Mechanism of surface hydrophobicity modification of ... · Published by Maney Publishing (c) W.S Maney & Son Limited Mechanism of surface hydrophobicity modification of wollastonite

Pub

lishe

d by

Man

ey P

ublis

hing

(c)

W.S

Man

ey &

Son

Lim

ited

Mechanism of surface hydrophobicitymodification of wollastonite powder

X. Hou1,2, H. Ding*1, Y. Liang1, Y. X. Zheng1, Z. D. Yang2 and H. N. Luo1

In this paper, the surface of wollastonite powder is modified by sodium stearate, and the amount

of modifier, modifying time, modifying temperature and slurry concentration are optimised. The

modifying mechanism is revealed by infrared radiation, scanning electron microscope and

particle size analyser. Results show that the surface of modified wollastonite powder should

change from hydrophilic to hydrophobic, and the contact angle should change from 11 to 68u.Sodium stearate is adsorbed on the surface of wollastonite through chemical bond. After being

modified, wollastonite powder has better dispersion, and it can be used in organic systems like

plastic and rubber.

Keywords: Wollastonite powder, Sodium stearate, Surface modification, Mechanism analysis

Wollastonite is a kind of calcium metasilicate mineralsalt. Its chemical formula is CaO.SiO2. Its theoreticalchemical composition is 51?75%SiO2 and 48?25%CaO,and its structural formula is Ca3[Si3O9].1 The crystalstructure of wollastonite is shown in Fig. 1. Three [SiO4]tetrahedra form [Si3O9] single chain, and the chainextends along the b axis. The chains are parallel to eachother, and the gaps between the chains are only filled byCa2z ions, forming [CaO6] octahedral. The [CaO6]octahedrals form the chains that are parallel to the b axiswith the edges.2

The physical and chemical properties of wollastoniteare stable. In addition, it has high whiteness, low thermalexpansion coefficient (6?561026 mm uC21 when thetemperature is from 25 to 800uC), low moisture absorp-tion (,4%), low electrical conductivity and low dielectricloss.1 Therefore, its physical properties and mechanicalproperties are excellent. It is widely used in coatings,plastics, rubbers and ceramics.

However, wollastonite is a kind of inorganic mineraland is hard to disperse in organic systems like plastic.Therefore, a series of researches have been carried out todo surface modification of wollastonite to make itsapplication wider. At present, the investigative contentof wollastonite include mechanochemical effect,3,4 stea-ric acid modification,5 titanate modification,6 surfacemodification of inorganic minerals,7–10 polymer modifi-cation,11 modified ceramic applications12 and so on.However, there is no research concerning surface hydro-phobicity modification of wollastonite powder and itsmechanism and application as an excellent non-metallicmineral resource.

In this paper, the surface of wollastonite powder ismodified by sodium stearate. The modifying mechanisms

are revealed by Fourier transform infrared spectroscopy(FTIR), scanning electron microscope (SEM) and parti-cle size analyser. Results show that the surface ofmodified wollastonite powder should change fromhydrophilic to hydrophobic, and the contact angle changefrom 11 to 68u. Sodium stearate is adsorbed on thesurface of wollastonite in chemical bond. After modifica-tion, wollastonite powder has a better dispersion, and itcan be used in organic systems.

Experimental

Raw materialsWollastonite is supplied by the Tianzhiyan Health andTechnology Company (Fig. 2). Through X-ray diffrac-tion, particle analysis and SEM, the particles are in anacicular or fibrous shape, and they disperse uniformlywith clear cleavage. The surface is smooth, and theparticle size distribution is uniform. D50 is 20?42 mm,and D90 is 40?18 mm. Sodium stearate is chemical purity,and it is supplied by Jingwen Culture Company, Beijing.

Instruments of characterisationBaxter BT-1600 Baxter distribution of particle imageanalyser was from Baite Instrument Company, Dandong,Liaoning Province; D/MAX2000 X-ray powder diffract-ometer was from the Rigaku Corporation, Japan; S-3500N SEM was from Hitachi electron microscopeCorporation, Japan; Spectrum 100 FTIR spectrometerwas from PerkinElmer Instrument Corporation, Shanghai;and the JC2000D contact angle measuring instrument wasfrom Zhongchen Digital Equipment Company, Shanghai.

