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INTERCALATION COMPOUNDS OF LAYERED DOUBLE HYDROXIDES WITH ANTIMICROBIAL BENZOATE
ANIONS AS FILLER OF BIODEGRADABILE POLYMERIC MATRICES FOR NEW PACKAGING SYSTEMS
Loredana TammaroLoredana Tammaro Department of Chemical and Food Engineering, University of Salerno, Italy
Sezione Tematica INSTM: 6. Materiali polimerici funzionali e strutturali
VI Convegno Nazionale sulla Scienza e Tecnologia dei Materiali (INSTM 2007)Perugia, 12-15 Giugno 2007
Outline
Structural and physical characterizationStudy of thermal properties
Preparation and characterization of composites based on hydrotalcite as model systems for “active food packaging”
Aim
Loredana Tammaro University of Salerno
Preparation of nano-hybrids:
Intercalation of active molecules in layered double hydroxides (LDH) Preparation of nano-bio-hybrids composites:
polymeric matrix: poly(-caprolactone) (PCL)
inorganic fillers: modified hydrotalcites
Advantages of “active packaging materials”
Controlled release systems are becoming part of a wide category of new food packaging concepts known as ‘‘active packaging materials’’ which have the aim of extending the shelf life of the packaged foodstuff, inhibiting the microbial growth and preserving its sensory propertiesAn eco-friendly solution is introducing the use of polymers either biodegradable or from renewable sources. However some properties of biodegradable polymers are not suitable for the applications in the food packaging field. Therefore many efforts are necessary to produce biodegradable materials with mechanical and barrier properties suitable for specific necessities. A good way to improve the performance of these systems is the incorporation of inorganic materials, with lamellar structure, into polymeric matrix at nanometric level
Loredana Tammaro University of Salerno
The idea!
The innovative idea of our research is based The innovative idea of our research is based on the fact that it is possible to fix by ionic on the fact that it is possible to fix by ionic bonds, on the inorganic lamellae of anionic bonds, on the inorganic lamellae of anionic clay, active molecules (antimicrobial or clay, active molecules (antimicrobial or antioxidants). These molecules not only can antioxidants). These molecules not only can improve the compatibility with the polymer improve the compatibility with the polymer matrix, but can be released with controlled matrix, but can be released with controlled kinetics in particular environments, tookinetics in particular environments, too
Loredana Tammaro University of Salerno
Biopolymers
Layered double hydroxides
Active molecules
filmfilmss
Nano-hybrid composite polymeric material
Nano-hybrid composite
membranesmembranes hydroghydrogelsels
fibersfibers
Scaffolds tissue engineering Drug releaseActive packaging
Chemical properties morphological and structural properties physical properties
Mechanical properties (tensile,toughness, hardness, impact, fatigue properties.and creep properties)barrier and mechanical properties
biodegradability biocompatibility release kinetics
Suture threads
Loredana Tammaro University of Salerno
Why PCL?
PCL is a biodegradable polymer with good processing properties
M. Vert, J. Feijen, A. C. Albertsson, G. Scott, E. Chiellini (eds.), Biodegradable Polymers and Plastics, Royal Society of Chemistry, London, 1992
"Layered Double Hydroxides: present and future" Vicente Rives Editor, Nova Science Publisher, INC. New York, 2001.
They can be prepared with simple procedures, at high level of purity, are cheap and eco-compatible and can be organically modified with a variety of organic anions, generally much more numerous than organic cations. This latter characteristic will make these layered compounds compatible with a large variety of polymers and it is easy to foresee the possibility to prepare interesting new hybrid polymeric materials
Why Layered Double Hydroxide?
