Hyperfine interactions studies on Pt–In/Nb2O5 catalysts

Pt–In/Nb₂O₅ catalysts were investigated using temperature-programmed reduction (TPR) and time differential perturbed angular correlation (TDPAC) experiments. The results indicated the presence of In–O surface complexes for low loading In/Nb₂O₅ and Pt–In/Nb₂O₅ catalysts after calcination. These complexes did not form a In₂O₃ crystalline phase. After reduction of the Pt–In/Al₂O₃ catalyst, In is present in different states. A fraction of In atoms is bonded to niobia surface, as a surface complex that does not show crystalline structure similar to bulk In₂O₃. Other fraction of In atoms interacts with platinum, in the form of an alloy, in locations that present trigonal symmetry.     

Half-sandwich samarium (III) diketiminate bromide as a catalyst for methyl methacrylate polymerization

Half-sandwich samarium(III) diketiminate bromide was successfully synthesized and was shown to be active in methyl methacrylate (MMA) polymerization. The effects of temperature, polymerization time and catalyst concentration were studied. Activities of ca. 18 kg of polymethacrylate (PMMA) per mol of samarium per hour were obtained under optimum conditions (0 °C and a MMA/catalyst molar ratio of 100/1), giving a polymer with a molar mass M_n>24,000 g mol⁻¹ and a molar mass distribution (M_w/M_n)<1.4. After 1 h of polymerization, conversions of MMA as high as 96% were observed.     

Effect of montmorillonite on the properties of thermosensitive poly(N‐isopropylacrylamide) composite hydrogels

Thermosensitive composite hydrogels containing various amounts of sodium montmorillonite (NaMM) and poly(N‐isopropylacrylamide) (pNIPAAm) were synthesized. Their equilibrium degree of swelling (DS) was measured in NaCl solutions of different ionic strength and at various temperatures. The DS decreased when increasing the clay content and no substantial shift in the phase transition temperature was noticed. The composite hydrogels investigated had a NaMM content ranging between 1.0 and 5.7 wt % (in 0.1M NaCl at 25°C). A considerable enhancement in the response to thermal stimuli was observed for NaMM contents >2–3 wt %. It is suggested that when the NaMM concentration approaches a critical value, the clay platelets can inhibit the formation of the hydrophobic skin layer that hinders shrinking in conventional pNIPAAm hydrogels. The effect of montmorillonite on the mechanical properties of the hydrogels was investigated by uniaxial compression tests, which showed that the modulus increases with the NaMM content. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1964–1971, 2004     

Effect of lithium and residual nitrate species on platinum dispersion in Pt/Al2O3 catalysts

The effect of lithium (ex LiNO₃) on the metallic dispersion of 0.8 wt% Pt/Al₂O₃ catalysts, prepared by different impregnation techniques, was investigated by temperature programmed reduction (TPR) and the frontal method of H₂ chemisorption. The temperature at which platinum precursor is reduced at a maximum rate (543 K) was not modified by 0.1 wt% lithium addition, whatever the preparation technique used. The dispersion values of platinum (70–90%), after reduction at 773 K, were slightly dependent on the preparation procedure. After the addition of 0.8 wt% lithium the TPR profile presented two well defind peaks and the dispersion values (20–50%), measured after reduction at 773 K, presented a significant decrease. The results are linked with the presence of residual nitrate ions, that had not been eliminated during calcination at 773 K in air, but had been decomposed under the reducing atmosphere of the TPR experiment.     

Effectiveness of the preparation of maleic anhydride grafted poly (lactic acid) by reactive processing for poly (lactic acid)/carbon nanotubes nanocomposites

An effective strategy to increase the properties of poly (lactic acid) (PLA) is the addition of carbon nanotubes (CNT). In this work, aiming to improve the surface adhesion of PLA and CNT a new compatibilizer agent was prepared by reactive processing, PLA grafted maleic anhydride (PLA-g-MA) using benzoyl peroxide and maleic anhydride. The effectiveness of the PLA-g-MA as a compatibilizer agent was verified for PLA/PLA-g-MA/CNT nanocomposites. PLA and PLA-g-MA samples were characterized by Fourier transform infrared spectroscopy (FT-IR) to confirm the grafting reaction of maleic anhydride on PLA chains and by rheological analysis to prove the changes in the matrix PLA after the graphitization reaction. Thermal (differential scanning calorimetry and thermogravimetric analysis), mechanical tests (Izod impact strength and tensile test), and morphological characterization were used to verify the effect of the compatibilizer agent. The preparation of PLA-g-MA by reactive extrusion processing proved satisfactory and the nanocomposites presented good thermal and mechanical properties. The addition of the PLA-g-MA also contributed to the greater distribution of CNT and can be used as an alternative for the production of PLA/CNT nanocomposites.     

