Novel Strategies for the Development of Improved Nanocellulose-based Polymer and Biopolymer Nanocomposites

Transcription

1 Novel Strategies for the Development of Improved Nanocellulose-based Polymer and Biopolymer Nanocomposites Novel Materials and Nanotechnology Group IATA, CSIC (Spain) Amparo López Rubio

2 INTRODUCTION Polymers in food packaging applications PROS Versatility of processing methods Wide variety of compositions and materials Interesting Cost/Performance ratios Blending, printing, thermo-welding Adaptable to product requirements: transparent/opaque, flexible/rigid CONS x Permeable to the transport of low molecular weight compounds Losses in food quality and safety x Petroleum-based polymers are not renewable Large volumes of waste Use of high barrier polymers: EVOH, PA, PK Use of biobased materials

3 INTRODUCTION Polymers in food packaging applications Biopolyesters (PLA, PHAs) - Biodegradability - Renewable character - Good processability - High rigidity - High transparency - Low thermal resistance - Excessive brittleness - Relatively low O 2 permeability (compared to benchmark PET) - High production costs CHALLENGE: Development of competitive biopolyesters, economically viable and with similar performance to that of petroleum-based polymers

4 INTRODUCTION Nanocomposite polymeric materials Strategies to tune the properties of polymeric materials: blending, multilayer systems, composite materials Nanofillers vs. microfillers: Lower loadings required Limited detrimental effect on the transparency, mechanical and barrier properties Higher specific area matrix/filler interface adhesion may be improved Nanocomposites: Composite materials containing typically low additions of nanofillers (at least one dimension <100 nm). Nanoclays Carbon nanotubes Cellulose nanowhiskers Metallic nanoparticles

5 INTRODUCTION Cellulose as a source of crystalline nanofillers Plant-derived (PC) - Wood, Cotton, Hemp, Sisal - Food by-products CELLULOSE Non-plant derived - Bacterial Cellulose (BC) - Tunicates cellulose Properties may be different depending on the source: purity, crystallinity, thermal stability leading to different properties of the extracted nanocrystals

6 INTRODUCTION Cellulose as a source of crystalline nanofillers Bacterial cellulose (BC): Synthesised by bacteria belonging to the genera Acetobacter, Rhizobium, Agrobacterium, and Sarcina. The most efficient production is carried out by Gluconacetobacter xylinus in a rich saccharide medium under static condition at around 30ºC. BC vs. PC - High degree of purity (not associated with hemicellulose and lignin) - Higher yield for the extraction of cellulose nanowhiskers - Higher crystallinity - Higher degree of polymerization - Higher water holding capacity

7 INTRODUCTION Extraction of cellulose nanowhiskers (Source: Lavoine et al. (2012) Carbohyd. Polym. 90, ) Mechanical desintegration Chemical treatment (acid hydrolysis) Microfibrillated cellulose (MFC) Cellulose nanowhiskers (CNW)

8 INTRODUCTION CNW in nanocomposite materials. Challenges CELLULOSE Soluble in polar solvents PLA Soluble in organic solvents PHBV Soluble in organic solvents - Low compatibility between BCNW and hydrophobic polymers (and organic solvents) NANOFILLER AGGLOMERATION - When drying, strong intermolecular hydrogen bonds are developed DIFFICULT TO RE-DISPERSE BCNW

9 INTRODUCTION Nanocomposite polymeric materials To improve the properties of the matrix it is crucial to obtain a high dispersion of the nanofiller and good matrix/nanofiller adhesion This is especially critical when developing nanocomposites through MELT COMPOUNDING Large scale production. Industrially applicable Difficulties associated to the dispersion of nanofillers within polymeric matrices Detrimental effect on composites properties Phase separation: Microcomposite High dispersion: Nanocomposite

10 BCNW AS NANOFILLER IN NANOCOMPOSITE MATERIALS

11 NANOCOMPOSITES OF EVOH INCORPORATING BCNW PRODUCED BY MELT COMPOUNDING M. Martínez-Sanz, R.T. Olsson, A. López-Rubio, J.M. Lagaron. Development of electrospun EVOH fibres reinforced with bacterial cellulose nanowhiskers. Part I: Characterization and method optimization, Cellulose (2011), 18, M. Martínez-Sanz, R.T. Olsson, A. López-Rubio, J.M. Lagaron. Development of bacterial cellulose nanowhiskers reinforced EVOH composites by electrospinning, Journal of Applied Polymer Science (2012) 124, M. Martínez-Sanz, A. López-Rubio, J.M. Lagaron. Nanocomposites of ethylene vinyl alcohol copolymer with thermally resistant cellulose nanowhiskers by melt compounding (I): Morphology and thermal properties, Journal of Applied Polymer Science (2013) 128, M. Martínez-Sanz, A. López-Rubio, J.M. Lagaron. Nanocomposites of ethylene vinyl alcohol copolymer with thermally resistant cellulose nanowhiskers by melt compounding (II): Water barrier and mechanical properties, Journal of Applied Polymer Science (2013) 128,

