Spherulites etched surface

Fig. 5.41 SEM of a molded polyacetal surface shows a smooth texture (A) with little surface detail. Etching for short times results in elongated pits, oriented in the direction of polymer flow (B). Longer etching times result in surface pits deeper below the surface, due to etching larger spherulites in the core (C). R actured cross sections of plated and etched surfaces do not show the structure near the surface (arrows) (D) except in EDS maps of the plating material (E) or at higher magnification (F).

Figure 10.17 Etched surface showing lamellar detail in a banded spherulite of poly(vinylidene fluoride). Moving outwards along the radius (arrowed) the lamellar orientation changes from being seen close to flat on [B] to being edge on [A]. In region [A] the very dark radial features are a consequence of material being stripped from the specimen surface during replication.

Figure 3.8 Structure of a spherulite in HDPE (high-density polyethylene) with radial oriented and branched lamellae in a SEM micrograph of a selectively etched surface (from [2]).

Fig. 4.15 Scanning electron micrograph of an etched surface of polypropylene crystallized at J28°C showing the structure of the individual spherulites and the spherulite boundaries at a magnification of 400 x (courtesy of M. Burke).

In the case of a semicrystalline polymer such as PP, the microstructural features are likely to appear at the scale of the spherulites (typically 5-100 pm in diameter) or even closer at the scale of the long period of the lamellar stacks (10-100 nm). In order to accede to the latter details, it was shown previously (48) that etching of the polished surface with oxidizing acids engraves the amorphous interstices and let the crystalline morphology appear lamellae, or at least stacks of lamellae, become visible. 

Lamellae within adjacent bands of a banded spherulite of linear polyethylene crystallized at 125 C. The specimen was cut open after crystallization, and lamellae are revealed by permanganic etching of the cut surface. The electron micrograph is of a carbon replica of the etched cut surface (after 0. C. BassetO. Scale bar=f 0 fim. 

Figure 4 Sperulitic morphology of bulk PP on a microtomed surface after chemical etching, SEM micrographs (a) lower magnification with a whole spherulite (b) higher magnification of the central part of a spherulite.

The early stages of deformation of a banded spherulite of linear polyethylene draw ratio 1-2. Replica of an etched cut surface. 

The morphology of banded spherulitic polyethylene as in Fig. 2.17 (left) illustrates this well. The orientation of crystals rotate periodically along the spherulite radius at A the resistant basal surfaces of the crystals are seen standing proud of the general etched plane at B the lamellae are displayed edge-on, so are somewhat less... 

Different specimen types yield a range of results upon ion or plasma etching. Multiphase polymers generally etch differentially, enhancing the contrast. Melt crystallized polymers can be etched to reveal the spherulites. Surface protuberances and particulate fillers can and do form cones or ridges when etched. Oriented semicrystalline polymers, on the other hand, appear to be the most controversial with respect to the resulting surface textures. Clearly, in such cases the specimen should be prepared by other methods for comparison, and control experiments are essential. There are problems in the industrial laboratory that can be solved, in part, by microscopy of surfaces prepared by etching techniques however, these are far fewer than those addressed by other specimen preparation methods. 

Peck and Kaye [204] immersed cellulose acetate specimens in acetone, at -50°C, and then flooded the surfaces with cold absolute alcohol, followed by replication which showed the skin, orientation, voids and pigment. Reding and Walter [21] etched PE with hot carbon tetrachloride (high density PE), benzene (low density PE) or toluene, which removed the amorphous material. Bailey [205] used a rapid xylene etch to reveal spherulites in PE and PP, while Li and Kargin... 

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