Role of Heat Treatment on the Performance of Polymers As Iron Oxide Dispersants

APPLICATION

❙ Z. Amjad Role of Heat Treatment on the Performance of Polymers as Iron Oxide Dispersants

The influence of heat treatment on the performance of various 1 Introduction polymers as iron oxide dispersants in an aqueous system has been investigated. The polymers evaluated include: homo-poly- Feed water available for domestic and industrial uses is gen- mers of acrylic acid, methacrylic acid, maleic acid; co-polymer of, erally contaminated with various forms of dissolved ions acrylic acid:2-acrylamido-2-methylpropane sulfonic acid; ter- (i. e., calcium, magnesium, carbonate, sulfate, etc.), colloi- polymers of acrylic acid:2-acrylamido-2-methyl propane sulfonic dal, and suspended matter (i. e., clay, silt, organic debris, cor- acid:sulfonated styrene, and acrylic acid:2-acrylamido-2-methyl- rosion products, etc.). The type, size, and concentration of propane sulfonic acid:t-butylacrylamide. It has been found that suspended particles affect their behavior in water systems. all polymers lose performance to a varying degree when ex- In addition, metal ions (i. e., Cu, Mn, Fe) present in feed posed to thermal treatment (150 °C, 200 °C, 20 hr). The perfor- water may get hydrolyzed and/or oxidized under conditions mance data also suggest that sulfonated styrene containing ter- typically encountered in domestic and industrial systems. polymer is a better iron oxide dispersant than the ter-polymer Maintaining this hydrolyzed and/or oxidized metal ions in containing 2-acrylamido-2-methylpropane sulfonic acid and ter- soluble and in dispersed forms can prevent the build-up of tiary butylacrylamide. In the case of co-polymer of acrylic acid:2- unwanted deposits on various substrates. acrylamido-2-methylpropane sulfonic acid, the thermal treat- Although feed waters contain a variety of suspended ment exhibits strong negative influence on the dispersancy matter, iron-based foulants (e. g., Fe2O3,Fe3O4, Fe(OH)3, power of the polymer. The results have been explained in terms FePO4) are generally considered to be one of the most chal- of loss of 2-acrylamido-2-methylpropane sulfonic acid and t-bu- lenging problems. The four major approaches to control tylacrylamide in the co- and ter-polymers, as determined by FT- iron oxide deposits are: (a) removing iron oxides (corrosion IR and NMR methods, leading to the formation of poly(acrylic products) from the systems (filtration), (b) inhibiting corro- acid). sion at its source (this is achieved by the use of corrosion inhibitors), (c) stabilizing Fe(II) and Fe(III) ions in the feed Key words: Polymer, dispersion, thermal stability water (involves the use of iron selective chelants), and (d) treating the feed or re-circulating water with iron oxide dispersant(s) to minimize iron oxide deposition within the system. The use of dispersant is generally considered to be the Einfluss einer Wärmebehandlung auf die Leistungsfähigkeit most economical method. von Polymeren als Eisenoxid-Dispergiermittel. Der Einfluss ei- The suspended particles typically encountered in indus- ner Wärmebehandlung wurde auf die Leistungsfähigkeit ver- trial water applications generally carry a slight negative schiedener Polymere als Eisenoxid-Dispergiermittel in wässrigen charge. Therefore, anionic polymers are normally the most Systemen untersucht. Bewertet wurden folgende Polymere: efficient dispersants because these anionic polymers in- Homopolymere von Acrylsäure, Methacrylsäure, Maleinsäure; crease the negative surface charge and keep particles in sus- Copolymere von Acrylsäure:2-Acrylamido-2-methylpropansul- pension. Cationic polymers can be used as dispersants but fonsäure; Terpolymere von Acrylsäure:2-Acrylamido-2-methyl- this requires relatively high polymer concentrations in order propansulfonsäure:sulfoniertes Styrol und Acrylsäure:2-Acryl- to first neutralize the negative surface charges and then to amido-2-methylpropansulfonsäure:t-Butylacrylamid. Es wurde transfer cationic charge to particles for efficient dispersion. gefunden, dass alle Polymere an Leistungsfähigkeit mit un- Suspension of clays, metal oxides, pigments, ceramic terschiedlichem Ausmaß einbüßen, wenn sie einer thermischen materials, and other insoluble inorganic particulate solids Behandlung (150 °C, 200 °C, 20 h) ausgesetzt werden. Die Leis- in aqueous systems through the use of small quantities of tungswerte zeigen, dass sulfoniertes Styrol mit Terpolymer ein synthetic polymers, polyphosphates and other polyelectro- besseres Eisenoxid-Dispergiermittel ist als ein Terpolymer mit lytes has become an increasingly important area of study 2-Acrylamido-2-methylpropansulfonsäure und tertiäres Butyl- with high technological relevance [1–4]. Dubin [5] in his in- acrylamid. Im Fall des Copolymers von Acrylsäure:2-Acrylamido- vestigation on the evaluation of polyphosphates, organopho- 2-methylpropansulfonsäure zeigt die thermische Behandlung ei- sphonates, poly(acrylic acid), P-AA; poly(maleic acid), P-MA; nen starken negativen Einfluss auf die Dispergierfähigkeit des and co-polymer of acrylic acid:maleic acid (P-AA:MA) as dis- Polymers. Die Ergebnisse sind erklärbar durch einen Verlust an persants for iron oxide showed that acrylic acid and maleic 2-Acrylamido-2-methylpropansulfonsäure und t-Butylacrylamid acid based polymers performed better than polyphosphates bei den Co- und Terpolymeren, was zu einer Ausbildung von and organophosphonates. The effectiveness of polymers as Polyacrylsäure führt und mittels FT-IR- und NMR-Methoden be- dispersants for clay and iron oxide has been the subject of stimmt wurde. numerous investigations. It has been reported that polymers containing different functional groups i. e., carboxyl, amino, Stichwörter: Polymer, Dispersion, thermische Stabilität sulfonic, amido, etc., are effective dispersants [5–7]. In addition, it has also been shown that polymer molecular weight plays an important role in dispersing suspended matter in

