Multimodal Polyethylene Composition for Homogeneous Sag-Resistant Pipes
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Solution Overview
Problem
Multimodal polyethylene compositions face compatibility issues due to high molecular weight components, leading to non-homogeneous blends with 'white spots' and sagging problems in extruded articles like pipes, which affect mechanical and surface properties.
Innovation Solution
A polymer composition comprising a base resin with three components: a very high molecular weight polyethylene component, a low molecular weight polyethylene component, and a high molecular weight polyethylene component, produced through a multistage polymerization process using Ziegler-Natta catalysts, ensuring improved homogeneity and sagging resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If ultra-high molecular weight polyethylene component is added to improve mechanical properties, then mechanical strength is improved, but compatibility problems occur leading to non-homogeneous blends with white spots
Solution Approach 1:
The invention segments the high molecular weight component into two distinct fractions: a very high molecular weight fraction (Mw > 3,000,000) at 5-20 wt% and a high molecular weight fraction (Mw = 500,000-3,000,000) at 20-70 wt%. This segmentation allows the very high molecular weight fraction to provide mechanical strength while the high molecular weight fraction acts as a compatibility bridge, preventing phase separation and white spot formation by better integrating with the low molecular weight matrix.
2Strength
If very high molecular weight polyethylene is incorporated to improve mechanical properties, then crack propagation is slowed, but blending time increases significantly to 15 minutes
Solution Approach 1:
The invention performs preliminary action by pre-blending the very high molecular weight fraction with the high molecular weight fraction before final mixing with the low molecular weight matrix. The high molecular weight fraction serves as a pre-prepared compatibility medium that facilitates faster and more efficient blending of the ultra-high molecular weight component, reducing overall blending time while maintaining homogeneity.
3Strength
If high molecular weight component is increased to improve mechanical properties, then strength is improved, but viscosity ratio between components increases causing particle separation
Solution Approach 1:
The invention applies parameter changes by carefully controlling the molecular weight distribution across two fractions and their respective proportions. The very high molecular weight fraction (Mw > 3,000,000) is limited to 5-20 wt% while the high molecular weight fraction (Mw = 500,000-3,000,000) is maintained at 20-70 wt%. This parameter optimization ensures the viscosity ratio remains within a range that allows homogeneous blending while still achieving the desired mechanical strength enhancement.
4Stability of the object's composition
If polymer composition is made more homogeneous to eliminate white spots, then surface quality is improved, but mechanical properties may be compromised
Solution Approach 1:
The invention creates a composite material structure with three distinct polyethylene fractions, each serving a specific function. The low molecular weight fraction (Mw < 500,000) provides processability and matrix continuity, the high molecular weight fraction (Mw = 500,000-3,000,000) provides mechanical strength and acts as a compatibility agent, and the very high molecular weight fraction (Mw > 3,000,000) provides enhanced mechanical properties and crack resistance. This composite approach achieves both homogeneity and mechanical property enhancement simultaneously.
Data Source
AI summary
A polymer composition and a process for the production of this composition comprising a base resin is disclosed herein. The base resin includes a very high molecular weight component, a low molecular weight component, and a high molecular weight component having a weight average molecular weight higher than the weight average molecular weight of the low molecular weight component but lower than the weight average molecular weight of the very high molecular weight component. An amount of the very high molecular weight component in the base resin is 0.5 to 8 wt %. The very high molecular weight component has a viscosity average molecular weight of greater than 1100 kg/mol. The composition has FRR21/5 of equal to or greater than 38, a melt flow rate MFR21 of equal to or greater than 6.5 g/10 min and a viscosity at a shear stress of 747 Pa (eta747) of 450 to 3000 kPas.