Lignin and lignin derivatives as copolymerizable colorants for polyesters

Colored shapable polyesters having copolymerized therein lignin or lignin derivatives are prepared by condensing the lignin or lignin derivatives into the polyester backbone during the polymerization reaction. The lignin moieties are thermally stable at the polymer processing temperatures and are nonextractable from the polyester backbone. These colored, shapable polyesters are particularly suitable for use in food, beverage, pharmaceutical, or cosmetic container applications.

FIELD OF THE INVENTION 
The present invention relates to polyesters having lignins or lignin 
derivatives copolymerized therein to impart color thereto and to a process 
for preparing the colored polyesters. 
BACKGROUND OF THE INVENTION 
Since polyester containers such as food containers, beverage bottles, 
pharmaceutical containers, cosmetic containers and the like made of 
polyester plastic materials combine the advantages of low cost and 
durability with ease of fabrication, there is an increasing demand for 
polyester containers. In many applications the polyester containers must 
be colored not only to make the container aesthetically pleasing, but also 
to minimize light transmittance and thereby protect the container contents 
from light degradation. As a result, several colorants have been developed 
for polyesters used in the container industry. However, present colorants 
suffer from a number of important disadvantages. For example, some dyes 
and pigments used to color polyesters are costly and thereby greatly add 
to the cost of the containers. Other colorants, such as iron oxide, cause 
the polyester to become clouded thereby obscuring from view the container 
contents. Still other colorant systems allow high light transmittance in 
the ultraviolet light range, e.g. 300 nm. to 450 nm., which tends to 
degrade the light sensitive contents of the container. Finally, other 
colorants tend to leach from the polyester container into the container 
contents and therefore cannot be used with foods, drugs and cosmetics. 
Accordingly, it is an object of the present invention to provide a 
polyester colorant that is non-extractable from the polymer. 
It is a further object of the present invention to provide a colored 
polyester which exhibits low light transmittance in the ultraviolet range. 
It is a still further object of the present invention to provide a low 
cost, amber-colored polyester having greater clarity than other 
amber-colored polyesters. 
These and other objects of the present invention will be apparent to one of 
ordinary skill in the art from the summary and detailed description which 
follows. 
SUMMARY OF THE INVENTION 
The present invention relates to a shapable, colored copolymer of a 
polyester having chemically linked into the polyester backbone 
color-imparting amounts of a compound selected from lignin and lignin 
compounds having functional groups chemically linkable with the polyester 
backbone. 
Another embodiment of the present invention relates to a process for 
preparing a colored copolymer of a polyester having chemically linked into 
the polyester backbone color-imparting amounts of a compound selected from 
the group consisting of lignin and lignin compounds having functional 
groups chemically linkable with the polyester backbone. The process 
includes the steps of polymerizing at least one diol with at least one 
compound selected from dicarboxylic acids, esters of dicarboxylic acids 
and anhydrides of dicarboxylic acids, in the presence of color-imparting 
amounts of a compound selected from lignin and lignin compounds which can 
be chemically linked in a polyester backbone, and recovering the resultant 
polyester. 
A third embodiment of the present invention relates to an article of 
manufacture, including containers useful in the packaging of foods, 
beverages, cosmetics and pharmaceuticals made from the polyester of the 
present invention. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Lignin used to provide the colored polyester materials of the invention is 
a well known compound and is produced commercially by pulping processes 
which are well documented in the literature. Useful colorant lignins 
include Kraft lignin, steam explosion lignin, acid hydrolysis lignin, 
organosolv lignin and the like. The lignin derivatives which may also be 
used as colorants in the present invention have functional groups which 
will condense during polymerization into a polyester backbone as, for 
example, carboxy, ester, hydroxy and hydroxyalkoxy. Thus, without 
limitation, useful lignin derivatives of the present invention include 
lignin esters, lignin ethers, carboxy lignins, hydroxyalkoxy lignins and 
the like. More specifically, the lignin derivatives include lignin 
acetate, lignin propionate, lignin butyrate, lignin ethyl ether, lignin 
methyl ether, carboxymethyl lignin, (hydroxyethoxy) lignin, 
(hydroxypropoxy) lignin and the like. It should be understood that the 
ester lignin derivatives can be fully oxy-acylated yet still be 
incorporated into the polyester by ester interchange. The lignin ether 
derivatives, however, would be prepared under conditions leading to 
etherification of lignin phenolic hydroxyls only, leaving the aliphatic 
hydroxyls free to react in the polycondensation stage. Other lignin 
derivatives suitable for use in the present invention and their prepartion 
are discussed in Sarkanen and Ludwig, Lignins: Occurrence, Formation, 
Structure, and Reactions, Wiley-Interscience, New York, 1971, hereby 
incorporated by reference. 
