Miscibility of Poly(vinylidene fluoride) and Cellulose Acetate Blends in Dimethyl Formamide

Transcription

1 sian Journal of Cheistry; Vol. 3, No. 4 (011), Miscibility of Poly(vinylidene fluoride) and Cellulose cetate lends in Diethyl Foraide M. SELV KUMR 1, and D. KRISHN HT 1 Departent of Chistry, Manipal Institute of Technology, Manipal , India Departent of Cheistry, National Institute of Technology, Karnataka, Surathkal, Srinivasnagar , India Corresponding author: Fax: ; Tel: ; E-ail: cheselva78@gail.co (Received: March 010; ccepted: 30 Noveber 010) JC-9340 The iscibility of poly(vinylidene fluoride) (PVDF) and cellulose acetate blends in diethyl foraide has been investigated by viscosity, density, refractive index and ultrasonic velocity studies. The polyer-solvent and blend-solvent interaction paraeters and heat of ixing have been calculated using the viscosity, density and ultrasonic velocity data. The results indicated the existence of positive interactions in the blend polyer solutions and that they are iscible in diethyl foraide in the entire coposition range between K. The study also revealed that the variation in the teperature does not affect the iscibility of poly(vinylidene fluoride) and cellulose acetate blends in DMF significantly. The presence of hydrogen bonding in the blends in the solid state has also been indicated by FTIR studies. SEM iages also supported the iscibility of blends. Key Words: Polyer solutions, Ultrasonic velocity, Viscosity, Interaction paraeter, Polyer blends, Miscibility, Cellulose acetate, Poly(vinylidene fluoride), Diethyl foraide. INTRODUCTION The study of iscibility and interactions present in polyer and solvent in a polyer blend solution syste is of great significance for engineering applications of polyers. They also provide substantial inforation on the processes involving polyer production and their uses 1,. Polyer blends are physical ixtures of structurally different polyers or copolyers, which interact through secondary forces with no covalent bonding which are iscible at olecular level. The basis of polyer-polyer iscibility ay arise fro any specific interaction, such as hydrogen bonding, dipole-dipole forces or charge transfer interactions in the syste 3,4. Polyer blend iscibility has been studied widely with a nuber of techniques 5-9. review of literature suggested that no previous studies have been done on the iscibility of poly(vinylidene fluoride) (PVDF) and cellulose acetate (C) in diethyl foraide (DMF). Hence as a part of our research progra on polyer blends and solutions 10,11 iscibility behaviour of PVDF and C blends in DMF is presented in this paper. The choice of the polyers is due to their pharaceutical, bioedical and industrial applications 1,13. Further, it ay also be noted that the polyers containing polar groups with a susceptibility to act as proton donors were found to be iscible with those having a tendency to act as proton acceptors due to a specific interaction like hydrogen bonding. The structures of PVDF and cellulose acetate are shown in Fig. 1. RO ( O O OR O ) n OR R = H, C O CH 3 Fig. 1. Structures of poly(vinylidene fluoride) and cellulose acetate EXPERIMENTL Poly(vinylidene fluoride) (olecular weight, 75000; lfa esar) and cellulose acetate (olecular weight, 70000; lfa esar) were used as received. DMF (Merck) was distilled before use. Preparation of polyer solutions: Dilute solutions of % (w/v) PVDF and cellulose acetate in DMF were prepared separately in different stoppered conical flasks. Solutions of lower concentrations were then prepared by appropriately diluting these stock solutions with DMF. Siilarly different blend copositions of 10/90, 0/80, 30/70, 40/60, 50/50, 60/

