Study On Synergistic Toughening Effect Of Nucleating Agent And Elastomer On Polypropylene

Blending polypropylene (PP) with various elastomers is thought to be one of the most effective methods to improve its unfavorable toughness. Besides elastomer parameters, the toughening effect is greatly determined by the matrix parameters, e.g. crystalline morphology and structure. However, the synergistic toughening effect of those two parameters in improving PP toughness has been seldom investigated. In this thesis, two highly active nucleating agents (NAs), i.e.α-form NA 1,3:2,4-bis (3,4-dimethylbenzylidene) sorbitol (DMDBS, Millad 3988) andβ-form NA aryl amides compounds (TMB-5), were selected to control the crystalline morphology and structure of PP matrix and the synergistic toughening effect of NA and elastomer on PP was studied through notched Izod impact testing (high test speed). By analysizing the dependence of such toughening effect on the dimensional matching elastomer particles and PP spherulites, we explain why a maximum elastomer particles is required to induce significantly improved toughness. And then, the toughening model has also been proposed to interpret experimental data and provide a fresh insight into the understanding of the synergistic toughening mechanism of NA and elastomer on PP. Moreover, the role of NA and elastomer in improving the fracture toughness of PP was also discussed using single-edge notched tensile (SENT) testing at low test speed. The major results are as follows:1. At high test speed (impact conditions), NA (either DMDBS or TMB-5) and ethylene-octene copolymer (POE) present a significantly synergistic toughening effect on PP. The addition of NA into PP/POE blends changes the fractured surface feature from multiple-craze to predominantly shear yield or shear yield involving materials cavitations and tearing.2. At high test speed, TMB-5 and ethylene-propylene-diene terpolymer (EPDM) show a dramatically synergistic toughening effect on PP. The introduction of TMB-5 into PP/EPDM blends induces the change of fracture feature from multiple-craze to predominantly shear yield or shear yield companioned with matrix cavitations and second-crack re-initiation. However, DMDBS has no apparent effect on the impact toughness of PP/EPDM blends, but makes the debonding of EPDM particles from PP matrix easier during deformation process.3. For PP/elastomer blends, the addition of NA doesn't influence the elastomer particles size and distribution apparently. The great improvement in impact toughness of the blends is mainly ascribed to the changes of crystalline morphology and structure of PP matrix induced by NA.4. The synergistic toughening effect of NA and elastomer on PP is strongly dependent on the elastomer particles size and distribution. The smaller the elastomer particles size and the lower the polydispersity, the more significant the synergistic toughening effect is.5. At low test speed (SENT testing), the presence of DMDBS in PP/POE and PP/EPDM blends leads to a slight deterioration in fracture toughness compared to the binary blends. The smaller the elastomer particles size, the more apparent the decrease of the crack propagation energy is. TMB-5 induces the simultaneous enhancement of crack initiation energy and crack propagation energy, but the major contribution is ascribed to the energy absorption during the crack propagation stage. Importantly, the toughening effect of TMB-5 in such blends depends on the TMB-5 content, 0.05 wt% TMB-5 provides optimum toughening effect for the blends.