I recently bought myself a travel mug. It's a real sweet one from MEC, double-walled 18/8 stainless steel, carabiner clip, one of the ones with a sealing and sippy lid, grippy bottom. Pretty much the most agro looking mug I've ever seen, let alone owned. It was purchased to replace by last travel mug, which I think lasted me all of a month. I'm not sure how, but I seem to lose travel mugs pretty regularly, despite my best efforts to keep them around.

And so I started to wonder... Is there really any point in me owning a travel mug? If they seem to evaporate faster than the hot black liquid inside, am I really doing the environment a favour by reusing? Am I just better off using a disposable cup, since that's all my $20 mugs ever turn out to be? I thought I'd look into it.

I managed to find some pretty good data on paper and polystyrene cups from Dr. Hocking at UVic. Everything was reduced to nice easy to read columns, from which I extracted the desired data in order to put them in a more confusing format for you, dear reader.

Paper:
So it takes, on average, 66.1 kJ of energy to make one gram of coated paper. Given a paper cup's mass of ~8.3 grams, we're talking about: 66.1 kJ/g x 8.3 g/cup = 549 kJ/cup... That's actually quite a bit, considering that the average human consumes 8000 kJ of energy a day to stay alive.

Polystyrene:
Producing PS takes about 104.2 kJ/g, more than the paper. The average polystyrene cup, however, requires much less material, having a mass of only 1.9 g/cup. This gives us 104.2 kJ/g x 1.9 g/cup = 198 kJ/cup. That's considerably less than the paper cup.

Stainless Steel:
Okay, so I know there are other types of travel mugs, but given the recent concerns of carcinogens in plastic ones, and the fact that I'm addicted to the sexy ball-burnished appearance of chromium-laden iron, we're only going to look at the stainless mug.

This data was a bit trickier to assemble. I found the masses for small travel mugs, but a significant portion of the mug is nylon (lid, handle, et c.). So I ballparked the mug to be 15% nylon by mass.

Now the energy intensity data I found for the stainless was not quite full-cost accounting. It factors in the coking, ore separation, mixing and hot rolling of the components, but does not include the extraction costs. A fully random uneducated fudge factor of 15% was added for scooping and piling and miscellaneous processing of the ore (actually, my favourite number is just 15% --of anything).

Now, because all the steel data were American, they were all in BTUs per imperial ton . Does anyone else know what a BTU is? Answer: Who cares, as long as it equals 1 055.05585 Joules.

This gives us (780 x 10^6) BTU/ton x 1.15 fudge factor = (897 x 10^6) BTU/ton

(897 x 10^6) BTU/ton x 1 055 J/BTU = 946335 x 10^6 J/ton = (946.335 x 10^6) kJ/ton

Now, again we've got this damned yankee unit of a 'ton' which we have to make into a tonne to be of any use to us at all.

(946.335 x 10^6) kJ/ton x 1.102 tons/t = (1 042.86 x 10^6) kJ/t

Now we've just got to make the tonnes into grams.


(1 042.86 x 10^6) kJ/t x 10^-6 t/g = 1 042.86 kJ/g


The energy intensity of the nylon component is 145.5 kJ/g.

Bear with me folks, we're almost there...

A 300g stainless mug I decided has 85% steel (300g x 0.85 = 255g), and 15% nylon (300g - 255g = 45g).

1 042.86kJ/g x 255g = 265929 kJ/cup(SS)

145.5 kJ/g x 45g = 6547.5 kJ/cup(N)

Total = 265929 kJ/cup(SS) + 6547.5 kJ/cup(N) = 272476.5 kJ/cup!

So the final tally is:

Paper: 549 kJ/cup
Polystyrene: 198 kJ/cup
Stainless Steel: 272476.5 kJ/cup

So the number of times you have to reuse a stainless steel mug is:
Vs. Paper: 496 times
Vs. Polystyrene: 1376 times

Number of times I used my last travel mug: ~20 times.

I really hope that the person who found my travel mug uses it a many, many times... until (s)he loses it. : )

Have a great day!

-Neil A.


--
Fancy cutting down all those beautiful trees...to make pulp for those bloody newspapers, and calling it civilisation...
-Sir Winston Churchill