MELT-STABLE POLYLACTIDE RESIN COMPOSITIONS CONTAINING PHOSPHITE ESTERS

Abstract

Polylactide resin compositions contain certain phosphite esters. The presence of the phosphite ester increases the rate of hydrolysis of the polylactide resin under conditions of moisture (including atmospheric moisture) at mildly elevated temperatures.

Claims

1. A polylactide resin composition comprising (a) at least one polylactide having a number-average molecular weight as measured by gel permeation chromatography against a polystyrene standard of at least 20,000 g/mol, the polylactide containing (i) 5 to 300 ppm by weight of Group 2-14 metals based on the weight of the polylactide, (ii) 0.1 to 2 parts by weight per 100 parts by weight of the polylactide of (ii-a) a polymer having multiple carboxylic acid, a number average molecular weight of at least 500 g/mol and at least one carboxylic acid group per 250 atomic mass units and/or (ii-b) a polyphosphoric acid which may be partially or completely neutralized, and/or residue thereof and (iii) no more than 0.6 parts by weight of lactide per 100 parts by weight of the polylactide, and (b) at least one phosphite ester compound having a number-average molecular weight of up to 5,000 g/mol, the phosphite ester compound containing 3 to 15% by weight phosphorus and wherein the phosphite ester compound contains, per phosphite phosphorus atom, from zero to one aryl group in which at least one ring carbon ortho to a ring carbon bonded directly to a phosphite oxygen is directly bonded to a tertiary carbon atom of a substituent group, and the polylactide resin composition containing sufficient phosphite ester compound to provide 0.01 to 32 g of phosphorus per kilogram of the polylactide in the polylactide resin composition.

2. The polylactide resin composition of claim 1 wherein the phosphite ester compound is one or more of bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite, bis(2,4-dicumylphenyl) pentaerythritol diphosphite, bis (octadecyl)pentaerythritol diphosphite, triphenyl phosphite, tridecyl phosphite, didecyl phenyl phosphite, phenyl neopentylene glycol phosphite ester and tris(4-nonylphenyl) phosphite.

3. The polylactide resin composition of claim 1 wherein the phosphite ester compound includes at least one at least one polyphosphite ester compound represented by either of structures I and II, wherein structure I is ##STR00004## wherein each R.sup.2, R.sup.3, R.sup.4 and R.sup.5 can be the same or different and independently selected from the group consisting of C.sub.1-20 alkyl, C.sub.3-22 alkenyl, C.sub.6-40 cycloalkyl, C.sub.7-40 cycloalkylene, C.sub.1-20 methoxy alkyl glycol ethers, C.sub.1-20 alky glycol ethers, and/or YOH; Y is selected from the group consisting of C.sub.2-40 alkylene, C.sub.2-40 alkyl lactone, R.sup.6N(R.sup.7)R.sup.8 wherein R.sup.6, R.sup.7, and R.sup.8 are independently selected from the group consisting of hydrogen, C.sub.1-20 alkyl, C.sub.3-22 alkenyl, C.sub.6-40 cycloalkyl, C.sub.7-40 cycloalkylene, C.sub.1-20 methoxy alkyl glycol ethers, C.sub.1-20 alky glycol ethers and/or YOH, m is an integral value ranging from 2 to 100 and x is an integral value ranging from 1 to 1000; and structure II is ##STR00005## wherein R.sup.10, R.sup.11, R.sup.12, R.sup.13 and R.sup.14 can be the same or different are independently selected from the group consisting of C.sub.1-20 alkyl, C.sub.2-22 alkenyl, C.sub.6-40 cycloalkyl and C.sub.704.sub.o cycloalkenyl; Y is selected from the group consisting of C.sub.2-40 alkylene, C.sub.2-40 aliphatic carboxylic acid esters and C.sub.3-40 cycloalkylenes, n is a number from 5 to 100, u is a number from 8 to 1000, v is a number from 1 to 1000 and w is a number from 1 to 1000.