PreparationTen grams of wollastonite was weighed and poured intoa three-neck flask, then added with distilled wateraccording to different concentrations. The three-neckflask was put into the water bath, preheated and stirredto disperse the particles uniformly. Sodium stearate(1?5%) was weighed and put into the three-neck flask at

1School of Materials Science and Engineering, China University ofGeosciences, Beijing 100083, China2Tongling County NiuShan Mining Co., Ltd., Anhui Province, China

*Corresponding author, email [email protected]

S1-260

� W. S. Maney & Son Ltd. 2013Received 16 October 2012; accepted 25 March 2013DOI 10.1179/1432891713Z.000000000227 Materials Research Innovations 2013 VOL 17 SUPPL 1

Pub

lishe

d by

Man

ey P

ublis

hing

(c)

W.S

Man

ey &

Son

Lim

ited

50uC and kept stirring for 30 min. The flow chart isshown in Fig. 3.

Results and discussion

Modification of wollastonite with differentamounts of sodium stearateThe effect on the modification of wollastonite withdifferent amounts of sodium stearate was studied at60uC. The modifying time was 30 min, and the slurryconcentration was 20%. Single factor experiments were

performed with 0?2, 0?5, 1?0, 1?5 and 2?0% sodiumstearate respectively. Activation index and dispersionstability of the modified wollastonite were also studied.The products at the bottom were partially taken out andobserved with microscope after 30 min. The results ofdispersion stability and activation index showed thatwhen the amount of the modifier was 1?5%, the effectshould be the best. Images of particle dispersion (Figs. 4and 5e) showed that modified wollastonite powdershould disperse in kerosene uniformly, and there shouldbe no sign of reunion; this result was consistent with thecharacterisation of dispersion.

2 a spectrum (XRD), b particles spectrum and c,d SEM spectrum of raw wollastonite powder

1 Crystal structure of wollastonite

3 Processing of modification of wollastonite powder

Hou et al. Surface hydrophobicity modification of wollastonite powder

Materials Research Innovations 2013 VOL 17 SUPPL 1 S1-261

Pub

lishe

d by

Man

ey P

ublis

hing

(c)

W.S

Man

ey &

Son

Lim

ited

Effect on modification of wollastonite atdifferent timesThe effect on the modification of wollastonite at differenttimes was studied at 50uC. The slurry concentration was20%, and the amount of sodium stearate was 1?5%. Singlefactor experiments were carried out at 10, 15, 30, 45 and60 min respectively. There were two extremes in the chart.During the modifying time, the absorption of sodiumstearate on wollastonite was physical absorption mainly.As time went on, chemical absorption formed at thecontact surfaces. When the absorption reached saturation,the modifying effect became worse instead of getting better.Thus, 30 min was the best modifying time. Images ofparticle dispersion (Figs. 6 and 7d) showed that modifiedwollastonite powder should disperse in kerosene uniformly,and there should be no sign of reunion. This result wasconsistent with the characterisation of dispersion.

Effect on modification of wollastonite atdifferent modifying temperaturesThe effect of modifying temperature on the modificationof wollastonite was studied in 30 min. The slurryconcentration was 20%, and the amount of sodiumstearate was 1?5%. Single factor experiments wereperformed at 40, 50, 60, 70 and 80uC. The product at

the bottom was partially taken out and observed with amicroscope after 30 min.

Figure 9 showed the effect of modifying temperatureon the modification of wollastonite. For the modifyingtemperature, the absorption of ionic surfactant usuallydecreases as temperature rise. The results of dispersionstability and activation index showed that when theamount of the modifier was 1?5%, the effect should bethe best. Images of particle dispersion (Figs. 8 and 9c)showed that modified wollastonite powder shoulddisperse in kerosene uniformly, and there should be nosign of reunion.

Effect on modification of wollastonitewith different slurry concentrationsThe effect on the modification of wollastonite withdifferent slurry concentrations was studied at 50uC. Themodifying time was 30 min, and the amount of sodiumstearate was 1?5%. Single factor experiments werecarried out with the amount of slurry concentration10, 15, 20, 25 and 30% respectively. The products at thebottom were partially taken out and observed with amicroscope after 30 min.

4 Effect of modifier dosage to wollastonite powder

5 Analysing of particles dispersion of wollastonite powder with different modifier dosage

6 Effect of modifier to wollastonite powder with different

times


S1-262 Materials Research Innovations 2013 VOL 17 SUPPL 1

Pub

lishe

d by

Man

ey P

ublis

hing

(c)

W.S

Man

ey &

Son

Lim

ited

The results of the dispersion stability and activationindex showed that the dispersion stability increased firstand decreased later. When the slurry concentration

reached 10 or 15%, the effects were very good. As slurryconcentration increased, wollastonite particles andsodium stearate could not contact with each othersufficiently, and it caused worse modification. The resultof dispersion stability (Figs. 10 and 11b) showed thatwhen slurry concentration was 10%, the effect should bethe best, and the activation index reached 95%. Inaddition, considering the production cost, the effect wasthe best when the slurry concentration reached 10%.

