Permanganate-acid etching

Figure 10.5. Secondary electron micrographs at two magnifications (note the 10-pm bars) of a 43 wt % polystyrene/HDPE specimen etched in potassium permanganate/ acid solution. The raised domains are polystyrene-rich.

Fig. 27 Transmission electron micrograph of etched cut surface of a linear polyethylene after crystallisation at 130.4 °C for 27 days followed by quenching. Etching was performed with permanganic acid. Note the continuity between dominant ridges and thinner S-shaped lamellae. From Bassett et al. [46] with permission from the Royal Society of London, UK...

Figure 7.25 Effect of etching with permanganic acid, creating a surface topography revealing lamellar details of the morphology. Dark areas indicate crystals.

The lamellar structure is best studied using TEM. Let us take polyethylene. Two methods of preparation are commonly used staining with chlorosulphonic acid/uranyl acetate and etching with permanganic acid. 

Figure 11.15 shows transmission electron micrographs of replicas of samples etched with permanganic acid. One of the advantages is directly noted. There are no blank areas. All crystals, irrespective of orientation, are revealed. It is possible to find areas where the crystals are seen from the side with the chain axis in the sample plane (Fig. 11.15, top... 

Figure 11.15 Transmission electron micrographs of replicas of polyethylene etched with permanganic acid. Micrographs of M. T. Conde Braha, Dept of Polymer Technology, Royal Institute of Technology, Stockholm.

Permanganic acid, a weaker acid than nitric acid, has been found to selectively remove the amorphous regions of polyolefins and many other crystalline polymers to reveal their internal lamellar organization. It was developed and has been applied by Olley and Bassett [328-330] and others [251, 252, 331] as a complementary method to chlorosulfonation. The original permanganate etching method involved the use of... 

Dehydrated calcium pimelate is added (between 0.01 and 0.5 wt %) as the nucleating agent to isotactic polypropylene to produce the (3 modification of iPP [63]. Following molding between two glass plates at 220°C thin films of the polymer are isothermally crystallized at 140°C-143°C in a microscopy hot stage. After the hedritic structures develop, the samples are quenched to room temperature. Prior to AFM examination, the specimens are etched with a 1% solution of potassium permanganate in a mixture of sulfuric and orthophosphoric acid [64, 65]. This procedure is described in detail in the literature Caution consult the literature for safety precautions ) and helps to remove preferentially amorphous phase of PP [64]. Thus, unlike in the many other examples discussed in Sect. 3.2, here the interior of a specimen is analyzed after its exposure. 

Caution Consult appropriate literature and ensure that safety regulations are being followed. Strong oxidants and acids are used. Conditions 0.7 % w/v of potassium permanganate in a mixture of sulfuric acid (95-97%, Merck) and phosphoric acid (85%, Aldrich) in the volumetric ratio of 2 1. Specimens are etched in 0.7 % w/v of the permanganic solution at room temperature typically over 5 h. The etched... 

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