Production of Green Star/Linear PLA Blends by Extrusion and Injection Molding: Tailoring Rheological and Mechanical Performances of Conventional PLA

Abstract

In this work, bio‐based products composed of blends of a star‐shaped poly(d,l‐lactide) (star‐PDLLA) and a conventional linear poly(l‐lactide) (linear‐PLLA) are produced by typical large‐scale manufacturing techniques for thermoplastic blends. In the first case, the two polymers are blended through melt extrusion, producing pellets that are subsequently compression‐molded into the final bio‐based polymer films. Alternatively, the star/linear poly(lactide) (PLA) materials are developed by direct blending through injection molding, a process that generally applies after a preblending extrusion step to ensure proper mixing. Thermomechanical degradation induced by the different processes is evaluated, and the performances of the final star/linear PLA products are thoroughly compared. The effect of the short‐branched, amorphous, star polymeric component on thermal, mechanical, and rheological properties of the conventional PLLA is comprehensively investigated, revealing that the star‐PDLLA incorporation promotes the formation of a more flexible and tougher material with reduced capability of crystallization. Most importantly, star‐PDLLA decreases the melt viscosity of the final material, while increasing the shear‐thinning behavior, hence facilitating melt flow during manufacturing. Such properties lead to enhanced material ductility and processability, with respect to typically brittle and viscous conventional PLLA‐based materials. Moreover, the tuning of final material performances can be achieved by simply varying the star‐PDLLA content.

Recycled HDPE/Natural Fiber Composites Modified with Waste Tire Rubber: A Comparison between Injection and Compression Molding

“…The gaps between the agglomerated particles and rHDPE in compression molded composites are clearly observed in Figure 4 a,c. Similar results reported impregnation problem in compression molded hybrid composites attributed to the difficulty of high viscosity resins in diffusing into fiber bundles and subsequently their agglomeration (cluster) in highly viscous matrices [ 27 , 33 ]. High filler/matrix interaction may also explain the higher mechanical properties of injection molded composites due to more effective stress transfer and better interfacial quality.…”

“…This can be attributed to the orientation of polymer chains during IM. In fact, direct injection of the specimens into the dumbbell-shaped mold induced chain orientation along the flow direction resulting in improved tensile properties along the longitudinal direction (anisotropy) [ 33 ]. Moreover, better distribution and dispersion of the fiber occurs due to a second melt-mixing step inside the injection molding screw barrel [ 37 ].…”

Recycled Tire Fibers Used as Reinforcement for Recycled Polyethylene Composites

“…For example, 30CF-INJ has 111% higher tensile strength and 94% higher tensile modulus but 27% lower elongation at break than 30CF-COM. This is ascribed to the secondary melt-mixing step in injection, as well as the orientation of the fibers and polymer chains during injection molding, as reported in the literature [30,31]. Similar observations were obtained from SEM images (Figure 7), indicating that the fibers are mainly oriented perpendicular to the cross-section in injection-molded samples, while the fiber orientation is predominantly random, displaying more entanglements in compression-molded samples.…”

Review on the Degradation of Poly(lactic acid) during Melt Processing

“…The M n of unprocessed PLA (69.3 kDa) decreased to 48.2 kDa during IM, and a further decrease was observed during IM and SSE to a M n of 42.9 kDa. A similar study was performed by Scoponi et al [93], where unprocessed PLA was compared with PLA that was processed via IM, TSE, and both co-rotating twin-screw extrusion and compression molding (TSE + CM). It was observed that the M n of unprocessed PLA (74.1 kDa) decreased to 52.8 kDa after IM, 39.2 kDa after TSE, and 22.5 kDa after TSE + CM.…”