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A considerable amount of acidic gas penetrates into the annulus between the internal pressure sheath and the outer protective sheath during the service of flexible risers, which will inevitably lead to corrosion of the metal functional layer. Many researchers have modified nanocomposites from the mass transfer perspective to reduce the materials' permeability coefficient. While permeation is an integrated process of heat and mass transfer process, heat distribution directly impacts gas permeation. Herein, the thermal conductivity of flexible riser liner materials is predicted for the first time by a combination of molecular dynamics and experiments, and then the radial temperature distribution under different seawater temperatures and internal fluid temperatures is investigated by finite element analysis. Finally, the effect of temperature distribution on the permeation coefficient was analyzed. The results demonstrate that the thermal conductivity can be predicted by molecular dynamics simulation, and the thermal conductivity of (polyvinylidene difluoride) PVDF/TiO2 decreases, while the thermal conductivity of PVDF/carbon nanotube (CNT) increases compared with pure PVDF. The temperature distribution of the internal pressure sheath material decreases when condensate water is present. As the fluid temperature rises from 30 to 110°C, the maximum increase ratio in the permeability of PVDF/CNT over PVDF increased from 3.6% to 14.8%, and the maximum decrease ratio of PVDF/TiO2 permeability coefficient compared with PVDF is from 1.2% to 4.6%. The results present a new idea to improve the barrier properties of materials by decreasing thermal conductivity. [ABSTRACT FROM AUTHOR]

Nitrile butadiene rubber (NBR) has received a lot of attention as a sealing material, and its tribological performance is a crucial factor in determining the efficiency with which it will operate under various operating situations. In this study, NBR specimens with varying degrees of cyanide content, namely low cyanide (DN401), medium cyanide (DN2850), medium‐high cyanide (DN3380), and high cyanide (DN4050), were selected to investigate their tribological behavior when subjected to NO.10 aviation oil. To emulate their frictional responses during startup and shutdown operations, all four types of NBR were assessed under dry conditions. As the cyanide content increased, the coefficient of friction (COF) dropped from 1.381 to 0.810 and wear rate dropped from 2.38 × 10−3 mm3/(N m) to 1.88 × 10−4 mm3/(N m). When employed in conjunction with NO.10 aviation oil, DN401 and DN3380 exhibited COFs of 0.0963 and a slightly higher value of 0.127, respectively. Following aging treatment at 80°C in NO.10 aviation oil, stress reduction reached 65.8%, indicating the poorest performance among the four variants of NBR. Considering the COF, wear rate, and aging performance, DN3380 emerges as the most favorable choice for practical applications, thereby offering valuable insights into the selection of nitrile rubber for sealing materials. [ABSTRACT FROM AUTHOR]

It is generally believed that the ultra‐high molecular weight polyethylene (UHMWPE) performances are closely related to its molecular weight. However, when we sintered two brands of UHMWPE powders with similar molecular weights, GUR 4012 and GUR 400 Fine, we found they demonstrate eminent differences in cryogenic properties. Particularly, the cryogenic impact strength of GUR 4012 is 236% higher than that of GUR 400 Fine. To explain such an amazing phenomenon, we characterized UHMWPE microstructures and investigated the structure–property relations through scanning electron microscopy, x‐ray scattering diffraction, differential scanning calorimeter, and dynamic mechanical analysis. We observed only a slight difference in crystallization behaviors between them, but the entanglement density of GUR 4012 is much higher than that of GUR 400 Fine. Accordingly, we put forward a potential mechanism to analyze the eminent differences in cryogenic impact strengths. This work may promote our comprehension of the relation between the structure and performances of UHMWPE, which is conducive to promoting UHMWPE performance and broadening its industrial applications. [ABSTRACT FROM AUTHOR]

Nanoparticles can act as a barrier to gas penetration in the polymer matrix. However, the agglomeration of nanoparticles has a negative effect on the comprehensive properties of nanocomposites. We envisioned surface modification of 25 nm TiO2 nanoparticles with KH550 to enable better dispersion in the polyvinylidene fluoride (PVDF) matrix and prepared PVDF/TiO2 composites by the melt blending method. The effects of adding modified nanoparticles into the matrix on the thermodynamic, mechanical, rheological, and gas barrier properties were studied. We find that the dispersion of TiO2 in the matrix significantly improved after modification, as observed in the SEM images. As a result, the mechanical properties of composites decreased with an increase in the content of nanoparticles, and PVDF/N‐TiO2 composites showed better mechanical and CO2 barrier properties. The permeability coefficient of PVDF/0.5% N‐TiO2 has the lowest permeability coefficient, which is 18.30% lower than primary PVDF. At a high shear rate, the viscosity of PVDF/N‐TiO2 with 0.5% and 1.0% content decreased, and the viscosity of 1.5% ratio was higher than that of primary PVDF. PVDF/0.5% N‐TiO2 has the best comprehensive performance and also possesses the advantages of simple preparation, low cost, and ease of industrial production. [ABSTRACT FROM AUTHOR]

When fabricating polymer nanocomposites (PNCs), it is difficult for nanoparticles to disperse stably in polymer matrix since their high‐surface energy can cause them to attract each other. In this paper, we review the effects of nanoparticle size, surface chemical properties, and thermodynamic parameters on the dispersion state of nanoparticles (including inorganic and organic particles) in PNCs and describe some key measures to promote the nanoparticles dispersion. The ideal nanoparticles dispersion in polymer melt is available when the particle size is smaller than the rotation radius of polymer chains and the particle surface is highly compatible or has interactions with the matrix. In polymer solution, establishing proper thermodynamic parameters is necessary to ensure the balance interactions among particles, solvents, and polymers, leading to the successful preparation of PNCs with ideal structure. These results could supply theoretical suggestions for the design of PNCs. Moreover, the equilibrium dispersion may be unavailable without reasonable kinetic parameters, even if the dispersion process is thermodynamically favorable. Therefore, more studies are required on both thermodynamics and kinetics of the dispersion process. [ABSTRACT FROM AUTHOR]

ABSTRACT In this study, the effects of carbon nanofiber (CNF) surface modification on mechanical properties of polyamide 1212 (PA1212)/CNFs composites were investigated. CNFs grafted with ethylenediamine (CNF- g-EDA), and CNFs grafted with polyethyleneimine (CNF- g-PEI) were prepared and characterized. The mechanical properties of the PA1212/CNFs composites were reinforced efficiently with addition of 0.3 wt % modified CNFs after drawing. The reinforcing effect of the drawn composites was investigated in terms of interfacial interaction, crystal orientation, crystallization properties and so on. After the surface modification of CNFs, the interfacial adhesion and dispersion of CNFs in PA1212 matrix were improved, especially for CNF- g-PEI. The improved interfacial adhesion and dispersion of CNFs in PA1212 matrix was beneficial to reinforcement of the composites. Compared with pure PA1212, improved degree of crystal orientation in the PA1212/CNF- g-PEI (CNF- g-EDA) composites was responsible for reinforcement of mechanical properties after drawing. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41424. [ABSTRACT FROM AUTHOR]