Macromolecular Reaction Engineering最新文献

In the recent years, the growing amounts and incorrect disposal of solid wastes have created serious negative environmental impacts, including land and water pollution. Chicken litter (CL) is a type of solid waste which is generated during chicken production, the appropriate final destination of which is still subject to technical discussion. Because CL is composed mostly of fibers, proteins, carbohydrates, and different minerals, the use of this material as a filler for the manufacture of polymer materials has been suggested. The main objective of the present work is the manufacture of polymer composites in situ polymerization using CL as a filler and succinic acid and 1,4-butanediol as monomers, considering that the fiber content in CL is ≈20 wt%. The obtained poly(butylene succinate) (PBS) composites are characterized by Fourier transformed infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), gel permeation chromatography (GPC), nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), degradability in distilled water, and compression analyses. The results show that the addition of CL to the mixture do not affect the course of the polycondensation reaction significantly. Furthermore, compression tests show that the compressive strength of test pieces increases with the CL content.

The solubility of different alkanes in polyethylene (PE) of different densities, as well as the solubility of the polymers in the alkanes, and the degree of swelling of the powders are studied as a function of temperature. It is found that the solubility of linear low-density polyethylene (LLDPE) is as much as 6 times greater than that of high-density polyethylene (HDPE) at the same temperature, and that LLDPE swells at least 50% more than HDPE the same diluent at the same temperature. The breakthrough curves also show that lighter alkanes swell the PE more at a given temperature than heavier ones. Also, the breakthrough points (the temperature at which the swelling versus temperature curves change slope) occur at lower temperatures for PE of lower density. Gel formation is observed for medium and low density polyethylenes in pentane and hexane. This quantitative information will be useful in developing process models for different industrial polymerization processes, as particle swelling can have a significant impact on slurry viscosity and the flow stability and solids loading of commercial reactors.

Polyurethanes are probably the most versatile among polymers of greater industrial use due to the possibility of being produced in a wide range of density, hardness, and mechanical properties and through different conversion processes. Its synthesis involves a great variety of raw materials and proportions between them. A mathematical model that describes the polyurethane foam formation can be very useful for the development of formulations and in the definition of the processing conditions, avoiding great consumption of time and errors in the development and experiments. The present work studies this process using industrial formulation. The kinetic parameters of the reaction between polyol with isocyanate are determined calorimetrically using the adiabatic temperature rise method, obtaining the values of activation energy 22.2 kJ mol⁻¹ and heat of reaction 91.8 kJ mol⁻¹. Data liquid–vapor equilibrium of the hydrofluorolefin blowing agent in a polyol mixture are obtained and treated with Flory–Huggins model with good agreement with experimental data (deviation of 1.6%). The mathematical model is satisfactory to describe the expanding process in a pilot scale, under different conditions.

The bis(imino)pyridyl iron-based ethylene oligomerization catalysts have the advantages of mild reaction conditions, high activity and high selectivity to linear α-olefins. However, barriers, such as high polymer content in the product mixture and large methylaluminoxane (MAO) dosage, are still limitations for the development of these systems at the industrial scale. In this study, new cocatalysts are prepared by the reaction of alkylaluminums with urea and its derivatives, and successfully used to activate iron-based catalysts. It is found that the type and molar ratio of alkylaluminum and urea have significant influence on the performance of the cocatalysts. The activity of the preferred triisobutylaluminum/urea activated systems reaches more than 3.0 × 10⁸ g (mol-Fe)⁻¹ h⁻¹, and the polymer content can be controlled to be less than 2 wt.%. Notably, the catalytic system exhibits good high temperature stability, the activity can still reach 1.0 × 10⁸ g (mol-Fe)⁻¹ h⁻¹ even at 120 °C. Further ¹H NMR studies show that alkylaluminum can react with the NH moieties of urea, forming complex alkylaluminum clusters, even aluminoxane-like structures. This study offers a promising family of cocatalysts, making it possible to simultaneously improve their performance and reduce their cost.

In order to obtain a pH and temperature sensitive hybrids with a controlled structure, synthesis of N-(alkyl)acrylamide-based semi-interpenetrating polymer network (semi-IPN) reinforced with silica (SiO₂) nanoparticles and functionalized with methacrylic acid units is carried out by optimizing the polymerization temperature. The study aims to understand the effect of polymerization temperature on the physical properties of semi-IPN hybrids. Changing preparation temperature between −30 and 23 °C leads to significant differences in physico-mechanical results, swelling tendency and adsorption ability, while silica nanoparticles strengthen hybrid walls, preventing their collapse during deswelling and providing rapid response. The hybrids prepared at higher temperatures are found to swell more and faster in water, while the lowest swelling is observed those prepared at 5 °C. The incorporation of SiO₂ particles into copolymer structure via physical crosslinking with network chains enhances the elasticity. The effect of polymerization temperature on adsorption is investigated using methylene blue as a model dye. Increasing polymerization temperature increases the adsorption rate and shortens time to reach the equilibrium point, and adsorption efficiency increases when polymerization temperature is lowered. The results show that semi-IPN hybrids loaded with silica nanoparticles can be used as alternative and potential adsorbents in the treatment of industrial wastes.

