Monday, September 18, 2006

Nalgene ≠ plastic

Last week, a bold pink note was posted the side of our tub for dirty plastic dishes that declared "Nalgene ≠ plastic" and also that "bottles and flasks ≠ cylinders and beakers". This is important because we were separating plastics from glassware so as to wash the former with a mild detergent and the latter with harsh ol' Sparkleen - sorting them correctly will economize on space and expensive Nalgene cleaning products. What the somewhat cryptic note was telling us was that PC ≠ PP (ie. Polycarbonate ≠ Polypropylene).

Polycarbonate (PC) is the strongest thermoplastic (meaning it can be heated to a melting point and reshaped). It is clear, autoclavable, and can handle high centrifugal forces. PC is composed of dihydric phenols joined through carbonate linkages. The linkages are subject to chemical reactions with bases and strong acids and can suffer hydrolytic attack during autoclaving. Nalgene flasks and media bottles are made from PC - this explains why they become foggy over time and why they require gentle detergents.

Polypropylene (PP) is translucent, autoclavable and has no known solvent. This sounds great, but a drawback is that polypropylene products are brittle at 0ºC and can crack or break if dropped.

An easy way to distinguish between products made from these two plastics is to look at transparency (PC products are transparent (see-through) whereas PP products are only translucent), check the bottom of the vessel for a PC or PP label, or (the geekiest way) stick them in water: PP is lighter than water whereas PC is heavier.


At 4:13 PM, Blogger Sally said...

ooo.. really? I always thought transparent is PP and translucent is PC... so I guess this is why I am just an undergrad and Andrew is a graduate! =P

At 5:09 PM, Blogger Heather Maughan said...

Thanks for the lesson in chemistry. Will you attach those molecular structures to the pink sign? That might help us distinguish between the two.

At 6:55 AM, Blogger Rosie Redfield said...

Major geekitude points!

At 9:24 PM, Blogger LindsayAWilson said...

Oh dear, I had been washing anything left in the basket in Spankleen. I thought Rosie had a gruge against cylinders.


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