Nanosilica enhanced fracture toughness of epoxy for marine environment applications

Thermosetting polymers are used in various industrial applications. Most epoxy systems show low fracture toughness, poor resistance to crack initiation and propagation. The use of nanoparticles in various polymers to improve performance has been evaluated in many studies [1]. In the marine environment, complex conditions such as high salinity, high pressure, high humidity and alkaline corrosion accelerate degradation of polymer and can lead to corrosion of marine vehicles, equipment, and oil exploration platforms to different degrees [2]. Mouritz et al. showed that flexural strength of a glass/unsaturated polyester composite decreased as the composite was exposed to seawater [3]. Due to the difficulties of large-scale production and adequate dispersion of nanofillers into epoxy, commercial nanofiller-modified epoxy is rare. One is Nanoresins, from Germany, with a concentration of 40 wt% nanosilica in diglycidyl ether of bisphenol A (DGEBA) epoxy resin [4]. The silica nanoparticles are synthesised in situ by a sol-gel manufacturing process, whereby the particle size and excellent dispersion of these particles remain unchanged during any further mixing and/or blending operations.

In this study, a further exploration of this commercial epoxy nanocomposite with 2 wt% nanosilica has been conducted in marine environment. The result (Fig.1) shows that the sea water immersion decreases the fracture toughness (KIC) in both neat epoxy and the nanocomposite. However, the increment of fracture toughness due to the nanosilica addition can complement that loss caused by salt water immersion, which makes the modified epoxy work functionally in marine environment to replace the neat epoxy in terms of fracture toughness. Fig. 2 shows the SEM of fracture surfaces of neat epoxy and the composite after different times of salt water immersion.


Fig. 1. The critical stress intensity factor KIC of neat epoxy (EP) and nanosilica reinforced epoxy composite (SEP).


Fig. 2. SEM images of fracture surfaces of (a) and (c) EP, (b) and (d) SEP after (a) and (b) 0 day, (c) and (d) 7 days of salt water immersion.

Blog post by Wei Han, Supervisor Dr Youhong Tang

1. Deng SQ, Ye L, Friedrich K. J Mater Sci2007; 42: 2766-2774.

2. Le Gac PY, Le Saux V, Paris M, Marco Y. Polym Degrad Stabil 2012; 97:288-296

3. Mouritz AP, Geliert E, Burchill P, Challis K. Compos Struct2001; 53: 21-41.

4. Sprenger S. Polymer 2013; 54: 4790-4797.

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