Aspects of sustainability and design engineering for the production of interconnected smart food packaging

RESEARCH ARTICLE Aspects of sustainability and design engineering for the production of interconnected smart food packaging Marı ´a Ine ´s Cabot, Amalia LuqueID*, Ana de las Heras, Francisco Aguayo Department of Design Engineering, Higher Polytechnic School, University of Seville, Seville, Spain *[email protected] Abstract In the present work, the problem of food wastage and the concept of sustainability are studied. An analysis of Life Cycle Assessment as a tool and of the innovative concept of Cradle to Cradle is also carried out, together with an exhaustive comparison of these two approaches. Based on these concepts, an integrated methodology is proposed for the design of interconnected smart products. The smart packaging systems currently available are studied theoretically and a practical case is analysed using the proposed methodology through the design and Life Cycle Assessment of a smart interconnected container that is able to detect the ethylene emitted by climacteric fruit, thereby minimizing food wastage. For the case under study, a major impact is observed of the selected plastics in the resources category, and of the smart system in the human health category. Introduction The objectives of the present work include research into various methodologies and innovative frameworks for the study of the sustainability of products and processes, specifically that of Life Cycle Assessment (LCA) and Cradle to Cradle (C2C). A comparison is made between these two approaches and a combined methodology is proposed, which then can be applied to the design of smart interconnected food packaging. Smart Products are mechatronic products that are additionally equipped with embedded systems enabling communication with other Smart Products using existing internet technologies [1,2]. The current definition of sustainability dates from 1987: "Sustainability or sustainable development is one that meets the needs of the present without compromising the needs of future generations"[3–5]. This encompasses three major stages that define the 3E strategy: economy, equity, and ecology, constituting the Triple Bottom Line [6], where the three dimensions are treated equally [7,8]. The last two stages in the history of sustainability involve eco-efficiency ("from cradle to grave") [9,10], which covers all stages of the life cycle, from the extraction of materials to the end of life of the products, and the eco-effectivity ("from cradle to cradle") [11–13], whose PLOS ONE | https://doi.org/10.1371/journal.pone.0216555 May 8, 2019 1 / 15 a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Cabot MI, Luque A, de las Heras A, Aguayo F (2019) Aspects of sustainability and design engineering for the production of interconnected smart food packaging. PLoS ONE 14(5): e0216555. https://doi.org/10.1371/journal. pone.0216555 Editor: Prakash Kumar Sarangi, Central Agricultural University, INDIA Received: December 13, 2018 Accepted: April 10, 2019 Published: May 8, 2019 Copyright: ©2019 Cabot et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper. No specific or private data have been used. Funding: The authors received no specific funding for this work. Competing interests: The authors have declared that no competing interests exist. objective is not only to assure the efficiency of the processes throughout the stages of the life cycle, but also to ensure that, at the end of the useful life of products, their materials can be reused or recycled [14]. The whole value chain of a product has the responsibility to explain that sustainability is not synonymous to recycling, recyclability, recycled content, biodegradability and other buzzwords, but that the efficiency of the supply chain resources should remain the top priority[15]. This is why any improvement to sustainability requires the knowledge of complete value chains, and a focus on a single section is insufficient since solving a problem in one place in the chain can result in the creation of a different problem in another part of the chain [16]. According to the FAO [17], "food waste" can be defined as food suitable for human consumption that is discarded as a result of negligence or a conscious decision to throw away food. The earlier a product is lost or wasted in the supply chain, the higher the environmental cost becomes, and hence preventing the avoidable generation of food waste in the supply chain represents the most advantageous option within the hierarchy of food wastage [18]. The design of the food container constitutes one of the principal causes of food waste [19], since many times food packages are difficult to empty. In addition to this consideration, they should also be easy to reseal in order to avoid biological deterioration, be provided in sizes that obviate food being left over, and supply the correct information (content, expiration date, etc.) in order to prevent fresh food from being discarded [20]. New packaging solutions enable the economic aspect of food wastage to be improved and interest in active and smart packaging is currently on the rise. Field research has been carried out on packaging characteristics and technologies [21]. This is evidenced by the number of patents and patent