Blends of rABS and SEBS: Influence of In-Situ Compatibilization on the Mechanical Properties.

In this study, the in-situ compatibilization reaction between recycled acrylonitrile-butadiene-styrene copolymer (rABS) and functional styrene-ethylene-butylene-styrene block maleic anhydride (SEBS-g-MAH) was confirmed, which contributed to the toughening phenomenon of rABS, especially the notched impact strength. As mechanical test that manifested, the rABS/SEBS-g-MAH blends are stronger and more ductile than the rABS/SEBS blends. Prominently, the former has great advantage over the latter in terms of improving the impact performance. Scanning electron microscope (SEM) images showed that the compatible segments that were generated by reaction not only improve the interface adhesion of rABS/SEBS-g-MAH blends but also promote the evolution of co-continuous structures, which can be evidently observed after etching. Furthermore, the SEM micrographs of tensile fracture surfaces indicated that the formation of the co-continuous phase and the improvement of interface adhesion are the most profound reasons for the excellent tensile properties of the rABS/SEBS-g-MAH blends. The impact fracture surface revealed that two-phase interface affects crack propagation and shear yielding absorbs more impact energy than simple interface debonding does at higher deformation rates. Meanwhile, rheological analysis demonstrated that the complex viscosity of the rABS/SEBS-g-MAH (80/20 wt%) blend with a co-continuous structure exhibits a maximum positive deviation at low frequencies from the theoretical value calculated using the rule of logarithmic sum, which indicated a connection between co-continuous structure and complex viscosity. In addition, the storage modulus vs. loss modulus curves of the blends revealed that the viscoelastic behavior of rABS/SEBS-g-MAH blends is very similar to that of rABS.

Morphology, Thermal, Mechanical Properties and Rheological Behavior of Biodegradable Poly(butylene succinate)/poly(lactic acid) In-Situ Submicrofibrillar Composites.

In this study, biodegradable poly(butylene succinate)/poly(lactic acid) (PBS/PLA) in-situ submicrofibrillar composites with various PLA content were successfully produced by a triple-screw extruder followed by a hot stretching-cold drawing-compression molding process. This study aimed to investigate the effects of dispersed PLA submicro-fibrils on the thermal, mechanical and rheological properties of PBS/PLA composites. Morphological observations demonstrated that the PLA phases are fibrillated to submicro-fibrils in the PBS/PLA composites, and all the PLA submicro-fibrils produced seem to have a uniform diameter of about 200nm. As rheological measurements revealed, at low frequencies, the storage modulus (G') of PBS/PLA composites has been increased by more than four orders of magnitude with the inclusion of high concentrations (15 wt % and 20 wt %) of PLA submicro-fibrils, which indicates a significant improvement in the elastic responses of PBS melt. Dynamic Mechanical Analysis (DMA) results showed that the glass transition temperature (Tg) of PBS phase slightly shifted to the higher temperature after the inclusion of PLA. DSC experiments proved that fiber morphology of PLA has obvious heterogeneous nucleation effect on the crystallization of PBS. The tensile properties of the PBS/PLA in-situ submicrofibrillar composites are also improved compared to neat PBS.

A Facile Fabrication of High Toughness Poly(lactic Acid) via Reactive Extrusion with Poly(butylene Succinate) and Ethylene-Methyl Acrylate-Glycidyl Methacrylate.

As is an excellent bio-based polymer material, poly(lactic acid) (PLA)'s brittle nature greatly restricts its extensive applications. Herein, poly(butylene succinate) (PBS) was introduced to toughening PLA by melt blending using a self-made triple screw extruder through in situ reactive with ethylene-methyl acrylate-glycidyl methacrylate (EGMA). The effect of EGMA concentrations on the mechanical properties, morphology, interfacial compatibility of PLA/PBS blends were studied. Fourier transform infrared (FT-IR) results demonstrated that the epoxy group of EGMA reacts with the hydroxyl groups of PLA and PBS, which proved the occurrence of interfacial reactions among the tri-component. The significantly improved compatibility between PLA and PBS after EGMA incorporation was made evident by scanning electron microscope (SEM) characterization results. Meanwhile, the contact angle test predicted that the EGMA was selectively localized at the interface between PLA and PBS, and the result was verified by morphological analysis of cryofracture and etched samples. The EGMA improves the compatibility of PLA/PBS blends, and consequently leads to a significantly increased toughness with the elongation at break occurring 83 times more when 10 wt % EGMA was introduced than neat PLA, while impact strength also enhanced by twentyfold. Ultimately, the toughening mechanism of PLA based polymers was established based on the above analysis, exploring a new way for the extensive application for degradable material.

