Maila Castellano

Analysis of Calorimetric Curves Detected During the Polymorphic Transformation of Isotactic Polybutene-1

Multiple endotherms detected on heating melt-crystallized i-polybutene-1(PBu-1) are associated to the polymorphic transformation from the tetragonal (Form II) to the hexagonal modification (Form I). During this transformation, a progressive increase of the intensity of the high temperature endotherm, at the expenses of that pertaining to the low temperature one, is observed in DSC heating curves. Depending on molecular characteristics of the constituent chains and crystallization conditions, the two endotherms may exhibit some extent of superposition. In these cases, a reliable procedure to analyze the whole thermal curve must be found and adopted in order to follow the progress of the transformation in quantitative terms.The same set of thermal curves, detected after various ageing times of melt-crystallized i-PBu-1, has been analyzed according to four different approaches. Comparison of the results shows that, with the exception of the analysis based on the ‘partial area’ routine, available to most instruments, all methods lead to equivalent results. The simplest approach, based on the mass balance during structural transformation, should be preferred whenever constant overall degree of crystallinity can be assumed throughout the whole process.

Reactive blending of polyamide 6,6 and Vectra A

In this paper, blends of Nylon 6,6 with the liquid crystal polymer Vectra A950 are considered; specifically we focused our attention on Nylon 6,6 modifications by interchange reactions that can occur in the melt, as a function of mixing conditions and blend compositions. Two matrix samples have been used, characterised by a slightly different relative amount of amine and carboxylic end groups, being the latter predominant in both cases. The dried polymers Nylon 6,6/Vectra, combined in weight ratios between 95/5 and 50/50, were subjected to reactive blending with different methods (single-screw extruder, Brabender, pyrex reactor). Pure Nylon samples have been also investigated as reference materials. The soluble Nylon 6,6-rich fraction of each blend was separated from the insoluble Vectra-rich one and used for molecular and spectroscopic characterisations. Thermal and morphological analyses, as well as testing of tensile properties, were carried out on the blends. Evidences of the occurrence of interchange reactions are given and the most probable ones are suggested.

Investigation on elastomer–silica interactions by inverse gas chromatography and image analysis aided transmission electron microscopy

A study on the interactions between silica and elastomers typically used in tire tread production has been carried out by inverse gas chromatography (IGC) and image analysis aided transmission electron microscopy (TEM/AIA). At infinite dilution, IGC has been performed using precipitated silica as the stationary phase to determine its surface properties and to calculate the adsorption free energy and enthalpy of low molecular weight analogues of elastomers, used as the eluates. Vulcanized samples based on different matrices employed in tire formulations, i.e., natural rubber, butadiene rubber, and styrene-butadiene rubber, have been investigated by TEM/AIA to determine the dispersion of the filler within the matrix as well as to achieve quantitative information on aggregate size and shape distribution of silica and, consequently, on the polymer-filler interactions. A comparison between thermodynamic predictions deduced by IGC and the results from morphological analysis concerning filled compounds shows a very satisfactory agreement.

Reactive blending of polyamide 6,6 and vectra A, 2. Role of a bifunctional epoxy coupler

In a previous paper Nylon 6,6/Vectra A blends have been prepared and investigated; in particular, our attention has been focused on Nylon 6,6 modifications due to interchange reactions that occur in the melt, as a function of mixing conditions and blend compositions, and improve the compatibility of the blend. The results indicated that only a small amount of copolymeric species form because of the low reaction kinetics and unfavorable physical and rheological aspects. In order to overcome these limits, a further research on Nylon 6,6/Vectra A blends has been carried out to test the role of modified processing conditions in the presence of a reactive additive able to improve the extent of reactions between blend components and the melt viscosity of the polyamide matrix. The potential of a Nylon 6,6 sample with predominant -NH 2 end-groups on its reactive blending with Vectra with or without the reactive third component has been investigated. Nylon and Vectra, combined in weight ratios between 90/10 and 50/50, were subjected to reactive blending with different methods (a laboratory Pyrex reactor, a singlescrew extruder, and a Brabender mixer). Neat Nylon samples have been also investigated as reference materials. Thermal and morphological analyses were carried out on the blends. The soluble Nylon 6,6-rich fraction of each blend was sepa- rated from the insoluble Vectra-rich one, and both were used for spectroscopic characterizations; mixed Nylon-Vectra copolymers have been recognized in both the soluble and insoluble fractions of the blends.

