oryahalom
"Researches claim to have developed new "nano-papers" incorporating tiny cellulose fibers, which they allege give them the strength of cast iron".
In my humble opinion, there is one problem in the cited sentence, although I'm not sure whether it should be categorized as a "pronoun ambiguity" error.
Logically, in case no pronoun is used, the sentence can be rewritten as follow:
Researches claim to have developed new "nano-papers" incorporating tiny cellulose fibers, which researchers allege give "nano-papers"/cellulose fibers the strength of cast iron".In the same sentence, how can pronouns "they" and "them" refer to 2 different nouns? As far as I'm concerned, in this case, "they" and "them" must refer to only one particular noun.
Also, I guess "them" may refer to "nano-papers", because in case pronoun "them" refers to "tiny cellulose fibers", that pronoun should be changed to "themselves" instead ("fibers" plays the role of both subject and object of the clause).
Expert
DmitryFarber, please correct me if I'm wrong. Thank you.