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Asian Journal of ChemistryVol. 21, No. 9 (2009), 7279-7283
Acoustical Studies on Hydroxypropyl Methylcellulose in
Alcohols and Methylene Chloride Mixture
K. RAJU* and C. RAKKAPPAN†
Department of Physics, Sri Venkateswara College of Engineering, Sriperumbudur-602 105, India
E mail: rajusvce@gmail.com
Ultrasonic velocity, viscosity and density for the solutions of
hydroxypropyl methyl cellulose (HPMC) in propan-1-ol, butan-1-ol,
pentan-1-ol and hexan-1-ol with methylene chloride (1:1) mixtures were
measured at 303 K. From the experimental data observed as a function
of concentration, various acoustical parameters such as, adiabatic com-
pressibility, internal pressure, intermolecular free length, free volume
and solvation number were calculated. The results are interpreted in
terms of molecular interactions occurring in the solutions.
Key Words: Ultrasonic velocity, Adiabatic compressibility, Polymer-
polymer interactions, Solvation number, Hydroxypropyl methyl
cellulose.
INTRODUCTION
Ultrasonic studies in polymer solutions and in solid polymer have been a subject
of extensive research activity in recent years1-4. It is also found that ultrasonic velocity
together with density and viscosity studies throw more light on the polymer-solvent
interactions5-7. Hydroxypropyl methyl cellulose (HPMC) is chosen for the present
investigation because of its great importance in various industrial applications.
Hydroxypropyl methyl cellulose are widely used in food, cosmetic and other daily
use chemical lines.
Hydroxypropyl methyl cellulose (HPMC) are mainly used as an adhesive and
coating film in tablets, increasing markedly rate of dissolution and release and
strengthen water proof for tablets and also used as a mixed dispersing agent. Tablets
coated with HPMC exhibit poor dissolution. Hydroxypropyl methyl cellulose
(HPMC) may be dispersed or wet with organic solvents such as alcohols. Hence, it is
planned to study the behaviour of the solutions of HPMC in alcohols with methylene
chloride mixture. In the present paper, the authors have reported the results of density,
viscosity and ultrasonic velocity studies of the solution of HPMC in methylene
chloride and alcohols (propan-1-ol, butan-1-ol, pentan-1-ol and hexan-1-ol) 1:1 mixture
at 303 K as a function of polymer concentration.
†Department of Physics (DDE), Annamalai University, Annamalai Nagar-608 002, India.
EXPERIMENTAL
The commercially available hydroxypropyl methyl cellulose (HPMC) (ca. MW
13000) was obtained from Fluka Company. The alcohols and methylene chloride
were obtained from BDH Company. They were used after standard purification8,9.
The HPMC + alcohol + methylene chloride solutions were prepared by adding
a known weight of polymer (HPMC) to a fixed volume of solvents viz., alcohols
and methylene chloride (1:1) and then stirring under reflux using a magnetic stirrer,
until a clear solution was obtained. Due to its high viscous nature, the low concentration
range of polymer were studied i.e., 0 to 0.5 % (weight %). 0.0 % corresponds to
alcohol and methylene chloride (1:1) mixture.
The ultrasonic velocity was measured using a Pulse echo interferometer (10 MHz)
by the standard procedure10. Accuracy in the measurement of the velocity is 0.01 %.
The density and viscosity of these solutions were measured using specific gravity
bottle and an Ostwald's viscometer, respectively. All the measurements were carried
out at 303 K.
Theory
From the measured values of density (ρ), viscosity (η) and ultrasonic velocity
(U) the following acoustical parameters were calculated.
The adiabatic compressibility (βad) has been calculated using the relation
βad = [U2ρ]-1
where, ρ is the density of the solution and U is the ultrasonic velocity of the solution.
The intermolecular free length (Lf) has been calculated using the formula
Lf = KT [βad]1/2
where, KT is a constant for different temperatures known as Jacobson constant11.
The internal pressure (πi) is calculated using the formula12
πi = bRT [Kη/U]1/2[ρ2/3/Meff7/6]
where b stands for the cubic packing factor which is assumed to be 2 for all liquids
and solutions, K, the temperature independent constant (4.28 × 109), R, the gas
constant (8.3143 J K-1 mol-1), T, the absolute temperature and Meff is the effective
molecular weight of the solution.
