Jen-Ray Chang

Infrared studies of thermal oxidative degradation of polystyrene-block polybutadiene-block-polystyrene thermoplastic elastomers

Thermal oxidative degradation of a polystyrene-block-polybutadiene-block-polystyrene thermoplastic elastomer (SBS rubber) has been conducted in an in-situ infrared cell. By monitoring the disappearance of trans-1,4 and vinyl-1,2 double bonds and the appearance of the hydroxyl and the carboxyl/ carboxylate groups in the FTIR spectra, the temperature, air, antioxidant, and molecular microstructure dependence of the polymer degradation was studied. The experimental results indicate that the 1,4-polybutadiene portion of the SBS polymer is easier to degrade than the 1,2-polybutadiene portion and the hydroxyl group appears concomitantly with the disappearance of the polybutadiene. Based on data from the temperature-programmed desorption (TPD) of H2O, it is concluded that the formation of hydroxyl group makes the polymer hydrophilic and promotes the H2O adsorption on it. The amount of H2O adsorption varies with the temperature and the process appears reversible. At low temperatures, the moisture adsorbed onto a degraded polymer sample amounts to approximately 7–10% of total hydroxyls. 1 wt% of Irganox 1076 (antioxidant) would effectively thwart the thermal oxidation process even at severe conditions as high as 225 °C for 12 h. No degradation occurs in an air-free environment.

Use of waste rubber as concrete additive

For resource reutilization, scrap tyres have long been investigated as an additive to concrete to form ‘Rubcrete’ for various applications and have shown promising results. However, the addition of rubber particles leads to the degradation of physical properties, particularly, the compressive strength of the concrete. In this study, a theoretical model was proposed to shed light on the mechanisms of decrease in compressive strength due to the addition of rubber particles as well as improvement in compressive strength through modification of particle surfaces. The literature suggests that the compressive strength can be improved by soaking the rubber particles in alkaline solution first to increase the inter-phase bonding between the rubber particles and cement. Instead, we discovered that the loss in compressive strength was due to local imperfections in the hydration of cement, induced by the addition of heterogeneous and hydrophobic rubber particles. Microscopic studies showed that the rubber particles disturbed the water transfer to create channels, which were prone to cracking and led to a loss in the compressive strength. Unexpectedly, no cracking was found along the surfaces of the rubber particles, indicating that the bonding strength between the rubber particles and cement phases was not the critical factor in determining the compressive strength. Therefore, a theoretical model was proposed to describe the water transfer in the Rubcrete specimens to explain the experimental data. In the model, the local water available for hydration (Q) is: Q=-A slv/6πν, where Q, A slv, and ν are mass flow rate (kg s-1), Hamaker constant (J), and dynamic viscosity (m2 s-1), respectively. By maximizing the quantity Q and, in turn, the Hamaker constant A slv, the compressive strength could be improved. The Hamaker constant A slv for water film on rubber particle surfaces was smaller than that for the hydrated cement particles; the water transfer rate was lower in the presence of rubber particles because the Hamaker constant A slv for water film on rubber particle surfaces was smaller than that on the hydrated cement particles. Thus, the compressive strength of Rubcrete could be improved by increasing the Hamaker constant of the system. This was achieved by increasing the refractive indices of the solids (n s). The refractive indices of materials increase with increases in functional groups, such as OH and SH on the surface. The model provided a possible mechanism for the efficacy of treating rubber particles with NaOH in improving the compressive strength. By using NaOH solution treatment, an oxygen-containing OH group was formed on the rubber surface to increase the Hamaker constant of the system, leading to higher compressive strength. Based on this mechanism, a novel method for modification of the rubber particles was also proposed. In this process, the rubber particles were partially oxidized with hot air/steam in a fluidized bed reactor to produce the hydrophilic groups on the surface of the particles. Preliminary results obtained so far are promising in accordance with the theory.

