Effect of Flax/PP pellets’ morphology on the mechanical properties of injection-molded parts

Abstract

Flax and polypropylene (PP) pultrudates of 4.76 mm in diameter were produced using a multi-die pultrusion system. The flax content was 50 vol.%. Pultrusion conditions were varied to produce four porosity content between 4% and 22%. The pultrudates were pelletized into lengths of 6 and 15 mm, and injection-molded with pure PP to reduce the part flax content to 25 wt.%. Results showed that well consolidated pultrudates, having porosities up to 8%, were more resilient to the pelletizing process such that the pellets remained structurally intact after the process. These pellets went smoothly through the hopper into the injection molding machine screw. Pellets with void content higher than 8% lost integrity during pelletizing leading to uniform mixing. Exposed fibers segregated from the polymer in the hopper leading to ununiform mixing. The highest mechanical properties improvement compared to pure PP was using 15 mm pellets that had a prorosity of 8%. The tensile modulus doubled at 4652 ± 113 MPa. The impact strength increased by almost five times at 10.5 ± 0.7 [Formula: see text]. 15 mm pellets provided 1.7 times the impact strength of the 6 mm pellets. These improvement are attributed to low flax fiber thermal degradation and improved fiber dispersion.

Effect of high pulling speeds on the morphologies of pultrudates in a thermoplastic pultrusion process

“…Figure 5 presents the typical cross-section microscopic photos of Flax/PP pultrudates with respect to the pulling speeds. Contrary to Alsinani et al , 26 the polymer in all cases had fully melted. The pultrudates’ cross-section is round in all cases.…”

“…This created a delay in polymer melting at higher speed. Moreover, as observed in Nawaf et al 26 the PP polymer melts progressively from the die surface to the center of the pultrudate. Therefore, since un-melted polymer fibers cannot flow around flax agglomerations, the area they occupied effectively compressed and pushed the flax yarns into the melted PP in contact with the die.…”

“…27 The melting point of the PP was 166.5 ℃ as obtained by DSC at heating rate of 10 °C/min. Details about the DSC procedure can be found in Alsinani et al 26 The PP fiber’s density was considered to be 0.91 g/cm 3 . 28 After melting, the PP density was considered to decrease to 0.75 g/cm 3 .…”

“…This can create significant discrepancies between the set and the actual material temperatures especially when the pulling speed is high. Alsinani et al 26 pultruded Flax/PP rods at four distant speed between 50 to 1000 mm/min. The pultruded rods were then cut into pellets for subsequent injection molding.…”

Effect of hybrid eco‐friendly reinforcement and their size on mechanical and flame retardant properties of polypropylene composites for technical applications

“…This synergy fosters a resilient reinforcement matrix, amplifying the composite's loadbearing capacity and its overarching mechanical properties. 47,48 However, this progression is not linear. The observed dip from LFF2/PP-L10 to LFF2/PP-L15, paralleling fiber length augmentation, underscores the intrinsic distribution challenges concomitant with lengthening fibers.…”