High Density Polyethylene Melt Strength via Molten Stream Mixing
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Solution Overview
Problem
There is a need for higher density low-density polyethylene (LDPE)-based compositions with a density greater than 0.920 g/cc while maintaining high melt strength to improve coating performance, foaming performance, barrier properties, and n-hexane extractable levels.
Innovation Solution
A process involving a free-radical, high-pressure polymerization configuration that includes adding a high-density polyethylene (HDPE) stream to a molten LDPE stream after separation but before solidification, achieving a composition with a density of at least 0.940 g/cc and maintaining high melt strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high pressure free-radical polymerization is used to produce LDPE, then melt strength is improved, but density remains too low (< 0.920 g/cc)
Solution Approach 1:
The patent combines LDPE (produced by high-pressure free-radical polymerization) with HDPE (produced by other polymerization methods) to create a composite polymer composition. This allows the final material to achieve both high melt strength (from LDPE) and high density (from HDPE), resolving the contradiction between these two properties.
Solution Approach 2:
The patent merges two different polymerization processes and their respective products (LDPE and HDPE) into a single composite material. By combining the advantageous properties of both polymers, the final composition achieves both high melt strength and high density simultaneously.
2Quantity of substance
If HDPE is added to increase density, then density is improved, but melt strength decreases
Solution Approach 1:
The patent carefully controls the composition ratio of LDPE to HDPE in the final mixture, optimizing it to achieve the desired balance between density and melt strength. By adjusting this parameter, the patent resolves the contradiction by finding the optimal composition point where both properties are satisfied.
Solution Approach 2:
The patent creates a composite material with a specific formulation that combines LDPE and HDPE in optimized proportions. This composite approach allows the material to exhibit both high density (from HDPE) and high melt strength (from LDPE) simultaneously.
3Strength
If tubular reactor with high reaction zone peak temperatures is used, then melt strength is improved, but product density decreases
Solution Approach 1:
The patent segments the polymerization process into two distinct parts: (1) LDPE production in a tubular reactor with high peak temperatures to maximize melt strength, and (2) HDPE production using other methods to provide high density. The final composite combines these separately optimized components.
Solution Approach 2:
The patent uses HDPE as an intermediary component to compensate for the low density resulting from tubular reactor LDPE production. By adding HDPE to the LDPE matrix, the final composite achieves the desired density while preserving the melt strength benefits of the tubular reactor process.
4Quantity of substance
If autoclave reactor system is used to increase density, then density is improved, but melt strength and n-hexane extractable levels worsen
Solution Approach 1:
The patent uses LDPE produced by high-pressure free-radical polymerization as an intermediary to restore melt strength that was lost when using autoclave reactors. The LDPE component acts as a melt strength enhancer while the HDPE provides the density benefit.
Solution Approach 2:
The patent creates a composite material that combines HDPE (from autoclave or other processes) with LDPE (from high-pressure free-radical polymerization). This composite formulation simultaneously achieves high density (from HDPE) and high melt strength with low n-hexane extractables (from LDPE).
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 composition exhibits enhanced coating and foaming performance, improved barrier and compression properties, and reduced n-hexane extractable levels, while maintaining high melt strength.
Implementation Method 1
an ethylene homopolymer formed by polymerizing a reaction mixture comprising ethylene using a free-radical, high pressure polymerization process
Data Source
Figure 1~2
AI summary
A process for producing a composition comprising A) an ethylene-based polymer that has a density greater than, or equal to, 0.940 g/cc, and B) an ethylene homopolymer formed by polymerizing a reaction mixture comprising ethylene, using a free-radical, high pressure polymerization process includes adding component (A) to a molten stream of component (B) after component (B) exits the separator and before component (B) is solidified in the pelletizer. A polymerization configuration for producing the composition includes at least one reactor, at least one separator, at least one pelletizer, and a device used to feed component (A), in the molten state, to a molten stream of component (B) before the pelletizer. The composition has a ratio of the melt strength of the composition to the melt strength of component (B) is greater than or equal to 1.04 and a density of greater than 0.920 g/cc.