Decoupling Wet and Dry Strength in Paper Products via SEPF

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Solution Overview

Problem

Paper products face a tradeoff between wet strength and softness due to the coupling of dry and wet strength, making it difficult to achieve high wet strength without compromising softness.

Innovation Solution

Incorporating surface-enhanced pulp fibers (SEPF) with high fibrillation and embossing/lamination to decouple wet and dry strength, allowing for higher wet burst to dry tensile strength ratios while maintaining softness.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If wet strength resins and refining are added to promote wet strength, then wet strength is improved, but dry strength also increases and softness decreases

Engineering Contradiction:

Improvewet strengthVSAvoidsoftness

Core Design Contradiction:

StrengthVSEase of operation

Solution Approach 1:

The invention segments the fiber population into two distinct groups: SEPF (surface enhanced pulp fibers) that provide wet strength through high fibrillation and surface area, and conventional fibers that maintain softness and contribute to dry strength. This segmentation allows each fiber type to fulfill specific functional requirements without compromising the other properties.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The SEPF are specifically engineered with enhanced surface properties (high fibrillation, increased surface area) that are localized to provide wet strength at the fiber surface, while the bulk fiber structure maintains conventional characteristics for softness. This local quality enhancement resolves the contradiction by concentrating strength-providing features where needed without affecting overall softness.

Inventive Principle:

Principle #3Local quality

2Strength

If the proportion of strengthening fibers is increased to increase dry strength and wet strength, then strength is improved, but softness decreases

Engineering Contradiction:

Improvedry strengthVSAvoidsoftness

Core Design Contradiction:

StrengthVSEase of operation

Solution Approach 1:

The fiber furnish is segmented into SEPF (1-20% by weight) for strength and conventional fibers (80-99% by weight) for softness. This segmentation enables the paper product to achieve high dry strength through SEPF without requiring a high proportion of strengthening fibers overall, thereby maintaining softness.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention changes the critical parameter of fiber surface area through high fibrillation of SEPF, achieving strength enhancement without increasing fiber proportion. This parameter change allows strength improvement while maintaining the softness-providing fiber composition.

Inventive Principle:

Principle #35Parameter changes

3Ease of operation

If embossing and lamination are applied to the paper product, then softness and comfort are improved, but dry strength decreases more than wet strength

Engineering Contradiction:

ImprovesoftnessVSAvoiddry strength

Core Design Contradiction:

Ease of operationVSStrength

Solution Approach 1:

The SEPF are pre-engineered with high fibrillation and surface area before embossing/lamination occurs. This preliminary action ensures that the fiber network has sufficient inherent strength to withstand the embossing/lamination process, and that the decoupled strength properties are already established before the softness-enhancing operations.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention converts the potential harm of embossing/lamination (dry strength loss) into a benefit by leveraging the decoupled strength mechanism. The high fibrillation SEPF maintain wet strength bonds during embossing/lamination while allowing controlled dry strength reduction, effectively using the process to enhance the wet/dry strength ratio.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

4Strength

If high fibrillation is applied to increase fiber surface area for wet strength, then wet strength is improved, but fiber length may be reduced

Engineering Contradiction:

Improvewet strengthVSAvoidfiber length

Core Design Contradiction:

StrengthVSLength of moving object

Solution Approach 1:

The invention changes the fiber morphology parameters by creating SEPF with extreme fibrillation and surface area while controlling fiber length reduction through optimized refining conditions. This parameter change allows maximum surface area development for wet strength while minimizing the negative impact on fiber length.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS12116732B2Paper products incorporating surface enhanced pulp fibers and having decoupled wet and dry strengths and methods of making the same

Publication Date: 2024.10.15 DOMTAR PAPER COMPANY LLC(US)

AI summary

A method of making a paper product can comprise making one or more sheets at least by, for each of the sheet(s), forming a web from one or more furnishes that comprise fibers dispersed in water. The fibers of the furnish(es) can comprise a plurality of first fibers that are hardwood fibers and a plurality of second fibers that include softwood fibers and surface enhanced pulp fibers (SEPF), the SEPF having a length weighted average fiber length of at least 0.20 mm. The method can comprise at least partially dewatering the web to form the sheet. The sheet(s) can be laminated and/or embossed such that a total dry tensile strength of the paper product is less than or equal to 90% of the sum of the total dry tensile strength(s) of the sheet(s).