Effect of Relative Humidity on the Optimum Flute Shape for Corrugated Fiberboard

Container stacking strength is an important performance requirement of corrugated fiberboard. The objective of this study is to examine theoretically how fluting geometry affects fiberboard strength and stiffness under standard relative humidity (RH) and high RH conditions. The fluted medium in a corrugated fiberboard is modeled as a connection of curved arc and straight flank segments passing through the middle plane of the cross section. Flute pitch, flute height, flank length, arc radius, and angle of wrap are reduced to a set of non-dimensional parameters, two of which can be chosen as independent. Thickness data on corrugated fiberboard in various flute profiles and weight grades are used to generate a set of representative flute profiles, which when combined further with mechanistic models on fiberboard edgewise crush strength and bending stiffness, enable strength and stiffness data from fiberboard to be used to predict average stressstrain properties of containerboard components. Using a standard set of papers as inputs, the strength and stiffness models are extrapolated to examine theoretically how mechanical properties and material savings are predicted to change for other arbitrary flute profiles. Predictions based on containerboard stress-strain properties at a standard 50% RH are compared with predictions based on stress-strain properties at 90% RH. The results quantify how an optimum flute profile strikes a balance among cost, runnability, strength, and stiffness considerations.. 4 International Symposium on Moisture and Creep Effects on Paper, Board and Containers Page 27 E.F.P.G., France, March 99