Synthesis and characterization of alkali modified styrene-maleic anhydride copolymer (SMA) for...

RESEARCH ARTICLE

Synthesis and characterization of alkali modifiedstyrene-maleic anhydride copolymer (SMA)for dispersion of carbon black

Suman Kumari & Dhirendra Nigam & Indira Nigam

Received: 16 July 2011 /Accepted: 2 February 2012 /Published online: 20 April 2012# Central Institute of Plastics Engineering & Technology 2012

Abstract Copolymer of styrene and maleic anhydride (MAn) were copolymerized inN, N-dimethylformamide (DMF) as a solvent and benzoylperoxide as initiator attemperature 80°C . The monomer feed ratio of styrene (Sty) and maleic anhydride(MAn) was varied in the range of 1:1 to 3:1. The acid values were about 480, 357 and295 where as the softening temperature were 155, 140 and 120 respectively. Thesynthesized copolymer were hydrolyzed by various alkali viz. NaOH, KOH andNH4OH. The above synthesized copolymer and alkali modified copolymers havebeen characterized by 1H-NMR, DSC, TGA, SEM Optical microscopy andpercentage solid settling etc. The results showed a broad overlapping peak between1.1 and 2.3 δ ppm and peaks between 7.0 and 7.4 ppm are due to methylene/methineand aromatic ring hydrogens of styrene respectively where as Methine protons ofmaleic anhydride appear between 3.1 and 3.6 ppm. The Tg of copolymer were foundto be greater than that of polystyrene indicating formation of a copolymer. Thethermal stability of the copolymers decreased with the increase in maleic anhydridecontent in the copolymer. The spherical shapes of beads can be ascertained from themicrophotograph for molar feed of Sty/MAn as 1:1 and these becomes irregular for2:1 and 3:1. Where as a fine network with smaller structure as well as the welldispersed grain taken by Scanning Electron Microscopy and Optical Microscopyconfirms better dispersion of carbon black when these alkali modified SMAcopolymers have been added. It was also found a remarkable decrease inpercentage solids when alkali modified SMA were added in the system ascompared to when no resin were added. This shows the addition of SMA not onlyimproves dispersion but also improves the stability of the system. Application ofthese alkali modified SMA copolymers as a dispersing agent to disperse a non- polarparticles like carbon black in water were studied with the help of Daniel Flow Method

Int J Plast Technol (December 2011) 15(2):112–132DOI 10.1007/s12588-012-9020-x

S. Kumari : I. Nigam (*)Department of Plastic Technology, Harcourt Butler Technological Institute, Kanpur 208002, Indiae-mail: [email protected]

D. NigamC&E Ltd., Panchkula, Haryana, India

and found that the sodium salts of SMA copolymers having molar feed ratio ofstyrene to maleic anhydride as 1:1 showed best dispersion for Carbon Black particles.

Keywords Styrene –maleic anhydride (SMAn) copolymers . Carbon black .

Dispersing ability . Hydrolysis . Hydrophilicity

Introduction

A colloidal suspension with particles dispersed in solution is thermodynamicallyunstable; thus, dispersants are normally used to stabilize the system. The mainfunction of the dispersant is to provide the particles with an electrostatic barrier [1–4] and/or steric hindrance [5, 6] to prevent the coagulation of particles, or to modifythe surface properties of the particles to be more compatile with the medium [7]. Aneffective dispersant normally has a tendency to effectively adsorb on particles. Thus,the structure and functional group of a dispersant can be designed for a specific typeof particles to be dispersed. As a result of the importance of dispersing technology inindustry, it attracts a wide range of attention in both academic research and industrialapplication [1, 8], Ping-Lin Kuo, et al. [9] studied the dispersing ability of anionic andZwitterionic aniline-formaldehyde condensates to dyes and the dispersing propertiesof the condensates are assessed by the viscosity method, scanning electron micros-copy (SEM), the final volume fraction after sedimentation, and adsorption behaviors.Comparing the results of the viscosity method with those of SEM and the finalvolume fraction after sedimentation, it can be concluded that a better-dispersed pastedisplayed by SEM shows a lower viscosity and a smaller final volume fractionYamauchi et al. [10] found that when anionic groups were introduced with copoly-merization of corresponding vinyl monomers with vinyl acetate into poly (vinylalcohol) (PVA) with an alkylthio end group. The polymers were investigated as adispersant for coal water slurry (CWM). Anionic groups such as sodium sulfonateand sodium carboxylate enhance remarkably the ability of PVAwith an alkylthio endgroup to disperse coal. Sodium polyacrylic acid with an alkyl end group also showeda good ability of dispersing coal and the order of the ability of dispersing coal in thesepolymeric dispersants along with sodium naphthalene sulfonate formaldehyde con-densate (NSF) varied by the kind of coal used. Our approach to adding hydrophilicityto styrene is incorporating maleic anhydride (MAn) moiety along its backbonestructure. Upon hydrolysis maleic anhydride converted into hydrophilic carboxylicacid, and this improves the hydrophilicity. Copolymers of maleic anhydride havebeen commonly used for the synthesis of water –soluble materials, such as thicknersin paints and coatings, industrial emulsifiers, pigments dispersants and flocculatingagents [11–14].

