Biodegradable polyester

Abstract

A substantially gel-free and substantially linear biodegradable polyester obtainable by reaction with a radical initiator starting from a precursor polyester provided with an unsaturated chain terminator, wherein the terminator has the formula: T-(CH2)n-CHCH2, wherein T is selected from hydroxylic, carboxylic, amine, amide or ester group, and n is an integer comprised between 0 and 13. The content of the unsaturated chain terminator is between 0.01 and less than 1% by moles with respect to the moles of repetitive units of the polyester precursor; and the content of the radical initiator is less than 0.08 wt % with respect to the quantity of the precursor polyester.

Claims

1. A biodegradable thermoplastic polyester comprising units deriving from at least one diacid and at least one diol, obtained by reaction with a radical initiator starting from a precursor polyester, said precursor polyester being an aliphatic-aromatic biodegradable polyesters having the aromatic part composed by at least one aromatic polyfunctional acid and the aliphatic part composed by at least one C6-C13 aliphatic diacid, and at least one aliphatic diol, and an unsaturated chain terminator, said terminator having the formula: T-(CH2)n-CHCH2, wherein T is selected from the group consisting of hydroxylic, carboxylic, amine, amide or ester group, and n is 8 or 9; wherein the content of said unsaturated chain terminator is between 0.01 and less than 1% by moles with respect to the moles of repetitive units of the polyester precursor; the content of said radical initiator is less than 0.08 wt % with respect to the quantity of said precursor polyester; said precursor polyester having a gel fraction lower than 5%(w/w),a melt strength at 180 C. of 0.9 to 3 grams, a Shear Viscosity of 300 to 2,000 Pas and a structure comprising the multiple repetition in linear sequence of repeating units of acids and diols held together by ester linkage, in which the quantity of diacids or hydroxyacids of one or more polyfunctional molecules, and the derivatives thereof, is at most 3% by moles, the content of said at least one aromatic polyfunctional acid acids being between 30 and 80% by moles with respect to the total molar content of dicarboxylic acids.

2. The biodegradable polyester according to claim 1 wherein said terminator T is a carboxylic or hydroxylic group.

3. The biodegradable polyester according to claim 1 wherein said unsaturated chain terminator is omega-undecenoic acid, omega-undecylenic alcohol or mixtures thereof.

4. The biodegradable polyester according to claim 1, wherein said at least one aromatic polyfunctional acid is a dicarboxylic aromatic compound of the phthalic acid type and/or ester thereof and/or a dicarboxylic aromatic compound compounds of vegetable renewable origin and/or ester thereof.

5. The biodegradable polyester according to claim 4, wherein said at least one aromatic polyfunctional acid is a mixture of a dicarboxylic aromatic compound of the phthalic acid type and/or ester thereof and a dicarboxylic aromatic compound of vegetable renewable origin and/or ester thereof.

6. The biodegradable polyester according to claim 4, wherein said at least one aromatic polyfunctional acid is terephthalic acid and and/or ester thereof.

7. The biodegradable polyester according to claim 4 wherein said at least one aromatic polyfunctional acid is 2,5-furandicarboxylic acid and/or ester thereof.

8. The biodegradable polyester according to claim 1, wherein said at least one C.sub.6-C.sub.13 aliphatic diacid is selected from the group consisting of adipic acid, pimelic acid suberic acid, azelaic acid, sebacic acid, undecandioic acid, dodecandioic acid, brassylic acid and mixtures thereof.

9. The biodegradable polyester according to claim 8, wherein said at least one C.sub.6-C.sub.13 aliphatic diacid is of vegetable renewable origin.

10. The biodegradable polyester according to claim 9 wherein said at least one aliphatic diacid of vegetable renewable origin is selected from the group consisting of azelaic acid, sebacic acid and mixtures thereof.

11. The biodegradable polyester according to claim 1 wherein said precursor polyester contains at least one hydroxy acid, lactide thereof and/or lactone, in a quantity between 0-49%, by moles with respect to the molar content of repeating units.

12. The biodegradable polyester according to claim 1 wherein said precursor polyester is blended with another precursor polyester of the same type and/or with another polymer of natural or synthetic origin having an unsaturated terminal group.

13. The biodegradable polyester according to claim 1 wherein with a polyester of the same type and with another biodegradable polymer either of synthetic or natural origin.

14. A blend of the biodegradable polyester according to claim 13, wherein said biodegradable polymer of natural origin is selected from the group consisting of starch, cellulose, chitin, chitosan, alginates, proteins, lignins and derivatives thereof.

15. The biodegradable polyester according to claim 1 wherein the content of said unsaturated chain terminator is between 0.01% and 0.5% by moles with respect to the moles of repetitive units of the polyester precursor.

