Long-Fiber Thermoplastics Are Hot
One hot growth area for thermoplastics in the next few years will be long fiber thermoplastics (LFT) as a metal replacement. They feature continuous fiber filaments running the full length of a plastic pellet, boosting strength, stiffness, and impact resistance over a wide temperature range. Pellet lengths can typically be specified in a 6 to 12 mm range while the fiber length in short fiber pellets is typically less than 1 mm.
One of the major suppliers is specialty compounder RTP Co. of Winona, MN, which uses a pultrusion process to manufacture LFT. In pultrusion, continuous fiber rovings are pulled through a polymer melt in a specialized die. The resulting composite strands are cooled and chopped into pellets. Loading levels are typically in the range of 40 to 50 percent. Glass fiber is the most popular reinforcement for cost reasons, but other materials provide different properties. Aramid fiber is used for wear requirements, while stainless steel fiber provides electrostatic dissipation (ESD) and electromagnetic interference (EMI) shielding properties. Carbon fiber provides additional benefits in flexural modulus while also providing ESD properties, according to RTP, which has an excellent FAQ on LFT.
Among recent news, Celanese Corp. announced the acquisition of the long-fiber reinforced thermoplastics business of FACT GmbH (Future Advanced Composites Technology) of Kaiserslautern, Germany, a business unit of The Ravago Group.
At last June’s National Plastics Exposition in Chicago, several LFT technocgies were on display. PolyOne Corp. launched the OnForce LFT compounds, which are optimized for surface finish, stiffness, and toughness. SABIC Innovative Plastics (LNP) showed its StaMax long-glass PP compounds for automotive applications. Several other companies also supply LFT, which is expected to grow at the rate of more than 20 per cent a year when economic conditions improve. The dominant matrix resins are polypropylene and nylon, although others are also widely used.
Photo:PolyOne
Ben Harrison, Kaysun Corporation commented:
As a designer and manufacturer of advanced plastics products and assemblies, Kaysun Corporation can also confirm that many of our customers are using LFTs for an increasing number and variety of applications – including metal replacement.
We also thought it might be helpful to share a few lessons we’ve learned along the way – since many of the manufacturing techniques and processes used for traditional plastics can damage the fibers in LFTs and reduce their strength, stiffness, and impact resistance.
To maintain the integrity of LFTs, manufacturers need to:
• use the right screw and barrel
• control the “charging” phase with optimal back pressures and screw RPMs in the plastic melting process
• pay attention to the runner and gate system so it is flowing freely and smooth
• use profile injection if needed to slow flow around high-shear areas
In addition, we’ve found that crystalline resins with long fibers are prone to warp, so tooling adjustments may be required to compensate.
Great blog, Doug!
Ben Harrison, CEO, Kaysun Corporation