The SMA resins can be modified by various alkalis through reactive anhydridegroup present on the polymer and these alkali salts of SMA resins are readily solublein water. Hydrolyzed SMA resins offer an interesting hydrophilic/hydrophobic bal-ance, which makes them excellent products for pigment wetting and dispersing. Thisapplication takes advantage of the SMA resin’s strong surfactant properties to gainother benefits such as high dispersion stability and high pigment/dispersing resinratios. Although some investigators have studied various modified SMA, the system-atic studies of alkali modified SMA resins to act as a dispersing agent for inorganic

Int J Plast Technol (December 2011) 15(2):112–132 113

pigments such as Carbon black in aqueous solution have not been reported. In thismanuscript, an effort has been done, to study the dispersion properties of alkalimodified SMA resins of varying characteristics. For this SMA copolymers withdifferent molar feed ratios were synthesized and characterized. The synthesizedSMA copolymers were then modified by further reactions with different alkalis likeSodium hydroxide (NaOH), Potassium hydroxide (KOH) and Ammonium hydroxide(NH4OH) to generate a SMA carboxylate salt solution.

The dispersing ability of these copolymers of varying chemical nature have beenstudied for dispersion of inorganic pigment like carbon black in aqueous solution.The effect of variation in molar feed ratio on dispersing ability of copolymers werestudied and co-related with their structure.

Experimental

Materials

These chemicals were used for synthesis of copolymers.Maleic-anhydride (MAn) (SD’s Lab Chem, Mumbai), Styrene (E. Merck,

Germany), Methanol and Acetone AR grade (SD’s Lab Chem, Mumbai), N,N-Dimethylformamide and Tetrahydrofuran AR grade (Qualikems, Chmecials,Delhi), Benzoylperoxide (Qualikems, Chmecials, Delhi), Sodium hydroxide andPotassium hydroxide (Qualikems Chemicals, Delhi), Ammonia 25% aqueoussolution (Qualikems Chemicals, Delhi), Carbon Black powder (E. Merck,Germany).

Synthesis of copolymer

For polymerization, styrene was purified by alkaline washmethod andmaleic anhydridewas recrystalized twice frommethanol. The copolymer of styrene and maleic anhydridewas prepared by radical polymerization. The monomer feed ratio of styrene: maleicanhydride (Sty: MAn) was taken as 1:1, 2:1 and 3:1. The reaction was carried out in athree neck flask using an oil bath having its temperature accurately controlled. The N, N-dimethylformamide (DMF) was used as a solvent and Benzoylperoxide (BPO) was usedas initiator. The reaction was carried out at 80°C for 4 h in a nitrogen atmosphere. Thepolymer was precipitated using methanol as nonsolvent. The homopolymer of polysty-rene was removed by dissolving copolymer in benzene solution, then filtering anddrying in oven at 50°C for 48 h.

Hydrolysis of SMA copolymers

The synthesized copolymers were hydrolyzed using three different alkali viz. Sodiumhydroxide (NaOH), Potassium hydroxide (KOH), and Ammonium hydroxide(NH4OH). The neutralization reaction of base has been shown in Fig. 1. Thetemperature for neutralization with NaOH, KOH and NH4OH was maintained at40, 65 and 70°C respectively. For this 100 ml of distilled water was taken in threeneck flask and weight amount of SMA resin was added to it with constant stirring.

114 Int J Plast Technol (December 2011) 15(2):112–132

The appropriate amount of aqueous alkali required to dissolve the sample the samplewas added into it with constant stirring for 2 h. Then a few drops of concentrated H2SO4

were added to it until the pH of solution becomes less than 4. The product wascollected as white powders by filtration and dried at 50°C for 2 days. The copolymershydrolyzed with sodium hydroxide are designated as SMAH11, SMAH21 andSMAH31 where the copolymer hydrolyzed with potassium hydroxide and ammoniumhydroxide was designated as SMAK11, SMAK21, SMAK31, SMAN11, SMAN21 andSMAN31 respectively for the mole ratio of styrene-maleic anhydride as 1:1, 2:1 and 3:1.The reaction of SMA copolymers with various alkalis is given in Fig. 1.

Characterization of copolymer and modified SMA copolymer

a) Nuclear Magnetic Resonance (1H-NMR) Spectra of SMA Copolymers:-The 1H-NMR spectra of SMA copolymer were recorded on a Bruker WM 250

from deurated THF-d8 solution at 60°C, a frequency of 62.9 MH2 respectively,and trimethylsilane (TMS) as internal reference.

b) Glass transition temperature (Tg) of SMA Copolymers:-The Tg of copolymers were determined by the thermograms obtained on

Perkin-Elmer DSC-7 at a heating rate of 10°C/min.c) Thermal analysis of SMA Copolymers:-

Thermogravimetry analysis was done using a Perkin-Elmer TG analyzer innitrogen at a heating rate 10°min–1 with 5±1 mg of powdered sample.

d) Scanning electron microscope (SEM) of SMA and modified SMA copolymers:-A small piece of the copolymer was cut and put on an aluminum sheet and

electrodeposited with a layer of gold. The surface morphology of the copolymerwas observed by an SEM electron probe microanalyzer, (Hitashi 5–570).

Fig. 1 Neutralization of SMA resin with base


e) Optical Microscope:-The optical microscope photograph of alkali modified SMA copolymers have

been taken on Motic BA 200 model No. 4x trinukulare.f) Percentage Solid Settling:-

The percentage solid settling after 72 h was determined by adding slurry ofTiO2 using various modified SMA resins to an emulsion of acrylate polymer(PMMA) (Mol. wt. 16123) and measuring the amount of solids settled on thebottom of the beaker.

Assessment of the dispersing abilities of the polymers

The Daniel Flow point Method was used for assessing the dispersing efficiency of thealkali modified styrene-maleic anhydride copolymers.

