BIODEGRADABLE ALIPHATIC POLYESTER IONOMERIC RESIN AND ITS
PREPARING METHOD
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to biodegradable aliphatic polyester
ionomeric resin and a preparing method thereof, more particularly to aliphatic
polyester ionomeric resin with significantly improved biodegradability prepared
by adding an ionic compound to polyaliphatic glycol having at least two hydroxyl
groups and polyaliphatic carboxylic acid having at least two carboxyl groups, and
a preparing method thereof.
Description of the Related Art
Commonly used polyester resin is an aromatic compound with large
molecular weight, which is produced by poly condensation of terephthalic acid
and ethylene glycol or terephthalic acid and 1,'4-butanediol. It is widely used in
fibers, bottles, films and so forth. However, since the aromatic polyester resin is
hardly decomposed when it is wasted, it often leads to serious environmental
pollution.
Accordingly, it has been under high social demands to develop
biodegradable plastics which may replace synthetic plastics considering
convenience and durability.
It is well known that aliphatic polyester is biodegradable (Journal of
Macromol. Sci-Chem., A-23(3), 1986, 393-409). It has been applied to the medicinal,
agricultural and fishery industries, as a result, researches on its use are in progress.
Biodegradable aliphatic polyester and copolyester resin compositions and
their preparing method thereof are disclosed in Korea Patent Publication Nos. 98-
082074, 99-009593, 00-0019012 and 01-0055721. However, the improvements of
the above-mentioned aliphatic polyester resin compositions have been largely
restricted to mechanical and physical properties, but not much advance was made
in biodegradability.
Although the conventional aliphatic polyesters exhibit a bit improved
biodegradability than aromatic polyester resins, they are disadvantageous in that
they decompose very slowly in nature thus not helping to reduce the
environmental pollution to the level of satisfaction.
SUMMARY OF THE INVENTION
The present inventors have found that biodegradability is greatly
improved when ionic compound is added to polyaliphatic glycol and
polyaliphatic carboxylic acid to prepare an aliphatic polyester resin composition.
Therefore, it is an object of the present invention to provide new
biodegradable aliphatic polyester ionomeric resin and a preparing method thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows αH-NMR spectrum of the aliphatic polyester ionomeric resin
prepared according to the Example 2 of the present invention.
FIG. 2 is a non-contact mode AFM (atomic force microscope) photograph
of the aliphatic polyester ionomeric resin prepared according to the Example 2 of
the present invention.
FIG. 3 is a non-contact mode AFM photograph of the aliphatic polyester
ionomeric resin prepared according to the Comparative Example 1 of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to biodegradable aliphatic polyester
ionomeric resin comprising glycol 41 to 54 wt% of polyaliphatic (including cyclic
aliphatic), 36 to 52 wt% of polyaliphatic carboxylic acid or acid anhydride thereof
and 1 to 23 wt% of aliphatic or aromatic alkali metal sulfonate, wherein the resin
polymers are chemically bonded to the alkali metal sulfonate.
The present invention also relates to a method of preparing biodegradable
aliphatic polyester ionomeric resin comprising the steps of esterifying at 170 to
220 °C of a mixture comprising 41 to 54 wt% of polyaliphatic (including cyclic
aliphatic) glycol, 36 to 52 wt% of polyaliphatic carboxylic acid or acid anhydride
thereof and 1 to 23 wt% of aliphatic or aromatic alkali metal sulfonate, and
performing polycondensation at 220 to 260 °C by adding a polycondensation
catalyst.
Hereunder, the present invention is described in more detail.
The present invention provides environment-friendly biodegradable
aliphatic polyester ionomeric resin prepared by adding an ionic compound to
polyaliphatic glycol having at least two hydroxyl groups and polyaliphatic
carboxylic acid having at least two carboxyl groups, which has significantly
improved biodegradability due to the ions inserted in the polymer chain, and a
preparing method thereof.
