Reactions

Letters to the editor

Clarifying 3 articles

As I appreciate C&EN for its technical accuracy, I wanted to share some corrections that should provide important context for your readers:

“Reversible Polymer Chemistry Could Make a Truly Recyclable Plastic” (May 6, 2019, page 8). While I share a strong interest in vitrimers and recycling, I take issue with the implication that no existing plastics are “truly recyclable,” when poly(ethylene terephthalate) (PET) is depolymerized and repolymerized industrially to make recycled PET (to give just one example). Chemical recycling technologies have existed for a long time. Their practical implementation is limited because they tend to be slow, be energy intensive, or require harsh conditions to proceed. Specific to the piece in question, your readers are invited to take an equally thin piece of polyamide 6 and place it in a vial of concentrated HCl overnight—they will see a result more or less identical to what is shown in your article. This will work with any reasonably hygroscopic polyamide. Does that make conventional polyamides “truly recyclable” also?

“Epoxide Synthesis Goes Green Thanks to Electrochemistry” (May 6, 2019, page 7). Here, it is important to understand that, in general, epoxidation reactions do not produce high direct CO₂ emissions and require high temperatures and pressures; the production of ethylene oxide is the exception. Likewise, while the epoxidation of higher olefins under mild conditions has been reported before, it has yet to provide us with the means to address the outsize environmental footprint of ethylene oxide production. Indeed, the researchers who carried out the work described in this article make no such claims in their publication, which is focused on the epoxidation of higher olefins. What deserves the attention here is the novel electrochemical approach used, which I agree is quite promising. I look forward to future developments along these lines.

“Kevlar, the Tough Material Used in Body Armor and Sporting Gear, Now Comes in Aerogel Form” (May 13, 2019, page 11). These are some impressive materials! However, they are not aerogels. While the term is much abused in the literature, if we care about accuracy, an aerogel is, by definition, a product of supercritical drying. Materials produced by freeze-drying, as these materials were, are properly termed cryogels. Neither the structure nor the properties will be the same. This should not detract from the results reported, but it’s important to get this right.

Daniel Schmidt
Lowell, Massachusetts