Various concentration viz. 0.5–5% of alkali modified SMA copolymer wereprepared in distilled water. These aqueous solutions of alkali modified SMA copol-ymer was taken in a burette and added to 20 g of carbon black dropwise with constantstirring and rubbing with a glass rod until a heavy and smooth paste was obtained.Then some more aqueous solution of modified copolymer was added gradually to thepaste until the mass achieves a consistency at which it could be stirred withoutsignificant resistance. A characteristic end point was reached when a thin and evenfilm material remained on the glass rod and the last drop fell at an intervals of 1–2 s.These drops appeared to break with an elastic snap back.

Then a graph of the amount of each aqueous solution of alkali modified copolymerrequired to reach the above end point against the concentration of the dispersing agentwas plotted to give a "U"-shaped curve, having a minimum that corresponds to theoptimum composition for efficient dispersion.

Results and discussion

Synthesis and characterization of SMA and hydrolyzed SMA copolymers

The SMA copolymers have been synthesized using a N, N-Dimethylformamide(DMF) as a solvent and benzoylperoxide (BPO) as a free radical initiator, takingmolar feed ratios of styrene and maleic anhydride as 1:1, 2:1 and 3:1 at 80°C. Theabove synthesized copolymers, have been designated in this work as SMA11,SMA21 and SMA31 respectively. The molecular weight of styrene-maleic anhydridecopolymers as obtained by Mark Houwink equation for SMA11, SMA21 andSMA31 are 1862, 2015 and 2276 where as the acid values for these copolymerwas found to be 480, 357 and 295 respectively which was determined and reported inour previous papers are in good agreement with the SMA series reported in literature[15]. This range of molecular weight of SMA copolymers with these acids valuescould be efficiently act as a dispersant to disperse carbon black in water aftermodification with various alkalis. It was also found through the FTIR spectra asreported in our previous paper that an alternating polymer was produced. An alter-native SMA is useful for acquiring the polycarboxylates of which charges arehomogenously separated and could be useful as pigment dispersants. The molecular


weight, acid values and softening temperature of SMA copolymers have been givenin Table 1.

Characterization of SMA and modified SMA copolymers

In the 1H-NMR spectrum of SMA copolymer, broad overlapping peaks between 1.1and 2.3 δppm and peaks between 7.0 and 7.4 δppm are due to methylene/methine andaromatic ring hydrogens of styrene respectively. Methine protons of maleic anhydrideappear between 3.1 and 3.6 δppm as the multiplet styrene/maleic anhydride ratio ofthe copolymer was calculated from the integration ratio of the peak at 7.0–7.4 δ ppm and2.0–2.75 δppm as shown in Fig. 2. This ratio was about 0.95:1. These results are ingood agreement with the reported values given in the literature [16]. As expected, analternating copolymer was produced under the experimental conditions used in this work.

Where as the 1H-NMR spectra of sodium salt of styrene-maleic anhydride copol-ymer has been shown in Fig. 3. As it is clear from the figure that decrease in theintegration peaks between 1:1 and 2.3 and 7.0 and 7.4 δppm as well as peak at 3.7δppm representative of anhydride group disappears indicating the transformation of aanhydride to carboxylate salt of SMA copolymers.

Thermal characterization of SMA copolymer

The DSC curve is highly suitable to polymer systems and can be used to determine,besides the affect of addition of a comonomer on the crystallinity of the polymer andproperties. The glass transition temperature of copolymers were determined from DSCthermograms as shown in Figs. 4, 5 and 6. The values of Tg observed for variouscopolymers of styrene-maleic anhydride synthesized by varying molar monomer feedratios from 1:05 and 3:1 have been given in Table 2. The Tg of copolymers werefound to be greater than that of polystyrene indicating formation of a copolymer. Theslightly decreasing glass transition temperature of copolymers when the molar feedratio of styrene and maleic anhydride was varied from 0.5:1 to 3:1 indicated theincreasing the concentration of maleic anhydride in the copolymer increase glass transi-tion temperature of copolymers. These results confirmed the formation of alternatingcopolymer. The similar observations have been reported by other investigators [17].

Thermal analysis of SMA copolymers

TGA which measures the weight loss at elevated temperatures has been used topredict the stability of polymeric materials because it is very simple and accurate.

Table 1 Properties of Sodium Salts of SMA Resins

S.No. SMA Copolymer Appearance Charge pH

1. SMAH11 Clear and fluid liquid Anionic 9-11

2. SMAH21 Yellowing Transparent and Fluid Anionic 9-11

3. SMA31 Dark Yellowish and fluid liquid Anionic 9-11


The thermogram obtained by plotting the percentage residual weight versus temper-ature for the various copolymers at varying composition are shown in Fig. 7. It isclear from the figure that polystyrene started a sharp weight loss from 300°C onwardsand by 420°C the decomposition was complete.

The copolymers underwent two stage weight loss, the first stage corresponding toabout 85% when he composition of styrene and maleic anhydride was approximate1:1 with higher styrene content the first stage weight loss along with decompositiontemperature increased. The copolymers decomposed at a lower temperature thatpolystyrene. The thermal stability of the copolymers decreased with the increase inmaleic anhydride content in the copolymer.

Since the compositions of the copolymers did not differ much, the thermalstabilities also did not differ appreciably. When the composition was 2:1 the stabilitywas close to that of polystyrene. It is known [18] that polystyrene decomposes mainlyby depropagation and that the controlling factor in the mechanism of the degradationis the nature of the side-group attached to the carbon atom at which the chain-scissionoccurs [19]. In case of copolymers about 15% residue was left after 400°C . Thismight be due to the result of thermal cyclisation of the anhydride units at such a hightemperatures.

