Autooxidation of Oriented Polyolefins

Abstract

The effect of the chemical structure of the polymer on its reactivity in the oriented state is studied, and causes of the effect of orientation drawing of polyolefins on the oxidation kinetics are identified.

The orientation drawing of the polymer is shown to be dependent on the nature of the latter which can either delay or accelerate the oxidation process. The effect of a delayed rate of oxidation for the samples of one drawing degree is determined by the nature of the side substitute in the monomeric link of the polymer.

The effect of the orientation drawing of the polymer on the change of parameters of oxidation (k ₂ k ₆ ^?0.5 [RH]), a decrease of the coefficients of solubility and diffusion of oxygen as well as the change in the polymer structure depending on its nature are considered.

Analysis of structural changes in the polymers due to orientation has shown that drawing of the polymer can result in localization of oxidation in defected zones of amorphous areas isolated from each other by transition chains in extremely straightened conformation. In this case, the oxidation kinetics of oriented polyolefins can be described with the use of postulates of the “zone” model developed by Yu. A. Shlyapnikov. Evaluation of the kinetic parameters of oxidation (k _2eff, k _6eff, θ) with the use of this model is made.

It is shown that the effect of the nature of the polymer is due to a change in activity of the C?H bonds participating in the oxidation process, peculiar features of changes in the structure and physical properties of the polymer in the process of orientation drawing, in terms of the “zone” model, to the rate of the expansion of the oxidation center, that is, the nature of the polymer determines the parameters k _2eff, k _6eff, θ in the oriented sample.     

亲水性聚烯烃纤维的改性方法研究进展

聚烯烃以其优异的性能、低廉的价格和越来越广泛的用途,日益成为一种重要的合成高分子材料的主体。但它极弱的亲水性限制了在一些领域的应用。介绍了近几年国内外通过化学接枝、等离子体接枝、辐射接枝、表面光接枝等方法对聚烯烃表面亲水性改性的研究进展。     

Effects of Active-Center Reduction of Plant-Type Ferredoxin on Its Structure and Dynamics: Computational Analysis Using Molecular Dynamics Simulations

“Plant-type” ferredoxins (Fds) in the thylakoid membranes of plants, algae, and cyanobacteria possess a single [2Fe-2S] cluster in active sites and mediate light-induced electron transfer from Photosystem I reaction centers to various Fd-dependent enzymes. Structural knowledge of plant-type Fds is relatively limited to static structures, and the detailed behavior of oxidized and reduced Fds has not been fully elucidated. It is important that the investigations of the effects of active-center reduction on the structures and dynamics for elucidating electron-transfer mechanisms. In this study, model systems of oxidized and reduced Fds were constructed from the high-resolution crystal structure of Chlamydomonas reinhardtii Fd1, and three 200 ns molecular dynamics simulations were performed for each system. The force field parameters of the oxidized and reduced active centers were independently obtained using quantum chemical calculations. There were no substantial differences in the global conformations of the oxidized and reduced forms. In contrast, active-center reduction affected the hydrogen-bond network and compactness of the surrounding residues, leading to the increased flexibility of the side chain of Phe61, which is essential for the interaction between Fd and the target protein. These computational results will provide insight into the electron-transfer mechanisms in the Fds.     

Activity and Mechanism of Action of Thio and Dithiobisphenols in the Stabilization of Polyolefins

Abstract

Diphenol substituted sulfides have been studied as stabilizers poypropylene against thermal oxidation. Both phenol groups of antioxidants are reacting with oxidation reaction centres, the sulfide group reacting with hydroperoxides.

The reaction of phenol-substituted disulfides with tert-butylhydroperoxide was also studied.

The role of unstable sulfur-containing intermediates is discussed.     

Fused Deposition Modeling of Polyolefins: Challenges and Opportunities

Polyolefins are the largest class of commercially available synthetic polymers that are extensively used in a variety of applications from commodities to engineering owing to their low cost of production, good physico-mechanical properties, light weight, good processability, and recyclability. Compared to conventional molding techniques, fused deposition modeling (FDM)-based 3D printing is a smart manufacturing technology for thermoplastics due to its low cost, ease of production of complex geometrical parts, rapid prototyping, and scalable customization. FDM 3D printing can be an ideal manufacturing technology for polyolefins to manufacture various complex parts. However, FDM 3D-printing of polyolefins is challenged bycritical printing problems like high warpage, dimensional inaccuracies, poor bed adhesion, and poor layer-to-layer adhesion. In this review, a fundamental understanding of polyolefins and their FDM 3D-printing process is established, and the recent progress of FDM 3D printing of polyolefins is summarized. Furthermore, strategies to overcome warpage and to improve mechanical strength of the 3D-printed polyolefins are provided. Finally, future prospectives of FDM 3D-printing of polyolefins are critically discussed to inspire prospective research in this field. It is believed that this review article can be tremendously useful for research work related to FDM of polyolefin-based materials.     