Structural investigation of catalyst deactivation of Pt/SDB for catalytic oxidation of VOC-containing wastewater

The stability of styrene-divinyl benzene copolymer (SDB)-supported Pt (Pt/SDB) catalysts for destruction of volatile-organic-compound (VOC) in wastewater was examined. The test reaction was wet oxidation of water-containing aliphatic alcohol and formaldehyde at 140 degrees C and 90 psig for 40 h. The catalytic performance tests indicated that activity of the Pt/SDB catalysts could be maintained for VOC concentration of 3 wt.%, whereas the catalysts deactivated rapidly for 10 wt.% VOC containing wastewater. In order to investigate the nature of catalyst deactivation, extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge (XANES) spectroscopy were used to characterize the fresh and used catalysts. After the reaction, there is no oxidation of Pt clusters observed in EXAFS and XANES spectroscopy suggesting that the oxidation reaction takes places via the adsorbed oxygen. The spectroscopy results further indicated that deactivation of the catalysts were mainly caused by the increase of Pd particle size. After the reaction, the Pt-Pt coordination number has no significant change for the 3 wt.% wastewater whereas increase from 5.6 to 6.2 for 10 wt.% wastewater. Combined with the fact that the catalysts fractured during the reactions, we suggested that Pt agglomeration was mainly caused by thermal migration of the metal clusters.

Regenerable adsorbent for removing ammonia evolved from anaerobic reaction of animal urine.

The waste gas evolved from biodegradation of animal urine contains ammonia causing environmental concerns. A new and effective method for removing ammonia from such waste gas using reactive adsorption is presented. In the process, activated carbon impregnated with H2SO4(H2SO4/C) is employed. Ammonia in the waste gas reacts with H2SO4 on the adsorbent instantaneously and completely to form (NH4)2SO4. The H2SO4/C adsorbent is high in NH3 adsorption capacity and regenerable. The NH3 removal capacity of this regenerable adsorbent is more than 30 times that of the adsorbents used normally in the industry. The spent H2SO4/C is regenerated by flowing low-pressure steam through the adsorbent bed to remove the (NH4)2SO4 from the adsorbent. The regeneration by-product is concentrated (NH4)2SO4 solution, which is a perfect liquid fertilizer for local use. Re-soaking the activated carbon with H2SO4 solution rejuvenates the activity of the adsorbent. Thus the H2SO4/C can be reused repeatedly. In the mechanism of this reactive adsorption process, trace of H2O in the waste gas is a required, which lends itself to treating ammonia gas saturated with moisture from biodegradation of animal urine.

EXAFS Peaks and TPR Characterizing Bimetallic Interactions: Effects of Impregnation Methods on the Structure of Pt-Ru/C Catalysts

To investigate bimetallic interactions, Pt-Ru/C catalysts were prepared by coimpregnation (Pt-R/C) and successive impregnation (Ru-P/C), while Pt/C, Ru/C, and reduced Pt-Rublack were used as reference. Those samples were characterized by XAS and TPR. When P-R phase-and-amplitude correction is applied to Fourier transformed (FT) EXAFS of Pt-Rublack at Pt edge, the characteristic peak of Pt-Ru interactions appears at 2.70 , whereas, when Pt-Pt correction is applied, the peak appears at about 2.5 . Detailed EXAFS analysis for Pt-R/C and Pt-R/C confirms the nature of the characteristic peak and further indicates that the interactions can semiquantitatively be determined by the relative intensity between Pt-Ru and Pt-Pt characteristic peaks. This simple method in determining bimetallic interaction can be extended to characterize Pt-Pd/-Al2O3. However, for Pt-Re/-Al2O3, Pt-Re interactions cannot be determined by the method because of the overlap of Pt-Pt and Pt-Re characteristic peaks due to similar phase functions.

Preparation of block copolymer SBSIS having various polystyrene block lengths via anionic polymerization and the properties research

Two types of linear pentablock copolymers SBSIS, namely, ends-big and middle-big type were prepared by anionic polymerization of styrene (St), isoprene (Ip) and 1,3-butadiene (Bd) in a nonpolar solvent. Various samples having a number average molecular weight (Mn) of 60,000 g/mole were synthesized and characterized. The correlation between molecular structure and characteristic properties allows us to understand the effect on physical properties of important parameters such as styrene content, linking method, monomer proportions, and magnitude of end segment.