Monday, November 28, 2011

Strawman Arguments

Everyone knows that you shouldn't compare apples to oranges, but then why can some people compare two items that are even more dissimilar and publish it as innovative research? That's what happened over the weekend, when researchers from the University of Sheffield compared silkworm silk to high density polyethylene (HDPE) (subscription required)(here is a open access review), and Surprise! Surprise! found that the silkworm is more efficient at polymer processing.

What a dreadful comparison. Chemically the two materials are entirely different - silk is a multiphase polyamide while the HDPE is a polyolefin. Moreover, the two materials aren't processed at the same temperatures, and yet this allows the researchers to win a strawman argument by showing that the silkworm is more energy efficient since it doesn't need heat and/or high shear to produce orientation in the silk.

Why didn't they compare a natural polyamide to a synthetic polyamide? Synthetic polyamides can be made at room temperature:
and you don't even have to look closely at the the synthetic strand to see that volumetric production rate for the synthetic polymer is more greater than for a silkworm.

A further fault in the comparison that the researchers made was that the silk is solvent spun (from water) while the HDPE used in this example was not (even though HDPE can be gel spun at room temperature).

While the mechanical properties of silkworm silk are different (tougher) than those of synthetic nylon, not necessarily better. Depending on what your design requirements are, tougher may not be desired at all.

And lastly, while silk does have a unique set of properties that scientists cannot yet match in one material, keep in mind that the silkworm was been developing their materials for millions of years while synthetic polymers have only been in existence for less than a century.

Why the researchers chose to overlook all these facts is beyond me. Surely they can't be that desperate for a publication that that they need to stoop this low for it.


3 comments:

milkshake said...

my guess is that they did few experiments carefully chosen to produce predetermined conclusions for a headline-grabbing publication with a minimum effort. You see, they have this Silk Studies lab there at the university and the UK research grant funding has been lousy for the last 10 years (and not about to improve any time soon). It does not hurt to remind everyone how awesome material is the natural silk and how economically significant and cutting-edge is the research they do on it.

Chris Holland said...

John, I'd be more than willing to pop you a copy of the research as given the comments in this blog it's pretty clear that you haven't had chance to read the original paper (which underwent a process called peer review).

In fact we addressed the vast majority of the commented shortcomings directly in the paper and upon reading it I'd hope to think you'd agree. However if we failed to communicate our findings and their correct context appropriately I'd be happy to follow up with an email conversation. Warmest regards Chris

Chris Holland said...

@ Milkshake, indeed it never hurts to remind people how impressive nature is, the difficulty is to show people precisely how much better she nature and that's the focus of this work. Furthermore by comparing natural and synthetic polymer systems we find that nature has plenty of tricks up her sleeves and potentially completely new classes of polymeric materials (which we refer to in the paper as aquametls).

@ John, I'd be more than willing to pop you a copy of the research as given the posting it's pretty clear that you haven't had chance to read the original paper (which underwent a process called peer review).

In fact we addressed the vast majority of the commented shortcomings directly in the paper and upon reading it I'd hope to think you'd agree.

However if you have any more queries as to why we did the research and what we believe the findings to be, I'd be more than happy to chat further over email. Warmest regards Chris