Circular economy of polyisocyanurate insulation materials

Amesbury, Robert 2022. Circular economy of polyisocyanurate insulation materials. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

This thesis proposes a method for the circular use of isocyanates in insulation foam. Its outcomes were twofold: A series of hemi-labile ligands were prepared and complexed to Zn and Al. These complexes were screened as initiators for the cyclotrimerisation of alkyl and aryl isocyanates. A wide variety of reactivity and substrate tolerance was observed, highlighting the roles of electronic effects and steric crowding around the metal centre as well as the role of hemi-lability. A chemical recycling method was developed with the aim of recovering isocyanates from polyisocyanurate (PIR) insulation products. The product was found to be oligomeric methylenedianiline (MDA), the parent amine of the isocyanate included in the PIR formulation (methylene diphenyl diisocyanate, MDI). The effects of temperature, feed ratio, stirring speed and additives on the production of MDA and the consumption of the urethane bond was probed. The conversion of MDA to MDI using triphosgene was achieved, however the reactivity of the MDI was found to be poor, attributed to impurities not removed during synthesis. This thesis is divided into 7 chapters: Chapter 1 provides an introduction and overview of the current technologies surrounding the synthesis and recycling of polyurethane and polyisocyanurate materials. Typical monomers, catalysts and additives and their influence on the material properties of the polymer are discussed. The subsequent bonds formed in the polymer are listed, and their influence on the properties, as well as challenges they pose on the recycling are also included. The benefits and drawbacks of each recycling technology is discussed, and potential opportunities for innovation are identified. Chapter 2 is focused on the synthesis of a series of salicyalaldimine ligands and their complexes of Zn and Al. There is an emphasis on the producing complexes with a range of steric and electronic environments around the metal centre as well as a varying the hemi-lability of donor groups on the ligand. These complexes are characterised by NMR spectroscopy; this includes discussion of the nature of the hemi-lability confirmed using variable-temperature NMR spectroscopy, single-crystal X-ray diffraction, and computational modelling. Chapter 3 discusses the activity of the Zn and Al complexes as initiators for isocyanate cyclotrimerisation. A wide variety of aryl and alkyl isocyanates are iv screened, with varying degrees of efficacy. The mechanism of the cyclotrimerisation catalytic cycle is discussed with the assistance of DFT and NBO calculations. Chapter 4 investigates a novel piece of isocyanate chemistry, enabled via Zn mediated C-H functionalisation with the goal of synthesising highly functionalised primary amines. The intermediate complexes, a series of 6-coordinate N-phenylacetamide complexes are characterised by NMR spectroscopy and single-crystal X-ray diffraction, and their solution and solid-state structures are discussed. The enantioselectivity of the reaction is investigated using NMR spectroscopy. Chapter 5 describes the development of a chemical recycling process of polyisocyanurate insulation foam. The effects of temperature, feed ratio, stirring speed, and additives are investigated using FTIR spectroscopy. The product composition, and the fate of various components of the insulation foam are discussed in detail with the aid of mass spectrometry and NMR and FTIR spectroscopy. The production of isocyanate from recycled material is also explored. Chapter 6 Contains full characterising data and experimental details for the complexes, ligands and additional compounds prepared in this thesis. Computational details and atomic coordinates of proposed structures are listed. Chapter 7 Provides a summary of the findings of the thesis and outlines further avenues of investigation for future work.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Chemistry
Date of First Compliant Deposit:	7 February 2023
Last Modified:	05 Jan 2024 05:37
URI:	https://orca.cardiff.ac.uk/id/eprint/156544

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