Natural fibre composites from polyethylene waste and hazelnut shell: dimensional stability,physical, mechanical and thermal properties

Within the framework of this study, the physical modification of high-density polyethylene waste foil was performed using finely ground hazelnut flour to produce a composite whose physical, mechanical and flammable properties make it possible to use inside and outside of buildings. Three mixtures were produced with filler shares of 11, 26 and 42 vol.% using equipment that is normally used in polymer processing, and no refining additives were applied. The produced materials were analysed for their processing (mass flow ratio), physical (density and moisture content) and mechanical properties (tensile strength, elongation at break and dynamic thermal analysis) and resistance to environmental factors (swelling and water absorption, thermogravimetric analysis and combustion heat). The particle size distribution of the filler and morphological properties of the composites (scanning electron microscopy) were also investigated. It was vital to obtain an inexpensive material with low absorptivity. The resulting materials are characterised by a low density, acceptable low absorptive and good mechanical properties; also, they can constitute an important fuel once their practical properties have been exploited.     

钴-聚吡咯-碳载Pt催化剂的制备及其单电池性能研究

采用脉冲微波辅助化学还原法制备了钴-聚吡咯-碳载Pt催化剂(Pt/Co-PPy-C),并将其作为阴极催化剂,组装单电池。考察了电池运行温度和氢气/空气计量比对单电池性能的影响,并与商业Pt/C催化剂进行了耐久性实验比较。 结果表明,运行温度为70 ℃,氢气与空气的计量比为1.2:2.5时单电池性能最佳。600 mA/cm²恒电流稳定运行150 h耐久性测试中,以Pt/Co-PPy-C为阴极催化剂的单电池平均电压衰退率为0.119 mV/h,是商业Pt/C催化剂的26%。耐久性测试前后,单电池的阴极电荷传递阻抗为7.176和8.767 Ω,均比商业Pt/C催化剂阻抗小;Pt颗粒粒径从2.46 nm增长到3.18 nm,均小于商业Pt/C催化剂的粒径。这表明,以Pt/Co-PPy-C催化剂为阴极催化剂制备的单电池性能优良,在质子交换膜燃料电池中有广泛的应用前景。     

Embedding Amorphous Molybdenum Sulfide within a Porous Poly(3,4‐ethylenedioxythiophene) Matrix to Enhance its H2‐evolving Catalytic Activity and Robustness

Amorphous molybdenum sulfide (MoS_x) is a promising alternative to Pt catalyst for the H₂ evolution in water. However, it is suffered of an electrochemical corrosion. In this report, we present a strategy to tack this issue by embedding the MoS_x catalyst within a porous poly(3,4‐ethylenedioxythiophene) (PEDOT) matrix. The PEDOT host is firstly grown onto a fluorine‐doped tin oxide (FTO) electrode by electrochemical polymerization of EDOT monomer in an acetonitrile solution to perform a porous structure. The MoS_x catalyst is subsequently deposited onto the PEDOT by an electrochemical oxidation of [MoS₄]^2? monomer. In a 0.5 M H₂SO₄ electrolyte solution, the MoS_x/PEDOT shows higher H₂‐evolving catalytic activities (current density of 34.2 mA/cm² at ?0.4 V vs RHE) in comparison to a pristine MoS_x grown on a planar FTO electrode having similar catalyst loading (24.2 mA/cm²). The PEDOT matrix contributes to enhance the stability of MoS_x catalyst by a significant manner. As such, the MoS_x/PEDOT retains 81 % of its best catalytic activity after 1000 potential scans from 0 to ?0.4 V vs. RHE, whereas a planar MoS_x catalyst is completely degraded after about 240 potential scans, due to its complete corrosion.     

A MODEL FOR CONCRETE DURABILITY DEGRADATION IN FREEZE-THAWING CYCLES

Up to now, how to control the durability of concrete structures is still a pending research topic in civil engineering. Owing to the fact that concrete durability can be affected by many non-mechanical factors, it is very difficult to research durability only based on mechanics.However, the phenomenon of failure caused by non-mechanical factors is similar to that caused by loads. As frost durability reflects the comprehensive durability of concrete in a certain sense,the specific failure process is analyzed and a damage model is introduced, which can describe the durability degradation process of concrete in the whole freeze-thawing cycle.     

