What is thermoplastic pultrusion?
Thermoplastic pultrusion is based on the classic pultrusion method, with thermoplastics used as the matrix material instead of thermoset resins.
In both methods, continuous fibres are impregnated with a plastic, with each fibre element enveloped in plastic and joined to its neighbouring fibre elements, allowing them to transmit force.
In thermoset pultrusion, this is very easy to accomplish, as thermosets in a liquid state are very thin (like water), which allows the fibres to absorb the matrix very effectively. Thermoplastics, on the other hand, have a much higher viscosity. It is difficult to impregnate fibres with this viscous plastic mass, so a process has been specially developed to enable this: thermoplastic melt pultrusion.
What is a continuous-fibre-reinforced thermoplastic profile?
Whenever high-strength profiles are required and the weight of the component needs to be kept as low as possible, continuous-fibre-reinforced profiles are the right choice. They can replace reinforcement elements made from aluminium or other metals, for example.
Continuous-fibre-reinforced thermoplastic profiles are manufactured on the basis of continuous thermoplastic pultrusion.
Here, the continuous fibre (often glass fibre) serves as the reinforcement material; it runs unidirectionally and impregnated with plastic matrix. The plastic matrix envelops each fibre filament and joins the individual fibre strands together. This causes forces to be distributed across the entire cross-section of the profile and creates a high level of strength.
Pultruded profiles support a wide range of applications:
They can be welded to other components or coated or used as reinforcement inserts. As the pultruded material is made of thermoplastic, it can easily be integrated into a larger thermoplastic system (e.g. an assembly). This creates new opportunities for designs that combine strength and sustainability, using the materials PA 6, PA 66 or PP. The good material compatibility properties also make recycling easier.
Light reinforcement and effective crash protection in HV batteries
High strength profiles for pressure plates in facades
Welding, insert moulding, overmoulding or thermoforming
What does thermoplastic pultrusion process involve?
- Selecting the materials:
The process begins with the raw material selection. In addition to the reinforcement fibres, which determine the mechanic properties of the final product, the thermoplastic matrix must also be selected for additional product properties and in relation to compatibility with the final overall system. - Feeding the continuous fibre:
The continuous fibre is wrapped around spools in the form of a roving. The fibres are unwound by the creel with the desired speed and tension. They are then pre-heated in the tensioner and given the desired shape with slight tension. - Impregnation and shaping:
In the extruder, the thermoplastic is melted and fed to the heated pultrusion tool. The reinforcement fibres pass through the tool, where they are incorporated into the plastic matrix. They are also shaped inside the tool. The profile is then cooled down until it has completely solidified. - Haul-off and trimming:
A caterpillar haul-off unit feeds the completed pultruded profile to the trimming unit where it is cut to the desired length. It is then dropped onto the discharge table.
Benefits
Recycling:
Toughness:
Heat and chemical resistance:
Shaping properties:
The main difference is the matrix material:
Thermoset pultrusion:
This method uses a chemically curing resin such as epoxy or polyester. The glass fibres are pulled through the liquid resin, impregnating them. The resin then cures in a special tool under controlled temperatures. These materials cannot be shaped or melted once they have hardened.
Thermoplastic pultrusion:
This method uses thermoplastics that are melted in an extruder. The continuous fibres are then impregnated in a tool. After impregnation of the fibres, the melts cool down and the profile becomes rigid. As thermoplastics can be remelted, they can easily be recycled and re-used.
Sindy Richter, Team Development