AKD Sizing Agents: Manufacturing Innovations, Application Strategies, and Food Safety Compliance

1. Introduction: The Evolution of AKD Manufacturing Technology

Alkyl Ketene Dimer (AKD) has established itself as the most widely used neutral sizing agent in modern papermaking, offering superior water resistance, enhanced paper strength, and compatibility with cost-effective calcium carbonate fillers. Since its first industrial development by Hercules Inc. in 1956, AKD technology has undergone continuous refinement—from traditional solvent-based synthesis to today’s green, solvent-free manufacturing processes, and from liquid emulsions to advanced redispersible powder formulations.

This article provides a comprehensive technical overview of AKD sizing agents, covering manufacturing innovations, application strategies, and the critical safety and regulatory considerations that govern their use in food-contact paper products. As global demand for sustainable, high-performance packaging materials continues to rise, understanding the full lifecycle of AKD—from synthesis to end-use application—has never been more important for papermakers and chemical buyers alike.

LY Chem Technology Co., Ltd. , with over two decades of experience in paper chemicals manufacturing, offers a complete range of AKD-based sizing solutions, including our LY-AKD301 internal sizing agent and LY-AKD302 surface sizing agent. Our products are manufactured under ISO 9001 quality management and are available with FDA, SGS, and RoHS certifications for export markets.

2. Manufacturing Innovations: From Solvent-Based to Green Synthesis

2.1 Traditional Solvent-Based AKD Synthesis

Historically, AKD has been produced through the reaction of triethylamine and fatty acyl chlorides in organic solvents—most commonly toluene. While this method yields AKD of acceptable quality, it presents significant drawbacks:

• Solvent residue: Toluene, classified as a carcinogenic substance by the World Health Organization, can remain as a residue in the final AKD product.
• Environmental pollution: The use of volatile organic solvents generates emissions and wastewater that require costly treatment.
• Application limitations: Solvent residues render traditionally manufactured AKD unsuitable for food-contact paper applications, severely limiting its market potential.

2.2 The Solvent-Free Revolution

In response to these challenges, researchers and manufacturers have developed solvent-free AKD synthesis processes that eliminate toluene and other organic solvents from production.

Key innovations in solvent-free AKD manufacturing include:

Higher reaction temperatures: The synthesis temperature has been raised from the traditional 25°C to 50–70°C, accelerating reaction rates and significantly improving product quality.

Reduced moisture content: The elimination of solvents reduces the moisture content of reactants, leading to higher-purity AKD.

Energy efficiency: The solvent-free process effectively reduces energy consumption while achieving near-zero wastewater discharge.

Superior product purity: Solvent-free AKD is typically free from toxic substances, making it particularly suitable for sensitive applications such as liquid food packaging paper where hygiene standards are paramount.

Leading manufacturers have patented continuous AKD preparation devices that enable high-purity, solvent-free production at industrial scale. These innovations have made solvent-free AKD the mainstream direction for the industry.

2.3 Redispersible Powder Sizing Agents: Enhancing Stability and Performance

While AKD emulsions have been the industry standard for decades, they face inherent challenges: short shelf life (typically 1–3 months), susceptibility to hydrolysis, and the need for careful temperature-controlled storage.

To overcome these limitations, researchers have developed redispersible powder sizing agents using starch and polyvinyl alcohol (PVA) as protective colloids. These powder formulations are typically prepared through spray drying—a process in which AKD emulsions containing protective colloids are atomized and dried to form free-flowing powders.

The advantages of redispersible powder AKD are substantial:

• Extended shelf life: Powder formulations are significantly more stable than liquid emulsions
• Improved storage stability: Reduced hydrolysis during storage
• Excellent redispersibility: The powder readily redisperses in water to form stable emulsions
• Superior sizing efficiency: Enhanced performance compared to conventional emulsions

This technology represents a significant advancement in AKD formulation, enabling papermakers to maintain consistent sizing performance while simplifying inventory management and reducing waste.

3. Application Strategies: Internal vs. Surface Sizing

AKD sizing agents can be applied through two distinct approaches—internal sizing and surface sizing—each offering unique benefits and optimal use cases.

3.1 Internal Sizing (Wet-End Sizing)

Internal sizing involves the addition of AKD emulsion directly to the pulp at the wet end of the paper machine. The AKD particles adsorb onto cellulose fibers through electrostatic interactions and, during the drying process, form covalent ester bonds with fiber hydroxyl groups—creating a permanent hydrophobic barrier.

