Flowability and fiber content homogeneity of natural fiber polypropylene composites in injection molding

Abstract

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 Multiwalled Carbon Nanotubes on the Rheological Behavior and Physical Properties of Kenaf Fiber-Reinforced Polypropylene Composites

“…As the shear rates increase, the friction between the composite materials increases at the early stage and produces a thermal effect, which reduces the viscosity of the melt feedstock. This finding is consistent with those from other research studies on fiber-reinforced composites [ 25 , 26 ].…”

Analysis of the Segregation Phenomena of Wood Fiber Reinforced Plastics

“…At a wood content of 30 wt.%, the largest segregation was observed, with a wood content increase of 60%. Consequently, the results are consistent with [16,17], although no cyclic alternating pattern of wood fiber content was observed. For comparison, flow spirals were made with a glass fiber reinforced PP containing 40 wt.% fibers.…”

“…Schröder limited her investigations to wood fiber-reinforced polypropylene. Ramzy et al [16] and El-Sabbath [17] made similar findings using hemp and sisal fiber-reinforced polypropylene. The influence of the matrix material in combination with long glass fibers on the rheological and mechanical properties of surface and core areas has been studied, for example, in [18].…”

Thermoplastic natural fiber based composites

“…The flowability decreases as the fiber loading is increased. Moreover, it has been shown by El Sabbagh et al[122] that the fiber content may change along the flow path, resulting in inhomogeneity of mechanical properties. As in extrusion, fiber dispersion and thermal degradation are important issues.…”