2 Analysis of test results
2.1 Decrease in Mechanical Properties of Corrugated Cardboard with Storage Time
The data measured before the storage test is compared with the performance indexes required by GB/T 6544-1999, and it can be seen that the D-2.2 sample satisfies the requirements for first-class products. However, after 6 months of storage, the side pressure strength decreased by about 25%; the burst strength decreased by about 14%. After 5 months of storage, the performance could not meet the requirements of the first-grade products specified in GB/T 6544-1999. The variation of the side pressure strength performance is not strong, and the fluctuation phenomenon occurs during the test. The reason for the analysis is the uneven coating of the corrugated cardboard. From the graph analysis, the bond strength decreased by 20% in 6 months of storage.
2.2 Corrugated box empty bearing compressive strength test results analysis
Corrugated boxes were subjected to compressive strength storage tests for 6 months and strength was reduced by 20%. According to its gross weight of 18kg, take the stacking height of 3m, which means that after loading the product, the height of each stack is 9 boxes. The safety factor is 3, and the qualified determination value of the empty box pressure bearing strength of the corrugated box is 4.23kN. From this, it can be seen that after the corrugated box was stored for 6 months, its empty container bearing strength was significantly reduced, but it still met the requirements for use.
2.3 Analysis of Causes for Decline in Mechanical Properties
The environmental factor that affects the mechanical properties of corrugated board is mainly humidity. The edge pressure strength, adhesive strength, and burst strength of the raised humidity corrugated board will be significantly reduced.
From Table 1, it can be seen that the monthly average relative humidity in the storage test environment is above 75%, sometimes reaching over 90%. In this environment, the moisture content of corrugated board exceeds the specified requirements (8% to 12%). Although performance testing is pre-treated and tested under the same temperature and humidity conditions, the corrugated board performance change is not completely reversible. Excessive water content will cause the corrugated board to become soft, causing the corrugated shape to change and the corrugation height to decrease; and the binder can be hydrolyzed to reduce the bond strength. When the humidity of the environment is restored to the prescribed humidity, the moisture content of the corrugated board can be restored to the qualified requirements, but the above effects cannot be restored. Therefore, long-term storage in wet environments can degrade the mechanical properties of corrugated board. The compressive strength of the empty box of the corrugated box is directly related to the side pressure strength of the corrugated cardboard other than the size and the structure of the box, so long-term storage in a humid environment will reduce the compressive strength of the corrugated box.
3 Conclusion
When corrugated boxes are stored in a relatively humid environment, the overall mechanical properties of the corrugated boxes are gradually reduced with time. The recommended storage time is generally not more than 4 months.
To maintain the good mechanical properties of the corrugated box and require a longer period of storage, the temperature and humidity of the storage environment should be controlled, especially the relative humidity should be controlled at (50 ± 10)%. (Wen/Cheng Xiaoqin Ma Ting Wang Yilin Zhang Yongzhi)