Resins for Directed Long Fiber Thermoplastic (D-LFT)
Long fiber thermoplastic molding is a newer technology where thermoplastic material is directly compounded with long glass fibers (rovings) and then molded in one operation. Polypropylene is the common resin choice for D-LFT, but others such as PET and PBT can be used depending on your desired results.
Injection molding is generally considered faster then most of the thermoset processes. However, it also has many of the drawbacks of a thermoplastic material, including heat instability. Thermoplastics cannot be exposed to final application temperatures that exceed or even come close to their processing temperatures without losing physical property performances. In this case glass reinforcements help, but your product is limited to conditions that do not exceed the molding temperature.
End products feature exceptional mechanical properties because fiber integrity and length are maintained with great consistency. This results in parts that are tough and flexible, with a Tg (glass transition temperature) of 60˚C, similar to other thermoplastic materials.
Directed Long Fiber Thermoplastic (LFT).
Long fiberglass is typical
Special Design Considerations
As with most thermoplastics, the shrink factor is high, compared to most thermoset materials. MFG’s dedicated Design Center can help you design your application to accommodate the shrink of this material. MFG’s Technical Design Guide for FRP Composite Products and Parts provides in-depth information for product designers. You can download it on the bottom of this page.
The term “long fiber” references the length in comparison to glass filled thermoplastics that use 1/8 to 1/4” lengths. The glass in this material is approximately 1.0” in length, and 40% glass by weight is typically used. MFG’s engineering team can tailor this for your product.
Because polypropylene is the lowest cost of the thermoplastics, it is the most common choice for LFT. But others can be used depending on the results you want to achieve.
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