Propylene Polymer Melt Flow via Metallocene Catalyst
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Solution Overview
Problem
Propylene polymers with high melt flow rates typically have high levels of extractables, which are undesirable for applications like food packaging and medical tools, and are often achieved through processes that introduce degradation residues such as peroxides, leading to properties like yellowing and increased extractables.
Innovation Solution
A polypropylene resin with specific molecular weight distribution, high isotactic pentads, low hexane and xylene solubles, and a metallocene-based catalyst system to achieve high melt flow rates without peroxidic residues, ensuring low extractables and improved properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If peroxides are added to increase melt flow rate, then melt flow rate is improved, but extractables and degradation residues increase
Solution Approach 1:
The patent changes the fundamental parameter of catalyst type from conventional Ziegler-Natta to metallocene catalyst, enabling high melt flow rates through catalytic mechanism rather than peroxide degradation. This parameter change resolves the contradiction by achieving high MFR (up to 1000 g/10min) without introducing harmful peroxidic residues or increasing extractables
Solution Approach 2:
The patent replaces the chemical degradation mechanism (peroxide breakdown) with a catalytic polymerization mechanism (metallocene catalyst). This substitution eliminates the need for peroxides while achieving the desired melt flow rate through controlled catalytic processes that do not generate harmful residues
2Ease of manufacture
If conventional Ziegler-Natta catalysts are used, then manufacturing is easier, but melt flow rate is limited to about 400 g/10′
Solution Approach 1:
The patent changes the catalyst parameter from conventional Ziegler-Natta to metallocene catalyst system, which fundamentally alters the polymerization mechanism to enable higher melt flow rates. The metallocene catalyst with its specific molecular structure and electronic properties allows for controlled polymerization that achieves MFR up to 1000 g/10min while maintaining process feasibility
3Speed
If polymer is degraded with peroxides or gamma rays to increase melt flow rate, then melt flow rate is improved, but yellowing index and extractables increase
Solution Approach 1:
Instead of degrading the polymer after synthesis to increase melt flow rate, the patent inverts the approach by using a metallocene catalyst during polymerization to directly produce high MFR polymer without degradation. This inversion eliminates the harmful effects of peroxide or gamma ray degradation such as yellowing and increased extractables
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 solution enables propylene polymers with high melt flow rates and low extractables, maintaining superior properties without the drawbacks of degradation residues, suitable for various applications including food packaging and medical tools.
Implementation Method 1
a metallocene-based catalyst system
Implementation Method 2
distribution of molecular weight Mw/Mn lower than 4; preferably lower than 3; more preferably lower than 2.5
Data Source
AI summary
A polypropylene resin comprising a propylene polymer endowed with the following characteristics: a) distribution of molecular weight Mw/Mn lower than 4; b) the melt-viscosity measured at a temperature of 250° C. in the shear rate range between 1000 1/s and 40000 1/s meet the following relationship: c) h 9*e(−0.00006*sr)+2 a. wherein h represents the melt-viscosity in Pas and sr the shear rate in 1/s d) the isotactic pentads (mmmm) measured with by 13C-NMR are higher than 90%; d) preferably higher than 92%; more preferably higher than 95% and most preferred higher than 96%; e) the hexane extractables according FDA regulations are preferably below 2.6 wt. %; and f) the xylene solubles are below 2 wt. %; with the proviso that the propylene polymer was not visbroken.