Silk is fast drying which makes it highly practical when managing your laundry or just going about your day-to-day business. This difference makes silk smoother to the touch and shinier to the eye, with an altogether luxurious feel. The structure of silk depends on the fibre source, and this is usually either China or India.
Together, all of these properties contribute to the lustrous look, excellent drape, and luxurious feel of silk. Here are some common silk material types you might come across. Some of these fabrics can also be made of polyester or nylon as a more affordable alternative. Most arthropod species produce silks used for building structures to capture prey and protect their offspring against environmental hazards [ 2 ].
The most investigated categories that have piqued the greatest amount of interest are spider silk and dragline silk in particular, produced by major ampullate glands and the cocoon silk of Bombyx mori B. The ongoing evolutionary optimization of silks from silkworms and spiders exhibit outstanding mechanical properties, such as strength and extensibility, as well as toughness, which outperform most other natural and man-made silk fibers Table 1 [ 3 , 4 ].
Due to its smooth texture, luster and strength, silks from natural silkworms have been extensively used in apparel and fashion applications for thousands of years [ 5 ].
Silks from spiders have also been utilized throughout history, such as sutures and fishing equipment in ancient Greece and Australasia. In contrast petrochemical-based synthetic polymers commonly used today, such as polyethylene, which is formed by polymerization of ethylene at high temperature and pressure, or under the presence of some metal-based catalysis, B.
Due to current trends in exploration of natural biological materials and the demand for environmentally friendly green materials, investigation of the applications of silk fibers has steadily gained prominence.
Silk fibers are emerging as candidates for applications in even non-apparel areas due in part to recognition for their extraordinary mechanical properties, as well as their biocompatibility and biodegradability.
Currently, the promotion of silkworm as bio-factory to produce silk fibers fitting for innovative and advanced functional biological applications is a big trend. Compared to silkworm silks, the potential commercial applications for many spider silks are still extremely finite due to reasons such as difficulty of high-density spider farming, which is limited by the cannibalistic nature of most spiders. Schematic overview of different silk types produced by female orb-weaving spiders Araneae.
Each silk type highlighted in red is tailored for a specific purpose. Reprinted from Ref. Copyright , with permission from Elsevier. Comparison of mechanical properties of natural silks and other synthetic fibers [a]. Artificial spinning is the most promising method of promoting the application of silk fibers, as it can output sufficient man-made fibers cost-effectively and with specific tailored properties.
Reconstituted silk protein is derived from B. Recent advances in transgenic technology enable the high level expression of recombinant proteins. Spider silk proteins have been produced by other organisms so that recombinant spider silk protein might be suitable for creation of artificial silk threads or other applications. Host organisms include bacteria, yeasts, animal cells and plants [ 3 ].
In order to biomimic native silks, the reconstituted or recombinant proteins used to spin artificial silks should possess amino acid similar to the ones found in native sites for sequence and composition. However, the properties of synthetic silk fibers currently do not meet the standards of native silks yet, as the composition, hierarchical structure and production conditions of natural silks all reportedly affect their mechanical properties [ 11 ].
Consequently, a profound knowledge of the natural formation process, chemical composition, relationships of structure and properties of silk fibers seems therefor imperative. Thanks to recent developments in modern analytical techniques, significant progress has been made with respect to the structural characterization of silk.
These techniques can provide molecular information about silk, including microscopic methods atomic force microscopy AFM , scanning and transmission electron microscopy SEM and TEM , and scanning transmission x-ray microscopy STXM and synchrotron x-ray diffraction wide-angle x-ray diffraction WAXD and small-angle x-ray scattering SAXS combined with synchrotron radiation. Solid-state nuclear magnetic resonance SS-NMR is a powerful technique because it allows for the study of molecular structure and dynamics of semi-crystalline and amorphous materials.
Raman and FTIR spectroscopy can provide the dominant conformational contents of a fiber. Raman microspectroscopy can be used to determine quantitative parameters characterizing the molecular structure orientation and conformation, amino acid composition of micrometer-sized biological samples. Additionally, we will explore material morphologies and applications of these silk fibers. Various studies have suggested that there is a strong connection between the structures of silk fibers and their physical e.
