GLYCOLIC ACID POLYMER

Abstract

The invention pertains to an improved branched glycolic acid polymer being obtained from polycondensation reaction of a monomer mixture comprising: (i) glycolic acid (GA); (ii) optionally, at least one hydroxyacid having only one hydroxyl group and only one carboxylic acid group different from GA [hydroxyacid (A)], wherein the molar amount of hydroxyacid (A) is of at most 5% moles with respect to the sum of moles of GA and hydroxyacid (A); (iii) at least one polyol comprising at least three hydroxyl groups and being free from carboxylic acid group [polyol (H)]; (iv) at least one alcohol comprising one or two hydroxyl groups and being free from carboxylic acid group [alcohol (AO)]; (v) optionally at least one carboxylic acid comprising one carboxylic acid group and being free from hydroxyl group [monoacid (C)]; and (vi) optionally at least one polyacid comprising at least two carboxylic acid groups and being free from hydroxyl groups [polyacid (O)], wherein the amount of polyacid (O) is such that the number of carboxylic acid groups thereof is comprised between 0.025 and 0.900% with respect to the overall number of hydroxyl groups of glycolid acid and of the hydroxyacid (A), if present.

Claims

1. A glycolic acid polymer (polymer PGA), said polymer PGA being obtained from polycondensation reaction of a monomer mixture comprising: (i) glycolic acid (GA); (ii) optionally, at least one hydroxyacid having only one hydroxyl group and only one carboxylic acid group different from GA (hydroxyacid (A)), wherein a molar amount of hydroxyacid (A) is of at most 5% moles with respect to sum of moles of GA and hydroxyacid (A); (iii) at least one polyol comprising at least three hydroxyl groups and being free from carboxylic acid group (polyol (H)); (iv) at least one alcohol comprising one or two hydroxyl groups and being free from carboxylic acid group (alcohol (AO); (v) optionally at least one carboxylic acid comprising one carboxylic acid group and being free from hydroxyl group monoacid (C); and (vi) optionally at least one polyacid comprising at least two carboxylic acid groups and being free from hydroxyl groups polyacid (O), wherein the amount of polyacid (O) is such that number of carboxylic acid groups thereof is comprised between 0.025 and 0.900% with respect to a overall number of hydroxyl groups of glycolid acid and of the hydroxyacid (A), if present.

2. The polymer (PGA) according to claim 1, wherein an amount of polyol (H) is such that the number of hydroxyl groups thereof is comprised between 0.050 and 1.200% with respect to the overall number of carboxyl groups of glycolic acid and of the hydroxyacid (A), if present; the amount of alcohol (AO) is such that the number of hydroxyl groups thereof is comprised between 0.010 and 0.750% with respect to the overall number of carboxylic groups of glycolic acid and of the hydroxyacid (A), if present; and the amount of monoacid (C), when present, is such that the number of carboxylic acid groups thereof is comprised between 0.010 and 2.0% with respect to the overall number of hydroxyl groups of glycolic acid and of the hydroxyacid (A), if present.

3. The polymer (PGA) according to either claim 1, wherein the hydroxyacid (A) is selected from the group consisting of lactic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid and 6-hydroxycaproic acid, and/or wherein the hydroxyacid (A) is present in an amount of at most 4% moles with respect to the sum of moles of GA and of hydroxyacid (A).

4. The polymer (PGA) according to claim 1, wherein the polyol (H) is selected from the group consisting of: triols; tetraols; polyols comprising 5 hydroxyl groups; polyols comprising 6 hydroxyl groups; and polyols comprising 8 hydroxyl groups; and/or wherein the polyol (H) is used in an amount such that the number of hydroxyl groups thereof is of at least 0.050% with respect to the overall number of carboxylic groups of glycolic acid and of the hydroxyacid (A), if present.