A number of colorimetric pH indicators (phenolphthalein, bromocresol green, 4-nitrophenol, phenol red, and bromothymol blue) are encapsulated within silica particles via an acid-catalyzed sol–gel process. The fabricated indicator is added during ethylene polymerization with a metallocene (Cp₂ZrCl₂) catalyst. Introduction of the indicator into the silica matrix affects the surface area, probably by partially blocking some of the pores. The encapsulated pH indicator reduces the catalytic activity by up to 17%, whereas adding a solution of the indicator reduced the catalytic activity by up to 34%. The crystallinities of the samples containing the silica-encapsulated pH indicators are lower than those of the samples to which the pH indicator is added in solution form. The prepared encapsulated colorimetric pH indicators are analyzed by diffuse reflectance UV-vis spectroscopy. The measured color values are distributed according to the CIE Lab lightness psychometric color space. Addition of the indicator in solution form (free) to the ethylene polymerization reaction does not result in indicator activity in acidic or alkaline media. The pH indicators incorporated into the polyethylene show color changes when exposed to acidic and alkaline media. Samples to which the unencapsulated pH indicators (free) are added exhibit lower catalytic activities and higher crystallinities than the samples containing the encapsulated pH.

In this work, solvent-free waterborne polyurethane-poly(meth)acrylate hybrid dispersions that can be used to formulate anticorrosive paints are synthesized. To achieve the anticorrosive protection, a phosphate containing polymerizable surfactant, Sipomer PAM 200 is incorporated to the hybrids. The presence of phosphate groups can produce an iron phosphate passivation layer to provide coatings with anticorrosive properties. These properties are tested in both mild and harsh corrosive environments. It is observed that when the films are dried at 60% relative humidity conditions, very poor anticorrosive protection is achieved because no phosphatization is obtained, but increasing the humidity to 85% during the drying step allows the formation of the passivation layer providing good anticorrosive properties.

Much effort has been done toward the development of new emulsifiers able to improve the latex stability. In this sense, ionic liquids based on imidazolium constitute a new category of stabilizer in study. Moreover, the near infrared (NIR) spectroscopy has been extensively investigated as a tool to follow the properties of polymerization reactions. In this study different ionic liquids are investigated as emulsifiers during the emulsion homopolymerization of the styrene and methyl methacrylate. A quantitative analysis method is developed to determine the properties of latex based on the joint use of the NIR spectra and partial least squares regression (PLS). Kinetic results indicate that the latex properties are greatly influenced by the type of ionic liquid. The current work shows that the NIR spectrophotometer can be successfully used for monitoring of the latex properties, enabling to track the polymerization dynamics even in the presence of ionic liquids.

Surface molecularly imprinted cellulose-synthetic hybrid particles are prepared via atom transfer radical polymerization (ATRP). The two-step process involves the immobilization of α-bromoisobutyryl bromide in the pristine microcrystalline cellulose, to generate ATRP macroinitiator particles, and then the creation of a crosslinked-imprinted shell in the particles surface considering ATRP of 4-vinylpyridine (4VP) and ethylene glycoldimethacrylate (EGDMA) with quercetin as imprinting template. Among the polymerization recipes tested, a system with ethanol as solvent preserves a final size of the hybrid particles suitable for application as adsorbent, while also incorporating the 4VP/EGDMA co-monomers. Testing of imprinted/non-imprinted particles for sorption/desorption of standard phenolic compounds shows the modification of the surface of the pristine cellulose and also the achievement of molecular imprinting (imprinting factor ≈2.6). Particles are used for the enrichment of flavonoids in olive leaf extracts and the special features of the developed molecularly imprinted adsorbents are again highlighted with this complex mixture of phenolic compounds. It is shown that production of fractions rich in luteolin-7-O-glucoside, apigenin-7-O-glucoside, or quercetin, among other flavonoids is possible (estimated enrichment factors up to 4). These results point up for the usefulness of natural-synthetic materials with processes to get high-added value compounds in the framework of circular bio-economy.

This work investigates the fitting performance of conventional rheological models and the development of multivariable rheological models to reproduce experimental rheological data of different industrial grades of linear isotactic polypropylene (iPP) having high mass average molar masses, Mm (164–404 kg mol⁻¹), at three temperature values (180–220 °C) over a wide range of shear rates (10⁻¹–10⁴ s⁻¹). A shear thinning behavior is found in all investigated conditions. However, a low shear rate primary Newtonian plateau for a short shear rate range is only identified for the smallest Mm among those investigated, and for higher Mm such primary plateaus are even found at shorter shear rate range. Among the investigated models, only Cross and Carreau–Yasuda models are effective to reproduce the data for a specific PP grade. Two modified models are proposed that incorporate three variables. In the modified Cross Model, it has been shown that the characteristic time (λ) between the Newtonian plateau at the low shear rates and the shear-rate range with shear-thinning behavior depends exponentially on the Mm, and it does not depend on the temperature. Both proposed models fit very well with the experimental data with shear thinning behavior for a wide range of Mm.