Interlamina fracture toughness and mechanical properties of glass fiber reinforced epoxy resin/laccol composites cured with cyanetyldietylentriamine hardner

Abstract

Epoxy resins are widely utilised as high performance thermosetting resins for many industrial applications but unfortunately some are characterised by a relatively low toughness. Laccol (LC) is a natural phenol with two hydroxyl groups in oc/o-position and long side unsaturated hydrocarbon substitute C17H31. Epoxy-laccol (EP-LC) oligomers were synthesized by reaction of epoxy resin Epikote 828 with LC (1:1 eq) at temperature 140 ± 2 °C for 4 hrs in niừogen condition. The mixture of EP-LC with Epikote 828 is named Epolac. Using Epolac, the effect of LC content on the mode I interlaminar fracture toughness (Gic) and mechanical properties of epoxy polymers were evaluated. The obtained testing results showed that the Izod impact strength of glass fabric/epoxy (GF/EP) composites significantly increased by 44.1 % from 179.05 KjW to 258.04 KJ/m2, while the mode-I interlaminar fracture toughness for crack initiation and propagation also improved by 29.5 % and 20.0 %, respectively, when 20 % LC was participated in the epoxy matrix. Results obtained from dynamic mechanical thermal analysis (DMTA) showed that the glass transition temperatures of the epoxy resin matrix were slightly reduced on the addition of laccol. The scanning electron microscopy (SEM) observation revealed that LC delayed the crack growth in GF/EP composite as well as the onset of matrix crack. The overall results have shown that it is possible to obtain excellent impact strength and the mode I interlaminar fracture toughness (Gic) with the use of laccol as a toughness agent for the epoxy resins.