Schäfer, Hannes
Loading...
4 results
Now showing 1 - 4 of 4
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, An investigation of PLA/Babassu cold crystallization kinetics(Springer, 2019-12-06); 22 31 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Surface-initiated ring-opening polymerization of ɛ-caprolactone as a feasible approach to modify flax yarn(Elsevier, 2022-01); ; ; Surface-initiated ring-opening (SI-ROP) polymerization of ɛ-caprolactone is known as possible modification method to increase the hydrophobicity of cellulosic substrates. In this study SI-ROP of ɛ-caprolactone is applied on native and mercerized flax yarn. By use of triazabicyclodecene as catalyst, SI-ROP at room temperature was possible and poly-ɛ-caprolactone (PCL) was linked with a weight content of 4–10% to flax yarns. Besides a lower hydrophilicity an increased surface energy was achieved for PCL modified flax yarn. Furthermore, the positive effect of PCL linkage on the fibers surface regarding adhesion potential to an epoxy matrix was shown via conducting fiber-pull-out tests. After SI-ROP of ɛ-caprolactone on flax fiber surface a reduction of fiber pull-out up to 33% was achieved, evoked by physical improvement e.g. better wettability of fiber with epoxy matrix as well as enhanced crosslinking between the hydroxyl groups of the surface grafted PCL and the epoxy resin.journal articleBand:15261 30 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Crystallization behavior of polycaprolactone/babassu compounds(Springer, 2020-03-02); ; ; ; Polycaprolactone/babassu compounds were prepared in a laboratory internal mixer, their melt crystallization behavior was investigated using a differential scanning calorimeter, and their kinetics was correlated using the Pseudo-Avrami model, with cooling rates ranging from 2.5 to 15 °C min−1. Babassu filler did not affect significantly crystallization parameters, with maximum differences of 1.2 K in temperature and 3% in crystallinity, within experimental uncertainty. Regarding Pseudo-Avrami parameters, data were correlated for the interval 5–95% conversion, which seems to be appropriate for processing applications; the uncertainty associated with Pseudo-Avrami individual parameters is less than 1%, whereas the “rate parameter” K was found to be well represented by a quadratic function.journal articleBand:14341 19 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Steuerung funktioneller Materialeigenschaften eines Polybenzoxazin-Netzwerks über die Integration von Poly(caprolacton)-Oligomeren(2019-07-17); ; ; The present dissertation deals with the specific control of the functional properties of a bisphenol A based polybenzoxazine (PBA-a). Therefore, the thermoset was combined with the thermoplastic oligomer poly(caprolactone) (PCL). The influence of covalently integrated versus unbound PCL on polybenzoxazines properties was the main focus of this cumulative work and for that reason systematically analyzed by varying the PCL content in the polymer mixtures. The polyester end groups were functionally modified with a tosyl leaving group. In contrast to the hydroxy-terminated basic structure, the modified PCL could be covalently integrated into benzoxazines network. The copolymers homogeneous morphology observed by scanning electron micrographs of PCL/PBA-a revealed that the covalent incorporation of the polyester chains could prevent phase separation of the components as occurred for the unmodified PCL/PBA-a blend-like structures. A slightly decreased network density, due to the incorporated PCL chains, reduced the brittleness of samples with low contents of modified PCL (wPCL 30 %). Thus, toughness values of up to 1.66 MPa were achieved compared to 0.48 MPa for neat PBA-a. By increasing the content of the tosylated PCL in the samples (wPCL = 30 - 50 %) network density was lowered accordingly, resulting highly flexibilized polymers with an almost 10 times increased elongation at break compared to PBA-a. Due to the macroscopic phase separation, a further increase of the amount of unmodified PCL led to samples with even higher brittleness. Polymers with high levels of tosyl-modified PCL (wPCL = 60 - 80 %) exhibited thermoresponsive shape memory properties, which could be attributed to the presence of both covalently incorporated and free PCL in these samples with mixed bonding mode. The combination of the widened network and increased crystallinity are key factors to the displayed shape memory effect. In this work, benzoxazine networks with variable and functional properties have been successfully prepared due to the covalent integration of PCL oligomers. The deeper understanding of the structure-property relationship will facilitate a broader application of polybenzoxazine based materials.doctoral thesis400 372