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Sustainable polymers from renewable resources
时间:2016-05-27 浏览:

Sustainable polymers from renewable resources

 

Renewable resources are used increasingly in the production of polymers. In particular, monomers such as carbon dioxide,terpenes, vegetable oils and carbohydrates can be used as feedstocks for the manufacture of a variety of sustainable materials and products, including elastomers, plastics, hydrogels, flexible electronics, resins, engineering polymers and composites. Efficient catalysis is required to produce monomers, to facilitate selective polymerizations and to enable recycling or upcycling of waste materials. There are opportunities to use such sustainable polymers in both high-value areas and in basic applications such as packaging. Life-cycle assessment can be used to quantify the environmental benefits of sustainable polymers.

 

Modern life relies on polymers, from the materials that are used to make clothing, houses, cars and aeroplanes to those with sophisticated applications in medicine, diagnostics and electronics.The vast majority of these polymers are derived from petrochemicals. Many polymers contribute considerably to an improved quality of life and a cleaner environment, for example, as materials that enable the purification of water or as polymer composites with improved fuel economy for aerospace applications. Only about 6% of the oil produced worldwide is used in the manufacture of polymers, yet there are environmental concerns associated with both the raw materials used to make them1 and their end-of-life options2. Although there is no panacea for these complex environmental problems, one option is to develop more-‘sustainable’ polymers. Research has focused mainly on replacing fossil raw materials with renewable alternatives and on developing end-of-life options that generate materials that are suitable for recycling or biodegradation. Where biomass from plants is used as the renewable raw material, the polymers are often referred to as bioderived. In terms of biodegradation, it is important to recognize that some petrochemical polymers are biodegradable, and that not all bioderived polymers will biodegrade. The potential for sustainable polymers is stimulated by policy, legislation and international agreements, including some negotiated at the 2015 United Nations Climate Change Conference (COP21) (ref. 3) in Paris on reducing CO2 emissions. Although the commercial application of bioderived polymers can benefit from improvements in environmental performance (as well as from supportive policy or legislation), it will also require favourable economics and material properties that are better than seen in conventional materials, including thermal resistance, mechanical strength, processability and compatibility. Taken together, these are tough criteria that could explain, in part, why there are few commercially successful sustainable polymers at present.

 

In 2014, for example, only 1.7 megatonnes of more than 300 megatonnes of polymers produced globally were bioderived, of which the three main products, by volume, were polyethylene terephthalate (PET), polyethylene and polylactide4. There are two general approaches to preparing sustainable polymers: lessening the environmental impact of conventional production, for example by using biomass to make known monomers or polymers such as PET and polyethylene; and the preparation of new, ‘sustainable’ structures, such as polylactide, from renewable raw materials.

 

This Review highlights some of the opportunities for creating sustainable polymers from four renewable raw materials: carbon dioxide, terpenes, vegetable oils and carbohydrates (Fig. 1). These feedstocks enable the production of polymers and materials with a wide range of properties and applications. (The use of modified natural polymers such as cotton, silk, thermoplastic starch, cellulose derivatives and natural peptides is not discussed, although the potential for producing polymers from lignin is mentioned briefly.) The examples highlighted have been selected because they address some of the overarching challenges of sustainable polymer production.

 

The first challenge is that transformation of renewable resources and the production of polymers must be highly efficient to reduce costs. Production can be made more efficient by using mixtures of raw materials, producing monomers of lower purity or through the ‘upcycling’ of waste materials from agriculture or industry. Second, sustainable polymers must show complementary or improved properties compared with the polymers available at present. Applications with high-value markets, such as thermoplastic elastomers, rigid plastics and polyols, might present more favourable economics than applications such as packaging. Third, life-cycle assessment should be used to quantify the impact of sustainable polymers and to compare them with existing petrochemical benchmarks; this technique is usually used to assess environmental impacts and outputs that are associated with polymer production. Although the need for such comparisons might seem obvious, there are complexities associated with selecting appropriate benchmarks, boundaries and data5. At present, materials in the early stages of development, particularly in academic labs, are not routinely examined by life-cycle assessment. Here we highlight examples of life-cycle assessment that demonstrate the improved sustainability of the polymers, and where the findings are relevant to the design and development of future materials.

 

Zhu Y, Romain C, Williams C K. Sustainable polymers from renewable resources[J]. Nature, 2016, 540(7633): 354-362.

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