242  Carl Hanser Publisher, Munich Tenside Surf. Det. 43 (2006) 5 Z. Amjad: Role of heat treatment on the performance of polymers as iron oxide dispersants

aqueous systems. Recently, the influence of polymer archi- been mostly overlooked. In the present paper, we report tecture in dispersing many ceramics has been the subject on the results of investigations conducted to gain informa- of numerous investigations. Results of these studies have tion about the impact of thermal treatment on the perfor- shown that acrylic copolymers containing acrylic acid group mance of a variety of polymers used as scale inhibitors and other monomers, such as alkyl ester group, possess and dispersants in high temperature applications. The poly- properties different from those of P-AA [8–10]. mers we have selected include: a) homo-polymers i. e., Thermal degradation of polymers is a well studied area. poly(acrylic acids), P-1, P-2; poly(methacrylic acid), P-3; However, there is little information available of real value to poly(maleic acid), P-4; b) co-polymer i. e., poly(acrylic acid: industrial technologists concerned with using low molecular 2-acrylamido-2-methylpropane sulfonic acid), P-5; and c) weight polymers. Polymers used in high temperature appli- ter-polymers i. e., poly(acrylic acid:2-acrylamido-2-methyl- cations should be able to sustain high temperature and pres- propane sulfonic acid:sulfonated styrene), P-6; poly(acrylic sure environments normally associated with boiler and ther- acid:2-acrylamido-2-methylpropane sulfonic acid: tertiary mal desalination operations. McGaugh and Kottle [11] butyl acrylamide), P-7; Poly(acrylic acid:methacrylic acid: studied the thermal degradation of poly(acrylic acid) and la- tertiary butyl acrylamide, P-8. In addition, an optical micro- ter the thermal degradation of an acrylic acid-ethylene co- scope was used to study the influence of dispersants on polymer. They used infrared and mass spectrographic analy- iron oxide particle size distribution. sis to examine the degradation processes that occurred in the temperature regions 25–150 °C, 150–275 °C, 275 to 350 °C and above 350 °C. Their results suggest that in air 2 Experimental (min heating) dry poly(acrylic acid) decomposes by forming an anhydride, probably a six-membered glutaric anhydride- 2.1 Materials type structure at temperature up to 150 °C. At 350 °C there is drastic unmeasurable change and strong unsaturation ab- Grade A glassware and reagent grade chemicals were used. sorption. Mass spectrographic analysis showed that carbon The iron oxide (Fe2O3,) used in this investigation was ob- dioxide was the major volatile product at 350 °C. tained from Fisher Scientific Co. It was characterized as he- Denman and Salutsky [12] briefly examined the thermal matite by x-ray diffraction (JCPDS phase SS664). The parti- stability of a sodium poly(methacrylate) and a sodium poly- cle size distribution (with majority of particles in the 50 to (acrylate). Under dry conditions they found no change to 150 micron range) was obtained using a Beckman Coulter 316 °C after one (1) hour but some charring at 371 °C. Mas- Counter Model LS320. The polymeric materials used as dis- ler [13] investigated the thermal stability of several homo- persants were selected from commercial and experimental polymers used in the boiler. It was demonstrated that under materials and are listed in Table 1. All dispersant solutions the experimental conditions employed (pH 10.5, 250 °C, were prepared on a dry weight basis. The desired concentra- 18 hr] that P-AA, P-MA; and poly(methacrylic acid), P-MAA tions were obtained by dilution. all underwent some degradation. In terms of molecular weight loss, P-MAA lost slightly less molecular weight than 2.2 Thermal treatment of dispersant P-AA which lost considerably less than P-MA. Additionally, P-AA and P-MAA had minimal performance changes A solution of polymer was prepared containing 10 % poly- whereas P-MA displayed a substantial loss in performance. mer (as active solids) at pH 10.5 using sodium hydroxide McGaugh and Kottle [14] in their study on the polymer to neutralize the polymer. Sodium sulfite was used as an thermal stability showed that P-AA forms an intramolecular oxygen scavenger. A known amount of polymer solution anhydride at temperatures below 150 °C. At higher tempera- was retained for characterization and performance testing. tures, this anhydride appears as an intermediate in the de- The balance was charged to a stainless steel tube. The carboxylation of P-AA. Gurkaynak et al. [15] performed very headspace was purged with