Chất làm cứng bề mặt giấy từ enzyme sinh học: Một cuộc cách mạng bền vững trong công nghệ làm cứng bề mặt giấy

1. Introduction: The Challenge of Starch Sizing in Modern Papermaking

Surface sizing is an indispensable process in modern papermaking, essential for improving paper surface strength, water resistance, and printability. Among the various surface sizing agents available, starch and its derivatives are the most widely used—accounting for the largest volume of any commercial product used for surface sizing of paper. Starch is applied in concentrations typically ranging from 6% to 12%, depending on the desired paper qualities.

For decades, oxidized starch has been the industry standard for surface sizing. However, the traditional chemical production process for oxidized starch has long presented significant drawbacks: high production costs, difficulty in controlling the degree of oxidation, and environmental pollution. The oxidation process consumes substantial quantities of bleaching agents, generates wastewater, and imposes operational complexities that limit production efficiency.

In response to these challenges, bio-enzyme sizing technology has emerged as a transformative alternative. By utilizing biological enzymes—primarily α-amylase—to modify native starch through a controlled enzymatic hydrolysis process, papermakers can now produce high-performance starch sizing agents with exceptional flexibility, cost-effectiveness, and environmental sustainability.

Công ty TNHH Công nghệ LY Chem. , with over two decades of experience in paper chemicals manufacturing, recognizes the transformative potential of bio-enzyme sizing technology. As a comprehensive supplier of papermaking chemical solutions, LY Chem supports papermakers in adopting sustainable, cost-effective technologies that improve product quality while reducing environmental impact.

2. The Science of Bio-Enzyme Sizing: Understanding the Mechanism

2.1 What Is a Bio-Enzyme Sizing Agent?

A bio-enzyme sizing agent (also known as a sizing enzyme or starch-converting enzyme) is a biological enzyme preparation that directly treats native (unmodified) starch to achieve the viscosity and performance characteristics required for paper surface sizing. These enzymes are typically α-amylase or α/β-amylase复合酶 preparations that hydrolyze starch polymers into lower molecular weight fragments, reducing viscosity to levels suitable for surface sizing applications.

2.2 The Enzymatic Hydrolysis Mechanism

Starch is a high-molecular-weight polysaccharide composed of glucose units linked by α-D-1,4 glycosidic bonds (in amylose) and α-D-1,6 glycosidic bonds (at branch points in amylopectin). Bio-enzyme sizing agents—primarily endo-acting α-amylases—function by randomly cleaving the α-1,4 glycosidic bonds within the starch polymer chain.

The mechanism proceeds as follows:

1. Gelatinization: When starch is heated to its gelatinization temperature in water, the starch granules swell and the polymer chains become accessible to enzymatic action.
2. Enzymatic Hydrolysis: The bio-enzyme randomly attacks and cleaves the α-1,4 glycosidic bonds, breaking the long starch polymer chains into shorter fragments. This reduces the molecular weight and, consequently, the viscosity of the starch paste.
3. Controlled Viscosity Reduction: The enzyme continues to reduce viscosity until the desired level is reached. Unlike chemical oxidation, which is difficult to control precisely, enzymatic hydrolysis can be terminated on demand by heating the paste above 95°C—a temperature at which the enzyme is irreversibly denatured and loses activity.
4. Viscosity Stabilization: Once the enzyme is inactivated, the viscosity remains stable and unchanged. This stability is one of the most significant advantages over traditional oxidized starch.

2.3 The Role of Temperature and pH

The enzymatic conversion process is highly dependent on temperature and pH:

• Optimal temperature range: 60–95°C
• Optimal pH range: 6.0–7.0 (with an acceptable range of 5.5–7.5)
• Enzyme inactivation: Heating to 95°C for 15–20 minutes ensures complete enzyme denaturation

The α/β-复合淀粉酶 system has been shown to provide superior control over the starch hydrolysis rate, yielding starch pastes with viscosity well-suited for surface sizing applications. Studies have demonstrated that under optimized conditions (α-amylase 90 mL/t, β-amylase 30 mL/t at 60°C), paper strength properties can be significantly enhanced.

3. Bio-Enzyme Sizing vs. Traditional Oxidized Starch: A Comparative Analysis

3.1 Limitations of Traditional Oxidized Starch

The conventional production of oxidized starch for surface sizing involves chemical oxidation using agents such as sodium hypochlorite or hydrogen peroxide. This process has been the industry standard for decades but presents multiple disadvantages:

Limitation	Impact
High production cost	Chemical reagents, energy consumption, and wastewater treatment drive up costs
Difficult oxidation control	Degree of oxidation is hard to regulate precisely, leading to inconsistent product quality
Environmental pollution	Chemical oxidation generates wastewater containing residual oxidants and byproducts
Limited concentration	Oxidized starch pastes cannot be easily prepared at high concentrations
Incomplete dissolution	Insoluble particles can cause pipe blockages and operational issues
Surface defects	Papers sized with oxidized starch may exhibit roughness and linting problems

3.2 Advantages of Bio-Enzyme Sizing Technology

Bio-enzyme sizing technology directly addresses each of these limitations:

1. Operational Simplicity
The enzymatic process is straightforward: simply mix native starch with water, add the enzyme, heat to gelatinization, and control viscosity through temperature management. No complex chemical handling or hazardous reagents are required. The process does not change pH, does not affect subsequent production, and is non-corrosive.

