Thermal degradation chemistry of poly(ethylene naphthalate) – A study by thermal volatilisation analysis

Although the fundamental degradation chemistry of poly(ethylene naphthalate), PEN, is thought to be similar to that of poly(ethylene terephthalate), PET, there is very little evidence in the literature to support this. This paper presents data on the thermal degradation of PEN, in comparison to PET, with particular reference to evolved gas analysis undertaken by thermal volatilisation analysis (TVA). Our thermal degradation studies highlight strong similarities in the degradation behaviour of PET and PEN, despite some evidence of increased thermal stability of PEN in comparison to PET. Identical primary and secondary thermal degradation mechanisms are proposed for PET and PEN, with radical degradation processes thought to dominate at high temperature.     

Optimum step-stress accelerated degradation test for Wiener degradation process under constraints

To assess a product's reliability for subsequent managerial decisions such as designing an extended warranty policy and developing a maintenance schedule, Accelerated Degradation Test (ADT) has been used to obtain reliability information in a timely manner. In particular, Step-Stress ADT (SSADT) is one of the most commonly used stress loadings for shortening test duration and reducing the required sample size. Although it was demonstrated in many previous studies that the optimum SSADT plan is actually a simple SSADT plan using only two stress levels, most of these results were obtained numerically on a case-by-case basis. In this paper, we formally prove that, under the Wiener degradation model with a drift parameter being a linear function of the (transformed) stress level, a multi-level SSADT plan will degenerate to a simple SSADT plan under many commonly used optimization criteria and some practical constraints. We also show that, under our model assumptions, any SSADT plan with more than two distinct stress levels cannot be optimal. These results are useful for searching for an optimum SSADT plan, since one needs to focus only on simple SSADTs. A numerical example is presented to compare the efficiency of the proposed optimum simple SSADT plans and a SSADT plan proposed by a previous study. In addition, a simulation study is conducted for investigating the efficiency of the proposed SSADT plans when the sample size is small.     

Degradation kinetics of fluvoxamine in buffer solutions: In silico ADMET profiling and identification of degradation products by LC-MS/ESI

The kinetics of hydrolysis of fluvoxamine maleate (FLV) has been investigated over the pH range 1.0–12.0 at 40, 60 and 80 °C. FLV degradation follows pseudo-first-order kinetics which is consistent with the kinetics of drugs that are not readily dissolved in aqueous medium. The hydrolytic degradation rate constant (k_obs) range from 0.92 (pH 6.0) to 13.8 × 10⁻⁴ min⁻¹ (pH 1.0). The k_obs represents the sum of six different degradation rate constants; the k_H has been found to be higher than k_OH. The FLV exhibits a typical rate- pH profile with a flat bottom over the pH range 3.0–6.0 which indicates its maximum stability at pH 6.0. Ten FLV degradants have been predicted by Zeneth software and among them four degradation products (D1, D2, D3 and D4) have been identified in degraded samples. The in-silico pharmacokinetics and toxicity of degradation products have been determined using Swiss ADME and admetSAR software. The toxicity profile reveals that D2 is both AMES toxic and carcinogenic while the rest of the products are non-AMES toxic and non-carcinogenic. All of the degradation products are high in causing fish toxicity thus their presence in pharmaceutical waste is alarming for environmental safety.     

CeO2 nanofibers-CdS nanostructures n–n junction with enhanced visible-light photocatalytic activity

In the present work, the n-cerium (IV) oxide (CeO₂)/n-cadmium sulfide (CdS) composite nanofibers were successfully synthesized via a facile electrospinning and hydrothermal synthesis strategy. The physicochemical properties of the synthesized composite nanofibers were investigated by using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), energy Dispersive X-Ray Spectroscopy (EDS), diffuse Reflectance Spectroscopy (DRS), Fourier-transform infrared (FTIR), photoluminescence (PL), Brunauer–Emmett–Teller (BET) and Raman spectroscopy analysis. The activities of the CeO₂/CdS were evaluated through the photocatalytic degradation of Rose Bengal (RB) in an aqueous solution under blue LED light radiation. CeO₂/CdS composites exhibit higher photocurrent density in photocurrent response experiment and smaller charge-transfer resistance in electrochemical impedance spectroscopy (EIS). Overall, the results confirmed higher charge separation efficiency in CeO₂/CdS composites compared to pristine CeO₂ nanofibers, and CdS, which is related to intimately contact among the CeO₂, and CdS. The present work provides a new approach to construct n-n heterojunction photocatalysts based on electrospinning and a deeper insight for the photocatalytic degradation activity. In addition, possible degradation mechanism and pathways were proposed according to the identified intermediates.     

