Degradation of a poly(ester urethane) elastomer. IV. Sorption and diffusion of water in PBX 9501 and its components

In preparation for studying the hydrolytic degradation of Estane® 5703 in the plastic‐bonded explosive PBX 9501, the sorption (solubility) and diffusion of water in PBX 9501 and each of its components are studied experimentally and modeled theoretically. Experiments are reported that measure the weight gain or loss due to a change in the relative humidity (RH). For all of the components, the equilibrium amount of water sorbed per gram of sample is linear in the RH at low relative humidities but curves upwards at higher relative humidities. This behavior is modeled with a water cluster model. Diffusion coefficients are determined by modeling the time dependence of the water concentrations assuming Fickian diffusion, and that fits the data for some of the materials. However, all the samples that contain the explosive HMX show much more complicated behavior at high relative humidities, and that is presented and discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

固体火箭发动机粘接界面湿热老化特性探究

对常用的加速老化寿命模型进行了归纳、总结,在分析其原理的基础上,针对固体火箭发动机粘接界面在湿热环境下的失效机理,提出合适的湿热老化寿命模型,可作为固体火箭发动机粘接界面湿热环境适应性研究的理论依据。     

Enhancement of hydrolytic stability and adhesion of waterborne polyurethanes

A new type of polyester polyol, with alkyl side groups, viz. poly(2,4‐diethyl‐1,5‐pentamethylene adipate) glycol (PDPAd) was synthesized and used to improve the hydrolytic stability of waterborne polyurethanes (PU). The results compared favorably with poly(tetramethylene adipate) glycol (PTAd)–based PU and blends of the two types of PU in terms of particle size, thermal, XRD, mechanical, dynamic mechanical, and swell behavior of the dispersion cast films in addition to hydrolytic stability and adhesion properties. Blends of PTAd‐based PU and PDPAd‐based PU gave significantly improved green (immediate) adhesion and hydrolytic stability due to the synergistic effects of crystallinity (heat of crystallization, high density) and amorphous regions (tack, high thermal stability). © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1961–1969, 2005     

Measurement of solubility and diffusion coefficients of ethylene in solid and molten low-density polyethylene with different melt indices

The diffusion behavior of ethylene in polyethylene is of great importance for the polymerization and degassing of polyethylene (PE) industry. Based on the gravimetric sorption and desorption measurement approach, an intelligent gravimetric analyzer is applied to obtain the solubility and diffusion coefficients of ethylene in solid low-density PE (LDPE) with different melt indices at 30°C to 70°C, 0 to 4 atm and in molten LDPE at 160°C to 230°C, 0 to 4 atm, respectively. Results indicate that both the solubility and diffusion coefficients of ethylene in solid LDPE are smaller than those in molten LDPE, while the dissolution enthalpy and diffusion activation energy of ethylene in solid LDPE are higher. In addition, one- and two-dimensional diffusion models are built and the effects of particle size, polymer properties, and operation conditions are systematically investigated on the diffusion behaviors of ethylene in solid and molten LDPE.     

Investigations on the adhesion and interfacial properties of polyurethane foam/thermoplastic materials

The adhesion and interfacial properties of polyurethane (PU) foams with thermoplastic (TP) materials were investigated using different techniques. The adhesion performance of PU foam with TP materials was evaluated using the peel test method, and the adhesion durability was checked after different climate treatments. X‐ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and contact angle measurements were used to study the surface and interface morphology of PU foam and TP material system. Three types of PU foam samples which differ in their composition and also five commercially available TP blends systems, based on poly(carbonate), poly(styrene‐co‐maleic anhydride), poly(acrylonitrile‐butadiene‐styrene), and silicone acrylate rubber have been used. The slow reacting foam shows the best adhesion properties with all the TP materials. The climate treatments strongly effected the PU foam adhesion durability with poly(carbonate) containing TP materials (70–80% loss in adhesion), but nearly no effect with poly(styrene‐co‐maleic anhydride). The samples with lowered adhesion could be separated by peeling without visible foam residues on the TP surface. AFM, XPS, and surface tension studies have shown that the surface properties of the TP material are still governed by the PU foam. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 479–488, 2007     

Diffusion and desorption of CO2 in foamed polystyrene film

Based on the existence of the pores in foamed polystyrene (PS), foamed‐non‐Fickian diffusion (FNFD) model was proposed, for the first time, to regress the desorption data obtained by gravimetric method. Results showed that FNFD model could accurately describe the diffusion behavior of CO₂ out of foamed PS, and well predict the solubility of CO₂ in foamed PS. The characterization of scanning electron microscopy indicated that there were abundant pores in the foamed PS, and the pores store most of CO₂, which would diffuse in the pores, adsorb to the wall of the pores, penetrate across walls of the pores, diffuse in the matrix of PS, and desorb out of PS. The mass of CO₂ in the pores of foamed PS was expressed as a function of foaming pressure and temperature according to foaming kinetics. Results showed that the values calculated by this function agreed well with the values obtained from the FNFD model. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45645.     