4. The polylactide resin composition of claim 1 which contains 5 to 300 ppm tin.

5. The polylactide resin composition of claim 1 wherein the polymer having multiple carboxylic acid groups, a number average molecular weight of at least 500 g/mol and at least one carboxylic acid group per 250 atomic mass units is present and is a homopolymer or copolymer of acrylic acid.

6. The polylactide resin composition of claim 1 wherein the polyphosphoric acid or residue thereof is present.

7. A method of making a polylactide resin composition of claim 1, comprising the steps of: a) polymerizing lactide in the presence of a Group 2-14 metal-containing catalyst to produce a crude polylactide containing 5 to 300 ppm by weight of Group 2-14 metals based on the weight of the polylactide; b) combining the crude PLA resin with a 0.1 to 2 parts by weight, per 100 parts of the polylactide, of (i) a polymer having multiple carboxylic acid groups, a number average molecular weight of at least 500 g/mol and at least one carboxylic acid group per 250 atomic mass units, and/or (ii) a polyphosphoric acid and/or residue thereof; c) before, simultaneously with, or after step b), devolatilizing the crude polylactide resin to reduce the lactide concentration to no greater than 0.6% of the combined weight of the polylactide and the remaining lactide and then d) after step b), combining the PLA resin at least one phosphite ester compound containing 3 to 15% by weight phosphorus and wherein the phosphite ester compound contains, per phosphite phosphorus atom, from zero to one aryl group in which at least one ring carbon ortho to a ring carbon bonded directly to a phosphite oxygen is directly bonded to a tertiary carbon atom of a substituent group, in an amount of sufficient to provide 0.01 to 32 g of phosphorus per kg of the polylactide in the polylactide resin composition.

8. The method of claim 7 wherein the phosphite ester compound is one or more of bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite, bis(2,4-dicumylphenyl) pentaerythritol diphosphite, bis (octadecyl)pentaerythritol diphosphite, triphenyl phosphite, tridecyl phosphite, didecyl phenyl phosphite, phenyl neopentylene glycol phosphite ester and tris(4-nonylphenyl) phosphite.

9. The method of claim 7 wherein the phosphite ester compound includes at least one at least one polyphosphite ester compound represented by either of structures I and II, wherein structure I is ##STR00006## wherein each R.sup.2, R.sup.3, R.sup.4 and R.sup.5 can be the same or different and independently selected from the group consisting of C.sub.1-20 alkyl, C.sub.3-22 alkenyl, C.sub.6-40 cycloalkyl, C.sub.7-40 cycloalkylene, C.sub.1-20 methoxy alkyl glycol ethers, C.sub.1-20 alky glycol ethers, and/or YOH; Y is selected from the group consisting of C.sub.2-40 alkylene, C.sub.2-40 alkyl lactone, R.sup.6N(R.sup.7)R.sup.8 wherein R.sup.6, R.sup.7, and R.sup.8 are independently selected from the group consisting of hydrogen, C.sub.1-20 alkyl, C.sub.3-22 alkenyl, C.sub.6-40 cycloalkyl, C.sub.7-40 cycloalkylene, C.sub.1-20 methoxy alkyl glycol ethers, C.sub.1-20 alky glycol ethers and/or YOH, m is an integral value ranging from 2 to 100 and x is an integral value ranging from 1 to 1000; and structure II is ##STR00007## wherein R.sup.10, R.sup.11, R.sup.12, R.sup.13 and R.sup.14 can be the same or different are independently selected from the group consisting of C.sub.1-20 alkyl, C.sub.2-22 alkenyl, C.sub.6-40 cycloalkyl and C.sub.704.sub.o cycloalkenyl; Y is selected from the group consisting of C.sub.2-40 alkylene, C.sub.2-40 aliphatic carboxylic acid esters and C.sub.3-40 cycloalkylenes, n is a number from 5 to 100, u is a number from 8 to 1000, v is a number from 1 to 1000 and w is a number from 1 to 1000.

10. The method of claim 7 wherein the polylactide resin composition contains 5 to 300 ppm tin.

11. The method of claim 7 wherein in step b the crude PLA resin is combined with the polymer having multiple carboxylic acid groups, a number average molecular weight of at least 500 g/mol and at least one carboxylic acid group per 250 atomic mass units.

