Anionic Cellulose Derivative Additive for Paper Wet Strength
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Solution Overview
Problem
The paper industry faces challenges in increasing the initial wet web strength (IWWS) of paper sheets made from short fiber pulp, which limits machine runnability and productivity, and relies heavily on softwood pulp due to its higher inter-fiber bonding properties, while hardwood pulp, such as eucalyptus, is cost-effective but lacks strength.
Innovation Solution
The use of a microfibrillated cellulose composition, a starch derivative, and an anionic cellulose derivative as additives during papermaking, with specific molecular weight and degree of substitution ranges, enhances the IWWS and dry tensile strength of paper sheets, allowing for improved properties and machine runnability even with short fiber pulp.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If softwood pulp is used to increase inter-fiber bonding and initial wet web strength, then machine runnability and productivity improve, but production costs increase due to slower growth rates and longer harvesting cycles
Solution Approach 1:
The patent introduces anionic cellulose derivative as an intermediary substance that mediates between hardwood fibers to create effective bonding. This additive acts as a bridge that compensates for the naturally weaker bonding properties of hardwood, enabling hardwood pulp to achieve strength levels previously only attainable with softwood pulp.
Solution Approach 2:
The invention changes the chemical parameters of the pulp system by introducing specific anionic cellulose derivatives with controlled molecular weights (300,000-800,000 g/mol) and degrees of substitution (0.3-0.65). These parameter changes fundamentally alter the bonding characteristics of hardwood fibers, transforming them from weakly-bonding to strongly-bonding materials suitable for high-speed machine runnability.
2Productivity
If hardwood pulp is used to reduce costs through fast growth and short harvesting cycles, then production costs decrease, but initial wet web strength and machine runnability deteriorate
Solution Approach 1:
The anionic cellulose derivative serves as a chemical intermediary that compensates for the inherent weakness of hardwood fiber bonding. By adding this substance, hardwood pulp achieves the necessary strength characteristics without compromising the economic advantages of using fast-growing hardwood species.
Solution Approach 2:
The invention creates a composite system combining hardwood pulp with anionic cellulose derivative additives. This composite approach allows the system to exhibit properties superior to the individual components, where the additive enhances the bonding characteristics of hardwood to levels comparable with or exceeding softwood pulp.
3Strength
If softwood pulp is used to achieve high dry tensile strength through long fiber length, then strength properties improve, but the complexity of the papermaking process increases due to the need for mixed pulp sourcing and processing
Solution Approach 1:
The invention applies local quality enhancement by introducing anionic cellulose derivative specifically at the fiber bonding interfaces within hardwood pulp. This targeted approach strengthens the critical bonding zones without requiring changes to the entire pulp structure or sourcing mixed wood types, simplifying the overall processing system.
Data Source
AI summary
A product includes a microfibrillated cellulose composition, a starch derivative, and an anionic cellulose derivative, as a combined preparation for simultaneous or separate use. The anionic cellulose derivative has a number average molecular weight comprised between 300000 g/mol and 800000 g/mol, and a degree of substitution comprised between 0.3 and 0.65. Additionally, a paper sheet includes the product as an additive to increase the initial wet web strength and/or dry tensile strength of the paper sheet.