Terpenes as a sustainable monomer source for 3D printable inks and resins

Additive manufacturing (AM) is the process by which 3D structures are built layer-by-layer, commonly from polymer based inks, resins or filaments. These techniques generally generate a reduced quantity of waste compared to other manufacturing techniques. AM is particularly useful for the production of complex and custom 3D parts across medical, automotive and aerospace industries.
However, as petrochemical sources of monomer deplete and the worldwide quantity of plastic waste continues to increase, it is key that renewably sourced and recyclable alternatives to these inks and resins are pioneered. The field of AM is therefore faced with two fundamental challenges with respect to sustainability, there is a limited range of renewably sourced polymers suitable for AM inks and a reliance on chemical crosslinking between polymer chains to rapidly induce cure hinders recyclability of printed products.The current lack of renewably sourced polymers suitable for AM can be attributed to the rapid reactivities necessary for sufficient print times and the strict viscosity range required of monomers, pre-polymers and printed polymers. Chemical crosslinks are commonly relied upon in AM as a method of rapidly obtaining high molecular weight polymers capable of supporting subsequent layers, crosslinks however tend to be irreversible which presents major challenges for achieving chemical circularity at the end of product life-time. Terpenes and their derivatives offer a particularly promising class of molecular building blocks for renewably sourced polymers. Firstly, terpenes can be sourced from a range of biobased feedstocks, for example -pinene and -pinene are readily obtainable from turpentine an abundant waste oil from the paper and pulp industry. Secondly, a versatile range of polymers can be derived through the functionalisation of terpene skeletons, including polyolefins, poly(meth)acrylates, polyesters and polyacrylamides. Finally, through copolymerisation of "glassy" cyclic terpenes with "rubbery" acyclic terpenes, a range of different materials with varying glass transitions temperature's can be achieved.

Living anionic polymerisation (LAP) offers opportunity to synthesise polymers with highly defined mass, dispersity, composition and architecture making it an ideal candidate to produce pre-polymers of highly defined viscosity. Group transfer polymerisation (GTP) displays extremely fast reaction kinetics producing high molecular weight polymers without crosslinks, and therefore presents a compelling alternative to the crosslinking chemistries commonly used across AM.

Thus, this project will investigate the LAP of terpene based monomers and the advantages it provides over radical polymerisations, particularly how molecular weight distribution impacts viscosity. The printability of these terpene pre-polymers will then be assessed, leading on to the printing of some novel terpene based formulations through either photoinitiated or two component printing techniques. GTP within a AM technique will also be trailed using terpene based monomers and pre-polymers to produce printed polymers with limited crosslinking, with a particular focus improving the reaction kinetics of some previously slow reacting monomers.

This CDT will deliver impact aligned to the following agendas:

People
A2P will provide over 60 PhD graduates with the skill sets required to deliver innovative sustainable products and processes into the UK chemicals manufacturing industry. A2P will inspire and develop leaders who will:
- understand the needs of industrial end-users;
- embed sustainability across a range of sectors; and
- catalyse the transition to a more productive and resilient UK economy.

Economy
A2P will promote a step change towards a circular economy that embraces resilience and efficiency in terms of atoms and energy. The benefits of adopting more sustainable design principles and smarter production are clear. For example, the global production of active pharmaceutical ingredients (APIs) has been estimated at 65,000-100,000 tonnes per annum. The scale of associated waste is > 10 million tonnes per annum with a disposal cost of more than £15 billion. Consequently, even a modest efficiency increase by applying new, more sustainable chemical processes would deliver substantial economic savings and environmental wins. A2P will seek and deliver systematic gains across all sectors of the chemicals manufacturing industry. Our goals of providing cross-scale training in chemical sciences with economic and life- cycle awareness will drive uptake of sustainable best practice in UK industry, leading to improved economic competitiveness.

Knowledge
This CDT will deliver significant new knowledge in the development of more sustainable processes and products. It will integrate the philosophy of sustainability with catalysis, synthetic methodology, process engineering, and scale-up. Critical concepts such as energy/resource efficiency, life cycle analysis, recycling, and sustainability metrics will become seamlessly joined to what is considered a 'normal' approach to new molecular products. This knowledge and experience will be shared through publications, conferences and other engagement activities. A2P partners will provide efficient routes to market ensuring the efficient translation and transferal of new technologies is realised, ensuring impact is achieved.

Society
The chemistry-using industries manufacture a rich portfolio of products that are critical in maintaining a high quality of life in the UK. A2P will provide highly trained people and new knowledge to develop smarter, better products, whilst increasing the efficiency and sustainability of chemicals manufacture.
To amplify the impacts of our CDT, effective public engagement and technology transfer will become crucially important. As a general comment, 'sustainability' styled research is often regarded in a positive light by society, however, the science that underpins its effective implementation is often poorly appreciated. The University of Nottingham has developed an effective communication portfolio (with dedicated outreach staff) to tackle this issue. In addition to more traditional routes of scientific communication and dissemination, A2P will develop a portfolio of engagement and outreach activities including blogs, webpages, public outreach events, and contribution of material to our award-winning YouTube channel, www.periodicvideos.com.

A2P will build on our successful Sustainable Chemicals and Processes Industry Forum (SCIF), which will provide entry to networks with a wide range of chemical science end-users (spanning multinationals through to speciality SMEs), policy makers and regulators. We will share new scientific developments and best practice with leaders in these areas, to help realise the full impact of our CDT. Annual showcase events will provide a forum where knowledge may be disseminated to partners, we will broaden these events to include participants from thematically linked CDTs from across the UK, we will build on our track record of delivering hi-impact inter-CDT events with complementary centres hosted by the Universities of Bath and Bristol.