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The heterogeneous formalization of poly(vinyl alcohol) accompanying crosslinking reaction-II.

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Die Angewalzdte Makromolekulare Chemie 25 (1972) 15-26 (Nr. 345)
From the Department of Textile Industrial Chemistry, Faculty of Textile Science
and Technology, Shinshu University, Ueda, Nagano, Japan
The Heterogeneous Formalization of
Poly(viny1 alcohol) accompanying Crosslinking
Reaction-I1
By KENJIOGASAWARA,
NORIYUKI
YAMAGAMI
and SHUJIMATUZAWA
(Eingegangen am 10. Januar 1972)
SUMMARY:
Poly(viny1 alcohol) (PVA) films were allowed to react with formaldehyde in
water containing salt and a n acid catalyst (the heterogeneous formalization).
The content of crosslinks increased with decreasing acid concentration under fixed
formaldehyde and salt concentrations. The crosslink contents of formalized PVA
were estimated in terms of the degree of swelling of formalized and acetylated PVA
in chloroform. The crosslink contents were calculated by means of FLORY’S
method.
One crosslink per 100 units of vinyl alcohol was estimated to exist for the sample
of the degree of swelling about 6.
ZUSAMMENFASSUNG :
Die heterogene Reaktion von Polyvinylalkohol(PVA)-Filmenmit Formaldehyd
wurde in Salz und Siiurekatalysator enthaltendem Wasser untersucht. Bei konstanter Formaldehyd- und Salzkonzentration steigt der Vernetzungsgrad mit abnehmender Siiurekonzentration. Der Vernetzungsgrad wurde mittels Quellungsmessungen an formalisiertem und dann acetyliertem PVA in Chloroform bestimmt.
Der Vernetzungsgrad wurde nach der FLoRYschen Methode berechnet. Eine
Probe mit dem Quellungsgrad von etwa 6 besitzt eine Vernetzung pro 100 Grundbausteine.
1. Introduction
The acetalization of poly(viny1 alcohol) (PVA) has been studied for a long
time mainly from the industrial points of view19 2. Now this reaction is indispensable for PVA t o endow the hydrophobic property.
It has recently been recognized that in the reaction of PVA with formaldehyde both intramolecular formalization and a n intermolecular one (crosslinking
reaction) occur3, 49 5 , 6 , 7. The formalization of PVA can be divided into two
classes :oneisin homogeneous systems and another is in heterogeneous ones. I n the
latter system, KAWASE7 has reported that the rate of the crosslinking reaction
of formaldehyde depends mainly on the rate of formalization. The content of
16
K. OGASAWARA,
N. YAMAGAMI,
and S. MATUZAWA
crosslinks is controlled by the relative rate of the crosslinking reaction t o t h a t
of the hydrolysis of the crosslinks formed. The authors8 have reported t h a t the
crosslinks consisting of polymeric formaldehyde were also an important factor.
In this paper, the authors report on the estimation of the crosslink content
method and the influence of
of formalized PVA quantitatively using FLORY'S
a n acid on the crosslinking reaction of PVA films.
2. Experimental
2.1 Preparation of the sample
2.1.1 PVA
Commercial PVA (Kurare Poval 120 D P = 2000) and its fractions were used
after the perfect saponification. The fractionation was carried out by the nonsolvent addition method using water as a solvent and n-propanol as a non-solvent.
The average degree of polymerization of the fractionated PVA was calculated from
intrinsic viscosity number by means of the equation9 [ q ] = 7.5 * 10-3 * P.
2.1.2 F o r m a l i z a t i o n
PVA films about 0.1 mm in thickness were obtained by casting and were exposed
to thermal treatment for 20 minutes at 50 "C or 150 "C. The treated PVA films were
formalized in mixtures of water, aqueous formaldehyde, sodium chloride and
hydrochloric acid at 60 "C.
2.2 Measurement of the degree of formalization
The formaldehyde content was determined by the colorimetric method using the
chromotropic acid &s a colour developerlo.
2.3 Acetylation of formalized P V A
The formalized PVA was acetylated in a mixture of pyridine and acetic anhydride in a similar manner as reported in the previous paper4.
