Multimodal Polyethylene Pipe for Slow Crack Growth Resistance
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Solution Overview
Problem
Polymer pipes used in tough soil conditions and hard installation scenarios lack sufficient slow crack growth (SCG) properties, requiring materials with SCG notch test results exceeding 5,000 hours, while maintaining a balance of processability, impact strength, modulus of elasticity, and rapid crack propagation resistance.
Innovation Solution
A multimodal polyethylene pipe composition with a base resin comprising two ethylene homo- or copolymer fractions, where one fraction has a lower average molecular weight than the other, and specific properties such as density, melt flow rate, comonomer content, and complex viscosity, enhancing SCG properties and pressure resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional polyethylene materials are used, then processability and manufacturing ease are maintained, but slow crack growth properties are insufficient for tough soil conditions
Solution Approach 1:
The patent uses a multimodal polyethylene composition comprising at least two ethylene polymer fractions with different molecular weight distributions. Fraction (A) has a first molecular weight distribution with MFR2 of 300-600 g/10min, while fraction (B) has a second molecular weight distribution with MFR2 of 1-20 g/10min. This composite structure combines the processability benefits of low molecular weight fractions with the superior SCG resistance of high molecular weight fractions, achieving SCG notch test results exceeding 5000 hours while maintaining acceptable processability.
2Reliability
If high molecular weight polyethylene is used to improve SCG properties, then slow crack growth resistance increases, but processability and manufacturing ease deteriorate
Solution Approach 1:
The patent segments the polyethylene material into two distinct molecular weight fractions with clearly defined characteristics. Fraction (A) with MFR2 of 300-600 g/10min provides excellent processability for extrusion, while fraction (B) with MFR2 of 1-20 g/10min provides the high molecular weight necessary for SCG resistance. The segmented structure allows each fraction to perform its specialized function without compromising the other, achieving SCG notch test results >5000 hours while maintaining extrusion processability.
3Reliability
If multimodal polyethylene composition is used to enhance SCG properties, then slow crack growth resistance and pressure resistance improve, but material complexity increases
Solution Approach 1:
The patent achieves improved pressure resistance and SCG properties by carefully controlling specific parameters of the multimodal composition. The base resin has density of 0.941-0.947 g/cm3, MFR2 of 10-50 g/10min, MFR5 of 0.15-0.50 g/10min, comonomer content of 1.5-3.0 wt.%, and complex viscosity η*2.7 of 200-400 kPa·s. These parameter specifications ensure consistent performance with SCG notch test results exceeding 5000 hours and pressure resistance meeting ISO 1167 standards, while maintaining manageable material complexity through defined composition ranges.
Data Source
AI summary
A pipe or a supplementary pipe article comprising a polyethylene composition comprising a base resin which comprises (A) a first ethylene homo- or copolymer fraction having an MFR2 in the range of 300 to 700 g/10 min, and (B) a second ethylene homo- or copolymer fraction, wherein fraction (A) has a lower average molecular weight than fraction (B), wherein the base resin has a density in the range of 0.945 to 0.949 kg/cm3 and an MFR5 in the range of 0.2 to 0.4 g/10 min and a comonomer content of higher than 2.0 wt.-% and a SHI(2.7/210) in the range of 55 to 100.