Volume 14, Issue 7- September 2013
WPCs Gain Acceptance
Fenestration profiles made of wood fiber-polymer composites (WPCs) continue to make inroads in the marketplace. The trend, driven by cost reductions stemming from volume-sensitive production efficiencies and ongoing improvements in their processing, performance and appearance, follows earlier acceptance for use in shingles, siding and decking components.
WPCs are a blend of one or more of several thermoplastic polymers (e.g., polyethylene blends, high-density polyethylene, polypropylene, polystyrene, styrene copolymers or vinyl) in various proportions along with wood or other natural fibers, particles or flakes. Additional compounding ingredients may include lubricants, stabilizers, modifiers, blowing agents, colorants, pigments, process aids and/or inorganic fillers. The resulting profiles provide the structural integrity and workability of wood along with the durability of a polymer.
1. The polymeric material component resists rot and insects, providing an inherently long product life and requiring minimal routine maintenance;
2. The cellulosic fiber content provides reinforcement, increasing the rigidity of the product, even under elevated temperatures;
3. WPCs can be worked like wood using ordinary tools and fastening techniques;
4. WPCs can be pigmented during processing or painted after installation;
5. WPCs are “green” products capable of virtually 100-percent recycled content.
As with other engineered polymeric materials, composites establish themselves in the marketplace and deliver their benefits only to the extent that their performance can be evaluated objectively and uniformly by specifiers. AAMA consensus standards provide the objective data for such evaluation and form the foundation of a quality assurance system for buyers, specifiers and fabricators of WPC products, as well as a reference point for national code organizations and local code officials. They also form the basis of AAMA certification programs for fenestration profiles.
Among the more recent additions to this family of performance standards—which includes AAMA 303 for PVC profiles, AAMA 304 for acrylonitrile-butadiene-styrene, AAMA 305 for fiberglass, AAMA 308 for cellular PVC, AAMA 310 for reinforced thermoplastic and AAMA 313 for molded aliphatic polyurethane elastomers—are AAMA 309, Standard Specification for Classification of Rigid Thermoplastic/Cellulosic Composite Materials and AAMA 311, Voluntary Specification for Rigid Thermoplastic Cellulosic Composite Fenestration Exterior Profiles. The latter serves as the basis for certification of profiles per the AAMA 109 profile certification program procedural guide.
Originally issued in 2004, AAMA 309 defines a cell classification system, resulting in a nine-digit designation number that defines various ranges of properties: resin type, percent cellulose content, specific gravity, impact resistance, flexural modulus, flexural strength, thermal expansion, temperature at which deflection can occur and percent weight change due to water absorption. Tests are specified that can be used to determine these properties. Lead content must be separately measured per ASTM E1753 and must not exceed 0.02 percent by weight.
The new edition of AAMA 309 adds a test method and performance criteria for solar heat buildup based on ASTM D4803, Standard Test Method for Predicting Heat Buildup in PVC Building Products.
The progress that AAMA’s Wood and Cellulosic Composite Material Council has made in staying ahead of the technological curve is due to the enthusiastic participation both of suppliers and manufacturers involved in the cellulosic composite industry. They serve as positive examples of AAMA’s ongoing document development consensus process.
Dean Lewis serves as educational and technical information manager for the American Architectural Manufacturers Association in Schaumburg, Ill.