The European Pultrusion Technology Assn. (EPTA) held its bi-annual World Pultrusion Conference, March 3-4, in Prague, Czech Republic. EPTA’s stated mission is to “support growth of the composite profiles industry by maximizing external communication efforts.”
EPTA president Luigi Giamundo, owner/CEO of Atp Srl Avanzate Tecnologie Plastiche (Barletta, Italy), welcomed 124 registrants from 24 countries — the largest EPTA delegation to date — to 23 presentations that covered market trends, machine and process innovations, new applications, sustainability and environment issues and raw material development.
Elmar Witten, managing director of conference organizer AVK – Federation of Reinforced Plastics e.V (Frankfurt, Germany), discussed pultrusion’s relative position in the broader composites marketplace. Of the 8.8 million MT of worldwide composites production volume, he reported, the European share was about 2.3 million MT, based on a survey conducted by JEC Composites (Paris, France) in 2014. Chopped fiber-reinforced thermoplastics accounted for 1.25 million MT and continuous fiber-reinforced thermoset — including pultruded products — made up about 1.04 million MT. Germany is the largest producer, followed by Scandinavia (Finland, Norway, Sweden, Denmark). One hundred companies in Europe produce ~98% of the composite products made in Europe, Witten added, primarily in glass fiber applications for automotive, construction and electrical/electronic sectors. Pultrusion production is growing slowly but steadily in that context, but at this time, the composites market is still dominated by processes that employ sheet molding and bulk molding compounds, followed by by hand layup and sprayup. Carbon fiber composites shows similar gradual growth in automotive and aerospace markets.
European Composites Industry Association (EuCIA)
Although EPTA is not yet a member, more than 10,000 companies and about 150,000 employees that are actively involved in composites production across Europe now have potential support of a European Composites Industry, EuCIA (Brussels, Belgium). EuCIA represents European national composite associations as well as industry specific sector groups.
One of its objectives is involvement in innovative developments for the composites sector—including development of a Life Cycle Aspects tool and a European design standard for pultruded rebar.
EuCIA’s Life Cycle Aspects (LCA) tool for the composites industry
Jaap van der Woude of EuCIA reported on an LCA tool project being embraced by the European composites community. LCA is a web-based eco-calculator that calculates the expected lifecycle, or service life of composite parts and their impact on the environment. A work in progress, it currently considers orthophthalic resins and glass fibers, and various processes that convert fiber and resin to a product. The Web-based calculator leads the user step-by-step through the procedure and will be available at no charge through 2016. It is privacy-protected, and EuCIA does not have access to the data input by a user.
Opportunities for pultruded composite rebar
Status of European design standard. André Weber, R&D director, Schoeck Bauteile GmbH (Baden-Baden, Germany), reported on the status of the rebar standards development effort in Europe. At this time, test procedures for material properties are in progress, as established by the European Technical Assessment (ETA) for regulation of construction projects. Weber said most composite rebar is unidirectional pultruded fiberglass. He noted that the problem with pultruded rebar is not any failure to achieve desired part strength but instead, achieving the bond with the concrete: The ribs on the rebar must be designed for it. Toward that end, Weber recommended a wedge-type angle on the rebar. Fire/heat resistance also is critical. He noted also that the rebar must be bent to go around corners and said that this technology is now available.
International consortium for sustainable concrete. On the same subject of composite rebar, Mikhail Vorobiev, global product manager – thermosets, Owens Corning Composite Solutions Business (Toledo, OH, US), announced the establishment of SEACON — an international project for sustainable concrete, using seawater, salt-contaminated aggregates and non-corrosive reinforcement (i.e., fiberglass composite rebar). SEACON brings members of the fiberglass composites and concrete communities together to combat the chlorides in seawater, along with air and de-icing mixes, that together lead to corrosion in steel rebar. As Earth’s climate change raises ocean levels, the challenge of seawater corrosion is expected to increase, and the need for solutions becomes increasingly critical.
This could be a major market for pultrusion. Projects are planned in Rome and Florida the summer of 2016, to be completed by 2017. OC’s Advantex ECR glass and vinyl ester resins are current leading material candidates.
MACHINE AND PROCESS INNOVATIONS
Pultrusion of curved or variable radii elements
Basic pultrusion is an automated process that continuously produces linear, constant cross-section profiles by pulling dry fibers through a resin chamber, then through a stationary heated die/mold, where the part is cured. The cured part is then pulled through an automated cut-off saw, where it is cut to a preprogrammed length.
