Polyacrylonitrile (PAN)/Montmorillonite (MMT) clay nanocomposite was prepared in a microwave oven using a transition metal Co(III) complex taking ammonium persulfate (APS) as initiator with a motive of converting hydrophobic PAN into hydrophilic nanocomposite material via nanotechnology by the inclusion of MMT to the virgin polymer. UV-visible spectral analysis revealed various interactions between the developed complex with other reaction components. The formation of the PAN/MMT nanocomposites was characterized by FTIR. Furthermore, as evidenced by X-ray diffraction (XRD), transmission electron microscopy (TEM), the composite so obtained was found to have nano-order. XRD and TEM were suggesting that montmorillonite layers were exfoliated during the polymerization process. An increasing in the thermal stability for the developed nanocomposite was recorded by thermogravimetric analysis (TGA). The water absorption and biodegradation properties were carried out for its ecofriendly nature and better commercialization.
A great deal of research on organic polymer-layered silicate nanocomposites have been carried out over the past decade due to their substantial enhanced physical properties over virgin polymers, even when prepared with a very small amount of layered silicate [
Unlike to a virgin polymer or conventional micro and macro composites, the improvement in properties of PLSNs is remarkable, including high moduli [
Microwave heating is rapidly developing as an alternative to conventional heating techniques used in thermally initiated polymerization. The interaction between the microwave energy and molecular dipole moments of the starting materials provides an effective, selective, clean, and fast synthetic method [
Further, study on green polymeric materials which avoid the use of any toxic or noxious components in their manufacture and could be naturally biodegradable, are in demand, as they reduce the hazardous effect of plastics and other polymeric compounds on environment. So far, biodegradable polymers, such as polylactide (PLA) [
Monomer, AN E merck India, was purified as reported earlier [
A mixture of 6.85 g of 70% ethylene diamine (en) (0.08 moL) and 10 ml of water was partially neutralized by the addition of 3 ml of concentrated nitric acid (0.048 moL). The resulting solution was added to a solution of 11.5 g of Co(NO3)2 6H2O (0.04 moL) and 6 g of sodium nitrite (0.087 moL) in 20 ml water. A vigorous stream of air was passed through the solution. The yellow trans-[Co(III)en2(NO2)2]NO3 began to precipitate after 20 minutes. The mixture was cooled in an ice bath and filtered. The yellow crystalline solid was recrystallised from boiling water, washed with alcohol and ether and air dried. The formation of the complex trans-[Co(III)en2(NO2)2]NO3 was confirmed by UV-visible spectral analysis (Scheme
Schematic representation of [Co(III)(en)2(NO2)2]NO3 complex (I), (b) coordination of monomer AN with [Co(III)(en)2
The polymerization experiments were carried out in a Kenstar (Model No. MOW 9811, 1200 W) domestic MW oven. The average bulk temperature at end of the reaction was measured by inserting a thermometer in the reaction mixture. All the experiments were done with water and benzene as solvent, and the temperature is less than 100°C. The polymerization experiment was carried out first in two parts. The first part was carried out in reaction vessel containing the requisite amount (0.1 M) of each trans-[Co(III)en2(NO2)2]NO3 with a known amount of AN in 4/5th part deionized water. At the same time, desired amount of MMT was dispersed in rest 1/5th part of water at same condition. The MMT suspension was added to the reaction vessel and stirred with constant velocity at N2 atmospheric pressure. Then requisite amount of initiator solution was carefully injected to the reaction mixture. For all the MW power studies, the exposure time was varied from 30 to 180 sec. After completing reaction, the polymerization was terminated by the addition of a 0.1 M solution of ferrous ammonium sulfate solution. The coagulated products were purified. The variations of different components along with conversions were tabulated in Table
Effect of variation of concentration of AN, APS, Co(III) complex, MMT, and time on the % of conversion and water absorbency.
