Polyester Composition Melt Strength via Chain Extender
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Solution Overview
Problem
Polyester compositions used in extrusion blow molding lack sufficient melt strength and recyclability, leading to issues such as hour-glass shape formation, thermal degradation, and increased manufacturing costs, while branched PET copolymers like Eastar Copolyester EB062 improve melt strength but hinder recyclability due to slow crystallization rates.
Innovation Solution
A polyester composition comprising a first polyester copolymer with a peak crystallization time of less than 45 minutes, a second polyester with a peak crystallization time of less than 45 minutes, and a chain extender like trimellitic anhydride, combined in a specific weight ratio, along with an optional branching agent, to enhance melt strength and crystallinity, enabling stable extrusion blow molding and recyclability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high molecular weight PET with I.V. of 1.0 dl/g or greater is used to increase melt strength, then the ability to form suitable parison improves, but processing temperature increases causing thermal degradation and yellowness
Solution Approach 1:
The patent changes the molecular weight parameter by using a blend of high molecular weight PET (I.V. ≥1.0) with lower molecular weight PET (I.V. 0.72-0.84), achieving sufficient melt strength while lowering the average molecular weight to reduce processing temperature and thermal degradation
Solution Approach 2:
The patent creates a composite polyester composition blending high molecular weight PET with lower molecular weight PET and cyclic carbonate additives, combining the melt strength benefits of high MW PET with the thermal stability and processability of lower MW PET
2Strength
If high molecular weight PET with I.V. of 1.0 dl/g or greater is used to increase melt strength, then parison formation ability improves, but the process window narrows making stable operation difficult
Solution Approach 1:
The patent adjusts the molecular weight distribution by blending high MW PET with lower MW PET, broadening the process window while maintaining sufficient melt strength for parison formation
3Strength
If branched PET copolymers like EB062 are used to increase melt strength, then process stability improves, but crystallization rate decreases causing sticking and agglomeration in recycling
Solution Approach 1:
The patent uses cyclic carbonate compounds as intermediaries that temporarily enhance melt strength during processing but decompose before recycling, allowing rapid crystallization in the recycling process without permanent branching
Solution Approach 2:
The patent changes the chemical structure temporarily during processing using cyclic carbonates, then restores the linear structure suitable for rapid crystallization by adding NaOH during recycling
4Productivity
If bottle grade PET with low melt viscosity is used for injection stretch blow molding, then processing speed improves, but melt strength is insufficient for extrusion blow molding
Solution Approach 1:
The patent changes the molecular weight parameter by blending high MW PET (I.V. ≥1.0) with bottle grade PET, achieving sufficient melt strength for EBM while maintaining processability
Solution Approach 2:
The patent creates a composite polyester composition blending high MW PET with bottle grade PET and cyclic carbonate additives, combining the processability of bottle grade PET with the melt strength of high MW PET
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 composition achieves improved melt strength, clarity, and recyclability, allowing for the production of containers with desirable aesthetics and physical properties, while enabling the use of regrind materials in PET recycling streams without causing sticking or agglomeration issues.
Implementation Method 1
from about 0.1 to about 5 wt% of a chain extender selected from the group consisting of trimellitic anhydride, pyromellitic dianhydride, trimellitic acid, haloformyl derivatives thereof, and combinations thereof
Implementation Method 2
a first polyester copolymer which does not show a peak crystallization time of less than about 45 minutes, a second polyester having a peak crystallization time of less than 45 minutes
Implementation Method 3
Air is injected to inflate the parison against the interior walls of the blow mold. Upon contact with the walls, the parison cools rapidly and assumes the shape of the mold
Data Source
Figure 1A~1B
Figure 2
Figure 3A
AI summary
Polyester compositions described herein have properties which are particularly suitable for extrusion blow molding (EBM). These properties relate primarily to the rate of crystallization and melt strength or melt viscosity. Articles prepared from the polyester compositions exhibit good clarity, aesthetics, and other physical properties. The polyester compositions also exhibit broad molecular weight distribution (MWD), resulting in improved processability and melt strength. The crystallization rate allows for good drying characteristics while also enabling the use of regrind. In addition, the compositions exhibit improved recyclability, such as in existing PET recycling streams. In one aspect, articles are prepared in an extrusion blow molding method by combining a dry first polyester copolymer component, a dry second polyester component, and a chain extender to form a feed material suitable for extrusion blow molding. In another aspect, a single component co-polyester and a chain extender are combined to form a feed material.