Chapter 2. Mechanical design and performance testing of corrugated
2.3 Factors affecting paper and paperboard performance
2.3.2 Mechanical hazards affecting packaging and fresh produce in the
When designing efficient packages, it is crucial to determine the damage severity of the handling and distribution environment (Jamialahmadi et al., 2008). A distribution environment includes all the environmental conditions the package and produce encounter during the postharvest journey from the grower to the consumer (Ragulskis et al., 2012; Jamialahmadi et al., 2011; Eagleton, 1995). Package handling, storage and transportation can result in various hazards within the distribution environment. These may include, among others, horizontal impacts or vertical drops, compression loads, transport vibration and shocks (Opara & Fadiji, 2018; Fadiji et al., 2016a, b, c; Pathare & Opara, 2014; Singh et al., 2009; Van Zeebroeck et al., 2007; Vergano et al., 1991). Any of these hazards or a combination
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of two or more can lead to package and produce damage. Assessing the distribution method and understanding the supply chain environment of a produce, can help to determine the type of hazards the produce will be subjected to and the extent of the hazards, which will consequently assist in designing the package that will effectively protect the produce (Jamialahmadi et al., 2008). Trucks, trains, ships and aircrafts are the main modes of transportation that have the potential of causing various hazards. It is important that package designers have an upfront knowledge on the modes of transportation to predict the likelihood of these hazards. An ideal package should be able to provide adequate protection needed by the produce, at the lowest possible overall cost (Robertson, 2012; Han & Park, 2007).
Vibration hazards
Vibration is an oscillating motion over time. During the postharvest journey of packaged produce inside corrugated paperboard packages, the produce undergo continuous movement during transit which may lead to package/produce damage (Fadiji et al., 2016b; Sittipod et al., 2009; Jarimopas et al., 2007). Packages being transported by truck, rail or aircraft are generally exposed to vibration. During transportation of packaged produce, vibration is affected by a number of factors such as the road roughness, travelling speed, number and load of axles, truck suspension (Idah et al., 2012; Vursavuş & Özgüven, 2004; Berardinelli et al., 2005, 2003a, b). Produce damage during vibration occurs when the acceleration the produce experiences is more than the acceleration of gravity (9.8 m s-2). When the acceleration is below this level, the packed produce does not move with respect to the carton or the nearest produce. During vehicle transportation, acceleration impact is experienced more at the top of the stacked cartons because the peak acceleration increases from the bottom of the carton to the top (Fadiji et al., 2016b; Van Zeebroeck et al., 2007; Slaughter et al., 1993; Hinsch et al., 1993).
To understand the behaviour of corrugated paperboard packaging under vibration, Park et al. (2011) characterised the properties of corrugated paperboard such as vibration transmissibility, resonant frequency, damping ratio and maximum dynamic stress, which are relevant to its application for protective packaging during transportation. A similar study by Guo and Zhang (2004) evaluated the dynamic cushion curve and analysed the resonance and vibration transmissibility of honeycomb paperboards. The authors reported the large effect honeycomb paperboard had in diminishing vibration in the high frequency region because vibration transmissibility at resonant frequencies that exist over 350 Hz is insignificant. In a recent study by Fadiji et al. (2016b), the authors determined the transmissibility of corrugated paperboard packages and incidence of apple bruise damage at three frequencies: 9, 12 and 15 Hz. The authors reported the range of packaging transmissibility to be from 100 to 250%, with the highest observed at 12 Hz. The incidence and severity of the apple bruising was also reported to be dependent on the type of package and the frequency of excitation. Table 2.3 shows range of vertical frequencies and maximum accelerations, which are encountered during transportation and distribution. Immobilising or restricting the movement of
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the produce, cautious handling and proper packaging have shown to minimise the losses of produce due to vibration hazard damage (Chonhenchob et al., 2009; Chonhenchob & Singh, 2003; Singh & Singh, 1992; Singh et al., 1992). In transport trailers, air-ride suspension has been used to minimise vibration hazards particularly during the shipment of produce that are sensitive to vibration injury (Pathare & Opara, 2014; Hinsch et al., 1993).
