Phenolic pultrusion technology now available for license.

Phenolic Pultrusion Technology Now Available for License

Pultrusion processing technology for recently introduced phenolic resins is now being made available to processors on a license basis. Several major pultrusion processors are exploring the technology, or trying to develop their own versions of it, in an effort to exploit what is expected to be a large market for flame-resistant building materials made from pultruded glass-reinforced phenolics. There's also interest from the aero-space sector in these new resins (see PT, March '89, p. 58).

Composite panels 16 in. wide pultruded from Plastics Engineering Co.'s Plenco 11956 phenolic resin were part of a joint display at the recent SPI Composites Institute conference in Dallas by Weyerhaeuser Co., the Tacoma, Wash.-based building-materials giant that sponsored and is patenting the process technology, and American Composite Technology (ACT) Inc. of Boston, which developed the process for Weyerhaeuser and is its first licensee.

ACT developed a custom-made system using an electrically heated die with resin injection chamber, plus ultra-sensitive pressure, speed and temperature controls. The injection-type die reportedly permits balanced infeed of resin and eliminates the recirculation of resin from a wet-bath impregnation station, which can lead to resin contamination. The pultruder used in the test program was built by Norway's Nordic Supply, and steel dies up to 2 ft wide were produced by Nordic Supply, Plenco, and ACT. The dies were specially designed to prevent distortion from differential expansion and shrinkage of the panels.

According to ACT president Johan D. Koppernaes, test panels were pultruded at a resin-injection pressure range of 20-60 psi, depending on material viscosity and pulling speed. It was not necessary to preheat the resin, which was cured at about 356 F, but the glass reinforcement was preheated to eliminate moisture and vacuumed to remove any contaminants.

NO ACID CATALYST NEEDED

The breakthrough in the process development was the introduction of the Plenco resin, which, unlike most phenolics, does not require an acid catalyst, eliminating the need for corrosion-resistant processing equipment. Most important, the moisture, volatile content and reactivity of the high-solids (81-86% after 3 hr at 275 F) phenolic were optimized to allow production of high-strength pultrusions with minimum void content (condensation reactions have been minimized). At 77 F, the 11956 resin has a viscosity of 7000-9000 cp (which drops dramatically as the material is heated), specific gravity of 1.119-1.170, moisture content of less than 2%, free formaldehyde content of 1-2%, and pH of 7.2-7.8 (essentially neutral). The material has a shelf life of about 30-60 days when stored below 70 F.

"We tried all sorts of resins from Europe, using all sorts of curing agents and additives, but they wore out the die. We had to find something that could make a million pieces without damaging the die, and was not corrosive, so you could fasten or glue to it," Koppernaes told PLASTICS TECHNOLOGY.

The proprietary process reportedly can accommodate 70% glass loadings. "It works just as easily on polyester," Koppernaes says.

In tests on cross-sections of 1.25-in. x 0.25-in. bars of pultruded phenolic or polyester reinforced with about 70% glass roving, the phenolic composite showed an interlaminar shear strength of 6060 psi vs. 5090 for the polyester, a flexural modulus of 5.07 million psi (vs. 5.10), and a flexural strength of 93,200 psi (vs. 93,300). In addition to smoke and flame resistance that's said to be far superior to polyester's (see photos), tests showed that phenolic panels have about twice the abrasion resistance of polyester.

Weyerhaeuser originally began the development program to pultrude wood fiber, then turned to phenolics as its interest in flame-resistant materials grew (the company was already considering a move into reinforced plastics). However, Weyerhaeuser has decided not to make pultruded products itself using the proprietary method, according to Charlotte Taylor, the company's manager of technology licensing. Taylor says several processors have expressed an interest in the technology, and Plenco has agreed to supply 11956 resin (patent applied for) to any licensee. Potential products include gratings, railings, cladding materials, ship housings, fire doors, and other building materials. At the conference in Dallas, representatives of pultrusion leader MMFG, Bristol, Va., held discussions with Weyerhaeuser concerning a potential license, according to informed sources. (CIRCLE 96)

OTHER STILL EXPERIMENTING

Pultrusion Technology Inc., Twinsburg, Ohio, a recently acquired subsidiary of MMFG, has been experimenting with pultruded phenolics with "moderate" success, according to general manager Jeff Martin. Martin says voids, primarily from water generated in the reaction, are a problem. Also, the surface finish of the material can be dictated by the style of reinforcement material used.

"We found we had to put a fine-fiber mat, or even a roving, right at the surface to prevent a very porous surface from developing. From a technical standpoint, that could be limiting. If you have to put roving at the surface, there are some applications where it might not be the laminate construction you would choose to meet physical property requirements," Martin says.

Dexter Corp.'s Pultrusions Div., Aurora, Ohio, currently is working with a proprietary phenolic system, according to David T. Balazek, v.p. for materials and process development. Dexter expects to pultrude some test panels in the next few months, he says.

"One of the biggest hurdless is evacuating the extreme condensation, which hurts both physical and mechanical quality because of void content. Another is making sure we get glass binders that are compatible with the phenolic resin," Balazek says. Dexter is working with Certain Teed Corp., Valley Forge, Pa., on glass binder development.

PHOTO : Burn tests conducted by Weyerhaeuser show the flame-retardant capability of phenolics. Polyester panel (left) is engulfed in flames after being exposed to heat source for 2 min; plywood (top, right) caught fire after 5 min; phenolic (bottom, right) only exhibited charring after 64 min. Weyershaeuser is patenting technology for pultruded phenolics.