Nguyen Thi Thu Trang

Effects of maleic anhydride grafted ethylene/vinyl acetate copolymer (EVA) on the properties of EVA/silica nanocomposites

AbstractTernary nanocomposites based on ethylene/vinyl acetate copolymer (EVA), maleic anhydride-grafted EVA (EVAgMA), and nanosilica were prepared in a Haake Rheomixer. The structure of the EVA/EVAgMA/silica nanocomposites was characterized by Fourier transform infrared spectroscopy and field emission scanning electron microscopy. The blending sequence was found to have a significant effect on the microstructure of EVA/EVAgMA/silica nanocomposites and the dispersion behavior of the nanosilica in the EVA matrix. The tensile properties (tensile strength and elongation at break), thermal behavior, crystalline structure and weatherability of the nanocomposites were also studied. The results showed that the above properties of the nanocomposites were enhanced remarkably using 1 wt% EVAgMA.

Effect of TiO2-Crystal Forms on the Photo-Degradation of EVA/PLA Blend Under Accelerated Weather Testing

Photo-degradation of poly (ethylene-co-vinyl acetate) (EVA)/poly (lactic acid) (PLA) blend and EVA/PLA/TiO2 nanocomposites was carried out under accelerated weather testing conditions by alternating cycles of ultraviolet (UV) light and moisture at controlled and elevated temperatures. The characters, properties, and morphology of these materials before and after accelerated weather testing were determined by Fourier transform infrared spectroscopy, colour changes, viscosity, tensile test, thermogravimetric analysis, and field emission scanning electron microscopy. The increases in the content of oxygen-containing groups, colour changes; the decreases in viscosity, tensile properties, and thermal stability of these materials after accelerated weather testing are the evidence for the photo-degradation of the blend and nanocomposites. After accelerated weather testing, the appearance of many micro-holes and micro-pores on the surface of the collected samples was observed. The photo-degradation degree of the nanocomposites depended on the TiO2-crystal form. Rutile TiO2 do not enhance the degradation, but anatase and mixed crystals TiO2 nanoparticles promoted the degradation of the nanocomposites. Particularly, the mixed crystals TiO2 nanoparticles showed the highest photo-catalytic activity of the nanocomposites.

Fabrication of poly (lactic acid)/hydroxyapatite (PLA/HAp) porous nanocomposite for bone regeneration

In this study, a poly (lactic acid)/hydroxyapatite (PLA/HAp) porous nanocomposite was fabricated by melt mixing method. Polyethylene oxide (PEO) was added into the nanocomposite to improve compatibility of HAp in the PLA matrix. A porous structure of the nanocomposite was created by using a salt (NaCl) which leaches in water. The influence of HAps weight, compatibiliser content of porous agent on morphology and mechanical properties of PLA/HAp nanocomposite was investigated by SEM and tensile testing method. The obtained results indicated that the nanocomposite containing 20 wt% HAp, 5 wt% PEO, and an amount of NaCl in proportion with PLA weight (1 : 1) had good mechanical properties with a promising Youngs modulus close to the one of cancellous bone (530 MPa) as well as a high porosity. The invitro tests of nanocomposite in simulated body fluids (SBF) were carried out and then pH of SBF solution, variation of material mass (Δm), morphology and phase structure of the nanocomposite were also estimated. The results showed that pH decreased, and Δm had positive or negative values depending on composition and surface of material formed by HAp crystals and the hydrolysis of PLA during immersion time.

Tensile, rheological properties, thermal stability, and morphology of ethylene vinyl acetate copolymer/silica nanocomposites using EVA-g-maleic anhydride