An understanding of the structure-property relationship requires background knowledge of local structure, including the component and composition of silk fiber, the conformation and orientation of constitutive units with respect to the fiber, and so on.
In principle, the full range of properties of silk fibers can be calculated from their structural morphology and chemical composition.
On the macroscopic level, the morphological structure of B. The silk thread diameter varies across types and species.
For example, coating the two core brins of B. Examples of silk fibers produced by silkworms and spiders and a schematic illustration. Silk fibers are normally polyamino acid-based fibrous proteins. The results confirmed that silk fibers are composed of well-oriented bundles of nanofibrils. Generally, the coatings of silk fibers function as glue.
However, recent studies have provided evidences that the coating may act as a fungicidal or bactericidal agent [ 20 ]. It may also have a role in the complex spinning process. Studies have demonstrated the presence of microvoids for both silk fibers [ 21 , 22 ]. Microvoids are thought to develop during the final stages of the spinning process, in which viscous protein aqueous is stretched or loaded into the fibers.
As two major families of silk proteins, fibroin is the chief component of silkworm silk fiber, while spidroin also named spider fibroin is the analogue in spider silk fiber.
The B. The main proteinaceous constituents of spider dragline silk are typically two major ampullate spidroins, MaSp1 and MaSp2, which are estimated to range from kDa or larger [ 26 - 29 ]. A common feature of fibroins is the high content of alanine and glycine residues. Figure slightly modified with permission from Ref.
Copyright Wiley Periodicals, Inc. The primary sequence plays an important role in defining basic materials. Despite being quite different in their primary structure, B. Both have large central core of repeated modular units Figure 4 , flanked by nonrepetitive amino- NRN [ 31 , 32 ] and carboxy- NRC [ 29 ] terminal domains Figure 3.
The light chain of B. It plays only a marginal role in the fiber [ 33 ]. The organization of the repeating modular units can differ significantly, as seen in the sequences of different protein types.
As the major component of B. In MaSp1, the modular units mainly consist of a subset of the sequence motifs Ala n followed by several GGX motifs, with X representing a variable amino acid.
The modular units are repeated up to several hundred times in the central core of B. The highly conserved sequence of nonrepetitive amino- and carboxy- terminal domains are essential for fiber formation and expected to be of functional relevance [ 35 - 39 ].
Moreover, the analysis of the hydropathicity of these fibroins reveals a pair of hydrophobic and hydrophilic counterparts. The central region of the protein is mostly hydrophobic, while the nonrepetitive amino- and carboxy- terminal domains are more hydrophilic [ 40 ]. Typical amino acid sequences of repetitive core of B. The highly repetitive Gly-Ala n and Ala n sequence motifs are highlighted in red.
The primary structural motifs have a preferred secondary structure and give rise to structures higher up the hierarchy. NMR, circular dichroism CD , IR and Raman spectroscopy were usually used to examine the chemical, conformational, and orientational information of secondary structures for silk proteins [ 41 - 51 ]. Using the approach of Porter, and reducing the complex secondary structure of silk proteins into fractions of ordered and disordered material, they are roughly equivalent to crystalline and non-crystalline phase of silk proteins, respectively [ 55 , 56 ].
The first Raman spectrum of B. Therefore, it is widely accepted that the B. Drummy et al. Tussah silk: Silk made from wild silkworms is called tussah silk. Bombyx-mori silk: It is also known as mulberry silk which is produced by domesticated silkworm.
Reeled silk or Thrown silk: It is term for silk fibre that is unwound from the silkworm cocoon. Spun silk: Silk made from broken cocoon from which the moths have already emerged and short fibres.
Weighted silk: When yarns are prepared for weaving, the skeins of yarn are boiled in a soap solution to remove the natural silk gum or sericin. Pure silk: If the natural gum or sericin is removed from the silk and no further material is added to increase the weight of the fibre it is called pure silk. Silk Fibre Types According to cocoons and silkworms There are four major types of silk of commercial importance, obtained from different species of silkworms which in turn feed on a number of food plants.
