Meaning
Composite materials composed of thermoplastic polymer matrices embedded with discontinuous glass fibers having lengths typically below one millimeter offer a balance of stiffness, strength and melt processability. Engineers specify short glass fiber reinforced thermoplastics to produce structural components that require higher dimensional stability than unfilled resins can provide. These materials flow easily through standard injection moulding equipment, making them suitable for complex geometries.
High shear forces during compounding and moulding set the final fiber length distribution.
Processing Behavior
Melt viscosity increases when glass fibers are added to the polymer matrix. Processing short glass fiber reinforced thermoplastics demands higher injection pressures and melt temperatures to prevent premature freezing in thin walls. These elevated temperatures can degrade the polymer matrix if residence times are too long.
Anisotropic Performance
Flow patterns during mold filling align the discontinuous fibers along the flow directions, creating directionally dependent mechanical properties. This alignment results in low thermal expansion along the flow path but high expansion across it, which can cause part warpage. Optimizing the gate location minimizes these differential shrinkage effects.
Recycle Economics
Mechanical recycling reduces the average fiber length through the regrinding process, leading to a loss of reinforcing efficiency. Blending virgin resin with regrind helps maintain acceptable stiffness while reducing material costs. Too much regrind content causes the mechanical properties to drop below the specified datasheet values.