nitrogen followed by tighten- short degradation tests on a 6000 MW (molecular weight) P- ing the fittings. The tube was then placed in the oven AA at high temperature and different pH levels. Results of maintained at the required temperature (either at 150 °C their study show that rate of decarboxylation depends upon or 200 °C). At known times tubes were removed from the various parameters i. e., solution pH, ionic strength, and oven, cooled to room temperature, and solution was trans- temperature. Hetper et al. [16] investigated the thermal be- ferred to vials for polymer characterization and perform- haviour of sodium, calcium, and magnesium polyacrylates. ance testing. They found that the main decomposition of the calcium and magnesium salts occurs in the temperature range 2.3 Polymer characterization 450–490 °C. It was suggested that the thermal degradation of the metal polyacrylates proceeds via side chain and main The molecular weights of polymers were determined accord- chain scission, without depolymerization. The thermal de- ing to the method described previously [13]. Nuclear mag- gradation of calcium and magnesium salts of P-AA has been netic resonance (NMR) spectra of polymers before and after recently studied by McNiell and Sadeghi [17]. Results of thermal treatment were obtained on a Brubaker AV-500 their study show some similarities to the behaviour of the NMR spectrometer. Attenuated total reflectance infra-red alkali metal salts of P-AA and to that of the alkaline earth (FT-IR) spectra of all polymers, neutralized to pH 10 with metal salts of P-MAA. NaOH solution were acquired as films on a Nicolet Magna During the last two decades, the influence of polymers 560 Fourier Transform Infrared (FT-IR) spectrometer. as precipitation inhibitors for scale forming salts i. e., calcium phosphate, calcium carbonate, calcium sulfate, bar- 2.4 Iron oxide particle characterization ium sulfate, calcium fluoride, calcium phosphonate, etc., has been the subject of numerous investigations [18–22]. At the end of experiments few drops of iron oxide suspen- However, the impact of thermal stability of polymers on sion in the presence and absence of polymers were removed the performance of polymers as scale inhibitors and as dis- for particle size characterization by Leica Mz16 stereo-optical persants for particulate matter especially iron oxide has microscope.

Tenside Surf. Det. 43 (2006) 5 243 Z. Amjad: Role of heat treatment on the performance of polymers as iron oxide dispersants

2.5 Iron oxide dispersancy iron oxide dispersed (%D) was calculated, after making cor- rection for the %T reading obtained in the absence of poly- A known amount (0.12 g) of iron oxide was added to syn- mer (90 % T), from %T readings (%D = 100 – 1.11 %T) mea- thetic water (600 mL) containing a known amount of poly- sured at 3 hr as the amount of iron oxide dispersed. The mer (dispersant) solution adjusted to pH 8 in a 800 mL bea- data presented in this study had good reproducibility (± 5% ker. The synthetic water used in dispersancy test was made or better). The performance of the polymer was determined by mixing standard solutions of calcium chloride, magne- by comparing the %D values of the slurries containing poly- sium chloride, sodium sulfate, sodium bicarbonate, and so- mer against control (no polymer). Greater dispersancy was dium chloride. The synthetic water has the following com- therefore indicated by higher %D value. position: 100 mg/L Ca, 30 mg/L Mg, 314 mg/L Na, 571 mg/L Cl, 200 mg/L SO4 and 60 mg/L HCO3. The pH 3 Results and Discussion of the synthetic water was adjusted to 8.0 with dilute NaOH and or HCl solutions. 3.1 Dispersant performance In a typical test, six experiments were run simulta- neously using a gang-stirrer. The gang-stirrer was set to A series of experiments were conducted to evaluate the per- 110 rpm (revolutions per minute) speed. At known time in- formance of polymers as iron oxide dispersants both with tervals transmittance readings (%T) were taken with a and without heat treatment. Table 1 shows the structures of Brinkmann PC/100 colorimeter with 420 nm filter. The ab- polymers evaluated in the present study. The experiments sorbance of several filtered (0.22 micron) suspensions with were designed to evaluate the performance of polymer as a low to high %T readings was measured at 420 nm. It was function of dosage, dispersant architecture, the impact of found that absorbance contribution due to dissolved species heat treatment, and calcium ion compatibility. was insignificant (< 3 %). Polymer performance as percent

