Iraqi Journal of Chemical and Petroleum Engineering 

 Vol.13 No.2 (June 2012) 29- 36 

ISSN: 1997-4884 

 

 

 

 

Effect of Annealing on the Crystallization of Poly Vinyl Chloride for 

Drug Delivery System 

 
Basma A. Abdul-Majeed, Hussain K. Hussain and Nagam A. Kafel Al-Sultanee 

Chemical Engineering Department, College of Engineering, University of Baghdad 

 

Abstract 

Poly vinyl alcohol has been studied for its ability to form crystallites by using 

annealing method. Semicrystalline films of poly vinyl alcohol (PVA) were prepared 

by casting 11.5 wt. % and 13 wt. % PVA aqueous solution onto glass slides at 

annealing temperature range 90 -120°C and duration time 15- 60 minute. This 

allowed the macromolecules to form crystallites, small regions of folded and 

compacted chains separated by amorphous regions where single PVA chain may pass 

through several of these crystallites. Degree of crystallinity of PVA films (hydrogels) 

was determined by method of density; on the other hand the swelling behavior was 

conducted by the determination of water uptake, wet degree of crystallinity, gel 

fraction and solubility. The results of PVA films showed that water uptake decreased 

with increasing temperature, time of annealing and PVA concentration, while degree 

of crystallinity increased, and gel fraction and solubility decreased with increasing 

temperature and time of annealing. The maximum dry and wet degree of crystallinity 

was 64% and 36% respectively at 120°C and 60 min. 

 

Key words: poly (vinyl alcohol)–annealing–swelling- crystallinity. 

 

Introduction 

Advances in polymer science have 

opened up possibilities for using a 

wide variety of polymeric materials as 

drug delivery systems. Biodegradable 

polymers, by virtue of their ability to 

degrade in the body naturally, offer 

enormous advantages over 

conventional drug delivery systems 

[1,2]. It eliminated the need for surgery 

and also does not elicit any adverse 

reactions from the body. Polymeric 

drug delivery systems are mainly 

intended to deliver the drug over a 

period of time. Some of the materials 

that are currently being used/studied 

for controlled drug delivery include 

poly methyl methacrylate, poly vinyl 

alcohol, polyacrylamide, polyethylene 

glycol, polylactic acid, polyglycolic 

acid, polylacticglycolic acid, and 

polyanhydrides [3]. Hydrogels of 

polymer are gaining increasing 

popularity in the area of controlled-

release drug delivery. These polymers 

are generally glassy in the dehydrated 

state but swell to become an elastic gel 

upon water penetration. The entrapped 

drug within the swelling matrix 

concomitantly dissolves and diffuses 

through the swollen network into 

surrounding aqueous environment. The 

rate of drug release from hydrogels is 

regulated by cross-linking density and 

the extent of swelling [4]. Poly vinyl 

Iraqi Journal of Chemical and 

Petroleum Engineering 

 

University of Baghdad 

College of Engineering 



Effect of Annealing on the Crystallization of Poly Vinyl Chloride for Drug Delivery System 

 

30                                        IJCPE Vol.13 No.2 (June 2012)               -Available online at: www.iasj.net 
 

alcohol (PVA) is a hydrophilic 

polymer with unique properties. It 

absorbs water, swells easily and it has 

extensively been used in controlled 

release applications [5]. Several 
methods have been explored to form 

semicrystalline PVA for use in 

biomedical applications. One early 

method studied by Peppas [6] explored 

crystallization by a slow dehydration 

process. Peppas et al. [7] studied 

formation of crystallites by a freeze-

thaw process. Thin amorphous films of 

PVA were frozen for 8 h at -20°C and 

then thawed for 4 h at 25°C. This cycle 

was repeated several times. They 

showed that as the number of freeze-

thaw cycles increased the stability of 

the crystallites during swelling 

increased. However, the total number 

of crystals in the hydro gel did not 

necessarily increase with increased 

freeze-thaw cycles. They also added 

PEG [8] to hydro gels formed by the 

freeze-thaw process, and showed that 

the resulting hydro gels exhibited 

increased stability during swelling. 

Other studies have used a combination 

of cross-linking and crystallization 

techniques to probe the characteristics 

of PVA hydro gels under various 

crystallization and swelling conditions. 

Mallapragada and Peppas [9] studied 

the effect of swelling on the crystalline 

regions of PVA hydro gels. The PVA 

networks were created by first cross-

linking aqueous solutions of PVA 

using electron-beam irradiation, 

followed by annealing to form 

crystallites. Using IR spectroscopy to 

compare the crystallinity before and 

after swelling, they showed that the 

swelling process did not affect the 

crystallites in the semicrystalline PVA; 

only the amorphous regions of the 

hydro gel were penetrated by the water 

molecules. Another technique for 
crystallization of PVA is annealing at a 

temperature between the glass 

transition temperature and the melting 

point; Mallapragada et al. [10] 

conducted some of the earliest 

experiments using this annealing 

process. These studies also explored 

dissolution mechanisms of PVA hydro 

gels that had been crystallized using 

annealing. Unlike previous works, 

these annealed films were not 

previously cross-linked, so the sole 

source of stability was the crystalline 

structure formed during annealing. 
Peppas N.A.,and Tennenhouse D.[11] 

study the preparations Semicrystalline 

films of poly vinyl alcohol by 

annealing amorphous PVA films at 

temperature 90, 100, 110
o
C for 60 min, 

the degree of crystallinity of the dry 

films was measured by differential 

scanning calorimetry[12,13].  
In this work, special emphasis is given 

to the methods of preparation, the 

optimization of the preparation process 

and the swelling behavior of the 

associated systems.  
 

Experimental Work 

1. PVA Film Preparation 
The films produced were made from a 

13% and 11.5% aqueous PVA 

solution. To prepare 13%  PVA 

solution,35 ml of deionized water was 

added to 5.3 g PVA(Mw=14000 , 

degree of hydrolysis=99.8%).To 

prepare 11.5%  PVA solution,45 ml of 

deionized water was added to 5.3 g 

PVA(Mw=14000,degree of hydrolysis 

99.8%). The PVA solution was stirred 

and heated at 85- 90°C for 4 to 6 h by 

using a water bath. The solution was 

allowed to cool for several minutes 

before use. The solution was then cast 

on to six 25.4x76.2 mm glass slides 

and spread uniformly over the slides 

using a glass rod. The films were 

allowed to dry at 25-30°C for at least 

24 h. 

 

 

 
 



Basma A. Abdul-Majeed, Hussain K. Hussain and Nagam A. Kafel Al-Sultanee 

 

-Available online at: www.iasj.net                IJCPE Vol.13 No.2 (June 2012)                                       31 
 

2. Annealing of the films 
The amorphous PVA and films were  

annealed in an oven at temperatures  

90,110 and 120°C for 15,30 and 60 

min with concentrations of 13% and 

11.5% aqueous PVA films. Once the 

films were removed from the oven and 

then peeled off from the glass slides 

and stored at room temperature. The 

resulting hydro gels were tested for 

their crystalline, swelling behavior,gel 

fraction and solubility. 

 

Tests of the Films  

1. Water Uptake 
The samples were submerged in 

deionized water at 37°C (the last level 

simulates water absorption at the 

temperature of the human body) until 

they reached equilibrium, which 

occurred after three to four days. After 

swelling, the weight and volume of the 

samples were again measured. The 

water uptake, or percent water 

incorporated into the hydrogel was 

calculated from Eq.1. 

 

       
     

  
                   …(1) 

 

where    is the weight of dry sample 
and    is the weight of swollen 
sample. 

The swelling behavior of PVA films 

was studied by measuring the amount 

of water incorporated into the sample. 

After the annealing process, the 

samples were weighted then swollen in 

water, later the swelling samples were 

weighted after swollen every two days 

nearly until the amorphous PVA was 

soluble. 

 

2. Calculation of the Samples 
Volume 

Volumetric measurements were taken 

by suspending the sample in heptane (a 

non-solvent), weighing, and 

calculating the volume, V, based on the 

weight of the heptane displaced. First 

the samples were weighing in air and 

then volumetric measurements were 

taken by suspending the sample in n-

heptane, weighing, and calculating the 

volume, V, based on the weight of   the 

heptane displaced. The volume, V, was 

calculated by Eq.2. 

