Short-wavelength near-infrared spectra of sucrose, glucose, and fructose with respect to sugar concentration and temperature

Short-wavelength near-infrared (SW-NIR) (700-1100 nm) spectra of aqueous solutions of sucrose, D-glucose, and D-fructose were monitored with respect to change in temperature and sugar concentration. Sugar OH and CH related vibrations were identified by analysis of the spectra of sugar solutions in deuterium oxide (D2O), and of sucrose-d8 solutions in D2O. Absorption spectra were explained in terms of the second and third overtones of OH stretching vibrations and the third overtone of CH2 and CH stretchings. In deuterated solutions, CH and CH2 higher overtone vibration bands became apparent. The major spectral effect of decreased temperature or increased sugar concentration was a decrease in absorbance at 960 nm and an increase in absorbance at 984 nm, interpreted as an increase in the degree of H bonding. Partial least-squares (PLS) calibrations on sugar concentrations (with spectra collected at several sample temperatures) relied strongly on the 910 nm sugar CH related bands, whereas calibrations on temperature depended equally on all OH associated vibrations (750, 840, 960, and 985 nm).     

Curing kinetics of divinyl ester resins with styrene

The curing reaction of a divinyl ester resin with different proportions of styrene—4, 20, and 40% by weight—was investigated by differential scanning calorimetry (DSC) using isothermal and dynamic modes. The different constraints on the reaction rate was globally considered, taken the reaction as divided in two regimens: below the vitrification regimen and during the vitrification regimen. Below the vitrification regimen, the autocatalytic model developed by Kamal was used to perform the analysis of the curing kinetics of divinyl ester resin with styrene. Experimental data from dynamic and isothermic runs, at a fixed composition, were simultaneously considered, while the actual temperature records (measured during the DSC runs) were also taken into account. The adjusted kinetic parameters took into account the gel effect on the radicals' termination rate and the structure constraints on the reactivity of pendant vinyls groups, present during this stage. During the vitrification stage, the diffusion control due to the low mobility of the reactive groups and molecules was incorporated into the overall rate constant according to the Rabinowitch model, which considers the two regimen contributions to the overall reaction rate kinetic. The Vogel–Fulcher relationship was adopted to express the temperature dependence of the rate constant during the vitrification stage. The method presented here has been satisfactorily applied to dynamic and isothermal curing reactions, allowing a simple and general kinetic expression useful in the design, optimization, and control of the processing of composites based on these thermoset polymers to be obtained. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1044–1053, 1999     

Toxicity assessment of heavy metal mixtures by Lemna minor L

The discharge of untreated electroplating wastewaters directly into the environment is a certain source of heavy metals in surface waters. Even though heavy metal discharge is regulated by environmental laws many small-scale electroplating facilities do not apply adequate protective measures. Electroplating wastewaters contain large amounts of various heavy metals (the composition depending on the facility) and the pH value often bellow 2. Such pollution diminishes the biodiversity of aquatic ecosystems and also endangers human health. The aim of our study was to observe/measure the toxic effects induced by a mixture of seven heavy metals on a bioindicator species Lemna minor L. Since artificial laboratory metal mixtures cannot entirely predict behaviour of metal mixtures nor provide us with informations relating to the specific conditions in the realistic environment we have used an actual electroplating wastewater sample discharged from a small electroplating facility. In order to obtain three more samples with the same composition of heavy metals but at different concentrations, the original electroplating wastewater sample has undergone a purification process. The purification process used was developed by Orescanin et al. [Orescanin V, Mikeli? L, Luli? S, Nad K, Rubci? M, Pavlovi? G. Purification of electroplating wastewaters utilizing waste by-product ferrous sulphate and wood fly ash. J Environ Sci Health A 2004; 39 (9): 2437-2446.] in order to remove the heavy metals and adjust the pH value to acceptable values for discharge into the environment. Studies involving plants and multielemental waters are very rare because of the difficulty in explaining interactions of the combined toxicities. Regardless of the complexity in interpretation, Lemna bioassay can be efficiently used to assess combined effects of multimetal samples. Such realistic samples should not be avoided because they can provide us with a wide range of information which can help explain many different interactions of metals on plant growth and metabolism. In this study we have primarily evaluated classical toxicity endpoints (relative growth rate, Nfronds/Ncolonies ratio, dry to fresh weight ratio and frond area) and measured guaiacol peroxidase (GPX) activity as early indicator of oxidative stress. Also, we have measured metal accumulation in plants treated with waste ash water sample with EDXRF analysis and have used toxic unit (TU) approach to predict which metal will contribute the most to the general toxicity of the tested samples.     

