纳米TiO2光催化降解有机物的机理及其影响因素的研究

对纳米TiO2光催化降解水中有机物的机理进行了研究，并对溴苯酚降解为目标反应，系统分析了紫外光强度、TiO2浓度、温度、溶液的pH值以及杂质等对光催化降解为溴苯酚程度的影响。优化这些因素可以提高纳米TiO2光催化降解率。     

Thermooxidative degradation of natural rubber/clay composite

The clay is treated with a reducing agent and an acid so as to obtain a clay containing various metal components with a variable‐valence state. Then, the clay is coprecipitated with natural rubber (NR) latex to prepare a vulcanized NR/clay composite. The degradation process of the NR/clay composite under hot air condition was studied dynamically by using a Fourier transform infrared spectrometer attaching an in situ sample cell and was also investigated using the TGA method. The test result obtained from the infrared spectrometry indicated that under low decomposition temperature, the decomposition products of the test samples mainly are ethylene, low molecular olefinic hydrocarbon, and carbonyl compounds. As the decomposition temperature rises, the low molecular olefinic hydrocarbon content decreases, the olefine with longer chain is formed, and a lot of alkane decomposition products are formed at the same time. When the content of the metal components with a variable‐valence state in clay such as Cu, Mn, Co, and Fe increases, the oxidation products containing the carbonyl group, the olefinic hydrocarbon, and CO₂ in the decomposition product of the test sample also increase. The TGA result clearly shows a shoulder peak that appears by the side of the main peak on the DTG curve of NR/clay composite. With the increase in the content of metal components with variable‐valence state in clay, the initial degradation temperature of the test sample (T₀), the degradation peak temperature (T_p1), and the final degradation temperature (T_f1) in first‐stage reaction, as well as the degradation peak temperature (T_p2) and the last final degradation temperature (T_f) in second‐stage reaction of all the test samples more or less shift to the direction of low temperature; besides, the activation energy (E) of the reaction of the test samples more or less decreases. This means that the metal components with variable‐valence state promote the oxidative degradation of the clay–rubber masterbatch. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3809–3815, 2006     

Sequence distribution and thermal properties of poly(butylene naphthalate terephthalate)

Poly(butylene naphthalate terephthalate) (PBNT) copolyesters were synthesized from bis(4-hydroxybutyl) terephthalate (BHBT) and bis(4-hydroxybutyl) naphthalate (BHBN) as starting materials. BHBT and BHBN were either homopolymerized or copolymerized at 260∼270 °C in the presence of titanium tetrabutoxide (TBT) as a catalyst to provide PBNT with various compositions. The copolyesters were characterized using inherent viscosity, X-ray, d.s.c., t.g.a. and ¹H NMR. The composition and sequence distribution of the copolyesters was determined from ¹H NMR spectra. The copolyesters exhibited a degree of randomness of about 1, indicating that the reactivity of BHBT and BHBN was almost the same. X-ray and d.s.c. showed PBNT copolyesters to be crystalline polymers. T.g.a. kinetics showed PBNT copolyesters to exhibit higher degradation activation energy, that is, better thermal stability, than PBTs.     

Photocatalytic degradation rate of oxalic acid on the semiconductive layer of n-TiO2 particles in the batch mode plate reactor Part I: Mass transfer limits

Organic compounds dissolved in water can be decomposed on a layer of n-TiO2 particles irradiated by u.v. light, which generates holes and electrons in the TiO2 material. Dissolved oxygen was used as electron scavenger and holes reacted with water to give OH radicals. The rate of degradation of the dissolved organic compounds by OH radicals is limited by the transfer of either oxygen or of theorganic compounds to the surface of n-TiO2 particles. The consequence of these limits is that, in the batch mode reactor with recirculation of the liquid, the dependence of the concentration of an organic compound on time has either a linear or an exponential form. Experiments with decomposition of oxalic acid in aqueous solutions using a plate reactor (60 cm × 120 cm) confirmed the analysis. Equations for evaluation of the mass transfer coefficient of the dissolved species to the surface of the plate reactor with a moving liquid fil m were developed for the case of the thickness of the Nernst diffusion layer being thinner than the thickness of the liquid. The experimentally obtained decomposition rate of oxalic acid was about 60 to 80% of the theoretical decomposition rate limited by oxygen flux through the film of a moving liquid. The present theory neglects the diffusion of oxygen into the porous layer of n-TiO2.     