Pultrusion is an automated process that eliminates the multi-sequence steps of hand layup, resin wet-out and cure of RTM, VARTM, autoclave and other molding operations. But it has the disadvantage of limited part shape capability. Over the years, pultruders have developed and experimented with innovative variations to overcome this disadvantage, successfully introducing non-linear, off-axis fibers into the part, and attempting to pultrude curved elements and variable radii, non-constant cross-section parts. The earliest curved variant was probably the Pulformer patented and built by W. Brandt Goldsworthy in the early 1980s as a contender for curved composite leaf springs for the automotive industry. Composite leaf springs are used on cars, today, but are mostly built by RTM rather than by curved pultrusion.
Klaus Jansen, general manager for Thomas Technik + Innovation KG, part of Thomas GmbH (Bremerverde, Germany) reported on the company’s efforts in the area of non-linear pultrusion. Jansen says Thomas can produce a constantly curved profile by moving the heated die mold instead of moving the profile through a stationary mold. Curved parts have been produced using polyester, vinyl ester and epoxy thermoset matrices, Jansen says (see first photo on left). Thomas has also developed methods for pultruding variable radii for linear pultrusion, using moving, segmented guide rails and a moving mold. Jansen claimed that the company can modify any pultrusion machine to perform variable radii/linear pultrusion. Future goals include a circular design for a coil spring using a torque drive with curvature control, on either a horizontal or vertical axis, with a rotating or moving guide rail.
PulPress for sandwich profiles
2016 EPTA Innovation Award
Evonik Industries AG (Essen, Germany) is also challenging the constraints of basic pultrusion. Sebastian Bühler of Evonik’s Composites Project House in Marl, Germany, reports on a PulPress variation of pultrusion developed in conjunction with Secar Technologie GmbH (Mürzzuschlag-Hönigsberg, Austria) that uses Rohacell high-temperature, closed-cell foam as a mandrel and sandwich core. Said to be compatible with both thermoplastic and thermoset polyester and epoxy matrices, the system operates with two dies, or presses: the first press heats and cures the sandwich; the second cools the cured part. Bühler maintains the PulPress automated process reduces the cost of sandwich profiles by up to 60% compared to RTM, and reduces cycle times and scrap — a particular advantage for the automotive industry, he notes. Buhler acknowledges a slight weight penalty, but sees this as a minor disadvantage relative to the substantially increased strength and bending stiffness of the PulPress sandwich structure.
Pull braiding and blow molding hollow complex shaped parts
Fraunhofer Institute for Chemical Technology (ICT, Pfinztal, Germany) also is studying the possibility of postforming a pultruded B-stage preform. Fraunhofer’s Renato Bezerra described this variation of basic pultrusion: A two-step curing resin is used with carbon fiber to pultrude a hollow, B-staged part into a blow molding machine where it can be postformed into complex shapes unattainable in standard pultrusion (See final image at left). The two-step resin is Daron isocyanate from Aliancys AG (formerly DSM Composite Resins, Schaffhausen, Switzerland).
Alternative method for fiber impregnation (prepregs)
The University of Stuttgart (Stuttgart, Germany) is developing an alternative method for fiber impregnation of prepreg fibers and tows. Markus Blandi reported the initial motivation was prepreg to build a space car — initially for the Stuttgart Academy of Fine Arts, then looking at the possibility of a space car for a “real car.” The impregnation process begins by winding fiber on a perforated spool. The spool is loaded into a container, and centered on a hollow resin intake tube at the bottom of the container. Early tests show resin flows evenly onto the surface of the fibers. The method achieved high-speed impregnation, and Blandi said it will accommodate all fiber types and a wide range of resin matrices. For pultrusion it is a ready prepreg system where the pultruder can chose its own resin system and fibers, and eliminate the need for a resin impregnation chamber.
In-line coating of pultrusions, graphene nanoplatelets bioepoxies
Nora Lardies reported on two European projects underway at AIMPLAS Plastics Technology Centre (Valencia, Spain). The first is for in-line coating of pultruded composites, called COALINE, using an advanced die design, microwave curing and curved sensors for controlling the degree of cure. Lardies reports that microwave curing of polyester and vinyl ester resins achieves best results when a microwave absorbent (called susceptors) is used (epoxy does not need susceptors). Examples of susceptors noted are metallic charges, organic dipolar additives and inorganic additives transparent to microwaves. The project achieved a profile cured under microwave energy alone and further work is planned to advance the technology.
