1.3 Text Natural protein fibres
Natural protein fibres such as wool and silk are obtained from animal hairs and animal secretions.All of these fibres are composed of protein in which the repeated unit is amino acid.The amino acids are linked to each other by the peptide bond（—CO—NH—）to form the protein polymer.Some of man-made fibres are also made from amino acids，but only animal fibres are the natural protein fibre.Natural protein fibres have higher moisture regain and warmth than natural cellulosic fibres.Natural protein fibres have good resiliency and good elastic recovery but have poor resistance to alkalis.[1]
1.Wool
In the category of animal hair fibres，wool is the most important fibre and produced in the largest amount；other animal hair fibres such as mohair，cashmere and vicuna are only produced on a small scale.Wool is the fur-like covering of sheep that are raised in many countries around the world.It is obtained by shearing the fibrous covering from the sheep.The shorn-off wool is dirty and about 50% of its weight consists of natural and other impurities such as grease，suint，sand，dirt，vegetable matter，etc.So the raw wool should be treated through a series of processes including sorting，scouring and carbonization before it is used in spinning.The ultimate wool quality relating to the fineness，length，physical strength，handle，luster，absorbency，etc.，depends on many factors including the processes mentioned above.It is also affected by the species of sheep，climatic condition under which the animal is raised，the health of the animal，and so on.[2]Major varieties of wool come from Merino，Leiester，Sussex and other breeds of sheep.Different species of sheep produce different types of wool in fibre length，diameter and other characteristics.Generally wool fibres are 1.5-5.0 inch in length and 14-40 μm in width.Wool fibres are roughly oval in cross-section and grow in a more or less wavy form with a certain amount of twist.The finer the wool，the more the crimp.[3] The morphological structure of wool fibre can be divided into three layers：the scaly covering layer（cuticle），the fibrillar layer（cortex）and medullary layer（medulla）.The cuticle controls the rate of diffusion of dyes and other chemicals onto the fibre.The cortex，however，controls the bulk properties of wool and has a greater receptivity to certain dyes.In the center of the wool is the medulla.
Chemically，the most important component in wool is keratin that is a complex protein and composed of 16 to 18 different amino acids.Keratin is amphoteric in nature.So wool can be dyed with acid or reactive dyes.
According to their fineness and length，wool can be divided into four types：fine wool，long wool，medium wool and carpet wool.Fine wools are very fine and soft and have good elasticity.They are used to spin worsted yarns and to make high-quality textiles such as uniform and jacket.Long wools are coarse，strong but long.They are mainly used to spin woollen yarns for coarse tweed，serge，blanket and overcoating fabrics.Medium wools fall between fine and long wools in fineness and length.They are used for fine tweed，serge，overcoatings，etc.Carpet wools have low spinnability and mainly used in the manufacture of carpet，rugs and upholstery fabrics.
2.Silk
Silk is produced by silkworms that are the larvae of a moth known as Bombyx mori.When the silkworm is ready to begin its transformation into a moth，it spins a cocoon around its body by extruding the content of the two silk glands from two tiny holes in its mouth.The two filaments solidify on coming in contact with air and form a composite thread.Silk filament is retrieved by treating the cocoon in hot water baths before the moth eats its way out.The hot water kills the moth and removes the wax inherent in the fibre.Under this condition，the silk fibre can be unwound from the cocoon.The process of unwinding the silk filament from the cocoon is known as reeling.In order to prevent silk yarn from breaking up in weaving process，the silk filaments are usually produced in the form of yarn by combining reeled strands from several cocoons together by giving a certain twist to hold them and the gum existing on silk helps to hold the strands together.[4] The product is called reeled silk that is a continuous filament maybe as long as three kilometers.There are some silk waste，such as broken cocoon，the beginnings and ends of the cocoon filament that are of inferior quality，which resulted from the various stages of processing.The silk waste can be used in the manufacture of spun silk that is a short length fibre like cotton and is spun into yarn on the cotton system.