Sample code | (AN) moL·dm-3 | (APS) × 102 MoL·dm-3 | (Complex) × 102 moL × dm-3 | (MMT) | Time in Sec | % conversion | Water absorbency |
---|---|---|---|---|---|---|---|
S0 | 7.0 | 2.0 | 2.0 | 0.0 | 180 | 55.45 | 09 |
S1 | 0.38 | 2.0 | 2.0 | 5.0 | 180 | 57.19 | 39 |
S2 | 0.76 | 2.0 | 2.0 | 5.0 | 180 | 64.08 | 42 |
S3 | 1.51 | 2.0 | 2.0 | 5.0 | 180 | 68.85 | 74 |
S4 | |||||||
S5 | 3.03 | 2.0 | 2.0 | 5.0 | 180 | 64.45 | 68 |
S6 | 3.79 | 2.0 | 2.0 | 5.0 | 180 | 58.43 | 59 |
S7 | 4.55 | 2.0 | 2.0 | 5.0 | 180 | 54.57 | 56 |
S8 | 2.27 | 0.5 | 2.0 | 5.0 | 180 | 25.05 | 56 |
S9 | 2.27 | 1.0 | 2.0 | 5.0 | 180 | 58.18 | 69 |
S10 | 2.27 | 1.5 | 2.0 | 5.0 | 180 | 72.65 | 75 |
S11 | 2.27 | 2.0 | 2.0 | 5.0 | 180 | 79.06 | 87 |
S12 | 2.27 | 2.5 | 2.0 | 5.0 | 180 | 68.06 | 79 |
S13 | 2.27 | 3.0 | 2.0 | 5.0 | 180 | 54.49 | 72 |
S14 | 2.27 | 3.5 | 2.0 | 5.0 | 180 | 48.56 | 64 |
S15 | 2.27 | 2.0 | 0.5 | 5.0 | 180 | 35.09 | 69 |
S16 | 2.27 | 2.0 | 1.0 | 5.0 | 180 | 54.54 | 77 |
S17 | 2.27 | 2.0 | 1.5 | 5.0 | 180 | 68.89 | 83 |
S18 | 2.27 | 2.0 | 2.0 | 5.0 | 180 | 79.06 | 87 |
S19 | 2.27 | 2.0 | 2.5 | 5.0 | 180 | 64.00 | 76 |
S20 | 2.27 | 2.0 | 3.0 | 5.0 | 180 | 56.75 | 69 |
S21 | 2.27 | 2.0 | 3.5 | 5.0 | 180 | 48.95 | 62 |
S22 | 2.27 | 2.0 | 2.0 | 1.25 | 180 | 53.41 | 65 |
S23 | 2.27 | 2.0 | 2.0 | 2.5 | 180 | 62.31 | 76 |
S24 | 2.27 | 2.0 | 2.0 | 5.0 | 180 | 79.06 | 87 |
S25 | 2.27 | 2.0 | 2.0 | 10 | 180 | 72.55 | 84 |
S26 | 2.27 | 2.0 | 2.0 | 15 | 180 | 69.06 | 80 |
S27 | 2.27 | 2.0 | 2.0 | 20 | 180 | 63.07 | 76 |
S28 | 2.27 | 2.0 | 2.0 | 25 | 180 | 56.08 | 73 |
S29 | 2.27 | 2.0 | 2.0 | 5.0 | 60 | 57.09 | |
S30 | 2.27 | 2.0 | 2.0 | 5.0 | 90 | 65.59 | |
S31 | 2.27 | 2.0 | 2.0 | 5.0 | 120 | 69.49 | |
S32 | 2.27 | 2.0 | 2.0 | 5.0 | 150 | 74.55 | |
S33 | 2.27 | 2.0 | 2.0 | 5.0 | 180 | 79.06 | |
S34 | 2.27 | 2.0 | 2.0 | 5.0 | 210 | 79.57 | |
S35 | 2.27 | 2.0 | 2.0 | 5.0 | 240 | 79.65 | |
S36 | 2.27 | 2.0 | 2.0 | 5.0 | 300 | 79.75 |
The IR spectra of PAN and PAN/MMT nanocomposite, in the form of KBr pellets, were recorded with a Perkin-Elmer model Paragon-500 FTIR spectrophotometer.
The incorporation of Na-MMT into the matrix was confirmed by using an XRD monitoring diffraction angle 2
Nanoscale structure of PAN/MMT was investigated by means of TEM (H-700, Hitachi Co.), operated at an accelerating voltage of 100 kV. The ultrathin section (the edge of the sample sheet perpendicular to the compression mold) by diamond knife with a thickness of 100 nm was microtomed at −80°C.
The surface morphology of PAN/MMT nanocomposite before and after biodegradation was studied by scanning electron microscopy (SEM) using Jeol Ltd, Japan and Model 5200 scanning electron microscope.
Tensile bars were obtained on a Van Dorn 55 HPS 2.8F mini injection molding machine under the following processing conditions: a melt temperature of 150°C, a mold temperature of 25°C, an injection speed of 40 mm/s, an injection pressure of 10 MPa, and a holding time of 2 s, with a total cycle time of 30 s. Tensile measurements on injection molded samples of nanocomposites were performed according to ASTM D-638-00 using an Instron test machine Model 5567. Tests were carried out at a crosshead speed of 50 mm/min and a 1 kN load cell without the use of an extensometer. All tests were performed at room temperature and the results were the average of five measurements. The highest value of standard deviation was 15%.
Thermal properties were measured by using Shimadzu DTA-500 system in air, from room temperature to 600°C at a heating rate of 10°C per min.
The UV-visible spectra of [Co(III)en2(NO2)2]NO3 complex vis-à-vis those of the monomer and the initiator were studied using a Perkin Elmer UV-visible spectrophotometer model Lambda-20.
