Analysis of Welded Joints by Using Novel Nanoscale IR Spectroscopy

Welding is a common joining method in plastics processing in which the macromolecules of the joining partners form a material bond across the interface. There are various models which try to explain the effective mechanisms in a weld. However, it has not yet been possible to prove the diffusion theory or any models based on it since polymer chains cannot be observed directly. For amorphous thermoplastics, analysis methods are extremely restricted because of their lack of long-range order. Joints consisting of PMMA and PC were manufactured by using hot plate welding and analysed with a novel investigation method, atomic force microscopy coupled with infrared spectroscopy (AFM-IR). This method permitted the identification not only of the weld but also of the polymers which had penetrated into each other. The interfacial region of the weld exhibited a width of approx. 50 nm and suggests the diffusion and thorough mixing of both polymers. Moreover, it was possible to prove this chemically in this way.