Interaction of fibroblast with poly(p-dioxanone) and its degradation products

In vitro techniques were used to evaluate the interactions between Fibroblastic cells and Poly(p-Dioxanone) PPDX and compared its performance with that of other polymeric substrates. In vitro biocompatibility was assessed by studying cell adhesion and cell growth of cells on the polymer films themselves as well as in media enriched with the degradation products of PPDX and Poly(glycolic)/Poly(L-lactide 90:10 copolymer (PGLA-910). Our results show that althought all polymers tested were suitable for initial attachment, PPDX proved to be the most favorable surface for cell growth; as cell density after 48 h of culture was similar to that obtained on tissue culture Polystyrene TCPS (control). No signs of cell damage were detected using scanning electron microscopy (SEM) where after 48 h. of cell seeding on PPDX, fibroblast exhibited a confluent cell multilayer similar to TCPS. In addition, the products of the hydrolytic degradation of PPDX had no citotoxic effect on the adherence and proliferation of fibroblastic cell on TCPS. The hydrolytic degradation starts in the amorphous regions, as the tie-chain segments in these regions degrade into fragments causing the pH decrease in buffer solution and weight loss of degradable polymers. The in vitro evaluation suggests that PPDX may be candidate biomaterial for the construction a cell-polymer matrix.     

Heterogeneous nucleation and self-nucleation of poly(p-dioxanone)

The changes in nucleation behaviour upon addition of Boron Nitride (BN), Talc and Hydroxyapatite (HA) to poly(p-dioxanone) (PPDX) were monitored by DSC and Polarised Optical Microscopy (PM). Self-nucleation DSC studies evidenced the existence of the usual three self-nucleation domains depending on the self-nucleation temperature (T _s) employed. By far the best nucleation agents for PPDX were its own self-nuclei and this result was independent of the presence or absence of any of the other nucleating agents employed; once Domain II was reached, self-nucleation dominated the nucleation process. BN and Talc were able to nucleate PPDX, thereby increasing its nucleation density, its dynamic crystallisation temperature upon cooling from the melt (T _c) and its enthalpy of crystallisation (H _c). BN was a better nucleating agent than talc. HA on the other hand caused an antinucleation effect on PPDX characterised by a decrease in its nucleation density, a decrease in its T _c and in H _c. Isothermally crystallised PPDX exhibited large banded spherulites whose morphology changed as a function of crystallisation temperature from single banded structures with a very clear Maltese cross to double banded spherulites. PPDX also shows a change in growth regime upon increasing crystallisation temperature (from Regime III to Regime II) according to the kinetic interpretation of growth rate data. BN did not cause any significant modification of the spherulitic growth kinetics (in Regime II) except for a small decrease in surface free energy of PPDX crystals (_e). On the other hand HA was found to increase the spherulitic growth rate and the overall crystallisation rate of PPDX, this increase was caused by a degradation process experienced by the polymer during the treatments involved in isothermal crystallisation that was only present in the samples with HA. It is postulated that the interaction between the phosphate groups on the surface of HA and the ester groups of PPDX are responsible for both the antinucleation effect and the catalysis of the hydrolytic degradation of PPDX.     

Carbonization behavior of polyoxadiazole fibers and films

The carbonization behavior of polyoxadiazole (POD) fibers was investigated in comparison with that of films by using wide- and small-angle X-ray scattering, scanning electron microscopy and measurements of density, mass, volume and dimensional changes. On heat-treating POD fibers and films at a degradation temperature of about 500 °C, small-angle X-ray scattering from a long-period structure appeared and disappeared again, which indicated inhomogeneous progress of the scission of POD molecules. This accounted for the ability of this polymer to keep the macroscopic precursor geometry during carbonization in spite of yielding a graphitizing carbon. During the volume reduction process, the nuclei of the carbon layer stacks formed immediately after degradation of POD were piled up parallel to the material surface. This led to autonomous increase in the preferred orientation of the carbon layer stacks at higher temperatures. When the interlayer spacing decreased below 0.340 nm, the carbon layer stacks assumed three-dimensional regularity. The degree of the stacking regularity was higher for the films than the fibers. The macroscopic precursor geometry imposed a stronger restriction on the growth of the carbon layer stacks in the fibers than in the films.     

