Audrey Durin

Influence of extrusion conditions on fiber breakage along the screw profile during twin screw compounding of glass fiber-reinforced PA

Abstract In the present study, Polyamide 12 was compounded with glass fibers in both laboratory and industrial twin screw extruders using various processing conditions (screw speed and feed rate). Dead-stop experiments were performed and samples were collected at different locations along the screws in order to determine the fiber length distribution and the extent of fiber breakage. Results show that significant fiber break-up occurs right after the addition of glass fibers to the molten matrix. Similarly fiber length distribution changes drastically at the first sampling location, near the glass fiber feeder. Processing conditions also influence the extent of degradation: it increases with screw speed and decreases with feed rate, which controls the residence time. Flow modelling has been used to calculate the flow conditions along the screw profile. It is shown that the modified Shon-Liu-White model previously proposed to describe the average fiber length evolution as function of specific energy is not able to correctly predict the evolution along the screw profile. In similar processing conditions, the large industrial extruder appears as less severe than the small laboratory one.

Comparison between 1D and 3D Approaches for Twin-Screw Extrusion Simulation

Abstract In this paper, numerical simulations of flows in a co-rotating intermeshing twin-screw extruder are performed using a previously presented 3D finite elements model. Some numerical improvements recently introduced are presented. The computations are performed for several processing conditions and screw arrangements. Values of specific energy, pressure and filled length are compared to the results issuing from the 1D Ludovic software in order to compare both approaches. The 3D simulation method is found to be more accurate to describe the effect of varying staggering angle and thickness of kneading discs. On the other hand, 1D model provides very satisfactory results for flows in screw elements.

A Study of Fiber Breakage during Compounding in a Buss Kneader

Abstract This paper is devoted to the study of fiber breakage during compounding with a polyamide matrix in a Buss kneader. Results showed a drastic decrease of glass fiber length during compounding, typically from 3500 to 350 μm. Fiber breakage depended on processing conditions: it increased with screw speed, but the effect of feed rate was less clear. Fiber breakage increased also with the severity of the screw profile. Characterizations of fiber length evolution along the screw profile have also been performed after dead-stop experiments. Generally speaking, fiber length evolution can be described using a modified Shon-Liu-White model, in which either the number of turns or the specific energy is considered.

On The Use Of Prototype Industrial Flows To Identify Viscoelastic Constitutive Equations For Polymer Melts

This study is devoted to the validation and identification of viscoelastic constitutive equations for entangled polymer melts using “classical” rheometry tests and fieldwise measurements (flow induced birefringence coupled to laser Doppler velocimetry) in prototype extrusion flows equipped with a transparent die. We studied two different polymers : a linear polystyrene (presented in this paper) and a branched low density polyethylene (will be presented during the conference), and tested the pertinence of “molecular” constitutive equations to predict their behaviour in a contraction flow exhibiting high elongational rates. First, a “classical” identification was performed using linear viscoelasticity, capillary and extensional rheometry for a polystyrene and polyethylene. Models predictions were then tested in extrusion flows using velocity (gradients) and (first principal) stresses (difference) measurements. It was shown that an extra adjustment of parameters for the very fast viscoelastic modes were need...

A Comparative Study of Fiber Break‐up During Compounding of Glass Fiber‐Reinforced Polyamide in Batch and Continuous Mixers

Glass fiber breakage during compounding was determined for both batch and continuous mixers including an internal mixer and two different co‐rotating twin screw extruders; of laboratory and industrial scales. The effect of processing conditions such as screw speed, feed rate and screw profiles on fiber damage was investigated. Finally, the results of experimental studies were discussed, compared and interpreted using a model for fiber breakage.