Ethylene/1-hexene copolymer catalyst system for mechanical strength
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Solution Overview
Problem
There is a need for new ethylene/1-hexene copolymers with specific properties such as density, melt index, molecular weight ratios, and cumulative detector fraction that existing polymers do not adequately provide, particularly for applications requiring improved mechanical strength and impact resistance.
Innovation Solution
Ethylene/1-hexene copolymers are produced using a gas-phase reactor system with a zirconocene catalyst and a hydrogenation catalyst, with a titanium to zirconium molar ratio of 0.100 to 0.700, achieving densities between 0.850 to 0.940 g/cm3 and enhanced Instrumented Dart Impact Peak Force, along with a cumulative detector fraction greater than 4% at a molecular weight of ≥1,000,000 g/mol.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If existing polymerization processes are used, then production is achieved, but the copolymers do not have the desired combination of density, melt index ratio, and molecular weight distribution
Solution Approach 1:
The patent applies parameter changes by systematically varying catalyst composition (zirconocene with specific ligands, aluminum alkyl activators), monomer ratios (ethylene to 1-hexene), and polymerization conditions (temperature, pressure, residence time) to achieve precise control over melt index ratio and molecular weight distribution while maintaining production efficiency
Solution Approach 2:
The patent uses composite catalyst systems combining zirconocene metallocene catalysts with aluminum alkyl activators and hydrogenation catalysts to create copolymers with tailored properties. The composite approach allows simultaneous optimization of multiple parameters including density (0.860-0.920 g/cm³), melt index ratio (I21/I2 ≤ 18.5), and molecular weight distribution (Mw/Mn = 2.0-3.5)
2Strength
If density is increased for stronger material, then mechanical strength is improved, but impact resistance and processability deteriorate
Solution Approach 1:
The patent applies local quality by creating copolymers with controlled composition distribution, where different molecular weight fractions have different comonomer contents. This results in a material that simultaneously exhibits high strength from crystalline regions and impact resistance from amorphous regions, with density optimized at 0.860-0.920 g/cm³
Solution Approach 2:
The patent creates a composite molecular structure with a blend of high molecular weight chains (providing strength and impact resistance) and lower molecular weight chains (providing processability). The molecular weight distribution (Mw/Mn = 2.0-3.5) is engineered to balance mechanical properties with ease of processing
3Strength
If molecular weight is increased for better mechanical properties, then strength is improved, but melt index and processability worsen
Solution Approach 1:
The patent applies dynamics by creating a polydisperse molecular weight distribution rather than a uniform structure. The broad distribution (Mw/Mn = 2.0-3.5) allows the material to exhibit high strength at low shear rates while maintaining good flow and processability at high shear rates during manufacturing
Solution Approach 2:
The patent optimizes the molecular weight distribution parameters by controlling catalyst activity and polymerization conditions to achieve Mw/Mn = 2.0-3.5 and Mz/Mw = 1.7-4.5, which balances mechanical strength with acceptable melt index (I21 = 0.1-50 dg/min) for various processing applications
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
The resulting copolymers exhibit improved mechanical properties, including increased melt strength and Instrumented Dart Impact Peak Force, while maintaining desired density and molecular weight ratios, making them suitable for various applications like films and molded articles.
Implementation Method 1
contacting a zirconocene catalyst and a hydrogenation catalyst with ethylene and hexene in a gas-phase reactor under polymerizable conditions
Data Source
AI summary
Embodiments are directed towards ethylene/1-hexene copolymers made from ethylene and hexene, wherein the ethyl-CA ene/1-hexene copolymer has a density from 0.850 to 0.940 g/cm3, a melt index (I21) from 0.1 to 50 dg/min, a melt index (I21/I2) ratio less than or equal to 18.5, a Mw(Abs)/Mn(Abs) from 2.0 to 3.5, a Mz(Abs)/Mw(Abs) from 1.7 to 4.5, and a cumulative detector fraction (CDFLS) at a molecular weight of ≥1,000,000 g/mol of greater than 100*(0.0536−I21*0.00224)%.