Short‐fiber‐reinforced thermoplastics. Part III: Effect of fiber length on rheological properties and fiber orientation

The effect of fiber length on fiber‐filled melt viscosity and on shear‐induced fiber breakage and orientation development in polystyrene was studied. The incorporation of fibers, increasing their length, results in an increasing viscosity over the entire shear rate range. Significant fiber length reduction was observed even at low shear rates. Determined fiber orientation distributions, as affected by shear rate and fiber length, are discussed. Orientation effects are expressed by a single orientation parameter which is used to account for the average fiber orientation contribution to the relative viscosity. Calculated orientation parameters indicate higher fiber orientation for shorter fibers. Fiber orientation in the flow direction increases with increasing shear rate and results in the expected viscosity decrease.