Spherulites banded type

It was noted in early session that sphemlitic structure of a polymer affects the mechanical properties of the polymer. Micrographs of PHB and PHB12 V crystals stractrrre, revealed using POM, are shown in Figure 12. The PHB V and PHBHHx show fine fibrillar structure of spherulites while PHB shows circular ring banded spherulites, both types of crystals display Maltese cross. 

Fig. 30a--c. Interaction between shear bands of type A with bands of type B a, and with spherulite boundaries perpendicular b and parallel c to shear band package A in PP 1320... 

Fig, 37a—d. Structure of shear fracture surface a SEM-micrograph of a shear fracture in PP 1120 (T = —80 °C) b secondary crack formation (white arrow) in one of the shear bands of type B in fine spherulitic PB-l (T = -196 °C) c traces of shear bands B containing fibrillated polymer substance on a shear fracture plane in fine spherulitic PP 1120 (T = —196 °C) d preferred shear fracture along spherulite boundaries (SB) of coarse spherulitic PP 1120 (T = —80 °C)... 

The ring-banded structure of spherulites (Fig. 7) is often seen in blends in which the amorphous components are miscible, i.e. both components are present in the melt at the growth surface, and it is frequently considered that such features are only seen in these situations. Detailed information on ring-banded spherulites is exempHfied in subsequent sections deaUng with individual blend types. To date there is no agreed explanation for the origin of this feature i.e. there is no explanation as to why the fibrils should twist in a regular... 

Figure 16.7 POM images showing the effect of stalk dendrites at < 46°C and branching costallization temperature on blend morpholo- dendrites at 7c=<48°C. Reprinted with per-gies for the PVME/PHA (20/80) blend, (a) Mai- mission from Ref. [57] 2010, Nature Pub-tese cross-type pattern at T < 38°C (b) Ring- lishing Croup, banded spherulites at 7 . = <42 C (c) Straight-...

Figure 7.34 shows the two main types of spherulites, non-banded (Fig. 7.34(a)) and banded (Fig. 7.34(b)). The boundaries of the spherulites are non-spherical but smooth after impingement. The boundaries of mature spherulites before impingement appear to be circular (spherical). Examination of the spherulite boundaries by transmission electron microscopy shows more irregular features. Low molar mass species may accumulate in the spherulite boundaries making them very brittle in samples with appreciable fractions of low molar mass species. 

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