European Polymer Journal 44 (2008) 2695–2701

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European Polymer Journal

journal homepage: www.elsevier .com/locate /europol j

Synthesis of alkali-soluble copolymer (butyl acrylate/acrylic acid) andits application in leather finishing agent

Jing Hu *, Jianzhong Ma, Weijun DengCollege of Resource and Environment, Shaanxi University of Science and Technology, Xi’an, Shaanxi 710021, People’s Republic of China

a r t i c l e i n f o

Article history:Received 29 November 2007Received in revised form 16 May 2008Accepted 21 May 2008Available online 3 July 2008

Keywords:Alkali-soluble copolymerSynthesisLeather finishing agentEmulsifier

0014-3057/$ - see front matter � 2008 Elsevier Ltddoi:10.1016/j.eurpolymj.2008.05.016

* Corresponding author. Tel./fax: +86 29 8613255E-mail address: hujing616@gmail.com (J. Hu).

a b s t r a c t

Alkali-soluble copolymer (butyl acrylate/acrylic acid) was synthesized via solution poly-merization and used as the emulsifier to prepare acrylic resin for leather finishing agent.The influence of the synthetic conditions, such as the contents of acrylic acid and the ini-tiator types on the properties of P(BA/AA) was investigated in detail. Fourier TransformInfrared Spectrometer (FTIR) indicated that the polymerization reaction of P(BA/AA) wascomplete without ‘‘AC@CA” absorption peak. Differential Scanning Calorimeters (DSC)analysis confirmed that the glass transition temperature (Tg) of P(BA/AA) was �44 �C,Transmission Electron microscope (TEM) indicated that the copolymer latex particles dis-persed evenly and were less than 100 nm. Moreover, in contrast to acrylic resin preparedwith sodium dodecylsulfate (SDS) and alkylphenol ethoxylates (OP-10) as the emulsifiers,the applied properties of light leather finished by acrylic resin in use of P(BA/AA) as theemulsifier were measured: The air permeability increased by 18.5% as well as the water-resistance by 28.08% and the wet rub fastness by half class, respectively.

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1. Introduction

With the improvement of the environment safeguardsand the finishing materials requirement, water-solublefinishing materials has become the research hotspot inthe leather finishing agent. However, the water-solubilityfinishing agent prepared via the conventional emulsionpolymerization also exhibited the disadvantages [1]: thelarge use of small molecular surfactants pollute the envi-ronment and limit the finishing materials properties suchas the freezing stability, the mechanical stability, the wetand dry rubbing resistance and so on. In order to avoidthese disadvantages, The polymer surfactants was ap-plied to the emulsion polymerization [2–9]. Liu et al.[3] reported that the alkali-soluble copolymer P(methylmethacrylate/ethyl acrylate/methacrylic) was used tosynthesize the emulsion polymerization of n-butyl meth-acrylate as the surfactants and the nucleus-shell latexes

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9.

of 40–80 nm were obtained. Sun et al. [4] prepared a no-vel macromolecule surfactant of PS21-acrylamide/acrylicacid/MMA copolymer via the homogeneous polymerization.Muller et al. [5] used polyelectrolyte block copolymers toprepare the emulsion of 100 nm. Doug et al. [6] studiedthe preparation of PBA emulsion in the presence of poly-styrene/a-methylphenylene/AA copolymer; Satoshi et al.[7] investigated the kinetic process of styrene emulsionpolymerization with MMA/methacrylic acid copolymeras the emulsifiers.

Although the results that the properties of the macromol-ecule emulsifiers are better than low-molecular-weightemulsifier have been reported already, the macromoleculeemulsifiers usually have be used after the purification. In aword, the process seems to be time-consuming. If the mix-ture of the macromolecule emulsifiers with the excellenceemulsifier property was obtained without the separation,this will be useful for the industry manufacture.

In this paper, the mixture of the macromolecule emulsi-fiers synthesized via solution polymerization without anypurification ways was employed to be copolymerized with

2696 J. Hu et al. / European Polymer Journal 44 (2008) 2695–2701

acrylate monomers for preparing leather finishing agentdirectly. Besides, the influence of synthesized conditionssuch as the contents of AA and the different initiator typeson the physical properties of alkali-soluble copolymer (BA/AA) was investigated in detail. At last, acrylic resin pre-pared with P (BA/AA) as the emulsifier was applied inleather finish and the applied properties were determined.

