Fiber surfaces, electron spectroscopy

In a pilot study, it was discovered that an ultraviolet zone (UVO) based method, which has been developed for surface treating wool fibers, could be used to oxidatively modify polymer surfaces. Electron spectroscopy for chemical analysis (ESCA) and contact angle results indicated that the treatment was effective on PE and a polyetheretherketone (PEEK). It produced changes in surface oxygen chemistry and free energy, which increased polarity and improved wettability of the surface. Composite lap shear tests showed that the treatment gave a marked improvement in adhesion and that an optimum joint strength is achieved at low treatment times (<1 min). 

Hopfgarten, F. (1978). Surface study of carbon fibers with ESCA and Auger electron spectroscopy. Fibre Sci. Technol. II, 61-19. 

Theories and instrumentation of Fourier transform IR spectroscopy and electron spectroscopy for chemical analysis are briefly reviewed. The possibility of using these techniques in detection and analysis of acid impurities distributed at surfaces of paper documents produced during the period from 1790 to 1983 is demonstrated. Results show that all of the papers tested contained carboxylic groups. The carboxylic acids found in the paper of 1790 are the results of oxidation and aging. Acids in other papers are due to fiber oxidation as well as the presence of rosin acids. These techniques show promise as nondestructive methods for elucidating chemical characteristics of surfaces of paper documents. 

The measurement of acidity in paper documents with cold- and hot-water extraction frequently distorts and damages the paper fibers and printing inks. Many paper conservators and museum curators have long desired a reliable and rapid method for the detection of acidity of paper documents in a nondestructive manner so that they can determine the acidity routinely to screen out valuable book documents for deacidification or other necessary preservation treatments. The objective of this chapter is to introduce two spectroscopic techniques, namely, Fourier transform IR spectroscopy (FTIR) and electron spectroscopy for chemical analysis (ESCA), for chemical analysis of paper surfaces. The effectiveness of these techniques in analyzing and determining the presence of acidic functional groups on paper documents is demonstrated. 

Robbins and Bahl [6] have examined the effects of sunlight and ultraviolet radiation on disulfide sulfur in hair via electron spectroscopy for chemical analysis [6]. Both UV-A (320-400 nm) and UV-B (290-320 nm) radiation were shown to oxidize sulfur in hair. The primary oxidation occurs closer to the hair fiber surface, producing a steep gradient of oxidized to less oxidized hair from the outer circumference of the hair to the fiber core. 

P. H. Wang, K. L. Hong, and Q. R. Zhu, Surface analysis of polyacrylonitrile-based activated carbon fibers by X-ray photo-electron spectroscopy, J. Applied Polym. Sci., 62,1987-91 (1996). 

Desimoni E, Cataldi TRI, Ceifidor UB, On the characterization of carbon fiber surfaces by X-ray excited Auger Electron Spectroscopy, Annali di Chimica, 82(5-6), 207-218, 1992. 

ABSTRACT. The paper details the use of scanning electron microscopy, surface reflectance infrared spectroscopy, Auger electron spectroscopy, ion scattering spectroscopy, secondary ion mass spectroscopy, and x-ray photoelectron spectroscopy in the analysis of polymeric adhesives and composites. A brief review of the principle of each surface analytical technique will be followed by application of the technique to interfacial adhesion with an emphasis on polymer/metal, fiber/matrix, and composite/composite adhesion. 

PVDF and PP sutures have very similar melting temperatures (165-175°C), but distinctively different level of crystallinity. PVDF has a level of crystallinity 59% 7%,whilePPhas43% 3%. Because ofthe lack ofan a alkyl group, PVDF could be sterilized by the conventional /-irradiation method, while PP requires the use ethylene oxide gas. Thus, PVDF could take advantage of the effidenqr and convenience of /-irradiation sterilization. like PP sutures, PVDF sutures should not have any Oj element in their chemical structure. However the surface of PVDF and PP sutures showed oxidation products as confirmed by electron spectroscopy for chemical analysis. The amounts of O2 element on the surface of PVDF and PP sutures were 7.4% and 7.9%, respectively. However, bulk FUR data failed to reveal such oxidation products. This suggests that oxidation of PVDF and PP is introduced during melt spinning of fibers and is mainly restricted to the surface of suture fibers. 