Table 1 Polymers tested

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3.1.1 Effect of dispersant dosage its marked influence in imparting more negative charge on iron oxide particles. The improved performance of P-5 over Figure 1 presents dispersancy data as a function of disper- P-1 may be attributed to the presence of two functional sant concentration for three polymers namely homo-poly- groups (i. e., carboxyl and sulfonic acid) compared to only mers of acrylic acid of varying molecular weight (MW), P-1, one functional group (i. e., carboxyl) present in P-1. MW 2000; P-2, MW 10000 and a co-polymer of acrylic acid:2-acrylamido-2-methylpropane sulfonic acid, P-5, MW < 15 000. It can be seen that polymer concentration strongly 3.1.2 Effect of heat treatment affects the performance of the polymer as iron oxide dispersant. For example, at a 0.25 ppm polymer concentration P-1 Figure 2 presents performance data for several polymers at exhibits poor performance (< 25 %D). However, as the poly- 1.0 ppm polymer concentration under standard test condi- mer concentration is increased by a factor of two (i. e., from tions. As shown in Figure 2, the homo-polymers (i. e., P-1, 0.25 to 0.50 ppm), polymer performance is significantly im- P-3, and P-4) before heat treatment provide relatively poor proved and maximum dispersancy is obtained at 1.0 ppm (< 50 %) iron oxide dispersion. Furthermore, the iron oxide concentration. As illustrated in Figure 1 further increase in dispersancy values for both heat treated and non-heat trea- polymer concentration (i. e., from 1.0 to 1.5 ppm) does not ted homo-polymers are very similar. This indicates that heat exhibit any significant improvement in dispersancy value. stress (exposure of aqueous solutions of these homo-poly- It is worth noting that under similar experimental condi- mers to 200 °C, 20 hr) has a negligible detrimental effect tions polymer performance as iron oxide dispersant de- (< 10 % loss in %D) on the dispersing power of the poly- creases with increasing molecular weight. For example, %D mers. The data presented in Figure 2 suggest that polymers values obtained in the presence of 1.0 ppm of P-1 (MW containing only carboxyl group do not significantly decarb- 2000) and P-2 (MW 10000) are 41 % and 11 %, respectively. oxylate under the test conditions. The observed decrease in polymer performance with in- Masler [13] in his investigation on the effect of thermal creasing MW is consistent with earlier studies on the disper- treatment (250 °C, 18 hr, pH 10.5) of several homo-polymers sancy of hydroxyapatite by polymers [23]. reported that P-MAA lost slightly less molecular weight than The %D data as a function of co-polymer (P-5) concentra- P-AA which lost considerably less molecular weight than P- tion is presented in Figure 1. It is evident from Figure 1 that MA. In terms of P-AA decarboxylated less than P-MAA P-5 is more effective in dispersing iron oxide than P-1 thus which decarboxylated less than P-MAA. In addition, it was suggesting the presence of sulfonic acid group in P-5 exhib- reported that P-MA lost ∼40 % activity as a calcium carbo-

Figure 1 Effect of polymer dosage on iron oxide dispersancy by homo- and co-polymer

Figure 2 Effect of heat treatment on the performance of homo-, co-, and ter-polymers as iron oxide dispersants

Tenside Surf. Det. 43 (2006) 5 245 Z. Amjad: Role of heat treatment on the performance of polymers as iron oxide dispersants

