Tannin–Phenol Formaldehyde Resins As Binders for Cellulosic Fibers: Mechanical Properties

doi:10.4236/nr.2011.22013

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Natural Resources, 2011, 2, 98-101

doi:10.4236/nr.2011.22013 Published Online June 2011 (http://www.scirp.org/journal/nr)

Tannin-phenol Formaldehyde Resins as Binders

for Cellulosic Fibers: Mechanical Properties

A. S. Hussein1*, K. I. Ibrahim1, K. M. Abdulla2

Polymer Research Center, University of Basrah; State Company for Petrochemical Industries, Basrah , Iraq.

E-mail: [email protected]

Received December 21st, 2010; revised May 11th, 2011; accepted May 20th, 2011.

ABSTRACT

In this study Eucalyptus tannin (T) was isolated from outer bark of Eucalyptus trees; as sodium phenoxide salt and used

as extender or copolymer into phenol formaldehyde (PF) resin at five percent (10, 20, 30, 40 and 50)% W/W. Tan-

nin-phenol formaldehyde (TPF) and tannin formaldehyde-phenol formaldehyde (TFPF) resins that synthesized in this

study were evaluated as adhesive material for cellulosic fibers by study the mechanical properties of the composite

sheets. The results show that the substitu ting of (PF) with tannin at (10-50)% W/W give resins with mechanical proper-

ties comparable or near to those of pure (PF), where the tensile strength at break (Tb) ranging from 15.15 Mpa to 22.27

Mpa as compared with 17.6 Mpa for pure (PF); while the impact strength properties (Im) of composites sheets in-

creased with increased the (T) percents which were about 5.16 KJ/m2 for (TPF-10%) and 7.21 KJ/m2 for

(TPF-50%) .On the other hand modification of (T) to tannin formaldehyde resin (TF) appear less performance at the

results of this study, this effect probably to low p enetration of (TFPF) resins between the small vo ids of cellulose fibers

when soaked it in resin solutions. In gene ral the results of this study ind icate that th e Eucalyptus tann in can be used for

partial sub stitution of (PF) to produce resins with feas ible mechanical properties and can be used in so me applications

of (PF) resins.

Keywords: Tannin, Tannin-formaldehyde Resins, Phenol- formaldehyde Resins, Mechanical Properties

1. Introduction

Tannins are one of the natural products which are widely

distributed in plant kingdom, they are composed of dif-

ferent phenolic compounds [1,2]. Tannins are generally

classified into two major types: hydrolysable tannin s and

condensed tannins, the hydrolysable tannins are mixture

of simple phenols and it has had medicinal and cottage

applications. Condensed tannins are polymeric phenolic

compounds comprising from flavon-3-ol repeating units;

Condensed tannins are known for their wide distribution

in various softwood and hardwood, and it constitute

about 90% of the total world production of commercial

tannins [3].

Many studies show that the phenolic natural of tannin

make it suitable for synthesis polymeric resins and adhe-

sives; Hergert [4] stated that (30-50)% W/W tannin re-

placement of the amino and phenolic resins have been

formulated into wood adhesives. Saayman [5] reported

tannin (Wattle tann in) utility i n PF resins fo r wood adh e-

sives requiring up to 30% of PF fortification to obtain a

fully water–resistant bond. Other studies deal with reac-

tion of tannin (Wattle tannin) with formaldehyde to syn-

thesis polymeric resins [6, 7].

The purpose of this study was to evaluate the per-

formance of Eucalyptus tannin as tannin sodium salt (T)

or as tannin-formaldehyde resin (TF) into PF as binders

for cellulosic fibers to produce composites sheets by

study their mechanical properties.

2. Experimental

2.1. Materials:

Tannin was isolated from the outer bark of Eucalyptus

tree, and used as crude without farther purification. Cel-

lulose fibers (pulp) were used as sheets from National

Company of Papers Industries, other chemicals used in

this study were:

Sodium hydroxide and phosphoric acid from Fluka

Chemical Company Inc.; phenol, ethanol and formalin

solution (37-41)% W/V from (H&W).

2. 2. Instruments:

The tensile properties were measured by using tensile

Tannin–phenol Formaldehyde Resins As Binders for Cellulosic Fibers: Mechanical Properties

strength instrument (I nstron model 1193), an d the impact

strength was measured by impact testing instrument

(Universal Pendulums model 6546/000), with 2J pendu-

lum energy.

The composite sheets that prepared from these resins

that synthesized in this study with cellulose fibers were

cut into tensile test sp ecimens (Dumbbell shape) and in to

impact test specimens by dumbbell cutter (Automatic

Hollow Dipunch, made by Ceast Company). The sam-

ples sheets were compression–molded using hydrolic

press (F. & R. AL-Haddad Co.).

Dimensions of the samples were measured by mi-

crometer (Brown & Shape micrometer); (TMT Notch

cutter model 43-15-1) was used for notching the impact

test specimens.

2.3. Isolation of Tannin:

The powder of Eucalyptus outer bark was refluxed with

sodium hydroxide solution 2% for 24 hr., and then the

miture allowed to cool and filtrated. Sodium tannin

phenoxide was used as tannin without naturalized or far-

ther purification, the yield of it is about (48 – 50)% per

total solids used (ba rk and so di um hydroxid e).

2.4. Resins Synthesis:

TF resin was synthesized adopting the following proce-

dure: 10 g tannin was dissolved in 50 ml water, the PH of

solution was adjusted to (10-11) by added some drops

from 10% NaOH solution, the temperature o f the soltion

raised to 80˚C with stirring for 75 min. Afterwards the

solution was allowed to cool to 60˚C, then 40 ml from

formalin solution was added, the temperature of the

mixture was kept at 60˚C; the reaction time was about 3

hr.

