Showing papers on "Polymer blend published in 2000"

Polymer synthesis and processing using supercritical carbon dioxide

Abstract: Carbon dioxide is a clean and versatile solvent for the synthesis and processing of a range of materials. This review focuses on recent advances in polymer synthesis and processing using liquid and supercritical CO2. The synthetic techniques discussed include homogeneous solution polymerisation, precipitation polymerisation, dispersion and emulsion polymerisation, and bulk polycondensation. The formation of porous polymers and polymer blends is also considered, and the specific advantages of CO2 in these processes are evaluated in each case. The use of CO2 as a solvent for polymer processing is reviewed from a materials perspective, with particular attention being given to the formation of polymers with well defined morphologies. The variable solvent strength associated with supercritical fluids has been utilised in areas such as polymer fractionation and polymer extraction. Plasticisation phenomena have been exploited for the impregnation and heterogeneous chemical modification of polymeric materials. The formation of microcellular polymer foams by pressure induced phase separation is considered, as is the use of CO2 for polymer particle formation, spray coating, and microlithography. The aim of the review is to highlight the wide range of opportunities available to the materials chemist through the use of carbon dioxide as an alternative solvent.

Mobility enhancement in conjugated polymer field-effect transistors through chain alignment in a liquid-crystalline phase

Abstract: A method is demonstrated by which liquid-crystalline self-organization in rigid-rod nematic conjugated polymers can be used to control the microstructure of the active semiconducting layer in solution-processed polymer thin-film transistors (TFTs). Enhanced charge carrier mobilities of 0.01–0.02 cm2/V s and good operating stability have been achieved in polyfluorene copolymer TFTs by preparing the polymer in a nematic glassy state and by aligning the polymer chains parallel to the transport direction with the help of an alignment layer. Mobility anisotropies of 5–8 for current flow parallel and perpendicular to the alignment direction have been observed that are of the same order of magnitude as optical dichroic ratios.

Self-Concentrations and Effective Glass Transition Temperatures in Polymer Blends

Abstract: In a miscible polymer blend the local environment of a monomer of type A will, on average, be rich in A compared to the bulk composition, φ, and similarly for B; this is a direct consequence of chain connectivity. As a result, the local dynamics of the two chains may exhibit different dependences on temperature and overall composition. By assigning a length scale (or volume) to particular dynamic mode, the relevant “self-concentration” φs can be estimated. For example, we associate the Kuhn length of the chain, lK, with the monomeric friction factor, ζ, and thus the composition and temperature dependences of ζ should be influenced by φs calculated for a volume V ∼ lK3. An effective local composition, φeff, can then be calculated from φs and φ. As lower Tg polymers are generally more flexible, the associated φ s is larger, and the local dynamics in the mixture may be quite similar to the pure material. The higher Tg component, on the other hand, may have a smaller φs, and thus its dynamics in the mixture w...

Mapping Polymer Heterogeneity Using Atomic Force Microscopy Phase Imaging and Nanoscale Indentation

Abstract: Polymer coatings often contain degradation-susceptible regions, and corrosion of the metallic substrate can occur directly underneath these regions. In this paper, the microstructure of model coating materials is investigated using atomic force microscopy (AFM). Specifically, AFM is used to study heterogeneity in thin film blends of polystyrene (PS) and polybutadiene (PB) as a function of annealing time at 80 °C. PS/PB blend films with thicknesses of approximately 250 nm are prepared by spin casting from solutions onto silicon substrates. Both topographic and phase imaging in tapping mode AFM are performed on these films under ambient conditions and at different force levels using a silicon tip. For certain force levels, phase imaging provides good contrast between the phase-separated PS and PB regions, primarily because of the large compliance difference between the two materials. This contrast decreases with increasing annealing time because thermal oxidation causes cross-linking in PB, and thus, the compliance of the PB region increases toward that of PS. Nanoscale indentation measurements are then made on the observed phase-separated regions to identify these regions as PS- and PB-rich and to better understand the influence of relative surface stiffness on the phase images. Cast and free-standing films of pure PS and pure PB are also studied as a function of annealing time using AFM, contact angle measurements, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). Results from studies of the individual PS and PB films are related to the AFM results for the blend films. The use of phase imaging for cure monitoring of polymers and for studies of chemically heterogeneous polymer systems is also discussed.

Miscibility Behavior of Polybenzimidazole/Sulfonated Polysulfone Blends for Use in Fuel Cell Applications

Abstract: Polybenzimidazole (PBI) and polysulfone (PSF) compose an immiscible polymer pair; the introduction however of functional groups such as sulfonate groups in the polymeric chain of PSF resulted in the formation of miscible blends with PBI. The miscibility behavior of a series of blends of PBI with sulfonated PSF (SPSF) at various sulfonation levels has been studied by dynamic mechanical analysis (DMA), FT-IR, and FT-Raman spectroscopy. DMA has shown that the sulfonation degree as well as blend composition controls the miscibility behavior of the studied system. In that respect, partially miscible or miscible blends were obtained when the sulfonation level is higher than 10 mol %. Since both polymers exhibit functional groups, which could participate in specific interactions, this possibility has been examined by FT-IR analysis. In absorption FT-IR spectra of PBI−SPSF specimens with high sulfonation degree and high PBI content, band shifts associated with the NH and sulfonate groups are accounted for the ind...

