Chemical modification of flax reinforced polypropylene composites

This paper presents an experimental study on the static and dynamic mechanical properties of nonwoven based flax fibre reinforced polypropylene composites. The effect of zein modification on flax fibres is also reported. Flax nonwovens were treated with zein coupling agent, which is a protein extracted from corn. Composites were prepared using nonwovens treated with zein solution. The tensile, flexural and impact properties of these composites were analysed and the reinforcing properties of the chemically treated composites were compared with that of untreated composites. Composites containing chemically modified flax fibres were found to possess improved mechanical properties. The viscoelastic properties of composites at different frequencies were investigated. The storage modulus of composites was found to increase with fibre content while damping properties registered a decrease. Zein coating was found to increase the storage modulus due to enhanced interfacial adhesion. The fracture mechanism of treated and untreated flax reinforced polypropylene composites was also investigated from scanning electron microscopic studies.     

Chemical imaging by direct methods

Chemical imaging is a very old principle of analysis. It has been used for many millions of years in biological tasting and smelling systems. Artificial versions of chemical imaging are traditional paper chromatography and the pH indicator strip used in chemical analysis, which directly result in real (visible) chemical images. In a recent article the indirect and direct chemical imaging methods are introduced, especially the evaluation methods for gas sensitive surfaces by direct pixelizing of the surface and interface potential changes. The scanned light pulse technique (SLPT) and the scanning vibrating capacitor are very effective tools for the chemical mapping of the surfaces. These methods are sensitive for the interface or surface potential shifts (adsorption induced work function shifts) respectively, that depend on the composition of adsorbed layers. Advantages and disadvantages, some technical limits, theory, practice and some results are discussed, too.     

Chemical imaging of latent fingerprint residues

In situ attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopic imaging has been used to obtain chemical images of fingerprints under controlled humidity and temperature. The distribution of lipid and amino acid components in the fingerprints from different donors left on the surface of the ZnSe crystal has been studied using an in situ FT-IR spectroscopic imaging approach under a controlled environment and studied as a function of time. Univariate and multivariate analyses were employed to analyze the spectroscopic dataset. Changes in the spectra of lipids with temperature and time have been detected. This information is needed to understand aging of the fingerprints. The ATR-FT-IR spectroscopic imaging offers a new and complementary means for studying the chemistry of fingerprints that are left pristine for further analysis. This study demonstrates the potential for visualizing the chemical changes of fingerprints for forensic applications by spectroscopic imaging.     

Chemical vapour depositedin-situ composites in the system Ti-Si-C

Chemical vapour deposited (CVD) SiC-ceramic composites were produced by adding TiCl₄ to the SiH₂Cl₂-C₄H₁₀-H₂ system previously used to prepare CVD -SiC. Experiments performed in a classical cold-wall reactor on a graphite substrate heated by Joule effect, were carried out at a constant hydrogen gas flow rate of 30 l h^–1, under atmospheric pressure and at a deposition temperature ranging from 1123–1373 K. Silicon, titanium and carbon elemental compositions were determined by electron probe microanalysis-wavelength dispersive spectrometry. Phase identifications were mainly performed by Auger electron spectroscopy and X-ray diffraction and additionally by Raman spectroscopy. Three- and two-phased materials were obtained: SiC-TiC-C, SiC-TiC and SiC-TiSi₂ with ratios 42<11. Temperature governed the dominance of the dispersed phases: lower for TiSi₂ and higher for TiC than TiC + C. At 1373 K, co-deposits were strongly textured, the -SiC [2 2 0] preferred orientation getting weaker as the deposition temperature decreased. Apparent crystallite size along the 2 2 0 direction decreased with temperature from about 15 nm to 10 nm. The deposition rate was almost independent of time and decreased with temperature from about 800 m h^–1 to 60 m h^–1. Arrhenius plots showed linear relationships with temperature and slope breaks at 1123 K, the temperature corresponding to the change of the dispersed phases in the SiC matrix.     

