Enzymatic degradation of poly(epsilon-caprolactone)/poly(DL-lactide) blends in phosphate buffer solution

Blend films of poly(epsilon-caprolactone) (PCL) and poly(DL-lactide) (PDLLA) with 0.5 weight fraction of PCL were prepared by means of solution casting and their degradation behavior was studied in phosphate buffer solution containing Pseudomonas (PS) lipase. Enzymatic degradation of the blend films occurred continuously within the first 6 days and finally stopped when the film weight loss reached 50%, showing that only PCL in the blends degraded under the action of PS lipase in the buffer solution. These results indicate the selectivity of PS lipase on the promotion of degradation for PCL and PDLLA. The thermal properties and morphology of the blend films were investigated by differential scanning calorimetry, wide-angle X-ray diffraction and scanning electron microscopy (SEM). The morphology resulting from aggregate structures of PCL in the blends was destroyed in the enzymatic degradation process, as observed by SEM. These results confirm again the enzymatic degradation of PCL in the blends in the presence of PS lipase. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.

Thermal degradation of short kevlar fibre thermoplastic polyurethane composite

The thermal degradation of short kevlar fibre-thermoplastic polyurethane (TPU) composites has been studied by Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). TGA showed that the thermal degradation of TPU takes place in two steps with peak maxima (T1max and T2ma,) at 383°C and 448°C, respectively. In the presence of 10-40 phr of short kevlar fibres, T1_ and T2max were shifted to lower temperatures. The temperature of onset of degradation was increased from 245 to 255°C at 40 parts per hundred rubber (phr) fibre loading. Kinetic studies showed that the degradation of TPU and kevlar-TPU composite follows first-order reaction kinetics. The DSC study showed that there is an improvement in thermal stability of TPU in the presence of 20 phr of short kevlar fibres.

Differential changes in transforming growth factor β isoform expression during postnatal cardiac growth

Transforming growth factor-β (TGF-β) is synthesised as an inactive precursor protein; this is cleaved to produce the mature peptide and a latency associated protein (LAP), which remains associated with the mature peptide until activation by LAP degradation. Isoform specific antibodies raised against the LAPs for TGF-β2and -β3were used to determine the myocardial levels of LAP (activatable TGF-β) and full length precursor (inactive TGF-β) forms during post-natal development in the rat. TGF-β2was present predominantly as the precursor in 2 day old myocardium. There was an age-dependent shift from precursor protein to LAP between 2 and 28 days. A corresponding increase in the level of mature (activatable) TGF-β2was found. TGF-β3was detected in significant quantities only as LAP. However, a four-fold increase in the expression of TGF-β3LAP was observed between 2 and 28 days. The substantial increases in activatable forms of TGF-β2and -β3that occur in myocardium during the first 28 days of life in the rat support a role for these proteins in post-natal cardiac development.

Thermal degradation of natural rubber/ZNO nanocomposites

Nanoparticies have been widely used to enhance the properties of natural rubber (NR). In the present paper a novel nanocomposite was developed by blending nano-ZnO slurry with prevulcanized NR latex, and the thermal degradation process of pure NR and NR/ZnO nanocomposites with different nano-ZnO loading was studied with a Perkin Elemer TGA-7 thermogravimetric analyzer. The thermal degradation parameters of NR/ZnO (2 parts ZnO per hundred dlY rubber) at different heating rates (Bs) were studied. The results show that the thermal degradation of pure NR and NR/ZnO nanocomposites in nitrogen is a one-step reaction. The degradation temperatures of NR/ZnO nanocomposite increase with an increasing B. The peak height (R_p) on the differential thermogravimetric curve increases with the increase of B. The degradation rates are not affected significantly by B, and the average values of thermal degradation rate C_p and C_f are 44.42 % and 81.04 %, respectively. The thermal degradation kinetic parameters are calculated with Ozawa-Flynn-Wall method. The activation energy (E) and the frequency factor (A) vary with ecomposition degree, and can be divided into three phases corresponding to the volatilization of low-molecular-weight materials, the thermal degradation ofNR main chains and the decomposition of residual carbon.

