Optimization of the reaction conditions and characterization of L‐lactic acid direct polycondensation products catalyzed by a non‐metal‐based compound

In this article, we deal with the investigation into a poly(lactic acid) (PLA) preparation process catalyzed by a non‐metal‐based compound. Low‐molecular‐weight PLA was synthesized by the direct melt polycondensation of L ‐lactic acid catalyzed by methanesulfonic acid (MSA). This study was focused on the investigation into optimal MSA concentration determination and into the temperature (130, 145, 160, 175, and 190°C) and time (6, 12, 18, and 24 h) influence on the structure (Fourier transform infrared spectroscopy), molecular weight (viscometric measurements and gel permeation chromatography), and thermal properties (differential scanning calorimetry) of the samples. The results show an optimal MSA content of 0.5 wt %. The highest molecular weight of PLA prepared by this method was reached after 18 h of reaction at 175°C (weight‐average molar mass = 17.2 × 10³ g/mol). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of sonication on anticorrosion properties of a sulfursilane film dopped with Ce (IV) on galvannealed steel

Currently, galvannealed carbon steel has been submitted to phosphatizing and/or chromatizing as surface pre-treatments; however, for economic and environmental issues, the viability of using silanes as an alternative pre-treatment has been studied. The aim of this work is to study the effect of sonication of the solvent solution (50/50%, m/m water/ethanol) with 50 ppm of Ce (IV) ions on the corrosion behavior of bis-1.2-[triethoxysilylpropyl]tetrasulfide (BTESPT) silane film deposited on galvannealed steel. The sonication influence on reactions has been studied and seems to promote the formation of small molecules starting from large ones, the change of the local pH and temperature, beyond the change of the solution viscosity. The corrosion resistance of the steel coated samples was evaluated by electrochemical impedance spectroscopy (EIS), linear polarization resistance (R_p) and potentiodynamic polarization curves. The molecular vibrational and chemical properties of the films were obtained by infrared (IR) and micro Raman spectroscopies. The physical characterization of sonicated solutions was performed by measuring their kinematic viscosity. The images from scanning electron (SEM) microscope were obtained to characterize the aspect and morphology of the film. The results showed that the sonication led to obtaining more homogeneous, compact and corrosion resistant silane films.     

The effect of microwave irradiation on poly(vinyl alcohol) dissolved in ethylene glycol

Poly(vinyl alcohol) (PVA) dissolved in ethylene glycol is subjected to microwave (MW) irradiation for 1 h to determine possible degradation. Fourier transform infrared spectroscopy results show that MW treatment produces a minor effect on the solutions. Ultraviolet–visible spectroscopy suggests that PVA could undergoes loss of hydroxyl groups followed by formation of unsaturated conjugated bonds although the extent of degradation is limited, whereas size exclusion chromatography indicates that MW irradiation do not cause significant changes in PVA molar mass and neither chain cleavage nor crosslinking reactions are observed. Hence, polymer degradation induced by MWs in solution can be considered as negligible for prospective applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

EQUILIBRIUM MOISTURE CONTENT OF CELLULOSIC MATERIALS AT HIGH TEMPERATURE

ABSTRACT

At the high drying rates now obtainable in high intensity drying; solids may reach quite high temperatures for very short drying times. Frequently the temperature stability of solids precludes measurement of their adsorption equilibrium moisture content at these elevated temperatures. A thermodynamic method is presented for calculating equilibrium moisture content at high temperature from measurements made at low temperature. The method, based on Gibbs surface excess free energy theory, involves no parameters requiring experimental measurement and eliminates the need for empirical extrapolations. Although demonstrated for three fibrous cellulosic materials, viscose yarn, cotton and kraft wood pulp, the procedure is applicable to any absorbent - water system. The examples show that the method is practical and convenient for application.     

雅在深处 乌克兰欧莱雅学院

<正>2003年,知名品牌欧莱雅进驻乌克兰,它仅仅用了两年的时间便从一个小小的代理处发展成为正式的欧莱雅集团附属公司并颇具影响力。如今,这里的员工也从最开始的寥寥10多人发展到了在全国范围内拥有150名员工。     

坐拥和风 香港Busy Suzie餐厅

<正>室内设计师Patrick Gilles和Doro-thee Boissier设计了一个全新的日式餐厅Busy Suzie,这间独特的环形炉端烧餐厅酒吧坐落于香港九龙尖沙咀1881 Heri-tage。1881 Heritage的前身是香港用于     

建筑英雄 Simone Micheli访谈录

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