The focus of this research was on the thermal conductivity and rheological properties of poly(ethylene glycol) with a molecular mass of 200 g mol
−1
(i.e., PEG200) loaded with four different types of ...multi-walled carbon nanotubes (MWCNTs) in a wide concentration range up to 10 mass%. MWCNTs used differ in size (both diameter and length) and the content of COOH (oxidized) functional groups on their surface. It was found that the use of oxidized, shorter and wider MWCNTs in PEG200 results in highest enhancement in thermal conductivity by 133% for 10 mass% MWCNTs-PEG200 nanofluids. Investigation of the shear rate dependence of dynamic viscosity (
η
) showed that the use of MWCNTs in concentrations greater than 0.1 mass% changes the Newtonian behavior of PEG200 and results in the shear-thinning behavior. This behavior is strongly influenced by the MWCNT concentration in the nanofluid. When comparing the same nanofluid concentration, the highest degree of MWCNT agglomeration in PEG200 nanofluids was observed when long, thin and pristine MWCNTs were used. The thermal conductivity results were correlated with the most commonly used theoretical models: Maxwell, Hamilton-Crosser, Xue, and Murshed. Dynamic viscosity results were correlated with Einstein, Brinkman, and Brenner-Condiff theoretical models. The best agreement with the experimental results was obtained by the Maxwell and Einstein models, indicating the formation of sphere-like MWCNT agglomerates in each PEG200 nanofluid studied.
A novel procedure that uses FTIR-ATR CO signal area (1690–1800 cm−1) and a standard test method that is used for determination of fatty acid methyl ester in diesel were applied for the quantification ...of ethyl, propyl, butyl, isobutyl, pentyl, isopenyl, hexyl, heptyl, octyl, decyl, and dodecyl fatty acid esters in diesel. These methods were examined in the range from 0.0 to 30.0 vol% of biodiesel in diesel. The obtained correlation between concentration and FTIR absorption was highly linear (R2 above 0.993, in most cases 0.999). Considering that diesel blends with butanol or higher alcohols with their corresponding fatty acid alkyl ester can satisfy the requirements for use in diesel engines, we tested if such blending would influence the results of those two methods. The results indicate that biodiesel can be quantified for blends with alcohol content up to 9 vol% of the total volume when signal area calibration is used.
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•FTIR methods for determination of biodiesel content in blends with diesel fuel.•Methods are applicable for biodiesels synthetized from different alcohols.•Influence of alcohol content on quantification of biodiesel in blends with diesel.
Proton exchange membrane water electrolysis (PEMWE) represents promising technology for the generation of high-purity hydrogen using electricity generated from renewable energy sources (solar and ...wind). Currently, benchmark catalysts for hydrogen evolution reactions in PEMWE are highly dispersed carbon-supported Pt-based materials. In order for this technology to be used on a large scale and be market competitive, it is highly desirable to better understand its performance and reduce the production costs associated with the use of expensive noble metal cathodes. The development of non-noble metal cathodes poses a major challenge for scientists, as their electrocatalytic activity still does not exceed the performance of the benchmark carbon-supported Pt. Therefore, many published works deal with the use of platinum group materials, but in reduced quantities (below 0.5 mg cm−2). These Pd-, Ru-, and Rh-based electrodes are highly efficient in hydrogen production and have the potential for large-scale application. Nevertheless, great progress is needed in the field of water electrolysis to improve the activity and stability of the developed catalysts, especially in the context of industrial applications. Therefore, the aim of this review is to present all the process features related to the hydrogen evolution mechanism in water electrolysis, with a focus on PEMWE, and to provide an outlook on recently developed novel electrocatalysts that could be used as cathode materials in PEMWE in the future. Non-noble metal options consisting of transition metal sulfides, phosphides, and carbides, as well as alternatives with reduced noble metals content, will be presented in detail. In addition, the paper provides a brief overview of the application of PEMWE systems at the European level and related initiatives that promote green hydrogen production.
