Synthesis and Properties of Phenolic Syntan with HRP Catalysis Shenghua Lva and Mingming Houb

College of Resource and Environment, Shaanxi University of Scicence & Technology, Xi’an 710021, Shaanxi, China

alsh630603@yahoo.com.cn (corresponding author), bhouming.2008@yahoo.com.cn,

Keywords: horseradish peroxides, gallic acid, enzymatic catalytic polymerization

Abstract. A phenolic syntan GA-SHBS had been synthesized by radical copolymerization of gallic

acid (GA) and sodium 4-hydroxybenzenesulfonate (SHBS) using horseradish peroxides

(HRP)/H2O2 as catalyst. The effects of monomer ratio, reaction temperature and HRP dosage on

syntan were discussed. The optimum performance of GA-SHBS was got when the molar ratio of

GA: SHBS is 1:1 in the presence of 5 mg HRP at 35℃ in pH 7.0. The chemical structure of

copolymer was characterized by means of FTIR and NMR. The mechanism of polymerization

between GA and SHBS and binding mechanism between syntans and leather fibers were proposed.

The copolymer was used in making leather as tanning agent and retanning agent respectively,

applied results showed that the Ts of tanned leather can reach to 75.6°C, re-tanned leather has the

merits of good uniformity, fullness, softness, fine grain and non-plastic feel etc. Syntan also has

good permeability, excellent tanning performance and dyeing effect.

Intorduction

Syntans are obtained by simple polymerization of organic compounds, it is widely used in leather

tanning and mainly for the tight leather, and it can replace most of the vegetable tanning agent. The

syntan can improve the permeability of vegetable tanning and the physical properties of leather.

With the development of tanning technology, variety of syntans increased rapidly, especially the

phenolic syntans. But general production process of phenolic syntans may lead to undesirable

environmental effects as they can accidentally or intentionally decompose and pollution was created

because of the release of formaldehyde. Meanwhile general synthesis technology was difficult to

expand the transform of monomer to full extent, largely reduced the utilization rate of monomer. So

it will be an inevitable trend to explore a new synthesis technology.

Enzyme is a kind of green and efficient biological material. In particular, some enzyme such as

horseradish peroxidase (HRP) can be used to synthesize polymer from some monomer together with

H2O2. There were many literatures in which the HRP/H2O2 was used as catalyst to prepare new

copolymer with special structure using monomer such as phenols and anilines [1-4]. In this paper,

copolymer GA-SHBS from gallic acid (GA) and Sodium 4-hydroxybenzenesulfonate (SHBS) was

obtained by copolymerization using HRP/H2O2 as catalyst. Application experiments were carried

out by using the copolymer as tanning agent and retanning agent, and it can enhance the physical

properties and fullness of leather by adsorbing or filling in the collagen fibers [5].The chemical

structure of the copolymer GA-SHBS was characterized by FTIR and NMR.

Experiment

Material. HRP was brought from Beijing Biosynthesis Co, Ltd, China. Hydrogen peroxide

(H2O2, 30 wt %) was supplied by Tianjin Chemical Reagent No.3 Plant, China. Gallic acid, sodium

4-hydroxybenzenesulfonate, formic acid and sodium bicarbonate, all were chemical reagent and

brought from Xi’an Chemicals Reagent Factory, China. Pickling pig skin and wet blue pig skin was

supplied by Hebei Liushi Manufacture of leather Co, Ltd, China.

Preparation of HRP solution. The enzymatic solution was obtained by dissolving 50 mg HRP

in 100 mL distilled water, and then stored in a refrigerator at 4 °C until using.

Applied Mechanics and Materials Vols. 80-81 (2011) pp 391-395Online available since 2011/Jul/27 at www.scientific.net© (2011) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMM.80-81.391

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Synthesis of GA-SHBS. 10.2 g gallic acid and 11.7 g sodium 4-hydroxybenzenesulfonate

(molar ratio of GA and SHBS is 1:1) were put into moderate deionized water. The pH of mixture

solution was adjusted to 7.0 with sodium bicarbonate and then 10 mL HRP solution was put into the

mixture and then heated up to 35°C. Add 13.6 g H2O2 (30 wt %) to the flask by dropping for 2 h.

