Bin-Yi Chen

Superior Impact Toughness and Excellent Storage Modulus of Poly(lactic acid) Foams Reinforced by Shish-Kebab Nanoporous Structure

Poly(lactic acid) (PLA) foams, with the combination of shish-kebab and spherulite nanoporous structure in skin and core layer respectively, was prepared using a novel technique comprising loop oscillating push-pull molding (LOPPM) and supercritical carbon dioxide low-temperature foaming process (SC-CO2LTFP). The foams present superior impact toughness which is 6-fold higher than that of neat PLA, and no significant decrease was observed for the storage modulus. Moreover, SC-CO2LTFP at soaking temperature ranging from 110 to 150 °C were performed to determine the evolution of pore morphology. The ultratough and supermoduli are unprecedented for PLA, and are in great need for broader applications.

Excellent properties and extrusion foaming behavior of PPC/PS/PTFE composites with an in situ fibrillated PTFE nanofibrillar network

In this work, we compounded polystyrene (PS) and polytetrafluoroethylene (PTFE) with poly(propylene carbonate) (PPC) via a triple-screw extruder to prepare multiphase composites that possess special properties and to improve the extrusion foaming ability of PPC. It was found that PS was immiscible with PPC and formed a dispersion phase, and PTFE was in situ fibrillated into the nanofibrillar network within the PPC/PS matrix. The introduction of rigid PS domains and PTFE nanofibrils showed remarkable effects on the properties of PPC. Compared with neat PPC, the PPC/PS/PTFE composites had a 12 °C higher glass transition temperature, 292% higher storage modulus in the glassy state characterized by dynamic mechanical analysis, and 1576% higher initial viscosity. Moreover, the physical network formed by PTFE nanofibrils effectively prevented the shear-thinning behavior of the polymer matrix. A significant influence of PTFE on the cell morphology was found in the extrusion foaming process. The cell density of PPC/PS/PTFE foams was four orders of magnitude higher than PPC foams. The compressive modulus and strength of the foamed PPC/PS/PTFE composites were 58 and 34 times higher than that of PPC foams, respectively. The great improvement in the mechanical performance was attributed to the synergistic effects of the enhanced CO2 affinity, the heterogeneous nucleation effect, and the changes in system melt viscosity.

The Effect of Talc on the Mechanical, Crystallization and Foaming Properties of Poly(Lactic Acid)

ABSTRACT Poly(lactic acid) (PLA)/talc composites containing different contents of talc were prepared by melt blending. Multiple properties of the prepared composites were investigated including mechanical, rheological and crystallization as well as foaming properties. Tensile test results indicated that the mechanical properties of the composite with 3% wt. talc showed significant reinforcement and toughening effect. When the talc content reached 10%, Youngs modulus of the composite was increased by 35% compared with pure PLA. The morphological results showed that the talc layers were partially delaminated and uniformly dispersed in the PLA matrix at low loading. Differential scanning calorimetry (DSC) and polarized optical microscopy (POM) results indicated that 3% wt. talc significantly increased the crystallinity of the PLA matrix. The thermogravimetric analysis (TGA) results demonstrated that the thermal stability of PLA/talc composites was enhanced as well. Moreover, talc at low loading could act as a plasticizer in the polymer flow, which was investigated by rheological tests. The batch foaming experiments revealed that 3% wt. talc loading had the most notable heterogeneous nucleation effect, with the cell size decreasing from 15.4 μm for neat PLA to 8.5 μm and the cell density increasing by 298%.

Morphology Evolution of the Microcellular Polymethyl Methacrylate with Supercritical CO2: Effects of Shear Stress and Orthogonal Vibration

This study presents a foaming system that was developed to generate shear stress as well as oscillatory mechanical vibration in an orthogonal direction. The microcellular processes of PMMA specimens blown with ScCO2 have been conducted to find the optimal processing parameters under the static conditions as well as dynamic conditions. It is evident that the cells are drawn into elliptical geometries sheared circumferential by the rotor rotation in isolation. However, the orthogonal pulsatile axial vibration superimposed on the polymer melt synchronously drives the oriented and elongated cells to isotropy as well as a more homogenous cells distribution and planar structure. GRAPHICAL ABSTRACT