1999 рік

Processing of intractable polymers using reactive solvents (monomers) has been studied extensively in our laboratory, notably the system poly(phenylene ether) (PPE)/epoxy (resin). PPE can be dissolved at elevated temperatures in epoxy resin and the solution can be easily transferred into a mould or into a fabric. Upon curing the epoxy resin, phase separation and phase inversion occurs and the originally dissolved PPE becomes the continuous matrix phase. The dispersed (cured thermoset) epoxy particles become an integrated part of the system and could act as fillers or as toughening agents, depending on the type of epoxy resin used. An important parameter for the (ultimate) physical and mechanical properties is the size of the dispersed particles. The aim of the present study is to control the morphology development in order to produce a dispersed phase in the sub-micron to nanometre range. The size of the dispersed phase will be determined by the competition between the coarsening rate, e.g. by the coalescence of dispersed droplets, and the vitrification and/or gelation rate induced by curing. For the coarsening process, the viscosity of the system plays an important role which is usually mainly determined by the temperature. However, in the case of PPE/epoxy, the viscosity can be controlled at a chosen curing temperature by adding polystyrene. The ternary phase diagram shows that the miscibility of PPE–polystyrene (PS) is retained upon the addition of epoxy at relatively low concentrations. However, thermally induced phase separation upon cooling occurs for solutions with an epoxy content of 30 wt% and more. Upon curing, a two phase morphology is obtained in which the PPE–PS phase acts, as expected, as one single phase. The size of the dispersed phase can be decreased by one order of magnitude if curing is performed at the glass transition temperature, Tg, of the initial solution, attributed to the high viscosity at Tg that slows down coalescence. During the additional post-curing steps, necessary to reach a maximum epoxy conversion, these original morphologies are maintained. In conclusion, by controlling the polymerisation temperature, relative with reference to the Tg of the original solution, the final morphology of the chemically induced phase separated systems can be tuned.

Детальніше...  

Co-continuous morphologies in a blend of poly(ether–ester) and polystyrene break up into a droplet/matrix morphology when subjected to a shear flow in a rheometer with a cone–plate configuration and are therefore not stable under shear. It is shown that the capillary number at these flow conditions is too small to maintain stable extended structures that are necessary for a co-continuous morphology. Co-continuity at such flow conditions is limited to the point of phase inversion, contrary to the range of co-continuity usually found after extrusion.

Детальніше...  

The substution reaction of poly(viny1 chloride) (PVC) with sodium thiobenzoate has been performed in two series of solvents differing in molecular structure. One series includes cyclohexanone and the other includes more basic solvents, such as N-methylpyrrolidone and N,Ndimethylformamide. The evolution of unreacted iso-, hetero- and syndiotactic triad contents with degree of substitution has been followed by 13C NMR spectroscopy. In the former type of solvent, the mm located at the end of long isotactic sequences react exclusively. Then, the heterotactic triad mr is involved in the reaction. The latter type of solvent does not discriminate between either structure from the outset of the reaction, as is the case for the former group of solvents at conversions higher than roughly 7%. Only a small fraction of mmr tetrads reacts occasionally by the central chlorine of its mr triad instead of the mm. Through the foregoing results, the mechanisms of substitution, as proposed in a previous work, have been confirmed to be independent of the type of solvent utilized. The approach to the local configurational nature of the mechanisms is discussed on the grounds of the FTIR results. The same reaction has also been studied in aqueous suspension in the presence of a phase-transfer catalyst. In this experimental system, the behaviour of the modified samples in relation to the evolution of the content of mmr and rrmr structures rather approximates to that obtained for basic solvents. On the whole, the results, as analysed in the light of earlier work, provide some novel ideas on the role of the tacticity-dependent microstructure and the related local conformations in the chemical reactions of PVC.

Детальніше...  

The surface morphology of compression-moulded PP/PET blends is investigated and compared to the bulk morphology. Before compression moulding the blends are prepared by melt mixing in a Brabender plastograph. Model experiments are developed to analyse the influence of the processing conditions and of the nature of the moulding surface on the surface and bulk morphologies. Films are prepared under different shear conditions with PI as the moulding surface. At low shear rates the bulk and surface morphologies (size and composition) are very similar. At high shear rates and when the PET is the dispersed phase, the nodules at the surface are highly deformed in the flow direction while the PET nodules remaining in the bulk are undeformed. The PET concentration at the surface increases above the bulk concentration. When PP is the dispersed phase, the surface concentration is much lower than the bulk concentration. The observed surface morphology for samples prepared with high shearing can be explained by an interplay between the flow field and the affinity of the dispersed phase for the moulding surface.

