregnated tows: Continuous tows of fibres are impregnated with thermoplastic powder giving a flexible ribbon or sheet
- Fibre Impregnated Thermoplastic, FIT: Powder impregnated continuous fibres encased in a polymer sheath
- Short and long fibre reinforced polymer pellets LFRT: compounded for subsequent extrusion or injection moulding
The secondary process is forming the component into the final product. The aim of any process is to coat the reinforcing fibres in thermoplastic and form into the desired shape.
Moulding Compounds
Large scale production of reinforced thermoplastics has so far centred on the injection moulding or extrusion of long and short fibre reinforced pellets. Here the fibres are incorporated to improve mechanical performance of the resultant moulding. The granules fall into two categories:
- short fibre - fibres of up to 3mm in length
- long fibre - fibres up to 13mm in length
During processing most fibres are damaged and the lengths are reduced.Note, the compounds with glass fibre are very abrasive so your tooling and barrel will need to be able to cope. The orientation of the fibres is determined by the shear profile within the die or mould. This can be hard to predict. The reinforcing effect is greatest in the direction of the fibre. Therefore, the processing parameters have to be carefully controlled to achieve the required stiffness and strength in the required direction. Please go to the Fibre Length page for more information. Need help with product design or material selection then we can help-go now to our consultancy page.
Commingled Fibres:
Commingled fibres are fibres of the polymer and reinforcement fibre intermingled together. As with all precursors they are only available in a fixed volume fractions, and limited range of colours, polymer types, additives etc. Interested in pultruding commingled fibres? We have a great deal of experience in this- we can pultrude profiles for you, set you up, refine your process. See our consultancy page for details of our services or contact us now.
Prepregs:
Prepregs are sheets or tapes of reinforcement fibres pre-impregnated with a thermoplastic resin. They can then be laid and stacked up to form a composite structure. Unlike thermoset prepreg they are not tacky and require very different treatment to their thermoset matrix counterparts. We manufacture unidirectional prepregs with high fibre alignment and high impregnation levels. Find out more about our prepregs made to order and our standard range of AtenPly prepregs. We can also help with the processing and manufacture of products using prepregs just contact us about our capabilities.
The potential of thermoplastic composites
The broader use of advanced composites is currently inhibited by high material and manufacturing costs. Thermoplastics are generally low cost. The processing steps for the manufacture of thermoplastic composites are much simpler than for thermoset as no chemical reactions are involved. However, existing thermoplastic composite manufacturing routes are all two stage processes. The full potential of thermoplastic composites will not be achieved until a one stage manufacturing method has been developed. Jonam Composites Ltd has developed such a one-stage manufacturing process that does not rely on expensive precursor materials producing a smooth, coloured, selectively reinforced profile. The resulting profile has the aesthetics of an extrusion with the performance of fibreglass pultrusions. Not only does this enable cheaper composites but the range of applications suitable for composites is enhanced due to the greater range of properties available with thermoplastics. For more information on the immense potential of thermoplastic composites please see our process technology page.
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