CUYAHOGA FALLS, Ohio—The silicone industry has gone a long way, even all the way to Mars, according to Oliver Franssen, global marketing director, elastomers/transportation for Momentive Performance Materials Inc.
Though the history of silicone is still relatively recent, it's made some great strides, he said in his presentation "The World Records of Silicones" at the recent International Silicone Conference held in Cuyahoga Falls.
After GE Chemist Eugene Rochow discovered the direct reaction process for making methylchlorosilanes in the early 1940s, it led to the development of applying silicones in our daily lives, he said. Silicone innovation has continued over a 75-year timeline, but time wasn't the measurement Franssen wanted to use.
"I want to invite you to look at this time axis on a whole different scale," he said. "We will talk about silicone applications in the distance to the human body."
Starting at a distance of -1 inch, Franssen began with silicones with the highest purity and intrinsic chemical stability compared to organic elastomers, with a baby pacifier.
"That's a really unique selling point of silicone elastomers," he said. "The inertness of the polymer and the fact that it is inorganic, it has a low absorption for UV and is therefore is more or less UV transparent. It is not attacked like natural rubber would be for baby pacifiers, so it does not need to be protected."
Silicone can make very soft materials without the risk of nitrous amines, which normally would not be healthy for the baby, Franssen said.
"That is the foundation of the big success of silicone elastomers in the medical industry," he said. "It is odorless and can comply with the USP standards, FDA and ISO standards."
Moving to a distance of 0 inches, silicone provides the highest permeability, making gas permeable contacts a possibility, he said.
"If I talk to somebody making tires about permeability, it is negative," he said. "By structure, silicone elastomers are highly, highly permeable to media. That can be fluid, that can be gaseous."
Silicone elastomers have high freedom of polymer chain motion and high solubility and diffusivity of penetrants. For an application like gas permeable contact lenses, the application calls for a product that has a high oxygen permeability, and "that is the reason for success of the silicone compounds for contact lenses," Franssen said.
Clarity and viscosity
With the highest transparency of all the elastomers, silicone elastomers do well at a distance of about an inch from the human body for items, such as underwater goggles, he said.
"There's nothing which can beat the silicone elastomers," he said. "Especially since 2008, when a new generation was brought to the market in terms of LSR with optical quality."
Polydimethylsiloxane polymers are highly transparent to visible light, making them a strong fit for applications requiring ultraclear elastomers and opening new opportunities for consumer goods and LED lights, Franssen said.
"Instead of tensile strengths and tear resistance and compression set, we now deal with a yellowing index, with Abbe number with chromatic aberration," he said.
Silicone elastomers boast the lowest hardness without plasticizer, so they work well at about 1.5 feet within arm's reach for items like the transparent sensor coupling pad for an automotive driver assistance camera, Franssen said.
"For plasticizer-free EPDMs, it's impossible to go 40 Shore A, but if you work with silicone rubber you can have no limit to the low end," he said.
The range of LSR hardness runs from about 5-90 Shore A, with substances of about 3-5 Shore A having "the consistency of pudding," he said.
Franssen borrowed an example from a fellow presenter at the event, Gabriel Geyne, application engineer for Sigmasoft Virtual Molding, to show off lowest viscosity for silicone, at about 2.5 feet. The part was a designer webbed wine bottle net, with thin material that still needed to keep enough strength to hold a bottle without dropping and breaking it.
Silicone has a very low viscosity with limited temperature dependency and excellent pumpability, he said.
"Viscosity of LSR is a factor two magnitudes lower than organic elastomers," Franssen said. "This is allowing you to make shear thinning, so it is getting even more liquid under stress, and has a very high flow length."