Nanofibrillar Cellulose Surface Layer for Tissue Strength
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Solution Overview
Problem
Existing tissue products face a challenge in achieving a balance between softness and strength, as increasing softness often inversely affects strength, and conventional methods like using surfactants or starch filaments can lead to issues like linting or reduced tensile strength.
Innovation Solution
Applying a layer of nanofibrillar cellulose to the surface of tissue webs during the papermaking process, which enhances strength without significantly compromising softness, and can be done using a spray application on the Yankee or air side of the paper machine, utilizing its high surface area and rheological properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If surfactants or starch filaments are applied to improve softness, then softness is improved, but tensile strength decreases or linting is exacerbated
Solution Approach 1:
The patent applies nanofibrillar cellulose with specific dimensional parameters (nanoscale diameter of 1-100 nm) to change the physical state of the tissue surface. This nanoscale parameter change allows the material to provide softness through increased surface area and fibrillar structure without the linting and strength reduction associated with conventional micrometer-scale starch filaments or surfactants.
Solution Approach 2:
The invention uses composite materials by combining nanofibrillar cellulose with the tissue substrate. The nanofibrillar cellulose forms a composite structure with the tissue fibers, creating a surface layer that provides softness while maintaining strength through the hierarchical structure of the composite material.
2Shape
If starch and polyvinyl alcohol filaments are deposited and thermally fused to provide softness, then softness is improved and linting is reduced, but the method is difficult to implement on existing papermachines and dispersibility is adversely impacted
Solution Approach 1:
The patent utilizes hydraulic principles by applying nanofibrillar cellulose in an aqueous suspension during the wet end of the papermaking process. The nanofibrillar cellulose is introduced into the wet web where it is deposited and bonded through hydraulic pressure and capillary action, eliminating the need for thermal fusion equipment and enabling implementation on existing papermachines.
Solution Approach 2:
The invention uses water as an intermediary medium to apply the nanofibrillar cellulose to the tissue web. The aqueous suspension of nanofibrillar cellulose serves as the intermediary carrier, allowing the material to be deposited and bonded without requiring thermal fusion or additional specialized equipment.
3Strength
If nanofibrillar cellulose is applied to increase strength, then tensile strength is improved, but softness may be compromised
Solution Approach 1:
The patent applies local quality by concentrating the nanofibrillar cellulose specifically at the tissue surface rather than throughout the entire web. This localized application provides strength enhancement at the surface level while preserving the softness characteristics of the bulk tissue material.
Solution Approach 2:
The invention segments the tissue structure into a bulk substrate layer and a surface nanofibrillar cellulose layer. This segmentation allows the bulk material to maintain its softness properties while the surface layer provides strength enhancement through the nanoscale fibrillar structure.
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 method results in unexpectedly high tensile strength increases while maintaining softness, with a minimal decrease in sensory softness, and does not require additional equipment on existing paper machines.
Implementation Method 1
The spray of NFC may be applied after the wet web is formed on the formation wire and immediately before transfer to a felt, however the application can also be done at the formation wire or at the felt, either on the Yankee or the air side of the sheet, depending on papermachine configuration.
Implementation Method 2
Nanofibrillar cellulose has been evaluated in a myriad of applications, from composite materials, colloids, food, adhesives, biomedical applications, building materials, additive in oil drilling fluids and in papermaking as strength additive and in coating formulations and adhesives.
Data Source
AI summary
A method of making a tissue basesheet includes: (a) forming a nascent web from an aqueous furnish of papermaking fiber; (b) applying an aqueous composition of nanofibrillar cellulose to a surface of the nascent web; and (c) drying the nascent web to provide the tissue basesheet. Typically the basesheet is constructed with a tissue substrate of cellulosic papermaking fiber having applied to a surface thereof a layer of nanofibrillar cellulose, the tissue substrate having a basis weight of from 15 g/m2 to 30 g/m2 and the layer of nanofibrillar cellulose having a coatweight of from 0.25 g/m2 to 3 g/m2. The product may be incorporated into 2-ply or 3-ply bath tissue.