Paper packaging exposed to moisture can lose up to 95% of its dry strength, leading to structural failures during transport and storage. Traditional wet-strength additives like polyamide epichlorohydrin (PAE) resins provide only partial protection, with measurements showing strength retention dropping significantly after 30 minutes of water exposure.

The fundamental challenge lies in maintaining fiber-to-fiber bonds under wet conditions while preserving the recyclability and sustainability advantages of paper-based materials.

This page brings together solutions from recent research—including metal ion coordination treatments, thixotropic clay-polymer barriers, composite structures with gradient foam layers, and specialized carboxymethylcellulose coatings. These and other approaches focus on practical, scalable methods to enhance wet strength while meeting commercial packaging requirements for food safety and recyclability.

1. Method for Inducing Hydrophobicity in Paper via Multivalent Metal Ion Coordination

MISSISSIPPI STATE UNIVERSITY, 2024

Simplified, cost-effective and scalable method to convert conventional hydrophilic paper into hydrophobic paper with improved water resistance and wet strength. The method involves immersing or spraying paper into a dilute solution of multivalent metal ions like Fe3+, Zr4+, etc, followed by drying. The metal ions coordinate with lignocellulosic fibers to induce hydrophobicity, water resistance and reduced water absorption. The metal-ion-modified hydrophobic paper retains high hydrophobicity, stability and wet strength after washing or storage.

2. Water-Resistant Paper with Dual-Layer Configuration Comprising Latex-Pigment Undercoat and Polyolefin-Acrylic Resin Layer

OJI HOLDINGS CORP, 2024

Water-resistant paper with improved printability, condensation resistance, and water resistance. The paper has a water-resistant layer on one side and an undercoat layer on the opposite side. The undercoat layer has specific smoothness and water absorbency. This allows the paper to have good print quality, prevent condensation, and still be water-resistant on the opposite side from the water contacting surface. The undercoat layer contains latex and pigment, and the water-resistant layer contains polyolefin or acrylic resins. The paper is suitable for packaging containers like cups that have both printed surfaces and contact with liquids.

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3. Filter Material with Biodegradable Non-Fibrous Binder for Enhanced Strength and Compostability

GLATFELTER GERNSBACH GMBH, 2024

Filter material for tea bags and other food packaging that uses a biodegradable binder to enhance strength and compostability. The filter contains fibers and a non-fibrous binder like polylactic acid, polyglycolic acid, or copolymers thereof. This binder enhances wet strength properties like tensile and crimp strength compared to traditional synthetic binders. The biodegradable binder also prevents water ingress into the crimped area, making the fold more permanent and reducing dust transfer through the filter. The biobased binder improves compostability and sustainability compared to fossil-based binders.

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4. Cellulose Fiber Pulp Mold Packaging with Enhanced Strength, Reduced Air Bubbles, and Water Repellency Through Additive Incorporation

THERMO LAB KOREA CO LTD, 2023

Pulp mold packaging made from cellulose fibers that is stronger, less prone to absorbing water, and has fewer air bubbles compared to conventional pulp mold packaging. The packaging is made by adding binders, defoamers, and water repellents to the cellulose pulp. The binders increase strength and elasticity, the defoamers remove air bubbles, and the water repellents prevent water absorption. The specific compositions of the additives are: binder with 79-81% water, pH 2.8-4.8, melting/freezing point 0°C, initial boiling point 90°C, boiling range 90-100°C, specific gravity 1.10-1.20; defoamer with 70-72% water, pH 5-

5. Food Packaging Paper with Primer and Functional Coating Layers for Crack Prevention and Oil-Water Resistance

LEE TAE HOON, 2023

Food packaging paper with improved crack prevention and oil and water resistance for preventing food spoilage when packaging foods like burgers and sandwiches. The paper has a primer layer on the substrate to prevent cracks, followed by a functional coating layer for oil and water resistance. The primer layer contains butyl acrylate, polybutylene adipate, butyl-2-propenoate, and polyethylene glycol. The functional layer has alcohol, fluorine compounds, paraffin wax, nitrocellulose, dicyclohexyl phthalate, and silicone resin. Coating the primer prevents cracks when folding the packaging. The functional coating provides oil and water resistance to prevent food absorption.