Tannin resins that synthesized consist of tannin-phenol

formaldehyde (TPF), and tannin formaldehyde–phenol

formaldehyde (TFPF); at five percent from tannin in the

final resin (10, 20 , 30 , 40 and 50 )% W/W.

PF resin was synthesized according to the procedure

described in references 8 and 9; TPF resins were synth-

sized by mixing the solution of predetermined weight of

tannin with the mount of PF that give required propor-

tion.

TFPF resins at (10, 20, 30, 40 and 50)% from tannin

were prepared by allowed the some method of TPF syn-

thesis.

2.5. Production of Composite Boards:

The composite boards were prepared by soaking the cel-

lulose fibers in 20% W/V of resin solutions for 24 hr.,

then dried at room temperature and cut into test speci-

mens. Test samples compressed under 150 psi pressure,

at (160-170)˚C for 10 min. The impact test samples had

dimensions of (1 cm width, 0.2-0.17 cm thickness and 5

cm length). While the tensile test samples had 11.5 cm

length, (0.2-0.17) cm thickness and 0.6 cm width.

3. Measurements:

The tensile properties were measured at across head

speed 50 mm/min. and recorder speed 10 mm/min.; five

samples were made for each test, the tensile strength

tests carried out at 25˚C and according to the ASTM–

D638-72(1986)[10a]. While the impact resistance acord-

ing to ASTM D256-56(1986)[10b].

4. Results and Discussion

Many study focused to reduced the cost of phenolic res-

ins and to reduced their toxicity on humans and on the

environment; some of this are used lignin and it's deriva-

tives [12-14], another tries about using of tannins or

other natural products [15,16].

In this study the effects of Eucalpytus tannin and it’s

methylol derivative on the adhesion properties of PF for

cellulose fibers was examined and evaluate the perform-

ance of these resins which contain tannin (T) or tannin

formaldehyde (TF) as binders resins by study the me-

chanical properties of final composites sheets that made

by it after thermal curing under press. The ten sile proper-

ties of materials evaluated the rigidity, cross-linking, and

flexibility of it. However the tensile strength of these

composites (resins) showed in Figure 1 and Figure 2; it

indicate that the tensile of the samples made by (10-30)%

tannin or tannin formaldehyde decrease relative to that of

the sample which made by pure PF resin, where the ten-

sile of the resins that contain tannin or tannin formalde-

hyde at all percent lower than of the pure PF except the

resins that contain (40-50)% W/W tannin have tensile

values higher than that of PF.

This behavior mean that tannin or tannin formaldhyde

resin decreased the amount of resins that act as binder

because tannin not contain reactive functional groups can

bonded in the network of resin matrix, on the other hand

Figure 1. Tensile strength of TPF resins-cellulose fibers

composite at different percent of tannin.

100 Tannin–phenol Formaldehyde Resins As Binders for Cellulosic Fibers: Mechanical Properties

Figure 2. Tensile strength of TFPF resins-cellulose fibers

composite at different percent tannin formaldehyde.

no significant effect to methylol groups of TF; Figure 2.

this may be result to some factors of TFPF resin solu-

tions or to method of cellulose fibers-resins samples

preparation. The results showed in Figure 1 and 2 indi-

cate that the tensile strength of the samples not continue

in decreasing at percent of 10%, 20% and 30% from T or

TF which about (15.15-15 .01) Mpa and (13.6-13.1) Mpa

respectively; in spite of reduce the amount of PF portion;

there are some effects for T or TF in the final properties

of the composites these effects may come from action of

tannin as fillers which generally increase the rigidity of

the samples or by act as extender with limit activity for

tannin ability to form methylol groups when react with

formaldehyde during hot press then can participate with

PF in the formation of network resins but at little func-

tional groups [17]; and the high density of polar func-

tional groups in tannin lead to th is behavior.

On the other hand, the impact strength of TPF resins

treated cellulose fibers (Figure 4 and 5) at T percent

10% and 20% were lower than that of pure PF.

While the resins of 30%, 40% and 50% TPF gave an

impact strength equal to that of pure PF about 7.2 KJ/m2,

this brittleness appears to be the result to the action of

tannin as fillers and also for behave of it as across-link-

ing agent for substituted the lower levels of PF that

needed to obtained similar mechanical properties. As can

see the modification of T to TF did not improved the

Figure 4. Impact strength of TPF resins–cellulose fibers

composites.

Figure 5. Impact strength of TFPF resins–cellulose fibers

composites.

adhesion properties of these resins (Figure 5); the ob-

served impact strength values of most composites that

contain TF were generally higher than this contain 100%

PF, only one resin (TFPF-10%) have impact value less

than others; this flexibility appear to be the result to low

diffusion of resins between the fibers. Therefore replace

the soaking method by mixing the resins with fibers me-

chanically is expected to give samples with better me-

chanical and adhesion properties due to facilitate the

diffusion and p enet rat i o n of re sins.

5. Conclusions

Used Eucalyptus tannin as tannin sodium salt into PF

resin at (10, 20, 30, 40 and 50)% W/W can produce cel-

lulose fibers-TPF composite sheets with mechanical

properties comparable to that made with pure PF. The

composed sheets produced by used tannin-formaldehyde

resin into PF resin show lower satisfactory results. At the

limited mechanical properties of this study; the used of

Eucalyptus tannin as TPF or TFPF resins appear to be

practically to reduced the ratio of PF in some of it's ap-

plications, Tannin act as filler or extender to participate

in the formation adhesive bonds but at lower level and

stiffness.

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