Double-Walled Polyurethane Capsules for High-Temperature Self-Healing

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Solution Overview

Problem

Conventional self-healing materials face challenges in incorporating thermally robust capsules that can survive high temperatures and shear stresses during the processing of polymeric materials, making it difficult to create self-healing versions of these materials.

Innovation Solution

The development of double-walled capsules with an inner polyurethane wall and an outer poly(urea-formaldehyde) wall, which are more thermally stable and can encapsulate healing agents, allowing for self-healing properties in materials processed at elevated temperatures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional single-walled capsules are used to encapsulate healing agents, then the capsule structure is simple and easy to manufacture, but the capsules cannot survive high temperatures and shear stresses during polymer processing

Engineering Contradiction:

Improvecapsule thermal stabilityVSAvoidcapsule structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent implements a double-walled capsule structure where an inner capsule wall containing the healing agent is nested within an outer capsule wall. The inner wall is formed from polyurethane precursor that reacts to form a crosslinked network, while the outer wall is formed from poly(urea-formaldehyde) precursor. This nested configuration provides thermal robustness through the outer wall's high-temperature stability while maintaining the healing agent containment function of the inner wall.

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The patent creates a composite capsule wall structure combining two different polymeric materials with complementary properties. The inner polyurethane wall provides flexibility and healing agent containment, while the outer poly(urea-formaldehyde) wall provides thermal stability and mechanical strength. This composite approach allows the capsule to withstand processing temperatures up to 200°C and shear stresses during polymer extrusion.

Inventive Principle:

Principle #40Composite materials

2Ease of manufacture

If processing temperature is increased to improve polymer processing performance, then the polymer can be processed more effectively, but the capsule shell degrades or the healing agent evaporates

Engineering Contradiction:

Improvepolymer processing capabilityVSAvoidcapsule degradation

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The patent changes the thermal parameters of the capsule wall materials to match or exceed the polymer processing temperature range. The outer poly(urea-formaldehyde) wall is specifically designed to maintain structural integrity at temperatures up to 200°C, allowing the capsule to survive standard polymer processing conditions without degradation or healing agent evaporation.

Inventive Principle:

Principle #35Parameter changes

3Strength

If conventional capsule formation methods are used, then the process is simple, but the capsules lack sufficient mechanical strength to survive high shear stresses during extrusion

Engineering Contradiction:

Improvecapsule mechanical strengthVSAvoidcapsule formation process

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The patent employs a composite wall structure where the outer poly(urea-formaldehyde) layer provides enhanced mechanical strength and resistance to shear stresses during extrusion, while the inner polyurethane layer maintains flexibility and healing agent containment. This composite construction achieves high mechanical strength without requiring complex multi-step formation processes.

Inventive Principle:

Principle #40Composite materials

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 double-walled capsules enable self-healing materials to be formed at high temperatures, previously impossible with conventional single-walled capsules, providing enhanced thermal stability and self-healing capabilities.

Implementation Method 1

emulsifying the mixture, adding a second component of the two-component poly(urea-formaldehyde) precursor system to the emulsified mixture, and maintaining the emulsified mixture at a temperature and for a time sufficient to form a plurality of capsules

Methodology Applied

Scientific EffectEmulsion polymerization: Photopolymerisation

Implementation Method 2

a first component of a two-component poly(urea-formaldehyde) precursor system... adding a second component of the two-component poly(urea-formaldehyde) precursor system

Methodology Applied

Scientific EffectCrosslinking: Chemical Bonding

Data Source

PatentUS8951639B2Thermally robust capsule system, and composites including the capsules

Publication Date: 2015.02.10 THE BOARD OF TRUSTEES OF THE UNIV OF ILLINOIS

AI summary

A method of making capsules includes forming a mixture including a core liquid, a polyurethane precursor system, a first component of a two-component poly(urea-formaldehyde) precursor system, and a solvent. The method further includes emulsifying the mixture, adding a second component of the two-component poly(urea-formaldehyde) precursor system to the emulsified mixture, and maintaining the emulsified mixture at a temperature and for a time sufficient to form a plurality of capsules that encapsulate at least a portion of the core liquid. The capsules made by the method may include a polymerizer in the capsules, where the capsules have an inner capsule wall including a polyurethane, and an outer capsule wall including a poly(urea-formaldehyde). The capsules may include in the solid polymer matrix of a composite material.