Water-absorbing polymer particles surface crosslinking
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Solution Overview
Problem
Existing methods for producing water-absorbing polymer particles struggle to achieve a balance between high centrifuge retention capacity, absorption under pressure, and swelling rate, often compromising on one property at the expense of others due to limitations in the degree of crosslinking and processing techniques.
Innovation Solution
A process involving polymerizing drops of a monomer solution in a gas phase with a solids content of at least 35% by weight and an average particle diameter of at least 150 μm, using ethylenically unsaturated monomers, crosslinkers, and initiators, which results in post-crosslinked polymer particles with enhanced properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the degree of crosslinking is increased to improve gel strength, then the absorption capacity decreases
Solution Approach 1:
The patent applies post-crosslinking selectively to the particle surface rather than throughout the entire particle. This creates a gradient structure where the surface has high crosslinking density (providing gel strength) while the interior maintains lower crosslinking density (preserving absorption capacity). The surface crosslinking is achieved by coating particles with crosslinking agents and applying heat, creating a differentiated structure that resolves the contradiction between strength and absorption.
2Productivity
If spray polymerization is used to combine polymerization and drying steps, then particle size control is limited
Solution Approach 1:
The patent performs polymerization in a liquid phase before the drying step, allowing particles to form and grow to desired sizes while still in the liquid medium. This preliminary particle formation enables better size control through parameters like monomer concentration and polymerization time, before the subsequent drying and surface crosslinking steps. The sequence of operations (polymerization → drying → surface crosslinking) allows each step to be optimized independently.
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 yields water-absorbing polymer particles with significantly improved centrifuge retention capacity, absorption under pressure, and swelling rate, meeting specific performance criteria such as CRC ≥ 20 g/g and FSR ≥ CRC^2 + b*CRC + c, with optimized coefficients for each property.
Implementation Method 1
by polymerizing drops of a monomer solution containing a) at least one ethylenically unsaturated monomer, b) at least one crosslinker, c) at least one initiator
Implementation Method 2
water-absorbing polymer particles with high absorption
Data Source
AI summary
The invention relates to method for producing post-cured water-absorbent polymer particles with a higher absorption by polymerising droplets of a monomer solution in a gas phase surrounding the droplets. The solids content of the monomer solution is at least 35 wt% and the polymer particles have an average diameter of at least 150 µm.