ELECTROSPUN EVOH FIBRES REINFORCED WITH BACTERIAL CELLULOSE NANOWHISKERS WITH POTENTIAL IN FOOD PACKAGING APPLICATIONS Novel Materials and Nanotechnology Group Marta Martínez-Sanz Richard T. Olsson Amparo López-Rubio Jose M. Lagaron
1. INTRODUCTION Plant-derived (PC) Wood Cotton, Hemp, Flax, Jute, Ramie, Sisal Glucose units linked by β-1,4-glycosidic bonds CELLULOSE Non-plant derived Bacterial Cellulose (BC) Tunicates cellulose BC vs. PC - High degree of purity (not associated with hemicellulose and lignin). - Higher water holding capacity. - Higher degree of polymerization. - Incorporation of additives in the culture medium ( in situ ).
1. INTRODUCTION BACTERIAL CELLULOSE Synthesized by Gluconacetobacter, in a rich C and N medium, static conditions, 28-30ºC. Highly hydrated pellicle (97% H 2 O) made up of an assembly of ribbon-shaped microfibrils, which are composed of a bundle of nanofibrils. High crystallinity (60-90%) Mechanical strength Low density (1600 Kg/m 3 ) Biocompatibility Dietary food (nata-de-coco) High mechanical strength paper Biomaterial in cosmetics and medicine Acoustic diaphragms Reinforcing agent in nanocomposites
1. INTRODUCTION BACTERIAL CELLULOSE. NANOCOMPOSITES REINFORCEMENT Cellulose acid hydrolysis Micro-/Nanocrystalline Cellulose (BCNW) Poor compatibility of BCNW with hydrophobic thermoplastic matrixes Electrospinning as a method for incorporating well-dispersed nanowhiskers in an EVOH matrix (*) (*) ES1641.712 Patent
2. OBJECTIVES Production and characterization of bacterial cellulose nanowhiskers (BCNW) by means of acid treatment. Incorporation of BCNW into an EVOH polymeric matrix by the electrospinning technique. Optimization of the incorporation method. Characterization of electrospun EVOH/BCNW fibres with different concentrations of BCNW.
3. MATERIALS AND METHODS BCNW PRODUCTION PROCESS Production of BC mats Incubation of Gluconacetobacter xylinum in a static culture medium. Production of mats in the air/liquid interface. Washing of mats with NaOH and boiling water.
3. MATERIALS AND METHODS BCNW PRODUCTION PROCESS H 2 SO 4 treatment Preferential digestion of amorphous domains Individual nanofibres/nanocrystals High degree of crystallinity Washing with H 2 O and centrifugation cycles Bacterial cellulose nanowhiskers (BCNW) are obtained as a precipitate after centrifugation. Centrifuged BCNW Freeze-dried BCNW
MORPHOLOGY 4. BCNW CHARACTERIZATION TEM SEM Nanofibres having a diameter< 60 nm which are aggregated after freeze-drying, forming bundles of width< 800 nm
4. BCNW CHARACTERIZATION CRYSTALLINITY INDEX 1800 1600 BC BCNW 1400 1200 BC BCNW Intensity 1000 800 CI (XD) (%) 65.2 85.6 600 400 CI (XD-CI) (%) 38.6 51.7 200 CI (XD-CII) (%) 26.7 34.0 0 5 10 15 20 25 30 35 40 45 2θ º D (002) (nm) 1.0 1.2 CELLULOSE I Parallel-up structure CELLULOSE II Anti-parallel chains structure
4. BCNW CHARACTERIZATION THERMAL STABILITY H 2 SO 4 treatment Amorphous fraction digestion Sulphate groups incorporation C.I. Thermal stability
5. OPTIMIZATION OF EVOH/BCNW ELECTROSPINNING METHOD Centrifuged BCNW + H 2 O 8% BCNW Cent. Ultraturrax US 8% BCNW Cent. US 5% EVOH29 isopropanol Freeze-dried BCNW + H 2 O Ultraturrax US 8% BCNW Liof. 8% BCNW Liof. US Electrospun EVOH fibres reinforced with BCNW
