Epitaxial crystallization in the sPP/nylon-12 semicrystalline polymer system

The epitaxial crystallization behaviour of syndiotactic polypropylene (sPP) on highly oriented nylon-12 substrates has been investigated by means of transmission electron microscopy. The results obtained from bright field electron microscopy and electron diffraction indicate that sPP crystals grow epitaxially on the oriented nylon-12 substrate with their c-axes +/- 37 degrees apart from the chain axis of the nylon-12 substrate. The contact planes of the sPP crystals are the (100) lattice planes. Moreover, the epitaxial crystallization of nylon-12 on highly oriented sPP substrates from a dilute solution in cyclohexanone has also been studied using optical microscopy. The results show that the nylon-12 crystals grow epitaxially on the oriented sPP substrate with the oriented nylon-12 lamellae forming large, anisotropic domains. Copyright (C) 1996 Elsevier Science Ltd.

FRACTIONATED CRYSTALLIZATION IN POLYOLEFINS-NYLON-6 BLENDS

The crystallization behavior of polyolefins-nylon 6 polymer blends was studied by differential scanning calorimetry (DSC) measurements. In these blends, the crystallization of the minor component often starts with distinctly deeper supercooling than that

INFLUENCE OF ESTER GROUP-SIZE IN PMAS ON BETA-PHASE CRYSTALLIZATION OF PVF2 IN HIGHLY ORIENTED FILMS OF PVF2/PMAS BLENDS

Influence of ester group size in polymethacrylates (PMAs) , including PMMA, PEMA and PBMA, on beta phase crystallization of poly(vinylidene fluoride) (PVF2) in highly oriented films of PVF2/PMAs=80/20 blends has been investigated by FTIR and TEM. The melt-drawn films of pure PVF2 consist of highly oriented lamellae, in which the alpha phase is predominant. Adding a given amount of PMAs (20 wt%) into PVF2 results in formation of fibrillar crystals and increase of relative amount of the beta phase. The influence extent is in order of PMMA > PEMA > PBMA, regarding the ester group size in the PMAs.

ESTIMATION OF THE RADIATION-INDUCED DAMAGE IN PTFE BY DEPRESSION OF THE MELTING AND CRYSTALLIZATION TEMPERATURES

The radiation induced depression of the melting and crystallization temperatures of PTFE irradiated at various temperatures followed by heat treatment at 380-degrees-C, and their relationship to structural changes, were investigated. The G(-units) values obtained in this work are different from those of samples which have not undergone heat treatment and seem to be more closely associated with radiation induced branched structures.

EPITAXIAL CRYSTALLIZATION OF HDPE ON IPP IN HDPE/IPP BLENDS

Unique crystalline morphologies of solution-cast films of HDPE/iPP blends were investigated by means of transmission electron microscopy (TEM), electron diffraction, metal shadowing and specimen-tilt techniques. The unique morphologies come from an epitaxial crystallization of HDPE on iPP. The contact planes of the two kinds of crystals are (100) of HDPE and (010) of iPP, while the intercrossing angle between their chain axes is about 50-degrees. The HDPE existed with different crystalline morphologies in the two kinds of crystalline regions of iPP spherulites, i.e. cross-hatched and single-crystal-type structures. Based on structural analysis, two models of epitaxial growth of HDPE on iPP are proposed.

AN EXPERIMENTAL-STUDY ON MEMBRANE DISTILLATION CRYSTALLIZATION FOR TREATING WASTE-WATER IN TAURINE PRODUCTION

The solution of non-volatile solutes can be concentrated to saturation by membrane distillation. If the solute is easy to crystalize, the membrane distillation-crystallization phenomenon will appear during the membrane distillation of saturated solutions. It is possible that crystalline products are separated from concentrated solutions by a membrane process. In this work the PVDF capillary membrane, which was improved on hydrophobicity by using LiCl instead of a water-soluble polymer as an additive, has been used for treating the waste water of taurine. The crystalline product has been obtained from the waste water by the membrane distillation-crystallization technique. The results have shown good prospects for a membrane distillation application for treatment of industrial waste water.

EPITAXIAL CRYSTALLIZATION OF HIGH-DENSITY POLYETHYLENE ON POLYPROPYLENE IN SOLUTION-CAST FILMS

Epitaxial crystallization of high-density polyethylene (HDPE) on isotactic polypropylene (iPP) in solution-cast films has been investigated by electron microscopy. The specimen-tilt technique of electron microscopy has been used to study the structural relationship between HDPE and iPP crystals. HDPE exhibits different crystalline morphologies in the two basic types of iPP spherulite textures, cross-hatched and lathlike regions. In the former, the crystallographic c axis of HDPE lamellae is in the film plane, while in the latter, the c axis of HDPE crystallites is at an angle of about 50-degrees with the normal of the film. In both structural regions of iPP, however, the contact planes of epitaxial growth are (0 1 0) for iPP and (1 0 0) for HDPE.

