Oxygen Tailoring HDPE Resin Sag Resistance
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Solution Overview
Problem
High-molecular-weight polyethylene resins used in sheet extrusion and thermoforming face challenges in processability and extrudability due to their high sag or drape, which limits their acceptance in the industrial thermoforming market, despite offering excellent mechanical properties.
Innovation Solution
The process of oxygen tailoring is used to increase the melt strength of chromium-catalyzed HDPE by exposing the molten resin to low levels of oxygen, promoting long chain branching without significantly affecting extensibility or elongational viscosity, thereby reducing sag in extruded sheets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high-molecular-weight polyethylene resins are used to improve mechanical properties, then strength and impact resistance are improved, but processability and extrudability deteriorate due to high sag or drape
Solution Approach 1:
The patent changes the molecular weight distribution parameters by blending HMW and LMW polyethylene components in specific ratios (30-70 weight percent HMW, 70-30 weight percent LMW). This parameter adjustment allows the resin to maintain high mechanical strength from the HMW component while the LMW component reduces sag and improves processability during extrusion and thermoforming operations.
2Strength
If high-molecular-weight polyethylene resins are used to improve tensile strength and puncture resistance, then mechanical performance is improved, but extrudability deteriorates
Solution Approach 1:
The patent creates a composite resin system combining two polyethylene components with different molecular weight characteristics. The HMW component (0.01-10 dg/min melt index) provides tensile strength and puncture resistance, while the LMW component (10-1000 dg/min melt index) acts as a processability enhancer that improves extrudability by reducing melt viscosity and sag during processing.
3Strength
If high-molecular-weight polyethylene resins are used to improve impact strength, then toughness is improved, but processability deteriorates due to increased sag
Solution Approach 1:
The patent adjusts the melt index parameter of the resin blend to achieve optimal processability. By incorporating LMW component (higher melt index: 10-1000 dg/min) with HMW component (lower melt index: 0.01-10 dg/min), the blend achieves a balanced melt index that maintains impact strength from the HMW fraction while the LMW fraction reduces sag and improves flow characteristics during extrusion and thermoforming.
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
This approach results in HDPE resins with improved sag resistance and melt strength, allowing for the production of sheets with reduced drape and enhanced rheological properties, making them more suitable for thermoforming applications without compromising their mechanical performance.
Implementation Method 1
contacting the HDPE resin with a gaseous medium comprising oxygen in the second melt zone, under conditions sufficient to promote at least some long chain branching
Data Source
AI summary
This invention relates to coupling of polyethylene resins, more specifically coupling of polyethylene resins for use in extruded profiles, especially extruded profiles for sheet extrusion and cut sheet thermoforming applications and geomembranes. The process involves conveying a HDPE resin through an extruder, wherein the extruder comprises a feed zone, a first melt zone downstream of the feed zone, a second melt zone downstream of the first melt zone, and a third melt zone downstream of the second melt zone. The resin is melted in the first zone, contacted with oxygen in the second melt zone, and contacted antioxidant in the third melt zone.