Plastic lumber makers move to standardize testing.

The first of several pending industry standards on plastic lumber has just been approved by the American Society for Testing and Materials (ASTM) in Philadelphia. The three-year old Plastics Lumber Trade Association (PLTA), based in Akron, Ohio, has been working with ASTM to develop nationally recognized test methods that will help establish a benchmark for minimum performance of plastic lumber. Four more standards are currently in the advanced development stages and awaiting a final ballot by ASTM.

Ten or eleven years ago, plastic "lumber" molded or extruded from recycled plastics gained an unsavory reputation as an unreliable performer. Manufacturers admit that use of a wide variety of recycled feedstocks to make plastic lumber with no standard specifications - or even test methods - led to inconsistent product performance. This hampered the acceptance of plastic lumber among civil engineers and city planners for use in structural applications such as decks, boardwalks, and sea walls.

Today, plastic lumber shows signs of growing maturity and acceptance in the market. Close to 60 North American manufacturers produced about 16 million board feet of plastic lumber in 1995. Those manufacturers agree that industry standards will help greatly to establish a foundation for continued growth.

FIRST STANDARD ARRIVES

In April, the first of five testing standards received ASTM approval and an official designation. A question of terminology must be resolved before the other four test methods are approved by the ASTM's Committee of Standards, the last stop before approval, says Kathie Morgan, manager of the ASTM D20 committee developing the test methods for plastic lumber. That question should be resolved by the next ASTM meeting in July, says Dr. Prabhat Krishnaswamy, senior researcher at Battelle, a Columbus, Ohio, consulting and research firm that helped create the tests.

"We need individual test methods for plastic lumber because the product is not made from a homogeneous plastic matrix. Some people test it using a wood or plastic standard, but a part of its strength comes from the skin layer, and a part comes from the outer structure, and then there is an inner core that is foamed or blown," says Malcolm G. McLaren, president of plastics consulting firm MG McLaren, P.C., Consulting Engineers in West Nyack, N.Y. Krishnaswamy says the heterogeneous structure of plastic lumber is why standard ASTM test methods - based on molded "dog-bone" samples or ones cut from fairly thin sheet - do not apply.

Up to now, plastic lumber producers have tested their products as they see fit. Now the materials can be tested in a uniform and accepted way that will give specifiers more confidence in their performance properties. "Test methods for flexural and compression properties will be key in the design parameters of plastic lumber in structural applications," says Krishnaswamy.

The "Test Method for Mechanical Fasteners in Plastic Lumber and Shapes" is the first approved standard, designated ASTM D6117-97. It pertains to pull-out resistance of objects like nails from the product. Still awaiting approval are four more testing standards:

* D6108, "Test Method for Compressive Properties of Plastics Lumber and Shapes."

* D6109, "Test Method for Flexural Properties of Unreinforced and Reinforced Plastic Lumber."

* D6111, "Test Method for Bulk Density and Specific Gravity of Plastic Lumber and Shapes by Displacement."

* D6112, "Test Method for Compressive and Flexural Creep and Creep Rupture of Plastic Lumber and Shapes."

MOVING TOWARD PERFORMANCE STANDARDS

The testing standards only recommend types of test equipment and methods of conducting and recording test procedures. The next step will be to use the tests to establish guidelines for minimum performance levels of plastic lumber - such as those that exist for plastic pipe, for instance.

Battelle has started work on a program in collaboration with the PLTA to evaluate the properties of various types of plastic lumber in order to establish a baseline property profile. So far, five lumber makers have sent products to be tested.

Establishing performance standards for outdoor residential decking boards - such as shear properties, weathering, hygrothermal cycling, and mechanical-fastener pull-out - is one of the top goals, says Krishnaswamy.

Consultant McLaren expects the PLTA to develop a chart listing recommended minimum physical properties for plastic lumber used in decking. The three-year Battelle/PLTA project will also create an information database of materials, properties, applications, and design guidelines.