Stemergy: Renewable Fibre Technology

Spunlaced Flax: New Possibilities For Eco-Friendly Composites

1 August 2010

By Janet Bealer Rodie, Managing Editor: Textile World

Norafin GmbH -- a Switzerland-based developer and manufacturer of durable spunlaced, needlepunched and composite nonwoven fabrics for applications such as apparel, automotive, filtration, industrial, medical, roofing and other applications -- has begun developing spunlaced and spunlaced composite roll goods for applications including roofing, automotive, packaging, sports equipment and filtration. The company sees flax fiber as an environmentally responsible alternative to glass and other high-tech fibers typically used for those applications, and the spunlace process offers advantages over needlepunching, which also is used to process flax for certain applications. Flax offers other advantages as well, according to Stuart Smith, business unit manager, Norafin (Americas) Inc., Hendersonville, N.C.

"Flax and other natural fibers have the potential to address both our short-term and future needs with respect to environmental considerations," Smith said during a presentation at the Techtextil North America Symposium earlier this year in Atlanta. In addition to natural fibers being renewable and biodegradable, he added, "on average, the production of natural fiber suitable for composites is about 60-percent lower in energy consumption than the manufacture of commonly used glass fiber." He also noted that natural fibers produce no more carbon dioxide when incinerated than they consume while growing.

Compared with other natural fibers, flax offers advantages in terms of its cultivation, as it requires no special soil conditions or pesticides, and also needs less water. In terms of performance characteristics, it offers better tensile strength and modulus, and lower elongation -- ranging between that of glass and aramid fibers. In addition to good tensile strength -- though lower than that of glass, aramid or carbon fibers -- and elongation properties, flax's other potential advantages for composite use include vibration absorption, ultraviolet (UV) resistance, moisture retention, low density, no static charge, low relative cost, a natural resistance to insects and bacteria, and hypoallergenic properties.

In addition, compared with glass fiber, flax is less abrasive to processing equipment, and it does not present the occupational safety and health hazards associated with glass fiber.

At the same time, Smith said, there are some drawbacks to using flax, and it is important to consider all factors in determining its optimal uses. For example, it is not inherently fire-resistant (FR), nor as durable as high-performance man-made fibers, although it can be treated to provide these properties; and its moisture-retaining and -absorbing properties can be a disadvantage with regard to the choice and application of resins as well as the dimensional stability of the composite. Irregular fiber dimensions and relatively short length also may pose problems, but they may be mitigated by process adjustments. Thermal stability becomes an issue at temperatures higher than 180°C, and fiber quality and price may fluctuate based on climactic conditions during the growing season.

For flax processing, spunlacing offers certain advantages over needlepunching. "Needlepunching is more mechanical, and the needles can break the fiber, whereas the water jets used in spunlacing are more gentle to the fiber," Smith explained. Norafin has configured its spunlace line in such a way that, in one production step, it can produce multi-layered constructions that may comprise different fibers, blends and constructions in each layer. Spunlacing is a cost-effective process that also yields improved web uniformity and homogeneity; allows fibers to be split to improve coverage and strength; and enables production of 3-D, apertured or custom patterned constructions. And the flax fiber itself has pectin, which causes the fiber to stiffen during the spunlace process. Smith said Norafin is working to optimize the process to handle the irregular fiber dimensions, but it also is necessary to cooperate with the fiber producers to ensure availability of the best flax grades for processing.

One spunlaced flax product already commercially available is Flaxline, a durable, hard-wearing, tear-resistant roofing membrane that is offered in Europe by France-based Soprema, a manufacturer of waterproofing membranes for various construction applications. Flaxline comprises flax fiber spunlaced with a scrim of recycled glass. The material has been tested for waterproofness according to the European standard EN 13111, and its vapor permeability is reported to exceed that of conventional roofing membranes available in Europe. In this application, the fiber's UV-resistant and anti-slip attributes contribute to its performance, as do its insect and bacteria resistance and light weight.

Other non-composite applications include biodegradable bags and covers, for which moisture absorption is a desirable property; and sunshades and sunscreens, for which flax's UV resistance and natural appearance are attractive.

Automotive applications, in particular, offer opportunities for the development of spunlaced flax composite products. Compared with glass fiber, flax has significantly lower density, Smith said, thereby enabling a lighter-weight composite that offers comparable performance. "This is key for the automotive industry, where it is used for sound absorption, strengthening and structural reinforcement," he noted. "A lot of flax is already used in automotive products, but it's needlepunched."

Smith added that the uniform strength and elongation of the spunlaced web enhances its moldability, and particular properties can be engineered into the product.

There also are potential composite applications in sports equipment. As a reinforcement layer in tennis racquets, spunlaced flax is lightweight and absorbs vibrations, and the surface patterning possibilities could be of interest. The fiber's UV resistance and natural wood-like appearance make it attractive as a construction material for boats and canoes.

Other possibilities include reinforcement in foot bridges, for which flax offers lightweight strength and a natural appearance; and in wind turbine blades, again because it is lightweight.

As part of its development efforts, Norafin also is exploring solutions to make the composite material 100-percent biodegradable. For such a material, a natural resin, such as a starch, would be used as a binder.

Source: http://www.textileworld.com/

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