Impact/drop hazards
Impact hazards may occur during handling, storage and transportation due to impacts from racks, forklifts, dropping of the packages, sudden braking and accelerating transportation system and shocks during transportation. The resulting effect of an impact hazard include bursting of the packages or bruising of the packed produce. There is no particular stage during the handling and distribution process at which impact hazard occurs, as it may occur at each stage of the process and is usually difficult to eliminate (Fadiji et al., 2016a; Opara & Pathare, 2014; Gołacki et al., 2009). Opening of package flaps causing the package to lose its function, distortion in package shape thereby reducing stacking abilities, and the splitting of the seams are among the adverse effects of impact hazards on corrugated paperboard packages (Fadiji et al., 2016a; Opara & Pathare, 2014; Pathare & Opara, 2014; Walker, 1992). During handling and transportation, some level of protection against shock may be required to prevent damage caused by impact depending on the packed produce. The use of rigid packages and adequate cushioning can reduce damage that may arise from impact hazard.
It is crucial to determine the potential drop height that packed produce may experience, the fragility of the produce and the resistance of the package to shock damage due to free fall. This is necessary because during transportation and storage, packages can fall onto the floor resulting in damage (Fadiji et al., 2016a; Pathare & Opara, 2014; Hammou et al., 2012). Some other factors such as forklifts bumping pallets, tossing the package horizontally during palletisation and sudden breaking or entering potholes during transportation could result in impacts. Drop testing is used to measure the ability of the package to retain and protect the packed produce from free fall (Fadiji et al., 2016a; Pathare & Opara, 2014; Hammou et al., 2012). Recently, an extensive impact study was done by Fadiji et al. (2016a) to determine the susceptibility of apple fruit packed inside ventilated corrugated paperboard packages at different drop heights. The authors reported that the incidence and susceptibility to bruise damage of apples was affected by package design and drop heights. In drop testing, the product of the weight of the packed produce and the drop height determines the potential energy of the package (Pathare & Opara, 2014; Poustis, 2005). The drop height is the vertical distance from the point the package was released to the impact surface, falling under the influence of gravity. During handling operations, imposed loads on the package are usually reported in terms of equivalent drop height (EDH). This is defined as the free fall height that is required to produce the same total velocity change as measured on the shock waveform (Eagleton, 1995). EDH is used for comparison between impacts by forces other
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than gravitational force. For an ideal free-falling package, the relationship between the total velocity change and EDH is given as:
(1 ) 2 eq
V e gh
(2.4)
where
e
is the coefficient of restitution, g is the acceleration due to gravity (m s-2), is the change in total velocity (m sV -1) and eq
h
is the equivalent drop height (m).Researchers have correlated several other mechanical parameters with the damage caused by impact hazards. Such parameters are the energy absorbed (Jarimopas et al., 2007; Bollen et al., 2001, 1999) and force (Brusewitz et al., 1991). The amount of absorbed energy by the impacted surface during drop is referred to as the coefficient of restitution: r i V e V (2.5)
where
V
r is the rebound velocity (m s-1) andV
i is the impact velocity (m s-1). For packed produce, the range of the coefficient of restitution is usually from 0.3 to 0.75. In packaging design, the value of 1 for coefficient of restitution is considered a worst-case value (Garcia‐Romeu‐Martinez et al., 2007; Brusewitz et al., 1991; Eagleton, 1995).Compression hazards
Compression is said to occur when a pushing force reduces the volume of an object. Compression hazards occurs during postharvest handling and distribution if the package at the bottom of the stack on the pallet is not sufficiently strong enough to withstand the load of the carton stacked on it. Compression loads on packages are generally associated with storage stacking (Eagleton, 1995). Static compression is a loading force that a package will endure when it is stacked vertically for an amount of time. The force being applied is not moving. A package may also encounter dynamic compression while being transported in the back of a truck. Dynamic compression occurs when there is a moving force being pressed against the object and can be observed during cushion testing. This form of compression may result from vibration and shocks in transportation by load amplification when the packages vibrate at the critical resonant frequencies. It is important to mention that very low vibration frequencies from transport operations such as the response of aircraft to gusts and ships rolling or pitching may result in dynamic compression loads on the packages (Eagleton, 1995). Equipment for mechanical handling such as slings, cargo nets, clamps on trucks, rail car coupling and strapping of the package could result in dynamic compression loads (Eagleton, 1995).
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To minimise this, carton boxes should not be stacked above their design requirements (Kader, 2002). In a report by Kader (2002), designing corrugated paperboard cartons to withstand more than four pallets high, particularly during storage is not economically feasible. Appropriate package design systems and good packaging offer vital protection to package and produce against compression hazards, and utilising strong packages able to withstand multiple stacking can help minimise this hazard thereby reducing the incidence and the extent of produce damage. The shallowness of packaging also determines the extent of damage as it should be shallow enough to prevent the packed produce in the bottom from damage that may arise from weight of the packages in the top layers.