Loredana Tammaro University of Salerno
Chemical Structure of LDH
Hydrotalcite: [MII1-xMIII
x(OH)2]x+[A n- . nH2O] inter
Structure of brucite
Ions of metals M(II) and M(III) six times coordinate with ions OH-
identifying octraedrals that form innumerable packed layers joined by ionic bonds and/or Van der Waals forces. The whole structure is constituted by the stacking of such layers, intercalating charge-balancing anionic species and water molecules
Loredana Tammaro University of Salerno
ISOMORPHOUS REPLACEMENT
Replacement of bivalent cations such as Mg2+ e Fe2+ present in the lattice with trivalent cations such as Al3+ creates positive charges balanced by the presence of counter-anions such as CO3
2-, Cl-, NO3- located into the interlamellar region
MODIFIED HYDROTALCITES
Although the hydrophilic nature of the clay minerals hinders their homogeneous dispersion into the polymer it has been possible to render the clays more compatible with the polymeric matrix
Loredana Tammaro University of Salerno
GENERALLYBy replacing the charge balancing anions (ex. NO3
-) with organofilic groups, such as long chain of carboxylic acid salts. In this way the miscibility of the oxide layers in the polymer matrix can be enhancedLDHs a unique class of layered solids to be used as host of
polymers, molecules bearing a negative charge and/or polymers copolymerized with a small amount of a negative charged monomer
Intercalation of active molecules in hydrotalcite- like compounds
Structural formula of: benzoate (Bz) (a), 2,4-dichlorobenzoate (DCB) (b), o-hydroxybenzoate (o-OHBz) (c), p-hydroxybenzoate (p-OHBz) (d) anions
COO- COO-
Cl
Cl
COO-
OH
COO-
OH
(a) (b) (c) (d)
Loredana Tammaro University of Salerno
A) Preparation of nano-hybrids
Preparation of ZnAl-2,4dichlorobenzoate (ZnAl-DCB) and ZnAl-p hydroxybenzoate (ZnAl-p-OHBz)
The intercalation of the benzoate derivatives were performed equilibrating 1 g of ZnAl-NO3 in 15 cm3 of solution water/acetone (1/1, v/v) 0.5 M of the anions obtained by titrating the corresponding acid forms with NaOH 1 M until the hydrolysis pH 7. The suspensions were stirred for 3 days. The obtained intercalation compounds were washed with CO2-free de-ionized water and dried at R. H.=75%
Preparation of ZnAl-Benzoate (ZnAl-Bz) and ZnAl-salycilate (ZnAl-o-OHBz)
The intercalation of benzoate and salicylate anions was achieved by equilibrating the nitrate form of hydrotalcite with an aqueous solution of the anion 0.5 mol/dm3 (molar ratio organic anions/ NO3
- = 3) for 24 hours at room temperature. The recovered solids were three times washed with CO2-free de-ionized water and dried at R.H.=75%
Loredana Tammaro University of Salerno
DENOMINATION
Acronyms of molecular ions intercalated into ZnAl-LDH,
interlayer distance and composition of the intercalation
compounds
Anion d (Å) CompositionBz 15,5 [Zn0.65Al0.35(OH)2]Bz0.35x1H2O
o-OHBz 15,5 [Zn0.65Al0.35(OH)2]o-OHBz0.27(NO3)0.08x1H2O
p-OHBz 15,3 [Zn0.65Al0.35(OH)2]p-OHBz0.2(NO3)0.15x0.66H2O
DCB 16,8 [Zn0.65Al0.35(OH)2]DCB0.32(NO3)0.03x1H2O
Loredana Tammaro University of Salerno
Structural analysis
XRPD of intercalation compounds dried over saturated NaCl solution (R.H.=75%): (a) ZnAl-NO3; (b) ZnAl-p-OHBz; (c) ZnAl-o-OHBz, (d) ZnAl-Bz and (e) ZnAl-DCB
Loredana Tammaro University of Salerno
Structural Model
Structural models of the intercalation compounds is proposed taking into account their chemical composition, interlayer distance, van der Waals dimension of the guests and considering that the intercalation process does not alter appreciably the structure of the layers.
Computer generated models showing the most probable arrangement of (a) o-OHBz; (b) p-OHBz; (c) DCB and (d) Bz anions between the LDH layers(d)
Loredana Tammaro University of Salerno
Thermogravimetric analysis
Weight losses:
1) 80°-300°C: co-intercalated water and dehydroxylation of the inorganic layers 2) 300°C -600°C: decomposition of organic guests3) > 600°C: formation of ZnO and ZnAl2O4TGA and DTA curves of the sample ZnAl-Bz. Operative
conditions: air flow; heating rate: 5°C/min
0 100 200 300 400 500 600 700 800 900 1000-60
-50
-40
-30
-20
-10
0TGA
EXO
% w
eigh
t los
s
T (°C)
DTA
Loredana Tammaro University of Salerno
Infrared Analysis
3600 3300 3000 2700 2400 2100 1800 1500 1200 900 600
(b)
T(a
.u.)
