Fracture strain LLDPE

Also included in Table I are the true fracture stress (of) calculated from the cross section of the fractured specimen, and the fracture strain (ef). The fracture stress dropped significantly, from 171 MPa for LLDPE to 100 MPa and 35 MPa for 10% and 25% PS, respectively. The fracture stress of the 37.5% PS blend was even lower, 8.5 MPa, but was still higher than the oy value of 5.9 MPa, so the blend deformed in a ductile manner. The blend with 50% PS fractured in a quasi-brittle manner at a stress of 7.0 MPa, which was slightly lower than cry for this composition. The large decrease in Of with increasing PS concentration was consistent with debonded PS particles that were not load-bearing during plastic deformation. 

The engineering fracture strain of the LLDPE-PS blends demonstrated transitional behavior. When the PS content was low, less than 30%, high fracture strains were observed with only a gradual decrease in fracture strain as the PS content increased. The stress-strain behavior was characterized as Type I in this composition range. This was followed by a sharp decrease in the fracture strain in a narrow composition range as the stress-strain behavior changed from Type I to Type II and Type III. 

Figure 8. Fracture strain of LLDPE-PS blends. The calculated fracture strain in the Type I fracture region, where equation 18 applies, is given by the solid curves for 1.0 A and 1.1 A. Data for all the blend compositions are included as open circles.

Microfibrils in the blend compatibilized with Kraton G probably formed by drawing of the rubbery shell of the core-shell particle. Important factors would have been the amount of rubber in the shell, the strength of the rubber, and the strength of adhesion to LLDPE. All these factors may have contributed in some degree to the high fracture stress and strain of the blend with Kraton G. The amount of compatibilizer in the shell differed for the various Kratons the thicker coating was certainly one of the reasons Kraton G gave better properties to the compatibilized blend than the Kraton D compatibiliz-ers. 

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