Table 1Formula of leather finishes

Prebase coat/g Base coat/g

APV(Cationic Polyu’ethane) 100H20 250 350IPA(iso-Propy1 alcohol) 10Black pigment 100Black dye liquid 20Resin 300

Resins of two base coat formulas were 1# acrylic resin and 2# acrylicresin dividedly. Crust material: black cow crust.

2. Experimental

2.1. Materials

Acrylic acid (AA), kalium persulfate (KPS), sodiumbisulphite (NaHSO3), iso-propyl alcohol (IPA), MMA, BA,ammonium persulfate (APS), sodium thiosulfate(Na2S2O3) and sodium hydroxide (NaOH) were all pur-chased from Tianjin No. 3 Chemical Reagent Factoryand used without further purification; Sodium dodecyl-sulfate (SDS) and alkylphenol ethoxylates (OP-10) werebought from China Research Institute of Daily ChemicalIndustry. Deionized water was applied for the polymeri-zation processes. APV (cationic aromatic polyurethane),black pigment and black dye liquid were industry classand provided by Lanxsess LTd.

2.2. Preparation of alkali-soluble copolymer (BA/AA)

A 250-mL 3-necked round-bottom flask was equippedwith a reflux condenser, a thermometer and a magneticstirring bar. The reactor flask, charged with dionized water(60 g), AA (variable) and BA (5.00 g) were immersed in awater bath at 82 �C. It was stirred at 350 rpm for 20 min.Then 10 g aqueous solution of variable initiators(1.5 wt%) was added to the flask. The reaction was keptat the same temperature for 1.5 h and pH was adjustedto 7.0 using an aqueous solution of NaOH (20 wt%).

2.3. Preparation of acrylic resin emulsion

1# Acrylic resin: A 250-mL 3-necked round-bottomflask was equipped with a reflux condenser, a thermome-ter and a magnetic stirring bar. The reactor flask chargedwith 70 g of latex including water and P (BA/AA) washeated to 80 �C in a water bath. It was stirred at 350 rpmfor 20 min. Then, the polymerization was started with10 g aqueous solution of KPS (1.5 wt%) and the mixtureof MMA (10 g) and BA(6 g) monomers added dropwiseand finished within 1 h. The reaction was kept at 85 �Cfor 2 h.

2# Acrylic resin: A 250-mL 3-necked round-bottom flaskwas equipped with a reflux condenser, a thermometer anda magnetic stirring bar. The reactor flask charged with 2 g ofSDS, OP-10 (the molar ratio of SDS and OP-10 is 1:2) anddeionized water (40 g) were heated to 50 �C for 20 min;After the mixture of MMA (3 g) and BA (2 g), 5 g aqueoussolution of KPS (1 wt%) were charged to the reactor for30 min at 80 �C. Then, the polymerization was started with15 g aqueous solution of KPS (1 wt%) and the mixture ofMMA (12 g) and BA (6 g) added dropwise and finishedwithin 1 h. The reaction was kept at 85 �C for 2 h.

2.4. The application in the leather finishes

Acrylic resin leather finishing agent (1#) prepared withthe emulsifier of copolymer P(BA/AA) and conventional ac-rylic resin (2#) prepared with the emulsifiers of SDS andOP-10 were applied in the parallel leather finish experi-ments. Then the applied properties of the leather after fin-ished were determined. The formula of leather finishedwas shown in Table 1.

Operations: The mixture of aqueous solution of ammo-nia (15 N), anhydrous ethanol and water were used toclean the crust in the ratio 3:2:95 (mass ratio). The leatherwas sprayed once with the prebase coat materials andhung up. Then the same procedure as outlined above wasfollowed with the base coat materials (total mass of thefinishing materials: 9 g).

2.5. Determination of applied property

Measurement of water vapor permeability: In accor-dance with method DIN EN 14268, DIN 53333*, IUP 15.Measurement of water resistance of light leathers: Inaccordance with reference [10,11].Measurement of fastness to rubbing (wet and dry) oflight leathers: In accordance with method DIN EN ISO11640, DIN 53339*, IUF450.Measurement of flexing endurance of light leathers: Inaccordance with method IUP20.

2.6. Characterization

2.6.1. Thermogravimetric analysis (TGA)Thermogravimetric analysis (TGA) was performed using

a PerkinElmer thermogravimetric analyzer under a streamof air. P(BA/AA) films were heated from 50 �C to 800 �C at ascanning speed of 10 �C/min.

2.6.2. FTIR analysisFourier transform infrared spectrometer (FTIR) analysis

of P(BA/AA) film after purification, BA and AA were per-formed by VETOR-2 FTIR (Bruker Company in German).

2.6.3. Thermal analysis (DSC)Differential Scanning Calorimeters analysis was carried

out on SHIMADZU DSC-204 (Netzsch Company in German).The samples were quickly cooled to�100 �C and equilibratedat that temperature for 3 min, then heated to 100 �C at thescan rate of 10 �C/min under nitrogen atmosphere.

J. Hu et al. / European Polymer Journal 44 (2008) 2695–2701 2697

2.6.4. TEM analysisEmulsion of P(BA/AA) after the phosphomolybdic acid

coloration was observed by JEM-10OCXII TEM (JOEL com-pany in Japan).

3. Results and discussion

3.1. Surface tension analysis

The influence of AA amount and the initiator type onthe surface tension of alkali-soluble copolymer was inves-tigated during the preparation of P(BA/AA). The surfacetension of alkali-soluble copolymer (BA/AA) is dependentupon the contents of AA, which belongs to the stronghydrophilic polyacrylic acid and sodium polyacrylate usedas the hydrophilic groups of the surfactants [12]. When thecopolymer (BA/AA) molecule assembles the surface layerbetween air and liquid state, the polar groups of copolymer(BA/AA) can interact with H2O molecule but their non-po-lar groups extend outside, which decreases the interfacearea of air and liquid state and the surface tension of thesolution. Besides, the remnant sulfate ion of initiators afterpolymerization initiated can become the polar end groupof copolymer like the polymer emulsifiers.

Fig. 1 shows that the surface tension of alkali-solublecopolymer (BA/AA) increases with the contents of AA rising,when the initiators of APS/NaHSO3 and KPS/NaHSO3 are usedduring the preparation. This is because that the interactionbetween the hydrophilic group (ACOOH) of copolymer andH2O molecule increases the interface area of air and liquidstate. But the surface tension of alkali-soluble copolymer(BA/AA) with the initiators of APS/Na2S2O3 and KPS/Na2S2O3

decreases, which belongs to the different reducers.

3.2. Instability analysis

Fig. 2 displays that the instability of P(BA/AA) with dif-ferent initiators is dependent on the contents of AA. This is

Fig. 1. Effect of AA contents and initiator typ

because the increase of the contents of AA leads to theimprovement of the system interface area and the surfaceGibbs function. Besides, with the hydrophilic groups inP(BA/AA) rising, the copolymer molecule cannot be effec-tively adsorbed the interface layer between the air and li-quid state to form the interface film.

Fig. 2 also demonstrates that the stability of P(BA/AA) isbest using oxidation–reduction initiator system of APS,which is attributed to the only sodium ion after the copoly-mer neutralized by NaOH. However, the stability of P(BA/AA) using oxidation–reduction initiator system of KPS islow. In conclusion, the different cations influence the sta-bility of P(BA/AA) drastically, which belongs to more watermolecules accompanied by Na+ and larger electrostaticrepulsive force caused by the hydrated cation(Na+).

3.3. TGA analysis

Fig. 3 and Table 2 demonstrate the thermogravimetricanalysis (TGA) curves of P(BA/AA) with different AAamount and the initiator of KPS and NaHSO3 (samples a,b, c, d in Fig. 3). Three weight-loss stages are observedfor P(BA/AA). These correspond to the evaporation of phys-ically adsorbed water, the decomposition of P(BA/AA), andthe decomposition of P(BA), respectively. With the con-tents of AA increased, the amount of P(BA/AA) increasesbut the amount of P(BA) decrease. Fig. 3 also shows thatthe weight of P(BA/AA) decreases at lower temperaturefor P(BA/AA) with higher content of AA.

3.4. FTIR analysis

The structures of alkali-soluble copolymer (BA/AA), BAmonomer and AA monomer shown in Fig. 4 display thatBA and AA were copolymerized completely. In P(BA/AA)curve, the unsaturated carbonous bonds monomers havebeen copolymerized completely without the extendingvibration of C@C absorption peak 1680–1620 cm�1. The

es on the surface tension of P(BA/AA).

Fig. 2. Effect of AA contents and initiator types on the instability of P(BA/AA).

Fig. 3. TGA ana1ysis (a-0.3AA, b-0.9AA, c-1.5AA, d-2.1AAt1; the initiator of KPS/NaHSO3).