12 EVOH nanocomposites Ethylene-vinyl alcohol copolymer (EVOH) Semi-crystalline materials with excellent gas barrier properties to oxygen and organic -(CH 2 -CH 2 ) m -(CH 2 -CHOH) n - BCNW AS NANOFILLER IN NANOCOMPOSITES compounds, considerable chemical resistance and high transparency. ethylene vinyl alcohol Hygroscopic material Deterioration of gas barrier and mechanical properties at high relative humidity conditions. Widely used as barrier layer in multilayer structures for food packaging applications.

13 EVOH nanocomposites BCNW AS NANOFILLER IN NANOCOMPOSITES EVOH-BCNW nanocomposites. Strategies BCNW Electrospinning Solution precipitation Freeze-drying EVOH-BCNW suspensions H 2 O/isopropanol EVOH+15%BCNW fibres EVOH+15%BCNW precipitate 2%BCNW ES 1-4%BCNW P 2%BCNW FD EVOH pellets MELT COMPOUNDING COMPRESSION MOLDING

14 EVOH nanocomposites BCNW AS NANOFILLER IN NANOCOMPOSITES Production of fibres by electrospinning Production of fibres in the submicron range through the action of an electric field. As the solvent in the polymeric jet evaporates, the material is collected in the metallic plate. Morphology: non-woven mat (fibres), capsules, nanoparticles Needle Metallic plate (collector) Syringe (polymeric solution) Pump Electrodes Applications: Biomedicine, textiles, nanocomposites, etc.

15 EVOH nanocomposites Morphology EVOH BCNW AS NANOFILLER IN NANOCOMPOSITES 2%BCNW ES 2%BCNW FD 2%BCNW P Direct melt mixing gives rise to high degree of BCNW agglomeration. Both pre-incorporation methods improve significantly the nanofiller dispersion.

16 P H 2 O (Kg m/s m 2 Pa) EVOH nanocomposites 1.4e e e e e e-15 Water permeability BCNW AS NANOFILLER IN NANOCOMPOSITES Water uptake 100% RH (%) X c (%) (XRD) D (m 2 /s) a (g/cm 3 ) EVOH 9.25 ± ± ± 0.04 e %BCNW P 7.93 ± ± ± 0.08 e e-15 2%BCNW P 8.62 ± ± ± 0.00 e EVOH 1%BCNW P 2%BCNW P 3%BCNW P 4%BCNW P 2%BCNW ES 2%BCNW FD 3%BCNW P 7.81 ± ± ± 0.07 e %BCNW P 7.05 ± ± ± 0.97 e %BCNW ES 6.99 ± ± ± 0.39 e %BCNW FD 7.12 ± ± ± 0.14 e The overall X c (XRD) increased with the addition of BCNW lower H 2 Osorption. The amorphous density decreased (higher free volume) higher H 2 O diffusion. Higher nanofiller loadings were required to reduce the PH 2 O: 4%BCNW P 22% PH 2 O drop. PH 2 O increased by 69% when directly melt mixing BCNW with EVOH due to increased H 2 O diffusion through the film (preferential paths in areas where BCNW were agglomerated).

17 EVOH nanocomposites Mechanical properties BCNW incorporation More rigid and brittle materials. BCNW AS NANOFILLER IN NANOCOMPOSITES BCNW FD 94% B (poor matrix-filler adhesion). Pre-incorporation methods Limited B drop (improved matrix-filler adhesion). Optimal loading: 3%BCNW P 36% E and minimum B reduction. 2.0 E E E B B EVOH 1%BCNW P 2%BCNW P 3%BCNW P 4%BCNW P 2%BCNW ES 2%BCNW FD E (GPa) EB (%)