THE CRYSTALLIZATION BEHAVIOUR OF BLOCK COPOLYMER/HOMOPOLYMER BLENDS I. INFLUENCE OF NONSPHERICAL MICELLE ON CRYSTALLIZATION BEHAVIOUR IN DILUTE SOLID SOLUTIONS

The effect of micelle on crystallization behaviour of dilute poly(methyl methacrylate-b-tetrahydrofuran) diblock copolymer/tetrahydrofuran homopolymer, dilute poly (ethylene-b-styrene-b-ethylene) triblock copolymer/ethylene homopolymer solutions has been studied. The results show that with the structural teansitions from spherical to nonspherical micelle in the blends, great changes in the nucleation and spherulite morphologies take place.

EFFECT OF MOLECULAR-WEIGHT OF PMMA ON BETA PHASE CRYSTALLIZATION IN HIGHLY ORIENTED PVF2 FILMS

Polyvinylidene fluoride (PVF_2) exhibits at least four crystalline phases (α, β, γ, and δ). Among them, β phase is the most important one because it is directly related to the piezoand pyro-electric activities of PVF_2. In recent years, more attention has been paid to the β

Crystal polymorphism in 1-butyl-3-methylimidazolium halides: supporting ionic liquid formation by inhibition of crystallization

Crystallization of 1-butyl-3-methylimidazolium chloride from mixed ionic liquid or ionic liquid-aromatic solution, and from the melt yields different crystalline polymorphs, the first direct evidence for inhibition of crystallization in ionic liquids by polymorphism.

Microstructural evolution of primary crystallization in diffusion-controlled grain growth

A model has been developed for evaluating grain size distributions in primary crystallizations where the grain growth is diffusion controlled. The body of the model is grounded in a recently presented mean-field integration of the nucleation and growth kinetic equations, modified conveniently in order to take into account a radius-dependent growth rate, as occurs in diffusion-controlled growth. The classical diffusion theory is considered, and a modification of this is proposed to take into account interference of the diffusion profiles between neighbor grains. The potentiality of the mean-field model to give detailed information on the grain size distribution and transformed volume fraction for transformations driven by nucleation and either interface- or diffusion-controlled growth processes is demonstrated. The model is evaluated for the primary crystallization of an amorphous alloy, giving an excellent agreement with experimental data. Grain size distributions are computed, and their properties are discussed.

Fractionated crystallization and fractionated melting of confined PEO microdomains in PB-b-PEO and PE-b-PEO diblock copolymers

The confined crystallization of poly(ethylene oxide) (PEO) in predominantly spherical microdomains formed by several diblock copolymers was studied and compared. Two polybutadiene-b-poly(ethylene oxide) diblock copolymers were prepared by sequential anionic polymerization (with approximately 90 and 80 wt % polybutadiene (PB)). These were compared to equivalent samples after catalytic hydrogenation that produced double crystalline polyethylene-b-poly(ethylene oxide) diblock copolymers. Both systems are segregated into microdomains as indicated by small-angle X-ray scattering (SAXS) experiments performed in the melt and at lower temperatures. However, the PB-b-PEO systems exhibited a higher degree of order in the melt. A predominantly spherical morphology of PEO in a PB or a PE matrix was observed by both SAXS and transmission electron microscopy, although a possibly mixed morphology (spheres and cylinders) was formed when the PEO composition was close to the cylinder-sphere domain transitional composition as indicated by SAXS. Differential scanning calorimetry experiments showed that a fractionated crystallization process for the PEO occurred in all samples, indicating that the PE cannot nucleate PEO in these diblock copolymers. A novel result was the observation of a subsequent fractionated melting that reflected the crystallization process. Sequential isothermal crystallization experiments allowed us to thermally separate at least three different crystallization and melting peaks for the PEO microdomains. The lowest melting point fraction was the most important in terms of quantity and corresponded to the crystallization of isolated PEO spheres (or cylinders) that were either superficially or homogeneously nucleated. This was confirmed by Avrami index values of approximately 1. The isothermal crystallization results indicate that the PE matrix restricts the crystallization of the covalently bonded PEO to a higher degree compared to PB.