wave number (cm-1)
(a)
FT-IR spectra of ZnAl-Bz: (a) room temperature; (b) after heating at 300°C for 24 hours
Spectrum (a)1) 3000-3750 cm-1 : lamellae OH
stretching involved in H- bonds with hydration water and carboxylic groups
2) 1537 cm-1 and 1397 cm-1 : asymmetric and symmetric stretching vibrations of the carbon-oxygen bonds of COO- group
3) 1595 cm-1 : in-plane skeletal vibration of monosubstituted aromatic ring
4) 719 cm-1 and 689 cm-1 : bending of the five adjacent hydrogen atoms of the ring
Spectrum (b)The broad band centred at 3420 cm-1 disappear because of the removal of hydration water and the condensation of OH group of the lamellae, while the typical –COO- stretching are still present
Loredana Tammaro University of Salerno
High Energy Ball Milling
Use of mechanical energy to blend different materials Advantages: No solvents
No high temperaturesPossibility to prepare composites using natural polymers (i.e. pectins, starch...) that don’t melt, but degrade with temperature
Possibility to incorporate into polymers, at low temperatures, inorganic solids with organic molecules thermally sensible
Loredana Tammaro University of Salerno
B) Nano-bio-hybrid incorporation in PCL
Operating conditions:
Cylindrical steel jar = 50 cm3
Steel balls (10 mm diameter)= 5Rotation speed = 580 r.p.m. Milling time = 1 hourTemperature= 25°CDifferent percentages (wt/wt) PCL-LDHs
Characterization of the composites: X-Ray
ZnAl-Bz (a) and the composites PCL/ZnAl-Bz3 (b), PCL/ZnAl-Bz6 (c), PCL/ZnAl-Bz11 (d)
ZnAl-DCB (a) and the composites PCL/ZnAl-DCB3 (b), PCL/ZnAl-DCB6 (c), PCL/ZnAl-DCB9 (d)
ZnAl-o-OHBz (a) and the composites PCL/ZnAl-o-OHBz4 (b),PCL/ZnAl-o-OHBz6 (c), PCL/ZnAl-o-OHBz11 (d)
ZnAl-p-OH (a) and the composites PCL/ZnAl-p-OHBz4 (b), PCL/ZnAl-p-OHBz7 (c), PCL/ZnAl-p-OHBz10 (d)
Loredana Tammaro University of Salerno
5 10 15 20 25 30 35 40
1.55 nm
1.94nm
(d)
(c)
(b)
(a)
Inte
nsi
ty (
a.u
.)
2
5 10 15 20 25 30 35 40
16.8 nm
(d)
(c)
(b)
(a)
Inte
nsi
ty (
a.u
.)
2
5 10 15 20 25 30 35 40
1.88 nm15.5 nm
(d)
(c)
(b)
(a)
Inte
nsi
ty (
a.u
.)
25 10 15 20 25 30 35 40
15.3 nm
(d)
(c)
(b)
(a)
Inte
nsi
ty (
a.u
.)
2
Characterization of the composites: FT-IR
1540 cm-1 : COO- antisymmetric stretching
1595 cm-1 : C=C stretching vibration
1650 1625 1600 1575 1550 1525 1500
(e)
(d)(c)
(b)
(a)
Ab
sorb
ance
(a.
u.)
Wavenumber (cm-1)
PCL (a), ZnAl-Bz (b) and the composites PCL/ZnAl-Bz3 (c), PCL/ZnAl-Bz6 (d), PCL/ZnAl-Bz11 (e) 0 2 4 6 8 10 12
LDHBz content (w/w%)
Ab
sorb
ance
(a.
u.)
Relationship between the infrared absorbance intensity of the band at 1540 cm-1 and the inorganic content of the nanohybrid ZnAl-Bz in the relative composites
Loredana Tammaro University of Salerno
Characterization of the composites: TGA
100 200 300 400 500 600 700 800
0
10
20
30
40
50
60
70
80
90
100
(c)
(e)
(d)
(b)(a)
Wei
gh
t (%
)
Temperature (°C)
PCL (a), PCL/ZnAl-Bz3 (b), PCL/ZnAl-Bz6 (c), PCL/ZnAl-Bz11 (d), ZnAl-Bz (e). Heating rate 5°C/min, in air flow
PCL displays one main degradation step with a Td midpoint value of 402°C, followed by a small tail at about 450°C. Incorporation of the nano-hybrid ZnAl-Bz within PCL anticipates the midpoint of thermal degradation, due to the lower degradation point of the ZnAl-Bz. Degradation temperature slightly decreases on increasing the ZnAl-Bz content.
