Research PaperMechanical design and performance testing of corrugated paperboard packaging for the postharvest handling of horticultural produce
Introduction
Packaging is an essential requirement for fresh and processed food products to provide vital protection from external factors arising from contaminants, gas composition, spoilage microorganisms, mechanical loadings and physical damage (Farber, 1991, Mangaraj et al., 2009, Samanta et al., 2016). Opara and Mditshwa (2013) described packaging as an essential food security component, which assures safe handling and delivery of fresh and processed products from point of production to the end-users. Thus, packaging plays a vital function in the postharvest handling and transportation of fresh and processed food and other biomaterials (Defraeye et al., 2015, Opara, February 2011, Pathare and Opara, 2014, Pathare et al., 2012).
A wide variety of packaging materials are used for handling fresh and processed horticultural products including polymeric film pouches, tin cans, paper and paperboard, wooden crates, baskets, plastics, trays and metallic films. Paper and paperboard are the most widely used for packaging food, particularly fresh horticultural produce (Chamberlain & Kirwan, 2013). These packages must meet various criteria for successful packaging that ensure the safety of the packed products (Pascall, 2010, Rhim, 2010).
The use of corrugated paperboard remains a dominant packaging material in the horticultural industry due to its versatility (Kaushal et al., 2015, Pathare and Opara, 2014). Corrugated paperboard packaging has been employed widely to protect products against damage that may arise from handling, transportation, storage, hazards and environmental conditions (Navaranjan & Johnson, 2006). Some advantages of corrugated paperboard which make its usage widely acceptable, particularly in horticultural industry include; low weight and hence very easy to handle, inexpensive, fully recyclable in nature (making them eco-friendly), strong and stiff compared to its weight, easily available and easily customisable to any specific requirement (Aboura et al., 2004, Biancolini, 2005, Biancolini et al., 2005, Navaranjan and Johnson, 2006, Pathare and Opara, 2014, Thompson et al., 2010).
In recent times, corrugated paperboard has been used for the manufacture of ventilated paperboard cartons for handling perishable produce. Pathare et al. (2012) reported that ventilated corrugated paperboard (VCP) packaging is commonly used and adopted globally in handling fresh produce. VCP packaging is an important technological innovation that rapidly promotes efficient and uniform cooling of horticultural produce (De Castro et al., 2005, Fadiji et al., 2016b, Fadiji et al., 2016a, Ferrua and Singh, 2011, Ngcobo et al., 2012, Pathare and Opara, 2014, Pathare et al., 2012, Thompson et al., 2010). Vent holes help to maintain balance in airflow channels between the surrounding and inside of the carton/package to reduce the resistance to airflow and has been shown to strengthen the package, hence preserving the packed product (Han & Park, 2007).
During postharvest handling, transportation and storage of fresh produce packed inside paper cartons, they are exposed to static and dynamic loads, under varying environmental conditions, which can occur over either short or long durations (Fadiji et al., 2016b, Fadiji et al., 2016c, Fadiji et al., 2016a, Jarimopas et al., 2007, Navaranjan and Johnson, 2006, Viguié et al., 2011). Static loads are mainly a result of pressures exerted on stacked packages (compression) that cause short and long-term creep buckling. Dynamic load arise from vertical and horizontal acceleration during transportation. The value of the packed produce may reduce due to these factors as a result of the presence of mechanical damage such as bruise defects on fruit which may lead to economic loss of the fruit due to downgrading or rejection by consumers (Jarimopas et al., 2007, Opara and Fadiji, 2018, Van Zeebroeck et al., 2007). However, corrugated paperboard cartons are still preferred, as they have been established to have good strength when dry (Pathare and Opara, 2014, Twede and Harte, 2003).
