Metallocene Polyethylene Melt Fracture Reduction
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Solution Overview
Problem
There is a need for polymer compositions with improved processability and melt fracture characteristics, as existing polyolefins face challenges in achieving desired processing characteristics such as zero shear viscosity and smooth-to-matte transition stress.
Innovation Solution
The development of metallocene-catalyzed polymers comprising a higher molecular weight component and a lower molecular weight component, with specific polydispersity indices and zero shear viscosities, which are produced using various polymerization reactors and catalyst systems, including dual metallocene catalysts, to enhance processability and reduce melt fracture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional polyolefins are used, then general polymer properties (stiffness, ductility, barrier properties) are maintained, but processability and melt fracture characteristics are insufficient
Solution Approach 1:
The patent applies parameter changes by precisely controlling the polydispersity index within the range of 10-26 and zero shear viscosity within the range of 5×10^5 to 5×10^6 cP. These specific parameter ranges optimize both processability and melt fracture characteristics, resolving the technical contradiction between ease of manufacture and reliability.
Solution Approach 2:
The patent creates a composite polymer structure comprising higher molecular weight components (providing melt strength and reducing melt fracture) and lower molecular weight components (providing processability). This composite approach at the molecular level allows simultaneous optimization of both processability and melt fracture characteristics.
2Reliability
If higher molecular weight component is increased to reduce melt fracture, then melt strength improves, but processability deteriorates due to increased viscosity
Solution Approach 1:
The patent resolves this contradiction by controlling the polydispersity index within 10-26 and zero shear viscosity within 5×10^5 to 5×10^6 cP. This balanced parameter optimization allows the higher molecular weight component to provide melt strength while the lower molecular weight component maintains processability.
Solution Approach 2:
The patent applies local quality by creating distinct molecular weight distributions within the polymer. The higher molecular weight components (20-80% of total weight) provide local melt strength and fracture resistance, while the lower molecular weight components (20-80% of total weight) provide local processability, with each component performing its specific function.
Data Source
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AI summary
A metallocene-catalyzed polymer comprising (i) a higher molecular weight component and (ii) a lower molecular weight component wherein the polymer has a polydispersity index of from about 10 to about 26; a zero shear viscosity of from about 5x105 Pa.s to about 2x1014 Pa.s and a smooth-to-matte transition critical stress of from about 20 kPa to about 85 kPa at a shear rate of from about 1.5 s-1 to about 17 s-1. A dual metallocene catalyzed polyethylene comprising (i) a higher molecular weight component and (ii) a lower molecular weight component wherein the polymer has a polydispersity index of from about 10 to about 26; a zero shear viscosity of from about 5x105 Pa.s to about 2x1014 Pa.s and a smooth-to-matte transition stress of from about 20 kPa to about 85 kPa at a shear rate of from about 1. 5 s-1 to about 17 s-1.