Zinc Stearate Research Articles

Evaluating the potential of nanoparticles for controlling zinc stearate release from low‐density polyethylene into food simulants

The present study addressed the effect of polymer nanocomposites with different loading contents of fume silica (nanospheres) and nanoclay (nanosheet) on migration of zinc stearate from packaging materials into food simulants. Specific migration levels of zinc stearate from neat low‐density polyethylene (LDPE) and LDPE/nanocomposites into two food simulants stored at 40°C for 10 days were determined by gas chromatography coupled with flame ionization detector. Differential scanning calorimetry (DSC) analysis showed that incorporation of nanoparticles, especially at 1 wt% loading level of nano silica, noticeably increased degree of crystallinity, which significantly reduced water vapour permeability. Nanocomposites had a lower migration of zinc stearate in comparison with neat polymer. Additionally, results of this study revealed that physical properties of the food simulant had dominant effect on migration of zinc stearate.

Multifunctionality of zinc carboxylate to produce acylglycerols, free fatty acids and fatty acids methyl esters

Hydrolysis of acid oils is an important alternative for the production of non-ionic surfactants and fatty acids that can be converted to fatty acid methyl esters (biodiesel) by esterification. In this work, hydrolysis of palm oil was initially carried out in subcritical water using zinc stearate as catalyst. The experiments were performed in a CSTR-type reactor where the effect of temperature (140–190 °C), palm oil-to-water MR (1:10–1:53) and catalyst amount (2–10 wt%) were evaluated. High contents of free fatty acids (up to 60 wt%) with 35 wt% diacylglycerols and 20 wt% monoacylglycerols were obtained. Also, zinc stearate maintained its catalytic activity for palm oil hydrolysis for five consecutive reuse cycles but changes in the catalyst chemical composition were observed, mostly due to the conversion of zinc stearate to zinc palmitate. However, by increasing the reaction time from 4 to 8 h at 190 °C, there was a decrease in the accumulation of free fatty acids and an increase in the accumulation of acylglycerols and this was a strong evidence for reaction reversion. After removal of water, palm oil hydrolysates still containing the reaction catalyst were subjected to simultaneous esterification and transesterification under similar reaction conditions, reaching a final monoester content of about 90 wt%. These values are 50 wt% higher than those obtained by direct transesterification using the same catalyst. Also, the resulting crude glycerin phase was colorless in appearance, indicating little contamination with reaction products and intermediates.

Synthesis and Study of Zinc Orotate and Its Synergistic Effect with Commercial Stabilizers for Stabilizing Poly(Vinyl Chloride).

Zinc orotate (ZnOr2), which is a new kind of poly(vinyl chloride) (PVC) stabilizer, is prepared in this work through the precipitation method, and its impact on the thermal stability of PVC is measured by thermogravimetric analysis (TG), Congo red test, and discoloration test. The results exhibit that the thermal stability of PVC is positively enhanced after the addition of ZnOr2. In contrast with a commercial thermal stabilizer, zinc stearate (ZnSt2), a noteworthy improvement was observed that ZnOr2 could postpone the “zinc burning” of PVC. This is principally ascribed to the Or anion in the structure of ZnOr2 being able to absorb the HCl released by PVC, and to supersede unstable chlorine atoms in the structure of PVC. In addition, blending ZnOr2 with calcium stearate (CaSt2) in diverse mass ratios can significantly accelerate the thermal stability of PVC. Optimum performance was achieved with a CaSt2:ZnOr2 ratio of 1.8:1.2. Moreover, an outstanding synergistic effect can be observed when CaSt2/ZnOr2 is coupled with other commercial auxiliary stabilizers. The initial color and long-term stability of PVC including CaSt2/ZnOr2 is significantly increased when pentaerythritol (PER) is added, while dibenzoylmethane (DBM) can only improve its long-term thermal stability.

Highly Luminescent Ag-In-Zn-S Quaternary Nanocrystals: Growth Mechanism and Surface Chemistry Elucidation.