2 Vol. 3, No. 4 (011) Miscibility of Poly(vinylidenefluoride) and Cellulose cetate lends in Diethylforaide , 70/30, 80/0, 90/10 ratio, along with the pure polyer solutions in DMF at nine concentrations between % (v/v) of the blends as well as pure coponents were prepared by ixing appropriate quantities of stock solutions of PVDF and cellulose acetate. Preparation of the blend fils: The blend solutions prepared as stated above were cast on clean Teflon dish. Fils were dried initially at roo teperature and were then kept in a vacuu oven at 40 ºC for 48 h to reove any residual DMF traces. The coplete reoval of DMF has also been confired by FTIR spectra of the fils. The absence of N-C=O bending and C-N stretching frequencies at 600 and 1300 c -1, respectively indicate the absence of DMF in the blend fil. Solution and solid state property easureents: The densities of individual and blend polyer solutions in DMF were easured with a Mettler Toledo Digital density eter odel Densito 30 PX. The teperature of the easureent was within an uncertainty of ± 0.1 ºC. The instruent was calibrated with standard density water supplied with the instruent. The estiated error in the density easureent was within ± 0.05 %. Dilute solution viscosities of PVDF, cellulose acetate and their blend solutions were easured at different teperatures using an Ubbelhode viscoeter with an accuracy of ± 0.1 %. Solution viscosities at different teperatures were deterined by equilibrating the viscoeter tube in a therostat aintained at a desired teperature for about 10 in before the flow tie easureent. The teperature of the bath was kept constant within an accuracy of ± 0.1 ºC. Ultrasonic velocity easureents were carried out on a fixed frequency continuous wave ultrasonic interferoeter (Model F81, Mittal Enterprises, New Delhi) operating at MHz using the standard procedure. The error in the easureent of ultrasonic velocity was within ± 0.1 %. Measureents at different teperatures were carried out by circulating water at required teperatures fro a therostatic bath, inside the double walled jacket covering the interferoeter cell. The accuracy of teperature aintenance was within ± 0.1 ºC. Measureents at different teperatures were carried out by circulating water at required teperatures fro a therostatic bath, inside the double walled jacket covering the interferoeter cell. The accuracy of teperature aintenance was within ± 0.1 ºC. The refractive index values of polyer solution were easured with a Mettler Toledo Refractoeter odel Refracto 30 GS. The uncertainty in the values was within ± units at all the teperatures. t least three independent readings of all the physical properties were taken for each ixture. The average of these values was used for the data analyses. FTIR, SEM: FTIR easureents of the polyblend fils were carried out at roo teperature using a Nicolet vatar 330 FTIR spectroeter. SEM iages of the blend fils were recorded on a Jeol Scanning electron icroscope. RESULTS ND DISCUSSION Solution property studies: Viscosity of the blend solutions were easured at 303, 313 and 33 K for different C/PVDF blend copositions at ratios of 10/90, 0/80, 30/70, 40/60, 50/50, 60/40, 70/30, 80/0, 90/10 along with the pure polyer solutions in DMF at seven concentrations, naely, % (v/v) of the blends as well as pure coponents. Density, refractive index and ultrasonic velocity of the polyer solutions were easured at three different teperatures indicated above for all the C/PVDF copositions at a concentration of % (v/v). Fro viscosity data, relative and reduced viscosities of the polyer solutions have been calculated and plotted against coposition/solution concentration (Figs. and 3).The plot of relative viscosity versus blend coposition (Fig. ) was linear for the entire coposition range. This behaviour is a characteristic of a iscible blend syste The plots of reduced viscosities of the coponent polyers and their blend copositions versus concentrations at different teperatures (Fig. 3) were also linear without any cross over indicating that the blends are copletely iscible. sharp cross over in the plots of reduced viscosity versus concentration is generally shown by iiscible blends. Relative viscosity % Weight of C Fig.. Relative viscosity versus coposition of C/PVDF blends at 303 K Fig. 3. Reduced (dl/g) C C/PVDF (80:0) C/PVDF (60:40) C/PVDF (50:50) C/PVDF (40:60) C/PVDF (0:80) PVDF Concentration (g/dl) Reduced Viscosity of C/PVDF blends at 313 K The interaction paraeter of the coponent polyers and their blend copositions have been obtained fro the plots of the reduced viscosity versus concentration and are given in Table-1. The slope of the curve gives the corresponding interaction paraeter value, which has been evaluated on the basis of classical Huggins equation 17,18. Krigbau and Wall 14 interaction paraeter b of the blends has been obtained fro the difference between the experiental and theoretical values of the interaction paraeters b 1 and b 1. Polyer 1-polyer interaction paraeter b can be calculated as follows:

3 1476 Kuar et al. sian J. Che. TLE-1 INTRINSIC VISCOSITY ND SLOPE OF REDUCED VISCOSITY VERSUS CONCENTRTION PLOTS OF CELLULOSE CETTE/ POLY(VINYLIDENE FLUORIDE) LENDS ND INDIVIDUL SOLUTIONS T DIFFERENT TEMPERTURES Cellulose acetate/ fluoride) (v/v) at 303 K curve at 303 K at 313 K curve at 313 K at 33 K curve at 33 K 0/ / / / / / / ( η sp C ) = ( η) + b where C = total concentration of polyers C 1 + C, (η sp ) is the specific viscosity and b represents the global interaction between all polyeric species defined by the equation, C (1) b = X 1 b 11 + X 1 X b 1 + X b () where X 1 and X weight fractions of polyer 1 and polyer, respectively, b 1 is the interaction paraeter of the blend syste which can be calculated fro eqn. and b 11 and b are respective individual interaction paraeters. The interaction paraeters b 11, b and b have been calculated fro the slopes of the plot of reduced viscosity versus concentration 16. The interaction paraeter b 1 was then calculated theoretically by using equation, b 1 = (b 11b ) 1/ (3) The difference ( b) calculated fro the theoretical b 1 fro eqn. 3 and the experiental b 1 with eqn. is given as, b = (b 1 - b 1 ) (4) If b > 0, blends are iscible and if b < 0 phase separation occurs. It has been found that b values are positive (Table-) for all blend copositions and at all studied teperatures. This suggests that the blends are iscible in the studied range. If η 1 and η are sufficiently apart, a ore effective paraeter µ, defined by Chee et al. 7 can be used to predict the copatibility. The relation is given by, b µ = (5) ( η η1) TLE- b ND k VLUES FOR THE CELLULOSE CETTE/ POLY(VINYLIDENE FLUORIDE) LENDS T DIFFERENT TEMPERTURES Cellulose acetate/ 303 K 313 K 33 K fluoride) (w/w) b k b k b k 0/100 0/ / / / / /0 where η 1 and η are intrinsic viscosities of pure coponent solutions. The blend is iscible when µ 0 and iiscible if µ < 0. The values of µ, calculated with aforeentioned expression at different teperatures for the present syste have been presented in Table-3. The results show that the µ values for the syste under study are all positive and sufficiently high, indicating the iscibility of the blends. High value of µ ay also be due to specific interaction of hydrogen bonding between the polyers. TLE-3 µ ND α VLUES FOR THE CELLULOSE CETTE/ POLY(VINYLIDENE FLUORIDE) LENDS T DIFFERENT TEMPERTURES Cellulose acetate/ 303 K 313 K 33 K fluoride) (w/w) µ α µ α µ α 0/100 0/ / / / / /0 Recently, Sun et al. 19 have suggested a new forula for the deterination of polyer iscibility as follows: K1[ η1] W + K1K [ 1[ W1 W α = K (6) {[ 1W1 + [ W } where, K 1, K and K are the Huggins's constants for individual coponents 1 and and the blend, respectively. The longrange hydrodynaic interactions are considered while deriving this equation. They have also suggested that a blend will be iscible when α 0 and iiscible when α < 0. The α values for the present syste at various teperatures have been listed in Table-3. The positive values at all teperatures indicate that the blends are iscible. Further, we have also carried out calculations to identify the iscibility of blends based on Huggins 17 constant. The Huggins constant is a paraeter which also could be used to express the interaction between unlike polyers 0. The k value was concerned with b as shown in the equations and b k k [ [ = (7) b (bw + bw ) = (8) [ [ W W