5. The polymer (PGA) according to claim 1, wherein the alcohol (AO) is a diol (D) which is characterized by a boiling point at atmospheric pressure, of at least 100° C., and/or a diol (D) which is preferably used in an amount such that the number of hydroxyl groups thereof is of at least 0.010% with respect to the overall number of carboxylic groups of glycolic acid and of the hydroxyacid (A), if present.

6. The polymer (PGA) according to claim 1, wherein the alcohol (AO) is a diol (D) which is selected from diethyleneglycol, 1,4-cyclohexane dimethanol, isosorbide, isoidide, dodecane 1,12-diol and mixtures thereof.

7. The polymer (PGA) according to claim 1, wherein the monoacid (C) is an aliphatic monoacid of formula: R.sub.Hm—COOH (formula C-1) wherein R.sub.Hm is a monovalent aliphatic group having one or more than one carbon atom, or an aromatic monoacid selected from the group consisting of benzoic acid, naphthoic acid and phenylacetic acid.

8. The polymer (PGA) according to ah claim 1, wherein the polyacid (O) is an aromatic diacid.

9. A method of making the polymer (PGA) according to claim 1, said method comprising polycondensing glycolic acid (GA), optionally at least one hydroxyacid (A), at least one polyol (H), at least one alcohol (AO), optionally at least one monoacid (C) and optionally at least one polyacid (O), as defined in claim 1 to form the polymer (PGA).

10. A composition (C) comprising the polymer (PGA) according to claim 1 and at least one additional ingredient, wherein the said ingredient may be selected from anti-oxidants, thermal stabilizers, buffers, UV and light stabilizers, pigments, lubricants, processing aids, hydrolytic stabilizers, reinforcing agents, tougheners, plasticizers, colorants, antistatic agents, flame retardants, nucleating agents and other processing aids.

11. The composition (C) according to claim 10, wherein the composition (C) comprises the polymer (PGA) according to claim 1 and from 10 to 60 wt % based on total weight of the composition (C), of reinforcing agents.

12. A method for producing a multilayer, optionally stretched, optionally thermoformed, product, said method comprising: (i) forming a multilayer resin laminate including at least one layer of the polymer (PGA) according to claim 1 or of a composition (C) comprising the polymer (PGA) and at least one additional ingredient, and at least one layer of a thermoplast different from the polymer (PGA), by processing from a melt; (ii) optionally stretching the multilayer resin laminate, (iii) optionally thermoforming the optionally stretched, laminate, so as to produce the multilayer, optionally stretched, optionally thermoformed, product.

13. An article comprising the polymer (PGA) according to claim 1, a composition (C) comprising the polymer (PGA) and at least one additional ingredient, or a multilayer, optionally stretched, optionally thermoformed, product comprising at least one layer of the polymer (PGA) and at least one layer of a thermoplast different from the polymer (PGA).

14. The article according to claim 13, wherein the article is a bottle, an article for hydrocarbon resource recovery, a film for packaging, a feminine hygiene product, a disposable pod, a structural component for electronic applications or a biomedical article.

15. The article according to claim 14, wherein the article is an open-dome bottle, an article for hydrocarbon resource recovery or a feminine hygiene product.

16. The method of claim 9, wherein the method includes a first step of polymerization in a molten state to form a pre-polymer and a second step of solid state polymerization (SSP) for increasing molecular weight of the pre-polymer.

Description

EXAMPLE 1 (ACCORDING TO THE INVENTION)

[0251] A 7.5 l stainless steel double jacketed reactor, equipped with heater, condenser, temperature and pressure sensors and mechanical stirrer was charged with 4500 g of a 70 wt % of an aqueous glycolic acid solution (GA; 41.420 mole, taken as 1.0000 mol basis), 10.004 g of trimethylolpropane (TMP; 0.075 mole, 0.0018 mol per mol of GA), 3.584 g of cyclohexanedimethanol (CHDM, 0.025 mole, 0.0006 mol per mol of GA) and 0.536 g of methanesulfonic acid (MSA; 0.006 mole, 0.00014 mol per mol of GA).

