Characterisation of the In-Situ Polymerisation Production Process for Continuous Fibre Reinforced Thermoplastics (Karakterisatie van het in-situ polymerisatie productieproces voor continu vezelsterkte thermoplasten)

De voordelen van een thermoplastische matrix in continu vezelversterkte composieten ten opzichte van thermoharders zijn ondermeer een verhoogde impactweerstand en de mogelijkheid tot heropsmelten van de matrix waardoor er meerdere recyclage-mogelijkheden zijn. Deze voordelen worden echter overschaduwd door de hoge smelviscositeit van de matrix die de impregnatie van de vezelversterking bemoeilijkt. In-situ polymerisatie van cyclische oligomeren, zoals CBT® hars dat polymeriseert tot de thermoplastische technische kunststof poly(butyleen tereftalaat), vereenvoudigt niet alleen de impregnatie, het laat bovendien toe om productiemethodes voor thermohardende composieten, zoals RTM, te gebruiken.In dit onderzoek wordt de mogelijkheid om composieten isotherm te produceren met CBT® hars aangetoond. Bovendien worden ook de resulterende matrix- en composieteigenschappen gekarakteriseerd. Hoewel het moleculair gewicht en de conversie dalen in aanwezigheid van glasvezels, hebben deze een berperkte invloed op de composieteigenschappen. Het isotherm karakter van het productieproces aan de andere kant leidt tot simultane polymerisatie en kristallisatie. Hierdoor worden georiënteerde, dikke lamellen met weinig verbindingsmoleculen gevormd wat leidt tot een bros matrixgedrag en een verlaagde impactweerstand van de composieten.Tenslotte werd een meer fundamentele studie van het kristallisatieproces uitgevoerd met behulp van synchotron straling. De bekomen morfologie bestaat uit een drie-fasen structuur opgebouwd uit semi-dense stapels. Deze stapels bestaan uit vloeibaar amorf afgewisseld met dense lamellen, die op hun beurt zijn opgebouwd uit kristallijne korrels en een dense, amorfe fractie.Ch1 Introduction 1 Ch2 Literature review 5 Ch3 Problem statement 49 Ch4 Materials and Methods 41 Ch5 Composites: Production and Properties 71 Ch6 Properties and morphology of pCBT 105 Ch7 Time-resolved X-ray measurements 125 Ch8 Conclusions and Outlook 167 AppA Production of a leaf spring prototype 171 AppB Principles of X-ray scattering 177 AppC Thermoplastic Polyurethanes 187status: publishe

In situ polymerization of thermoplastic composites based on cyclic oligomers

The high melt viscosity of thermoplastics is the main issue when producing continuously reinforced thermoplastic composites. For this reason, production methods for thermoplastic and thermoset composites differ substantially. Lowering the viscosity of thermoplastics to a value below 1 Pa.s enables the use of thermoset production methods such as resin transfer molding (RTM). In order to achieve these low viscosities, a low viscous mixture of prepolymers and catalyst can be infused into a mold where the polymerization reaction takes place. Only a limited number of polymerization reactions are compatible with a closed mold process. These polymerization reactions proceed rapidly compared to the curing reaction of thermosets used in RTM. Therefore, the processing window is narrow, and managing the processing parameters is crucial. This paper describes the production and properties of a glass fiber reinforced polyester produced from cyclic oligoesters.status: publishe

Properties of poly(butylene terephthatlate) polymerized from cyclic oligomers and its composites

The high viscosity of thermoplastic matrices hampers fiber impregnation. This problem can be overcome by using low viscous polymeric precursors such as cyclic butylene terephthalate (CBT® resins), which polymerize to form a thermoplastic matrix. This allows thermoset production techniques, like resin transfer molding (RTM), to be used for the production of textile reinforced thermoplastics. Due to the processing route and more specifically the time-temperature profile, inherent to the RTM process, the crystallites of the matrix consist out of well-defined, thick and well-oriented crystal lamellae. Together with a high overall degree of crystallinity and a low density of tie molecules, these large and perfect crystals cause polymer brittleness. Matrix brittleness lowers the transverse strength of unidirectional composites to below the matrix strength, but leaves the mechanical properties in the fiber direction unaffected. Although not a valid option for the RTM production route, crystallization from a truly random melt and at a sufficiently high cooling rate would substantially improve the ductility.status: publishe

Friction induced vibration in windscreen wiper contacts

This research is aimed at understanding the mechanisms that give rise to friction induced noise in automotive windscreen wipers, with a focus on frequencies between 500 and 3500 Hz. To study this phenomenon, experimental friction, sound, and high-speed video measurements are combined with finite element modeling of a rubber wiper/glass contact. In agreement with previous research, simultaneous sound and friction measurements showed that wiper noise in this frequency range results from the negative damping effect caused by the dependence of friction on speed in the mixed lubrication regime. Furthermore, during sliding, the friction induced noise recorded by the microphone occurred in one of two frequency ranges (close to 1000 Hz and between 2000 and 2500 Hz). These coincided closely with the eigen-frequencies of first two bending modes, predicted by finite element modeling. Experimental observations also showed the wiper to be oscillating backward and forward without any torsional motion and that the thickness of the glass had no effect on the emitted noise. These observations highlight how friction induced noise—although caused by conditions within contact—has characteristics that are determined by the structure of the excited component. A number of additional findings are made. Most importantly, both experiment and finite element modeling showed that the presence of water in contact with the wiper modulates the frequency and amplitude of the emitted noise by effectively adding mass to the vibrating system. While this is occurring, Faraday-like standing waves are observed in the water. In addition to this, friction induced vibration is shown only to occur for glass surfaces with intermediate surface energies, which is possibly due to high contact angles preventing water reaching the contact. Based on the understanding gained, a number of suggestions are made regarding means of reducing windscreen wiper noise