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Poly(L-lactide) (PLLA) is a renewable and completely biodegradable material. However, due to its semirigid molecular chain, asymmetric carbon atoms, and poor regularity of the molecular chain, PLLA has poor crystallization ability and is almost amorphous under the traditional processing conditions, resulting in poor toughness and thermal resistance that severely limit its widespread use. In this work, biodegradable poly(ε-caprolactone) (PCL), a rubbery polymer, was added into PLLA to promote the mobility of PLLA molecular chains and then exerted the strong shear flow field generated by multiflow vibration injection molding (MFVIM) technology. The results demonstrate that the coexistence of ductile PCL and strong shear field could improve the crystallization ability and thermal resistance of PLLA significantly. The crystallinity increases to 40.7% and the Vicat softening temperature is up to 138.4 °C. Finally, a strength−toughness-balanced PLLA material is obtained, which can widen the application range of PLLA.

To date, many advanced polymer processing technologies have been developed to tune the morphology of semicrystalline polymers, such as multiflow vibration injection molding (MFVIM). By adjusting the processing fields, i.e., shear and thermal fields, the material can be imparted with great mechanical properties, good electrical/thermal conductivity, or biomimic structure, by manipulating chain's orientation, crystal's arrangement, or hierarchical structure distribution. Despite the era of intelligent manufacturing approaching, there is rarely any report on the computer simulation of these advanced processing technologies. In this work, the processing fields of the MFVIM isotactic polypropylene/high-density polyethylene (iPP/ HDPE) part are successfully simulated using Moldflow by designing a special model. Different thermal gradients can be realized in the plate part by setting different mold temperatures. The experimental results correlate well with the simulation results, and both of them illustrate that the mold temperature plays an important role in the morphology of dispersed PE phase resulting in different physical properties.

The effect of thermal annealing on the mechanical properties and microstructure of polymers has been studied intensively. Nevertheless, sparse work investigated the influence of annealing on the mechanical properties of materials with alternated structure. In this work, the evolution of properties and microstructure of iPP samples with different structure after annealing were discussed. Note that annealing plays a little role on microstructure of all the specimens, whereas its effect on the variation of impact strength of different samples does not show the similar trend. For sample CIM and V1, impact fracture toughness does not improve significantly after annealing within the range of temperature used. But the promotion of the impact strength of sample V2 is extremely remarkable (from 29 KJ/m2 to 90.5KJ/m2), which can be attributed to better interfacial adhesion, resulting in violent crack deflection and plastic deformation, the formation of microfibers and the better ability of load transfer.