Multimodal EPDM Thermoplastic Vulcanizate Composition
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Solution Overview
Problem
Current methods for producing thermoplastic vulcanizates with ethylene-propylene-diene monomer (EPDM) elastomers face challenges in achieving a balance between molecular weight and oil extension, leading to high viscosities that hinder processability and result in inferior properties, while attempts to reduce molecular weight and oil extension have not successfully matched the performance of high molecular weight unimodal rubbers.
Innovation Solution
A thermoplastic vulcanizate composition is developed using a multimodal polymer composition dynamically cured with a curing agent, comprising 45-75 wt% of a first polymer fraction and 25-55 wt% of a second polymer fraction, both polymerized using Ziegler-Natta catalyst systems in a series of reactors, with the addition of 10-50 phr extender oil, achieving a number average molecular weight of 60,000 to 350,000 g/mol and a Mooney viscosity below 90 ML(1+4@125°C).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high molecular weight EPDM elastomers are used to achieve high elasticity and performance, then the Mooney viscosity increases above 100 ML(1+4@125°C), but processability deteriorates and manufacturing becomes difficult
Solution Approach 1:
The patent segments the polymer composition into two distinct fractions with different molecular weights. The first fraction has Mooney viscosity of 130-300 ML(1+4@125°C) providing elasticity, while the second fraction has Mooney viscosity of 20-100 ML(1+4@125°C) ensuring processability. This segmentation allows each fraction to fulfill its specific function without compromise.
Solution Approach 2:
The patent changes the molecular weight distribution parameter by introducing a bimodal structure. Instead of using a single high molecular weight polymer, it combines high MW and low MW fractions in specific ratios (40-80 wt% first fraction, 20-60 wt% second fraction). This parameter change enables the compound to exhibit both high elasticity and good processability.
2Ease of manufacture
If extender oil is added to reduce the apparent viscosity of high molecular weight EPDM, then processability improves, but the rubber capacity of the plant is reduced and manufacturing capacity deteriorates
Solution Approach 1:
The patent replaces expensive extender oil with a cost-effective alternative: a low molecular weight polymer fraction. This second fraction serves as both a processability enhancer and a rubber component, eliminating the need for non-rubber extender oils while maintaining or improving manufacturing capacity.
Solution Approach 2:
The patent changes the composition parameter from adding extender oil to using a bimodal polymer blend. The low viscosity fraction (20-100 ML) acts as an internal lubricant and process aid, replacing the function of extender oil while contributing to the rubber matrix structure and maintaining rubber capacity.
3Productivity
If molecular weight and oil extension are reduced to improve production capacity, then processability improves, but the performance fails to match unimodal high molecular weight rubbers
Solution Approach 1:
The patent segments the polymer fractions to assign different functions: the high molecular weight first fraction (40-80 wt%) provides mechanical strength, elasticity, and performance characteristics, while the low molecular weight second fraction (20-60 wt%) provides processability and flow characteristics. This functional segmentation ensures both performance and productivity requirements are met.
Solution Approach 2:
The patent creates a composite polymer system combining two fractions with complementary properties. The bimodal blend acts as a composite material where each component contributes its strengths, resulting in a compound that exhibits both high performance and high production capacity, surpassing the limitations of unimodal systems.
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
This approach enhances the balance of elasticity, processability, and physical properties, allowing for improved production capacity and performance comparable to unimodal high molecular weight rubbers with reduced extender oil quantities, thereby increasing plant capacity and cost-effectiveness.
Implementation Method 1
both polymerized using Ziegler-Natta catalyst systems in a series of reactors
Implementation Method 2
These rubber particles are crosslinked to promote elasticity
Data Source
AI summary
The disclosure is directed to a thermoplastic vulcanizate composition comprising a dynamically-cured rubber; from about 20 to about 300 parts by weight of a thermoplastic resin per 100 parts by weight rubber and from about 30 to about 250 parts by weight additional oil per 100 parts by weight rubber; wherein the rubber comprises a multimodal polymer composition cured with a curing agent, the multimodal polymer composition comprising 45 to 75 wt % of a first polymer fraction and 25 to 55 wt % of a second polymer fraction, each comprising ethylene, a C3-C10 alpha-olefin, and a non-conjugated diene. A method of producing the thermoplastic vulcanizate is also disclosed.