Description

EXAMPLES

Example 1

(1) a) Synthesis of the Precursor Polymer PP [poly(butylene terephthalate-co-butylene sebacate) at 56% by Moles of Aromatic Units Containing 0.15% by Moles of Omega Undecenoic Acid]

(2) A 25 l reactor, provided with a mechanical stirrer, an inlet for nitrogen flow, a condenser and a connection to a vacuum pump, was loaded with the following:

(3) TABLE-US-00001 dimethyl ester of terephthalic acid (DMT) 3313 g (17.08 moles) sebacic acid 2711 g (13.42 moles) 1,4-butanediol 3156 g (35.07 moles) omega-undecenoic acid 8.43 g (0.046 moles)

(4) The temperature was gradually increased under vigorous stirring and nitrogen flow to 210 C. The reaction was continued until 90% of the theoretical quantity of light by-products was distilled. The temperature was then increased to 240 C. and the system was subjected to a pressure of 0.6 mmHg. The reaction was continued for 120 min.

(5) 7.0 kg of polymer are obtained with shear viscosity of 674 Pas at a flow gradient =100 s.sup.1, Thermal Stability Constant 0.7.Math.10.sup.4 at 180 C., melt strength<1 at 180 C., molecular weight M.sub.n of 55140 and Melt Flow Rate (MFR) of 11 g/10 min (measured at 190 C. and 2.16 kg according to the standard ASTM D1238).

(6) b) Reactive Extrusion of the Precursor Polyester PP and Preparation of the Biodegradable Polyester BP According to the Invention

(7) 100 kg of the precursor polyester PP obtained in a) was made to react with 12 g of alpha,alphadi-(tert-butylperoxy)diisopropylbenzene (corresponding to 0.012% in weight) in a twin screw extruder whose principal characteristics are: extruder temperature profile: 30-100-200-170-150x3-160 C. twin screw rotation speed: 240 rpm active degassing

(8) A biodegradable polyester PB having the following properties is obtained: Shear viscosity of 1011 Pas Thermal Stability Constant 0.51.Math.10.sup.4 at 180 C. Melt Strength 1.6 g at 180 C., Gel fraction: <1%

(9) The polyester is odorless.

(10) Characterization of the Biodegradable Polyester BP According to Example 1.

(11) 2 grams of biodegradable polyester BP are placed in a 250 ml Erlenmeyer flask together with 100 ml of methanol and 0.5 g of lithium methylate and are refluxed until complete dissolution of the polymer and until a limpid solution is obtained (approximately 8 hours).

(12) 1 ml of the solution containing the polyester is taken to a pH of around 7 by a cationic exchange resin charged with H.sup.+. The sample thus obtained is then diluted 1 to 50 with methyl isobutyl ketone and analyzed by GC-MS. The instrument used is a Thermo Trace-DSQ II gas chromatograph provided with split/splitless injector used in splitless configuration (injector temperature 300 C.) and a Trace TR-5MS capillary column (length 15 m, diameter 0.25 mm, stationary phase 95% dimethyl-/5% diphenyl-polysiloxane and stationary phase thickness 0.25 m). The carrier gas used for analysis is He (flow 1.2 ml/min) The elution program consists in a temperature ramp that starts from 100 C. up to 300 C. with a gradient of 15 C./min. The injected volume is of 1 microliter.

(13) The mass detector is provided with electronic impact ionization set at 220 C. with positive ionization and was set in Total Ion Current mode between 40 and 600 m/z.

(14) FIG. 1-a shows the gas chromatographic trace obtained by analyzing the sample of biodegradable polyester according to Example 1. The gas chromatographic trace shows one chromatographic peak, with retention time of 3.52 minutes, which can be used for the identification of the biodegradable polyester according to Example 1.

(15) FIG. 1-b shows the gas chromatographic trace obtained by analyzing a sample of a poly(butylene terephthalate-co-butylene sebacate) at 56% by moles of aromatic units without unsaturated chain terminator which was previously subjected to reactive extrusion with 0.012% in weight of alpha-di(t-butyl peroxy)diisopropylbenzene. The gas chromatographic trace shows no peak at or around the retention time of 3.52 minutes.

(16) FIG. 2-a shows the detail of the mass spectrum of the peak at 3.52 minutes of the gas chromatographic trace shown in FIG. 1-a. Said peak is referable to the reacted unsaturated chain terminator of Example 1 after the reaction of its terminal double bond.

(17) FIG. 2-b shows a detail of the gas chromatographic trace of FIG. 1-b corresponding to a retention time of 3.52 minutes. FIG. 2-b has no peak corresponding to the chromatographic peak of the polyester according to Example 1.

Example 2

(18) Starch Based Blend

(19) 63 parts in weight of the biodegradable polyester BP obtained in Example 1 were mixed with 5 parts of poly-L-lactic acid (Mn of 130 000, MFR at 190 C., 2.16 kg of 3.5 g/10 min, lactide residue of less than 0.2% and D-isomer content of around 6%), 23.4 parts starch, 3.5 parts water and 5 parts glycerol in a Haake Rheocord 90 Rheomex TW-100 twin screw extruder.