Surface morphology of the SMA copolymers and modified SMA copolymers

The surface appearance and structure of the styrene-maleic anhydride (SMA) copol-ymer was observed using Scanning Electron Microscopy (SEM). The microphoto-graphs taken by the electron microscope.

The microphotographs taken by the electron microscope of the SMA copolymershaving the molar feed ratios of sty/MAn as 1:1, 2:1 and 3:1 are shown in Figs. 8, 9and 10. The spherical shapes of beads can be ascertained from the microphotographfor molar feed of Sty/MAn as 1:1 and these spherical shapes becomes irregular for 2:1and 3:1. It is also obvious from the figure that these copolymer possess a porousstructure.

Fig. 2 1H-NMR spectrum ofSMA copolymer

Fig. 3 1H-NMR spectrum ofSodium Salt of SMA copolymers


Where is case of alkali modified SMA copolymers an increase in porosity ofpolymer structure can be observed. This may be because of introduction of hygro-scopic moieties on the polymer structure introduced through reactions with alkalis asshown in Fig. 11.

Optical microscopy of alkali modified SMA copolymer

The dispersion of Carbon black pigment particles without containing any dispersantshave been shown in Fig. 12 and those containing alkali have been shown in Fig. 13.The well dispersed grains in photographs as compared to agglomerated particle asshown in above figure confirms better dispersion of Carbon black when alkalimodified SMA was added.

Dispersibility of carbon black

The primary function of a pigment dispersant is to surround a suspended pigmentparticles with a barrier envelope that by either ionic repulsion or steric hindranceprevent random contact with other particles. This is turn avoids adhesion and

Fig. 4 DSC thermogram oftypical Sty-MAn copolymers at aheating rate of 10°C min–1 innitrogen for 1:1

Fig. 5 DSC thermogram of atypical Sty-MAn copolymer at aheating rate of 10°C min-1 innitrogen for SMA2:1


flocculation. In order to acquire a stable dispersion, a dispersant is usually added tohelp suspend solid particles in liquid. The main function of the dispersant is toprovide the particles with electrostatic charges or with steric hindrance to produce abarrier and for the formation of electrical barrier to aggregation, ionic dispersants aregenerally used.

When the solid to be dispersed is essentially nonpolar (e.g. hydrobic carbon) andthe dispersing medium is aqueous conventional dispersant (containing one terminalhydrophilic group and a long hydrophobic group) may be used, since adsorption ofthe ion onto the essentially uncharged solid particles causes them all to acquire acharge of same sign and to repel each other. An electrical barrier to aggregation willthen have been formed. In addition, the adsorbed dispersant ions will be oriented withtheir hydrophobic groups towards the nonpolar particles and their hydrophilic headstoward the aqueous phase, producing a lowering of the solid–liquid interfacialtension. The efficiency of adsorption in this case increases with increases in thelength of the hydrophobic group, longer chain compounds can be expected to bemore efficient dispersing agents for this type of particle than shorter-chain ones.Krishnan, et al. [20] studied the interactions of acetylenic diol dispersants (surfynol104 and Surfynol 440) with maleic anhydride copolymers (SMA1000H, SMA3000Hand SMA1440H) by dynamic surface tension method and found that acetylenic diol

Table 2 Glass transition temper-ature (Tg) of Styrene (Sty) andMaleic anhydride (MAn) copoly-mers at varying molar feed ratio

Monomer Molar feed ratio Tg of Copolymer

0.5:1 154

0.8:1 147

1:1 145

1.5:1 136

2.0:1 131

2.5:1 123

3.0:1 118

4:1 113

Fig. 6 DSC thermogram of atypical Sty-MAn copolymer at aheating rate of 10°C min-1 innitrogen for SMA3:1


dispersants interacted with maleic anhydride copolymers forming simple complexesand complex structures in the bulk that dramatically increased solution viscosity forhigh polymer concentrations and dispersants doses. The extend of interactionsincreases with increasing polymer hydrophobicity and the amount of ethylene oxidein the dispersant mol. structure. Both hydrophobic and hydrogen bonds seem to beinvolved in the polymer/dispersant interactions and for the low dispersant concentra-tion polymer/dispersant interactions can be described as simple dispersant adsorptionon the “adsorption sites of the polymer chain. In our case the dispersing ability ofvarious synthesized alkali modified SMA11 copolymer has been studied using asimpler method viz Daniel Flow Method. For this the aqueous solution havingfractional concentration varying in the range of 0.5–5% of alkali modified SMA indistilled water has been used for dispersion of 20 g of the carbon black. The amountof dispersant solution required to disperse the carbon black have been plotted as afunction of fractional concentration of dispersant in solution. Such plots obtained forcopolymers SMAH11, SMAK11, SMAN11 have been given in Fig. 14. The amountof aqueous solution required to disperse the carbon black in absence of any dispersantis as high as 55.2 ml as shown in Fig. 14. and on addition of sodium salt of SMA11

Fig. 7 TGA traces in nitrogen ata heating rate of 10°C min-1 for(__) Polysty, (⋯⋯) Sty-co-MAn(2:1) and (—.—) Sty-co-MAn(1:1)