The presented research is focused on the synthesis of alloyed Ag-In-Zn-S colloidal nanocrystals from a mixture of simple metal precursors such as AgNO3, InCl3, zinc stearate combined with 1-dodecanethiol (DDT), 1-octadecene (ODE), and sulfur dissolved in oleylamine (OLA). In particular, the focus is on the effect of the solvent (ODE vs 1,2-dichlorobenzene (DCB)) and the type of sulfur precursor (S/OLA vs S/ n-octylamine (OCA)) on the metal precursors reactivates and on the chemical composition, crystal structure, and luminescent properties of the resulting nanocrystals. The replacement of ODE by DCB as a solvent lowers the reactivity of metal precursors and results in a 3-fold decrease of the photoluminescence quantum yields (Q.Y.) values (from 67% to 21%). This negative effect can be fully compensated by the use of S/OCA as a source of sulfur instead of S/OLA (Q.Y. increases from 21% to 64%). NMR studies of the isolated organic phase indicate that the S/OLA precursor generates two types of ligands being products of ( Z)-1-amino-9-octadecene (OLA) hydrogenation. These are "surface bound" 1-aminooctadecane (C18H37NH2) and crystal bound, i.e., alkyl chain covalently bound to the nanocrystal surface via surfacial sulfur (C18H37-NH-S crystal). Highly luminescent Ag-In-Zn-S nanocrystals exhibit a cation-enriched (predominantly indium) surface and are stabilized by a 1-aminooctadecane ligand, which shows more flexibility than OLA. These investigations were completed by hydrophilization of nanocrystals obtained via exchange of the primary ligands for 11-mercaptoundecanoic acid, (MUA) with only a 2-fold decrease of photoluminescence Q.Y. in the most successful case (from 67% to 31%). Finally, through ligand exchange, an electroactive inorganic/organic hybrid was obtained, namely, Ag-In-Zn-S/7-octyloxyphenazine-2-thiol, in which its organic part fully retained its electrochemical activity.

High performance metal stearates thermal stabilizers for poly vinyl chloride

Low thermal stability of poly vinyl chloride (PVC) is one of the most serious problems that facing its processing. In the present study some single and mixed metal stearate soaps were prepared, characterized and evaluated for their performance in enhancing and imparts the thermal stability of PVC. Accordingly, calcium stearate, barium stearate, zinc stearate and also the mixed metal stearate salt of calcium, zinc and barium were prepared by the double decomposition of sodium stearate and single or mixed metal acetate solutions. The prepared metal stearates were characterized via spectroscopic analysis (FT-IR and XRD) in addition to micro analysis and thermal gravimetric analysis (TGA). The results showed that the prepared metal stearates are good thermal stabilizers for PVC; also the thermal stability of the prepared (Ca/Ba/Zn) stearate was enhanced when melamine, ammonium poly phosphate, magnesium hydroxide and Ca/Zn phosphate are mixed with it.

A Study of the Regularities of the Solid-Phase Synthesis of Metal Stearates

Features of the solid-phase synthesis of metal stearates (calcium, barium, zinc, and silver stearates) on a Bridgman anvil-type device were studied. Factors of the solid-phase reaction between reagents were determined. The activation volumes of the reactions between stearic acid with calcium oxide and silver oxide were determined. The initial rates of the solid-phase synthesis of silver and calcium stearate were calculated. The rates of synthesis of metal stearates in liquid and solid phases were compared. The data showed that metal carboxylates could be synthesized in a solution-less medium.