Development of sandwich panels combining Sisal Fiber-Cement Composites and Fiber-Reinforced Lightweight Concrete

This research proposes the development of an innovative structural panels based on the use of thin outer layers of Sisal Fiber-Cement Composites (SiFCC) together with a core layer of Polypropylene Fiber-Reinforced Lightweight Concrete (PFRLC).The influence of sisal fibers was studied in two different ways, short sisal fibers (50 mm) randomly distributed in the matrix, and long unidirectional aligned sisal fibers (700 mm) applied by a cast hand layup technique. Lightweight aggregates and polypropylene fibers were used in the concrete layer forming the panel's core in order to reduce its density and improve its post-cracking tensile strength and energy absorption capacity.The behavior of the sandwich panels in four-point bending test is described, and the various failure mechanisms are reported. Mechanical properties of both SiFCC and PFRLC were obtained, which were also used in the numerical simulations. Pull-off tests were performed to evaluate the bond strength between the outer SiFCC layers and the core PFRLC. The results revealed that the long sisal fibers were more effective in terms of providing to the panel higher flexural capacity than when using short sisal fibers, long fibers ensured the development of a deflection hardening behavior followed by the formation of multiple cracks, while short sisal fibers promoted a softening response after cracking.     

Influence of ethylene glycol vapor annealing on structure and property of wet-spun PVA/PEDOT:PSS blend fiber

In this study, blend fibers composed of poly(vinyl alcohol) and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) were prepared via wet-spinning technology. Ethylene glycol (EG) vapor annealing was employed to improve the electrical conductivity and tensile properties of blend fibers. The effects of EG vapor annealing on structures and properties of blend fibers were investigated in detail by analyzing the changes in chemical constituent and structure, molecular structure, surface morphology, surface chemical composition, electrical conductivity, and tensile properties. FTIR spectroscopy indicates that EG vapor annealing does not change the chemical constituent and structure of blend fibers. Raman spectroscopy shows that vapor annealing leads to conformational changes of PEDOT chains from benzoid structure to quinoid structure. AFM and SEM images show that surface morphology of blend fibers become smoother after vapor annealing. XPS measurement shows that EG vapor annealing induces significant phase separation between PEDOT and PSS, forming an enriched PSS layer on the surface of blend fibers, thus leading to a thinner insulating PSS layer between PEDOT grains. This conformational change is beneficial to improve the electrical conductivity of blend fibers. The resultant blend fiber reached conductivity up to 20.4 S cm^?1. The mechanical properties of blend fibers were also improved by EG vapor annealing, with the Young’s modulus and tensile strength increasing from 3.6 GPa and 112 MPa to 4.4 GPa and 132.7 MPa, respectively.     

Recrystallization behavior of a co-cast AA3xxx–AA6xxx aluminum alloy laminate — Effect of annealing conditions and cold reduction levels

The annealing behavior of a laminated AA3xxx–AA6xxx alloy system is investigated at temperatures and conditions which represent fine particle presence or dissolution in the AA6xxx (i.e. core) layer, as well as 60 or 80% cold reduction levels. The through-thickness microstructural characteristics of the cold rolled and annealed laminates are analyzed using various methods. It is found that the average grain size of the AA3xxx (i.e. clad) layer is generally finer than that of the core layer and the grains are more equiaxed in that layer for all conditions studied. The annealed microstructure of the core layer is also more strongly affected by the change in the annealing conditions. The dependencies of the average grain size and grain size aspect ratio on the annealing conditions are dictated by the presence, size, distribution and thermal stability of particles. A higher level of cold reduction results in reversing the trend of change in the grain size aspect ratios of both layers with annealing temperature in the range of 380 to 420 °C (1 h), while it yields characteristics similar to that obtained by 60% reduction when annealing is conducted for 30 s at 540 °C. These results are explained through the microstructural evolution parameters that are affected by cold rolling and annealing conditions.     

湿法纺聚丙烯腈原丝的微观结构分析

利用扫描电镜和透射电镜研究了聚丙烯腈(PAN)纤维在湿法纺丝工艺中的微观形貌与结构演变.测试分析证实,初生纤维的结构会遗传至PAN原丝,PAN原丝为皮芯多层结构,最外面是一层极薄的表皮,向内依次为表层、内层、芯部.表皮的片层结构薄且致密,其分子链结晶度高且晶粒沿轴向取向度好.柱状表层的层状结构中晶粒分布均匀、沿轴向定向较好.由表皮至内层,层状结构的厚度逐渐增加,芯部组织较疏松.建立了PAN原丝的结构模型.     

