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21.3 Cloudiness Troubleshooting 197
21.3.4.2 Material: Moisture Content
High moisture content on materials can lead to excessive splay that results in a
clear part looking cloudy. Verify the moisture content when processing hygro-
scopic materials. See Chapter 9 on drying for more information.
21.3.4.3 Material: Semi-Crystalline Nucleation
The way that semi-crystalline materials crystalize will impact how clear or opaque
some materials end up being. A nucleated polypropylene can end up being fairly
clear because the nucleation forms small crystals fast. If the nucleation level of the
material varies the level of clarity will also vary. A polypropylene that does not
contain nucleating agents will tend to be opaque and cloudy in normal appearance.
The nucleation effect with semi-crystalline materials will be impacted by wall
stock, mold temperature, and melt temperature. Rapid cooling freezes the material
in a more “amorphous” state and will maximize the clarity of the material.
