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 Samples of composites are withdrawn after each processing extruder element to study the effect of this element on the fiber dimension.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.
Influence of rapid heat cycle molding and filler type on warpage of injection molded parts out of PP-based compounds AIP Conference Proceedings 1779, 020005 (2016) Abstract. As an index of viscosity, flowability of natural fiber polypropylene composites is assessed by spiral mold test using injection molding machine. The effect of the processing parameters like the injection temperature at 180-220°C, injection pressure at 500-1000 bar and the mold temperature of room temperature and 80°C on flowability is studied. The investigated parameters are the fiber shape (Non branched straight cellulose versus low flexural stiffness and branched hemp fibers), fiber length (0.5 versus 1.5 mm chopped cellulose fibers) and fiber content Wf (10 versus 30 wt%). The results show that the most significant parameters in a descending order are the pressure, temperature and the mold temperature. Another aspect of the product quality is the homogeneity of the fiber content through the whole injected spirals. Therefore samples are taken out at even distances along the spiral. The cut samples are dissolved to extract fibers and calculate the fiber content. Fiber content definition along the injected spirals proved that it is not constant and the deviation in its measurements can reach to almost 30% from the nominal value. The results prove the separation of fibers before being injected specially in cases of low pressure and low injection temperatures. Secondly, the fiber content varies in a cyclic way. The number of cycles increases with the increase of temperature and pressure but with smaller amplitude of variation. The variation of the fiber content in cellulose fluctuates around an almost constant value which is not the case with hemp variation. Thirdly, the fiber content shows in most of the cases a parabolic trend with a minimum point just shortly after the input injection point. Fourth, the change in fiber length behaves more or less like change in fiber content especially at both low pressure and temperature. Fifth, the variation in fiber content (Wfmax -Wfmin) along the spiral is clear in composites with hemp fibers at high processing temperature / pressure . These results about variation in fiber content are studied in terms of the measured fiber dimensions. Fiber length is defined by the dynamic image analysis system QICPIC. Fiber length proves that the longer the fiber length, most likely the higher the fiber content. However, these results are still in need to be deeply analyzed and better understood in order to open the door in future for robust simulation.
Influence of initial fiber length on the mechanical and tribological properties of hemp fiber reinforced plantsderived polyamide 1010 biomass composites AIP Conference Proceedings 1914, 070003 (2017) Abstract. The hydrophilic nature of natural fibres and the hydrophobic behaviour of standard polymers such as polypropylene and other polyolefins are the major cause for the lack of adhesion between fibre and matrix in natural fibre reinforced plastics (NFRP's). To overcome this incompatibility of fibre and matrix, different coupling agents can be incorporated into the compound. Our investigations revealed the bonding capability of three dendritic polyesters and one thermoplastic polyurethane in a flax fibre/PP compound. The treatment with different amounts of coupling agent led to an increase in mechanical properties such as bending strength, tensile strength and most of all CHARPY impact strength. In addition, it was possible to make a correlation between IR spectra and the chemical and physical interactions between fibre, matrix and adhesive. Therefore a relationship between intermolecular forces and mechanical properties could be concluded.
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