Spherulites banded polyethylene

Macrospherulites of polyethylene glycols that have diameters of up to about 2 cm (Figure 8) have been reported (88). When viewed between crossed Polaroids , the characteristic Maltese cross patterns and spherulitic banding that are seen in microscopic spherulites are apparent in these spherulites and can be seen with the naked eye (Figure 9). 

Figure 37 A banded spherulite of polyethylene crystallized at 122" C, showing lamellar re-orientation approximately every...

Figure 11 Left Spherulites of a Ziegler-Natta isotactic poly(propylene) with Mw = 271,500 g/mol and mmmm — 0.95, isothermally crystallized at 148°C. Right Banded spherulites of a linear polyethylene with Mw = 53,600 g/mol slowly cooled from the melt.

Fig. 16a-c Polarised photomicrographs of different linear polyethylenes showing a non-banded spherulites, b banded spherulites (from [115] with permission from Elsevier, UK) and c axialites. Scale bars represent 20 pm... 

A preferentially and a sheaf-like aggregation with random in-plane orientation are observed for the thinner films (thicknesses of 0.1, 0.2 and 0.4 pm in panels a-c). By contrast thick films (0.6 pm and thicker, panel d) show a morphology that resembles the well known (bulk) spherulitic form with a banded structure, characteristic of linear polyethylene crystallized from the melt at moderately high undercooling. 

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. 

Banded spherulities of linear polyethylene within a commercial pellet. Optical micrograph of a thin section viewed between crossed polars. Note that sequences of spherulites have nucleated along lines, here in black contrast, which are probably a legacy of extrusion (after D. C. Bassett.). Scale bar -10 un. 

Fig. 11. Portion of a banded spherulite of linear polyethylene (Sclair 2907). This sample has been annealed at 0-5 GPa and 230°C. Replica of an etched...

Ring-banded spherulites were more commonly seen in blends of PCL with polymers with which there was miscibility in the amorphous phase (cf. PVC and chlorinated polyethylenes. Sects. 8 and 9). The initial copolymers were immiscible with PCL but it was considered that miscibility was enhanced by the formation of different copolymer structures on heating during processing. 

SAXS data show that the quantized thicknesses are not established immediately but that the long period passes through a nonintegrally folded (NIF) form, in which surfaces will not be well defined (77). There are also new infrared data showing that 001 surfaces of solution-crystallized deuterated re-alkanes are inherently disordered (117). Similarly, linear nucleation has shown that for most crystallization conditions, polyethylene fold surfaces form as 001 in a stressed condition from which they subsequently transform to S-profiles, with banding (65). Monodisperse re-C294H5go also forms banded spherulites of the once-folded form when quenched (113), signifying that, in this condition, its basal surfaces are stressed. 

Fig. 7. (a) Banded spherulites of poly(trimethylene glutarate) viewed between crossed polars in a polarizing microscope. From Ref 118.. (b) lamellar texture in a banded spherulite of butyl-branched linear low density polyethylene crystallized at 124°C. From Ref. 119. 

Fig. 4.21 Portion of a banded spherulite of linear polyethylene, also showing a spherulite boundary, as revealed by one hour etching using 2% w/w potassium permanganate in concentrated sulfuric acid as described by Naylor and Phillips [275]. The micrograph is of a chromium shadowed carbon replica studied in the TEM where each disk-like object in the bands is composed of lamellae nucleated at that point by a screw dislocation. (From Phillips and Philpot [274] used with permission.)...

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... 

Shahin MM, Olley RH (2002) Novel etching phenomena in poly(3-hydroxy butyrate) and poly (oxymethylene) spherulites. J Polym Sci B Polym Phys 40 124—133 Shahin MM, Olley RH, Blissett MJ (1999) Refinement of etching techniques to reveal lamellar profiles in polyethylene banded spherulites. J Polym Sci Polym Polym Phys 37 2279-2286 Shanks RA, Amarasinghe G (2000) Crystallisation of blends of LLDPE with branched VLDPE. Polymer 41 4579 587... 

Crystalline lamellae can be arranged in different ways, from a parallel arrangement in stacks or bundles, sheaf-like structures, up to spherulites with a radial arrangement of lamellae (typical of HDPE, (high-density polyethylene), or polypropylene (PP)) or twisted lamellae, arranged in concentric rings (banded spherulites, typical of LDPE (low-density polyethylene), as in Fig. 1.9). Depending on the polymer and thermal treatment, the spherulites can reach diameters of up to several tens or hundreds of microns. 

Figure 10.15 Banded spherulite in low-density polyethylene after staining with chlorosulphonic acid. Although the lamellar structure is well resolved at the centre of the object, in other regions morphological detail is less distinct.

Figure 7.36 Transmission electron micrograph of polyethylene with banded spherulites etched with a mixture of potassium permanganate, sulphuric acid and phosphoric acid (M. Hedenqvist, Dept of Polymer Technology, Royal Institute of Technology, Stockholm, Sweden).

Figure 3.15. Two images of a thin melt cast film of high density polyethylene the region is 200 x 250//m. The left hand image was taken in crossed polars. The radial Maltese cross is due to the extinction position. The spherulites in this material have dark circumferential bands. The crystals twist as they grow, and their orientation in these bands has the optic axis perpendicular to the specimen plane. The right hand image is the same area when a first order red plate is also used. The blue and yellow colors show that the spherulites are negative. (See color Insert.)...

Figures 3.15 and 3.16 show spherulites in crossed polars and with the sensitive tint plate. In crossed polars, the spherulites are bright except at the four perpendicular radial directions where the crystals are in the extinction position. High density polyethylene (see Fig. 3.15) produces spherulites that are unusually perfect, and also have circumferential dark bands. The bands are regions of apparent isotropy where the optic axis is perpendicular to the specimen plane. With the first order red plate placed so that its slow direction is at -l45° (top right to bottom left of the image), the...

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