12. The method of 7 wherein in step b) the crude PLA resin is combined with the polyphosphoric acid.

13. A polylactide resin composition comprising (a) at least one polylactide having a number-average molecular weight as measured by gel permeation chromatography against a polystyrene standard of at least 20,000 g/mol having dissolved or dispersed therein (b) at least one polyphosphite ester compound containing 3.5 to 15% by weight phosphorus and being represented by either of structures I and II, wherein structure I is ##STR00008## wherein each R.sup.2, R.sup.3, R.sup.4 and R.sup.5 can be the same or different and independently selected from the group consisting of C.sub.1-20 alkyl, C.sub.3-22 alkenyl, C.sub.6-40 cycloalkyl, C.sub.7-40 cycloalkylene, C.sub.1-20 methoxy alkyl glycol ethers, C.sub.1-20 alky glycol ethers, and/or YOH; Y is selected from the group consisting of C.sub.2-40 alkylene, C.sub.2-40 alkyl lactone, R.sup.6N(R.sup.7)R.sup.8 wherein R.sup.6, R.sup.7, and R.sup.8 are independently selected from the group consisting of hydrogen, C.sub.1-20 alkyl, C.sub.3-22 alkenyl, C.sub.6-40 cycloalkyl, C.sub.7-40 cycloalkylene, C.sub.1-20 methoxy alkyl glycol ethers, C.sub.1-20 alky glycol ethers and/or YOH, m is an integral value ranging from 2 to 100 and x is an integral value ranging from 1 to 1000; and structure II is ##STR00009## wherein R.sup.10, R.sup.11, R.sup.12, R.sup.13 and R.sup.14 can be the same or different are independently selected from the group consisting of C.sub.1-20 alkyl, C.sub.2-22 alkenyl, C.sub.6-40 cycloalkyl and C.sub.704.sub.o cycloalkenyl; Y is selected from the group consisting of C.sub.2-40 alkylene, C.sub.2-40 aliphatic carboxylic acid esters and C.sub.3-40 cycloalkylenes, n is a number from 5 to 100, u is a number from 8 to 1000, v is a number from 1 to 1000 and w is a number from 1 to 1000, is (i) a linear or branched C.sub.2 to C.sub.24 alkylene group; (ii) a residue, after removal of hydroxyl groups, of a glycol ether or a glycol polyether, a homopolymer or copolymer of ethylene glycol, and/or propylene glycol having 4 or more ether units and formula weights (after removal of hydroxyl groups) of up to 1000 g/mol; and (iii) an o-, m-, or p-dialkyl cyclohexane, in which the alkyl groups have 1 to 4 carbon atoms.

14. A process for hydrolyzing a polylactide resin, comprising immersing a polylactide composition of claim 13 in liquid water at a temperature of 25? C. to 80? C.

15. A process for hydrolyzing a polylactide resin, comprising immersing a polylactide composition of claim 13 in liquid water at a temperature of 25? C.to 80? C.

16. A process for hydrolyzing a polylactide resin, comprising contacting the polylactide composition of claim 13 in air having relative humidity of at least 50% at a temperature of 35? C. to 80? C.

17. A method for treating a subterranean formation comprising a) introducing a treatment fluid containing a liquid phase and particles of the polylactide composition of claim 1 into the subterranean formation, such that a mass of the particles is deposited in the subterranean formation, and then b) hydrolyzing the deposited particles in the subterranean formation by exposing the deposited particles to an aqueous medium and an elevated temperature such that the deposited particles lose at least 50% of their starting mass due to hydrolysis.

Description

Examples 1-15 and Comparative Samples A-C

[0077] Examples 1-15 and Comparative Samples B and C are prepared by melt-blending PLA Resin 1 with a phosphite ester compound (as indicated in Table 1) in a twin-screw extruder. The amount of phosphite ester compound is selected to provide phosphorus levels in the product as indicated in Table 1 below. Comparative Sample A is prepared by passing a sample of PLA Resin 1 through the twin-screw extruder under the same operating conditions but without any additive.

