2 - Ecole Nationale Supérieure des Arts et Industries Textiles (ENSAIT) Roubaix, France. The extraordinary interest and swift expansion of biopolymers is ...
INTERREG efface les frontières Union Européenne – Fonds Européen de Développement Régional
Polylactide (PLA) – (silver/clay) hybrid nanocomposites designed for films and fibres with multifunctional end-use properties M. Murariu, L. Bonnaud, A. Gallos1, G. Fontaine1, M. Ferreira2, A. Cayla2, D. Dumont2, C. Campagne2, S. Bourbigot1, E. Devaux2 and Ph. 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 1 - Ecole Nationale Supérieure de Chimie de Lille (ENSCL), Villeneuve d’Ascq Cedex, France 2 - Ecole Nationale Supérieure des Arts et Industries Textiles (ENSAIT) Roubaix, France
Introduction The extraordinary interest and swift expansion of biopolymers is connected to the demand for more environmentally-sustainable products and to the increased restrictions for the use of polymers with high “carbon footprint” of petrochemical origin. Polylactide or polylactic acid (PLA), one of the most promising candidates for future developments, is currently receiving considerable attention not only for conventional utilization such as packaging and textile materials, but also for engineering applications (automotive, electrical and electronics industry, etc.). To tune up the PLA properties, promising developments are expected especially in the field of nanotechnology. This study was focused on the preparation of (silver/clay) hybrid nanocomposites based on PLA as matrix, products designed for production of films and fibres with multifunctional properties. The aim of communication is to discuss selected aspects regarding the beneficial effects of silver (3D morphology) and clay (1D) nanoparticles (NPs) co-addition into PLA matrix, and to evidence the main synergies and their key-role in obtaining specific features (antibacterial activity and fire resistance, respectively).
Materials and experimental procedure Two PLA grades supplied by NatureWorks LLC for realization of films (4032D (PLA1): Mn(PS) = 133500, dispersity (Mw/Mn) =1.94, D-isomer = 1,4%) and fibres (6202D (PLA2): Mn(PS) = 94000; Mw/Mn= 1.89, D- isomer ≤ 2%) were used for melt-compounding with 0.3 wt.-% silver and various loadings (2-6 wt.-%) of organo-modified layered silicates (OMLS) via Leistritz twin-screw extruders. Selected samples were used to produce films and fibers. Ag spherical nanoparticles of 20 and 35 nm were supplied by IOLITEC, Germany. They were surface treated with oleic acid (≈ 2%). Two OMLS supplied by Southern Clay Products, Inc., i.e. Cloisite 10A (C10A : (organo)modified - MMT with “benzyl, dimethyl, hydrogenated tallow ammonium”, modifier concentration: 125 meq/100g clay, d(001)= 19.2Å) and Cloisite 30B (C30B : (organo)modified - MMT with “bis-(2-hydroxyethyl) methyl hydrogenated tallow ammonium”, modifier concentration: 90 meq/100g clay, d(001)= 18.5Å) were used in the frame of experimental program to produce PLA nanocomposites for films and fibres, respectively. Ag NPs are between clay layers
Results and discussion TGA of PLA2- C30B- 0.3% Ag Effect of clay
Weight (%)
40
0
5
3
(under air, 20°C/min)
-40
-80
-120
Why (silver/clay) hybrid nanocomposites
7 PLA2 PLA2- 4% C30B- 0.3% Ag PLA2- 6% C30B- 0.3% Ag
80
0
100
200
300 Temperature (°C)
400
500
Deriv. Weight (%/°C)
120
1D
PLA
1
It is reported that the well dispersed nanoclay creates a “tortuosity” and a large internal surface within the polymer and this increases the efficiency of Ag ions. Presence of Ag NPs between clay nanolayers can lead to long-lasting effectiveness and uniform antibacterial effects. Expected multifunctional properties (rigidity, thermal stability, barrier and fire retardancy (FR) by addition of clays, antibacterial effect due to silver), while a good processing is one key-condition…
3D TEM of PLA2 - 4% C30B- 0.3% Ag
-1 600 Universal V4.5A TA Instruments
Morphology, thermal and FR properties Fire retardancy (FR): UL94 HB and cone calorimeter fire testing PLA2 - 4% C30B- 0.3% Ag
UL94 : HB, C30B (≥ 4 wt.%) leads to a harder char
TGA confirms an evident gain in thermal stability for PLA hybrid nanocomposites containing OMLS (C10 or C30B) ascribed to a good clay dispersion. Once more, the FR properties attributed to presence of clays are confirmed by cone calorimeter testing (e.g., 4% C30B decreases the RHR peak by 30%) or using the horizontal burning test UL 94 (cat. HB) which confirms also formation of an important charring.
Antibacterial properties: The antibacterial tests (ISO 20743/
RHR (kW/m2)
JIS L1902) on fibres have shown that even in presence of 0.1% Ag, PLA asses good antibacterial performances after 18 hours towards both gram positive and gram negative bacteria. However, due to a higher surface area, the antibacterial effect was more evident for fibers than for films (after 24h, protection only towards gram positive bacteria at 0.1% Ag, JIS Z 2801). ASTM E2149-10* "Dynamic Shake Flask" test was used in the case of hybrid nanocomposites. The first analyses with E. coli confirm Ag effectiveness (at ≤ 0.3%), i.e. the decrease by 90% in bacteria number during 24h, for instance, without obvious correlation to clay loading, thus additional investigations are required at longer time.
Time (s)
Good distribution and dispersion of C30B, Ag difficult to be evidenced
XRD: peaks at 38.2°, 44.4°, 64.6° and 77.5° due to Ag NPs, evidence of intercalated and exfoliated clay morphologies
1
2
PLA2 as matrix
Conclusions & Acknowledgements Authors thank the Wallonia Region, Nord-Pas de Calais Region and European
PLA, OMLS and silver NPs have been used for melt-compounding in twin-screw extruders Community for the financial support in the frame of IINTERREG IV - NANOLAC project. They are grateful to Anne–Laure Dechief, Yoann Paint and Lisa Dangreau to produce PLA hybrid nanocomposites for films and fibres with multifunctional properties (Materia Nova, Belgium) for assistance in the realization of samples and analyses.
PLA- (silver/clay) nanocomposites: good processing, nanofiller dispersion, improvements This work has been also supported by the European Commission and Région in thermal stability, etc. and specific end-use properties (flame retardancy, antibacterial, Wallonne FEDER program (Materia Nova), Interuniversity Attraction Pole program of the Belgian Federal Science Policy Office (PAI 6/27) and by FNRS-FRFC. expected longer antibacterial activity), additional R&D works are further considered References Novel bio-products with higher added value allowing the larger application of biobased PLA
[1] Murariu M, Doumbia A, Devaux E, Dubois Ph. et al., Biomacromolecules 2011, 12:1762-1771. [2] Shameli, K et al., Int. J. Nanomedicine 2011, 6:581—590. [3] Zhang, Y et al., J. Inorg. Biochem. 2013, 118:59-64.