Effect of glassy carbon addition and photodegradation on the biodegradation in aqueous medium of poly (3-hydroxybutyrate-co-3-hydroxyvalerate)/glassy carbon green composites

The use of biodegradable polymers is an interesting way to reduce the polymeric waste accumulation in the environment. However, the addition of fillers to biodegradable polymer matrices may decrease their biodegradability. Glassy carbon (GC) is a promising carbon material that can be employed as a filler in the production of antistatic packaging utilized to protect electronic components. The use of a biodegradable polymeric matrix such as poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) can be an excellent alternative for the preparation of green composites to be used in these packages. This work aims to evaluate the effect of the GC addition and the GC particle size on the biodegradability of the PHBV matrix, as well as to study the result of the employment of a previous photodegradation treatment on the biodegradation in aqueous medium of PHBV/GC composites. Scanning electron microscopy, residual weight measurement (%) and surface roughness showed that GC does not interfere negatively with PHBV biodegradability. Differential scanning calorimetry analysis and residual weight measurement permitted to suggest that the increase in the crystallinity degree of PHBV and PHBV/GC samples occasioned by the ultraviolet radiation hindered the water and enzyme access to the bulk of the materials, decreasing the biodegradability.     

Antimicrobial PLA/TPS/gelatin sheets with enzymatically crosslinked surface containing silver nanoparticles

In the present work, poly (lactic acid)/thermoplastic starch/gelatin sheets were produced by calendering–extrusion process and silver nanoparticles (AgNPs, synthesized by chemical reduction with d ‐glucose), were incorporated at sheet surfaces to promote antimicrobial activity. A gelatin solution containing AgNPs was enzymatically crosslinked as a layer at sheets surface using transglutaminase. AgNPs presented 63 nm (z average size) and spherical shape (scanning electron microscopy, SEM) while morphology analysis showed that sheets presented internal porosity. Mechanical properties (Young modulus, elongation at break, and tensile strength) and water vapor permeability presented significant difference in function of gelatin amount added to sheets formulation due to increased internal porosity. Antimicrobial activity was demonstrated against Bacillus cereus, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa for the AGNPs solution as well as for the surface treated films. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43039.     

Structural,thermal, and gas transport properties of HDPE/LLDPE blend‐based nanocomposites using a mixture of HDPE‐g‐MA and LLDPE‐g‐MA as compatibilizer

Nanocomposites based on high density polyethylene (HDPE)/linear low density polyethylene (LLDPE) blend were prepared by melt compounding in a twin‐screw extruder using organoclay (montmorillonite) as nano‐filler and a 50/50 wt% mixture of maleic anhydride functionalized high density polyethylene (HDPE‐g‐MA) and linear low density polyethylene (LLDPE‐g‐MA) as the compatibilizing system. The addition of a maleated polyethylene‐based compatibilizing system was required to improve the organoclay dispersion in the HDPE/LLDPE blend‐based nanocomposite. In this work, the relationships between thermal properties, gas transport properties, and morphology were correlated. The compatibilized nanocomposite exhibited an intercalated morphology with a small number of individual platelets dispersed in the HDPE/LLDPE matrix, leading to an significant decrease in the oxygen permeation coefficient of the nanocomposites. A decrease in the carbon dioxide permeability and oxygen permeability with increase of nanoclay was observed for the compatibilized nanocomposites. The carbon dioxide permeability of the compatibilized nanocomposites was lower than the carbon dioxide permeability of the uncompatibilized nanocomposites even with the low intrinsic barrier properties of the compatibilizer. These effects were attributed to a good dispersion of the inorganic filler, good wettability of the filler by the polymer matrix, and strong interactions at the interface that increased the tortuous path for diffusion. Theoretical permeability models were used to estimate the final aspect ratio of nanoclay in the nanocomposite and showed good agreement with the aspect ratio obtained directly from TEM images. POLYM. ENG. SCI., 56:765–775, 2016. © 2016 Society of Plastics Engineers