Epoxy-layered silicates nanocomposites based on diglycidyl ether of bisphenol A and an anhydride-curing agent have been successfully synthesised. A manufacturing process using hand lay-up, vacuum ...bagging, and hot pressing techniques was developed to produce glass fibre-reinforced laminates with this nanocomposite matrix. Transmission electron microscopy indicated that silicate layers dispersed in the epoxy matrix present a long-range order with an interlamellar spacing of about 9
nm. X-ray diffraction analysis confirmed this nanostructure both in the nanocomposites and in the fibre-reinforced composite based on the same matrix. Scanning electron micrographs of the laminate with a nanocomposite matrix showed that nanolayers are apparently sticking at the surface of the glass fibre, improving possibly in this manner the interfacial properties of the fibres. Flexural testing of the laminates showed that the nanolayers improve the modulus and the strength, respectively, by 6% and 27%. Dynamic mechanical analyses of the epoxy and nanocomposite plates and their corresponding laminates showed a systematic glass transition temperature decrease of the nanocomposite based materials. This explains probably the larger water uptake observed at 50
°C in the plate and the laminate based on a nanocomposite matrix as compared with those based on the pristine epoxy.
A high performance liquid chromatography column (HPLC) Hypercarb® packed with porous graphite has proven to discriminate polyolefin molecules due to differences in their adsorption and desorption ...behaviour. While linear polyethylene (PE) and syndiotactic polypropylene (sPP) are adsorbed on the graphite packing, isotactic polypropylene (iPP) is not adsorbed. The column operates at 160°C with 1-decanol as sample solvent and mobile phase. We have now tested this HPLC system for separations of random propene/1-alkene and ethylene/1-hexene copolymers: While copolymers of propene with 1-butene, 1-hexene and 1-octene copolymers eluted in size exclusion mode without adsorption, propene/1-octadecene and ethylene/1-hexene copolymers are strongly retained and eluted only after application of a linear gradient starting from 1-decanol and ending with pure 1,2,4-trichlorobenzene. The retention of propene/1-alkene (>11 carbons in the side chain) copolymers increases with the concentration of comonomer, making this HPLC system suitable to separate these copolymers according to their chemical composition. In contrast, the retention of ethylene/1-hexene samples decreases with increasing 1-hexene content. Branching in this case shortens the length of continuous methylene sequences of the polymer backbone, which are expected to adsorb in a planar conformation to the graphite layers. This is the first report on the separation of short chain branched polyolefins by high-temperature adsorption liquid chromatography.
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The use of spin-diffusion NMR for the measurement of domain sizes in multiphase materials is becoming increasingly popular, in particular for the study of heterogeneous polymers. Under conditions ...where
T
1 relaxation can be neglected, which is mostly the case at high field, analytical and approximate solutions to the evolution of spin diffusion are available. In order to extend the technique to more general conditions, we performed a comprehensive study of the diffusion of magnetization in a model copolymer at low field, where
T
1 tends to be of the same order of magnitude as the typical spin-diffusion time. In order to study the effects of
T
1 and to delineate the optimal
T
1 values for back correction prior to applying the initial-rate approximation, we developed a numerical simulation based on the diffusion equation and including longitudinal relaxation. We present and discuss the limits of simple correction strategies for initial-slope analysis based on apparent relaxation times from saturation-recovery experiments or the spin-diffusion experiments themselves. Our best strategy faithfully reproduces domain sizes obtained by both TEM investigations and full simultaneous fitting of spin-diffusion and saturation-recovery curves. Full fitting of such independent data sets not only yields correct domain sizes, but also the true longitudinal relaxation times, as well as spin-diffusion coefficients. Effects of interphases with distinct mobility on spin-diffusion curves, as well as practical hints concerning the reliable component decomposition of the detected low-resolution FID signal by help of different magnetization filters are also discussed in detail.
The present paper aims to study the possibility to modify the properties of poly(vinyl alcohol) (PVA) hydrogels prepared in the presence of different salt types (Na2SO4, NaCl and NaNO3) in order to ...extend the nature of the salts already used in obtaining films or gels, to expand their concentration domains and to explain the increase of film strain, concomitantly with the increase of their crystallinity. The morphology of the PVA based hydrogels has been studied by Scanning Electronic Microscopy (SEM), the interaction between the PVA macromolecular chains and salts has been determined by Fourier Transform Infrared Spectroscopy (FTIR), while the mechanical properties of the cryogels have been investigated by oscillatory dynamic mechanical measurements. The gels swelling in water have been monitored by gravimetric method in order to evidence the alteration of the PVA cryogel properties such as crystallinity and porosity determined by the salt addition to the initial PVA aqueous solution. The data reported show that the ions present in the PVA solution influence the interaction between PVA-water and PVA-PVA chains; their influence on the salt-based PVA hydrogels follow the Hofmeister lyotropic series.
