Biodegradable aliphatic-aromatic copolyester for use in nonwoven webs
View Patent ↗A method for forming a biodegradable aliphatic-aromatic copolyester suitable for use in fibers is provided. In one embodiment, for example, an aliphatic-aromatic copolyester is melt blended with an alcohol to initiate an alcoholysis reaction that results in a copolyester having one or more hydroxyalkyl or alkyl terminal groups. By selectively controlling the alcoholysis conditions (e.g., alcohol and copolymer concentrations, catalysts, temperature, etc.), a modified aliphatic-aromatic copolyester may be achieved that has a molecular weight lower than the starting aliphatic-aromatic polymer. Such lower molecular weight polymers also have the combination of a higher melt flow index and lower apparent viscosity, which is useful in a wide variety of fiber forming applications, such as in the meltblowing of nonwoven webs.
1. A fiber comprising a biodegradable aliphatic-aromatic copolyester terminated with a C 1 -C 10 alkyl group, a C 1 -C 10 hydroxyalkyl group, or a combination thereof, wherein the copolyester has a melt flow index of from about 5 to about 500 grams per 10 minutes, determined at a load of 2160 grams and temperature of 190° C. in accordance with ASTM Test Method D1238-E.
2. The fiber of claim 1 , wherein the melt flow index of the copolyester is from about 20 to about 250 grams per 10 minutes.
3. The fiber of claim 1 , wherein the copolyester has an apparent viscosity of from about 10 to about 500 Pascal-seconds, determined at a temperature of 170° C. and a shear rate of 1000 sec −1 .
4. The fiber of claim 1 , wherein the copolyester has an apparent viscosity of from about 30 to about 250 Pascal-seconds, determined at a temperature of 170° C. and a shear rate of 1000 sec −1 .
5. The fiber of claim 1 , wherein the copolyester has a number average molecular weight of from about 10,000 to about 70,000 grams per mole, a weight average molecular weight of from about 20,000 to about 125,000 grams per mole, and a polydispersity index of from 1 to 3.
6. The fiber of claim 1 , wherein the copolyester has a number average molecular weight of from about 20,000 to about 60,000 grams per mole, a weight average molecular weight of from about 30,000 to about 110,000 grams per mole, and a polydispersity index of from 1 to 3.
7. The fiber of claim 1 , wherein the copolyester has a melting point of from about 80° C. to about 160° C.
8. The fiber of claim 1 , wherein the copolyester has a glass transition temperature of about 0° C. or less.
9. The fiber of claim 1 , wherein the copolyester has the following general structure:
wherein,
m is an integer from 2 to 10, in some embodiments from 2 to 4, and in one embodiment, 4;
n is an integer from 0 to 18, in some embodiments from 2 to 4, and in one embodiment, 4;
p is an integer from 2 to 10, in some embodiments from 2 to 4, and in one embodiment, 4;
x is an integer greater than 1;
y is an integer greater than 1; and
R 1 and R 2 are independently selected from straight chain or branched, substituted or unsubstituted C 1 -C 10 alkyl groups and straight chain or branched, substituted or unsubstituted C 1 -C 10 hydroxyalkyl groups.
10. The fiber of claim 9 , wherein m and n are each from 2 to 4.
11. The fiber of claim 9 , wherein the copolyester is derived from polybutylene adipate terphthalate.
12. A nonwoven web comprising the fiber of claim 1 .
13. The nonwoven web of claim 12 , wherein the web is a meltblown web.
14. A nonwoven laminate comprising a spunbond layer and a meltblown layer, wherein the spunbond layer, the meltblown layer, or both, are formed from the web of claim 12 .