Water-Redispersible Polymer Powders Storage Stability
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Solution Overview
Problem
Vinyl acetate-ethylene and styrene-(meth)acrylic ester copolymers used in building material dry formulations face challenges in maintaining redispersibility and storage stability, especially under humid and warm conditions, due to their low glass transition temperatures leading to film formation and blocking issues.
Innovation Solution
The production of these copolymers as water-redispersible powders is enhanced by incorporating water-soluble inorganic salts like alkali metal sulfates and magnesium sulfate, along with desiccants such as polyvinyl alcohols, during the drying of aqueous dispersions, to improve storage stability and redispersibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polymer powders are stored under humid and warm conditions, then film formation and blocking occur, but redispersibility deteriorates
Solution Approach 1:
Water-soluble inorganic salts (alkali metal sulfates and magnesium sulfate) are introduced as intermediary substances during drying to form a protective shell around polymer particles. This shell prevents direct polymer-polymer contact and film formation during storage, while being completely soluble in water to allow full redispersibility when water is added later
Solution Approach 2:
The invention changes the chemical composition parameters of the drying environment by adding specific inorganic salts (alkali metal sulfates at 0.1-5% w/w and magnesium sulfate at 0.1-5% w/w). These parameter changes modify the drying process to create a protective crystalline shell that maintains particle separation during storage but dissolves completely upon water addition, restoring redispersibility
2Reliability
If desiccants are used during drying to prevent film formation, then storage stability improves, but redispersibility may be compromised
Solution Approach 1:
The invention creates a composite protective layer combining inorganic salt crystals (alkali metal sulfates or magnesium sulfate) with organic desiccants. This composite structure provides dual functionality: the inorganic salt framework prevents polymer particle contact and film formation, while the water-soluble nature of both components ensures complete redispersibility when water is added
Solution Approach 2:
The inorganic salts act as intermediary substances that mediate between the polymer particles during drying, forming a protective barrier without permanently binding to the polymer. This intermediary shell prevents direct polymer-polymer interaction during storage but dissolves completely in water, allowing full redispersibility to be restored
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 improves the redispersibility and storage stability of the polymer powders, reducing sedimentation and maintaining mechanical properties like tensile bond strength and flexural strength in building products, even after long-term storage under adverse conditions.
Implementation Method 1
drying aqueous dispersions comprising protective-colloid-stabilized vinyl acetate-ethylene and/or styrene-(meth)acrylic ester copolymers, one or more water-soluble inorganic salts, and one or more desiccants
Implementation Method 2
drying the corresponding aqueous polymer dispersions in the presence of desiccants
Implementation Method 3
On redispersing the polymer powder in water, the desiccant dissolves and an aqueous redispersion forms in which the original polymer particles (primary polymer particles) are as far as possible present once again
Data Source
AI summary
Vinyl acetate-ethylene and/or styrene-(meth)acrylic ester copolymers along with processes for preparing the same and uses for the same. Wherein the vinyl acetate-ethylene and/or styrene-(meth)acrylic ester copolymers are in the form of water-redispersible powders for producing hydraulically-setting building material dry formulations. Where the storage stability of the protective-colloid-stabilized vinyl acetate-ethylene or styrene-(meth)acrylic ester copolymers in the form of water-redispersible powders is improved by drying aqueous dispersions comprising protective-colloid-stabilized vinyl acetate-ethylene and/or styrene-(meth)acrylic ester copolymers, one or more water-soluble inorganic salts, and one or more desiccants. Where the water-soluble inorganic salts are selected from the group consisting of alkali metal sulfates and where the desiccants are selected from the group comprising polyvinyl alcohols, polyvinyl acetals, nonionic polyvinylpyrrolidones, nonionic poly(meth)acrylamides, polysaccharides and proteins.