Interfacial evaluation of single Ramie and Kenaf fiber/epoxy resin composites using micromechanical test and nondestructive acoustic emission

Interfacial shear strength (IFSS) of environmentally friendly natural fiber reinforced polymer composites plays a very important role in controlling their overall mechanical performance. The IFSS of various Ramie and Kenaf fiber/epoxy composites was evaluated using the combination of micromechanical test and nondestructive acoustic emission (AE) to find the optimal conditions for desirable final performance. Dynamic contact angle was measured for Ramie and Kenaf fibers and correlated the wettability properties with interfacial adhesion. Mechanical properties of Ramie and Kenaf fibers were investigated using single-fiber tensile test and analyzed statistically by both unimodal and bimodal Weibull distributions. The effect of clamping on the real elongation for both Ramie and Kenaf fibers was evaluated as well. Two different microfailure modes, axial dedonding and fibril fracture, coming from fiber bundles and single fiber composites (SFC) were observed under tension and compression. They were evaluated optically and also determined by AE and their FFT analysis nondestructively.     

Evaluation of reinforcement on the mechanical behavior of partially bonded fiber/matrix interface

This paper aims at introducing a new natural composite used as soil stabilizer with particular application in geotechnical engineering. The fibers introduced in the present study could be used as effective soil reinforcement. This research proves the feasibility of the use of modified jute/polypropylene in lime and cement composites and studies their effects on the tensile and compressive strength of the matrix. In general, the optimal mechanical performance of natural composites and durability depends on the optimization of the interfacial bond between natural fiber and matrix. Since the fibers and matrices are chemically different, strong adhesion at their interfaces is needed for an effective transfer of stress and bond distribution throughout an interface. In this paper a theoretical approach for the identification of elastic modulus in composite interfaces is proposed in detail with a reasonable error. The theoretical approach is based on the method using a sum of least squares criterion. The approach is applied through optimization techniques, using analytical sensitivities and correlating adhesion with Young's modulus. The validity and potentiality of the proposed technique is discussed and the results demonstrated the versatility, accuracy, and efficiency of the presented approach. The applied method also appears to be a simple way of predicting the modulus of elasticity in composite interfaces. This leads to a discussion of the most promising stabilization methods for soil reinforcement and the outlook for the future.     

Spurious Effects in Perturbative Calculations

We show spurious effects in perturbativecalculations due to different orderings of inhomogeneousterms while computing corrections to Green functions fortwo different metrics. These effects are not carried over to physically measurable quantities likethe renormalized value of the vacuum expectation valueof the stress-energy tensor.     

Potential space estimates in local Hardy spaces for Green potentials in convex domains

Let Ω be a bounded co.nvex domain in Rn(n≥3) and G(x,y) be the Green function of the Laplace operator -△ on Ω. Let hrp(Ω) = {f ∈ D'(Ω) :(E)F∈hp(Rn), s.t. F|Ω = f}, by the atom characterization of Local Hardy spaces in a bounded Lipschitz domain, the bound of f→(△)2(Gf) for every f ∈ hrp(Ω) is obtained, where n/(n 1)＜p≤1.     

Cellulosic fibre-reinforced green composites

Increased environmental awareness and societal needs serve as a catalyst for developing new eco-friendly materials like green composites. In the recent past, researchers have reported the results of their studies on green composites of different plant fibres and various biodegradable matrices. This article is an overview of the various aspects of green composites. Composites based on important biodegradable matrices like rubber, poly (lactic acid), poly(butylene succinate), poly(hydroxybutanoate) and soy-based matrices have been discussed. Special emphasis has been given to natural rubber-based green composites.     

离子缔合物二级散射光谱的分析应用2: 汞(II)-硫氰酸盐-感性三芳基甲烷染料体系

研究了[Hg(SCN)4]^2^1与结晶紫、孔雀石绿、亮绿或碘绿等碱性三芳基甲烷染料的离子缔合配合物的二级散射(DS)和"反二级散射"(ADS)光谱, 以及这类散射光谱的特征、影响因素和反应的适宜条件。确定了散射光强度与溶液中汞(II)浓度的关系。提出了用二级散射光谱测定痕量汞的新的高灵敏分析方法, 并对反应机理和两种二级散射发生变化的原因作了初步的讨论。     

Determination of the interfacial properties between modified soy protein resin and kenaf fiber