Predicting the Structure and Dynamics of Membrane Protein GerAB from Bacillus subtilis

Bacillus subtilis forms dormant spores upon nutrient depletion. Germinant receptors (GRs) in spore’s inner membrane respond to ligands such as L-alanine, and trigger spore germination. In B. subtilis spores, GerA is the major GR, and has three subunits, GerAA, GerAB, and GerAC. L-Alanine activation of GerA requires all three subunits, but which binds L-alanine is unknown. To date, how GRs trigger germination is unknown, in particular due to lack of detailed structural information about B subunits. Using homology modelling with molecular dynamics (MD) simulations, we present structural predictions for the integral membrane protein GerAB. These predictions indicate that GerAB is an α-helical transmembrane protein containing a water channel. The MD simulations with free L-alanine show that alanine binds transiently to specific sites on GerAB. These results provide a starting point for unraveling the mechanism of L-alanine mediated signaling by GerAB, which may facilitate early events in spore germination.     

Biomolecular Structure and Dynamics with Neutrons: The View from Simulation

The characterization of the structure and internal dynamics of biomolecules is essential to understanding their biological function. Neutron scattering probes similar time- and length-scales to molecular dynamics simulation. Hence, simulation models of biomolecules have become invaluable in the interpretation of experimental neutron data. Here, we report on advances in the application of simulation in developing neutron scattering to investigate internal protein motions and, as an example of industrial relevance, in the derivation of physical models of use in biofuel renewable energy research.     

气体在水中的分子动力学模拟

采用分子动力学（ＭＤ）模拟的方法在常温及工业应用背景条件下对ＣＨ４、ＮＨ３、ＣＯ２、Ｏ２这些气体在水中的结构及扩散情形进行了研究。ＭＤ模拟可以为这些涉及到气体在水中的工业应用情形的机理提供分子水平的解释,同时ＭＤ模拟还可为一些不易实验测定扩散性质的体系提供工程初步设计和过程开发所需的数据。     

The Use of Molecular Dynamics Simulation Method to Quantitatively Evaluate the Affinity between HBV Antigen T Cell Epitope Peptides and HLA-A Molecules

Chronic hepatitis B virus (HBV), a potentially life-threatening liver disease, makes people vulnerable to serious diseases such as cancer. T lymphocytes play a crucial role in clearing HBV virus, while the pathway depends on the strong binding of T cell epitope peptide and HLA. However, the experimental identification of HLA-restricted HBV antigenic peptides is extremely time-consuming. In this study, we provide a novel prediction strategy based on structure to assess the affinity between the HBV antigenic peptide and HLA molecule. We used residue scanning, peptide docking and molecular dynamics methods to obtain the molecular docking model of HBV peptide and HLA, and then adopted the MM-GBSA method to calculate the binding affinity of the HBV peptide–HLA complex. Overall, we collected 59 structures of HLA-A from Protein Data Bank, and finally obtained 352 numerical affinity results to figure out the optimal bind choice between the HLA-A molecules and 45 HBV T cell epitope peptides. The results were highly consistent with the qualitative affinity level determined by the competitive peptide binding assay, which confirmed that our affinity prediction process based on an HLA structure is accurate and also proved that the homologous modeling strategy for HLA-A molecules in this study was reliable. Hence, our work highlights an effective way by which to predict and screen for HLA-peptide binding that would improve the treatment of HBV infection.     

NPT系综分子动力学模拟水的密度和扩散系数

采用常温常压(NPT)系综分子动力学方法模拟了298.15K、0.1013MPa条件下水的密度和自扩散系数,模拟结果与实验值一致,相对误差分别为1.74%和3.83%。     

Contact Oxidation and Adhesive Interaction of Polyolefins with Metals

Polymer-metal systems: adhesive joints of metals, metal-polymer composites, polymeric coatings on metals etc., are of great practical interest. The polyolefin-based systems (large supply, widespread, cheap polymers, distinguished by high chemical resistance, anticorrosive capacity and other valuable properties) and steel (including steel of the common grades, which are in great need of rust protection) are wisely used. One of the basic requirements, guaranteeing high serviceability of the abovementioned systems, is a strong and durable adhesive interaction between polymer and metal. In this paper, the most essential research results, obtained in our laboratory, in the field of controlling the processes of adhesive interaction between polyolefin melts and steel surfaces, have been generalized (for more detail, see Ref. 1).     

