Yüksek molekül ağırlıklı akrilamid polimerlerinin sentezi ve flokülant olarak değerlendirilmesi

Abstract

Son yıllarda akrilamid polimerlerin endüstriyel kullanım alanları çok artmıştır. Bu yaygın kullanım alanlarının en önemlisi flokülasyon işlemidir. Flokülasyon işlemlerinde genellikle yüksek molekül ağırlıklı poliakrilamidler tercih edilmektedir. Ancak yüksek molekül ağırlıklı poliakrilamid sentezi sırasında jelleşme olayının meydana gelmesinden dolayı bazı zorluklarla karşılaşılmaktadır. Ay rıca bu tip polimerlerin üretimi bazı özel firmaların tekelindedir ve üretim yöntemleri patentlidir. Bu çalışma, yüksek molekül ağırlıklı poliakrilamid sentezi ve flokulant olarak değerlendirilmesi için yapılan araştırma ve deney sonuçlarını içermektedir. Bu amaçla akrilamidin, 4,4-Azobis (4 siyano pentanol) azo başlatıcısı varlığında ısısal polimerizasyonunda reaksiyon zamanı ve başlatıcı konsantrasyonuna göre dönüşüm ve molekül ağırlığı değişi mi incelenmiştir. Ayrıca ısısal polimerizasyonla elde edilen poli- akri lamı" di erin, akrilamid ile Ce(IV) varlığında redoks polimerizasyonuyla zincir büyütülmesi gerçekleştirilmiştir. Akrilamidin, polietilenglikol segmentleri içeren poli azoesterlerile önce ısısal polimerizasyonu ve buradan elde edilen poliakrilamid-polietilenglikol kopolimerinin, akrilamid ile Ce(IV) varlığında redoks polimerizasyonu ile zincir büyütülmesi gerçekleştirilmiştir. Elde edilen homopolimer ve kopolimerler jar testinde kullanılarak flokülant aktiviteleri bazı ticari polimeri eri nki ile karşılaştırılmıştır.