TABLE-US-00001 TABLE 1 Sample Phosphite Additive mmol P/kg g P/kg A* None 0 0 1 Phosphite Ester 1 2.36 0.07 2 Phosphite Ester 1 11.79 0.365 3 Phosphite Ester 1 117.9 3.65 4 Phosphite Ester 2 2.36 0.07 5 Phosphite Ester 2 11.82 0.366 6 Phosphite Ester 2 118.2 3.66 7 Phosphite Ester 3 11.79 0.365 8 Phosphite Ester 3 122.9 3.81 9 Phosphite Ester 4 11.9 0.369 10 Phosphite Ester 4 115.7 3.58 11 Phosphite Ester 5 11.79 0.365 12 Phosphite Ester 5 117.2 3.64 13 Phosphite Ester 6 2.36 0.07 14 Phosphite Ester 6 11.79 0.365 15 Phosphite Ester 6 112.4 3.49 B* Phosphite Ester A 11.79 0.365 C* Phosphite Ester A 116.0 3.59 *Not an example of the invention.

[0078] 5 The various materials are subjected to hydrolysis to determine relative rates of hydrolysis. The hydrolysis rate of Comparative Sample A is assigned a relative value of 1.0. The weight-average molecular weight of a sample of each material is measured by GPC relative to polystyrene standards. A portion of each sample is placed in an open aluminum container and subjected to conditions of 50? C. and 80% relative humidity (RH) in a humidity chamber. A sample is removed every 48 hours for 10 molecular weight measurement. The removed sample is first dried in a vacuum oven at 40? C. for 24 hours to remove water and thereby stop any further hydrolysis, and then evaluated by GPC. The slope of the natural logarithm of the molecular weight versus time is evaluated, and a relative (compared to Comparative Sample A) rate of hydrolysis is calculated. Higher numbers indicate faster hydrolysis. Results are as indicated in Table 2.

TABLE-US-00002 TABLE 2 Hydrolysis Data in Humidity Chamber at 50? C. and 80% RH Starting Slope Relative g Mw Ln(M.sub.w)/ Hydrolysis Sample Phosphite Additive P/kg (g/mol) day Rate A* None 0 208,737 ?0.0432 1.00 1 Phosphite Ester 1 0.07 204,910 ?0.0796 1.84 2 Phosphite Ester 1 0.365 173,644 ?0.1404 3.25 3 Phosphite Ester 1 3.65 206,589 ?0.1637 3.79 4 Phosphite Ester 2 0.07 196,585 ?0.0571 1.32 5 Phosphite Ester 2 0.366 158,640 ?0.1175 2.72 6 Phosphite Ester 2 3.66 205,262 ?0.2614 6.05 7 Phosphite Ester 3 0.365 203,618 ?0.0929 2.15 8 Phosphite Ester 3 3.81 201,072 ?0.0815 1.89 9 Phosphite Ester 4 0.369 210,832 ?0.1017 2.35 10 Phosphite Ester 4 3.58 206,729 ?0.1197 2.77 11 Phosphite Ester 5 0.365 212,568 ?0.1002 2.32 12 Phosphite Ester 5 3.64 207,115 ?0.1118 2.59 13 Phosphite Ester 6 0.07 212,741 ?0.0619 1.43 14 Phosphite Ester 6 0.365 212,515 ?0.1261 2.92 15 Phosphite Ester 6 3.49 226,148 ?0.2031 4.70 B* Phosphite Ester A 0.365 206,876 ?0.0411 0.95 C* Phosphite Ester A 3.59 207,030 ?0.0350 0.81 *Not an example of the invention.

[0079] It is seen from the data in Table 2 that Phosphite Esters 1-6 each provides, at an equivalent phosphorus loading, a much faster rate of hydrolysis than the control (Comparative Sample A). At a phosphorus loading of about 0.36 g/kg, the presence of Phosphite Ester 1 more than triples the rate of hydrolysis under these mild hydrolysis conditions. An even greater acceleration is achieved if the amount of Phosphite Ester is increased to provide 3.65 g P/kg. The hydrolysis rate is nearly doubled even at the very low loading of Example 1. Phosphite Ester 2 is seen to nearly triple the hydrolysis rate at a phosphorus loading of 0.354 g/kg, and to increase it by over six times at a phosphorus loading of 3.65 g/kg.