Raw silk is composed of two proteins：fibroin and sericin.Fibroin is the actual fibre protein.Sericin is the gummy substance and holds the filament together.The average composition of raw silk is 70%-75% fibroin，20%-25% sericin，2%-3% waxy substances and 1%-1.7% mineral matter.Sericin is amorphous and dissolves in hot soap solution.Fibroin is the form of a filament thread and dissolves in 5% sodium hydroxide solution at boiling point.The chemical composition of fibroin and sericin is shown in table 1-3.
Table 1-3 Amino add compositions of fibroin and sericin
Both of fibroin and sericin are built up of 16-18 amino acids，out of which only glycine，alanine，serine and tyrosine make up the largest part of the silk fibre，and the remaining amino acids containing bulky side groups are not significant.Fibroin contains only a minimal amount of amino acids as side chain.The low number of large side groups enables the protein molecules to be densely packed.The degree of crystallinity of silk is about 65%-70%.The degree of polymerization of silk fibroin is uncertain，with DP of 300 to 3000 having been measured in different solvents.[5] The isoelectric point of silk is about 5.
Silk fibres are translucent with some irregularity in diameter along the fibre.They have smooth surface and a distinctive triangular cross-sectional dimension，so silk fibres have a lustrous appearance.Silk has high tenacity and relatively good moisture regain.It is warm and pleasant to touch and comfortable to wear.It is dyeable with a variety of dyes.It also has the ability to adsorb metallic salts，which can be used in the manufacture of the specific weighted silk goods.So silk has excellent wearing performances and is essentially used in luxury articles，usually associated with high fashion.
New words
1.secretion[si'kri:∫ən]n.分泌物，分泌
2.vicuna[vi'kju:nə]n.驼马，驼马绒，驼马毛织品
3.suint[swint]n.羊毛脂汗
4.sorting['sɔ:tiŋ]n.分类，分级，挑选
5.carbonization[,kɑ:bənai'zei∫ən]n.碳化（作用），炭化（作用），碳化物
6.Merino[mə'ri:nəu]n.美利奴绵羊，美利奴羊毛，美利奴毛织物
7.Leiester[li:estə]n.雷伊斯特绵羊，雷伊斯特羊毛
8.Sussex['sʌsiks]n.苏塞克斯绵羊，苏塞克斯羊毛
9.twist[twist]n.捻度，经纱，缝纫丝线 v.加捻
10.cortex['kɔ:teks]n.皮层，皮质；树皮
11.medullary[me'dʌləri]adj.骨髓的，髓质的
12.medulla[me'dʌlə]n.骨髓
13.keratin['kerətin]n.角蛋白
14.overcoating['əuvəkəutiŋ]n.大衣料，外套料
15.spinnability['spinə'biliti]n.可纺性
16.cocoon[kə'ku:n]n.茧
17.gland[ɡlænd]n.腺
18.retrieve[ri'tri:v]v.重新得到
19.unwound['ʌn'waund]adj.未卷绕的，未加捻的，松散的 v.解舒
20.reeling[ri:liŋ]n.摇纱，缫丝，络丝
21.strand[strænd]n.绳，线中的一股，单纱
22.fibroin['faibrəuin]n.丝心蛋白，丝素
23.sericin['serisin]n.丝胶
24.glycine['ɡlaisi:n]n.氨基乙酸，糖胶
25.alanine['ælə,ni:n]n.丙氨酸
26.serine['seri:n]n.丝氨酸
27.tyrosine['tirəsi:n]n.酪氨酸
28.tenacity[ti'næsitil]n.韧性，韧度，强度
Phrases and expressions
1.amino acid 氨基酸
2.peptide bond 肽键
3.moisture regain 回潮率，回湿率
4.elastic recovery 弹性回复
5.worsted yarn 精纺毛纱
6.woolen yarn 粗纺毛纱
7.Bombyx mori 中国桑蚕
8.reeled silk 绞丝
9.spun silk 绢丝
10.isoelectric point 等电点
11.cross-sectional 横截面的，横切面的
12.wearing performance 服用性能
Notes
[1] Natural protein fibres have higher moisture regain and warmth than natural cellulosic fibres.Natural protein fibres have good resiliency and good elastic recovery but have poor resistance to alkalis.
