Studies on the photodegradation of polyurethane foam

Student thesis: Doctoral Thesis

Abstract

Polyurethane (PU) is an extraordinary polymer well known for its superior mechanical properties, extensive applications, and tailorable formulations. However, specific chemistries used for their synthesis can make them susceptible to light absorption and photodegradation. This can adversely affect their lifetimes in the many industries to which they are applied. Many studies into their photodegradation have been carried out since the 1960s, primarily involving PU coatings, adhesives, and elastomers. The degradation of their foamed materials has been less commonly studied but becoming of greater interest in the field. The initial focus of this research was to fully understand the photodegradation of PU foam in a natural setting. To do so, PU foams synthesised using common, light-sensitive materials were subjected to accelerated conditions of solar radiation within a weatherometer. To identify the photochemical and photooxidative changes these materials were capable of in an outdoor setting, oxidative and non-oxidative weathering conditions were employed. The results of the oxidative and non-oxidative weathering studies demonstrate that chemical changes occur through the Photo-Fries Rearrangement of MDI, Norrish Type I and II reactions of carbonyl groups and photooxidation of the polyol segment. This study highlights the detrimental impact of an oxidative environment on foam chemistry and the consequential effects these changes have on their physical and mechanical properties. Exposure to solar radiation caused hardening of the foam surface which became increasingly friable upon increasing exposure. Exposing PU foams to the full spectrum of solar radiation demonstrated the photodegradative reaction that can occur simultaneously. Implementing specific wavelength studies of the foam took this research further by focusing on the effects of ultraviolet (UV) and visible (vis) light. This study showed that short wavelengths of light caused the most substantial chemical changes and was concluded to be the result of more photochemical changes coinciding with PU photooxidation. It was also demonstrated that the PU foam samples were also sensitive to light within the visible region. The photooxidative studies highlighted significant chemical changes to the foam’s polyol component and marked the final focus of this research study. Despite the absorption of light by ether-based polyols is not scientifically feasible, the work confirms their sensitivity to light and the reasoning behind this. Specific wavelength studies accentuated the impact of shorter, high-energy wavelengths of light on polymeric material. This was addressed through significant mass loss, extensive chemical changes, and the induced volatility of the polyol. Characterisation of the polyols chemical changes provided insightful evidence for the photodegradation pathway of the PU foam leading to the proposal of a full mechanistic pathway.
Date of Award23 May 2023
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde & EPSRC (Engineering and Physical Sciences Research Council)
SupervisorJohn Liggat (Supervisor) & Peter Cormack (Supervisor)

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