Figure 10.10 Auger electron spectroscopy profile of a fiber which reveals that the fiber surface (left side) is primarily Si and O. (Sputter rate is about 10 nm/min.)... 

Inorganic nanofibers are usually characterized by wide angle x-ray diffraction (WAXD) to establish the crystallinity of the fibers, transmission electron micrograph (TEM) images to demonstrate the crystallite morphology, and Fourier transform infra-red (FTIR) spectroscopy to confirm the surface chemistry. A few the studies have also employed Raman... 

Hossain et al. [45] studied the effects of surface modification of jute libers and nanoclay on jute-Biopol green composites. Four subsequent chemical treatments including detergent washing, dewaxing, alkali treatment, and acetic acid treatment were performed to facilitate better bonding between the fiber and matrix. The scanning electron microscopy and Fourier transform infrared spectroscopy study confirmed improved fiber surfaces for better adhesion with matrix after final treatment. Enhanced thermal... 

Here only the most relevant issues will be summarized, because several mainstream reviews [4,5,7,8,12], as well as a more personal account by Sherwood [13] based on his extensive experience with x-ray photoelectron spectroscopy of carbon fibers are available. Of special interest are the mechanisms of transfer of oxygen, protons, and electrons to and from the carbon surface. The first two mechanisms have been clarified significantly over the past few decades unfortunately, however, the transfer of electrons—the most relevant one for the applications of interest here—is not well understood therefore, here we can offer more questions than answers. But based on a careful scrutiny of the literature, we can at least formulate some of the more plausible mechanisms as an attempt to guide future research in this area. 

For information on the analysis of surfaces by IR radiation instead of electrons, a complimentary technique known as reflection absorption infrared spectroscopy (RAIRS), see (a) http //www.uksaf.org/tech/rairs.html (b)http //www.cem.msu.edu/ cem924sg/Topicll.pdf For example, the development of fibers/fabrics that will actively adsorb and surface deactivate chemical and biological warfare agents — of increasing importance as new modes of terrorist activity continue to emerge. For more information, see (a) http //web.mit.edu/isn/(Institute of Soldier Nanotechnologies at M.I.T.). (b) Richards, V. N. Vohs, J. K. Williams, G. L. Fahlman, B. D. J. Am. Ceram. Soc. 2005,88,1973. 

Gel-permeation chromatography" is used to compare the pore structure of jute, scoured jute and purified cotton cellulose. Both native and scoured jute have shown greater pore volumes than cotton. The effects of alkali and acid treatment on the mechanical properties of coir fibers are reported." Scanning electron micrographs of the fractured surfaces of the fibers have revealed extensive fibrillation. Tenacity and extension-at-break decrease with chemical treatment and ultraviolet radiation, whereas an increase in initial modulus and crystallinity is observed with alkali treatment. FTIR spectroscopy shows that the major structural changes that occur when coir fibers are heated isothermally in an air oven (at 100, 150 and 200 °C for 1 h) are attributable to oxidation, dehydration and depolymerization of the cellulose component. 

The association of several techniques to study the same system is always advantageous. For the specific case of surfaces, techniques like XPS, contact angle, diffuse reflectance infrared with Fourier transform, surface area and pore size measurements, scanning electron microscopy appear frequently associated. This is the case for the study of carbon or glass fibers [ 105-109], activated carbons [110], and polymeric films obtained by plasma polymerization [111]. In Section 5, the specific combination of diffuse reflectance spectroscopies in the region of UVA is and XPS will be emphasized. 

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