2. Precise Viscosity Control
The greatest advantage of bio-enzyme sizing is the ability to precisely and flexibly control viscosity at the production site. Viscosity can be adjusted according to real-time production requirements by varying enzyme dosage or hydrolysis time—a flexibility that oxidized starch cannot match.

3. Reduced Cost
The economic benefits are substantial:

• Enzyme usage is minimal—typically 0.01–0.03% relative to dry starch or 50–150 mL per ton of dry starch
• A few yuan worth of enzyme (50–400 grams per ton of starch) can replace one ton of oxidized starch
• Starch usage can be increased by 15–30% while maintaining or improving performance
• A pilot plant test demonstrated cost savings of 53.5 yuan per ton of paper when replacing oxidized starch with enzyme-converted starch

4. Environmental Sustainability
The bio-enzyme process eliminates the need for chemical oxidants, reducing wastewater pollution and energy consumption. The enzymatic conversion is a biological process that generates no hazardous byproducts.

5. Superior Paper Properties
Papers produced with bio-enzyme-sized starch exhibit:

• Increased surface smoothness and reduced linting/dusting
• Độ bền bề mặt được nâng cao and printability
• Improved tensile strength, burst index, and folding endurance
• Better fiber bonding due to improved penetration and adhesion

6. High Concentration Capability
Bio-enzyme sizing enables the preparation of high-concentration, low-viscosity starch pastes—a combination that oxidized starch cannot achieve. Higher concentrations mean greater sizing application per pass and improved production efficiency.

3.3 Performance Comparison: Data from Industry Applications

Study: Enzyme-Converted Starch in Lightweight Paper Sizing

Using α-amylase to prepare high-concentration, low-viscosity starch sizing agent for 60 g/m² lightweight paper:

• Optimal conditions: α-amylase 0.2‰ (relative to dry starch); hold at 80°C for 20 minutes; rapidly heat to 98°C and hold for 30 minutes
• Product properties: 9.0% solids; viscosity 5.5–6.5 mPa·s at 60°C
• Result: Surface strength increased by 23% compared to oxidized starch

Study: Enzyme-Converted Starch in Carbonless Copy Paper Base Stock

Compared with oxidized starch sizing:

• Longitudinal stiffness: Increased by approximately 30 mN·mm
• Độ bền bề mặt: Increased by approximately 0.1 m/s
• Cost savings: 53.5 yuan per ton of paper

Study: Enzyme-Converted Starch in Corrugating Medium

Using α/β-复合淀粉酶 under optimized conditions (60°C, 90 mL/t α-amylase, 30 mL/t β-amylase):

• Độ bền kéo: Increased by 20.7% compared to unsized paper
• Độ bền nén vòng: Increased by 31.8% compared to unsized paper

4. Application Process: How to Use Bio-Enzyme Sizing Agents

4.1 Intermittent (Batch) Cooking Process

The batch process is the most commonly used method for preparing bio-enzyme-sized starch pastes:

Step 1: Starch Slurry Preparation
Add the required amount of clean water and starch to the cooking vessel according to the target solids concentration. Mix thoroughly to form a uniform slurry.

Step 2: Enzyme Addition
Add the pre-measured bio-enzyme (typical dosage: 0.01–0.03% relative to dry starch, or 50–150 mL per ton of dry starch). Mix thoroughly to ensure uniform enzyme distribution throughout the slurry.

Step 3: Steam Cooking
Begin heating with steam. The temperature should be raised progressively according to the starch viscosity profile. The principle is to heat directly to 95°C in a single step.

Step 4: Temperature Control
Monitor the viscosity during heating. Enzymatic hydrolysis accelerates as the starch gelatinizes and the enzyme becomes active.

Step 5: Enzyme Inactivation
Once the target viscosity is reached, hold at 95°C for 15–20 minutes. This heat treatment completely inactivates the enzyme, stabilizing the viscosity.

Step 6: Cooling and Application
Cool the paste to the application temperature of 55–65°C. Special cases may require adjustment according to the manufacturer’s specifications.