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6. Paper Coating Agent Comprising Low Glass Transition Temperature Copolymer and Carnauba Wax

DIC CORP, 2023

A paper coating agent that provides oil and water resistance, as well as heat sealability, for paper. The coating agent contains a copolymer made from a carboxylic acid with a double bond and a (meth)acrylate, carnauba wax, and water. The copolymer has a glass transition temperature of 30°C or less. This coating agent can be applied to paper to impart oil and water resistance, and when heat sealed, forms a bonded layer. It allows replacing plastic coatings and sealing films on paper packaging, reducing plastic use and facilitating recycling.

7. Laminated Sheet Structure with Waterproof Paper, Photocurable Resin, and Adhesive Layers

TOPPAN PRINTING CO LTD, 2023

Decorative sheets, packaging boxes, and packages with improved moisture resistance for containing items like liquids. The sheets have a waterproof paper layer, a photocurable resin layer, and an adhesive layer. The waterproof paper provides moisture barrier and the photocurable resin layer adds water resistance. The adhesive layer bonds the layers together. This enables the sheets to maintain strength when contacting moisture. The sheets can be used in boxes and packages for items like liquids without delamination or peeling when exposed to moisture. The photocurable resin can be UV curable and contain acrylic monomers. The waterproof paper can have a resin component matching the photocurable resin.

8. Unbleached Kraft Paper Packaging with Primary Cellulose and Polyolefin or PLA Coating

MONDI AG, 2023

Packaging material made from unbleached kraft paper that doesn't tear when stretched and maintains elasticity over time. The paper contains at least 90% primary cellulose with a length-weighted mean fiber length between 2.0 and 2.9 mm and less than 5% fillers. It has a grammage between 65 and 170 g/m2. The kraft paper is coated with a polyolefin or PLA in small amounts to improve wet strength. The material can be formed into sleeves, bands, or loops by pivoting, folding, and closing the paper. The high strength-to-weight kraft paper replaces plastic packaging while avoiding the environmental issues of wet strength agents.

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9. Water-Resistant Paper with Ethylene Copolymer Layer and Pigment Coating

OJI HOLDINGS CO LTD, 2023

Water-resistant paper with improved water resistance, blocking resistance, moldability, and heat-sealability compared to existing water-resistant papers. The paper has a water-resistant layer on one side of the paper substrate, with specific melting point ranges and resin composition. The water-resistant layer contains an ethylene-(meth)acrylic acid copolymer and a copolymer of ethylene and an unsaturated hydrocarbon other than ethylene. The ethylene copolymer/other copolymer mass ratio is 50/50 to 90/10. The copolymer with an unsaturated hydrocarbon other than ethylene likely contributes to the second melting point range of 100-120°C. The paper also has a pigment coating layer between the paper substrate and the water-res

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10. Biodegradable Reinforced Paper Packaging with Plant-Based Resin Fiber Bonding and Low-Density Polyethylene Coating

PAPEIS AMALIA LTDA, 2022

Biodegradable reinforced paper packaging material with increased strength and impermeability compared to conventional paper packaging. The material uses a biodegradable plant-based resin to chemically bond fibers within the paper layer and coat the surface with biodegradable low-density polyethylene. This reinforces the paper while maintaining minimal weight. The resin also improves wetting barrier properties. The reinforced paper packaging is biodegradable and reduces costs compared to using thicker paper or adhesives.

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11. Additive Comprising Bacterial Cellulose for Enhanced Mechanical and Permeability Properties in Recycled Paper-Based Packaging

MODERN KARTON SANAYI VE TICARET ANONIM SIRKETI, 2022

An additive containing bacterial cellulose that can be used as a sustainable, biodegradable and renewable raw material source in the paper industry, especially in the production of packaging boxes. The additive improves air permeability, water absorbency and mechanical properties of the final product compared to using 100% recycled paper. It allows using 100% recycled paper as raw material in packaging boxes by adding 5-40% bacterial cellulose to compensate for the strength and performance issues of recycled paper.

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12. Paper Substrate with Waterproof Resin Coating for Ice and Frozen Product Packaging

JUJO PAPER CO LTD, 2022

Paper packaging material for storing ice and frozen products that has waterproof properties to prevent melting water from seeping through. The packaging material is made by coating a waterproof resin layer onto at least one side of a paper substrate. The resin contains a synthetic resin like styrene or acrylic, and wax. The resin layer has low moisture permeability to prevent water leakage. The coated paper can be processed into bags for packaging ice and frozen products. The coating is heat-sealable and peels easily from frozen products.

