WO2010016801A1

WO2010016801A1 - Melt-stable and hydrolysis resistant hydroxy acid polymer

Info

Publication number: WO2010016801A1
Application number: PCT/SG2009/000265
Authority: WO
Inventors: Lianlong Hou; Shaofeng Wang; Bo JING; Siok Ling Sherlyn Yap
Original assignee: Hydrochem S Pte Ltd
Current assignee: Hydrochem S Pte Ltd
Priority date: 2008-08-07
Filing date: 2009-07-27
Publication date: 2010-02-11
Anticipated expiration: 2011-02-07

Abstract

There is disclosed a method for stabilizing hydroxy acid polymer comprising the steps of (a) adding an organic peroxide to a hydroxy acid polymer melt composition containing catalyst that catalyses the polymerization reaction to form the hydroxy acid polymer; and (b) adding at least one stabilizing agent to the hydroxy acid polymer melt composition, wherein said stabilizing agent is selected to at least partially reduce the rate of depolymerization of the hydroxy acid polymer within said melt composition.

Description

Melt-Stable and Hydrolysis Resistant Hydroxy Acid Polymer

Technical Field

The present invention generally relates to melt stable hydroxy acid polymer compositions having improved hydrolysis resistance properties.

v Background

In recent years, hydroxy acid polymers, such as lactic acid polymers, have gained increasing economic importance as a substitute for petroleum-based polymers. The imminent depletion of oil resources worldwide has necessitated the development of alternative substitutes to these polymers. Furthermore, the continued depletion of landfill space and its associated hazardous incineration waste have led to an urgency to develop novel biodegradable polymers which can be converted to desired articles or devices.

A biodegradable polymer with similar strength properties of a petroleum-based polymer, yet based on renewable resources is highly favored. These strengthened polymers could be used in existing plastic molding equipment to manufacture a myriad of industrial and consumer goods, thereby easing the transition to biodegradable polymers and reducing the dependency for petroleum-based polymers .

Attention is directed to hydroxy acid polymers mostly because of its ^λΛenvironmentally friendly" properties as these polymers are synthesized from lactic acid (derived from corn, a renewable plant feedstock) and biodegrades after use, if composted. This renewable crop-based polymer represents an important substitute for petroleum-based polymers . The manufacture of lactic acid polymers via the polymerization of lactic acids or lactide or its corresponding polymers thereof, is well known in the industry. However, the presence of undesired chemical moieties in the polymer such as hydroxyl or carboxyl end groups, imparts instability to the polymer formed. Moreover, the presence of impurities such as residual activators, monomers and oligomers from polymerization reactions further accelerates the degradation of the polymer.

The concept of instability has both positive and negative aspects. A positive aspect is the favorable biodegradation for composting the polymers at the end of its shelf life. However, a negative aspect of such instability is the accelerated polymer degradation during processing at elevated temperatures. This instability has hampered the development of many lactic acid polymer resins suitable for commercial use.

Recent advancements have focused on improving the mechanical and physical properties of the polymers, such as strength, stiffness, moldability, dimensional stability and thermal stability.

These advancements have been centered on manufacturing polymer compositions having additive agents to impart positive stability to the polymer. One known process for producing lactic acid polymers with modified strength and dimensional stability comprises incorporating an elastomer into the polymer via melting both components together in an additional phase, wherein preferably, the elastomer has functional groups, which form covalent bonds with the polymer. However, this method relies on the use of an additional compatibilizing agent, i.e. plasticizers, to improve the binding of the components together in the polymer, thus resulting in an increase in processing costs .

It has been generally accepted that the main polymer degradation pathway is initiated by the hydrolysis of ester groups in the polymer chain. The unwanted side products formed further propagates other degradation pathways. For example, water produced as by-products of the polymerization reaction causes excessive loss of molecular weight of the polymer. To overcome this deficiency, many have attempted to stabilize the polymer through capping the polymer ends, removing impurities formed, and deactivating any catalysts remaining from the polymerization step. More recently, stabilizing agents that prevent hydrolysis have been incorporated into the polymer.

One known process to produce hydrolysis stable polymers comprises incorporating stabilizing agents such as carbodiimide compounds and phosphorus antioxidants into the polymer resin. However, this process relies on melt temperatures of 185°C that may further degrade the polymer since it is very sensitive to high temperatures.

Other stabilizing agents that have been reported include hygroscopic polyhydroxy compounds, multifunctional carboxylic acids, and water scavengers such as anhydrides, acyl chlorides, isocyanates, alkoxy silanes, clay, alumina, silica, zeolites, calcium carbonate, sodium sulfate, bicarbonates and mixtures thereof.

It is possible to manufacture a myriad of these polymers having different compositions of stabilizing agents. However, prior attempts at stabilizing the polymers using these agents have found limited success in disclosing a general melt processing method to fit within the commercial requirements for manufacturing of fibers, films, sheets and foams. This is due to the complexity of the process methods at high temperatures in relation to the use of the stabilizing agents. It may be possible to lower the melt-processing temperature, but it may result in a significant deterioration of the physical properties, thus increasing the economic cost of the production process .

