Fig. 2(d) shows that Charpy impact strength value of neat phenolic specimen (P) was improved when modified with nitrile rubber particles,
for instance the increases being 56 and 37% in the specimens PR0.5 and PR1, respectively.
This is reasonable due to the ‘rubber toughening’ effect of nitrile rubber domains in the phenolic matrix.
However, increasing rubber content decreases the improvement so that the specimen having highest rubber content (PR3) had lower impact strength than the neat phenolic specimen (P).