Fig. 8 SEM photograph ofSMA11 copolymer


i.e., SMAH11 the aqueous solution required to disperse the same amount of carbonblack reduces. It drops to 30.1 ml in the presence of 0.5% of SMAH11 and decreasesas concentration of SMAH11 increases in the solution. It keep on decreasing until theconcentration of SMAH11 in aqueous solution reaches at some minimum concentra-tion beyond which when the concentration of modified SMAH11 in the solution isincreased the amount of aqueous solution required to disperse gm of pigmentparticles starts increasing as shown in Table 3. As per the principle of Daniel FlowMethod, the concentration at which the amount of aqueous solution required todisperse the carbon black is the least is termed as optimum concentration of thatdispersant. The optimum concentration for NaOH modified SMA11 is 11.6 ml whichis about 81% less than the aqueous solution required for dispersion of 20 g carbonblack when no copolymer is present in it. The optimum concentration observed in thisway for SMA11 copolymers modified with different alkalis have been found to be4%. The amount of aqueous solution of these copolymers required to disperse thesame. The amount of aqueous solution of these copolymers required to disperse thesome amount of carbon black at optimum concentration is given in Table 3. ForSMAH11 the volume is about 11.6 ml of dispersant of optimum concentration and13.9 ml for SMAK11 and 15.2 ml for SMAN11 respectively. Thus it is obvious from

Fig. 9 SEM photograph ofSMA21 copolymer

Fig. 10 SEM photograph ofSMA 31 copolymer


the above results that alkali modified SMA resins can improve dispersion of carbonblack in the water. The reasons for better dispersion with the addition of alkalimodified copolymer is the presence of reactive ionic carboxylic groups which oftenexcellent dispersing agents for solids in aqueous media. Thus these ionic groups canimpart high surface charges to the solid particles onto which they adsorb and thetendency to adsorb on the surface of a solid particle of an individual functional groupattached to the backbone of the polymer is low, the number of such groups in themonomer must be large enough, so that the total adsorption energy of the molecule issufficient to firmly anchor the particle surface.

The formation of carboxylic groups can be confirmed by comparing the IR spectraof sodium modified SMA copolymers with that of unmodified SMA11 where inreduction of anhydride peak as well as characteristic peak of carboxylic group has

Fig. 11 SEM photographs of al-kali modified SMA copolymer

Fig. 12 Optical microphotographof the Carbon black particlewithout containing anydispersant


been observed in the later in our previous paper [21]. When these hydrophilic SMAcopolymer is added for dispersion of carbon black particles it gets adsorbed on thesurface of particles by anchoring through carboxylic groups and thus preventsagglomerations of the particles, hence making dispersion more efficient. Ping-LinKuo et al. [22]. Synthesized Butyl-substituted naphthalene sulfonate formaldehydecondensates (C4NSF) as dispersants and were compared to unmodified naphthene-sulfonate formaldehyde condensates (NSF) in their ability to disperse nonpolar

Fig. 13 Optical microphoto-graphs of the alkali modifiedCarbon black particles

Fig. 14 Daniel flow data forSMAH11, SMAK11 andSMAN11 for dispersion ofCarbon black


particles (carbon black) and polar particles (TiO2) in water. Their dispersing abilitywas evaluated by both a viscosity method and a microscopy method. For dispersingcarbon black in water, it was found that using C4NSF as dispersing agents result in alower viscosity, a lower yield by the viscosity method and a more homogenousdispersion of particles determined by microscopy, and the result indicate that thebutyl group enhances the dispersing ability of C4NSF. He also found that fordispersing TiO2 in water, C4NSF results in a higher viscosity and a higher adsorptionamount of dispersed system than NSF, the result were interpreted in term of thehydrophobic interaction between the butyl groups and the bridging effect.

Parfitt et al. [23] studied the dispersion of rutile powder in aqueous surfactantsolution and the effectiveness of the whole dispersion process for pure rutile inaqueous solutions of sodium dodecylsulfate and dodecyl trimethylammonium bro-mide has been assessed by measurements of optical density following various periodsof agitation, and these measurement are compared with measurements of contactangle and of the stability and electrophoretic mobility of dispersions prepared byultrasonic irradiation. The results are considered in terms of wetting and of resistanceto coagulation as predicted by the Deryaguin –Landau-Verwey-Overbeek theory ofcolloid stability. The part played in the overall process by each of the three stages isclearly indicated and good agreements is found with theoretical predictions. Dick etal. [24] studied the adsorption of Alkylbenzene sulfonate (A.B.S.) surfactants at theAlumina- Water interface and found branching decreases the contribution of hydrobicinteractions to two dimensional condensation (hemi-micelle formation) at the solid–liquid interface as well as branching also displaces the shear plane out from theinterface and that vertical orientation for adsorbed molecules is more likely thanhorizontal orientation.

Voronov et al. [25] found that the polymer peroxide surfactant obtained bycopolymerization of a peroxide monomer with maleic anhydride either by physicalor chemical sorbed on the dispersed phase surface, for example, on minerals fillersand latex particles. Subsequent initiations of graft copolymerization from the surfacegave interfacial compatibilizing polymer layers in H2O emulsions and dispersed-filled-polyethylene. The morphology of the resulting filled polymer was character-ized by SEM. Shixing et al. [26] studied the synthesis of poly (styrene-maleicanhydride) (PSMA)/TiO2 nanocomposite via in situ hydrolysis of a multi-component solution (PSMA dissolved in THF/H2O/acetylacetone, acidification withHCl, addition of Ti(OBu-n)4 and heating, volatilization of THF) and found that thismethod improve the dispersion of TiO2 particles in the PSMA matrix by preventingtheir aggregation. The nanocomposite was investigated by Fourier-transform IR

Table 3 Daniel Flow data forSMAH11, SMAK11 and SMAN11for dispersion of carbon black