Mechanism of modification onwollastonite

The analysis of contact angle before and aftermodificationThe optimal experimental condition is as follows:the amount of sodium stearate, 1?5%; modifyingtemperature, 50uC; modifying time, 30 min; and slurryconcentration, 10%. The flow chart of the modificationwas shown in Fig. 3. The contact angle was measuredwith distilled water (Fig. 12).

7 Analysing of particles dispersion of wollastonite powder with different time

8 Effect of modifier to wollastonite powder with different

temperature

9 Analysing of particles dispersion of wollastonite powder with different temperature



Pub

lishe

d by

Man

ey P

ublis

hing

(c)

W.S

Man

ey &

Son

Lim

ited

The contact angle of wollastonite changed from 11 to68u after modification (Fig. 12), and the contact anglereached a hydrophobic one [63u (Ref. 13) and 65u(Refs. 14 and 15)]. It can be concluded that the surfaceof wollastonite changed from hydrophilic to hydropho-bic, and it had a promising outlook of using in organicsystems.

Infrared radiation analysis before and aftermodificationInfrared radiation (IR) spectra of the modified wollas-tonite under the condition of modifier of 1?5%,modifying temperature of 50uC, modifying time of30 min and slurry concentration of 10% were recordedthrough a Nicolet IR100/200 spectrophotometer usingthe standard KBr pellet technique (Fig. 13).

The characteristic absorption bands of methyl andmethylene groups in sodium stearate appeared at 2917and 2849 cm21 respectively. Low frequency of char-acteristic absorption bands of methyl appeared at1385 cm21. The characteristic absorption bands of thecarboxyl group were 1558 and 1440 cm21 (Fig. 13a).Figure 13c was the IR spectrum of the modifiedwollastonite. Compared with Fig. 13b, the characteristicabsorption bands at 2917 and 2843 cm21 representedmethyl and methylene groups in sodium stearate.Compared with Fig. 13a, the characteristic absorptionband that represented –C5O function group 1750 cm21

disappeared after modification,5 and two strong peaksappeared at 900 and 1200 cm21. The characteristicabsorption band of 900 cm21 moved 30 cm21 to lowerfrequency compared with Fig. 13b. It is thought that

10 Effect of slurry concentration to wollastonite powder

11 Analysing of particles dispersion of wollastonite powder with different slurry concentration

12 Analysing of contact angle of wollastonite powder a before and b after modification



Pub

lishe

d by

Man

ey P

ublis

hing

(c)

W.S

Man

ey &

Son

Lim

ited calcium stearate formed, and C17H35COO–Ca absorbed

on the surface of wollastonite by coordination bond.16,17

Modification mechanism of wollastonite

R{COONa?R{COO{zNaz (1)

R{COO{zCa½Si3O9�z?R{COOCa½Si3O9� (2)

Figure 14a shows the [100] cleavage plane of wollasto-nite crystal. It can be seen that a large amount of Caz

was exposed at the cleavage plane of wollastonite.Figure 14b shows the surface schematic diagram ofwollastonite crystal’s cleavage plane. The function groupof calcium hydroxyl was not stable, and it was easy toform Caz. As a result, it was easy to form R–COOCa[Si3O9] with R–COO2 of sodium stearate, andthe formed compound could absorb on the surface ofwollastonite. Figure 14c shows the schematic diagram ofthe modified wollastonite. Obviously, R–COOCa[Si3O9]was stable and able to absorb on the surface ofwollastonite by coordination bond. Specific reactionmechanisms were shown in equations (1) and (2).

ConclusionsThe hydrophobic wollastonite powders were synthesisedvia a modification route in the present work. Based onoverall investigation on the modification data, thedispersion stability and the activation index of modifiedwollastonite powder were the optimum when the dosageof sodium stearate, the modification temperature, themodification time and the slurry concentration were1?5%, 50uC, 30 min and 10% respectively. The structureproperties of the modified wollastonite powder arecharacterised by contact angle measuring instrumentand FTIR. Results show that the contact angles ofmodified wollastonite powder were changed from 11 to68u, and sodium stearate is adsorbed on the surface ofthe wollastonite powder by coordination bond.

