LFTs | technology
Demand for long fi bre thermoplastics (LFTs) continues to grow as the materials displace both metal and more costly polymer in a range of applications, writes Peter Mapleston
LFTs: the lightweight alternative
The strong growth in use of long fi bre reinforced thermoplastics (LFTs) continues as an increasing number of specifi ers appreciate their ability to combine high strength with low weight. These injection mouldable compounds - mostly, but not exclusively, based on polypropylene - fi nd their way into a whole raft of demanding applications that would otherwise require the use of either metals or short fi bre-reinforced compounds based on much more expensive matrix resins. This article looks at the technologies used to make LFTs, reviewing the roots of these technologies as well as looking forward to some emerging production options. In the early days there were essentially just two ways
to make LFTs. One was a melt impregnation process sharing some similarities to thermoset composite pultrusion technology; the other was derived from wire coating technology. The former was considered best for quality as it provided optimal wetting of the individual fi bres, while the latter was best for quantity as lines could be run faster. What linked the two processes was that material coming out of the die head contained continuous fi bres running parallel with the fl ow direction. The continuous product was then pelletized and it is this stage that determined the maximum fi bre length in the LFT. LFT pellets are typically around 10-13 mm long and can be processed on regular injection moulding
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machines (although modifi cations may be required to the screw and nozzle to reduce fi bre degradation). Some types may measure 25 mm or longer. Although these latter grades are not ideal for injection moulding they are well suited to stamping processes. While the fi rst LFTs were compounds of glass fi bres
and polyamides, today polypropylene is by far the most popular polymer. Over the years, both processes have been refi ned, variants have come along – some of which add the fi bres well before the die head to yield more variation in fi bre length and orientation in the pellets – and new polymer/fi bre combinations have been developed. The range of applications has also grown considerably and, although growth has not matched some of the earliest predictions, this is proving to be a vibrant market. The global LFT market is estimated at upwards of
350,000 tonnes (not including LFT-D that are converted in-line into fi nished parts) and over the last decade or so has been growing on average at around 12%/yr. In a 2014 report on polypropylene-based LFTs, Compound- ing World parent company Applied Market Information predicted future growth would be around 8% annually, but suggested that overall growth could accelerate with the introduction of new materials, as automotive OEMs continue with their lightweighting strategies, and as adoption of LFT technology increases in Asia.
May 2016 | COMPOUNDING WORLD 29
Main image: LFTs present an alternative to metals and other more
costly engi- neering
compounds in applications requiring high
strength at low weight
PHOTO: PLASTICOMP
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