• Fages, Jacques
• Sescousse, Romain
• Jiménez, Jennifer Andrea Villamil
• Benezet, Jean-Charles
• Moigne, Nicolas Le
• Sauceau, Martial

Abstract

In many industrial fields, the development of porous and light polymer composite structures is of great interest because of their several advantages compared to a massive solid of the same chemical nature. Batch foaming of polymers is a discontinuous process carried out normally in an autoclave. The samples are saturated in a pressurised vessel, andtheir foaming is achieved by inducing an instability into the system. Gas solubility in polymers increases with pressure but decreases with temperature. Therefore, in the batch foaming process, the instability can be induced by a sudden drop in pressure (pressure quenching) or by a raise in temperature thus causing polymer foaming1.Pressure quenching is largely used for its ease of implementation. This foaming technology has been used for different polymers including PLA-based composites. Silk, cellulose1, jute, and wood flour have been studied as fillers in PLA foams. The operating conditions have a great influence on final foam morphology, as well as fillers nature and content. In general, fillers enhance the crystallization kinetics and PLA melt strength. Foams with reduced cell size and expansion ratio and increased cell density can be obtained compared to pure PLA foams2.This work is intended to explain the effects of size and aspect ratio of fibres as well as its content, on the characteristics of PLA foams obtained by supercritical CO2-assisted batch process by pressure quenching, which have not been studied until today.Cellulose fibres (Rettenmaier France) of different aspect ratios were compounded with PLA by extrusion and, then injected in discs, to be analysed and foamed afterwards. A complete characterisation of the crystallisation phenomenon of composites through isothermal and non-isothermal DSC, microscopic and rheological studies have been made in order to understand the effect of fibre characteristics on the solidification and crystallisation phenomena. The initial fibres size and aspect ratio and the ones within the composites have been evaluated through image analysis; in the case of the fibres embedded in thecomposites, an extraction process was necessary.Temperatures going from 100 °C to 140 °C have been employed at a CO2 pressure of 15 MPa, firstly for pure PLA foaming, in order to determine the most appropriate operating conditions for the composites. An analysis of fibre effects on foam morphology, crystallinity, and foaming temperature is ongoing. Figure 1 shows first foams of pure PLA obtained atdifferent temperatures.Understanding the role of the filler size and aspect ratio, as well as the effect of supercritical CO2 and operating conditions on cell morphology of a composite foam, will allow to control its microstructure and therefore its characteristics.

Topics

• porous
• density
• impedance spectroscopy
• polymer
• extraction
• melt
• extrusion
• strength
• composite
• differential scanning calorimetry
• wood
• cellulose
• crystallization
• crystallinity
• quenching