Tannin Based Foams and its derived Carbon Foams G. Tondi1-2, A. Pizzi2, A.Celzard2-3

1 FHS – University of Applied Science – Salzburg. 136a Marktstraße, 5431 Kuchl (Austria)

2 ENSTIB - LERMAB, UHP – Nancy. 27 rue du Merle Blanc, 88051 Epinal (France)

3 Institut J.Lamour UMR-CNRS 7198, 54506 Vandouvre-les-Nancy, (France)

Context : Natural foams

Abstract :

Polyurethane is the most versatile foam world-wide recognized. It is used for many applications in

both rigid and elastic applications. The challenge, in this field, consists in developing new materials

with the following features: Environmentally friendly, resistant to fire and cheap. Tannin foams are 95%

natural, strongly resistant to fire and not really expensive ( around 2-4 €/Kg).

100 m

Condensed Mimosa tannin mixed with:

Copolymerization agent: Furfurylic

alcohol;

Blowing solvent: Diethylether;

Hardener: Formaldehyde;

Moderator: Water;

When the solution is homogeneous...

Catalyst: p-toluensulphonic acid.

How to prepare it?

Context : Carbon foams

Since many years carbon has started to be considered the “material of the future”

due to its extremely wide range of properties. Nowadays many materials are

proposed as carbon precursor, but not many natural solutions are found,

especially for highly porous carbons. Tannin derived carbon foam because of its

properties and its price (10-15 €/Kg) is a really interesting opportunity.

Tannin-based rigid foams are networked structures obtained by polycondensations of polyflavonoid

tannins and furfuryl alcohol.

Carbon foam derived by pyrolisis of such a natural precursor have been synthesized. Physical and

chemical properties of both, tannin foams and derived carbon foams have been evaluated.

Tannin foams have shown interesting properties such has their complete resistance to fire, their high

water uptaking and their remarkable low thermal conductivity.

During the carbonization process, the foams rearrange the structure producing a glass-like carbon

foam. This vitreous carbon foams have good electrical conductivity, low thermal conductivity and good

mechanical strength. O

OH

OH

OH

OH

OH

O

OOH

n

O

OH

OH

OH

OH

OHn H+

O

OH

OH

OH

OH

OH

OH

2

O

OH

OH

OH

OH

OHO

OH

OHOH

HO

H+

HCHO

H2O

OOHn

H+ O O O

In acid environment furfuryl alcohol and flavonoids condense. The furanic ring is highly reactive in

position 5 and it can create crosslinked structures. The polymer becames more and more rigid

because this reaction can happen in several point of the oligomeric tannin-chain obtaining a fully

branched copolymer.

Chemistry:

Two simultaneous reactions take place: the autocondensation of furfuryl alcohol (That will follow Diels-

Alder mechanism) and the formilation of flavonoids.

These reactions are even faster than the condensation between furfuryl alcohol and flavonoids.

The final polymer have to be considered made of the mixed sum of these condensations.

• The development of the foam takes place in 60-90 seconds.

• No external energy required. Exothermic polymerization.

• The structure lost the most of the solvent in 24 hours and , in the meantime, the polymer becomes rigid.

Conclusions :

Perspectives :

Results and discussions :

Organic tannin foams and their carbonized derivatives are different materials. Their properties are

reported in the tables below:

Intrinsic properties of tannin and carbon foams are similar. Only two remarkable characteristics are different.

Wall density is clearly different because the skeletons are based respectively on tannin-furanic polymers

and carbons. Average cells diameter is also not the same: During the carbonization process, indeed, the

foam lose 50% of its volume.

Features Tannin Foams Carbon Foams

Bulk Density (g/cm3) 0,04 – 0,15 0,04 – 0,15

Walls Density (g/cm3) 1,55 1,98

Anisotropy 1-3 1-3

Cells diameter(mm) 370 - 195 250 - 135

Porosity (%) 95 - 97 94 - 96

Open cells(%) 94-96 93-95

Surface Area (m²/g) 0,5 - 1 0,5 - 1

Connectivity 1,0 1,0

Tortuosity 1,17 – 1,28 1,20 – 1,35

Features Tannin Foams Carbon Foams

Compression Resistance(MPa) 0,15 – 0,5 0,3 – 0,9

Elastic Modulus (MPa) 100-300 250-600

Water Uptake (%) 100 - 500 50-200

Thermal conductivity (W/m K) 0,03 0,035 – 0,044

Electrical conductivity(S/cm) Not conduct 1,34 - 4

Coeff. Thermal dilatometry (ppm/K) - 2-4

Permeability (m²) 10-9 - 10-11 10-11- 10-14

Flame resistance Bunsen (1400°C)

10 min.

Air/Acetylene

(3000°C) 30 sec.

Organic and carbon foams are deeply diverse: Mechanical, thermal and electrical properties are different.

These two porous structures can be useful for extremely different applications.

Mainly three lines of development have to be considered: Further characterizations of the two materials, acoustic properties and heavy metal adsorption tests.

New formulations of the foam can be considered: More elastic blends with natural latex, tailored dimensions of pores, use of different fillers to increase mechanical and insulating properties.

Scale up of the process and resolution of several problems related to stirring systems and temperature controlling .

Completely different trend for

Extrinsic properties …

Several Applications have been proposed for the two foams. Their high amount of pores suggests immediately to use these products as insulating materials:

Poster section: Thursday 7th, October. 1st International Conference on Processing Technologies for the Forest and Biobased Products Industries

Insulation of Buildings

• Extremely low thermal conductivity;

• Fire resistant;

• Natural and cheap.

Water and shock Absorber

• High affinity for water;

• Strong energy absorption.

Katalytic support / Filter

• Low cost precursor;

• Vitreous Carbon;

• Easy Activation.

Thermal Shield

• High resistance to thermal shock;

• Lightweight material

• Energy absorption

Tannin based Organic Foams Derivate Carbon Foams

N2

5 K/min

900

C

2 h

Carbonization: