JEC COMPOSITES MAGAZINE - Issue #45 - November/December 2008 - 68

KNOW-HOW Biopolymer …/… The “green” challenge: high-performance PLA (nano)composites moulding, extrusion, compression moulding, etc. Furthermore, to enhance their performance and enlarge their field of application, adding a third component to PLA-AII composites (impact modifier, flame retardant, plasticizer, etc.) can be another alternative of choice. Fig. 6: Notched impact strength (Izod) of PLA-40 wt% AII composites with/without impact modifier (ASTM D 256 Method A, 3.46 m/s impact speed, 0.668 kg hammer). For unfilled PLA, impact strength = 2.6 KJ/m². Fig. 4: SEM pictures of the fractured surfaces (BSE mode) of unfilled PLA and highly-filled PLA-AII composites showing fine inorganic filler dispersion. Fig. 5: PLA-AII composites delivered as granules and mechanical test specimens as produced by injection moulding. Highly filled PLA composites with improved impact properties Unfortunately, at filler contents higher than 20 wt%, filled composites have low impact strength properties that become poorer with increasing CaSO4 (AII) content. Because these composites do not have the impact resistance required for some potential applications, they need to be impact modified in order to fulfil industry requirements. As for other mineral-filled polymers (PA, PET, PBT, etc.), adding an impact modifier, a plasticizer, etc. can be an alternative to increase impact strength performance [5, 6]. Among the commercially available impact modifiers (IM) suitable for improving PLA toughness, some specific ethylene or acrylic-based copolymers were very recently considered. In order to prepare filled composites with improved impact strength properties, selected IM that had previously been evaluated with the PLA matrix (Biomax Strong 100 (BS)DuPont, Paraloid BPM500 -Rohm and Haas, Lotader AX 8900 Arkema) were mixed within PLA and CaSO4 (AII). Interestingly enough, adding up to 10 wt% IM to highly filled composites (40 wt% filler) leads to an attractive two-to-three-times higher impact strength compared to the compositions without modifier (Fig. 6), while the glass transition temperature (Tg) of PLA matrix was unchanged. Ternary PLA-based (nano)composites with advanced flame retardant properties PLA-based composites are being considered more and more for the production of electrical or electronic devices (e.g., housings for notebook computers) that require excellent mechanical and flame-retardant properties. Mineral-filled composites, and more particularly AII-filled PLA composites, are of interest for these applications but, unfortunately, cannot be recommended for applications where advanced flame-retardant properties are sought. Polymer-based nanocomposites (PNCs) have attracted much attention from both the academic and industrial worlds. Because of this widespread interest, they are an important topic for R&D. PNCs are known to be a radical alternative to conventionally filled polymers due to their significantly improved properties (stiffness, thermal stability, fire retardancy, lower permeability, etc.), even at (nano)filler contents as low as 1-5 wt%. In this context, we have discovered [7] that the co-addition of AII and organo-modified layered silicates (OMLS) has synergistic effects on PLA flame retardancy by both significantly increasing time to ignition (tig) and decreasing maximum rate of heat release (HRR), as evidenced by cone calorimetry (Fig. 7), while specific UL 94HB fire testing reveals non-dripping properties. On the one hand, the materials containing either neat PLA or PLA with a high amount of CaSO4 (about 40-50 wt% AII) are characterized by intensive dripping and a total absence of charring behaviour. On the other hand, even though OMLSfilled PLA binary compositions no longer generate flamed droplets upon burning, the combustion speed is higher. Remarkably, the co-dispersion of both OMLS (3 wt%) and AII (40 wt%) in PLA compositions results in synergistic flameretardant properties, i.e. low combustion speed, absence of dripping and intensive char formation, while preserving attractive thermo-mechanical and melt-processing properties. Finally – and interestingly enough – in the perspective of targeted applications, it is worthwhile to point out that advanced flame-retardant properties, i.e. V0 rating according to jec composites magazine / No45 November-December 2008

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

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #45 - November/December 2008