Introduction
In the corrugated cardboard manufacturing industry, adhesives play a crucial role in bonding the linerboards and fluted medium together to create strong, durable packaging materials. Among the various adhesives used, starch-based adhesives are the most widely adopted due to their cost-effectiveness, sustainability, and strong bonding properties.
This article explores the importance of starch adhesive in cardboard production, its advantages over synthetic adhesives, the formulation process, and best practices for application in a production line.
What is Starch Adhesive?
Starch adhesive is a natural, biodegradable glue made from plant-derived starches, such as:
- Corn starch
- Tapioca starch
- Potato starch
- Wheat starch
Starch adhesive is water-based and becomes sticky when heated or mixed with alkali solutions, making it ideal for corrugated board bonding.
Why is Starch Adhesive Used in Cardboard Production?
Strong Bonding Performance
- Creates high-strength adhesion between corrugated fluting and linerboards.
- Ensures structural integrity even under stress or weight.
Eco-Friendly & Biodegradable
- Derived from natural sources, making it 100% biodegradable and recyclable.
- Safer for food packaging applications compared to synthetic adhesives.
Cost-Effective
- Starch adhesives are cheaper than synthetic glue and widely available.
- Reduces overall production costs without compromising quality.
Moisture Resistance with Additives
- When combined with borax or resin additives, starch adhesive provides better water resistance.
Non-Toxic & Food-Safe
- Starch-based glues contain no harmful chemicals, making them safe for food packaging.
How is Starch Adhesive Prepared?
1. Ingredients & Chemical Composition
Starch adhesive is made using a combination of:
- Raw starch (corn, tapioca, potato, or wheat) – the main binding agent.
- Borax (sodium borate) – improves viscosity and bonding strength.
- Caustic soda (sodium hydroxide) – gelatinizes the starch, activating adhesion.
- Water – used as a base for mixing and application.
2. Starch Adhesive Formulation Process
Mixing: Starch is dissolved in water to create a slurry.
Cooking: The solution is heated to activate gelatinization and enhance stickiness.
Addition of Additives: Borax and caustic soda are added to increase bonding efficiency.
Cooling & Storage: The adhesive is stored in temperature-controlled tanks for production use.
Application of Starch Adhesive in a Cardboard Production Line
Starch adhesive is applied at multiple stages during corrugated cardboard production. Here’s how it works:
1. Corrugation & Fluting Stage
- Starch adhesive is applied to the fluted medium to bond it with the linerboard.
- A precise glue roller system ensures even distribution of adhesive.
2. Bonding of Multiple Layers
- In double-wall and triple-wall cardboard, starch glue is used to bond additional liner layers.
- The adhesive must set quickly to maintain production speed.
3. Drying and Curing
- Heat is applied using steam-heated rollers to accelerate drying.
- Proper temperature control prevents glue over-drying or under-bonding.
4. Quality Control
- The adhesive application is monitored through viscosity tests.
- Any issues, such as uneven bonding or glue buildup, are corrected in real time.
Factors Affecting Starch Adhesive Performance
To ensure optimal bonding and cardboard durability, manufacturers must control several factors during adhesive application.
1. Temperature & Humidity
- Ideal glue temperature: 55°C – 65°C (131°F – 149°F).
- High humidity can weaken the bond, so drying must be carefully controlled.
2. Viscosity of Adhesive
- The glue should have moderate viscosity (18 – 25 seconds in a viscosity cup test).
- Low viscosity = Weak bonding.
- High viscosity = Glue buildup and slower drying.
3. Application Thickness
- Excess adhesive can cause warping or excessive moisture absorption.
- Too little adhesive can result in poor bonding.
4. pH Balance
- Maintaining a pH level between 8 – 10 ensures proper gelatinization.
- Too acidic or too alkaline glue can reduce adhesive effectiveness.
Common Problems in Starch Adhesive Application & Solutions
| Problem | Cause | Solution |
|---|---|---|
| Delamination (Peeling Layers) | Low glue viscosity or under-bonding | Adjust adhesive formulation & viscosity |
| Warping or Curling | Excess moisture in adhesive | Reduce glue thickness & optimize drying |
| Glue Drying Too Fast | Overheating during production | Lower glue temperature & adjust curing time |
| Weak Bonding | Incorrect pH level or low gelatinization | Adjust caustic soda levels for better activation |
Future Trends in Starch Adhesive Technology
1. Bio-Based Enhancements for Stronger Adhesion
- Scientists are developing starch-based adhesives with natural reinforcements for higher bonding strength.
- Future adhesives may include cellulose nanofibers for added durability.
2. Improved Water & Heat Resistance
- New formulations using organic additives are making starch adhesives more resistant to moisture.
- Enhances the use of corrugated cardboard in humid environments.
3. Automated Glue Application Systems
- AI-powered monitoring systems are now automating glue viscosity adjustments in real time.
- Reduces material waste and ensures consistent bonding.
Summary
Starch adhesive is the most widely used bonding agent in corrugated cardboard production, offering strong adhesion, sustainability, and cost efficiency.
By optimizing viscosity, temperature, and drying conditions, manufacturers can ensure:
- Stronger bonds and better cardboard durability.
- More sustainable, biodegradable packaging.
- Cost-effective and high-speed production lines.
With advancements in starch adhesive technology, the future of eco-friendly cardboard manufacturing looks promising.