Cationic Polymer Dewatering for Paper Dry Strength
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Solution Overview
Problem
The paper industry faces challenges in producing paper or cardboard with good dry strength due to rising recycling rates, shorter cellulose fibers, and the use of cheaper raw materials, which often result in reduced basis weight and compromised dry strength.
Innovation Solution
A process involving the addition of a water-soluble polymer P to an aqueous fiber suspension, followed by dewatering on a water-permeable base to form a wet paper structure with a specific dry content range, enhancing the dry strength of the final paper or cardboard product.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If recycling rates of waste paper are increased, then environmental sustainability is improved, but dry strength of paper or board deteriorates due to shorter cellulose fibers
Solution Approach 1:
A cationic polymer is introduced as an intermediary substance between the fiber suspension and the dewatering process. This polymer mediates the interaction between fibers and water, enhancing fiber bonding during dewatering to compensate for the weaker bonding capacity of shorter recycled fibers, thereby maintaining dry strength despite high recycling rates
Solution Approach 2:
The invention changes the chemical parameters of the fiber suspension by adding a cationic polymer, which alters the electrochemical properties of the system. This parameter change improves fiber-to-fiber bonding during dewatering, counteracting the negative effect of shorter fibers from recycling and preserving dry strength
2Quantity of substance
If basis weight of paper or board is reduced to save raw materials, then material cost is decreased, but dry strength deteriorates
Solution Approach 1:
By adding a cationic polymer to change the chemical parameters of the fiber suspension, the invention enhances fiber bonding efficiency. This allows achieving adequate dry strength with reduced basis weight, as the polymer compensates for the lower fiber mass through improved bonding mechanics during dewatering
3Strength
If cationic polymer is added to aqueous fiber suspension, then dry strength is improved, but polymer cost increases
Solution Approach 1:
The invention optimizes the concentration parameters of the cationic polymer addition, using the minimum effective amount to achieve the desired dry strength improvement. By precisely controlling the polymer dosage and its interaction parameters during dewatering, cost-effective reinforcement is achieved without excessive polymer consumption
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 effectively increases the dry strength of paper or cardboard, addressing the industry's need for improved mechanical properties despite recycling and material cost constraints.
Implementation Method 1
adding a polymer P to an aqueous fiber suspension... The resulting paper or board has good dry strength
Implementation Method 2
dewatering this aqueous fiber suspension containing polymer P on a water-permeable substrate
Data Source
AI summary
The invention relates to a method for manufacturing paper or cardboard, containing the following steps: (A) adding a water-soluble polymer P to a first aqueous fibrous material suspension, which has a dry content of between 0.1 wt% and 6 wt%, the polymer P being obtainable by polymerizing the following to form a polymer V: (i) 33 to 83 mol% of a monomer of formula I, in which R1 means H or C1-C6 alkyl, (ii) 6 to 56 mol% of diallyldimethylammonium chloride, diallyldiethylammonium chloride or a salt form of a monoethylenically unsaturated monomer having a quaternized nitrogen as the only charge-carrying group at a pH value of 7, (iii) 11 to 61 mol% of a monoethylenically unsaturated carboxylic acid, a monoethylenically unsaturated sulfonic acid or a monoethylenically unsaturated phosphonic acid, or salt forms thereof, (iv) 0 to 50 mol% of one or more ethylenically unsaturated monomers different from a monomer (i), (ii) and (iii), the total amount of all monomers (i), (ii), (iii) and (iv) being 100 mol%, and hydrolyzing the N-C(=O)R groups of the units of the monomers of formula (i) polymerized into the polymer V, primary amino or amidine groups thus being formed, to form the polymer P, at least 87% of the units of the monomers of formula (i) polymerized into the polymer V being hydrolyzed, with respect to the number of all units of the monomers of formula (i) polymerized into the polymer V, (B) dewatering the second aqueous fibrous material suspension containing polymer P on a water-permeable base to form a wet paper structure, which has a dry content of between 18.5 wt% and 25 wt%, (C) dewatering the wet paper structure, the paper or the cardboard thereby being produced. The produced paper or cardboard has good dry strength. The invention further relates to a paper or cardboard that can be obtained by the method, and to the polymer P.