Brittle paper: what can it stand?

Posted by mdever on April 5, 2019 in conservation, GLAM sector, manuscripts, materiality, paper, preservation, research

Taking a literal turn in our thinking around materiality and the archived page, the following recent publications examine the mechanics of aged and brittle paper:

Abstract: The ability to determine the condition of paper (e.g. its brittleness) and its permanence is a need in libraries and archives. This study investigates various bend tests and applies these tests to aged paper with the goal of finding easy, non-destructive tests to determine the mechanical properties of paper. The cantilever test was previously shown to accurately assess mechanical properties of paper-based materials, such as elastic and bending moduli as well as the bending length. This work investigates the hanging pear loop and clamped fold tests and compares the results with those found with the cantilever test. The results show that the strain and curvature induced by the two tests are much larger than those experienced in the cantilever test. This large strain and curvature induce plastic behaviour and make the hanging pear loop and clamped fold tests inappropriate for use on paper-based materials.

“The Bending Mechanics of Aged Paper” by Andrea K. I. Hall, Thomas C. O’Connor, Molly K. McGath and Patricia McGuiggan, published in Journal of Applied Mechanics | Volume 85 | Issue 7 | (2018).

Abstract: Brittleness in paper is one of the primary reasons library books are removed from circulation, digitized, or have their access limited. Yet, paper brittleness is difficult to characterize as it has multiple definitions and no single measurable physical or chemical property associated with it. This study reevaluates the cantilever test as applied to aged papers. In this nondestructive test, the deflection of a strip of paper held horizontally is measured across its length. The deflection data are then fit to nonlinear bending theories assuming large deflection of a cantilever beam under a combined uniform and concentrated load. Fitting the shape of the deflection profiles provides bending and elastic moduli, the bending length, and confirms that the paper sheets respond linearly. The results are compared to those calculated from a simplified single point measurement of the maximum deflection of the cantilevered sample. Young’s modulus measured by the cantilever test is lower for paper-based materials than that measured by tensile testing, and the bending modulus was found to correlate with the destructive Massachusetts Institute of Technology (MIT) fold endurance test (see below).

The MIT Flex Tester – MIT Folding Endurance Tester is used for determining the folding endurance strength of paper and paperboard using hang type weight method.