by Liz White, editor
Polyurethane industry experts are getting increasingly enthusiastic about wider use of the material in the composites field.
And after a great surge of interest over the last couple of years in use of carbon fibre to reinforce plastic car parts, the industry is settling to the task of getting polyurethanes more widely recognised and used in the composites sector, as described by various experts UTI spoke to at the JEC Composites show in Paris, 27-29 March 2012.
This task seems to be more advanced in the US in the wider composites market, while in Europe, the automotive sector's use of PU composites is further ahead, largely driven by some of the innovative German OEMs.
PU supplier Bayer has teams for all three regions - the US, Europe, Asia - dedicated to developing PU composites, and it is putting a lot of resources and energy behind this, "because we see it as a very big growth opportunity for PU," said Harry George, manager, new markets, with Bayer MaterialScience llc, based in Pittsburgh, Pennsylvania.
Demand for lighter and lighter parts for all type of transport uses is forcing suppliers to adapt, and this gives scope for new opportunities, as George's European colleague Claudio Pauler, marketing manager for BaySystems for diversified industries, pointed out.
"One reason for optimism for me is that really the industry is now changing and it's a good opportunity to introduce new materials, new technology and new resins," said Pauler, speaking 27 March at Bayer's stand at the JEC show.
Developments in lightweight and electric vehicles, mean that "the sector is much more open to new solutions. I believe it is a good window of opportunity for us to introduce new ideas," he emphasised.
PU wind blades on the way
George is a firm believer that PU can take a wider share in the composites business, and is genuinely optimistic about the future for urethane resins in uses such as wind blades.
BMS is developing PU resin-infusion technology which can eventually be used for wind blades, he said, and also "vacuum-assisted RTM (resin transfer moulding) for structural parts, which are on display here.".
BMS studies show that while PU's static properties are comparable to epoxy, in dynamic properties - which includes fatigue resistance, crack propagation, inter-laminar shear and so on - PU is significantly better, 10 times better, than epoxy, George said.
This has high value in uses such as wind-blades and he is sure that PU use here is a realistic long-term goal. PU offers higher strength to enable the part to be thinner, and hence lighter.
"As offshore wind becomes a bigger part of the industry, the blades have to become much larger," George explained. "We are looking at blades 100-m long." With some existing technologies, "they're reaching a point where they can't get the properties they need to make a 100-m blade," he said.
BMS is talking to major wind-blade makers, although confidentiality agreements mean George cannot say who it is working with.
The blades could use glass or carbon fibre reinforcement: "It could be either," said George, and BMS has also assessed reinforcement with nano-materials.
The timescale for commercial applications is longish: "I think it's within the next three years probably," George said. Since it's a high-risk area, and the liability if a wind blade fails is obviously significant, a lot of testing needs to be done, he added.
Growth rates in wind blades are "double-digit every year in all regions," with China growing fastest, because of government support, and the US next, George added.
George noted that in China it is possible that "half the wind blades that are in place today aren't connected to the grid. ... They don't have the infrastructure.".
Pultrusion and filament winding develop
BMS is expanding its pultrusion capabilities globally, and developing new applications in Europe, the US and in China, with structural uses developing well," said George.
"We're developing some new formulations in the US, one for a soya-based resin that has bio-content," for a major manufacturer of PVC windows. The weakness of PVC means these windows have metal inserts - either steel (Europe) or aluminium (US). But the thermal performance of aluminium doesn't allow them to meet energy demands in the US, he said.
BMS' material is intended to replace the aluminium inserts. The soya material, green in colour, has a renewable content of about 2 percent of the final polymer, which is "an added bonus, rather than big demand." It offers "the same physical, same mechanical properties as our standard material," he added.
BMS is also progressing in filament winding, where PU offers "process advantages, compared to current vinyl ester or epoxy resins.".
George pointed out that, "If you filament wind an epoxy tank, it has to be post cured to get to the final properties." Customers make a tank which then needs post-curing for up to 2h. "With PU they can wind it and take it off and it cures without an oven in only 30 min," he said.
Filament winding could be used for natural gas tanks for vehicles, for water tanks and for tapered electrical utility poles.
RS Technologies in Canada is using filament-wound PU for this, George said. The company also uses pultrusion, but its high-tension poles are all done by filament winding of PU. "That was the strongest material they could find," George said.