2.4 The degree of swelling and solubility
The acetylated sample was swollen in pyridine or chloroform for 48 hours a t
30 "C and the degree of swelling was determined using the following equation :
Degree of swelling (D.S) =
w,- w
W
where W, is the weight of the swollen sample and W the dried sample after swelling.
The solubility is represented in weight percentage :
where A is the dissolved weight and B the undissolved one in the acetylating
mixture.
16
Heterogeneous Formalization of Poly(viny1 dcohol) 11
2.5 Determination of the molecular weight between crosslinks (Mc)
According to FLORY'S
equation" we evaluated Mc from the degree of swelling in
chloroform:
where Vzg is the volume fraction of polymer in the equilibrium swelling, x1 the
interaction parameter, e specific gravity of polymer which is 1.21 at 3OoC, M the
molecular weight of original PVA and V1 the specific volume of the solvent. Vzg
was estimated by means of the following equation:
1
v2g =
+
(el@'). D.8 1 '
where e' is the density of chloroform a.s a solvent, which is 1.47 at 30°C, was
determined from the second virial coefficient A2 of osmosis in chloroform solution
by the following equation :
where R is the gas constant, T the absolute temperature, V the specific volume
of the polymer and V1 the molecular volume of the solvent. The second virial
coefficient was 1.23 . 10-5 for the sample containing the formal Iinkage of about
50 mole yo.Thus the interaction parameter X i was calculated a s 0.354.
3 . Results
3.1 The efiect of acid on the crosslinking reaction
lhfractionated PVA film heat treated a t 50 "Cwas used and the formalization
reaction was carried out under various reaction conditions. Table 1 shows
the results of the reactions in solutions containing from I to 5 % of formaldehyde and table 2 shows the results of the reactions in solutions containing
from 10 to 20% of formaldehyde, respectively. The rate of formalization increased with increasing formaldehyde and acid concentration.
The relation between the degree of formalization and that of swelling are
shown in Fig. 1 to 3. Fig. 1 shows the result in the case of 5 % acid concentration and Fig. 2 and 3 show the results in the cases of 10 yo and 15 yo acid
concentration, respectively. As can be seen from these figures, the slope of the
straight lines becomes steeper with increasing acid concentration.
3.2 The eQect of formaldehyde concentration on the crosslinking reaction
Fractionated PVA (DP = 2790) was formalized a t various formaldehyde
concentrations under 4.5 yo acid and 10 yo sodium chloride concentration.
Solubility in the acetylation mixture and the degree of swelling in pyridine are
17
K. OGASAWARA,N. YAMAGAMI,
and S. MATUZAWA
9
0
4
0
I
rl
uj
t-
*
el
03
us3
10
51
"rn
3
-z
1.91
9'8P
L'89
L'99
LI'O
I
9'0
E
PZ
8P
PZ
8P
E
EE
6'98
Z'E8
9 7L
6'ZI
I
9'0
9.L1
LI'O
12
1'8P
T'EL
0'89
81
E
Z'OZ
P'TZ
6'81
1'98
L'Z8
L'I L
9P
19
P'ZI
L'8
L'8
L'8
9'8
9'6
9Z
LI
61
92
PF
82
(OL)
91
OT
(08)
9
01
P
9
Z
0'01
E'06
ple
o.
(YO)
HC1
NaCl (Yo)
(HzO(Y0))
Reaction conditions
Reaction
time (hrs)
Degree of
formalization (mole yo)
Degree of
swelling
(YO)
Solubility
K.
OGASAWARA,
N.
YAMAGAMI,
and
s. MATUZAWA
100
0
0
20
40
6 0 80 100
Degree of formalization (mole%)
Fig. 1. Relationship between the degree of formalization and swelling of samples
formalized at constant acid concentration of 5 yo, sodium chloride concentration of 10 yo and various formaldehyde concentrations.
3 40
0)
4
t o
0
0
0" 20
0
20
Fig. 2.
