Determination of plasticizers efficiency for nylon by molecular modeling

Polyamides are semicrystalline polymers useful in a wide range of applications in the plastics industry. Some applications require higher flexibility and workability of the polyamides, therefore, plasticizers are added to ease compounding and processing procedures and produce the desired product properties. The goal of this study was to estimate plasticizers efficiency in plasticizing Nylon 66/6 copolymer (molar ratio 80/20, respectively) using computational tools and to compare the calculated estimations to experimental results. Four plasticizers were studied: glycerin mono stearate, benzene sulfonamide, methyl 4-hydroxybenzoate (M4HB), and diethylhexyl phthalate. Plasticizers efficiency was determined by calculating cohesive energy density, solubility parameters, free volume and interaction intensities of pristine nylon, and the nylon–plasticizer blends. It was found that the efficiency of the plasticizers increases with the degree of interaction intensity between the plasticizer and polymer chains and that M4HB molecules cause the largest changes in free volume. This finding correlates with the experimental results, based on reduction of polymer glass transition temperature (T _g). The highest calculated plasticization efficiency was obtained for M4HB, for which the decrease in T _g was the most significant.     

水滑石类热稳定剂在PVC型材中的应用

介绍了水滑石类热稳定剂的基本情况,通过对比试验研究了水滑石类热稳定剂与铅盐类热稳定剂的热稳定性能及在PVC型材中的应用效果,并对试验结果进行了思考与讨论,建议改进水滑石类热稳定剂。     

Mechanism of action of PVC thermal stabilizers

Based on experimental data, changes of properties of plasticized PVC containing stearates of Ca, Zn, Cd, and Pb stabilizers during thermal degradation are discussed. The mechanism of action of these stabilizers is described in kinetic form.     

Spectroscopic studies of ligand exchange reactions in alkyl- and estertin PVC stabilizers

It has long been appreciated that mercaptoester/Cl exchange equilibria in mono- and dialkyltin mercaptoester/chlorides are important in understanding the stabilization of PVC by alkyltin mercaptoesters (1–3). More recently, IR studies have demonstrated the existence of similar equilibria in mixed mono-/dialkyltin systems; it has been suggested that these exchange reactions may be the source of synergism in the mixed mono-/dialkytin mercaptoester stabilizers (4). The ability to study these systems by IR and NMR methods is based upon the phenmenon of carbonyl to Sn coordination in these compounds and its sensitivity to molecular environment, principally the electronegativity of the tin atom. Our previous studies have now been extended to include estertin (β-carboalkoxyethyltin) mercaptoesters and mercaptoester/chlorides. In contrast to the simple alkyltin systems, the position of the respective mercaptoester/Cl exchange equilibria are dominated by carbonyl to Sn coordination from the ester group of the β-carboalkoxyethyl moiety. Based on the same phenomenon of carbonyl to tin coordination, the nature of alkyl- and estertin mercaptoesters containing alkyltin sulfides has been looked at to a very limited extent.     

Combined molecular dynamics-finite element multiscale modeling of thermal conduction in graphene epoxy nanocomposites

We developed a multiscale scheme using molecular dynamics (MD) and finite element (FE) methods for evaluating the effective thermal conductivity of graphene epoxy nanocomposites. The proposed hierarchical multiscale approach includes three different scales. First, we used MD simulations for the investigation of thermal conduction in graphene epoxy assembly at atomic scale. Our results suggest that thermal conductivity of single layer graphene decline by around 30% in epoxy matrix for two different hardener chemicals. Using MD, we also calculated thermal boundary conductance (TBC) between crosslinked epoxy and graphene sheet. In the next step, using the results obtained by the MD method, we developed FE based representative volume elements (RVE) of the nanocomposite in order to evaluate the thermal conductivity at the microscale. Finally, nanocomposite effective thermal conductivity was obtained using FE homogenization of an ensemble of microscale RVEs. The validity of the proposed approach was confirmed by comparing predicted results with experimental results in the literature.     

延迟焦化加热炉热效率的机理建模与实时估计应用

在延迟焦化装置中,焦化炉热效率是操作先进性关键评价指标,然而实际工业生产中难以在线测得加热炉热效率。本文基于机理建模,推导了管式加热炉状态空间预测模型。为降低干扰影响,提出了一种基于粒子滤波的联合估计方法来修正加热炉热效率模型预测,并分析了其收敛性。实际应用结果证实了所提方法的可行性和有效性,为实现延迟焦化装置先进控制奠定了基础。     

Strength of aluminium titanate/mullite composites containing thermal stabilizers

This work contains a study on the room temperature-fracture strength of three aluminium titanate-based materials containing mullite and different thermal stabilizers (namely Fe₂O₃ and MgO). The highest inert strength was reached by the material sintered without any stabilizer. The MgO-doped material had a comparable inert strength, but a significantly higher Weibull modulus. Finally, the Fe₂O₃-doped material showed the worst mechanical properties. In all cases, a critical load above which strength degraded was apparent. These behaviours have been analyzed in terms of the type of additives and the particular microstructures. Conclusions about the potential use of these materials are briefly stated.     

Use of small-scale testing to predict Cal 133 performance

The use of the cone calorimeter to predict the performance of upholstered furniture in open-flame ignition tests such as Cal 133 is reviewed. Fabric-fire blocker-foam composite tests are correlated to full-scale chair burn results for a wide range of upholstery fabrics. The ACT/DFA study as well as CBUF models are discussed. © 1997 John Wiley & Sons, Ltd.     

