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.     

Degradation of acrylonitrile–ammonium itaconate copolymers

Acrylonitrile–ammonium itaconate copolymers were prepared by H₂O/dimethyl formamide suspension polymerization technique. Differential scanning calorimetry results of the degradation of acrylonitrile–ammonium itaconate copolymers in air are presented. The apparent activation energy of degradation of the copolymer was calculated using the Kissinger method. Effects of copolymerization conditions on the apparent activation energy of copolymer were studied. Increasing the dimethyl formamide concentration in the solvent mixture leads to a rapid increase in the degradation apparent activation energy of acrylonitrile–ammonium itaconate copolymer. The value of the degradation apparent activation energy of the copolymer synthesized in dimethyl formamide solvent increases up to 168.3 kJ mol^?1. The apparent activation energy decreases quickly along with an increase in ammonium itaconate concentration, and this change becomes less prominent as the weight ratio of ammonium itaconate/acrylonitrile goes beyond 6/94, ΔE_a = 89.4 ± 2.0 kJ mol^?1. The apparent activation energy shows a trend of increase with increasing copolymerization temperature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1708–1711, 2005     

Lifetime assessment of epoxies by the kinetics of thermal degradation

The kinetics of thermal degradation of 4,4′‐diaminodiphenylsulfone (DDS)‐cured glycidylethers (DGBA) and glycidylamines (TGDDM) have been studied by isothermal annealing. Thermal degradation proceeds via first‐order kinetics with activation energies of 138 (DGBA/DDS) and 95 kJ/mol (TGDDM/DDS). From these data the temperature‐dependent lifetime can be calculated. Based on the heat distortion temperature and 20 years' service as criteria, the upper service temperature is found to be around 115–120°C. In spite of the different activation energies and bond stabilities, only marginal differences in the upper allowed service temperatures between these resins were found. Only slight improvements can be expected by optimizing the cure conditions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1881–1886, 2004     

坡缕石/Al掺杂CdS复合材料光催化降解罗丹明B

采用溶剂热法制备了坡缕石/Al掺杂CdS复合材料(PGS/CdS-Al),运用XRD、XPS、SEM、UV-Vis DRS及PL对材料的结构、形貌以及光学性能进行了表征.结果表明,Al元素成功掺杂到CdS中,CdS的晶体结构没有改变,但其禁带宽带变宽.可见光照射下,该复合材料对孔雀石绿、亚甲基蓝、甲基橙、结晶紫、罗丹明B有机染料均有光催化降解活性,且对罗丹明B的光催化降解效果最好.光照40 min,质量浓度为0.67 g/L 15％PGS/CdS-Al(15％为PGS的负载量,以生成的CdS质量计)对30 mL质量浓度为20 mg/L罗丹明B的降解率为98.7％,反应主要活性基团是h+.该降解反应符合一级动力学,反应速率常数为0.067 min–1.     

水溶液中纳米二氧化钛光催化降解甲基橙的影响因素

用沸腾回流直接水解法制备了粒径为25～35 nm纯锐钛矿型纳米二氧化钛(TiO2).用X射线衍射和透射电镜表征材料的结构与形貌.用该催化剂催化降解甲基橙,研究了催化剂用量、甲基橙的起始浓度、溶液pH值、光强度、溶液中添加金属离子的影响.结果表明:在较强紫外光照射下,当甲基橙的起始浓度为0.02 g/L,TiO2用量为1.0g/L,光催化效率最高.酸性条件有利于光催化降解甲基橙.掺加Fe3 或Zn2 的光催化效率显著增加.掺加Mn2 或Ca2对光催化活性没有影响.在紫外光区域(366 nm),样品对催化降解水溶液中甲基橙的活性较高.     

