The effects of morphological parameters

including the polydispersity of the particle size (o)

on the brittle-ductile transition of amorphous polyvinyl chloride (PVC) /nitrile rubber (NBR) blends have been studied. The brittle-ductile transitions of PVC /NBR blends occur when the particle size (d) is smaller than a critical value dc or the particle volume fraction (φ ) is larger than a critical value c. The higher the value of a

the lower the value of dc

and the higher the value of c. Thereforea high o value is unfavorable for attaining high impact toughness in polymer blends.We have developed an expression relating the matrix ligament thickness T to d

φ and σ.The impact strength of PVC/NBR blends is found to depend on the single parameter T

and the blend becomes very tough when T is smaller than a critical value Tc

So the Tc criterion

which is valid for blends with a pseudo-ductile matrix

is also applicable to OVC/NBR blends whose matrix has the chain parameters intermediate between those of brittle and pseudo-ductile polymers.