Polyurethane-based composites are making significant commercial advances, as illustrated by new applications in decking and electrical utility poles that were unveiled at the recent Composites 2005 show in Columbus, Ohio, sponsored by the American Composites Manufacturers Association. The first PUR lumber has arrived in decking and fencing, and PUR composites are also cracking the utility pole market, particularly the transmission-pole segment, where typical polyester-based composites have yet to penetrate.
Other news from the show included a new process called Tool-less Engineered Composites, which promises cost savings by using a thermoformed skin as a “mold” and backing it with reinforced composite using a vacuum-bag process. Other developments included a new vinyl ester blend for closed-mold boat manufacturing, innovative computer software to control FRP dispensing, and a new spray gun for highly filled resins.
PUR lumber is a first
A new form of plastic lumber utilizes Baydur PUR system from Bayer MaterialScience. Lifetime Lumber, manufactured by Century Products LLC, Anaheim, Calif., is claimed to be the first PUR lumber manufactured in a continuous process. Fly ash, a waste product from electric utility plants, comprises about 65% of its weight. Fly ash is an inexpensive but highly structured filler that reduces material cost, according to James Mahler, senior v.p. of business development. The fly ash is supplied by Headwaters Resources.
This lumber has a combination of strength, flexibility, and resistance to water absorption that is unlike wood or other competing composite products, according to Mahler. The material’s water absorption is about 0.41%.
Due to the material’s high strength and sag resistance, the 2 x 6 in. PUR lumber can be manufactured for 24-in. joist spans, compared with 16 in. to 18 in. for typical composite products. This results in up to 30% savings in substructure costs, the company claims.
The patent-pending continuous process produces about 1500 linear ft/hr. It consists of a special forming unit with a series of conveyors that apply pressure to create the grain, dimensions, and other physical features.
Lifetime Lumber is primarily available in the western U.S. for decking and fencing. It is available in redwood and gray colors and tongue-and-groove configurations. Pricing is competitive with other plastic lumber at $2.15 to $2.45/ft. Century Products also sees strong promise in fencing.
PUR for utility poles
Another new PUR composite development is fiberglass-reinforced utility poles, an application currently dominated by polyester composites. A new alternative comes from RS Technologies in Calgary, Alberta, which manufactures the RStandard modular composite utility pole using its own Version PUR resins and a patented filament winding process. The RStandard pole, made in lengths up to 135 ft, is the first use of composites for electrical transmission poles, according to RS Technologies. Polyester composites are used mostly for smaller distribution poles. The RStandard pole is also the first two-part, all-PUR system; it competes with a hybrid urethane pole also on the market.
An aromatic version of the Version PUR resin is used in the inner layer of the pole while an aliphatic version is used on the outside of the pole. The outermost aliphatic layer has uv resistance built into the material, thereby eliminating the need for surface veils or coatings and saving labor and material costs. The two-component Version PUR material is 100% solids and is VOC- and HAP-free, according to the company. It is claimed to be stronger and tougher than polyester, vinyl ester, or epoxy and offers a greater strength-to-weight ratio. In addition, proprietary fiber-placement technology reduces the amount of reinforcement to make poles with strength equal to or better than those made with traditional thermosets.
RS Technologies’ patented filament winding system performs zero-degree winds, placing glass reinforcement perfectly in the axial plane of the pole, explains Mark Warren, chief technology officer. Typical filament winding processes can wind at minimum angles of 7° to 8°. Placement of fiberglass and resin reportedly can be optimized to reduce thickness and overall pole weight. RS Technologies developed some of its own machinery. The company has married various features into one production system that can wind one metric ton of material per hour. In most cases, standard mandrels, heaters, and control systems designed for other thermosets can be used without modification.
The modular poles come in 15-ft and 30-ft segments 10 to 15 mm thick, which are tapered and nested together. They are said to offer significant storage, transportation, installation, and maintenance benefits compared with standard one-piece composite poles, while prices are competitive. The company is working on larger transmission poles up to 200 ft long.
Custom thermoformer Plastics Unlimited, Preston, Iowa, sees promise for its process that combines a thermoplastic skin and a thermoset composite backing that is cured in a closed mold. The patent-pending Tool-less Engineered Composite (TEC) process involves placing a thin (typically 0.09-in.) thermoformed skin in a simple holding fixture, where it’s backed with FRP composite using a vacuum-bag system.
Cost reduction is a major advantage because a composite part can be manufactured without the expense of composite tooling, according to Terry Kieffer, president of Plastics Unlimited. Manufacturers can also avoid VOCs with thermoformed skins as a replacement for gel coats. Impact resistance is another benefit, with parts exhibiting notched Izod values up to 18 ft-lb/in.
In its commercial debut, TEC was used to manufacture an air scoop for a John Deere tractor combine. The 0.09-in.-thick thermoformed skin was Spartech’s WeatherPro G, a tri-layer coextrusion of an ABS substrate, a weatherable ASA color layer, and a clear, glossy acrylic cap. The skin is backed with fiberglass mat and a 30% soy-based polyester from Ashland. The resin is poured over the mat before the vacuum bag is laid on top.
For production volumes up to 10,000 parts, TEC can compete with RIM, RTM, and compression molding, according to Kieffer. It is also seen as competitive with thermoforming alone in applications where a high-performance sheet resin may be prohibitively costly. Kieffer says TEC has some similarities to Genmar Holdings’ VEC Shield process which also incorporates a composite back-up of thermoformed skins. However, the VEC Shield closed-mold RTM process uses two tools and is more capital-intensive, claims Kieffer.
Several other applications in marine, medical, agriculture, and recreational vehicles are in development. Kieffer adds that licensing arrangements are possible.
New resins & equipment
In material news, AOC announced a vinyl ester blend for closed-mold manufacturing of marine parts. This HydroPro blend enabled Baja Marine Corp. in Bucyrus, Ohio, to convert to closed molding for its boat hulls and liners, according to Baja v.p. of operations Bill Regan. “This resin gives us the surface appearance and strength we’re looking for in our high-performance boats,” he explains. AOC says Baja Marine is one of the first boat makers in North America to switch from open molding to closed molding. Baja adjusted the material’s cure cycle to suit both its closed-mold processes—resin infusion and its own variation of RTM Lite called FAST (Fiber-reinforced Advanced System Technology).
AOC also introduced a high-heat-resistant vinyl ester called Vipel F086. It has 35% styrene content and an HDT of 330 F. This novolac vinyl ester is aimed at reinforcing thermoplastic liners in dual-laminate applications and for hot chemical environments such as gas pipes and quench vessels.
New open-mold resins from Reichhold included a low-styrene vinyl ester for marine parts and spas. Hydrex 100-LV contains 35% styrene and cures with standard MEKP. It is a direct offset to Ashland’s AME 6000 product, says Reichhold. Targeted uses include skin coating of boats and spas.
Reichhold also unveiled a “universal” polyester resin for bonding to both acrylic and ABS in tub/shower applications. Previously, manufacturers required two separate resin systems. Polylite 33315-00 has 35% styrene content and can take up to 55-60% filler.
In equipment news, a new internal-mix spray-up system with a needle-less design was introduced by GlasCraft. The Formula gun has specially hardened valves and can dispense heavily filled materials at high volume while maintaining an accurate and controlled spray pattern, the company says.
The developmental MAC system from Magnum Venus Products is one of the first computer systems that both monitors and controls a range of process variables in FRP dispensing. The computer software is tied directly to the dispensing equipment and automatically controls output, catalyst flow, material ratio, and mold temperature for open and closed molding. Magnum Venus says manufacturers are demanding stricter control over FRP production due to the rising cost of materials.