The resistance of functionalised PET samples to hydrolytic degradation

  • Kimberley Miller

Student thesis: Doctoral Thesis


It is well documented in the literature that poly(ethylene terephthalate) (PET) undergoes hydrolysis. PET has been previously used in short lifetime applications such as food packaging and textile fibers. The condition that PET is exposed to when used in these applications allows hydrolysis to occur very slowly, and so does not cause any concern. In recent years PET has been considered for more long term outdoor applications such as use in solar cells. In these applications, it is a concern that PET is a hydrolysis sensitive polymer.One of the tried and tested ways to reduce the impact of hydrolytic degradation is to involve lowering the carboxyl end group concentration. An esterification reaction between PET and epoxides will successfully lower the carboxyl end group concentration. Three epoxides were investigated, namely; Cardura, Heloxy and Vikolox.Reliable titration and nuclear magnetic resonance (NMR) methods were utilised during this PhD to detect the esterification reaction and how quickly it was occurring. All three epoxides were shown to be subjected to the esterification reaction with the model compounds benzoic acid and poly(ethylene isophthalate) (PEI). Cardura, however, was shown to have a greater extent of reaction with carboxyl end groups than the other epoxides. The NMR data obtained for the 3 epoxides clearly show that a higher level of esterification reaction is occurring in Cardura when compared to Heloxy and Vikolox (after 1 minute at 150 oC, all epoxide groups were reacted in the Cardura samples, whereas no reaction was detected in the other 2 epoxide samples).;DuPont Teijin Films (DTF) requires the additive they will use to be capable of being manufactured in a reactive extrusion process. Their current processing lines could be easily modified to include a liquid feed, preventing the substantial capital costs that would otherwise be required to manufacture the new product. A small scale system was established to determine if the selected additives could be added in this way; all three epoxides could successfully be added in this manner. Though all three epoxides could be added, the carboxylic end group concentration of the PET samples containing Cardura was reduced the most. With the addition of 6% Cardura the carboxylic acid was reduced from 41.54 to 7.56 equivalence per 106 grams, but was only reduced to 17.28 and 18.02 equivalents per 106 grams for samples of PET containing 6% Heloxy and 6% Vikolox respectively. The fact that the carboxyl end group concentration of the samples containing Cardura is significantly lower allows Cardura to be added in a lower concentration, which is desired in order to minimise raw material costs.For Cardura to be a suitable additive, it must display extrusion stability when exposed to various conditions. Additionally, the chosen additive must not have any adverse effects on the polymer samples properties such as clarity, molecular weight, crystallinity and melting point. Cardura was shown to have good extrusion stability and no adverse effect on the polymer sample. Cardura was shown to increase the resistance to hydrolytic degradation but to not have any adverse effects on the thermal or thermal-oxidative degradation of the polymer samples. The data gathered in this thesis indicates that Cardura could be utilised to increase the resistance of PET to hydrolytic degradation in long term outdoor applications such as solar cells.
Date of Award10 Nov 2017
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council) & Dupont Teijin Films UK
SupervisorJohn Liggat (Supervisor) & Peter Skabara (Supervisor)

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