Preparation and characterization of calcium carbonate/low‐density‐polyethylene nanocomposites

Calcium carbonate/low‐density‐polyethylene (LDPE) nanocomposites have been prepared by melting blend with twin‐screw extruder. The mechanical properties of composites and the dispersion of the nanoparticles were studied. The reinforcement mechanism was discussed. The results show that not only the tensile property but also the flexural modulus of the system have been evidently increased by the addition of calcium carbonate. The calcium carbonate particles have been dispersed in the matrix in the nanometer scale. The reinforcement mechanism of the calcium carbonate lies on that the calcium carbonate particles, acting as hetero‐nuclei, can induce higher crystallinity at the matrix‐particle interface compared to regions away from the interface. Consequently, in the process of the tensile test, the nanocomposites have better tensile yield strength. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Heterogeneously assisted oxidation of adsorbates from carbonmonoxide, methanol and ethanol by hydrogen peroxide solutions on platinum electrodes in sulphuric acid

The influence of hydrogen peroxide on the adsorption and oxidation of carbon monoxide, methanol and ethanol adlayers on porous Pt electrodes were studied in 2 M sulphuric acid solution by means of cyclic voltammetry and differential electrochemical mass spectrometry (DEMS). The oxidation of adsorbed species is observed at electrode potentials far less negative than those required for electrochemical adsorbate oxidation. The oxidation by H₂O₂ is dependent on its concentration in solution, as well as on the adsorbates and their coverages. In all cases the isolated adlayers are oxidised by dissolved H₂O₂. However, the presence of H₂O₂ during adsorption partially inhibits adlayer formation from CH₃OH and C₂H₅OH, but avoids almost completely the adsorption of carbon monoxide. The removal of the residues from the surface by dissolved hydrogen peroxide probably occurs through O_ad species formed during the heterogeneous decomposition reaction of H₂O₂ on Pt.     

Preparation and characterization of eugenol‐grafted chitosan hydrogels and their antioxidant activities

The hydrogels composed of chitosan and eugenol were prepared to enhance and sustain antioxidant activities. The vinyl groups of eugenol monomer were directly grafted on the amino groups of chitosan, using ceric ammonium nitrate. The graft of eugenol onto chitosan was confirmed by using Fourier‐transform infrared and proton nuclear magnetic resonance spectroscopies. Results from the swelling behavior, thermal stability, and wide‐angle X‐ray diffraction revealed that the equilibrium water content decreased with increase of graft yields, because of the hydrophobicity of eugenol, although the introduction of eugenol as a side chain disturbed the ordered arrangement of chitosan's crystalline structure. The eugenol‐grafted chitosan hydrogels showed lower pH sensitivity in comparison with chitosan alone, because the amino groups, which were pH sensitive, of chitosan were grafted with eugenol. The scavenging activity of the tested hydrogels increased with graft yield of eugenol, because phenolic groups in the eugenol could play a major role as potent free‐radical terminators, in the results of improved antioxidant activity in eugenol‐grafted chitosan hydrogel in comparison with chitosan alone. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99:3500–3506, 2006     

Impregnation of X Zeolite with Alkaline Hydroxide During the Synthesis

Enhancement of the basic properties of the X zeolite with FAU framework has been carried out during synthesis, without further treatment such as ion-exchange or impregnation. Control of the washing stage enables retention of the optimum amount of alkaline hydroxides, which increases the basic catalytic activity of X zeolite in the alkylation of toluene. This alkaline hydroxides neither affect the FAU framework nor the silicon/aluminium molar ratio of the X zeolite. The optimum (Na + K)/Al molar ratio of the improved catalyst was 1.06 corresponding to a washing volume of 200 mL. This X zeolite presented better catalytic activity than a cesium-zeolite prepared by ion-exchange. The presence of hydroxysodalite impurity in the X zeolite increased the amount of impregnated alkaline hydroxides but not the catalytic activity. The present study shows that it is possible to increase the basic properties of the X zeolite directly in the synthesis process.     