13. Water-Soluble Coating Composition with Acrylate Polymer and PVA Composite for Paper and Fiber Materials

ECO MAP CO LTD, KOH BYIUNG KUK, HAN CHUNG KU, 2022

A water-soluble coating composition for paper and packaging materials that allows recycling and reduces waste. The coating composition contains a water-soluble acrylate-based polymer, PVA, and a PVA composite with a metal ion like calcium, magnesium, or zinc. The coating composition is prepared by mixing the acrylate polymer with calcium hydroxide generated by adding calcium oxide to water. The PVA is added last. This composition provides thermal adhesion, water resistance, and oil resistance. It enables reuse of paper packaging when discarded after use by avoiding contamination of the recycling stream. The coating composition can be applied to paper, nonwoven fabric, or fiber materials like masks, diapers, filters, or packaging.

14. Aqueous Dispersion of Ethylene-Vinyl Alcohol Copolymer and Cellulose Nanofibers with Specified Ethylene Content

KURARAY CO, 2022

Aqueous dispersion and emulsion containing ethylene-vinyl alcohol copolymer and cellulose nanofibers for improved water resistance, strength, and barrier properties in films, coatings, papers, multilayer structures, and adhesives. The ethylene unit content of the ethylene-vinyl alcohol copolymer is 1-20 mol%. This range provides dispersibility, storage stability, and coatability while maintaining water resistance, tensile strength, and fracture properties compared to PVA-CNF dispersions.

15. High Wet Tensile Strength Paper Wrapper for Electrically Heated Aerosol-Generating Articles

Philip Morris Products S.A., 2022

Paper wrapper for electrically heated aerosol-generating articles like vape devices that prevents tearing when removing the device from the vape. The wrapper has a wet tensile strength of at least 5 N/15 mm when wet, tested using a specific method. This high wet strength prevents tearing when the wrapped vape is heated and the moisture inside wets the paper. It allows easy removal without wrapper fragments getting into the vape device. The wrapper also optionally has a dry tensile strength of at least 10 N/15 mm.

16. Aqueous Dispersions Containing Ethylene-Vinyl Alcohol Copolymer and Cellulose Nanofibers with Defined Ethylene Content and Nanofiber Concentration

KURARAY CO, 2021

Aqueous dispersions and emulsions containing an ethylene-vinyl alcohol copolymer and cellulose nanofibers for making films with improved properties like water resistance, tensile strength, and reduced breakage compared to using just the copolymer. The ethylene unit content of the copolymer is 1-20 mol%. The nanofibers are dispersed in the aqueous medium containing the copolymer at 0.1-40 parts by mass. This composition improves film properties compared to just the copolymer alone. The dispersions and emulsions can be used to make films, coatings, papers, and packaging materials with enhanced properties.

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17. Method for Synthesizing Hyperbranched Superabsorbent Material via Temperature Gradient Reaction of Lewis Base and Organic Acid

PINGHU JINGXING PACKING MATERIAL CO LTD, 2021

Preparation of a hyperbranched structure super absorbent functional material and its application in paper sizing material for packaging. The method involves mixing a Lewis base substance like glycerol or triethanolamine with an organic acid like terephthalic acid or citric acid in a temperature gradient reaction. The gradients are at room temperature, 40-100°C, and 100-160°C. This produces a super absorbent functional material with a hyperbranched structure. The material is used as a packaging paper sizing to improve wet strength.

18. Coated Liner Paper with Dual Composition for Enhanced Strength and Waterproofing in Honeycomb Board Fabrication

Pearson PB Co., Ltd., Kang Gun-woo, Choi Deok-young, 2021

A packaging material with improved strength and waterproofing for export packaging applications. The material is made by coating the outer and inner surfaces of liner paper used in corrugated cardboard with specific compositions. The first coating contains epoxy, melamine, methanol, and water. The second coating contains a waterproofing agent (paraffin wax and polyolefin) and vinyl acetate emulsion. Applying and curing these coatings on the liner paper improves its strength and water resistance. The coated liner paper is then used to manufacture honeycomb boards with hexagonal cores. The honeycomb boards are heat-treated and laminated with polyethylene for the final packaging material.

