Fracture behaviour of controlled‐rheology ethylene–propylene block copolymers

Abstract

The evolution of the molecular weight distribution and the thermal, mechanical and fracture behaviour of controlled-rheology ethylene-propylene block copolymers (ca 8 wt% ethylene content) has been analysed. Various concentrations of di-tertbutylperoxide were utilized. The melt flow index increased with the peroxide content due to the reduction of the molecular weight and the narrowing of the molecular weight distribution. However, the thermal behaviour and degree of crystallinity were not improved and some mechanical properties, such as the tensile strength and elongation at break, presented an anomalous behaviour. This trend can be explained by the presence of the elastomeric phase. The addition of peroxide influenced strongly the J -R curves obtained via the elastic-plastic fracture mechanics approach. The slope of these curves was markedly reduced with addition of peroxide to almost being flat for the highest concentration. This loss of ductility and the sudden decrease of the fracture toughness values with an increasing amount of peroxide were mainly due to the reduction in the molecular weight.

Study on β-Nucleated Controlled-Rheological Polypropylene Random Copolymer: Crystallization Behavior and a Possible Degradation Mechanism

“…21,22,25 As for copolymerized PP, studies on controlled-rheological block copolymerized polypropylene (PPB) indicate that PP matrix degrades while the long ethylene sequence tends to branch and cross-link by macroradical recombination, which results in the presence of high residual masses and much less increased MFR, compared to that of CRPPH. 25,26 Thus, the similar MFR results of CRPPR and CRPPH might suggest that there are almost no branching or cross-linking reactions in our experiment.…”

“…Moreover, it can be seen from Figure 1 that the MFR values increase almost linearly with DCP concentration, and the extent of the increase is comparable to that of CRPPH reported in previous work. 26 As mentioned above, the difference of molecular structure between PPR and PPH is the random insertion of ethylene comonomers in propylene sequence. When PPH molecular chains react with free radicals, hydrogen abstraction from PPH backbones proceeds preferably at the site of the tertiary carbon atom, which leads to the β-fragmentation reaction of tertiary alkyl radicals.…”

In the melt, grafting of polycarbonate onto polystyrene-block -poly(ethylene-butylene)-block -polystyrene-grafted -maleic anhydride: Reactive extrusion

“…The vGP plots reflect the occurrence of a tail of long relaxation times. As already described in the introduction, when immiscible PET and PC blends have been studied , the values of the phase angle decrease (in the case of heterogeneous polymer melts, they reflect a general increase of the elasticity) and the maximum loss angle shifts to the high modulus (the interfacial energy increases and so, the interfacial area), proving the compatibilization of PET and PC. In this study, the PC and KFG do not have to be compatibilized.…”

“…In the field of chemical polymer modification or polymerization, this process plays an important role . Bulk polymerization , polymer functionalization , and grafting reactions are examples of the wide field of reactive extrusion. The use of twin‐screw extruders as chemical reactors is explained by its mixing capability (even with high viscosity materials), and its modularity for a better control of chemical reactions .…”

Relating fracture behavior to spherulite size in conrolled‐rheology polypropylenes

“…Although extensive studies have been focused on the reactive mechanism, the rheological and crystallization behavior as well as the mechanical properties of controlled rheology PPs [3–8, 12–14, 16–19, 34], few reports are concerned with the influence of the spherulite size and distribution on the fracture mechanics parameters [35–37]. Salazar et al [35, 36] analyzed the evolution of the fracture toughness under Elastic–Plastic Fracture Mechanics (EPFM) of different grades of PP homopolymer [35] and ethylene‐propylene block copolymers [36] prepared controlling the addition of di‐ tert ‐butylperoxide (DTBP) in reactive extrusion. In turn, Sheng et al [37] analyzed the effect on the fracture behavior under Post‐Yield Fracture Mechanics approach through the evaluation of Essential Work of Fracture (EWF) of rheology controlled ethylene‐propylene block copolymers films.…”