Isothiazolinone biocides are a broad-spectrum, highly effective class of microbial inhibitors widely used in industries such as coatings, adhesives, papermaking, metalworking fluids, and water treatment. However, they are prone to degradation and ineffectiveness in formulations due to factors such as pH, temperature, metal ions, and redox reactions.
I. Chemical Properties of Magnesium Oxide
Magnesium oxide is an alkaline, low-solubility inorganic oxide that gradually hydrates into magnesium hydroxide in aqueous systems, creating a slow and controllable alkaline environment. It also possesses:
Buffering capacity: Suppresses pH fluctuations.
Adsorption/chelation: Can chelate certain metal ion impurities.
High-temperature resistance: Thermally stable and does not decompose.
These properties make magnesium oxide an excellent stabilizing additive.
II. Mechanism of Enhancing Isothiazolinone Stability
1. pH Buffering Stabilization
Isothiazolinones are prone to hydrolysis and inactivation in acidic environments. Magnesium oxide neutralizes free acids and establishes a mildly alkaline buffering environment, maintaining the pH within the stable range of the biocide (4–8), significantly slowing hydrolysis.
2. Inhibition of Metal-Catalyzed Degradation
Isothiazolinones are susceptible to catalytic oxidation or complexation inactivation by soluble metal ions (e.g., Fe³⁺, Cu²⁺). Magnesium oxide reduces the active concentration of metal ions through ion exchange and surface adsorption, minimizing catalytic degradation pathways.
3. Prevention of Oxidative Reactions
The alkaline nature of magnesium oxide helps neutralize or inhibit the attack of certain peroxides or acidic oxidants on isothiazolinones, reducing free radical or oxidative degradation pathways.
4. Synergistic Antimicrobial Enhancement
Studies have shown that the alkaline environment created by magnesium oxide also exhibits mild inhibitory effects on certain bacteria or molds, synergistically improving the overall antimicrobial and antifungal efficacy of isothiazolinones.
III. Practical Application Scenarios
1. Waterborne Coatings/Adhesives
Prevents biocide ineffectiveness caused by acidification or metal contamination in storage tanks.
Extends pot life and shelf life.
2. Metalworking Fluids/Water Treatment Agents
Neutralizes acidic byproducts generated in the system, reducing corrosion risks and maintaining biocide activity.
3. Papermaking/Emulsion Polymerization
Buffers pH fluctuations to prevent degradation during high-temperature processes.
IV. Usage Recommendations
Select high-purity, low-impurity magnesium oxide to avoid introducing additional metal ion contamination.
Pre-disperse or prepare a masterbatch according to the formulation system to ensure uniform distribution.
Determine the optimal dosage during the formulation development stage through small-scale trials, typically in the range of 0.1–1.0% (specific amounts should be optimized for each system).