Blends spherulites

Growth Rate of Miscible Polymer Blend Spherulites Crystallized Isothermally from the Melt Measured by Polarizing Optical Microscopy [74]... 

Mesoscale Morphologies in Polymer Blends Spherulites and Miorocrystallites... 

To confirm the shape of the spherulites described by the Avrami exponent, polarized optical micrographs of the isothermal crystallized melt blends were taken, and are shown in Figure 20.26 [44],... 

The morphology of the spherulites was in the form of a Maltese Cross , which was confirmed by the Avrami exponent value in the DSC study. The spherulite size of the binary blends was smaller than that of pure PET and PEN. 

The structure of crystalline polymers may be significantly modified by the introduction of fillers. All aspects of the structure change on filling, crystallite and spherulite size, as well as crystallinity, are altered as an effect of nucleation [9]. A typical example is the extremely strong nucleation effect of talc in polypropylene [10,11], which is demonstrated also in Fig. 2. Nucleating effect is characterized by the peak temperature of crystallization, which increases significantly on the addition of the filler. Elastomer modified PP blends are shown as a comparison crystallization temperature decreases in this case. Talc also nucleates polyamides. Increasing crystallization temperature leads to an increase in lamella thickness and crystallinity, while the size of the spherulites decreases on... 

The isothermal crystallization of PEO in a PEO-PMMA diblock was monitored by observation of the increase in radius of spherulites or the enthalpy of fusion as a function of time by Richardson etal. (1995). Comparative experiments were also made on blends of the two homopolymers. The block copolymer was observed to have a lower melting point and lower spherulitic growth rate compared to the blend with the same composition. The growth rates extracted from optical microscopy were interpreted in terms of the kinetic nucleation theory of Hoffman and co-workers (Hoffman and Miller 1989 Lauritzen and Hoffman 1960) (Section 5.3.3). The fold surface free energy obtained using this model (ere 2.5-3 kJ mol"1) was close to that obtained for PEO/PPO copolymers by Booth and co-workers (Ashman and Booth 1975 Ashman et al. 1975) using the Flory-Vrij theory. 

Blends of polyphenylenevinylene with water-soluble polymers have been prepared by mixing solutions of the sulfonium precursor with polyethyleneoxide, hydroxy-propylcellulose and polyvinylmethylether317). Polyethyleneoxide forms spherulites which impose a spherulitic texture to the polyphenylenevinylene that is retained after transformation. As a result of this open network, high conductivities are reached at only 10% conducting polymer. 

Figure 10.5 shows scanning electron micrographs of blend samples that were prepared as described in the Experimental Section . The etchant preferentially attacks polyethylene, producing a topography in which the polystyrene-rich domains are raised above the polyethylene domains. The interlamellar amorphous material provides a location for styrene to penetrate and polymerize. A considerable amount of polystyrene is present in the center of the spherulites. This is due either to amorphous polyethylene that is present in these locations or to voids that develop during crystallization... 

The morphology of a polyethylene blend (a homopolymer prepared from ethylene is a blend of species with different molar mass) after crystallisation is dependent on the blend morphology of the molten system before crystallisation and on the relative tendencies for the different molecular species to crystallise at different temperatures. The latter may lead to phase separation (segregation) of low molar mass species at a relatively fine scale within spherulites this is typical of linear polyethylene. Highly branched polyethylene may show segregation on a larger scale, so-called cellulation. Phase separation in the melt results in spherical domain structures on a large scale. 

One might expect the nodule diameter of pure LDPE to be the same as that in the amorphous rubber/LDPE blend. This could result if the same proportion of LDPE nucleated the crystals and if no amorphous EPDM lay inside the LDPE crystallites. However, the concentration of crystallites would be lower in the blend. It is impossible for us to measure the concentration of crystallites in this blend. The resolution is inadequate and the etching depth is not accurately known. We will have to look at blends containing less LDPE to see if the crystallite concentration decreases. No spherulites are seen in these blends by polarized optical microscopy. However, these nodules are too small for optical resolution, and may indeed be spherulites or aggregates of lamellae. 

Microscopic examination of these samples show for the PET-rich blends the presence of very small spherulites. The PBT-rich blends show very low birefringence, low turbidity, and no organized structures. The SALS patterns are circularly symmetrical. 

Microscopic examination of the samples crystallized at 130°C shows very low turbidity and birefringence for the PBT samples the turbidity in the blends increased, and small spherulites were present for PET. The samples crystallized at 110°C again showed small spherulites for PET, and no organized structures were observed in the blends of intermediate composition although their turbidity was quite high with samples of very high PBT composition, the turbidity was lost. 

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