The arduous task of formulating the correct composition amount that confers greatest stability to the polymer has yet to be adapted for the manufacture of commercially desired articles or devices.

There is a need to provide a method for incorporating the various stabilizing agents into the polymer without accelerating the degradation process.

There is also a need to provide a melt-stable lactic acid polymer composition having increased melt-stability properties, and that exhibits sufficient compostability or degradability after its useful life to be manufactured into useful polymeric materials suitable as replacements for petroleum-based polymers that overcome, or at least ameliorate, one or more of the disadvantages described above .

Summary

According to a first aspect, there is provided a method for stabilizing hydroxy acid polymer comprising the steps of:

(a) adding an organic peroxide to a hydroxy acid polymer melt composition containing catalyst that catalyses the polymerization reaction to form the hydroxy acid polymer; and

(b) adding at least one stabilizing agent to the hydroxy acid polymer melt composition, wherein said stabilizing agent is selected to at least partially reduce the rate of depolymerization of the hydroxy acid polymer within said melt composition.

Advantageously, the hydroxyl acid polymer, such as biodegradable polylactic acid, has a longer "shelf-life" and does not degrade as fast relative to hydroxyl acid polymers which do not have organic peroxides and stabilizing agents therein.

The catalyst is used to catalyze the polymerization of hydroxy acid polymer. However, upon completion of the polymerization reaction, the catalyst may undesirably promote the depolymerization of the hydroxy acid polymer.

Advantageously, the organic peroxide is added to the hydroxy acid polymer so that the catalyst is deactivated.

The organic peroxide may also act as a coupling agent, which aids in coupling the de-polymerized hydroxy acid polymer polymers together again.

During or after polymerization, the formed hydroxy acid polymer may decompose into smaller polymers due to instability. Advantageously, the stabilizing agent acts as a coupling agent. More advantageously, the stabilizing agent is capable of neutralizing the acid by-products.

Yet more advantageously, the stabilizing agent is capable of removing the water by-products. These acid and water by-products may further propagate degradation of the hydroxy acid polymer.

Advantageously, when the stabilizing agent is used in combination with the organic peroxide, the stability of the hydroxy acid polymer can be improved and the degree of degradation of the hydroxy acid polymer can be greatly reduced.

According to a second aspect, there is provided a method for stabilizing hydroxy acid polymer, such as polylactic acid (PLA), comprising the steps of: (a) adding about 0.01 wt% to about 1 wt% organic peroxide to a hydroxy acid polymer melt composition containing catalyst that catalyses the polymerization reaction to form the hydroxy acid polymer; and

(b) adding stabilizing agent to the melt composition to at least partially reduce the rate of depolymerization of the hydroxy acid polymer within said melt composition, the stabilizing agent comprising about 0.01 wt% to about 5 wt% anti-oxidant, about 0.01 wt% to about 5 wt% acid scavenger and about 0.1 wt% to about 10 wt% inorganic additive.

According to a third aspect, there is provided a method for stabilizing polylactic acid (PLA) comprising the steps of:

(a) adding about 0.01 wt% to about 1 wt% organic peroxide to a PLA melt composition containing catalyst that catalyses the polymerization reaction to form the PLA; and

(b) adding stabilizing agent to the melt composition to at least partially reduce the rate of depolymerization of the hydroxy acid polymer within said melt composition, the stabilizing agent being selected from at least one, preferably at least two and more preferably at least three, of the following: (i) about 0.01 wt% to about 5 wt% anti-oxidant, (ii) about 0.01 wt% to about 5 wt% acid scavenger; (iii) about 0.1 wt% to about 10 wt% inorganic additive; and (iv) about 0.05 wt% to about 10 wt% water scavenger.

According to a fourth aspect, there is provided a hydroxy acid polymer composition comprising an organic peroxide and at least one stabilizing agent, wherein said stabilizing agent is selected to at least partially reduce the rate of depolymerization of the hydroxy acid polymer.

Advantageously, the hydroxy acid polymer composition as disclosed herein is melt-stable and hydrolysis resistant. More advantageously, the average molecular weight of the hydroxy acid polymer obtained is at least about 25,000, or at least about 50,000.

According to a fifth aspect, there is provided a hydroxy acid polymer composition comprising about 0.01 wt% to about 1 wt% organic peroxide and stabilizing agent selected to at least partially reduce the rate of depolymerization of the hydroxy acid polymer, the stabilizing agent being selected from the group consisting of about 0.01 wt% to about 5 wt% anti-oxidant , about 0.01 wt% to about 5 wt% acid scavenger and about 0.1 wt% to about 10 wt% inorganic additive.

According to a sixth aspect, there is provided a polylactic acid (PLA) ^' composition comprising about 0.01 wt% to about 1 wt% organic peroxide and stabilizing agent selected to at least partially reduce the rate of depolymerization of the hydroxy acid polymer, the stabilizing agent comprising at least one, preferably at least two and more preferably at least three, of the following: (i) about 0.01 wt% to about 5 wt% anti-oxidant, (ii) about 0.01 wt% to about 5 wt% acid scavenger; (iii) about 0.1 wt% to about 10 wt% inorganic additive; and (iv) about 0.05 wt% to about 10 wt% water scavenger. Definitions

The following words and terms used herein shall have the meaning indicated:

The term "hydroxy acid" as used herein means a carboxylic acid in which one or more hydrogen atom of the alkyl group has been replaced by a hydroxyl group.