半导体光催化氧化在有机废水处理中的应用与研究进展

简要介绍了半导体光催化氧化降解有机物的作用机理,重点阐述半导体光催化氧化在处理有机废水中的应用,并就该技术之不足对其应用前景和发展方向作了展望。     

Zinc hydroxystannate and zinc stannate as flame‐retardant agents for flexible poly(vinyl chloride)

The flame‐retardant and smoke‐suppressant properties of inorganic tin compounds such as zinc hydroxystannate (ZHS) and zinc stannate (ZS) were investigated in a comparison with alumina trihydrate, magnesium hydroxide, and Sb₂O₃ through the limiting oxygen index test and smoke density test. The flame‐retardant mechanisms were studied through the char yield test, SEM, quantitative analysis, thermogravimetry and differential thermal analysis. The thermal degradation in air of flexible PVC treated with the above compounds was studied by thermal analysis from ambient temperature to 800°C. The results showed that tin compounds such as ZHS and ZS could be used as a highly effective flame retardant for flexible PVC, and it appears that the tin compound may exert its action in both the condensed and vapor phases, but mainly in condensed phases as a Lewis acid. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1469–1475, 2005     

防火涂料热降解的测试研究技术

介绍了防火涂料热降解的测试研究技术,并举例说明了这些技术在研究防火涂料热降解过程及机理中的作用,评述了各种测试研究技术的特点,说明采用多种测试技术联用是分析防火涂料热降解的方向。     

Kinetics of the thermal degradation and thermal stability of conductive silicone rubber filled with conductive carbon black

The kinetics of the thermal degradation and thermal stability of conductive silicone rubber filled with conductive carbon black was investigated by thermogravimetric analysis in a flowing nitrogen atmosphere at a heating rate of 5°C/min. The rate parameters were evaluated by the method of Freeman–Carroll. The results show that the thermal degradation of conductive silicone rubber begins at about 350°C and ends at about 600°C. The thermal degradation is multistage, in which zero‐order reactions are principal. The kinetics of the thermal degradation of conductive silicone rubber has relevance to its loading of conductive carbon black. The activation energies are temperature‐sensitive and their sensitivity to temperature becomes weak as temperature increases. In addition, the conductive silicone rubber filled with conductive carbon black has better thermal stability than that of silicone rubber without any fillers. Also, conductive silicone rubber filled with conductive carbon black has better thermal stability than that of silicone rubber filled with the same amount of silica. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1548–1554, 2003     

Kinetics of the enzymatic degradation of poly(vinyl acetate) in solution

The enzymatic degradability of poly(vinyl acetate) was investigated in toluene solutions at various temperatures with hog pancreas lipase. The polymer degraded by specific scission to yield oligomeric products with a molecular weight of 700. Continuous distribution kinetics were used to determine the rate coefficients. The variation of the rate coefficients with the temperature indicated an optimum at 55°C. The p‐toluene sulfonic acid catalyzed degradation of poly(vinyl acetate) was also investigated. The degradation mechanism was random chain scission, and the energy of activation for degradation was determined from the variation of the rate coefficients with the temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2579–2582, 2003     

On the thermal stability of xanthan gum

The thermal stability of xanthan gum in dilute aqueous solutions at 90°C is considered. The relative viscosity as a function of ageing time is discussed, and it has been found to depend on the polymer concentration and conformation as well as on the salt content. The effectiveness of a quencher demonstrates the existence of a free-radical process in the degradation. During ageing, the molecular weight first decreases by rapid random hydrolysis of the main chain and loss of the pyruvate and acetate substituents. Later, oligomers are formed corresponding to a breakdown of both the side chain and the main chain. The identification of cellodextrins in the oligomer pool demonstrates the second effect.