In general, ionomer refers to a material containing a small number of ionic
groups in the nonpolar polymer chain. Since the polar ions present in the
nonpolar chain attract each other, it has totally different physical properties from
those of other polymers. The biodegradable aliphatic polyester ionomeric resin of
the present invention is prepared by adding an ionic compound to polyaliphatic
glycol and polycarboxylic acid to introduce ionic groups to the polymer chain of
the polyester resin. Hence, the aliphatic polyester resin has significantly
improved biodegradability.
As polyaliphatic glycol, those having 2 to 20 carbon atoms, including cyclic
aliphatic glycol, may be used. As glycols, those having hydroxyl groups at both
ends or those having ether groups may be used. As glycol having hydroxyl
groups at both ends, diol or its structural isomer, such as ethylene glycol, 1,3-
propanediol, neopentylglycol, propylene glycol, 1,2-butanediol, 1,4-butanediol,
1,6-hexanediol and 1,9-nonanediol, may be used alone or in combination. For the
glycol having ether groups, diethylene glycol, triethylene glycol or polyethylene
glycol (molecular weight being 900 or smaller) may be used alone or in
combination.
As polyaliphatic carboxylic acid, an acid anhydride thereof or a derivative
thereof, those having 2 to 12 carbon atoms, including cyclic aliphatic carboxylic
acid, are preferable. For example, polyaliphatic carboxylic acid selected from
oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid,
sebacinic acid, azelaic acid, nonanedicarboxylic acid and dimethylsuccinic acid, an
anhydride thereof or a derivative thereof may be used alone or in combination.
The polyaliphatic glycol is used in 41 to 54 wt%, and the polyaliphatic
carboxylic acid is used in 36 to 52 wt%. If the content of the polyaliphatic glycol
is below 41 wt%, the resulting polymer may have a low molecular weight. In
contrast, if it exceeds 54 wt%, the reaction is proceeded at a slower rate.
As an ionic compound, aliphatic or aromatic alkali metal sulfonate,
preferably sodium aliphatic or aromatic sulfonate, may be used. For example,
sodium 1,4-dihydroxybutanesulfonate, sodium dimethyl-5-sulfoisophthalate,
sodium diethyl-5-sulfoisophthalate, sodium dibutyl-5-sulfoisophthalate, sodium
dimethyl-5-sulfoterephthalate, sodium diethyl-5-sulfoterephthalate or sodium
dibutyl-5-sulfoterephthalate may be used alone or in combination. The above
ionic compound is used in 1 to 23 wt%. If the content is below 1 wt%, the ionic
compound does not offer significant effect. In contrast, if it exceeds 50 wt%, the
melt polymerization becomes difficult because the ionic salt becomes less soluble.
The biodegradable aliphatic polyester ionomeric resin of the present
invention with ionic compound introduced, has inherent viscosity of ranging from
0.1 to 2.3, melting point of ranging from 104 to 114 °C and glass transition
temperature of ranging from -22 to 3 °C . More importantly, it has 1.2 to 5 times
superiorities in biodegradability to the conventional aliphatic polyester resins.
Hereunder, the preparing method of aliphatic polyester ionomeric resin of
the present invention is described in detail.
First, 41 to 54 wt% of polyaliphatic (including cyclic aliphatic) glycol
having at least two hydroxyl groups, 36 to 52 wt% of polyaliphatic carboxylic
acid having at least two carboxyl groups, an acid anhydride thereof or a derivative
thereof and 1 to 23 wt% of ionic compound are added at 170 to 220 °C for
esterification. If the reaction temperature is below 170 °C, the esterification is
proceeded at a slower rate. In contrast, if it exceeds 220 °C, the monomers may be
decomposed.
After the esterification is completed, polycondensation is proceeded at 220
to 260 °C in the presence of polycondensation catalyst. For the polycondensation
catalyst, magnesium acetate, tetrapropyl titanate, zinc acetate, tetrabutyl titanate,
dibutyl tin oxide, tetrapropyl titanate, calcium acetate, titanium isopropoxide,
titanium butoxide, tin chloride or tetraisopropyl titanate may be used alone or in
combination. The catalyst is used in 0.05 to 2 wt% for the total aliphatic polyester
ionomeric resin weight. If the catalyst content is below 0.05 wt%, it becomes
difficult to increase molecular weight because the catalyst activity does not last
long. In contrast, if it exceeds 2 wt%, the polymer may be discolored. If the
condensation polymerization temperature is below 220 °C, the reaction is
proceeded at a slower rate. In contrast, if it exceeds 260 °C, thermal
decomposition may occur. The polycondensation is carried out under high
vacuum, preferably at 0.1 torr or lower. If the pressure exceeds 0.1 torr, it
becomes difficult to obtain large molecular weight. Preferably, the
polycondensation is proceeded for 50 to 250 minutes, although dependent on the
catalyst content.
