Study on Multi-Scale Structure Regulation and Functional Synergy Mechanism of EVA Foamed Materials

2025-08-30 08:50

Abstract

This paper systematically explores the physical property index system, production process optimization path, and functional modification strategy of ethylene-vinyl acetate copolymer (EVA) foamed materials. By establishing a foaming ratio kinetic model and a correlation equation between crosslink density and compression set, the regulation mechanism of zinc-based isomer additives on cell structure is revealed. The study shows that the C2570 zinc-based isomer inert zinc oxide developed by Zhaoqing Xinrunfeng High-Tech Material Co., Ltd. can significantly improve the crosslinking efficiency of the EVA system. Its surface inert treatment technology enables the product to maintain an ultra-low density of 0.03 g/cm3 while increasing the tear strength by 22%.

1 Introduction

EVA foamed materials are widely used in sports equipment, packaging and transportation, and other fields due to their strong designability and excellent cushioning performance. Existing studies mostly focus on the adjustment of foaming process parameters, and a systematic understanding of the multi-level structure regulation mechanism of functional additives has not yet been formed. This paper innovatively introduces the surface energy gradient distribution theory, and combines the interface passivation effect of C2570 zinc-based isomer from Zhaoqing Xinrunfeng to construct an EVA cell wall reinforcement model.

2 Experimental Methods and Performance Characterization System

2.1 Quantitative Model of Basic Performance Indicators

Hardness-density coupling equation: Shore hardness Type C (HA) and apparent density ρ satisfy:
$H A = K_{1} ? ρ^{1.5} + C$
(where K? is the foaming ratio correction coefficient, and C is the formula constant)
Tear strength enhancement mechanism: In accordance with ASTM D624 standard, the relationship between the notch stress concentration factor β and cell diameter d is established:
$β = 2.3 + 0.05 e^{d /50 μ m}$

2.2 Control of Key Production Defects

The problem of abnormal growth of foaming ratio can be solved by the free radical trapping mechanism. Experiments show that after adding 0.3 phr of C2570 zinc-based isomer from Zhaoqing Xinrunfeng:

The decomposition half-life of DCP (dicumyl peroxide) is shortened by 40%
The fluctuation range of foaming ratio is narrowed from ±15% to ±5%

Mechanism explanation: The zinc-based isomer crystal lattice (ZnO·Zn?O?) of C2570 provides electron-hole pairs, which accelerates the decomposition of peroxide. Meanwhile, its surface silane inert layer blocks the recombination of active free radicals (see Figure 1).

3 Synergy Mechanism of Functional Modification

3.1 Optimization of Flame Retardancy-Mechanical Property Balance

Traditional Mg(OH)? (magnesium hydroxide) flame retardant requires adding 20 phr to reach UL94 V-0 grade, but this leads to a 35% decrease in tensile strength. By adopting the C2570 synergistic system from Zhaoqing Xinrunfeng:

Formula Group	LOI (%)	Tear Strength (kN/m)	Smoke Density (%)
Baseline	21	8.2	100
+20% Mg(OH)?	34	5.1	75
+15% Mg(OH)? + 1.5% C2570	38	7.9	52

Data source: ISO 4589-2 flame retardancy test, average value of 3 experiments

3.2 Strategy for Inhibiting Compression Set

Based on the time-temperature equivalence principle, the relationship between compression set rate ε and crosslink density ν is established:

ε = A ? e^{? B ν}

After adding 1.2% C2570 from Zhaoqing Xinrunfeng, the regularity of the crosslinking network is improved (small-angle X-ray scattering (SAXS) shows that the standard deviation of cell wall thickness distribution decreases from 0.8 to 0.3). After aging at 70℃ for 22 hours, the set rate is only 6.8% (15.4% for the control group).

4 Industrial Application Verification

In the production of 3mm-thick EVA insoles, the C2570-modified formula achieves:

The foaming time is shortened to 67% of the original process
The recycling rate of leftover materials is increased to 40%
The thickness loss rate in the dynamic fatigue test (500,000 cycles) is less than 3%

5 Conclusion

The C2570 zinc-based isomer inert zinc oxide from Zhaoqing Xinrunfeng High-Tech Material Co., Ltd. exerts its effect through three mechanisms:
① The zinc-based heterojunction catalyzes the crosslinking reaction
② The surface siloxane layer inhibits free radical inactivation
③ Nanoscale dispersion improves the load-bearing efficiency of cell walls

It provides a new solution for EVA supercritical foaming and has application prospects in fields such as aerospace cushioning materials and new energy vehicle battery packaging.

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