Contact Oxidation and Adhesive Interaction of Polyolefins with Metals

Polymer-metal systems: adhesive joints of metals, metal-polymer composites, polymeric coatings on metals etc., are of great practical interest. The polyolefin-based systems (large supply, widespread, cheap polymers, distinguished by high chemical resistance, anticorrosive capacity and other valuable properties) and steel (including steel of the common grades, which are in great need of rust protection) are wisely used. One of the basic requirements, guaranteeing high serviceability of the abovementioned systems, is a strong and durable adhesive interaction between polymer and metal. In this paper, the most essential research results, obtained in our laboratory, in the field of controlling the processes of adhesive interaction between polyolefin melts and steel surfaces, have been generalized (for more detail, see Ref. 1).     

Effects of Cardiolipin on the Conformational Dynamics of Membrane-Anchored Bcl-xL

The anti-apoptotic protein Bcl-xL regulates apoptosis by preventing the permeation of the mitochondrial outer membrane by pro-apoptotic pore-forming proteins, which release apoptotic factors into the cytosol that ultimately lead to cell death. Two different membrane-integrated Bcl-xL constructs have been identified: a membrane-anchored and a membrane-inserted conformation. Here, we use molecular dynamics simulations to study the effect of the mitochondrial specific lipid cardiolipin and the protein protonation state on the conformational dynamics of membrane-anchored Bcl-xL. The analysis reveals that the protonation state of the protein and cardiolipin content of the membrane modulate the orientation of the soluble head region (helices α1 through α7) and hence the exposure of its BH3-binding groove, which is required for its interaction with pro-apoptotic proteins.     

Normal Mode Dynamics Comparison of Proteins

Sequence and structure comparisons are fundamental techniques that enable exploration of the sequence and structural spaces of proteins. Homology detection, function prediction, and protein classification rely on these techniques. However, protein structures are dynamic, rather than static, and such protein dynamics play a key role in a wide range of biological activities. Therefore, protein dynamics comparison algorithms may shed light on the relationship between proteins′ dynamics and function. Here, we review different strategies for comparing dynamics of proteins. Special emphasis is given to newly developed algorithms that compare dynamics of proteins with no apparent sequence or structural similarity and to the qualitative differences between these algorithms.     

受限于碳纳米管中水分子微观结构的分子动力学模拟研究

利用分子动力学模拟研究受限于不同管径中水分子的微观结构,改变温度,做出受限水分子的径向分布函数图,并对比说明。通过做水分子在碳纳米管内的均方位移与时间关系图,利用Einstein法算出不同管径中水分子的扩散系数,与利用Knudsen扩散公式计算出的水分子的扩散系数进行比较。     

Assessing the effect of molecular weight on the kinetics of backbone scission reactions in polyethylene using Reactive Molecular Dynamics

Kinetics of polymer bond scission, the initial step in thermal decomposition of polyethylene and other vinyl polymers, was investigated as a function of the number of repeat units using an improved Reactive Molecular Dynamics (RMD) approach, which is introduced here. The rate of scission per bond is shown to depend on the degree of polymerization, an effect not captured by the conventional practice of modeling polymer decomposition with small-molecule Arrhenius parameters. In the new approach, implemented in an open-source C++ code RxnMD, well-behaved reactive force fields are generated using switching functions that activate and attenuate terms obtained from a conventional, non-reactive force field. In this way, predefined reaction types are modeled accurately by interpolating smoothly between non-reactive potential energy terms describing reactants, transition states, and products.     

Study on the Characteristics of Gas Molecular Mean Free Path in Nanopores by Molecular Dynamics Simulations

This paper presents studies on the characteristics of gas molecular mean free path in nanopores by molecular dynamics simulation. Our study results indicate that the mean free path of all molecules in nanopores depend on both the radius of the nanopore and the gas-solid interaction strength. Besides mean free path of all molecules in the nanopore, this paper highlights the gas molecular mean free path at different positions of the nanopore and the anisotropy of the gas molecular mean free path at nanopores. The molecular mean free path varies with the molecule’s distance from the center of the nanopore. The least value of the mean free path occurs at the wall surface of the nanopore. The present paper found that the gas molecular mean free path is anisotropic when gas is confined in nanopores. The radial gas molecular mean free path is much smaller than the mean free path including all molecular collisions occuring in three directions. Our study results also indicate that when gas is confined in nanopores the gas molecule number density does not affect the gas molecular mean free path in the same way as it does for the gas in unbounded space. These study results may bring new insights into understanding the gas flow’s characteristic at nanoscale.