The possibilities and limitations of analyzing by scanning electron microscopy wool blended with two unmedullated specialty fibers, mohair and cashmere, were studied. The measurement of the height of the cuticle scale at the scale edge was used as an objective criterion for distinguishing between the wool and the specialty fibers. For both blend types and for the experimental procedure used, the mean absolute error of 1% was less than a third of the mean confidence distances and compared well with the accuracy of the chemical methods of analyzing fiber blends. The remaining errors were attributed to purely random variations, so that systematic errors of any kind can largely be excluded.Labeling textiles to indicate their composition requires analytical means for control, not only for the final product but also for the raw materials and during all stages of processing. Besides the legal aspects of labeling, the price difference of the components for various common fiber blends is a major motivation for developing exact analytical procedures.Quite common fiber blends for high quality textile goods are blends of sheep's wool, hereafter referred to simply as wool, with other fine animal hair fibers, e.g., mohair, cashmere, camel hair, angora, etc., referred to as specialty fibers [ 1,12].
Part I of this series described the analysis of blends of the specialty fibers mohair and cashmere with sheep's wool by scanning electron microscopy (SEM), assuming equal densities and circular cross sections for the components. A bias may be expected in the analysis of other noncircular and medullated specialty fibers through systematic errors in determining the fiber diameters and densities. To determine whether the SEM method is subject to such a bias, blends were prepared of wool with angora rabbit hair, which can be regarded as an extreme example of noncircularity and med ullation. The results show that the blends can satisfactorily be analyzed by introducing a specific density for angora rabbit hair of 1.15 g/cm 3. No systematic bias of the results due to cross-sectional irregularities or to a density distribution of the rabbit hair could be detected. For the angora/wool blends, the errors of analysis compare favorably with those of cashmere/wool and mohair/wool blends.
Although wool and other keratinous materials consist of highly crosslinked protein matter and thus are virtually insoluble and resistant to biological attack, some insect larvae are able to digest and use them as food. The digestion of wool by these moth and beetle species involves processes that are not yet fully understood. Scanning electron microscopic investigations of larvae excreta have helped to shed more light on this subject by showing the breakdown of wool and the digestion of the morphological components of wool by moth and beetle larvae, on the basis of the remaining wool fragments. The feces of all larvae species, excreted after feeding on untreated and mothproofed wool, were found to contain wool fragments in different stages of degradation. In the last stage of degradation, the wool was broken down to its fibrillar structures. Microscopic observations of the excreta indicated a preferential breakdown in the larval gut of some of the low sulfur regions of the wool.Wool and other keratinous materials are subject to attack as a primary food source for the larvae of several moth and beetle species. The larvae of some thirty species of moth (Lepidoptera), some fifteen species of beetles (Coleoptera), and several hundred species of bird lice (Mallophaga) are able to break down keratins. Only a few of these insect species are considered as serious fabric pests, however, the most important being the larvae of the webbing clothes moth (Tineola bisselliella), the case-bearing clothes moth (Tinea spp.), the brown house moth (Hofmannophila pseudospretella), the furniture carpet beetle (Anthrenus spp.), and the black carpet beetle (Attagenus spp.), variant strains of them being present in nature [ 15]. The ability of these insect larvae to break down crosslinked protein material, especially wool, is unusual. Extensive research work exploring the digestive mechanisms and enzyme systems of some of these wool pests has already been described, e.g., by Linderstrom-Lang and Duspiva [9], Waterhouse [ 15], and more recently by Ward [ 13,14] and Baker [ I ]. The actual course of the digestion process still raises questions. ' A wide range of commercial moth-and beetle-proof ing agents permits the effective control of keratin-digesting pests, though up to now there are several unsolved problems with respect to the biology, application methods, and environmental aspects of the different product systems and their biologically active iDpdents [4]. Further fundamental research activities, aimed at a better understanding of the biological and biochemical mechanisms of wool-feeding insects, are necessary for the effoctive control of insect pests. In our previous work, we examined the breakdown of mothproofed and nonproofed wool by moth and beetle larvae by analyzing their excreta [5-71. Characterization of the larvae feces by means of amino acid analysis and SDS-polyacrylamide gel dectropboresis is given elsewhere [7]. This paper deals with scanning electron microscopic observations of moth-and bottle-type feces, excreted ...
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