Effects of polyol molecular weight on properties of benzoxazine–urethane polymer alloys

Recently, a new thermoset resin namely benzoxazine (BA) resin has been developed. The polymer possesses several outstanding properties, such as, ease of synthesis, low viscosity, near‐zero shrinkage, lack of by‐product upon curing, high thermal stability, and high mechanical property. Moreover, the benzoxazine resins can be alloyed with various types of resins because of the various function groups in their structure. In this work, urethane elastomer (PU) is used to enhance toughness of the polybenzoxazine. The effects of polyol molecular weights on the properties of BA: PU polymer alloys are investigated. The experiment reveals that the similar curing peaks of the matrices at various polyol molecular weights, with the same urethane mass fraction, in the resin mixtures are obtained. The glass transition temperature increases from 160°C of polybenzoxazine to 240–245°C in the 70:30 BA:PU system. In addition, the char yield increases when the higher molecular weight of polyol is added. The flexural modulus of polybenzoxazine decreases from 6.2 GPa to be in the range of 2.2–2.8 GPa when 30 wt% of PU is presented in the alloys. Furthermore, the synergism with ultimate flexural strength is observed in the 90:10 BA:PU alloy for all molecular weights of the polyol used. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

The nature of surface species on modified Pt-based catalysts for the SCR of NO by C<Subscript>3</Subscript>H<Subscript>6</Subscript> under lean-burn condition

The catalytic activity behavior for the selective catalytic reduction of NO by C₃H₆ under excess oxygen and the nature of surface species on the active sites of Pt/Al₂O₃ catalyst after adding a second metal (Fe, Sn, Co, Cr or W) were investigated. It has been found that an important role of second metals is on TONs of C₃H₆ and NO conversions and the nature of surface species produced on the catalyst surface at low temperature instead of the catalytic activity behavior towards the temperature programmed reaction. Although the introduction of each second metal distinctly disturbs the characteristic of surface species, the reaction mechanism is presumably similar. The observation of few surface species and the investigation about their reactivity indicate that few mechanisms are simultaneously proceeding at the same reaction condition.     

Deactivation of the metal and acidic functions for Pt, Pt-Sn and Pt-Sn-K using physically mixed catalysts

The effect of K addition on the amount and dispersion of carbon deposition on metal sites and support sites was investigated on a physical mixture for hexane dehydrogenation. TPO, BET and ESR experiments were used for characterization. The K addition significantly decreases catalyst deactivation involving the amount of coke deposits and the density of carbon radicals on the metal and support sites because of ensemble and electronic effects, especially on the metal sites. Coke on the metal sites associated with carbonaceous species rich in hydrogen is less polymerized than coke on the support sites, corresponding to a more graphitic-like carbon.     

Roles of Pt and alumina during the combustion of coke deposits on propane dehydrogenation catalysts

Temperature programmed oxidation of coke deposited on Pt based propane dehydrogenation catalysts reveals that the deposited coke can be categorised into three groups according to their burning temperatures. When coke was separated from the catalyst, however, only one TPO peak could be observed. Experimental results suggest that γ-Al₂O₃ enhances the coke burning process by increasing coke surface area contacts to oxygen. Pt may also act as a catalyst for the coke combustion reaction. Experiments also show that changing dehydrogenation reaction temperature, variation of H₂/HC ratios, addition of only Sn or Sn and an alkali metal (Li, Na and K) can significantly affect the amount of each coke formed. Sample weight used in the temperature programmed oxidation (TPO) experiment also affects the resolution of TPO spectrum.