[0080] Phosphite Esters 3-6 also provide significant acceleration of the hydrolysis rate. Phosphite Ester A has no effect on hydrolysis rate.

[0081] Another set of hydrolysis experiments is performed in similar manner, except the hydrolysis conditions are 40? C. and 80% RH. Results are as indicated in Table 3.

TABLE-US-00003 TABLE 3 Hydrolysis Data in Humidity Chamber at 40? C. and 80% RH Starting Slope Relative g Mw Ln(Mw)/ Hydrolysis Sample Phosphite Additive P/kg (g/mol) day Rate A* None 0 208,737 ?0.0046 1.00 1 Phosphite Ester 1 0.07 204,910 ?0.0111 2.41 2 Phosphite Ester 1 0.365 173,644 ?0.0226 4.91 7 Phosphite Ester 3 0.365 203,618 ?0.0212 4.61 9 Phosphite Ester 4 0.369 210,832 ?0.0230 5.00 11 Phosphite Ester 5 0.365 212,568 ?0.0219 4.76 13 Phosphite Ester 6 0.07 212,741 ?0.0120 2.61 14 Phosphite Ester 6 0.365 212,515 ?0.0230 5.00 B* Phosphite Ester A 0.365 206,876 ?0.0052 1.13 *Not an example of the invention.

[0082] Under these still milder conditions, Phosphite Esters 1 and 3-6 still provide significant acceleration of hydrolysis rates.

[0083] A third set of hydrolysis experiments is performed in similar manner, except the samples are submersed in DI water at 50? C. Results are as indicated in Table 4.

TABLE-US-00004 TABLE 4 Hydrolysis Data for Samples Submersed in DI Water at 50? C. Starting Slope Relative g Mw Ln(Mw)/ Hydrolysis Sample Phosphite Additive P/kg (g/mol) day Rate A* None 0 208,737 ?0.0506 1.00 1 Phosphite Ester 1 0.07 204,910 ?0.0692 1.37 2 Phosphite Ester 1 0.365 173,644 ?0.1169 2.31 4 Phosphite Ester 2 0.07 196,585 ?0.0614 1.18 5 Phosphite Ester 2 0.366 158,640 ?0.1101 2.12 7 Phosphite Ester 3 0.365 203,618 ?0.0587 1.16 9 Phosphite Ester 4 0.369 210,832 ?0.0606 1.20 11 Phosphite Ester 5 0.365 212,568 ?0.0625 1.23 14 Phosphite Ester 6 0.365 212,515 ?0.0630 1.25 B* Phosphite Ester A 0.365 206,876 ?0.0487 0.96 *Not an example of the invention.

[0084] This data illustrates the effect of changing from hydrolysis in humid air to hydrolysis in liquid water. Phosphite Ester A has a slightly negative effect on hydrolysis rate. Phosphite Esters 3-6 increase hydrolysis rate slightly. Phosphite Esters 1 and 2 provide very significant increases in the hydrolysis rate under these conditions.

[0085] Examples 2 and 9 and Comparative Samples A and C are taken for thermophilic aerobic respirometry (58? C.) according to ASTM D5338-15, as follows.

[0086] An inoculum is prepared from a compost having a water content of 45-55% water, obtained from an industrial composting plant, sieved through a 4.76-mm sieve. This compost has an activity within the range of 50 to 150 mg CO.sub.2 per gram of volatile solids over 10 days, per ASTM D5338 ? 9.1. It has an ash content of less than 70% and a pH between 7 and 8.2. It has heavy metal contents below the maximum allowable for good microbial health and activity.

[0087] Samples of each of Examples 2 and 9 and Comparative Samples A and B are ground and sieved to produce test samples having a particle size of 0.5 to 1.0 mm. 40 g of the test samples are added to 480 g of inoculum and CO2 production is measured over a 90-day period according to the ASTM method. The cumulative CO2 production and absolute biodegradation data are as indicated in Table 5.

