Predicting the laser weldability of dissimilar polymers

The determination of whether two dissimilar polymers are weldable is still largely trial-and-error. Here we suggest a correlation between laser weld strength and the ratio of the equilibrium interpenetration depth (w∞) of two immiscible polymers to the maximum entanglement tube diameter of the two polymers (amax). Taking the weld strength from a published chart of qualitative weld strength, we find a correlation coefficient between this and the ratio w∞/amax of 0.67, where w∞ is based on the simple Hildebrand solubility parameter. ncouraged a quantitative study of the laser weld strength. This was done using a through transmission laser welding process with 0.4% carbon black as an absorber. The laser welds were tensile tested and relative weld strengths obtained. This strength was compared to the w∞/amax ratio, where w∞ is based on experimentally determined Hansen solubility parameters. The results suggest weldability between dissimilar polymers is obtainable when w∞/amax is greater than 0.15.