Interlamellar cavitation

Cavitation is often a precursor to craze formation [20], an example of which is shown in Fig. 5 for bulk HDPE deformed at room temperature. It may be inferred from the micrograph that interlamellar cavitation occurs ahead of the craze tip, followed by simultaneous breakdown of the interlamellar material and separation and stretching of fibrils emanating from the dominant lamellae visible in the undeformed regions. The result is an interconnected network of cavities and craze fibrils with diameters of the order of 10 nm. This is at odds with the notion that craze fibrils in semicrystalline polymers deformed above Tg are coarser than in glassy polymers [20, 28], as well as with models for craze formation in which lamellar fragmentation constitutes an intermediate step [20, 29] but, as will be seen, it is difficult to generalise and a variety of mechanisms and structures is possible. 

Fig. 19a, b Early stages of irreversible deformation in a thin film of a iPP deformed at room temperature and post-stained with Ru04 vapour, showing a interlamellar cavitation and b lamellar shear at a later stage in the deformation process [26]... 

Fig. 30a-c TEM micrograph of microdeformation in different parts of the crack-tip deformation zone at a y3 nucleated (iPP/5 wt% iPP-MAH)-PA 6 interface, a Crazing in an a-rich region, b extensive interlamellar cavitation in a /5-rich region and c lamellar shear in a /5-rich region [177]... 

Fig. 5 TEM of a section through part of the fracture surface of the third generation HOPE tested with K,- = 0.12 MPam in Igepal (Table 1, FNCTJ) (a) overview (b) detail of regions of interlamellar cavitation behind the fracture surface.

Sonawane et al. [90] investigated the affect of ultrasound and nanoclay for the adsorption of phenol. Three types of nanoclay tetrabutyl ammonium chloride (TBAC), N-acetyl-N,N,N trimethyl ammonium bromide (CTAB) and hexadecyl trimethyl ammonium chloride (HDTMA), modified under sonication, were synthesized which showed healthier adsorption of phenol within only 10 min in waste water. The interlamellar spacing of all the three clay increased due to incorporation of long chain quaternary salts under cavitational effect. 

Fig. 24. Schematic representation of the possible deformation processes of a stack of crystal lamellae (a) the initial state, (b) interlamellar shear, (c) interlamellar separation, (d) intralamellar block shear, (e) intralamellar fine shear (not shown bending and rotation of lamellae), and (f) cavitation within the amorphous regions.

These local deformation modes are similar to the situation in semicrystalline polymers with a parallel arrangement of crystalline lamellae (stiff) and amorphous layers (soft) compare Figs. 2.20 and 2.21. Due to the larger number of molecular defects (chain ends, weak entanglements) in the amorphous phase of semicrystalline polymers, cavitation and interlamellar separation often occur. Contrary to this, block copolymers with less molecular defects in the soft layers (PB) can easily deform with chevron formation (6,25). 

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