Advantages of internal AKD sizing:

• Simple application: Added directly to the pulp system with minimal process modification
• Lower cost: No additional equipment required beyond standard wet-end chemical addition systems
• Uniform distribution: Sizing agent is distributed throughout the sheet, providing bulk water resistance
• Enhanced internal bond strength: Improves overall sheet integrity

Limitations:

• Curing time required: Traditional formulations require 12–24 hours for full sizing development
• Surface roughness: Internally sized papers may have higher surface roughness
• Potential for surface defects: Issues such as waxy spots can occur if sizing is not properly controlled

3.2 Surface Sizing

Surface sizing involves the application of AKD or other sizing agents to the surface of already-formed paper at the size press, after the sheet has been partially dried.

Advantages of surface AKD sizing:

• High retention: Sizing agent retention approaches 100%, minimizing waste
• Superior surface properties: Significantly improves surface strength, water resistance, smoothness, and printability
• Reduced two-sidedness: Minimizes the difference between top and bottom sheet surfaces
• Enhanced physical strength: Improves ring crush index and burst index

Limitations:

• Higher cost: Requires additional equipment (size press) and sizing materials
• Additional process step: Adds complexity to the papermaking process

3.3 Strategic Selection: Which Approach Is Right for Your Application?

The choice between internal and surface sizing—or a combination of both—depends on the specific requirements of the final paper product:

Application	Recommended Approach	Rationale
Liquid packaging board	Internal sizing (hard sizing)	AKD provides excellent resistance to fruit juice, lactic acid, and other aggressive media
Corrugated medium (fluting)	Internal sizing	Provides compression resistance and moisture resistance for box strength
Linerboard for high-precision printing	Surface sizing	Enhances printability and surface smoothness
Food packaging paper	Internal + surface sizing	Dual approach ensures maximum barrier performance and regulatory compliance
Fast-moving consumer goods packaging	Internal sizing	Cost-effective for short-transport, lightweight applications

LY Chem’s AKD solutions address both application approaches:

• LY-AKD301 (Internal AKD Sizing Agent) — Ideal for wet-end addition, delivering superior water resistance and aging resistance for cultural paper, coated paper, and packaging base paper
• LY-AKD302 (Surface AKD Sizing Agent) — Designed for size-press application in combination with starch, shortening curing time while improving ring crush strength and burst strength for corrugating medium and linerboard

4. Food Safety and Regulatory Compliance

4.1 The Food-Contact Challenge

AKD is widely used in the manufacture of paper and board for food-contact applications to increase wetting stability. However, unbound AKD residues can hydrolyze and decarboxylate into dialkylketones—non-intentionally added substances (NIAS) that have the potential to migrate into fatty foods in contact with these packaging materials.

This migration potential has made food-contact compliance a critical consideration for AKD manufacturers and papermakers serving the food packaging sector.

4.2 FDA Regulations (United States)

The U.S. Food and Drug Administration (FDA) addresses AKD under 21 CFR 176.120 (“alkyl ketene dimers”). Key provisions include:

• AKD and its hydrolysis products (dialkyl ketones) may be used in paper and paperboard
• The combined total of AKD and dialkyl ketones must not exceed 0.4% by weight of the paper and paperboard
• The petition dossier for this approval covers comprehensive studies of potential exposure through the packaging chain, including complete toxicity studies for the hydrolysis product

4.3 BfR Regulations (Germany)

In Germany, the Federal Institute for Risk Assessment (BfR) has established specific regulations for paper and board intended for food contact under Recommendation XXXVI (“Papiere, Kartons und Pappen für den Lebensmittelkontakt”):

• Part B, additives, paragraph I.11: Dialkyl (C10-C18) diketene (may contain up to 65% iso-alkyl groups) — maximum 1.0%
• Recommendation XXXVI/2 (“Papiere, Kartons und Pappen für Backzwecke” — papers for baking purposes) — maximum 0.5%

Additionally, the BfR has established a specific migration limit (SML) of 5 mg/kg for the transfer of dialkylketones into foodstuffs.

4.4 European and Other International Standards

The European Union regulates food-contact materials under Regulation (EC) No 1935/2004. Other national approvals for AKD in food-contact applications include the Dutch Warenwet regulations.