Vegetation net primary productivity and its response to climate change during 2001-2008 in the Tibetan Plateau.

Alpine ecosystems are highly sensitive to global climate changes. The Tibetan Plateau is one of the areas that are most sensitive to global climate change. Increases in temperature and changes in precipitation can impact the plateau's ecosystem productivity. Net primary productivity (NPP) is one of the most important factors in the carbon cycle of terrestrial ecosystems. In this paper, a light-use-efficiency model was used to estimate the net primary productivity in the Tibetan Plateau. The model is based on a 1-km×1-km-resolution map of vegetation type, multi-temporal 500-m-resolution MODIS data and daily meteorological data. The spatial distribution pattern and dynamic change of the annual NPP from 2001 to 2008 are analyzed. Then, we analyzed the response of the NPP to temperature and precipitation changes. The results show that the mean annual NPP of alpine ecosystems in the Tibetan Plateau is equal to 0.472 Pg C and that the NPP exhibits significant seasonal and interannual variation due to the combined effects of temperature and precipitation changes. Finally, to analyze the effect of temperature and precipitation on the inter-annual change of the NPP, the correlation coefficient between temperature, precipitation and the NPP was computed. It was found that the relations among air temperature, precipitation and the NPP in the Tibetan Plateau region are different. The annual average temperature increase had a significantly positive effect on the vegetation NPP (R(2)=0.83). In contrast, the annual precipitation changes had a weakly negative effect on the vegetation NPP (R(2)=0.373).

Enzyme enhanced quantitative determination of multiple DNA targets based on capillary electrophoresis.

In the current paper, enzyme enhanced simultaneous quantitative determination of multiple DNA targets based on capillary electrophoresis (CE) was described. We used three biotin-modified DNA probes, which reacted with avidin-conjugated horseradish peroxidase (avidin-HRP) conjugate to obtain the HRP labeled probes, to hybridize with three corresponding targets. The resulting mixture containing double-strand DNA (dsDNA)-HRP, excess single-strand DNA (ssDNA)-HRP and remaining avidin-HRP was separated by capillary electrophoresis, and then the system of HRP catalyzing H(2)O(2)/o-aminophenol (OAP) reaction was adopted. The catalytic product was detected with electrochemical detection. With this protocol, the limits of quantification for the hybridization assay of 21-, 39- and 80-mer DNA fragments were of 1.2 x 10(-11), 2.4 x 10(-11) and 3.0 x 10(-11)M, respectively. The multiplex assay also provided good specificity without any cross-reaction.

Label-free electrochemical detection of short sequences related to the hepatitis B virus using 4,4'-diaminoazobenzene based on multiwalled carbon nanotube-modified GCE.

A novel label-free electrochemical DNA biosensor based on 4,4'-diaminoazobenzene (4,4'-DAAB) and multiwalled carbon nanotube (MWNT)-modified glassy carbon electrode (GCE) for short DNA sequences related to the hepatitis B virus (HBV) hybridization detection was presented. Differential pulse voltammetry (DPV) was used to investigate hybridization event. The decrease in the peak current of 4,4'-DAAB was observed on hybridization of probe with the target. This electrochemical approach was sequence specific as indicated by the control experiments, in which no peak current change was observed when a noncomplementary DNA sequence was used. Numerous factors affecting the target hybridization were optimized to maximize the sensitivity. Under optimal conditions, this sensor showed a good calibration range between 7.94 x 10(-8) M and 1.58 x 10(-6) M, with HBV DNA sequence detection limit of 1.1 x 10(-8) M.