The free volume (Vf) was calculated by using the relation13,
Vf = [Meff U/Kη]3/2
where, the symbols have their usual meaning.
The solvation number, the number of solvent molecules taking part in solvation
of a repeat unit was calculated by using the Passynsky equation14,
Sn = [m/mo][1-(β/β0)][(100-x)/x]
where β and β0 are the adiabatic compressibility of polymer solution and the solvents
respectively, m and m0 are the molecular weight of the polymer repeat unit and the
solvent respectively and x is the weight of the polymer in 100 g of solution.
Then these parameters are correlated with concentration (c).
7280 Raju et al. Asian J. Chem.
RESULTS AND DISCUSSION
The solution property parameters namely, density (ρ), viscosity (η) and ultrasonic
velocity (U), adiabatic compressibility, internal pressure, intermolecular free length,
free volume and solvation number for HPMC in alcohols and methylene chloride
(1:1) mixtures at 303 K are presented in the Table-1.
TABLE-1
VARIATION OF ULTRASONIC VELOCITY AND RELATED PARAMETERS WITH
CONCENTRATION OF HRDROXYPROPYL METHYLCELLULOSE (HPMC) IN
ALCOHOLS AND METHYLENE CHLORIDE (1:1) MIXTURES AT 303 K
Conc.
(wt %) U
(ms-1) ρ
(kg m-3) η × 103
(Nsm-2) βad × 1010
(N-1m2) Lf (Å) πi × 10-6
(pascal)
Vf × 108
(m3 mol-1)
Sn × 10
HPMC in propan-1-ol + methylene chloride (1:1)
0.0 1074.8 0960.1 00.644 9.0160 0.600 0505.06 15.330 -
0.1 1080.6 0980.7 01.260 8.7320 0.591 0738.46 05.653 13.04
0.2 1081.3 1000.2 02.807 8.5500 0.584 1115.71 01.703 09.26
0.3 1082.5 1016.2 03.568 8.3970 0.579 1269.33 01.191 08.19
0.4 1085.4 1030.6 07.022 8.2360 0.573 1793.79 00.433 07.74
0.5 1087.1 1041.5 10.103 8.1240 0.570 2163.32 00.252 07.07
HPMC in butan-1-ol + methylene chloride (1:1)
0.0 1090.2 0984.0 00.706 0.8550 0.584 0496.49 15.626 -
0.1 1096.4 0995.9 01.413 8.3520 0.578 0705.44 05.575 07.58
0.2 1097.6 1012.6 02.247 8.1970 0.572 0898.26 02.788 06.77
0.3 1100.0 1032.1 04.269 8.0070 0.565 1251.61 01.069 06.94
0.4 1102.8 1036.2 07.818 7.9350 0.563 1694.69 00.433 05.89
0.5 1105.7 1048.2 10.710 7.8030 0.558 1994.74 00.271 05.78
HPMC in pentan-1-ol + methylene chloride (1:1)
0.0 1118.0 0993.6 00.780 8.0520 0.567 0479.29 15.461 -
0.1 1122.6 1004.4 01.575 7.9000 0.562 0683.68 05.435 05.81
0.2 1124.2 1021.2 02.412 7.7480 0.556 0854.35 02.877 05.80
0.3 1125.4 1039.3 04.401 7.5969 0.551 1166.18 01.170 05.79
0.4 1128.0 1051.6 08.110 7.4730 0.546 1592.69 00.469 05.52
0.5 1129.6 1056.6 11.303 7.4170 0.544 1883.45 00.286 04.84
HPMC in hexan-1-ol + methylene chloride (1:1)
0.0 1150.8 1024.4 00.871 7.3700 0.542 0479.19 14.812 -
0.1 1155.6 1042.9 01.424 7.1800 0.535 0618.10 07.143 07.55
0.2 1158.3 1050.9 02.540 7.0920 0.532 0828.29 03.011 05.52
0.3 1160.5 1052.8 03.809 7.0530 0.531 1013.90 01.645 04.19
0.4 1161.9 1053.3 08.441 7.0320 0.530 1507.56 00.499 03.34
0.5 1165.7 1056.9 13.386 6.9630 0.527 1898.39 00.252 03.22
From the Table-1, it has been observed that all the four systems are behaving in
a similar manner for all the concentrations. It can be seen that all these parameters
except adiabatic compressibility, intermolecular free length, free volume and solvation
Vol. 21, No. 9 (2009) Acoustical Studies on Hydroxypropyl Methylcellulose 7281
number are found to increase with increase of concentration of polymer. The adiabatic
compressibility of the polymer solutions decreased with concentration and the remai-
ning parameters intermolecular free length, free volume and solvation number also
show the same dependency.
