Macromolecular Reaction Engineering最新文献

The crystallinity of Linear Low-Density Polyethylene (LLDPE) is influenced significantly by short-chain branches (SCBs) present in the backbone of the polymer. Despite the importance of this aspect, with only a few linear comonomers being currently used in the commercial production of LLDPE. It is found that by introducing branched comonomers, the melting point and crystallinity of LLDPE can be influenced to a greater extent than with linear comonomers. Since only a few linear comonomers are currently used in the production of LLDPE, the characterization of LLDPEs with branched comonomer has been often overlooked. By combining High-Temperature-Size-Exclusion Chromatography (HT-SEC), Nuclear Magnetic Resonance (NMR) spectroscopy, and Infrared (IR) spectroscopy, it is shown that standard HT-SEC analysis using an IR detector is also applicable to polymers containing branched comonomers.

Front Cover: In article number 2300006, Nermin Orakdogen and co-workers deal with temperature-optimized synthesis of N-(alkyl)acrylamide-based semi-interpenetrating polymer network reinforced with silica nanoparticles and functionalized with methacrylic acid units by varying the polymerization temperature. The gelation is performed at different temperatures to evaluate the formation mechanism. The mechanical properties, swelling properties and susceptibility to stimuli show a wide dependence on the polymerization temperature.

Ethylene/1-hexene copolymerization with two MgCl₂-supported Ziegler-Natta catalysts containing no internal electron donor or diethylphthalate (DEP) is conducted for different polymerization time . Effects of DEP on active center distribution are studied by fractionating each copolymer sample into boiling n-heptane soluble (C7-sol) and insoluble (C7-ins) fractions, and counting the number of active centers in the copolymer fractions . The main effect of introducing DEP in the catalyst are reduction in the Ti content and significant increase in the proportion of active centers producing C7-ins fraction. The propagation rate constants of ethylene insertion (k_pE) and 1-hexene insertion (k_pH) are respectively estimated by linear fitting/extrapolating the change of apparent propagation rate constants (k_pi)_a with polymer yield according to a simplified multi-grain particle model. In both catalysts, k_pE in the C7-ins fraction is 9–12 times larger than that in the C7-sol fraction, and k_pH in the C7-ins fraction is 3–4 times larger than that in the C7-sol fraction. The two groups of active centers have distinctly different catalytic properties. Introducing DEP reduced the k_pE and k_pH values and the extent of diffusion limitation . In summary, addition of electron donor in MgCl₂-supported Z-N catalyst significantly changed the active center distribution and catalytic properties of its two groups of active centers.

The reactivity of different polyethylene modifiers based on acrylic acid (AA) and maleic anhydride (MA) with polyamide 6 (PA6) is investigated, using several degrees of functionalization. The polymer blends are processed in an internal mixer and injection molded. Mechanical, rheological, infrared spectroscopy, thermal, thermomechanical properties, and morphology are evaluated. The torque rheometry results show that higher functionalization degrees favored a high reactivity with PA6. As a consequence, there is an increase in the viscosity of the polymer blends, which is reflected in the reduction of the melt flow index (MFI), compared to PA6. High impact strength and elongation at break properties confirm the blends' compatibility. The elastic modulus and the tensile strength maintain high values, suggesting a balance of mechanical properties. In addition, the polymer blends' heat deflection temperature (HDT) and thermal stability properties are comparable to neat PA6. The morphology obtained by scanning electron microscopy show dispersed and refined particles in the PA6 matrix, indicating stabilization at the interface. Incorporating only 10% of high-density polyethylene grafted with acrylic-acid (HDPE-g-AA) is very efficient in optimizing the properties of PA6, contributing to broadening the range of applications for the processing industry.

Polymer and many other flows exhibit non-Newtonian rheological behavior. For some materials, the thermal dependence of viscosity is also essential to be established. It can be described by considering an activation energy, estimated by using the viscosity measurements at different temperatures. Nevertheless, the test temperatures must be reliable and accurate. An annular measuring device (TRAC: Thermo-Rheo Annular Cell) is previously proposed for highly robust temperature measurement and viscosity identification by inverse method, which exploits the viscous dissipation in the flow. This work explains how critical viscosity points, identified thanks to the TRAC, can be used to estimate the activation energy with different approaches involving the principle of time-temperature superposition. Thanks to the thermal characteristics of the annular flow, the thermal dependence of viscosity can also be estimated from direct temperature measurements to perform fast analysis, without using inverse method.

Soft sensors (SS) are of importance in monitoring polymerization processes because numerous production and quality variables cannot be measured online. Adaptive SSs are of interest to maintain accurate estimations under disturbances and changes in operating points. This study proposes an adaptive SS to online estimate the mass conversion in the emulsion copolymerization required for the production of Styrene-Butadiene rubber (SBR). The SS includes a bias term calculated from sporadic laboratory measurements. Typically, the bias is updated every time a new laboratory report becomes available, but this strategy leads to unnecessarily frequent bias updates. The SS includes a statistic-based tool to avoid unnecessary bias updates and reduce the variability of the bias with respect to classical approaches. A control chart (CC) for individual determinations combined with an algorithmic Cusum is used to monitor the statistical stability of the average prediction error. The adaptive SS enables a bias update only when a loss of said statistical stability is detected. Several bias update methods are tested on a simulated industrial train of reactors for the latex production in the SBR process. The best results are obtained by combining the proposed CC-based approach with a previously developed Bayesian bias update strategy.

This work uses sol–gel and sonochemical methods to prepare bimetallic PdCu catalysts supported on modified ZrO₂ with Ti and Al. The catalysts are tested for vinyl acetate synthesis from ethylene, acetic acid, and oxygen, varying the reaction temperature for two catalysts prepared, which show higher activity. Catalysts characterization results show bimetallic species and distort alloys with a dispersed distribution of active metal onto the support. The in situ reaction by DRIFT-MS identifies the surface formation of main intermediates like palladium acetate monomers and mono and bidentate intermediates, associated to vinyl acetate formation, like vinyl hydrogenated species over PdCu. Finally, this behavior will be attributed to the bimetallic distortions of PdCu samples, provided by interaction effects between PdCu and supports, indicating a more exposition of PdCu species suitable for the reaction, according to high-resolution transmission microscopy electron microscopy results for PdCu/ZrTi sample. Thus, this sample exhibits a minimal formation of sub-products and catalytic stability for 18 hh. These results evidence the participation of hydroxyls and oxygen vacancies of the catalyst in the catalytic reaction measured in situ, monitoring the products formed at the reactor outlet. Finally, it is proposed a reaction pathway as a function of reaction conditions.

In this paper, a detailed description of particle adsorption/diffusion model in batch systems is presented. The phenomenological equations are based on a mechanism combining mass transfer by convection from bulk phase to particle surface, intraparticle mass diffusion and equilibrium adsorption processes. The change of bulk and particle concentration is modeled through differential mass balance equations, leading to a system of one ordinary differential equation and one partial differential equation. When adsorption equilibrium follows a linear relationship, this system of equations can be solved by the Laplace transform method. The purpose of this paper is the development of a generalized analytical solution, that is rewritten specifically for each of the traditional particle shapes: slab, cylinder, and sphere. Finally, this analytical solution is evaluated through several simulations in different batch conditions and compared to simulated experimental data, showing the capability of this analytical solution to predict batch adsorption processes when adsorbate concentration is low. This result clearly indicates the feasibility of applying the analytical solution presented in this paper, which is based on phenomenological concepts, to describe the adsorption kinetics of processes, when the linear isotherm can be considered adequate to represent the adsorption equilibrium.