Choosing the right thermoplastic Part 4 - Ultimate Performing Long Fiber

Welcome to part 4 in our series on plastic compounding. Our friends over at RTP Company have written a white paper to answer the question "“How do I choose the correct thermoplastic composite to meet the application?”". They have broken it down as follows:

1) Resin Morphology
2) Cost Comparison
3) Temperature Resistance
4) Property Enhancement Using Aspect Ratio
5) Ultimate Performing Long Fiber

Today's blog post is on Ultimate Performing Long Fiber.

The preceding physical property data indicates that the aspect ratio of the additive has a direct correlation to the strength, modulus, and heat distortion properties, and possibly the impact resistance of the composite. To maximize the performance of the composite, one should maximize the aspect ratio of the reinforcement fiber. To do this, you could minimize the fiber diameter and/or maximize the fiber length, which is the logic behind the long fiber composites. Long fiber composites are manufactured by a pultrusion process where a fiber roving is pulled through a die in which the base resin is forced to impregnate the individual fibers in the roving. The impregnated fiber rovings are pulled out of the die and into a pelletizer that cuts the strands into pellets. The fiber length in the pellets will be the same as the pellet length, which for most materials is 1/2 inch. If a 17 micron diameter fiber is used, this would result in a fiber aspect ratio of about 750 for a long fiber composite, which is about 10 times larger than that of chopped fiber compounds typically produced via the extrusion compounding process.

Prior to long fiber compounds, if one was looking to improve the impact resistance of a chopped fiber composite, the typical approach would be to add a rubber based impact modifier. This would improve the toughness of the material but would reduce the strength, modulus, and heat distortion of the composite. The effect of having an
extremely high aspect ratio fiber in long fiber composites has been the improvement of all the physical properties, which is depicted in this spider chart for 40% glass fiber nylon materials.

By having the ultimate in strength, modulus, impact, and heat distortion, long fiber composites have become the choice for demanding applications, such as replacing metal in load bearing applications. The high aspect ratio in the long fiber composites also allows these materials to have excellent creep resistance.

Well that concludes this series. Thanks to Kirk Fratzke and author Steve Maki of RTP for contributing this information.


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