nate inhibitor after heat treatment at 250 °C for 18 hr. It is 20 hr), the iron oxide dispersancy decreases drastically (by a interesting to note that under similar experimental condi- factor 4). For example, % iron oxide dispersancy values ob- tions P-AA and P-MAA lost only ∼5–8 % inhibitory activity tained for co-polymer (P-5) before and after heat treatment thus suggesting that carboxyl content in the polymer plays were 84 % and 14 %, respectively. It is worth noting that an important role in inhibiting the precipitation of calcium the performance of heat treated co-polymer is similar to that carbonate. Gurkaynak et al. [14] investigated the high tem- obtained for poly(acrylic acid), P-2 (Fig. 2), of similar mole- perature degradation of P-AA in aqueous solution as a func- cular weight (∼10 000). The observed marked decrease in P- tion of pH, ionic strength, and temperature. Results of their 5 performance clearly indicates that 2-acrylamido-2-methyl- study show that rate of decarboxylation of P-AA decreases propane sulfonic acid (SA) present in P-5 underwent serious with increasing pH (i.e, COO– is relatively more stable than degradation upon exposure to heat treatment thus leading to COOH) and the rate of decarboxylation increases rapidly as the formation of poly(acrylic acid). the temperature is increased from 250 °C to 350 °C. The dis- Iron oxide dispersancy data for ter-polymers (i. e., P-6, P- persancy data presented in Figure 2 suggest that there was 7, and P-8) are also illustrated in Figure 2. As shown, all of no significant loss of dispersancy or carboxyl content under the three ter-polymers in the absence of heat treatment show the experimental conditions employed in the present condi- excellent (> 80 %) dispesancy power. It is evident from Fig- tions (200 °C, 20 hr, pH 10.5). The insignificant loss in dis- ure 2 that P-6, P-7 and P-8 upon heat treatment (200 °C, persancy or decarboxylation as observed in the present in- 20 hr) lost significant dispersancy ability. For example, %D vestigation is thus consistent with previously reported values obtained for P-6, P-7, and P-8 before heat treatment studies on the thermal stability of P-AA in alkaline pH [14]. were 89 %, 86 % and 82 %, respectively compared to 32 %, Comparative dispersion data on several co- and ter-poly- 20 %, and 15 %, respectively obtained for heat treated ter- mers are presented in Figure 2. As illustrated, both the copolymers. As shown in Table 1, the structural difference be- and ter-polymers in the absence of thermal stress exhibit ex- tween P-6 and P-7 is due to the presence of a third mono- cellent (> 80 %) iron oxide dispersion. However, when these mer i. e., sulfonated styrene, SS, in P-6 versus tertiary butyl co-and ter-polymers are exposed to heat stress (200 °C, acrylamide, t-BuAm, in P-7. Similarly, in P-7, SA has been

Figure 3 Plots of molecular weight loss due to heat treatment for various polymers

Figure 4 FT-IR spectra of poly(acrylic acid) before and after heat treatment at 200 °C for 20 hr

246 Tenside Surf. Det. 43 (2006) 5 Z. Amjad: Role of heat treatment on the performance of polymers as iron oxide dispersants

replaced with methacrylic acid to yield P-8. From the data Figure 2 also shows a comparison of the ter-polymers presented in Figure 3 it is clear that upon subjecting the that have the same baseline performance before heat treat- ter-polymers to heat treatment, P-7 and P-8 lost more inhibi- ment. However, as the polymers are exposed to 150 °C and tory power compared to P-6. The observed decrease in per- 200 °C, a marked decrease in polymer performance is ob- formance between these two-ter-polymers suggests that SS served. It should be noted that compared to P-6, P-7 lost is thermally more stable than the t-BuAm and SA. more dispersancy power at both temperatures. The observed difference in ter-polymer performance suggests better stabi- 3.1.3 Effect of temperature lity of SS over t-BuAm. The influence of temperature on the thermal stability of 3.2 Polymer characterization polymers was also investigated at both 150 °C and 200 °C. The performance data presented in Figure 2 illustrate excel- 3.2.1 Molecular weight lent thermal stability for the poly(methacrylic acid), P-3, and two poly(acrylic acid), P-1 and P-2 evaluated at both 150 °C It is well known that molecular weight of a polymer has pro- and 200 °C. The baseline performance (without heat treat- found effects on its performance in domestic, biological, and ment) for the two acrylic acid-based ter-polymers is better industrial applications. For example, a low molecular weight than for the homo-polymers tested. (2000 to 10 000) polymers are effective precipitation inhibi-

Figure 5 FT-IR spectra of co- polymer (P-5) before and after heat treatment at 200 °Cfor 20 hr

Figure 6 FT-IR spectra of ter- polymer (P-7) before and after heat treatment at 200 °Cfor 20 hr

