This critical review provides a survey illustrated by recent references of different strategies to achieve a sustainable conversion of biomass to bioproducts. Because of the huge number of chemical products that can be potentially manufactured, a selection of starting materials and targeted chemicals has been done. Also, thermochemical conversion processes such as biomass pyrolysis or gasification as well as the synthesis of biofuels were not considered. The synthesis of chemicals by conversion of platform molecules obtained by depolymerisation and fermentation of biopolymers is presently the most widely envisioned approach. Successful catalytic conversion of these building blocks into intermediates, specialties and fine chemicals will be examined. However, the platform molecule value chain is in competition with well-optimised, cost-effective synthesis routes from fossil resources to produce chemicals that have already a market. The literature covering alternative value chains whereby biopolymers are converted in one or few steps to functional materials will be analysed. This approach which does not require the use of isolated, pure chemicals is well adapted to produce high tonnage products, such as paper additives, paints, resins, foams, surfactants, lubricants, and plasticisers. Another objective of the review was to examine critically the green character of conversion processes because using renewables as raw materials does not exempt from abiding by green chemistry principles (368 references).

Conversion of biomass to selected chemical products

Much has been written about theory and practice in the law, and the tension between practitioners and theorists. Judges do not cite theoretical articles often; they rarely "apply" theories to particular cases. These arguments are not revisited. Instead the Essay explores the working and interaction of theory and practice, practitioners and theorists. The Essay starts with a story about solving a legal issue using our intellectual tools - theory, practice, and their progenies: experience and "gut." Next the Essay elaborates on the nature of theory, practice, experience and "gut." The third part of the Essay discusses theories that are helpful to practitioners and those that are less helpful. The Essay concludes that practitioners theorize, and theorists practice. They use these intellectual tools differently because the goals and orientations of theorists and practitioners, and the constraints under which they act, differ. Theory, practice, experience and "gut" help us think, remember, decide and create. They complement each other like the two sides of the same coin: distinct but inseparable.

Of Theory and Practice

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.

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Sustainable polymers from renewable resources

Conversion of Biomass into Chemicals over Metal Catalysts

Trends in bioconversion of lignocellulose: Biofuels, platform chemicals & biorefinery concept

The circular economy (CE) is perceived as a sustainable economic system where the economic growth is decoupled from the resources use, through the reduction and recirculation of natural resources. In the shift towards the CE, quantifying the circularity of products and services (or their contribution to the CE) is crucial in designing policies and business strategies, and prioritizing sustainable solutions based on evidence. New circularity metrics are being developed for that purpose, but they often present contradiction in both form and content, which contributes to confusion and misunderstanding of the CE concept. This review aims to map methodological developments regarding circularity metrics for products and services, in order to: (1) identify the foundations of circularity metrics used so far and their applications, (2) evaluate the validity of current circularity metrics, based on predefined requirements and a CE definition anchored in the sustainability concept, and (3) provide recommendations on how to measure circularity. The literature search provided a wide variety of CE metrics being developed and applied (seven measurement indices, nine assessment indicators and three assessment frameworks). However, none of them are addressing the CE concept in full, potentially leading to undesirable burden shifting from reduced material consumption to increased environmental, economic or social impacts. Additionally, new metrics under-represent the complexities of multiple cycles and the consequences of material downcycling. Circularity metrics intended to sustainable decision making should be comprehensive enough to avoid burden shifting, and clearly indicate how the benefits of recycling are allocated between the primary and secondary products.

Towards sustainable development through the circular economy—A review and critical assessment on current circularity metrics