4.5 Implications for Papermakers

For paper manufacturers serving the food packaging sector, the regulatory landscape demands:

1. Careful selection of AKD suppliers: Choose manufacturers that can demonstrate compliance with relevant food-contact regulations
2. Control of AKD addition levels: Ensure that AKD and dialkylketone content remains below regulatory limits
3. Migration testing: Verify that dialkylketone migration into food simulants and actual foods remains below SMLs
4. Documentation: Maintain comprehensive records of raw material specifications and finished product compliance

LY Chem Technology Co., Ltd. addresses these requirements through our LY-WA403 food-grade PAE wet strength resin and our full range of AKD sizing products, all available with FDA, SGS, and RoHS certifications. Our solvent-free manufacturing processes ensure that our AKD products are free from toluene and other harmful solvent residues, making them suitable for the most demanding food-contact applications.

5. Market Outlook and Industry Trends

5.1 Global AKD Market Growth

The global Alkyl Ketene Dimer (AKD) market demonstrates robust growth, driven by increasing demand from the paper manufacturing sector—particularly for packaging applications:

• Market valued at USD 460 million in 2024
• Projected to reach USD 485 million in 2025
• Expected to grow to USD 720 million by 2032
• CAGR of 5.8% during the forecast period

The Asia-Pacific region currently dominates AKD consumption, accounting for over 45% of global demand, with China being the largest producer and consumer. The China market alone accounted for nearly 35% of global paper production capacity in 2024, with AKD consumption in this sector growing 6.8% year-over-year.

5.2 Key Market Drivers

Sustainable Packaging Growth: With the paper and paperboard packaging sector expected to grow at over 4% annually through 2032, demand for AKD as a sizing agent continues to rise. This growth aligns with increased e-commerce activities and environmental regulations phasing out single-use plastics.

Technological Advancements: Recent innovations in AKD wax emulsion formulations have enhanced sizing performance while reducing consumption rates by up to 15% compared to traditional products. Major producers have developed thermally stable variants that maintain effectiveness across broader pH ranges (6.5–8.5), enabling wider application in recycled paper streams.

Cost-Effectiveness: AKD-based solutions have proven 20–25% more cost-effective than rosin alternatives in neutral/alkaline papermaking conditions.

Bio-Based AKD Development: While currently accounting for less than 10% of total production, renewable-sourced AKD is projected to capture nearly 30% market share by 2032 as sustainability mandates tighten globally.

6. Conclusion: The Future of AKD Sizing Technology

AKD neutral sizing technology has evolved dramatically since its introduction in 1956. From traditional solvent-based synthesis to today’s green, solvent-free manufacturing processes, and from liquid emulsions to advanced redispersible powder formulations, AKD technology continues to advance in response to the paper industry’s evolving needs.

Key trends shaping the future of AKD sizing include:

• Sustainability: Solvent-free manufacturing and bio-based AKD precursors reducing environmental impact
• Performance enhancement: Improved formulations offering faster curing, better stability, and reduced consumption rates
• Regulatory compliance: Increasing focus on food-contact safety and migration limits
• Application expansion: Growing use in recycled paper streams and specialty applications

LY Chem Technology Co., Ltd. stands at the forefront of these developments. With over two decades of experience in paper chemicals manufacturing, we offer a comprehensive range of AKD-based sizing solutions designed to meet the diverse needs of modern papermakers:

• LY-AKD301 (Internal AKD Sizing Agent) — Superior water resistance and aging resistance for cultural paper, coated paper, and packaging base paper
• LY-AKD302 (Surface AKD Sizing Agent) — Enhanced ring crush strength and burst strength for corrugating medium and linerboard
• Solvent-free manufacturing — Ensuring our products are free from toluene and other harmful residues
• Food-grade compliance — Available with FDA, SGS, and RoHS certifications for food-contact applications

As the global paper industry continues its transition toward sustainable, high-performance, alkaline papermaking, LY Chem remains committed to providing innovative chemical solutions that empower papermakers to meet the challenges of tomorrow—today.

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

References

1. Baidu Baike – Sizing Agent (施胶剂)
2. Baidu Baike – Paper Sizing Agent (造纸施胶剂)
3. Tech110 – Alkyl Ketene Dimer (AKD) – Solvent-Free Production
4. CNKI – Solvent-Free Synthesis of AKD – Research and Exploration
5. FDA 21 CFR 176.120 – Alkyl Ketene Dimers
6. BfR Recommendation XXXVI – Papers, Boards and Cardboards for Food Contact
7. Stanford University – Dialkyl Diketene Dimers in Food Contact Materials
8. 24Chemical Research – Alkyl Ketene Dimer (AKD) Market Insights 2025
9. Patsnap – Device and Method for Continuously Preparing High-Purity AKD Without Solvent
10. OECD SIDS – Alkyl Ketene Dimers