Blends of two polymers, poly(ethene-co-styrene) (PES) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), were examined with tapping mode atomic force microscopy (AFM) using various values of the ...driving amplitude A 0 and set-point amplitude ratio r sp = A sp/A 0, where A sp is the set-point amplitude. In height and phase images of PPO/PES blend samples, the relative contrast of chemically different regions depends sensitively on the r sp and A 0 values. As the tip−sample force is increased from small to large, both phase and height images of PPO/PES blend samples can undergo a contrast reversal twice. This makes it difficult to assign the features of height and phase images to different chemical components without performing additional experiments. Phase and height images were interpreted by analyzing several factors that affect the dependence of phase shift and amplitude damping on r sp and A 0.
The crystallization behavior of poly(1-butene) (P1b) was investigated by polarized light microscopy (PLM), atomic force microscopy (AFM), wide-angle X-ray scattering (WAXS), dilatometry, and also by ...time- and temperature-resolved small-angle X-ray scattering experiments (SAXS). Observations in the PLM indicate a temperature-dependent change in the mechanism of crystallization. When crossing a certain critical crystallization temperature, the morphology changes from spherulites to quadratic, platelike single crystals. Investigations of samples with different molar mass show that the transition temperature is molar mass-dependent; on decreasing the molar mass the transition shifts to lower temperatures. As proved by WAXS, both the spherulites and the single crystals are of the metastable form II. The morphological change is also observed in AFM images obtained after a rapid cooling of the samples to room temperature; the difference in the morphological appearance is preserved through the transformation from form II to form I. According to dilatometric measurements, the change in the crystallization mechanism leads to variations in the temperature dependence of the crystallization rate and also to a steplike increase in the crystallinity. The results of SAXS experiments show that the formation of P1b crystallites is governed by the same general laws as for other polymers studied before. Both the crystallization temperature, T c, and the melting temperature, T f, are linearly dependent on the reciprocal crystalline layer thickness, d c -1, but with different slopes and different limiting temperatures for d c -1 → 0. The observations are again indicative for a crystal development in two steps: First an initial form appears which then transforms into the final lamellar crystallites. As a new feature, in direct correspondence to the two different crystallization mechanisms observed microscopically, two different crystallization lines (d c -1 vs T c) show up, indicating the occurrence of two different initial states. On the other hand, only one common melting line (T f vs d c -1) is found, which means that the two crystallization mechanisms produce crystallites with similar surface free energies. We discuss the peculiar crystallization properties of P1b by comparing the radius of gyration R g of the chains in the melt with the crystal thickness d c and propose that the change in the crystallization mechanism could be due to a change from folded-chain to chain-extended crystallization, taking place when d c gets larger than R g.
Medium to high molar mass isotactic polypropenes with different amounts of stereoirregularities were characterised with respect to their crystallisation behaviour and for comparison a random ...copolymer of ethene and propene with 5.8
wt% ethene is used. The influence of stereoregularity and crystallisation temperature on the γ-content of the crystallised samples is studied by means of wide angle X-ray scattering, atomic force microscopy and light microscopy. The paper deals also with the temperature rising elution fractionation of an i-PP with large amounts of stereoirregularities and the influence of a nucleation agent on the γ-content. It is shown that effects which render the chainfolding in lamellae more difficult, enhance the formation of the γ-modification. The necessity of chainfolding in isotactic polypropene is discussed in terms of a model that is based on the number of chains that emerge from the lamellae surfaces of the α- and the γ-modification, respectively.
Blends of poly(styrene)-block-poly(ethene-co-but-1-ene)-block-poly(styrene) (SEBS) with isotactic polypropylene (i-PP) and with atactic polypropylene (a-PP) were prepared under different thermal ...treatments. On the basis of the phase imaging of tapping-mode atomic force microscopy (TMAFM), we investigated the nanostructures and the morphologies of these blends as well as their dependence on blending history. The observed macrophase separation in i-PP/SEBS blends is caused by the incompatibility of the two polymer components. The microphase separation of the SEBS component depends on the thermal treatment. The morphology of a-PP/SEBS blends exhibits domains that span a wide range of sizes from 15 μm down to 15 nm. Our work shows that TMAFM phase imaging is an important and competitive tool for studying the microphase separation of polymers.
The reaction of hydrazine with ethyl glycolate results in 1,2‐bisglycoylhydrazine, a monomer that was used for the lipase‐catalyzed synthesis of biodegradable poly(ester hydrazide)s. The polymers ...derived from the hydrazide‐containing monomer and vinyl‐activated adipic, suberic, and sebacic acid, respectively, showed low melting temperatures of 136 to 141 °C and are thermally stable up to 300 °C. The aliphatic poly(ester hydrazide)s (PEHs) are highly crystalline, as proven by polarization microscopy and atomic force microscopy. Further, the PEHs represent the first described biodegradable poly(hydrazide)s. They degrade in the presence of lipase at 37 °C within a few weeks.
Synthetic route to poly(ester hydrazide)s.
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