No abstract

Hydrolysis degradation of a set of drawn poly(lactic acid) (PLA) fibers was induced by an accelerated weathering test, radiating ultraviolet (UV) light under a certain temperature and humidity. The fine features of the transient behavior of the PLA fibers were captured by near-infrared (NIR) hyperspectral imaging. The PLA fibers showed a gradual decrease in mechanical property (e.g., tensile strength), indicating hydrolysis degradation. Thus, the detailed analysis of the spectral variation, in turn, offers useful information on the molecular-level degradation behavior of the drawn PLA fibers. The variation of the spectral intensity as well as band position shift of the crystalline band of PLA was analyzed. The spectral intensity of the crystalline band of PLA showed gradual decrease, suggesting the decrease in molecular weight induced by the hydrolysis degradation. In addition, the crystalline band also exhibited a coinciding shift to the lower wavenumber direction with the weathering test, revealing cleavage-induced crystallization of the PLA samples. Consequently, the hydrolysis degradation induced by the weathering test substantially accelerates predominant degradation of the amorphous structure of the PLA and such variation of the molecular structure, in turn, brings less ductility to the PLA fiber.

Living metathesis polymerization of [o- (trifluoromethyl)phenyl] acetylene, a phenylacetylene with an electron-withdrawing group, has been achieved by using molybdenum-based three-component catalysts. Thus polymerization by MoOCWt-BuiSn-EtOH (1:1:0.5 mole ratio) catalyst in toluene at 30 °C produced a polymer having a narrow molecular weight distribution; MjMa = 1.06. Upon three consecutive additions of fresh monomer feeds to completely polymerized systems, the M" of the polymer increased in direct proportion to monomer conversion, while the MjM" remained < 1.1. The initiator efficiency was ca. 0.10. The M0CI5n-ButSn-EtOH (1:1:0.5) catalyst also induced living polymerization, though the MJMn (ca. 1.20) was somewhat larger. Effects of catalyst components and polymerization conditions have been studied.

Alkaline fuel cells have received significant interest in recent years relative to acid fuel cells, because of advantages when operating under alkaline conditions, which include enhancement of the electrode reaction kinetics, especially at the cathode, as the cathode catalyst is not subjected to corrosion.[1] Consequently, non-noble metals or inexpensive metal oxides can be used as catalysts. [2] In addition, high energy density liquids and gases such as ethanol, hydrazine, and ammonia can be adopted as fuels.[3] Anion exchange polymers are widely viewed as promising candidates for electrolyte membranes; however, a major challenge in the development of such polymers is their stability at high pH, [4] because both the main chain and functional groups are easily degraded by hydroxide ion attacks. In addition, the poor chemical stability of current anion exchange polymers means that the operating temperature is limited to 80 8C or less; therefore, this type fuel cell is typically operated between 50 and 60 8C.[5]Operating a fuel cell at elevated temperatures provides the anode catalyst with high tolerance to CO, which is useful for both acid and alkaline fuel cells.[6] Additional benefits include small polarization loss, good drainage at the anode, and effective heat dissipation from the fuel cell system. A few anion-conducting electrolyte materials capable of operating at intermediate temperatures (100-200 8C) have been reported, such as KOH-doped polybenzimidazole (PBI) [6] and hydroxide ion-intercalated Mg-Al layered double hydroxide (LDH). [7] However, the reaction of KOH in the former electrolyte with CO 2 present in the air to form K 2 CO 3 is a possibility, and the hydroxide ion conductivity of the latter (0.03 S cm À1 at 200 8C) is not sufficiently high to achieve satisfactory cell performance. Further increases in chemical stability and conductivity would enhance the position of intermediate-temperature anion exchange membranes as the preferred electrolyte material for practical alkaline fuel cells.In this study, metal pyrophosphates (MP 2 O 7 ) were studied as anion-conducting electrolytes for intermediate temperature applications. The metal pyrophosphate structure can be described as a network of MO 6 octahedra sharing corners with P 2 O 7 units, characterized by the presence of intersecting zigzag tunnels delimited by pentagonal windows.[ .[9]The resultant proton conductivity reaches approximately 0.1 S cm À1 at 200 8C.[10] An opposite effect is expected by the partial substitution of Sn 4+ cations with high-valency cations, which would result in hydroxide ion exchange capability because of charge compensation for the high-valency cations. We demonstrate the hydroxide ion conduction of pentavalent cation-doped SnP 2 O 7 at intermediate temperatures using electrochemical measurements, including complex impedance, gas concentration cells, and H/D isotope replacement methods. Moreover, Sn 0.92 Sb 0.08 P 2 O 7 , which exhibits the highest hydroxide ion conductivity among the tested compounds, is characteri...