European cars focus on lightweight
In automotive composites, the BMS expert said, "there's a lot going on in Europe. Automotive light-weighting is a bigger focus than in the US.
Most innovation here is being done in Germany, by OEMs such as BMW and Mercedes, the BMS team feels. Some German companies are coming out with high-speed RTM for epoxies, "but we think PU offers better value in processing and properties," George said.
Again RTM can use glass or carbon fibre with PU as the resin matrix, and the user gains better dynamic properties than with current materials, he said.
Pauler pointed out that automotive manufacturers will only accept new processes if they are cost-effective solutions for lightweight and with good mechanical properties. "You have to offer a cost-efficient solution that allows large-scale production with a certain flexibility," he said.
But Pauler feels structural automotive uses for PU composites are feasible, perhaps with carbon-fibre-reinforced parts. For example, BMS was involved in developing the polyurethane diesel engine cover that won a JEC innovation award (see PU Engine below) .
George said in his experience, people tend to look at composite solutions because of some kind of regulation - the need for lighter weight, or in the US, thermal performance in windows.
"Polyurethane in composites offers special solutions to a customer with specific problems," he said. For example, in the container industry, "one company we are working with wanted to replace wood flooring with PU pultruded flooring," he said. The solution costs more initially, but the lifetime savings are good.
Structural car composites will take a while
After the excitement at last year's JEC event about use of carbon fibre for structural parts in the automotive sector, things have quietened down.
A structural polyurethane/carbon fibre composite part developed by BASF and on show at last year's JEC show is not in production yet - although several projects are ongoing, pointed out Andreas Wolf, BASF's European segment leader for exterior automotive parts.
"To be honest, you need a long breath for this, especially when you are approaching the structural parts, where you intend to substitute steel or aluminium," he added. "We are aware that this will take a few years until there is a certain market penetration," he commented.
For automotive OEMs such as Volkswagen AG, it takes several years for such projects to reach production, but developments are gaining pace, and BASF has been involved in four projects with Tier 1s and OEMs in the last year, involving RTM - which is mainly an epoxy process, Wolf acknowledged.
Laminate structure now the focus.
The BASF expert said for both OEMs and Tiers "it does not matter whether it is epoxy, PU, polyamide (PA), or whatever. They want the best-performing product.".
"If you are dealing with end-consumer OEMs, they are not interested in the material's hardness and tensile strength.".
Wolf feels straightforward comparisons of epoxy and PU materials are not necessarily the most helpful approach. BASF tried this for a few years, he said, but "we came to the conclusion that you cannot just compare the raw material properties, you always need to see it in the context of the laminate structure. ... You can have a good resin, but in the composite structure it might fail," he said.
"For sure we think PU will have some advantages versus epoxy," but at present this is not a fruitful approach, he indicated.
As a result, BASF now has a team for lightweight composites, to evaluate technologies and develop applications, Wolf said.
"We focus on laminate structures, using PU, epoxy, reactive PA, and also in combination with different foam cores," Wolf said.
Customers want a view on "the whole laminate structure and its design issues," he said.
BASF can now simulate these kinds of structures, and see how a design would look if made in PU RTM or epoxy RTM, in combination with foam cores, Wolf said.
The group has developed PU foam cores which can withstand the pressure/temperature in the RTM process, where epoxy injection temperatures are up to 140°C, Wolf said.
In a project with the EDAG Group, BASF has developed a roof module for a hard top, and simulated the design for this part, Wolf said.
The part already exists in steel: "We wanted to find out if there are advantages in making such a roof module in a composite material.".
The composite part offers "significant weight advantages," greater than 60 percent over steel and 30 percent over aluminium, Wolf said. This part weighs 2.8 kg in a composite, 4.5 kg in aluminium, and over 7 kg in steel, he said.
"It is very interesting... to see the weight advantages with CFR laminates," he added.
"We have proven the possibilities with our material and design, know-how, to reduce weight significantly without losing mechanical stiffness properties, that is the main message." This adds to the confidence of the team, he said.
"What's interesting here is that all relevant part-specific tests have been simulated on this part, and flexural strength has also been simulated," Wolf said.
As a core structure, foam has advantages over paper honeycomb for composite sandwiches, in allowing homogeneous pressure distribution, and no surface defects in RTM, he added. Foam also adds thermal insulation and structural stiffness, combined with low weight, he said.
BASF first makes the PU foam part, and applies the fibreglass layers either side. Then it puts the complete preform into the mould and injects the resin.
