Textiles, degradation natural fibers

Natural fibers may be adversely affected by sunlight, air pollutants, acids and alkali, bleaches and other oxidizing agents, and chemical finishing processes. However, the effects of photochemical degradation are by far the most problematic in the conservation of textiles and therefore have received the most attention. 

Photochemical degradation of natural fibers depends on the atmospheric conditions in which the textiles are exposed, stored, or displayed, on... 

Up to the present time conservators were interested in preserving textiles made from natural fibers. With time, however, as present day materials incorporating man-made fibers are collected, concerns will arise as to their preservation and display. In this chapter, I survey the different types of man-made fibers, discuss environmental factors that can degrade them, and indicate methods for the identification or estimation of such damage. Also, I indicate where precautions need to be taken in their cleaning and display. 

Deterioration. The causes of degradation phenomena in textiles (155—158, 164) are many and include pollution, bleaches, acids, alkaUes, and, of course, wear. The single most important effect, however, is that of photodegradation. Both ceUulosic and proteinaceous fibers are highly photosensitive. The natural sensitivity of the fibers are enhanced by impurities, remainders of finishing processes, and mordants for dyes. Depolymerization and oxidation lead to decreased fiber strength and to embrittlement. 

Geotextiles are available as mats, textiles, webs, nets, grids, and sheets. When retention of the contained material is desired synthetic polymers such as polypropylenes, polyesters, nylons, PEs, and PVCs are used because they resist rapid degradation. When only shortterm retention is needed natural materials such as cotton are used. Geotextiles are not always made from fibers, but include film materials such as PE and polypropylene sheets used to retain moisture but retard weed growth in gardens. 

Even if the particulate represents a contaminant, it is useful to know the nature of that contaminant. Once the textiles are examined visually and with magnification, examination of the particulate by microscopy should be undertaken. Identifying features of the fiber or of other materials that comprise the particulate may be difficult to see, possibly because they are occluded with soil or were damaged in active use or in long-term degradation. Therefore, additional analyses might be needed. 

The two most common natural textile fibers encountered in modern fabrics have contrasting responses to soil burial. Under most soil burial conditions cellulose will degrade rapidly whereas wool will decay at a slower rate. These phenomena are demonstrated by the degradation of textile fibers from the Experimental Earthworks Project (Janaway 1996a). Figures 7.9 and 7.10 compare wool and linen buried in the chalk environments at Overton Down for 32 years. The linen is denatured to the point that there is little surviving morphology, whereas the wool retained some fiber structure. 

The development of methods and tests for preserving natural textile fibers is surveyed. The effect of the environment in which the textiles are stored or exposed, chemical, physical, and biological agents responsible for their degradation, and test methods for evaluating their performance and extent of damage are discussed. Emphasis is on cotton, wool, and silk, with selected references on other cellulosic fibers such as jute and linen. 

The influence of the environment on degradation of natural textile fibers is well documented. Most research has been directed towards assessing how well materials withstand weathering or outdoor exposure although there has been increased emphasis on preservation of textiles in storage, particularly as objects of art in museums. 

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