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Thermoset materials commonly used for producing fibre-reinforced plastics (FRP) are not easily recyclable and repairable. Existing concepts are mainly based on milling and burning. The Fraunhofer Research Institution for Polymeric Materials and Composites PYCO has developed a new concept that extracts the resin from fibre-reinforced parts. Furthermore, the resin can also be extracted from a selected area for repair.
(Published on March-April 2009 – JEC Magazine #47)
Fraunhofer PYCO's work focuses on lightweight composites, microelectronics and optoelectronics.
Focusing on thermosets
Fraunhofer PYCO's thermosets are used in the field of adhesives, coatings, varnishes, binders, inmoulds and gelcoats, castings, foams, prepregs, RTM and pultrusion. The following properties can be designed: high flame retardancy, high fracture toughness, minimum volume shrinkage upon curing, fast and latent curing at a time, disbonding ability, water vapour and oxygen barrier properties, adjusted thermal coefficient of expansion, adjusted refraction index, reworkability and recyclability.
The institute develops polymer systems along the whole supply chain, from monomers up to the finished part. The scientists synthesise monomers and prepolymers that can include co-reactants, flame retardants, tougheners, fillers or modifiers. The processability of the systems is then tested and the first prototype parts are manufactured in close cooperation with customers. Finally, the finished parts are characterised and their quality is evaluated.
The institute uses state-of-the-art material characterisation methods and inhouse developed methods such as optical crack tracing, volume dilatometry, nano TMA/TGA/DVS for thin polymer films, and determination of water vapour and oxygen permeation rates.
Recycling and repair issues
The existing concepts mainly use milling and burning methods. The resulting products do not have the same properties as the starting materials. This is a major disadvantage. The state-of-the-art processes for repairing thermosets are complex and difficult to implement. Special component preparation is required to repair thermosets, which ends up being quite expensive and involves many working hours.
The institute has developed a new recycling concept. As the substances obtained from decomposition have defined properties, they can be reused as basic chemicals. This is a critical advantage compared with currentlyaccepted recycling processes. Overall, this concept saves energy and production costs while reducing CO2 emissions. The reclaimed reinforcement, which is not destroyed or damaged, is similar to the initial reinforcement, which means it can be reused for producing new parts. Using the same reinforcement repeatedly is especially cost-effective for expensive fibres and preforms like carbon and aramid. In this case, the cost saving potential could be significant.
Fraunhofer PYCO also uses this concept to repair damaged parts. The resin in the damaged area is extracted through a special operation (see Figure) and then a new resin is applied in the corrupted area. The resulting component has the same properties and characteristics as a new one.
About Fraunhofer PYCO
The chemists, physicists, engineers and technicians at the Fraunhofer Research Institution in Teltow, Germany, and at the Chair of Polymer Materials of Brandenburg Technical University Cottbus (BTU), develop highly cross-linked polymers (thermosets) for all applications, especially for lightweight construction and micro- and opto-eclectronics.
The decomposition process is initialised by a special chemical agent, so unintentional recycling during the product lifetime is not possible. No expensive equipment is required for recycling and repairing damaged parts, and the procedure uses a low process temperature which further lowers costs. The resin used for the recycling or repairing process can be adapted to all common manufacturing processes, including prepregs, hand lay-up, vacuum bagging, autoclave or resin transfer moulding (RTM).