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The use of natural fibers in composites is predominantly limited to the car industry, where polypropylene is used as the matrix material. There is also widespread use of natural fibers in epoxy resins. With unsaturated polyester (UP) resins, the use of natural fibers has been difficult because the water content in the fibers affects the curing process. The fibers, therefore, need to be dried first. This requires an oven, which uses a large amount of energy and has a negative impact on the CO2 footprint.
In addition, the dried fibers need to be stored in confined conditions to avoid absorbing moisture from the air. For this reason, the use of natural fibers in UP resin composites is only successful in small sized end products.
Natural fibers such as flax contain up to 12% water. Curing composites that use natural fibers is challenging, if not impossible, when using standard cobalt-based curing systems. Cobalt carboxylates are prone to hydrolysis under the influence of water and then become unreactive for the curing process.
To address this issue, Nouryon has introduced its range of Nouryact® accelerators, which are not sensitive to water when curing UP resins. This gives an advantage to customers who work in moist conditions and use wet filler materials, such as non-dried natural fibers. Nouryon has also shown that structural composites based on non-dried flax fibers and different grades of UP and vinyl ester (VE) resins can be produced in a vacuum infusion process.
Laminates made with non-dried flax fibers, and Nouryact proved to have the same mechanical properties as dried flax fibers in combination with a traditional curing system.
« Curing with Nouryact accelerators allows for our customers to easily switch from glass to flax fibers while maintaining mechanical properties », said Roel Zuijderduin, Global Technical Development Manager. Drying flax and keeping it in confined storage is not necessary. In fact, the mechanical properties of the non-dried flax fiber composite using UP or VE resins are similar to an epoxy-based laminate using dried fibers under the same conditions. Since the pre-drying and separate storage of dried flax fibers is no longer needed, it makes the use of these natural fibers easy and cheap. This can allow more companies to start using bio-fibers for their composite end-products.
Nouryon is glad to be active in the SSUCHY project through its Polymer Catalyst unit, which produces and develops curing systems, including peroxides and accelerators for room-temperature curing, for polyester based thermosetting resins. « Our task in the SSUCHY project is to develop novel curing systems for bio-based resins, which meet labelling requirements and are not water sensitive. Within the four-year project we have developed new combinations of peroxides and metal based accelerators which are not water sensitive », said Mark Gu, Global Segment Leader.
Discover Nouryon’s cure systems for bio-fiber reinforced composites in this video: