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Studies on the thermal degradation of thermosetting polyimides and their composites
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
2022 (English)Licentiate thesis, comprehensive summary (Other academic)Alternative title
Studier av termisk degradering i härdplastpolyimider och dess kompositer (Swedish)
Abstract [en]

The thesis contains a background and reflections section, an introduction, and three appended articles. The first section is reserved for some of the background and basics on polymers and polymer composites and a discussion on their effect on our everyday lives. The introduction gives a brief recap of the project. The articles contain the research that was performed on the thermal oxidation of thermosetting polyimides and their composites during the project.

The first article covered the thermal oxidative degradation of satin weave and thin-ply composites made by resin transfer molding with carbon fibers and thermosetting polyimide. The degradation was studied by weight loss measurements and X-ray computed microtomography. The weight loss measurements showed that the initial desorption stage during ageing followed Fickian behavior and the proposed model. It was also observed that the satin weave composites formed crack clusters that grew into a network of cracks, voids and delaminations throughout the specimens as the ageing time progressed, while the thin-ply composites only formed delaminations at the free edges.

The second manuscript studied the behavior of the neat polyimide resin when aged for up to 1500 hours in ambient air, and compared it with a newly developed polyimide formulation, with slightly altered chemical composition. The reduced amount of internal crosslinkers in the newer formulation was expected to enhance the fracture toughness of the material. Three-point bending, differential scanning calorimetry, dilatometry, weight loss, light optical microscopy and nanoindentation experiments were performed and highlighted the differences in the thermal and mechanical properties of the two formulations. A slight increase in the fracture toughness was observed, while the glass transition of the new formulation had decreased.

The third manuscript was aimed at continuing the discussion from the second article on the differences between the two thermosetting polyimides. Thermogravimetric scans showed that the polyimide formulations behaved very similarly under thermal oxidative tests. The initial analysis gave indications that the model could capture well the degradation at high temperatures, but is not adequate in predicting long-term degradation at temperatures around 288–400 °C.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2022.
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Keywords [en]
Polymer composites, Polyimide, Thermal oxidative degradation
National Category
Textile, Rubber and Polymeric Materials Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
URN: urn:nbn:se:ltu:diva-93613ISBN: 978-91-8048-188-5 (print)ISBN: 978-91-8048-189-2 (electronic)OAI: oai:DiVA.org:ltu-93613DiVA, id: diva2:1704105
Presentation
2022-12-20, E632, Luleå tekniska universitet, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2022-10-17 Created: 2022-10-17 Last updated: 2023-08-31Bibliographically approved
List of papers
1. Thermal oxidative aging of satin weave and thin-ply polyimide composites
Open this publication in new window or tab >>Thermal oxidative aging of satin weave and thin-ply polyimide composites
2022 (English)In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 43, no 5, p. 2615-2627Article in journal (Refereed) Published
Abstract [en]

The weight loss and damage development of satin weave and thin-ply carbon fiber-reinforced polyimide composites are studied during high temperature (288 and 320°C) aging in air. Two distinct regions are identified in the weight loss measurements—a rapid initial desorption and a subsequent slower weight loss, which is attributed to matrix degradation. The initial desorption stage is modeled by combining material constitutive properties from literature, micro-mechanics and a one-dimensional Fickian diffusion model. Two different damage patterns are observed by using optical microscopy and X-ray computed tomography on specimens before and after aging. Crack clusters form a network in satin weave composites, while edge delaminations are observed in thin-ply laminates, which are known for their enhanced resistance to matrix cracking.

Place, publisher, year, edition, pages
John Wiley & Sons, 2022
National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-89750 (URN)10.1002/pc.26561 (DOI)000763429300001 ()2-s2.0-85125530795 (Scopus ID)
Note

Validerad;2022;Nivå 2;2022-05-31 (johcin)

Available from: 2022-03-18 Created: 2022-03-18 Last updated: 2024-04-05Bibliographically approved
2. The Influence of Ethynyl In-Chain Crosslinkers on the Properties of 6FDA-Based Polyimides
Open this publication in new window or tab >>The Influence of Ethynyl In-Chain Crosslinkers on the Properties of 6FDA-Based Polyimides
2022 (English)In: Materials, E-ISSN 1996-1944, Vol. 16, no 1, article id 169Article in journal (Refereed) Published
Abstract [en]

Two 4,4′-(hexafluoroisopropylidene)diphthalic anhydride-based thermosetting polyimide formulations with varied amounts of crosslinking sites were compared to understand the influence of crosslinking density on fracture toughness, glass transition temperature and thermal oxidative stability. The thermal and mechanical properties of both materials were investigated through a series of single-edge notched beams, differential scanning calorimetry, dilatometry, weight loss, light optical microscopy and nanoindentation experiments. It was found out that the reduced crosslinking resulted in slightly increased fracture toughness but decreased the Tg of the material. No significant difference could be observed in the thermal oxidative stability with the experimental techniques considered.

Place, publisher, year, edition, pages
MDPI, 2022
Keywords
Polyimide, Fracture toughness, Thermal oxidative aging, DSC, Nano-indentation
National Category
Textile, Rubber and Polymeric Materials
Research subject
Machine Elements; Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-93612 (URN)10.3390/ma16010169 (DOI)000909327000001 ()36614507 (PubMedID)2-s2.0-85145654445 (Scopus ID)
Note

Validerad;2023;Nivå 2;2023-01-16 (hanlid);

This article has previously appeared as a manuscript in a thesis.

Available from: 2022-10-14 Created: 2022-10-14 Last updated: 2024-07-04Bibliographically approved
3. Assessing the thermo-oxidative degradation of thermosetting polyimides
Open this publication in new window or tab >>Assessing the thermo-oxidative degradation of thermosetting polyimides
(English)Manuscript (preprint) (Other academic)
Keywords
Polyimide, 6FDA, Thermo-oxidative degradation, TGA, Isoconversional analysis, Thermodynamic parameters
National Category
Textile, Rubber and Polymeric Materials
Identifiers
urn:nbn:se:ltu:diva-93614 (URN)
Available from: 2022-10-14 Created: 2022-10-14 Last updated: 2024-04-05

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