Highly Refined Cellulose Films: High-Shear Mixing for Fewer Pinholes
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Solution Overview
Problem
Existing methods for manufacturing microfibrillated cellulose (MFC) films face challenges with poor drainage and strength properties due to floc formation, which affects barrier properties, particularly in paper- or paperboard machine processes.
Innovation Solution
A method involving deflocculating and diluting an aqueous pulp suspension of highly refined cellulose fibers using a high shear mixer before feeding it to a paper-making machine headbox, reducing floc formation and improving suspension uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If MFC suspension is applied on a porous substrate and dewatering is performed by draining water through the substrate, then film formation is achieved, but pinholes are formed in the film deteriorating barrier properties
Solution Approach 1:
The invention applies preliminary action by treating the MFC suspension with a cationic polymer before dewatering to prevent flocculation. This pre-treatment modifies the suspension properties in advance, ensuring uniform fiber distribution and preventing pinhole formation during the subsequent dewatering process, thereby maintaining barrier properties without requiring post-processing corrections
Solution Approach 2:
The invention changes key parameters of the suspension by adding a cationic polymer, which alters the electrical charge and interaction properties of the MFC fibers. This parameter change prevents flocculation and maintains suspension stability during dewatering, enabling pinhole-free film formation while preserving barrier properties
2Manufacturing precision
If MFC films are made by casting technology with drying by evaporation, then uniform thickness distribution and smooth surface are achieved, but the slow diffusion of water restricts drying rate and forms shrink tensions
Solution Approach 1:
The invention replaces the slow evaporation-based drying mechanism with a mechanical dewatering process using a porous substrate. This substitution enables rapid removal of water through drainage, dramatically increasing productivity while the cationic polymer treatment ensures uniform fiber mat formation prevents pinholes and reduces shrink tensions
Solution Approach 2:
The invention introduces a cationic polymer as an intermediary substance that mediates between the MFC fibers and water during dewatering. This intermediary prevents fiber aggregation, ensures uniform distribution, and maintains suspension stability during rapid drainage, enabling both high productivity and manufacturing precision
3Productivity
If dewatering speed is increased to improve productivity, then drying rate increases, but pinholes are formed in the film
Solution Approach 1:
The invention applies preliminary action by pre-treating the MFC suspension with a cationic polymer before high-speed dewatering. This pre-treatment establishes stable fiber-suspension interactions that prevent flocculation even under rapid drainage conditions, enabling high productivity without pinhole formation
Solution Approach 2:
The invention changes the suspension parameters by adding a cationic polymer, which fundamentally alters the flow and interaction characteristics of the MFC suspension. This parameter change enables the suspension to withstand high dewatering speeds while maintaining uniform fiber distribution and preventing pinhole formation
Data Source
AI summary
The present invention relates to a method for manufacturing a film comprising highly refined cellulose fibers in a paper-making machine, the method comprising the steps of: a) providing an aqueous pulp suspension comprising at least 20% by dry weight of highly refined cellulose fibers having an SR (Schopper-Riegier) value in the range of 80-100 at a consistency in the range of 0.8-3 wt % and; b) deflocculating and diluting the aqueous pulp suspension to a lower consistency in the range of 0.1-1.5 wt % by injecting the aqueous pulp suspension into an aqueous stream using a high shear mixer to obtain a diluted aqueous pulp suspension; and c) feeding the diluted aqueous pulp suspension to a headbox of the paper-making machine.