Detailed Explanation of Key Influencing Factors
1.Materials and Formulation
PVC Resin: PVC itself contains chlorine atoms, which gives it good resistance to most inorganic acids, alkalis and salts. However, organic solvents such as esters, ketones, aromatic hydrocarbons and chlorinated hydrocarbons may cause it to swell or dissolve.
Plasticizer: Adding plasticizers (e.g. phthalates) can improve flexibility, but excessive addition will reduce chemical resistance, especially increasing sensitivity to oils and solvents.
Stabilizer: Used to prevent PVC from decomposing under heat and light during processing and service. For example, lead salt stabilizers (such as tribasic lead sulfate) have good thermal stability but are toxic and affect weather resistance; while organotin stabilizers are more suitable for products with high transparency and environmental requirements. Insufficient or improper stabilizers will lead to accelerated aging of pipes in chemical media.
Other Additives: Fillers, impact modifiers and others also affect the final chemical stability.
2.Processing Technology
Improper control of processing temperature, mixing uniformity, extrusion or injection molding processes may lead to poor plasticization, internal stress concentration or micro defects. These will become breakthrough points for chemical medium corrosion and reduce chemical resistance.
3.Environment and Application Conditions
Type and Concentration of Chemical Media: This is the most direct factor. The resistance of PVC varies with the concentration of the medium. For example, it can resist concentrated hydrochloric acid, sulfuric acid below 90%, nitric acid of 50–60%, and caustic soda below 20%, but it cannot withstand strong oxidizing acids such as fuming sulfuric acid and concentrated nitric acid.
Temperature: An increase in temperature will significantly accelerate the chemical corrosion process. The long-term service temperature of PVC is generally not suitable to exceed 55–60 °C.
Time and Stress: Long-term immersion and continuous mechanical stress (such as internal pipe pressure) act synergistically to aggravate chemical attack, which may lead to stress cracking.