Core-shell emulsion polymers for fiber cement impact resistance
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Solution Overview
Problem
Fiber cement articles, such as roof tiles and boards, face limitations in hail impact resistance due to the use of alternative fibers like polyvinyl alcohol, which do not meet stringent mechanical property standards, and existing elastomeric particles fail to enhance impact resistance due to poor bonding with the cement matrix.
Innovation Solution
Incorporating core-shell aqueous emulsion polymers with a crosslinked rubbery core and a grafted acrylic or vinyl shell into fiber cement articles, where the core has a glass transition temperature of -20 to -140°C and the shell has a temperature of 20 to 170°C, along with reinforcing fibers, to improve impact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If alternative fibers like polyvinyl alcohol are used to replace asbestos fiber, then health and safety restrictions are met, but mechanical properties such as hail impact resistance are limited
Solution Approach 1:
The patent combines alternative fibers (polyvinyl alcohol) with a cement matrix and elastomeric particles to create a composite material that maintains health safety compliance while achieving improved hail impact resistance through the synergistic interaction of components
Solution Approach 2:
The patent modifies the mechanical properties of fiber cement articles by changing the chemical composition parameters, specifically incorporating elastomeric particles with specific glass transition temperatures and cement formulations to enhance impact resistance while maintaining fiber substitution
2Strength
If elastomeric particles are added to the cement matrix, then impact resistance may be improved, but poor bonding occurs due to hydrophobicity of elastomers versus hydrophilicity of cement
Solution Approach 1:
The patent uses cement as an intermediary material that bridges the hydrophobic elastomeric particles and the hydrophilic fiber matrix, enabling effective stress transfer and bonding despite the inherent incompatibility between elastomer and cement materials
Solution Approach 2:
The patent selects elastomeric particles with specific properties (glass transition temperature below -50°C, specific size ranges) and optimizes cement composition to achieve proper bonding and stress transfer, transforming the material parameters to resolve the bonding issue
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 use of core-shell emulsion polymers significantly enhances the impact resistance of fiber cement articles by up to 35% as measured by the Gardner Universal Impact Tester, improving their durability and compliance with mechanical standards.
Implementation Method 1
the effective transfer of stress from the cement matrix to the particulate elastomers dispersed therein
Implementation Method 2
core-shell aqueous emulsion polymers having a crosslinked rubbery core with a calculated glass transition temperature (calculated Tg) of from -20 to -140 °C
Data Source
AI summary
The present invention provides fiber cement articles, such as roof tiles having improved impact and hail resistance and methods for making them. The fiber cement articles comprise cement, an optional filler, reinforcing fibers, such as poly(vinyl alcohol) fibers or a mixture of cellulosic and synthetic fibers, one or more core-shell aqueous emulsion polymers having a crosslinked rubbery core with a calculated glass transition temperature (calculated Tg) of from -20 to -140 °C, and an at least partially grafted acrylic or vinyl shell polymer having a calculated Tg of from 20 to 170 °C, and having a Z-average primary particle size of from 55 to 800 nm, or, preferably, from 140 to 650 nm. The solids weight ratio of the crosslinked rubbery core to the shell of the core-shell aqueous emulsion polymer may range from 85:20 to 97:3.