Beitrag zur Charakterisierung des Werkstoffverhaltens von aPA 6 für die Realisierung eines robusten T-RTM-Prozesses

Die Herstellung von thermoplastischen Faserverbunden im T-RTM-Prozess wurde in den letzten Jahren im Rahmen von Forschungs- und Entwicklungsprojekten anhand mehrerer Anwendungen demonstriert. Die Verwendung der reaktiven, niederviskosen Monomerschmelze ermöglicht die schnelle Infiltration von Faserhalbzeugen, ist jedoch sehr empfindlich gegenüber äußeren Einflüssen. Einer der größten Einflussfaktoren ist Wasser, das in Form von Luftfeuchtigkeit in Kontakt mit den zu verarbeitenden Materialien kommt. Die während der Verarbeitung eingebrachten Wassermoleküle reduzieren die Reaktivität der Monomerschmelze. Eine reproduzierbare Produktion ist ohne die Berücksichtigung und Kompensation des Wassereinflusses nicht möglich. Ziel der Arbeit ist es zunächst, den Wassereinfluss auf die anionische Polymerisation von ε-Caprolactam zu quantifizieren. Zuerst wird der theoretische Wassereinfluss anhand der chemi-schen Reaktionsgleichungen berechnet, um die Größenordnung des Einflusses zu ermitteln. Die anschließende Charakterisierung der Wasseraufnahme der Matrixkomponenten und Glasfaserhalbzeuge gibt Aufschluss über das Sorptionsverhalten der Materialien und deren maximale Feuchtebeladung. Ein bestehendes Reaktionskinetikmodell und ein Viskositätsmodell werden im ersten Teil der Arbeit so erweitert, dass die Kinetik und der Viskositätsverlauf in Abhängigkeit der Anzahl der in der Schmelze vorhandenen Aktivator- und Katalysatormoleküle berechnet werden können. Im Rahmen dieser Arbeit wird eine Möglichkeit aufgezeigt, den Wassereinfluss durch Zugabe von Aktivator und Katalysator zu kompensieren. Die Bestimmung des Verhältnisses, bei der Reaktion von Wassermolekülen mit Aktivator- bzw. Katalysatormolekülen, wird für eine Kompensation des Wassers benötigt. Diese Kompensation bietet den Vorteil, bereits im Material befindliches Wasser zu binden, sodass die ursprüngliche Reaktionskinetik wiederhergestellt werden kann. Im zweiten Teil dieser Arbeit wird der Wassereinfluss auf die anionische Polymerisation im T-RTM-Prozess untersucht. Die Analyse des Druckverlaufs in der Kavität während der Polymeri-sation zeigt, dass der Druckverlauf als Indikator für das Stattfinden der Polymerisation genutzt werden kann. Anschließend wird der Einfluss der Wasserzugabe und die Kompensation anhand der physikalischen (Restmonomergehalt, Molekulargewicht) und mechanischen Eigenschaften (Zug- und Biegeeigenschaften) polymerisierter aPA 6- und glasfaserverstärkter Proben ermittelt. Des Weiteren werden die mechanischen Eigenschaften unverstärkter und verstärkter Platten nach der Kompensation des Wassereinflusses charakterisiert. Es kann gezeigt werden, dass die Steifigkeit und Festigkeit nach der ersten Kompensation des Wassers vergleichbar mit den Eigenschaften der Referenzproben sind. Diese Arbeit liefert einen Beitrag zum Verständnis des Wassereinflusses und dessen Kompensation für die Verarbeitung von ε-Caprolactam zur präziseren Definition der Prozessparameter und Prozessfenster im T-RTM-Prozess. Die Einfüllzeit der Matrixkomponenten, Trocknungszeit der Glasfasern, Handlingszeit der Glasfaserhalbzeuge vom Ofen bis ins Werkzeug und Injektionszeit werden anhand der ermittelten Ergebnisse abgeleitet. Es kann gezeigt werden, dass Glasfasern mit entsprechendem Sizing eine sehr geringe Feuchtebeladung besitzen und dadurch eine geringe Rolle bei der Beeinflussung der anionischen Polymerisation spielen. Die Hygroskopie der Matrixkomponenten verursacht eine schnelle Feuchtebeladung während der Einfüllzeit. Deshalb ist die Definition der maximalen Einfüllzeit ein wesentlicher Parameter bei der Realisierung eines reproduzierbaren T-RTM-Prozesses

Moisture adsorption and desorption behavior of raw materials for the t-rtm process

The use of fiber reinforced plastics (FRPs) has significant potential to reduce the weight of components. As regards the sustainability of these components, thermoplastic matrices offer more potential for recycling than thermoset ones. A possible manufacturing process for the production of thermoplastic FRPs is thermoplastic resin transfer molding (T-RTM). In this very moisture-sensitive process, ε-caprolactam in addition to an activator and catalyst polymerizes anionically to polyamide 6 (aPA6). The anionic polymerization of aPA6 is slowed down or even completely blocked by the presence of water. This study analyses the sorption behavior of the matrix, fiber, binder and core materials for the production of anionic polyamide 6 composites, which are processed in the thermoplastic RTM process. Water vapor sorption measurements are used to determine the adsorption and desorption behavior of the materials. The maximum moisture loading of the materials provides information about the water adsorption capacity of the material. This knowledge is crucial for correct handling of the materials to achieve a fast process and good properties of the final product

Enhanced Piezoresponse and Nonlinear Optical Properties of Fluorinated Self-Assembled Peptide Nanotubes

