Polystyrene fracture energy

The Fracture Energy of Low Molecular Weight Fractions of Polystyrene... 

The fracture energy of polystyrene is a combination of the plastic energy needed to form crazed material from uncrazed material, the energy to create the exposed surface in the craze, the elastic strain energy stored in the craze, and the energy to create new surface when the craze ruptures (5, 9). As the molecular weight decreases, the amount of crazing and... 

Fracture energy of polystyrene at 23 C after drawing above the glass transition at s, showing effect of molecular orientatioi direction (after L J. Broutman and F. J. McGany). 

One might wonder whether it is possible to correlate the interfacial fracture energy of an incompatible polymer pair more precisely to the width of the interface. Such a correlation clearly exists at a qualitative level. For example, polystyrene is substantially less miscible with poly(2-vinyl pyridine) (PVP) than it is with PMMA. This is reflected via equation (4.2.4) in the width of the... 

Figure 7.3. Fracture energies of interfaces between polystyrene and poly(/)-methyl styrene) of various relative molecular masses (A, PS 1 250 000 and PpMS 570 000 o, PS 310 000 and PpMS 570 000 and O, PS 862 000 and PpMS 157 000) as functions of their interfacial widths, measured by neutron reflectivity. After Schnell et al. (1998).

Figure 7.4. Fracture energies of interfaces reinforced by block copolymers as a function of the effective areal density of chains crossing the interface. Triangles and squares are for polystyrene/poly(2-vinyl pyridine) interfaces reinforced with styrene-2-vinyl pyridine block copolymers (Creton et al. 1992) circles are for poly(xylenyl etherypoly(methyl methacrylate) interfaces reinforced with styrene-methyl methacrylate block copolymers (Brown 1991a, b). After Creton et al. (1992).

Figure 7.9. Interfacial reinforcement of a polystyrene/poly(vinyl pyridine) interface by a high relative molecular mass deuterated styrene-vinyl pyridine block copolymer, with degrees of polymerisation of each block 800 and 870, respectively. Circles (right-hand axis) show the measured interfacial fracture energy as a function of the areal chain density of the block copolymer 2, whereas crosses show the fraction of dPS found on the polystyrene side of the interface after fiacture. The discontinuity in the curves at 2 = 0.03 nm is believed to reflect a transition from failure by chain scission to failure by crazing. After Kramer et al. (1994).

The formation of such grafts must modify the interfacial tension in a similar way to block copolymers, as discussed in chapter 6. The mechanical effect of grafting has been studied by Norton et al. (1995), who looked at the effect on fracture energy of grafting polystyrene with a carboxy end-group at an interface between polystyrene and a thermosetting epoxy resin. The unmodified... 

Figure 7.15. The fracture energy against the crack velocity for a polyisoprene elastomer in contact with a polystyrene substrate, in the presence and absence of a layer of styrene-isoprene copolymer. The relative molecular masses of the styrene and isoprene blocks were 60 000 and 66 000, respectively. 0,11 = 0.053 , 2 = 0.01 and , 2 = 0. After Creton et al. (1994).

In summary. Fig. 15 shows the molecular weight dependence of the fracture energy for polystyrene in which the three solutions are graphed for the three pertinent regions. (1) When M < Me, the nail solution (Eq. 4.1) applies to very fragile glasses. (2) When < M < M, disentanglement predominates and Eq. 8.9 applies such that little bond rupture occurs. (3) When M > M, bond rupture dominates and Eq. 8.14 applies. 

Figure 1 shows the molecular weight dependence of the fracture energy for polystyrene in which the three solutions are represented for the three pertinent regions involving pullout, disentanglement and bond rupmre mechanisms. 

The fracture energy, for a brittle polymer such as polystyrene, is reported to be of the order of 10 joules/m" or 0.1... 

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