Polypropylene Resin Melt Strength via Non-Aromatic Electron Donors
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Solution Overview
Problem
Conventional polypropylene homopolymer and copolymer resins formed by traditional Ziegler-Natta catalysts have low melt strength and are unsuitable for high-processing-rate applications like injection molding, blown films, and thermobond fibers due to their low molecular weight distribution and lack of strain hardening, which limits their use in converting processes such as blown film, multi-layer applications, sheeting, and thermoforming.
Innovation Solution
A polypropylene resin with at least 50 mol% propylene, a molecular weight distribution (MWD) greater than 5, and a branching index of at least 0.95, produced using a Ziegler-Natta catalyst system comprising a non-aromatic internal electron donor and external organosilicon compounds, which enhances melt strength and processing capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional Ziegler-Natta catalysts with aromatic internal electron donors are used, then stereoregularity and crystallinity are improved, but melt strength and processability deteriorate
Solution Approach 1:
The patent changes the chemical parameters of the electron donor system by replacing aromatic internal electron donors with non-aromatic alternatives (such as cyclic ethers, esters, or amides) and adjusting the ratio of internal to external electron donors. This parameter change modifies the catalyst's polymerization behavior to produce polymers with improved melt strength while maintaining adequate stereoregularity.
Solution Approach 2:
The patent employs a composite electron donor system combining multiple components (non-aromatic internal electron donor plus external electron donors) to achieve synergistic effects. This composite approach allows the catalyst to produce polymers with both sufficient stereoregularity and improved melt strength, resolving the contradiction between these two properties.
2Strength
If highly crystalline polypropylene is produced, then flexural modulus and melting point are improved, but melt flow rate deteriorates
Solution Approach 1:
The patent modifies the electron donor parameters to control the degree of crystallinity and molecular weight distribution. By using non-aromatic internal electron donors and optimizing the external electron donor system, the patent achieves a balance where the polymer maintains high flexural modulus through adequate crystallinity while improving melt flow rate through controlled molecular weight distribution and reduced gel content.
3Stability of the object's composition
If molecular weight distribution is kept narrow (MWD 3-4.5), then polymer uniformity is improved, but converting process suitability deteriorates
Solution Approach 1:
The patent changes the catalyst system parameters, specifically the electron donor composition and ratios, to broaden the molecular weight distribution (MWD > 5). This parameter change enables the polymer to exhibit strain hardening behavior and improved melt strength, making it suitable for various converting processes like blown film, sheeting, and thermoforming, while still maintaining adequate compositional uniformity.
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 polypropylene resin exhibits improved melt strength, stiffness, and processing characteristics, making it suitable for applications such as blown film, multi-layer applications, sheeting, and thermoforming, replacing HDPE in certain uses and improving production efficiency.
Implementation Method 1
contacting propylene monomers at propylene polymerization conditions with a catalyst system comprising a Ziegler-Natta catalyst
Data Source
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AI summary
Polypropylene resin comprising at least 50 mol% propylene, an MWD (Mw/Mn) of greater than 5, a branching index (g') of at least 0.95, and a melt strength of at least 20 cN determined using an extensional rheometer at 190°C. A catalyst system comprising a Ziegler-Natta catalyst comprising a non-aromatic internal electron donor, and first and second external electron donors comprising different organosilicon compounds, and a method to produce a polypropylene resin comprising contacting propylene monomers at propylene polymerization conditions with the catalyst system are also disclosed.