Anionic Polymer Spray for Paper Strength via Aldehyde Crosslinking
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Solution Overview
Problem
The papermaking process faces limitations in enhancing paper strength due to challenges such as high conductivity and anionic trash in process water, which affect the adsorption and effectiveness of traditional wet end additives, leading to limited fiber surface interaction and sheet formation issues.
Innovation Solution
The introduction of a wet end composition comprising a cationic or amphoteric polymer with a net positive charge, combined with an anionic polymer functionalized with aldehyde groups, is sprayed onto the paper sheet to enhance fiber bonding and strength, utilizing a specific ratio of mono-reacted to di-reacted aldehyde groups to improve paper strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional wet end additives are applied to increase paper strength, then fiber surface adsorption is improved, but effectiveness decreases due to high conductivity and anionic trash in recycled process water
Solution Approach 1:
The patent uses a cationic polymer as an intermediary substance that first adsorbs to the fiber surface in the wet end, creating positive charge sites. The anionic polymer with aldehyde groups then interacts with these cationic sites to form crosslinks. This two-stage intermediary approach overcomes the direct adsorption problems caused by high conductivity and anionic trash in recycled water.
Solution Approach 2:
The invention creates a composite polymer system combining cationic and anionic polymers with aldehyde groups. This composite approach allows the cationic polymer to overcome water chemistry challenges while the anionic polymer with aldehyde groups provides crosslinking functionality, achieving superior strength improvement beyond what single polymers can provide.
2Strength
If dual component wet end additive programs are used to overcome water chemistry challenges, then paper strength is improved, but sheet formation deteriorates due to flocculation from cationic-anionic interactions
Solution Approach 1:
The patent segments the strength enhancement process into two distinct locations: wet end application of cationic polymer and dry end spray application of anionic polymer with aldehyde groups. This spatial segmentation prevents the cationic and anionic polymers from interacting in the slurry, avoiding flocculation and maintaining good sheet formation while still achieving strength improvement through subsequent crosslinking.
Solution Approach 2:
The cationic polymer is applied in advance in the wet end to adsorb onto fiber surfaces and create positive charge sites. This preliminary action prepares the fiber surface for subsequent anionic polymer crosslinking at the dry end, enabling strength enhancement without compromising sheet formation during the forming process.
3Strength
If more cationic polymer is added to adsorb to anionic fiber surfaces, then paper strength increases, but the capacity of fiber surface sites becomes limited
Solution Approach 1:
The patent changes the chemical state of the fiber surface by first applying cationic polymer to create positively charged sites, then using anionic polymer with aldehyde groups to form crosslinks. This parameter change in charge state and chemical functionality allows continued strength improvement without being limited by the original anionic site capacity of the fibers.
Solution Approach 2:
The cationic polymer acts as an intermediary that transforms the fiber surface properties, converting anionic sites to cationic sites. This intermediary transformation enables the subsequent anionic polymer to interact and form crosslinks, effectively bypassing the limitation of original fiber surface site capacity.
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
This approach significantly increases paper strength by forming a polymer network between the sprayed additives and wet end additives, resulting in improved dry strength and surface strength, with the anionic polymer spray demonstrating a dramatic increase in strength beyond traditional methods.
Implementation Method 1
the cationic polymer can be used to adsorb to the anionic fiber surface
Implementation Method 2
The anionic polymer with aldehyde groups reacts with the fiber surface to form crosslinked networks
Implementation Method 3
spraying an effective amount of a composition onto the paper sheet
Data Source
AI summary
The present disclosure provides methods and compositions for strengthening paper. The methods may include a step of spraying an anionic polymer onto a paper sheet to increase the strength of the paper sheet. The anionic polymer may have amino groups, amide groups, or a combination of amino groups and amide groups. These groups may be functionalized with an aldehyde. Methods may also include a step of adding a wet end composition to a wet end of the papermaking process.