(20) The thermal profile was maintained between 120 and 190 C. The final water content of the granule was equal to 0.8%.

(21) The granules thus obtained were made into film on a 40 mm Ghioldi machine having die gap=1 mm, flow rate 20 kg/h to obtain a film with a thickness of 20 m. The film obtained was subjected to mechanical characterization tests. Each parameter was determined by means of at least 6 replicates on randomly obtained specimen of films. The values herewith reported correspond to the arithmetic mean of these replicas.

(22) Mechanical properties (tear) (ASTM 192223 C. and 55% relative humidity, film thickness 31 m).

(23) Tear strength (N/mm) 163

Comparison Example 1

(24) a) Synthesis of poly(butylene terephthalate-co-butylene sebacate) at 56% by Moles of Aromatic Units Containing 1.2% by Moles of Omega-Undecenoic Acid

(25) A 25 l reactor, provided with a mechanical stirrer, an inlet for nitrogen flow, a condenser and a connection to a vacuum pump, was loaded with the following:

(26) TABLE-US-00002 dimethyl ester of terephthalic acid 3313 g (17.08 moles) (DMT) sebacic acid 2711 g (13.42 moles) 1,4-butanediol 3156 g (35.07 moles) omega-undecenoic acid 67.45 g (0.366 moles)

(27) The temperature was gradually increased under vigorous stirring and nitrogen flow to 210 C. The reaction was continued until 90% of the theoretical quantity of light by-products was distilled. The temperature was then increased to 240 C. and the system was subjected to a pressure of 0.6 mmHg. The reaction was continued for 120 min.

(28) 7. kg of polymer are obtained with shear viscosity of 540 Pas at a flow gradient =100 s.sup.1, Thermal Stability Constant 1.7.Math.10 at 180 C., melt strength<1 at 180 C., molecular weight M.sub.n of 43000 and Melt Flow Rate (MFR) of 14.4 g/10 min (measured at 190 C. and 2.16 kg according to the standard ASTM D1238).

(29) b) Reactive Extrusion of the Polyester According to Step a)

(30) 100 kg of the polyester obtained in a) was made to react with 600 g of alpha,alphadi-(tert-butylperoxy)diisopropylbenzene (corresponding to 0.6% in weight) in a twin screw extruder whose principal characteristics are: extruder temperature profile: 30-100-200-170-1503-160 C. twin screw rotation speed: 240 rpm active degassing

(31) A polyester having the following properties was obtained: Shear viscosity: not detectable Thermal Stability Constant: not detectable Melt Strength: not detectable Gel fraction .>5%

Comparison Example 2

(32) a) Synthesis of the Precursor Polymer PP [poly(butylene terephthalate-co-butylene sebacate) at 56% by Moles of Aromatic Units Containing 2% by Moles of Omega Undecenoic Acid]

(33) A 25 l reactor, provided with a mechanical stirrer, an inlet for nitrogen flow, a condenser and a connection to a vacuum pump, was loaded with the following:

(34) TABLE-US-00003 dimethyl ester of terephthalic acid 3313 g (17.08 moles) (DMT) sebacic acid 2711 g (13.42 moles) 1,4-butanediol 3156 g (35.07 moles) omega-undecenoic acid 112.4 g (0.61 moles)

(35) The temperature was gradually increased under vigorous stirring and nitrogen flow to 210 C. The reaction was continued until 90% of the theoretical quantity of light by-products was distilled. The temperature was then increased to 240 C. and the system was subjected to a pressure of 0.6 mmHg. The reaction was continued for 120 min.

(36) 7.0 kg of polymer were obtained with shear viscosity of 260 Pas at a flow gradient =100 s.sup.1, Thermal Stability Constant 1.24.Math.10.sup.4 at 180 C., melt strength<1 at 180 C., Melt Flow Rate (MFR) of 35 g/10 min (measured at 190 C. and 2.16 kg according to the standard ASTM D1238).

(37) b) Reactive Extrusion of the Precursor Polyester PP and Preparation of the Biodegradable Polyester PB According to the Invention

(38) 100 kg of the precursor polyester PP obtained in a) was made to react with 24 g of alpha,alphadi-(tert-butylperoxy)diisopropylbenzene (corresponding to 0.024% in weight) in a twin screw extruder whose principal characteristics are: extruder temperature profile: 30-100-200-170-1503-160 C. twin screw rotation speed: 240 rpm active degassing

(39) A biodegradable polyester PB having the following properties is obtained: Shear viscosity of 2674 Pas Thermal Stability Constant 0.41.Math.10.sup.4 at 180 C. Melt Strength 11 g at 180 C., Gel fraction: >5%