Grafted Crosslinked Cellulose for Wet Bulk and Permeability
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Solution Overview
Problem
Cellulosic fibers used in absorbent products tend to collapse upon wetting, reducing their liquid retention capacity and inhibiting liquid distribution, and existing crosslinking methods face challenges in enhancing both wet bulk and liquid permeability without compromising other performance properties.
Innovation Solution
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 to create intra-fiber chain-to-chain and chain-to-cellulose crosslinks, improving wet bulk and liquid permeability while maintaining or exceeding the performance of non-grafted crosslinked cellulose fibers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If cellulosic fluff pulp is used to provide high bulk liquid absorbent fiber structure, then the dry bulk and capillary structure are improved, but the structure collapses upon wetting which reduces wet bulk and liquid retention capacity
Solution Approach 1:
The cellulose fibers are pre-treated with grafting and crosslinking modifications before use in absorbent products. This preliminary chemical modification creates a more stable fiber structure that resists collapse upon wetting, allowing the fibers to maintain their bulk and porosity in the wet state. The crosslinked gel structure formed during grafting creates internal support that prevents structural collapse when the fibers absorb liquid.
2Volume of stationary object
If crosslinked cellulose fibers are used to enhance wet bulk, then the wet bulk and liquid acquisition rate are improved, but liquid permeability decreases due to increased capillary pressure
Solution Approach 1:
The invention optimizes the crosslinking parameters including the type of crosslinking agent (monomeric vs. polymeric polycarboxylic acids), crosslinking density, and molecular weight of crosslinking agents to achieve the desired balance between wet bulk and liquid permeability. By controlling these parameters, the fiber structure maintains adequate porosity for liquid flow while developing sufficient stiffness to preserve wet bulk.
3Ease of manufacture
If monomeric polycarboxylic acid crosslinking agents are used, then the crosslinking process is simplified, but the crosslinked fibers undergo reversion to non-crosslinked condition with short shelf-life
Solution Approach 1:
The invention uses composite crosslinking systems combining polycarboxylic acid crosslinking agents with additional crosslinking mechanisms or complementary agents. This composite approach creates multiple crosslinking bonds within the fiber structure, significantly enhancing the stability and shelf-life of the crosslinked cellulose fibers while maintaining process feasibility. The multi-component crosslinking system prevents reversion to the non-crosslinked state.
4Reliability
If polymeric polycarboxylic acid crosslinking agents are used to resist aging and reversion, then the shelf-life is improved, but the complexity of the crosslinking process and material costs increase
Solution Approach 1:
The invention optimizes parameters of polymeric polycarboxylic acid crosslinking agents including molecular weight, degree of polymerization, and carboxyl group density to achieve effective crosslinking with reduced process complexity. By carefully selecting and tuning these parameters, the invention achieves stable crosslinked structures with good shelf-life while minimizing the complexity of the crosslinking process and material costs.
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 in-plane radial permeability, with improved medium absorption pressure values, effectively addressing the limitations of traditional crosslinked cellulose fibers by achieving higher liquid retention and distribution capabilities.
Implementation Method 1
reacting the monomer with the cellulosic substrate in the presence of a grafting initiator to produce a grafted cellulosic material
Implementation Method 2
crosslinking the grafted cellulosic material by treating the material with a crosslinking agent adapted to effect crosslinking of one or more of the cellulosic substrate or the polymer chains
Data Source
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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.