Microhardness of polymers

Abstract: Preface 1. Introduction 2. Microhardness determination in polymeric materials 3. Microhardness of glassy polymers 4. Microhardness of crystalline polymers 5. Microhardness of polymer blends, copolymers and composites 6. Microhardness of polymers under strain 7. Application of hardness techniques to the characterization of polymer materials Author index Subject index.

Polypropylene-based adhesive compositions

Abstract: An adhesive blend is described that can include a semi-crystalline copolymer of propylene and at least one comonomer selected from the group consisting of ethylene and at least one C4 to C20 α-olefin, the copolymer having a weight average molecular weight (Mw) from about 15,000 to about 200,000; a melt index (MI) from about 7dg/min to about 3000 dg/min as measured by ASTM D 1238(B), and a (Mw/Mn) of approximately 2. Various production processes are also described. Also described are adhesive compositions and methods for making adhesive compositions having polymers or polymer blends with melt flow rates (MFRs) equal to and above 250 dg/min at 230NC. Certain specific embodiments of the invention involve the use of a free radical initiator, e.g., a peroxide.

High-Throughput Measurement of Polymer Blend Phase Behavior

Abstract: Introduction. Because of successes in pharmaceuticals research, combinatorial and high-throughput methods for searching composition space1-3 have received increasing attention for the synthesis and discovery of new inorganic materials,4-6 catalysts,7,8 and organic polymers.9,10 Combinatorial methods can also allow rapid scanning of parameter space to make fundamental measurements and develop physical models for polymers. One limitation is the difficulty of preparing parallel libraries and performing highthroughput screening with conventional instrumentation and sample preparation. Recently, we developed a combinatorial technique for investigating polymer thin film dewetting phenomena by using sample libraries with orthogonal gradients in thickness and temperature to create a large database of dewetting information in a few hours of experiments.3,11 This report describes high-throughput measurement of cloud points for polymer blends utilizing a novel sample deposition method for creating two-dimensional composition (φ), temperature (T) libraries. In the sample libraries, T and φ are varied orthogonally, and optical microscopy is used to detect phase separation and microstructure. The cloud points determined with this high-throughput method are validated by comparison to conventional light scattering results and singlecomposition controls. Library Preparation. Three steps are involved in preparing composition gradient films: gradient mixing (Figure 1a), deposition (Figure 1b), and film spreading (Figure 1c). Two syringe pumps (Harvard PHD2000)12 (Figure 1a) introduce and withdraw polymer solutions to and from a mixing vial at rates I and W, respectively, where I ) W ) 1.7 mL/min. Pump I contained mass fraction xPS,O ) 0.080 of polystyrene (PS, Mr ) 96.4 kg/ mol, Mr/Mn ) 1.01, Tosoh)13 in toluene. The vial was loaded with an initial M0 ) 2.0 mL of mass fraction xPVME,O ) 0.080 of poly(vinyl methyl ether) (PVME, Mr ) 119 kg/mol, Mr/Mn ) 2.5)14 in toluene from pump W. The infusion and withdrawal syringe pumps were started simultaneously while vigorously stirring the vial solution, and a third syringe, S, was used to manually extract solution from the vial. A mass balance of the transient mixing process gives the mass fraction of PS, xPS, in the vial at any time t (minutes) as

Morphology development and control in immiscible polymer blends

Abstract: Most immiscible polymer blends are produced by melt compounding in extruders. The melting and mixing process can generate morphologies ranging from disperse drops to fibers to lamella to cocontinuous structures. Controlling these morphologies is critical to performance of the final blend. This paper reviews recent research, from our group which reveals how these morphologies develop during compounding and how they can be stabilized with reactions at the interface between the two polymers.

Novel Microporous Poly(vinylidene fluoride) Blend Electrolytes for Lithium‐Ion Batteries

Abstract: In the present paper, novel microporous poly(vinylidene fluoride)‐hexafluoropropylene copolymer (PVDF-HFP) blend electrolyte/electrode films were obtained as the result of phase separation between PVDF-HFP and polyethylene oxide (PEO) oligomer additives, which were cast from a common solvent. Upon solvent evaporation and removal of the additives, an interconnected microporous morphology was formed. The additives can either be removed from the films by vacuum evaporation or methanol extraction. The conductivities of the methanol extracted microporous (pore sizes range from 1 to 5 μm) films formed from PVDF-HFP/PEO oligomer blends after electrolyte activation are more than 70% higher than those of the methanol extracted nanoporous (pore size in range from 10 to 100 nm) films prepared from PVDF-HFP/dibutyl phthalate blends. Microporous films formed by vacuum evaporation had conductivities similar to solvent extracted nanoporous separators. Battery performance tests were carried out using lithium cobalt dioxide as the cathode and mesocarbon microbeads as the anode. The cells prepared using extracted microporous PVDF-HFP/PEO oligomer blend films as separators show more than 40% higher specific discharge capacity at the C/2 rate, and 70% higher rate capability than those using extracted nanoporous separators. © 2000 The Electrochemical Society. All rights reserved.