In this article, we present a study on the properties of ethylene vinyl acetate copolymer/silica nanocomposites prepared in absence and presence of EVA-g-maleic anhydride as a compatibilizer between silica nanoparticles and ethylene vinyl acetate matrix. A series of ethylene vinyl acetate/silica nanocomposites with different contents of silica nanoparticles were prepared by solution method. EVA-g-maleic anhydride with 0.5 wt% maleic anhydride groups was added to all ethylene vinyl acetate/silica nanocomposites. Fourier transform infrared, field emission scanning electron microscopy, rheology behavior, and thermogravimetry analysis were used to characterize the structure, morphology, rheological, and thermal properties of the nanocomposites, respectively. The Fourier transform infrared spectra and field emission scanning electron microscopy micrographs showed that the hydroxyl groups on the surface of silica nanoparticles interact with maleic anhydride groups in EVA-g-maleic anhydride and lead to a finer dispersion of individual silica nanoparticles in the ethylene vinyl acetate matrix. The rheological properties and thermal stability of ethylene vinyl acetate/silica nanocomposites were significantly increased after adding EVA-g-maleic anhydride into the nanocomposites. Mechanical properties including tensile strength and elongation at break of the nanocomposites were mainly affected by the content of silica nanoparticles. For the tensile strength as well as elongation at break of the nanocomposites, a maximum value was observed at the content of 0.5 wt% of silica nanoparticles. The addition of EVA-g-maleic anhydride into ethylene vinyl acetate/silica nanocomposites resulted in a further improvement of mechanical properties of the nanocomposites.

Influence of Cd:Se precursor ratio on optical properties of colloidal CdSe tetrapods prepared in octadecene

Colloidal CdSe tetrapods were synthesized by chemical method in octadecene with the initial Cd:Se precursor ratios from 6:1 to 1:10 and the different monomer concentrations. Their stoichiometry and optical properties were investigated using the energy dispersion X-ray, absorption and photoluminescence spectroscopy. It was found that the CdSe tetrapods are Cd rich for all of the obtained sizes. Their stoichiometry was almost not changed during the growth and depends on the initial precursor ratio. The double-peak structure corresponding to the optical transitions in the core and arms of CdSe tetrapods was observed clearly in both the optical absorption and photoluminescence spectra for the Cd:Se precursor ratios from 2:1 to 1:2. The influence of the initial Cd:Se precursor ratio and monomer concentration on the growth of CdSe tetrapods and their optical properties has been analysed and discussed.

Sustainable composite materials based on ethylene-vinylacetate copolymer and organo-modified silica

Abstract Silica nanoparticles (SNPs) were modified by different amounts of 3-aminopropyltriethoxysilane (APTES). Nanocomposites based on ethylene vinyl acetate copolymer (EVA) and modified SNP (m-SNP) were prepared by the melt mixing method. They were characterized by Haake torque measurement, differential scanning calorimetry (DSC), horizontal burning test, scanning electron microscopy. Accelerated weather testing of the nanocomposites was performed according to ASTM D4329 (cycle A) for 168 h. The Haake torque indicates that the relative melt viscosity of EVA/m-SNPs is slightly higher than that of EVA/SNP nanocomposites. The DSC and burning test results show that m-SNPs decrease crystallinity degree and flammability of EVA. After accelerated weather testing, the relative amount of C=O groups in EVA/m-SNP nanocomposites is lower than that in EVA/SNP nanocomposites. Micro crack of EVA/m-SNP nanocomposite is smaller than that of EVA/SNP nanocomposite. In our study, the EVA/m-SNP nanocomposites with good tensile properties, flame and weather resistance can be used as sustainable materials in some technique fields.

Effect of Porous Structure and Acidity of ZSM-5/SBA-15 Catalyst on 1,3,5-Triisopropylbenzene Cracking Catalytic Activity

ZSM-5/SBA-15 composite materials with different acidities and mesoporous system formations were successfully synthesized by three-step method. The catalysts were characterized by XRD, HR-TEM, BET, EDX and TPD-NH3 methods. It showed that the Si/Al molar ratio had effect on the formation and property of materials. Among synthesized catalysts with the different Si/Al molar ratios of 30 (HZSC-30), 50 (HZSC-50), 70 (HZSC-70), HZSC-50 catalyst had better mesoporous system formation and acidity. These properties helped this catalyst to have higher catalytic activity in 1,3,5-triisopropylbenzene cracking reaction than other studied catalysts in term of higher benzene product yield. In comparison to HZSM-5 microporous material that had the similar Si/Al molar ratio of 50, it showed that the formation of mesopore system of HZSC-50 catalyst had a major improvement on the cracking catalytic activity.

