Material Drying
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Bubbles/pores on the surface of linear low-density polyethylene extruded products
Problem Phenomenon
Bubbles or pores appear on the extrudate surface or cross-section, and product density decreases.
Bubbles not only affect appearance but also reduce product mechanical strength and pressure resistance; they are common in pipe and profile extrusion.
Cause Analysis
(1) Raw material moisture content exceeds the standard; moisture vaporizes at high temperature to produce bubbles
(2) Poor screw venting; air is entrained in the melt
(3) Barrel temperature is too high; material thermal degradation produces gas
(4) Screw speed is too fast, and venting time is insufficient
(5) Raw material has high content of low-molecular volatiles
Solution
(1) Fully dry the raw material; control linear low-density polyethylene moisture content below 0.02%
(2) Check venting section design, and use a vented extruder if necessary
(3) Appropriately lower barrel temperature to a reasonable value within the 190-250°C range
(4) Reduce screw speed to increase material residence time in the venting section
(5) Select raw material grades with low volatile content
Key Takeaway
Bubbles are caused by moisture vaporization or gas entrainment and need to be solved from raw '2079851475616104451 and the venting system.
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