I use this blog as a soap box to preach (ahem... to talk :-) about subjects that interest me.

Tuesday, July 27, 2010

Toilet paper woes

Paper is manufactured by pressing together moist fibres and then drying them. The quality of the paper largely depends on the nature and length of the fibres that are used. In general, better and stronger papers are made with longer fibres. And that is why it is difficult to make good quality recycled papers: the recycling process breaks down the fibres, thereby automatically reducing the tensile strength of the resulting paper. Not surprisingly, given its use, toilet paper is close to the... ahem... bottom of the quality scale. The problem with toilet paper is that it has to be cheap while being strong enough to prevent fingers from “breaking through”. An unpleasant experience that most of us have had to endure at one time or another. Ideally, toilet paper should also be soft rather than scratchy or, worse, slippery. To top it off, toilet paper should also readily dissolve in water in order to minimise the risk of clogging the sewers. And what about the presence of possible allergens? And the colour? And the smell? The list of requirements imposed on such a humble product is almost endless. Modern toilet paper also has the added feature of being perforated, to allow for an easy separation of segments. It doesn’t always work as it should, but it is of great help.

When I was a child, my mother bought rolls of toilet paper with jokes printed on it. Unfortunately, after a trial period, we had to switch back to unprinted paper when it turned out that we all unrolled the paper to read more jokes, without then being able to roll it back as well as it had originally been. But I am digressing... My apologies. Toilet paper has always been a subject of interest to me!

The toilet paper manufacturers try to balance the conflicting requirements of softness, strength, and low cost by layering the paper. This is what it means when you read that the paper has two or four plies. Incidentally, I believe that three-ply papers don’t exist because the manufacturing process doubles the number of layers in successive paths, thereby only allowing for a number of plies equal to a power of two.

Unfortunately, the layering process is not sufficient to provide enough strength to reliably prevent the dreaded “breaking through”. That’s why I (like, I suspect, everybody else) use more than one segment of paper to achieve the required strength. But the question is: how do you do it? Do you break individual segments that you then overlap or do you take a single multi-segment section that you then fold? Figure 1 shows the solution I arrived to after decades of studies and experiments.

Figure 1: Giulio’s simple fold

By folding the two elements at an angle, I significantly improve the strength of the paper. This is because the fibres are aligned with the longer side of each segment. Therefore, by folding the paper at an angle, I introduce a “meshing” effect of the fibres. Incidentally, the fact that the fibres are aligned with the edge of the roll is what makes the perforation necessary. To convince yourself of it, try to cut out a picture from a newspaper. You will not manage to rip the top and bottom along straight lines, because the fibres are aligned with the left and right sides of the page. The same happens with toilet paper.

The best solution would be to rip off two individual segments and cross them at right angles or, in general, to rip off N segments and cross them at angles which are multiple of 180/N degrees. For example, three segments would be arranged as shown in Figure 2.

Figure 2: The optimal technique

But I confess that I cannot be bothered, and a simple fold with an angle of eight degrees (as shown in Figure 1) sufficiently adds to the strength of the segments. At least for me, that is!

No comments:

Post a Comment