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Relationship Between Crystallinity & Clarity in Clear Polypropylene Sheet

Posted by Natalie K. MacVarish on June 15, 2018
UltraClear Polypropylene TrayPolypropylene is a semi-crystalline polymer, and characteristic of these type of polymers, PP appears hazy in its natural state. But there are also clarified PP resins that offer drastically improved clarity, haze and overall aesthetics when compared to “neat” PP. So how does this work? Continue reading to learn more about the relationship between crystallinity and clarity in polypropylene sheet.

 

As noted above, PP is a semi-crystalline polymer, which is what contributes to the haze appearance in its natural state. At the molecular level, semi-crystalline polymers exhibit organized and tightly packed molecular chains. The areas of crystallinity are called spherulites and can vary in shape and size with amorphous areas existing between the crystalline areas. The degree of crystallinity affects many characteristics of the polymer such as stiffness, as well as the chemical and thermal resistance of the material.

Polypropylene normally crystallizes slowly, forming collections of large and complex crystals or spherulites. The growth of these spherulites is initiated around microscopic “sites” naturally present in the material. This phenomenon is called nucleation. Without the addition of a clarifying additive, the size of the spherulites grow to be larger than the wavelength of visible light, resulting in light scattering and hazing the material.

Natural PP vs UltraClear PPThe addition of the clarifying agent increases the rate of crystallization throughout the polymer. Because there are more crystals packed into the same space, the crystals grow smaller, allowing for light transmission and enhanced clarity. So now you can take advantage of all of the wonderful characteristics inherent to PP while still achieving a part with the visual appeal desired by todays consumers.  To learn more visit Milliken Chemical.


To learn more about UltraClear Polypropylene and clarified impact copolymer polypropylene sheet options from Impact Plastics, check out our website or contact our team today!

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Topics: ultraclear polypropylene, clear polypropylene, polyproyplene sheet

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