Towards sustainable engineering plastics: Synthesis and characterisation of semi-aromatic polyamides based on renewable 2,5-furandicarboxylic acid (FDCA)

Abstract

The production and use of plastics is expected to double in the next 20 years from the current 407 million tons per year. Almost 99% of these plastics are produced from non-renewable fossil-based feedstocks. The anticipated volume growth in plastic production and increasing world population and urbanisation will place severe burden on these unsustainable resources. The net emission of greenhouse gases into the atmosphere and challenges associated with the disposal of these materials are other factors that is driving the research in this area towards more sustainably sourced materials. 2,5-furandicarboxylic acid (FDCA) has been termed as a “sleeping giant” due to its unexplored potential as a renewable monomer and a platform chemical.
Chapter 1 of this thesis introduces the subject area of research with focus on furanic monomers and polymeric material produced from them. Literature related to polyamides in general and furan-based polyamides (FPAs) in particular has been reviewed and presented in this chapter.
In Chapter 2, preliminary investigations into the synthesis of a model furan-based polyamide PA6F, were carried out using an eco-friendly and solvent-free melt polymerisation approach. A two-step synthesis, combining oligomerisation and polycondensation steps, was developed and tested in a small scale thin-film reactor. A range of catalysts were screened to facilitate the amidation of FDCA. Titanium(IV) isopropoxide (TIPT) and titanium(IV) citrate (TIC) were found to be active catalysts for PA6F production. The reaction conditions were optimised in order to produce a reasonably high molecular weight polymer. PA6F produced after optimisation, demonstrated significantly higher molecular weights (Mw ~ 46 kg/mol) and better thermal properties (Tg ~ 130 ᵒC) compared to those synthesised using conventional method.
Chapter 3 explores the up-scaling potential of PA6F by synthesis in a 250 mL glass reactor using the conditions and best performing catalysts identified in Chapter 2. The effect of catalyst loadings, polycondensation temperature and reaction stoichiometry was assessed. PA6F structure and properties were also investigated in more detail using a range of analytical techniques. The resulting polymers again showed consistently better molecular weights. The incorporation of HMDA in slight excess showed positive impact on the molecular weights. On the other hand, DSC, DMA and WAXD revealed a predominantly amorphous nature of PA6F.
The scope of catalytic melt polymerisation technique was further extended in Chapter 4 by employing some common aliphatic diamines used in the polyamide production. In addition to PA6F synthesised earlier, four other FPAs (PA4F, PA8F, PA10F and PA6MF) were produced using TIPT catalyst. The polymer structures and thermomechanical properties were investigated. Depending on the methylene chain length, the Mw of the obtained polymers ranged between 23 – 36 kg/mol, while the glass transition temperatures were in the range of 97-140 ᵒC. All polymers showed exceptional thermal stability during TGA. PA10F, a 100% bio-based polyamide, displayed the highest thermal stability (Td-max = 446 ᵒC) among tested FPAs. However, all FPAs were found to be mainly amorphous, as confirmed with DSC, DMA and WAXD analysis.
To address the FPA’s lower tendency to crystallise, copolymerisation of two other aromatic diesters, i.e. DMTPA and DMTDC, was explored in Chapter 5. Again, the analogous catalytic melt polymerisation technique was employed to synthesise PA6F/6T and PA6F/6S type copolymers containing different ratios of DMTPA and DMTD. DMTPA was found to be more effective monomer to induce some degree of crystallisation when 50 mol% of DMFDC was replaced by DMTPA in the copolymer. The semi-crystalline nature of the 50/50 sample was confirmed with help of DSC, DMA and WAXD analysis. Furthermore, taking the advantage of renewable nature of C10 diamine, PA10F/10T random and block copolymers were also produced. It was validated that block copolymers displayed semi-crystalline behaviour at a significantly lower proportion of non-renewable DMTPA compared to random copolymers.

Date of Award	11 Oct 2021
Original language	English
Awarding Institution	University of Bath
Supervisor	Matthew Davidson (Supervisor) & Janet Scott (Supervisor)