Surface studies on the additive migration and diffusion in the windowseal rubber component influencing adhesion to coating

As rubber formulations are complex mixtures of different additives, many of them often migrate and diffuse to the surface, resulting in poor adhesion of windowseal rubber to coating. The present work was conducted to identify and quantify the diffusion behavior of additives of different rubber samples [masterbatch and final automotive ethylene propylene diene (EPDM) rubber compounds] using different complementary techniques such as contact angle measurements, X-ray photoelectron spectroscopy (XPS), size exclusion chromatography (SEC), and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The influence of different methods of processing (milling and extrusion) on the diffusion behavior and change in rubber surface chemistry was investigated. Contact angle measurements using scanning Wilhelmy and sessile drop methods over prolonged time mainly showed an increase in the polar component of the surface energy for the samples, although the total surface energy did not change significantly. XPS analysis showed that in masterbatch samples, the main additive excluded on the surface was the zinc salt of fatty acid. The diffusion coefficient of zinc stearate was found to be 1.083 x 10^-7 cm²/s from contact angle measurement, which is in good agreement with other stearate diffusants in the rubber matrix. Sulfur diffusion over time was more pronounced in the milled final sample. SEC indicated a mixture of additives with different molecular weights extracted from the sample surfaces, such as PE wax, oil, and zinc salt of fatty acid (Aktiplast), indicating that these particular additives migrate to the surface.     

Effect of inert fillers on diffusion and controlled release of penetrant in polymer matrices

This study investigates the characteristics of leaching into a solvent of an active used as termiticide, Bifenthrin® (a synthetic pyrethroid) entrapped in polymer, and the effect of layered silicates on this diffusion. Two contrasting solvents, water and acetone, were used to understand this phenomenon; the active is soluble in acetone but has very low solubility in water. The data are used to understand the migration characteristics of Bifenthrin when encapsulated in polyurethane to form a termite barrier. The absorption characteristics of Bifenthrin in polyethylene were also studied for comparison. Bifenthrin-polyurethaneblends containing 0, 0.5, and 5% of layered silicates were prepared and monitored for the release of Bifenthrin. Using the time-concentration dependence of the active in polymer, diffusion coefficients of Bifenthrin from the polymer were inferred assuming Fickian diffusion. The presence of silicates had no significant effect on the diffusion behavior. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Calculation of pressure in a solid-propellant rocket motor with the use of a real dependence of the solid propellant burning rate on pressure

Five variants of calculating the burning rate of a solid propellant as a function of the pressure in a solid-propellant rocket motor are considered. Two variants of analytical expressions are proposed for approximating real dependences. In all variants, the pressure in the rocket motor can be presented by simple analytical expressions as a function of solid propellant parameters, charging conditions, and structural factors of the charge and motor.     

Organofunctional silanes as adhesion promoters: direct characterization of the polymer/silane interphase

Organofunetional silanes can be used as coupling agents to promote the adhesion of organic matrices to inorganic substrates. Silane coupling agents are of the general structure YSi(OR)₃, where Y is an organofunctional group selected for bonding to organic polymers while (OR) is a hydrolyzable group on silicon which can react with surface hydroxyl groups on the substrate. One mechanism of adhesion promotion by silanes has been postulated to be the interdiffusion of the coupling agent and the polymer to form an interpenetrating network. This paper reviews some earlier results using X-ray photoelectron spectroscopy to probe the polymer/silane interphase region and gives new results obtained using the technique of sputtered neutral mass spectrometry (SNMS). It was demonstrated that SNMS had the sensitivity necessary to detect the polymer/coupling agent interphase. It was found that interdiffusion of the coupling agent with the polymer was maximized when the solubility parameters of the polymer and coupling agent were matched.     

Diffusion coefficient and equilibrium solubility of water molecules in biodegradable polymers

The diffusion coefficient and solubility of water molecules were measured in polyglycolide (PGA), poly(L ‐lactide) (PLLA), poly[(R)‐3‐hydroxybutyrate] (PHB), poly(ϵ‐caprolactone) (PCL), and Skygreen^R (SG). The diffusion coefficient and equilibrium solubility decreased in the order SG > PCL > PLLA > PHB > PGA and PGA > SG > PLLA > PHB > PCL, respectively. The diffusion coefficient and solubility of water at low sorption temperature in PHB varied according to the initial crystallinity of the matrix polymer even though crystallization of PHB molecules took place during the sorption experiment. In contrast, the amorphous PLLA and the crystalline PLLA showed an almost identical diffusion coefficient and solubility of water, in spite of the fact that the amorphous PLLA remained practically amorphous during the whole sorption procedure. A strong correlation existed between the water solubility and the surface tension or contact angle of the polymer matrix. The water diffusivity in PGA was almost 2 orders of magnitude lower while water was more soluble in PGA with a lower heat of sorption than that corresponding to the other more hydrophobic polymers, indicating that the transport of water molecules in PGA followed the solution–diffusion model. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1716–1722, 2000     

