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This answer to the question How to clean and preserve a cicada's molted exoskeleton (exuvia)? states:

The exuvia is made of cross-liked chitin, and will not decay. You don't need any special preservatives as all. If you need to get the mud off, just rinse it as you said, in soapy water, let it dry, and you are done. Simple.

Wikipedia's Chitin says only:

Chitin is a modified polysaccharide that contains nitrogen; it is synthesized from units of N-acetyl-D-glucosamine (to be precise, 2-(acetylamino)-2-deoxy-D-glucose). These units form covalent β-(1→4)-linkages (like the linkages between glucose units forming cellulose). Therefore, chitin may be described as cellulose with one hydroxyl group on each monomer replaced with an acetyl amine group. This allows for increased hydrogen bonding between adjacent polymers, giving the chitin-polymer matrix increased strength.

I'm not a chemist, but "increased hydrogen bonding between adjacent polymers" doesn't sound the same as cross-linked polymers. So I would like to ask for an answer based on sources other than Wikipedia:

Question: Is the chitin in an insect's exoskeleton cross-linked? If it depends on the type of insect, then the focus should be on "a cicada's molted exoskeleton (exuvia)" as discussed in the linked answer.

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  • $\begingroup$ I'm not sure I've tagged correctly. $\endgroup$ – uhoh Aug 18 at 11:13
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    $\begingroup$ Crossliking implies covalent bonds between adjacent polymer chains. I did a non-exhaustive search and it seems that there is no example of naturally crosslinked chitin. There seems to be a mention of a crosslinked protein, though. $\endgroup$ – WYSIWYG Aug 19 at 8:13
  • $\begingroup$ @WYSIWYG that's my understanding as well, thanks! $\endgroup$ – uhoh Aug 19 at 8:16
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much like cellulose, chitin strands are bonded to other strands by hydrogen bonds. here is a slide share with a breakdown of the structure.

It is crosslinked in the sense strands are linked to other strands in such a way that most enzymes cannot access it to break it down. this is the same thing that makes wood last untreated. In a strictly chemistry sense it is not a crosslinked polymer (which requires covalent or ionic bonding) but it still has crosslinking. Your hitting a difficulty in jargon.

source.

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  • $\begingroup$ Thanks for the clear and sourced answer, this clears things up! $\endgroup$ – uhoh Aug 20 at 0:27
  • $\begingroup$ I would say that the requirement for "covalent or ionic bonding" as in the Wikipedia article is just usage of an English term that has no intrinsic chemical definition. And the difference between an ionic bond and a hydrogen bond is only a matter of degree. If the hydrogen bonds are specific (which they are) I would say that it is perfectly valid to talk about chitin being "crosslinked by hydrogen bonds". However an article on preserving dead beasties is hardly attempting chemical. I think this question would have been better on SE Chemistry and voted to close on that basis. $\endgroup$ – David Aug 20 at 12:39
  • $\begingroup$ In polymer chemistry (and also in biochemistry) crosslinking always refers to covalent bonds (or very short covalently bonded chains) between two polymer chains. $\endgroup$ – WYSIWYG Aug 21 at 8:05

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