Modeling and simulating chemical reactions

Many students are familiar with the idea of modeling chemical reactions in terms of ordinary differential equations. However, these deterministic reaction rate equations are really a certain large-scale limit of a sequence of finer-scale probabilistic models. In studying this hierarchy of models, students can be exposed to a range of modern ideas in applied and computational mathematics. This article introduces some of the basic concepts in an accessible manner and points to some challenges that currently occupy researchers in this area. Short, downloadable MATLAB codes are listed and described

Mezclas poliméricas cristal líquido/olefinas: morfología y propiedades de transporte

Se han preparado mezclas con diferentes composiciones a partir de un copolímero de etileno-1-octeno, sintetizado con un catalizador de tipo metaloceno y un polímero cristal líquido. La caracterizción estructural y morfológica de las películas obtenidas se realizó mediante difracción de rayos X, calorimetría diferencial de barrido y microscopía electrónica de barrido, mientras que el estudio de las propiedades físicas se ha llevado a cabo mediante análisis mecanodinámico, microdureza y ensayos esfuerzo-deformación, poniendo especial énfasis a la evaluación de sus propiedades de transporte de oxígeno

A Comparison of the Effect of Silk Fibroin Nanoparticles and Microfibers on the Reprocessing and Biodegradability of PLA/PCL Blends

In this research, the effect of reprocessing on the properties of poly(lactic acid)/poly(ε-caprolactone) (PLA/PCL) blends reinforced with silk nanoparticles (NP) and silk microfibers (SF) was investigated. In this regard, the multiple extrusion process was applied to the PLA/PCL based composites and their morphology, thermal stability, intrinsic viscosity, water absorption, mass loss, barrier, and mechanical properties were studied and compared. The results of atomic force microscopy showed that silk nanoparticles were mainly located in the PLA matrix and partially at the phase interphase with a thickness of layers around 80 nm. The scanning electron microscopy results illustrated a good dispersion of NPs in the blend and poor adhesion between SFs and the polymer matrix. The thermogravimetric analysis results showed that the presence of bio-fillers stabilized the thermal properties of composites and decreased the thermo-mechanical degradation of recycled materials. Furthermore, the addition of NPs and SFs improved the barrier properties of materials and led to a decrease in the value of water absorption and mass loss of PCL/PCL composites. The results of microhardness and impact tests also demonstrated that the mechanical properties of neat PLA/PCL blends are deteriorated by increasing the number of reprocessing cycles; however, the incorporation of both NPs and SFs improved the mechanical performance of recycled PLA/PCL composites. The results suggest that the use of silk fillers represents a cost-effective and environmentally friendly way of improving the properties of reprocessed PLA-based plastic

Color and degradation in cellulosic materials of different composition and degree of grinding

Degradation of cellulosic materials at low or moderate temperatures is a matter of the utmost interest for the paper and textile industries, for the conservators of museums and libraries, as well as in the field of the compound materials of thermoplastic matrix and cellulosic reinforcements, at the manufacturing and processing whereof temperatures higher than 200°C are reached, which produces an important degradation and reduces the yields of the final materials. At the same time, it is a matter of scientific interest due to its great complexity, since different degradation mechanisms coexist, which are not yet well-known. The main consequences of degradation at these temperatures are the loss of strength, related to a reduction in the degree of polymerization of the pulp, and the colouring of the material, due to the formation of chromophors in some degradation processes. Numerous factors influence the gravity of degradation, among which the temperature, the presence of oxygen, the moisture, pH and the light can be highlighted. Determinant are also the chemical composition and the cellulosic material structure, although some key aspects, such as the colouring kinetics of different cellulosic materials, or the effect of certain processing conditions or of certain additives on the thermal colouring of the material are still little-known. The influence of the chemical composition and of the freeness on the colour and the kinetics of the thermal yellowing of different cellulosic materials has been studied in this work. The study was based upon brown kraft pulps of Eucalyptus globulus, refined at different degrees. As reference material a Whatman paper was used, which can be considered as a practically pure pulp. As experimental techniques, the diffuse reflectance spectroscopy (IR and UV-Visible) and the colorimetry of solids have been applied. The first results indicate that the colour depends on the chemical composition and on the freeness, the materials of higher freeness being more coloured. The relationship between freeness and colouring speed is, in turn, complex. The colouring kinetics depends to a large extent on the chemical composition, the presence of lignin being the most influent factor

Amino-Modified Halloysite Nanotubes to Reduce Polymer Degradation and Improve the Performance of Mechanically Recycled Poly(lactic acid)