复合材料盒段耐久性／损伤容限试验研究

纤维增强复合材料结构的耐久性／损伤容限设计是目前飞机设计中极为关注的问题，但是，有关这方面的理论分析尚未成熟，本文通过对复合材料盒段的耐久性／损伤容限的试验研究，得到一些有关复合材料结构耐久性／损伤容限设计的结呆，可供复合材料结构设计和进一步理论探讨引介。     

ZrP-Nafion115复合膜的直接甲醇燃料电池原位稳定性

以商品Nafion115膜中的水合纳米离子簇为微反应器,通过化学键将磷酸氢锆(ZrP)纳米粒子锚合在Nafion115膜中,制备了ZrP-Nafion115复合膜。通过XRD及原位恒流放电等方法研究了复合膜在直接甲醇燃料电池(DMFC)工况条件下的稳定性,并进一步揭示了ZrP在Nafion115膜中发生化学锚合作用的反应机理及微观结构。结果表明:使用了ZrP-Nafion115复合膜的DMFC在恒流放电(100 mA/cm~2)过程中,可以在0.4 V以上的电压中稳定运行至少116 h,且ZrP纳米粒子没有明显流失。     

Durability and integrity studies of environmentally conditioned interfaces in fibrous polymeric composites: Critical concepts and comments

Fibre reinforced polymer (FRP) composites are the most promising and elegant material of the present century. Their durability and integrity in various service environments can be altered by the response of its constituent i.e. fibre, polymer matrix, and the existing interface/interphase between the fibre and polymer matrix, in that particular environment. The interphase is generally manifested by chemical bonding, molecular segregation and also by van der Waals bonding. The sizing of fibres generally influences the chemistry and character of the interface/interphase and might generate structural gradient in the polymer matrix. Their susceptibilities to degradation are dependent of the nature of environments and each of the constituents' responds differently and uniquely. Amongst the three constituents, the interface/interphase has a very critical role to play on the performance and reliability of FRP composites. The reduced glass transition temperature of the interphase may induce low modulus area, which subsequently affects fracture toughness and local stresses of the composite. These result in high fracture toughness at ambient temperatures, but significantly reduced performance at high temperatures.     

Relevance of High Temperature Oxidative Stability Testing to Long Term Polymer Durability

In polymer degradation and durability studies, as well as predicting shelf-life for medical devices, one is confronted with the need for accurate prediction and difficulties of long term real-time evaluation. Various ways to accelerate the degradation process have met with mixed success. However, recently, in our own studies, a ‘master curve’ like behavior was found to be valid for polypropylene samples studied. Evidently, for samples obeying the master curve, very few data points at high temperatures can be scaled to obtain reasonably accurate estimates on long term durability. Nevertheless, in a reference medium density polyethylene (MDPE) film material, the high temperature oxidative induction time data appear to diverge when run under air atmosphere compared with oxygen environments. In this article, we will present data on many of the polymer systems studied with an emphasis on extrapolation schemes for high temperature accelerated data to lower temperature very long-term durability. In this context, polymer and antioxidant reactivity toward oxygen, morphology, and mechanical property dependence on extent of degradation all need to be considered. And the potential and limitations of this approach will be discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of boron addition on the structure and properties of iron phosphate glasses

Effects of boron addition on the glass forming characteristics, structure and properties of iron phosphate glasses with nominal compositions of xB₂O₃-(40−x)Fe₂O₃-60P₂O₅ (x = 2-20, mol%) and xB₂O₃-(100−x)[Fe₂O₃-60P₂O₅] (x = 2-20, mol%) have been investigated by DTA, XRD, IR and Mössbauer spectroscopy. Although there were some weak local surface crystallizations on especially most of the glasses in group B, all of the compositions formed glass. DTA spectra showed two exothermic peaks corresponding to crystallizations along with an endothermic glass transition peak. T_g increased with increasing B₂O₃ content for the glasses in the first series which indicates that the addition of B₂O₃ increases the thermal stability of glasses in this series while the opposite is observed in the second series. The dissolution rates of boron containing bulk glasses were found to be around 10⁻⁹ gr/cm² min which are comparable to that of the base iron phosphate glass. When the B₂O₃ content was above 14%, new bands related to BO₄ tetrahedral groups have been observed in the IR spectra. The Mössbauer isomer shift values of boron doped glasses were found to be a little lower than that of base glass but both iron ions had distorted octahedral coordination in all glasses. The fraction of Fe²⁺ ions in glasses (Fe²⁺/∑(Fe²⁺ + Fe³⁺)) was found to be 23% for the base glass while it was 10-22% for the boron doped glasses.     

Improved lifetime of PEM fuel cell catalysts through polymer stabilization

A novel approach to increase lifetime of Pt/C catalysts was demonstrated and shown that Nafion-stabilized Pt catalyst (denoted here as Nafion-Pt/C) synthesized by a colloid route gives rise to an enhanced durability as compared to a conventional Pt/C catalysts commonly used in PEM fuel cell. A high catalytic activity of the catalyst is also observed by both CV (cyclic voltammetry) and ORR (oxygen reduction reaction) measurements. This catalyst durability in comparison with conventional Pt/C is increased directly by electrochemically-accelerated durability test (ADT). The loss rate of electrochemical active area (ECA) for Nafion-Pt/C catalysts is only 0.004 m² g⁻¹ cycle⁻¹, compared to a value of 0.012 m² g⁻¹ cycle⁻¹ for Pt/C. This indicates the catalyst is three times higher durability than Pt/C.