Tensile, Thermal, Dielectric and Morphological Properties of Polyoxymethylene/Silica Nanocomposites

This paper presents the tensile, thermal, dielectric and morphological properties of composites based on polyoxymethylene (POM) and nanosilica (NS) prepared by melt mixing method at 190 °C. Based on the torque readings, the processing of POM/NS composites were found to be easier in comparison to only POM. The FT-IR spectra analysis of the POM/NS nanocomposites showed the presence of peak at approximately 910 cm-1, attributed to the Si-O and C-O groups in NS and POM on the POM/NS nanocomposite. The absorption at these peaks increased on gradually increasing the content of NS. Tensile property testing (tensile strength, elongation at break, and Youngs modulus) indicated that the tensile strength of POM/NS nanocomposites increases as the NS content increases from 0.5 wt.% to 1.5 wt.%, and sharply dropped when the NS content was more than 2 wt.%. A similar trend was observed for Youngs modulus and elongation at break of the nanocomposites. The DSC analysis of the nanocomposites showed that the melting temperature (Tm) of POM/NC composites increased in the presence of low weight % of NS which can be attributed to the interaction between POM and NS leading to the rising crystallinity of all nanocomposites. POM/NS have a slightly higher temperature resistance as confirmed from the TGA analysis and POM/NS 1.5 wt.% had the maximum degradation temperature (Tmax) value and consequently the lowest weight loss. The dielectric constant of the nanocomposites increased from 3.26 to 3.56, while the dielectric loss tangent and volume resistivity were dropped, corresponding to the NS content from 0.5 to 2 wt.%. The SEM images of POM/NS nanocomposites demonstrated that the NS particles were dispersed relatively regularly into POM with a size in the range of 100 to 500 nm. They were dispersed more regularly into the polymer matrix at 1.5 wt.% NS. Based on the obtained results, the suitable NS content for the preparation of the POM/NS nanocomposites was found to be 1.5 wt.%.

Polylactic Acid/Chitosan Nanoparticles Loading Nifedipine: Characterization Findings and In Vivo Investigation in Animal

This paper presents the results of zeta potential, water contact angle, atomic force microscopy image, in vitro solubility, and content of heavy metals in polylactic acid (PLA)/chitosan (CS) nanoparticles loading nifedipine. In addition, the In Vivo test of the PLA/CS nanoparticles loading nifedipine in the mice is also one of highlights of this work. The Zeta potential result shows that the charged surface of the PLA/CS nanoparticles loading nifedipine is neutral, negative or complex depending on nifedipine content. Nifedipine plays a role in increase of hydrophobic property, swelling degree and regular surface as well as decrease of surface rough of the nanoparticles. The PLA/CS/nifedipine nanoparticles are dissolved in the solutions with pH 6.8, pH 4.5 and pH 1.2. The In Vivo test of PLA/CS nanoparticles loading nifedipine on mice was evaluated by the change in diastolic pressure, systolic pressure, arterial pressure and heart rate. The obtained results confirm that the PLA/CS nanoparticles loading nifedipine is suitable to apply in the treatment of hypertension patients lately.

Study on characteristics, properties, and morphology of poly(lactic acid)/chitosan/hydroquinine green nanoparticles

Abstract Poly(lactic acid)/chitosan (PLA/CS) green nanoparticles containing hydroquinine (Hq) were prepared by emulsion method. The content of Hq was 10–50 wt% compared with the weight total of PLA and CS. The characteristics of these nanoparticles were analyzed by Fourier transform infrared (FTIR), differential scanning calorimetry, field emission scanning electron microscopy (FESEM), and particle size analysis. The wavenumbers of C=O, C=N, OH, and CH3 groups in FTIR spectra of the PLA/CS/Hq (PCHq) nanoparticles shifted in comparision with neat PLA, CS, and Hq that proved the interaction between these components. The FESEM images and particle size analysis results showed that the basic particle size of PCHq nanoparticles ranged between 100 and 200 nm. The Hq released from PLA/CS nanoparticles in pH 2 and pH 7.4 solutions was determined by ultraviolet-visible method. The obtained results indicated that the linear regression coefficient of calibration equation of Hq in the above solutions approximates 1. The Hq release from the PCHq nanoparticles includes fast release for the eight first testing hours, and then, controlled slow release. The Hq released process was obeyed according to the Korsmeyer-Peppas kinetic model.