We have developed a beta nucleant masterbatch that can be added to a non-nucleated polypropylene resin to produce unique oriented film products,as well as enhance the properties and processability of injection molded and thermoformed polypropylene.When PP resins containing this masterbatch are extruded under the proper conditions,the resulting sheets contain high levels of beta crystallinity.When these sheets are subsequently stretched to produce either monoaxial (MOPP) or biaxial (BOPP) oriented polypropylene film,the beta crystals transform into alpha crystals and develop microvoids.The microvoids scatter light resulting in an opaque/white film,and also reduce the density of the final film.Under certain circumstances it is possible to produce a microvoided film that has very high moisture vapor transmission rates,so that the film is "breathable" while also being waterproof.For thermoforming applications we have demonstrated that a beta crystalline PP sheet has a broader processing window than that of a conventional PP sheet,can be run at faster cycle rates,and produces a final thermoformed part with improved material distribution and physical properties.This latter attribute allows the part weight to be reduced thereby resulting in a significant cost and raw material savings.When the beta nucleant masterbatch is used to produce an injection molded polypropylene part,the stiffness/impact balance is improved,and the final part has dramatically improved impact strength without a significant loss in stiffness.
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