Creep Properties of Corrugated Fibreboard Protective Cushions
Multi-layered corrugated fibreboard, has inrecent years been gaining attention as a replacement for polymeric materials for protective packaging for environmental reasons. The properties of pre-compressed multilayered corrugated fibreboard make it a sustainable replacement for poly-foam and polystyrene. Pre-compressed multilayered fibreboard cushions have most of the structural resistance and damping removed, they behave more like a soft spring.
The performance of pre-compressed multilayered corrugated fibreboard as a protective cushion is influenced by the amount of moisture present. The material stiffness is also dependent on the amount of moisture present.
Static compression testing can be carried out to obtain stiffness data by measuring load versus controlled deflection, with stiffness being the load required to deflect a specified distance. The creep properties can be obtained by measuring deflection with a controlled force overa period of time, that is, creep is a measure of deflection per time under aconstant force.
There have been many materials used in the protective packaging area over many decades, such as expanded polystyrene (EPS) and poly-foams. These materials have been difficult to re-cycle and generally end up in landfill. Paper based materials tend to be more amenable tore-cycling, although more expensive to manufacture.
Corrugated fibreboard has been used in the packaging industry for many years mainly as containers and boxes to pack goods for transportation. This material has however can also be used as protective cushions inside containers usually constructed in multiplelayers pre-compressed multi-layered corrugated fibreboard cushions, which is the essence of this study, consists of layers of virgin board glued together then compressed to remove the rigidity and to create a spring like structure.
The virgin board usually consists of corrugated fibreboard sheet sandwiched between two plain sheets as shown in Figure 1.1.
The flute configuration can be of the following sizes as shown in Table 1-1 with the size shown in yellow being acommonly used size in cushioning.
It is felt that the pre-compressed corrugated fibreboard is a good substitute for polymeric materials such as poly-foams and EPS which are commonly used in the packaging industry. As with all cushioning materials it is necessary to determine the cushioning characteristics prior tousing as a protective cushion.
Within the dynamics and vibrations research group at Victoria University and else where much research has been carried out into the application of virgin and precompressed multi-layered corrugated fibreboard cushions for protective packaging in storage and delivery container sboxes.
The main focus has been on the shock attenuation or cushioning characteristics, methods to produce cushion curves using simple compression data and modeling of cushion dynamic behavior and producing records such asimpact failure as shown in Figure 1.2.
Another dimension to cushion testing is to take into account that when packaged products are in stored in boxes for longer lengths of time, such as in storage, there is a tendency for protective cushions to experience creep or time dependent deformation. The protective cushions lose thickness that leads to a slackening off to the interface between the cushion and the packaged product. This would create direct deterioration of the cushioning effect or loss of support during impact or vibration, and subsequently lead to product damage.
One method to overcome this is to allow more cushioning, but to establish how much, requires some knowledge of the creep behaviour. As this product is a paper product there is also the question of humidity affects the creep performance. There has been work produced on the creep behaviour of corrugated fibreboard storage boxes particularly with respect to the effect of humidity.
However there seems to be little work on the creep behaviour of corrugated fibreboard protective cushions, especially when the cushions are pre-compressed. There is then a need to study Creep Behaviour of Pre-compressed Corrugated Fibreboard protective cushions. The pre-compression process reveals knowledge of the static compression characteristics of the material which is an adjunct to the creepprocess.
The work for this study is described in the following chapters: The literature review in chapter two talks discusses static compression and creepin corrugated fibreboard and proposes the methodology for this study. Chapter three describes static compression and creep testing procedure. Chapter four provides the analysis of the experimental results and modelling processes. Chapter five contains discussion and main conclusions.