来源期刊：Carbohydrate Polymers: Scientific and Technological Aspects of Industrially Important Polysaccharides
Nanocomposites of polyvinyl acetate (PVAc) reinforced with two different TEMPO-oxidized cellulose nanofibrils (CNF) were prepared by casting/evaporation method. These two sets of CNF, designed as CNF-O-5 min (5 min of oxidation) and CNF-O-120 min (120 min of oxidation), are different by their surface charge, geometrical characteristics and crystallinity index. The weight fraction of CNF was changed from 1 to 10 wt%. The mechanical and thermal properties of the nanocomposite films were studied by dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and tensile tests, and their morphology was investigated by scanning electron microscopy (SEM). For all nanocomposites, increasing amounts of CNF led to a significant increase in the mechanical properties (increase in Young's modulus and tensile strength) and in the water uptake. On the other hand, the lost of transparency became very significant when the weight fraction of CNF exceeded 3 wt%. The comparison between the two sets of CNF showed that PVAc/CNF-O-5 min nanocomposite films had a tendency to display higher tensile strength and elastic modulus than those of PVAc/CNF-O-120 min films. In addition, the water uptake is higher for PVAc/CNF-O-120 min. Finally, the thermal stability analyses for PVAc/CNF films show that shorter and more charged fibrils (CNF-O-120 min) appear to slightly increase the thermal stability compared to other larger and less charged fibrils (CNF-O-5 min). All these results are discussed in connection with the CNFs characteristics.
GHEORGHE HUBCA;CAMELIA HODOSAN;PAUL OCTAVIAN STANESCU
年/卷/期：2006 / 43 / 4
The present work investigates the possibility to control the alcoholysis reaction in order to obtain various sorts of polyvinyl alcohol with a predetermined degree of alcoholysis and high block copolymer character.On this purpose,two methods are suggested: quantitative determination of methyl acetate (resulted as a by product of the alcoholysis reaction) existing at a certain time in the system,and termination of the alcoholysis reaction according to a predetermined calibration curve.
Analytical parameters including sensitivity in the QCM sensing system are critical to understand its sensing mechanism. We investigated the QCM analytical parameters after the QCM electrode surface was modified with polyvinyl acetate (PVAc) nanofiber for primary alcohols' vapor detection. The PVAc nanofibers were prepared by electrospinning method and were observed using a scanning electron microscope (SEM). The modified QCM sensing system was used to test the vapor of primary alcohols. The QCM sensitivity for methanol, ethanol, n-propanol, n-butanol, and n-pentanol was found to be 6.8 +/- 0.4, 13.1 +/- 0.5, 25.2 +/- 1.1, 39.7 +/- 1.9, and 51.9 +/- 2.6 Hz mg(-1) L, respectively. The limit of detection for npentanol vapor was 0.023 mg/L, which the highest of all. The shortest response time was 4s, when it was exposed to methanol vapor. The intermolecular interaction between the active surface and gaseous molecules is believed to responsible for frequency shift. The concentration of the analyte in the air is linearly correlated to the compound vapor pressure. The results could provide a new promising way to detect vapor of structurally similar of volatile organic compounds (VOCs) by QCM. (C) 2019 Elsevier B.V. All rights reserved.
Elena Vismara;Khadija Ajmi;Imene Manai;Maroua Haddad;Moktar Hamdi;Hassib Bouallagui
来源期刊：Journal of hazardous materials
年/卷/期：2018 / 358 / Sep.15
The Fenton reaction as an oxidative degradation process was used for industrial chemical wastewater (ICW) pretreatment. The biodegradation of pretreated ICW was performed, in aqueous environment under aerobic condition, by a defined fungal consortium. The central composite design (CCD) was used to study the effect of nitrogen and phosphorus addition and the concentration of the pollution on the removal of polyvinyl alcohol (PVA) and organic compounds. The interaction between parameters was modeled using the response surface methodology (RSM). Results of optimization showed COD, PVA and color removal yields of 97.8%, 98.5% and 99.75%, respectively with a supplementof 1.4?gL?1of (NH4)2SO4, 1.2?gL?1of KH2PO4and 75% of concentrated ICW. Enzymatic analysis proved that laccase and lignin peroxidase were involved in the biodegradation with 45 UIL-1and 450 UIL-1, respectively. Furthermore, the analysis of metabolic products using Fourier transforms infrared spectroscopy (FTIR) and nuclear magnetic resonance (1HNMR) showed clearly the mineralization of organic compounds and the formation of formic acid and ethanol. Therefore, the effective treatment of ICW was achieved by developing an integrated chemical and biological process which met the requirement for a safety effluent respectful for environment without risks for public health.
