Gas permeabilities of polyurethane films for fresh produce packaging: Response of O2 permeability to temperature and relative humidity

Thermoplastic shape memory polyurethane (SMPU) polymers were synthesized, cast to films, and their gas barrier properties were characterized. In addition, performance of an optical method was assessed by measuring oxygen permeability (P_O2) of the films. P_O2 of the SMPU film was at least two times higher than that of low density polyethylene (LDPE and increased at higher relative humidity. Permselectivity (P_CO2/P_O2) of the SMPU film was 15, which is approximately three times higher than for LDPE. The film absorbed circa 18% water vapor at 98% relative humidity. The optical method agreed very well (maximum 20% deviation) with a standard carrier gas method in P_O2 measurement. Overall our results show that SMPU is an attractive polymer for fresh produce packaging.     

鲜蒜嫩鳞被中半胱氨酸肽的制备及其对豆类铁锌生物利用率的影响

离子交换层析结合制备液相方法从鲜蒜嫩鳞被中制备2种半胱氨酸肽(γ-GCPs):(SC2RC7)-γ-L-谷氨酰-S-烯丙基-L-半胱氨酸(1)和(SC2RC7)-γ-L-谷氨酰-S-丙基-L-半胱氨酸(2)。产物结构经HPLC-MS,CD和1H NMR,13C NMR分析并与标准品比对确定。利用体外模拟胃、肠消化实验检测其对豆类铁锌生物利用率的影响。结果表明,5 g豆粉中添加0.01 mmol的化合物1和化合物2分别使黄豆铁生物利用率从1.88%提高到6.73%和4.42%,绿豆铁生物利用率从2.52%提高到12.04%和9.38%;使黄豆锌生物利用率从13.37%提高到23.95%和20.58%,绿豆锌生物利用率从15.98%提高到28.44%和27.05%。     

A New Testing Method to Investigate the Compacting Behaviour of Fresh Concretes Under Impact Loading

This paper presents a new instrumented Proctor test using a Hopkinson bar which allows for the original measurement of forces and velocities during the impact loading on soft fresh concrete samples. For this purpose, the specific points of using low impedance Nylon bar as well as the two-point measurement method to recover coupled waves are discussed. The whole test consists of successive impacts of low velocity (less than 3 m/s) exerted on the compressible specimen of a fresh concrete. The proposed original measurement allows for a quantitative comparison of the behaviour of the fresh concrete submitted to quasi-static and impact compaction. It shows that impact compaction is more efficient than quasi-static case. However, the increase of the impact velocity seems to reduce the efficiency. There exists probably an optimal loading path. The further understanding of the behaviour of fresh concrete under low velocity impact should be an interesting way to improve the industrial compacting process.     

Adsorptive scavenging of cationic dyes from aquatic phase by H3PO4 activated Indian jujube (Ziziphus mauritiana) seeds based activated carbon: Isotherm,kinetics, and thermodynamic study

In the present work, a cost-effective Indian jujube seeds derived activated carbon (IJSAC) prepared via o-phosphoric acid chemical activation, is studied for the sequestration of acriflavine (AF) and Victoria blue B (VB) from the aquatic environment. The activated carbon is characterized by Fourier transform infrared spectroscopy, N₂-adsorption/desorption isotherm, scanning electron microscopy techniques and point of zero-charge measurement. The specific surface area (S_BET) of 571 m²/g with a pore radius of 22.45 Å specifies mesoporous nature of the IJSAC. The implication of operational conditions on the adsorption of both dyes onto IJSAC assessed by batch methodology, establish the optimal conditions as dosage (1.5 and 2.5 g/L), contact time (60 min), pH (8 and 10), and initial concentration (130 and 140 mg/L) for AF and VB uptake, respectively. The Freundlich adsorption isotherm model (R² = 0.99) appropriates the equilibrium data suggesting multilayer adsorption onto heterogeneous surface sites, while pseudo-second order (R² = 0.95–0.99) is the best fit kinetic model. The liquid film and intraparticle diffusion modelling demonstrate that the adsorption process of these dyes is governed by both the steps. Maximum Langmuir adsorption capacity is 113.6 mg/g for acriflavine and 92.78 mg/g for Victoria blue B. Thermodynamic studies indicate endothermic and spontaneous adsorption of dyes. The adsorption mechanism for the uptake of AF and VB by IJSAC most probably involves hydrogen bonding, electrostatic and π-π interactions. Based on its high adsorption capacity, relatively faster kinetics, and reusability, IJSAC can be perceived as a proficient and effective adsorbent for cationic dyes removal from the liquid waste.     

