Poly fracture surfaces

The appearance of the individual microcapsules is shown in Fig. 1. Most individual microcapsules are approximately spherical and show a surface made up of deposited plates of poly(DL-lactic acid) in which the drug is embedded. Many of the larger microcapsules are cemented together by further plates of poly(DL-lactic acid). The effect of compression on these microcapsules is shown in Fig. 2. At a compressive force of 2 kN (Fig. 2(a)) the electron micrograph of the tablet fracture surface shows that the microcapsules, while distorted, remain essentially intact and rounded, with a relatively open porous structure to the tablet as a whole. At 10 kN force (Fig. 2(b)) the microcapsules at the fracture are flattened, cracked and distorted so that the fracture surface shows a far less open, porous aspect. Both of these microcap tablets have a very different appearance from that produced by the simple mixture (Fig. 3), where the individual plates of poly(DL-lactic acid) are mixed with the drug crystals in an open structure from which release would be easily... 

Fig. 1 Fracture surface of granular (bulk-polymerized) poly(tetrafluorethylene (PTFE). The sample was held in the melt at 380 °C for an unspecified time followed by slow cooling and fracture after immersion in liquid N2. (Reprinted from Ref. [1] with permission from Wiley-Interscience)...

Fracture Surface Morphology and Phase Relationships of Polystyrene/Poly(methyl Methacrylate) Systems... 

A second method consists in observing the composite fracture surfaces. For example, in the case of MWNTs in a poly (hydroxy-aminoether) matrix, C. Bower et al. (70) observed a lot of pulled out nanotubes and concluded that the load transfer from polymer to nanotube was not sufficient to fracture the nanotubes. In the same time, a lot of kinked MWNTs were observed, which were believed to be plastically deformed. 

The microstructure of this type of material was studied as early as 1952 by Fischer and Isenbarth (1). These authors demonstrated by thin section transmission microscopy that a two-phase microstructure was present in a number of materials available commercially for restoring tooth structure. In 1955 Helmcke reported similar findings with electron microscopic studies of fracture replicas (2, 3). Then in 1958, Smith examined at low magnification fracture surfaces in materials made from denture base polymers attention centered on a system of ridges concentric with a mirror region (4). In retrospect, this phenomenon was similar to that observed in one-phase samples of poly (methyl methacrylate) (5). Subsequently, in 1961, Smith showed that the microstruc-... 

Kojima M, Magill JH (1986) Fracture surface morphcdogy of poly(bis(trifluoroethoxy)phospha-zene]. J. Mat Sci., 21 2651 see also Makromol. Ctemie IS6 649 (1985)... 

Figure 6. Sketch and details of a fracture surface of poly(EGDM). Reproduced lth permission from Ref. 31 Copyright 1982, John Wiley Sons, Inc.

Figure 9.15 Cryo-SEM image of the fracture surface of a coated layer of poly(styrene-co-acrylic acid, 50° C) spheres 850 nm in diameter dried for 8 min in room air. The adjacent top surface shows obliquely...

Fig. 11. Fracture surfaces ( x200) of fibre-epoxy composites using (a) glass fibre, (b) heat treated poly (p benzamide) fibre.

Finally, a word about the fracture properties of poly(p-benzamide) fibre. Not unexpectedly it appears that the extreme axial properties of the fibre have to be paid for in terms of very poor transverse properties. Indeed the higher the modulus the greater is the tendency for the fibre to exhibit a failure mode consisting of fibrillation and splintering. Words cannot describe this as well as the Stereoscan photograph (Fig. 10) and Fig. 11 which compares fracture surfaces in a glass fibre-epoxy composite (a) and a poly(p-benzamide)-epoxy composite (b) prepared in the authors laboratories. 

Skin/core morphologies are common in blends of LCP s and thermoplastic polymers and they play a significant role in defining the properties of both extruded and injection molded samples. Usually, LCP s in the skin have a higher degree of orientation than in the core when the blends are extruded or injection molded (Husman et al. 1980 Hedmark et al. 1989 Lee 1988). Baird et al. (Baird and Mehta 1989 Baird and Sukhadia 1993) observed a skin/core morphology in blends of PA 66 with HBA/HNA and 40 PET/60 PHB and 20 PET/80 HBA copolyesters. More LCP fibers were present in the skin than in the core for both systems. Isayev and Swaninathan (1994) also reported shell-core structure in the fracture surfaces of injection molded blends of HNA/HBA liquid crystalline copolyesters and poly (etherimide). 

Figure 12.6 Matching fracture surfaces of a cleavage sample of poly(methyl methacrylate) showing colour alternation (green filter). (Reproduced from Berry, in Fracture 1959 (eds B. L. Averach et al.,), Wiley, New York, 1959, p. 263)...

Blended matrices of maleated natural rubber and poly(methyl methacrylate) were prepared by mechanical mixing, and the fractured surface morphology of... 

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