来源期刊：Journal of Adhesion Science and Technology: The International Journal of Theoredtical and Basic Aspects of Adhesion Science and Its Applications in All Areas of Technology
年/卷/期：2018 / 32 / 17/20
Polyvinyl acetate (PVA) adhesive is one of the most common types of adhesives has been used in the wood industry for decades. However, many drawbacks are still associated with this adhesive including low water resistance, poor bond strength, and low viscosity. In this reported study, two additives, sulfanilamide and N,N-dimethylethylenediamine, were used to modify a PVA adhesive to improve its comprehensive practical performance. The prepared adhesive samples were characterized by Fourier transform infrared spectroscopy (FT-IR). Furthermore, the thermal decomposition characteristics of the PVA adhesives were studied using Thermal Gravimetric Analysis (TGA) and Differential Scanning Calorimetry analysis (DSC) combined with the Kissinger method. The experimental results showed that when compared to the pure PVA adhesive, the solid content, viscosity, dry bond strength, and wet bond strength of the modified PVA adhesive (PVA+N,N-dimethylethylenediamine+sulfanilamide) were improved by 34.8, 41.4, 47.0 and 35.2%, respectively. FT-IR analysis indicate that these two additives altered the chemical bond ratio that resulted from the generation of new chemical bonds, which explained the improved performance of the modified PVA adhesive. The pure PVA adhesive possessed two thermal decomposition steps, while the modified PVA adhesive (PVA+N,N-dimethylethylenediamine+sulfanilamide) exhibited only one thermal decomposition step. The thermal decomposition process of the pure PVA adhesive is characterized by a quick thermal decomposition stage and a slow thermal decomposition stage. Since the H>0, S<0 and G>0 in the thermal decomposition process it can be concluded that the decomposition reactions of the PVA adhesive were non-spontaneously endothermic and the entropy decreased during the reaction.
An improvement to a previously published suspension polymerization process for the production of spherical core/shell PVAc/PVA particles is described. To increase the settling time of the beads in the suspension, an expansion stage was introduced. The core/shell structure was obtained through the partial hydrolysis of the PVAc. The particle density was manipulated through addition of a solvent during the suspension polymerization stage and posterior expansion of the polymer beads obtained at the end of the process. This technique allows for effective reduction of the density of the final polymer beads. The expansion stage exerts also a beneficial effect on particle drying, avoiding particle aggregation during post-polymerization processing of the polymer beads.
来源期刊：International Journal of Biological Macromolecules: Structure, Function and Interactions
Chitosan-g-polyvinyl acetate (Cs-g-PVAc) was synthesized successfully using redox copolymerization using potassium persulfate as initiator. TiO2 and TiO2 doped ZnO which previously prepared by sol-gel technique added for preparing emulsion from polymer - metal oxide nanocomposites. Cotton fabrics were treated with prepared emulsions using citric acid and sodium hypophosphite. XRD measurements prove that the prepared TiO2 nano particles corresponded to anatase phase with average crystallite size d = 15.98 nm where the crystallinity and crystallite size decreased for Zn doped TiO2 where d = 11.7 nm. FFIR indicates that the exhibition of grafting process and formation polymer metal oxide nanocomposite. Samples treated with Copolymer showed the highest antibacterial properties. However, the copolymer doped with TiO2 and TiO2/ZnO showed lowest contact angle and affects positively on its photocatalytic performance. SEM and TEM micrographs confirmed that the prepared metal oxides are in nano scales, where TiO2 is smaller than TiO2/ZnO which effects on the band gap of TiO2/ZnO to be larger than TiO2 and consequently decreased on the photocatalytic properties TiO2/ZnO of samples compared to TiO2 sample under the halogen lamp. (C) 2018 Elsevier B.V. All rights reserved.
Mushtaq, Asim;Mukhtar, Hilmi;Shariff, Azmi Mohd
来源期刊：Journal of the Chemical Society of Pakistan
年/卷/期：2019 / 41 / 1
The solubility parameter is calculated to express the magnitude and nature of the interactive forces between the polymers and solvents. It measures the affinity between the components of a mixture. To improve the prediction of the solubility parameter, the group contribution method is used to calculate the overall solubility parameter as suggested by Hildebrand. Hildebrand's method is used to predict the interaction between the polymers and solvent. In this study, calculate the solubility parameters of polysulfone (PSU), polyvinyl acetate (PVAc) polymers and dimethylacetamide (DMAc) solvent by Hildebrand method. The PSU and PVAc solubility were found to be 1.52H and 1.7H, respectively. These solubility values show that both polymers were dissolved readily in the DMAc solvent, resulting in a true solution.
In order to develo a sulphuric-acid-resistant mortar at a low cost a new idea to modify cement mortar by using soluble soda glass (sodium silicate) and polymer latex as main and supplementary modifying materials,respectively was proposed.In light of an explratory test including five kinds of polymer latexes,the polyvinyl acetate latex was chosen as the supplementary modifier.Four different mortars,namely soluble glas-polyvinyl acetate modified mortar,polyvinyl acetate modified mortar,soluble glass modified mortar and unmodified mortar were then made for a detailed contratest research.The contratest results showed that the sulphuric acid resistance of the soluble glass-polyvinyl acetate modified mortar was significantly higher than that of the other kinds of mortars.