Marius Murariu, Samira Benali, Yoann Paint, Jean-Marie Raquez, Leila Bonnaud and Philippe Dubois. Laboratory of Polymeric and Composite Materials, ...
INTERREG efface les frontières Union Européenne – Fonds Européen de Développement Régional
Current progress in the production of PLA - ZnO nanocomposites Marius Murariu, Samira Benali, Yoann Paint, Jean-Marie Raquez, Leila Bonnaud and Philippe Dubois
Laboratory of Polymeric and Composite Materials, Center of Innovation and Research in Materials & Polymers (CIRMAP), Materia Nova Research Center & University of Mons, 20 Place du Parc, 7000 - Mons, Belgium CIRMAP: To the best of our knowledge, the first study with positive results
Introduction The role of nanotechnology and of bioplastics is increasing together in applications requiring high performance materials (automotive, electrical & electronic products, etc.) where the carbon footprint, biodegradability or recycling possibility is considered an additional advantage. Polylactide (PLA), a polyester produced from renewable resources, has a key-position in the market of biopolymers for various applications (packaging, fibers, appliance/technical parts). Following the studies accomplished by CIRMAP, for the first time was reported production of PLA- ZnO nanocomposites (via melt-blending technology and using a specifically treated nanofiller to limit polyester degradation). These new nanocomposites have been successfully extrapolated in the production of fibers, films, or other materials, showing multifunctional properties (anti-UV, antibacterial, barrier, etc.) The aim of this communication is to assess the beneficial effects of a designed chain extender on the performances of PLA-ZnO nanocomposites.
Materials and experimental procedure PLA was supplied by NatureWorks LLC as grade (4032D) for realization of films (Mn(PS) = 133 500, dispersity (Mw/Mn) =1.94, D-isomer = 1,4%). Silane treated ZnO nanofiller (ZnO(s)) was supplied by Umicore Zinc Chemicals (Belgium) as Zano 20 Plus (surface treated with triethoxy caprylylsilane, ZnO content 96%). Ultranox 626A was selected as thermal stabilizer and used at preferred percentage of 0.3 wt-% in PLA.
Joncryl ADR- 4300F was kindly supplied by BASF as PLA chain extender with mild-epoxy functionality (Mw= 5500, epoxy equivalent by weight 445 g/mol). PLA-ZnO(s) nanocomposites containing up to 5% nanofiller and 0.5-1% chain extender were obtained by meltcompounding using a twin-screw extruder Leistritz (extrusion temperatures in the range 185 – 200 °C, speed of the screws = 150 rpm, throughput: 2 kg/h). The nanocomposites were processed by injection molding and extrusion (as films).
Mn values assessing for chain extender effectiveness, some larger dispersity
Max. tensile strength of PLA nanocomposites
Results and discussion
(ASTM 638, v=5 mm/min, specimens* type ISO ½)
Joncryl as additive for PLA & PLA-ZnO(s)
In all cases improved thermal stability, possibility of processing at higher temperature 100
220 °C
Weight (%)
(under air)
80
Joncryl is an oligomeric styrene–acrylic chain extender with mild-epoxy functionality obtained by the copolymerization of styrene, BMA, MMA and GMA (WO2003066704 A1). Glycidyl functions (from GMA) can react with both end groups (–COOH and –OH) of PLA leading to high molecular weight polymer, with beneficial effects on rheological, thermal and mechanical properties.
Why Joncryl? Especially at high ZnO(s) loading, following the long residence time at the temperatures of processing (e.g., spinning), is quite difficult to limit the decrease of PLA molecular weights (ZnO degrading effects), even using nanofiller treated by silanes.
240 °C
60
PLA- 5% ZnO[s] PLA- 5% ZnO[s]- 1% Joncryl
The key role of chain extender addition
TGA under isothermal conditions (at 220 °C & 240 °C) 40 10
30
50 Time (min)
70 Universal V4.5A TA Instruments
TEM pictures of PLA - 3% ZnO(s)- 1% Joncryl displaying the good distribution of ZnO(s) rods
ZnO nanoparticles
In presence of 1 wt.% chain extender, Mn values are nearly two times higher with respect to PLA coming from nanocomposites without Joncryl, assessing for the effectiveness of this additive. Its addition has a key key-role in improving the ability of processing by extrusion (preserving a low MFI, better melt strength, viscosity, etc.) TGA confirms the significant increasing in thermal stability for PLA-ZnO(s) nanocomposites following the addition of Joncryl. The samples containing chain extender show a higher T5% (the onset of thermal degradation), with 10 to 20 °C greater than those of the nanocomposites without this additive. Furthermore, the specific enduse properties following ZnO(s) addition are maintained, whereas the improved tensile strength in the mechanical testing is ascribed to the effective (reactive) role of Joncryl.
Conclusions & Acknowledgements
* made by injection molding
The onset of thermal degradation (T 5%) of films (°C)
ZnO(s), % 1 3 5
Joncryl loading 0% 1% 305 315 294 304 280 301 1-3% ZnO(s) 5% ZnO(s)
(Films ~100 microns thickness)
(RE)CONFIRMATION: ZnO is absorbing the harmful UV radiation, lower transmittance at 5% ZnO(s)
-PLA, ZnO(s) nanofiller and a selected chain extender (Joncryl) have been mixed via Authors thank the Wallonia Region, Nord-Pas de Calais Region and twin-screw extruders to yield to nanocomposites with specific end-use properties, while European Community for the financial support in the frame of the IINTERREG IV - NANOLAC project. They thank all collaborators from the groups of Prof. limiting the decrease of PLA molecular mass and depolymerization ability of ZnO -PLA/ZnO(s)- chain extender nanocomposites, the way to high performance products: better processing, improved molecular & thermo-mechanical parameters, good nanofiller distribution, anti-UV properties… -Innovative products: confirmations in production of fibers and films, the MB approach as alternative
Serge Bourbigot (ENSC Lille, France) and of Prof. Eric Devaux (ENSAIT Roubaix, France) for helpful discussions and all mentioned companies for supplying raw materials. This work has been also supported by the European Commission and Région Wallonne FEDER program (Materia Nova), Interuniversity Attraction Pole program of the Belgian Federal Science Policy Office (PAI 6/27) and by FNRS-FRFC.
