激光闪射法测量耐火材料的热物理性能

介绍了应用激光闪射法测量耐火材料比热容、热扩散系数以及导热系数等热物理性能的原理,列举应用实例说明了测试方法,并且讨论了影响实验数据准确性的因素。     

稳态平板法测导热系数的补充实验研究

以建陶坯体为研究对象,针对目前平板法测量圆饼状固体材料导热系数的常见问题,采用蜡封方法避免水分沿圆周方向的逸出,分析湿度对导热系数的影响。试验结果表明:坯体导热系数随温度和含水率的升高而升高,并首次针对不符合尺寸要求的实验样品采用简化的实验方法,推导出其导热系数的计算公式。     

有机玻璃在新能源汽车中的应用

将有机玻璃与传统无机玻璃进行对比,分析了有机玻璃应用发展现状和性能特点,同时介绍了有机玻璃在新能源汽车中的应用,最后以车窗为例,对有机玻璃的性能进行了测定。结果表明:除聚碳酸酯玻璃外,有机玻璃和无机玻璃的耐磨性均符合ECE R43《关于安全玻璃材料认证的统一规定》,另外这三种材料的抗冲击性均符合规定,且施加涂层能增强玻璃材料的耐磨性,但对其强度影响很小;采用有机玻璃作为车窗材质的汽车内平均计权隔声量比无机玻璃更低,且在人耳能听到的低频段,有机玻璃的隔声性能更好。     

侧面散热对导热系数测量的影响研究

稳态平板法测量导热系数因方法简单直接在测量材料的导热系数中广泛应用。但通过数值模拟和实验发现侧面散热对导热系数测量影响明显,采用大空间自然对流换热实验关联式对实验数据处理公式进行修正,在实验中得到较满意结果。利用数值模拟和实验对影响侧面散热的主要因素如环境温度、热源温度、样品厚度、试样导热系数进行研究,发现环境温度降低、热源温度增加、试样厚度的增加以及试样导热系数的减小,都会导致传热温差增加,侧面散热的绝对量和占总传热量的比例也随之增加。     

热老化橡胶的导热率的测量和分析

为了适应测量热老化橡胶的导热率,改进了传统的稳态法测定导热率的测量方法.用该方法测量了热老化橡胶的导热率,并对热老化橡胶的导热率的变化机理进行了初步探讨.     

数值法在处理HDPE和SBR流变实验数据上的应用

本文着重介绍用数值分析的方法,处理恒速率型流变仪测得的流变实验数据,采用二次插值法,建立适当的数学模型,计算在恒应力条件下聚合物的粘度值。由理论分析及实验实例证明,模型的选择是合理的,计算出的结果是符合聚合物流变性的一般规律。     

数值方法在桥梁结构分析中的应用

结构分析数值方法、结构试验方法与求解析解是结构分析的三种主要方法。随着计算科学的迅速发展及其在工程技术等领域中的广泛应用,数值方法已成为近似求解工程结构问题的重要工具。     

热探针法测量陶瓷粉末导热系数的实验研究

以Al2O3粉末为例,在分析探针法测量原理的基础上,用热探针法对Al2O3粉末的导热系数进行测量,研究在不同含水率和温度下Al2O3粉末导热系数的变化情况。试验结果发现,Al2O3粉末的导热系数随着秸秆密度,温度和含水率的增加而增加,并基本呈线性关系。     

应用数值方法于化学工程

化学工程中的许多问题都是用数学方程描述的 ,求解数学方程成了解决化学工程中问题的重要方法。本文将对计算机辅助数值方法求解化学工程问题做一综述     

Damping Properties of Polyorganosiloxane/Poly(methyl methacrylate) Interpenetrating Networks

Interpenetrating polymer networks (IPNs) based on polyorganosiloxane/poly(methyl methacrylate) were prepared via sequential polymerization and the damping and mechanical properties of these materials were studied. The effects of crosslinking in both the first‐ and second‐formed networks were investigated. The experimental results show that the extent of damping of the IPNs was decreased and shifted to higher temperature as the content of poly(methyl methacrylate) was increased; the mechanical properties such as tensile strength and hardness (Shore A) were increased with increasing poly(methyl methacrylate) (PMMA) content. The loss factor peak becomes narrower with increasing crosslinker level in the first‐formed network (polysiloxane network), while increasing crosslinker content in the second‐formed network (PMMA network) results in a broadening of the IPN transition peak and moves the IPN transition to higher temperatures as well.     