Influence of process parameters on the workability characteristics of sintered Al and Al–Cu composites during cold deformation

An experimental investigation on the process parameters affecting the workability characteristics of sintered aluminium (Al) and aluminium–copper (Al–Cu) composites during cold forging has been carried out. Cylindrical billets of Al, Al–3%Cu and Al–6%Cu with height to diameter ratio (aspect ratio) of 0.45 and 0.9 were cold deformed under three different frictional conditions (nil/no lubricant, graphite lubricant and zinc stearate lubricant). As such, some important process parameters influencing the workability of these composites such as the initial preform geometry and different volume percent of Cu addition to the Al composite preforms on the relative density, R and physical parameters such as stresses affecting the workability stress index, β have been investigated. Also, the effects of the different frictional conditions on the same are presented. It was established that the nil/no lubricant condition and preforms of the lower aspect ratio yielded improved densification, higher values of stresses and better workability. Furthermore, Al–Cu composites were developed to yield better combined properties such as improved densification and workability than monolithic Al. However, the addition of Cu reduced the axial strain to fracture. As such, a decrease in the densification and the workability characteristics was noted with an increase in the volume percent of Cu.

FERRONIOBIUM ALLOY FINES AGGLOMERATION THROUGH BRIQUETTING

Brazil is the largest producer of Niobium alloys, with a production of 58,000 tons of Nb2 O5 concentrate in 2016, corresponding to a 92.81% of the world production. The Brazilian Niobium ores grades vary from 0.51 to 2.71%. Ferroniobium (Fe-Nb) is an iron niobium alloy with niobium content of 60-70%. It is the main source for niobium alloying of HSLA steel and covers more than 80% of the worldwide niobium production. In 2014, Brazil produced 51,737 tons of Fe-Nb, being around 90% of it for exportation. In the final stage of the Fe-Nb production, the alloy needs to be crushed in a jaw crusher, which generate fine particles (around 26% of the feed below 10 mm at Niobras/CMOC). The selling price of the fine particles have a significant loss in the market, since the fine particles cannot be used directly in steelmaking. A process to agglomerate the Fe-Nb fine particles into briquettes with size and chemical composition similar to original products was developed. Organic binders were used as well as a lubricant agent. The briquettes were characterized both physically and chemically. For the physical characterization, the briquettes were tested for mechanical and water resistance, thermal shock and Brinell hardness. Briquettes containing addition of 3% of zinc stearate, 2% of iron powder, and 1% of water reached a Niobium content above 62% and contaminants levels of below the standard Fe-Nb specifications. The results indicate that Fe-Nb alloy fines can be technically and economically agglomerate by briquetting.

Utility of Zinc (Lignin/Silica/Fatty Acids) Complex Driven From Rice Straw as Antioxidant and Activator in Rubber Composites

This article presents a method to precipitate zinc (lignin/silica/fatty acids) complex (Zn LSF complex) from the black liquor of pulped rice straw and studying the efficiency of it as green activator and antioxidant in natural rubber composites. The results obtained revealed that the investigated zinc complex has dual function as activator and antioxidant in natural rubber composites. This evaluation was supported by physico‐mechanical properties of the vulcanizates which showed a considerable improvement of rheometric characteristics, tensile strength, strain at break, hardness, Young's modulus, thermal oxidative aging, and thermal stability of NR composites. The composite loaded with 7 phr of Zn LSF complex as activator exhibited the best mechanical properties in comparison with the same concentrations of control activator zinc stearate. Also, results revealed that Zn LSF complex is efficient as antioxidant in NR vulcanizates compared conventional antioxidants, namely polymerized 2,2,4‐trimethyl‐1,2‐dihydroquinoline. POLYM. ENG. SCI., 59:E196–E205, 2019. © 2018 Society of Plastics Engineers

Effect of electron‐beam irradiation on the thermal vulcanization of a natural rubber compound

ABSTRACTThe influence of electron‐beam irradiation on the thermal vulcanization curing kinetics of a natural rubber compound was investigated by means of rheometric tests [moving die rheometry (MDR)] and differential scanning calorimetry (DSC). Differences in the storage moduli of compounds with different radiation doses were observed and assigned to a plasticizer effect by the zinc stearate mainly formed in the mixing stages; this compound migrated to the interphase region. This fact was confirmed by Fourier transform infrared spectroscopy. From the measurements performed by MDR and DSC testing, the induction time (to) was analyzed in the frame of the Claxton–Liska model, whereas the kinetic behavior of the nonirradiated and pre‐irradiated compounds were satisfactorily fitted with the Isayev–Deng and Kamal–Ryan models. Additionally, both curing characterization techniques corroborated the fact that the pre‐irradiated rubber compound showed an earlier t o and a lower activation energy in comparison with the nonirradiated compound. These facts were attributed to the effect of irradiation on the free sulfur content present in the rubber compound, which promoted more activated precursor species to crosslink with rubber. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47216.