[0252] The reactor was then closed and purged three times using alternatively vacuum and nitrogen. The reaction solution was heated rapidly to 50° C. under mechanical stirring. Pressure was reduced to 600 mbar and heating was pursued from 50° C. up to 100° C. over 30 min. The water distillation was started. The temperature was slowly raised to 130° C. over 60 min to gently pursue the water distillation. When most of the water was removed, the temperature was increased faster to 220° C. over 30 min.

[0253] Once 220° C. was reached, the pressure was progressively decreased down to 30 mbar over 30 min. Temperature was then finally raised up to 230° C. and kept steady for the rest of the synthesis. The vacuum was applied for 270 min more to increase the GA conversion.

[0254] The reaction mixture was then brought back to atmospheric pressure using nitrogen. The PGA was drawn from the kettle through the bottom valve and recovered in SS trays over dry ice. The hard solidified PGA mass was taken out and weighed. Crude yield: 2.10 kg (˜88%).

[0255] The polymer was grinded into small particles with less than 2 mm diameter using a high speed grinder, classified through a 2 mm sieve and further dried in a vacuum oven at 90° C. overnight.

[0256] In order to obtain an homogeneous particle size distribution and consistency, the powder was pelletized on a 19 mm diameter BRABENDER extruder, equipped with a 25 L/D monoscrew having a compression ratio of 3:1. The die was a one strand die (2 mm hole) and the strand was “die faced cut” in dry conditions. Screw speed used was 60 rpm and the temperature profile was kept low (flat temperature profile of 195° C., 4 heating zones in the extruder; 1 heating zone in the die), to cope with the low viscosity of the pre-polymer melt polymerized. Typical output was around 2.1 kg/h. Pellet size obtained was approximately 2 mm diameter and approximately 3 mm length.

[0257] The pellets so-obtained were introduced in a double wall rotary tumbler unit for uniform mixing and further polymerization in the solid state by applying heat and pulling vacuum. The tumbler used had a 15 l total volume/6 l useful volume. About 2 kg of polymer was used per batch.

[0258] After closing the tumbler, rotation was started at 8 rpm. The vacuum pump was started to reach 5-10 mbar vacuum in the tumbler. Simultaneously the tumbler was flushed with nitrogen (flow rate set at 50 l/h). Oil circulating in the double wall was heated in order to ramp up the temperature from room temperature to 214° C. in 16 h.

[0259] The tumbler was equipped with a sampling valve so that a specimen of reduced quantity of the polymer could be carefully taken out to analyze the melt viscosity using a parallel plate rheometer, at different times of solid state polymerization (SSP). After achieving the desired melt viscosity, the heating was stopped, the SSP was discontinued and the product was cooled down.

[0260] After 66 hours of SSP at 214° C., 1.8 kg of a PGA polymer having a melt viscosity of 647 Pa×sec at a shear rate of 10 sec.sup.1 was obtained.

[0261] The residual MSA in the final PGA after SSP was titrated according to the described method and found to be 0.005 mol % in regard to GA units.

EXAMPLE 2 (ACCORDING TO THE INVENTION)

[0262] The reactor described in Example 1 was charged with 4500 g of a 70 wt % of an aqueous glycolic acid solution (GA; 41.420 mole, taken as 1.0000 mol basis), 8.892 g of trimethylolpropane (TMP; 0.066 mole, 0.0016 mol per mol of GA), 9.557 g of cyclohexanedimethanol (CHDM, 0.066 mole, 0.0016 mol per mol of GA) and 0.536 g of methanesulfonic acid (MSA; 0.006 mole, 0.00014 mol per mol of GA).

[0263] The exact same protocol as Example 1 was applied and 2.20 kg of PGA were recovered (crude yield 92%).

[0264] The exact same protocol to pelletize the powder and increase melt viscosity by SSP was applied as in Example 1.

[0265] After 78 hours of SSP at 214° C., 1.8 kg of a PGA polymer having a melt viscosity of 634 Pa×sec at a shear rate of 10 sec.sup.−1 was obtained.