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19. Papermaking Process Incorporating Sequential Polymer Addition for Enhanced Moisture Resistance

ANHEUSER BUSCH INBEV SA, 2021

A process for producing paper and cardboard with improved moisture resistance for packaging beverage containers. The process involves adding specific polymers to the pulp during papermaking to enhance wet strength and tear resistance. The polymers include a cationic polymer, an anionic polymer, and a cationic starch. The addition order and reaction time between the polymers can be varied.

20. Papermaking Process Incorporating Polymer-Starch Network for Enhanced Moisture Resistance

ANHEUSER BUSCH INBEV SA, 2021

A process for producing label paper and packaging board for beverage containers that has improved moisture resistance without using traditional moisture-resistant additives like epichlorohydrin or melamine. The process involves adding specific polymers and starch to the papermaking process to form a network mixture with the wood fiber pulp. The cationic polymer, anionic polymer, and cationic starch are added in specific amounts to the pulp feed. This network improves the paper's moisture resistance properties, like wet shear and wet breakage, without compromising printability or integrity.

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21. Composite Material Comprising Cellulose Nanofibers and Anionic Gelling Polysaccharide with Ionically Crosslinked Interpenetrating Networks

CELLUTECH AB, 2020

Composite material made from cellulose nanofibers (CNF) and an anionic gelling polysaccharide, like alginate or carrageenan, that has impressive toughness and hygroplastic behavior in wet conditions as well as increased rigidity and extensibility in the wet state. The composite is prepared by mixing CNF with the gelling polysaccharide, then crosslinking with multivalent ions like calcium. The synergistic interpenetrating networks formed by the CNF and gelling polysaccharide provide wet resistance and stability without impairing dry properties. The composite can be used as a film, packaging material, or 3D-formed object that maintains properties in wet environments.

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22. Process for Producing Paper with Polyamide Epichlorohydrin, Carboxymethyl Cellulose, and Cationic Starch Additives

ANHEUSER BUSCH INBEV SA, 2020

A process for producing label paper or board paper for beverage container packaging that provides high wet strength and tear resistance. The process involves adding specific chemicals to the paper production process. The chemicals include a polyamide epichlorohydrin resin, carboxymethyl cellulose, and cationic starch. These chemicals are added in controlled amounts during the paper manufacturing steps. The resulting paper has improved wet strength and tear resistance to prevent label delamination or beverage container falling out of packaging when exposed to moisture.

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23. Process for Producing Label Paper and Packaging Board with Sequential Addition of Polyamide-Epichlorohydrin Resin, Carboxymethyl Cellulose, and Cationic Starch

ANHEUSER BUSCH INBEV SA, 2020

A process for producing label paper and packaging board for beverage containers that provides improved wet strength and tear resistance. The process involves adding specific chemical additives in a specific order during the paper making process. The steps include supplying wood fiber pulp, followed by adding a polyamide-epichlorohydrin resin, then carboxymethyl cellulose, and finally cationic starch. The order and reaction times between the additives are crucial for optimal wet strength and tear resistance.

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24. Coating Composition for Food Packaging Paper with Plasticized Cellulose Derivative and Smectite Clay Particles

COSCO Paper Co., Ltd., COSCO PAPER Corporation, 2019

Eco-friendly coating for food packaging paper that is reusable without generating harmful substances. The coating improves durability and reusability of food packaging paper without using harmful plastics like polyethylene. The coating is made from a water-soluble resin, plasticized cellulose derivative, slip agent, dispersant, and smectite clay particles. The cellulose derivative is plasticized to improve flexibility. The slip agent prevents sticking. The dispersant helps the particles mix. The smectite clay particles provide weatherability. The coating enables multiple reuses without agglomeration and pollution issues compared to plastic coatings.

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25. Biodegradable Paper Packaging with Reinforced Chemical Pulp Fiber Bonding and Moisture Barrier

CHROMA PAPER LLC, 2019

Biodegradable reinforced paper packaging material that reduces costs and improves the preservation of goods using packaging material that is substantially impermeable and with increased mechanical strength with a minimum weight. The packaging material uses a biodegradable vegetal based resin to create a strong chemical pulp fiber bonding that penetrates inside the paper web while simultaneously the same vegetal based resin creates a barrier against moisture. The packaging material also has a controlled thermo-sealing area on one side with a layer of polyethylene for sealing. This allows the packaging to be compostable and reduces reliance on adhesives for sealing.

