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The benefits of Ahlstrom Glassfibre’s CBT-compatible glass-fibre reinforcements and Cyclics’ CBT resins were combined to develop a new platform of composite materials with properties that bring new opportunities to the wind power and marine markets.
(Published on October-November 2005 – JEC Magazine #20)
KAY RÖKMAN, R&D DIRECTOR, AHLSTROM GLASSFIBRE OY, FINLAND OLIVER HANITZSCH, DIPL. ENGINEER, SENIOR ACCOUNT MANAGER CYCLICS EUROPE GMBH, GERMANY
Cyclics CBT® resins are a small, ring-shaped or macrocyclic form of polybutylene terephthalate (PBT) resin, a well-known engineering thermoplastic. From a practical standpoint, it is a form of PBT that melts at a much lower temperature and has a radically lower viscosity that is close to that of water. Combined with Ahlstrom’s reinforcements, CBT resins can easily and rapidly wet out fibres, offering substantial benefits in composites processing for the marine industry. The water- like viscosity of the resins enables the use of conventional reinforc ements, such as spray-up roving, woven roving, combination products and multiaxials. An added value is that no special flow layer is needed. CBT® resins offer an opportunity to produce parts with epoxy-like mechanical properties while eliminating the workerexposure risks of epoxies and the generation of volatile organic compounds (VOC) during processing. In addition, the resulting composites are recyclable due to the thermoplastic nature of CBT resin.
The best of both
Simply put, Cyclics resins start off as a solid and are heated to a liquid for moulding. The included catalyst then converts the material at temperature into a tough, strong thermoplastic. The resins essentially represent the best of both thermoplastics and thermosets. They achieve a breakthrough in the processing of thermoplastics, because they process in a low-viscosity, or water-like form similar to most thermosets, but solidify to become a thermoplastic with the attending material advantages. Cyclics resins can be used in addition to or in place of conventional thermoplastics where there is a meltviscosity issue to overcome. They can also replace thermosetting resins in many applications, because they process similarly and offer significant processing, physical-pro p e rty and recycling advantages.
In addition to being tough, the composites with Cyclics resins and Ahlstrom glass fibres can be re-melted and recycled or re- shaped, unlike thermosets. Moreover, the resins do not release regulated organic compounds, such as styrene, which are subject to a variety of government regulations that limit operational flexibility and capacity unless the moulder implements expensive control technologies. Different aspects of the conversion from cyclic oligomers to highmolecular- weight PBT thermoplastic and the range of processing options for making parts are what give Ahlstrom-Cyclics composites significant advantages over other materials.
Some key attributes of the composites with Cyclics resins and the resulting applications are as follows:
As a matrix, Cyclics CBT® resins do not restrict the choice of production process. They can be used in RTM, vacuum moulding, spray-up, thermoforming and pre-pregging. The polymerized resin can be used as a matrix in semi-finished products – or organosheets – which are thermoformed into the final shape.
Due to its excellent and fast wet out, CBT® resin allows for increased production rates in RTM / infusion processing. The ability to use high fibre volumes makes it possible to redesign parts in terms of weight, without compromising mechanical properties.
Processing advantages - Solid form. - CBT resin melts to a very low viscosity. - Thermoformability. - Adjustable reaction times resistance. - No heat released in reaction. - Improved worker safety. - No toxic or regulated air emissions. - Long shelf life.
The resin’s low melt viscosity guarantees higher-quality production p a rts with fewer voids. Cyclics resins do not need post-curing, so parts can be de-moulded immediately after polymerisation, releasing the mould for the next cycle.
No release of volatile toxic gases
It is well known that the absence of volatile emissions improves the quality of surface finish. Therefore, Cyclics resins reduce potential surface rework. The VOC-free material also allows healthier working conditions.
No self-generated heat
In order to avoid possible runaway heating during epoxy moulding, which can ruin a boat made by reactive systems, many manufacturers currently slow down the reaction time of epoxies. CBT® resin allows manufacturers to make thick parts faster and more reliably, because there is no risk of self-generated heat degrading the part during processing.
Both in-house scrap and post-consumer parts can be ground and remoulded, with or without additional resin, to improve initial cost and provide an attractive option for reclaiming parts at the end of their initial use.
Increasingly, the life cycle of a material is impacting the buying decisions of consumers and the waste-management requirements of governments.