Why do plastic profiles exhibit embrittlement?

Due to physical limitations, plastic shaped products may experience brittle PVC materials during the production process. The main reason is that the plastic products have become brittle due to unreasonable PVC formula and mixing process. There are several reasons why the formula and mixing process are unreasonable:
Hot mix feeding sequence, temperature setting, and curing time: There are many components in the PVC-U formula, and the feeding sequence of additives should help improve the complementary effect of additives, overcome the effect of mutual repulsion, and enable the additives that should be dispersed in the PVC resin to fully enter the interior of the PVC resin. Generally, the temperature of hot mixing is about 120 ℃. When the temperature is too low, the materials cannot achieve gel and mixing uniformity. Some materials above this temperature may decompose and volatilize, and the dry mixed powder will turn yellow.
Excessive or insufficient stabilizers: The function of stabilizers is to degrade, react with the released hydrogen chloride, and prevent discoloration during PVC processing. Excessive use of stabilizers can delay the plasticization time of the material, resulting in insufficient plasticization when the material is exported to the mold, and incomplete fusion between the molecules in the formula system. When the dosage is too low, it will cause the degradation or decomposition of relatively low molecular weight substances in the formula system, causing damage to the stability of the intermolecular structure of each component. Therefore, excessive or insufficient use of stabilizers can cause a decrease in the strength of the profile and cause it to become brittle.
Excessive filling: With the development of technology, most of the materials now use ultrafine lightweight activated calcium carbonate, even nanoscale calcium carbonate. It not only increases rigidity and filling, but also has the function of modification. However, the amount of filling is not infinite, and its proportion should be controlled. Some manufacturers now add calcium carbonate to 20-50 parts by mass in order to reduce costs, which greatly reduces the physical and mechanical properties of the profiles and causes the brittle phenomenon of the profiles mentioned in this chapter.
Quantity of impact modifier added: Impact modifier is a polymer that can increase the total breaking energy of polyvinyl chloride under stress. At present, the main types of impact modifiers for hard polyvinyl chloride include CPE, ABS, etc. When blended with PVC, they can effectively improve the impact resistance, processability, weather resistance of hard polyvinyl chloride, and improve the welding corner strength within a certain range.
After experimental verification, the impact strength of ACR is about 30% higher than that of CPE. Therefore, PVC/ACR blend system should be used as much as possible in the formula, and when modified with CPE and the dosage is less than 8 parts by mass, it often causes the profile to become brittle.
Excessive use of external lubricants: The solubility of external lubricants with resin is low, which can promote the sliding between resin particles, thereby reducing frictional heat and delaying the melting process. This effect of lubricants is significant in the early stages of the processing process. If the lubricant dosage is not appropriate, it may cause flow marks, low yield, turbidity, poor impact, rough surface, adhesion, poor plasticization, etc., causing brittle profiles.