August 2005

Volume 6 Issue 7 August 2005

WPC: Wood, Plastic Composites & Wise Plausible Choice
by Bill Thornton

Wood Plastic Composites (WPC) are beginning to appear in a growing number of fenestration product components. WPCs are made from a blend of wood (cellulosic) or natural fibers and various types of plastic polymers, such as high density polyethylene, polypropylene, polystyrene, styrene copolymers and vinyl and vinyl blends.

Performance Benefits
Manufacturers formulations are usually proprietary, but on average yield superior performing fenestration products offering an assortment of benefits to the manufacturer, fabricator and the consumer. These include:

• Resistance to rot and insects provides a long product life cycle, thus reducing warranty issues due to failures from rot or insect infestation dramatically.
• The ability to use the profiles without special tools or skills.
• The ability to be colored through and embossed to match other competitive materials, providing rich, beautiful wood looking textures.
• The ability to be labeled “green.” Some WPC manufacturers processes utilize virtually 100-percent recycled content from post consumer polymeric waste and wood fiber scrap from large wood processors such as furniture or window producers.

Close tolerance “fit and function” component parts required for use in fenestration component parts. Some manufacturers have the technical expertise to extrude complex shapes with tolerance as close as +/- .015. Others produce “blanks” and then run these through typical wood molding machinery to achieve a specified shape to tolerance.

In 2002, the WPC industry began to develop performance standards and specifications utilizing protocols established within the American Architectural Manufacturers Association (AAMA). Ultimately, this formed the foundation of a quality assurance system for buyers, specifiers and fabricators, as well as a reference point for code organizations and code officials concerned about the performance of fenestration products.

These objectives have borne significant achievements over the past several years. For example, AAMA 309-04, Standard Specification for Classification of Rigid Thermoplastic/Cellulosic Composite Materials establishes minimum requirements for the structural performance, physical requirements, weight and dimensional requirements for profiles made of WPC. This standard spells out how to construct a nine-digit designation number that defines various ranges of properties such as: resin type, percentage of cellulosic 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. Various tests are specified that can be used to determine these properties. The resulting class designation number can be decoded easily using a table in the AAMA 309-04 Standard.

New Standards Set the Stage
AAMA’s new Voluntary Specification for Rigid Thermoplastic Cellulosic Composite Fenestration Exterior Profiles is expected this year. This new standard establishes the minimum requirements for dimensional stability, screw withdrawal, thermal cycling, weatherability, heat resistance, heat build up, and lead content of rigid thermoplastic cellulosic profiles used in windows, doors and skylights.

Also scheduled for release in the fall of this year is AAMA’s Performance Requirements for the Lamination of Wood and Cellulosic Composite Profiles. This new standard will set the performance requirements for laminations when tested per the procedures outlined in AAMA 307. It establishes acceptable levels of weatherability and appearance of laminations on either interior or exterior surfaces of a profile over a period of many years.

With regard to UV weathering performance, for example, the laminate must meet the same guideline as those for integral color PVC profiles as specified in AAMA 303 and ASTM D4726. There must be no more than 10DE units color change after 2000 hours accelerated test for exterior surfaces. The Standard also references a 90-degree angle peel-off test method for determining the level of adhesion for the laminate to the substrate when subjected to simulated cyclic weatherability conditions. Exterior peel adhesion test are at low temperature and high temperature and after water immersion per ASTM D1183-96.

Architects, specifiers and those fenestration manufacturers interested in stipulating the composition and verifying the performance of the latest generation of WPC window and door profiles, as well as comparing their properties and performance to those of others, will find these new AAMA standards of high interest. Code referencing and product inclusion in manufactured goods certification programs should not be far behind.

Bill Thornton is president and CEO of Integrated Composite Technologies Inc. Thornton also serves as the first vice president of AAMA’s wood and cellulosic composite materials council.