Degradation behavior of amorphous silicon nitride fibers in low atmospheric pressure

We investigated the degradation behavior of amorphous silicon nitride (Si₃N₄) fibers in low air pressure and presumed the evolution mechanism. The obtained Si₃N₄ fibers were characterized by tensile strength, X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and elemental analysis after being annealed (air pressure: 1 Pa–0.1 MPa, temperature: 1000–1600 °C, dwell time: 0–4 h). When air pressure was lower than 100 Pa or higher than 1000 Pa the strength of fibers dropped sharply. Due to the moderate partial pressure of oxygen in 100–1000 Pa, both active oxidation and passive oxidation were restrained resulting in the best mechanical property of fibers in 100–1000 Pa. Besides air pressure, annealing time also affected the thermal behavior of fibers. Firstly Si₃N₄ fibers were passive oxidized to form SiO₂ layer on the surface, and then Si₃N₄ decomposed into free Si and SiO₂ released gaseous SiO. Finally crystallization inside of fibers and formation of nanowires on the outer surface played the leading role in the progress of degradation.

     

Electrospun polymer nanofibers with internal periodic structure obtained by microphase separation of cylindrically confined block copolymers

Continuous fibers are described having concentric layer or aligned sphere microphase-separated, styrene-isoprene block copolymer morphologies. The fibers are obtained by a two-fluid coaxial electrospinning technique in which the desired block copolymer is encapsulated as the core component within a polymer shell having a high glass transition temperature (Tg). The fibers range in diameter from 300 to 800 nm, and the block copolymer core ranges from 50 to 500 nm. Subsequent annealing of the fibers above the upper Tg of the block copolymer but below the Tg of the shell polymer results in microphase separation of the block copolymer under cylindrical confinement. The resulting fibers exhibit improved long-range order. This two-step strategy creates the opportunity to fabricate continuous nanofibers with periodic internal structure.     

壳聚糖中空纤维膜的制备及其结构研究

采用干湿相转化成膜的方法,纺制了壳聚糖中空纤维膜,研究了干燥方法及成膜条件对膜结构的影响.实验发现自然干燥导致膜的严重收缩,最终形成整体致密的膜结构;采用乙醇-正己烷液-液交换干燥,能够有效地避免膜结构的完全致密化,最终形成整体非对称的膜结构.成膜条件的研究结果表明,壳聚糖浓度的提高,更易形成致密层增厚的膜结构;而凝胶温度及凝胶液组成中氢氧化钠浓度的升高,有利于形成致密层更薄,支撑层孔径更大的整体非对称膜结构.进一步的研究表明,整体非对称结构的壳聚糖中空纤维膜可以应用于渗透汽化分离碳酸二甲酯/甲醇混合物,突破恒沸组成的限制,具有较好的应用前景.     

The influence of the fiber drawing process on intrinsic stress and the resulting birefringence optimization of PM fibers

The propagation properties of optical fibers can be significantly influenced by intrinsic stress. These effects are often undesired but in some cases essential for certain applications, e.g. in polarization maintaining (PM) fibers. In this paper, we present systematic studies on the influence of the fiber drawing process on the generated stress and demonstrate an approach to significantly increase the stress induced birefringence of PM-fibers. It is shown that the thermal stress caused by the material composition is superimposed with the mechanical stress caused by the fiber fabrication process. This intrinsic stress has a strong effect on the optical and mechanical properties of the glass and thus influences the fiber stability and modal behavior. By applying a thermal annealing step, the mechanical stress due to the fiber drawing process can be canceled. It is shown that this annealing step compensates the stress reducing influence of the drawing process on the birefringence of PM-fibers with panda structure. The comparison of the intrinsic stress states after fabrication with the state after the additional high temperature annealing step clearly shows that it is possible to improve the overall birefringence of panda fibers using appropriate preparation steps.     