applications granted in recent years [22]. The objective of the present case study is to study the environmental impacts of a smart interconnected rigid plastic container, whose main purpose is to store climacteric fruit in the refrigerator of a standard household. This container monitors the ethylene content emitted by the fruit during its ripening process and informs consumers via a Bluetooth connection that the fruit it contains has reached its optimum for consumption, thus preventing food from being wasted. This container is designed to be transported from the house to the supermarket every time a purchase thereof is made, which implies a saving in the disposable plastic containers commonly used in the packaging of this type of product. The rest of the paper is organized as follows: Section 1 deals with the concept of sustainability, food waste, and the importance of packaging for its minimization, and this section concludes with the explanation of the case study. In Section 2, which corresponds to materials and methods, Life Cycle Assessment Methodology and Cradle to Cradle Philosophy are studied, the Smart Packaging concept is analysed, the MOSFET Sensors are chosen as the appropriate smart technology, and the choice of plastics for the manufacture of the container is explained.‘ Metal-oxide semiconductor field-effect transistor (MOSFET) sensors rely on a change of electrostatic potential. A MOSFET sensor comprises three layers: a silicon semiconductor; a silicon-oxide insulator; and a catalytic metal (usually palladium, platinum, iridium, or rhodium), also called the gate [23]. A MOSFET requires a thin semiconducting layer, which is separated from a gate electrode by the gate oxide dielectric, and also requires source and drain electrodes of width W (channel width) separated by a distance L (channel length) [24]. In Section 3, where the theory and calculations are discussed, the objective and scope are outlined and the inventory of mass and energy is analysed. The end of life of the packaging is then discussed. Section 4 presents the results of the comparison between the approaches of Life Cycle Assessment and Cradle to Cradle in terms of impact characterization, evaluation by standardized category, and single score by component, obtained from SimaPro software. In Aspects of sustainability and design engineering for the production of interconnected smart food packaging PLOS ONE | https://doi.org/10.1371/journal.pone.0216555 May 8, 2019 2 / 15 the subsequent discussion section (Section 5), the basic discrepancies between the two methods, the measurement of C2C principles with LCA, and the application of C2C principles to the case study are all discussed, and a process optimization is carried out. Finally, Section 6 presents the conclusions. Materials and methods Methodology of Life Cycle Assessment (LCA) Life Cycle Assessment is a methodology developed in the 1970s to measure the impact of a product, service, or process throughout its life cycle, from the time its raw materials are obtained to their end of life and subsequent management [25]. Based on the collection and analysis of inputs and outputs of the system (natural resources, emissions, waste, and by-products) to obtain quantitative data on their potential impacts on the environment [25], LCA considers that all the stages involved in the life cycle of a product/ activity are responsible for its environmental consequences. Certain studies indicate that agricultural production constitutes the hotspot in the life cycle of food products, and that LCA can assist in identifying the most sustainable options [26]. The European Union has indicated that LCA is the best tool for the evaluation of the potential environmental impact of products [27]. The LCA methodology consists of 4 steps (Fig 1): Step 1: Definition of objectives and scope [28–30]; Step 2: Inventory analysis [28,31]; Step 3: Impact evaluation [27]; Step 4: Interpretation of results [29]. The LCA method is dynamic, and the four stages in which it is performed are related to each other in such a way that, as results are obtained, then the data, hypotheses, system limits, and/or objectives, can all be modified or improved. Cradle to Cradle Philosophy (C2C) Cradle to Cradle is an innovation framework used since the 1990s in order to design products and services that are beneficial in economic, well-being, and environmental terms, in order to achieve a sustainable world [33]. Cradle to Cradle (C2C) offers a positive vision of the future, where products are radically redesigned to be beneficial both to humans and the environment. This concept is not based on the reduction of negative impacts (as in LCA), but on the increase of positive impacts [13,34,35]. A transition towards a circular economy requires consumers and companies to shift towards models of utilisation rather than of ownership. The C2C approach proposes replacing eco-efficiency with eco-effectivity, where the challenge is to make positive net contributions to the built environment with the aim of achieving "zero status”: zero residual emissions, zero use of resources, and zero toxicity, while taking up the banner of the declared goal of “doing good” instead of simply avoiding “doing much wrong” [36]. The basis of the C2C philosophy is that, although nothing good can be achieved