Syndiotactic Polystyrene/Organoclay Nanocomposites: Synthesis via In Situ Coordination‐Insertion Polymerization and Preliminary Characterization

Summary: Syndiotactic polystyrene (sPS)/organophilic clay nanocomposites were obtained by in situ coordination‐insertion polymerization of styrene. Two cationic surfactants (alkylammonium and alkylphosphonium) were used for the intercalation of montmorillonite (MMT). For each organically modified clay, three protocols were performed using an MAO‐activated hemi‐metallocene catalyst, in order to compare the influence of experimental conditions on the composite microstructure and on its thermal stability. The microstructures of nanocomposites were investigated by wide angle X‐ray scattering and DSC. Partially exfoliated or intercalated materials were obtained in all cases and a decrease of crystallinity is observed. Thermal properties were also studied by DSC and thermogravimetric analysis. The presence of clay does not have a strong influence on the sPS thermal transitions but the thermal decomposition process of the material was slowed down in the presence of few organoclay percents, particularly in the degradation beginning. The influence of these two organically modified clays on the thermal stability of the material is discussed.

Gel and suspension formed from the combination of cloisite with toluene (left) and styrene (right), respectively.     

Preparation of pH‐sensitive poly(vinyl alcohol‐g‐methacrylic acid) and poly(vinyl alcohol‐g‐acrylic acid) hydrogels by gamma ray irradiation and their insulin release behavior

A series of pH‐responsive hydrogels were studied as potential drug carriers for the protection of insulin from the acidic environment of the stomach before releasing in the small intestine. Hydrogels based on poly(vinyl alcohol) networks grafted with acrylic acid or methacrylic acid were prepared by a two‐step process. Poly(vinyl alcohol) hydrogels were prepared by gamma ray irradiation (50 kGy) and then followed by grafting either acrylic acid or methacrylic acid onto these poly(vinyl alcohol) hydrogels with subsequent irradiation (5–20 kGy). These graft hydrogels showed pH‐sensitive swelling behavior and were used as carriers for the controlled release of insulin. The in vitro release of insulin was observed for the insulin‐loaded hydrogels in a simulated intestinal fluid (pH 6.8) but not in a simulated gastric fluid (pH 1.2). The release behavior of insulin in vivo in a rat model confirmed the effectiveness of the oral delivery of insulin to control the level of glucose. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 636–643, 2004     

Lignan contents in sesame seeds and products

Sesame seed (Sesamum indicum L.) is a rich source of furofuran lignans with a wide range of potential biological activities. The major lignans in sesame seeds are the oil‐soluble sesamin and sesamolin, as well as glucosides of sesaminol and sesamolinol that reside in the defatted sesame flour. Upon refining of sesame oil, acid‐catalyzed transformation of sesamin to episesamin and of sesamolin to epimeric sesaminols takes place, making the profile of refined sesame oils different from that of virgin oils. In this study, the total lignan content of 14 sesame seeds ranged between 405 and 1178 mg/100 g and the total lignan content in 14 different products, including tahini, ranged between 11 and 763 mg/100 g. The content of sesamin and sesamolin in ten commercial virgin and roasted sesame oils was in the range of 444–1601 mg/100 g oil. In five refined sesame oils, sesamin ranged between 118 and 401 mg/100 g seed, episesamin between 12 and 206 mg/100 g seed, and the total contents of sesaminol epimers between 5 and 35 mg/100 g seed, and no sesamolin was found. Thus, there is a great variation in the types and amounts of lignans in sesame seeds, seed products and oils. This knowledge is important for nutritionists working on resolving the connection between diet and health. Since the consumption of sesame seed products is increasing steadily in Europe and USA, it is important to include sesame seed lignans in databases and studies pertinent to the nutritional significance of antioxidants and phytoestrogens. It is also important to differentiate between virgin, roasted and refined sesame oils.     