The term "hydroxy acid polymer" as used herein means polymer of repeating hydroxy acid monomer units. The "hydroxy acid polymer" refers to a hydroxy acid polymer having a molecular weight of more than 25,000, preferably more than 50,000. In some embodiments, the molecular weight of the hydroxy acid polymer is about 25,000 to about 350,000.

The terms "polymerize", "polymerizing", "polymerization" and grammatical variations thereof, means not only "homopolymerization" but also "copolymerization" . The terms are to be interpreted broadly to include any process whereby monomer molecules react with each other, or with a polymer chain of hydroxy acid polymer, in a chemical reaction to form larger molecular weight polymer chains of hydroxy acid polymer. The polymerization mechanism can be cationic, anionic, coordination or free radical polymerization. The hydroxy acid polymer chains may be linear chains or a three-dimensional network of polymer chains. For example, the terms may include ring- opening reaction of cyclic dimers with hydroxy acid polymer to thereby increase the molecular weight of said hydroxy acid polymer.

The term "catalyst" is to be interpreted broadly to include any substance that increases the rate of reaction of the aliphatic hydroxycarboxylic acid, or polymerization of said hydroxy acid polymer, without being substantially consumed in the reaction. The term "coupling agent" as used herein means a reagent that may be capable of joining or coupling one hydroxy acid or hydroxy acid polymer to another hydroxy acid or hydroxy acid polymer. When a hydroxy acid polymer decomposes, the coupling agent may also be capable of joining the depolymerized hydroxy acid polymer polymers together.

The term "depolymerization" as used herein refers to a reduction in the molecular weight of a hydroxy acid polymer by the breaking of bonds in the hydroxy acid polymer to produce shorter polymer chains of lower molecular weight.

The term "rate of depolymerization" refers to the degree of depolymerization of the hydroxy acid polymer over a particular time period.

The word "substantially" does not exclude

"completely" e.g. a composition which is "substantially free" from Y may be completely free from Y. Where necessary, the word "substantially" may be omitted from the definition of the invention.

Unless specified otherwise, the terms "comprising" and "comprise", and grammatical variants thereof, are intended to represent "open" or "inclusive" language such that they include recited elements but also permit inclusion of additional, unrecited elements.

As used herein, the term "about", in the context of concentrations of components of the formulations, typically means +/- 5% of the stated value, more typically +/- 4% of the stated value, more typically +/- 3% of the stated value, more typically, +/- 2% of the stated value, even more typically +/- 1% of the stated value, and even more typically +/- 0.5% of the stated value.

Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

Disclosure of Optional Embodiments

Exemplary, non-limiting embodiments of a method for stabilizing hydroxy acid polymer comprising the steps of

(a) adding an organic peroxide to the hydroxy acid polymer, and (b) adding at least one stabilizing agent to the hydroxy acid polymer, will now be disclosed.

In one embodiment, the organic peroxide is added in an amount in the range of from about 0.01 wt% to about

3 wt%, or from about 0.01 wt% to about 2 wt%, or from about 0.01 wt% to about 1 wt%, or from about 0.02 wt% to about 0.5 wt%, or from about 0.05 wt% to about 0.2 wt%.

In one embodiment, the organic peroxide is selected from the group consisting of dilauroyl peroxide such as benzoyl peroxide, dialkanoyl peroxide such as lauroyl peroxide, alkylperoxy-alkylacetate such as tert- butylperoxy-diethylacetate, alkylperoxy-alkylhexanoate such as tert-butylperoxy-2-ethylhexanote, alkylperoxy- butyrate such as tert-butylperoxyisobutyrate, alkylperoxy acetate such as tert-butylperoxyacetate, alkylperoxy- benzoate such as tert-butylperoxybenzoate, dibenzoylperoxide, di-tert-butyl peroxide, and dicumyl peroxide.

The stabilizing agent is selected to at least partially reduce the rate of depolymerization of the hydroxy acid polymer. Then stabilizing agent may be at least one of, preferably at least two of, more preferably at least three of an antioxidant, a water scavenger, an acid scavenger, an inorganic additive and mixtures thereof . In one embodiment, the acid scavenger is selected from the group consisting of epoxy, oxazoline, isocyanate and mixtures thereof.

In one embodiment, the water scavenger is selected from the group consisting of isocyanate, carbodiimide, anhydride, acyl chloride, desiccant material and mixtures thereof .

The desiccant material may be selected from the group consisting of carbonate, bicarbonate, alumina, calcium oxide, sodium sulfate, silica gel, zeolite, clay, and mixtures thereof.

The epoxy matrix agent may be selected from the group consisting of an acrylic polymer epoxy resin, glycidyl methacrylate and epoxidized soybean oil. The epoxy matrix agent may also be an oligomer or prepolymer with at least three epoxy groups, and the number average molecular weight is less than about 5,000.