Tenside Surf. Det. 43 (2006) 5 247 Z. Amjad: Role of heat treatment on the performance of polymers as iron oxide dispersants

tors and dispersing agents for particulate matter whereas Figures 4, 5, and 6, respectively. Figure 7 shows the FT-IR high (> 100,000) molecular weight polymers are poor preci- spectra for P-6 before and as well as after 20 hr of heat treat- pitation inhibitors but may be effective flocculants. ment at 200 °C. In all cases, polyacrylic carboxylate (Na) salt, All polymers (synthetic and natural) degrade as a result of which is near 1,565 cm–1 shifted to a 7–8 cm–1 lower fre- exposure to elevated temperature and pressure. The extent quency after heat treatment. The reason(s) for this is not of degradation depends upon several factors including tem- fully understood, but may reflect a change in pH caused by perature, duration of heat treatment, and polymer architec- the heat treatment. ture. The polymers used in the present study lost molecular For those samples containing sulfonic acid group (i. e., weight as a result of their thermal degradation. Figure 3 de- Figures 5, 6, and 7), the amide carbonyl band near picts the “% molecular weight loss” for homo-, co-, and ter- 1,655 cm–1 diminishes and eventually disappears during polymers. The data show that there is small loss of molecu- heat treatment, as the amide functionality is oxidized. As lar weight for homo-polymers (i. e., P-1, P-3) after heating at the amide carbonyl diminishes, a complementary carboxy- 200 °C. Figure 3 also shows that ter-polymers are degraded late salt band near 1,565 cm–1 grows; this band is indistin- to a lesser extent than P-5 copolymer. For example, the mo- guishable from the carboxylate salt band observed in poly- lecular weight loss obtained for ter-polymers was ∼11 % acrylate salt type products (i. e., P-1). As the sulfonic acid compared to 22 % loss in the case of co-polymer. As dis- component is degraded, the primary sulfonate salt asym- –1 cussed earlier the loss in co- and ter-polymers performance metric SO3 stretch band near 1,195 cm shifts to an ap- as a result of heat treatment is far greater (60 to 80 %) than proximately 15 cm–1 higher frequency. The position of –1 the observed (10 to 20 %) loss in molecular weight. This sug- asymmetric SO3 stretch band near 1,047 cm is essentially gests that the decrease in polymer performance as an iron unchanged. However, the relative intensity of this band is oxide dispersant is due to degradation of the functional somewhat less in heat-treated samples than in the untreated group(s) rather than the cleavage of the polymer backbone. samples. The spectra in Figure 7 indicate that the majority of the thermal degradation occurred after only 4 hr. Further- 3.2.2 FT-IR spectroscopy more, the greater heat stability of P-6 vs. P-7 is evident by comparing the spectra in Figures 7 and 6, respectively. It Before and after thermal treatment FT-IR spectra of P-1, P-5, should be pointed out that observations made in FT-IR and P-7 are shown in investigation on polymer samples regarding structural

Figure 7 FT-IR spectra of ter- polymer (P-6) before and after heat treatment at 200 °C for 4 hr and 20 hr

Figure 8 Calcium ion compatibility of homo-, co-, and ter-polymers before and after heat treatment at 200 °C for 20 hr

248 Tenside Surf. Det. 43 (2006) 5 Z. Amjad: Role of heat treatment on the performance of polymers as iron oxide dispersants

changes during heat treatment agree well with NMR charac- rylic acid homopolymer (i. e., P-2) does not significantly im- terization data obtained for polymer samples before and pact the compatibility of P-2 with calcium ion. For example, after heat treatment. calcium compatibility values obtained in the absence and presence of heat treatment are 5 and 4.5 ppm polymer/ 3.3 Calcium ion compatibility 1000 mg Ca, respectively. The data presented in Figure 8 also suggest that all SA-containing co- and terpolymers are It has been reported that a polymer's ability to complex affected by thermal treatment. With the exception of P-6, hardness ions is affected by polymer molecular weight [24]. all co- and terpolymers became significantly less tolerant to Higher molecular weight polymers typically exhibit better Ca. For example, Ca ion tolerance values obtained for P-5 complexing ability than the low molecular weight polymers. and P-7 are > 100 ppm before thermal stress compared to However, polymers that complex hardness can also, if used ∼2 ppm obtained when these polymers are subjected to ther- at high concentrations, form insoluble calcium salts which mal stress (200 °C for 20 hr). Because the resultant polymer exhibit inverse solubility [24]. in both cases (P-5 and P-7) is essentially a poly(acrylic acid) Calcium ion compatibility of several polymers exposed to P-AA, the poor compatibility obtained for both polymers is thermal stress (200 °C for 20 hr) was studied using a stand- consistent with high molecular weight water polymerized ard test method as described previously [24]. The results P-AA [24]. shown in Figure 10 indicate that thermal treatment of ac- 4 Particle Size Characterization by Optical Microscopy

The iron oxide particles collected at the end of dispersancy experiments were also evaluated for particle morphology and size by optical microscopy. Figure 9 presents micro- graphs of iron oxide particles in the absence of polymer (Fig- ure 9A), in the presence of 1.0 ppm P-6 (Figure 9B) and in the presence of 1.0 ppm P-6 heat treated at 200 °C for 20 hr (Figure 9C). It is evident from Figures 9A and 9B that whereas ter-polymer exhibits marked effect in breaking down (or de-agglomerating) large iron oxide particles, heat treated ter-polymer shows poor performance in terms of de- agglomeration. Amjad and Zuhl [25] recently studied the effect of polymers on iron oxide particle size distribution in aqueous solution. It was found that in the presence of poly- (A) mers the iron oxide particle size distribution shifts from lar- ger particle size (> 50 micron) to smaller (< 5 micron) particle. In addition, it was also observed that heat treated co- and ter-polymers show less effect on particle size distribution profiles. The results obtained in the present investigation on iron oxide dispersancy by heat treated and non-treated polymers are consistent with the changes observed in iron oxide particle size distribution profiles in the presence of polymers.