After H2O2 was dropping out, the reaction temperature was maintained at 35°C for 3.5 h. Then the

reaction solution was cooled down to the room temperature. The product was separated and purified

with absolute ethanol.

Tanning process. Pickling pig skin → Weighing (100% gain) → Detect shrinkage temperature

(Ts) → Acid bating (pH∼2.5) → Neutralizing (pH∼5.5, 0.5 h) → Tanning (for 4 h) → Fatliquoring

oiling (55°C)→ Feed formic acid (decrease the pH to 3.0, 0.5 h) → Oscillate for 1 h → Stay

overnight → Detect shrinkage temperature (Ts).

Retanning process. Wet blue pig leather → Weighing → Detect shrinkage temperature (Ts) and

thickness → Washing → Neutralizing (pH∼5.5, 0.5 h) → Tanning (for 4 h) → Fatliquoring

oiling(55°C)→ Feed formic acid (decrease the pH to 3.0, 0.5 h) → Oscillate for 1 h → Washing →

Detect shrinkage temperature (Ts) and thickness.

FTIR Test. FTIR spectra were recorded on EQUINOX-55 spectrometer (Bruker, Bremen,

Germany).The polymer and KBr mixture was used to record the FTIR spectra.

NMR Test. 1H-NMR spectra was recorded on INOVA-400MHz spectrometer (Varian, Palo Alto,

USA). Samples were prepared in deuterated dimethyl sulphoxide (DMSO-d6).

Measurement of leather thickness. The thickness of retanned leather was measured before and

after retanning. The thickness value was calculated by equation (1).

100%1

12×

−=

d

ddT (1)

T is the increased rate of thickness. d1 is the thickness of wet blue before retanning. d2 is the

thickness of wet blue after retanning.

Test for Ts and Mechanical properties of leather. Ts of leather were measured by Digital

Leather Shrinkage Temperature Tester MSW-YD4 before and after tanning. Mechanical properties

of leather were measured by electronic universal testing machine, including tensile strength and tear

strength.

Results and discuss

Effects of influencing factors on applied properties of copolymer. Enzyme is a kind of

temperature-sensitive material, it could exhibit high catalytic activity under optimum temperature.

Fig. 1 shows the effect of the different reaction temperature on Ts of the leather. The Ts of the leather

tanned by copolymer can reach to 75.6°C when the reaction temperature is 35°C in the presence of

5 mg HRP in pH 7.0.

Fig. 2 shows that HRP has significant effects on Ts of the pickling skin. Although HRP is a

highly efficient biological catalyst, from Fig. 2 we can see once reduce the amount of it, the Ts of

pickling skin be reduced at the same time. The Ts of the leather can obtain maximum 75.6°C when

the dosage of HRP is 5mg, and the Ts have not change with the increase the amount of HRP. Taking

into account the price of HRP, the optimal dosage of HRP is 5mg.

Effects of influencing factors on applied properties of copolymer. Enzyme is a kind of

temperature-sensitive material, it could exhibit high catalytic activity under optimum temperature.

Fig. 1 shows the effect of the different reaction temperature on Ts of the leather. The Ts of the leather

tanned by copolymer can reach to 75.6°C when the reaction temperature is 35°C in the presence of

5 mg HRP for 3.5 h in pH 7.0.

Fig. 2 shows that HRP has significant effects on Ts of the pickling skin. Although HRP is a

highly efficient biological catalyst, from Fig. 2 we can see once reduce the amount of it, the Ts of

pickling skin be reduced at the same time. The Ts of the leather can obtain maximum 75.6°C when

the dosage of HRP is 5mg, and the Ts have not change with the increase the amount of HRP. Taking

into account the price of HRP, the optimal dosage of HRP is 5mg.

