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Solid state polylactid-poly(methyl methacrylate) precurors for the in-line production of foam core sandwich structures

Type of publication Peer-reviewed
Publikationsform Proceedings (peer-reviewed)
Publication date 2015
Author Yonghoon Yoon Smole Joze Rheme Martin Thoemen heiko Plummer Christopher J.G. Manson Jan-Anders,
Project A new generation of ultra-light bio-based particleboard produced with an in-line foaming step
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Proceedings (peer-reviewed)

Title of proceedings 20th International Conference on Composite Materials
Place Compenhag

Abstract

The overall aim of this work is to develop precursors suitable for the in-line production of lightweight bio-based foam core sandwich structures with consolidated wood particle facings, using a non-VOC blowing agent. A preliminary study of poly(D,L-lactide) (PDLLA)/CO2 showed that solid expandable precursors could be prepared by impregnation with CO2 under both subcritical and supercritical conditions. However, because the particleboard process involves temperatures, T, well above the effective glass transition temperature, Tg, of the PDLLA/CO2, foam collapse tended to occur during consolidation of facings. The PDLLA was therefore extrusion-compounded with poly(methyl methacrylate) (PMMA) in order to increase its Tg. That the thermal characteristics of the PLA could be modified by blending with PMMA was confirmed by differential scanning calorimetric measurements of Tg and the evolution of the corresponding α-transition from dynamic mechanical analysis over a wide range of compositions. The uptake of liquid CO2 during impregnation at 10 °C and 5 MPa was found to decrease with PMMA content, but the subsequent desorption rates were comparable with those obtained with unmodified PDLLA. It was consequently possible to adapt an impregnation and conditioning procedure developed previously for PDLLA to give solid granular precursors from PDLLA-50 wt% PMMA blends that were stable during handling at room T, but contained sufficient CO2 for the generation of low density foams at T in the vicinity of 100 °C, as required by the particle-board process, in which water vapour is the primary vector for heat transport. The free expansion behaviour of the precursors was investigated systematically as a function of T, in order to establish process windows and investigate process-structure-property relationships. Model foam-core particleboard sandwich structures were then successfully prepared using an open hydraulic press and a single thermo-mechanical cycle, in which consolidation of the facings using a conventional binder and foam expansion took place simultaneously.
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