The aliphatic polyester ionomeric resin of the present invention comprising
polyaliphatic glycol, polyaliphatic carboxylic acid and ionic compound has
improved water permeability due to introduction of ionic groups in the polymer
chain, and thus significantly improved biodegradability.
EXAMPLES
Hereinafter, the present invention is described in more detail by the
following Examples. However, they shall not be construed as limiting the scope
of the present invention.
Examples 1 to 9 and Comparative Examples 1 to 2 : Preparation of aliphatic
polyester resin
After purging an empty 400 mL 4-bulb condensation reactor with nitrogen
gas, a mixture according to the composition in Table 1 below was added.
Esterification was carried out at 200 °C . After adding the above mixture, the
reaction was terminated 90 to 120 minutes after there is no more evaporation of
water at 200 °C . Water generated during esterification was removed from the
reaction system using a distillator.
After esterification was completed, polycondensation was carried out.
Oligomer prepared in the esterification step was cooled to 100 °C, and 0.58 g of
titanium isopropoxide catalyst was added. After mixing well, pressure was
slowly lowered to high vacuum (0.1 torr or below). Slowly heating to 230 °C,
polycondensation was proceeded for 150 to 180 minutes to obtain polyester resin.
Introduction of sodium ions in the aliphatic polyester ionomeric resin
prepared according to the Example 2 of the present invention was identified by
Η-NMR. The Η-NMR spectrum is shown in FIG. 1.
Ion clusters are formed on the surface of the polyester ionomer. FIG. 2 is
a non-contact mode AFM photograph showing the surface of the aliphatic
polyester ionomeric resin prepared according to the Example 2 of the present
invention. And, FIG. 3 is a non-contact mode AFM photograph of the aliphatic
polyester ionomeric resin prepared according to Comparative Example 1.
Dispersed ion clusters measuring about 50 nm were found in FIG. 2, but not in FIG.
3.
Experimental Example: Physical property measurement of aliphatic polyester
resin
Physical properties of polyester resins prepared in Examples 1 to 9 and
Comparative Examples 1 to 2 were measured by the following method. The
result is shown in Table 2 below.
Inherent viscosity was measured at 30 °C using phenol and 1,1,2,2-
tetrachloroethane. Melting point was determined with a differential scanning
calorimeter (DSC) at a heating rate of 10 °C/min. Glass transition temperature
was determined by the peak value of the tan δ curve using dynamic mechanical
analysis (DMA). Tensile strength and elongation were determined using a
universal testing machine (UTM). Hydrolysis test was performed under pH 12.
Resin film with thickness ranging from 0.2 to 0.25 mm was cut into 2 x 5 cm size.
The samples were completely immersed in caustic soda solution at 40 °C . Weight
loss was checked every day for 30 days.
Table 1
Table 2
As shown in Table 2, the aliphatic polyester ionomeric resin of the present
invention has significantly improved biodegradability.
As described above, the aliphatic polyester ionomeric resin of the present
invention has improved hydrophilicity due to introduction of ionic groups in the
polymer chain. Therefore, it has resulted in significant improvement in
hy dr oly zability .
The aliphatic polyester ionomeric resin of the present invention may
outstandingly reduce environmental pollution when used in place of the
conventional non-decomposable plastics. Because it can be processed into a
variety of plastic gods, including consumer goods, agricultural goods and
industrial films, it is expected to have a great commercial value with regard to
ever-increasing international environment regulations.
While the present invention has been described referring to the preferred
embodiments, those skilled in the art will appreciate that various modifications
and substitutions can be made thereto without departing from the spirit and scope
of the present invention as set forth in the appended claims.