 

V = (Wair - Wheptane) /ρheptane       …(2) 
 

Where Wair is the weight of the sample 

in air, Wheptane is the weight of the 

sample in heptane and ρheptane is 
0.6840g/ml. 

 

3. Density of Gels   
The density of dry gels was determined 

by hydrostatical weighing by [kit YDK 

01LP in n-heptane (EN 1183-1:2004)]. 

The density of gels was calculated by 

Eq.3. 

 

                          …(3) 
 

where    is the weight of the sample 
in air,    is the density of the liquid (n-
heptane), and   is the weight of the 
sample in the liquid. 

 

4. Degree of Crystallinity  
The semicrystalline films were 

characterized by measuring the degree 

of crystallinity, X, after annealing. The 

degree of crystallinity of the samples 

was calculated by Eq.4: 

 
 

  
 

 

  
 

     

  
                              …(4) 

 

Where a   =1.345 g/cm³ for 100% 
crystalline PVA,   =1.269 g/cm³ [ 89 
] for 100%amorphous PVA, and    is 

the density of the sample. The “wet 

degree of crystallinity” Xwet, was 

calculated by Eq.5. This value 

indicates the volume of crystallites in 

the hydrogel compared to the total 

volume of the swollen hydrogel. 

 

Xwet = X * Vdry / Vswollen                …(5) 



Effect of Annealing on the Crystallization of Poly Vinyl Chloride for Drug Delivery System 

 

32                                        IJCPE Vol.13 No.2 (June 2012)               -Available online at: www.iasj.net 
 

To calculate the degree of crystallinity 

X of the samples, first the dry 

annealing films were weighted in air 

and then in n-heptane; after that the 

were samples swollen in water by 

using magnetic stirrer for 4h, and later 

the swollen samples were weighted in 

air heptane once more. 

 

Results and Discussion 

Effect of Annealing Temperature on 

the Water Uptake of PVA Films 

Thin films of PVA were annealed at 

temperatures of 90, 110 and 120
o
C( 

above the glass transition temperature 

of 85°C) for 15 min to investigate the 

effect of annealing temperature on 

water uptake of the films. Fig.1 and 

Fig 2 show that water uptake increased 

with time until it reached nearly 

constant value after 20 day. Water 

uptake was decreased with increasing 

annealing temperature for 13% and 

11.5% PVA related to the effect of  

density of the films. 

The increasing of density was caused 

by the effect of annealing temperature 

on the inner composition of the 

polymer. Increasing  the temperature of 

annealing caused in compacting of 

polymer molecules which result in 

decreasing the voids among polymer 

molecules. Consequently the porosity 

decreased and the permeability of the 

polymer for liquids and gases 

decreased [14]. This behavior indicates 

clearly the increase in the crystalline 

phase in comparison with the 

amorphous one, or it can be said that 

the system is more packed with 

crystallite. 

 

 

 
Fig.1, Relation between water uptake and time 
of swelling for different annealing temperature, 

t=15 min, 13% PVA 

 

 
Fig.2, Relation between water uptake and time 

for different annealing temperature, t=15 min, 

11.5% PVA 

 

Effect of Annealing Time on the 

Water Uptake of PVA Films 

The effect of annealing time on the 

water uptake of polyvinyl alcohol films 

was investigated. The  films of PVA  

were anneallied for different times (15, 

30 and 60 min) at annealing 

temperature of 120
o
C. Figures 3 and 4 

show the effect of annealing time on 

the water uptake with constant 

annealing temperature using 13% and 

11.5% PVA, respectively. These 

figures illustrate  that  increasing the 

annealing time causes decreasing the 

water uptake, which can be attributed 

to the increase in density.  

