Deformation, yield and fracture of elastomer‐modified polypropylene

Abstract

ABSTRACT:In recent decades, great attention has been devoted to the toughening of isotactic poly(propylene) (PP) with elastomers such as ethylene-propylene rubber (EPR). The most important reasons for this interest are the moderate cost and favorable properties of PP. This article is focused on the role of EPR in the deformation and fracture mechanism of PP/EPR blends with different volume fractions of elastomer phase. Differential scanning calorimetry (DSC), tensile tests, and microscopy techniques were used in this study. The fracture mechanism of isotactic PP toughened by EPR (PP/EPR) has also been studied by three point bending (3-PB) and four point bending (4-PB) tests. Rubber particle cavitation appears to be the main mechanism of microvoid formation, although some matrix/particle debonding was observed. The investigation of the toughening mechanism shows that a wide damage zone spreads in front of the pre-crack. Optical microscopy (OM) illustrates that, in pure PP, crazing is the only fracture mechanism, and no evidence of shear yielding is found, while in PP blends craze-like features associated with shear yielding are observed, which have been identified as high shear localized dilatational bands. This type of deformation pattern supports a model previously proposed by Lazzeri 1 to explain the interparticle distance effect on the basis of the stabilization effect on dilatational band propagation exerted by stretched rubber particles.

Effect of both uncoated and coated calcium carbonate on fracture toughness of HDPE/CaCO3 nanocomposites

“…Thus, one may conclude that the fracture toughness measurements for all the nanocomposites (including unfilled HDPE) cannot satisfy the LEFM requirements. This is similar to what proposed by Zebarjad et al 25 during determination of fracture toughness of PP and its blend and what reported by Hooley and Moore 26 In fact, they showed that plane strain fracture toughness of PE can be achieved at room temperature if the sample thickness is more than 255 mm. 26 The simple fact that the injection machine necessary to mold such thick samples does not yet exist, it means it would be absurd to compare hypothetical fracture results obtained on samples of such thickness.…”

“…25,[33][34][35][36][37][38] Since the scientists who studied fracture behavior of the materials believe that the main part of fracture energy is due to making plastic zone or stress whitening zone in front of precrack, the current research has been concentrated on this subject. Figure 8 points out the effect of SWZ on fracture toughness for the materials.…”

Modification of fracture toughness of isotactic polypropylene with a combination of EPR and CaCO3 particles

“…With regarding the results of our previous works [22][23][24][25][26][27][28][29] and current study, the effect of combination of CaCO 3 and EPR on deformation and fracture behaviour of PP can be summarised similar to what proposed by Zebarjad et al [29] for PP-EPR-GF. In fact, addition CaCO 3 leads the dominant fracture mechanism of PP from shear yielding to crazing.…”

New toughened polypropylene/organophilic montmorillonite nanocomposites

“…Traditional toughness reinforcement of PP by the addition of rubber 1,2 or elastomer 3 decreases the strength and rigidity of the materials; this especially weakens the thermal stability of the materials. In this study, we focused on a new method for enhancing the toughness of PP by adding organophilic montmorillonite (OMMT) while retaining the material's high strength, rigidity, and thermal stability.…”