Fiber reinforced plastic

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File:Monsanto House of the Future.jpg

The Monsanto House of the Future (designed by G.H. Dietz,Hamilton and Goody, constructed at Disneyland, Anaheim, Calif.,1957) was built using modular fiber reinforced plastic walls filled with foam insulation. The building was demolished in 1967.

Fiber reinforced plastic (FRP) (also fiber reinforced polymer) encompasses materials like acrylics, vinyls, phenolics, and polyesters that are reinforced with fibers like asbestos, carbon fibers, and glass fibers. Glass fiber with unsaturated polyester resin is the most commonly used building component. Additives like fillers, catalysts, and coloring agents are added to produce rigid materials that have a continuous reinforcement and varying chemical properties.

History

The first visible evidence of fiber reinforced plastic was in 1713. Rene Reaumur presented a “glass cloth” to the Paris Academy of Science. The material proved too thick and weighted for modern use, and remained useless until 1930 when it was refined. In 1938 Owens-Corning Fiberglas began manufacturing fiberglass fabric made of continuous filaments that had been twisted together to create a glass yarn. Berzelius, a Swedish chemist, produced the first polyester in 1847, followed D. Vorlander’s creation of unsaturated resins. In 1926 the General Electric Company first introduced a commercial alkyd resin they called Glyptal. 7 years later, Carleton Ellis received a patent for using polyesters as a reinforced plastic. In 1940, Ellis received another patent for copolymerizing polyester and styrene which created the first moldable resin. Allyl castings soon replaced glass and low-pressure laminating resins were used to manufacture pieces with glass cloth and resin. Reinforced plastics were available before World War II but the techniques and resins available required more heat and pressure that the glass fibers could withstand. With the development of cold low-pressure molding resin, glass fibers could now be used for reinforcement. In 1944 FRP boats were being manufactures by Winner Manufacturing. The Society of Plastic Industry saw the potential for this material and soon developed a low-pressure division (later know as the reinforced plastics division).

Manufacturing Process

There are two distinct processes used to create FRP components. The first process is known as contact molding. Contact molding uses an open mold while machine molding requires a matched mold. The type of process selected depends on the length of the run, the component’s size, and the quality of the surface required. Contact molding is used to fabricate buildings and uses a polyester resin that requires no heat to cure. This process only requires one mold that should have a smooth surface treated with a gel coat that will help release the materials after they cure. This gel may be mixed with a synthetic surfacing material to provide a resin-rich surface and balance the laminate. A fine glass tissue is embedded in the gel coat to prevent the reinforcing fibers extruding through the surface. Once the gel is completely dry, a resin coat is brushed over the top and can be impregnated by hand or with a spray gun. A resin coat is brushed over the gel and a fiber-reinforcing mat is pressed into the mix. The mat is then rolled or pressed into this mix until the mat becomes saturated. More layers can be applied if they are required. They spray up process allows the resin and chopped fibers to be mixed together by the spray gun. Rolling the area is still required so that the laminate may consolidate. Pressure and heat can be applied, though they are not necessary, to speed up the curing process. While the resin is still fresh, molding and trim are added. Machine molding allows for better quality and can also allow a finish on both face surfaces. Sheeting is manufactured in machine molding only. The resin and reinforcement are placed between two release films and rolled in order to remove air bubbles. These sheets then pass through an oven where the material is corrugated and the mixture cured. Plaskon introduced the idea of automatic injection molding in 1946.

