Chlorinated Rubber

1. Physical Properties:
   · Appearance: White or cream-colored, odorless powder or flake solid
   · Density: ~1.5-1.7 g/cm³
   · Thermal Stability: Stable below 130°C; decomposes releasing hydrogen chloride at higher temperatures
   · Solubility: Insoluble in water, ethanol; soluble in aromatic hydrocarbons (toluene, xylene), esters, ketones, chlorinated hydrocarbons, etc.
   · Film Formation: Forms hard, transparent, continuous films

2. Chemical Properties:
   · High chlorine content (65-68%), providing excellent flame retardancy and chemical inertness
   · Excellent corrosion resistance to inorganic chemicals such as acids, alkalis, salts, and oxidizers
   · Good weather resistance, although prolonged UV exposure may cause film chalking
   · Very low permeability to water, water vapor, and oxygen, offering outstanding barrier protection
   · Good compatibility with various plasticizers and resins (e.g., alkyd resins, epoxy resins)

Extended Explanation of Production Processes: Aqueous vs. Solvent Method

The production of Chlorinated Rubber has historically relied on two primary processes: the Solvent Process and the Aqueous Process. Understanding the difference is crucial for evaluating product quality, environmental impact, and regulatory compliance.

1. Solvent Process (Traditional - Now Obsolete)

• Basic Principle: Natural or synthetic rubber was dissolved in chlorinated organic solvents, primarily carbon tetrachloride (CCl₄), to form a homogeneous solution. Chlorine gas (Cl₂) was then introduced in the presence of a catalyst. Post-reaction, the product was isolated by precipitation in water or solvent distillation.

• Process Characteristics:

  • Homogeneous Reaction: Efficient and uniform reaction in solution, leading to consistent product quality.

  • Solvent Issue: Relied on carbon tetrachloride (CCl₄), a highly toxic solvent and a potent ozone-depleting substance (ODS).

  • Complex Post-Treatment: Required complex solvent recovery systems; risk of residual solvent in the final product.

  • High Environmental & Safety Risk: The use of toxic, volatile solvents posed significant risks to operators and the environment. This method is now banned under the Montreal Protocol.

2. Aqueous Process (Modern - Industry Standard)

• Basic Principle: Rubber is broken down into fine particles or a slurry and dispersed in an aqueous (water) phase to form a stable suspension. Chlorination is carried out by introducing chlorine gas into a pressurized reactor. Dispersing agents and catalysts are added to ensure smooth reaction and product stability. The final product is obtained after neutralization, washing, dehydration, and drying.

• Process Characteristics:

  • Heterogeneous Reaction: Reaction occurs in a water suspension, eliminating the need for organic solvents.

  • Eco-Friendly & Safe: Completely eliminates the use of ODS and toxic solvents, making the process safer and environmentally sustainable.

  • Pure Product: The product is free from organic solvent residues, is typically whiter in color, and offers better thermal stability.

  • Technical Barrier: Requires advanced technology for dispersion, catalysis, and process control to ensure uniform chlorination and controlled molecular weight distribution.