What are the causes of the cracking phenomenon of PVC profile extrusion in the raw material formula? And what are the solutions?

What are the causes of the cracking phenomenon of PVC profile extrusion in the raw material formula? And what are the solutions?

①Excessive fillers;

②The types and addition amounts of impact modifiers selected, generally speaking, the impact strength of ACR is about 30% higher than that of CPE. When CPE is used for modification, if the dosage is lower than 8 quality parts, the profiles are prone to become brittle. 
③Excessive or insufficient stabilizers. When the dosage of stabilizers is too high, it will delay the plasticization time of the materials, resulting in insufficient plasticization at the material outlet die, and the molecules in the formula system cannot fully fuse, and the intermolecular structure is not stable. When the dosage is too low, it will cause the degradation or decomposition of relatively low-molecular substances in the formula system, which will damage the stability of the intermolecular structure of each component. Excessive or insufficient dosage of stabilizers is likely to cause the reduction of profile strength and brittleness of the profiles. 
④Excessive dosage of external lubricants. The external lubricants have poor compatibility with the resin, thus resulting in poor density and plasticization of the profiles, and poor impact performance, causing brittleness of the profiles. 


The solutions mainly include: 

①Reduce the dosage of fillers. More often, ultrafine lightweight activated calcium carbonate or even nano-sized calcium carbonate is used. It not only increases the rigidity and filling effect but also has the role of modification. The dosage is generally controlled within 20-50 quality parts. Try to use less heavy calcium carbonate as much as possible. Due to the irregular particle shape and relatively coarse particle size of heavy calcium carbonate, its compatibility with the PVC resin matrix is poor. When the dosage is large, it will have adverse effects on the color appearance and performance of the profiles.
②Use an appropriate dosage of impact modifiers, and try to use multiple impact modifiers in combination to improve the impact modification effect. 
③Use a reasonable stabilizer system, and try to use composite heat stabilizers to improve the heat stabilizer effect and reduce the dosage of heat stabilizers.
④Select an appropriate external lubricant, and try to reduce the dosage of lubricants.
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