Pinnacle Launches New Ultra-High Impact Polypropylene

Stiffness and ability to withstand impact are both critical properties for many applications where polypropylene is used. These properties are reported using standardized tests so that users can choose materials that best satisfy real-world demands. At any given melt flow there is an inverse relationship between stiffness and impact resistance(1). The higher the impact strength the softer the finished part, while stiffer parts tend to have lower ability to absorb impacts. For this reason end users must often sacrifice one property to achieve acceptable performance in the other.

Polypropylene impact copolymers are chosen to perform in tough environments. Many applications would benefit from a part that has both high stiffness and high impact. For example, a plastic shovel needs to have a high tolerance to impact, yet be stiff enough to shovel snow or dirt without excessive bending.

Points on this graph represent all of the commercially available, advertised impact copolymers. Only products having both high melt flow and high impact are plotted(2). The line in this graph illustrates the inverse relationship between stiffness and impact in polypropylene. As you can see most producers must formulate the product with a trade off, electing either higher flex, or high impact, but not both. Typically, more rubber is added to increase impact. However, as more rubber is added the stiffness decreases because of the soft elastic nature of the rubber. As you can plainly see, there is a cluster around the line that represents the typical balance between flex and izod.

The highlighted data point shows how Pinnacle's recently improved impact copolymers stand-out from the crowd! Here you can see that Pinnacle's 4220H 20 melt flow impact stands well away from the line that represents the competition. Pinnacle can produce a resin with both high impact and superior stiffness.

At Pinnacle we have refined our process so that we can achieve superior combinations of melt flow, impact resistance and stiffness. Of course, we can also increase the softness producing very high impact with softer flex mods for those applications that require softness and high impact. Pinnacle is proud to offer the most versatile range of impacts available to the market.

  1. Flexural Modulus or "flex mod" is the standard measure of the stiffness of a material. Flex mod is measured in psi or pounds per square inch using a standard ASTM D790A test method. It can be expressed as the pounds per square inch (psi or kpsi) it takes to deform a material, usually measured at 1% deformation. The higher the value the stiffer the material, lower values represent softer materials. Resistance to impact is measured by the Notched Izod test and can be expressed as ft.-lb/in based on ASTM D256 where higher values indicate that more force is required to fracture a part. Parts with lower izod values would break more easily on impact.
  2. The property of impact resistance also goes down as melt flow goes up. This makes high impact polymers with high melt flow very difficult to produce.