EPDM Interpolymer Foam Composition Melt Elasticity
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Solution Overview
Problem
Current polymer compositions for foams face challenges in achieving high expansion and smooth surface quality while minimizing water absorption, particularly due to the delicate balance of cross-linking and melt elasticity, which is influenced by molecular weight and long-chain branching, and existing EPDM products like VISTALON 8800 and KELTAN 7341A are high in molecular weight but have relatively high water absorption.
Innovation Solution
A composition comprising an ethylene/alpha-olefin/nonconjugated polyene interpolymer with specific properties, including a weight average molecular weight greater than 200,000 g/mole, a peak area from 21.3 to 21.8 ppm in 13C NMR, and a tan delta of less than 1.0 at 190°C, comprising 40-60 weight percent ethylene, which enhances melt elasticity and reduces water absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high molecular weight EPDM products are used, then foaming characteristics and compression set are improved, but water absorption increases
Solution Approach 1:
The invention changes the molecular weight parameter of the EPDM polymer to a specific range (200,000-500,000 g/mol) and controls the long-chain branching content (5-20%) to optimize the balance between foaming characteristics and water absorption. This parameter optimization resolves the contradiction by finding the sweet spot where both foaming performance and low water absorption are achieved.
Solution Approach 2:
The invention creates a composite polymer system by incorporating specific amounts of oil (5-30 phr) and crosslinking agents into the EPDM matrix, forming a multi-component system that achieves superior foaming characteristics while controlling water absorption through the synergistic interaction of components.
2Reliability
If melt elasticity is increased for better expansion, then foaming characteristics improve, but viscosity increase during expansion cycle worsens
Solution Approach 1:
The invention optimizes the molecular weight (200,000-500,000 g/mol) and long-chain branching content (5-20%) parameters to achieve the desired melt elasticity range. This controlled parameter adjustment ensures sufficient expansion while limiting excessive viscosity increase during the foaming process.
Solution Approach 2:
The invention introduces dynamic control of viscosity through time-dependent crosslinking during the foaming process. The crosslinking reaction progresses during expansion, dynamically adjusting the viscosity to maintain optimal foaming characteristics while preventing excessive viscosity buildup that would hinder expansion.
3Stability of the object's composition
If cross-linking is increased for better foam structure, then closed cell content improves, but melt elasticity decreases
Solution Approach 1:
The invention applies preliminary crosslinking before the foaming process to establish a适度 crosslinked network structure that provides good closed-cell content. This pre-crosslinking action ensures the foam structure stability while maintaining sufficient melt elasticity for proper expansion during the actual foaming step.
Solution Approach 2:
The invention uses dynamic crosslinking control where the crosslinking degree is adjusted at different stages of the foaming process. Initial crosslinking provides structural stability for closed-cell formation, while controlled progression of crosslinking during expansion maintains melt elasticity for continued foam growth.
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 solution results in foams with improved expansion characteristics, smooth surface quality, and reduced water absorption, leading to low foam densities and high closed-cell content, offering better dimensional stability and sealing performance.
Implementation Method 1
The melt elasticity of the polymer is related to its molecular weight and degree of long-chain branching present
Implementation Method 2
The foaming process is a delicate balance of the cross-linking of the EPDM and expansion
Implementation Method 3
The observed water absorption relates directly to the foamed structure and number of closed cells present in the foam
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention provides a composition comprising a first composition that comprises an ethylene/alpha-olefin/nonconjugated polyene interpolymer that has the following properties: A) a Mw greater than, or equal to, 150,000 g/mole; and B) a peak area from 21.3 ppm to 21.8 ppm that is greater than, or equal to, 3.0 percent of the total integral area from 19.5 ppm to 22.0 ppm, as determined by 13C NMR; and wherein the first composition has a tan delta (190C at 0.1 rad/sec) less than, or equal to, 1.0.