The kenaf fiber/soy protein resin interface was characterized. The soy protein isolate (SPI) was modified using a polycarboxylic acid, Phytagel^® (PH), to make an interpenetrating network-like (IPN-like structure) structure of the resin. The effects of different PH contents on the interfacial properties were characterized using single fiber composite (SFC) tests and optical microscopy. Kenaf fiber strength was characterized using tensile tests. Kenaf fibers were extracted from nonwoven mats. The length of each kenaf fiber was extended by gluing it to long polyethylene filaments on both sides. After drying the glue, dog-bone shaped SFC specimens were prepared using pure and modified SPI resins. The dried SFC specimens were taken out from the mold and hot-pressed (cured) at 120°C. The interfacial shear strength (IFSS) was calculated using the shear-lag analysis. Single fiber tensile tests at different gauge lengths were performed. The average stresses were computed by fitting the data to Weibull distribution. These values were used in the calculation of the IFSS. After the SFC tests, the specimens were observed under the optical microscope to characterize the fiber fracture modes and the region around the fiber fracture. The SFC tests showed that the IFSS is a function of the PH content which controls the resin shrinkage. It was also seen that the interfacial failure mode is also a function of the PH content. These finding were confirmed by the microbead tests in which E-glass fibers were used with the modified SPI resins.     

Nanocellulose enhanced interfaces in truly green unidirectional fibre reinforced composites

One of the main problems in fabricating natural fibre reinforced polymers is the poor adhesion between intrinsically polar plant fibres and non-polar polymer matrices. We have developed a truly green technique of modifying natural fibre (hemp and sisal) surfaces to improve the interaction between the fibres and polymers by attaching nano-scale bacterial cellulose to the fibre surfaces. These modified natural fibres were then incorporated into the renewable polymers cellulose acetate butyrate (CAB) and poly-L-lactic acid (PLLA). Unidirectional natural fibre reinforced composites were manufactured to investigate the impact of the surface modification on the fibre and interface dominated composite properties. Both the tensile strength parallel as well as perpendicular to the fibres of the composites reinforced by bacterial cellulose modified natural fibres were found to increase significantly, especially in the case of a PLLA matrix. In case of modified sisal reinforced PLLA the parallel strength increases by 44% and the off-axis composite strength by 68%. Scanning electron microscopy observations of the composite fracture surfaces confirm the improved interaction between the fibre and the polymer matrix.     

Green tea polyphenols in combination with copper(II) induce apoptosis in HeLa cells

In the present investigation we report that the natural antioxidant green tea polyphenols (GTPs) could induce apoptosis in HeLa cells in the presence of copper cation. After treatment with low concentrations of GTP (5-15 M) plus 2 M Cu²⁺, HeLa cells died gradually as measured by the MTT assay. Agarose gel electrophoresis analysis of DNA extracted from HeLa cells exposed to GTP/Cu²⁺ showed typical internucleosomal DNA fragmentation (DNA ladder), which was also confirmed by DNA content analysis by flow cytometry. Morphological observation of HeLa cells treated with GTP/Cu2+ by transmission electronic microscopy also showed typical apoptotic features including cell shrinkage, chromatin condensation, and the formation of apoptotic bodies. Laser confocal microscopy determination of intracellular calcium level revealed that exposure to GTP/Cu²⁺ triggered increase of cytosolic calcium ion, which may be involved in the process of apoptosis. This evidence suggested that GTPs might be used as potential therapeutic agent for the treatment of cancer.     

Redifferentiation of human hepatoma cells induced by green tea polyphenols

A novel approach for the treatment of cancer is the differentiation therapy in which cancer cells are induced to attain a mature phenotype when exposed to differentiation inducers. To examine the effects of polyphenols extracted from green tea, i.e. ( – )-epicatechin (EC), ( – )-epigallocatechin (EGC), ( – )-epicatechin gallate (ECG) and ( – )-epigallocatechin gallate (EGCG), on the proliferation and redifferentiation of human hepatoma cell line SMMC-7721, we measured the changes of cell growth, cell surface charge and cell morphography after treament with green tea polyphenols. It was found that the growth curve of treated cells was decreased remarkably, cell surface charge of treated cells was decreased and the microvilli on the surface of treated cells were reduced obviously. It confirmed that green tea polyphenols could reverse malignant phenotypic characteristics and induced redifferentiation of SMMC-7721 cells. The ability of green tea polyphenols to inhibit reactive oxygen species (ROS)-mediated oxidative damage of DNA was also assessedin vitro by measuring the conversion of supercoiled pBR322 plasmid DNA to the open circular and linear forms. It was found that green tea polyphenols could significantly inhibit the oxidative damage of DNA induced by a water-soluble azo initiator 2,2-azobis(2-amidinopropane hydrochloride) (AAPH). However, they could promote the oxidative damage of DNA induced by H₂O₂ and Fe²⁺ at high concentrations. The relationship between the anti-cancer activity and antioxidation-prooxidation activity of green tea polyphenols is discussed.