Locally Controllable Surface Foaming of Polymers Induced by Graphene via Near-Infrared Pulsed Laser

Our study proposed an efficient and environment-friendly strategy to realize the locally controllable surface foaming on polymers via a near-infrared pulsed laser. This laser foaming was induced by the multilayer graphene (MLG), and only 0.05 wt % MLG gave the polymer an excellent foaming performance with good smoothness and a foaming height of 0.41 mm. Benefited from programming and automatically controlling the laser system, foamed patterns of arbitrary shapes with three-dimensional appearance could be accurately written on the polymer surface. Scanning electron microscopy confirmed that the uniform cells produced by laser foaming were mainly ellipsoidal with closed-cell structures (D = 31.5 μm); moreover, the surface foam had three layers with a total thickness of 633.7 μm. X-ray photoelectron spectroscopy (XPS) revealed the surface carbonization of the foam during laser foaming. Both attenuated total reflection Fourier transform infrared spectroscopy and XPS confirmed the weak oxidation of the polypropylene (PP) matrix caused by laser because of the appearance of C–O and CO groups on foams. Besides, the Raman depth imaging demonstrated the layered carbonization distribution in the foam surface. The micro-Raman spectroscopy confirmed that the amorphous carbon and the sp/sp² carbon (CC/CC) were two main carbonized products of PP. This study also proposed the mechanism of polymer laser foaming induced by MLG.