Composite resins based on novel and highly reactive bisglycidyl methacrylate monomers

Three new bisglycidyl monomers; 1,4‐bis((2‐hydroxy‐3‐methacryloxypropoxy) methyl)benzene (MB‐Phe‐OH), 1,4‐bis(2‐hydroxy‐3‐methacryloxypropoxy)2‐cis‐butene (MB‐Cis‐OH), and 1,7‐bis(2‐hydroxy‐3‐methacryloxypropoxy)heptane (MB‐1,7‐OH); were synthesized and used as Bis‐GMA/TEGDMA (bisphenolglycidyl methacrylate/triethylene glycol dimethacrylate) composite resin additives. Flexural properties and double bond conversion of the dental resins composed of silanizated inorganic filler and organic matrices containing new monomers were evaluated. The composite resins formulated, using the monomers MB‐Cis‐OH and MB‐1,7‐OH, have mechanical properties and double bond conversion comparable with those of Bis‐GMA/TEGDMA composite resin used as control. The composite containing the new monomer MB‐Phe‐OH has better flexural properties (flexural strength 65.01 MPa and flexural modulus 5675.91 MPa) than the control composite resin (flexural strength 52.85 MPa and flexural modulus 4879.72 MPa); this could be attributed to the molecular structure of the monomer and its high double bond conversion level of 74.19%. The new bisglycidyl methacrylate monomer MB‐Phe‐OH could be potentially useful in the development of new organic matrices for dental composite resins with high double bond conversion and enhanced mechanical properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40971.     

Comparative effects of two different crosslinkers on the properties of vegetable oil-based polyurethanes

Thermoset polyurethanes (PUs) were prepared from a polyol derived from castor oil, 4,4′-methylene diphenyl diisocyanate (MDI) and different trifunctional low-molecular-weight crosslinkers, biobased glycerol (Gly) and petroleum-derived trimethylolpropane (TMP). The synthesis was carried out in bulk and without catalyst via one-step polymerization varying the components equivalent weight ratio, Polyol:MDI:Gly and Polyol:MDI:TMP, respectively. The physicochemical, morphological, thermal, dynamic–mechanical, and mechanical properties of the PUs were determined. The success of the reaction between the polyol and MDI was confirmed by Fourier transform infrared spectroscopy. The dynamic–mechanical and the mechanical properties as well as hardness were determined and related to the concentration of the low-molecular-weight crosslinkers utilized (Gly or TMP). However, important differences were observed between the synthesized two series, due to phase separation produced during the curing reaction, which affected more the materials prepared from TMP. Scanning electron microscopy images and dynamic–mechanical results confirmed this difference, related to the reactivity of primary and secondary hydroxyls present in the crosslinkers. Thermogravimetric analysis also showed to be sensible to the different structure of the crosslinkers with TMP leading to more thermally stable samples. Finally, measurements of water contact angle indicated that the surfaces were mostly hydrophobic with minor differences between the samples. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48741.     

Vegetable oil/styrene thermoset copolymers with shape memory behavior and damping capacity

The mechanical and damping properties as well as the shape memory behavior of copolymers obtained by cationic copolymerization of tung oil with styrene with different stoichiometric ratios are presented and analyzed in this work. The glass transition temperatures are close to room temperature for all the copolymers, and generally increase with the content of styrene. A similar trend is observed for the modulus, which exhibits values from 4.89 MPa for the copolymer with 30 wt% styrene to 13.92 MPa for the copolymer with 70 wt% styrene. These hard elastomers present shape memory behavior with high recovery and fixity ratios, as well as high damping quality (damping factors 0.4 and 1.38 at 28.9 and 43.3 °C, for the tung oil homopolymer and the copolymer with 70 wt% styrene, respectively), opening possibilities for practical applications that require material response close to room temperature. Copyright © 2012 Society of Chemical Industry     

Preparation and characterization of transition metal-modified lacunary Keggin 11-tungstophosphates supported on carbon

Transition metal-modified lacunary Keggin heteropolycompounds [PW₁₁O₃₉M]⁵⁻, with M = Ni²⁺, Co²⁺, Cu²⁺, or Zn²⁺, were synthesized and characterized. These heteropolycompounds were used to prepare the carbon-supported catalysts. Both the heteropolycompounds and the carbon-supported catalysts showed FT-IR spectra with the characteristic bands of these compounds and provided an indirect measure of the interaction strength between M and the oxygen of the central tetrahedron group of the Keggin structure. The anion decomposition of the modified compounds takes place at equal or lower temperature than that of the bulk and supported parent lacunary [PW₁₁O₃₉]⁷⁻ anion. The species present on the support surface may be highly dispersed as a non-crystalline form, as a result of the interaction with the support surface groups. The activity of the synthesized catalysts in isopropanol dehydration, reflecting their acidity, increases as the reduction temperature of the decomposition products of the heteropolycompounds decreases. It may be assumed that the generation of acid sites is a result of the interaction of hydrogen, donated by isopropanol during its decomposition, with the M cation, leading to M reduction and protons.     

Moisture absorption effects on the thermal and mechanical properties of wood flour/linseed oil resin composites

The thermal and mechanical behavior of new natural polymeric composite materials after exposure to humid environments must be well known and understood in order to predict their performance in final applications. For this reason, composites made from unsaturated polyesters based on linseed oil and filled with wood flour were exposed to environments of different relative humidities and their final properties were measured. In general, the equilibrium moisture content increased as the wood flour percentage increased. Dynamic mechanical tests performed in temperature scan mode were carried out in order to monitor the changes resulting from moisture absorption on the main transition temperature of the matrix (T_α). The temperature of this transition decreased as the amount of absorbed water increased, but the effect was partially reversible by re‐drying the samples. The mechanical properties were also strongly affected by moisture. The flexural modulus and ultimate stress of the composites decreased after equilibration in humid environments. Copyright © 2006 Society of Chemical Industry