While this is a complex two-step process, Wolf said that the automotive sector is "playing with a lot of ideas" to optimise and automate it for higher volume production.
A big breakthrough may be some way off, with major uses commencing between 2016 and 2020, he said, "because we are talking about structural parts and replacing metal components.".
Plenty of technologies are being studied, including CF RTM and sandwich structures, and Wolf thinks it "will not be one structure, one technology, one material.".
Dow offering PU/epoxy/carbon fibre.
Dow looks at automotive as a dedicated market with its own sales/marketing teams. "Our strategy is to be a solutions provider to automotive," said Jon Penrice, head of Dow's European formulated systems business, in an interview at UTECH Europe.
For automotive, Dow is very interested in composite technology, and in this context has signed a joint venture in carbon fibre in Turkey.
"If you look at what you need to compete in composites, it's carbon fibre, epoxy, polyurethane," Penrice said, noting that availability of glass fibre is relatively good, "so the three we now offer [epoxy, PU and CF] give us good differentiation.".
Discussing PU use in composites, Penrice said this is "still an incredibly young industry and therefore rather conservative. It starts in one place, with epoxy used in aerospace and some in automotive," he said.
"But the concept of lightweighting can be applied in many places," Penrice noted.
As many other commentators observed, Penrice feels epoxy with glass or carbon fibre, and also PU will be used as the industry matures. Segments with winning technology will emerge: "some of those will be PU," he added.
And he emphasised: "We're just gearing up now to really increase our resources into composites, and are really segmenting the market here.".
Dow's Automotive Systems unit has just opened a new European Technology Center for composite applications in Freienbach near ZŸrich, which it says allows the unit to be a strategic partner for OEMs on composites, especially carbon fibre solutions.
Dow says the centre offers "comprehensive infrastructure" to develop composite applications and the appropriate joining technology.
A 200-m² laboratory will be equipped with a 120-tonne high-pressure RTM machine, with test/development facilities for resins and adhesives.
Henkel offers fast-curing PU composite resin at JEC
Henkel offers fast-curing PU composite resin at JEC At JEC Europe, adhesives producer Henkel presented its new Loctite MAX2 polyurethane for resin transfer moulding (RTM).
Henkel said that composites based on carbon or glass fibre are gaining momentum due to the opportunity for "enormous weight savings over traditional part construction, with no loss in mechanical performance." Such composites started in aerospace where pre-impregnated fibres (prepregs) are manually laid up and then baked into composites, but many uses are now penetrating into the automotive industry.
Processes such as RTM are suited for high-volume automotive production, Henkel said, and its new composite matrix resin based on PU offers improved economics and throughput. Compared to standard epoxy resins, the new PU type cures significantly faster, said Henkel. During injection, it impregnates the fibres efficiently without stressing the fibres since the resin viscosity is lower. Another PU product, the adhesive Macroplast UK 1340, will help manufacturers of wind blades raise productivity and cut costs.
Henkel said using polyurethane adhesives is "an obvious way of accelerating rotor blade bonding." Traditionally, blade shells and spars have been bonded using two-component epoxies, which reliably meet extremely high mechanical specifications, but Henkel said they are rapidly reaching their limits in terms of automation.
New technologies are needed to speed up and automate production. Macroplast UK 1340 satisfies the specific mechanical requirements for blades and makes rotor-blade production more efficient. PU adhesives react much faster than traditional epoxy resins, and produce substantially less reaction heat. As a result, this two-component adhesive cuts both the length and the temperature of the cure phase, said Henkel.
In a four-month test, technicians subjected a 40-m Enercon rotor blade bonded with the new adhesive to stresses and strains that would normally occur over a period of 20 years. The bonded joints passed this programme of static and dynamic tests specified in IEC 61400-23.
PU engine housing wins PURTrain team a JEC award
The idea of train parts being made using paper seems a little far-fetched - until you remember that paper honeycombs are quite commonly used as a composite base, and give strong products when impregnated with resin.
"To demonstrate the material, we manufactured a component that is subject to significant stresses ... the diesel engine housing for a train," said Jan Kuppinger, an ICT scientist, in a piece on the Fraunhofer website.
The objective is to make lighter trains which are more economical to run.
The housing is located beneath the train, where it shields the engine against flying stones as well as protecting the environment from any oil that might escape. It is also flame retardant, meeting the rail fire safety standards of CEN/TS 45545 standard.
