Hydrophilic Polyurethane Foam Water Retention Under Compression
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Solution Overview
Problem
Hydrophilic foams used in water management systems for roofs tend to lose water-holding capacity when under compressive force, reducing their effectiveness in capturing and retaining rainwater.
Innovation Solution
A hydrophilic polyurethane foam is developed using a reaction mixture comprising water, a quasi-prepolymer with specific oxyethylene units and diphenylmethane diisocyanate, and surfactants, which maintains high water-holding capacity even under compressive forces, forming a multilayer structure for efficient water management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If hydrophilic foam is used to absorb and hold water in roofing systems, then water capture capacity is improved, but water retention under compressive force deteriorates
Solution Approach 1:
The patent modifies the chemical composition parameters of the foam by specifying precise ratios of oxyethylene units (55-75 wt%), water content (20-80 parts per 100 parts quasi-prepolymer), and isocyanate index (0.5-50). These parameter changes create a foam structure that maintains cell integrity under compression while preserving water-holding capacity, directly resolving the contradiction between water absorption and compression resistance.
Solution Approach 2:
The invention creates a composite polyurethane foam system combining hydrophilic components (oxyethylene units, water) with hydrophobic components (diphenylmethane diisocyanate, polymer backbone). This composite structure provides both high water affinity for absorption and structural rigidity for compression resistance, simultaneously achieving both improved water-holding capacity and maintained retention under load.
2Strength
If a weight-bearing layer is constructed on top of hydrophilic foam, then structural load-bearing capacity is improved, but foam compression increases reducing water retention
Solution Approach 1:
The patent formulates the foam with built-in compression resistance properties through its chemical composition and cell structure before the weight-bearing layer is installed. The foam's inherent structural stability, achieved through controlled crosslinking and cell wall strength, cushions against subsequent compressive loads from roofing structures, preventing premature water loss and maintaining capacity throughout the system's service life.
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 foam retains a significant proportion of its water-holding capacity under compressive forces, making it suitable for use in water containment systems like blue and green roofs, effectively managing rainwater without significant water loss.
Implementation Method 1
Hydrophilic foams have been proposed for use in immobilizing captured water. These foams act as 'sponges' to absorb and hold the water.
Implementation Method 2
a) water, b) a quasi-prepolymer, which quasi-prepolymer has an isocyanate content of 5 to 15% by weight and contains 55 to 75 weight percent of oxyethylene units
Data Source
AI summary
Hydrophilic polyurethane foam is made from a diphenylmethane-based quasi-prepolymer having specified isocyanate and oxyethylene contents. The foams have an unusually good capacity for retaining water even when under compressive forces. They also exhibit at most moderate swelling when saturated with water. The foam is useful as a layer of a water containment system such as a green roof or blue roof system.