[0266] The residual MSA in the final PGA after SSP was titrated according to the described method and found to be 0.005 mol % in regard to GA units.

EXAMPLE 1(C) (COMPARATIVE EXAMPLE)

[0267] Using the same equipment and protocol as for Example 1, a load of 4500 g of a 70 wt % of an aqueous glycolic acid solution (GA; 41.420 mole, taken as 1.0000 mol basis), 8.892 g of trimethylolpropane (TMP; 0.066 mole, 0.0016 mol per mol of GA), 6.193 g of isophthalic acid (IPA, 0.037 mole, 0.0009 mol per mol of GA) and 0.819 g of methanesulfonic acid (MSA; 0.009 mole, 0.00021 mol per mol of GA), was converted into 2.15 kg of PGA (crude yield 90%).

[0268] The exact same protocol to pelletize the powder and increase melt viscosity by SSP was applied as in Example 1.

[0269] After 63 hours of SSP at 214° C., 1.8 kg of a PGA polymer having a melt viscosity of 582 Pa×sec at a shear rate of 10 sec.sup.−1 was obtained.

[0270] The residual MSA in the final PGA after SSP was titrated according to the described method and found to be 0.005 mol % in regard to GA units.

EXAMPLE 2(C) (COMPARATIVE EXAMPLE)

[0271] Similarly, a load of 4500 g of a 70 wt % of an aqueous glycolic acid solution (GA; 41.420 mole, taken as 1.0000 mol basis), 8.892 g of trimethylolpropane (TMP; 0.066 mole, 0.0016 mol per mol of GA) and 0.536 g of methanesulfonic acid (MSA; 0.006 mole, 0.00014 mol per mol of GA), was converted into 2.20 kg of PGA (crude yield 92%).

[0272] The exact same protocol to pelletize the powder and increase melt viscosity by SSP was applied as in Example 1.

[0273] After 48 hours of SSP at 214° C., 1.8 kg of a PGA polymer having a melt viscosity of 738 Pa×sec at a shear rate of 10 sec.sup.−1 was obtained.

[0274] The residual MSA in the final PGA after SSP was titrated according to the described method and found to be 0.005 mol % in regard to GA units.

[0275] Tan δ and hydrolysis resistance measured on the PGA obtained in the different examples, according to the methods described above, are given in Table 1.

[0276] The melt viscosity over time at 260° C. and 10 s.sup.−1 (melt stability) for the PGA obtained in the different examples is given in Table 2.

TABLE-US-00001 TABLE 1 Melt viscosity Resistance to (Pa × sec at a shear hydrolysis Run rate of 10 sec.sup.−1) Tan δ (hours) Example 1 647 2.6 180 Example 2 634 2.7 195 Example 1(C) 582 2.5 150 Example 2(C) 738 2.4 155

[0277] From the results given in Table 1, it can be seen that the PGA obtained according to the invention are characterized by a significant improvement of resistance to hydrolysis compared to the PGA obtained according to the comparative examples.

TABLE-US-00002 TABLE 2 sec min Example 1 Example 2 Example 1(C) Example 2(C) 6 0.1 100%  100%  100%  100%  600 10 97% 98% 88% 84% 900 15 88% 90% 72% 73% 1200 20 80% 83% 61% 64% 1500 25 73% 76% 52% 58%

[0278] From the results given in Table 2, it can be seen that the PGA obtained according to the invention are characterized by a melt stability over time which is significantly improved compared to the melt stability over time of the PGA obtained according to the comparative examples.

[0279] This leads to significant benefits in terms of the PGA processing window for typical melt processing techniques. Such more stable PGA is easier to handle and has a more predictable rheological behavior during pelletization, compounding, injection molding, blow molding, compression molding and film extrusion. This also reduces the need for extra moisture protection on the equipment. It also allows the polymer to be melt processed more than one time without the melt strength falling below an acceptable level for typical melt processes.