Lightweight Polypropylene/Polylactic Acid Composite Foams with Controllable Hollow Radially Gradient Porous Structures for Oil/Water Separation

The structural characteristics of the polymer composite foams play an important role in their properties. Herein, the polypropylene/polylactic acid (PP/PLA) composite foams with the controllable hollow radially gradient porous structures are designed and prepared by the supercritical CO2-assisted foam extrusion coupled with postdrawing auxiliary technology. The above structures consist of the dense skin layer, hollow-core, closed-cell, and open-cell. Under the constant extrusion foaming temperature and pressure, the outer diameter of the as-prepared foams can be adjusted from about 9.8 mm to 5.7 mm, while the inner diameter changes from about 5.5 mm to 1.7 mm, by adding the PLA to regulate the viscoelasticity and thermodynamic differences of the polymeric melt. Besides, the formation mechanism of the hollow radially gradient porous structures is theoretically analyzed. The as-prepared PP/PLA composite foams exhibit outstanding oil/water separation performance, which show potential application in wastewater treatment.