Bantjes, A.

Froehling, P.E.

Koenhen, D.M.

Smolders, C.A.

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Swelling of linear polymers in mixed swelling agents: predictability by means of solubility parameters

University of Twente Research Information

[ Notes to the Editor Swelling of linear polymers in mixed swelling agents; predictability by means of solubility parameters P. E. Froehling, D. M. Koenhen, A. Bantjes and C. A. Smolders Laboratory for Macromoleculer Chemistry, Twente University of Technology, PO Box 217, Enschede, The Netherlands (Received 26 March 1976; revised 19 May 1976) INTRODUCTION The solubility behaviour of polymers can be predicted to a reasonable ex- tent by applying the Hildebrand rela- tion I which connects the energy of mixing of two compounds to their individual energies of vaporization: - V(61 - 62 )  2 (1 )  ~bl~b 2 where ~ m i x  is the energy of mixing; (I) 1 andS2, the volume fractions of the components; V, the total volume of one mole of the mixture and 51, 62, the Hildebrand solubility parameters of both components, defined by: 6 = (cohesive energy density) 1/2 k V m ]  (2) where z2tEva p is the energy of vapor- ization and Vm is the molar volume. From equation (1) it is clear that a smaller difference in 6 between two compounds results in a diminished energy of mixing. A decrease in 2XEmi x gives a higher degree of swelling and eventually complete solubility may result. The applicability of equation (1) has been extended by Hansen 2, who divided the solubility parameter into contributions from disperse (6d), dipole (6p) and donor/acceptor or hydrogen-bond (6h) interactions, and represented 6 as: (3) which may be taken as a vector sum. It is possible to express each of the solubility parameter components for a mixture of two solvents as: 6m,iW-d~lSl,i+~262,i; i=d,p, h (4) This relation can be used only when there are no specific interactions upon mixing, since these interactions (e.g. additional donor/acceptor interactions) do not obey the geometric mean rule. The values of the components of 8 have been reported for numerous com- pounds, and methods to calculate them from other physico-chemical properties of solvents and polymers are progress- ing rapidly 3. The often encountered enhanced interaction of polymers with solvent pairs can be explained by the vector concept of the solubility parameter, of which a representation is given in Figure 1. The affinity of a solvent mixture X (on the line A-B)  with respect to a polymer is inversely proportional to its distance to P, the location of the poly- mer in the 5d, 8p, 8 h space. It is evi- dent that for the given spatial con- figuration of A, B and P there exists a point M at which the energy of mix- ing is at a minimum and swelling should reach a maximum. The appli- cation of the solubility parameter con- cept to the interaction of polymers with solvent mixtures has been con- fined up to now to qualitative aspects of the solubility of linear polymers 2'4 and the swelling behaviour of cross- linked elastomers s. We wish to report here on the application of the same concepts to the swelling of linear poly- mers by swelling agent/non-solvent mixtures. The systems studied are shown in Table 1. Toluene, trichloroethylene and n-butyl acetate are well-known swelling agents for poly(vinyl chloride), while methanol and nitromethane are strict non-solvents 2. For the combina- tion n-butylacetate/nitromethane a deviating behaviour may be expected, as these solvents show mutual inter- action on account of their respective electron donating and accepting char- acter 6. The other two solvent pairs do not show specific interactions which may cause deviations. EXPERIMENTAL Poly(vinyl chloride), Breon S 110/10 (BP Ltd), was a very pure preparation according to i.r. spectrum and elemen- tary analysis. From gel permeation chromatography (solvent tetrahydro- furan, stationary phase Styragel-Waters Associates) the molecular weight dis- tributionwas calculated as 7 ~ / ~ n  = 28 000, Mw = 56 000 using calibration samples of PVC from Pressure Chemi- cal Co. All solvents were analytical grade quality. PVC films were cast from a 15% so- A 6 h Figure I Spatial representation of solvent mixture/polymer interaction Table I Solubil i ty parameters of PVC and solvents. Values are taken from ref 3 Compound 6 d 6 0 6 h PVC 9.15 4.9 1.5 Toluene 8.82 0.7 1.0 Trichloroethylene 8.78 1.5 2.6 n-Butylacetate 7.67 1.8 3.1 Nitromethane 7.70 9.2 2.5 Methanol 7.42 6.0 10.9 POLYMER, 1976, Vol 17, September 835 Notes to the Ed i t o r  lution in tetrahydrofuran. The dry films (about 0.5 mm thick) was cut into pieces o f " 2 0 0  mg. The pieces were immersed in the solvent mixtures, and (after rapid blotting with filter ~: 0.6 paper) weighed after 2, 6 and 20 h .