Thermal degradation kinetics and mechanism of epoxidized natural rubber

Thermal resistance is one of the most dominative properties for polymer materials. Thermal degradation mechanisms of epoxidized natural rubber (ENR) and NR are studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The results show that, the introduction of epoxy groups into the NR molecular main chain leads to a remarkable change in the degradation mechanism. The thermal stability of ENR is worse than that of NR. For the first thermooxidative degradation stage, the thermal decomposition mechanism of ENR is similar to that of NR, which corresponds to a mechanism involving one-dimensional diffusion. For the second stage, the thermal decomposition mechanism of ENR is a three-dimensional diffusion, which is more complex than that of NR. Kinetic analysis showed that activation energy (E?), activation entropy (?H) and activation Gibbs energy (?G) values are all positive, indicating that the thermooxidative degradation process of ENR is non-spontaneous.

The effects of mechanical stress, environment and cathodic protection on the degradation and failure of coatings: An overview

Organic coatings have been used in conjunction with cathodic protection as the most economical method of corrosion protection by the oil and gas pipeline industry. In a bid to prolong the life of the pipelines, the degradation and failure of pipeline coatings under the effects of major influencing factors including mechanical stress, the environmental corrosivity and cathodic protection have been extensively investigated over the past decades. This paper provides an overview of recent research for understanding coating degradation under the effect of these factors, either individually or in combination. Electrochemical impedance spectroscopy remains the primary and the most commonly used technique of studying the degradation of organic coatings, although there have been attempts to use other techniques such as electrochemical polarization (both dynamic and static), electrochemical noise, Scanning Kelvin Probe, Fourier Transform Infrared Spectroscopy, Differential Scanning Calorimetry and Dynamic Mechanical Analyser. Major knowledge and technological gaps in the investigation of the combined effects of mechanical stress, environmental corrosivity and cathodic protection on coating degradation have been identified.

Differential Toxicity of Disperse Red 1 and Disperse Red 13 in the Ames Test, HepG2 Cytotoxicity Assay, and Daphnia Acute Toxicity Test

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The influence of soil and landfill leachate microorganisms in the degradation of PVC/PCL films cast from DMF

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Thermal degradation of a composite solid propellant examined by DSC - Kinetic study

The thermal decomposition of ammonium perchlorate (AP)/hydroxyl-terminated-polybutadiene (HTPB), the AP/HTPB solid propellant, was studied at different heating rates in dynamic nitrogen atmosphere. The exothermic reaction kinetics was studied by differential scanning calorimetry (DSC) in non-isothermal conditions. The Arrhenius Parameters were estimated according to the Ozawa method. The calculated activation energy was 134.5 W mol(-1), the pre-exponential factor, A, was 2.04.10(10) min(-1) and the reaction order for the global composite decomposition was estimated in 0.7 by the kinetic Shimadzu software based on the Ozawa method. The Kissinger method for obtaining the activation energy value was also used for comparison. These results are discussed here.

Indirect polarographic and cathodic stripping voltammetric determination of cefaclor as an alkaline degradation product

Cefaclor is not reducible at a mercury electrode, but it can be determined polarographically and by cathodic stripping voltammetry as its initial alkaline degradation product which is obtained in high yield by hydrolysis of cefaclor in Britton-Robinson (B-R) buffer pH 10 at 50 degrees C for 30 min (reduction peak at pH 10, -0.70 V). Differential pulse polarographic calibration graphs are linear up to at least 1 x 10(-4) mol l(-1). Recoveries of 93% of the cefaclor (n = 3) were obtained from urine spiked with 38.6 mu g ml(-1) using this polarographic method with 1 ml urine made up to 10 ml with pH 10 buffer. Using cathodic stripping voltammetry and accumulating at a hanging mercury drop electrode at -0.2 V for 30 s, linear calibration graphs were obtained from 0.35 to 40 mu g ml(-1) cefaclor in B-R buffer pH 10. A relative standard deviation of 4.2% (eta = 5) was obtained, and the limit of detection was calculated to be 2.9 ng ml(-1). Direct determination of cefaclor in human urine (1 ml of urine was made up to 10 ml with pH 10 buffer) spiked to 0.39 mu g ml(-1) was made (recovery 98.6%). (C) 1999 Elsevier B.V. B.V. All rights reserved.