392 Information Engineering for Mechanics and Materials

FTIR of GA-SHBS. The FTIR data of the copolymer is showed in Fig. 3. The broad vibration

absorption peak at 3531cm-1

and 3473 cm-1

corresponds to -O-H of phenol, the wavenunber moves

to the high frequency due to the effect of hydrogen bonding. The stretching vibration absorption

peak at 1222 cm-1

corresponds to -C-O of GA-SHBS. The stretching vibration absorption peak at

1631 cm-1

and 1348 cm-1

correspond to the symmetry and anti symmetric of carboxylate, it proves

the product contains a large number of -OH and -COO-. The absorption peaks 1176 cm-1

and 1033

cm-1

correspond to the S=O anti-symmetric stretching vibration and symmetric stretching vibration.

The vibration absorption peak of aromatic ring is at 1504 cm-1

and 1593 cm-1

appear deformation

vibration absorption peak. 650 cm-1

to 900 cm-1

belong to the C-H of benzene ring’s bending

vibration peak. Absorption peaks at the range of 1911 cm-1

prove that the benzene ring of

copolymer was substituted at 1, 2, 3, 5. The results indicate that the copolymer was obtained using

HRP/H2O2 as catalyst. 1H-NMR of GA-SHBS. Fig. 4 shows the

1H-NMR spectrum of the copolymer. The data are

analyzed as follows.1H-NMR (400 MHz, DMSO-d6): 3.387 (H1), 6.681(H2), 7.422(H3). The peaks

H1, H2 correspond to the hydroxyl groups of phenols respectively. The characteristic peak of H in

benzene ring was H3. 1H-NMR proves that copolymer contain hydroxyl groups.

Mechanism of polymerization. Radical polymerization consists of three steps composed of

radical initiation, radical coupling and radical transfer. Polymerization mechanism of GA and SHBS

is a couple-initiate process. The copolymerization of phenols is initiated by HRP/H2O2. The

synthetic process and the reaction mechanism of GA-SHBS are depicted in Fig. 5. In Fig. 5, the first

section indicates that under the catalysis of HRP/H2O2, the free radicals of GA and SHBS were

produced. The second section of polymerization is the radicals of GA and SHBS combined with

each other to form the dimer. The third section is the active site of the monomer radical transfer to

the dimer, therefore a dimer radical was formed, then two dimer radicals couple together to form a

trimer. Repeat of this process makes the chains of polymers grow.

Applied Mechanics and Materials Vols. 80-81 393

Applying results analysis. Table 1 and Table 2 show the effect of molar ratio between GA and

SHBS on the applied properties of copolymer. Table 1 shows the effect of GA dosage on the Ts of

pickling skin were investigated. The Ts of pickling skin has increased from 44.2 to 47.2°C when the

molar ratio of SHBS: GA is 1.0:0, this is because homopolymer of SHBS has no cross-linking with

collagen fibers. But the Ts of pickling skin have improved with the increase of GA in dosage. The Ts

of pickling skin increased from 43.1 to 65.5°C when the molar ratio of SHBS and GA was 1.0:0.5.

The Ts of pickling skin can reach to 75.6°C from 45.0°C when the molar ratio of SHBS and GA is

1.0:1.0. This is because -OH and -SO3 of polymer bond with the leather fibres and produce more

cross-linking. Then proportion of GA was kept unchanged, the effect of SHBS dosage on the Ts of

pickling skin were investigated. The Ts of pickling skin increased from 43.5°C to 64.3°C when the

molar ratio of SHBS and GA is 0.5:1.0. The Ts of pickling skin increased from 45.4 to 64.8°C when

the molar ratio of SHBS and GA is 0:1.0. It is because the poor acting force between copolymer and

fibers with the reduction of SHBS.

