Materials Girl

Guess who’s sitting on their couch, happy as a pig in slop, watching How It’s Made? What, you too? Though I enjoy pliers and clogs as much as the next person, it’s the textiles I love. Complements of the Science Channel I bring you: synthetic leather production. 

Photo from the FIFA factory

The majority of pleather is comprised of a petroleum based plasticizer and powdered vinyl, also included in the mix is a flame retardant solution. This polymer pancake batter is then piped into a tub full of coloring agents. Where did you think hot pink pleather came from? The legging stork? In order to apply texture to the surface the now brilliantly (or modestly, no judgment) colored goo is spread onto a roll of textured paper, this creates a thin top layer and provides stability to the liquid mix for further processing. After being heat set the now dry polymer mix is covered with another layer called the “foam” and heads back into the oven. With the application of heat the second layer expands, adding body. A fabric backing (which looked like a fine jersey knit) is adhered to the back, further increaseing the durability of the leather. Print treatments and a protective coating finish the production.

Cool stuff about pleather: It you light it on fire (don’t do this at home) it will self extinguish in 2 seconds! Also, even after processing it retains its thermoplastic properties, so it can be vacuum formed, wow.

Remember a paragraph ago when I mentioned that a hefty amount of pleather is comprised of plasticizer? Plasticizers are used to lower the glass transition temperature of a polymer, keeping it soft and pliable. The vacuum forming that is possible with pleather make it the perfect choice for automotive interiors, dash boards, door panels and so on. As a car gets older you often see cracks begin to appear in the dash, after long enough the plasticizers evaporate, and the brittle nature of the main polymer is revealed. What about when a car is new, and the dash is shiny and beautiful? The parts are still full of plasticizer, and that’s the source of that “new car” smell.

Remember Indiana Jones and The Temple of Doom? Remember the snake pit? Good. You’re half way to understanding a fancy polymer chemistry concept.

Polymers are what we like to call Macromolecules, meaning simply that they are really big. To compare: if a water molecule were the size of a nickel, a polyethylene molecule would be 1/4 of a mile long. Back to Indiana Jones, so it’s a nice warm day in the snake pit and the snakes are wiggling happily to and fro, over and under, in a giant swirly spaghetti blob. Now you decide to drive your Land Rover (so British) through this snake room, and what do the snakes do? They slither out of the way, minimal dead snakes, maximum driving efficiency. Now what about a cold day in Egypt? (un-likely but necessary for this example) The snakes are moving very little now, stacked and entangled with each other. Here comes the Land Rover again, and things get messy this time around. (A shout out to Macrogalleria for this metaphor)

This is the exact (ish) way that polymers function, just think of all those snakes as long molecular chains. When they get cold, below their Glass Transition Temperature (Tg), they will break. Ever left a plastic bucket outside overnight in winter? Enough said. Ever put a rubber ball into liquid nitrogen? Do it. 

Glass transition isn’t just for breaking stuff, it’s also very useful for imparting desirable properties to the polymer products in everyday life. A rubber band is only functional when flexible, and above its Tg. While those clear plastic wine glasses, the ones that always break, are below their Tg. The many states of semi-crytaline polymers, bringing variety and functionality to plastics all around you.