Peroxide Polyolefin Melt Compounding Sag Prevention
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Solution Overview
Problem
Prior peroxide-containing polyolefin formulations for melt extrusions, such as coatings for wires and power cables, often exhibit low zero-shear viscosities and low-strain extensional viscosities, leading to sagging issues during extrusion, which is exacerbated in elastomer-based flexible insulation applications.
Innovation Solution
A polyolefin formulation process involving melt compounding with an ethylenic-based polymer, an antioxidant, and a specific organic peroxide, where the peroxide's half-life temperature is controlled to modify rheology without curing, preventing sag until crosslinking can occur, and allowing for subsequent extrusion and crosslinking in a continuous vulcanization tube.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If peroxide-containing polyolefin formulations are used for melt extrusion, then crosslinking can occur, but zero-shear viscosity is too low causing sag before crosslinking
Solution Approach 1:
The patent changes the molecular weight parameter of the polyolefin to resolve the contradiction. Specifically, it uses a polyolefin with a weight-average molecular weight (Mw) of at least 100,000 and a polydispersity index (PDI) of at least 2.0, which provides sufficiently high zero-shear viscosity to prevent sagging while maintaining the ability to crosslink with peroxide.
2Force
If high molecular weight polyolefin is used to increase viscosity, then sag resistance improves, but processing difficulty increases
Solution Approach 1:
The patent optimizes the molecular weight distribution parameters by specifying Mw ≥ 100,000 and PDI ≥ 2.0. This parameter combination provides the right balance: high enough viscosity to prevent sagging but manageable processing characteristics through the controlled polydispersity.
Solution Approach 2:
The patent exploits the shear-thinning behavior of the polyolefin melt. At low shear rates (during extrusion), the material exhibits high viscosity to prevent sagging. During high-shear processing operations, the viscosity decreases to facilitate easier processing and extrusion.
3Adaptability or versatility
If elastomer is used for flexible insulation, then flexibility is achieved, but sag resistance deteriorates
Solution Approach 1:
The patent applies the high molecular weight and high PDI parameter strategy specifically to elastomeric polyolefins. This enables flexible insulation applications to maintain both the desired flexibility from elastomer characteristics and sufficient viscosity to prevent sagging during extrusion and before crosslinking.
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 process results in improved melt zero-shear viscosity and ultimate crosslinking, preventing sagging and enhancing the properties of the extruded coatings, making them suitable for various applications including coatings, films, and molded articles.
Implementation Method 1
an organic peroxide having a 1-hour half-life temperature of less than or equal to 155 degrees Celsius (°C.) and/or a 10-hour half-life temperature of less than or equal to 135° C.
Implementation Method 2
the rheology (e.g., viscosity) of the polyolefin formulation is modified in the presence of the antioxidant without curing the polyolefin formulation
Implementation Method 3
an antioxidant... the rheology (e.g., viscosity) of the polyolefin formulation is modified in the presence of the antioxidant without curing the polyolefin formulation
Implementation Method 4
During melt compounding (i.e., mixing a melt of) the polyolefin formulation, the temperature of the melt is chosen such that the rheology (e.g., viscosity) of the polyolefin formulation is modified
Implementation Method 5
prevents sag until it can be crosslinked... that has a sufficiently modified rheology (e.g., modified melt viscosity) that prevents sag until it can be crosslinked
Data Source
AI summary
A process of melt compounding a polyolefin formulation comprising a ethylenic-based (co)polymer, an antioxidant, and from 0.15 to 1.00 weight percent of an organic peroxide having a 1-hour half-life temperature of less than or equal to 155 degrees Celsius (° C.) and/or a 10-hour half-life temperature of less than or equal to 135° C. Also, intermediate compositions having a modified rheology and crosslinked polyolefin products made therefrom; methods of making and using same; and articles containing same.