by making small changes in a system that is fundamentally wrong, the bad things can still be reduced a little [37]. Aspects of sustainability and design engineering for the production of interconnected smart food packaging PLOS ONE | https://doi.org/10.1371/journal.pone.0216555 May 8, 2019 3 / 15 The aspiration of C2C for the built environment involves the promotion of smart designs that enjoy a positive synergic relationship with the environment. This can only be achieved by taking inspiration from natural flow systems where the sun is the main source of energy and where process waste is metabolized biologically to feed nourishment for other biological processes [33]. It is emphasized that the products should be designed as biological nutrients or technical nutrients, the former composing the naturesphere, which is metabolized and regenerated by nature, and the latter composing the technosphere, which is maintained in closed cycles of manufacture, reuse, and recovery [37]. This philosophy prioritizes supra-recycling, where of a material or product without use, destined to be waste, is transformed into another material or product of equal or greater utility or value, and the waterfall model, where the materials are kept within a technical cycle for a certain number of iterations, until losing their properties before returning to the biological cycle [13]. This framework raises 3 principles. The first is the concept of closed cycles, where the waste of one process constitutes the food of another process, thereby rejecting the eco-efficient approach of striving to reduce the amount of waste, and stating that the vision should be to design systems with products that other processes can absorb as nutrients [37]. This principle also incorporates the concept of toxicity of the material [33]. The second principle involves the use of sustainable energy and proposes that the energy demanded by industrial activity be obtained preferably from renewable sources, such as energy from the sun [33], instead of exploiting abiotic resources in the form of fossil fuels, which devastates regions where these materials have been stored [14]. Fig 1. ISO 14040:2006. Adapted from [32]. https://doi.org/10.1371/journal.pone.0216555.g001 Aspects of sustainability and design engineering for the production of interconnected smart food packaging PLOS ONE | https://doi.org/10.1371/journal.pone.0216555 May 8, 2019 4 / 15 The third principle is called "celebrating diversity" and is based on the fact that diversity favours the resilience and robustness of the product and the associated system, thereby guaranteeing security in a changing world [14]. Therefore, in order to improve the resistance of a system, diversity is necessary. Focusing on only one criterion could cause instability and imbalance in a broader context [13]. Smart packaging systems In legal terms, these are known as "intelligent materials and objects in contact with food" and can be defined as the materials and objects that control the state of packaged foods or their surroundings [38]. These include systems employed to detect, perceive, and record any changes within the package during its life cycle [39] and to communicate this information related to the quality or safety of the packaged product [18] in order not only to improve safety and quality, but also to warn about potential problems during the transport and storage of food [39]. Unlike active packaging, smart packaging does not intend to release components into the food [40]. The emergence of smart packaging systems has contributed towards a significant change in the existing perception of packaging, since they transform the traditional communication functions of packaging into intelligent communications [22], and interact with the consumer in terms of their ability to detect changes in the environment of the products [41]. Controlling the state of food content and alerting the consumer when food begins to deteriorate or is no longer fit for consumption has the potential to eliminate the waste caused by today’s "use by" dates that are necessarily conservative. While the smart package may require more resources for its production, the food supply system it supports will become much more sustainable [16]. One concept of smart packaging includes a system of interactions between the product, the package, and the environment as can be observed in Fig 2. If this technology were combined with low-impact packaging systems, there would be an increase in the environmental sustainability of the packaging and food preservation solution. Furthermore, if the contained food were produced using processes and products of low environmental impact, all the packaged food would be more sustainable [43]. Intelligent technology: MOSFET sensors A sensor can be defined as a device used to detect, locate, and/or quantify energy or matter that gives a signal for the detection or measurement of a physical or chemical property to which the device responds [41]. Chemical sensors generally contain two basic components connected in series: a molecular chemical recognition system (receptor) and a physicochemical transducer [44]. Receptors are based on the detector selectivity of the sensor, and can transform, in a continuous and reversible way, a chemical or physical parameter into