That of sustainability is a broad concept that goes far beyond the simple environmental aspect. Thus, to define a product, process or service as “sustainable,” it must be so from the environmental, economic and social perspectives.

The engineering and subsequent application of polymeric materials has, undoubtedly, brought benefits to the human species: electronics, medicine, renewable energy, food, and transportation are just some of the areas in which plastics have sanctioned a radical change. The #plasticfree campaign demonizes and condemns the use of plastics but, tends to divert attention from the real problem: “the use that is made of plastics.” Plastics are engineered materials: flexibility, strength, light weight, excellent thermal, electrical and chemical properties are just some of the reasons why we simply cannot do without them. In fact, plastics make an immense contribution to environmental sustainability because of their recyclability, which, however, raises questions about the quality of the secondary raw material, and their energy-saving potential. A 2016 study conducted by Trucost for the American Chemistry Council tried to quantify the beneficial impact of using plastics compared to possible alternatives. For all possible application areas of polymeric materials, it was imagined to replace them with one or more different materials and calculate the related potential environmental impacts. The materials considered as alternatives to plastics are as follows:

• Steel, iron and tin
• Aluminum
• Glass
• Paper and Cardboard
• Fabrics
• Wood
• Rock wool
• Leather
• Resin and rubber

From studies by Denkstatt (2011) and Franklin Associates (2013), through Trucost data, the substitution ratios between plastics and other materials are derived and are shown in the following table.

For each sector of the consumer goods market, the distribution of materials that make up the alternative was also calculated for the product to provide the same function. The following figure shows, briefly, the compositions of the various alternatives.

_{¹ Denkstatt. 2011. The impact of plastics on life cycle energy consumption and greenhouse gas emissions in Europe}

_{² Franklin Associates. 2013. Impact of Plastics Packaging on Life Cycle Energy Consumption and Greenhouse Gas Emissions in the United States and Canada}

Once the substitution ratios were calculated, the environmental impact throughout the life cycle was assessed using a cradle-to-grave approach: this approach, typical of the Life Cycle Assessment methodology, examines processes from the extraction of raw materials to the end of life (EoL) of the product, whether disposal or recycling. Life Cycle Assessment is a standardized methodology, and standardized by UNI EN ISO 14040 of 2006 and UNI EN ISO 14044 of 2018, which allows precisely to assess the potential environmental impacts associated with a process, product or service.

Quantification of potential environmental impacts is then done through computational models that transform matter and energy flows into “global warming,” “eutrophication,” “acidification,” etc. These same models also allow environmental impacts to be transformed into damage to human health, ecosystem and resource consumption. Environmental impacts retain a concrete physical meaning while damages are synthetic parameters that allow, more easily, decision-making in the case of comparisons between products, processes and services. In addition, the calculated impacts have been expressed in monetary terms ($) so as to assess their social cost.

PLASTIC VS. ALTERNATIVES: ENVIRONMENTAL COSTS

The study shows that the environmental cost of a ton of plastic is slightly higher than that of a ton of alternative material (average value, ed.). What really makes a difference, however, is how 400% alternative material is needed to ensure the same functionality for the product. Consequently, for the same object (or functional unit), plastic provides an environmental cost equal to 25% of the alternative.

Aluminum, often referred to as a plastic substitute, accounts, on average, for 6 percent by mass of the mix of alternative materials used to replace polymeric materials. It is responsible, however, for about 39 percent of environmental costs, due to the high energy demand of production processes. The same argument can be made for glass, however, which boasts the highest recyclability (100 percent) and thus returns potentially lower environmental impacts and costs.

THE BENEFIT OF MORE SUSTAINABLE USE OF PLASTICS
Plastic proves to be more sustainable than potential alternatives, but the environmental cost associated with its use throughout the consumer goods sector could, however, soon exceed $209 billion.

More sustainable use of polymeric materials could therefore help reduce the magnitude of these environmental costs:

• Bioplastics-have the potential to reduce greenhouse gas emissions by 30 to 80 percent compared to traditional plastics. They could lead to problems of competition between land to be devoted to agricultural or biomass production. One possible solution is to use residues from other production sectors or to use high-efficiency biomass that requires small-scale land to produce;
• Biodegradable plastics-they can be traditional plastics or bioplastics and have additives that increase their biodegradability. This solution could solve the problem of plastic accumulation in the environment but could negatively impact the net greenhouse gas balance. It may, moreover, still be necessary to set up collection and treatment facilities because the rate of degradation would be a function of the composition of the plastic material. A recent study also explains how the adoption of current plastics biodegradation technologies does not appear to reduce the amount of polymeric materials impacting the oceans;
• Designing for recycling-designing plastic packaging with the recycling phase in mind could maximize the recoverability of polymeric materials. With this in mind, there are guidelines to help manufacturers at the design stage.

CONCLUSIONS
Imagining the replacement of plastics by modern society is a thought that leaves much to be desired. Our society is so deeply based on polymeric materials that it is inextricably linked to them. The main motivation for this is that plastic is a profoundly effective and efficient material. What needs to change, then, is how it is used and to rethink processes and products to make them even more efficient:

1. Imagining powering polymer materials manufacturing processes with renewable energy would help significantly reduce their impact in terms of greenhouse gas emissions (-15% to -30%), air, water and land pollution. This would result in a decrease in environmental costs of up to $15 billion;
2. Rethinking products by making them use less plastic (e.g., by switching from rigid to flexible packaging) could lead to an additional reduction in environmental costs of up to $15 billion;
3. Transportation, along with production, of plastics materials accounts for about 25 percent of total environmental costs (about $50 billion). The use of more effective and efficient propulsion systems (electric, hydrogen, hybrid, low emission) could reduce this value by up to $11 billion;
4. The implementation of circular economy policies resulting in improved collection and recycling systems could have huge impacts in Europe, Asia and North America by reducing the flows of plastics that end up in the oceans.