A critical review of the literature on the various aspects of natural fibers and biocomposites with a particular reference to chemical modifications is presented in this paper. A notable disadvantage of natural fibers is their polarity which makes it incompatible with hydrophobic matrix. This incompatibility results in poor interfacial bonding between the fibers and the matrix. This in turn leads to impaired mechanical properties of the composites. This defect can be remedied by chemical modification of fibers so as to make it less hydrophilic. This paper reviews the latest trends in chemical modifications and characterizations of natural fibers. The structure and properties of natural fibers have been discussed. Common chemical modifications and their mechanisms have also been elaborated. The importance of chemical modifications and the resultant enhancement in the properties of the composites have also been reviewed. Recent investigations dealing with chemical modifications of natural fiber-reinforced composites have also been cited. POLYM. COMPOS., 29:187‐

Recent Developments in Chemical Modification and Characterization of Natural Fiber-Reinforced Composites

Separate relativistic Hartree-Fock solutions for atoms in their initial and final states are used for calculating the radiative decay of a $K$-vacancy state. The matrix-element calculations include the exchange effects of the nonzero overlap of wave functions from different subshells. Results are presented for the filling of the vacancy by the $p$ electrons for a set of elements from $Z=10\mathrm{to}98$. The Hartree-Fock theory is also used for calculating the rates of production of multiple-vacancy states in the decay process. In contrast to earlier single-potential calculations, the calculated values of ratios of the rates of the $K$ x-ray components are in good agreement with the experimental values.

Exchange corrections of K x-ray emission rates

Reinforcement of natural rubber with silica/carbon black hybrid filler

Calculations of mass energy-transfer and mass energy-absorption coefficients for photon energies from 1 keV to 100 MeV have been developed, based on a re-examination of the processes involved after the initial photon interaction. The probabilities for the initial interaction are from the current photon interaction cross-section database at the National Institute of Standards and Technology. The calculations then take into account (1) electron binding effects on the Compton-scattered photon distribution; (2) the complete cascade of fluorescence emission after ionization events in any atomic subshell, including those associated with incoherent scattering and triplet production; and (3) the radiative energy losses of the secondary electrons and positrons slowing down in the medium, including the emission of bremsstrahlung, characteristic X rays from impact ionization, and positron in-flight as well as at-rest annihilation quanta. Consideration of the processes in (3) goes beyond the continuous-slowing-down approximation and includes the effects of energy-loss straggling. Results for the mass energy-absorption coefficient are compared with those from recent tabulations.

Calculation of Photon Mass Energy-Transfer and Mass Energy-Absorption Coefficients'

Experimental K and L relative x-ray emission ratess

Inner shell ionization of copper, silver and gold by electron bombardment

We report the results of an analysis of the available experimental data on electron-induced K-shell ionization which show that the data can be described by the Bethe theory of ionization corrected for relativistic energies by a classical correction. This analysis, which extends over five orders of magnitude in the ratio of bombarding energy to ionization potential, appears to be superior to the available theoretical treatments, and suggests where further work would be useful. (AIP)

Semiempirical analysis of electron-induced K -shell ionization

Absolute doubly differential bremsstrahlung cross sections from Xe, Kr, Ar, and Ne have been measured for electron bombarding energies of 28 and 50 keV. Bremsstrahlung photons have been detected at $90\ifmmode^\circ\else\textdegree\fi{}$ to the incident electron beam at energies ranging from 5 keV up to the kinematic end point. The results are compared with predictions of ordinary bremsstrahlung and of total bremsstrahlung that include polarizational bremsstrahlung from the target atom calculated in the stripping approximation. All previous absolute cross sections have been from thin-film solid targets and have not shown any polarizational bremsstrahlung contribution. The present results, the first from free atoms, provide definitive evidence for the contribution of polarizational bremsstrahlung to the photon spectrum from electron bremsstrahlung.

Absolute doubly differential cross sections for electron bremsstrahlung from rare gas atoms at 28 and 50 keV.

Carbon Black and silica as reinforcers of rubber polymers: Doppler broadening spectroscopy results

As part of an experiment to study atomic-field bremsstrahlung produced by electron bombardment of rare-gas atoms in the 4- to 10-keV energy range, we have determined the characteristic x-ray production cross section for the $K$ shell of argon and the $L$ shells of krypton and xenon. We compare our results for the inner-shell ionization cross section with the Bethe theory, the plane-wave Born approximation of McGuire, and the classical binary encounter theory as well as with previous experiments. Using the observed validity of classical scaling over this energy range, and the known average $K$-shell fluorescence yield for argon, we have determined the average $L$-shell fluorescence yield for xenon and krypton.

C.A. Quarles

Papers

Inner shell ionization of copper, silver and gold by electron bombardment

Semiempirical analysis of electron-induced K -shell ionization

Absolute doubly differential cross sections for electron bremsstrahlung from rare gas atoms at 28 and 50 keV.

Carbon Black and silica as reinforcers of rubber polymers: Doppler broadening spectroscopy results

Characteristic x-ray production by electron bombardment of argon, krypton, and xenon from 4 to 10 keV