Differential expression of members of the IGF system in OPU-derived oocytes from Nelore (Bos indicus) and Holstein (Bos taurus) cows

The insulin-like growth factor (IGF) system is related to quality of oocytes and embryos. The aim of this study was to investigate the mRNA levels of IGF1 and IGF2 and their receptors, IGFR1 and IGFR2, as well as IGFBP2, IGFBP4, and PAPP-A in oocytes from Nelore compared to Holstein cows. Pools of oocytes (20 oocytes/pool) from Nelore (n=8 pools) and Holstein (n=4 pools) were obtained via ovum pick-up (OPU, 10 sessions) and cumulus cells and zona pellucida were removed. The pools were submitted to total RNA extraction. Expression of members of the IGF system was assessed by real time RT-PCR. The mRNA expression of IGF1 and IGF2, IGFR1 and IGFR2, IGFBP2 and IGFBP4 was significantly higher (P<0.01) in oocytes from Holstein whereas the expression of PAPP-A was significantly higher (P<0.05) in oocytes from Nelore cows. The high PAPP-A expression and the low expression of IGFBP2 and IGFBP4 are associated with more efficient degradation of IGFBPs, which results in greater bioavailability of IGF in Nelore oocytes when compared to the Holstein. © 2013 Elsevier B.V.

Comparison of the nanoparticles performance in the photocatalytic degradation of a styrene-butadiene rubber nanocomposite

Much has been talking about the advantages of polymeric nanocomposites, but little is known about the influence of nanoparticles on the stability of these materials. In this sense, we studied the influence of both oxides of zirconium and titanium, known to have photocatalytic properties, as well as the influence of synthetic clay Laponite on the photodegradation of styrene-butadiene rubber (SBR). SBR nanocomposites were prepared by the colloidal route by mixing commercial polymer lattices and nanometric anatase TiO2, monoclinic ZrO2 or exfoliated Laponite clays colloidal suspensions. To better understand the degradation mechanisms that occur in these nanocomposites, the efficiency of different photocatalysts under ultraviolet radiation was monitored by FT-IR and UV-vis spectroscopies and by differential scanning calorimetric. It was observed that TiO2 and ZrO2 nanoparticles undoubtedly acted as catalysts during the photodegradation process with different efficiencies and rates. However, when compared to pure SBR samples, the polymer degradation mechanism was unaffected. Unlike studies with nanocomposites montmorillonite, exfoliated laponite clay effectively acts as a photostabilizer of polymer UV photodegradation. Copyright © 2012 Wiley Periodicals, Inc.

Differential Expression of IGF Family Members in Heat-Stressed Embryos Produced In Vitro from OPU-Derived Oocytes of Nelore (Bos indicus) and Holstein (Bos taurus) Cows

Contents The IGF system is related to embryo quality. We aim to determine the effect of the heat stress on the mRNA expression of IGF1 and IGF2, IGFR1 and IGFR2, IGFBP2 and IGFBP4, and PAPPA in in vitro production (IVP) blastocysts from Nelore and Holstein after ovum pick up (OPU) to better understand the differences between these breeds.Oocytes from four Nelore and seven Holstein were collected in six OPU sessions. Following in vitro maturation and fertilization using six Nelore or Holstein sires, embryos were divided into control (cultured at 39 degrees C) and heat stress (HS; exposed to 41 degrees C for 9h). Blastocysts were submitted to RNA extraction. The IGF1 expression was higher in blastocysts under HS in both breeds, and the expression of IGFBP2 and IGFBP4 was higher in Holstein blastocysts under HS. The high PAPPA expression and the low expression of IGFBP2 and IGFBP4 are associated with a more efficient degradation of IGFBPs, which results in greater IGF bioavailability in Nelore blastocysts and may contribute to the superior HS tolerance in Nelore, when compared to Holstein.

Differential environmental impacts on small and medium size rivers from center of São Paulo State, Brazil, and regional management perspectives

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Bioremediation with White-Rot Fungi at Fisherville Mill: Analyses of Gene Expression and Number 6 Fuel Oil Degradation

Extracellular enzymes that white-rot fungi secrete during lignin decay have been proposed as promising agents for oxidizing pollutants. We investigated the abilities of the white-rot fungi Punctularia strigosozonata, Irpex lacteus, Trichaptum biforme, Phlebia radiata, Trametes versicolor, and Pleurotus ostreatus to degrade Number 6 fuel oil in wood sawdust cultures. Our goals are to advise bioremediation efforts at a brownfield redevelopment site on the Blackstone River in Grafton, Massachusetts and to contribute to the understanding of decay mechanisms in white-rot fungi. All species tested degraded a C10 alkane. When cultivated for 6 months, Irpex lacteus, T. biforme, P. radiata, T. versicolor and P. ostreatus also degraded a C14 alkane and the polycyclic aromatic hydrocarbon phenanthrene. Gene expression analyses of P. strigosozonata indicate differential gene expression in the presence of Number 6 oil and on pine and aspen sawdust.