Propylene 1-Hexene Copolymer Slow Crack Resistance
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Solution Overview
Problem
Polypropylene pipes used for pressure applications face challenges in balancing high resistance to slow crack propagation, thermal resistance, and rigidity while minimizing the risk of material washout by pressurized fluids, as existing copolymers often compromise on these properties.
Innovation Solution
A β-nucleated propylene 1-hexene copolymer with a comonomer content of 1.0 to 3.0 wt.%, a xylene soluble fraction of 2.5 wt.% or less, and a β-modification of at least 50%, which includes β-nucleating agents such as dicarboxylic acid derivatives and quinacridone compounds, is developed to enhance slow crack propagation, stiffness, and impact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If propylene copolymers are used to improve resistance to slow crack growth, then slow crack growth resistance is improved, but thermal resistance and rigidity deteriorate
Solution Approach 1:
The patent applies parameter changes by precisely controlling the comonomer content within 1.0 to 3.0 wt.-% range and limiting xylene soluble fraction to 2.5 wt.-% or less. This specific parameter optimization allows the copolymer to achieve improved slow crack growth resistance while maintaining adequate thermal resistance and rigidity, resolving the contradiction between reliability and strength properties.
Solution Approach 2:
The patent creates a composite material system by combining propylene with controlled amounts of comonomers (1.0-3.0 wt.-%) to form a copolymer structure. This composite approach at the molecular level enables the material to exhibit both improved slow crack growth resistance from the copolymer structure and maintained rigidity through the propylene base matrix, thus resolving the contradiction between reliability and strength.
2Reliability
If comonomer content is increased to improve slow crack growth resistance, then slow crack growth resistance is improved, but the risk of material washout increases
Solution Approach 1:
The patent resolves this contradiction by establishing an optimal parameter range for comonomer content (1.0-3.0 wt.-%) and constraining the xylene soluble fraction to 2.5 wt.-% or less. This parameter optimization ensures sufficient slow crack growth resistance while preventing excessive material washout, as the comonomer content is high enough to improve crack resistance but low enough to maintain material stability against washout.
3Strength
If propylene homopolymer is used to maintain high thermal resistance and rigidity, then thermal resistance and rigidity are maintained, but resistance to slow crack growth deteriorates
Solution Approach 1:
The patent creates a copolymer composite material that combines propylene with controlled comonomer content (1.0-3.0 wt.-%). This composite structure maintains the rigidity and thermal resistance characteristics of the propylene base while incorporating the comonomer segments that improve slow crack growth resistance, thus resolving the contradiction between strength and reliability.
Solution Approach 2:
The patent applies parameter changes by optimizing the comonomer content to 1.0-3.0 wt.-% and limiting xylene soluble fraction to 2.5 wt.-% or less. This controlled modification from pure homopolymer creates a copolymer that maintains the desirable thermal and mechanical properties while improving slow crack growth resistance, resolving the contradiction between strength and reliability.
4Reliability
If higher comonomer content is used to improve slow crack growth resistance, then slow crack growth resistance is improved, but stiffness deteriorates
Solution Approach 1:
The patent resolves this contradiction by precisely controlling the comonomer content within 1.0 to 3.0 wt.-% range. This optimized parameter range provides sufficient slow crack growth resistance improvement while limiting the negative impact on stiffness, as the comonomer content is high enough to enhance crack resistance but low enough to preserve the stiffness required for pipe applications.
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 propylene copolymer exhibits superior slow crack propagation performance, high stiffness, and excellent impact resistance, maintaining thermal resistance while minimizing material washout, as demonstrated by improved Izod impact resistance and flexural modulus.
Implementation Method 1
The present invention relates to a propylene copolymer... produced in the presence of a ziegler natta catalyst
Implementation Method 2
being partially crystallized in the β-modification, preferably having a β-modification of at least 50 %
Data Source
AI summary
Propylene copolymer a. comprising at least 1-hexene as a comonomer, b. having a comonomer content in the range of 1.0 to 3.0 wt.-%, c. having a xylene soluble fraction equal or below 2.5 wt.-%, and d. being partially crystallized in the ß-modification.