硫黄在NR硫化胶中的溶解及扩散

根据分配定律,测定了４０℃时硫黄在ＮＲ硫化胶中的溶解度为１０４,硫黄在胶料与硫化胶之间的分配因子Ｋ为０８４,由此计算出４０℃时硫黄在胶料中的溶解度为１２４。根据硫黄实验扩散曲线计算硫黄在硫化胶中的平均扩散系数Ｄ为３２×１０－５ｍｍ２·ｓ－１,由此推算出４０℃下任意贮存时间内硫黄从胶料向硫化胶迁移的理论扩散曲线。     

超临界CO2在聚合物中的溶解度和扩散性研究

用重量分析法测量了静态条件下CO2在聚苯乙烯(PS)中的溶解度,研究了溶解度与压力和温度的关系,估算了CO2在聚合物PS中的扩散系数。用Henry系数表示了溶解度与温度的关系。实验压力在5-30MPa范围、温度在40-200℃范围。实验数据表明:CO2在PS中的溶解度随着压力的增加而增加,但随着温度的增加而降低。CO2在PS中的扩散系数随饱和时间增加而增加。当吸附量达到一定值时,扩散系数呈下降趋势。     

CL-20在推进剂和发射药中的应用

对CL-20在国内外推进剂和发射药中的研究应用进行了综述。含cL一20的推进剂虽然感度稍高,但有着输出能量高、低特征信号及燃烧产物对环境污染小等优点。CL-20作为低敏感、高能填充剂可用于制造高能、低敏感发射药,在某些推进剂和发射药配方中得到了应用。     

Research on the Crack Mechanism of High-Burning-Rate Propellant in the solid rocket motor

Through the analysis and calculation to the flow field in the solid rocket motor using high-burning-rate propellant, the authors believe that the existence of pressure difference between the inside and outside of the propellant tube causes the propellant crack. In this paper, the design method to eliminate the pressure difference is discussed. The theoretical results were certified by the experimental results.     

CO_2在固态聚丙烯/滑石粉复合材料中的溶解和扩散

利用重量分析的方法测定了温度分别为343.15、373.15和393.15 K,压力0~16 MPa范围内,CO2在聚丙烯(PP)、PP/滑石粉和界面改性PP/滑石粉复合材料中的溶解度和扩散系数。CO2在未经界面改性PP/滑石粉复合材料中的溶解度低压下大于而高压下小于其在纯PP中的溶解度,在经过界面改性的PP/滑石粉复合材料中的溶解度小于其在纯PP和未经界面改性复合材料中的溶解度。CO2在PP/滑石粉复合材料中的扩散系数小于其在纯PP中的扩散系数,填料含量越大扩散系数越小。通过S-L状态方程关联了CO2在纯PP和经过界面改性的PP/滑石粉复合材料非晶区的溶解度,并计算了CO2对聚合物基体的溶胀情况,证实了填料对聚合物分子链运动的阻碍作用。     

Diffusion rates in a dense matrix of methane-producing microorganisms

The diffusion rate of a species, in a dense matrix of methane-producing microorganisms, was determined experimentally. To this end, a specially designed diaphragm diffusion cell was utilized. The experimental results revealed that the effective diffusion coefficient in a microorganism matrix was 22–33% of the diffusion coefficient in pure water.     

A Model for the Diffusion of Moisture in Adhesive Joints. Part I: Equations Governing Diffusion

A methodology is proposed to relate the diffusion coefficient of small penetrant molecules in polymers to temperature, strain, and penetrant concentration. The approach used is based on well-known free volume theories. It is assumed that the transport kinetics is governed by the constant redistribution of the free volume, caused by the segmental motions of the polymeric chains. An expression for the diffusion coefficient is inferred from the temperature, strain, and penetrant concentration dependence of the free volume. The stress dependence of solubility is predicted from the Hildebrand theory. It is shown that the resulting constitutive equations exhibit many features desirable for joint durability studies. Finally, a non-Fickian driving force arising from differential swelling is included in the governing equations.     

Solubility and diffusion in latex films formed from high glass transition temperature particles

In situ steady-state fluorescence measurements were used to study the dissolution of polymer films. These films were formed from pyrene labeled poly(methyl methacrylate) (PMMA) latex particles that were sterically stabilized by polyisobutylene. Annealing was performed above the glass transition temperature at 180°C at 1-h time intervals for film formation. Desorption of pyrene labeled PMMA chains was monitored in real time by the change of pyrene fluorescence intensity. Dissolution experiments were performed in various solvents with different solubility parameters, δ, at room temperature. Diffusion coefficients, D, in various solvents were measured and found to be around 10⁻¹⁰ cm²/s. A strong relation between D and δ was observed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1493–1502, 1998     

Time calculation for the after-cure cooling process of the cast modified double base propellant in a large rocket motor

An unsteady heat conduction model is proposed to calculate the temperature distribution of the case-bonded rocket motors and the time required for the cooling process based on the experimentally determined thermal and mechanical parameters of a cast modified double base propellant (CMDB) and its glass steel shell. The resultant value of the time is then used to derive the corresponding stress relaxation modulus, which is compared with the modulus data obtained from uniaxial tensile stress relaxation experiments to see if the internal stress has been thoroughly relaxed within this period of time.