Uses and Installation

After World War II, manufacturers saw the opportunity to expand into new markets. Car bodies and boats were built out of this practical material, which developed the FRP products for construction. Corrugated fiber-reinforced translucent sheets were introduced in the late 1940s and soon dominated the construction industry. The sheets were popular because they had a high strength to material content ratio. New techniques for creating stronger or color sheets emerged but few manufacturers could surpass the standard dimensional consistency. Two pioneering products in the 1960s included Sanpan panels produced by Panel Structures and Kalwall panels produced by the Kalwall Corporation. Kalwall was developed by Robert Keller, who became familiar with FRP during World War II. He later developed a light-transmitting building panel that could be used as a large wall when pieced together. This material was self-supporting and ideal for odd shaped ceilings, like the U.S Pavillion at the 1958 World’s Fair in Brussels. This building required 2,000 Kalwall panels that covered 72,000 square feet of floor with a span of 302 feet. These panels consisted of two sheet of reinforced plastic sheeting bonded to a non rigid polysulfide to an interlocking aluminum grid. Fiber reinforced plastics were used extensively throughout the 1950s and 1960s because of it plasticity and moldability. They were created in sheet forms and developed with a concentration on structural applications. A variety of prototype houses and buildings defined the plastic’s potential for construction. Sandwich panels’ popularity rose during the war as they were being used for covers on radar equipment. Acorn Houses produced the first building with sandwich panels for the radar research laboratory at the Massachusetts Institute of Technology. The building was covered with a honeycomb paper core that was sandwiched between skins of clear polyester reinforced with glass cloth. Shell structures were also important for FRP’s development, applying the rigidity of the curved plate or folded plate forms. Folded plate forms are composed of a series of triangular folds that achieve stiffening with thin sheet material. Albert G. H. Dietz recognized that the use of FRP could solve design problems that would otherwise be unsolvable. In 1959, Dietz created a shelter using 90 parasol shells for the American National Exhibition in Moscow. The tulip form had reinforcement at the edges and ribs. Each tulip was made of six petals and supported on a central column. In 1964, the New York World’s Fair saw the use of FRP for several pavilion enclosures, most using sandwich style construction. The Monsanto House of the future (Hamilton and Goody) greatly influenced this style. The house was built at Disneyland and used plastics as the main building materials, rather than as substitutes. The building had a simple cross supported on a central core which allowed for only two types of FRP floor and roof section. The house was extremely popular until its time of demolition. FRP is popular as cladding for buildings as well as for prefabrication of complete rooms or houses. FRP was also popular in gutters and flashings, roof lights, and plastic forms for concrete. The quality of FRP depended heavily on how effective the joints are. FRP is known for extreme expansion and joints should be capable of moving to cause less stresses. Often, other materials were used to cover the joints of the FRP to compensate for the expansion and permitting movement. FRP standards were developed in the 1950s. Without performance information on fire resistance, this material could not be put in walls or roofs under some building codes. A special gel coat was developed to provide necessary performance requirements.

Conservation

It is difficult but not impossible to repair FRP, a characteristic that most plastics lack. Matching the materials or the finish can be especially difficult because different degrees of transparency occur in translucent FRP.

Deterioration

Principal forms of polymer breakdown are bio-, photo-, atmospheric, and hydrolytic degradation. Water, humidity, mechanical damage and manufacturing defects are common causes of deterioration. Ultraviolet lights can cause yellow, which can be delayed by an inhibiting coating that absorbs the energy from the ultraviolet light source. Heavy dirt deposits prove to last longer than clean sheets because the dirt helps to block out the sun. Wicking of water along the glass fibers can cause whitening by attacking the resin-fiber. A gel coat can usually inhibit the deterioration but may not meet fire-resistance requirements. Wicking can also take place through spots of impact damage that occurs before or after installation. It allows organic growth and erosion of the reinforcements. Erosion will appear in colored panels as dark lines but in translucent panels is obvious by light diffraction that will appear as a bloom that obscures light transmission. Sandwich panel construction relies heavily on the core and the facing material. Trapped air can be difficult to remove in the manufacturing process and can cause expansion when warmed. These expansions can cause a rippling effect on the surface. Differential movement happens between the outer skin and the insulating core; panel flexing can also produce issues in small corrugations caused by differential movement between the resin and fiber face. FRP failures in components can be caused by manufacturing defects in the design or installation. Scratching is a main cause of erosion and occurs by a flawed installation. The environment can also have a significant effect on the mechanical performance. Failure from cracking can occur with a few hours when the material is placed under stressed when installed.

Conservation Techniques

Fiber reinforced plastic can usually be cleaned with a soapy water mixtures. This should remove most dirt build-up and biological growth. Rinsing with water every four to five years is recommended to remove loose dirt and build-up. Abrasive cleaners can be used but may damage the gel coat. It is best to remove dirt build-up with a rubbing compound. Acetone is capable of removing polishes but should be applied with caution. Graffiti is easy to remove from newer FRP installations, applying a solvent with a cotton swab and wiping the cleaner off after a short period of time should remove most graffiti. Translucent areas can be polished with nonabrasive window cleaners but testing is strongly recommended. Minor cosmetic damage should first be cleaned with a solvent. Then, a tapered edge is formed along the damaged area and sanding to remove any coatings slightly beyond the damaged area. A resin filler is applied and then cured, sanded, and smoothed. Structural damage may require backing strips and thicker laminated around the area. Holes can be repaired by cutting out the damaged area and washing the adjacent area with methyl ethylketone. Then, adding a new FRP section is possible with proprietary adhesives. Self-colored and transparent laminates host a significant range of other problems. Repairs are usually visible unless the entire panel is replaced. Some coatings can be applied in attempt to match the color but may prove more troublesome than the replacement itself. Contacting the manufacturer may be required for proper repair of these pieces.

Replacement

Small replacements may be impossible because of the price. Custom replacements for buildings can be produced with hand or spray lay-in molds. Color matching proves most difficult in replacement, however.

References

• Walker, Anthony J.T. "Fiber Reinforced Plastic." Twentieth-century Building Materials: History and Conservation. By Thomas C. Jester. New York: McGraw-Hill, 1995. 142-47. Print.