Today's KNOWLEDGE Share : Epoxy Resin Composites properties Modified by Nanofiller

Today's KNOWLEDGE Share

Mechanical Properties of the Epoxy Resin Composites Modified by Nanofiller under Different Aging Conditions

Epoxy resin (EP) is a typical cross-linked thermosetting polymer material, which has many outstanding advantages, such as good mechanical properties, strong stability and bonding ability, low shrinkage, excellent heat resistance, chemical resistance, and fire-retardant. Therefore, it is widely used in the field of surface coating, adhesives, composite manufacturing, civil engineering, etc.. However, the performance of EP is degraded in harsh environments, including humidity, high-temperature, hygrothermal, and radiation conditions, which decreases their lifetime and durability.

The hygrothermal aging condition has strongly deteriorated the mechanical performance of the EP. Under the hygrothermal aging condition, EP will absorb water, leading to the deterioration in the physical and chemical properties of the resin because of hydrolysis, plasticization, and matrix swelling. To reduce the damage and deterioration of the resin in a hygrothermal environment, some nanofillers are used, such as carbon nanotube (CNT), graphene nanoplatelet (GNP), graphene oxide (mGO), nanoclay, and nano-silicon carbide (n-SiC). Nanoclay is one of the commonly used nanofillers to improve multiple properties of the EP because of its low cost, high aspect ratio, unique chemical properties, high mechanical properties, and thermal stability. Halloysite nanoclay is from silicate minerals and is also named halloysite nanotube (HNT) due to its hollow nanotube structure. Due to its excellent properties, HNT is widely used in the research of composite materials. Previous research work shows that the addition of HNTs into polymers can significantly enhance mechanical properties, which improves the tensile strength, flexural strength, and durability of EP, and delay the degradation behavior of the EP in a humid environment.

The aging behavior of resin composites is related to several variables, such as temperature, corrosion medium, additives, and aging time. Uthaman et al.  considered the effects of water and acid solutions at different temperatures on the properties of EP. The reduction in tensile strength of the resin is depending on the soaking time and temperature, and a long soaking time and high temperature accelerate the aging behavior. Shettar et al. studied the effect of thermal shock cycling (TSC) on the properties of EP. Under the condition of TSC, the tensile strength of neat EP was reduced by 6%-11%, and the bending strength decreased by 8%-15%. The tensile strength and bending strength of EP added with nanoclay decreased by 7%-13% and 9%-17%, respectively. It can be attributed to stress formation at the nanoclay/epoxy interface due to the mismatch coefficient of thermal expansion, and therefore, the addition of nanoclay is not helpful to improve aging resistance under thermal shock cycling (TSC) conditions. Ulus et al. investigated the effect of the addition of halloysite nanoclay on the properties of the resin in a saltwater environment. They found that after 6 months of aging, the tensile strength and flexural strength of neat EP decreased by about 37.4% and 41.9%, respectively, while the tensile strength and flexural strength of EP with halloysite nanoclay decreased by about 28% and 35.1%, respectively.

Although some studies have investigated the aging behavior of resin composites under hygrothermal and thermal shock cycle conditions, there is little research on coupled aging factors, e.g., a combination of soaking aging and thermal shock cycle; therefore, the effects of single condition aging and coupling aging on the mechanical properties of neat EP and HNT/EP nanocomposites were investigated. The accelerated aging conditions were set as water soaking (20°C, 40°C, and 60°C), thermal shock cycling (TSC), and soaking coupled with subsequent thermal shock cycling (composite aging). The degradation in mechanical properties under these conditions was studied to obtain a comprehensive understanding of the effects of the aging condition and nanofiller on EP in a variety of applications.

source:S. J. Lu, T. Yang, X. Xiao, X. Y. Zhu, J. Wang, P. Y. Zang, J. A. Liu