Duromere Matrixsysteme aus nachwachsenden Rohstoffen für den Einsatz in naturfaserverstärkten Verbundwerkstoffen

Translated title of the contribution: Thermoset matrix systems made of renewable resources for the use in natural fiber reinforced composite materials

Andrea Todorovic

Research output: ThesisDoctoral Thesis

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Abstract

High-performance composites allow the production of stable components and component structures with a very low weight, because of their high strength and stiffness combined with low density. Due to their outstanding property profile, they have a high potential for use as lightweight materials, which makes them a particularly resource-efficient class of materials. As environmentally conscious thinking plays an increasingly important role, the development of bio-based materials (matrix, fiber) with lower environmental impact and a lower carbon footprint is of great importance. In the case of established bio-composites, the reference to nature in most cases refers only to the used reinforcement fibers (plant fibers). Thermosets made from petrochemical raw materials are still predominantly used as matrix materials. Therefore, this doctoral thesis deals with the development of a thermoset matrix (epoxy) based on renewable resources for composites with natural fiber reinforcement. Special focus is on reducing the use of ecologically critical and toxicologically dubious ingredients and additives, while maximizing thermo mechanical properties and bio-based carbon content. In order to obtain a bio-based epoxy resin, epoxidized hemp or linseed oil is thermally cross-linked with an anhydride (methyltetrahydrophtalic anhydride, MTHPA), an amine (triethylenetetramine, TETA) or a Lewis acid (ytterbium(III)trifluoromethanesulfonate, Yb(TF)3). The highest storage modulus and glass transition temperature were achieving with epoxidized linseed oil and MTHPA. The pronounced hydrolysis of anhydrides is identified as critical, which is particularly problematic when using natural fibers (inherently wet), since moisture leads to a hydrolytic degradation of the hardener and consequently to a lower cross-linking density and correspondingly reduced mechanical performance profile. In addition, anhydrides are produced from petrochemically based raw materials, resulting in a bio-based carbon content of max. 60 % (with regard to the whole resin system). In order to increase the bio-based carbon content, crystalline citric acid was used as a hardener. Without the addition of accelerators or other additives, citric acid and epoxidized linseed oil were used to develop a fully bio-based epoxy resin and optimized with regard to its property profile and curing conditions. Subsequently, on the basis of this resin system and flax fiber reinforcement a toxicologically and ecologically compatible (with regard to processing and use) composite with a bio-based carbon content of 100 % was analyzed with regard to morphological properties. The storage modulus and glass transition temperature were analyzed by DMA. This system has also shown a certain sensitivity to moisture (hydrolysis of epoxy groups). Systematic studies showed, that a negative influence of moisture on the cross-linking reaction and consequently on the mechanical performance of the resin system or the composite is largely avoidable by pre-drying of fibers. The results demonstrate that biogenic raw materials are also suitable for the production of high-performance materials and thus make an important contribution to the transition to a bio-based industry.
Translated title of the contributionThermoset matrix systems made of renewable resources for the use in natural fiber reinforced composite materials
Original languageGerman
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Bonten, Christian, Assessor A (external), External person
  • Stana Kleinscheck, Karin, Assessor B (external), External person
  • Kern, Wolfgang, Co-Supervisor (internal)
  • Pinter, Gerald, Supervisor (internal)
Publication statusPublished - 2021

Bibliographical note

embargoed until null

Keywords

  • epoxidized plant oil
  • biobased epoxyresin
  • moisture sensitivity
  • natural-fiber reinforced composite
  • high-performance material

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