energy, while a transducer converts this energy into a useful analytical signal, that is, an electrical signal. In comparison with indicators, sensors are fast, accurate, and reliable, although their application in packaging systems is often more complicated. Indicators are more commercialized than sensors because they are more economical and can be verified at a glance; however, they fail to provide information on the quality of food in real time [39]. It is of special importance that the reaction with ethylene in the chosen sensor is reversible, since the container will be reused. The technology chosen for the smart part of the container includes metal-oxide semiconductor field-effect transistor (MOSFET) sensors. These sensors comprise three layers: a silicon Aspects of sustainability and design engineering for the production of interconnected smart food packaging PLOS ONE | https://doi.org/10.1371/journal.pone.0216555 May 8, 2019 5 / 15 semiconductor, an insulator of silicon oxide, and a catalytic metal (Pd, Pt, Ir, Rh) called the "gate" [45]. An MSP430 microcontroller, connected to the electric current, is attached to the sensors. Plastics chosen for the manufacture of the container The packaging is made of plastic since it is in this material that most innovations are made. There is also an addition of two plastic layers, so that the desired physical and barrier properties are achieved. The property of resistance is a major priority, since it holds the key to achieving the desired useful life and minimizes any damage in the transport of the food to the supermarket. The use of bioplastics was considered, but these materials have less favourable barrier and mechanical properties than common plastics, and would result in an undesirable increase in the input of material. In addition, conversions involving energy consumption are required to move bioplastics from biological raw materials to useful molecules [16]. On the other hand, the use of biodegradable plastics was also considered; their useful life is approximately 6 months, during which they gradually lose their properties. Logically, since a container with a long shelf life is desired, this is not an option, at least initially. Finally, the container is composed of an outer layer of Polyethylene Terephthalate (PET), with high hardness and low oxygen permeability and an internal layer of High Density Polyethylene (HDPE), which provides impact resistance and low moisture permeability. A mixture of 75/25 PET/HDPE is used, and as an adhesive, the copolymer commercially known as Surlyn (a copolymer of ethylene and 6.5% by weight of methacrylic acid partially neutralized with zinc) is chosen, since its operation has been observed in studies, such as [46]. Fig 2. Product-packaging-environment interaction for smart packaging. Adapted from [42]. https://doi.org/10.1371/journal.pone.0216555.g002 Aspects of sustainability and design engineering for the production of interconnected smart food packaging PLOS ONE | https://doi.org/10.1371/journal.pone.0216555 May 8, 2019 6 / 15 Theory and calculations For the Life Cycle Assessment of the interconnected smart packaging, SimaPro Software and the Ecoindicator 99 methodology are used. Objective and scope Life Cycle Assessments should be based on a defined service unit: the functional unit delivered to a consumer through the value chain. Therefore, for the present study, one (1) interconnected intelligent plastic PET/HDPE bilayer container with a volume of 5L was chosen as the functional unit [16]. The scope of the Life Cycle Assessment covered the transport and extrusion of PET and HDPE granules, the coextrusion of the laminates obtained, the thermoforming of the final packaging, the coupling of the sensors in the container, the distribution of the containers in the Spanish territory, the use of the container, and then the analysis of its possible disposal at the end of its useful life. The Ecoindicator 99 methodology is used, and hence the scope of this LCA covers the following impacts: climate change, depletion of the ozone layer, acidification/eutrophication (combined), carcinogenesis, organic respiratory compounds, inorganic respiratory compounds, ionizing radiation, eco-toxicity, land use, mineral resources, and fossil resources. Inventory analysis Mass inventory. The measures of the container are established under the consideration that it has to be transportable, and consistent with the purchases made by a family type, which is set at 2 Kg of climacteric fruit per week (12 medium apples), which corresponds to a volume of 4560 L, and that it should be rectangular in shape in order to be practical at the time of placing it inside the refrigerator. The final measurements are determined: length 0.25m, width 0.20m, and height 0.10m, with a lid length of 0.25m, width 0.20m, and height 0.02m, thereby establishing a total volume of 5000L. The thickness is set at 1cm of which considered a logical measure and approximately 0.0075m is PET and 0.0025m HDPE. The masses of the sensor and the MSP430 microcontroller employed are both estimated at 0.05Kg. The masses of PET, HDPE, and Surlyn are determined by the container measurements and the density of the materials, resulting in values of 2.15 kg of PET, 0.99 kg of HDPE and 0.24 kg of Surlyn per container. Energy