TABLE-US-00005 TABLE 5 Composting Results after 90 days Absolute Cumulative CO.sub.2 Biodegra- Sample Phosphite Additive g P/kg production (mg) dation, % A* None 0 77,376 58.0 2 Phosphite Ester 1 0.365 98,049 86.3 9 Phosphite Ester 4 0.369 87,141 71.4 B* Phosphite Ester A 0.365 76,785 57.3

[0088] The blank reactor exhibits a cumulative CO.sub.2 production of 34,741 mg. Absolute biodegradation is calculated from the following equation:

[00001]$\mathrm{Absolute}\mathrm{Biodegradation}\left(\%\right)=\frac{{\mathrm{Sample}}_{{\mathrm{CO}}_2}}{\mathrm{sample}\mathrm{mass}?\mathrm{carbon}\mathrm{content}\left(\%\right)?44/12}$

where Sample.sub.CO2 is calculated accordingly:

Sample.sub.CO.sub.2Reactor.sub.CO.sub.2?Blank.sub.CO.sub.2

[0089] For the samples subjected to biodegradation testing, carbon content is 50%.

[0090] These results demonstrate that the presence of Phosphite Esters 1 and 4 each greatly accelerates biodegradation under compositing conditions, whereas Phosphite Ester A provides no benefit.

Examples 17-19 and Comparative Samples D-F

[0091] Examples 17-19 and Comparative Samples E and G are prepared by melt-blending PLA Resin 2 or PLA Resin 3 with a phosphite ester compound (as indicated in Table 6) in a twin-screw extruder. The amount of phosphite ester compound is selected to provide phosphorus levels in the product as indicated in Table 6. Comparative Samples D and F are prepared by passing a sample of PLA Resin 2 and PLA Resin 3, respectively, through the twin-screw extruder under the same operating conditions but without any additive.

TABLE-US-00006 TABLE 6 Phosphite Sample PLA Resin Additive mmol P/kg g P/kg D* 2 None 0 0 E* 2 A 11.8 0.366 16 2 1 11.8 0.366 17 2 4 11.8 0.366 F* 3 None 0 0 G* 3 A 11.8 0.366 18 3 1 11.8 0.366 19 3 4 11.8 0.366 *Not an example of the invention.

[0092] Examples 16-19 and Comparative Samples D-G each are subjected to hydrolysis at conditions of 50? C. and 80% relative humidity (RH), in the manner as described for the previous examples. Results are as indicated in Table 7.

TABLE-US-00007 TABLE 7 Hydrolysis Data in Humidity Chamber at 50? C. and 80% RH Slope Relative PLA g Ln(M.sub.w)/ Hydrolysis Sample Resin Phosphite Additive P/kg day Rate.sup.1 C* 2 None 0 ?0.0311 1.00 D* 2 Phosphite Ester A 0.366 ?0.0357 1.15 16 2 Phosphite Ester 1 0.366 ?0.0895 2.88 17 2 Phosphite Ester 4 0.366 ?0.0823 2.65 E* 3 None 0.366 ?0.0334 1.0 F* 3 Phosphite Ester A 0.366 ?0.0420 1.26 18 3 Phosphite Ester 1 0.366 ?0.1307 3.91 19 3 Phosphite Ester 4 0.366 ?0.0991 2.97 *Not an example of the invention. .sup.1Relative to Sample C, for Comparative Sample D and Examples 16 and 17; relative to Sample E, for Comparative Sample F and Examples 18 and 19.

[0093] PLA Resins 2 and 3 are treated with a polyphosphoric acid instead of the polyacrylic acid used to treat PLA Resin 1. The rate of hydrolysis of PLA Resins 2 and 3, when no phosphite ester is present (Samples C and E) is significantly less than that of PLA Resin 1 (Sample A, See Table 2). This indicates that the polyphosphoric acid (or residues thereof) present in PLA Resins 2 and 3 does not facilitate hydrolysis; to the contrary its presence appears to slow the hydrolysis rate by 20% to 30%.

[0094] Similar to the results with PLA Resin 1, Phosphite Ester A provides very little increase in hydrolysis rate under these conditions, whereas very significant increases in hydrolysis rate are seen with Phosphite Esters 1 and 4.