 

40

45

50

55

60

65

70

75

0 10 20 30

w
a

te
r 

u
p

ta
k

e
 

day 

T=90 °C
T=110 °C
T=120 °C

0

10

20

30

40

50

60

70

80

0 10 20 30

w
a

te
r 

u
p

ta
k

e
 

day 

T=90 °C
T=110 °C
T=120 °C



Basma A. Abdul-Majeed, Hussain K. Hussain and Nagam A. Kafel Al-Sultanee 

 

-Available online at: www.iasj.net                IJCPE Vol.13 No.2 (June 2012)                                       33 
 

 
Fig.3, Relation between water uptake and 

annealing time for T=120
o
C, and 13% PVA 

 

 
Fig.4, Relation between water uptake and 
annealing time for T=120

o
C and 11.5% PVA 

 

Effect Concentration of PVA on the 

Water Uptake of PVA Films 

The effect of the concentration of PVA 

on the water uptake of polyvinyl 

alcohol films with time was 

investigated. The PVA films were 

annealed at constant temperature of 

120
o
C for constant annealing time of 

30 min to investigate the effect of the 

concentration of PVA on the water 

uptake of the films.  Figure 5 shows 

the effect of increasing concentration 

of PVA on water uptake with time of 

swelling. The increase in polymer 

concentration leads to a decrease in the 

water uptake of the films. From the 

results of the previous sections, 

increasing the density caused the 

decreasing of the water uptake of the 

polymer; increasing the concentration 

means the increasing of the density, 

thus the increasing of the polymer 

concentration carried out the 

decreasing of the water up take which 

was caused by the decreasing of the 

permeabilityof the polymer. The 

increase in the density means that the 

interstituoas distance between the 

adjacent molecules will become less 

leading to less porosity and hence less 

water uptake. During the annealing 

process, some of the amorphous phases 

changes into folded compact chains 

which are distributed through the 

amorphous phase. This can be 

considered as crosslinking but of 

physical type. These points of physical 

crosslinkings are considered as crystals 

or crosslinking agents or centre. 

 

 
Fig.5, Relation between water up take and 

swelling time for different concentration of 

PVA at annealing temperature of 120
o
C and 

annealing time of 30 min 

 

Effect of Annealing Temperature on 

the Degree of Crystallinity of PVA 

Films 

The effect of annealing temperature on 

the degree of crystallinity of polyvinyl 

alcohol films was investigated. Fig.6 

shows the effect of the annealing 

temperature on the degree of 

crystallinity with different annealing 

time. The increase in the annealing 

temperature leads to  the increase of 

the degree of crystallinity, which 

results from increasing the density of 

the polymeric samples. The annealing 

process causes the appearance of 

aggregation of the polymer chains; 

consequently the crystal regions will 

grow with the increase of annealing 

temperature [10,13]. The physical 

35

45

55

65

75

0 5 10 15 20 25 30

w
a

te
r 

u
p

ta
k

e
 

day 

t=15 min
t=30 min
t=60 min

0

10

20

30

40

50

60

70

80

0 10 20 30

w
a

te
r 

u
p

ta
k

e
 

day 

t=15 min
t=30 min
t=60 min

20

25

30

35

40

45

50

55

60

0 10 20 30

w
a

te
r 

u
p

ta
k

e
 

day 

11.5% PVA

13% PVA



Effect of Annealing on the Crystallization of Poly Vinyl Chloride for Drug Delivery System 

 

34                                        IJCPE Vol.13 No.2 (June 2012)               -Available online at: www.iasj.net 
 

crosslinking causes the polymer to be 

packed with crystals with less inner 

distances. 

 

 
Fig.6, Relation between the degree of 

crystallinity of PVA and annealing temperature 

for different annealing time, 11.5% PVA 

 

Effect of Annealing Time on the 

Degree of Crystallinity of PVA Films 

The Effect of annealing time on the 

degree of crystallinity of polyvinyl 

alcohol films was investigated as show 

in Fig.7. The degree of crystallinity 

increased with increasing time of 

annealing.  
 

Comparison Between Dry and Wet 

Crystallinity of PVA Films 

A comparison between dry and wet 

crystallinity of polyvinyl alcohol films 

at different temperatures and constant 

annealing time was investigated as 

shown in Fig.8, while Fig. 9 shows a 

comparison between the dry and wet 

crystallinity of the samples annealed 

for different annealing times at 

constant temperature. As expected, the 

rate of swelling differs in both dry and 

wet films. The wet crystallinity of the 

samples was much lower than that of 

the dry crystallinity. This was readily 

explained by the water incorporated 

into the polymer network during 

swelling. The amorphous regions of 

the hydrogel swelled, allowing water to 

penetrate the network and became 

entrained in the hydrogel. This 

expansion of the network and 

incorporation of water caused the 

overall weight and volume of the 

hydrogels to increase during swelling. 