Chemical imaging sensor and laser beacon

Design and functional aspects of PANSPEC, a panoramic-imaging chemical vapor sensor (PANSPEC is an abbreviation for infrared panoramic-viewing spectroradiometer), were advanced and its optical system reoptimized accordingly. The PANSPEC model unites camera and fused solid-state interferometer and photopolarimeter subsystems. The camera is an eye of the open atmosphere that collects, collimates, and images ambient infrared radiance from a panoramic field of view (FOV). The passive interferometer rapidly measures an infrared-absorbing (or infrared-emitting) chemical cloud traversing the FOV by means of molecular vibrational spectroscopy. The active photopolarimeter system provides a laser beam beacon. This beam carries identification (feature spectra measured by the interferometer) and heading (detector pixels disclosing these feature spectra) information on the hazardous cloud through a binary encryption of Mueller matrix elements. Interferometer and photopolarimeter share a common configuration of photoelastic modulation optics. PANSPEC was optimized for minimum aberrations and maximum resolution of image. The optimized design was evaluated for tolerances in the shaping and mounting of the optical system, stray light, and ghost images at the focal plane given a modulation transfer function metric.     

Nuclear magnetic resonance imaging of polymers and polymer composites

Since its inception in the early 1970s, the nuclear magnetic resonance (NMR) imaging technique has developed to the point that it is now used as a routine clinical diagnostic tool in many hospitals. As a result, virtually all; research in NMR imaging was until recently directed towards mapping the water and lipid distribution contained in human soft tissue, and it is only within the last few years that a start., has been made in exploring the non-medical applications of NMR imaging. In this review article we discuss some of the many applications of NMR imaging to studies of the production and evaluation of 'advanced materials', particularly polymers and polymer composites, and review some ofthe studies which have already been undertaken. It is hoped that this article will be read both by polymer scientists and engineers interested in this powerful new research tool for studying their materials, and also by those already involved in other aspects of NMR imaging who are seeking challenging new problems.     

Chemical recycling of glass fibre reinforced composites using subcritical water

A hydrolysis process is applied to degrade an unsaturated polyester resin based on DCPD (dicyclopentadiene) and crosslinked with styrene, as the matrix of a composite material reinforced with long glass fibres. Subcritical conditions of water (200 °C < temperature < 374 °C and pressure < 221bars) were chosen regarding the involved chemistry for the case of simple esters. Several experiments were realised to measure the effects of the process parameters on the efficiency of hydrolysis, on the quality of the recovered fibres and finally on the nature of the recovered organic products. A washing of the fibres is necessary and appears to be an important step of the process realised in batch conditions. The identification of the recovered organic products indicates that monomers of the resin are obtained but also that secondary reactions occur during the hydrolysis process.     

Chemical reaction of SiCp/Al composites during multiple remelting

In the present study, the chemical reaction of SiCp/Al composites during multiple remelting above the liquidus was investigated using Differential Scanning Calorimetry and Transmission Electron Microscope. The experimental results indicated that the chemical reaction of SiC particles increased with increasing remelting temperature and the number of recycling runs. After reaching a certain degree of reaction, no further change occurred during subsequent remelting. The chemical reaction in SiCp/Al composite during multiple remelting could be suppressed by controlling the remelting temperature when silicon was present in the aluminum matrix. When 8 wt% silicon was added to the aluminum matrix, the chemical reaction between SiC particles and aluminum was completely suppressed even during multiple remelting above the liquidus.     

Chemical feasibility of lithium as a matrix for structural composites

The chemical compatibility of lithium with tows of carbon and aramid fibres and silicon carbide and boron monofilaments was investigated by encapsulating the fibres in liquid lithium and also by sintering. The lithium did not readily wet the various fibres. In particular, very little lithium infiltration into the carbon and aramid tows was achieved and the strength of the tows was seriously degraded. The strength of the boron and silicon carbide monofilaments, however, was not affected by the liquid lithium. Therefore lithium is not feasible as a matrix for carbon and aramid fibres, but a composite containing boron or silicon carbide fibres in a lithium matrix may be feasible for specialized applications.     

