Nanofibrillated Cellulose Refining with Variable Specific Edge Loading
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Solution Overview
Problem
Current processes for producing nanofibrillated cellulose require high energy consumption and do not efficiently produce longer fibers, leading to increased manufacturing costs and environmental concerns due to chlorine bleaching agents.
Innovation Solution
A novel method involving a series of mechanical treatments with specific refiner configurations that significantly reduce energy consumption by varying the specific edge loading (SEL) between initial and subsequent refining stages, using disc refiners with different blade and groove configurations to achieve higher energy efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple stages of homogenization or refining are used to achieve nanosized cellulose fibril, then the desired nano-sized product is obtained, but the energy consumption becomes very high
Solution Approach 1:
The refining process is divided into multiple stages with progressively decreasing specific edge loading (SEL). The first stage uses high SEL (1.5-8.0 J/m) for initial fibrillation, followed by second and third stages with lower SEL (0.05-1.5 J/m) for further refinement. This segmentation allows each stage to perform a specific function, achieving nanosized fibrils with reduced total energy consumption compared to uniform high-intensity refining.
Solution Approach 2:
The patent changes the SEL parameter across different refining stages. By decreasing the SEL from the first stage (1.5-8.0 J/m) to subsequent stages (0.05-1.5 J/m), the process optimizes energy efficiency while maintaining the nanosized fibril structure. This parameter change allows the system to achieve the desired manufacturing precision with significantly reduced energy consumption.
2Manufacturing precision
If conventional refining processes are used to produce nanofibrils, then nanocellulose is obtained, but the fiber length is significantly reduced
Solution Approach 1:
The patent applies dynamic control of refining intensity by varying the SEL across stages. The first stage uses higher SEL to initiate fibrillation while preserving fiber length, and subsequent stages use lower SEL to gradually refine the fibrils without excessive fiber shortening. This dynamic approach maintains longer fiber lengths (0.2-2.0 mm) compared to conventional single-stage or multi-stage refining with uniform high intensity.
3Manufacturing precision
If chlorine-containing bleaching agents are used for pulp bleaching, then effective bleaching is achieved, but environmental harm and equipment corrosion increase
Solution Approach 1:
The patent replaces harmful chlorine-containing bleaching agents with oxygen-based compounds (ozone, peroxide, oxygen). This substitution eliminates the formation of chlorinated organics and chloride corrosion products, converting a harmful bleaching process into an environmentally benign one. The oxygen-based agents achieve effective bleaching without the harmful by-products, thus benefiting both the environment and equipment longevity.
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 reduces energy consumption by 2-30% compared to traditional processes, allowing for the production of nanofibrillated cellulose with improved fiber length and properties, such as increased tensile strength and reduced yield stress, while minimizing environmental impact.
Implementation Method 1
The method comprises first and second mechanical refining of the cellulosic fibers using refiners to produce the nanofibrillated cellulose
Implementation Method 2
Mechanical refining requires a great deal of energy to mechanically and physically break the cellulose fibers into smaller fragments
Data Source
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AI summary
A scalable, energy efficient process for preparing cellulose nanofibers is disclosed. The process employs treating the cellulosic material with a first mechanical refiner with plates having a configuration of blades separated by grooves, and subsequently treating the material with a second mechanical refiner with plates having a configuration of blades separated by grooves different than the first refiner. The plate configurations and treatment operations are selected such that the first refiner produces a first SEL that is greater than the SEL of the second refiner, by as much as 2-50 fold. An exemplary high first SEL may be in the range of 1.5 to 8 J/m. Paper products made with about 2% to about 30% cellulose nanofibers having a length from about 0.2 mm to about 0.5 mm, preferably from 0.2 mm to about 0.4 mm have improved properties.