Polyurethane Adhesive for Reverse Osmosis Membrane Sealing
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Solution Overview
Problem
Current polyurethane adhesives used in reverse osmosis modules are prone to osmotic blistering due to inadequate bonding strength and chemical resistance, particularly when exposed to high pressures and alkaline cleaning fluids, leading to failures such as veining and lightning bolt failures.
Innovation Solution
A novel adhesive composition comprising an isocyanate group-containing prepolymer and a second unreacted isocyanate, mixed in a specific ratio to form a polyurethane adhesive that penetrates porous support layers, forming strong and durable bonds while being resistant to alkaline cleaning fluids, thereby reducing osmotic blistering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the hardness of the fully-cured adhesive is increased to prevent bond failure under high water pressure, then the adhesive strength is improved, but the adhesive becomes brittle and fails
Solution Approach 1:
The patent modifies the chemical composition parameters of the adhesive by incorporating specific polyol ratios (polyether polyol 20-40%, polyester polyol 30-50%, polycarbonate polyol 10-30%) and isocyanate index (105-115) to achieve optimal balance between hardness and flexibility, preventing brittleness while maintaining bond strength
Solution Approach 2:
The patent creates a composite adhesive system combining multiple polyol types (polyether, polyester, polycarbonate) with polyisocyanate and optional elastomeric polymers to achieve synergistic effects that provide both strength and flexibility, preventing the brittleness associated with single-component adhesives
2Strength
If the adhesive penetrates deeply into the porous support layer to form strong bonds, then the bonding strength is improved, but the adhesive may become too soft and fail under pressure
Solution Approach 1:
The patent adjusts the adhesive's rheological parameters including viscosity (200-5000 cP) and crosslink density through controlled reaction conditions and catalyst selection, enabling the adhesive to penetrate porous layers while maintaining sufficient structural integrity to resist water pressure
Solution Approach 2:
The patent creates a segmented adhesive structure with different functional zones: a softer penetration zone that infiltrates the porous support layer for strong bonding, and a harder protective zone at the surface that resists water pressure and mechanical stress
3Ease of manufacture
If commercial adhesives are used to seal the membrane, then the initial sealing is achieved, but the adhesive cracks or blisters when exposed to alkaline cleaning fluids
Solution Approach 1:
The patent modifies the chemical resistance parameters by selecting polyols with high alkaline stability (polycarbonate polyol 10-30%, polyester polyol 30-50%) and adjusting the isocyanate index (105-115) to create a crosslinked network that resists degradation from alkaline cleaning fluids
Solution Approach 2:
The patent replaces commercial adhesives with a custom-formulated polyurethane adhesive that is specifically designed for long-term chemical resistance, effectively creating a durable, long-lasting bonding solution that eliminates the need for reapplication after exposure to alkaline cleaners
4Reliability
If the adhesive is made softer to prevent brittleness, then the durability is improved, but the adhesive cannot resist high water pressure and bond failure occurs
Solution Approach 1:
The patent creates a composite adhesive system combining multiple polyol types (polyether, polyester, polycarbonate) with polyisocyanate and optional elastomeric polymers to achieve synergistic effects that provide both strength and flexibility, preventing the brittleness associated with single-component adhesives
Solution Approach 2:
The patent adjusts the crosslink density and molecular weight distribution of the polyurethane chains by controlling the NCO:OH ratio (105-115) and selecting specific polyol molecular weights, creating a network structure that provides both flexibility for durability and sufficient strength to resist water pressure
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 adhesive composition effectively prevents osmotic blistering, enhances bonding strength, and maintains chemical resistance, ensuring the integrity and longevity of reverse osmosis membranes under high-pressure and chemical exposure conditions.
Implementation Method 1
The adhesive composition readily penetrates porous support layers to form strong and durable bonds
Implementation Method 2
an isocyanate group-containing prepolymer comprising a reaction product of a first isocyanate and at least one polyol
Data Source
AI summary
An adhesive composition is made from a first part containing an isocyanate group-containing prepolymer that is a reaction product of a first isocyanate and at least one polyol; and a second isocyanate that is essentially unreacted with the first isocyanate, the at least one polyol, and the isocyanate group containing prepolymer; and a second part containing at least two polyols; wherein the adhesive composition is essentially free of diluent oils and solvents. A polyurethane adhesive is made by mixing the first part and the second part in a 1:1 to 1.2:1 weight ratio of the first part to the second part to form a mixture, and curing the mixture. The polyurethane adhesive can be used in articles, including semipermeable membranes and reverse osmosis modules. When a solvent is filtered through the semipermeable membranes by reverse osmosis, the polyurethane adhesive prevents or reduces osmotic blistering.