26. Method for Producing Laminated Paper Packaging Material with Cellulose Nanofiber Coating

TOPPAN PRINTING CO LTD, 2019

A method for producing a laminated paper packaging material with improved strength, smoothness, and water resistance. The method involves coating a base paper made from acid-resistant paper with a water-based coating containing cellulose nanofibers. The nanofiber coating provides a smooth, uniform layer with good adhesion to the base paper. The nanofiber content, coating amount, and fiber diameter are optimized to prevent penetration between the base paper fibers. This prevents chalking, film thickness unevenness, and strength failure. The nanofiber coating also improves water resistance by forming a barrier against moisture ingress.

27. Reinforced Paper Packaging with Vegetable-Based Resin Bonding and Polyethylene Sealing Layer

CHROMA PAPER LTD, 2018

Biodegradable reinforced paper packaging material that provides improved mechanical strength and moisture resistance compared to conventional paper packaging. The material is made by treating a paper web with a vegetable-based resin to bond the fibers internally. It also has a polyethylene layer on one side for sealing. The vegetable resin provides strength and moisture resistance. The material is biodegradable and compostable.

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28. Paper Wrapper for Electrically Heated Aerosol-Generating Articles with Enhanced Wet and Dry Tensile Strength

PHILIP MORRIS PRODUCTS SOCIETE ANONYM, 2018

Paper wrappers for electrically heated aerosol-generating articles like electronic cigarettes that have improved strength to prevent tearing during removal. The wrappers have a wet tensile strength of at least 5 N/15mm when measured according to a specific test. This higher wet strength compared to conventional wrappers prevents tearing when the article is removed from the heating device. The wrappers also preferably have a dry strength of at least 10 N/15mm.

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29. Coating Composition with Acrylic Resin and Titanium Dioxide for Cardboard Box Durability

PARK SANG WOON, Park Sang-woon, 2018

A coating composition for improving the durability of packaging boxes like cardboard boxes used for shipping fruits. The coating composition contains an acrylic resin, filler, titanium dioxide, dispersant, defoaming agent, and water. It can be applied to the inside or outside of cardboard boxes and dried to form a coating layer that enhances the durability of the boxes during transport and storage. The composition also optionally contains additives like antibacterial, deodorant, binder, and flame retardant agents.

30. Copolymer Latex Coating with Acrylic and Reactive Silicone for Paper Packaging Waterproofing

Shim Myung-sik, APEC, 2016

Eco-friendly waterproofing agent for food packaging that replaces polyethylene coatings on paper containers. The waterproofing agent is a copolymer latex made by emulsion polymerization using acrylic monomers, carboxylic acid monomers, and a reactive silicone polymer. The copolymer has glass transition temperatures between -15°C and 15°C. It provides barrier properties against water, oil, and alcohols for paper packaging without needing post-processing. The latex can be coated directly onto paper using existing equipment.

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31. Latex-Based Waterproofing Agent for Food Packaging Papers with Emulsion Polymerized Acrylic and Carboxylic Acid Monomers

SHIM MYOUNG-SIK, 2016

Eco-friendly waterproofing agent for food packaging papers that can replace polyethylene coatings and enable recycling of the paper. The agent is a latex made by emulsion polymerization of acrylic and carboxylic acid monomers in the presence of a reactive emulsifier and polyfunctional silicone. The latex has glass transition temperatures of -15 to 15°C, containing repeating units derived from the acrylic monomer and carboxylic acid monomer in proportions of 70% or more. The latex provides barrier properties for water, oil, and alcohol resistance. It enables recycling of the paper by coating the waterproofing agent during paper manufacturing instead of post-processing with polyethylene.

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32. Packaging Paper with PVA-Silicone Coating for Water and Oil Resistance in Rolled Foods

LEE SEUNG GOO, YOU YOUNG SUN, 2015

Eco-friendly packaging paper for rolled foods like sushi that provides good water resistance and oil resistance without using aluminum foil. The paper has specific physical properties and a coating composition that combines water resistance, oil resistance, packaging ease, and robustness. The base paper has a wet tensile strength of 0.1-0.7 kN/m. The coating uses a water-soluble PVA-based solution with a silicone resin emulsion to enhance durability and water repellency. The coating formulation and paper properties are optimized together for rolled food packaging. The paper can be recycled by dissolving the coating in water or an alkali solution.

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