Introduction

Abstract Polymers have always been indispensable in meeting human needs, as they have properties attractive for many purposes. However, they also bring environmental challenges that are being addressed in many ways. Originally only natural polymeric materials such as wood were available, but now there are also many synthetic polymers: the plastics and elastomers. They are thermoplastics or thermosets, depending on whether their molecules are separate or connected by crosslinks: this determines how they are formed into shape. Polymers are used sometimes in engineered products requiring stiffness and strength greater than they possess. Then their mechanical properties are enhanced by fibre reinforcement, for example. Synthetic polymers now play essential roles in most manufactured products. The need to achieve sustainability, including reduction of dependence on fossil fuels, is stimulating rapid growth in recycling of polymers after use, and new sources for polymers are being developed, based on biomass instead of oil.