 

 
Fig.7, Relation between the degree of 

crystallinity and time of annealing for different 

annealing temperature, 11.5% PVA 

 

 
Fig.8, Relation between the degree of 

crystallinity and temperature of annealing for 

dry and wet films 

 

 
Fig.9, Relation between the degree of 

crystallinity and time of annealing for dry and 

wet films  

 

54

56

58

60

62

64

66

85 95 105 115 125

 
d

e
g

re
e

 o
f 

cr
y

st
a

ll
in

it
y

 

Temp. of annealing 

t=15 min
t=30 min
t=60 min

53

55

57

59

61

63

65

5 10 15 20 25 30 35 40 45 50 55 60 65

d
e

g
re

e
 o

f 
cr

y
st

a
ll

in
it

y
 

time of annealing 

T=90 °C

T=110 °C

T=120 °C

0

10

20

30

40

50

60

70

85 95 105 115 125

d
e

g
re

e
 o

f 
cr

y
st

a
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in
it

y
 

Temp. of annealing 

X

Xwet

0

20

40

60

80

10 30 50 70

d
e

g
re

e
 o

f 
cr

y
st

a
ll

in
it

y
 

time of annealing 

X Xwet



Basma A. Abdul-Majeed, Hussain K. Hussain and Nagam A. Kafel Al-Sultanee 

 

-Available online at: www.iasj.net                IJCPE Vol.13 No.2 (June 2012)                                       35 
 

Long-Term Stability of Hydrogels 
Long term stability of hydrogels was 

investigated. As noticed from the 

previous results, the increasing of 

annealing temperature and time of 

annealing causes the decreasing of the 

water uptake, and since the gel fraction 

is a function of the water uptake; 

therefore the gel fraction behaves 

exactly the same as the water uptake. 

On the other hand the solubility is 

inversely proportional to the 

crystallinity, or it behaves inversely.   

Fig. 10 shows the effect of annealing 

temperature and time of annealing on 

gel fraction of PVA films, where the 

increasing of annealing temperature 

and time of annealing causes the 

decreasing of the gel fraction. Fig.11 

shows the effect of annealing 

temperature and time of annealing on 

the solubility of the PVA films, where 

the increasing of annealing temperature 

and time of annealing results in the 

decreasing of the solubility. 

 

 
Fig.10, Relation between Gel fraction of the 

polymer and annealing time at different 

annealing temperature, 11.5% PVA 

 

 
Fig.11, Relation between Solubility of the 

polymer and annealing time at different 

annealing temperature, 11.5% PVA 

 

Conclusions 

Increasing the annealing temperature 

leads to a decrease in water uptake, an 

increase of density, and an increase of 

the crystallinity of PVA films with 

constant time of annealing. Increasing 

time of annealing leads to decreasing 

in the water uptake, increasing density 

and increasing of the crystallinity of 

PVA films at constant annealing 

temperature. Increasing density leads 

to decreasing in the water uptake and 

increasing crystallinity of the PVA 

films. The wet crystallinity of the 

samples was much lower than that of 

the dry crystallinity for the PVA films. 

The results show that increasing the 

annealing temperature and annealing 

time causes the decrease of the gel 

fraction and solubility for the PVA 

films. 
 

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1. Peppas N.A., Huang Y. - Polymers 
and gels as molecular recognition   

agents. - Pharmac. Res., 19, 578-

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2. Santini, J., John T., et al., 
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3. Peppas, L.B., Polymers in 
Controlled Drug Delivery, in 

110
135
160
185
210
235
260
285
310
335
360

10 30 50 70

G
 %

 

annealing time 

T=120 °C

T=110 °C

T=90 °C

11.5% PVA 

0.05

0.06

0.07

0.08

0.09

0.1

10 30 50 70

S
 %

 

annealing time 

T=90 °C

T= 110 °C

T=120 °C

11.5% PVA 



Effect of Annealing on the Crystallization of Poly Vinyl Chloride for Drug Delivery System 

 

36                                        IJCPE Vol.13 No.2 (June 2012)               -Available online at: www.iasj.net 
 

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