Issue link: http://cp.revolio.com/i/586959
22 ista views • October 2015 • www.ista.org Long Term Corrugated Container Compression Performance > CONTINUED FROM PAGE 21 Popil and Hojjatie, writing about the Effects of Component Properties and Orientation on Corrugated Container Endurance, provided the data in Figure 6 (Popil, Hajjatie; 2010). While not the related to the points they were making, it is interesting to note that BCT alone does not seem to predict box lifetime - other factors are clearly involved. It is notable that two identical sample groups (18A-1 and 18A- 2) have essentially the same BCT values but 18A-1 lasted nearly twice as long as 18A-2. Most notable is sample group 33A, which has slightly higher BCT than groups 20AQ and 26A, yet survived 6 times longer. Popil and Hojjatie also showed that using water vapor barrier coatings on box exterior surfaces can increase lifetime by a factor of 8, by limiting hygroexpansive strain in the outer linerboard. Note that in their testing, temperature was held constant while relative humidity was cycled from 50 to 80%. This shows that coatings will protect boxes from the damaging effects of cyclic Relative Humidity levels which are external (my emphasis) to the boxes. An interesting line of inquiry would be the effects of moisture pressure gradients caused by temperature changes, acting upon existing moisture, contained either in the component papers or the interior of the box. One might begin by testing coated boxes which enter testing with high moisture content (rather than beginning with boxes preconditioned to a "dry" state per TAPPI T402), as would be expected in hot humid climates, such as found in many of today's low cost manufacturing regions (e.g. southeast Asia, southern and interior China), and test with cyclic temperature, to determine the effects of moisture trapped in the box material and interior. This would mimic the moisture scenario which is common in many parts of Asia. Would the high starting moisture content of the box components, plus moisture inside the box trapped by an exterior coated liner, significantly reduce box life, due to cyclic temperature and resultant absorption-desorption cycles? A similar question could be asked with respect to moisture trapped by pallet load stretch-wrap. Preliminary, unpublished testing performed at HP indicates that pallet stretchwrap effectively prevents significant moisture migration into the load, in time scales similar to 24 hour diurnal temperature/RH cycles. Thus, like box coatings, pallet stretchwrap may be effect in mitigating the impact of cyclic RH levels outside the load from affecting the coated boxes and wrapped loads. However, coatings and stretchwrap will not prevent internal moisture already present in box component papers, and the box interior, from creating moisture change pressure gradients, caused by diurnal temperature changes. Figure 6: Cyclic Humidity Cycles to Failure for Various Mediums, with Associated BCT (Popil, Hojjatie; 2010)