Blends of thermoplastic starch and polyesteramide: Processing and properties

Abstract: The blending of thermoplastic starch (TPS) with other biodegradable polyesters such as polyesteramide could be an interesting way to produce new biodegradable starch-based materials. Different mixes of wheat starch and polyesteramide (BAK) were melt blended by extrusion. After pelletization, granules were injection molded to produce test specimens. A range of blends was studied with glycerol (plasticizer)/starch content ratios varying from 0.14 to 0.54. BAK concentrations were up to 40 wt %, TPS remaining as the major phase in the blend. Various properties were examined with mechanical, thermomechanical (dynamic mechanical thermal analyzer) and thermal (differential scanning calorimetry) analysis. Hydrophobicity was determined with contact angle measurements. Thanks to the knowledge of the properties of each polymeric system, we analyzed the blends' behavior by varying each component concentration. The material aging was also studied. We showed that structural changes occurred during several weeks after injection. We noticed a certain compatibility between both polymeric systems. The addition of BAK to TPS matrix allowed us to overcome the weaknesses of pure thermoplastic starch: low mechanical properties, high moisture sensitivity, and high shrinkage in injection, even at 10 wt % BAK. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1117–1128, 2000

Medical devices made from polymer blends containing low melting temperature liquid crystal polymers

Abstract: A medical device, at least a portion of which is composed of a polymeric material in which the polymeric material is a melt blend product of at least two different thermoplastic polymers, one of the thermoplastic polymers being a thermoplastic liquid crystal polymer (LCP) having a melting point of less than 250° C. The portion of the device made from the melt blend may be a catheter body segment or a balloon for a catheter. The LCP blends suitably also include a non-LCP base polymer having a melting point in the range of about 140° C. to about 265° C.

Critical Experimental Comparison between Five Techniques for the Determination of Interfacial Tension in Polymer Blends: Model System of Polystyrene/Polyamide-6

Abstract: A critical review and experimental comparison between different techniques for the determination of interfacial tension are presented for a model polymer pair. Five experimental methods were applie...

Effects of Annealing on the Surface Composition and Morphology of PS/PMMA Blend

Abstract: Films of polystyrene (PS) and poly(methyl methacrylate) (PMMA) blend have been annealed at a temperature above their glass transition temperatures for up to 48 h. Surface chemical compositions of the cast and annealed films were measured by X-ray photoelectron spectroscopy (XPS) while surface topographical changes were followed by atomic force microscopy (AFM). The blend films spin-cast from chloroform produce nonequilibrium surfaces with a significant excess of PMMA. The polymer component with a lower surface free energy, PS, is shown to segregate to the surface upon annealing. The PS surface concentration of the films, containing 50% PS:50% PMMA in the bulk, was evaluated using the ester peak in XPS C 1s spectra (sampling depth ∼ 9 nm) and found to increase from ∼5% (freshly spin-cast film) to a saturated level of ∼47% after 17 h of annealing. AFM imaging reveals evolution of blend morphology with annealing time. The spin-cast films prior to annealing exhibit pitted topography with typical pit size of ∼...

Poly(ε-caprolactone) Blends

Abstract: Poly(e-caprolactone) is unusual in being considered compatible with several polymers to produce useful polymer blends. Such blends have been widely investigated both with regard to producing blends with enhanced physical or mechanical properties and to plasticizing rigid polymers with a polymeric plasticizer which will not leach from its substrate. These several materials have potential practical applications. In addition, blends of poly(e-caprolactone) are probably the most widely investigated series of blends involving one or more crystallisable components and, in this context, provide information which enhances the general understanding of polymer blends.

Poly (D,L-lactic acid)/poly (∈-caprolactone) blend membranes: preparation and morphological characterisation

Abstract: With the aim of exploring possible application of the concept of blend compatibilisation into the field of biodegradable membranes, a study of the influence of random copolymer poly(D,L-lactide-co-∈-caprolactone) on the properties of corresponding homopolymer blends has been conducted. Blends of plain homopolymers and blends containing 5 and 10 wt% of a copolymer of suitable composition have been prepared in the melt and characterised for their molecular interactions using thermal, dynamic-mechanical, mechanical (tensile tests) and morphological analyses. The blends are characterised by a good dispersion of the poly-∈-caprolactone (PCL) minor phase into the poly(D,L-lactic acid) (PDLLA) matrix and better mechanical properties compared to plain PDLLA, and such characteristics further improve when adding the copolymer. Microporous blend membranes consisting of PDLLA and PCL were then prepared by a phase inversion method and characterised by scanning electron microscopy. The addition of compatibilising agent led to a highly homogeneous structure, while in absence of compatibiliser a clear phase separation occurred.