Irradiation spherulite

Just above the melting point the polymer is visually quite viscous and numerous observations have been made that the polymer exhibits a memory effect, that is to say, on recooling the melt crystallites will appear in the same sites where they had been before melting the polymer. Hartley, Lord and Morgan (1954) state It is reasonable to suppose that there will be a few localities in the crystalline polymer which have a very high degree of crystalline order, and therefore the melt can contain, even at considerable temperatures above the observed melting or collapse point, thermodynamically stable minute crystals of the polymer . Especially if the polymer has been irradiated so as to contain a few crosslinks as in irradiated polyethylene, then flow is inhibited and spherulites can be made to appear on recrystallization in the same sites that they had before the polymer was melted, Hammer, Brandt and Peticolas (1957). However, as mentioned above, the specific heat of irradiated polyethylene in the liquid state is identical with that of the unirradiated material, within the limits of experimental error. Dole and Howard (1957). 

Fig. 11a and b. Micrographs of craze tips in a solvent-produced, spherulitic film of PP 1120 before a and after long time irradiation in the TEM b... 

Figure 5.4 shows the heating curves of melt-crystallized PTOX cooled from the melt at a rate of 64 C/min, or the 2nd run of the 80% sample used in Fig. 5.1. The profile of the heating curve changes more sharply with increasing dose, although Ts remains constant in all samples, except those irradiated with 10 kGy. Quite similar results were obtained in two types of POM, a spherulite crystal and an oriented...

Figure 8. Appearance between crossed polars of various morphological features associated with the inversion wall defects in LC spherulites. (a) Successive radial initiation, (b) initiation by extrinsic factors, (c) rejection and reorientation of inversion walls in interspherulitic boundaries, and (d) spherulitic growth in confined regions. The material is a 25 75 E7 NOA65 LCpolymer blend UV-irradiated with 4.5 J/cm. (Reproduced from Ref. 11 Copyright American Chemical Society).

Figure 10. Polarizing micrographs depicting the isotropization behavior during heating of LC spherulites in a 25 75 E7 NOA65 LCrpolymer blend UV-irradiated with 4.5 J/cm at 25°C. (a) Heated to 61.5 C, (b) 61.6 C, and (c) 61.8°C. (d) Cooled to ambient after complete isotropization at 62 C and further heating to 65 C.

Figure 1.9 Banded spherulites in LORE with a radiai arrangement of iameiiae, twisted in concentric rings (irradiation-induced fixation of the materiai, UDS, TEM)...

On the other hand, an electron beam can initiate processes in the polymeric material that yield an increase in material contrast. Spherulites with a radial arrangement of lamellae have been made clearly visible in an HEM micrograph in Fig. 1.65 through the use of irradiation-induced contrast enhancement. Similar effects of contrast enhancement can be used in polyethylenes (see Fig. 1.9 and Figs. 2.69, 2.70) [1,5]. 

Irradiation Reduced degree of crystallinity decrease in crystallization rate changes in spherulitic structure 84, 85... 

Mass loss destroys the sample to a greater or lesser extent, but it can be regarded positively as an etching process using the electron beam, and put to use. Two polymers in a blend or copolymer may have little contrast initially, but one phase loses more mass and the contrast increases or reverses [220]. Even in a homopolymer, the cracks and voids that appear can sometimes be related to the microstructure, making it more visible. For example, cracks form in molded poly(oxymethylene) samples during irradiation in the SEM [215], which follow spherulite radii and show up the oriented skin (e.g., see Fig. 4.34). 

Figure 3.22 Contrast enhancement by the physical effect of /-irradiation in semi-crystalline LDPE (/-irradiation with a dosage of 20 MGy) [15] (a) banded spherulites and (b) lamellae inside the concentric bands.

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