An Experimental Investigation on the Effect of Sintering Temperature and Holding Time to the Characteristics of Fecual Powder Compacts Formed at Elevated Temperature

This paper presents the experimental investigation on the effect of sintering schedule to the final properties of FeCuAl powder compacts formed at elevated temperature through a lab-scale uniaxial die compaction rig. Iron (Fe) powder ASC100.29 was used as a main powder constituent and mixed with elemental powders which are copper (Cu) and aluminum (Al). The weight percentage of powder mass was divided into four, i.e., iron (91.7 wt%), copper (7.5 wt%), aluminum (0.5 wt%), and zinc stearate (0.3 wt%) as lubricant. All the powders were mixed through mechanical blending at a rotation speed of 30 rpm for 30 min. The mixed powder mass was compacted at 150˚C by 425 MPa of axial loading from upward and downward simultaneously. Subsequently, the defect-free green compacts were sintered under controlled argon gas atmosphere at three different sintering temperatures, i.e., 800˚C, 900˚C and 1000˚C for 120 min, 150 min and 180 min, respectively at constant sintering rate of 10˚C/min. Afterwards, the sintered samples were characterized for their physical properties, electrical properties, mechanical properties and their microstructures were evaluated. The results revealed that higher flexure stress was acquired by sample sintered at 1000˚C for 120 min and their microstructures were found to be better, i.e., the particles were bonded perfectly.

Synthesis and Degradation of Cadmium-Free InP and InPZn/ZnS Quantum Dots in Solution.

This study advances the chemical research community toward the goal of replacing toxic cadmium-containing quantum dots (QDs) with environmentally benign InP QDs. The InP QD synthesis uniquely combines the previously reported use of InP magic-sized clusters (MSCs) as a single-source precursor for indium and phosphorus to form InP QDs, with zinc incorporation and subsequent ZnS shelling, to form InPZn/ZnS QDs with luminescence properties comparable to those of commonly used cadmium-containing luminescent QDs. The resulting InPZn/ZnS QDs have an emission quantum yield of about 50% across a broad range of emission peak wavelengths and emission peaks averaging 50 nm fwhm. The emission peak wavelength can be easily tuned by varying the Zn/In ratio in the reaction mixture. The strategy of using zinc stearate to tune the emission properties is advantageous as it does not lead to a loss of emission quantum yield or emission peak broadening. Although the initial optical properties of InP and InPZn/ZnS QDs are promising, thermal stability measurements of InPZn QDs show significant degradation in the absence of a shell compared to the CdSe QDs particularly at increased temperature in the presence of oxygen, which is indicative of thermal oxidation. There is no significant difference in the degradation rate of InP QDs made from molecular precursors and from MSCs. Additionally, the emission intensity and quantum yield of InPZn/ZnS QDs when purified and diluted in organic solvents under ambient conditions decrease significantly compared to those of CdSe/ZnS QDs. This indicates instability of the ZnS shell when prepared by common literature methods. This must be improved to realize high-quality, robust Cd-free QDs with the capability of replacing CdSe QDs in QD technologies.

