Wide‐angle x‐ray diffraction studies are reported on polyacrylonitrile (PAN) (homopolymer powder and fiber samples) and its random copolymers with methyl methacrylate (MMA) and methacrylonitrile (MAN). A new method of determination of degree of order which involves resolution of the individual maxima in the diffraction pattern is described and compared with the methods used in the literature. Comparison of the results on untreated fibers with those on untreated homopolymer powder samples, and the effect of heat treatment, suggest the molecular rod conformation of the PAN molecules in the amorphous phase. Heat treatment or the orientation induces a parallel alignment of the molecular rods in the amorphous phase, similar to the cyrstalline structure of PAN. Copolymerization with both the comonomers MMA and MAN produces qualitatively similar effect on the structure of PAN, which depends on the comonomer content. Below a critical comonomer content c* (c* = 12 mol % for MMA and 25 mol % for MAN comonomer), the crystalline lattice remains that characteristic of PAN, whereas above the critical comonomer content some modification in the crystalline lattice is apparent.

The deformation and fracture behavior of several dynamic vulcanizate blends of isotactic polypropylene with ethylene‐propylene‐diene rubber (EPDM) was examined and compared with those of uncrosslinked blends of PP/EPDM. These blends were prepared by melt mixing in an internal mixer at 190°C in a composition range of 10–40 wt % EPDM rubber. The variation in yield stress, the strength of fibrils of the craze, and the number density of the EPDM rubber domains (morphology fixation) that are dominant factors for enhancing interfacial adhesion and toughness in dynamic vulcanizate blends were evaluated. The ductility and toughness of these materials were explained in light of the composition between crack formation and the degree of plastic deformation through crazing and shear yielding. The physicomechanical properties including the hardness, yield stress, Young's modulus, percentage elongation, impact strength, flexural strength, and flexural modulus of dynamic vulcanized blends were found to be consistent and displayed higher values compared with uncrosslinked blends. The nucleation effect of the crosslinked particles and the decrease of crystallinity of the EPDM rubber were also considered to contribute to the improvement in the impact strength. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2089–2103, 2000

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This article investigates the synthesis of superabsorbent hydrogels (SAHs) based on acrylamide and acrylic acid by solution polymerization in the presence of N,N 0 -methylenebisacrylamide (NMBA) as a cross-linker and potassium per sulphate as initiator. In this work the acrylamide content was varied in a large range of 30-70% (mole of total monomer) in feed, in order to study its effect on swelling behavior. The results indicate that when acrylamide content present in the hydrogels was increased from 17.23-35.85% (mole of the total monomer); then equilibrium water absorbency also increased from 276-573 (g water/g sample). But when acrylamide content was further increased from 35.85-50.24%, then equilibrium water absorbency abruptly decreased. The equilibrium water absorbency of various copolymeric hydrogels was also investigated in different concentration of saline solutions. The effect of SAHs on growth of seeds of lentil was also studied. The hydrogels were also characterized by fourier-transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), scanning electron microscopy (SEM); and network parameters such as average molecular weight between cross-links (Mc) and cross-link density (q) were determined to explain the swelling behavior.

A series of novel superabsorbent hydrogels based on acrylic acid (AAc), acrylamide (AM), and sodium humate (SH) were prepared by free-radical solution copolymerization for removal of dye and metal ion from waste water. Ammonium per sulfate was used as initiator and N,N 0 methylene bisacrylamide as crosslinker. The hydrogels were characterized with the help of FTIR and SEM. In this study the concentration of SH was varied in the range of 0.50-4.76 wt % based on total monomer content and the resulting hydrogels were investigated for the effect of SH on swelling and diffusion kinetic parameters such as equilibrium swelling ratio, initial swelling rate, swelling rate constant, maximum swelling at equilibrium, and type of diffusion, etc. Hydrogel having 2.43 wt % SH content showed the maximum water absorbency of 724 g of water per gram of hydrogel. Swelling exponent found in the range 0.68-0.79 thus suggesting Non-Fickian diffu-sion mechanism. The swelling behavior was also studied in different concentrations of salt solutions [sodium chloride (NaCl), magnesium chloride (MgCl 2 ), and ferric chloride (FeCl 3 )]. The synthesized superabsorbent hydrogels were used for the adsorption of Cu 2þ ions and methylene blue (MB) dye from their aqueous solutions. The influence of SH concentration on the Cu 2þ ions and MB molecules binding capacity of hydrogels was tested. The chelation behavior was modeled using Langmuir isotherm. The maximum binding capacity for Cu 2þ ion was 299 mg/L at 1000 mg/L, initial Cu 2þ ion concentration and 269 mg/L at 320 mg/L, initial MB dye molecules concentration per gm of AAc/ AM/SH containing 2.43 wt % SH content.