A situation common to individuals across a diverse student body is the failure to effectively erase graphite marks ingrained on paper using certain types of erasers. Encountering this situation more than a couple times over a week may cause the user to arrive at the ensuing question: Why are some erasers more effective at erasing pencil marks than those from other brands? This article will attempt to address this question by analyzing the two most prevalent factors of eraser quality, namely material engineering and age.
Before diving into the following analysis, we must provide a precise definition. First, what is an eraser? The definition of an eraser for the purpose of this analysis will be that of a stationery tool produced using rubber or vinyl for the application of removing marks of graphite from paper. This definition therefore excludes kneaded erasers (mouldable erasers used by artists) and fibreglass erasers (extremely durable erasers that can be used to erase scratches on cars).
The first major factor is material engineering. To understand why this is so important, one must consider the microscopic forces at play when an eraser rubs away graphite from paper.1 To begin, consider why pencil marks adhere to paper. Pencil marks are composed of graphite — an allotrope, or arrangement, of carbon. Graphite adheres to paper, which is composed mostly of cellulose fibres. Cellulose is a polymer of glucose; in other words, it is a long chain of tightly-bound sugar molecules. London dispersion forces — a usually weak type of ‘intermolecular force’, or a force between molecules — hold the graphite to the paper. When one rubs an eraser — composed of an organic, or carbon-based, compound known as polyvinyl chloride (PVC) and, in the eraser market, as vinyl — against pencil marks, the eraser removes the graphite from the paper because the intermolecular forces between vinyl and graphite are stronger than those between cellulose and graphite.2 Both vinyl and graphite are relatively non-polar while cellulose has many polar hydroxyl (OH) groups. Certain brands of erasers work more effectively than others because erasers from different brands are composed of different proportions of vinyl and synthetic rubber — another organic substance. Vinyl erasers are softer than the rubber, and allow parts of the eraser bonded to graphite to rub off more easily.2
The second major factor is age. According to a 2014 report by The Atlantic, materials science Professor Rigoberto Advincula of Case Western Reserve University stated, “over time, some of the rubber properties can be lost because of oxidation or chemical degradation. Some of the plastic can also soften or even harden because of different environmental conditions.” The article further suggested one could potentially mitigate these age-related factors by using hermetic (air-tight) storage. As hypothesized by engineering professor Henry Petroski of Duke University, “If you had a pencil with an eraser from a hundred years ago and it had been hermetically sealed, — aka sealed in an air-tight container — it might still work.”
As stated in this article, the two primary factors for why your eraser is smudging graphite all over your exam are your choice of eraser brand and the eraser’s age. One might consider the presentation of these two factors to be the most important part of this article. However, the knowledge of the fundamental scientific theories behind these factors is even more important. Understanding the chemical concepts of intermolecular forces and molecular structure gives one the potential to understand phenomena in fields extending far beyond those in related to eraser manufacturing. I believe that out of all the memories you have, your understanding of general chemistry should be among the last of the items you should ever wish to erase.
References
(All website listed were accessed in October 2016.)
- H. Schwedel, Why do erasers suck at erasing? October 2014, www.theatlantic.com/technology/archive/2014/10/why-do-erasers-suck-at-erasing/381025/
- M. Trimarchi, (2013, February 26). How do erasers erase? February 2013,
http://science.howstuffworks.com/innovation/everyday-innovations/erasers-erase1.htm.
[This article was sent in by Jennifer Pitts-Lainsbury from University of Toronto Schools, Toronto, Ontario. Not only is it interesting, but it is a great example of what high school students can do.]