天然蛋白质纤维比天然纤维素纤维的回潮率和保暖性高。此外，天然蛋白质纤维有良好的弹性和弹性回复，但其耐碱性较差。
[2] The ultimate wool quality relating to the fineness，length，physical strength，handle，luster，absorbency，etc.，depends on many factors including the processes mentioned above.It is also affected by the species of sheep，climatic condition under which the animal is raised，the health of the animal，and so on.
羊毛最终的质量如细度、长度、机械强度、手感、光泽、吸水性等取决于许多因素，包括上面提到的加工工艺。同时也受羊的品种、饲养地的气候条件、动物的健康状况等因素的影响。
[3] Wool fibres are ronghly oval in cross-section and grow in a more or less wary form with a certain amount of twist.The finer the wool，the more the crimp.
羊毛纤维的横切面近似椭圆形，生长过程中形成或多或少的卷曲，带一定捻度，越细越卷曲。同时，羊毛的质量越高，卷曲度越高。
[4] In order to prevent silk yarn from breaking up in weaving process，the silk filaments are usually produced in the form of yarn by combining reeled strands from several cocoons together by giving a certain twist to hold them and the gum existing on silk helps to hold the strands together.
为了防止蚕丝在织造过程中断裂，蚕丝通常以纱的形式生产，即几个蚕茧的单丝通过给予一定的捻度而结合在一起，并通过丝上保留的胶质物使这些单丝结合在一起。
这里，“the silk filaments are produced in the form of yarn by combining reeled strands from several cocoons together by giving a certain twist to hold them”与“the gum existing on silk helps to hold the strands together”为并列句结构。后一句说明蚕丝上的丝胶对并丝也有作用。
[5] The degree of crystallinity of silk is about 65%-70%.The degree of polymerization of silk fibroin is uncertain，with DP of 300 to 3000 having been measured in different solvents.
蚕丝的结晶度大约是65%～70%。丝素的聚合度是不确定的，在不同的溶剂中测定的聚合度从300到3000都有。
这里，“DP”是“degree of polymerization”的缩写。
Exercises
Ⅰ.Answer the following questions.
1.Why should the raw wool be treated before spinning？And how to treat？
2.What factors does the ultimate wool quality rely on？
3.What types of wools can be divided into according to their fineness and length？
4.How do we produce silks？
5.What is the composition of raw silk？
Ⅱ.Translate the following sentences into Chinese.
1.The amino acids are linked to each other by the peptide bond（—CO—NH—）to form the protein polymer.
2.The shorn-off wool is dirty and about 50% of its weight consists of natural and other impurities such as grease，suint，sand，dirt，vegetable matter，etc.
3.The morphological structure of wool fibre can be divided into three layers：the scaly covering layer（cuticle），the fibrillar layer（cortex）and medullary layer（medulla）.
4.Medium wools fall between fine and long wools in fineness and length.They are used for fine tweed，serge，overcoatings，etc.
5.When the silkworm is ready to begin its transformation into a moth，it spins a cocoon around its body by extruding the content of the two silk glands from two tiny holes in its mouth.
6.They have smooth surface and a distinctive triangular cross-sectional dimension，so silk fibres have a lustrous appearance.
Reading material Wool farming
In large wool-producing countries，sheep are usually rounded up towards the end of spring in sheep stations and prepared for shearing.Animals may be washed a couple of days before shearing to reduce the dirt and grease present on the wool.They are then segregated according to their age，sex and type，as each class would produce a different quality of wool，and crowded into small pens where they are effectively forced to sweat，which will soften the wax on their skin，making it easier to remove the fibres by shearing.They are pulled out of the pen one by one and sheared using mechanical or，more usually，electrical shears.A skilled shearer will take about two and a half minutes to shear a sheep.Once the shearing is complete，the animal is allowed to return to the open.
The wool is removed in one piece because grease and entanglement hold it together.This is now referred to as a fleece.The fleece is tidied up and visible bits of dirt and extra-short fibres are removed.Before it is sold，wool classing is carried out by professional assessors who examine the animals prior to shearing with respect to their health，living condition，age and breed.The shornoff wool or fleece is then appropriately classed according to fibre length，fineness，fibre character e.g.luster and overall condition-dirt and grease content.
The sale is carried out either by direct transaction or，more traditionally，by public auction.