I. Introduction

The paper manufacturing industry is a complex chemical processing operation involving multiple stages such as fiber slurry preparation, pulping, bleaching, and sheet formation. During these processes, mechanical agitation, chemical reactions, and the presence of surfactants often generate excessive foam. This foam not only reduces production efficiency but can also lead to paper quality defects. Defoamers, as essential papermaking additives, effectively control foam during production, playing an indispensable role in ensuring continuous operation and product quality.

II. Foam Formation and Its Hazards in Papermaking

(1) Causes of Foam

Foam in papermaking primarily arises from:

1. Natural resins, fatty acids, and other surfactants present in raw materials

2. Chemical additives such as sizing agents and strengthening agents

3. Air entrainment due to mechanical stirring and pulp pumping

4. Accumulated surfactants in wastewater recycling systems

(2) Hazards of Foam

1. Impact on Production Operations: Foam can cause slurry overflow and difficulty in level control, disrupting continuous and stable production.

2. Reduced Product Quality: Foam leads to defects like "foam holes" and "fish eyes," affecting paper appearance and strength.

3. Increased Energy Consumption: Foam reduces slurry density, increasing pumping energy costs.

4. Environmental Pollution: Overflowing foam worsens the production environment and raises cleaning costs.

III. Classification and Characteristics of Defoamers

(1) Classification by Chemical Composition

1. Mineral Oil Defoamers:

   • Main components: Mineral oil as a carrier with hydrophobic particles (e.g., silica)

   • Characteristics: Low cost, suitable for general foam control

   • Disadvantages: Lower efficiency, may affect paper sizing

2. Silicone-Based Defoamers:

   • Main components: Polydimethylsiloxane and its derivatives

   • Characteristics: Extremely low surface tension, excellent defoaming and foam suppression

   • Advantages: Low dosage, high efficiency, minimal impact on paper properties

   • Disadvantages: Higher cost, potential deposition issues

3. Polyether Defoamers:

   • Main components: Ethylene oxide/propylene oxide copolymers

   • Characteristics: Combined defoaming and foam suppression, heat-resistant

   • Advantages: Suitable for high-temperature, highly alkaline conditions

   • Disadvantages: Less effective at low temperatures

4. Composite Defoamers:

   • Combination of different defoaming components

   • Characteristics: Integrates advantages of multiple ingredients, designed for specific issues

   • Advantages: Wide applicability, stable performance

(2) Classification by Form

1. Oil-Based Defoamers: Traditional form, easy to disperse

2. Emulsion Defoamers: Good water dispersibility, convenient to use

3. Powder Defoamers: Easy to transport and store

4. Paste Defoamers: High concentration, cost-effective

IV. Application of Defoamers in Papermaking

(1) Pulping Section

1. Digestion Process: High-temperature alkaline conditions cause foam from resins and fatty acids, requiring alkali- and heat-resistant defoamers.

2. Washing and Screening: Mechanical action during pulp and black liquor separation generates foam, reducing washing efficiency.

3. Bleaching Section: Hydrogen peroxide bleaching tends to produce foam, necessitating specialized defoamers.

(2) Papermaking Section

1. Stock Approach System: Foam forms at the fan pump and cleaners, affecting sheet formation uniformity.

2. White Water System: Closed-loop recycling accumulates surfactants, requiring high-efficiency foam suppressants.

3. Coating Process: Binders and dispersants in coating formulations generate foam, impacting coating quality.

(3) Wastewater Treatment

Papermaking wastewater contains high organic content, leading to foam during aeration treatment, requiring environmentally friendly defoamers.

V. Selection Criteria for Defoamers

1. Specificity: Choose based on foam characteristics (pH, temperature, system composition).

2. Compatibility: Should not react adversely with other papermaking chemicals.

3. Efficiency: Low dosage with long-lasting effects.

4. Environmental Compliance: Must meet eco-friendly standards without affecting paper recyclability.

5. Cost-Effectiveness: Balance between cost and performance.

VI. Trends in Defoamer Development

1. High-Efficiency Composite Types: Development of multifunctional formulations for improved performance.

2. Eco-Friendly Variants: Biodegradable, non-toxic products.

3. Smart Defoamers: Systems that automatically adjust dosage based on foam conditions.

4. Specialized Defoamers: Tailored solutions for specific processes and paper grades.

VII. Conclusion

Defoamers play a crucial role in paper production by ensuring efficiency and product quality. As papermaking technology advances and environmental regulations tighten, defoamer innovation continues to evolve. In the future, high-efficiency, eco-friendly, and multifunctional defoamers will dominate the market, supporting sustainable development in the paper industry. Paper manufacturers should select defoamers scientifically based on their specific processes and continuously optimize usage strategies for the best economic and technical outcomes.