Nanofibrillated Cellulose PVOH Adhesive for Soft Multi-Ply Sheets
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Solution Overview
Problem
Conventional glue-bonded multi-ply absorbent sheets face challenges in achieving optimal bonding strength and softness due to the balancing act required in adhesive viscosity, where glue that is too viscous fails to penetrate and glue that is too thin requires excess application, leading to wicking issues and compromised bulk and emboss quality.
Innovation Solution
A pseudoplastic polyvinyl alcohol adhesive containing nanofibrillated cellulose, which modifies viscosity to enable better penetration and retention, reinforcing the interface between plies and allowing for softer products with less glue, characterized by fibrils 4-20 nm wide and 500-2000 nm long, or exhibiting a 80% viscosity reduction as shear rate increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the glue is too viscous, then the glue maintains its position on the web surface, but it does not penetrate the ply sufficiently to achieve strong bonding
Solution Approach 1:
The adhesive composition exhibits shear-thinning behavior where viscosity decreases under shear stress during application and penetration, then recovers at rest to prevent wicking. This dynamic viscosity adjustment allows the glue to penetrate plies effectively during bonding while maintaining position afterward, resolving the contradiction between penetration and position maintenance.
Solution Approach 2:
The patent modifies the rheological parameters of the adhesive by adding shear-thinning agents to conventional PVOH glue, changing its viscosity characteristics from static to dynamic. This parameter change enables the glue to adapt its flow properties during different stages of the bonding process, achieving both sufficient penetration and position retention.
2Quantity of substance
If the glue is too thin (low viscosity), then the glue penetrates the web easily, but excess glue is required to overcome wicking into the web
Solution Approach 1:
The shear-thinning adhesive allows controlled penetration during application when viscosity is reduced under shear, then rapidly increases viscosity at rest to prevent excessive wicking into the web. This dynamic behavior reduces the need for excess glue application while ensuring sufficient penetration for strong bonding.
Solution Approach 2:
By changing the rheological parameters of the adhesive composition to include shear-thinning characteristics, the patent enables the glue to have low viscosity during application for easy penetration, then high viscosity at rest to minimize wicking and glue consumption.
3Strength
If increased marrying roll pressure is used to improve bonding, then the glue penetration and bond strength improve, but bulk, softness and emboss quality suffer
Solution Approach 1:
The patent changes the rheological parameters of the adhesive to exhibit shear-thinning behavior, allowing effective bonding at lower pressing forces. The dynamic viscosity adjustment enables sufficient glue penetration and bond strength without requiring high marrying roll pressure, thereby preserving bulk, softness, and emboss quality.
Solution Approach 2:
The patent replaces reliance on high mechanical pressing force with a chemically-modified adhesive system that provides enhanced bonding through improved glue penetration and interfacial adhesion. This substitution allows achieving strong bonds without the mechanical pressure that would compromise product quality.
4Strength
If more glue is applied to achieve sufficient bonding, then the bond strength improves, but the product softness decreases due to excess glue presence
Solution Approach 1:
By modifying the adhesive's rheological parameters to include shear-thinning behavior, the patent enables effective bonding with reduced glue application. The dynamic viscosity control ensures sufficient penetration and adhesion strength while minimizing excess glue residue that would compromise product softness.
Solution Approach 2:
The patent creates a composite adhesive system combining conventional PVOH glue with shear-thinning agents (nanofibrillated cellulose and/or xanthan gum), achieving enhanced bonding performance with lower glue quantities. This composite formulation maintains product softness while providing sufficient bond strength.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The use of nanofibrillated cellulose in the adhesive composition results in enhanced bonding strength and softer products with reduced glue usage, demonstrated by increased panel softness and peel test plybond values, while maintaining comparable adhesion levels.
Implementation Method 1
Nanofibrillated cellulose (NFC) is a shear-thinning material, so it flows more as shear is applied, and recovers viscosity as shear decreases
Implementation Method 2
NFC has the additional benefit that it can reinforce the interface between plies after drying
Data Source
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AI summary
A multi-ply absorbent sheet includes a first absorbent ply of cellulosic sheet; a second absorbent ply of cellulosic sheet; and a ply bonding adhesive interposed between the first absorbent ply and the second absorbent ply, the ply-bonding adhesive thereby adhering said absorbent plies together. The ply-bonding adhesive comprises polyvinyl alcohol and nanofibrillated cellulose. In a particularly preferred embodiment the adhesive is applied as a dilute aqueous composition to tissue plies and the nanofibrillated cellulose has a Characteristic Breaking Length of 6.5 km or above.