The other project reported was development of a bioepoxy resin system comprising epoxy resin and commercial graphene nanoplatelets. In trials at the pilot plant level, fiberglass/bioepoxy rebars achieved improved mechanical properties in tensile strength, modulus and elongation, compared to pultruded rebar using polyester resin and bioepoxy with 0.5% graphene.
Miniature thermoplastic pultrusion
Fraunhofer Institute for Production Technology IPT (Aachen, Germany) is developing thermoplastic micro-pultrusion and micro-pullwinding processes for diameters less than 1mm, primarily for applications in medical devices that are used in MRI imaging, where metal materials can distort the image. Alexander Brack, research associate for Fraunhofer IPT, described thermoplastic micro-pultrusion and micro-pullwinding trials in both reactive and non-reactive processes. (Reactive processing achieves polymerization of the polymer directly in the forming tool.)
For reactive pultrusion, Fraunhofer found use of prepolymers for fiber impregnation of thermoplastics improved the results. First trials were performed with PA6 and PA12. Good results were achieved, but the best results were achieved using Elium liquid thermoplastic acrylic resin from Arkema Inc. (Paris, France) and polybutylene terephthalate (PBT).
For non-reactive trials, PA6, PA12 and PEEK were tested, reinforced with carbon fibers. In this category, the processing of fully consolidated thermoplastic prepregs (tapes) achieved the best mechanical properties.
The study concluded that pultrusion with thermoplastic polymers can be miniaturized and the subsequent forming of both pultruded and pullwound micro-profiles is possible (see second photo down, on left).
In-situ pultrusion for lightweight automotive structural part
In-situ pultrusion is one method described for producing reinforced thermoplastic parts. Stefan Epple presented a study by the University of Stuttgart for replacing heavy metal sheets with lightweight sheets of pultruded fiber-reinforced thermoplastic polymer. Fibers cannot be impregnated with thermoplastic resin by pulling the fibers through a resin bath, because the surrounding humidity would disturb the chemical reaction, Epple says. For in-situ pultrusion, the two thermoplastic reactive components are mixed together and injected into a first-stage heated die mold, in a modified resin injection molding (RIM) process. Fiber reinforcements are pulled through the first die and through a second stage of the die, which is temperature-controlled for the process. The “cured” part is then pulled into an automated cutting unit.
Thermoplastic pultrusion of braided tape preforms
Christian Garthaus, scientific assistant, reported on work being done at the Technische Universitat Dresden – ILK (Dresden, Germany) on an “efficient, automatable manufacturing processes for structurally loaded, fiber-reinforced thermoplastic (FRTP) profile structures with integrated metallic load introduction elements.” ILK’s stated goals are 1) cost effective manufacture of load-adapted, high-quality, semi-finished profile structures by pultrusion; 2) develop a modular approach for individual functionalization, according to the application; and 3) to demonstrate the potential of the approach by taking advantage of the thermoformability and weldability of the thermoplastic material.
The process begins with impregnation of the carbon unidirectional tape. These tapes are braided into tape preforms, through an in-line braiding wheel. The braided tape preforms are then pultruded to consolidated profile structures. In the thermoplastic pultrusion process, the material passes through a preforming die, and thence into a heating chamber. Next the still malleable part enters a compaction and forming die, where it is consolidated into final form. And then it is cooled and solidified (cured). Garthaus explains, “The consolidated profiles are locally functionalized with positive-lock functional elements. In the so-called injection forming process the thermoplastic injection molding compound is used to locally mold the thermoplastic pultruded profile around the functional elements.”
Pultrusion of carbon fibers in a thermoplastic resin film process
Lisa Mueller, M.Sc., reported on Faserinstitut Bremen e.V. exploration into the automated, cost-effective pultrusion of carbon profiles using a resin film infusion process. Woven fabric and resin film were layed up and pulled together through a forming press, where the resin film is pressed into the fabric in the through-thickness direction, impregnating the fibers. Adhesion is achieved at room temperature, and increased through contact pressure in the forming press. (A release foil is needed to smooth the pulling force.) The most effective layup comprised two layers of fabric on the top, one layer of fabric on the bottom, and all eight film layers between the fabric layers. This resulted in the resin flowing to the outside of the layup, pushing air out of the laminate. Further trials, analyses and crash tests are planned to continue the exploration.