A comparison of the increased temperature accelerated degradation of Poly(d,l-lactide-co-glycolide) and Poly(l-lactide-co-glycolide)

Bioresorbable polymers composed of Poly(lactide), Poly(glycolide) and their related copolymers have become increasingly popular for the preparation of bone substitute constructs. In vitro tests assessing the degradative changes in physicochemical, mechanical, and biological properties of bioresorbable polymers are generally carried out at 37 °C, in pH 7.4 phosphate-buffered saline (PBS). However, long degradation times, varying from months to years make it difficult to assess these polymers at their late stages of degradation. An increased temperature accelerated degradation methodology, that simulates the long-term degradation of Poly(d,l-lactide-co-glycolide) and Poly(l-lactide-co-glycolide), has been validated in this study. Samples were degraded in PBS, under sterile conditions. Degradation temperatures of 47 °C, 57 °C and 70 °C were selected and compared to physiological temperature, 37 °C. At predetermined time intervals, samples were retrieved and evaluated for changes in mass, swelling, molecular weight, crystallinity, and thermal properties. The results from this study suggest that the degradation mechanism at elevated temperatures is similar to that observed at 37 °C. It is recommended that 47 °C is adopted by the research community to accelerate the degradation of these polymers. It is hoped the application of this methodology could be used as a valuable tool, prior to the assessment of the long-term biocompatibility of these polymers.     

石墨相氮化碳可见光下活化过一硫酸盐氧化降解光惰性邻苯二甲酸二甲酯的机理研究（英文）

近几年过一硫酸盐(PMS)活化技术备受关注,其中利用太阳能活化PMS具有可持续和环保的优势,但PMS本身不吸收可见光.因此,本文提出利用具有可见光响应的石墨相氮化碳(g-C3N4)激发产生光电子进而活化PMS.首先利用三聚氰胺前驱体通过热缩聚法制备g-C3N4,通过X射线衍射(XRD)、傅里叶变换红外光谱(FT-IR)、紫外-可见光漫反射(UV-Vis)、荧光光谱(PL)、透射电镜(TEM)、N2吸附脱附测试(BET)、电化学等一系列方法对g-C3N4进行表征,研究其表面性质及光学性能.结果显示, g-C3N4具有典型的片层结构和可见光活性,禁带宽度为2.7 e V.本文选取光惰性的内分泌干扰物邻苯二甲酸二甲酯(DMP)为目标污染物,系统地研究了其降解动力学和降解机理.研究发现,在短波紫外光(254和300nm)照射下,直接光解和·OH参与的反应机理能实现DMP的光降解,而在可见光照射下g-C3N4介导的光催化过程不能使DMP分解;但当添加PMS时,体系主导自由基由·O2–转化为SO4·–和·OH,从而实现DMP的有效降解和矿化.研究还发现,高浓度的PMS和高剂量的g-C3N4均可以提高PMS的活化量和相应的DMP降解效率,但提高催化剂剂量的方式能更充分的利用PMS.尽管高浓度的DMP阻碍了PMS和光催化剂g-C3N4的有效接触,但可以提高PMS的利用率.当p H低于零电荷点(5.4)时, DMP的降解效率较高.此外,使用两种淬灭剂(乙醇和叔丁醇)与DMP进行竞争性实验,结合电子自旋共振检测,表明SO4·–和·OH都是体系主要的自由基.此外,还对g-C3N4的可持续性能进行考察,四次循环实验结果显示,该催化剂具有良好的可重复利用性.对DMP降解进行总有机碳测定,发现降低了19%.最后,利用液相色谱质谱联用对DMP降解产物进行定性定量分析,发现DMP主要通过SO4·–和·OH对苯环的攻击以及脂肪族链的氧化断键这两种途径进行降解.综上可见,利用可见光激发g-C3N4产生的光电子能有效活化PMS降解顽固型有机污染物,可为实现太阳能活化PMS技术提供有力的技术参考.     