Synthesis of 2‐monoglycerides by alcoholysis of palm oil and tuna oil using immobilized lipases

Commercial immobilized lipases were used for the synthesis of 2‐monoglycerides (2‐MG) by alcoholysis of palm and tuna oils with ethanol in organic solvents. Several parameters were studied, i.e., the type of immobilized lipases, water activity, type of solvents and temperatures. The optimum conditions for alcoholysis of tuna oil were at a water activity of 0.43 and a temperature of 60 °C in methyl‐tert‐butyl ether for ～12 h. Although immobilized lipase preparations from Pseudomonas sp. and Candida antarctica fraction B are not 1, 3‐regiospecific enzymes, they were considered to be more suitable for the production of 2‐MG by the alcoholysis of tuna oil than the 1, 3‐regiospecific lipases (Lipozyme RM IM from Rhizomucor miehei and lipase D from Rhizopus delemar). With Pseudomonas sp. lipase a yield of up to 81% 2‐MG containing 80% PUFA (poly‐unsaturated fatty acids) from tuna oil was achieved. The optimum conditions for alcoholysis of palm oil were similar as these of tuna oil alcoholysis. However, lipase D immobilized on Accurel EP100 was used as catalyst at 40 °C with shorter reaction times (<12 h). This lead to a yield of ～60% 2‐MG containing 55.0‐55.7% oleic acid and 18.7‐21.0% linoleic acid.     

Curing and pyrolysis of cresol novolac epoxy resins containing [2‐(6‐oxido‐6H‐dibenz(c,e)(1,2)oxaphosphorin‐6‐yl)‐1,4‐naphthalenediol]

This study investigates the curing kinetics, thermal properties and decomposition kinetics of cresol novolac epoxy (CNE) with two curing agents, 2‐(6‐oxido‐6H dibenz(c,e)(1,2) oxaphosphorin‐6‐yl)‐1,4‐benzenediol (ODOPN), and phenol novolac (PN). In comparison with the conventional PN system, introducing ODOPN, a phosphorus‐containing bulky pendant group, into CNE increases T_g by 33°C, char yield from 30% to 38%, and LOI from 22 to 31. The DSC curing study reveals that the E_a of the CNE/ODOPN epoxy can be obtained by Kissinger's method. The resulting E_a values indicate that the catalytic effect of EMI is insignificant on CNE/ODOPN but is marked on CNE/PN, whose E_a was reduced from 131.5 to 75.6 KJ/mole. This result may be caused by the fact that the symmetric diol attached to the 1 and 4 positions of the naphthalene ring in ODOPN sets up a steadily resonating structure and inhibits the catalytic action. Further investigating the conversion ratio with curing temperature yielded experimental data that agreed closely with Kaiser's model. The orders of the autocatalyzed reaction, m, and the crosslinking reaction, n, are close to 0.5 and 1.0, respectively, independently of the scan rate. Finally, the TGA decomposition study by Ozawa's method demonstrates that the mean E_a declines with the phosphorus content, because the easy decomposition of the phosphorus compound in the initiation stage facilitates the formation of an insulating layer. However, results in this study further reveal an increasing tendency for E_a with decomposition conversion for an ODOPN/PN mixture with the ODOPN content of over 50%, probably because of the retardation of gas diffusion by the insulating layer of phosphorus compound.     

Lignin‐based polycondensation resins for wood adhesives

Lignin‐based wood adhesives are obtained that satisfy the requirements of relevant international standards for the manufacture of exterior‐grade wood particleboard. Formulations based on low molecular mass lignin and presenting an increase in the relative proportion of reactive points yield better results than the higher molecular mass lignin used in the past. These lignins allow a higher proportion of hydroxymethylation during preparation of methylolated lignins. These lignin‐based adhesives also yield acceptable results at particleboard pressing times that are sufficiently low to be of industrial significance. Lignin‐based wood adhesives, in which a nonvolatile nontoxic aldehyde (glyoxal) is substituted for formaldehyde in their preparation, are prepared and tested for application to wood panels such as particleboard. The adhesives yield good internal bond strength results for the panels, which are good enough to comfortably pass relevant international standard specifications for exterior‐grade panels. The adhesives also show sufficient reactivity to yield panels in press times comparable to that of formaldehyde‐based commercial adhesives. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1690–1699, 2007