Volume 6 Issue 10 November 2005
Meeting the Market Demand
by Larry Livermore
Door and window profiles of wood and cellulosic composites (a.k.a., wood fiber-polymer composites, (WPCs) are beginning to make noticeable inroads in the fenestration profile marketplace. Driven by cost reductions stemming from volume-sensitive production efficiencies and ongoing improvements in their processing, performance and appearance, the trend is following on the heels of earlier and more widespread use in shingles, siding and decking components.
WPCs are made of a blend of one or more polymers (e.g., polyethylene blends [PE], high-density polyethylene [HDPE], polypropylene [PP], polystyrene [PS], styrene copolymers or vinyl [PVC or PVC blends or copolymers]) in various proportions along with wood or other natural fibers, particles or flakes.
Setting the Standard
Architects and specifiers have been putting the AAMA family of performance standards for polymeric profiles to good use for some time. These include AAMA 303-05 for profiles made of PVC, AAMA 304-04 for ABS, AAMA 305-04 for fiberglass, AAMA 308-04 for cellular PVC and AAMA 310-04 for reinforced thermoplastic.
Now, similar performance standards for WPCs join this family to aid in verifying the performance of this latest generation of window and door products. These new standards are:
Voluntary Specification for Rigid Thermoplastic Cellulosic Composite Fenestration Exterior Profiles (AAMA 311-05). This new specification establishes the minimum performance requirements for rigid thermoplastic cellulosic composite exterior profiles used in doors, windows and skylights, including those with decorative finishes such as paint or laminates.
• Dimensional stability. The percentage of shrinkage at an elevated temperature–an excellent indicator of any internal or residual stresses in the profile that may have resulted from the extrusion process);
• Screw withdrawal. Measures the ability of the profile to be held to an adjoining object);
• Thermal cycling. Measures the effect of changes in temperature and humidity on weight and appearance);
• Weatherability. Color retention and impact resistance for varying North American climatic regions);
• Heat-resistance. Resistance to blistering, cracking or delamination due to temperatures up to 284 degrees Fahrenheit);
• Heat build-up. Temperature rise above ambient air temperature caused by absorption of solar energy); and
• Lead content. Cannot exceed the U.S. safety standard of less than 0.02 percent by weight.
ASTM standards and test methods are referenced where applicable. For the purpose of in-process quality control of extrusions, tests for dimensional stability, screw withdrawal, thermal cycling and heat resistance must be conducted on samples selected from each extrusion machine at least every 12 hours.
Performance Requirements for the Lamination of Wood and Cellulosic Composite Profiles (AAMA 312-05). This newly-released standard establishes performance requirements for the lamination of wood and cellulosic composite profiles intended for either interior or exterior use. It sets forth test methods to test for appearance weatherability (ultraviolet color hold), chemical resistance and adhesion of the laminate to the substrate (resistance of adhesives to a 90-degree Fahrenheit peel-off test after prolonged exposure to cyclic laboratory-simulated aging conditions, i.e., extremes of temperature and humidity).
Related specifications issued earlier include the Standard Specification for Classification of Rigid Thermoplastic/Cellulosic Composite Materials (AAMA 309-04).
This document spells out how to construct a nine-digit designation number that defines various ranges of properties: resin type, percentage cellulose content, specific gravity, impact resistance, flexural modulus, flexural strength, thermal expansion, temperature at which deflection can occur and percentage weight change due to water absorption. Tests are specified that can be used to determine these properties. The resulting class designation number is decoded easily by a table in the standard.
Larry Livermore serves as technical standards manager for the American Architectural Manufacturers Association in Schaumburg, Ill. He may be reached at firstname.lastname@example.org.
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