These are: Mulberry Tasar Eri Muga Except mulberry, other varieties of silks are generally termed as non-mulberry silks. Mulberry The bulk of the commercial silk produced in the world comes from this variety and often silk generally refers to mulberry silk.
Tussah: Tasar Tussah is copperish colour. It is a finer variety of tasar generated by the silkworm, Antheraea proyeli J. These feeds on natural food plants of oak. Which is found in abundance in the sub-Himalayan belt of India. China is the major producer of oak tasar in the world.
This comes from another silkworm which is known as Antheraea pernyi. Oak is mainly used for furnishing, dress materials and sarees. Types of Silk Fibre. Bafta is a popular blend of tasar and cotton. Shawls and mufflers are also produced using a blend of oak tasar.
With other natural fibers like wool, cotton, etc. This silk can be styled into beautiful dresses, stoles and scarves. Tasar fabric can also be printed, hand-painted. Even embroidered into traditional sarees and beautiful dress-materials. Endi or Errandi, Eri is multivoltine silk spun from open-ended cocoons like other varieties of silk.
Eri silk is the product of the domesticated silkworm, Philosamia ricini. It feeds mainly on castor leaves. Ericulture is a household activity practiced mainly for protein rich pupae, a delicacy for the tribal.
While worms spin silk in the wild in parts of China, India, and Europe, wild silk is never available in large enough quantities to satisfy the needs of full-blown textile production. Cultivation of domesticated silk originated in China. One piece of archaeological evidence dates the use of silk textiles in China back to BC, and the ancient Chinese certainly used silk as early as BC. While historical records of the origin of silk manufacturing in China are largely lacking, Chinese legends credit Empress Leizu with the development of sericulture , which is the art of making silk.
In the early days of Chinese culture, only the nobility wore silk, but as Chinese civilization developed and became wealthier, commoners started wearing this soft and durable fabric as well.
Silk production in China eventually led to the development of prominent pre-industrial trade routes. The Silk Road stretched from China to Western Europe, and Chinese merchants traveled up and down this trade route to exchange silk for the commodities of distant nations.
For generations, the secrets of sericulture were the most prized and guarded pieces of knowledge of the Chinese nobility, but eventually, information on how to make refined silk spread to Korea and India during the first few centuries AD.
India, Thailand, and other Asian nations already had highly-developed sericulture processes at this point, but the Chinese method of making silk was considered to be superior. Based on limited legends and historical records, silk may have also been produced in the West during the distant past. Whatever the case may be, silk was highly prized by Westerners as far back as Roman times, and the popularity of this rare and mysterious substance only grew during the Medieval period.
By the 11th century AD, silk production was widespread throughout Europe. Many Italian city-states, such as Lucca, Venice, and Florence, were highly economically reliant on silk production during the Middle Ages, and the silk industry gradually spread to France and Spain.
King James I introduced silk production to the New World in the 17th century, and American states such as Connecticut and Massachusetts rapidly became hubs of silk production. World War II cut America off from Asian silk, and as a result, American corporations developed synthetic replacements such as nylon. While the silk industry has expanded greatly during the last century, the processes used to make this fabric are still largely the same as they were in the ancient world.
Once silkworm breeders have harvested silkworm cocoons, they usually expose them to high heat to prevent the mature worms from emerging. After the cocoons have been heated, silk producers carefully unravel the threads that the silkworms meticulously put into place. To do so, the silk cocoons may be boiled briefly to remove a small amount of the sericin in the cocoons, which is the glue-like substance that silkworms excrete to form their metamorphosis chambers.
Silkworms make cocoons out of one long strand of fiber, which means that a fully unraveled cocoon results in a single string of silk. To unravel a cocoon, a silk worker or an automated machine will brush the cocoon to find the loose end and load it through a porcelain eyelet onto a reel that unravels silk strand. As the silk strand loads onto the reel, it is automatically attached to another strand to make a continuous string.
The sericin in the silk strand helps the strands stick together. Next, silk producers twist these long strings together to make yarn. Silk producers may perform a variety of post-production processes to create silk yarn that has certain desired attributes, and then the silk yarn is put through a roller to make it more uniform.
0コメント