The colorants of the invention are chemically linked and incorporated in 
the polyester backbone during the copolymerization by a condensation 
reaction either through esterification or by ester interchange. The 
polyesters of the present invention may be linear, thermoplastic, 
crystalline, or amorphous polyesters and are produced by copolymerizing 
one or more diols and one or more dicarboxylic acid esters or anhydrides 
thereof in the presence of lignin or lignin derivatives. In general, the 
diol components contain 2 to 18, preferably 2 to 12 carbon atoms. 
Illustrative of suitable diol components are ethylene glycol, 
1,4-cyclohexanedimethanol, 1,2-propanediol, 1,3-propanediol, 
1-2-butanediol, 1,3-butanediol, 1,4-butanediol, 
2,2-dimethyl-1,3-propanediol, 1,6-hexanediol, 1,2-cyclohexanediol, 
1,4-cyclohexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 
3,8-bis(hydroxymethyl) tricyclo-[5.2.1.0]-decane, 4,8-bis(hydroxymethyl) 
tricyclo-[5.2.1.0]-decane, 5,8-bis(hydroxymethyl) 
tricyclo-[5.2.1.0]-decane and diols containing one or more oxygen atoms in 
the chain such as diethylene glycol, triethylene glycol, dipropylene 
glycol, tripropylene glycol and the like. Cycloaliphatic diols can be 
employed in their cis- or trans-configuration or as a mixture of both 
forms. The dicarboxylic acid components are preferably aliphatic, 
alicyclic, or aromatic dicarboxylic acids, including the anhydrides and 
esters of the dicarboxylic acids. Examples of acid components of the 
polyester of the invention are terephthalic acid, isophthalic acid, 
1,4-cyclohexanedicarboxylic acid, 2,6 naphthalene dicarboxylic acid, 
1,3-cyclohexanedicarboxylic acid, succinic acid, glutaric acid, adipic 
acid, sebacic acid, 1,12-dodecanedioic acid and the like, and the 
anhydrides and esters thereof. Also, in place of the dicarboxylic acids it 
is possible, and often preferable to use functional acid derivatives of 
the dicarboxylic acids such as the dimethyl ester, diethyl ester and 
dipropyl ester of the dicarboxylic acid. The polyesters of the present 
invention are prepared using typical polycondensation techniques that are 
well known in the art. Generally, 2 moles of diol per one mole of 
dicarboxylic acid are placed in a reaction vessel with a color-imparting 
amount of a colorant selected from lignin, at least one lignin derivative, 
or mixtures thereof, and a polycondensation catalyst. The reaction vessel 
is heated with stirring and with a nitrogen sweep over the reaction 
mixture to distill off the theoretical amount of water or alcohol from the 
reaction vessel. The reaction vessel is then heated for an additional time 
period at reduced pressure, removed from the heat and allowed to cool in a 
nitrogen atmosphere to solidify the colored polyester. 
A preferred catalyst for use in the above reaction is a solution of 
acetyltriisopropyl titanate which contains 0.03 grams of titanium per 
milliliter. However, other polycondensation catalysts commonly employed in 
polyester formation condensation reactions may be used as well. 
The amount of lignin and lignin derivatives copolymerized with the diol and 
diacid components of the invention can vary but in all instances will be 
an amount sufficient to impart an amber color to the resulting polyester. 
Normally, the amount of lignin of lignin derivative will fall in the range 
of 0.05 to about 10 weight percent of the resultant polyester, preferably 
about 0.1 to about 5 weight percent of the resultant polyester. 
From experimentation it has been determined that the best mode of the 
present invention is represented by linear thermoplastic polyesters having 
an inherent viscosity of about 0.4 to about 1.2. The preferred acid 
reactant comprises at least 50 mole percent terephthalic acid and the 
preferred diol reactant comprises at least 50 mole percent ethylene glycol 
or 1,4-cyclohexanedimethanol. The preferred polyesters include about 0.1 
to about 5 weight percent of a copolymerizable lignin or lignin 
derivative. 
