Material Drying
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Bubbles/Pores on the Surface of Block Copolymer Polypropylene Extruded Products
Problem Phenomenon
Bubbles or pores appear on the surface or cross-section of the extrudate, and the product density decreases.
Bubbles not only affect the appearance, but also reduce the mechanical strength and pressure resistance of the product, and are common in pipe and profile extrusion.
Cause Analysis
（1）The moisture content of the raw material exceeds the standard, and the water vaporizes at high temperature to produce bubbles
（2）The screw venting is poor, and air is entrained in the melt
（3）The barrel temperature is too high, and the material thermally degrades to produce gas
（4）The screw rotation speed is too fast, and the venting time is insufficient
（5）The content of low-molecular volatiles in the raw material is high
Solution
（1）Fully dry the raw material, and control the moisture content of block copolymer polypropylene below 0.02%
（2）Check the venting section design, and use a vented extruder when necessary
（3）Appropriately reduce the barrel temperature to a reasonable value within the 200-270°C range
（4）Reduce the screw rotation speed to increase the residence time of the material in the venting section
（5）Select raw material grades with low volatile content
Key Takeaway
Bubbles are caused by water vaporization or gas entrainment, and need to be solved from raw '2079851475616104451 and the venting system.
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