The stabilizing agent may comprise carbodiimides such as N, N' -dicyclohexylcarbodiimide, N, N' -diisopropyl carbodiimide, bis (2, 6-diisopropylphenyl) carbodiimide, l-ethyl-3- (3-dimethylaminopropyl) -carbodiimide, stabaxol-P

(Brenntag NV, Belgium) , stabaxol-P200 (Brenntag NV,

Belgium) , stabaxol-100 (Brenntag NV, Belgium) and stabaxol-I (Brenntag NV, Belgium) , anhydrides such as

ALTFONA^® 5151 (Shanghai Gelun Chemical Technology Co., Ltd, China) and maleic anhydride, oxazolines and isocyanates such as 1, 6-hexamethylene diisocyanate, 4, 4' -methylene- bis (cyclohexyl isocyanate) , lysine diisocyanate methyl ester, butane diisocyanate. In one embodiment, the stabilizing agent may comprise a biodegradable polyester. The biodegradable polyester may be selected from the group consisting of polybutylene succinate, polyhydroxyalkanoate, polycaprolactone, poly (vinyl alcohol) and mixtures thereof. The stabilizing agent may also comprise inorganic additives such as clay, alumina, silica gel, calcium carbonate and calcium bicarbonates . The inorganic additives are water scavengers that are capable of tying up water during storage . The stabilizing agent may also comprise antioxidants such as phosphite antioxidants, hindered phenolic compounds such as trialkyl phosphites, mixed alkyl/aryl phosphites, alkylated aryl phosphites, sterically hindered aryl phosphites, aliphatic spirocyclic phosphites, sterically hindered phenyl spirocyclics, sterically hindered bisphosphonites, hydroxyphenyl propionates and mixtures thereof.

The stabilizing agent may comprise a weight percentage of peroxide, based on the weight of the hydroxy acid polymer, in the range of from about 0.01 wt% to about 1.0 wt%, from about 0.02 wt% to about 0.5 wt%, from about 0.05 wt% to about 0.2 wt%.

The stabilizing agent may comprise a weight percentage of epoxy matrix agent, based on the weight of the hydroxy acid polymer, in the range of from about 0.01 wt% to about 5.0 wt%, from about 0.05 wt% to about 2.5 wt%, from about 0.1 wt% to about 2.0 wt% .

The stabilizing agent may comprise a weight percentage of carbodiimide matrix agent, based on the weight of the hydroxy acid polymer, in the range of from about 0.05 wt% to about 10.0 wt%, from about 0.25 wt% to about 7.5 wt%, from about 0.5 wt% to about 5.0 wt% .

The stabilizing agent may comprise a weight percentage of antioxidant, based on the weight of the hydroxy acid polymer, in the range of from about 0.01 wt% to about 5.0 wt%, from about 0.05 wt% to about 2.5 wt%, from about 0.1 wt% to about 2.0 wt%.

The stabilizing agent may comprise a weight percentage of inorganic additive, based on the weight of the hydroxy acid polymer, in the range of from about 0.1 wt% to about 10.0 wt%, from about 0.5 wt% to about 7.5 wt%, from about 1.0 wt% to about 5.0 wt%.

In one embodiment, the stabilizing agent may comprise at least one of an epoxy matrix agent, a carbodiimide matrix agent, an antioxidant and an inorganic additive. The organic peroxide, epoxy matrix agent, carbodiimide matrix agent, antioxidant and inorganic additive may be added in the sequence as listed above. In another embodiment, the organic peroxide, epoxy matrix agent, carbodiimide matrix agent, antioxidant and inorganic additive are added in at least two separate steps during melt processing. Advantageously, this prevents the occurrence of undesirable side reactions between the different agents.

In one embodiment, a mixture of the peroxide, antioxidant and epoxy matrix agent may first be added to the hydroxy acid polymer followed by a mixture of the epoxy matrix agent, carbodiimide matrix agent and inorganic additive.

In one embodiment, the adding step (b) is undertaken in an extruder or a mixer. The extruder may be a co- rotating twin screw extruder or a counter-rotating twin screw extruder. In one embodiment, the adding step (b) comprises the step of adding at least three stabilizing agents. The at least three stabilizing agents may be mixed together prior to adding to said hydroxy acid polymer. The at least three stabilizing agents may also be added directly to said hydroxy acid polymer without first mixing the said stabilizing agents together. The at least three stabilizing agents may also be added sequentially to said hydroxy acid polymer. In one embodiment, the adding step (b) is undertaken at the same time as adding step (a) . In another embodiment, the adding step (b) is undertaken after adding step (a) .

There is disclosed a hydroxy acid polymer composition comprising an organic peroxide and at least one stabilizing agent, wherein said stabilizing agent is selected to reduce the rate of depolymerization of the hydroxy acid polymer.

The hydroxy acid polymer may have a weight average molecular weight of from about 25,000 to about 350,000, or from about 30,000 to about 300,000, or from about 40,000 to about 250,000, or from about 50,000 to about 200,000.