% SMAH11 SMAK11 SMAN11

0.5% 30.1 35.2 38.0

1% 23.0 24.6 26.8

2% 16.3 18.8 20.8

3% 13.8 15.5 17.0

4% 11.5 13.8 15.5

5% 13.5 16.3 18.3


spectroscopy, transmission electron microscopy, and X-ray diffraction. TiO2 is bond-ed with PSMA in the form of the covalent bond and found that the composites existedas a 3-dimensional net with separation of nanometer-sized TiO2 anatase micro-phaseinside and with the increasing content of Ti(OBu-n)4 as reactant, the mean particlessizes of TiO2 increased. Kohji et al. [27] studied the effects of secondary polymercovalently attached to monodisperse, poly (maleic anhydride-styrene) modified col-loidal silica on dispersibility in organic solvent. Thus it was found that waterinsoluble SMA resin become water soluble after treating with different alkalis andwere found to be act as an efficient dispersant of nonpolar particle like carbon black.

Effect of alkali used for modification It was found that the alkali modified SMA resinact as a dispersing agent as it has been adsorb onto a solid particle and to produce aadsorption energy barrier of sufficient height to disperse the particle in a liquidmedium. In order to study this, the SMA has been modified by three different alkalisviz NaOH, KOH and NH4OH. On comparing the results the amount of 0.5% ofaqueous solution of SMAK11 and SMAN11 required to disperse 20 g of carbon blackis 24.4 ml and 26.2 ml respectively as compared to 23.2 ml for 0.5% SMAH11containing aqueous solution. Similarly at 1% concentration of SMAK11 andSMAN11 copolymers the amount of aqueous solution required to disperse 20 g ofcarbon black is 18.8 ml and 21.0 ml as compared to 16.4 ml for SMAH11 copolymersas shown in Table 3. The optimum concentration also varies with alkali used formodification as it has been shown in Figs. 14, 15 and 16. For SMAK11 and SMAN11the optimum concentration is 13.9 ml and 15.2 ml respectively as compared to11.6 ml for SMAH11 copolymers. If the dispersing agent is ionic in nature ionicfield is developed and they bound the particle more tightly and can reduce the surfacetension of water to much lower values than the obtainable with dispersants containinghydrocarbon groups. Thus because of the difference in basicity of sodium hydroxide,potassium hydroxide and ammonium hydroxide, the tendency for complete ionizationand water solubility is higher in case of NaOH as compared to KOH and NH4OH anddue to presence of a stronger ion on sodium modified SMA anchors carbon blackparticle, also prevents the agglomeration of the particle to a greater extent and betterdispersion is formed in this case as compared to other two alkali modifiedcopolymers.

Pina et al. [28] studied the adsorption of a polyelectrolyte, which is a hydrolyzedstyrene-maleic anhydride (HSMA) copolymer, on TiO2 and for that the adsorptionisotherms are dependent on the pH and on the total ionic strength of the solution,which can be varied both by increasing the concentration of the polyelectrolyte andby addition of an external monovalent salt like KNO3. He also found that theadsorption isotherms displays a plateau followed by an increasing adsorption at smallsalt concentration.

The ionic strength effect shows that this increasing adsorption cannot attributed topolydispersity and model is langmuirian. He also found that the interaction near thesolid substrate are electrostatic between the discrete, possible of the surface and theHSMA copolymer and non electrostatic such as H-bond. The interaction near thesolid surface are predominant for small ionic strength where as interaction inside theadsorbed layer are predominant for high ionic strength as the repulsion between theHSMA copolymers segment is quantitavily diminished.


On comparing the results of dispersions studies of alkali modified SMAH11 forcarbon black is best because of the higher ionic strength in solution which in turnmore tightly bound counterion thus prevent coming together of the particles hencecoagulation. Thus they permit extension of the dispersant molecule into the aqueousphase (thus creating a steric barrier to coalescence) with an increase in the free energyof the system. The decrease in free energy resulting from hydration of ionic hydro-philic groups may compensate for the free energy increase due to the increasedcontact of the hydrophobic group with the aqueous phase in this case of alkalimodified SMA copolymer in these studies.

Effect of maleic anhydride content For this three copolymers having the molar feedratios of Sty/MAn as 1:1, 2:1 and 3:1 have been synthesized. These copolymers havebeen modified with three different alkalis and used for studying dispersion of carbonblack. On comparing the result of Daniel Flow studies of sodium modified SMA11,SMA21 and SMA31 for dispersibility given in Figs. 14, 15 & 16 respectively, it hasbeen observed that the efficiency of dispersant is much dependent on the reactivegroups present on a polymer which were responsible for dispersion. Thus the plot forDaniel Flow studies for the modified copolymers having molar feed ratio for styrene-maleic anhydride as 2:1 and 3:1 as referred as SMAH21, SMAK21, SMAN21 andSMAH31, SMAK31 and SMAN31 has been given in Figs. 15 and 16 respectively.