At the JEC show, Florian Wafzig, of Fraunhofer ICT's polymer engineering group, told UTI that that this part carries the weight of the engine through a metal layer on the fixing parts. The composite replaces an all-metal part, and adds sound damping, he said.
"By using this new material, we can reduce the component's weight by over 35 percent - and cut costs by 30 percent," Kuppinger said.
The group included train developer Bombardier GmbH, machinery maker KraussMaffei Kunststofftechnik GmbH, PU materials supplier Bayer MaterialScience AG and processor DECS GmbH, and worked as part of the PURtrain project, funded by the German Federal Ministry of Education and Research (BMBF).
BMS' role was to develop the fire-retardant formulation, said Dr Andreas Hoffman, of BMS' polyurethanes business unit for EMEA, talking to UTI at the JEC show.
This honeycomb, with glass-fibre mats top and bottom, sprayed with urethane, is the "same PU technology used for load-floor applications," Hoffmann pointed out.
The partners optimised the fibre-spraying process, by developing a mixing chamber which allows even more complex structures to be produced in any required size.
"This is the first time it has proved possible to use this process to manufacture such a large and complex component that also satisfies the structural requirements," said Kuppinger.
To determine the thickness of the PU top layers, the researchers used computer tomography.
ICT says the prototype passed its first strength test "with flying colours." If field tests prove successful, the material could be used for roof segments, side flaps and wind deflectors for the vehicle industry, with the process ramped up to produce volumes of 250 to 30 000 units.
Bombardier will be carrying out trials on this component in the next few months, Wafzig said.
Parts are now being further tested before commercial use, agreed Hoffmann. The technology can be used for all types of motor housing, load floors, roof modules, where weight saving is needed, he said.
CSM process ideal for vehicle load floors, Hennecke says
For German PU equipment specialist Hennecke GmbH, a new cutting process for glass fibre rovings for its CSM (composite spray moulding) process is "really a revolution," claims Detlef Hohn, sales manager for CSM.
And Hohn also said that Hennecke's CSM process has become state-of-the-art technology for vehicle load floors. "More than 90 percent of the load floors which are made use our CSM technology," Hšhn said.
In load floors, a lot of areas need extra reinforcement for weight bearing and to add handles. CSM allows easy addition of chopped fibre at specific points where reinforcement is necessary.
Over 45 systems are running worldwide, "some 52 machines, for this load-floor technology," Hohn added. It is being used for all types of vehicle, from the cheapest Opel Corsa, to top-end models, he said.
"We have a lot of machines running in China to make load floors for German and US models made there," explained Hohn, noting that the technology will also be exploited widely in trucks, since truck OEMs are now very interested in lightweighting.
Hennecke developed its new glass-fibre cutter because in the previous system the blade would become blunt and have to be changed after cutting 100 kg of fibreglass, Hohn explained.
Now it has a system with ten times longer service life, significantly reducing downtime, maintenance and costs. Hennecke says this is thanks to a new cutting process that needs "neither a knife roller nor blade."
For a processor making dashboards, which weigh about 3 kg and consist of a third by weight of glass-fibre, 1000 parts can be made without touching the cutting system.
Hennecke's system cuts the glass fibre outside the mixhead, a more versatile approach than cutting inside the mixhead, Hohn said. For cutters in the mixhead, spare part costs are high since all parts must be hardened to handle chopped fibre.
"We are using a standard mixhead, so the life- time of the head is much longer than that of competing systems," Hohn said.
With Hennecke's CSM system, users can spray 100 percent of PU or glass fibre or any ratio in between. "We have a 100-percent spray and also 100-percent LFI application both in one," he said.
The cutter is a little smaller than previously, which means that "for parts where you want to go deeper into the mould, it is easier now," said Hohn.
Hennecke's cutter also makes it simple to change glass fibre length. Rovings are guided into the cutting unit via a patented pressurised-air mechanism.
Hohn said the task is to break the fibre where you want to: "If you tear it with too much strength, you destroy the rovings." Using air pressure produces much less tension, and "as the robot goes back you cut it in the other direction," Hohn said, allowing less damage.
Hohn cited a US customer who was fascinated by this movement of rovings, because his present system damages rovings a lot.
Hennecke is aiming parts made of fibre-reinforced PU layers, with a paper honeycomb core, at truck cabins, interior parts - at any sector looking for weight saving, he said.
