Why does silk have lustre and cotton dull in appearance inspite of both being natural fiber?

Question

Why does silk have lustre and cotton dull in appearance inspite of both being natural fiber?

Answer 1

Silk only has luster when processed.  Raw silk looks like rough cotton, I have a raw silk skirt.

Answer 2

Silk is made by the insects as two long, fine strands of protein bound together by a gummy protein. In the raw state this gum is not removed so raw silk, called tussah, lacks the sheen and creamy color of refined silk. The raw silk is a slightly darker yellowish tan from the gum. Once this is washed out the fibroin filaments reveal their smooth surface and reflect light to produce the luster and soft drape.

Fibroin is the silk filament protein – The fiber is not a simple repeat of two or three amino acids it is a complex sequence containing nearly 20 amino acid residues in it. The fibroin fiber's structure is glassy and naturally reflective. SerIcin is the gummy protein that is washed out, recovered and used in other ways.

http://209.85.173.104/search?q=cache:SAP...

http://faculty.washington.edu/yagerp/sil...

http://www.sciencedirect.com/science?_ob...

Cotton must be mercerized or treated to produce luster it is not inherent in the fiber. Cotton is a rod of cellulose that dries into a coiling ribbon when the boll opens and the water evaporates. To provide the soft shine the fiber is treated with alkalies while being pulled taut. This make the fiber return to a round shape and straightens it so it reflects light well. The basic recipe is to hold cotton with a specific tension for ten minutes in a bath of 21%-23% caustic soda (NaOH), at room temperature to alter the cellulose's shape enough to acquire a lustrous surface and reflect light well.

The longer the fiber the fewer ends fluff out after the thread is twisted together. These ends make the thread less smooth. The smoother the surface the more light is reflected so sometimes when the cotton thread is spun it is further treated with heat to remove the fine surface fuzzy ends that stick out to improve shine.

http://fiberarts.org/design/articles/mer...

Cellulose is not protein it is actually glucose sugar molecules  polymerized into long chains. Whether made into fabric or paper it must be treated to become glossy. This is why glossy paper is more expensive.

http://www.patentstorm.us/patents/531867...

Answer 3

Silk doesn't have cellulose and cotton has cellulose. Also silk is produced by silk worms which add some of their body proteins during their production.

Answer 4

Both are natural fibres but there is a basic difference in the chemical composition of both the fibres. Silk fibre (obtained from silk worms) is a  protein and cotton (from cotton plant) is made up of cellulose. Due to the basic difference in the chemical compostion there is a difference in the texture.

Answer 5

silk thread is produced from silk worms which has luster

whereas cotton is an agricultural crop and the thread is processed through mill process in various stages. Cotton is more absorbent than silk and looses its luster during thread making process. Cotton needs humid climate whereas silk worms are reared in conditional atmosphere.

Hence silk has a better luster than cotton.