掺Fe3+A-TiO2粉末的制备及其可见光催化降解碱性品红

以硫酸钛为原料用水热法制备了掺Fe3+TiO2粉末,用SEM测定了样品的形貌和晶型,研究了以自制的掺Fe3+ A-TiO2对碱性品红溶液的光催化降解作用.结果表明:所制备的TiO2为锐铁矿型TiO2(A-TiO2).可见光照射下,用自制的掺Fe3+A-TiO2降解碱性品红溶液的最佳条件是:2mg·L-1的碱性品红溶液中...     

Catalytic effect of lucunary heteropolyanion containing molybdenum and tungsten atoms on decolorization of direct blue 71

In this research,a lucunary Keggin structure,[PMo₂W₉O₃₉]^7- was selected as an efficient homogenous catalyst for degradation of an azo dye（direct blue 71） and a simple method was developed for degradation of DB71.The method is based on the oxidation of azo dye in the presence of a lucunary Keggin form of polyoxometalates,K₇[PMo₂W₉O₃₉]? 19H₂O,as a homogenous catalyst at room temperature.The reaction is monitored spectrophotometrically by measuring the absorbance of dye atλ=585 nm.Some parameters including concentration of catalyst,concentration of H₂O₂,pH and reaction time were investigated and optimized. Results show that K₇[PMo₂W₉O₃₉]? 19H₂O is more efficient in the presence of hydrogen peroxide.Degradation of dye in the presence of the catalyst and H₂O₂ could lead to the disappearance approximately 65%of dye after 60 min.But degradation for the same experiment performed in the absence of catalyst or in the absence of H₂O₂ was 22%or 5%respectively.Approximately 87% azo dyes has been eliminated after 90 min in the presence of catalyst,H₂O₂ and optimize conditions(0.6 g/L of K₇[PMo_2- W₉O₃₉H₉H₂O,0.08 mol/L hydrogen peroxide and room temperature).     

The metathetic degradation of polyisoprene and polybutadiene in block copolymers using Grubbs second generation catalyst

A degradation study of polystyrene-polybutadiene-polystyrene and polyisoprene-polystyrene-polyisoprene in both dichloromethane and hexane solvents is presented. Alternative solvents for metathetic degradation provide the potential for greener chemistry, better selectivity, and control over the products. The catalyst concentration and solvent selection both determine the products formed. The degradation of polyisoprene and polybutadiene in a particular solvent was controlled by the solubility of polyisoprene/polybutadiene, and by its solubility relative to polystyrene. A large difference in solubility between the polymers in the selected solvent provides an additional driving force for block separation, encouraging reaction close to the interface between different blocks. Furthermore, solubility of the block copolymer speeds the degradation reaction. This tailoring of the reaction mechanism yields a new control over the products of polymer degradation.     

Degradation kinetics of poly(lactic-co-glycolic) acid block copolymer cast films in phosphate buffer solution as revealed by infrared and Raman spectroscopies

Poly(lactic-co-glycolic) acid (PLGA) is an important copolymer used in drug delivery platforms where controlled release is required. In this work we investigated the in vitro degradation of four PLGA copolymers with L/G molar compositions of 50/50, 65/35, 75/25 and 95/5. ATR-IR and Raman spectroscopies were used to differentiate and quantify the degradation rates of glycolic and lactic units. Both techniques were used to determine the polymer composition as a function of degradation time and the degradation rate constants for the hydrolysis of glycolic and lactic units were calculated using a 1st order kinetics approach. Our results revealed a two stage process for the degradation of PLGA cast films in PBS in agreement with our previous work. The degradation rate constant for glycolic unit was found to be 1.3 times higher than for lactic units. In addition the degradation rate constants for L and G units were shown to decrease proportionally with increasing initial lactic content of the copolymer used to prepare the films.