40
60
80
100
Degree of formalization (mole%)
Relationship between the degree of formalization and swelling of samples
formalized at constant acid concentration of 10 yo, sodium chloride concentration of 15 yo and various formaldehyde concentrations.
CH20: 1 % ( 0 )5;% (0);
10% ( 0 )20%
; (0).
Heterogeneous Formalization of Poly(viny1 alcohol) I I
40
60
80
100
Degree of formalization (mole%)
20
Fig. 3. Relationship between the degree of formalization and swelling of samples
formalized at a formaldehyde concentration of 20 yo, hydrochloric acid
concentration of 15 yo and sodium chloride concentration of 15 yo.
shown in table 3. Evidently the crosslinking reaction occurs readily a t the
higher concentration of formaldehyde, whereas it does not a t lower concentrations a t constant acid concentration. The crosslinking was not recognized in
the case of an acid concentration of 4.5 yo and a formaldehyde concentration
within 0.4 yo.
3.3 Estimation of the crosslink content from the degree of swelling
Three samples of fractionated PVA (DP = 1280, 2070, 2970) were used. The
formalization was carried out a t various formaldehyde concentrations above
0.5 a t an acid concentration of 4.5 yo.Mc of formalized and acetylated PVA
was estimated using FLORY’Sequation. The results are shown in table 4. Mc
decreased with increasing formaldehyde concentration.
‘x
4. Discussion
4.1 The eflect of mid on the crosslinking reaction
As is evident from Fig. 1 to 3, the crosslink content increases with increasing
formaldehyde concentration under constant acid concentration. These results
23
K. OUASAWARA,N. YAMAGAMI,
and S. MATUZAWA
Table 3.
Effect of formaldehyde concentration on crosslink content.
HC1: 4.5 yo,Degree of formalization : 64 mole yo.
CHzO
(yo)I
0.2*
0.4
0.5
1.o
2.0
10.0
Solubility
1 Degree of swelling
-
0
0
-
Remarkable
20.2.
9.5
8.1
X
X
X
X
*
Degree of formalization: 57 mole yo.
0:Soluble in the acetylating solution.
X : Insoluble in the acetylating solution.
Table 4.
Determination of the crosslink content.
Degree Of
polymerization
1280
2070
2970
CHzO
('0)
Degree of
formalization (mole yo)
Mc
-
-
-
-
50.5
52.2
51.1
0
0
0
5.0
48.8
X
0.5
0
-
-
0.7
1.o
44.6
47.3
50.7
X
5.0
62.0
X
34.7
21.3
7.4
56 900
37 300
9 900
0.5
0.7
1.0
5.0
48.6
49.7
X
0.5
0.7
1.o
25.1
23.5
10.0
29.8
14.7
13.6
6.9
63.3
66 100
29 500
23 900
8 900
-
23.2
15.2
53 100
31 500
48.7
57.3
: Insoluble in the acetylating solution.
24
Degree of
swelling
0.5
0.7
1.0
0: Soluble in the acetylating solution.
x
Solubility
X
X
X
X
X
X
X
-
9.2
14 700
Heterogeneous Formalization of Poly(viny1 alcohol) I I
show that the crosslinking reaction occurs more readily a t the high formaldehyde concentration than a t the low formaldehyde concentration. This is in agreement with the results of KAWASE~,
who has reported that the content of crosslinks increased with increasing formaldehyde concentration whereas it was
independent on the concentrations of sulfuric acid and of sodium sulfate whena
heat treated (at 230 "C) PVA was formalized in a moderately concentrated
formaldehyde solution. He concluded this to be due to the increase in the probribility of intermolecular formalization and to the amount of isolated hydroxyl groups increasing the rate of the formalization reaction and considered
moreover that the crosslinks formed between isolated hydroxyl groups have
considerable stability.
TAXAKA
and
~ ~ZAVITSAS~~
have reported that the more concentrated the
formaldehyde solution was, the less monomeric formaldehyde was present. I n
the reaction of cellulose with formaldehyde, GUTHRIE14 pointed out that the
crosslinks are polymeric formaldehyde. The authors8 also pointed out from the
reitction in methanol that the polymeric formaldehyde was the crosslink. The
presence of polymeric formaldehyde also is an important factor for the intermolecular formalization.