Acknowledgements

This work was financially supported by theFundamental Research Funds for the CentralUniversities (grant no. 2011PY0169) and the National

a crystal structure cleavage plane (100); b functional groups of cleavage plane; c after modification14 Schematic diagram of wollastonite powder

13 Analysing of IR of a raw wollastonite b before and b after modification



Pub

lishe

d by

Man

ey P

ublis

hing

(c)

W.S

Man

ey &

Son

Lim

ited

Natural Science Foundation of China (grantno. 51144011).

References1. H. W. Ma, D. M. Liu, L. B. Liao, Z. M. Bai, et al: ‘Industrial

minerals and rocks’; 2011, Beijing, Chemical Industry Press.

2. W. Y. Zhao, C. Q. Peng and Q. J. Zhang: ‘Evolution process of

crystal structute during synthesizing silica materials from wollas-

tonite’, J. Chin. Ceram. Soc., 2004, 32, (8), 975–981.

3. W. R. Wu and Z. L. Pan: ‘TEM study on surface behavior of

wollastonite by mechanicochemical activation’, Acta Mineral.

Sinica, 2000, 20, (4), 397–400.

4. W. R. Wu, Z. L. Pan, H. Zhao, Z. B. Guo et al: ‘Mechanism of

mechanochemical activation on wollastonite’, Bull. Mineral. Petrol.

Geochem., 1999, 18, (4), 274–276.

5. Y. L. Zhao, S. Y. Shen and F. Su: ‘The infrared spectrum study on

modified mechanism by stearic acid for wollastonite’, Conserv.

Utilization Min. Resour., 2003, 2, 17–20.

6. H. Ding, S. C. Lu and G. X. Du: ‘Surface modification of

wollastonite by the mechano-activated method and its properties’,

Int. J. Miner. Metall. Mater., 2011, 18, 83–88.

7. J. Z. Zhao, Z. C. Wang, L.W. Wang, H. Yang, M.Y. Zhao, et al:

‘The synthesis and characterization of TiO2–wollastonite compo-

site’, Mater. Lett., 1998, 37, 149–155.

8. N. N. Tao, J. Z. Zhao and Y. P. Guo: ‘Preparation and

characteristics of core-shell rutile titania/wollastonite at room

temperature’, Mater. Chem. Phys., 2004, 84, 58–62.

9. S. Sharma, V. P. Soni and J. R. Bellare: ‘Chitosan reinforced

apatite–wollastonite coatingby electrophoretic deposition on tita-

nium implants’, J. Mater. Sci., Mater. Med., 2009, 20, 1427–1436.

10. X. Y. Liu and C. X. Ding: ‘Plasma sprayed wollastonite–TiO2

composite coatings on titanium alloys’, Biomaterials, 2002, 23,

4065–4077.

11. X. W. Yuan, A. J. Easteal and D. Bhattacharyya: ‘Influence of

surface treatment on hybrid wollastonite–polyethylene composite

resins for rotational moulding’, J. Mater. Sci., 2008, 43, 6057–

6063.

12. H. H. Rodrı’guez, G. Vargas and D. A. Cortes: ‘Electrophoretic

deposition of bioactive wollastonite and porcelain–wollastonite

coatings on 316L stainless steel’, Ceram. Int., 2008, 34, 1303–1307.

13. L. Jiang and L Feng: ‘Bioinspired intelligent nano structure

interfacial materials’; 2007, Beijing, Chemical Industry Press.

14. E. A. Vogler: ‘Structure and reactivity of water at biomaterial

surfaces’, Adv. Colloid Interface Sci., 1998, 74, (1–3), 69–117.

15. J. M. Berg, L. G. Tomas Eriksson, P. M. Claesson and K. G. N.

Borvet: ‘Three-component Langmuir–Blodgett films with a con-

trollable degree of polarity’, Langmuir, 1994, 10, (4), 1225–

1234.

16. G. H. Liu, Y. J. Huang, Z. H. Peng, Q. S. Zhou, X. B. Li, et al:

‘Flocculation mechanism of dicalcium silicate in concentrated

sodium aluminate solutions by sintering process’, Chin. J.

Nonferrous Met., 2010, 20, (10), 2051–2056.

17. J. Ruiren, W. B. Hu and X. J. Hou: ‘Mechanism of selective

flocculation of hematite from quartz with hydrolyzed polyacryla-

mide’, Colloids Surf., 1987, 26, 317–331.



Mechanism of surface hydrophobicity modification of ... · Published by Maney Publishing (c) W.S Maney & Son Limited Mechanism of surface hydrophobicity modification of wollastonite

Documents