INTERCALATION COMPOUNDS OF LAYERED DOUBLE HYDROXIDES WITH ANTIMICROBIAL BENZOATE ANIONS AS FILLER OF BIODEGRADABILE POLYMERIC MATRICES FOR NEW PACKAGING

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


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


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


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?


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


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


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)


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%


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


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


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)


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


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


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


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)


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


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)


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


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.


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


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..

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INTERCALATION COMPOUNDS OF LAYERED DOUBLE HYDROXIDES WITH ANTIMICROBIAL BENZOATE ANIONS AS FILLER OF BIODEGRADABILE POLYMERIC MATRICES FOR NEW PACKAGING