Stiffened Paper via Chemical Crosslinking
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Solution Overview
Problem
The papermaking industry faces challenges in enhancing the dry-strength and mechanical properties of paper products made from recycled cellulose fibers, which are often shorter and less effective than those from virgin fibers, leading to issues like paper failures during printing and increased costs due to the need for lamination or costly chemical additives.
Innovation Solution
A papermaking process that incorporates a crosslinker, such as glyoxal or zirconium-containing crosslinkers, into the pulp slurry to increase the stiffness and rigidity of the paper, allowing for the production of unlaminated sheets with mechanical properties comparable to laminated products, without the need for lamination or high-cost additives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If lamination is used to increase the strength of paper products, then the stiffness and rigidity are improved, but the production cost and operational complexity increase
Solution Approach 1:
The patent extracts the lamination process from the production system and replaces it with a chemical crosslinking approach. By removing the need for lamination equipment and processes while achieving similar stiffness and rigidity through crosslinkers, the solution reduces operational complexity and production costs.
Solution Approach 2:
The patent substitutes the mechanical lamination process with a chemical crosslinking mechanism. Instead of physically bonding layers together through pressure and heat, the invention uses chemical crosslinkers to create molecular bonds between cellulose fibers, achieving the same structural reinforcement with simpler equipment requirements.
2Strength
If surface sizing is applied to improve dry-strength properties, then the surface strength is improved, but the equipment requirements and cost increase
Solution Approach 1:
The patent merges the dry-strength improvement function into the paper formation process itself rather than applying it as a separate surface treatment. By incorporating crosslinkers during the forming stage, the solution achieves internal strength enhancement without requiring separate sizing equipment or processes.
Solution Approach 2:
The patent applies the strengthening action preliminarily during the paper formation process rather than afterward. By adding crosslinkers to the pulp slurry before forming, the solution builds strength into the paper structure in advance, eliminating the need for subsequent surface sizing operations.
3Strength
If wet-end additives are used to internally strengthen fiber products, then the mechanical properties are improved, but the additive retention and effectiveness decrease
Solution Approach 1:
The patent changes the chemical parameters of the additives by using crosslinkers that form permanent molecular bonds rather than temporary physical adsorptions. This parameter change ensures that the strengthening agents remain bonded to the cellulose fibers throughout the paper formation process and do not wash away with the white water.
Solution Approach 2:
The patent creates a composite structure at the molecular level by forming crosslinks between cellulose fibers and crosslinker molecules. This composite approach ensures that the strengthening agents become an integral part of the paper matrix, improving retention and effectiveness compared to simple additive mixing.
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 process achieves increased stiffness and rigidity in paper products, matching the properties of laminated sheets while maintaining or reducing other mechanical strengths, allowing for higher basis weights without adding to the total finish caliper, thus reducing production costs and operational challenges.
Implementation Method 1
incorporates a crosslinker, such as glyoxal or zirconium-containing crosslinkers, into the pulp slurry to increase the stiffness and rigidity of the paper
Data Source
AI summary
A process for making a stiffened and rigid paper includes preparing a pulp slurry consisting essentially of water, a cellulosic pulp, a crosslinker, and a starch, and optionally a binder; draining the liquid from the pulp slurry to form a web; and drying the web. Alternatively, a process for making a stiffened and rigid paper includes the step of adding at least one crosslinker at one or more locations, such as at the wet-end, dry-end, or at both ends of the papermaking process. Suitable crosslinkers include a glyoxal-containing crosslinker, a gluteraldehyde, a polyfunctional aziridine, a zirconium-containing crosslinker, a titanium-containing crosslinker, and an epichlorohydrin, and mixtures thereof. When a binder is employed, it can be added either in the dry or wet form. Provided is a neutral or alkaline process to produce a paper product having the improved mechanical properties of a laminated product in the Z-direction, without a lamination step.