Key Process Parameters:

• Water pH: 5.5–7.5 (optimal: 6.0–7.0)
• Enzyme dosage: 0.5–2.0‰ relative to dry starch (cultural paper); 0.5–1.0‰ (board paper)
• Starch concentration: 5–10%
• Application temperature: 55–65°C

4.2 Continuous Cooking Process

The continuous cooking process follows essentially the same principles as the batch process but offers significant advantages for large-scale production:

• Fully automated process control ensures consistent quality
• Precise control of all process parameters: starch concentration, enzyme dosage, conversion temperature, conversion time, and inactivation temperature
• Uniform molecular weight and stable viscosity of the finished paste
• Improved paper quality and machine runnability (reduced paper breaks, cleaner dryer surfaces)
• Reduced sizing consumption while maintaining equivalent product quality

4.3 Practical Tips for Successful Application

1. Enzyme compatibility: Bio-enzyme sizing agents are compatible with most anionic and nonionic size press additives. They work well with AKD for enhanced water resistance.
2. Enzyme stability: Enzymes are protein-based materials. Prolonged contact may irritate skin, eyes, and mucous membranes. Appropriate personal protective equipment is recommended.
3. Storage: Bio-enzyme products should be stored in a cool, dry place. Liquid products typically have a shelf life of 6–12 months.
4. Avoid freezing: Enzyme preparations should not be frozen.
5. Trial optimization: The optimal enzyme dosage should be determined through laboratory trials based on the specific starch type and target viscosity.

5. Industry Applications and Case Studies

5.1 Large-Scale Paper Machine Application

Case Study: Sun Paper Industry (太阳纸业)

Sun Paper’s Tianzhang #19 machine (wire width 4,950 mm, design speed 1,300 m/min) successfully implemented bio-enzyme sizing technology. The results were impressive:

• Raw material change: Switched from oxidized cationic cassava starch to native cassava or corn starch
• Process simplification: Eliminated the oxidation and cationization steps
• Energy savings: Reduced energy consumption
• Emission reduction: Lowered environmental pollution
• Cost reduction: Significantly reduced surface sizing chemical costs

5.2 Lightweight Paper Production

For 60 g/m² lightweight paper, α-amylase-converted starch at 9.0% solids with viscosity of 5.5–6.5 mPa·s at 60°C delivered a 23% improvement in surface strength compared to conventional oxidized starch sizing.

5.3 Corrugating Medium Production

Using α/β-复合淀粉酶 under optimized conditions produced a sizing agent that increased:

• Độ bền kéo: +20.7%
• Độ bền nén vòng: +31.8%

5.4 Carbonless Copy Paper Base Stock

A pilot-scale trial demonstrated that enzyme-converted starch sizing:

• Increased longitudinal stiffness by 30 mN·mm
• Increased surface strength by 0.1 m/s
• Reduced production cost by 53.5 yuan per ton of paper

6. Quality Control and Troubleshooting

6.1 Common Issues and Solutions

Issue: Yellow foam formation

• Cause: Incomplete enzyme inactivation or starch degradation
• Solution: Ensure proper heat treatment (95°C for 15–20 minutes); consider using inorganic carriers with cationic modification

Issue: Rod plugging and roll sticking

• Cause: Undissolved starch particles or incomplete gelatinization
• Solution: Improve mixing; ensure proper cooking temperature profile

Issue: Uneven sizing

• Cause: Inconsistent viscosity or enzyme activity
• Solution: Control enzyme dosage and cooking conditions precisely; consider using α/β- systems for better control

6.2 Monitoring Key Parameters

To ensure consistent sizing quality, papermakers should monitor:

• Starch paste viscosity: The primary indicator of enzymatic conversion degree
• Solids content: Determines application rate and coverage
• Temperature: Critical for both enzymatic activity and inactivation
• pH: Affects enzyme activity and stability

7. Conclusion: The Future of Sustainable Sizing

Bio-enzyme sizing technology represents a paradigm shift in paper surface sizing—moving from resource-intensive chemical processes to sustainable, precise, and cost-effective biological conversion. The advantages are compelling:

• Environmental: Eliminates chemical oxidants, reduces wastewater pollution, and lowers energy consumption
• Economic: Reduces chemical costs, enables higher starch concentrations, and improves production efficiency
• Quality: Enhances paper surface strength, smoothness, printability, and physical strength properties
• Operational: Provides unprecedented flexibility in viscosity control at the production site

The technology has been widely adopted by major paper mills worldwide. In China, leading mills have transitioned from oxidized starch to enzyme-converted starch systems, achieving significant cost savings and quality improvements.

Công ty TNHH Công nghệ LY Chem. , with over two decades of experience in paper chemicals manufacturing, is committed to supporting papermakers in adopting sustainable, high-performance technologies. As the industry continues to pursue greater sustainability and efficiency, bio-enzyme sizing technology will play an increasingly central role in the future of papermaking.

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For more information about LY Chem’s complete range of papermaking chemical solutions, please contact our technical sales team.

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