JEC COMPOSITES MAGAZINE - Issue #45 - November/December 2008 - 67

- synthesis of new polymer architectures with tailored and controlled molecular structures, - catalysis in macromolecular chemistry, - preparation and characterization of composites and nanocomposites, - design of environmentally friendly polymeric/(nano)composite materials. Innovations in bio-based polymers: PLA-AII (nano)composites for packaging and technical applications High-performance CaSO4(AII)-filled PLA composites PLA-AII compositions with up to 50 wt% AII were prepared under optimized conditions by melt-compounding technology and the resulting composites were fully characterized to shed some light on the effect of adding filler to PLA (Galastic grade PLA supplied by Galactic SA, Belgium; Mn = 74,500 and D-LA content = 4%). First, it appears that adding AII to PLA does not detrimentally affect PLA molar masses [3]. Moreover, these two products from the same source as origin (LA fabrication process) can be melt-mixed to produce polymer composites with remarkable mechanical properties. For instance, tensile strength remained at a level higher than 35 MPa at filler contents as high as 50 wt%, without any filler surface treatment (Fig. 3), while rigidity (Young’s modulus) increased by more than 65% with respect to neat PLA. The Mabiolac project: PLA composites filled with calcium sulphate from the lactic acid fabrication process The Mabiolac R&D project was implemented as part of the Interreg III programme (Wallonie-France) in close collaboration with ENSC Lille and ENSAIT Roubaix (France). The project focuses on the original production of novel (nano)composite materials using PLA as polyester matrix for targeted applications in rigid packaging, in the field of technical and engineering applications, and in the production of textile fibres. It is well known that incorporating mineral fillers in PLA can be a worthwhile solution to reduce its overall cost and improve specific properties such as rigidity, dimensional stability, heat deflection temperature, processability, etc. Selected results related to the preparation and characterization of new highlyfilled PLA composites engineered with specific end-use properties such as high tensile strength/rigidity, toughness/impact strength or flame-retardant properties, are summarized here. The basic building block for PLA, lactic acid (LA), can be produced through chemical synthesis or carbohydrate fermentation. In conventional processes, LA obtained by carbohydrate fermentation is isolated by neutralization with Ca(OH)2 to precipitate its calcium salt (calcium lactate), followed by sulphuric acid treatment to obtain the main product (LA). This procedure produces large amounts of hydrated calcium sulphate, i.e., about one kilogram of gypsum is formed as by-product for each kilogram of LA [3, 4]. This inorganic filler, adequately prepared, was found to be a potentially worthwhile solution to produce PLA-based composites. Like other aliphatic polyesters, PLA is stable in the molten state, provided that it is adequately stabilized and intensively dried before processing, with a 250-ppm maximum acceptable water content. Therefore, to produce PLA composites, it is of prime importance to dry the polyester resin, but also to dehydrate the filler prior to melt compounding. To produce high-performance PLA composites and prevent polyester degradation by hydrolysis, it was demonstrated that it is important to use the β-anhydrite AII form generated by dehydration of gypsum hemihydrate (D50: 9 μm) at 500°C, which proved to be much more suitable for melt-blending with PLA with respect to other CaSO4 anhydrite forms, which are by far too sensitive to atmospheric water absorption [3]. This behaviour makes it possible to preserve polyester molecular weights and thermomechanical properties of the final products. Fig. 3: Tensile strength at break of neat PLA compared to PLA-AII composites (ASTM D-638, 1mm/min, type V specimens). Furthermore, to achieve the desired end-use properties, the adhesion/interfacial properties between the polymer matrix (PLA) and filler (AII) were tuned up by adding different coating/compatibilizer agents (silanes, titanates, stearic acid, etc.). As an illustration, PLA-based compositions with an inorganic content as high as 40 wt% in an AII surface treated by silane agents displayed mechanical properties comparable to those of some filled engineering polymers, e.g. a tensile strength around 55 MPa. Moreover, predictive mathematical models for filled thermoplastics confirm favourable interactions between the dried AII particles and PLA matrix, even for a filler without any previous surface treatment. This is remarkably evidenced by SEM (Scanning Electron Microscopy) images of the fractured surfaces of highly filled composites, showing excellent filler dispersion throughout the polyester matrix (Fig. 4). In terms of thermo-mechanical properties, PLA-AII composites (Fig. 5), which can be easily obtained after melt-compounding as granules, are attractive for rigid packaging or technical applications, due to good thermal stability and excellent processability with traditional techniques such as injection No45 November-December 2008 / jec composites magazine

JEC COMPOSITES MAGAZINE - Issue #45 - November/December 2008

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