Self-assembled L,L-diphenylalanine (FF) nanostructures offer an attractive platform for photonics and nonlinear optics. The nonlinear optical (NLO) coefficients of FF nanotubes depend on the diameter of the tube [S. Khanra et al. Phys. Chem. Chem. Phys. 19(4), 3084-3093 (2017)]. To further enhance the NLO properties of FF, we search for structural modifications. Here, we report on the synthesis of fluorinated FF dipeptides by replacing one ortho-hydrogen atom in each of the phenyl groups of FF by a fluorine atom. Density-functional theoretical calculations yield insights into minimum energy conformers of fluorinated FF (Fl-FF). Fl-FF self-assembles akin to FF into micron-length tubes. The effects of fluorination are evaluated on the piezoelectric response and nonlinear optical properties. The piezoelectric d15 coefficient of Fl-FF is found to be more than 10 times higher than that of FF nanotubes, and the intensity of second harmonic generation (SHG) polarimetry from individual Fl-FF nanotubes is more than 20 times that of individual FF nanotubes. Furthermore, we obtain SHG images to compare the intensities of FF and Fl-FF tubes. This work demonstrates the potential of fluorine substitution in other self-assembled biomimetic peptides for enhancing nonlinear optical response and piezoelectricity

Moisture sorption of ɛ-caprolactam and its influence on the anionic polymerization in the thermoplastic RTM-process - An overview

Thermoplastic fibre reinforced composites (FRPs) offer, in comparison to duromeric composites, a range of advantages. Higher impact strength, simple functionality and good recyclability are the main features of these composite parts. Thermoplastic resin transfer moulding (T-RTM) is an already extensively investigated manufacturing method for such components. As matrix components "-caprolactam is used in combination with activator and catalyst. The anionic ringopening polymerization (aROP) is sensitive to external influences such as water. The chemical reactions of the matrix components with water are examined in detail and explained according to their probability of occurrence. Since water absorption in the process cannot be excluded when materials are processed in series production, the sorption behaviour of the materials is very important. This has not yet been characterized in detail, which is why this paper considers the basics of sorption measurement of the materials used in the T-RTM process, and discusses suitable measurement methods. Finally, a calculation of the deactivated amounts of activator and catalyst in relation to the reaction rate serves as a basis for further experiments of cycle time optimization in the T-RTM process

Influence of water during manufacturing of APA6 in the thermoplastic RTM process

The thermoplastic resin transfer molding (T-RTM) process has the potential for high-volume production of high performance fiber-reinforced components in the automotive industry. The fast anionic polymerization of APA6 and the development of robust injection equipment lead to short cycle times. The sensitivity against water of the reactive APA6 is well known. All resin components from the manufacturer are dried to achieve water content below 200 ppm. In T-RTM high-performance composite manufacturing fibers, binder systems or core materials are needed. During the manufacturing (preforming, handling, infiltration) of these materials it is necessary to ensure that the total amount of water is small enough to achieve good polymerization. Previous studies established the influence of water for non-activated polymerization. However, there is no knowledge about the influence of water during T-RTM manufacturing using fast-reacting activated polymerization. In this paper, different concentrations of catalyst are investigated to analyze the influence of water in the T-RTM process during curing of the resin. Residual monomer content and viscosity number was measured to analyze the conversion of manufactured plates. To characterize the impact on the mechanical properties, tensile tests were performed. The results show the possibility to monitor the anionic polymerization during the manufacturing by observing the trend of the cavity pressures. In addition, the influence of water on the conversion and the resulting mechanical properties can be compensated by the concentration of the catalyst

Compensation of Water Influence on Anionic Polymerization of ε-Caprolactam: 1. Chemistry and Experiments

The activated anionic ring opening polymerization of ε-caprolactam to polyamide 6 is highly sensitive to external influences such as water. Based on an initial theory, preliminary reaction kinetic tests are carried out with the aim of compensating the influence of the water by increasing the activator and catalyst concentration. Different formulations of activator and catalyst were studied to understand the influence of water on the concentration of activator and catalyst. It was found that the compensation of added water with activator and catalyst restores the original reaction time. The test plates produced are examined with regard to their mechanical characteristics and the polymer properties. The results of the mechanical characterization show no significant impairment after compensation of the added water. The physical properties of the matrix show degradation with repeated compensation. However, the residual ε-caprolactam content remains below the critical value of 1% for three of the four investigated formulations

Characterization of the interlaminar shear strength of fibre metal laminates with reactively processed thermoplastic matrix

The interface shear strength of fibre metal laminates with thermoplastic matrix is characterised by edge shear tests. Therefor eleven different surface treatments of the metal surface (DC04) are tested. The treatments are combined in three steps. First, a mechanical or chemical treatment is applied. Second, the mechanical or chemical treatment is combined with an adhesion promoter and at least a mechanical treatment and chemical treatment are combined and finished with adhesion promoter

Moisture Adsorption and Desorption Behavior of Raw Materials for the T-RTM Process

The use of fiber reinforced plastics (FRPs) has significant potential to reduce the weight of components. As regards the sustainability of these components, thermoplastic matrices offer more potential for recycling than thermoset ones. A possible manufacturing process for the production of thermoplastic FRPs is thermoplastic resin transfer molding (T-RTM). In this very moisture-sensitive process, ε-caprolactam in addition to an activator and catalyst polymerizes anionically to polyamide 6 (aPA6). The anionic polymerization of aPA6 is slowed down or even completely blocked by the presence of water. This study analyses the sorption behavior of the matrix, fiber, binder and core materials for the production of anionic polyamide 6 composites, which are processed in the thermoplastic RTM process. Water vapor sorption measurements are used to determine the adsorption and desorption behavior of the materials. The maximum moisture loading of the materials provides information about the water adsorption capacity of the material. This knowledge is crucial for correct handling of the materials to achieve a fast process and good properties of the final product