Physical Properties of Plasticized Poly(vinyl chloride) Blended with Poly(methyl methacrylate) Nanoparticles Synthesized by Differential Microemulsion Polymerization

In this work, poly(methyl methacrylate) (PMMA) nanoparticles synthesized by differential micro emulsion polymerization were used to improve the physical properties of plasticized poly(vinyl chloride) (PVC). PVC, plasticizer (40 phr), heat stabilizer (2 phr), and lubricant (0.2 phr) were melt-mixed with varied amount of the PMMA nanoparticles (3, 5, 7, and 9 phr) on a two-roll mill, followed by compression molding. The results showed that the tensile strength, Young's modulus, tear strength, and thermal stability were improved, but the elongation at break deteriorated with increased PMMA content. Moreover, the flammability of the plasticized PVC was not improved by the PMMA nanoparticles.     

电容式湿度传感器电容式湿度传感器——交联的聚甲基丙烯酸甲酯的感湿性能

运用本体聚合法合成了聚甲基丙烯酸甲酯（ＰＭＭＡ）和分别用三种交联剂交联的ＰＭＭＡ。以ＰＭＭＡ和交联的ＰＭＭＡ为感湿膜制成电容式湿度传感器,在１０％～９０％ＲＨ范围内,这些传感器的电容随相对湿度呈线性规律变化。交联的ＰＭＭＡ传感器具有正的温度系数,但与乙酸丁酸纤维素（ＣＡＢ）传感器相比,ＰＭＭＡ的温度依赖性更小。交联的ＰＭＭＡ传感器能耐有机蒸气,在饱和丙酮蒸气中放置３０ｍｉｎ后,３次测试循环后在９０％ＲＨ下传感器电容的变化约为１％。在高温、高湿、油烟气等各种苛刻环境中放置预定时间后,传感器的漂移一般在±２％ＲＨ范围内。     

自聚甲基丙烯酸甲酯的结构及性能

通过核磁共振波谱、热失重分析仪、差示扫描量热仪及凝胶渗透色谱研究了自聚甲基丙烯酸甲酯(PMMA)的分子链结构、热稳定性、相对分子质量及其分布,并对PMMA的自引发聚合机理进行了探讨。结果表明,与引发剂引发合成PMMA相比,自聚PMMA的相对分子质量更高,分布更宽;自聚PMMA分子链内均含有热不稳定的过氧键,致使其在130 ℃便开始降解,但它对PMMA的热稳定性没有影响;自聚合是由氧与甲基丙烯酸甲酯单体（MMA）反应形成低相对分子质量过氧化物引发的。     

Synthesis and thermal properties of poly(methyl methacrylate)‐poly(L‐lactic acid)‐poly(methyl methacrylate) tri‐block copolymer

Poly(methyl methacrylate)‐poly(L ‐lactic acid)‐poly(methyl methacrylate) tri‐block copolymer was prepared using atom transfer radical polymerization (ATRP). The structure and properties of the copolymer were analyzed using infrared spectroscopy, gel permeation chromatography, nuclear magnetic resonance (¹H‐NMR, ¹³C‐NMR), thermogravimetry, and differential scanning calorimetry. The kinetic plot for the ATRP of methyl methacrylate using poly(L ‐lactic acid) (PLLA) as the initiator shows that the reaction time increases linearly with ln[M]₀/[M]. The results indicate that it is possible to achieve grafted chains with well‐defined molecular weights, and block copolymers with narrowed molecular weight distributions. The thermal stability of PLLA is improved by copolymerization. A new wash‐extraction method for removing copper from the ATRP has also exhibits satisfactory results. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Temperature Limit of Inhibition of Thermo- oxidative Degradation of Polystyrene and Poly(methyl methacrylate) by Antioxidants

Abstract

Investigation has been made on the influence of aromatic and sterically hindered amines, sterically hindered phenols, S- and P-containing compounds on the thermo-oxidative degradation of PS and PMMA by a DSC method under oxygen. The oxidative degradation of antioxidants themselves has been studied under the identical conditions. The dependences of the temperature of the onset of degradation of the polymers on antioxidant concentrations have been obtained. It has been shown that the upper temperature limit of inhibition of the thermo-oxidative degradation of PS and PMMA by well-known effective antioxidants is in the range 280–295°C and depends insignificantly on the chemical structure of polymer. The suggestion was made that the value of the temperature limit of inhibition depends to a great extent on intensive oxidative decomposition of antioxidant itself.     