Table 1 The effect of molar ratio of monomers on leather’s Ts

Tannage

SHBS :GA (mol)

Ts of tanning and retanning leather (°C)

Before

tanning

After

tanning

Before

retanning

After

retanning

1.0:0.0 44.2 47.2 106.6 107.2

1.0:0.5 43.1 65.5 108.3 109.5

1.0:1.0 45.0 75.6 108.7 110.2

0.5:1.0 43.5 64.3 107.8 109.6

0.0:1.0 45.4 64.8 109.2 110.8

Table 1 shows that the GA-SHBS has small contribution to the Ts of wet blue leather. The Ts

improved to 110.2°C from 108.7°C when the molar ratio of SHBS and GA is 1.0:1.0. Table 2

shows the thickening increment rate of leather reach to 30% when the molar ratio of SHBS and GA

is 1.0:1.0. In particular when the molar ratio of SHBS and GA is 0:1.0, the thickening rate of wet

blue leather can achieve 56.9%. It is because the -OH and -COOH of copolymer easy to produce the

hydrogen bond and form a copolymer macromolecules like the vegetable tanning agents. When

used it as tanning agent, portion of it penetrate into the fibres and produce cross-linking with

collagen between groups, another part of it deposition or absorption with the collagen fibres, both of

them have greatly improved on the thickness of leather. The results of Table 1 and Table 2 show

that the GA-SHBS has best application performance when the molar ratio of GA and SHBS is

1.0:1.0.

394 Information Engineering for Mechanics and Materials

Table 2. The effect of molar ratio of monomers on thickness and mechanical properties of leather

Tannage

SHBS :GA

(mol)

Thickeness of

retanned leather (mm)

Mechanical properties

of retanned leather

Before

retanning

After

retanning

Tensile strength

(N/mm2)

Tear strength

(N/mm)

1.0:0.0 0.65 0.68 6.20 21.40

1.0:0.5 0.58 0.67 10.64 36.92

1.0:1.0 0.62 0.81 14.87 52.23

0.5:1.0 0.60 0.85 11.81 41.42

0.0:1.0 0.67 1.03 9.42 32.67

Summary

The copolymer GA-SHBS was carried out under catalytic synthesis of HRP/H2O2. The effect of

molar ratio of monomers, reaction temperature, dosage of HRP and reaction time were investigated.

The results show that they can affect the physical properties of leather distinctly. The optimization

synthesis condition is the molar ratio of monomer GA and SHBS is 1:1 in the presence of 5 mg

HRP at 35°C in pH 7.0. The chemical structure of graft copolymer were characterized by FTIR and

NMR. The mechanism of polymerization between GA and SHBS, binding mechanism between

syntans and leather fibers were both proposed. Application results show that the product has good

selective filling and excellent permeability for leather, used it for main tanning, the Ts of leather can

reach to 75.6°C. The good fullness, exquisite surface and excellent mechanical properties of leather

are obtained by the syntan of GA-SHBS.

References

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(2005)33-36.

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[3] S. Lv, G. Liu, Y. Ma, Preparation and properties of starch-polyacrylamide graft copolymer with

HRP catalysis, China leather. 39 (2010)15-19.

[4] S. H. Lv, G. Liu, Y.F.Ma, Study on preparation and properties of copolymer of

p-hydroxybenzoic acid and sulfanilic acid with HRP catalysis, Journal of Functional Materials.

41 (2010)1427-1431.

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Applied Mechanics and Materials Vols. 80-81 395

Information Engineering for Mechanics and Materials 10.4028/www.scientific.net/AMM.80-81 Synthesis and Properties of Phenolic Syntan with HRP Catalysis 10.4028/www.scientific.net/AMM.80-81.391

DOI References

[2] S. Sgalla, G. Fabrizi and S. Cacchi, Horseradish peroxides in ionic liquids Reacions with water insoluble

phenolic substrates, Journal of Molecular Catalysis B: Enzymatic. 44 (2007) 144-148.

http://dx.doi.org/10.1016/j.molcatb.2006.10.002