In one embodiment, the hydroxy acid polymer is poly (lactic acid) (PLA) .

Examples

The invention is described in detail with reference to the following Examples. The disclosed examples are to support the better understanding the contents of the invention and are not intended to restrict the technical scope of the invention. Drying

The pelletized lactic acid polymer-based resins and their corresponding stabilized polymers were dried in a rotational vacuum drier at a temperature of from 40 degree C to 85 degree C for a period of 12 hours to 76 hours. The dried lactic acid polymer-based resins and stabilized polymers were then vacuum-packed in aluminum- plastic composite bags.

American Society for Testing and Materials (ASTM) Standards

The dried lactic acid polymer-based resins and stabilized polymers were injected into different specimens for measuring of the mechanical and thermal properties according to the ASTM standards. Specifically, ASTM D638 was used for measuring tensile strength, ASTM D1238 was used for measuring melt flow rate, ASTM D256 was used for measuring Izod notched impact strength, and ASTM D790 was used for measuring flexural strength and modulus.

Gel Permeation Chromatography (GPC)

The weight-average molecular weight (Mw) of the lactic acid polymer was generally determined using GPC at a column temperature of 45 degree C, using chloroform as the solvent. A refractive index detector was used with relative molecular weight calibrations using polystyrene standards .

Differential Scanning Calorimeter (DSC) DSC measurements were performed on a QlO Differential Scanning Calorimeter (TA Instruments, United States of America) in a nitrogen atmosphere (mass flow of 50 ml/min) with a heating and cooling rate of 10 degree C per minute. Calibration was achieved using indium standard samples. All measurements were performed from 20 degree C to 180 degree C for 3 min to erase any previous thermal history, and then passed through subsequent cooling and heating cycles .

Reduced Viscosity (RV) RV was measured according to ASTM D1243 and ASTM D2857. The polymer samples were first weighed and then dissolved in chloroform solvent. The solution and viscometer were placed in a constant temperature water bath. The liquid was then brought above the upper graduation mark on the viscometer. The time for the solution to flow from the upper to lower graduation marks was recorded for calculating the corresponding viscosity.

Acid Number (AN) AN was determined using Titrando 809 with Touch Control System (Metrohm AG, Switzerland) according to ASTM D664, using chloroform as a solvent for dissolving the samples.

Hydrolytic Stability Test (Water)

The hydrolytic stability test was conducted under water conditions, according to the following process.

1) Weighing out a sample amount (accuracy of up to 4 decimal place) into a glass beaker, 2) Transferring (using a measuring cylinder) a certain volume of water into the glass beaker,

3) Putting in a magnetic stirrer into the glass beaker carefully, 4) Placing the glass beaker containing the sample and water solvent onto a hotplate magnetic stirrer,

5) Setting the stirring speed at 200 rpm and the temperature of hotplate at 80 degree C,

6) Recording down the time when the temperature of the solution reached 80 degree C (measured by a temperature sensor placed in the solution) ,

7) Collecting the sample carefully from the beaker with a metal/plastic spoon at different treating time,

8) Testing samples collected for their reduced viscosity ^■ and/or acid number, including the untreated samples, according to the standard testing methods .

Hydrolytic Stability Test (Buffer Solution)

The hydrolytic stability test was also conducted under buffer solution conditions. The process used was the same as that for the hydrolytic stability test conducted under water conditions as described above, except that sodium phosphate buffer solution having a pH value of 7.0 was used instead of water.

Surface Treating of Calcium Carbonate

TC-114 (titanate coupling agent) was diluted with 1:1

(wt/wt) fluid wax. 2 kg calcium carbonate and 40 g of the diluted coupling agent solvent were charged into a high speed mixer (SHR-A, Zhangjiagang City, Xinrong Machinery CO., LTD, China) for mixing at 600 rpm at 110 degree C for 5 min.

Master Batch (MB) Preparation 1 Surface treating of calcium carbonate as described above was conducted. 2 kg polybutylene succinate (PBS) and 2.04 kg of the surface treated calcium carbonate were charged into a high speed mixer for mixing at 900 rpm, at 30 degree C for 3 min. The Master Batch prepared accordingly is hereinafter referred to as "MBl".

Master Batch (MB) Preparation 2

Surface treating of calcium carbonate as described above was conducted. 2 kg polybutylene succinate-co- polylactic acid copolymer (PBSA) and 2.04 kg of the surface treated calcium carbonate were charged into a high speed mixer for mixing at 900 rpm, at 30 degree C for 3 min. The Master Batch prepared accordingly is hereinafter referred to as ^XNMB2".

Master Batch (MB) Preparation 3

Surface treating of calcium carbonate as described above was conducted. 4 kg PBSA, 2.04 kg surface treated calcium carbonate, 200 g ADR 4385 and 400 g octadecyl-3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate were sequentially charged into a high speed mixer for mixing at 900 rpm, at 30 degree C for 3 min. The Master Batch prepared accordingly is hereinafter referred to as "MB3". Master Batch (MB) Preparation 4

Surface treating of calcium carbonate as described above was conducted. 2 kg Ecoflex® FBX 7011 (BASF, United States of America), 2.04 kg surface treated calcium carbonate and ^' 400 g octadecyl-3- (3, 5-di-tert-butyl-4- hydroxyphenyl) propionate were sequentially charged into a high speed mixer for mixing at 900 rpm, at 30 degree C for 3 min. The Master Batch prepared accordingly is hereinafter referred to as "MB4".