Chemical shrinkage characterization techniques for thermoset resins and associated composites

Control and optimization of curing process is very important for the production of high quality composite parts. Crosslinking of molecules of thermoset resin occurs in this phase, which involves exothermy of reaction, chemical shrinkage (Sh) and development of thermo-physical and thermo-mechanical properties. Exact knowledge of the evolution of all these parameters is required for the better understanding and improvement of the fabrication process. Sh is one such property of thermoset matrix, which is difficult to characterize due to its coupling with thermal expansion/contraction. A number of techniques have been used to determine volume Sh of thermoset matrix, which later on has been used to find tensor of Sh for the simulation of residual stresses and shape distortion of composite part, etc. Direct characterization of volume Sh of composites has also been made by some authors. Though not much, but some work has also been reported to determine the Sh of composite part in a specific direction. In this article, all the techniques used in the literature for the characterization of Sh of resin and composite are reported briefly with their respective advantages, disadvantage and important results.     

Chemical activation of calcium aluminate cement composites cured at elevated temperature

The influence of sodium sulfate, as an activator, on the hydration of calcium aluminate cement (CAC)–fly ash (FA)–silica fume (SF) composites was investigated. Different mixes of CAC with 20% pozzolans (20% FA, 20% SF and 10% FA + 10% SF) were prepared and hydrated at 38 °C for up to 28 days. The hydration products were investigated by XRD, DSC and SEM. The results showed that sodium sulfate accelerated the hydration reactions of calcium aluminate cement as well as the reactions of FA and SF with CAH₁₀ and C₂AH₈ to form the strätlingite (C₂ASH₈). The later reactions prevent the strength loss by preventing the conversion of CAH₁₀ and C₂AH₈ to the cubic C₃AH₆ phase. The acceleration effect of Na₂SO₄ on the reactivity of fly ash was more pronounced than on the reactivity of silica fume with respect to reaction with CAH₁₀ and C₂AH₈ phases.     

Chemical imaging of iron oxides and oxyhydroxides using near infrared Raman imaging microscopy

Abstract

A new method of identifying and mapping the distribution of both iron oxides and oxyhydroxides using near infrared Raman imaging microscopy NIRIM is reported. This technique offers an important alternative to conventional spectroscopic techniques that provide spatially averaged data. The NIRIM instrument used for these studies combines fibre bundle image compression hardware and multivariate signal processing software to identify and map different iron minerals and corrosion products. The NIRIM images clearly distinguish hematite, magnetite, wustite, goethite, and lepidocrocite microstructures. The first chemical maps of naturally occurring iron minerals and corroded steel surfaces obtained using NIRIM spectral images, classified with the aid of a library of pure compound spectra, are presented.     

Chemical synthesis of hydroxyapatite/poly(ε-caprolactone) composites

Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂)—biodegradable polymer composites as bone replacement scaffolds were synthesized by a colloidal non-aqueous precipitation technique at room temperature. The starting materials used for synthesizing hydroxyapatite (HA) were Ca(NO₃)₂·4H₂O and H₃PO₄ with a Ca/P ratio of 1.67 while poly(ε-caprolactone) (PCL) was used as the biodegradable polymer. The composites were prepared containing up to 34.5 wt.% HA and PCL polymer without any evidence of phase separation. This paper describes, the synthesis and structure of the HA/PCL composites. In addition, the pH changes during precipitation, the yield of the chemical reaction, and the possible existence of any bond between the ceramic and the polymer including the microstructure of the composites were studied. Finally, the mechanical and thermal properties of the composites were investigated. The results of these studies are described and discussed.     

Chemical activation of calcium aluminate cement composites cured at elevated temperature

The influence of sodium sulfate, as an activator, on the hydration of calcium aluminate cement (CAC)–fly ash (FA)–silica fume (SF) composites was investigated. Different mixes of CAC with 20% pozzolans (20% FA, 20% SF and 10% FA + 10% SF) were prepared and hydrated at 38 °C for up to 28 days. The hydration products were investigated by XRD, DSC and SEM. The results showed that sodium sulfate accelerated the hydration reactions of calcium aluminate cement as well as the reactions of FA and SF with CAH₁₀ and C₂AH₈ to form the strätlingite (C₂ASH₈). The later reactions prevent the strength loss by preventing the conversion of CAH₁₀ and C₂AH₈ to the cubic C₃AH₆ phase. The acceleration effect of Na₂SO₄ on the reactivity of fly ash was more pronounced than on the reactivity of silica fume with respect to reaction with CAH₁₀ and C₂AH₈ phases.     

