TWI Industrial Member Report Summary 423/1990
By S M Stevens
Engineering thermoplastics are increasingly used to replace metals in a variety of applications, as they are light, flexible, tough and corrosion-resistant. The properties of semicrystalline polymers such as polyethylene (PE) and polypropylene (PP) are determined by a number of factors, including the crystallinity and molecular conformation. Crystallinity is dependent on the thermal history of the polymer and would therefore be expected to be influenced by welding.
However, few data exist on the crystallinity developed in welds, and it is difficult to determine this by established techniques. This report describes an evaluation of Fourier transform infrared (FTIR)-microspectrometry for the quantitative determination of crystallinity in PE and PP parent materials, and the subsequent application of the method to PE and PP hot plate and vibration welds.