Master Batch (MB) Preparation 5

Surface treating of calcium carbonate as described above was conducted. 2 kg Ecoflex® FBX 7011 (BASF, United States of America) , 2 kg Talc, 200 g ADR 4385 and 200 g octadecyl-3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate were sequentially charged into a high speed mixer for mixing at 900 rpm, at 30 degree C for 3 min. The Master Batch prepared accordingly is hereinafter referred to as ^λλMB5".

Master Batch (MB) Preparation 6

Surface treating of calcium carbonate as described above was conducted. 2 kg PBSA, 2.04 kg surface treated calcium carbonate, 100 g ADR 4385 (epoxy matrix agent) , 100 g pentaerythritolyl tetrakis [3- (3, 5-di-t-butyl-4- hydroxyphenyl) propionate and 100 g tris (2, 4-di-t- butylphenyl) phosphite were sequentially charged into a high speed mixer for mixing at 900 rpm, at 30 degree C for 3 min. The Master Batch prepared accordingly is hereinafter referred to as "MB6". _.

Example 1 (Comparative Example)

Preparation of stabilized lactic acid polymers by adding peroxide

The stabilized lactic acid polymer was prepared according to the steps as described below.

(a) 5 kg lactic acid polymer was charged into a high speed mixer.

(b) 5 g tert-butyl peroxy benzonate (i.e. 0.1 wt% of lactic acid polymer) was charged into the same high speed mixer for mixing with the lactic acid polymer at a speed of 900rpm for 3 min, at 30 degree C.

(c) All the materials were added into the hopper of an co-rotating extruder (SHJ-36, Nanjing Jieya Extrusion Equipment CO., LTD, China) . The temperature setting within the extruder was divided into six zones. The corresponding temperatures from zone 1 to zone 6 were 120 degree C, 190 degree C, 200 degree C, 190 degree C, 180 degree C, 170 degree C. The die temperature was set at 160 degree C and the melt temperature was 180 degree C. The extruder was preheated and the motor speed was set at 20 Hz and the feeding speed was set at 15 Hz.

(d) The sheets extruded from the extruder die were passed through cooling water, and then pelletized.

(e) The pellets were dried in a rotational vacuum drier (Twin Cone, Wenzhou Feilong M&EEngineering CO., LTD,

China) according to the drying method as mentioned above. During drying, the temperature did not exceed 85 degree C. After drying, the moisture content of lactic acid polymer was below 500 parts-per-million by weight. (f) No other additive was added in this Example, as shown in Table 1 below. (g) The properties of the lactic acid polymer obtained were measured according to above mentioned methods. The results were tabulated in Table 3.

(h) The data in relation to the reduced viscosity and acid number of the stabilized lactic acid polymer obtained under different treating conditions (as described above) were tabulated in Tables 4 and 5 below.

Example 2 Preparation of stabilized lactic acid polymers by adding peroxide, phosphite antioxidant and epoxy matrix agent

(i) 5 kg lactic acid polymer was charged into a high speed mixer.

(ii) 5 g (i.e. 0.1 wt% of lactic acid polymer) tert- butyl peroxy benzonate, 20 g (i.e. 0.4 wt% of lactic acid polymer) tris (nonylphenyl) phosphate (TNPP) antioxidant and 5 g (i.e. 0.1 wt% of lactic acid polymer) ADR 4385 (epoxy matrix agent) were charged into the same high speed mixer for mixing with the lactic acid polymer at a speed of 900rpm for 3 min, at 30 degree C.

(iii) All the materials were added into the hopper of a co-rotating extruder (SHJ-36, Nanjing Jieya Extrusion Equipment CO., LTD, China) . The temperature setting within the extruder was divided into six zones. The corresponding temperatures from zone 1 to zone 6 were 120 degree C, 190 degree C, 200 degree C, 190 degree C, 180 degree C, 170 degree C. The die temperature was set at 160 degree C and the melt temperature was 180 degree C. The extruder was preheated and the motor speed was set at 20 Hz and the feeding speed was set at 15 Hz.

(iv) The sheets extruded from the extruder die were passed through cooling water, and then pelletized. (v) The pellets were dried in a rotational vacuum drier

(Twin Cone, Wenzhou Feilong M&EEngineering CO.^', LTD,

China) according to the drying method as mentioned above.

During drying, the temperature did not exceed 85 degree C.

After drying, the moisture content of lactic acid polymer was below 500 parts-per-million by weight.

(vi) No other additive was added in this Example, as shown in Table 1 (for Examples 2 to 7; or Table 2, for Examples 8 to 14) below.

(vii) The properties of the lactic acid polymer obtained were measured according to above mentioned methods. The results were tabulated in Table 3 below.

