Low Formaldehyde Vinyl Ester/Ethylene Copolymers via Redox Initiation
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Solution Overview
Problem
Existing vinyl ester/ethylene emulsion copolymers used in self-leveling flooring screeds and ceramic tile adhesives often contain high levels of formaldehyde, which is a human carcinogen, and conventional redox initiator systems contribute to its generation, posing a regulatory and health risk.
Innovation Solution
A formaldehyde-free redox initiator system comprising t-butyl hydroperoxide as an oxidizing agent and erythorbic acid or sulfinic acid-based compounds as reducing agents is used in the emulsion polymerization of vinyl ester/ethylene monomers, along with a stabilizing system of polyvinyl alcohol, to produce copolymers with low formaldehyde content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional redox initiator systems (sodium formaldehyde sulfoxylate) are used in emulsion polymerization, then polymerization efficiency is improved, but formaldehyde content in the copolymer increases
Solution Approach 1:
The patent extracts and removes the formaldehyde-generating component (sodium formaldehyde sulfoxylate) from the redox initiator system and replaces it with alternative reducing agents (ascorbic acid, erythorbic acid, or sodium sulfite) that do not generate formaldehyde, thereby eliminating the harmful factor while maintaining polymerization functionality
Solution Approach 2:
The patent changes the chemical composition parameters of the redox initiator system by substituting the reducing agent component, specifically replacing sodium formaldehyde sulfoxylate with ascorbic acid, erythorbic acid, or sodium sulfite, which alters the reaction pathway to avoid formaldehyde generation while preserving polymerization efficiency
2Object-generated harmful factors
If erythorbic acid is used as reducing agent with controlled hydrogen peroxide, then formaldehyde content is reduced, but copolymer discoloration occurs
Solution Approach 1:
The patent employs t-butyl hydroperoxide as a short-lived oxidizing agent that decomposes completely during polymerization, leaving no residual oxidant to cause subsequent discoloration of the copolymer, while still enabling effective redox initiation with erythorbic acid
Solution Approach 2:
The patent changes the oxidizing agent from hydrogen peroxide to t-butyl hydroperoxide, which has different decomposition characteristics and does not cause copolymer discoloration, thereby resolving the discoloration issue while maintaining formaldehyde-free polymerization
3Object-generated harmful factors
If formaldehyde-free redox initiator system is used, then formaldehyde content is reduced, but adhesive and flow properties may be impaired
Solution Approach 1:
The patent utilizes the polymerization exotherm and in-situ generated radicals from the redox initiator system to drive the polymerization process without external intervention, ensuring complete monomer conversion and optimal polymer network formation that delivers excellent adhesive and flow properties
Solution Approach 2:
The patent creates a composite redox initiator system combining t-butyl hydroperoxide oxidizing agent with ascorbic acid/erythorbic acid/sodium sulfite reducing agents, which synergistically generates radicals that initiate efficient polymerization while maintaining all required performance properties
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 resulting copolymers exhibit excellent adhesive and flow properties, early strength on curing, and low formaldehyde content (<5.0 ppmw), meeting industry standards and regulatory requirements while maintaining performance in self-leveling flooring screeds and ceramic tile adhesives.
Implementation Method 1
a free radical redox polymerization initiator system comprising t-butyl hydroperoxide as an oxidizing agent and at least one of a sulfinic acid-based compound and erythorbic acid or a salt thereof as a reducing agent
Implementation Method 2
emulsion copolymerization of a monomer mixture comprising at least one vinyl ester, ethylene
Data Source
AI summary
A vinyl ester/ethylene copolymer is prepared by emulsion copolymerization of a monomer mixture comprising at least one vinyl ester, ethylene, a stabilizing system comprising polyvinyl alcohol and a free radical redox polymerization initiator system comprising i-butyl hydroperoxide as an oxidizing agent and at least one of a sulfuric acid-based compound and erythorbic acid or a salt thereof as a reducing agent. The monomer mixture comprises from 70 wt % to 95 wt % of said at least one vinyl ester and from 5 wt % to 30 wt % of ethylene based on the total weight of monomers in said mixture and the copolymer has a formaldehyde content of less than 5.0 ppmw as determined by ISO-15173.