Chemical functionalization of carbon nanotubes for the mechanical reinforcement of polystyrene composites

An organometallic approach was used to functionalize multiwalled carbon nanotubes with n-butyllithium. This procedure was repeated two more times to achieve a higher degree of multiwalled carbon nanotube functionalization. The functionalized nanotubes have been characterized by Fourier transform infrared and Raman spectroscopy, thermogravimetrical analysis, scanning electron microscopy and sedimentation studies. It was possible to form stable suspensions of the functionalized nanotubes in tetrahydrofuran and they were used to make nanotube polymer composites. The mechanical properties of these new nanotube polymer composites were tested and they were found to show an increase of up to 25% in their Young's moduli and up to 50% in their tensile strength over pure polystyrene.     

Chemical imaging of surface reactions by multiplexed capillary electrophoresis

A new technique for in situ imaging of surface reactions and screening heterogeneous catalysts by using multiplexed capillary electrophoresis was developed. By bundling together the inlets of a large number of capillaries, an aligned imaging probe can be created that can be used to sample directly products formed at a surface with spatial resolution determined by the outer diameter of the capillaries. In this work, we used surfaces made of platinum, iron, or gold wires to generate electrochemical products for imaging. Various shapes were recorded including crosses, squares, and triangles. A model multifunctional catalytic surface consisting of both iron and platinum electrodes in the shape of a cross was also imaged successfully. Each of the two wires produced a different electrochemical product that could be subjected to capillary electrophoresis to provide chemical selectivity. On the basis of the collected data, we were able to distinguish the products from each wire in the reconstructed image.     

Chemical imaging with a confocal scanning Fourier-transform-Raman microscope

Traditional approaches in confocal microscopy have focused on techniques to generate volumetric intensity or phase images of an object. In these different imaging modes the scattered optical-field properties depend on local refractive index and absorption, properties not unique to a given material. We report here on a confocal microscope that uses Raman scattered light to generate volumetric chemical images of a material. We designed and built a prototype instrument, called a confocal scanning laser Raman microscope, that combines a confocal scanning laser microscope with a Fourier-transform-Raman spectrometer. The high depth and lateral spatial resolution of the confocal optics design define a volume element from which the Raman scattered light is collected, and the spectrometer analyzes its spectral content. The sample is scanned through the microscope probe volume, and a chemical image isgenerated based on the content of the Raman spectrum extracted from each scan position in the sample. The results inclu e instrument characterization measurements and examples of confocal chemical imaging.     

炭纤维织物复合材料微结构超声成像方法

超声波在炭纤维织物复合材料中树脂囊界面声压反射系数可达 21 %,在层间界面的反射则与树脂层的厚度和声波频率有关,在缺陷界面则会产生绝对反射。研究了入射声波在织物复合材料内部树脂囊、编织纤维束和层间界面产生的声波反射信息,揭示织物复合材料内部铺层和层间界面微结构的三维分布特征。结果表明,采用高分辨率超声成像方法,可以较好地再现织物复合材料中的树脂囊和纤维束形状、取向、铺层方向及层间界面等三维分布特征,为织物复合材料提供一种有效的微结构表征和缺陷检测方法。      

Chemical preparation,direct-current conductivity and thermopower of polyaniline and polypyrrole composites

Polyaniline and polypyrrole composites were synthesized by doping during polymerization with a variety of organic and inorganic groups. Their direct-current (d.c.) conductivity was measured and their activation energy was estimated at room temperature. From thermopower measurements on polypyrrole composites a metallic p-type conductivity in the fibrils was revealed, although for polyaniline an n-type to p-type change of the carriers into the metallic islands was displayed at about 320 K. The introduction of the various groups, in addition to this change in the electrical properties, also resulted in conducting polymers capable of surface complexation with metal ions.