Theoretical Comparison Between Nylon and Silk

Nylon is a linear polymer that contains the amide bonds CONH (Tetsuya et al. 1998). Natural polymers, such as protein, also have amide groups in their molecular structure. However, nylon with the exception of nylon-1, is resistant against proteolytic enzymes, whereas protein is easily hydrolyzed by these enzymes (Tetsuya et al. 1998). Nylon has the same structure as silk but different behaviors in the degradation process. One is degradable, but the other one is non-degradable .

Silk and Nylon 6,6 are considered to be twin polymers because both of them have a similar structure, but these twins have different behaviors in the decomposition process. Nylon was the result of research directed by Wallace Hume Carothers at du Pont. Nylon gained rapid attention for use in stockings and in making parachutes (Katz 1981).

To find the problem the whole pathway of producing nylon (Crude oil —> Naphtha —> Benzene —» hexamethylene diamine —> Adipic acid —» Nylon 6,6) needs supervision.

Nylon 6,6 is the most commercially successful polyamide and has been widely used for a long term. One of the most popular topics is the relationship between the microstructure of nylon and its twin polymer (silk), because the knowledge about it is very important for controlling the physical and mechanical performance. (Lu et al. 2004; Ramesh 1994; Keller 1994)

As it is shown in the whole pathway from crude oil to plastic, nylon 6,6 is synthesized by reacting adipic acid with hexamethylene diamine.

Nylons (polyamides) have the characteristics of amide groups in the chain, which can form hydrogen bond with each other.

H-bonds connect neighboring chain segments and form an extended planar sheet such that NH groups are able to form strong hydrogen bonds (H-bonds) with the CO group, which causes a crystal structure of nylon. The intermolecular contains the H-bonds. The formation of the extended sheets dominates the structure.

As shown in Figure 9.27, nylon has a symmetrical structure with the same monomers in the chain. This is common in most synthetic polymers. In the whole process, from crude oil to nylon (and many other oil-based-polymers), large molecules (macromolecules) are broken down into small molecules that build the body of future polymers. This is a linearized process, which is rare in nature. Since everything in nature is non-linear and consequently sustainable, o o p II II

-f o—oh2—CH2—OH2—E::H2— C—NH—CH2—CH2—CH2—CH2 —CH2—CH2—NH^

Six carbon atoms Six carbon atoms o

Adipic acid Hexamettiylene diamine o h

"N

Nylon 6,6

Figure 9.28 Nylon synthesis (Website 14).

-f-c—ch2—ch2—ch2—ch2—c—nh—ch2—ch2—ch2—ch2— ch2—ch2—nh^

Amide group

Figure 9.29 Amide group in nylon (Website 14).

Figure 9.29 Amide group in nylon (Website 14).

most synthetic processes disagree with natural processes (Khan et al. 2005).

At first look at the silk chemical structure, it seems that nylon and silk have exactly the same structure. However, one is degrad-able and harmless, and the other is non-degradable and resistant to decomposition process. So, where is the point that makes these two materials different?

From the structure of silk (Figure 9.31), it can be seen that it has four, five, or six carbons between amide units. Nature acts much more economical by using only one carbon between amide groups (website 13). Nature substitutes this carbon with several different functional segments and groups (Website 13). In other words, in synthetic production the same groups of molecules are used, but nature uses diverse groups for building a polymer. In fact, this difference is apparent not only between silk and nylon but also in most polymers that have been imitated from the nature.

Nature uses diverse groups of monomers for a polymer like silk, and, more importantly, there are different kinds of silk in nature, such as silks produced by spiders, for which little study has been done. The amino acid sequence repeats in spider fibroins, but each

/ \ /

H-C-R

H--C

-R

H

O, 23

\

/

\

C =

:0-

- -H-

-N

c=o

/

\

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H-N

C:

=o-

- -H-

-N

\

/

\

H-C-

-R-

- - R

-C-

-H

H-C-R

/

\

/

o=c

N-

-H-

- -0

= C

\

/

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N-

-H-

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= C

N-H

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R-C-H

R-C

-H

R

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:0-

--H-

-N

c=o

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-f-C — CH2—CH2—CH2—CH2—C — NH — CH2—CH2—CH2—CH2 —CH2—CH2 —NH^

_[_ CH—C—C -]- This is nature's poiyamide. This is a synthetic polyamide,

| | " Nylon 6,6. In nature, each repeat unit has a specific and

R H different R group. The nature of the R groups and the order in which they come can give infinitely variable properties. How's that for tailored microstructure! The synthetic grows dull in comparison, each repeat unit exactly the same. How feeble are we.

Figure 9.32 Differences between natural silk and synthetic silk (nylon) (Website 13).

of the seven glands' produced proteins has a unique amino acid composition (Anderson 1970). The compositions of most spider silks are similar to those of the textile silk produced by the silk moth B. mori. Here is how we can understand how nature produces silk and how weak synthetic processes are in imitating it:

"B. mori fibroin is known to contain multiple repeats of a hexa-peptide and the hexapeptide GAG AGS occurs in blocks of 8-10 repeats, separated by another repeating motif that is more variable. These two large sequence blocks repeat four or five times between a small, approximately 30 residue, section of non-repetitive sequence called the 'amorphous domain.' Thus, B. mori fibroin contains a preponderance of long crystal forming blocks, which establishes a strong potential for crystal formation, and this probably accounts for the high crystal content of B. mori silk." (Gosline et al. 2002, 3299; Mita et al. 1994)

This example illustrates the complexity and diversity of silk in the polymer world compared to synthetic silks (nylons), which are simple and repeatable.

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Responses

  • duenna
    What is the different between silk and niron.?
    2 years ago
  • RYLEY
    What do the structures of nylon and silk have in common?
    2 years ago
  • fausto sabbatini
    Are the properties of Nylon similar to that of silk?
    1 year ago
  • jennifer
    What is difference between nylon and silk?
    1 year ago
  • abbie
    Why is nylon referred to as artificial silk?
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  • semhar tewolde
    What do the structures of nylon and silk have in commo?
    1 year ago
  • Elisa
    What do nylon and silk have in common structurally?
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  • ayesha
    What do structes of nylon and silk have in common chemistry?
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  • Victoria
    How do the structures of silk and nylon compare?
    1 year ago
  • Massawa
    What is the difference between nylon stockings and silk stockings?
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