An update on the road to better plastics for a sustainable future

Three Perspectives and an Editorial highlight issues and advances in developing plastics that are more sustainable and easier to recycle. First, Marc A. Hillmyer discusses advances in making plastics and other polymers from plants, which are both an abundant and "renewable" source. Scientists have developed commercially viable processes for producing some of the key starting materials, or "monomers," from plant matter; for other such monomers, research is progressing. Another approach is to create completely new plant-based plastics. Precise control over modifying bio-based compounds can be challenging, but Hillmayer notes that scientists are working on addressing these deficiencies with new additives, comonomers, and control of mac­romolecular architectures. Another major challenge, he says, is not only converting these abundant resources into useful compounds, but doing so efficiently. Fundamental research is needed to find highly active and selective catalysts, and high-yielding and atom-economic metabolic pathways, he says. A Perspective by Jeannette M. Garcia and Megan L. Robertson evaluates why only a small percentage of plastic waste is recycled. Roughly half of the annual global produc­tion of solid plastics, or 150 million tons, is thrown away worldwide each year. In the U.S. alone, plastic waste costs an estimated $8.3 billion. The authors discuss a number of challenges when it comes to recycling, including those related to sorting different types of plastic, the energy required to recycle plastics, and expanding recycling technologies to be able to reuse tra­ditionally nonrecyclable polymers. Key ways to address these issues include the development of better catalysts, new polymers that are easier to recycle, and of ways to recycle mixed plastics, which may be aided by advanced computational modeling and data analytics, Garcia and Robertson say. In a third Perspective, Ann-Christine Albertsson and Minna Hakkarainen highlight challenges in developing degradable plastics. For many applications, plastic needs to be durable, yet that same characteristic means that plastic persists in natural environments. Scientists have attempted to engineer plastics that degrade more easily; however, natural environments can vary greatly in terms of factors that contribute to degradation, such as humidity, microorganisms, oxy­gen, sunlight, and temperature, the authors note. They say that, so far, the most widely accepted "environ­mentally degradable" polymer materials are based on aliphatic polyesters or starch with biodegradable chemi­cal bonds, which they say show some promise but still may not degrade rapidly or fully in all natural envi­ronments. Ultimately, the authors stress that scientists should learn from biological systems that often combine weak or switchable linkages with hierarchical structures, such as wood. In an accompanying Editorial, Ellen MacArthur underscores the urgent need for policymakers and business leaders to embrace more sustainable plastic practices. She notes that policy approaches that make plastic producers responsible for the entire product life cycle can be particularly effective; such approaches have recently been introduced in EU legislation. Shifting away from types of plastic that currently cannot be recycled will require a great degree of redesign and innovation, MacArthur emphasizes.

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