So, about the whole endocrine disruptors thing. What exactly is the chemical composition of various different types of plastics, and what leads some of them to have a greater propensity toward being an endocrine disruptor than others? First of all, let’s start out with the chemical composition of endocrine disruptors and the endocrine system itself.
Steroids are one of the primary signalling and controlling factor in the endocrine system. Steroids, as we know, have been extensively studied and the chemical structural composition of them is well known. Namely, the chemical diagrams of steroids are distinctively visually recognizable by their inclusion of hexagonal and pentagonal loop structures. Specifically, steroids are defined to include three four-element carbon rings and one five-element carbon ring.
20190204/https://en.wikipedia.org/wiki/Steroid
Now, let’s take a look at the chemical structure of a few known endocrine disruptors. Phthalates have a distinctive 6-element carbon ring structure within them. Although a phthalate isn’t strictly a steroid per-se in its chemical structure, we know that they do in fact chemically interact with the endocrine systemm in a disruptive way, and you can intuitively reason that part of that is due to their similarity in structure.
20190204/https://en.wikipedia.org/wiki/Phthalate
Now, don’t be surprised that Bisphenol A has an even more similar structure to a steroid, with two 6-element carbon rings. Bisphenol S is quite similar to Bisphenol A, also two two 6-element carbon rings. Yet, due to the subtle differences in the chemical structure of Bisphenol S, it is purportedly even more disruptive to the endocrine system than Bisphenol A.
20190204/https://en.wikipedia.org/wiki/Bisphenol_A
20190204/https://en.wikipedia.org/wiki/Bisphenol_S
Now, let’s take a look at the chemical structures of our plastics. To start, polyethylene, polypropylene, and polylactic acid do not contain 5-element or 6-element carbon rings. Furthermore, none of the intermediates used to produce polylactic acid contain 5-element or 6-element carbon rings. Acrylic (Poly(methyl methacrylate)) also does not contain 5-element or 6-element carbon rings, but be forewarned that additives are typically used with Acrylic.
20190204/https://en.wikipedia.org/wiki/Polyethylene
20190204/https://en.wikipedia.org/wiki/Polypropylene
20190204/https://en.wikipedia.org/wiki/Polylactic_acid
20190204/https://en.wikipedia.org/wiki/Acrylic_glass
20190204/https://en.wikipedia.org/wiki/Lactic_acid
20190204/https://en.wikipedia.org/wiki/Lactide
Polyethylene still has environmental caveats, though maybe this is sheerly due to the volume of disposable polyethylene products produced. Polyethylene outgasses the greenhouse gases methane and ethylene, especially low density polyethylene (LDPE), the flexible formulation suitable for plastic bags. These are not endocrine disruptors, though, and both essentially pose no risk to humans in very low quantities.
20190204/https://www.independent.co.uk/news/science/polythenes-story-the-accidental-birth-of-plastic-bags-800602.html
Let’s also overview some basic visual and structural properties of these fairly safe plastic chemicals while we’re at it. Low-density polyethylene (LDPE) and Acrylic are great for transparent plastics. PLA can be transparent. High-density polyethylene (HDPE) is translucent instead of transparent. Polypropylene has a crystalline structure that makes its pure form white, but it can be made translucent under certain formulations that might, for example, incorporate some polyethylene. Polyethylene is very vulnerable to degradation from UV light, and polypropylene is somewhat vulnerable. Polyethylene has a lower melting point around 120 degrees Celsius, but polypropylene, polylactic acid, and Acrylic have higher melting points around 160 degrees Celsius. All of these plastics are thermoplastics, so they are recyclable. So far, this all sounds pretty good for 3D printing, I must say.
Now, let’s venture over to the more dangerous side of affairs: the plastics known to contain or be able to readily transform into endocrine disruptors or be carcinogens.
Polycarbonate contains two 6-element carbon rings. In high temperatures and high humidity, polycarbonate readily transforms into Bisphenol A, a known endocrine disruptor. It’s no wonder then, that during 3D printing, the fumes from polycarbonate have been reported to cause quite the severe headaches, headaches that took several minutes away from exposure to resolve. Once endocrine disruptors are breathed in through airborne dust, they readily enter the bloodstream.
20190204/https://en.wikipedia.org/wiki/Polycarbonate
Polyurethane contains two 6-element carbon rings. The burning of polyurethane produces a variety of chemicals hazardous to human health, and polyurethane spray foam emits some hazardous gases during or after application.
Decomposition from fire can produce significant amounts of carbon monoxide and hydrogen cyanide, in addition to nitrogen oxides, isocyanates, and other toxic products.[41] Because of the flammability of the material, it has to be treated with flame retardants (at least in case of furniture), almost all of which are considered harmful.[42][43]
20190204/https://en.wikipedia.org/wiki/Polyurethane
Polyethylene terephthalate (PET) thermoplastic, due to the inclusion of phthalates, naturally contains endocrine disruptors.
