Natural materials fibers

Because of low prices and steadily rising performance on the part of technical and standard plastics, the application of natural fibers came to a near halt. The current critical discussion about preservation of natural resources and recycling led to a reflection about natural materials, the focus centuring on regrowing raw materials [2]. 

The feeling of a spider web may be unsettling, but a similar natural material has been used for centuries to make silk fabric that is prized for its smooth texture. Silkworms produce the silk fibers used to make clothing. They feast on mulberry leaves and convert the molecules from these leaves into silk, from which they spin cocoons. 

Silk fibers or monolayers of silk proteins have a number of potential biomedical applications. Biocompatibility tests have been carried out with scaffolds of fibers or solubilized silk proteins from the silkworm Bombyx mori (for review see Ref. [38]). Some biocompatibility problems have been reported, but this was probably due to contamination with residual sericin. More recent studies with well-defined silkworm silk fibers and films suggest that the core fibroin fibers show in vivo and in vivo biocompatibility that is comparable to other biomaterials, such as polyactic acid and collagen. Altmann et al. [39] showed that a silk-fiber matrix obtained from properly processed natural silkworm fibers is a suitable material for the attachment, expansion and differentiation of adult human progenitor bone marrow stromal cells. Also, the direct inflammatory potential of silkworm silk was studied using an in vitro system [40]. The authors claimed that their silk fibers were mostly immunologically inert in short and long term culture with murine macrophage cells. 

In 1923 one of Mark s superiors handed him a piece of hemp and asked that he study its molecular structure. Hemp was one of the many natural materials we now recognize as macromolecules which to then defied structural analysis. After much thought and work, also including X-ray studies, he concluded that the hemp fiber contained crystals. On examination, so also did cotton, wood and flax. 

While direct, this method is the most difficult experimentally due to the diminutive nature of fiber diameters and the uncertainty involved with contact angle measurements and hysteresis. The value i ) can also be measured on flat sheets of the fiber material but due to fabric finishes and different surface properties incurred during manufacture, the surface energetics of the sheet and fiber may be very dissimilar. Therefore, the value of co8i i was determined in the following manner from detergency data. The Kubelka-Munk Equation (12-13),... 

Most minerals occur in a variety of morphologies. Although it is not exhaustive, the list we recorded as occurring in fibrous form (Appendix 1) contains more than 350 entries, each with a reference. The format follows that proposed in Dana s System of Mineralogy, (Palache, et al., 1944), one of the standard references in the field. The names of fibrous minerals are alphabetically arranged within each chemical group that is, elements, oxides, hydroxides, carbonates, sulfates, phosphates, and so on. A similar, parallel system has been adopted for the list of synthetic fibers (Appendix 2). The list of synthetics includes glassy fibers produced from natural materials, as well as whiskers. 

Natural fibrous materials are identified somewhat by chance. For example, there are seven vanadate and seven vanadium oxysalt minerals on the list of fibrous minerals. These species are composed of a rare element, vanadium, but the fibrous samples may have attracted attention because they are often brightly colored. Vanadinite [Pb5(V04)3Cl] for example, is bright orange-red. Further, the list of natural mineral fibers we have compiled contains seventy-seven phosphate species. So many phosphates are listed because detailed descriptions of these mostly quite rare minerals were readily available (Nriagu and Moore, 1984). 

Fibrous Full of fibers, or formed of fibers (OED), with dimensions unspecified but implied, by comparison, to be similar to the natural materials thread and hair (see Fiber). Aggregates of any size of individual fibers may form relatively thick fibrous bundles, thus becoming visible to the naked eye. 

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. 

In view of the various level of structural organization, it is worthwhile to draw a comparison between natural silk fibers (silkworm silk and spider silk) and man-made silk-based materials. 

Fibers are used in a wide variety of applications and are composed of diverse materials. Natural animal and plant fibers, including wool, silk, cotton, hemp, ramie, flax, jute, and sisal, have long been used for clothing, baskets, fishing nets, and rope. Ropemaking has been an essential skill for thousands of years, a key element in the advancement of civilizations via the oceans. The natural mineral fiber asbestos is in the silicate family. We have encountered glass fibers previously in the text (see Chapter 7). 

Celluloid combines synthetic and natural materials. Its successor, Bakelite, is originally completely synthetic, composed of carbolic acid mixed with formaldehyde. Later forms of bakelite also included cellulose fiber and natural pigments. 

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. 

In much the same way, natural polymeric fibers like wool, cotton, silk, etc., are often touted as superior to anything that is man-made or synthetic. But is this fair There is no doubt that natural fibers have a unique set of properties that have withstood the test of time (e.g., it is difficult, but not impossible, to match silk s feel or cotton s ability to breathe ). On the other hand, consider Lycra , a completely synthetic fiber produced by DuPont (Figure 1-12) that has a truly amazing set of properties and is the major component of Spandex (a material that keeps string bikinis on ). Or consider the wrinkle-free polyester fibers used in clothing and the stain proof nylon and polyacrylonitrile polymers used in carpets. The point here is that polymers, be they natural" or synthetic, are all macromolecules but with different chemical structures. The challenge is to design polymers that have specific properties that can benefit mankind. 

We have seen that many useful synthetic materials are polymers. Thus it should not be surprising that a great many natural materials are also polymers starch, hair, silicate chains in soil and rocks, silk and cotton fibers, and the cellulose in woody plants, to name only a few. 

The world textile industry is one of the largest consumers of dyestuffs. An understanding of the chemistry of textile fibers is necessary to select an appropriate dye from each of the several dye classes so that the textile product requirements for proper shade, fastness, and economics are achieved. The properties of some of the more commercially important natural and synthetic fibers are briefly discussed in this section. The natural fibers may be from plant sources (such as cotton and flax), animal sources (such as wool and silk), or chemically modified natural materials (such as rayon and acetate fibers). The synthetic fibers include nylon, polyester, acrylics, polyolefins, and spindex. The various types of fiber along with the type of dye needed are summarized in Table 8.2. 

With a great number of substances available for use as his starting materials, the chemist has succeeded in making fibers and plastics which e for many purposes superior to natural materials. This field of chemistry, that of synthetic giant molecules, is still a new field, and we may look forward to further great progress in it in the coming years. 

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