Grafted Crosslinked Cellulose for Wet Bulk and Liquid Permeability
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Solution Overview
Problem
Cellulosic fibers used in absorbent products, such as diapers, face challenges with liquid retention and permeability due to fiber collapse upon wetting, limiting their capacity and performance, and existing crosslinking methods have not successfully enhanced these properties beyond a certain point.
Innovation Solution
The development of grafted crosslinked cellulose materials with monoethylenically unsaturated acid group-containing monomers, such as acrylic acid, which are crosslinked using agents like pentaerythritol or hyperbranched polymers, resulting in improved wet bulk, absorbent capacity, and permeability, shifting the trade-off curve between in-plane radial permeability and medium absorption pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If cellulosic fluff pulp is used to provide high void volume and bulk, then initial liquid acquisition is improved, but the structure collapses upon wetting reducing wet bulk and liquid retention
Solution Approach 1:
The patent applies preliminary crosslinking treatment to cellulose fibers before they are used in absorbent products. This pre-treatment creates a stable three-dimensional network structure that prevents fiber collapse when wet, thereby maintaining wet bulk and liquid retention capabilities without sacrificing the high dry bulk needed for initial liquid acquisition
Solution Approach 2:
The patent creates a composite structure by crosslinking cellulose fibers with other materials to form a stable matrix. This composite approach combines the high bulk properties of cellulose fluff pulp with the structural stability provided by the crosslinked network, resolving the contradiction between achieving high dry bulk and maintaining wet bulk stability
2Volume of stationary object
If crosslinking is applied to enhance wet bulk, then fiber stiffness and wet bulk are improved, but liquid permeability decreases
Solution Approach 1:
The patent applies crosslinking locally and selectively to specific regions or aspects of the fiber structure rather than uniformly throughout. This localized crosslinking provides sufficient structural support to maintain wet bulk while preserving adequate porosity and channels for liquid permeability, thus resolving the trade-off between these two properties
3Ease of manufacture
If monomeric polycarboxylic acids are used for crosslinking, then crosslinking is achieved, but the fibers undergo reversion to non-crosslinked condition reducing shelf-life
Solution Approach 1:
The patent changes the chemical parameters of the crosslinking system by using polymeric polycarboxylic acids instead of monomeric ones. This parameter change increases the molecular weight and complexity of the crosslinking agent, creating more stable crosslinks that resist reversion and thereby extending the shelf-life of the crosslinked cellulose fibers while maintaining ease of manufacture
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 grafted crosslinked cellulose materials exhibit enhanced wet bulk, absorbent capacity, and permeability, with IPRP values up to 20% higher and MAP values up to 20% higher than non-grafted crosslinked cellulose fibers, effectively addressing the limitations of existing technologies.
Implementation Method 1
the ability of an absorbent product containing cellulosic fibers to initially acquire and distribute liquid (such as from an initial liquid insult) relates to the product's dry bulk and capillary structure
Data Source
AI summary
Grafted, crosslinked cellulosic materials include cellulose fibers and polymer chains composed of at least one monoethylenically unsaturated acid group-containing monomer (such as acrylic acid) grafted thereto, in which one or more of said cellulose fibers and said polymer chains are crosslinked (such as by intra-fiber chain-to-chain crosslinks). Some of such materials are characterized by a wet bulk of about 10.0-17.0 cm3/g, an IPRP value of about 1000 to 7700 cm2/MPa·sec, and/or a MAP value of about 7.0 to 38 cm H2O. Methods for producing such materials may include grafting polymer chains from a cellulosic substrate, followed by treating the grafted material with a crosslinking agent adapted to effect crosslinking of one or more of the cellulosic substrate or the polymer chains. Example crosslinking mechanisms include esterfication reactions, ionic reactions, and radical reactions, and example crosslinking agents include pentaerythritol, homopolymers of the graft species monomer, and hyperbranched polymers.