Детальніше...  

Mobility and orientation of amorphous chains in cold drawn films of isotactic polypropylene (PP) are studied by 2H-NMR as a function of the annealing temperature. It is shown that the deformation is not affine. The relaxation of amorphous chains in materials annealed with free and clamped ends appears respectively at T* < Tg 1 508C and at Tac < 808C. Above these transition temperatures, corresponding to the onset of the chain mobility in the amorphous and crystalline states, the orientation of amorphous chains decreases linearly with the temperature. These reports show that the 2H-NMR technique provides important information on the plastic deformation of semi-crystalline polymers.

Детальніше...  

Poly(c-caprolactone) (PCL) was found to be miscible with uncured polyester resin, i.e. oligoester (OER), as shown by the existence of a single glass transition temperature (T,) in each blend. However, PCL was judged to be partially miscible with crosslinked polyester resin (PER) which was concluded from the results of thermal analysis. Fourier-transform infrared (FT-i.r.) studies revealed that intermolecular hydrogen bonding interaction between the components is an important driving force to the miscibility of PCL/OER blends and the partial miscibility of crosslinked PCL/PER blends. The importance of entropy contribution to the miscibility of thermosetting polymer blends is also shown from the FT-i.r. results. The spherulitic morphology of the blends was remarkably affected by crosslinking. The birefringent spherulites were observed in the uncured PCUOER blends, whereas a distinct pattern of extinction rings, which was absent either in the pure PCL or in the uncured PCUOER blends, was apparent in the crosslinked PCL/PER blends.

Детальніше...  

The styrene-crosslinked mixed polyesters derived from maleic anhydride, 2,2-di-(4-hydroxypropoxyphenyl)propane and 1,2-propylene glycol were studied by means of high-resolution 13C n.m.r. in the solid state (CP/MAS). The proton spin–lattice relaxation time, T1H and H spin–lattice relaxation time in the rotating frame, T1r were determined and compared with corresponding values calculated for hypothetical mixed ester/styrene copolymers. The results, found to be consistent with T g data, were interpreted in terms of the mixing, copolymer and crosslinking effects.

Детальніше...  

Macromonomer with styrenic polymerizable group was synthetized by anionic polymerization of ethylene oxide initiated by a mixture of potassium p- and m-vinylbenzyl alcoholate. The corresponding alcohol was prepared by modified two-step method described by Bamford et al. (Polymer 1973;14:330) using vinylbenzyl chloride as a starting material. Emulsion polymerization of styrene was carried out in the presence of either a styrenic macromonomer of poly(ethylene oxide) or conventional surfactants ethoxylated alkylphenol. In all cases small particle size of less than 75 nm in diameter were produced.

Детальніше...  

Reactive blending of polysulfone (PSU) and polyamide 6 (PA) was carried out at 2O:SO (PSU-PA) wt. ratio using a gram-scale mixer (Mini-Max Molder). Three PSUs with different functional groups were prepared and used: maleic anhydride-grafted PSU (PSU-MAH), carboxylic acid-grafted PSU (PSU-COOH) and phthalic anhydride-terminated PSU (PSU-PhAH), having almost same molecular weight (M, = ca. 20 k) and functional group content (ca. 90 pmole g-l). The change in PSU particle size with mixing time was investigated by light scattering and transmission electron microscopy. As expected, all reactive systems yielded finer particles via faster size reduction process, compared with non-reactive system. Attainable particle diameters were: ca. 1 pm for non-functionalized PSU, ca.

Детальніше...  

PS, PP and Nylon plate parts designed with gas channels having five different types of cross-section but with same section area were gasassisted injection moulded (GAIM). Mechanical properties of GAIM parts were investigated via tensile and bending tests. Effects of part thickness, shape and associated dimensions of gas channels on tensile and bending properties of GAIM parts were examined. It was found that maximum tensile load and ultimate tensile stress show only slight influence from gas channel design and part thickness except Nylon parts which exhibit significant dependence on part thickness due to degree of crystallinity. Gas channel design, introducing additional moment of inertia, results in part structural reinforcement. Part stiffness and maximum bending load basically increases linearly with the moment of inertia and the section modulus of the plate, respectively. Gas channel design attached with top rib (shapes D and E) show the best effect of structural reinforcement. For brittle PS parts, plates with semicircular gas channel (shape A) exhibit maximum flexural strength. PS parts with rectangular gas channel design (shape B) can absorb more bending energy than the other designs. The present study provides part designers with a design guideline for choosing the most effective gas channel design to achieve a specific objective of part structural performance.

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