The evaluation of molecular orientation and structural changes in polypropylene welds

TWI Industrial Member Report Summary  439/1991

S M Stevens

Scope

Polypropylene (PP) is a widely used semicrystalline thermoplastic, and its mechanical properties are influenced by a number of factors, including morphology, orientation of the polymer chain, and crystallinity. These factors are dependent on the thermal history and manufacturing process, and will be influenced by welding.

There have been few studies on the molecular changes induced in a polymer by the welding process. This report describes the use of polarised Fourier transform infrared (FTIR)-microspectrometry and differential scanning calorimetry (DSC) to evaluate molecular orientation, and structural changes, respectively, in PP hot plate and vibration welds. In addition, X-ray diffraction (XRD) measurements on parent materials were used in interpretation of the DSC weld results.