Effect of extruder elements on fiber dimensions and mechanical properties of bast natural fiber polypropylene composites

Abstract

Illusions and facts about aspect ratio and the corresponding mechanical properties of the polypropylene flax are studied in this work. Selection of extruder elements controls significantly the fiber final dimensions. Hence, the load transfer efficiency can be improved. Different extruder layouts are tried. First and second trials investigate the mixing degree effect using kneading elements with eight and four kneading elements, respectively. The third and fourth trials keep four kneading blocks but differentiate in using multiprocessing element MPE and toothed elements, respectively. All the four configurations are tested at different shearing rates namely 100, 200, and 300 rpm and different fiber loadings 10, 20, and 30 wt %. Polypropylene (PP) with high flowing properties and slivers flax natural fibers are used. The output extruded strands are mechanically tested. The third and fourth configurations showed superiority to the normal kneading profiles regarding the mechanical properties. Samples of composites are withdrawn after each processing extruder element to study the effect of this element on the fiber dimension. Measurement of extracted fibers is carried out by two methods namely dynamic image analysis machine and secondly normal microscopic investigation. Weibull distributions are defined for fiber geometry distributions for the different locations on the extruder configuration. Also, the effect of the shear rate and the extruder configuration on the final dimensions of the fibers extracted from the composite. The results show the correlation between extruder configuration and fiber aspect ratio and hence the composite overall strength. However, further processing like injection molding erases the pre-extrusion effect.

Non-destructive automatic determination of aspect ratio and cross-sectional properties of fibres

“…The microstructure of such materials is formed during the manufacturing processes that typically include, e.g., pelletization, compounding, extrusion and moulding, each of which affect the geometry and distribution of the precursors [5]. Information on the microstructure of the material [6,7] evolving through the different processing stages may be used to optimize the processing chain and the properties of the final product through selection of proper processing methods [8,9] and their parameters [10].…”

Mechanical and Thermal Properties of Polypropylene Composites Reinforced with Lignocellulose Nanofibers Dried in Melted Ethylene-Butene Copolymer

“…It has been reported that using fillers with a larger aspect ratio in composites results in a higher reinforcing efficiency, owing to the effective transfer of stress from the matrix to the filler [11,12,13]. However, the reinforcing effects of the LCNFs and wood flour on the moduli and stresses determined by the flexural and tensile tests were almost similar.…”

Development of natural fiber/engineering plastics composites with flame retardance properties

“…Reverse element helps in filling the previous element and proper material pumping. Special elements like multi process element (MPE) decrease the fiber damage during process [13]. Application of vacuum has positive effect but it is not essential if the input materials are well dried.…”

“…Hu et al reported the extrusion of PE/ flax at 110-150 rpm [12]. El-Sabbagh et al studied the effect of the fiber size in dependence on the speed up to 300 rpm using different screw designs [13]. So it is required to design a screw with low shearing stress (less kneading elements in other words) as well as high speed to ensure less dwell time in the extruder.…”