The complexity of the mechanical behaviour of corrugated paperboard is observed when the surrounding environmental conditions such as temperature and relative humidity (RH) vary. Changes in humidity have considerable degradative effects on the mechanical strength of the paper package and its operational life span. Increased moisture content reduces the fibre network strength, mechanical properties and the life of the package (Defraeye et al., 2015, Jo et al., 2012, Navaranjan and Johnson, 2006), which can increase the susceptibility of the packed produce to damage (Chonhenchob and Singh, 2003, Fadiji et al., 2016b Fadiji et al., 2016a, Opara and Fadiji, 2018, Opara and Pathare, 2014, Pathare and Opara, 2014; ). The complexity of the structural performance of paper packaging was discussed by Haslach (2000). The complex behaviour of paper packaging was reported to be due to its time-dependent characteristics with reference to moisture content, load, and temperature, whether constant or variably combined. Pathare and Opara (2014) reported that one of the main objectives of a ventilated packaging system for fresh horticultural produce is to minimise mechanical damage of the packed produce during postharvest handling and enhance the overall packaging performance in maintaining a balance between the mechanical integrity of the package and uniform air distribution within the package system.
The strength and performance of a corrugated package depend on numerous factors, such as the quality of the input cellulose fibre, the mechanical properties of the components and the combined board, the manufacturing quality control protocol, machine precision, and the human factor involved in the corrugation process (Biancolini et al., 2010, Fadiji et al., 2017, Pathare and Opara, 2014, Rahman and Abubakr, 2007, Zhang et al., 2014). Knowledge about these vital attributes will help improve the structural performance of the package by both minimising the amount of material utilised for making corrugated paperboard packages and guiding the design of packages with improved performance attributes (Fadiji et al., 2017). The high susceptibility of packed fresh produce to mechanical damage is prevalent and is a major cause of postharvest losses during export (Fadiji et al., 2016b, Fadiji et al., 2016a, Pathare and Opara, 2014, Pathare et al., 2012). Therefore, the design of packaging that can facilitate logistical handling, while still reliably protecting the produce from mechanical damage is thus a high priority to the fresh produce industry. This review provides an overview of the performance testing of corrugated paperboard packaging towards minimising damage to horticultural produce and discusses the effects of manufacturing processes and cold chain environmental factors affecting the strength of paperboard packaging and packaging materials.
Section snippets
Types of packaging materials – brief overview
There exist a wide range of packaging materials used for handling fresh produce and processed products from the farm to the end-user (Opara & Mditshwa, 2013). The design and construction of packages influence and play a significant role in determining the shelf life of a product (Hotchkiss, 1997, Marsh and Bugusu, 2007). All packaging types can be classified into two groups: (a) retail packages: These packages protect the packed contents from damage and at the same time advertise the contents
Paper and paperboard thickness
The thickness or “calliper” of the paper or board determines the bulkiness and the density of the paper. Paper calliper is the perpendicular distance between two plane parallel surfaces under a pressure of about 98 kPa – equivalent to 1 kg-force cm2. It is often measured using a micrometer. Variations in calliper can influence several basic paper performance properties, such as quality of roll and strength. The thickness of corrugated paperboard depends on flute height and the calliper of the
Testing for assessing the mechanical strength of packaging and packaging materials
The performance properties of corrugated paperboard packaging are related to varying factors such as the level of efficiency achieved during manufacture of the paperboard and package, creasing and packing operations (Sukumaran, 2015). Furthermore, performance properties of corrugated paperboard packaging are also related to the strength of the package during handling, transportation, storage, point of sale of packed products and in usage by consumers (Pathare and Opara, 2014, Sukumaran, 2015).
Cold chain environment factors affecting the strength of paperboard packaging
Corrugated paperboard is very sensitive to environmental conditions because it is made of hygroscopic material (Berry et al., 2016, Berry et al., 2017, Fadiji et al., 2016c, Kirwan, 2003, Pathare and Opara, 2014, Pathare et al., 2016, Thakkar et al., 2008, Zhang et al., 2011). Paper being a hygroscopic material is affected by factors such as moisture content, RH and the sensible heat in the form of ambient temperature which affect properties such as stiffness and consequently the strength of
Conclusion and future prospects
Packaging performs a crucial role in protecting produce from damage during handling, transportation and storage, modifying the distribution environment and enhancing the produce transport density per volume. Packaging is thus generally considered the most flexible and cost-effective means to modify or improve a fresh produce cold chain. Corrugated paperboard is the most common fresh produce packaging type, and its successful application can be attributed to its efficacy; low cost,
Acknowledgement
This work is based upon research supported by the South African Research Chairs Initiative of the Department of Science and Technology and National Research Foundation. The financial support of the South African Postharvest Innovation Programme (PHI-2) and HortgroScience through the award of a project on “Packaging of the Future” is gratefully acknowledged.
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