Polyethylene Pipe Composition SCG and RCP Resistance
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Solution Overview
Problem
Current polyethylene pipe technologies fail to achieve a balanced combination of thermal, mechanical, and processing properties, particularly lacking superior resistance to slow crack growth (SCG), rapid crack propagation (RCP), and long-term burst performance at elevated temperatures, while maintaining performance at 23°C.
Innovation Solution
A polyethylene composition comprising a blend of high molecular weight and low molecular weight ethylene-based interpolymers, with specific density and melt index ranges, and a viscosity average molecular weight coefficient less than −0.0032, is developed to enhance SCG, RCP, and burst performance at 60°C and higher temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional polyethylene pipe technologies are used, then basic pipe functionality is achieved, but superior resistance to slow crack growth (SCG), rapid crack propagation (RCP), and long-term burst performance at elevated temperatures cannot be achieved simultaneously
Solution Approach 1:
The patent uses a composite polyethylene composition combining a first polyethylene resin and a second polyethylene resin with different molecular weight distributions. The first resin (higher molecular weight) provides superior SCG, RCP, and high-temperature burst performance, while the second resin (lower molecular weight) maintains processing properties and low-temperature performance. This composite approach enables simultaneous achievement of multiple performance requirements that cannot be met by single-resin systems.
Solution Approach 2:
The patent applies local quality by assigning different functional roles to different components of the polyethylene composition. The higher molecular weight resin specifically targets and improves SCG, RCP, and high-temperature burst resistance, while the lower molecular weight resin maintains processability and low-temperature ductility. This functional differentiation within the composition allows optimization of specific properties without compromising overall performance balance.
2Reliability
If polyethylene composition is optimized for superior SCG, RCP, and high-temperature burst performance, then reliability improves, but processing properties and performance at 23°C may deteriorate
Solution Approach 1:
The patent employs parameter changes by carefully controlling the molecular weight distribution characteristics of each resin component. The first resin has a weight average molecular weight (Mw) of 50,000-500,000 and a specific Mw/Mn ratio range, while the second resin has Mw of 10,000-100,000 with complementary distribution characteristics. By adjusting these molecular weight parameters and their ratios in the composition, the patent achieves superior high-temperature reliability while maintaining adequate processing properties and 23°C performance.
Data Source
AI summary
The invention is related to compositions suitable for the fabrication of pipes, and other articles, with excellent performance properties. The invention provides a composition, comprising a blend, wherein said blend comprises a high molecular weight ethylene-based interpolymer and a low molecular weight ethylene-based interpolymer, and the high molecular weight ethylene-based interpolymer is a heterogeneously branched linear or a homogeneously branched linear ethylene-based interpolymer, and has a density from 0.922 g/cc to 0.929 g/cc, and a high load melt index (I21) from 0.2 g/10 min to 1.0 g/10 min, and the low molecular weight ethylene-based interpolymer is heterogeneously branched linear or a homogeneously branched linear ethylene-based interpolymer, and has a density from 0.940 g/cc to 0.955 g/cc, and a melt index (I2) from 6 g/10 min to 50 g/10 min. The blend has a single peak in an ATREF profile eluting above 30° C., and has a coefficient of viscosity average molecular weight (CMv) less than −0.0032 in the log(calculated Mv) versus elution temperature, said CMv calculated in the range of elution temperatures from 70° C. to 90° C. The Mv is the viscosity average molecular weight.