Citric Acid Buffer Nonwoven Binder for Wipe Dispersibility
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Solution Overview
Problem
Current disposable wet wipes cause clogging in wastewater treatment equipment due to inadequate dispersibility, and existing binders that rely on pH differences between the wipe lotion and water to achieve dispersibility often lose strength if the pH of the lotion shifts above 5.5.
Innovation Solution
A method for forming a dispersible nonwoven substrate involving emulsion polymerization, neutralization with specific amines or alkali hydroxides, and immersion in an aqueous medium with a citric acid and sodium citrate buffer to maintain a pH below 5.5, ensuring the wipes remain strong during use and disintegrate effectively in water.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pH-dependent binders are used to achieve dispersibility, then dispersibility is improved, but tensile strength is lost when pH shifts above 5.5
Solution Approach 1:
The invention changes the pH parameter control strategy by introducing a buffer system (citric acid and sodium citrate) that maintains pH between 4.0 and 5.5, preventing the pH shift that causes binder failure. This allows the wipe to maintain tensile strength during use while ensuring dispersibility when exposed to wastewater treatment conditions.
Solution Approach 2:
The buffer system acts as an intermediary between the binder and the external environment (wastewater). It mediates the pH conditions, preventing direct interaction between high pH wastewater and the pH-sensitive binder, thereby protecting the binder's functionality and maintaining both strength and dispersibility.
2Reliability
If disposable wipes are made for ease of disposal, then dispersibility is improved, but equipment clogging occurs
Solution Approach 1:
The invention optimizes the binder composition parameters (emulsion polymer with controlled molecular weight and acid monomer content) to achieve complete dispersibility into individual fibers, ensuring that wipes break down sufficiently to prevent equipment clogging while maintaining usability.
3Strength
If lotion pH is maintained between 4 and 5.5 for binder stability, then tensile strength is preserved, but pH shift occurs over time
Solution Approach 1:
The buffer system (citric acid/sodium citrate) serves as an intermediary that stabilizes the pH environment, preventing spontaneous pH shifts that would otherwise occur over time or with environmental exposure, thereby maintaining binder effectiveness.
Solution Approach 2:
The buffer system provides beforehand cushioning against pH changes. By pre-establishing a buffer capacity in the lotion formulation, the system is prepared to resist pH shifts before they can occur, ensuring long-term stability of the binder and wipe strength.
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 method ensures the nonwoven substrates maintain tensile strength while ensuring dispersibility, with the addition of a citric acid/sodium citrate buffer maintaining wipe integrity and strength over time, preventing premature loss of tensile strength.
Implementation Method 1
neutralizing the emulsion polymer with a neutralizer selected from the group consisting of an amine having a pKb of 4 to 7, an alkali hydroxide, and combinations thereof to form the aqueous nonwoven binder
Implementation Method 2
immersing the contacted heated nonwoven substrate in an aqueous medium having a final pH of less than 5.5 to provide a dispersible nonwoven substrate wherein the aqueous medium contains a buffer comprising a mixture of citric acid and sodium citrate
Implementation Method 3
heating the contacted nonwoven substrate to a temperature of from 120°C to 220°C to form a heated contacted nonwoven substrate
Data Source
AI summary
A method for forming a dispersible nonwoven substrate comprising the steps of: a) emulsion polymerizing at least one mono-ethylenically unsaturated monomer an emulsion polymer; and b) neutralizing the emulsion polymer with a neutralizer selected from the group consisting of an amine having a pKb of 4 to7, an alkali hydroxide, and combinations thereof to form the aqueous nonwoven binder; c) contacting a nonwoven substrate with said aqueous nonwoven binder to form a contacted nonwoven substrate; d) heating the contacted nonwoven substrate to a temperature of from 120°C to 220°C to form a heated contacted nonwoven substrate; and e) immersing the contacted heated nonwoven substrate in an aqueous medium having a final pH of less than 5.5 to provide a dispersible nonwoven substrate wherein the aqueous medium contains a buffer comprising a mixture of citric acid and sodium citrate is disclosed.