(viii) The data in relation to the reduced viscosity and acid number of the stabilized lactic acid polymer obtained under different treating conditions (as described above) were tabulated in Tables 4 and 5 below (also refer to Table 6 below for data obtained in relation to Examples 3 to 5 and 8 to 12) .

Example 3 Preparation of stabilized lactic acid polymers by adding peroxide, phosphite antioxidant, epoxy and carbodiimide matrix agent

The steps for preparation of the stabilized lactic acid polymer in this Example were the same as those in Example 2 above except that in ^'step (vi) , 4024 g of the treated and dried lactic acid polymer, followed by a mixture of 8 g (i.e. about 0.2 wt% of lactic acid polymer) ADR 4368C (epoxy matrix agent), 16 g (i.e. about 0.4 wt% of lactic acid polymer) octadecyl-3- (3, 5-di-tert-butyl-4- hydroxyphenyl) propionate ("1076") and 40 g (i.e. about 1.0 wt% of lactic acid polymer) stabaxol P (carbodiimide matrix agent) were charged into the high speed mixer for mixing at a speed of 900 rpm, at 30 degree C for 3 min.

The lactic acid polymer was then extruded and pelletized in accordance with steps (iii) to (v) as described above.

Example 4

Preparation of stabilized lactic acid polymers by adding peroxide_r phosphite antioxidant , propionate antioxidant _r epoxy matrix agent and inorganic additive

The steps for preparation of the stabilized lactic acid polymer in this Example were the same as those in

Example 2 above except that after step (v) , an additional step of surface treating of calcium carbonate as described above was conducted.

Further, in step (vi) , 4024 g of the treated and dried lactic acid polymer, followed by a mixture of 4 g (i.e. 0.1 wt%) ADR 4385 (epoxy matrix agent), 82 g (i.e. 2.0 wt%) surface treated calcium carbonate and 16 g (i.e. 0.4 wt%) octadecyl-3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate (1076) were charged into the high speed mixer for mixing at 900 rpm, at 30 degree C for 3 min.

The lactic acid polymer was then extruded and pelletized in accordance with steps (iii) to (v) as described above. Example 5

Preparation of stabilized lactic acid polymers by adding peroxide, phosphite antioxidant, propionate antioxidant , epoxy matrix agent, carbodiimide matrix agent and inorganic additive

The steps for preparation of the stabilized lactic acid polymer in this Example were the same as those in Example 2 above except that in step (ii) , only 5 g (i.e. 0.1 wt%) tert-butyl peroxy benzonate and 20 g (i.e. 0.4 wt%) tris (nonylphenyl) phosphate (TNPP) antioxidant were charged into the high speed mixer.

Further, after step (v) , an additional step of Master Batch (MB) preparation 1 as described above was conducted.

The lactic acid polymer was then extruded and pelletized similarly to steps (iii) to (v) as described above except that the corresponding temperatures within the extruder from zone 1 to zone 6 were 70 degree C,

120 degree C, 140 degree C, 130 degree C, 130 degree C,

120 degree C. The die temperature was set at 120 degree C and the melt temperature was set at 130 degree C. The extruder was preheated and the motor speed was set at 15

Hz and the feeding speed was set at 17 Hz.

The pellets were dried in a rotational vacuum drier at 45 degree C until the moisture content was below 500 ppm.

In step (vi) , 4020 g of the treated and dried lactic acid polymer, followed by 162 g MBl, 20 g (i.e. 05. wt%) ADR 4385 (epoxy matrix agent), 16 g (i.e. 0.4 wt%) octadecyl-3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate and 40 g (i.e. 1.0 wt%) stabaxol P (carbodiimide matrix agent) were charged into the high speed mixer for mixing at 900 rpm, 30 degree C for 3 min. The lactic acid polymers was then extruded and pelletized in accordance with steps (iii) to (v) as described above.

Example 6

Preparation of stabilized lactic acid polymers with adding peroxide, phosphite antioxidant, epoxy matrix agent, propionate antioxidant, carbodiimide matrix agent and inorganic additive The steps for preparation of the stabilized lactic acid polymer in this Example were the same as those in Example 2 above except that in step (ii) , 10 g (0.2 wt%) ADR 4385 instead of only 5 g ADR 4385 was used, and after step (v) , an additional step of Master Batch (MB) preparation 2 as described above was conducted.

The lactic acid polymer was then extruded and pelletized similarly to steps (iii) to (v) as described above except that the corresponding temperatures of the extruder from zone 1 to zone 6 are 70 degree C, 120 degree C, 140 degree C, 130 degree C, 130 degree C, 120 degree C. The die temperature was set at 120 degree C and the melt temperature was set at 130 degree C. The extruder was preheated and the motor speed was set at 15 Hz and the feeding speed was set at 17 Hz. The pellets were dried in a rotational vacuum drier at 45 degree C until the moisture content was below 500 ppm.

