Preparation and Some Properties of a Nanocomposite of Polyacrylonitrile with Acetylene Black

Polymer Journal, Vol. 36, No. 10, pp. 812—816 (2004) Preparation and Some Properties of a Nanocomposite of Polyacrylonitrile with Acetylene Black y Arjun MAITY and Mukul BISWAS Department of Chemistry, Presidency College, Calcutta-73, India (Received April 15, 2004; Accepted July 12, 2004; Published October 15, 2004) ABSTRACT: Conducting nanocomposites of polyacrylonitrile (PAN) with acetylene black (AB) were prepared via K2CrO4–NaAsO2 initiated redox polymerization of acrylonitrile in presence of AB suspension in aqueous-methanol medium at 60 C. Prolonged extraction of PAN–AB composite by DMF failed to extract the loaded polyacrylonitrile completely from the acetylene black, as confirmed by FT IR studies. SEM analyses revealed the formation of agglom- erates of particles of nonuniform sizes and shapes. TEM analysis indicated that average particle diameters of the PAN– AB composite were in the range of 120–250 nm. Thermal stability of the PAN–AB composite was appreciably improved relative to that for the unmodified base polymer. The dc conductivity of the PAN–AB composite was in the range of 10À4–10À2 S/cm depending on the amount of AB in the PAN–AB composite, a value remarkably improved relative to that of the PAN homopolymer (>10À11 S/cm). [DOI 10.1295/polymj.36.812] KEY WORDS Polyacrylonitrile / Acetylene Black / K2CrO4–NaAsO2 Redox System / Thermal Stability / Conductivity / Considerable research interest has been shown late- capable of initiating the polymerization of N-vinylcar- ly in the modification of fundamental polymers like bazole. Interestingly, this system led to the simultane- polyacrylonitrile (PAN), polymethylmethacrylate ous formation of a PNVC–AB composite with a con- (PMMA), polystyrene (PS), etc. with a view to en- ductivity in the order of 10À2 S/cm. Earlier, Japanese hancing the scope of practical application of these ma- groups8–13 reported the polymerization of vinyl mono- terials. A widely investigated method in this direction mers like styrene, -methystyrene, isobutyl vinyl is the preparation of conducting polymer blends and ether (IBVE), N-vinyl-2-pyrrolidone (NVP) in the composites of the speciality conducting polymers presence of carbon black (CB) and external catalyst such as polyaniline (PANI), polypyrrole (PPY), and vis-a-vis formation of graft composites in the systems. polythiophene (PTP) with conventional polymers like Biswas et al.14–17 also explored the initiation of the PAN, PMMA, PS, etc. Several workers1,2 reported on polymerization of the NVC by Orient black (N220), the preparation of conducting polymeric blends/com- Vulcan XC-72, etc. without any external oxidant. posites of PPY–PVc and PPY–PMMA via electro- In this background, we wish to describe in this ar- chemical and oxidative polymerization methods re- ticle a novel procedure for the preparation of a highly 3 spectively. Stanke et al. synthesized a conducting conducting PAN–AB composite via K2CrO4–NaAsO2 graft copolymer film of PMMA and PPY by oxidative initiated redox polymerization of acrylonitrile in aque- 4,5 polymerization of pyrrole with FeCl3. Ruckenstein ous alcoholic medium and also report some relevant described preparation and evaluation of polyaniline/ properties of the PAN–AB composite. poly(alkylmethacrylate) and polypyrrole/poly(alkylmethacrylate) composites with high electrical conduc- EXPERIMENTAL tivity (6 S/cm). In an alternative process, blending polymers with Materials and Methods conducting fillers, such as natural graphite flake, car- Acrylonitrile (Aldrich, USA) was freed from inhib- bon black, and powders, to prepare electrically con- itor by successive washings with dilute sodium carbo- ducting composites has been extensively investigated nate solution, dilute sulphuric acid and finally with in the past few decades. In this context, Chen et al.6 distilled water. It was kept over-night over calcium prepared conducting PMMA/graphite nanosheet com- chloride and distilled in an all glass apparatus. The posites via in-situ polymerization of methylmethacry- fraction boiling at 77–78 C was collected and stored late (MMA) by benzoyl peroxide in aqueous alcohol carefully. Acetylene black (SENCO India, Chenai, In- solution in presence of expanded graphite (EG). We dia) was preheated by heating at 120 C for 2 h in vac- recently reported7 that acetylene black (AB)- the uum prior to use. Potassium chromate (Riedel, Ger- purest form of highly conducting carbon black, was many) and sodium arsenite (Riedel) were used as yTo whom correspondence should be addressed (Tel: +91-33-2521-3556; Fax: +91-33-2234-6075; E-mail: mukul [email protected]). 