PET-MXD6 Polyester Composition for Oxygen Barrier and Impact Strength
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Solution Overview
Problem
Thermoplastic polyester compositions for food packaging face challenges in achieving both effective gas barrier properties and mechanical strength while maintaining cost-effectiveness, as existing additives often compromise processing and mechanical properties, leading to increased production costs and complex processing requirements.
Innovation Solution
A polyester composition blending 90-97 wt.% of polyethylene terephthalate or polyethylene naphthalene with 2-6 wt.% of poly-m-xylidene (MXD6), 1-5000 ppm of cobalt salt, 0.1-1000 ppm of ethylene glycol, and 0.1-1000 ppm of pyromellitic dianhydride (PMDA), along with optional carbon black, to achieve low viscosity and enhanced gas barrier and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If additives such as polyamide and cobalt salts are added to enhance gas barrier properties, then oxygen permeability is reduced, but mechanical properties and processing characteristics deteriorate
Solution Approach 1:
The patent uses a composite material system consisting of PET base polymer, MXD6 polyamide (2-6 wt%), and cobalt salt (1-5000 ppm). This composite structure allows the polyamide to form a barrier network that reduces oxygen permeability while the controlled low amounts and specific interaction with cobalt salt prevent severe degradation of mechanical properties. The composite approach enables simultaneous achievement of gas barrier enhancement and mechanical property retention.
Solution Approach 2:
The patent optimizes the concentration parameters of additives to resolve the contradiction. By limiting polyamide content to 2-6 wt% and cobalt salt to 1-5000 ppm, the patent finds an optimal parameter range where gas barrier properties are significantly improved without causing excessive deterioration of mechanical properties. This parameter optimization allows the system to operate in a window where both requirements are satisfied.
2Strength
If higher amounts of polymer are used to thicken container walls to improve impact strength, then mechanical strength is improved, but production costs increase and processing becomes more difficult
Solution Approach 1:
The patent changes the compositional parameters by incorporating MXD6 polyamide and cobalt salt, which modify the material properties to achieve better impact strength at the same wall thickness. This compositional parameter change eliminates the need to increase wall thickness, thereby maintaining ease of manufacture and avoiding increased processing difficulty associated with thicker walls.
Solution Approach 2:
The patent applies local quality enhancement by concentrating the barrier and strength-enhancing components (MXD6 and cobalt salt) in specific amounts within the polymer matrix. This localized enhancement of properties through controlled additive distribution allows the material to achieve superior impact strength without requiring uniform thickening of the entire container wall, thus maintaining processing ease.
3Strength
If longer cooling times are required to solidify thicker preforms, then impact strength is improved, but production cycle time increases
Solution Approach 1:
The patent changes the material composition parameters by adding MXD6 polyamide and cobalt salt, which enhance impact strength at the original preform thickness. This compositional modification eliminates the need to increase preform thickness and subsequently extend cooling times, thereby maintaining short production cycle times while achieving the desired impact strength.
4Strength
If more crystallinity is formed in thicker preforms, then mechanical strength is improved, but processing complexity and production time increase
Solution Approach 1:
The patent modifies the compositional parameters by incorporating MXD6 and cobalt salt, which provide the necessary mechanical strength through a different mechanism (barrier network formation and polymer interaction) rather than relying on increased crystallinity. This approach simplifies processing by eliminating the need to control and maximize crystallinity development, thereby reducing processing complexity.
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 gas barrier properties with reduced oxygen permeability and higher burst pressure compared to standard PET, while maintaining lower production costs through optimized processing conditions, including lower injection and blowmoulding pressures and temperatures, resulting in lighter, stronger containers.
Implementation Method 1
MXD6 is an aliphatic polyamide resin which contains meta-xylylene groups in the molecule... MXD6... has been described as advantageous for enhancing gas barrier properties
Implementation Method 2
Transition metal salts, such as cobalt salts, can be added to the polyamide containing PET to catalyze and actively promote the oxidation of the polyamide polymer, thereby further enhancing the oxygen barrier characteristics
Implementation Method 3
catalyze and actively promote the oxidation of the polyamide polymer, thereby further enhancing the oxygen barrier characteristics
Implementation Method 4
Carbon black is a known additive for enhancing heating rate of a preform to blowmoulding temperature
Data Source
Figure 1~2
Figure 3(a)~3(b)
Figure 4~5
AI summary
The present invention concerns a polyester composition suitable for food and beverage packaging, said polyester composition being obtained by blending:(a) 90-97 wt.% of a thermoplastic polyester selected from polyethylene terephthalate, polyethylene naphthalene, and mixtures thereof, (b) 2-6 wt.% of MXD6, (c) 1-5000 ppm of a cobalt salt, (d) 0.1-1000 ppm ethylene glycol (EG), and (e) 0.1-1000 ppm of pyromellitic dianhydride (PMDA).