In this study biodiesel was produced from waste sunflower cooking oil and ethanol using N,N′,N″-tris(3-dimethylaminopropyl)-guanidine as new catalyst, which allows to avoid unwanted side-reaction of ...saponification. The influence of process variables on the conversion was investigated using experimental design and response surface methodology. Independent factors were varied in the following range: molar ratio of alcohol/oil from 3:1 to 15:1; catalyst concentration from 0.5 to 3 wt%; reaction temperature from 40 to 80 °C; and reaction time from 40 to 200 min. An empirical model of the process was developed. With this model and the goals of minimizing the independent factors in the tested range and maximizing the conversion, the optimization resulted in the following conditions: 1.13 wt% of catalyst, a molar ratio of 11.16:1, temperature of 67.96 °C, and a reaction time of 80 min. With those optimal conditions, the conversion predicted by the model was 94.6%.
•Biodiesel production from waste cooking oil and bioethanol with guanidine catalyst.•Process optimization for: temp., time, wt% catalyst, and molar ratio of reactants.•The optimal conditions were: oil/alcohol = 1/11.16, temp. = 68 °C, wcatalyst = 1.13 wt%.•At optimal conditions the conversion was 94.6%.
Since conventional catalysts for biodiesel production have problems with saponification, ten guanidine derivatives were investigated in this study for their catalytic activity in the production of ...biodiesel from rapeseed oil and methanol. The most active catalyst was selected for process optimization. The influence of process parameters (reaction time, mass percent of catalyst and alcohol to oil ratio) on the transesterification process was evaluated using a design of experiments following a 33 factorial Box-Behnken design of experiments in conjunction with response surface methodology. An accurate quadratic model was developed (p-value < 0.001, F-value 65.90, R2 0.990) and used for process optimization. The resulting optimal conditions were 1.8 wt% of catalyst, methanol to oil ratio of 6.2:1, and a reaction time of 80 min with a predicted yield of 99.2 mol%. The optimal conditions were verified on a larger scale (1 kg), obtaining a yield of 96.5 mol%, confirming the accuracy of the quadratic model. In addition, the obtained biodiesel was characterized with respect to the main physicochemical and application properties.
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Polylactide (PLA) composites with three types of fillers, calcium carbonate, barium sulfate, and mica, have been prepared. Methods of preparation were melt mixing in a Brabender plasticorder at ...190 °C and solution mixing in chloroform. The concentration of added fillers was: 0.1, 1, and 5 mass% (only by melt mixing). Thermal properties of prepared composites were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis. The dispersity of filler in matrix was examined by scanning electron microscopy. There was no agglomeration in any composites. Results of DSC analysis reveal the influence of preparation method on thermal transitions. By the melt mixing method, the introduced filler hindered crystallization but caused mostly just a slight increase in
T
g
relative to pure PLA (57.4 °C). By solution-mixing method, the absence of crystallization is noticed in all samples. Concurrently composites displayed
T
g
higher for ca. 5–6 °C relative to pure PLA (53.3 °C), with the exception of composite with smallest content of calcium carbonate nanofiller. Thermal stability is improved in all composites, regardless of the filler used and preparation method. It is especially pronounced regarding decomposition temperature (5 mass% loss) where the increase ranges from 11 up to 55 °C in case of melt mixing and 17–35 °C for solution mixing.