inventory. Three energy inputs are determined. The first is production: extrusion, coextrusion, and thermoforming are observed within this stage. The second entry is that of use: the sensor is considered as turned on once every 6 hours, and this sensor determines the shelf life of the container itself, since it is in contact with the atmosphere of the food and is estimated to have greater use than the other components. Its useful life is 15 months. The main elements of this stage include the MOSFET sensor, for which a measurement time of 10 min and a maximum current of 0.1 A are determined, leading to a calculated consumption of 24840000J, and the microcontroller MSP430, which in active mode consumes 0.00025A, and in real-time clock mode (when the sensor is not measuring) consumes 1e-6A, with a total consumption calculated for the 15 months at 62100J. The third entry occurs during the distribution, for which trucks are chosen that transport 40 tons and comply with the Euro 5 standard. It is assumed that the acquisition of the inputs Aspects of sustainability and design engineering for the production of interconnected smart food packaging PLOS ONE | https://doi.org/10.1371/journal.pone.0216555 May 8, 2019 7 / 15 for the container, and their distribution is carried out in Spain. A distance of 500 km is therefore used, which constitutes the average distance between the main Spanish cities. For this stage, post-consumer waste collection is excluded. Discussion of the end of life of the container Multilayer plastic is not recyclable, and hence end-of-life scenarios may initially only include incineration and disposal to landfills [47]. On the other hand, PET does not degrade in landfills, and it has been shown that there is no degradation of organic compounds in landfills due to the presence of an anaerobic environment [48], therefore, this scenario is not an option for the container in this study either. The possible option for the smart packaging involves incineration, carried out with energy recovery. Results Life Cycle Assessment (LCA) and Cradle to Cradle (C2C) comparison To begin with, C2C is a philosophy that establishes clear objectives at the beginning of the process, while LCA proposes the identification of "hotspots" together with the measurement of the environmental burden of a product [49]. The C2C approach enhances the creation of beneficial products, while in the LCA, products contaminate by definition, since they consume resources and finally produce some type of waste at the end of life [49]. Regarding intellectual property, in the case of C2C, the McDonough Braungart Design Chemistry (MBDC) [11] in Charlottesville, Virginia, owns the Cradle to Cradle trademark and the Environmental Protection Encouragement Agency (EPEA) in Hamburg, Germany holds the licence for its use. The C2C Product Innovation Institute (California) is in charge of the certification of the products. On the other hand, the LCA has been developed by a global community of professionals and is not owned by anyone in particular. Part of its coordination is under the authority of the UNEP-SETAC Lifecycle, and it is ISO 14040/44 that defines the applicability framework [49]. In terms of communication and marketing, C2C places the client as part of the solution through the purchase of certified products, while the LCA communicates the hotspots that can be reduced through redesign [49]. The LCA can be used to compare different but functionally similar products while the C2C compares one product in the different stages of its optimization [49]. The C2C approach states that the best source depends on the local situation, while for the LCA the best source depends on the calculation of environmental impacts [49]. Impact characterization It is clear that the greatest environmental impact in most categories is led by the intelligent system components (Fig 3). Impact assessment by standardized category First, the category of greatest impact is that of the consumption of resources, and is led by the chosen plastics (PET and HDPE). This impact arises from the fact that they are non-renewable raw materials (Fig 4). This is followed by the category of human well-being, where there is a high impact of the electronic components of the intelligent system (microcontroller, sensor, and cable). The third Aspects of sustainability and design engineering for the production of interconnected smart food packaging PLOS ONE | https://doi.org/10.1371/journal.pone.0216555 May 8, 2019 8 / 15 and last category of impact involves the quality of the ecosystem, which lies far below the other two aforementioned categories. Single score per component The greatest total impact is observed to be caused by PET, which is closely followed by that of the sensor, and then by the microcontroller (Fig 5). Fig 3. Results of the characterization of LCA for intelligent interconnected packaging in the SimaPro software. https://doi.org/10.1371/journal.pone.0216555.g003 Fig 4. Standardized impact values in the different categories of the LCA for smart interconnected packaging in the SimaPro software. https://doi.org/10.1371/journal.pone.0216555.g004 Aspects of sustainability and design engineering for the production of interconnected smart food packaging PLOS ONE | https://doi.org/10.1371/journal.pone.0216555 May 8, 2019 9 / 15