On comparing the results as shown in these plots it has been observed that for all thecopolymers studied SMA11 is giving better dispersibility as compared to SMA21 andSMA31. It was found that when 0.5% of SMAH11 copolymer has been used fordispersion, the amount of aqueous solution required to disperse 20 g of carbon blackparticle is 23.2 ml when 1% SMAH11 is used it is 16.4 ml. when SMAH31 is used atsame concentrations the amount of aqueous solution required is 27.4 ml and 22.6 mlrespectively as shown in Tables 4 and 5. These results shows that the amount ofaqueous solutions required at optimum concentration observed for sodium modifiedSMAH21 and SMAH31 copolymers is 16.2 ml and 18.0 ml respectively as comparedto 11.6 ml observed for SMAH11. The similar behaviour has been observed for SMAcopolymer modified with KOH and NH4OH, as minimum optimum concentration


Table 4 Daniel Flow data forSMAH21, SMAK21 and SHAN21for dispersion of carbon black


0.5% 32.5 38.8 40.2

1% 24.5 26.3 28.8

2% 20.5 22.5 26.4

3% 17.0 19.6 21.4

4% 16.3 18.2 20.4

5% 20.0 22.0 23.8


value has been observed for SMAK11 as compared to SMAK21 and SMAK31 andfor SMAN11 as compared to SMAN21 and SMAN21, the amount of aqueoussolution of these copolymers at optimum concentrations have been given in Table 3.Thus it is obvious from these results that among the various copolymers studied theminimum amount of aqueous solution is required in the case of sodium modifiedcopolymer, synthesized with molar feed ratio of styrene and maleic anhydride as 1:1.Gudrun et al. [29] studied the interaction between the oppositely charged polymerspoly (dimethyldially ammonium chloride) (PDADMAC) and poly (maleic acid co-styrene) in the presence of clay can be used for strong surface modification and foundthat the conditions of reaction (type of stirrer, time) strongly influence the particleproperties like particle size and adsorption behaviour/surface charge. The highersurface charge and the greater diameter of particles was obtained with an anchorstirrer, where as the formation of larger particles and the precipitation of the complexis prevented by the stronger shear forces of the leaf stirrer. Thus, all SMA11 copoly-mers are giving better results in dispersing 20 g of carbon black particles as comparedto SMA21 and SMA31 when modified with any of three alkalis studied. The highsoftening temperature as well as higher acid value in the case of SMA11 because ofthe presence of large number of maleic anhydride units that can generate a greaternumber of complexed carboxyl groups which form strong hydrogen bond withvarious alkalis make them SMA11 as more efficient dispersing agents as comparedto SMA21 and SMA31 which has a large number of polystyrene as compared tocarboxylic groups which cause antibridging effect due to which a more coagulation isfound and made the less affective dispersant for non-polar particles like carbon black.

Percentage solid settling

The percentage solid settling after 72 h was determined for all modified SMA andcompared to system in which no resin was added. The results have been given as barchart in Fig. 17. A remarkable decreases in percentage solid was observed whenalkali modified SMA was added in the system as compared to when no resin wasadded. When SMAH11 was added the least solid was settled after 72 h. which was4.5% as compared to 16.6% when no resin was used. This shows the addition ofSMA not only improves dispersion but also improves the stability of the system.

Being an oxide and tend to retain and outside layer of water molecules, andexhibits a surface change in water. This isoelectric pH value corresponding to thepH where the negative and positive charges on the oxide pigment surface just

Table 5 Daniel Flow data forSMAH31, SMAK31 andSMAN31 for dispersion of carbonblack


0.5% 34.7 40.0 43.6

1% 27.5 32.4 34.8

2% 22.5 25.0 27.8

3% 19.0 21.2 23.4

4% 18.0 20.0 22.5

5% 21.2 24.0 27.5


neutralized each other is 4.7 for TiO2 . As the pH was adjusted away from thisisoelectric pH a change imbalance starts to develop that leads pigments particlerepulsion. Presence of SMAH, SMAK or SMAN on the surface of TiO2 alters therelative balance of positive and negative charges on the surface and also alters theisoelectric pH value. The addition of these improves the dispersion stability. Separa-tion of TiO2 particles due to repulsion of like ionic charges on the particle surface isgreatly facilitated by increasing the steric barrier that separate them.

The introduction of adsorbing layer of SMAH acts to increase the thickness ofadherent water layer on TiO2 many times more effectively sterically hinder closeinterparticle contact and prevent agglomeration. This results in more stable dispersionas buffering barrier comes between particles.

Conclusion

1. Styrene-maleic anhydride copolymer can be synthesized using benzoylperoxide(BPO) as an initiator and N1N Dimethyl-formamide (DMF) as a solvent at thetemperature of 80°C.

2. The acid value and the softening temperature was higher when styrene andmaleic anhydride ratio in the feed is taken as 1:1 as compared to when the feedratio was 2:1 and 3:1.

3. The SMA copolymer modified with alkalis like NaOH, KOH and NH4OH andare water soluble.

4. The Nuclear Magnetic Resonance of SMA copolymers have been observedthrough 1H-NMR spectra confirms the formation of styrene-maleic anhydridecopolymers.

5. The glass transition temperature (Tg) of SMA copolymers was found to begreater then that of polystyrene indicating formation of a copolymer.

Fig. 17 Optimum Concentrationof dispersant as a function ofvarious alkalis used for disper-sion of Carbon black


6. The thermal analysis of SMA copolymers showed that the copolymers underwent two stage weight loss and the thermal stability of the copolymers de-creased with the increase in maleic anhydride content in the copolymer.

7. The effectiveness of water soluble alkali modified SMA copolymer as dispersantfor nonpolar carbon black particles could be assessed by Daniel Flow Method.

8. The amount of aqueous solution required to disperse 20 g of inorganic pigmentparticles decrease when these modified SMA copolymers are added in thesolution and thus these polymers has ability to function as a dispersing agents.

9. From the analysis of dispersion of inorganic pigment particle in aqueous solution byDaniel Flow Method an inversion in the required amount of aqueous solution wasobservedwhen concentration of thesemodified SMA copolymers was increased. Theconcentration at that point of minimum was designated as optimum concentration.