20190204/https://en.wikipedia.org/wiki/Polyethylene_terephthalate
Polystryrene thermoplastic contains one 6-element carbon ring. It is suspected of being an endocrine disruptor, and its chemical precursor, styrene, is a known carcinogen under elevated exposure.
20190204/https://en.wikipedia.org/wiki/Polystyrene
20190204/https://en.wikipedia.org/wiki/Styrene
Acrylonitrile butadiene styrene (ABS) thermoplastic, due to the inclusion of styrene, contains 6-element carbon rings. Butadiene in particular is a known carcinogen and a suspected endocrine disruptor, even though it does not contain 6-element carbon rings.
20190204/https://en.wikipedia.org/wiki/Acrylonitrile_butadiene_styrene
Polycarbonate is a very tough plastic with high impact strength. Polycarbonate, polyethylene terephthalate, and polystyrene are transparent thermoplastics. ABS is an opaque thermoplastic. Polyurethane is a thermoset plastic, although there are thermoplastic formulations available. Polycarbonate is very vulnerable to degradation from UV light, and polyurethane and ABS are somewhat vulnerable.
Ouch! That’s the price you pay for the stronger plastics. You’re trading your safety from endocrine disruptors for increased material strength. For rigid plastics, there is a ready inventory of usable plastics that do not contain endocrine disruptors. However, many of the materials chosen for their synthetic rubber-like quality contain endocrine disruptors. Polyurethane, ABS, SBR (styrene butadiene), PVC. This is something will cover in a later blog article.
JJJ TODO LINK!
A word on epoxies. After construction, epoxies have properties similar to thermoset plastics. Bisphenol A and Bisphenol S are two epoxies cover that are known endocrine distruptors. So, are all epoxies bad? Well, checking out the Wikipedia article, it appears that in theory, the definition of epoxies is such that do not require the application of harmful chemicals. In practice, virtually all of the commonly used chemicals used to either formulate or work with epoxies pose some sort of high health hazard.
20190204/https://en.wikipedia.org/wiki/Epoxy
Also, many synthetic polyesters are known to be environmentally hazardous, if only for the fact that when used in clothing, the microplastics that wash off are not biodegradable. PLA, a biodegradable polyester thermoplastic, does not have this problem, but it is definitely more expensive than the alternatives. The following polyesters have 6-element carbon rings: polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, Vectran. In other words, the semi-aromatic and aromatic polyesters. Many of the Wikipedia articles of the various polyester formulations are lacking on the environmental, health, and safety impacts.
20190204/https://en.wikipedia.org/wiki/Polyester
One thing I didn’t comment very much about is a detailed study of the chemical breakdown and intermediates when the various plastics are burned. Many of the plastics are touted to release harmful chemicals when burned, even though their pristine form is relatively harmless. This is something that I would need to study further.
So, now you wonder. What are the chemicals involved in paper, cloth, and photographic film? Now, most of us know what this is quite readily off the top of our head. Cellulose, the main structural component of the cell wall of plants. Cellulose does not contain 6-element carbon rings: there are hydrogen oxygen molecules in the 6-element ring to break apart at. Cotton cloth is almost pure cellulose. Cellulose acetate is used as the film base of photographic film. What about fleece/wool? Fleece/wool is composed out of proteins, so it’s quite a bit different in chemistry. Polypeptides, amino acids, macromolecules, you name it. Nylon thermoplastic is made out of polyamides, which is a pretty simple carbon-based chemical structure with no 6-element or 5-element carbon rings. The gelatin emulsion of photographic film is gelatin, of course, which is derived from collagen, a protein that is the main structural element of animal skin, bones, etc.
20190204/https://en.wikipedia.org/wiki/Cellulose
20190204/https://en.wikipedia.org/wiki/Cotton#Fiber_properties
20190204/https://en.wikipedia.org/wiki/Cellulose_acetate
20190204/https://en.wikipedia.org/wiki/Wool
20190204/https://en.wikipedia.org/wiki/Protein
20190204/https://en.wikipedia.org/wiki/Amino_acid
20190204/https://en.wikipedia.org/wiki/Nylon
20190204/https://en.wikipedia.org/wiki/Polyamide
20190204/https://en.wikipedia.org/wiki/Gelatin
20190204/https://en.wikipedia.org/wiki/Collagen
Now, we covered a lot of biomolecules there, but what about lipids? Well, lipids don’t appear to have as wide of a use for structural materials, though they may be used for soaps and glues, we know. Go figure, lipids are fat, and you can’t do body-building with fat alone. However, the carbon chains of lipids can be conceivably broken down and reformulated into useful parts of plastic molecules, just as fat would get burned during exercise. Ha, funny.
20190204/https://en.wikipedia.org/wiki/Lipid