Spherulite morphology poly

Significant variation of the ultimate mechanical properties of poly(hexamethylene sehacate), HMS, is possible by con-trol of thermal history without significant variation of percent crystallinity. Both banded and unbanded spherulite morphology samples obtained by crystallization at 52°C and 60°C respectively fracture in a brittle fashion at a strain of r O.Ol in./in. An ice-water-quenched specimen does not fracture after a strain of 1.40 in./in. The difference in deformation behavior is interpreted as variation of the population of tie molecules or tie fibrils and variation of crystalline morphological dimensions. The deformation process transforms the appearance of the quenched sample from a creamy white opaque color to a translucent material. Additional experiments are suggested which should define the morphological characteristics that result in variation of the mechanical properties from ductile to brittle behavior. 

In conclusion, the deformation behavior of poly(hexamethylene sebacate), HMS, can be altered from ductile to brittle by variation of crystallization conditions without significant variation of percent crystallinity. Banded and nonbanded spherulitic morphology samples crystallized at 52°C and 60°C fail at a strain of 0.01 in./in. whereas ice-water-quenched HMS does not fail at a strain of 1.40 in./in. The change in deformation behavior is attributed primarily to an increased population of tie molecules and/or tie fibrils with decreasing crystallization temperature which is related to variation of lamellar and spherulitic dimensions. This ductile-brittle transformation is not caused by volume or enthalpy relaxation as reported for glassy amorphous polymers. Nor is a series of molecular weights, temperatures, strain rates, etc. required to observe this transition. Also, the quenched HMS is transformed from the normal creamy white opaque appearance of HMS to a translucent appearance after deformation. 

Figure 6.22 (66) illustrates the spherulite morphology for poly(ethy-lene oxide)-h/oc -polystyrene. Two points should be made. First, the glass... 

Yang et al. [39], on their part, observed that the fractionate crystallization of poly(butylenes adipate) (PBA) was affected by the content and the crystalUzation temperature of the PBA component. At PBA/ PBS composition of 70/30, PBA showed its highest crystallinity value. However, observation of the PBA revealed that the presence of PBS helped to manipulate the spherulite morphology. 

Lee JK, Choi MJ, Im JE, Hwang DJ, Lee KH. Spherulite morphology and crystallization behavior of poly(trimethylene terephthalate)/poly(ether imide) blends. Polymer 2007 48 2980-7. 

Yang J, Pan P, Hua L, Dong T, Zhu B, Inoue Y, et al. Fractionated crystallization, polymorphic crystalline structure and spherulite morphology of poly(butylenes adipate) in its miscible blend with poly(bntylenes succinate). Polymer 2011 52 3460-8. 

The topographical AFM images of poly(ethylene vinyl acetate) films with various thicknesses ranging from 20 to 460 nm are shown in Fig. 33 [80]. The bulk-like spherulites are seen in the 460-nm film. In thick films, the surface morphology of the film is very similar to the bulk. As the thickness decreases to 152 nm, more small spherulites are observed. This is possibly due to the... 

The effects of morphology (i.e., crystallization rate) (6,7, 8) on the mechanical properties of semicrystalline polymers has been studied without observation of a transition from ductile to brittle failure behavior in unoriented samples of similar crystallinity. Often variations in ductlity are observed as spherulite size is varied, but this is normally confounded with sizable changes in percent crystallinity. This report demonstrates that a semicrystalline polymer, poly(hexamethylene sebacate) (HMS) may exhibit either ductile or brittle behavior dependent upon thermal history in a manner not directly related to volume relaxation or percent crystallinity. 

Li L-S (1986) On the morphology and structure of poly(p-phenylene terephthalamide) single crystals and spherulites. J. Macromol. Sci.-Phys., B25 215... 

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