This study assesses the environmental impact of polyethylene terephthalate (PET) bottle-to-fibre recycling using the methodology of life-cycle assessment (LCA). Four recycling cases, including mechanical recycling, semi-mechanical recycling, back-to-oligomer recycling and back-to-monomer recycling were analysed. Three allocation methods are applied for open-loop recycling, i.e. the “cut-off” approach, the “waste valuation” approach and the “system expansion” approach. Nine environmental impact indicators were analysed, i.e. non-renewable energy use (NREU), global warming potential (GWP), abiotic depletion, acidification, eutrophication, human toxicity, fresh water aquatic ecotoxicity, terrestrial ecotoxicity and photochemical oxidant formation. The LCA results are compared with virgin PET fibre and other commodity fibre products, i.e. cotton, viscose, PP (polypropylene) and PLA (polylactic acid). The LCA results show that recycled PET fibres offer important environmental benefits over virgin PET fibre. Depending on the allocation methods applied for open-loop-recycling, NREU savings of 40–85% and GWP savings of 25–75% can be achieved. Recycled PET fibres produced by mechanical recycling cause lower environmental impacts than virgin PET in at least eight out of a total of nine categories. Recycled fibres produced from chemical recycling allow to reduce impacts in six to seven out of a total of nine categories compared to virgin PET fibres. Note that while mechanical recycling has a better environmental profile than chemical recycling, chemically recycled fibres can be applied in a wider range of applications than mechanically recycled fibres.

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Open-loop recycling: A LCA case study of PET bottle-to-fibre recycling

Biobased plastics have experienced fast growth in the past decade thanks to the public concerns over the environment, climate change and the depletion of fossil fuels. This perspective provides an overview of the current global market of biobased plastics, their material properties, technical substitution potential and future market (for 2020). In addition, the technology and market development of three biobased plastics, namely polylactide (PLA), biobased polyethylene (PE) and biobased epoxy resin, are discussed in detail. The emerging biobased plastics market is still small compared to traditional biobased polymers and biomaterials. The global capacity of the emerging biobased plastics was only 0.36 million tonnes in 2007. However, the market grew strongly between 2003 and 2007 (approx. 40% per year). The technical substitution potential of biobased plastics replacing petrochemical plastics is estimated at 90%, demonstrating the enormous potential of biobased plastics. Global capacity of biobased plastics is expected to reach 3.45 million metric tonnes in 2020. Starch plastics, PLA, biobased PE, polyhydroxyalkanoates (PHA) and biobased epoxy resin are expected to be the major types of biobased plastics in the future.

Present and future development in plastics from biomass

Apart from conventional uses of polysaccharide materials, such as food, clothing, paper packaging and construction, new polysaccharide products and materials have been developed. This paper reviews life cycle assessment (LCA) studies in order to gain insight of the environmental profiles of polysaccharide products (e.g. viscose or natural fibre polymer composites) in comparison with their conventional counterparts (e.g. cotton or petrochemical polymers). The application areas covered are textiles, engineering materials and packing. It is found that for each stage of the life cycle (production, use phase and waste management) polysaccharide-based end products show better environmental profiles than their conventional counterparts in terms of non-renewable energy use (NREU) and greenhouse gas (GHG) emissions. Cotton is an exception, with high environmental impacts that are related to the use of fertilisers, herbicides, pesticides and high water consumption. The available literature for man-made cellulose fibres shows that they allow to reduce NREU and GHG emissions in the fibre production phase. No study has been found for the fabric production and the use phase of man-made cellulose textiles.

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Life cycle assessment of polysaccharide materials: a review

Man-made cellulose fibres have played an important role in the production of textile products for more than 70 years. The purpose of this study is to assess the environmental impact of man-made cellulose fibres. Life cycle assessment (LCA) was conducted for three types of fibres (i.e. Viscose, Modal and Tencel) produced by Lenzing AG. The functional unit is one tonne of staple fibre. The system boundary is cradle to factory gate. We compared the LCA results with other commodity fibres, namely cotton, PET and PP. Primary energy demand, water use, land use and the CML baseline impact categories were assessed. Sensitivity analyses were carried out to understand the influence of different allocation methods. In addition, three single score methods were introduced and applied. The LCA results show that four modern man-made cellulose fibre products, namely Tencel, Modal, Viscose (Austria) and Tencel (2012), have the lowest overall impact among all fibres studied. Viscose (Asia) has a higher overall impact than the other man-made cellulose fibres and is comparable to PET. Cotton is identified as the least preferred choice due to its high ecotoxicity impacts, eutrophication, water use and land use. The LCA results are influenced by the allocation methods applied; however, the ranking of all fibres does not change.

Li Shen

Papers

Towards sustainable development through the circular economy—A review and critical assessment on current circularity metrics

Open-loop recycling: A LCA case study of PET bottle-to-fibre recycling

Present and future development in plastics from biomass

Life cycle assessment of polysaccharide materials: a review

Environmental impact assessment of man-made cellulose fibres