Plastic Chair Failure

Our client, a restaurant owner, was being sued by a customer that was injured when a leg broke off a one-piece molded beige colored plastic (polypropylene) chair. Failure analysis of the plastic chair revealed dark colored particles embedded in the material on the fracture surface. Microscopic analysis revealed that the fracture originated at one of the embedded brown particles. Analysis of the particles revealed that the particles consistent of polyethylene and brown pigment. The brown pigment was purchased as a color concentrate using polyethylene as the carrier resin. Unfortunately, uniform mixing of polyethylene based color concentrate into polypropylene is difficult. The large dark brown pigment particles acted as defects in the material causing the failure. This finding revealed that the cause of the injury was the defectively manufactured chair and was not the fault of our client (the restaurant owner).