From an environmental point of view, mechanical recycling is, in general, a good end-of-life option for poly(lactic acid) (PLA), one of the most important biobased polymers. However, the degradation of PLA during the service life and, especially, during the mechanical recycling process, leads to a decrease in the properties of PLA, thus reducing the applications of the recycled plastic. The main aim of this work was to study the addition of small amounts of halloysite nanotubes, during the recycling step, as the basis of a cost-effective method for improving the properties of the recycled PLA. Raw halloysite was modified with an aminosilane, and 2% by weight of both raw and modified halloysite were melt compounded with PLA previously subjected to accelerated ageing. The addition of the nanotubes led to recycled materials with improved properties because halloysite reduces the degradation of PLA by blocking the carboxyl groups, generated during the ageing and washing steps, which catalyze the degradation during the recycling process. This effect was more intense in the silanized nanotubes, because the carboxyl groups were effectively blocked by acid–base interactions with the amino groups of the chemical modification. The properties of the recycled plastic with only 2 wt% of silanized halloysite were very close to those of the virgin plastic.The authors would like to thank the Centro Nacional de Microscopía Electrónica of the Universidad Complutense de Madrid (Spain), for the collaboration in the TEM measurements. This work was supported by MINECO-Spain (Grant Number CTM2017-88989-P) and Universidad Politécnica de Madrid (project UPM RP 160543006).Peer Reviewe

Biodegradable Nanocomposites Developed from PLA/PCL Blends and Silk Fibroin Nanoparticles: Study on the Microstructure, Thermal Behavior, Crystallinity and Performance

Recently, the use of natural materials has grown in the plastics industry. In this study, novel bio-nanocomposites were developed from poly(lactic acid)/poly(ε-caprolactone) (PLA/PCL) blends and silk fibroin nanoparticles (SFNP). SFNP were successfully synthesized from silk fibroin (SF) and analyzed by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The obtained results revealed that the well-ordered structures in SF were changed to the amorphous structures in SFNP. Then (PLA/PCL) blends containing 10–30% of PCL were prepared and characterized. According to the obtained results, the PLA/PCL (70/30) blend was selected as the optimized sample for further studies. The scanning electron microscopy results illustrated that the addition of 1% of SFNP into this blend improved the compatibility between PLA and PCL and reduced the PCL droplet sizes from 1.170 ± 92 to 794 ± 46 nm. The results from TGA analysis indicated that the presence of SFNP enhanced the thermal stability of materials at high temperatures. The crystallization kinetics results revealed that while SFNP promoted the crystallization of neat PLA, the crystallization rate of PLA/PCL blend was decreased upon the incorporation of nanofiller. Furthermore, the PLA/PCL/SFNP exhibited higher microhardness and barrier properties than the neat blend. The results suggest that the developed bio-nanocomposites are promising materials for demanding applications such as food packaging.The authors thank Perstorp Co. Ltd., Sweden, for supplying the PCL Capa™ 6800, MINECO-Spain (Project CTM2017- 88989-P) and Universidad Politécnica de Madrid (Project UPM RP 160543006). This project has received funding from the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 860407 BIO-PLASTICS EUROP

Fourier Transform Infrared Spectroscopy study of polymorphism in propylene-co-1-pentene copolymers: Trigonal form identification

Several regularity bands of the new trigonal form of iPP are identified in a real time FTIR study on a series of random propylene-co-1-pentene copolymers within a broad 1-pentene composition range. Some of them have been already reported for propylene-1-hexene copolymers. Moreover the coexistence of the different crystalline structures developed by these copolymers have been studied. Analysis of the real time evolution of IR regularity bands during heating of these copolymers confirms that when trigonal polymorph is developed its presence affects either the location or intensity of other common regularity bands. Conventional X-ray experiments at room temperature have been also performed to attain the required information on the different polymorphs existing at those distinct compositions analyzed. Additionally, DSC measurements and real-time variable temperature synchrotron experiments have been carried out to ascertain the phase transformations that take place on heating.The financial support of MICINN (Project MAT2010-19883) is acknowledged. Dr. J. Arranz-Andrés is also grateful to MICINN for his fundingPeer Reviewe

Thermo and photo-oxidation of functionalized metallocene high density polyethylene: Effect of hydrophilic groups

Incorporation of a small content of undecenoic acid is proposed as an approach to introduce polar groups within the macromolecular architecture of high density polyethylene-based materials in order to promote an easier degradation after their useful service life. The influence of these hydrophilic groups during thermo and photo-oxidation processes has been then evaluated by several complementary techniques. In addition to different degradation rates, distinct ratios of oxidized species (lactones, ketones, carboxylic acids, esters and aldehydes) are found depending on: a) the initial material (neat high density polyethylene or ethylene-co-undecenoic acid copolymer); b) the type of oxidation (thermo or photoinduced); and c) the absence or presence of a specific prodegradant additive. An important increase of crystallinity has been observed in the final oxidized samples, indicating that the extent of degradation is rather significant.Peer Reviewe