The colored copolymers of the present invention including lignin and lignin 
derivatives are shapable and thermally stable at polymer processing 
temperatures. Therefore, the colored copolymer of the invention can be 
shaped using polymer-shaping processes well known in the art. These 
polymer-shaping process include, for example, molding, fiber or sheet 
forming and the like. The greatest utility for the novel polyesters of the 
invention however will be as container bottles and the like. Thus, the 
colored polyesters of the present invention are suitable for use in food 
containers, beverage bottles, pharmaceutical containers, cosmetic 
containers and the like. The polyesters of the invention are particularly 
useful for the above applications because the color-inducing lignin or 
lignin derivative is not extractable from the polyester product and does 
not leach out of containers of the polyester into the container contents. 
Another advantage of the lignin colorant is its low cost in comparison to 
other colorants presently in use. In addition, the amber-colored polyester 
incorporating the lignin or lignin derivative exhibits greater clarity as 
compared to amber-colored polyesters prepared using colorants such as iron 
oxide. The amber colored polyesters of the present invention also exhibit 
low light transmittance at ranges of 300 nm to 450 nm as compared to 
colored copolymers using other colorant systems. Accordingly, the 
polyester of the invention provides light sensitive container contents 
greater protection from damaging light in the ultraviolet range.

The following two examples illustrate the preparation of lignin 
derivatives; 
EXAMPLE 1 
Preparation of Lignin Acetate 
A mixture of 100.0 g of lignin, 500 mL of acetic acid, 100 g of acetic 
anhydride, and 0.5 g of sodium acetate was stirred at ambient temperature 
for 48 hours, poured into 2 litres of water, and the precipitated lignin 
acetate was recovered by filtration. This lignin acetate (yield, 
approximately 108 g) was shown by analysis to contain 13.3.% acetyl by 
weight. 
EXAMPLE 2 
Preparation of (2-Hydroxyethoxy) Lignin 
A solution of 100 g of lignin in 600 mL of water containing 40.0 g of 
sodium hydroxide was treated with 75.0 mL of ethylene oxide and stirred at 
120.degree. C. for 8 hours. The resulting reaction mixture was acidified 
and filtered to give 102 g of solid product. A sample of this 
(2-hydroxyethoxy) lignin was fully acetylated with acetic anhydride in 
pyridine and analyzed by .sup.1 H NMR spectroscopy and acetyl analysis. 
The sample contained 14.1% acetyl, all of which was aliphatic according to 
the NMR analysis. 
Typical amber-colored polyesters prepared in accordance with this invention 
are as follows: 
EXAMPLE 3 
Preparation of Poly(ethylene terephthalate) Copolymerized with 0.9 wt % 
Lignin 
A total of 97 g (0.5 moles) of dimethyl terephthalate, 62 g (1.0 mole) 
ethylene glycol, 0.87 g (0.9 wt %) lignin, and 0.29 mL of an n-butanol 
solution of acetyltriisopropyl titanate which contains 0.03 g Titanium per 
mL is placed into a 500-mL, single-neck, round-bottom flask equipped with 
a nitrogen inlet, stirrer, vacuum outlet, and a condensing flask. The 
flask is heated with stirring at 200.degree. C. in a Belmont metal bath 
for 1 hour and at 210.degree. C. for 2 hours with a nitrogen sweep over 
the reaction mixture. When the theoretical amount of methanol has 
distilled from the reaction mixture, the metal bath temperature is 
increased to 280.degree. C. The flask is heated at 280.degree. C. at a 
reduced pressure of 0.5 to 0.1 mm mercury for 35 minutes. The flask is 
removed from the bath and is allowed to cool in a nitrogen atmosphere 
while the polyester solidifies. The flask is broken, the polyester is 
removed from the stirrer, and the polyester is ground to pass 3 mm using a 
Wiley mill. The ground polyester has an inherent viscosity of 0.86 
determined at 25.degree. C. in a 60/40 weight mixture of 
phenol/tetrachloroethane at a concentration of 0.5 g/100mL. Amorphous film 
of the polyester is bright amber colored. 
EXAMPLE 4 
Preparation of Poly(ethylene terephthalate) Copolymerized with 0.6 wt. % 
Acetylated Lignin 
A total of 97 g (0.5 moles) dimethyl terephthalate, 62 g (1.0 mole) 
ethylene glycol, 0.58 g (0.6 wt %) acetylated lignin, and 0.29 mL of a 
n-butanol solution of acetyltriisopropyl titanate which contains 0.03 g 
Titanium per mL is placed into a 500 mL, single-neck, round-bottom flask 
equipped with a nitrogen inlet, stirrer, vacuum outlet, and a condensing 
flask. The ester interchange and polymerization of this polymer are 
carried out as in Example 3. The resulting polymer has an inherent 
viscosity of 0.58. Amorphous film of the polyester is bright amber 
colored. 