In order to contribute to the demanded sustainability transparent poly(methyl methacrylate) (PMMA) composites with cellulose nanocrystals (CNC) up to high shares of 50 wt% were prepared by in situ ...radical polymerization in green solvent Cyrene. The weight average molecular weights of PMMA were in the range from 144,000 to 160,000 g mol−1 and the dispersity was in the range of 1.49 to 1.89 with high conversion of monomer to polymer. The DSC thermal analysis showed that the glass transition temperature of pure PMMA was at 99°C while in composites increased from 103°C up to 129°C with the increase of CNC from 1 wt% to 50 wt%. TGA shows that the addition of CNC does not have a significant effect on the thermal stability of PMMA. In composites Young's modulus increases with the increasing CNC ratio and composites with 50 wt% of CNC showed more than twice the modulus of the PMMA matrix. The SEM images indicate uniform distribution of CNC in polymer matrix. The transparent and semitransparent PMMA/cellulose composites of improved sustainability with higher modulus of elasticity and glass transition temperature can be used as lightweight materials for a wide range of technical and everyday applications as well as optical lenses or acoustic lenses for ultrasound transducers and other devices.
Highlights
Cellulose nanocrystals/PMMA composites fabricated by a green in situ process.
Synthesized PMMA matrices have high molecular weights.
Improved elastic modulus and glass transition temperature were achieved.
Prioritizing eco‐friendly chemicals for a greener production approach.
Preparation by in situ synthesis and characterization of poly(methyl methacrylate) composites with cellulose nanocrystals from 1 to 50 percentages by weight.
This work presents a correlation method that uses 1H NMR spectra for determining the conversion during transesterification of vegetable oil with 10 alcohols: methanol, ethanol, 1-propanol, ...2-propanol, 1-butanol, 2-butanol, isobutanol, 1-pentanol, isopentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-decanol, 1-dodecanol, and benzyl alcohol. Conversions ranging from 70 to 99%, depending on primary alcohol used, are obtained using organic catalyst N,N′,N″-tris(3-(dimethylamino)propyl)guanidine. Catalysts, alcohols, and intermediate products can cause signal overlapping, debilitating the use of the conventional 1H NMR method. Thus, our method uses the correlation between the triplet signal of α-carbonylmethylene and two signals of unsaturated parts of the fatty acid chain, where signal overlapping does not occur, hence, adding robustness and flexibility to the method. The method is applicable for unsaturated oils and is not affected by the amounts of residual alcohol, catalyst, or intermediate products, making it ideal for conversion determination and in situ monitoring of complex mixtures. In addition, we present a systematic analysis of the 1H NMR spectra of biodiesels produced with the mentioned alcohols.
The copolymerization reactivity ratios for 2-N-morpholinoethyl methacrylate (MEMA) with dodecyl methacrylate (DDMA) or styrene (ST) were estimated. The efficiency of the prepared polymers for ...dispersion of MWCNT in toluene was also studied. A wide range of copolymer compositions (all 10 mol% steps) were prepared using tert-butyl peroxy-2-ethylhexanoate (0.02 mol dm−3) as initiator isothermally (70 °C) to low conversions (< 10 wt%). In the case of DDMA/MEMA copolymerization, there is a slight tendency for both monomers to react more with MEMA. The reactivity ratios obtained are r(DDMA) = 0.86 and r(MEMA) = 1.05. The reactivity ratios for the copolymerization of ST/MEMA are both <1 and are r(ST) = 0.35 and r(MEMA) = 0.59, indicating a higher reactivity of each monomer with the other monomer. The addition of small amounts (10 mol%) of MEMA to DDMA homopolymer significantly increases its thermal stability (the temperature at 50 wt% loss is 46 °C higher). For ST/MEMA, the addition of MEMA gradually decreases the thermal stability (the temperature difference at 50 wt% loss between the homopolymers is 25 °C). The best dispersion of MWCNT in toluene is obtained with the ST/MEMA copolymer containing 42 mol% MEMA, as shown by UV–Vis measurements and visual inspections after the gravity test. The obtained results contribute to the further development of polymeric surfactants and stimuli-responsive polymers.
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•Reactivity ratios of DDMA/MEMA are close to 1 means ideal copolymerization.•Reactivity ratios of ST/MEMA are <1 means non-ideal copolymerization with azeotropic point at 62 mol% MEMA.•Best dispersion of MWCNT in toluene showed ST/MEMA copolymer with 42 mol%. MEMA.