812 Conducting Composite of Polyacrylonitrile with Acetylene Black the oxidant and the reductant respectively. All other composite was confirmed to contain PAN along with solvents were of analytical grade and were freshly dis- AB. tilled before used. Characterization and Property Evaluation Polymerization of Acrylonitrile with K2CrO4–NaAsO2 Intrinsic viscosity of PAN homopolymer was deter- Redox System mined with an Oswald viscometer in DMF solution at K2CrO4 (0.2 g) was dissolved in 30 mL of water– 25 C and molecular weight was calculated using the methanol mixture (3 mL MeOH) in a Pyrex flask to Ueberreiter–Springer equation ½¼1:66 Â 10À5 Â which 1.5 mL of acrylonitrile was injected. The sys- M0:81.18 The FT IR spectrum of PAN–AB composite tem was kept under stirring at room temperature under was taken on a JASCO-410 instrument in pressed N2 atmosphere for 10 min and thereafter, 0.3 g of KBr pellet. Dispersion of PAN–AB composite in 2- NaAsO2 was dissolved into this solution. Then the to- propanol was microsprayed on a mica substrate. The tal system was kept at 60 C for 6 h. Thereafter, the sample was sputter coated with gold layer and a white polymer was centrifuged, washed in succession Hitachi S-415 A scanning electron micrograph was with distilled water, methanol, and acetone and finally used to take the micrograph. Thermogravimetric anal- dried in vacuum for 12 h. yses were performed on a Shimadzu DT-40 instrument. Direct current (dc) conductivity measurements Preparation of PAN–AB Nanocomposite were made on pressed pellets with a silver coating, us- In a Pyrex flask, 0.02–5 g of AB was added to ing the conventional four-probe technique. 30 mL of water–methanol mixture (3 mL methanol) under sonication for 1 h to make a suspension of AB RESULTS AND DISCUSSION in which 0.2 g of K2CrO4 was dissolved and 1.5 mL of acrylonitrile was injected. Thereafter, 0.3 g of General Features of Composite Formation NaAsO2 was added to it. The system was kept at Table I presents some results on the polymerization 60 C with stirring for 6 h under N2 atmosphere. The of AN vis-a-vis composite formation of polyacryloni- total black mass was washed in succession with dis- trile with acetylene black. 85% PAN homopolymer tilled water, methanol and acetone and finally dried was formed when the polymerization was conducted in vacuum for 12 h. under conditions summarized in Table I. Entries 1–8 The total PAN–AB composite thus obtained was indicate that the percent conversion of PAN homo- extracted with DMF through continuous refluxing polymer decreased with increasing weight of AB at for one week at 50 C. The total separated mass was fixed amount of redox system and monomer in the in- centrifuged, a process repeated at least four times until itial feed. A notable feature was that after prolonged the extract did not yield any precipitate with methanol extraction of PAN–AB composites with DMF at due to any residual surface adsorbed PAN. This resi- 60 C, some residual amount of PAN (last column, due was finally dried at 60 C for 12 h under vacuum. Table I) was found to be present in the PAN–AB After various physicochemical characterizations, the composite. This could be due to fact that PAN homo- Table I. Some typical data on composite formationa of polyacrylonitrile with AB Weight of Weight % of polymer Entry composite (g) % polymer of AB graftedc per g of b No (g) before reflux after reflux formed composite with DMF with DMF 1 0.02 0.73 0.09 57 78 2 0.03 0.63 0.14 50 78 3 0.04 0.56 0.15 45 73 4 0.05 0.53 0.18 40 72 5 0.10 0.50 0.25 33 60 6 0.20 0.45 0.36 21 44 7 0.30 0.52 0.365 18 35 8 0.50 0.73 0.70 19 28 a Experimental conditions: weight of AN ¼ 1:2 g, weight of K2CrO4 ¼ 0:1 g, weight of NaAsO2 ¼ 0:3 g, total volume = 30 mL (water ¼ 27 mL and MeOH ¼ 3 mL), temperature ¼ 60 C, time of polymerization = 6 h; b% polymer formed in the control experiment (without AB; using same experimental conditions mentioned above) was 85%; % polymer in the composite ¼½ðcolumn 3 À column 2Þ=1:2Â 100 c% grafting ¼½ðcolumn 4 À column 2Þ=column 4Â100 Polym. J., Vol. 36, No. 10, 2004 813 A. MAITY and M. BISWAS polymer was grafted on the acetylene black surface. Table II. FT IR absorption characteristics of PAN– Biswas and Maity recently reported19 that the poly- homopolymer and of PAN–AB composite merization of acrylonitrile by K2CrO4–NaAsO2 redox Absorption of PAN–AB PAN Assignments system occurred via free radical pathway as follows: composite (cmÀ1) 2939 2924 C–H stretching vibration NaAsO2 þ H2O ¼ NaH2AsO2 ðref 20Þ 2245 2260 CN stretching vibration À 6þ 5þ H2AsO3 þ Cr ¼ H2AsO3 þ Cr ðref 21Þ 1454 1460 C–H bending vibration Initiation H2AsO3 þ CH2 ¼ CH{CN À! H2AsO3{CH2{C H{CN Propagation H2AsO3{CH2{C H{CN þ nCH2 ¼ CH{CN À! H2AsO3{(CH2{CH(CN))n{CH2{C H{CN It is well established8–17 by ESR studies that carbon black systems have unpaired electrons.

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