Co-Extruded PET Parison Melt Strength and Recyclability
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Solution Overview
Problem
Extrusion blow molding (EBM) processes face challenges with high molecular weight PET resins due to their slow crystallization, leading to recyclability issues, such as sticking, thermal agglomeration, and bridging, and standard ISBM-grade PET lacks adequate melt strength for forming acceptable parisons, resulting in containers with reduced strength and visual defects.
Innovation Solution
Co-extrusion of two PET polymers with different intrinsic viscosities, where a higher IV polymer provides strength and a lower IV polymer includes post-consumer recycled PET, allowing for the formation of a parison that can be blow molded into a container compatible with standard recycling streams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high molecular weight PET resin is used for EBM processing, then melt strength is improved, but crystallization speed decreases causing recyclability issues
Solution Approach 1:
The invention divides the PET resin system into two distinct segments: a high molecular weight PET component (providing melt strength with IV ≥ 0.90) and a low molecular weight PET component (accelerating crystallization with IV < 0.90). This segmentation allows each component to perform its specialized function without compromising the other, resolving the contradiction between melt strength and crystallization speed.
Solution Approach 2:
The invention creates a composite PET resin system by combining high molecular weight PET and low molecular weight PET in specific ratios (at least 20% by weight of the high IV component). This composite approach leverages the complementary properties of both components: the high IV resin provides structural integrity and melt strength, while the low IV resin promotes rapid crystallization, thereby resolving the performance trade-off.
2Ease of manufacture
If amorphous or slow-crystallizing co-polymer is used for easier EBM processing, then processability is improved, but recyclability deteriorates due to sticking and thermal agglomeration
Solution Approach 1:
The invention changes the molecular weight parameters of the PET resin system by incorporating both high IV (≥0.90) and low IV (<0.90) components. This parameter adjustment allows the resin to achieve optimal processing characteristics (through the low IV component's faster crystallization) while maintaining recyclability (through the high IV component's structural integrity and resistance to thermal degradation).
Solution Approach 2:
The invention creates a homogeneous blend of high and low molecular weight PET resins that crystallize uniformly. The low IV component accelerates overall crystallization without creating the heterogeneous, slow-crystallizing structure of amorphous co-polymers. This homogeneous crystallization behavior prevents sticking and thermal agglomeration during recycling while maintaining ease of EBM processing.
3Reliability
If standard ISBM-grade PET with low IV is used, then recyclability is improved, but melt strength decreases preventing proper parison formation
Solution Approach 1:
The invention segments the PET resin functionality by assigning the melt strength requirement to the high IV component (≥0.90) and the recyclability requirement to the low IV component (<0.90). This segmentation allows the high molecular weight resin to provide adequate melt strength for parison formation while the low molecular weight resin maintains recyclability compatibility, resolving the contradiction between these two requirements.
Solution Approach 2:
The invention formulates a composite PET resin system combining high IV and low IV PET components in specific proportions (at least 20% high IV by weight). This composite structure provides synergistic effects: the high IV component ensures sufficient melt strength for extrusion and parison formation, while the low IV component maintains compatibility with standard recycling streams, thereby resolving the melt strength vs. recyclability contradiction.
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 method produces containers with improved strength, clarity, and recyclability, capable of passing drop tests and suitable for commercial use, while maintaining compatibility with standard recycling programs.
Implementation Method 1
they tend not to be able to carry their own weight and/or the resins may extrude too quickly to form a desired capturable parison
Implementation Method 2
The co-extruded parison may be subsequently blow molded to form a container
Data Source
AI summary
An extruded PET parison includes a first extruded polymer comprising PET, and a second extruded polymer comprising PET. In embodiments, the first extruded polymer and the second extruded polymer are co-extruded, and the first extruded polymer has an intrinsic viscosity that is higher that the intrinsic viscosity of the second extruded polymer. A monolayer embodiment is also disclosed. In embodiments, a monolayer extruded PET container is comprised of bottle grade PET resin that has been solid stated and may have an IV from about 0.96 to about 1.4.