5. OPTIMIZATION OF EVOH/BCNW ELECTROSPINNING METHOD 8% Centrifuged BCNW 8% Freeze-dried BCNW Viscosity (cp) Mean diameter (nm) 5% EVOH 27.27 224.47 8% Centrifuged BCNW 1387.70 190.98 8% Freeze-dried BCNW 33.97 381.54 8% Centrifuged BCNW US ---- 285.50 8% Freeze-dried BCNW US 353.24 248.52
5. OPTIMIZATION OF EVOH/BCNW ELECTROSPINNING METHOD %INCORPORATION OF BCNW Calibration curve: Intensity of FT-IR bands vs. %BCNW I(1165cm I(838cm 1 1 base) base) C-O-C asymmetric stretching in cellulose II allomorph skeletal vibrations and CH 2 rocking of EVOH 10 I(1165-base)/I(838-base) 8 6 4 2 y = 0.2382x - 0.5219 R 2 = 0.9959 0 0 10 20 30 40 50 BC nanowhiskers (%)
5. OPTIMIZATION OF EVOH/BCNW ELECTROSPINNING METHOD %INCORPORATION OF BCNW % Incorporación BCNW 8% Cent. BCNW 8% Cent. BCNW US 8% F-d BCNW 8% F-d BCNW US EVOH
5. OPTIMIZATION OF EVOH/BCNW ELECTROSPINNING METHOD THERMAL PROPERTIES T m (ºC) ΔH (J/g EVOH) T g (ºC) EVOH 191.4 (0.7) 73.4 (0.4) 61.8 (0.6) EVOH + 8% Centrifuged BCNW 188.3 (0.6) 56.9 (1.1) 72.4 (0.3) EVOH + 8% Centrifuged BCNW (US) 187.8 (0.8) 57.0 (0.4) 70.8 (0.1) EVOH + 8% Freeze-dried BCNW 187.5 (1.2) 75.1 (3.5) 64.7 (0.5) EVOH + 8% Freeze-dried BCNW (US) 185.2 (0.7) 72.04 (1.4) 72.3 (0.2) Centrifuged BCNW Freeze-dried BCNW US T g Reinforcing capacity
6. CHARACTERIZATION OF EVOH FIBRES WITH DIFFERENT BCNW CONCENTRATIONS 8% Cent. BCNW % Incorporation T g - 4.1% EVOH + 40% BCNW 5.75% Solids - 4.6% EVOH + 25% BCNW - 4.8% EVOH + 20% BCNW - 5.0% EVOH + 15% BCNW - 5.5% EVOH + 5% BCNW 0 200 400 600 800 1000 1200 1400 Diameter (nm) % BCNW Fibres' diameter More uniform size distribution
6. CHARACTERIZATION OF EVOH FIBRES WITH DIFFERENT BCNW CONCENTRATIONS THERMAL STABILITY 40%BCNW T d = 125ºC 15%BCNW T d = 150ºC 5%BCNW T d = 162ºC Cellulose degradation EVOH T d = 300ºC
6. CHARACTERIZATION OF EVOH FIBRES WITH DIFFERENT BCNW CONCENTRATIONS THERMAL PROPERTIES T m (ºC) ΔH (J/g EVOH) T g (ºC) T m % BCNW H m EVOH 190.6 (0.8) 79.1 (1.6) 63.0 (0.6) 5% BCNW 188.8 (0.4) 69.1 (0.8) 63.9 (0.4) T g 15% BCNW 188.2 (2.0) 43.9 (0.3) 67.8 (0.1) 20% BCNW 185.5 (0.1) 37.9 (0.9) 75.0 (0.2) BCNW hinder crystallization: - More amorphous material. - Smaller or more defective crystals. 25% BCNW 187.2 (0.8) 33.8 (1.5) 76.2 (0.3) 40% BCNW 184.4 (0.2) 49.7 (2.0) 76.5 (0.2) Tg (ºC) 78 76 74 72 70 68 66 64 62 0 10 20 30 40 50 % BCNW
6. FIBRAS ELECTROESTIRADAS DE EVOH CON DIFERENTES CONCENTRACIONES DE BCNW %INCORPORATION OF BCNW 5% BCNW 15% BCNW 20% BCNW 25% BCNW 40% BCNW 1165 cm -1 Cellulose 838 cm -1 EVOH
7. CONCLUSIONS Acid treatment with H 2 SO 4 is an effective way of extracting bacterial cellulose nanowhiskers. - CI increases from 65% to 86%. - Nevertheless, thermal stability decreases. It is possible to obtain EVOH/BCNW fibres by means of the electrospinning technique. - BCNW incorporation is reflected in a stiffening effect (increase in the T g ) of the fibres. - The degree of incorporation and T g relative increase are higher when incorporating BCNW as a partially hydrated precipitate. - Thermal stability of fibres decreases as a consequence of sulphate groups. - It is possible to effectively incorporate BCNW in concentrations up to 20% BCNW.