One gram each of the powdered sample (PAN, PAN/MMT) was palatalized by using 10 tons of pressure of around 0.05 cm of thickness and 1.5 cm of diameter. The pellet was then immersed in water at room temperature until equilibrium was reached. The water absorption was determined by weighing the swollen pellet after it had been wrapped between the folds of filter paper. The water absorbency [
In the present work, the activated sludge water was collected [
A cultured medium was prepared by taking nutrient broth. In that medium, Bacillus cereus (gram-positive stain) was inoculated separately. The pure cultures were maintained separately in the incubator. The nutrient broth so prepared was sterilized for 45 m at a pressure of 15 lb/in2 at 80°C. Then to 10 ml of sterilized broth 0.1 g, each of the samples, that is, PAN, PAN/MMT nanocomposites were added aseptically in separate test tubes, and each tube of samples were supplemented with inoculum of different bacterial stains separately.
The degradation of samples by B. cereus was monitored in time intervals of 1, 7, 15, and 30 days. After the required time period, the samples were washed repeatedly with deionised water, oven dried at
Na2CO3, phenolphthalein indicator.
The cultured sample (“
From the series of experiments, it was found that the PAN was intercalated into gallery structure of silicate by the catalytic action of [Co(III)(en)2(NO2)2]NO3 complex. The complex initiating system helps to stabilize the emulsion latex to a high conversion level in the absence of added emulsifier (Table
Absorption peaks for PAN, PAN/MMT nanocomposite are shown in Figures
FTIR spectra of (a) PAN and (b) PAN/MMT (5 %w/v) nanocomposite.
XRD has been used to evaluate the degree of interaction of the layered silicates with the polymer matrix. The systematic arrangement of the silicate layers of the intercalated composites has been elucidated by XRD in calculating interlayer spacing with the help of Bragg’s equation. Figure
XRD of PAN/MMT nanocomposites (a) 5%, (b) 10 %w/v, and (c) pure MMT clay.
TEM micrographs of PAN/MMT nanocomposites (a) 5% and (b) 10 %w/v.
The internal structure of PAN/MMT nanocomposite was further conformed by TEM Figure
The thermal properties of the nanocomposite materials have been evaluated by TGA as shown in Figure
TGA of (a) PAN, (b) PAN/MMT (5 %w/v) nanocomposite, (c) PAN/MMT (10 %w/v) nanocomposite, and (d) MMT Clay.
The mechanical properties, including Young’s modulus, elongation at break, toughness, yield stress, and yield strain of all the nanocomposites prepared in this study, together with the corresponding values of the virgin polymer, are given in Table
Comparative data of mechanical properties (±error point) of PAN and PAN/MMT nanocomposites.
Sample code | Young’s model. (MPa) | Elong. at break (%) | Toughness, (MPa) | Yield strain (%) | Yield stress (MPa) |
---|---|---|---|---|---|
S0 | |||||
S22 | |||||
S24 | |||||
S25 | |||||
S27 |
The results of the study on the polymerization of AN initiated by APS catalyzed by, [Co(III)(en)2(NO2)2]NO3 were tabulated in Table
The UV-visible spectra of various mixtures like [Co(III)(en)2(NO2)2]NO3, [Co(III)(en)2(NO2)2]
UV-visible spectra of (a) Co(II)(NO2)2, (b) [Co(III)(en)2
It was found that the conversion and the
From Table
The above complexation mechanism is explained earlier on the basis of the spectral data and Scheme
From Table
The effect of variation in monomer concentration on water absorbency of the nanocomposite showed very interesting results (Table
The effect of initiator concentration was studied and presented in Table
As reported in our earlier publications, here also the synthesis of the nanocomposite was carried out in the presence of a new complex to catalyze the reaction as well as to avoid the use of any added emulsifier. Accordingly, the synthesis of the nanocomposite was carried out under different [Co(III)(en)2(NO2)2]NO3 concentrations; however, for concentration
The water absorbency was found to increase with MMT concentrations 1.25 to 5 moL·dm-3 and then decreased as shown in Table
From the comparative biodegradation study of PAN, PAN/MMT, it was found that PAN showed low accelerated rate of degradation by weight loss initially, but after 21 days, it was slowed down. The PAN/MMT nanocomposite showed tremendous rate of degradation in activated sludge as shown in Figure
Biodegradation by activated sludge of (a) PAN, (b) PAN/MMT (5 %w/v) on time versus weight loss.
SEM of PAN/MMT nanocomposites (a) before and (b) after 30 days biodegradation.
The weight loss data in Figure
Biodegradation by bacteria (
Again, the rate of degradation was also measured by calculating the amount of CO2 evolved from the cultured medium at interval period of times. The results in Figure
Biodegradation by bacteria (
PAN/MMT nanocomposites are prepared by using a Co(III) complex in a domestic microwave oven. In microwave oven, the polymerization took place very fast and consumed very less time. The fast polymerization reactions occurred by fast decomposition of initiator due to the complex. The formation of nanocomposites was characterized by FTIR, further confirmed from XRD and TEM. Due to the bond between PAN and MMT, the thermal stability of PAN/ MMT nanocomposite is increased. The mechanical properties of PAN/MMT nanocomposites, UV-visible spectra of complex and the mechanism of polymerization were studied. The biodegradation of the samples was also studied for their better commercialization.