Cascade ultrafiltration and competing ligand exchange for kinetic speciation of aluminium, iron, and nickel in fresh water

Kinetic speciation of nickel, aluminium, and iron in fresh water has been investigated by cascade ultrafiltration followed by competing ligand exchange of the ultrafiltered fractions. Graphite furnace atomic absorption spectrometry was used to measure the kinetics of metal complex dissociation. Dissolved metal species were fractionated by cascade ultrafiltration. Metal speciation in each ultrafiltered fraction was then characterized as free metal ions, “labile” metal complexes (with dissociation rate constants ≥10⁻³ s⁻¹), “slowly labile” metal complexes (with dissociation rate constants >10⁻⁶ s⁻¹), and “inert” metal complexes (with dissociation rate constants <10⁻⁶ s⁻¹). The experimental results were compared with the predictions of a computer-based equilibrium speciation model, the Windermere humic aqueous model (WHAM) V. Cascade ultrafiltration coupled with kinetic speciation of the metal species in each molecular weight cut-off (MWCO) fraction provided a more comprehensive picture and insight into the physical and the chemical characteristics of the metal species than either ultrafiltration or measurement of dissociation kinetics alone.     

乙二胺改善硅胶柱高效液相色谱法分离和测定糖

本文研究了用乙二胺作为硅胶柱改善剂的高效液相色谱法，对操作条件进行了探讨。采用示差折光检测器检测，含０．０１％乙二胺的乙腈－水（７２：２８，Ｖ／Ｖ）作流动相，在硅胶柱上成功地分离了果糖，葡萄糖，蔗糖，麦芽糖，乳糖和棉三糖。定量地分析了几种鲜桃汁中糖的含量。     

Separation of copper(II) and aluminium(III) from fresh waters by solid phase extraction on a complexing resin column

The solid‐phase extraction (SPE) of copper(II) and aluminium(III) from fresh waters on an ion‐exchange complexing resin containing iminodiacetic groups (Chelex 100) has been examined. Quantitative recovery of the metal ions was related to the breakthrough profile that, for some samples, could not be evaluated directly. A method is suggested for evaluation, instead, of the sorption curves, on the basis of passing different volumes of sample through the column. This enables evaluation of important properties, for instance the central point of the breakthrough curve, V_f. The column used was a small one, containing 0.10 g dry Chelex 100. The metal ion was eluted with a small volume of acid solution, 10 mL of 0.5 mol L^–1 HNO₃; this resulted in good preconcentration factors. For copper(II) it was found that fresh waters of similar composition could have different V_f in the same column. This was ascribed to different reaction coefficients (α_M(I)) of copper(II) in the considered samples, which affects V_f. By use of the proposed SPE procedure it is possible to evaluate the reaction coefficient of copper(II). The values of α_M(I) for two different drinking waters at pH 7.7 were found to be 3.70×10¹² and less than 4.40×10¹¹. Similar results were obtained for aluminium(III).     

A water-in-oil emulsion containing Kelex-100 for the speciation analysis of trace heavy metals in water

A water-in-oil (w/o) emulsion containing Kelex-100 (7-dodecenyl-8-quinolinol) and Span-80 (sorbitan monooleate, non-ionic surfactant) was ultrasonically prepared from 1.0 mol l⁻¹ hydrochloric acid and a (1 + 3) mixture of toluene and n-heptane. The resulting emulsion was gradually injected into water sample and dispersed as numerous tiny globules (0.01-0.1 mm in diameter). Dissolved inorganic species (free metal species) of heavy metals (e.g., Fe, Co, Cu, Cd, and Pb) were selectively transported through the oil layer into the internal aqueous phase of the emulsion, leaving other species, such as humic complexes and suspended particles (larger than 1 μm), in the sample solution. After collecting the dispersed emulsion globules, they were demulsified and the heavy metals in the segregated aqueous phase were determined by graphite-furnace atomic absorption spectrometry. The emulsion-based separation method allowed the selective collection of free metal species with a high concentration factor of 100, whereas the conventional solvent extraction did not offer such discrimination. This unique property of the emulsion method was successfully applied to the selective determination of free species of heavy metals in fresh water samples.     

An optimum design method for robotic tracked-vehicles operating over fresh concrete during straight-line motion

This paper addresses the general problem of the design of tracked base travel systems for special purpose vehicles and/or robotic machines that may be required to move over weak surfaces or over a lightly bonded terrain composed of fresh concrete. For the special case of a vehicle travelling on a very soft fresh concrete during construction, the paper presents detailed comparative studies of the tractive performance of several tracked vehicles with alternative slump values and mean contact pressure configurations. To complete these studies a detailed simulation-analytical method was used. From this, it was established that the simulation analysis method is useful for predicting land locomotion performance of specially designed small tracked vehicles running over fresh concrete of different consistencies during driving and braking action. This work was done for straight-line motion. Some possibilities for the real-time optimum control method of the tractive and braking performance of automated and robotic vehicles are also outlined.