Cross-linked cellulosic fibers
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Solution Overview
Problem
Existing methods for producing soft and bulky tissue products with sufficient tensile strength face challenges such as the use of irritating cross-linking agents like formaldehyde and polycarboxylic acids, which result in odor, toxicity, high costs, and low cross-linking efficiencies, while also causing discoloration and unpleasant odors.
Innovation Solution
The process involves reacting oxidized polyols, such as oxidized sugars with at least two aldehyde groups, with cellulosic fibers under specific conditions to create cross-linked fibers, which are then used to manufacture tissue products with enhanced bulk and reduced water retention values without the drawbacks of traditional cross-linking agents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If formaldehyde or formaldehyde addition products are used to crosslink cellulosic fibers, then bulk and strength are improved, but irritating effects on skin and eyes, odor, and low fiber brightness occur
Solution Approach 1:
The patent replaces formaldehyde with alternative crosslinking agents (polycarboxylic acids, dialdehydes, isocyanates) that achieve the same crosslinking function without the harmful side effects. These alternative agents provide the necessary strength improvement while eliminating skin and eye irritation, odor, and brightness loss associated with formaldehyde.
Solution Approach 2:
The patent changes the chemical parameters of the crosslinking agent from formaldehyde to other compounds such as polycarboxylic acids (citric acid, adipic acid), dialdehydes (glutaraldehyde), or isocyanates. This parameter change maintains the crosslinking effectiveness for improving strength and bulk while eliminating the harmful effects of formaldehyde vapor on skin and eyes.
2Object-affected harmful factors
If dialdehyde crosslinking agents such as glutaraldehyde are used, then many disadvantages of formaldehyde are overcome, but production cost becomes too high for commercial success
Solution Approach 1:
The patent identifies and promotes the use of cheaper alternative crosslinking agents such as polycarboxylic acids (citric acid, adipic acid, succinic acid) and other dialdehydes that are less expensive than glutaraldehyde. These alternatives maintain the benefits of reduced odor and improved brightness while achieving commercial viability through lower production costs.
Solution Approach 2:
The patent changes the economic parameter by selecting crosslinking agents with more favorable cost structures. Polycarboxylic acids and certain dialdehydes are chosen because they provide effective crosslinking at lower costs compared to glutaraldehyde, enabling commercial success while still overcoming the disadvantages of formaldehyde.
3Ease of manufacture
If polycarboxylic acid such as citric acid is used to crosslink fibers, then cost competitiveness and improved resilience are achieved, but discoloration (yellowing) and unpleasant odors occur
Solution Approach 1:
The patent changes the chemical structure parameters of the polycarboxylic acid crosslinking agents. By selecting specific acids (citric acid, adipic acid, succinic acid, malic acid) and controlling molecular weight and purity, the patent achieves cost competitiveness while minimizing discoloration and odor. The crosslinking mechanism is optimized to reduce chromophore formation.
Solution Approach 2:
The patent promotes the use of inexpensive polycarboxylic acids that provide cost-competitive crosslinking solutions. These agents maintain the economic advantages over formaldehyde and dialdehyde agents while process optimizations reduce the harmful effects of discoloration and odor.
4Volume of stationary object
If through-air drying is used to increase sheet bulk, then bulk is improved, but satisfactory softness requires calendering which negates much of the bulk obtained
Solution Approach 1:
The patent changes the physical-chemical parameters of the cellulosic fibers through crosslinking, which modifies fiber-fiber interactions and moisture behavior. This enables the tissue web to maintain softness without requiring aggressive calendering, thereby preserving the bulk achieved through through-air drying. The crosslinked structure provides sufficient strength and surface properties to eliminate the need for post-drying calendering.
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 resulting cross-linked cellulosic fibers exhibit improved brightness, color stability, reduced odor, and increased bulk, while maintaining comparable strength to non-cross-linked fibers, with water retention values at least 30% less than comparable fibers, thus addressing the limitations of previous methods.
Implementation Method 1
treating a portion of the papermaking furnish with chemicals that facilitate the formation of covalent bonds between adjacent cellulose molecules
Implementation Method 2
This process is commonly referred to as cross-linking
Implementation Method 3
reacting a polyol and an oxidizing agent selected from the group consisting of a periodate, a peroxide, a hypochlorite, and combinations thereof, and optionally a metal ion, to yield an oxidized polyol
Data Source
AI summary
Disclosed are processes for manufacturing cross-linked cellulosic fibers, as well as cross-linked fibers prepared by the same and tissue products comprising the novel cross-linked cellulosic fibers. The cross-linked fibers are manufactured by reacting an oxidized sugar having at least two aldehyde groups with a plurality of cellulosic fibers to yield treated fibers and heating the treated fibers at a temperature greater than about 140° C. to cure the treated fibers. The instant cross-linked fibers are manufactured without well-known cross-linking agents such as formaldehyde or polycarboxylic acids. As such the present cross-linked cellulosic fibers have good brightness and color and resist yellowing. Further, the cross-linked cellulosic fibers are generally free from off odors. Like prior art cross-linked fibers however, the instant cross-linked cellulosic fibers have enhanced properties, such as improved wet bulk, compared to uncross-linked fibers.