Exposing Sustainable Mortars with Nanosilica, Zinc Stearate, and Ethyl Silicate Coating to Sulfuric Acid Attack

Obtaining durable materials that lengthen the service life of constructions and thereby contribute to sustainability requires research into products that improve the durability of cementitious materials under aggressive conditions. This paper studies the effects of sulfuric acid exposure on four mortar types (control mortar, mortar with nanosilica, mortar with zinc stearate, and mortar with an ethyl silicate coating), and evaluates which of them have better performance against the acid attack. After 28 days of curing, the samples were exposed to a sulfuric acid attack by immersing them in a 3% w/w of H2SO4 solution. Physical changes (mass loss, ultrasonic pulse velocity, open porosity, and water absorption), and mechanical changes (compressive strength) were determined after the sulfuric acid exposure. A scanning electron microscope (SEM) was used to characterize the morphology of the surface mortars after the exposure. The control mortar had the highest compressive strength after the acid attack, although of the four types, the zinc stearate mortar showed the lowest percentage of strength loss. The zinc stearate mortar had the lowest mass loss after the acid exposure; moreover, it had the lowest capillary water absorption coefficient (demonstrating its hydrophobic effect) both in a non-aggressive environment and acid attack.

Effects of heat treatment and lubricant on magnetic properties of iron-based soft magnetic composites with Al2O3 insulating layer by one-pot synthesis method

Abstract In this work, we investigated the effects of heat treatment and lubricant on the magnetic properties of iron-based soft magnetic composites by one-pot synthesis method. Scanning electron microscopy (SEM) revealed that the surface of the coated Fe powder was coated with different thickness of Al2O3 insulating layer. The experiment results indicated that using lubricant in the coated iron-based compacts presented higher permeability, higher resistivity, lower core loss over the wide frequency range compared with those without using lubricant after heat treatment at 773 K. The above effects would be reduced with the increase of the thickness of the alumina coating. As the heat treatment temperature raised from 573 K to 773 K and even higher 873 K, zinc stearate continued to decompose, and its decomposition product carbon reacted with the iron oxide of the thinner coating. As a result, the frequency stability of the permeability decreased especially at high frequencies, the resistivity decreased significantly, and the eddy current loss increased significantly. When the alumina insulation layer became thick, the effects of zinc stearate and its leaving carbon after decomposition on the properties of the pressed magnet decreased.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ ЦЕЛЕВОГО МОДИФИЦИРОВАНИЯ ЭПОКСИДНЫХ МАТРИЦ И УГЛЕПЛАСТИКОВ НА ИХ ОСНОВЕ НА ТЕМПЕРАТУРУ В ЗОНЕ РЕЗАНИЯ ПРИ ОБРАЗОВАНИИ ОТВЕРСТИЙ

PURPOSE. The paper studies the effect of the special modification of epoxy matrices and epoxy matrix-based polymer composites on thermophysical parameters of machining processes under hole formation. A goal is set to produce experimental samples from matrices and experimental panels from carbon fiber plastics based on modified matrices. It is necessary to reveal whether there is any dependence of machining process thermal effects on the modification degree of matrices and carbon fiber plastics. METHODS. Experimental methods are used to achieve the purposes of this work. The experiment includes: production of experimental panels (binder preparation, liquid-phase combination with a dry filler, impregnation and vacuum-pressure oxidation molding); checking of their quality and mechanical properties (non-destructive testing of experimental panels by acoustic methods and standard mechanical tests); measurement of the cutting temperature under hole drilling in the sample made of experimental panels (infrared thermography of the hole formation zone). RESULTS AND THEIR DISCUSSION. It has been determined that the matrix samples feature the lowest heat release in the intervals from 0.1 to 0.3% wt depending on the type of the tool used. The peaks of the lowest heat release of the matrix-based carbon plastic samples are shifted to the range from 0.2 to 0.5%. The decrease in the maximum temperature in these ranges is due to the antifriction properties of the zinc stearate modifier: the coefficient and friction forces are reduced. Further increase in the modifier concentration leads to the recovery or even excess of the thermal effects relative to the initial unmodified matrices and carbon fiber plastics (0 % zinc stearate). This fact can presumably be explained by the decrease in cutting efficiency at reduced friction coefficients. The shifts of the peaks to the right and their “widening” for carbon fiber plastic samples is probably related to the thermophysical properties of the filler, which change the conditions of heat removal from the contact zone of friction bodies (a part and a processing tool). It is the carbon fiber plastic that is of some practical interest being a composite combination of a matrix and a carbon filler, which demonstrates more advantageous values of the thermal parameters of machining processes according to the study results. CONCLUSIONS. It has been shown that modification does not have any negative effect on the mechanical properties of modified composition-based carbon plastic. The dependences of the thermal effects of the machining processes under the hole formation in the samples on zinc stearate modifier concentration have been revealed. This fact proves the effectiveness of modification.

