Fracture modifying interfacial adhesion

The modification of bitumen with SBS copolymer powder was done using the mechanochemically devuicanized GRT (Zhu et al., 2009). The penetration index, softening point, 5°C ductility, aging behavior, and rheological properties of bitumens modified by 8,10, and 12 wt.% GRT/SBS mixtures were measured. In comparison with the bitumen modified by incorporation of 5.5 wt.% SBS alone, the majority of properties of the blends were improved, except their penetration. Rheological properties indicated that at high temperatures 10 wt.% GRT/SBS-modified bitumen was better than SBS-modifled bitumen. The SEM observation of the fractured surfaces showed that bitumens mixed with the GRT/SBS powder had a better interfacial adhesion with matrix than with SBS alone. 

Mondragon et al ° reported that unmodified and modified NR latex were used to prepare thermoplastic starch/NR/MMT nanoeomposites by twin-screw extrusion. After drying, the nanoeomposites were injection moulded to produce test specimens. SEM of fractured samples revealed that chemical modification of NR latex enhanced the interfacial adhesion between NR and thermoplastic starch (TPS), and improved their dispersion. X-ray diffraction (XRD) showed that the nanoeomposites exhibited partially intercalated/exfoKated structures. Surprisingly, transmission electron microscopy (TEM) showed that clay nanoparticles were preferentially intercalated into the rubber phase. Elastic modulus and tensile strength of TPS/NR blends were dramatically improved from 1.5 to 43 MPa and from 0.03 to 1.5 MPa, respectively, as a result of rubber modification. 

The scratch resistance of polypropylene was improved by blending 20 wt% PPE/HIPS blend (Noryl PX0844) as a modifier and 5 % styrene-ethylene/ propylene diblock copolymer (Kraton G) as a compatibilizer (Sue 2001, 2002). It appears that the fracture energy dissipation in the PP matrix occurs by craze promotion around the dispersed particles of PPE/HIPS blend and thus preventing crack formation, while the compatibilizer promoted the PP/PPE interfacial adhesion. 

Some authors have refused to accept the role of interfacial adhesion on the toughening of thermoset resins. Lavita and co-workers [190] reported that non-reactive rubber can toughen BPA-modified epoxy, but the mechanism was not fully discussed. Huang and co-workers [194] showed that when the second phase consists of micron-size rubber particles, the interfacial bonding has only a modest effect on the fracture properties of blends. 

The molecular weight of the reactive polymers, thus of the constitutive blocks of the compatibilizer, is also critical for efficient entanglements with the phases to be compa-tibilized. Indeed, good interfacial adhesion is essential for stress transfer from one phase to the other one to be efficient and for cracks initiated at the interface to be prevented from growth until catastrophic failure occurs. Kramer et al. studied the fracture mechanism of the polystyrene/poly(2-vinylpyridine) interface modified by the parent di-block copolymer. They found that the minimum degree of polymerization of PVP for entanglement (Npvp) was 255, below which the PVP block was pulled out in slow crack opening experiment [93, 94]. 

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