Microstructure evolution upon annealing of accumulative roll bonding (ARB) 1100 Al sheet materials: evolution of interface microstructures

The microstructure evolution upon annealing of 1100 aluminum samples that were accumulative roll bonding (ARB) processed were studied with the use of transmission electron microscopy. It was found that the ultra-fine microstructure resulted from the ARB process was not stable. Specifically, a two-stage grain growth behavior was observed, in which a relatively slower rate of grain growth was followed by a more rapid grain growth rate at higher annealing temperature. The bonding interfaces that were unique to the roll bonding process were found to have a significant influence on the grain growth behavior when the grain size of the material was of similar dimension as the bonding interface separation. Discontinuous pockets consisting of smaller grains were found to have formed upon annealing. These pockets represented the remnants of the heavily deformed layer from wire brushing.     

ZnO/GO纳米材料基热稳定钙钛矿太阳能电池

为了使钙钛矿太阳能电池在高温退火后能够保持稳定, 本研究通过电化学方法制备出氧化锌/氧化石墨烯纳米粒子, 并将其运用到钙钛矿太阳能电池中作为电子传输层使用。通过原位掠入射X射线衍射(GIXRD)、X射线衍射(XRD)、扫描电子显微镜(SEM)和紫外-可见吸收光谱(UV-Vis)等方法对沉积在氧化锌和氧化锌/氧化石墨烯纳米材料上面的甲胺铅碘的结构、形貌以及电池性能变化进行分析测试。结果表明: 氧化锌/氧化石墨烯对于甲胺铅碘有保护作用, 沉积在氧化锌/氧化石墨烯上面的甲胺铅碘薄膜稳定性更高, 电池性能更加稳定, 为将来大面积应用提供了一定的指导。     

Microstructural evolution of Hi-NicalonTM SiC fibers annealed and crept in various oxygen partial pressure atmospheres

It is expected that in the future SiC fiber-reinforced ceramic-matrix composites (CMCs) will be used in high temperature and hostile environments. In this study, Hi-Nicalon^TM SiC fibers were annealed and crept at 1500 °C for 1 hour in air, an argon flow and an ultra high-purity argon flow in order to investigate the effects of atmospheres and load conditions on the decomposition behavior and microstructural evolution of the fibers. After the fibers were annealed and crept in air, a silica layer with cracks was formed on the fiber surface. Under the creep load, the silica layer became thicker and porous due to the oxidation mechanism change from diffusion of ionic oxygen to transportation of oxygen molecules. An oxygen-enriched amorphous layer was formed at the fiber surface in the case of annealing in an argon flow, whereas SiC crystals were produced by the gas-phase reaction on the fiber surface when the fiber was crept in an argon flow. In an ultra high-purity argon flow, SiC crystals grew on the surface of both annealed and crept fibers. Growth of -SiC grain was enhanced under low oxygen partial pressure atmospheres and creep load.     

碳纤维制造过程中径向差异表征及演变机理

为优化PAN基碳纤维结构,采用AES表征PAN纤维在低温碳化与高温碳化后C,N,O沿纤维径向的分布,并用以阐明预氧化碳化过程径向差异的形成机理.结果表明:预氧丝径向结构不均匀,由外向内氧化程度降低;预氧时物理阻隔与化学阻隔导致径向形成氧浓度梯度,热物理传递与化学反应放热导致径向形成温度梯度.低温碳化时,热物理传递与化学反应放热形成温度梯度加剧了预氧时的径向差异;纤维分3部分,最外层氧含量低,由氧化程度高的预氧皮层外部强烈脱氮脱氧形成,最内层由氧化程度低的预氧芯层转化而成;中间是过渡层,一部分由氧化程度较高的预氧皮层内部少量脱氧脱氮而成,氧含量高,而后过渡到预氧程度低的低含氧量芯部.高碳丝径向组分差异变小,纤维分两部分,外层厚度仅为纤维直径的10%,是碳含量逐渐降低的过渡性皮层,其余部分为组成均一的芯层.     

Performance of functionally graded sandwich composite beams under shock wave loading

The dynamic behavior of sandwich composites made of E-Glass Vinyl-Ester (EVE) facesheets and graded Corecell™ A-series foam was studied using a shock tube apparatus. The foam core was monotonically graded based on increasing acoustic wave impedance, with the foam core layer of lowest wave impedance facing the blast. The specimen dimensions were held constant for all core configurations, while the number of core layers varied, resulting in specimens with one layer, two layer, three layer, and four layers of foam core gradation. Prior to shock tube testing, the quasi-static and dynamic constitutive behavior (compressive) of each type of foam was evaluated. During the shock tube testing, high-speed photography coupled with the optical technique of Digital Image Correlation (DIC) was utilized to capture the real-time deformation process as well as mechanisms of failure. Post-mortem analysis was also carried out to evaluate the overall blast performance of these configurations. The results indicated that increasing the number of monotonically graded foam core layers, thus reducing the acoustic wave impedance mismatch between successive layers, helped maintain structural integrity and increased the blast performance of the sandwich composite.     