In all the 4 systems studied, the velocity is gradually increasing with concen-
tration at room temperature. The increase in velocity with polymer concentration
in alcohols with methylene chloride is due to the interaction between polymer and
solvent molecules. At lower concentrations, the interaction is between the polymer
and the solvent molecules. As the concentration increases, one macromolecule may
influence another indirectly by way of mutual interaction. In more concentrated
solutions and bulk polymers, direct segment-segment interaction will exist15. This
vander Wall's interaction causes association between the molecules of HPMC and
alcohols in the lower concentrations and in the higher concentrations, in addition to
polymer-solvent interactions, polymer-polymer interaction may be responsible for
the increase in ultrasonic velocity16.
The rapid decrease in adiabatic compressibility with increase of concentration
in alcohols with methylene chloride systems clearly indicates the formation of a more
number of tightly bound systems. Since the velocity increase with concentration
and the density does so, the compressibility must decrease with concentration. This
could be caused by more rigid liquid structure associated with hydrogen bonding
of HPMC with alcohols. Such reductions in compressibilities have been found in
the solutions of cellulose derivatives which are attributed to change in compressi-
bilities of the solvent molecules concerned in solutions17. This implies the increase
of density with concentration, which leads to a decrease in compressibility.
At lower concentrations, the number of hydrogen bonds formed may be less
and at higher concentrations, it may be more due to polymer-polymer interactions.
In the polymer solutions, the hydrogen bond is formed between the hydrogen of the
methyl group in HPMC and the oxygen of hydroxyl group in alcohols18. At lower
concentrations of HPMC in alcohols with methylene chloride mixtures, the mole-
cules are not closer and thus the intermolecular free length will be high. As the
concentration increases, the molecules come closer through segment-segment inter-
action and thereby decreasing the intermolecular free length19.
As it is known that the internal pressure is increased in hydrogen bonded systems20,
the internal pressure increases with increase of concentration for all the four systems.
This increased internal pressure and decreased intermolecular free length confirms
the formation of hydrogen bonding between polymer and alcohols and the interaction
between polymers at higher concentrations. Thus an increase in internal pressure
and decrease in free volume suggest that there is a strong cohesive force between
the molecules21.
The solvation numbers decreased with increase in polymer concentration indica-
ting the increased polymer-polymer interaction with concentration. Higher solvation
numbers obtained at lower concentrations of HPMC may be due to the presence of
7282 Raju et al. Asian J. Chem.
interactions between the polymer and the solvent molecules. The lower solvation
number values obtained at higher concentrations may be due to the lesser interac-
tion with the solvent caused by the larger size of the repeat unit and also due to the
higher molecular weight of the sample used. This observation is again in line with
the previous results22.
Thus, on the basis of experimental findings it is concluded that, as the concen-
tration of HPMC increases, in all the four systems, the motion of HPMC molecule
is affected by the mutual interaction between the macromolecules and solvent mole-
cules in one hand and the interaction between one macromolecule with another.
The first type of mutual interaction is termed as hydrodynamic screening, which is
significant in determining the viscous flow properties of dilute polymer solutions.
In more concentrated solutions direct segment-segment interaction may exist. Thus,
in low concentrations HPMC and solvent interaction dominates whereas in higher
concentrations HPMC-HPMC interaction exists.
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(Received: 2 March 2009; Accepted: 21 August 2009) AJC-7763
Vol. 21, No. 9 (2009) Acoustical Studies on Hydroxypropyl Methylcellulose 7283
