6. Conclusions
The FTIR and HNMR analysis evidenced the presence of hydroxyl, carbonyl and epoxy functional groups in the chain of LNR. It can be concluded that the reduction in Tg of EP with increasing rubber content is an indication of the plasticization effect of LNR. Slight decreases in the tensile and flexural strengths were also observed. The incorporation of LNR led to a significant improvement of the fracture toughness of the EP. The toughening effect becomes more apparent at high testing speed.
SEM analysis indicated that the dispersed rubber particles act as stress concentrators during fracture, which induces delocalized plastic deformation of the matrix around the particles. On adding LNR some of the rubber particles accompanied by stress whitening zones developed on the fracture surface of modified EP this stress whitening effect is related to the local plastic deformation at the crack tip. This might explain the observed increase in fracture toughness compared with unmodified EP.