毛竹工艺纤维高温饱和蒸汽-机械分离及其物理力学特性

采用高温饱和蒸汽对高含水率新鲜毛竹竹材进行热处理,再通过辊轧制备竹材工艺纤维(由多根纤维组成),并运用光学显微、纳米压痕(NI)等分析技术研究了提取的工艺纤维的微观结构、化学组分、力学性能及吸湿特性.研究结果表明:高温饱和蒸汽处理可使细胞壁中半纤维发生降解,薄壁细胞由于壁薄更易受到破坏,在机械外力下薄壁细胞和维管束成功...     

Influence of Annealing Atmosphere on Epitaxial Growth Process of the CeO2 Buffer Layer for Coated Conductors

The epitaxial growth of the buffer layer on a textured metal substrate has a significant influence on the performance of coated conductors, which provides the potential to support a high current for electric utility and high magnetic field applications at 77 K. In this paper, we have fabricated the CeO₂ buffer layer on YSZ (yttria-stabilized zirconia) (00l) single crystal substrates by the chemical solution deposition (CSD) method in different annealing atmospheres. The results show that both the thermal decomposition behavior of the precursor solution and the annealing atmosphere have an important effect on the epitaxial growth process of the CeO₂ buffer layer. The large oxygen partial pressure in annealing atmosphere is to the disadvantage of the epitaxial growth of CeO₂ (00l) crystal face with high energy. Moreover, the epitaxial growth of the CeO₂ (00l) crystal plane goes against a decrease in the surface roughness of the CeO₂ film. Therefore, it can be considered that the orientation growth of the CeO₂ buffer layer and its surface morphology evolution may be related to the thermal decomposition behavior of precursor solution and the change of oxygen vacancies concentration.     

Transverse core fiber alignment in short-fiber injection-molding

Frequently it is observed that fibers in the core of short-fiber injection moldings lie predominantly in the plane of the plaque and perpendicular to the mold-fill direction. Such orientation of core fibers does nit appear to be explicable by the fluid mechanics of mold-filling, and an entrance-induced orientation argument does not account for an orientation which is transverse to both the mold-fill and thickness directions. The present work investigates the development of fiber orientation during the mold-filling process by examining through-thickness microstructures in a series of controlled short shots. Comparison of these microstructures with that of a fully packed injection molding indicates that the transverse orientation of fibers throughout the core layer did not occur until after the mold was full. Hence, the transverse orientation of core fibers may be attributed to stresses developed during the packing stage of the injection molding process.     

The relationship of crystallization behavior,mechanical properties,and morphology of polypropylene nanocomposite fibers

This study aimed at the fabrication of lightweight and high performance nanocomposite fibers. Polypropylene/multiwalled carbon nanotubes (PP/MWCNTs) nanocomposite fibers (0–5 wt% of MWCNTs) were prepared via melt spinning process. The MWCNTs were dispersed in the dispersing agent before mixing with PP powder. After mixing, the dispersing agent was removed. Then the nanocomposites were spun into fibers. The fibers were spun and stretched with 7.5 draw ratios. Crystallization behavior and thermal properties of PP/MWCNTs nanocomposite fibers were studied using the differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA). The DSC curves of PP/MWCNTs nanocomposite fibers showed the crystallization peak at a temperature higher than that of neat PP fibers. These results revealed that the MWCNTs acted as nucleating sites for PP crystallization. The additions of MWCNTs into PP leaded to an increase in both crystallization temperature and crystallization enthalpy. However, no significant changes in the melting temperatures of the PP nanocomposites were detected. Degradation temperature of samples obtained from the TGA curves showed increase thermal degradation behavior for the PP/MWCNTs with the content of MWCNTs. It was found that the increase of tensile strength and modulus corresponded well with the increase of crystallinity of the composite fibers.