Storage and transportation of corrugated boxes can expose them to varying and often fluctuating environmental conditions. This can negatively impact the corrugated material’s moisture content and the effectiveness of the glue used in manufacturing. Moisture and temperature are important considerations when discussing the strength and longevity of corrugated boxes.
Moisture Content Takes a Leading Role
Water is used in the corrugated board production and aids in creating the liner board, forming the flute structure, and as part of the starch adhesive that combines them. However, once the corrugated is manufactured, moisture regulation is critical, so the corrugated board is dried to achieve a moisture content of 10-12% to optimize it for strength and prevent box manufacturing issues, such as:
- Softening of the board
- Poor creasing
- Printing difficulties
Maintaining the moisture content of the corrugated box plays a critical role in its performance.
Relative Humidity Impacts Moisture Content
Once a box is formed, both before and after it is filled with product, maintaining its moisture content is critical to maintaining the box’s compression strength.
- Too dry, and the corrugated and glue can crack.
- Too much moisture can lead to weakened cellulose fibers, delamination, and weakened glue bonds.
Both cases can lead to failure. The moisture content of the box is determined by environmental relative humidity.
Relative humidity is the amount of water the air can hold at a given temperature, so there is a direct relationship between temperature and humidity. Colder temperatures hold less moisture. This is why dew forms when the temperature drops. During the day, the warmer air picks up moisture, and as the air cools in the evening, it releases it as dew.
The moisture content of corrugated materials prefers a state of equilibrium with atmospheric humidity. When relative humidity increases, the corrugated board will pull moisture from the air until it reaches the same moisture content level. If the relative humidity is low, the corrugated will give up moisture.
Impact of Storage and Transportation
Storage and transportation can expose corrugated boxes to fluctuations in temperature and humidity. Improper and fluctuations in relative humidity can be seen in:
- Arid or humid geographical location
- Seasonal fluctuations
- Daily changes over time
These can result in the box structure breaking down, leading to a reduction in strength and, eventually, failure.
The ideal temperature and humidity are 72° F, 50% RH1.
Boxes under stress from a load, such as stacked on a pallet, are even further impacted by increased humidity. Fluctuations in humidity can impact it even further. Studies have shown that corrugated under a constant load with cycled moisture has experienced accelerated creep or deformation of the material, leading to premature box failure.
Although it would be difficult to calculate the reduction of strength under fluctuating conditions over time, the chart below (Protective Packaging for Distribution, 2010) is used to determine the compression strength loss over time under various environmental conditions. The multipliers can be used to calculate compression loss for specific situations.
|Storage time under load||10 days – 37 percent loss||0.63|
|30 days – 40 percent loss||0.60|
|90 days – 45 percent loss||0.55|
|180 days – 50 percent loss||0.50|
|Relative humidity, under load (cyclical RH variation further increases compressive loss)||50 % RH – 0 percent loss||1.00|
|60 % RH – 10 percent loss||0.90|
|70 % RH – 20 percent loss||0.80|
|80 % RH – 32 percent loss||0.68|
|90 % RH – 52 percent loss||0.48|
|100% RH – 85 Percent Loss||0.15|
|Best Case||Worst Case|
|Columnar, Aligned||Up to 8 percent loss||1.00||0.92|
|Columnar, misaligned||10-15 percent loss||0.90||0.85|
|Interlocked||40-60 percent loss||0.60||0.40|
|Overhang||20-40 percent loss||0.80||0.60|
|Pallet deck board gap||10-25 percent loss||0.90||0.75|
|Excessive handling||10-40 percent loss||0.90||0.60|
Contact Progress to Ensure Structural Integrity in Any Environment
Our team has worked with countless companies whose boxes have faced just about every environmental condition imaginable. We have the experience to ask the right questions to ensure the boxes we provide you will meet your product’s needs and will remain structurally sound. Contact us to get started on your next project.