Over the next few weeks, the ARM blog will highlight the takeaway points from some of the key presentations given at ARM’s 40th Annual Meeting in New Orleans. The first of these posts comes from Tom Wyszynski, a new inductee in the Rotational Molding Hall of Fame, who summarizes the key points of his presentation on Septmember 27.
Polypropylene is an incredible polymer. Contrary to what some may think, there is a place for it in rotational molding. Designers, engineers, and molders need to remember it is not polyethylene – and it is not trying to be polyethylene.
The characteristics of polypropylene are very different from those of polyethylene – and that’s a good thing. PP has the ability to do well in higher temperature conditions than does PE. Polypropylene has very good chemical resistance and a very high flexural modulus. Many types of tanks, bins, and assorted containers are molded from polypropylene.
The high melt point and deflection temperature allow polypropylene to handle applications polyethylene could never touch. Those same thermal traits allow polypropylene to be disinfected using and autoclave. The 120°C operating temperature of an autoclave is almost at the melt point of some LLDPEs. Food and pharmaceutical applications love the fact this polymer can be sterilized via autoclave.
The copolymer polypropylenes being produced today for rotomolding are light years ahead of the compounds available years back. Careful selection and incorporation of impact modifiers as well as thermal and ultraviolet light stabilizers have really improved polypropylenes. While polypropylene may not have the impact resistance of PE many applications simply are not impact sensitive.
We deal with many things in our lives that are not impact resistant yet they serve a function. Polypropylene has a place in rotational molding but it needs to be the correct application.
Tom Wyszynski is a technical manager for rotomolding resins at A. Schulman and was inducted into the Rotational Molding Hall of Fame in September 2016.