As with other machinery makers, Hennecke has been starting to do business in RTM equipment for carbon-fibre-reinforced parts, with epoxy materials, despite being a polyurethane specialist. Hohn indicated that if Hennecke sees a chance to do business, "we take it."And as other commentators noted, Hohn said that epoxy resins "have more odour issues," and are slow reacting. "So the aim is also to develop PU RTM parts," using Hennecke's Streamline machine which is able to work with PU and epoxy systems, Hohn said.
Hennecke has a relationship with injection-moulding machine producer Engel for composites, and has been involved in a project making a die-cast part which uses a PU system. Here Hohn showed a panel that Hennecke has been involved with, using a technology called Touchskin from Magna Exteriors and Interiors.Touchskin is a plastic film incorporating electronic circuits, which can be moulded into shape, incorporated into an injection-moulded plastic panel and coated with a smooth Clearmelt polyurethane.
A prototype made for Magna is for the centre tunnel around a gearshift. The haptic interface responds to fingertip touch, so drivers can change settings using the 'scroll and tap' technology we are all familiar with in our phones, iPads and so on.The advantage of this technology is that "you can integrate some electrical functionality into these parts, without adding separate knobs and other equipment," said Hohn, so the production cycle can be streamlined.
Structural parts require new learning curve
A major demand in the EU is to meet CO2 emissions levels, which is producing strong demand for weight reduction, with BMW's megacity vehicle, now the i3, for example, making much use of carbon-fibre-reinforced (CFR) parts.
For new electric vehicles, processors need to learn how to design and produce such parts in lightweight composite materials, Wolf said. BASF is at the beginning of a learning curve here, he added and needs to learn how to simulate performance, safety features and more.
"I have the feeling we learn a little more every day, and are making big progress ... learning very fast, along with the Tier 1s and OEMs," Wolf said.
Carmakers have been looking at weight reduction for decades. But now the demand is getting more immediate. Now new lightweight composites "offer the chance to penetrate areas such as structural parts," the BASF expert said.
Frimo, Huntsman cooperating in RTM with polyurethanes
As the pace of development in composites accelerates, more companies are aiming to tie resin technology in with appropriate processing techniques. The latest example of this is a cooperation agreement between Frimo and Huntsman Polyurethanes to develop cost-effective solutions for high-volume composite manufacturing.
This deal with Frimo is "aimed very firmly at developing PU composites for automotive ... products to meet the lightweighting needs of the automotive OEMs," said Nick Webster, head of Huntsman Polyurethanes for Europe, in an 18 April interview at the UTECH Europe event in Maastricht, The Netherlands.
Frimo specialises in process technology, with tooling and equipment for PU processing, and experience in resin transfer moulding (RTM).
Huntsman has purchased a Frimo RTM pilot unit for its technical centre in Everberg, Belgium. This will allow Huntsman to expand testing and validation of its new Vitrox range of PU_matrix resins for automotive fibre composites.
Andy Walton, Huntsman's automotive business manager, and Karl-Heinz Stelzl, Frimo's director of advanced technology, said, "The industry needs innovative solutions that enable high-volume scalability, whilst optimising and driving down fibre composite part costs."
The venture will bring "some exciting top technology to the area of fibre-reinforced composites," Webster claimed.
Frimo has an impressive ability to design processing equipment and optimise process flow, "and we think we have got some for pretty special chemistry," said Webster, referring to Huntsman's Vitrox polyurethane resin for RTM.
The aim is to develop serious mass production technology for lightweight composites, in affordable, efficient, fast cycles time, using Frimo machinery, Webster said. This makes PU_RTM a reality for OEMs who are looking for lightweight solutions.
Webster said the object is not just to get the right performance, it is also about processing and economics, about cost efficiency.
"With Vitrox and Frimo we think we get the right combination of really fast cycle times, and great product properties and also, from Frimo, low clamping pressures," Webster said.
Webster said Huntsman is in contact with OEMs looking to make lightweight components, including body panels and structural parts.
"The jury is still out on where composites or other materials will fit in the vehicle, this is a development journey," said Webster, noting that Huntsman is "working with at least one of the big OEMs towards serious-scale production."
"We think that the Vitrox chemistry we've come up with, that allows really fast cycle times, is one of the enabling steps towards making this real," the Huntsman executive said.