Oberflächenmodifizierung von Fasermaterialien und textilen Halbzeugen zur Verwendung in Faserverbundwerkstoffen

authored by: Natalie Vellguth
supervised by: Franz Renz
Abstract: In the plastics sector, composites with the advantageous properties of fibers as reinforcing material and the plastic matrix as force transmitter are used for special applications. The compatibility of the two materials is essential for processing and the resulting composite properties. In addition to high-performance fibers such as carbon, natural fibers are also being used more and more fre-quently, which show more advantageous properties in certain areas of application, such as han-dling, availability, (energy) costs and, at the same time, ecological aspects such as the CO2 foot-print. Natural fibers as reinforcement components cannot compete with high-performance fibers, but are interesting for many applications in which these high requirements are not necessary. Due to their chemical structure and composition, natural fibers are hydrophilic and thermally stable up to about 200 °C, which is why processing with a hydrophobic plastic matrix and plastics with melting points >200 °C is challenging. The use of natural fibers in engineering thermoplastics, which have higher melting temperatures, is therefore not readily possible at present. The aim of this work is to realize the processing of natural fibers also at temperatures in the melting temper-ature range of engineering thermoplastics. In the present work, semi-finished textiles made of flax are used for this purpose and incorporated into two different polyamides. The flax used is coated with a thermoset resin system based on an epoxy resin to protect it from thermally induced degradation and compared with a standard pro-cess for adhesion-promoting sizing, silanization with aminopropyltriethoxysilane. The polyamide matrices used are a petro-based polyamide 6, an engineering thermoplastic with a melting tem-perature >200 °C, and a bio-based PA variant polyamide 11. The latter has a melting temperature below 200 °C. The methods are combined in each case in order to be able to draw conclusions about individual treatment steps. The processing of the materials takes place on a laboratory scale. Coating is carried out by means of manual coating by using rollers to achieve uniform distribution of the resin system. Silanization takes place on the scale of the targeted composites accordingly in plastic tanks. Treated and un-treated fabrics are pressed into composites using a hot press and polyamide films as matrix mate-rial, and individual test specimens are sawn from the resulting composites. The main characteri-zation methods include mechanical and thermal tests. For this purpose, tensile and bending tests are carried out on the specimens and their mechanical properties are investigated. Furthermore, a thermogravimetric analysis is used to relate the changes in properties of different treatments to thermal decomposition processes. Additionally, the samples will be exposed to various influences such as climate changes and isothermal treatments and then mechanically characterized in order to determine the effects of temperature and humidity on the fibers and the corresponding com-posites as a function of the fiber pretreatment. Due to the thermoset coating, changes in the resulting mechanical properties can be observed. Overall, the stretchability of the semi-finished textile products and their corresponding composites is reduced. With the aid of the coating, even after isothermal treatments in the hot press at 230 °C and after 600 s, higher mechanical properties are recorded than with untreated fibers. In addition, TGA measurements show that the degradation of uncoated fibers and fibers in the composite starts earlier and lasts for a longer period. Thermoset-coated fibers, on the other hand, degrade punctual and later.
Organisation(s): Institute of Inorganic Chemistry
Type: Doctoral thesis
No. of pages: 130
Publication date: 2023
Publication status: Published
Sustainable Development Goals: SDG 13 - Climate Action
Electronic version(s): https://doi.org/10.15488/14118 (Access: Open)