Poly(lactic acid)/Organo-Montmorillonite Nanocomposites: Synthesis,Structures, Permeation Properties and Applications

Polylactic acid (PLA)/organo-montmorillonite nanocomposites were prepared by the solution casting method using chloroform as solvent. The clays were organically modified by four different modifiers, ternary amine with two alkyl (tallow) tails, primary amine containing silane with a single tail, ammonium salt with a single alkyl (tallow) tail, and ammonium salts with two alkyl (tallow) tails. The structural characterization of the nanocomposite films was performed using Raman spectroscopy and the internal structure of the nanocomposites in the nanometer range was studied using wide-angle X-ray diffraction analysis. All the nanocomposites exhibited superior improvement when compared to neat PLA. Differential scanning calorimetry (DSC) was performed to study the thermal behavior of the prepared composites. Among the used clay types, M24 was the most effective in improving the water vapor and oxygen barrier properties. Water vapor and oxygen permeability of the nanocomposite films were decreased up to 80 and 49% when using M24 clay, respectively. Surface properties of the films were investigated with dynamic contact angle measurements. The migration studies of neat PLA and nanocomposites were performed for three types of food simulants.     

A new specific metal ion chelated‐poly(N‐vinylimidazole) gel sorbents for albumin adsorption‐desorption

Poly(N‐vinylimidazole) (PVIm) hydrogels were prepared by γ‐irradiating binary mixtures of N‐vinylimidazole‐water in a ⁶⁰Co‐γ source having 4.5 kGy/h dose rate. These affinity gels having different swelling ratio of Cu(II)‐chelated, Co(II)‐chelated and plain PVIm in acetate buffer were used in the albumin adsorption studies. Bovine serum albumin (BSA) adsorption on these gels from aqueous solutions containing different amounts of BSA at different pH adjusted with acetate and phosphate buffer was investigated in batch reactors. The adsorption capacities of BSA on/in the gels were decreased dramatically by increasing the ionic strength (I) adjusting with NaCl. BSA adsorption capacities of the metal ion‐chelated gels were higher than the plain PVIm gel even if the swelling ratio of the metal ion‐chelated gels was very low comparing to the PVIm gel. The rigidity of the metal ion‐chelated gel is very high and it can be used for the column applications. More than 95% of BSA were desorbed in 3 h in the desorption medium containing KSCN for PVIm gel and EDTA for metal ion‐chelated gels. These results indicate that PVIm and metal ion‐chelated PVIm gels are very efficient to remove BSA and the different metal ion‐chelated PVIm gels show different affinity for BSA or biomolecules.     

Electrochemical,spectroscopic, and thermal studies on interactions of linear poly(acrylic acid) with uranyl ions in aqueous solutions

The formation of complexes between linear poly(acrylic acid) (PAA) and uranyl ions in aqueous solutions was studied with conductometry, potentiometry, thermal analysis, Fourier transform infrared, and luminescence spectroscopy methods. The stoichiometry of the PAA/UO complex on repeating units of a PAA basis was determined to be 2:1. IR spectroscopy studies made on solid complexes showed that the carbonyl stretching absorption band of PAA was shifted to a higher wave number, and a new band at 1749 cm^?1 in the polycomplex spectrum was observed, confirming the existence of specific interactions between the carboxylate groups of PAA and metal ions. Luminescence spectroscopy studies showed an increase in the intensity of the uranyl‐ion emission spectra and new band formation at 483 nm, further confirming the interaction of UO ions with PAA in aqueous solutions. The thermal behavior of PAA/UO complexes further proved strong interactions in the complex structure. The thermal degradation of the polycomplexes included the main stages of destruction of both PAA and uranyl nitrate. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1610–1618, 2004     

Investigation of complex formation between poly(N-vinyl imidazole) and various metal ions using the molar ratio method

The complex formation of poly(N-vinyl imidazole) (PVIm) with various metal ions was studied. UV-vis spectroscopy was employed to study the interaction of PVIm and metal ions in aqueous solution. Formation constants of PVIm-metal complexes were calculated by applying a “mole ratio” method. The stoichiometric ratios between polymer and metal ions were found to be␣4. The stability constants for the complexes of PVIm with bivalent transition metal ions were in agreement with the Irving-William series. The biggest formation constant was found for the PVIm-Cu²⁺ complex system. Received: 4 January 1999 Accepted in revised form: 1 February 1999     

Radical Cyclization of Fluorinated 1,3‐Dicarbonyl Compounds with Dienes Using Manganese(III) Acetate and Synthesis of Fluoroacylated 4,5‐Dihydrofurans