MATERIALS AND ENVIRONMENT
Biotrickling filtration alternative for control of VOC emissions
Carmen Gabaldon, Department of Chemical Engineering at the University of Valencia (Valencia, Spain), described a new method for operational control of volatile organic emissions (VOCs) from pultrusion processing. Biotrickling filtration uses a filter bed 10-12m high, filled with an inert packing, to filter emissions, releasing the treated air into the atmosphere or to a recirculation tank. A major purpose is to remove styrene emissions, and Exel Composites Plc in Oudenaarde, Belgium, has plans for installing Biotrickling Filtration in its pultrusion facility to explore this approach as a sustainable and cost-efficient alternative for styrene emission control in its pultrusion facilities. Gabaldon reports operating costs are about 25% lower than using a concentrator and catalytic oxidizer for emissions control.
Styrene Classification and labeling update
Casper Albraktsen, Reichhold LLC2 (Research Triangle Park, NC, US) presented an update of regulation trends in Europe for the styrene monomer broadly used in unsaturated polyester resins (UPR) and vinyl ester. While styrene has not yet been listed as one of the Substances of Very High Concern (SVHC), it is listed as a potential endocrine disruptor and styrene occupational exposure limits have been established. Albraktsen does not think use of styrene will be banned — but this is under discussion.
Reichhold is a member of the European UP/VE Resin association: The UPR sector group of the European Chemical Industry Council. Known as Cefic, the Council’s published guidelines for safe handling of styrenated resins are found on the website http://www.upresins.org/safe-handling-guides
Building strength in pultrusion resins
Andreas Horbach, technical service manager for Aliancys AG (Schaffhausen, Switzerland) emphasized a new vision of innovation since its spin-off from DSM Composite Resins. Horbach stressed the importance of low profile additive (LPA) systems in resins for superior shrinkage compensation, especially critical in automotive applications. He said the company is taking the lead in pultrusion resins and looking for input from pultruders. Horbach reported Aliancys’ Daron resins for pultrusion are demonstrating better transverse strength, higher temperature resistance, and improved mechanical strength in flexural and tensile properties and even in interlaminar shear strength, for both glass and carbon fiber profiles.
Basalt fibers for pultrusion
Giorgi Gogoladze of Basal Fibers (Tbilisi, Georgia) discussed the production and advantages of basalt fibers for pultrusion. To form the fibers, basalt stone is crushed and then melted at 1400°C and passed through a bushing. For pultrusion, the fibers receive sizing in two applications: the first as the fibers exit the bushing and are wound onto what is called a spinning cake; the second as they are wound from the spinning cake onto the roving package. Basalt production is said to use the least energy consumption and produce the lowest CO2 emissions compared with not only aluminum and steel but glass and carbon fiber as well. Gogoladze argues that for pultruded rebar, basalt has good resistance to acid and alkali in concrete, as well as corrosion- and UV-resistance. (Concrete tends to eventually degrade glass fiber, he said.) Further, basalt is non-magnetic, non-conductive and non-hygroscopic.
Optimized pultrusion formulations
Gerard Reestman of BYK Chemie GmbH (Wesel, Germany) presented detailed coverage of the advantages for the pultrusion process of various additives into the resin, from air-release additives that act in the resin to reduce air in the mix and the resin bath, to wetting and dispersion (W&D) additives, and processing additives. Reestman listed W&D additives said to help control viscosity of filled systems, improve wet-out of the fibers, and which are designed to prevent the separation of shrink-control additives, among other advantages. Processing additives are designed to improve color, water resistance, surface appearance, bonding and paint adhesion.
Pigments and fillers affecting performance
Ron van der Leeuw, sales manager – thermosets EMEA for Chromaflo Technologies Corp. (Ashtabul, OH, US) reviewed the effect of pigments and fillers on the performance of pultruded parts: “To give a glimpse into the exciting world of color.” Van der Leeuw pointed out that while a colorant is only a minor component in a pultruded part, the effect of the colorant and pigments is significant. Putting 2% colorant in a matrix is a cost-effective way to add not only color, but opacity, UV resistance, resistance to acid, alkali and solvents, and heat resistance.
Similarly, fillers can affect shrinkage and warpage, cost, rheology, density, corrosion and UV resistance, flame/smoke/toxicity ratings and appearance of the part.
Reports from Asia
Growth in China has been consistent in the past 10 years, except for the years of 2009 and 2013, in which expansion slowed due to world economic and other crises, according to a report by James Wang, Jushi Group, a major supplier of fiberglass in China.
D.A. Gajjar, Dhanshree Impex (Gujarat, India), reported on anticipated growth of pultrusion in India and worldwide, with 60% of that growth in industrial applications. Dhanshree is a manufacturer and exporter of various FRP pultruded profiles, including threaded rod and insulating rod for high voltage applications.