10. Among the three alkalis used for modification of SMA copolymer the sodiummodified SMA copolymer of all three types of copolymer viz. SMA11, SMA21and SMA31 have been found to give best dispersion as in this case theminimum amount of aqueous solution was required to disperse the inorganicpigment particles at the optimum concentration.

11. Among all the copolymers synthesized the SMA11 having molar feed ratio ofstyrene-maleic anhydride as 1:1 copolymer modified by any of the three alkalishas shown best dispersion when added to 20 g of inorganic pigment particles asstudied by Daniel Flow Method.

This was because of presence of higher number of carboxylic groupspresent on SMA11 which was required for Hydrogen bonding with hy-droxyl groups of alkalis as compared to those present on SMA21 andSMA31 for carbon black.

12. It was also found that the introduction of adsorbing layer of hydrolyzed styrene-maleic anhydride copolymers acts to increase the thickness of adherent waterlayer on pigment particles many times more effectively sterically hinder closeinterparticle contact and prevent agglomeration. This results in more stabledispersion as buffering barrier comes between particles.

13. The spherical shapes of beads can be ascertained from the microphotographsobserved through Scanning. Electron Microscopy (SEM) for molar feed ratio ofSty/MAn as 1:1 and these spherical shapes becomes irregular for 2:1 and 3:1.

Where as the surface morphology observed through SEM for dispersed carbonblack pigment with alkali modified SMA copolymer a fine network with smallerstructure as a result of addition of these modified SMA resins. The networkstructure was one of the reasons for better dispersion of these pigment particles.

14. The well dispersed grain of the pigment particles as compared to agglomeratedones taken by Optical microscope also confirms better dispersion of carbonblack when these alkali modified SMA copolymers was added.

References

1. Parfitt GD (1981) Dispersion of powders in liquids; Applied Science Publishers, Inc.. 3rd ed2. Sato T, Ruch RJ (1980) Stabilization of colloid dispersions by polymer adsorption. Marcel Dekker, Inc,

New York


3. Ottewill RHJ (1977) Colloid Interface Sci 58:3574. Napper DH (1983) Polymeric stabilization of colloidal dispersions. Academic Press Inc, San Diego5. Napper DHJ (1977) Colloid Interface Sci 58:3906. Heller W, Pugh TLJ (1960) Polym Sci 67:2037. Patton TCJ (1970) Paint Technol 45:6668. Gooch JWJ (1988) Coat Technol 60:379. Kuo PL, Wey BS, Chen WHJ (2003) Appl Polym Sci 48(11):1953–196110. Yamauchi J, Terada K, Sato T, Okaya TJ (2003) Appl Polym Sci 55(11):155311. Cascaval CN, Chitanu G, Carpov A (1996) Thermochim Acta 275:22512. Ebdon SR, Towns CRJ (1986) Macromol Sci Rev Macromol Chem Phys 26:52313. Maeda H (1991) Adv Drug Deliv Rev 6:18114. Jarm V, Bogdanic G (1990) Thermochim Acta 171:3915. Kroschwitz JI (1987) Encyopedia. Polym Sci Engg. 9:266–269, John Wiley & Son New York16. Atici OG, Akar A, Rahimian R (2001) Turk J Chem 25:259–26617. Baruah SD, Narayan CL (1996) J Appl Polym Sci, 649–65618. Sadhir RK, Smith JDB, Castle PM (1983) J Polym Sci Polym Chem 5:1315–132919. Blazzo M, Szekely T (1974) Eur Polym J 10(8):733–73720. Krishnan R, Sprycha R (1999) Sun Chemical Corporation, Carlstadt, NJ, USA, Colloids and Surfaces,

A: Physicochemical and Engineering Aspects, 149 (1–3), 35521. Kumari S, Nigam D, Agarwal D, Nigam IJ (2007) Appl Polymer Sci 103:319422. Kuo PL, Lin JS, Wey BSJ (1992) Appl Polym Sci 47(3):52123. Parfitt GD, Wharton DGJ (1972) Colloid Interface Sci 38(2):43124. Dick SG, Fuerstenau DW, Healy TWJ (1971) Colloid Interface Sci 37(3):59525. Voronov S, Datsyuk V, Seredyuk V, Bednarska O, Oduola K, Alder H, Puschke C, Pich A,Wagenknecht U

(2000) State University "Lvivska Polytechnica", Lvov, Ukraine. J Appl Polym Sci 76(8):122826. Shixing W, Mingtai W, Yong L, Lide Z (1999) Institute of Solid State Physics, Chinese Academy of

Science, Hefei. Peop. Rep. China. J Mater Sci Lett 18(24):2009–201227. Kohji Y, Junji S, Hiroyasu N, Michio K (1999) Department of Applied Chemistry, Kyushu Institute of

Technology, Kitakyushu, Japan. J Colloid Interface Sci 214(2):18028. Pina A, Nakache E, Feret B, Depraetere P (1999) Groupe “Polymers at Interfaces: Laboratoire de

Chimie Moleculaire at Thio-organique, UMR CNRS 6507, Caen, Fr. Colloid and Surface, A: Physi-cochemical and Engineering Aspects, 158 (3) 375

29. Gudrun P, Siegfried B, Heide-Marie B (2000) Inst Polymer Res Eng 279:10–18


Synthesis and characterization of alkali modified styrene-maleic anhydride copolymer (SMA) for...

Documents

Transcript of Synthesis and characterization of alkali modified styrene-maleic anhydride copolymer (SMA) for...