The Effect of Epoxidized Palm Oil on the Properties and Performances of Epoxy Resin

Epoxidized Palm Oil (EPO) has the potential to enhance epoxy resin properties as well as to reduce the cost of the material. In this work, EPO was blended with epoxy prepolymer, a diglycidyl ether of bisphenol A (DGEBA) at various compositions ranging from 0 to 2 % wt. The EPO/DGEBA system was cured with m-xylylenediamine (m-XDA). The aim of the study was to graft EPO chains to the epoxy network in order to form interpenetrating polymer network (IPN).

The EPO was first prepolymerised with m-XDA at various temperatures and reaction times. The reaction between m-XDA and EPO was confirmed by using Fourier Transform infrared (FTIR) spectrometer and viscometer. The resulting products were then mixed with the epoxy prepolymer and allowed to react at 60 °C for 1 hr and 120 °C for another 3 hours. The fully reacted DGEBA/m-XDA /EPO blend was characterized by using scanning electron microscopy (SEM), differential scanning calorimeter (DSC), thermal gravimetric analysis (TGA), tensile test, dynamic mechanical analysis (DMA) and hardness indentation. The SEM study shows that the morphology ranging from phase separated (opaque) to miscible (transparent) are dependent on the reaction time between m-XDA and EPO. A miscible blend was obtained when m-XDA and EPO were reacted at 120 °C for more than two hours. Based on this processing parameter, homogeneous and transparent modified epoxy systems with EPO composition ranging from 0-20 % wt were produced.

The results from DSC and DMA show that the incorporation of EPO into the epoxy system reduced the glass transition temperature (Tg) substantially. This phenomenon is attributed to a loose network of epoxy resin system, which may increase the free volume. The decomposition curve of modified epoxy resin analyzed by TGA shows a similar trend to those of neat epoxy system, indicating that EPO modified epoxy resin still possesses good thermal stability. A reduction in the mechanical properties as analyzed by tensile test, DMA and hardness indentation was observed. The imperfect network also has caused a reduction in tensile strength. But, significant improvements on strain and toughness were observed in 20 % wt EPO modified epoxy resin. Water uptake increased slightly as the amount of EPO was increased. The increase in free volume allows a much easier ingress of water into the loose epoxy network. When the environment temperature was increased from 25 °C to 50 °C, more water was absorbed. The temperature increase also allowed the polymer segment to vibrate faster causing the epoxy resin to absorb more water.