5 Summary

The heat stability of several homo-, co-, and ter-polymers under simulated boiler water conditions has been investigated. The results indicate that all polymers undergo some degradation under the conditions employed in this study. (B) For polymers before heat stress, the co- and ter-polymers provide significantly better iron oxide dispersion than the homo-polymers. However, after heat stress, P-6 is clearly a better overall iron oxide dispersant than P-7 and P-8 which performs better than co-polymer (P-5). Iron oxide dispersion data also suggest that heat treatment of all the homo-polymers tested does not significantly degrade their performance. Heat stress testing data indicate that homo-polymers lost slightly less molecular weight than ter-polymers which lost less molecular weight than co-polymers. Furthermore, polymer that is susceptible to heat degradation experience molecular weight and performance loss as the heat treatment is increased from 150 °C to 200 °C. (C) The FT-IR and NMR analysis of the polymers exposed to heat treatment reveal that the SA containing co-polymer (P-5) Figure 9 Optical micrograph of iron oxide dispersed in the absence of poly- and SA and t-BuAm containing ter-polymers (P-7, P-8) under- mer (A), in the presence of 1 ppm of ter-polymer (P-6) before heat treatment (B), and in the presence of 1.0 ppm of heat treated P-6 at 200 °C for 20 hr went more severe degradation than ter-polymer containing (C) sulfonated styrene (P-6).

Tenside Surf. Det. 43 (2006) 5 249 Z. Amjad: Role of heat treatment on the performance of polymers as iron oxide dispersants APPAR. INFORMATION

References 23. Amjad, Z.: accepted for publication in Phos. Res. (2006). 24. Amjad, Z.: Tenside Surfactant Detergent 42 (2005) 2. 1. Shen, Zhi-Gang, Chen, Jian-Feng, Zou, Hai-kui and Yun, J.: J. Coll. Interface Sci. 25. Amjad, Z. and Zuhl, R.: accepted for presentation at the Annual Convention of 275 (2004) 158. Association of Water Technologies, Charlotte, NC (September, 2006). 2. Binner, J. G. P. and McDermott, A. M.: Ceramic International 32 (2006) 803. 3. Nagaragan, M. K. N.: Tenside Surfactant Detergent 28 (1991) 4. Received: 09. 06. 2006 4. Kessler, S. M.: Paper No. 02402, CORROSION/2002, NACE International, Revised: 04. 08. 2006 Houston, TX (2002). 5. Dubin, L.: Paper No.118, CORROSION/84, NACE International, Houston, TX (1984). 6. Liu, Y. and Gao, L.: Materials Chemistry and Physics 82 (2003) 362. ❙ Correspondence to 7. Garris, J. P. and Sikes, S. S.: Colloids and Surfaces A: Physiochemical and En- gineering Aspects 80 (1993) 103. 8. Jean, J. H. and Wang, H. R.: J. Amer. Ceram. Soc. 71 (1988) 62. Z. Amjad 9. Davies, J. and Binner, J. G. P.: J. Eur. Ceram. Soc. 20 (2000) 277. Performance Coatings 10. Hackley, V. A.: J. Amer. Ceram. Soc. 81 (1998) 2421. Noveon, Inc. 11. McGaugh, M. C. and Kottle, S.: J. Polym. Sci., Part A-1, 6 (1968) 1243. 9911 Brecksville Road 12. Denman, W. L. and Salutsky, M. L.: in Proceedings of the 28th International Brecksville, OH 44141 Water Conference, Pittsburgh, PA (1967). 13. Masler, W. F.: in Proceedings of the 43rd International Water Conference, Pitts- burgh, PA (1982). The author of this paper 14. McGaugh, M. C. and Kottle, S.: J. Polym Sci. B 5 (1967) 817. 15. Gurkaynak, A., Tubert, F., Yang, J., Matyas, J., Spenser, J. and Gryte, C.: J. Polym. Zahid Amjad, received his M.Sc. in Chemistry from Punjab University, Lahore, Paki- Sci. A 34 (1996) 349. stan, and his Ph.D. in Chemistry from Glasgow University, Scotland. He is currently a 16. Hetper, J., Balcerowiak, W. and Beres, J.: J. Thermal Anal. 20 (1981) 345. Research Fellow in the Performance Coatings Group of the Noveon, Inc. His areas 17. McNeill, I. C. and Sadeghi, S. M. T.: Polymer Degradation and Stability 30 of research include interactions of polymers with different substrates in aqueous (1990) 267. solution, and applications of water soluble and water swellable polymers in perso- 18. Amjad, Z., Klepetsanis, P. G. and Koutsoukos, P. G.: Chem. Engn. Trans. 1 nal care, pharmaceutical, and industrial water systems. (2002) 755. 19. Klepetsanis, P. G., Kladi, A., Koutsoukos, P. G. and Amjad, Z.: Progr. Colloid Polym. Sci. 115 (2000) 106. 20. Amjad, Z., Zibrida, J. F. and Zuhl, R. W.: Mat. Perf. 39 (2000) 54. You will find the article and additional material by enter- 21. Wilson, D.: Paper No. 8, CORROSION/98, NACE International, Houston, TX (1998). ing the document number TS100312 on our website at 22. Dogan, O., Akyol, E., Baris, S. and Oner, M.: Chapter No. 14 in Advances in Crystal Growth Inhibition Technologies, Amjad, Z. (Ed), Kluwer Academic Pub- www.tsdjournal.com lishers, NY, NY (2000).

