Polypropylene Foam Melt Strength via Peroxide-Diene Crosslinking
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Polypropylene foams face limitations due to low melt strength and high gel content, especially at high extrusion screw speeds, making them unsuitable for industrial applications despite their attractive properties like high modulus, tensile strength, and heat resistance.
Innovation Solution
A polypropylene composition is developed using a metallocene catalyst and post-reactor peroxide treatment in the presence of conjugated or non-conjugated dienes, resulting in a composition with low xylene hot unsoluble content and high melt strength, maintaining desirable properties even at high screw speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional peroxide treatment is applied to improve melt strength, then gel content increases, but this leads to undesirable low melt strength and poor processability at high extrusion speeds
Solution Approach 1:
The patent applies parameter changes by modifying the peroxide treatment conditions - specifically using controlled peroxide dosage (0.3-1.0 wt%) and temperature (20-90°C for at least 2 minutes) to achieve the desired balance between melt strength improvement and gel content control, enabling industrial-scale extrusion at high screw speeds without excessive gel formation
2Productivity
If high extrusion screw speed is used to increase productivity, then production rate improves, but gel formation increases leading to poor melt strength
Solution Approach 1:
The patent applies preliminary action by pre-mixing the polypropylene with peroxide and diene compounds in a controlled manner before extrusion, allowing the chemical modifications to be established in advance. This pre-treatment ensures that when high screw speed extrusion occurs, the material already has optimized properties without generating excessive gels during the high-speed processing
3Strength
If polypropylene is used for foam applications, then attractive properties like high modulus and heat resistance are achieved, but low melt strength and high gel content limit processability
Solution Approach 1:
The patent introduces diene compounds as intermediaries that mediate between the polypropylene base resin and the peroxide treatment. The dienes (0.3-2.0 parts per weight per 100 parts polypropylene) act as reactive intermediaries that control the crosslinking reaction, enabling the material to achieve both the desired mechanical properties and improved processability for foam 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 solution achieves a polypropylene composition with improved melt strength and reduced gel content, enabling commercially attractive production rates and enhanced processability, suitable for various industrial applications.
Implementation Method 1
a polypropylene being made in the presence of a metallocene catalyst
Implementation Method 2
post reactor peroxide treatment in the presence of at least one conjugated or non-conjugated, linear or branched diene containing 4 to 20 carbon atoms
Data Source
AI summary
The present invention is concerned with a polypropylene composition comprising a polypropylene base resin, the polypropylene composition having - a XHU content of less than 1.25 wt.-%; - a F30 melt strength of at least 30 cN, determined in the Rheotens test at 200°C; and - a melt extensibility v30 of at least 200 m/s, determined in the Rheotens test at 200°C. In another aspect the present invention is concerned with a polypropylene composition having an MFR (2.16 kg, 230 °C, ISO 1133) of 1.0 to 5.0 g/10 min comprising a polypropylene base resin, the polypropylene base resin being obtainable by producing an intermediate polypropylene having an MFR (2.16 kg, 230 °C, ISO 1133) of 0.5 to 2.5 g/10 min in the presence of an asymmetric catalyst; mixing the intermediate polypropylene with peroxide and at least one diene at a temperature of 20 to 90 °C for at least 2 minutes to form a pre-mixed material; melt mixing the pre-mixed material in a melt mixing device at a barrel temperature in the range of 180 to 300 °C, whereby the melt mixing device is a melt mixing device includes a feed zone, a kneading zone and a die zone, whereby an initial barrel temperature T1 is maintained in the feed zone, a barrel temperature T2 is maintained in the kneading zone and a die barrel temperature T3 is maintained in the die zone, whereby the barrel temperatures T1, T2, and T3 satisfy the following relation: T1 < T3 < T2. In yet another aspect the present invention is concerned with a process for the production of a polypropylene composition having - a XHU content of less than 1.25 wt.-%; - a F30 melt strength of at least 30 cN, determined in the Rheotens test at 200°C; and - a meit extensibility v30 of at least 200 m/s, determined in the Rheotens test at 200°C whereby an asymmetric catalyst derived intermediate polypropylene having an MFR (2.16 kg, 230 °C, ISO 1133) of 0.5 to 2.5 g/10 min is mixed with peroxide and at least one diene at a temperature of 20 to 90 °C for at least 2 minutes to form a pre-mixed material; and the pre-mixed material is melt mixed in a melt mixing device at a barrel temperature in the range of 180 to 300 °C. In yet another aspect the present invention is concerned with foam comprising the polypropylene composition according to the present invention. The present invention is further concerned with the use of the polypropylene composition for producing foamed articles.