[0095] Examples 16-19 and Comparative Samples D-G each are subjected to hydrolysis in 50? C. liquid water, in the manner as described for the previous examples. Example 16 is evaluated twice with the average result being reported. Results are as indicated in Table 8.

TABLE-US-00008 TABLE 8 Hydrolysis Data for Samples Submersed in DI Water at 50? C. Slope Relative PLA g Ln(M.sub.w)/ Hydrolysis Sample Resin Phosphite Additive P/kg day Rate.sup.1 C* 2 None 0 ?0.0435 1.00 D* 2 Phosphite Ester A 0.366 ?0.0391 0.90 16 2 Phosphite Ester 1 0.366 ?0.0884 2.0 17 2 Phosphite Ester 4 0.366 ?0.0393 0.90 E* 3 None 0.366 ?0.0384 0.88 F* 3 Phosphite Ester A 0.366 ?0.0385 1.00 18 3 Phosphite Ester 1 0.366 ?0.0816 2.13 19 3 Phosphite Ester 4 0.366 ?0.0422 1.10 *Not an example of the invention. .sup.1Relative to Sample C, for Comparative Sample D and Examples 16 and 17; relative to Sample E, for Comparative Sample F and Examples 18 and 19.

[0096] As before, the rate of hydrolysis of PLA Resins 2 and 3, when no phosphite ester is present (Samples C and E), is significantly less than that of PLA Resin 1 (Sample A, See Table 4). The presence of polyphosphoric acid (or residues thereof) appears to slow the hydrolysis rate by 14-25% in this test.

[0097] Again, it is seen that the performance of the phosphite ester is quite different when the sample is exposed to liquid water rather than merely humid air. Phosphite Ester A has an adverse effect hydrolysis rate under immersion conditions. The presence of Phosphite Ester 1 causes a doubling of the hydrolysis rate. A smaller but still positive increase in hydrolysis rate is seen with Phosphite Ester 4.

Examples 20 and 21 and Comparative Samples G and H

[0098] Examples 20 and 21 and Comparative Sample G are prepared by melt-blending PLA Resin 4 with 1.8 weight-% Phosphite Ester 1, 1 weight-% Phosphite Ester 2 and 1.4 weight-% lauric acid, respectively, in a twin-screw extruder. Comparative Sample H is PLA Resin 4 by itself.

[0099] Mass loss of the solid (undissolved) material is performed according to the following protocol. Approximately 2 grams samples, accurately weighed, are added to multiple vials which are also accurately weighed. The vials are then sealed and placed in oven and maintained at 50? C. The vials are removed one-by-one periodically over time. The liquid phase is separated from the remaining solids via decanting, and the vials containing residual solids are then dried to constant weight at 40? C. under vacuum. Mass loss is evaluated from the difference in initial and final weight for each vial as a function of time. The time at which 50% of the starting mass is lost is reported as t.sub.1/2. Testing is continued until the 95% of the starting mass of the sample has hydrolyzed and become dissolved in the liquid phase. Results are as indicated in Table 9.

TABLE-US-00009 TABLE 9 Hydrolysis Data for Samples Submersed in DI Water at 50? C. Additive Time to 95% Sample Additive Amount t.sub.1/2, days dissolution, days 19 Phosphite Ester 1 1.8% 9.5 19 20 Phosphite Ester 1 .sup.1% 12 20 G* Lauric Acid 1.4% 14.5 22 H* None N/A 17.5 24 *Not an example of the invention.

[0100] PLA Resin 4 by itself loses half of its mass in 17.5 days and 95% its mass in 24 days on this test. Adding 1.4% lauric acid, a known hydrolysis accelerant, decreases t.sub.1/2 by about 17%. Although not shown in Table 9, melt blending higher concentrations of lauric acid to PLA Resin 4 does not decrease t12 significantly.

[0101] Adding Phosphite Ester 1 to PLA Resin 4 results in much larger decreases in t.sub.1/2 (31-43%) than does lauric acid. The 95% hydrolysis in a reduced period of time is an appealing feature to well operators screening degradable diverters.