18 NANOCOMPOSITES OF PLA INCORPORATING BCNW PRODUCED BY MELT COMPOUNDING M. Martínez-Sanz, A. López-Rubio, J.M. Lagaron. Dispersing bacterial cellulose nanowhiskers in polylactides via electrohydrodynamic processing, Journal of Polymers and the Environment, in press. M. Martínez-Sanz, A. López-Rubio, J.M. Lagaron. Optimization of the dispersion of unmodified bacterial cellulose nanowhiskers into polylactide via melt compounding to significantly enhance barrier and mechanical properties, Biomacromolecules (2012), 13,

19 PLA nanocomposites Polylactic acid (PLA) Thermoplastic aliphatic biopolyester derived from fermentation of natural resources such as starch and sugarcanes. BCNW AS NANOFILLER IN NANOCOMPOSITES Highly transparent and rigid. Relatively low heat stability and barrier properties. Applications in biomedicine, biodegradable packaging, mulch films, drug delivery systems, etc.

20 PLA nanocomposites BCNW AS NANOFILLER IN NANOCOMPOSITES PLA-BCNW nanocomposites. Strategies BCNW Electrospinning Solution precipitation Freeze-drying PLA-BCNW EVOH-BCNW PLA+15%BCNW fibres suspensions HFP suspensions H 2 O/isopropanol EVOH+15%BCNW precipitate 1-3%BCNW ES 1-2%BCNW P 1-2%BCNW FD PLA pellets MELT COMPOUNDING COMPRESSION MOLDING

21 PLA nanocomposites Morphology BCNW AS NANOFILLER IN NANOCOMPOSITES PLA 2%BCNW ES 2%BCNW FD PLA-EVOH 2%BCNW P Optimized BCNW dispersion with pre-incorporation methods. Phase separation between PLA and EVOH weak adhesion. Incorporation of BCNW improves PLA-EVOH adhesion.

22 PLA nanocomposites Mechanical properties BCNW AS NANOFILLER IN NANOCOMPOSITES 17% E and 14% tensile strength by incorporating 2%BCNW ES and 3%BCNW ES Strong filler-filler interactions E E E B B 10 8 Slight reduction in the ductility of the material with the incorporation by ES Improved matrix-filler adhesion PLA 1%BCNW ES 2%BCNW ES 3%BCNW ES 1%BCNW FD 2%BCNW FD PLA+16%EVOH 1%BCNW P 2%BCNW P E (GPa) EB (%)

23 PLA nanocomposites Water barrier BCNW AS NANOFILLER IN NANOCOMPOSITES 2e-14 The incorporation of highly dispersed crystalline BCNW limits the water P H 2 O (Kg m/s m 2 Pa) 2e-14 1e-14 5e-15 diffusion up to 43% PH 2 O drop for 3% BCNW ES. Reduction of -OH groups after FD 0 limited H 2 Osorption. PLA 1%BCNW ES 2%BCNW ES 3%BCNW ES 1%BCNW FD 2%BCNW FD PLA+16%EVOH 1%BCNW P 2%BCNW P However, the poor dispersion and adhesion of BCNW FD results in increased PH 2 O.

24 PLA nanocomposites BCNW AS NANOFILLER IN NANOCOMPOSITES Oxygen barrier 3.0e e-18 0%RH 3.0e e-18 80%RH PO 2 (m 3 m/ m 2 s Pa) 2.0e e e-18 PO 2 (m 3 m/ m 2 s Pa) 2.0e e e e e PLA 1%BCNW ES 2%BCNW ES 3%BCNW ES 1%BCNW FD 2%BCNW FD PLA+16%EVOH 1%BCNW P 2%BCNW P 0.0 PLA 1%BCNW ES 2%BCNW ES 3%BCNW ES 1%BCNW FD 2%BCNW FD PLA+16%EVOH 1%BCNW P 2%BCNW P At 0%RH All the nanocomposites present reduced PO 2, mainly due to reduced sorption. At 80%RH Only nanocomposites with low BCNW loading (1wt.-%) presented significant PO 2 reductions. The incorporation of BCNW increases the diffusion coefficient due to a stronger plasticization effect of the amorphous phase by H 2 O molecules.