Investigation of Fullerenes as High Temperature Stabilizers of Poly(methyl methacrylate) and Polystyrene

Abstract

Investigation has been made on the effects of fullerenes C₆₀ and C₇₀ on the degradation of PMMA and PS under helium and oxygen by a DSC method. The dependences of the temperature of the onset of the thermal and thermo-oxidative degradation of the polymers on concentration of C₆₀ and C₇₀ have been obtained. The temperature limits of effective inhibition of the polymers by fullerenes have been determined. The temperature limit depends on the chemical structure of polymer, namely it is considerably greater in the degradation of more stable polymer. In the thermo-oxidative degradation of the polymers with addition of fullerenes, the temperature limit of inhibition of less stable PS is much less and of more stable PMMA is considerably greater than that in the presence of well-known antioxidants. It was concluded that fullerenes are more effective high temperature inhibitors of the thermo-oxidative degradation of PMMA than well-known antioxidants. The suggestion was made that the thermo-oxidative degradation of polymers initiates the oxidation of fullerenes.     

Poly(methyl methacrylate) and polyacrylonitrile dispersions stabilized by gelatin

Methyl methacrylate was polymerized in an aqueous medium in the presence of gelatin using potassium persulfate as initiator. The dispersion mode of polymerization, when the monomer is completely miscible with water, was investigated and compared with an emulsion process, which proceeds at higher monomer concentration. Spherical and relatively uniform polymer particles were formed. Macroscopic precipitation of polymer is prevented by combination of the steric stabilization by grafted gelatin and of repulsive electrostatic interactions from the initiator residues attached to the particle surface. Static and dynamic light scattering have been used to determine the molar mass (molar mass of the whole dispersion particle, M_wD ～ 10⁸-10⁹ g mol^?1) and hydrodynamic radius (R_hD ～ 50-120 nm) of the particles. The number of particles per unit volume does not depend on overall monomer concentration, and it is higher, and therefore the particle size is smaller, than that observed for the soapless emulsion polymerization. The addition of gelatin may be thus used to modify the particle size. Acrylonitrile dispersions were prepared under similar conditions. Unlike methyl methacrylate, this monomer does not swell the polymer particles. While poly(methyl methacrylate) particles are spherical and relatively uniform, the polyacrylonitrile dispersions consist of polydisperse aggregates of tiny polymer particles.     

Thermal and photolytic degradation of plates of poly(methyl methacrylate) containing monomer

Specimens of 1.5 mm thick absorber-free poly(methyl methacrylate) (PMMA) containing ～0.6% monomer but no absorber have been photolytically degraded in air at 50°, 85° and 115°C and thermally degraded in air at 115° and 125°C. Specimens were exposed to a simulated solar spectral range. Degradation was followed by gel permeation chromatographic determinations of molecular weight as a function of depth in the specimens. The results show increased photodegradation at the plate faces (back and front) over that occurring in the centres, and a rapidly attained constant amount of degradation for thermal degradation. Degradation mechanisms are proposed. The thermal degradation is ascribed to weak links and unspent initiator. Photolytic initiation is ascribed, at least in part, to degradation of the ester group by wavelengths in the range 300 to 330 nm. The effect of oxygen is to convert alkyl radicals into peroxyl radicals, some of which form alkoxyl radicals which tne undergo β-scission to give in-chain ruptures. Where the oxygen concentration is low, monomer changes non-tertiary alkyl radical sinto tertiary radicals by addition to the monomer double bond. After their peroxidation by molecular oxygen, tertiary radicals react with one another to give alkoxyl radicals and subsequent chain scission rather than undergoing the Russell termination reaction with no chain scission characteristic of non-tertiary peroxyl radicals. The effect of temperature is mostly to decrease the importance of the cage effect and to allow the initial radicals formed to diffuse away from one another. The products of photo-oxidation absorb the shorter (300 to 330 nm) radiation significantly and progressively shield the remainder of the plate as degradation proceeds.     

Influence of composition and molecular mass on the morphology,crystallization and melting behaviour of poly(ethylene oxide)/poly(methyl methacrylate) blends

Results are reported on the influence of composition and molecular mass of components on the isothermal growth rate of spherulites, on the overall kinetic rate constant, on the primary nucleation and on the thermal behaviour of poly(ethylene oxide)/poly(methyl methacrylate) blends. The growth rate of PEO spherulites as well as the observed equilibrium melting temperatures decrease, for a given T_c or ΔT, with the increase of PMMA content.Such observations are interpreted by assuming that the polymers are compatible in the undercooled melt, at least in the range of crystallization temperatures investigated. Thermodynamic quantities such as the surface free energy of folding σ_e and the Flory-Huggins parameter χ₁₂ have been obtained by studying the dependence of the radial growth rate G and of the overall kinetic rate constant K from temperature and composition and the dependence of the equilibrium melting temperature depression ΔT_m upon composition, respectively.