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Polyurethane backing improves carpet performance.

Polyurethane backing and cushion has enhanced the durability of carpeting

Traditionally, tufts of carpet fibers have been held in place with a latex backing which bonds the fibers to a woven polypropylene or other synthetic backing. While this system has sufficed for years, new developments using polyurethanes instead of latex improve performance and offer water resistance.

By adopting polyurethane-backed carpet, the industry can offer commercial and even residential carpet users better performance.

Carpet Components

Nylon is the most popular carpet fiber, representing two-thirds of the pile fibers used in the United States, followed by polypropylene, polyester, wool and other, the latter making up only about three percent of the market.

The carpet yarn is tufted through a primary backing, usually made of woven polypropylene, in loops, cut piles or a combination of both textures. The fiber is then bonded to the backing with latex or polyurethane. A secondary backing, usually of woven polypropylene, adds dimensional stability to the carpet and facilitates easy installation and, eventually, removal of the carpet.

How well the carpet fiber is "locked" into the primary backing is a key to the performance and durability of the carpet and an area where polyurethanes' performance clearly surpasses that of latex.

"Tuft bind," as this property is known, is a measure of the force needed to pull a fiber out of the backing. A carpet's tuft bind is important for performance, safety and aesthetic reasons.

Tests conducted on polyurethane-backed carpet produced by Pacificrest Mills using polyurethane chemicals from Bayer Corporation and Arco Chemical Company, have shown an average tuft bind of 20 pounds (ASTM D-1335). Similar latex-backed carpet usually exhibit a tuft bind as much as 25 percent lower.

The delamination strength of polyurethane-backed carpet is another area where it generally outperforms latex-backed carpets. This criteria measures the resistance necessary to separate the secondary backing from the primary backing. Polyurethane-backed carpet styles from Pacificrest Mills' Natural Resource line averages a six-pound delamination strength (ASTM D-3936) which is sustained under wet/dry cycling, unlike latex, which loses its strength.

Edge ravel is another area where the benefits of polyurethane backing is clear. While manufacturers of both latex- and polyurethane-backed carpet suggest installers use a special sealant on the cut edges of the carpet to prevent edge ravel or unravel, the superior tuft bind of a polyurethane-backed carpet gives it superior performance in terms of edge ravel.

Polyurethane pre-coated carpet also significantly reduces pilling an fuzzing.

Water Resistance

In addition to the superior tuft bind and delamination strength, polyurethanes out-perform latex as a carpet backing because they do not dissolve in water, weakening the hold on the carpet fibers.

Water from steam cleaning and other water-based cleaning methods can cause latex-backed carpet to weaken, especially if the carpet is exposed to foot traffic prior to drying. Polyurethane carpet backing, on the other hand, is not affected by a regular maintenance schedule and can endure even a rigorous scrubbing. The Carpet and Rug Institute recommends periodic cleaning every six to 12 months for high-traffic areas to remove accumulated soil not removed by regular vacuuming.

In addition to water resistance, polyurethane-backed carpet exhibits anti-microbial properties and, unlike latex, is mildew and mould resistant.

Carpet Cushion

While approximately 85 percent of carpet applications are direct laminates, carpet cushion can be the key to creating superior performance and is a growing application for commercial markets. Polyurethane cushion is usually selected in residential applications because of the more luxurious feel. A firm, energy-absorbing carpet cushion can also preserve the appearance and extend the life of the carpet by reducing the impact of foot traffic on the yarn.

Polyurethane foam cushion is available for all carpet styles, but only a polyurethane pre-coated backed carpet can offer an integral, chemically-bonded polyurethane foam cushion. In this case, the polyurethane backing and cushion are produced in a single operation, creating a bond between the carpet and cushion that is stronger than possible with a secondary bonding operation. A secondary backing can also be applied to the foam to ease installation and removal.

The Future

While approximately 300 million pounds of polyurethane materials are used as backing and cushion in North American commercial and residential markets, more carpet mills are beginning to offer polyurethane-backed carpet. As consumers, facilities managers and specifiers recognize the benefits of polyurethane-backed carpet, polyurethanes' market share will increase, especially in the high-end installations where durability and performance are critical.

Joyce A. Gaetano, a chemical engineer is the Marketing Manager, Carpet Backing/Froth Foam with Bayer Corporation's Polymer Division, Pittsburgh, PA, has been marketing polyurethanes for 18 years in the furnishings, construction and transportation markets.
COPYRIGHT 1997 Chemical Institute of Canada
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Author:Gaetano, Joyce A.
Publication:Canadian Chemical News
Date:Feb 1, 1997
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