The superior chemical resistance of PVC waterstops compared to rubber stems from fundamental differences in molecular structure and material composition:
Chlorine-rich Polymer Backbone
PVC contains highly electronegative chlorine atoms (≈57% by weight) covalently bonded to the carbon chain. This polar structure creates strong intermolecular forces, forming a dense barrier against chemical penetration. In contrast, natural rubber's polyisoprene backbone (C₅H₈) and synthetic rubbers like NBR/SBR lack such inherent chemical inertness.
Inertness to Oxidation
The C-Cl bonds in PVC resist oxidation reactions that degrade rubber's unsaturated carbon-carbon bonds. Rubber vulcanization introduces sulfur crosslinks that remain vulnerable to ozone, oxygen, and strong acids. PVC's saturated structure prevents chain scission even under prolonged UV/chemical exposure.
Hydrophobic Nature
PVC's hydrocarbon base combined with chlorine's electronegativity results in low water absorption (<0.5%), minimizing hydrolysis risks. Rubbers like EPDM/NBR absorb 3-8% water, accelerating degradation in acidic/alkaline environments.
Additive Synergy
PVC formulations incorporate UV stabilizers (e.g., titanium dioxide) and thermal stabilizers (e.g., lead/ca-zinc compounds) that enhance chemical resistance. Rubber antioxidants/plasticizers often migrate or decompose under chemical stress.
Performance in Specific Media
Acids: PVC withstands ≤20% HCl and ≤50% H₂SO₄ at 20°C, while rubber swells in concentrated acids.
Alkalis: PVC resists ≤20% NaOH solutions, outperforming rubber which degrades in strong bases.
Oils/Solvents: PVC's chlorine barrier repels non-polar hydrocarbons better than NBR/CR rubbers.