EXAMPLE 5 
Preparation of Poly(ethylene terephthalate) Copolymer Containing 3.5 Mole % 
1,4-Cyclohexanedimethanol and 0.9 Wt. % Lignin 
A total of 97 g (0.5 moles) dimethyl terephthalate, 2.52 g (0.0175 moles) 
1,4-cyclohexanedimethanol (70% trans isomer, 30% cis isomer), 60.9 g 
0.9825 moles) ethylene glycol, 0.88 g (0.9 wt %) lignin, and 0.29 mL of a 
n-butanol solution of acetyltriisopropyl titanate which contains 0.03 g 
titanium per mL is placed in a 500 mL, single-neck, round-bottom flask 
equipped with a nitrogen inlet, stirrer, vacuum outlet, and a condensing 
flask. The ester interchange and polycondensation of this polymer are 
carried out as in Example 3. The resulting polymer has an inherent 
viscosity of 0.60. Amorphous film of the polyester is bright amber 
colored. Gas chromatographic analyses on a hydrolyzed sample of the 
polyester show that the polyester contains 3.5 mole % 
1,4-cyclohexanedimethanol. 
EXAMPLE 6 
Preparation of Poly(ethylene terephthalate) Copolymer Containing 31 Mole % 
1,4-Cyclohexanedimethanol and 0.6 wt % of Lignin Propionate 
A total of 97 g (0.5 moles) dimethyl terephthalate, 23 g (0.16 moles) 
1,4-cyclohexanedimethanol (70% trans isomer, 30% cis isomer), 52.1 g (0.84 
moles) ethylene glycol, 0.66 g (0.6 wt. %) lignin propionate, and 0.33 mL 
of a n-butanol solution of acetyltriisopropyl titanate which contains 0.03 
g titanium per mL is placed into a 500-mL, single-neck, round-bottom flask 
equipped with a nitrogen inlet, stirrer, vacuum outlet, and a condensing 
flask. The flask and contents are heated at 200.degree. C. for 120 minutes 
and at 225.degree. C. for 70 minutes with a nitrogen sweep over the 
reaction mixture. When the theoretical amount of methanol has distilled 
from the reaction mixture, the metal bath temperature is increased to 
275.degree. C. The flask is heated at 275.degree. C. at a reduced pressure 
of 0.5 to 0.1 mm mercury for 80 minutes. The flask is removed from the 
bath and is allowed to cool in a nitrogen atmosphere. Film of the 
resulting amorphous polymer is bright amber colored. The polymer has an 
inherent viscosity of 0.76. Gas chromatographic analyses on a hydrolyzed 
sample of the polyester show that the polyester contains 31 mole % 
1,4-cyclohexanedimethanol. 
EXAMPLE 7 
Preparation of Poly(hexamethylene terephthalate) Copolymer Containing 20 
Mole % 1,4-Butanediol and 0.6 Wt. % of Lignin Butyrate 
A total of 97 g (0.5 moles) dimethyl terephthalate, 85 g (0.72 moles) 
1,6-hexanediol, 25.2 g (0.28 moles) 1,4-butanediol, 0.73 g (0.6 wt %) 
lignin butyrate, and 2.28 mL of n-butanol solution of titanium 
tetraisopropoxide which contains 0.0053 g Titanium per mL placed into a 
00-mL, single-neck, round-bottom flask equipped with a nitrogen inlet, 
stirrer, vacuum outlet, and a condensing flask. The flask and contents are 
heated at 200.degree. C. for 60 minutes and at 210.degree. C. for 120 
minutes with a nitrogen sweep over the reaction mixture. When the 
theoretical amount of methanol has distilled from the reaction mixture the 
metal bath temperature is increased to 260.degree. C. The flask is heated 
at 260.degree. C. at a reduced pressure of 0.5 to 0.1 mm mercury for 62 
minutes. The flask is removed from the bath and is allowed to cool in a 
nitrogen atmosphere while the copolyester crystallizes. Film of the 
polyester is amber colored. The polymer has an inherent viscosity of 0.81. 
Gas chromatographic analyses of a hydrolyzed sample show that the 
polyester contains 20 25. mole %, 1,4-butanediol and 80 mole % 
1,6-hexanediol. The polyester has a melting point of 130.degree. C. and a 
heat of fusion of 9.4 calories per gram. 
This invention has been described in detail with particular reference to 
certain preferred embodiments thereof, but it is to be understood that 
variations and modifications can be effected within the spirit of the 
invention and the scope of the invention is to be determined from the 
claims appended hereto.