4 Vol. 3, No. 4 (011) Miscibility of Poly(vinylidenefluoride) and Cellulose cetate lends in Diethylforaide 1477 The factor k, is a theoretical value derived fro the geoetric eans of k and k as 0.5,t (k k ) k = (9) The deviation fro the theoretical value also provides inforation about the interaction between unlike polyers as shown in k = k k (10), theoretical The positive k value indicates that the polyer ixture in solution-state is iscible. Table- shows the k values for present syste, which are positive for all the copositions up to 33 K indicating the iscibility of the blends in this teperature range 9. The heat of ixing ( H ) was also used as a easure to study the blend copatibility 1-3. ccording to Schneier, H of the polyer blends is given by 1/ W H = W1M 1ρ1( δ1 δ ) Mρ + (1 W 1) M1ρ1 (1 W ) (11) where W, M and ρ are the weight fraction of the polyer, the onoer olecular weight and the polyer density, respectively and δ represents the solubility paraeter of the polyer. The δ values of poly(vinylidene fluoride) [13.6 (cal/c 3 ) 1/ ] and cellulose acetate [1. (cal/c 3 ) 1/ ] were taken fro the literature 4 and these values were used to calculate H with eqn. 11. Fig. 4 shows the variation of H versus blend coposition. It is evident fro the figure that the variation follows alost a linear pattern, without any reversal (increase followed by decrease or vice-versa) in the trend. This behaviour further confirs that the blend solutions are iscible in the studied range of copositions and teperature. Further, the heat of ixing calculated at different teperatures did not vary significantly and in fact, as is seen in the Fig. 4, the H values for various teperatures are alost overlapping. This behaviour shows that the effect of teperature on iscibility of the blends is not very significant. Heat Heat of of ixing ( H, KJ) KJ) K % Weight of of C C Fig. 4. Heat of ixing of C/PVDF blends at different teperature To confir the iscibility behaviour of the blends further, the ultrasonic velocity, adiabatic copressibility, density and refractive index values of the blend solutions have been easured at five different teperatures. diabatic copressibility has been calculated by using the forula, β ad 1 = ν ρ (1) where ν = ultrasonic velocity and ρ = density. Ultrasonic velocity, adiabatic copressibility, density and refractive index of the blend solutions have been plotted against blend copositions at different teperatures (Figs. 5-7) and they are found to be linear. For incopatible blend solutions, these plots are non-linear showing distinct phase inversion at interediate copositions. Hence these results provide further supporting evidence for iscible nature of the studied blends in the entire coposition range. The iscibility ay be due to the presence of interolecular interactions such as hydrogen bonding between the blend polyers. Ultrasonic velocity (/sec) (/s) Ultrasonic velocity diabatic copressblity 4.9x10-10 diabatic copressibility copressblity (kg (kg 1 s -1 s ) ) x %% Weight of C Fig. 5. Ultrasonic velocity and adiabatic copressibility versus coposition of C/PVDF blends at 303 K Density (Kg/ 3 ) 3 ) Fig K % Weight of of C C Effect of teperature on the variation of density with the coposition of 1 % w/v of C/PVDF blend in solution FTIR spectroscopy: To confir the presence of hydrogen bonding in the blends and hence the iscibility of blends in the solid state, FTIR spectra of the individual and blend polyer fils have been easured at roo teperature. lthough the changes in energies, bond lengths and electron densities with the foration of hydrogen bonds are actually quite sall and about two to three orders of agnitude saller than typical cheical changes, FTIR spectroscopy is very sensitive to the foration of hydrogen bond 5-7. If the groups involved in the hydrogen bond foration in a blend syste