During the last two decades, the industrial use of acrylamide (AA) polymers has increased tremendously. The main uses of polyacry- lamides involve water treatment, mining and paper manufacture. In some uses such as flocculation, the objective is to attain a very high molecular weight. To obtain high molecular weight polyacryla- mide (PAA), aqueous polymerization using conventional azo, peroxy or redox initiators usually encounters with geletion which is difficult to deal with. However, there are several processes suitable for the production of high molecular weight soluble polymers. These include incremental addition of peroxy or activator compound to polymeriza tion mixture containing redox initiator, radiation induced polymeri zation under controlled conditions of monomer concentration, radia tion intensity, total dose and the pH of the reaction mixture, emul sion polymerization and nuclear radiation polymerization in the pre sence of additives. In the first part of this study, aqueous polymerization of AA carried out thermal under the action of 4-4'-Azo-bis(4-cyanopenta- nol) (ACP). The thermal polymerization was carried out at different durations and initiator concentrations. Variations in monomer con version and molecular weight of PAA as a function of these parameters were observed. The conversion is directly proportional to the amount of initiator used and polymerization time up to the certain level and thereafter levels off. While the molecular weight decreases with increasing initiator concentration. These results indicate that polymerization of AA with ACP shows the general behaviour of this type of initiation. AA polymerization by means of ACP is expected to yield PAA molecules with one hydroxy! groups per chain since chain termination is be lived to be mainly by disproportionation. ÇH3 0H-CH2-CH2-CH2- C - £ CHe-CH]- CN C=0 Whether or not the production polymer possesses one or two hydr- oxyl end groups depends mainly on the ratio, of disproportionation to combination for particular polymerization. By taking this fact into account in the present study chain extention of PAA was accomp lished via redox polymerization in the presence of AA as indicated below. VI- -fCH2-CH}n- I NHo -OH + Cedv) " " " m CH2=CH C=0 NH2 -fCH2-ÇH]n- 0-[CH2-CH]-m c=o I NH2 C=0 I NH2 Typical results of this polymerization are given in Table 1. It is interesting to note that PAA with lower molecular weight ap pears to undergo chain extension more efficiently indicating the importance of hydroxyl group concentration. The efficiency of the chain extension is affected also by the amount of monomer in the redox system. Table 1 Chain Extension of PAA by Redox Polymerization' a: Ce(IV) =2.4xl0"4 mol/1 in all cases b: Values of Mn estimated from measurements of (n) in water at 3Q°C Chain, extention was also performed in a different sequence of the above procedure. In this way, initially polymerization of AA was conducted by means of ACP-Ce(IV) redox system provided the for mation of PAA with one (-N=N-) group per chain. Thermal decomposi tion of the azo linkage produces two polymeric radicals per chain, which gives rise to the chain extension in the presence of AA. The increase in. the molecular weight of the starting polymer was found to be 21%. vxx These results indicate the efficiency and convenience of using ACP-Ce(IV) combined system to prepare high molecular weight PAA in aqueous solution via a two-step procedure which avoids the problems associated with aqueous gel. In the next step of the study, acrylamide-etilenglycol copoly mers were synthesized. To do this polyazoesters (PAEs) was used. Recently, special attention has been devoted to PAEs possessing polyethyleneglycol (PEG) and hydroxy! functions capable of forming free radicals in conjuction eerie salts according to following reac- ti ons. PEG H0{CH2CH20İı ?*? PEG, 9 CH3 S - ij-n-C-C-N^N-C^C-foCHjCHjjn-OH + Ce(lV) CH3 CH3.0-PEG-N=N-PEG-0- +Ce(lfl) + H+ CHrCH NH2 PAAm-PEG-N-N-PEG-PAAm These radicals initiate polymerization of an appropriate mono mer present in the system without effecting the central thermosen- sitive azo groups. Resultant polymers may be used as initiators to prapere multiphase block copolymers. Thus the polymerization of AA was carried out in aqueous solution by thermolysis of PAEs with dif ferent molecular weights. The conversion Vs time and molecular weight vs time graphs are given in Fig.l and Fig. 2. As can be seen the conversion is directly proportional to polymerization time up to certain level and thereafter levels off, whereas molecular weight is unaffected. It is also interesting to note that the molecular weight of PEG segment present in the initial PAE influences the mo lecular weight of the resultant PAA. Chain extension of these polymers via oxidatTon of terminal OH groups by Ce(-IV) in the presence of AA were studied and the results given in Table 2 were obtained. VXXX o '<ö t- > e o Fig.l. Conversion- Polymerization Time ReTations For Different PAEs in Aqueous Polymerization of ftcryl amide. AA =2.1 mol/1, PAE =55 g/1 °<=PAE 1500, a=PAE 10000 Table 2 Chain Extension of PAA-PEG by Redox Polymerization0,-4 a: AA =2 mol/î, Ce(IV) =2.4x10 * mol/1 b: Values of Mn estimated from measurements of (n) in water at 30°C As can be seen from Table 2, both polymers underwent signifi cant chain extension, PAA with lower molecular weight being more efficiently. It appears from this result that hydroxyl concentration plays an important role in the redox polymerization step. In the last stage of the study, polymers obtained either by redox polymerization or by thermolysis of the azo groups or in their xx X 3" 2 u 2 3 4 Time, (hr. ) Fig. 2. Molecular Weight- Polymerization Time for Different PAEs in Aqueous Polymerization of Ac ryl amide AA =2.1 mol/1, PAE=55 g/1, °=PAE 1500, a=PAE 10000 chain extended form and some commercial polymers were used as floccu- lants to clear an aqueous solutions of colloidal tinea! solids. Full description of polymers used in Jar-tests are given in Table 3. The effectiveness of the polymers listed in Table 4 to aggre gate the suspension was determined via Jar- test. Differences in flocculation activity between commercial polymers and polymers obta ined in this study could be due to differences in molecular weight distribution, or unknown structural variations such as branching. In this connection it should be pointed out that, because of the complexity of the procedure, some inconsistencies and anomalies may be observed for different type of flocculants, i.e. flocculants obtained by different synthetic procedures, and each flocculant should be considerent separetly. However, one thing is quite ob vious from Table 4, polymers obtained in this study give better transparency of the separated suspension than those of commercial polymers. It is also interesting to note that polymers with PEG segments were more efficient than homopolyac ryl amides, e.g. less polymer solution is required for similar transparency. Attachment of PEG segments to PAA flocculants may provide additional advantage in practical applications since these groups reduce adhession of flocculated clay during filtration process. Notably molecular a: Values of Mn estimated from measurements of (n) in water at 30°C b: Commercial polymer c: Thermal polymerization at 60°C d: Redox polymerization by Ce(IV) weight increase by chain extension improves the flocculation effici ency. It was understood from the additional experiments that incre mental flocculant addition is more effective on the flocculation efficiency. a: Optimum polymer dosage =13 mg/1 b: Optimum polymer dosage =9.8 mg/1