Thermal degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)

The degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate), a member of the Nodax family of polymers, were investigated using transient constant shear rate and dynamic time sweep rheological tests. The rate of chain scission at several times and temperatures was correlated with viscosity data and verified using molecular weight determination of the degraded samples. The experimental results show that the molecular weight and the viscosity of Nodax decrease with time over the range of temperatures that were studied (155–175°C). The degradation kinetics, which exhibited first‐order behavior, were determined as a function of the flow history and thermal history. An apparent activation energy of 189 ± 5 kJ/mol for thermal degradation was found by modeling variations in the rate with temperature using an Arrhenius law model. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 66–74, 2005     

185nmUV降解水中4-CP、4-NP和RhB的研究

本文以对氯苯酚（4-cP）、对硝基苯酚（4-NP）和罗丹明B（RhB）为模型有机物（以4-CP和4-NP为小分子模型有机物，以RhB为大分子模型有机物），分别研究了185nmUV对水中这3种模型有机物的降解规律、性能和效果．研究结果表明，185nmUV直接对水中4-CP、4-NP和RhB有很好的降解效果．研究内容包括：185nmUV降解模型有机物的浓度、TOC（Totalorganic carbon）浓度、185nmUV降解模型有机物过程中溶液pH及电导率变化、以及降解模型有机物过程中产生的无机离子等几个方面．     

Photoelectrocatalytic degradation of rhodamine B using Ti/TiO2 electrode prepared by laser calcination method

The method of Ti/TiO₂ photoelectrode prepared by using laser calcination method instead of oven calcination process was introduced. The prepared TiO₂ film was observed with AFM and XRD. Photoelectrocatalytic degradation of rhodamine B (RB) using this electrode was investigated, and anodic potential and pH were optimized. The laser power applied in this electrode preparation was also discussed, and it indicated that TiO₂ particle prepared with high laser power was crystallized adequately and the photoelectrocatalytic ability was satisfactory. RB degradation was investigated under different conditions, and it showed that photoelectrocatalytic degradation could achieve efficient and complete mineralization of organic pollutant. The photoelectrocatalytic oxidation using the Ti/TiO₂ electrode calcinated by laser was compared with that of the electrode calcinated by furnace, and it showed that the reaction rate of RB degradation using the electrode by laser was faster than that by furnace. Additionally, electrochemical impedance spectroscopy (EIS) was performed at the two different photoelectrodes, which verified the higher photocatalytic activity of the laser-treated electrode further.     

Thermal and flow properties of oils from salmon heads

Thermal and flow properties of unrefined oils from the heads of red or pink salmon were evaluated. Major thermal degradation of the salmon oils occurred between 200 and 450°C. Red and pink salmon oils were completely decomposed at 533 and 668°C, respectively. The phase transition of salmon oils occurred over a wide range of temperatures. The melting points of −69.6 to −0.36°C and −64.7 to 20.8°C were observed for red and pink salmon oils, respectively. The enthalpy was 40 j/g for red salmon oil and 39 j/g for pink salmon oil. Specific heat capacity ranges of 0.8 to 1.6 and 1.3 to 2.3 j/g/°C were observed for red and pink salmon oils, respectively. Both salmon oils exhibited Newtonian flow behavior. Red salmon oil required higher magnitudes of energy (kj·mol⁻¹) to flow than pink salmon oil. The viscosity of salmon oils was temperature-dependent and could be predicted by the Arrhenius equation.     

Al_2O_3负载TiO_2光催化氧化剂的制备与性能试验

以钛酸四丁酯为钛源、Al2O3为载体,采用浸渍法制备了一系列TiO2/Al2O3复合氧化物光催化剂。以光催化降解甲醛为探针反应,考察了催化剂的光催化活性。并采用XRD、SEM技术对催化剂进行了表征。考察了催化剂的焙烧温度、钛含量、反应温度等因素对甲醛光催化降解率的影响。结果表明:400℃是制备TiO2/Al2O3光催化剂的最佳焙烧温度;在TiO2负载质量为5.0%的复合氧化物光催化剂催化效果最好,甲醛的降解率达到58.4%。随着反应温度的升高,复合氧化物光催化剂的催化性能下降,由25℃时的58.4%的甲醛降解率下降到50℃时的4.8%。