ABSTRACT:Miscibility and crystallization behavior of biodegradable poly(butylene succinate) (PBSU) and poly(vinylidene fluoride) (PVDF) blends, where two components are crystallizable have been investigated by differential scanning calorimerty and optical microscopy. From cloud point observation of the blends they are found to have lower critical solution temperature behavior. Spherulites of PVDF grew linearly with crystallization time and the growth rate decreased with increase in PBSU content The interaction parameter x, 2 , obtained from melting point depression of PVDF gave the value of -0. 139. However,

ABSTRACT:Miscibility, crystallization behavior and morphology of blends prepared from two crystalline polymers, poly(butylene succinate) (PBSU), and poly(vinylidene chloride-co-vinyl chloride) [P(VDC-VC)] have been examined by polarized optical microscopy and differential scanning calorimetry. It is found that PBSU is miscible with P(VDC-VC) since each blend showed a single glass transition temperature T •. Spherulitic morphology and the melting behavior of the blends were strongly dependent upon the crystallization kinetics and some unique phenomena were found out: (i) in contrast to the other results reported so far, growth rate G of low-Tm component (PBSU) was decreased greatly with increasing high-Tm component [P(VDC-VC)] content, (ii) for the PBSU/P(VDC-VC) (40: 60) blend crystallized at 90oC (i.e., the growth rate of the two components was appproximately the same) so called interlocked spherulites were formed, where PBSU spherulites grown through the interlamellar regions of P(VDC-VC) spherulites, (iii) for the blends crystallized during fast cooling conditions from the melt (e.g., faster than IOoC min-1 ), only one melting peak appeared corresponding to PBSU and no noticeable melting peaks of high-T m component P(VDC-VC) were observed. Hence, it is seen that the crystallization behavior of high-T m component is heavily affected by the low-T m component. Therefore, kinetic factors are the most important one in controlling the crystallization behavior and the morphology of the crystalline/crystalline blends.KEY WORDS Poly(butylene succinate) j Poly(vinylidene chloride-co-vinyl chloride) / Polymer Blend I Spherulitic Morphology j Crystallization Kinetics / Miscibility between two amorphous polymers have been studied intensively by many researchers, especially in relation to phase separation dynamics. Miscibility between crystalline and amorphous polymers has also been examined, and a number of miscible blends are known. 1 -9 On the other hand, few studies have been reported on the miscibility and crystallization behavior of polymer blends between two crystalline polymers. A miscible crystalline/crystalline polymer blend is a rare phenomenon and only a few pairs have been reported to form miscible systems [e.g., poly(c-caprolactone) (PCL)/poly(vinylidene chloride), 10 · 11 poly(3-hydroxybutyrate) (PHB)/poly(ethylene oxide) (PEO), 12 PHB/poly-(L-lactide)13]. This is because the crystalline polymer pairs having attractive interactions between the two components are very rare. Manley et a/. 14 -17 recently have reported a series of miscibility and crystallization behavior of poly(1,4-butylene adipate) (PBA) and poly-(vinylidene fluoride) (PVDF) where both constituents are crystalline polymers. In the PBA/PVDF blends, the melting points of the two components have been ca. 100°C apart, the crystallization behavior and morphology of the low-Tm component (PBA) are seriously influenced by the presence of the spherulitic microstructure of the high-Tm component (PVDF).Recently, we have reported miscibility and crystall...

A novel method for the fabrication of silica/perfluoropolymer nanocomposites was investigated, whereby nano-sized silica particles without surface modification were dispersed uniformly through mechanical breakdown of loosely packed agglomerates of silica nanoparticles with low fracture strength in a polymer melt during direct melt-compounding. The method consists of two stages. The first stage involves preparation of the loose silica agglomerate, and the second stage involves melt-compounding of a completely hydrophobic perfluoropolymer, poly(tetrafluoroethyleneco-perfluoropropylvinylether), with the loose silica agglomerates prepared in the first stage. In the first stage, the packing structure and the fracture strength of the silica agglomerate were controlled by destabilizing an aqueous colloidal silica solution with a mean primary diameter of 190 nm via pH control and salt addition. In the next stage, the silica/perfluoropolymer nanocomposite was fabricated by breaking down the prepared loose silica agglomerates with low fracture strength by means of a shear force inside the polymer melt during melt-compounding.

A new approach for the preparation of organic/inorganic nanocomposites was investigated in which nano-sized silica particles without surface modification were dispersed by the mechanical smashing of strength-controlled porous silica agglomerates in molten resin during direct melt-compounding. The method consists of two stages. The first stage involves preparation of the strength-controlled agglomerated silica nanoparticles with pore structure, and the second stage involves meltcompounding of a thermoplastic resin with the silica agglomerates prepared in the first stage. In the first stage, on the basis of the theory of stability of an aqueous colloidal silica solution, the pore structure and the fracture strength of the silica agglomerate could be controlled by pH-control and electrolyte ion-addition to the colloidal solutions of silica nanoparticles. In the next stage, primary silica nanoparticles could be dispersed in some matrix resins such as a poly(ethylene-ran-vinyl alcohol) and polystyrene uniformly by the proposed mechanical approach by the use of the high shear stress acting on porous silica agglomerates inside these melt-compounded resins. Organic/inorganic nanocomposites 983 Dimensionless Interaction Energy, E T / kT Distance between Two Particle Surfaces, H / nm Conditions of colloidal silica solution KBr-addition pH-control Figure 4. Effects of KBr-addition and pH-control on dimensionless energy versus distance profile of DLVO interaction between two silica particles with d p,Silica ¼ 12 nm at the beginning stage of the evaporation step of aqueous solvent at 353 K. Organic/inorganic nanocomposites 987 Figure 11. SEM micrographs of selected areas of silica nanoparticle-dispersed PS composites (volume fraction of silica, V f,Silica ¼ (a) 0.025, (b) 0.049 and (c) 0.098). Bright spots in the circles are examples of dispersed primary silica particles.

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