Effect of EVA Cross-Linking Degree on Its Mechanical Properties (1)

Abstract: This study investigates the impact of varying cross-linking degrees on the mechanical properties of EVA, a material commonly used in the photovoltaic industry. EVA samples with different cross-linking levels were prepared by adjusting lamination process parameters, and their mechanical properties were systematically tested. After analyzing the data, it was found that an optimal cross-linking degree of approximately 85% provides the best balance of tensile strength, elongation at break, and adhesion between EVA and both the glass and backsheet. This level ensures superior performance in photovoltaic module packaging.

1. Introduction

Ethylene-vinyl acetate (EVA) is a copolymer known for its excellent flexibility, toughness, and impact resistance, largely due to the presence of polar vinyl acetate units that reduce crystallization. However, as a linear polymer, EVA has limited heat resistance and cohesive strength, which restricts its use in high-performance applications. In the solar photovoltaic industry, EVA is modified with additives such as coupling agents, initiators, and antioxidants to improve its thermal and chemical stability. During the lamination process, EVA undergoes cross-linking, forming a three-dimensional network structure. The degree of cross-linking directly influences the final properties of the material, including mechanical performance and long-term durability.

If the cross-linking degree is too low, the EVA may not fully form a dense network, leading to poor adhesion, reduced tensile strength, and weak bonding with the glass and backsheet. On the other hand, excessive cross-linking can make the material brittle, reducing flexibility and potentially causing cracks in the EVA or delamination from the glass and backsheet. It also affects aging resistance, making the material more prone to degradation over time. Therefore, finding the right balance in cross-linking is crucial for ensuring the reliability and longevity of photovoltaic modules.

With numerous EVA manufacturers in the domestic solar industry, there are significant variations in composition and performance across different models and brands. As a result, there is no universally accepted standard for the optimal cross-linking degree that maximizes both adhesion and mechanical properties. This paper addresses this gap by selecting three representative EVA models and conducting a detailed comparative analysis of their mechanical behavior under different cross-linking conditions. The findings provide valuable insights for optimizing the packaging process in photovoltaic module manufacturing.

2. Experimental Section

2.1 Main Raw Materials

In this study, three representative EVA films commonly used in the industry were selected as test samples. Additional materials, such as the backsheet, tempered glass, and high-temperature cloth, were also included. The key performance characteristics of these materials are summarized in Table 1 below.

Table 1: Test Raw Materials and Their Performance Description

*Note: Image shows typical EVA film samples and testing setup.*

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