The use of natural fibers in unsaturated polyester resins has been limited to date because biofibers need to be dried first and then processed immediately after to obtain high-quality composites. Examples of natural fibers used for polyester biocomposites include flax, jute and bamboo.

Biocomposites

Biocomposites polyester

The use of natural fibers 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. In unsaturated polyester (UP) resins, the use of natural fibers has been difficult because the water content in the fibers deteriorates the curing process. The fibers therefore need to be dried first. This is an elaborate step as it requires an oven, which is costly in daily operation, and a large amount of energy consumption, which has a negative impact on CO2 footprint.

In addition, dried fibers need to be stored in confined conditions to avoid absorbing moisture when exposed to air. For this reason, the use of natural fibers in UP resin composites is only successful in small end products.

To address this issue, AkzoNobel has successfully introduced a range of Nouryact® accelerators, which are not sensitive to water when curing UP resins. This gives an advantage to our customers who work in moist conditions and use wet filler materials, such as non-dried natural fibers. AkzoNobel has also successfully 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.

Natural fibers like flax are known to contain up to 12% water. Curing composites based on such water-rich reinforcements 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.

Laminates, which were made with wet (undried) 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. 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 an epoxy-based laminate using the same but dried fibers produced 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.

Contact us today to learn more about how our biocomposites can improve your curing process.

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