Unfilled polypropylene has rather low impact and stiffness. As a result, polypropylene materials are often modified to improve their mechanical properties. To improve stiffness the polypropylene can be compounded with short glass fiber (SGF-PP) or long glass fiber (LGF-PP). Key benefits of glass reinforced polypropylene compounds include significant increase in tensile, flexural, and heat performance.
SGF-PP is produced on co-rotating twin screw extruders. The combination of specially sized short glass fibers, the PP matrix and the chemical coupling define the final material properties.
LGF-PP is produced by pultrusion to achieve increased fiber length in both pellets and final parts. The glass fibers are typically arranged in a parallel manner in the pellets, with each having the same length as the pellet itself.
Important application properties of the long fiber reinforced thermoplastics compared with the corresponding short fiber reinforced materials are:
- Markedly higher mechanical properties
- Higher notched impact strength
- Reduced creep tendency
- Very good stability at elevated temperatures in humid conditions
Property comparisons of General Purpose PP, SGF-PP, and LGF-PP:
|Polypropylene||General Purpose||40% SGF-PP||40% LGF-PP|
|Tensile Strength||4,700 psi (32 MPa)||13,000 psi (90 MPa)||17,500 psi (121 MPa)|
|Flexural Modulus||200,000 psi (1,400 MPa)||1,000,000 psi (6,900 MPa)||1,200,000 psi (8,300 MPa)|
|Notched Izod Impact||1 ft-lb/in (53 J/m)||2 ft-lb/in (107 J/m)||5 ft-lb/in (267 J/m)|
|HDT @ 264 psi (HDT @ 1.8 MPa)||120°F (49°C)||285°F (141°C)||315°F (158°C)|