5 1478 Kuar et al. sian J. Che. Refractiveindex index ηη d Refractive d K % Weight Weight of of CC % 100 Fig. 7. Effect of teperature on the variation of refractive index with the coposition of % w/v of C/PVDF blend in solution at different teperatures are carbonyl and hydroxyl oieties, then the vibration frequencies of both the groups are expected to show a red shift due to hydrogen bond foration copared to the non-interacting group frequencies. In the present case, the carbonyl frequency of pure PVDF at 1735 c-1 decreased to 173 c-1 in the 50:50 C/PVDF blend indicating the foration of a weak hydrogen bond between coponent polyers, which can contribute to the iscibility of the blends. This enhanceent in the -OH stretching frequencies ay be attributed to the presence of intra and interolecular hydroxyl-hydroxyl as well as hydroxylo-hydrogen bonding interactions in cellulose acetate which occurs at lower frequencies (3469 c-1) and the sae being changed to interolecular hydroxyl-carbonyl hydrogen bonding interactions in the blend syste. Siilar observations have also been reported in the case of iscible blends of polyvinyl alcohol and polyvinyl pyrrolidone. Hence the FTIR spectral results also coplient the results obtained by solution studies, ascertaining the presence of specific interactions and iscibility of the of the blend syste studied6-8. SEM Study: Fig. 8 shows SEM iages of 50:50 C/PVDF blend. s can be seen fro the iages, the blend exhibits unifor orphological features without any phase separation or aggregation indicating the iscibility of the blend5,9. Conclusion The iscibility behaviour of PVDF and cellulose acetate blends in DMF has been studied in the teperature range K. The iscibility has been analyzed by solution viscosity, ultrasonic velocity and refractive index easureent of the blend solutions and calculating various interaction paraeters based on these data. The results indicated that the blends are iscible in the entire coposition range between K. The FTIR study of the blend fils also indicated the presence of weak specific interactions supporting the results of solution studies. The SEM iages of the blend fil showed unifor orphological features indicating coplete blend iscibility. Fig. 8. SEM iages of 50:50 C/PVDF blend: () low agnification and () high agnification REFERENCES D.R. Paul and S. Newan, 1978, Polyer lends, Vols. 1 and, New York (1981). H. Thopa, Polyer Solutions, utterworth Scientific, London (1956). M.M. Colean, J.F. Graf and P.C. Paiter, Specific Interactions and the Miscibility of Polyer lends, Technoic, Lancaster (1991). D.F. Varnell, J.P. Runt and M.M. Colean, Polyer, 4, 37 (1983). Y. Liu and M.C. Messer, J. Phys. Che., 107, 9774 (003). X. Zhang, D.M. Kale and S.. Jenekhe, Macroolecules, 35, 38 (00). K.K. Chee, Eur. Poly. J., 6, 43 (1990). R. Paladhi and R.P. Singh, Eur. Poly. J., 30, 51 (1994). U.S. Toti and T.M. inabhavi, J. Mebr. Sci., 8, 199 (004). D.K. hat and M. SelvaKuar, J. Poly. Environ., 14, 385 (006). M. Selvakuar and D.K. hat, Indian J. Che. Technol., 14, 57 (007). T. Ishikiriyaa and M. Todoki, J. Poly. Sci. : Poly. Phys., 33, 791 (1995). C.. Herold, K. Keil and D.E. runs, ioche. Pharacol., 38, 73 (1989). W.R. Krigbau and F.T. Wall, J. Poly. Sci., 5, 505 (1950). G.R. Williason and. Wright, J. Poly. Sci., 3, 3885 (1965). G.V. Thoas and G. Nair, J. ppl. Poly. Sci., 6, 9 (1996). M.L. Huggins, J.. Che. Soc., 64, 716 (194). Y.P. Singh and R.P. Singh, Eur. Poly. J., 19, 535 (1983). Z. Sun, W. Wang and Z. Fung, Eur. Poly. J., 8, 159 (199). P.D. Hong, H.T. Huang and C.M. Chou, Poly. Int., 49, 407 (000). P.J. Flory, Principles of Polyer Cheistry, Cornell University Press, New York (1953)..O. Schneier, J. ppl. Poly. Sci., 17, 175 (1973). S. Krause, J. Macrool. Sci. Poly. Rev., 7, 51 (197). J. randrup, E.H. Iergut and E.. Grulke, Polyer Handbook, Wiley Interscience, New York (1999). D.J. Hourston and D. Hughes, Polyer, 19, 535 (1978). Y. He,. Zhu and Y. Inoue, Prog. Poly. Sci., 9, 101 (004). M.M. Colean and P.C. Painter, Prog. Poly. Sci., 0, 1 (1995). Q. Guo, J. Huang and X. Li, Eur. Poly. J., 3, 43 (1996). V. Rao, P.V. shokan and M.H. Shridhar, Polyer, 40, 7167 (1999).