A novel high performance composite material that could have implications for the use of thermoplastics in the automotive industry was presented by DOW Automotive at the JEC Composites Show in Paris on Thursday.
Peter Cate (Market Development Manager for DOW Automotive UK) promoted the use of pCBT, a reactive thermoplastic with ultra-low viscosity, combining the processing benefits of thermosets with the toughness of thermoplastics. The presentation was one of six lectures provided as part of the JEC Automotive Forum which looked at new composite solutions for the automotive sector.
Structural composites can provide the potential weight savings required to achieve automotive industry fuel economy targets with pCBT composites particularly able to assist in overcoming some of the main challenges associated with composite use, such as:
Faster Processing to meet vehicle volume demand (Significantly improved balance of Stiffness and Impact Toughness performance versus thermoset products, enhancing durability
Environmental benefits in production (no VOC emissions)
Thermoplastic Recycling potential to assist with ELV directives (critical when replacing recyclable steel / aluminium components).
One of the reasons why composites still only form a small part of the automotive industry compared with traditional materials, is in part because steel is still regarded as a safe bet and relatively cheap, particularly at face value and when ignoring the product life cycle.
Speaking to DOW prior to the presentation, Peter Cate suggested that the integration of composites into the automotive sector partly relies on the industry to convince the OEM’s of the benefits of composites, and of the manufacturers to convince themselves that the advantages that outweigh the challenges of adopting a new manufacturing method.
DOW looked at this problem along with a number of issues that such as recyclability (especially with new EU ELV (End of Life) directives coming in place in 2006), improving cycle times, and material stiffness which maximises durability, all of which led DOW to a renewed interest in thermoplastics and in particular the qualities of CBT resin produced by the Cyclics Corporation.
Since 2002, DOW invested heavily in the CBT technology, mirroring Cyclics’ own investment, with the recent announcement of the first full-scale plant in Schwarzheide, Germany substantially increasing CBT (cyclic form of butylene terephthalate) production.
DOW Automotive have signed an exclusive agreement with Cyclics to develop CBT within the automotive sector and have spent some time applying science and innovation to develop catalysts and other additives for the CBT, which is then polymerized to create unique and valuable pCBT products.
CBT are solid (granules or powder) which at room temperature melt above ~150ºC and rapidly polymerize above ~180ºC to form pCBT. CBT resins melt to a water-like viscosity when heated and with the use of a catalyst polymerize into the engineering thermoplastic polybutylene terephthalate (PBT). Some of the key advantages are that CBT combines the processing advantages normally associated with thermosets, with the performance advantages of thermoplastics. DOW commented that during processing, the ultra-low processing viscosity of CBT also enables excellent filler wet-out, and high filler loading capabilities, but with no VOC emissions.
pCBT (Poly Cyclic Butylene Terephthalate) was highlighted at JEC as being the resin that could provide further impetus in integrating composite use within the automotive and other industry sectors due to a number of benefits that pCBT can provide, which include the ability to :
Accelerate production of structural composite parts for increased volume builds, something seen as a growth area by OEM’s;
Provides a unique balance of stiffness and toughness in the composite part, potentially reducing the amount and cost of reinforcement required (an important factor when considering the worldwide shortage of supply in carbon fibres.
Enabling significant part weight savings for reduced vehicle emissions, and,
Helping to meet environmental and recycling considerations.
The sale of the Derakane business of DOW in the latter part of last year may have been perceived by the industry as a lack of confidence by DOW in facilitating composite use in the automotive industry, despite the fact that they continue to sell epoxy resins today.
Ashland purchased the Derakane epoxy vinyl ester resin business from DOW as a move to strengthen Ashland’s current product portfolio of thermoset resins and according to Ted Harris, vice president of Ashland Specialty Chemical, “thermoset chemistries was core to the company’s long-term, strategic focus”.
At the time of the announcement in November 2004, the move towards thermoplastics became clear when Juan Antonio Merino, general manager of Dow’s Thermoset Systems business suggested that “in today’s environment, continued success (of the Derakane business) would require us to broaden our market participation and product offering. This would involve investing in polyester, which lies outside of our established core capabilities. We are pleased to have found a strategic buyer with the business model required to strengthen and maximize the value of the business and give customers a strong and proven supplier for the future..”.
Following the agreement with Cyclics, Dow began to develop CBT solutions for composite applications, utilising several manufacturing processes including compression moulding; powder pre-pregs manufactured using unpolymerized CBTTM to bind a glass or carbon fibre mat, which can then be compression moulded into pCBT thermoplastic composites and liquid moulding (RTM), where one- or two-component CBT systems are introduced into the mould, and where the low viscosity melt penetrates and wets out glass or carbon fibre pre-forms before polymerizing to form pCBT thermoplastic composites.
DOW see huge potential in the use of pCBT, and the presentation at JEC was testament to this faith. They see that structural composites can provide the potential weight saving required to achieve automotive industry fuel economy targets. In particular, they regard pCBT composites as being integral to overcoming some of the main challenges associated with composite use.
DOW have identified three application areas for potential pCBT use. These are semi-structural composites, where the current use of, for example, PP GMT or SR-PP replacements can be made where higher modulus at temperature is required in service.
Structural parts to replace epoxy composites, especially where cycle time, durability, or recyclability is an important issue.
And finally in exterior body panels within the truck, bus/rail sector where pCBT can be introduced into truck cab panels and eventually Class A passenger car body panels with appropriate surfacing technology.
It is not clear what products will be introduced later this year from DOW as they were unable to confirm whether any official agreements have been made with OEM’s. However, the official line is that developments with many customers are at an advanced stage and that there should be some announcements throughout the year.
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