Styrene–diene block copolymers as embedding matrices for polymer-dispersed liquid crystal films

Abstract Composite films made of the nematic mixture E7 or the nematic single component K15 embedded in styrene–diene triblock copolymers have been prepared by the solvent cast method from homogeneous solutions; their phase separation behaviour has been investigated by calorimetric and morphological analyses as a function of mixture and matrix compositions, diene nature, casting solvent and evaporation time. Three copolymeric samples of comparable molecular weight have been used; two of them, based on polybutadiene, differ in their styrene content (30 and 55% by weight), in the third the major fraction of soft segments (75%) is made of polyisoprene. Films based on homopolymeric polystyrene and polybutadiene have been also prepared and tested as reference materials. The results reveal a substantially different solubility of the liquid crystal (LC) in the two phases of the copolymer micro-heterogeneous structures. The droplet size, shape and distribution that characterise the film morphology change considerably upon increasing the LC concentration in the blends, varying the casting solvent or lowering the evaporation rate; moreover a significant role is played by the nature of the elastomeric fraction. The dependence of morphological features on the various parameters is tentatively discussed in terms of both the affinity between the casting solvent and the matrix blocks and the critical surface tensions of LC and copolymer components.

A Morphometric Investigation by TEM/AIA on Elastomer-Based Compounds Filled with an Untreated Precipitated Silica

Abstract An accurate morphological investigation has been carried out on vulcanized compounds based on different matrices, butadiene rubber, natural rubber and styrene-butadiene rubber, filled with 35phr of a precipitated silica. The analysis has been performed by using transmission electron microscopy (TEM) and automated image analysis (AIA) to achieve quantitative information on the filler dispersion. Significant differences in the aggregate size and shape distribution of silica within the different matrices which, in principle, can be related to the polymer-filler interactions, have been found. The results are in a very satisfactory agreement with thermodynamic predictions obtained by inverse gas chromatography. The use of two complementary techniques, TEM/AIA, allows attainment, in a reasonably short time, quantitative information on the filler dispersion and, consequently, on the performances of these elastomers-based composite materials.

Fluoro-modified elastomeric polyurethanes: effects of synthesis procedure on properties and morphology

Fluorinated polyurethanes characterized by a segmented structure, containing hard segments based on 4,4′-methylenebis (phenylisocyanate) (MDI), chain-extender 1,4 n-butandiol (BDO), and soft blocks like perfluoropolyether (PFPE), and poly-ε-caprolactone (PCL) were synthesized keeping constant the equivalent ratio among reagents, but varying the experimental conditions. Copolymers show a complex micro- and macrostrucrture with different morphology and calorimetry, similar tensile properties and undistinguishable, but strongly upgraded surface properties. The morphology should be governed by the different fluorine content of the polymeric chains along with the hard segment structure; tensile properties are little influenced by the morphology. All these characteristics are interpreted in terms of polymerization procedure which results to be a key parameter for ruling the composition of the different polymeric chains, due to a very limited mutual solubility of the reagents. Surprisingly, a beneficial effect of the catalyst dibutyltindilaurate for the increase of the reaction kinetics among segregated phases in the reaction mass was observed.

Alginate-polymethacrylate hybrid hydrogels for potential osteochondral tissue regeneration

Porous scaffolds based on alginate-polymethacrylate hybrid hydrogels intended for bone and cartilage regeneration were prepared through controlled calcium ions diffusion from an agar mould. The double interconnected network of such materials combines into a single porous structure maintained by both noncovalent crosslinks (calcium ions for alginate) and covalent crosslinks (polymethacrylate crosslinked by the addition of mixtures of mono and bifunctional monomers). The alginate component ensures the appropriate micro-environment to mimic the extra-cellular matrix, whereas the polymethacrylate improves the mechanical performances of the hybrid hydrogels, helping to overcome the mechanical limitations of the alginate component. Morphological characterization and porosity analysis of the hybrid scaffolds were assessed by scanning electron microscopy and micro-computed tomography. Relative concentration and distribution of calcium ions were evaluated by atomic absorption and dispersive X-ray analysis, respectively. Uniaxial compressive mechanical tests were conducted to evaluate the compressive elastic modulus of the hybrid hydrogels that was correlated with their swelling ratio and crosslinking degree. As was envisaged a much higher modulus (about seven times) was obtained for the hybrid Alg/HE hydrogel than with alginate alone.

Dependence of surface properties of silylated silica on the length of silane arms

Amorphous precipitated Zeosil 1165 MP silica was silylated with low grafting degrees of organosilicons bearing different alkoxy and hydrocarbon tails, like monomethoxy(dimethyl)octadecylsilane (DMODMS), monomethoxytrimethylsilane (TMMS), trimethoxymercaptopropylsilane (MPTS), and 3-octanoylthio-1-propyltriethoxysilane (NXT®). Thermogravimetry and Elemental Analysis were used to determine the degree of silane grafting and the final number of free silanol OH groups/nm2 on the modified Zeosil surface. Free energy, enthalpy and entropy of adsorption of hydrocarbon probes were determined by Inverse Gas Chromatography at infinite dilution and dispersive component,

EPR spin labelling studies of molecular dynamics in elastomer-silica composites

\gamma_{s}^{d}