192
280
383
192
274
383
245
341
383
325
383
205
0
50
100
150
200
250
300
350
400
450
LDHBz
PCL-LDHBz3
PCL
LDH-DCB
PCL-LDHDCB3
PCL
LDHo-OHBz
PCL-LDHo-O
HBz3PCL
LDHp-OHBz
PCL-LDHp-O
HBz3PCL
Mid
po
int
Tem
per
atu
re (
°C)
Loredana Tammaro University of Salerno
Conclusion
Layered double hydroxides intercalated with anionic active molecules based on benzoic acid and derivatives have been prepared and characterized
The nano-bio-hybrids, having antimicrobic properties, dispersed into PCL have been prepared and physically characterized
They can constitute model systems for “active food packaging” applications
Loredana Tammaro University of Salerno
Work in progress….
Analysis of mechanical properties Analysis of mechanical properties
Analysis of Analysis of controlled release through UV controlled release through UV spectroscopy of the active moleculesspectroscopy of the active molecules
ReferencesPetersen, K., Nielsen, P. V., Bertelsen, G., Lawther, M., Olsen, M. B., Nilssonk N. H. and Mortenseny G. Trends in Food Science & Technology;1999, 10: 52-68.M. Chasin, R. Langer (Eds), Biodegradable polymers as drug delivery systems. Marcel Decker, New York, 1990.
Loredana Tammaro University of Salerno
Thanks to:
Dr. Francesca Montanari, Dr. Morena Nocchetti, Prof. Umberto Costantino Department of Chemistry, University of
Perugia, Italy
This work was supported by PRISMA 2005 project entitled “Nanobiohybrids in polymeric matrices as
controlled delivery of active molecules”
My scientific group: My scientific group:
Dr. Valeria Bugatti, Dr. Giuliana Gorrasi, Prof. Vittoria VittoriaDr. Valeria Bugatti, Dr. Giuliana Gorrasi, Prof. Vittoria VittoriaDepartment of Chemical and Food Engineering, University of Salerno, Italy
Loredana Tammaro University of Salerno
Synthesis of the carbonate form: MgAlCOSynthesis of the carbonate form: MgAlCO33
The method used for the preparation of the carbonate form was the hydrolysis of urea The method used for the preparation of the carbonate form was the hydrolysis of urea in the in the
presence of mixture of M(II) (Mgpresence of mixture of M(II) (Mg2+2+) and M(III) (Al) and M(III) (Al3+3+) “Costantino ) “Costantino et al.et al. (1998a)”. (1998a)”.
Solid urea was added to 0.5 mol/dmSolid urea was added to 0.5 mol/dm33 metal chloride solutions (MgCl metal chloride solutions (MgCl22 and AlCl and AlCl33), having molar ), having molar fraction Al(III)/Al(III)+Mg(II) equal to 0.33, until the molar ratio of urea/Mg(II)+Al(III) fraction Al(III)/Al(III)+Mg(II) equal to 0.33, until the molar ratio of urea/Mg(II)+Al(III) reached the value 3.3.The clear solution was heated, under stirring, at temperature between 60 reached the value 3.3.The clear solution was heated, under stirring, at temperature between 60 and 100°C for 72 hours. The solid, separated from the solution, was washed with distilled and 100°C for 72 hours. The solid, separated from the solution, was washed with distilled
water, then dried at 80°C and stored in a desiccator with Pwater, then dried at 80°C and stored in a desiccator with P44OO1010 at room temperature. at room temperature.Synthesis of the chloride form: MgAlClSynthesis of the chloride form: MgAlCl
This form has been obtained by titrating at room temperature the carbonate form, This form has been obtained by titrating at room temperature the carbonate form, dispersed in 0.1 mol/dmdispersed in 0.1 mol/dm33 NaCl aqueous solution with a 0.1 mol/dm NaCl aqueous solution with a 0.1 mol/dm33 HCl solution by HCl solution by means of aRadiometer automatic titrator operating at pHstat mode and pH=5. After means of aRadiometer automatic titrator operating at pHstat mode and pH=5. After titration the solid waswashed with COtitration the solid waswashed with CO2 2 free deionized water and finally dried over free deionized water and finally dried over phosphorus pentoxidephosphorus pentoxide..