Table 2TGA results of P(BA/AA)

AA(g) The first weightloss (wt%)

The second weightloss (wt%)

The third weightloss (wt%)

0.3 16.68 55.18 16.78(below 289.4 �C) (289.4–432.63 �C) (432.63–657.43 �C)

0.9 10.54 70.25 11.45(below266.989 �C)

(266.98–455.69 �C) (455.699–695.28 �C)

1.5 10.77 74.65 7.84(below 221.16 �C) (221.16–464.39 �C) (464.39–670.21 �C)

2.1 10.863 75.86 5.4(below 202.63 �C) (202.63–471.38 �C) (471.38–687.05 �C)

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wide absorption peak 3000 cm�1 and the absorption peak2600–2800 cm�1 of ACOOH are disappeared and insteadof another wide absorption peak 3836 cm�1 of P(BA/AA)affected by extending vibration of AOH. The absorptionpeak 1733 cm�1 belongs to the extending vibration ofC@O and the absorption peak 2872 cm�1 is the extendingvibration of ACH3.

3.5. DSC analysis

Fig. 5 shows that there is the only glass transition tem-perature (Tg = �44 �C) in alkali-soluble copolymer P(BA/

J. Hu et al. / European Polymer Journal 44 (2008) 2695–2701 2699

AA), which may be that of P(BA/AA) and P(BA) mixtures.Based on FOX Formulation, the glass transition tempera-tures (Tg) of P(BA/AA) with 0.3 g AA and the initiator ofKPS/NaHSO3 calculated is about �45.7 �C. The glass transi-tion temperature of PBA is �54 �C.

3.6. TEM analysis

Fig. 6 demonstrates that the latex particles of alkali-sol-uble copolymer(BA/AA)is kept below 100 nm and disperseseven, which is because the addition of AA increase thehydrophilic groups of the emulsifiers and ensure the

Fig. 4. FTIR analysis (a-AA, b-BA, c-P (B

Fig. 5. DSC analysis of P(BA/AA)

water–oil latex particles formed during the early periodof the copolymer.

3.7. Applied properties

Table 3 demonstrates that the physical mechanicalproperties of light leather finished by acrylic resin usingP(BA/AA) as the emulsifier was improved evidently in con-trast to the conventional emulsifiers such as the waterresistance increased by 28.08% and the water vapor perme-ability improved by 18.5%. Besides, the wet rubbing fast-ness is improved by half class. The reason for these is

A/AA); AA = 0.3 g, KPS/NaHSO3).

(AA = 0.3 g, KPS/NaHSO3.

Fig. 6. TEM analysis of P(BA/AA) (AA = 0.3 g, the initiator of KPS/NaHSO3).

Table 3Physical and mechanical properties of finished leather

Type Water vaporpermeability ml(cm2 h)

Water resistance (the quality ofleather after 0.25/h water uptaking)

Dry rubbingfastness class

Wet rubbingfastness class

Flexing endurance

Leather finished by 1#acrylic resin

1.99 67.49 4/5 1/2 Perfect coating after100,000 Times flex

Light leather finishedby 2# acrylic resin

1.68 93.84 4/5 3 Perfect coating after100,000 Times flex

Ratio in contrast to 2#acrylic resin

18.5% �28.08% 0 0.5 0

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that acrylic resin prepared by the emulsifier of alkali-solu-ble copolymer (BA/AA) avoids the water-uptaking reactionof the small surfactants and the obtained film is even andtransparent.

4. Conclusion

Alkali-soluble copolymer (BA/AA) was synthesized viasolution polymerization and used as the emulsifier to pre-pare acrylic resin for leather finishing agent. The propertiesof the copolymer P(BA/AA) are dependent on the syntheticconditions, such as the contents of acrylic acid and the ini-tiator types. Fourier Transform Infrared Spectrometer(FTIR) indicated that the polymerization reaction of P(BA/AA) was complete without ‘‘AC@CA” absorption peak. Dif-ferential Scanning Calorimeters (DSC) analysis confirmedthat the glass transition temperature (Tg) of P(BA/AA)was �44 �C, Transmission Electron microscope (TEM) indi-cated that the copolymer latex particles dispersed evenlyand were less than 100 nm. Moreover, in contrast to acrylicresin prepared with sodium dodecylsulfate (SDS) andalkylphenol ethoxylates (OP-10) as the emulsifiers, the ap-plied properties of light leather finished by acrylic resin in

use of P(BA/AA)as the emulsifier were measured: The airpermeability increased by 18.5% as well as the water-resis-tance by 28.08% and the wet rub fastness by half class,respectively.

Acknowledgements

This investigation was supported by National 863 Foun-dation (Item No.: 2008AA03Z311), National NaturalScience Foundation (Item No.: 20674047) and the TeamWork Project of Science Innovation of Shaanxi Universityof Science and Technology (Item No.: SUST-A03).

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