NIR-Kameras im erweiterten Infrarot L.O.T.-Oriel bietet Kameratypen basierend auf drei Detektor- eine großformatige Kamera mit 640 × 512 Pixel lieferbar, in materialien an. InGaAs hat hervorragende Detektionseigen- Europa ohne jede Lizenz. schaften im nahen Infrarot und ist daher das bevorzugte Material zwischen 900 nm und 1700 nm. Hier übertrifft es Ansprechpartner: an Empfindlichkeiten alle anderen Materialien. Herr Stefan Wittmer Beim „extended“ InGaAs handelt es sich um ein dotier- L.O.T.-Oriel GmbH & Co. KG tes InGaAs, das bis „hinauf“ zu 2500 nm eingesetzt werden Im Tiefen See 58, D-64293 Darmstadt kann, allerdings mit deutlich reduzierter Gesamtempfind- Tel.: +49(0)61 51-88 06-63, E-mail: [email protected] lichkeit im Vergleich zum Standardmaterial. Internet: http://www.lot-oriel.com/de Diese Kameras benötigen daher mindestens einen drei- stufigen Peltierkühler, um das Rauschen bei langer Integra- tion zu reduzieren. Aber auch in der tiefgekühlten Variante wird der Detektor des „extended“ InGaAs gegenwärtig aus- schließlich für Anwendungen genutzt, bei denen das Objekt intensiv strahlt, beispielsweise bei Laserstrahl-Analysen. Eine Alternative ist die Verwendung einer MCT-Kamera (Quecksilberkadmiumtellurid). Diesen Detektor gibt es in einer Variante für den Spektralbereich von 850 nm bis 2500 nm. Er bietet im Vergleich zum „extended“ InGaAs eine fast vierfach höhere Quanteneffizienz und somit eine hohe Empfindlichkeit. Die Herstellung von hochwertigen MCT Focal Plane- Arrays mit nur wenigen Defekten ist zudem Routine. Die notwendige Kühlung auf 200 K wird mit einem thermoelek- trischen TE4-Kühler erreicht. Dadurch bleibt das Kamera- modell XEVA-MCT kompakt mit nur 11 × 10 × 9cm3. Die XEVA-MCT gibt es gegenwärtig in zwei Varianten mit 60 Hz und 100 Hz, jeweils im Vollbild 320 × 240 Pixel. Im Vergleich zum MCT-Detektor hat der InSb-Detektor eine ähnlich hohe Bildqualität und Empfindlichkeit im Be- reich zwischen 1700 nm und 2500 nm, aber er erweitert den Bereich bis 3000 nm. Ein entscheidender Nachteil des InSb-Detektors ist allerdings die Notwendigkeit der Küh- lung auf 77 K, die einen leistungsstarken und lebensdauer- begrenzenden Stirling-Kühler voraussetzt. Zudem sind die Optiken im erweiterten MID-Bereich um ein Vielfaches teu- rer als Optiken, die lediglich bis 2,5 lm transparent sind. Andererseits gibt es neben der Standard 60 Hz-Version und der 100 Hz-High Speed-Variante bei InSb-Kameras eine 350 Hz-Vollbild-Super High Speed-Kamera. Zudem ist auch

250 Tenside Surf. Det. 43 (2006) 5