In order to quantitatively study the effect of the modulus ratio of matrix polymer to toughening modifier on the brittle-ductile transition (BDT) of the blends, the modulus ratio of polypropylene (PP) to impact modifier at various temperatures was obtained from dynamic mechanical analysis (DMA) results. The modulus ratio changed continuously from nearly 1 to more than 100 by increasing temperature from − 100 to 50 °C. Accordingly, the impact property of the PP/POE blends within a wide composition range was studied at various temperatures by notched impact strength test. The variations of the notched impact strength with the modulus ratio were thereby obtained for various PP/POE blends. The result shows that a clear sharp BDT appeared with increasing the modulus ratio and the critical modulus ratio is 10, that is, the modulus of impact modifier must be one tenth of that of polymer matrix in order to be effective. In addition, the effect of the microstructure on the BDT of PP/POE blends was also studied.

In this study, the brittle-ductile transition of poly(ethylene-co-octene) (POE) toughened high density polyethylene (HDPE) was studied in terms of HDPE molecular weight, elastomer content and temperature. The relation among HDPE molecular weight, critical elastomer content and temperature, the relation among critical interparticle distance (IDc), HDPE molecular weight and temperature at critical brittle-ductile transition point were given. From these relations, the high impact HDPE blends with the lowest elastomer content, i.e. with the lowest rigidity loss, could be obtained. The results show that the lowest modulus loss for high impact HDPE/POE blend reduces markedly with the increase of HDPE molecule weight.

Impact resistance for elastomer toughened high density polyethylene (HDPE) at low temperature was determined by its brittle-ductile transition temperature (TBD). Following our previous work, i.e. the effect of HDPE molecular weight on the brittle-ductile transition of POE toughened HDPE (Wang et al. in J Polym Res 29:1–8, 2022), we studied the effect of elastomer modulus because the modules ratio of matrix polymer to elastomer plays an important role in brittle-ductile transition. In this study, four elastomers with different glass transition temperatures (Tg) were employed. The modules ratios of the HDPE to the elastomers were obtained by dynamic mechanical analysis (DMA) measurement, respectively. The notched impact strengths for the HDPE blends with different elastomers were tested at various temperatures. The results showed that the notched impact strength appeared a clear sharp transition when the modulus ratio of the HDPE to elastomer reached 10 by increasing temperature, indicating that the HDPE could not be toughened effectively when the modulus ratio of the HDPE to elastomer is smaller than 10. This is the first time to quantitatively give the effect of elastomer toughened thermal plastic polymers on the brittle-ductile transition in experiment. Moreover, the result directly indicated that the Tg of elastomer must be low enough in order to obtain lower TBD of elastomer toughened HDPE.