Superhydrophobic brass and bronze meshes based on electrochemical and chemical self-assembly of stearate

The preparation and characterization of superhydrophobic membranes formed on metal meshes (brass and bronze) by coating from stearic acid is presented. The membranes were prepared by two methods: electrolysis and acid etching. The electrolysis process is a one-step method performed by anodizing the mesh in ethanol solutions of stearic acid. Stearic acid concentration, support electrolyte concentration and electrolysis time were systematically varied. Nanostructures, including nanotubes, are induced on the metallic filaments. Analysis by FTIR, XRD, XPS and SEM of surfaces and precipitated material indicate that formed nanostructures are assemblies of metallic stearates on the surface (copper and/or zinc stearates). Superhydrophobicity (contact angles larger than 150°) was only achieved (in the electrolysis method) in cases where the formation of nanotubes was observed. On the other hand, the acid etching process is a two-step method: immersion of the meshes in acid solution of CuCl2 or FeCl3, oxidizing the surface with formation of inorganic salts nano crystals, followed by immersion in stearic acid solution. Organic nanostructures (nanoribbons and/or nanopetals) were observed after the second step. Superhydrophobic surfaces (contact angles between 150 and 170°) were obtained for all the membranes.Both kind of membranes (electrolysis and etching) resulted effective in oil-water separation.

EFFECT OF SOME ADDITIVES ON PROCESSBILITY, MECHANICAL PROPERTIES AND MORPHOLOGY OF POLYOXYMETHYLENE/SILICA NANOCOMPOSITES

Using additives for polyoxymethylene/silica (POM/SiO2) nanocomposite system is one of suitable solutions to improve processbility, mechanical properties, especially, elongation at break of the material. In this paper, the effect of some additives on the processbility, mechanical properties and morphology of polyoxymethylene/silica (POM/SiO2) nanocomposite was investigated. Zinc stearate (under the commercial name ultraflow – UTF), ethylene-vinyl acetate copolymer (EVA), linear low density polyethylene (LLDPE) and polylactic acid grafted 5 wt.% of polyethylene glycol (PELA) were used as additives for the nanocomposites. The obtained results showed that the preparing process of the POM/SiO2 nanocomposite becam more easily in the presence of PELA, UTF and EVA, corresponding to a lower torque and mixing energy. The PELA caused decrease in the E-modulus or hardness and increase in elongation at break as well as tensile strength of the POM/SiO2 nanocomposites. The SEM images showed that POM and nanosilica were less compatible in the nanocomposite using EVA, LLDPE and UTF and they were more compatible with using PELA.

The Effect of Zinc Stearate Modification on Aging Characteristics of Asphalt Binder

Different types of modifiers have been investigated to improve aging characteristics of asphalt binders. In this research, the effect of zinc stearate modification has been studied on aging resistance of asphalt binder. For this purpose, viscous flow properties and other rheological characteristics of neat and modified asphalt binders have been evaluated by using conventional experimental tests and superpave protocol test. In order to evaluate rheological behavior of asphalt binder in presence of zinc stearate, a neat asphalt binder sample with three modified samples containing 0.5, 1 and 2 wt% of zinc stearate were aged by means of the Rolling Thin Film Oven Test (RTFOT). The Brookfield rotational viscosity (RV) was implemented at six different temperatures from 100 to 200 degree of centigrade. Furthermore, the dynamic shear rheometer (DSR) was used for evaluating complex modulus (G*) and phase angle (δ) of all neat and modified samples at 10, 20, 30, 40, 50 and 60°C in frequency sweep mode. To evaluate effect of adding zinc stearate by using viscosity results, proportion of asphalt binder’s viscosity after aging to its viscosity before aging was defined as viscosity aging index (VAI). Results showed that adding zinc stearate to neat asphalt binder reduces the viscosity aging index. Results of frequency sweep test indicated that zinc stearate causes the values of complex shear modulus in aging asphalt binder approach to neat state which means the effect of zinc stearate modification is positive for improving aging resistance of asphalt binder.

