Higher melt-flow rates without secondary processing have been achieved by four new grades of polypropylene from Montell, called Pro-fax Ultra. With a balance between good stiffness and impact resistance, the materials? melt-flow rates range from 35 to 100. The key to this balance is the generation of high-melt-flow products straight out of the reactor, which do not require the peroxide typically used to improve melt flow. No peroxide means improved organoleptics (odor and taste qualities) in packaging applications. Also, the materials? better melt flow means lower processing temperatures, resulting in shorter cycle times.
Three of the four nucleated grades are antistatic and slip modified, and all are easy to color match with the absence of peroxide?s yellowing properties, according to company sources. One application for the 35-MFR SG833 grade is an ice cream container in which greater impact resistance is needed due to the product?s extreme cold temperature environment.
The 55-MFR SG853 grade is slated for use in DVD cases and housewares, or in a wagon (pictured) for holding children?s blocks. Toy manufacturer Ritvik chose SG853 instead of high-density polyethylene because it ran faster, maintained the part?s critical impact requirement, and offered high gloss, reports Montell. Both 100-MFR grades (SG982 and SG973) are intended for thin-wall dairy containers?such as yogurt cups?that previously were made of polyethylene and polystyrene, as well as polypropylene.
The balance between stiffness and impact resistance can be measured in the polypropylene?s properties: flexural modulus ranges from 170,000 to 210,000 psi, and notched Izod spans 2.3 to .8 ft-lb/in at 23C. Montell reports that Pro-fax Ultra comes at a slight premium compared to the company?s current standard PP.
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