Fiber-Reinforced Polypropylene Melt Flow and Impact Strength
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Solution Overview
Problem
Fiber-reinforced polypropylene compositions face challenges in achieving high flowability without compromising mechanical properties such as flexural modulus, impact strength, and elongation at break, particularly due to the negative correlation between glass fiber content and flowability.
Innovation Solution
A fiber-reinforced composition comprising a heterophasic propylene copolymer, a propylene homopolymer or copolymer, fibers, and optionally an elastomer and compatibilizer, where the heterophasic copolymer contains no more than 45 wt.% elastomeric copolymer, ensuring a high melt flow rate while maintaining mechanical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If glass fiber content is increased to improve mechanical properties, then strength and stiffness are improved, but flowability deteriorates
Solution Approach 1:
The patent changes the molecular weight distribution parameters of the polypropylene matrix by using a bimodal mixture with specific MFR2 ratios. The low molecular weight fraction (MFR2 > 500 g/10 min) reduces viscosity to improve flowability, while the high molecular weight fraction (MFR2: 0.1-30 g/10 min) maintains mechanical strength. This parameter optimization allows processing at lower injection pressures and temperatures while preserving impact strength.
Solution Approach 2:
The patent creates a composite polymer system combining two polypropylene fractions with different molecular characteristics. The low molecular weight fraction acts as a flow promoter while the high molecular weight fraction provides structural integrity. This composite approach at the polymer level enables simultaneous achievement of good flowability and mechanical properties, which then supports higher glass fiber content without sacrificing processability.
2Object-generated harmful factors
If melt flow rate is increased to improve flowability, then processability is improved, but mechanical performance deteriorates
Solution Approach 1:
The patent segments the polypropylene matrix into two distinct molecular weight fractions, each performing a specific function. The low molecular weight fraction (MFR2 > 500 g/10 min) is responsible for flowability and processability, while the high molecular weight fraction (MFR2: 0.1-30 g/10 min) maintains mechanical strength. This segmentation allows each component to optimize its specific function without compromising the other.
Solution Approach 2:
The patent optimizes the MFR2 parameter by creating a bimodal distribution rather than using a single molecular weight polymer. The specific ratio and characteristics of the two fractions are tuned to achieve the desired balance: the low MFR2 fraction provides excellent flowability for thin-wall molding, while the high MFR2 fraction ensures adequate impact strength and structural performance.
Data Source
AI summary
Fiber reinforced composition comprising a heterophasic propylene copolymer, a propylene homopolymer and/or a propylene copolymer, and fibers, wherein the propylene copolymer comprises not more than 2.0 wt.-% C2 to C10 α-olefins other than propylene, the propylene homopolymer and the propylene copolymer have a melt flow rate MFR2 (230° C.) of at least 500 g/10 min, and the composition has a melt flow rate MFR2 (230° C.) of at least 10 g/10 min.