Synergistic efficiency of combined HALS–UV absorber polymerizable stabilizers

The influence of combined 2,2,6,6‐tetra methylpiperidine ? 2‐hydroxyphenyl‐benzotriazole [1,3,5]triazine polymerizable stabilizers on the photostability of their copolymers with methyl methacrylate as well as the interaction of the photoreactive HALS and UV absorber fragments in the combined molecules have been studied. Chemical bonding of the stabilizers in the polymer was confirmed spectrophotometrically. The participation of the combined stabilizers in the polymerization did not affect considerably the molecular weight and the molecular weight distribution of the copolymers. A significant stabilizing effect against photodegradation was determined. Strong synergistic interaction between different HALS and UV absorber fragment in the combined stabilizers was established. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2408–2415, 2006     

稀土化合物作为高分子材料热稳定剂的研究进展

稀土化合物作为高分子热稳定剂具有优良的长期热稳定性,无毒环保,与其它热稳定剂具有协同作用。本文主要介绍了稀土热稳定剂在聚氯乙烯、硅橡胶和天然橡胶上的应用,概述了稀土与其它热稳定剂的协同作用与机理,并对稀土热稳定剂的应用和研究前景进行了展望。     

The thermal characteristics of epoxy resin: Design and predict by using molecular simulation method

Trial-and-error approaches for experimentally designing and optimizing the polymer matrix for advanced composites are time-consuming and expensive. The simulation for curing behavior and structure–property relationships of epoxy resins can provide a guideline for designing resin matrix which will possess desirable properties. So far there are few reports in which the accuracy of the molecular simulation for the different amine-epoxy systems are addressed. In this paper, an atomistic modeling technique was used to theoretically investigate the curing and thermal transition behavior of two epoxy resin matrices containing amine curing agent with different chemical structures i.e. diaminodiphenyl methane (DDM)/diglycidyl-4,5-epoxycyclohexane-1,2-dicarboxylate (TDE85) and diaminodiphenyl sulfone (DDS)/TDE85 to give help for designing high heat-resistant epoxy matrix. The simulated results successfully predicted that the reaction process was catalyzed in the early stage of the curing and the slight modification in the diamine structure resulted in significant change in the curing and glass transition behavior of epoxy resin. As the bridging group of diamine changed from methylene to sulphone, the reactivity of diamine toward epoxy declined and the glass transition temperature increased from about 190 °C to about 230 °C. This simulated method presented a good agreement with experimental data, and can be used to design and predict high performance resin matrix for advanced composites.     

Non-oxidative thermal degradation of amines: GCMS/FTIR spectra analysis and molecular modeling

Aqueous amino solvents, such as monoethanolamine (ETA/MEA), methyl diethanolamine (MDEA) or amine blends, are the most widely used solvents in commercial CO₂ or acid gas separation applications. These commercial solvents have various disadvantages, such as the possibilities of the solvent to be degraded. This research examines the impact of non-oxidative thermal degradations on the performance of the CO₂ absorption and the degradation mechanism of amine solvents. The impact of degradation was conducted by measuring the CO₂ solubility of solvent that had been heated to 120°C for 2 h. Although the performance of CO₂ absorption was not significantly reduced, the degradation of amines was found. Supported by Fourier Transform Infrared (FTIR) and Gas Chromatography/Mass Spectrometer result, the suspected products of non-oxidative thermal degradation of MDEA were MEA and acetone.     

提高管式加热炉热效率的途径

探讨影响加热炉热效率的因素,通过降低排烟温度,降低过剩空气系数,减少不完全燃烧损失和散热损失,进行设备改造和使用正确的操作等途径来提高加热炉热效率。     

航空燃料高温裂解条件下热稳定添加剂的研究进展

介绍了供氢剂和结焦抑制剂两类热稳定剂抑制航空燃料高温（>400 ℃）热裂解期结焦的研究进展。评述了一元、二元供氢剂以及含磷、有机硒、含硫结焦抑制剂的抑焦机理及其抑焦效果,并提出今后的研究方向。     

Weatherable rigid PVC: The effect of light and thermal stabilizers

Rigid PVC compositions used in outdoor applications such as siding, profiles, windows, and soffit predominantly contain a tin mercaptide thermal stabilizer. It is well known that tin mercaptides impart outstanding thermal stability to vinyl compounds, however, it is also well known that they provide only marginal light stability. Mercaptides can be used in these applications primarily because they are combined with high levels of titanium dioxide. They are not well suited for dark colored PVC and compositions without titanium dioxide. These require a more weatherable thermal stabilizer, such as a tin carboxylate. In this paper, principles for formulating rigid weatherable vinyl will be discussed. The influence of thermal stabilizers and the interdependence of light stabilizers and thermal stabilizers on PVC photostability will be emphasized. Data will be presented showing how one can formulate weatherable dark brown and pastel PVC through the use of tin carboxylate thermal stabilizers, the appropriate light stabilizers, and pigments. Traditional approaches to achieving weatherability will be compared to what can be attained by capitalizing on the latest advances in stabilization technology. Finally, methods for reducing TiO₂ concentration will be shown.     

Adsorbed metal ions as stabilizers for the thermal degradation of polyacrylamide

The thermal degradation of polyacrylamide has been studied in the presence of various metal ions using thermogravimetry. The thermal decomposition of the polymer in general occurs at higher temperatures in the presence of metal ions than with the pure polymer. Empirical measures of the stabilizing effect of the metal ions have been made by determining the temperatures of 12% and 50% decomposition, and the integral procedural decomposition temperature (IPDT). For main group metal ions, the stabilizing effect, as measured by the difference in ipdt between polymer-metal complex and copolymer, was inversely proportional to the radius of the metal ion, suggesting that the strength of the complex between the ion and polymer is important in determining stability. Transition metal ions, in contrast, showed no simple dependence of stabilizing effect on ionic radius, but showed, instead, a dependence upon the ligand field stabilization energy.