Antimicrobial itaconimido aromatic hydrazide derivatives for inhibition of the thermal degradation of rigid PVC

A series of novel itaconimido aromatic hydrazide derivatives has been synthesized by a low-temperature solution condensation reaction of N-[4-(chlorocarbonyl)phenyl]itaconimide with an equimolar amount of benzhydrazide, salicylhydrazide, p-aminobenzhydrazide or p-aminosalicylhydrazide. The structure of the synthesized derivatives was elucidated on the basis of elemental analyses, FTIR, 1H-NMR, and mass spectroscopy. All the hydrazide derivatives were screened for antibacterial activity against Bacillis subtilis and Streptococcus pneumoniae as Gram-positive bacteria and against Escherichia coli as Gram-negative bacteria and for antifungal activity against Aspergillus fumigatus, Geotricum candidum and Syncephalastrum racemosum fungi by agar well diffusion method. They showed good antimicrobial activity as judged by their high inhibition zone diameter and low minimum inhibition concentration. They are more potent against Gram-positive bacteria than against Gram-negative bacteria. Some of the hydrazide derivatives displayed comparable or even better antibacterial and antifungal activities than the reference bactericides or fungicides. The hydrazide derivatives are characterized by high thermal stability and could be cyclodehydrated into the corresponding 1,3,4-oxadiazole derivatives in the temperature region of 240–285 °C by losing water from the hydrazide groups as illustrated by thermogravimetric analyses (TG) and differential scanning calorimetry (DSC) in nitrogen. This is not a true degradation, but rather a thermochemical transformation reaction of the hydrazide derivatives into their corresponding 1,3,4-oxadiazole derivatives. The hydrazide derivatives were investigated as thermal stabilizers for rigid PVC using thermogravimetric analysis technique, in nitrogen. They exhibited a higher stabilizing efficiency relative to dibasic lead carbonate (DBLC), cadmium–barium–zinc (Cd–Ba–Zn) stearate complex and di-n-octyltin bis (isooctylmercaptoacetate) (n-octyltin mercaptide, n-OTM) industrially thermal stabilizers as shown by their higher initial decomposition temperature and higher residual weight percent at particular temperatures. Their stabilizing efficiency is also illustrated by lower rates both of discoloration as well as degree of chain scission of the polymer during degradation. The stabilizing efficiency increased with the introduction of electron-donating substituent groups into these derivatives.

Response surface study and kinetic modelling of biodiesel synthesis catalyzed by zinc stearate

This contribution reports experimental and theoretical studies on the transesterification of soybean oil with methanol catalyzed by zinc stearate. This reaction produces fatty acid methyl esters (FAME) and glycerol, and di- and monoglycerides as intermediate products.Response Surface Methodology was used to study the relationship between process variables and triglyceride conversion, FAME yield and initial rate. An increase in the catalyst concentration and in the methanol/oil molar ratio increased triglyceride conversion and FAME yield and decreased the initial turnover frequency values. The latter was associated with the formation of an emulsion in the reaction medium.A kinetic study of the reaction was performed. Two models were proposed. Model 1 assumed a complete mixing of the dissolved catalyst with the reactants and a second-order mechanism for the forward and reverse reactions, where the reaction system could be described as pseudo-homogeneous and the catalyst was dissolved in the reaction medium. Model 2 supposed that the dissolved catalyst formed part of a macro emulsion, with mass transfer resistance in the boundary layer around the droplets. The kinetic constants were determined, and Model 2 showed a better fit to the experimental data. The model and the kinetic parameters allow to generate reaction operation strategies.