Radical cyclizations of fluorinated 1,3‐dicarbonyl compounds with dienes mediated by Mn(OAc)₃ afforded 4,5‐dihydrofurans containing difluoroacetyl, trifluoroacetyl, or heptafluorobutanoyl groups in good‐to‐excellent yields. Additionally, 2‐(difluoromethyl)‐4,5‐dihydrofurans and a 4,7‐dihydrooxepin derivative were obtained as unexpected products in the reaction of 4,4‐difluoro‐1‐phenylbutane‐1,3‐dione with 1,3‐diphenylbuta‐1,3‐diene. The radical cyclization of symmetrical dienes such as 2,3‐dimethylbuta‐1,3‐diene and 1,4‐diphenylbuta‐1,3‐diene with 1,3‐diketones furnished the corresponding products in low yields. However, treatment of 1‐phenylbuta‐1,3‐diene with 1,3‐dicarbonyl compounds afforded 4,5‐dihydrofurans containing fluoroacyl groups. The radical cyclizations with 3‐methyl‐1‐phenylbuta‐1,3‐diene and 1,3‐diphenylbuta‐1,3‐diene led to 4,5‐dihydrofurans in good yields, since Me and Ph groups at C(3) of these dienes increase the stability of the radical intermediate.     

Macroporous Poly(Acrylamide) Hydrogels: Swelling and Shrinking Behaviors

Macroporous poly(acrylamide) hydrogels have been synthesized by using poly(ethylene glycol) (PEG) with three different molecular weights as the pore‐forming agent. Scanning electron microscope graphs reveal that the macroporous network structure of the hydrogels can be adjusted by applying different molecular weights of PEG during the polymerization reaction. The swelling ratios of the PEG‐modified hydrogels were much higher than those for the same type of hydrogel prepared via conventional method. However, the swelling/deswelling ratios of the PEG‐modified hydrogels were affected slightly by the change in the amount of the PEG. Scanning electron microscopy experiments, together with swelling ratio studies, reveal that the PEG‐modified hydrogels are characterized by an open structure with more pores and higher swelling ratio, but lower mechanical strength, compared the conventional hydrogel. PAAm has potential applications in controlled release of macromolecular active agents.     

Barrier properties of polylactic acid/layered silicate nanocomposites for food contact applications

Polylactic acid/layered silicate nanocomposite films were prepared by solution casting technique. Four types of organo modified montmorillonite and an unmodified bentonite were used as inorganic fillers. The structural characterizations were done by FTIR/ATR and dispersion of the layered silicates was determined by XRD. XRD results showed that the prepared nanocomposites showed flocculated, intercalated and exfoliated structure. The highest crystallinity degree obtained was 28. Overall migration tests were studied with food simulants included distilled water, 3% acetic acid, 95% ethanol. The migration values of all the prepared films were found to be below the allowed limit (10 mg/dm²). The best result in oxygen gas transmission and water vapor transmission rates were 233.4 cm³ mm/m² day MPa and 98.3 g/m² day, respectively. Consequently the oxygen barrier property has increased by 34% and water vapor barrier property increment was 65% when compared to pure PLA film.     

Radical Cyclization Reactions via Manganese(III) Acetate Leading to 2‐Thienyl‐Substituted Dihydrofuran Compounds

The 2‐thienyl‐substituted 4,5‐dihydrofuran derivatives 3 – 8 were obtained by the radical cyclization reaction of 1,3‐dicarbonyl compounds 1a – 1f with 2‐thienyl‐substituted conjugated alkenes 2a – 2e by using [Mn(OAc)₃] (Tables 1–5). In this study, reactions of 1,3‐dicarbonyl compounds 1a – 1e with alkenes 2a – 2c gave 4,5‐dihydrofuran derivatives 3 – 5 in high yields (Tables 1–3). Also the cyclic alkenes 2d and 2e gave the dihydrobenzofuran compounds, i.e., 6 and 7 in good yields (Table 4). Interestingly, the reaction of benzoylacetone (=1‐phenylbutane‐1,3‐dione; 1f ) with some alkenes gave two products due to generation of two stable carbocation intermediates (Table 5).     

Effects of mechanical and thermal stresses on electric degradation of polyolefins and related materials

Degradation under the simultaneous effects of mechanical stress and temperature in polyolefins (PE, PP), composites on their basis (PE+PP fibre, PP+PP fibre, PP+glass fibre) and radiation low-density polyethylene (X-LDPE) used in high-voltage cables obeys the thermofluctuation theory of Zhourkov (in certain σ and τ₀ intervals) based on the theory of Arrhenius is presented in the following form: τ_σ = τ₀ exp[(U₀ − γσ)/ RT] (1) where τ is durability. τ₀ is a constant (10⁻¹²-10⁻¹³s) equal to period of vibrations of atoms around equilibrium position, U₀ is the activation energy of the mechanical destruction process (at σ = 0), γ is a structure-sensitive parameter, T is absolute temperature and R is universal gas constant. Electric degradation under the effects of electric field and temperature in the materials mentioned above obeys the equation: τ_E = τ₀ exp[(W₀ − χE)/ RT] (2) Here, τ_E, W₀ and χ are analogous to τ_σ, U₀ and γ, respectively. It is assumed that the following equation is valid under the simultaneous effects of E, σ and T: τ_σ,E = τ₀ exp[(U₀ − (γσ + χE))/ RT]. (3) electric degradation