Polyethylene Melt Strength via Side Feed Dosage
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Solution Overview
Problem
High-pressure polymerization processes for polyethylene, such as tubular and autoclave reactors, often result in polyethylene with insufficient melt elasticity, which limits its properties for applications like extrusion coating.
Innovation Solution
A side feed dosage unit is introduced into the polymerization reactor system, specifically a side feed extruder, to inject additional polymer, adjusting CTA concentrations and reaction conditions to broaden the molecular weight distribution and improve melt strength without altering the melt index.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional high-pressure polymerization processes (tubular or autoclave reactors) are used, then polyethylene production is achieved, but the melt elasticity is insufficient
Solution Approach 1:
The patent combines two different polyethylene materials with distinct molecular weight distributions to create a composite product. The first material (from continuous polymerization) provides base properties, while the second material (from batch polymerization with added CTA) contributes broader molecular weight distribution and enhanced melt elasticity. This composite approach resolves the contradiction by achieving superior melt elasticity without fundamentally redesigning the entire manufacturing process.
Solution Approach 2:
The patent divides the polyethylene production process into two separate polymerization stages: a continuous polymerization step followed by a batch polymerization step. Each stage produces polymer with specific characteristics, and the final product is a blend of both. This segmentation allows optimization of each stage independently, achieving the desired melt elasticity while maintaining manufacturing feasibility.
2Strength
If CTA concentration is increased to broaden molecular weight distribution, then melt strength improves, but melt index changes
Solution Approach 1:
The patent applies different CTA concentrations at different stages of the polymerization process. The batch polymerization step uses higher CTA concentration to broaden molecular weight distribution and improve melt strength, while the continuous polymerization step maintains standard conditions to preserve melt index consistency. This localized application of quality control resolves the contradiction by achieving both improved strength and consistent melt index through staged processing.
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 increases the Mw/Mn ratio by at least 20%, enhancing melt strength, elastic properties, and broadening the molecular weight distribution, enabling better performance in extrusion coating and other applications with consistent melt index.
Implementation Method 1
an initiator such as for example an organic peroxide, azodicarboxylic acid ester and azodicarboxylic acid dinitrile that decompose into radicals
Implementation Method 2
the reactor tube, which is provided on the outside with a jacket through which cooling water flows in order to remove the generated heat of reaction via the wall
Implementation Method 3
cooling water flows in order to remove the generated heat of reaction
Implementation Method 4
In the polyethylene high-pressure process polyethylene is prepared by radical polymerisation in supercritical ethylene
Data Source
AI summary
The invention relates to a high-pressure polymerisation process for the preparation of polyethylene. A polymer is added to the extruder via a side feed dosage unit wherein the MFI sf of the polymer added via the side feed dosage unit has a higher value than the melt flow index (MFIend ) of the polyethylene end product and wherein the Mw/Mn of the end product increases at least 15% compared to the product wherein no polymer is dosed via the side feed.