~ immersion. Ecluilibrium was attained ~ 0.4 after 6 h at 20~C. All experiments were carried out in triplicate. ~. 0.2 O RESULTS The results of the swelling experiments are plotted in Figures 2 - 4 ,  together with the calculated polymer/solvent distances in the ~ space: a = [(gp.s  - ap~,)2 + ( g a s  - ga.p) + (gh.S -- gh.p)2] 1/2 (5) where the subscripts S and P refer to solvent and polymer respectively. Values of 8 were taken from Koen- hen 3. The values of the solvent mix- tures were calculated according to equation (4). It is clear that for the solvent pairs toluene/methanol and tri, chloroethylene/nitromethane which do not show donar/acceptor interactions upon mixing, the maximum in the swelling curve coincides with the calcu- lated composition at which the distance in g-space is minimal. The magnitude of the relative increase in swelling with relation to the pure solvents appears to be proportional to the calculated de- crease in A. It should be pointed out that the g values for PVC as given by Hansen 2 re- sult in a poorer agreement between the calculated and measured extreme values of A and degree of swelling. In the case of the donor/acceptor solvent pair Figure 2 Calculated interaction parameter A and measured relative weight increase of PVC in toluene/methanol mixtures IO 5 ._c "~ 6 3<1 Cn .~ 4 2 121 o o'.5 ~.o Volume fraction nitromethan¢ Figure 3 Calculated interaction parameter A and measured relative weight increase of PVC in trichloroethylene/nitromethane mixtures IO 6 4 ~ - 5 6 ~ 4 i m 3- 3< I  -~ 2 2 g ' "I 0 0 5  I'O Volume fraction nitromethan¢ Figure 4 Calculated interaction parameter A and measured relative weight increase of PVC in n-butylacetate/nitromethane mixtures n-butyl acetate/nitromethane no maxi- mum occurs in the swelling curve, con- trary to expectation. Caution should therefore be exer- cised in the application of the solubility parameter concept in mixtures of sol- vent which may interact through donor/ acceptor forces. ACKNOWLEDGEMENT The g.p.c, measurements were carried out by G. van de Ridder. REFERENCES 1 Hildebrand, J. H. and Scot~, R. L. 'The Solubility of Non-Electrolytes', Dover, New York, 1949 2 Hansen, C. M. J. Paint Technol. 1967, 39, 104 3 Koenhen, D. M. and Smolders, C. A. J. Appl. Polym. Sci. 1975, 19, 1163 4 Chen, S. A. J. Appl. Polym. Sci. 1971, 15, 1247 5 Beerbower, A. and Dickey, J. R. ASLE Trans. 1969, 12, 1 6 McClellan, A. and Pimental, G. 'The Hydrogen Bond', Freeman, San Francisco, 1960 7 Evans, J. M. Polym. Eng. Sci. 1973, 13, 401 8 Cardenas, J. N. and O'DriscoU, K. F. J. Polym. Sci. (Polym. Lett. Edn) 1975, 13, 657 A method for the calculation of optimum filler content in amorphous and semi- crystalline polymers S. C. Shea* OeDartmen t of  Polymer and Fibre Science, University of  Manchester Institute of Science and Technology, Manchester, UK (Received 22 March 1976; revised 13 May 1976) INTRODUCTION Currently more and more additives are being used in polymers, particu- larity the polyolefins. These additives include f'fliers, flame retardants, pig- * Present Address: Van Leer Research Laboratories, Passfield, Hampshire, UK ments etc. Consequently, it is desir- able to be able to predict the concen- tration of additive above which the mechanical properties significantly deteriorate. This communication de- tails a method of calculating an opti- mum f'flier concentration using prin- ciples well known in the surface coat- ing industry. While this proposed tech- nique will be illustrated using high den- sity polyethylene, it is thought that since the equations presented here are of a general nature, they may be more widely applicable. Of the many tests available elongation at break is prob, ably the most sensitive and will be used here to compare experimental results with theory. THEORY Consider a polymeric material to which 836 POLYMER,  1976, Vol 17, September 

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Swelling of linear polymers in mixed swelling agents:predictability by means of solubility parameters

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Swelling of linear polymers in mixed swelling agents; predictability by means of solubility parameters

Swelling of linear polymers in mixed swelling agents; predictability by means of solubility parameters

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