The Evoluon of Starch in Paper Manufacturing: From Nave to Modified Starches

Twinkle Parikh – Managing Partner – Sanjay Adhesives

The paper manufacturing industry has seen substantial advancements over the years, with starch playing a pivotal role in improving both the quality and cost-efficiency of paper production.

Historically, native starches such as corn starch were used in various stages of paper production. However, as demands for higher-quality products and more sustainable practices grew, the industry shifted towards modified starches.

Among the most commonly used starch types today are dry-end starch and wet-end starch, including oxidized starch and cationic starch. These starches offer numerous advantages over traditional native starches, revolutionizing the papermaking process.

Native Starch: Limitations and Challenges

Native starch, particularly native corn starch, has been employed in paper manufacturing, mainly for sizing applications. While it is effective in certain contexts, native starch comes with inherent limitations that can undermine the efficiency and quality of paper production:

1. Viscosity Variability:
   Native starch tends to exhibit significant viscosity fluctuations. For instance, its viscosity can range from 750 to 1000 Centipoises when measured with spindle no. 6 at 20 rpm at 75°C in a 5% solution. These variations make it challenging to maintain a consistent quality in the paper, particularly when precise viscosity control is necessary for high-speed production.
2. Concentration Limitations:
   Increasing the concentration of native starch to enhance its effect can result in a solution that is too viscous, hindering proper application and potentially compromising the final product’s characteristics.
3. Machine Speed Constraints:
   The application of native starch often requires slower machine speeds to achieve optimal paper quality. This reduction in machine speed directly impacts productivity and can lead to inefficiencies in the manufacturing process.

To address these challenges, papermakers have introduced enzyme-based treatments to modify native starch and improve performance. However, this solution can lead to unintended consequences, such as the conversion of starch into sugar increasing the overall hygroscopicity tendency, which negatively affects the paper’s burst factor and overall strength.

Dry-End Starch: The Rise of Oxidized Starch

One of the most notable advances in starch usage is the development of dry-end starch, which is introduced into paper pulp during the drying process. Typically added in powder or granular form, oxidized starch is a widely used variant due to its superior performance compared to native starch. Oxidized starch brings multiple benefits to the papermaking process:

1. Consistent Viscosity:
   Oxidized starch offers a more stable viscosity profile compared to native starch, ensuring uniform application across the paper surface. This consistency not only facilitates better coverage but also supports higher machine speeds, enhancing productivity without compromising quality.
2. Improved Strength:
   The inclusion of oxidized starch significantly strengthens the paper, making it more durable and less prone to tearing. This enhanced strength is particularly beneficial in applications requiring high resistance to mechanical stress or folding.
3. Better Printability:
   Oxidized starch improves the surface properties of the paper, which in turn facilitates better ink adhesion. This results in improved print quality, making oxidized starch a valuable addition in paper types used for printing and publishing.

In addition to oxidized starch, uncooked cationic starch is often used in multi-ply paper machines to further enhance paper quality. Cationic starch has a positive charge, which allows it to bond more effectively with cellulose fibers, contributing to superior strength, printability, and water resistance.

Applications of Cationic Starch

• Pulp Storage Chest:
  When introduced into the pulp storage chest, cationic starch serves as a fixative, improving the retention of fibers in the wet end of the papermaking process. This not only optimizes fiber utilization but also enhances the overall consistency and quality of the paper.
• Thick Stock Pump:
  Dosing cationic starch near the thick stock pump bolsters the dry strength of the paper. This results in a product that is stronger and more resilient, meeting the demands for higher performance in commercial and industrial applications.

By strategically incorporating these modified starches throughout the production process, manufacturers can significantly enhance both the quality and efficiency of their papers produced.

Wet-End Starch: The Role of Cationic Starch in Paper Formation

While dry-end starches are added during the drying phase, wet-end starch is introduced earlier in the papermaking process, when the pulp is mixed with water and other chemicals. Wet-end starch is essential for improving paper formation, drainage, and retention properties. It helps produce a more uniform sheet of paper with improved opacity and overall strength.

Among the most effective wet-end starches is cationic starch, which has become increasingly popular in paper manufacturing for several reasons:

1. Enhanced Plybond Strength:
   Cationic starch increases the plybond strength of paper, improving its performance in printing and writing applications. This makes it particularly useful in applications requiring high-quality printing surfaces, such as packaging and stationery.
2. Better Retention:
   Cationic starch enhances retention properties by promoting better fiber bonding and reducing fiber loss during the papermaking process. This not only improves efficiency but also contributes to higher yield and lower waste.

Polymerized Starch: A Premium Option for Plybond Strength and RCT

Another modified starch gaining attention in some Western countries is polymerized starch, which is used to enhance the plybond strength and Ring Crush Test (RCT) of paper. Polymerized starch is particularly useful for high-strength applications, where increased plybond strength is crucial for paper durability and resistance to tearing. However, its higher cost has limited its adoption in certain regions.

In India, polymerized starch is not commonly used in paper production due to its higher price compared to oxidized starch and cationic starch, which offer a more cost-effective solution for improving paper strength and printability. The cost-effectiveness of oxidized and cationic starches makes them the preferred choice in many developing markets.

Modified Starches: A Game-Changer in Paper Manufacturing

The introduction of modified starches—such as oxidized starch and cationic starch—has significantly transformed the paper industry. These starches offer a more cost-effective and sustainable alternative to traditional resins, which were once commonly used to improve paper quality. However, resins come with their own set of challenges, including:

1. High Cost:
   Resins are generally more expensive than starches, leading to higher production costs for paper manufacturers.
2. Environmental Concerns:
   The use of resins can contribute to environmental pollution, particularly in aquatic environments, as they are often not biodegradable and can harm marine life.
3. Limited Functionality:
   Resins are less versatile than modified starches and cannot be tailored as easily to meet the specific needs of paper manufacturers.

In contrast, modified starches provide several advantages:

1. Cost-effectiveness:
   Modified starches are significantly more affordable than resins, helping to reduce overall production costs.
2. Environmental Sustainability:
   Being biodegradable and non-toxic, modified starches present a much more environmentally friendly option, aligning with the growing demand for sustainable manufacturing practices.
3. Improved Functionality:
   Modified starches can be customized to meet specific paper properties such as strength, stiffness, and printability, making them highly versatile for different paper grades and applications.

Conclusion

The evolution of starch in paper manufacturing has been marked by a shift from traditional native starch to modified starches, driven by the need for improved quality, higher efficiency, and sustainability. Oxidized starch and cationic starch have emerged as key players in this transformation, offering consistent viscosity, enhanced strength, and superior printability, all while being more cost-effective and environmentally friendly than resins.

As the paper industry continues to evolve, the role of modified starches is set to grow even further, driving both innovation and sustainability in paper production. The move towards modified starches—such as oxidized and cationic starch—represents a critical step forward in improving paper quality while reducing environmental impact, making them a superior choice compared to native starches and resins. Manufacturers are encouraged to adopt these modified starches as part of their commitment to high-quality, sustainable paper products.