25 BCNW AS BASE MATERIAL FOR HIGH BARRIER FILMS M. Martínez-Sanz, A. López-Rubio, J.M. Lagaron. High-barrier coated bacterial cellulose nanowhiskers films with reduced moisture sensitivity, Carbohydrate Polymers, 98,

26 BCNW-BASED HIGH BARRIER FILMS Aqueous suspension of BCNW 332ºC BCNW films with high transparency and high thermal stability

27 BCNW-BASED HIGH BARRIER FILMS BCNW Films. Morphology and barrier properties Highly packed structure of layered nanofibres. Relatively high water permeability. Excellent oxygen barrier at low %RH. Sharp increase in the PO 2 at high %RH conditions. Behavior typical of hydrophilic materials, ascribed to the plasticization effect of H 2 O molecules. COATING WITH P H 2 O 75%RH P O 2 0%RH P O 2 80%RH HYDROPHOBIC MATERIALS (Kg m/m 2 s Pa) (m3 m/m2 s Pa) (m3 m/m2 s Pa) TO PRESERVE THE Film BCNW 3.55 ± 1.11 e ± 0.13 e ± 0.24 e -18 Film PLA 1.31 ± 0.01 e -14 (*) 2.61 ± 0.16 e ± 0.13 e -18 Film PHB 0.14 ± 0.03 e -14 (*) 0.23 ± 0.00 e ± 0.06 e -18 BARRIER PROPERTIES EVEN AT HIGH RELATIVE HUMIDITY (*) Measured at 100%RH

28 Coated systems BCNW-BASED HIGH BARRIER FILMS Casting PLA/PEG + BCNW + casting PLA/PEG Delamination of the multilayer system Casting PLA + BCNW + casting PLA

29 Coating approaches BCNW-BASED HIGH BARRIER FILMS PLA electrospun fibres Annealing BCNW Film Silanes

30 Coating approaches BCNW-BASED HIGH BARRIER FILMS BCNW-APTS BCNW-PLA 9 m 5 m BCNW-VTMS 0.8 m

31 BCNW-BASED HIGH BARRIER FILMS Coated systems. Barrier properties BCNW 43.8º P H 2 O 75%RH (Kg m/m 2 s Pa) Water uptake (%) D (m 2 /s) P O 2 80%RH (m3 m/m2 s Pa) Film BCNW 3.55 ± 1.11 e ± e ± 0.24 e -18 BCNW-PLA 1.19 ± 0.48 e ± e ± 0.08 e -18 BCNW-APTS 1.86 ± 0.33 e ± e ± 0.12 e -18 BCNW-PLA 77.8º BCNW-VTMS 3.28 ± 1.18 e ± e ± 0.20 e -18 Film PLA 1.31 ± 0.01 e -14 (*) 0.95 ± e ± 0.13 e -18 (*) Measured at 100%RH PH 2 O dropped by ca. 66% and PO 2 was reduced by ca. 97% by coating with annealed PLA electrospun nanostructured fibres. PLA limited water sorption due to its hydrophobicity. The inner BCNW layer provided a highly crystalline and compacted structure, which limited water diffusion through the system.

32 CONCLUSIONS The use of pre-incorporation techniques, in particular electrospinning, was proven to be an efficient strategy for avoiding BCNW agglomeration in melt compounded nanocomposites (both hydrophilic and hydrophobic matrices). The reduction in the ductility might be limited or even avoided by increasing the dispersion of BCNW or by improving the matrix-filler adhesion. At low RH, all the nanocomposites containing BCNW presented reduced PO2 due to the blocking capacity of the highly crystalline nanofiller. At high RH, lower PO2 reductions were attained due to the distortion of the hydrogen bonds established between the cellulose chains and/or with the polymeric matrix. It was possible to produce high barrier materials based on BCNW films coated with annealed PLA electrospun nanostructured fibres. This novel coating approach guaranteed a good adhesion between the different layers. Thus, the detrimental effect of moisture on the barrier properties of BCNW was strongly limited.

33 Acknowledgements Marta Martínez-Sanz MICINN (MAT C02-01 project) and the EU FP7 ECOBIOCAP project.

34 STSM PLA-BCNW nanocomposites through in-situ polymerization Challenges: Avoid BCNW degradation during the process Solutions: Chemical modification of the BCNW?? Increasing thermal stability of BCNW?? Any group wanting to host our PhD student for this specific tasks??

35 PROJECT PROPOSAL HORIZON 2020: Food safety, bioeconomy, waste valorisation Novel cellulose-based biopolymeric packaging materials with antimicrobial properties Cellulose for Characterization controlled release?? Demonstration Modification of cellulose (companies) surface for attaching antimicrobial substances

36 Novel Strategies for the Development of Improved Nanocellulose-based Polymer and Biopolymer Nanocomposites Novel Materials and Nanotechnology Group IATA, CSIC (Spain) Amparo López Rubio