The crosslink content decreased with increasing acid concentration. As is
recognized by TAKAHASHI15, the swelling power of acid and formaldehyde for
PVA film is large, so the degree of swelling of PVA film in the reaction solution
containing higher amounts of acid is large especially a t the initial reaction
stage. Therefore, intramolecular reaction occurs mainly a t the high acid concentration. As the formalization is promoted, the intermolecular reaction occurs
readily with decreasing degree of swelling of PVA film. The difference between
KAWASE'S
and our results is due to the samples used. Therefore, we suppose
that crosslink formation is also affected by the distance between the intermolecular hydroxyl groups. The degree of swelling of PVA film during the formalization reaction is also a very important factor.
According to FLORY,
the limit of the degree of formalization is 86.5 mole yo16.
But values of the degree of formalization over 86.5 mole yo were obtained.
Though the formalized PVAs were washed with distillated water again and
then steeped in hot water (80 "C) for 2 hours, the degree of formalization did not
decrease. The excess formaldehyde seems not to be due to the adhesion of the
unreacted formaldehyde, but to the polymeric crosslinks.
4.2 Crosslink content of formalized P V A
The degree of polymerization between crosslinks was calculated from the
values in table 4 using the following equation:
25
K. OGASAWARA,
N. YAMAGAMI,
and S. MATUZAWA
A
(loo.
where A is the degree of formalization and X is the average degree of polymerization between crosslinks. X value was 100 for the sample of the degree of
swelling of about 6, and X was 1000 for the sample of the degree of swelling of
about 30. Therefore one crosslink is estimated t o exist per 100 units of vinyl
alcohol for the sample of the degree of swelling of about 6 and 1000 units of
vinyl alcohol for the sample of t h e degree of swelling of about 30.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
26
I. SAKURADA,
S. REE,E. NAGAI,and T. TAKESHIRO,
Studies on synthetic fibers,
Japan, l(1943) 252.
I. SAKURADA,
N. NAKAMURA,
and Y. SAKAGUCHI,
Kobunshi Kagaku 8 (1951)476,
9 (1952) 20, 82.
H. SUYAMA
and M. UZUMAKI,
J. SOC. Fiber Sci. Tech., Japan 18 (1962) 96.
S. MATUZAWA,T. IMOTO,
and M. OKAZAKI,
Kobunshi Kagaku 25 (1968) 25.
S. MATUZAWA,
T. IMOTO,
and K. OGASAWARA,
Kobunshi Kagaku 25 (1968) 173.
S. MATUZAWA
and T. IMOTO,
J. SOC. Fiber Sci. Tech., Japan 24 (1968) 386.
H.KAwA~E
O.MORIMOTO,
,
and T.MOCHIZUKI,
J.Soc. Chem. Ind.,Japan74(1971)
1014, 1218, 1223, 1228.
S. MATUZAWAand K. OGASAWARA,
Angew. Makromol. Chem. 23 (1972) 157.
A. NAKAJIMA
and K. FURUTATE,
Kobunshi Kagaku 6 (1949) 460.
K. OGASAWARA,
N. NAKAMURA,
and S. MATUZAWA, Makromol. Chem. 149
(1971) 291.
P. J. FLORY,Principles of Polymer Chemistry, Cornell Univ. Press, New York,
1953, p. 579.
S. TANAKA,
T KURACHI,
M. TSUGE,Y. SATO,and M. KAWAKITA,
J. SOC. Chem.
Ind., Japan 66 (1963) 1598.
A. A. ZAVITSASand R. D. BEAULIEU,
Am. Chem. SOC., Div. Org. Coatings and
Plastics Preprints. 27 (1) (1967) 100.
J. D. GUTHRIE,Text. Res. J. 37 (1967) 40.
N. TAKAHASHI
and K. ONOSATO,
J. SOC. Chem. Ind., Japan 63 (1960) 1540.
P. J. FLORY,J. Amer. Chem. SOC. 61 (1938) 1518.
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