In step (vi) , 4028 g of the treated and dried lactic acid polymers, followed by 162 g MB2, 16 g (0.4 wt%) octadecyl-3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate and 40 g (1.0 wt%) stabaxol P (carbodiimide matrix agent) were charged into the high speed mixer for mixing at 900 rpm, 30 degree C for 3 min.

The lactic acid polymers was then extruded and pelletized in accordance with steps (iii) to (v) as described above.

Example 7

Preparation of stabilized lactic acid polymers by adding peroxide, phosphite antioxidant, epoxy matrix agent, propionate antioxidant _r carbodiimide matrix agent and inorganic additive

The steps for preparation of the stabilized lactic acid polymer in this Example were the same as those in Example 4 above except that in step (ii) , 10 g (instead of only 5 g) ADR 4385 (epoxy matrix agent) was used, and after step (v) , an additional step of surface treating of calcium carbonate as describe above was conducted.

In step (vi) , 4028 g of the treated and dried lactic acid polymer, followed by a mixture of 82 g (2.0 wt%) surface treated calcium carbonate, 16 g (0.4 wt%) octadecyl-3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate (1076) and 4O g (1.0 wt%) stabaxol P (carbodiimide matrix agent) were charged into the high speed mixer for mixing at 900 rpm, at 30 degree C for 3 min. The lactic acid polymer was then extruded and pelletized in accordance with steps (iii) to (v) as described above. Example 8

Preparation of stabilized lactic acid polymers by adding peroxide, propionate antioxidant , propionate antioxidant, epoxy matrix agent, carbodiimide matrix agent and inorganic additives

The steps for preparation of the stabilized lactic acid polymer in this Example were the same as those in Example 7 above except that, as shown in Table 2 below, in step (vi) , 4028 g of the treated and dried lactic acid • polymer, followed by a mixture of 82 g (2.0 wt%) surface treated calcium carbonate, 32 g (0.8 wt%) octadecyl-3-

(3, 5-di-tert-butyl-4-hydroxyphenyl) propionate (1076), 80 g (2.0 wt%) N,N'-dicyclohexylcarbodiimide (DCC) and 200 g

(5 wt%) Talc were charged into the high speed mixer for mixing at 900 rpm, at 30 degree C for 3 min.

Example 9

Preparation of stabilized lactic acid polymers by adding peroxide, phosphite antioxidant, epoxy matrix agent, propionate antioxidant and inorganic additive

Example 2 above except that in step (ii) , 10 g (0.2 wt%) octadecyl-3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate was also charged into the high speed mixer.

Further, after step (v) , an additional step of Master Batch (MB) preparation 3 as described above was conducted. The lactic acid polymer was then extruded and pelletized similarly to steps (iii) to (v) as described above except that the corresponding temperatures of the extruder from zone 1 to zone 6 are 70 degree C, 120 degree C, 140 degree C, 130 degree C, 130 degree C, 120 degree C. The die temperature was set at 120 degree C and the melt temperature was set at 130 degree C. The extruder was preheated and the motor speed was set at 15 Hz and the feeding speed was set at 17 Hz. The pellets were dried in a rotational vacuum drier at 45 degree C until the moisture content was below 500 ppm.

In step (vi) , 4032 g of the treated and dried lactic acid polymer, followed by a mixture of 264 g MB3, 4 g (0.1 wt%) ADR 4385 (epoxy matrix agent) and 8 g (0.2 wt%) octadecyl-3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate were charged into the high speed mixer for mixing at 900 rpm, at 30 degree C for 3 min.

Example 10

Preparation of stabilized lactic acid polymers by adding peroxide, phosphite antioxidant , epoxy matrix agent, propionate antioxidant, carbodiimide matrix agent and inorganic additive

The steps for preparation of the stabilized lactic acid polymer in this Example were the same as those in Example 7 above except that in step (vi) , 4028g of the treated and dried lactic acid polymer, followed by 80 g

(2.0 wt%) surface treated calcium carbonate, 16 g (0.4 wt%) octadecyl-3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate, 40 g (1.0 wt%) ALTFONA® 5151 and 4 g (0.1 wt%) ADR 4385 were charged into the high speed mixer for mixing at 900 rpm, at 30 degree C for 3 min

Example 11

Example 2 above except that after step (v) , an additional step of Master Batch (MB) preparation 4 as described above was conducted.

The lactic acid polymer was then extruded and pelletized similarly to steps (iii) to (v) as described above except that the corresponding temperatures within the extruder from zone 1 to zone 6 were 70 degree C, 120 degree C, 130 degree C, 130 degree C, 120 degree C, 110 degree C. The die temperature was set at 120 degree C and the melt temperature was set at 130 degree C. The extruder was preheated and the motor speed was set at 15 Hz and the feeding speed was set at 15 Hz. The pellets were dried in a rotational vacuum drier at 45 degree C until the moisture content was below 500 ppm.

In step (vi) , 4024 g of the treated and dried lactic acid polymer, followed by a mixture of 176 g MB4, 16 g (0.4 wt%) ADR 4385 (epoxy matrix agent), 16 g (0.4 wt%) octadecyl-3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate and 80 g (2.0 wt%) N, N' -dicyclohexylcarbodiimide (DCC) were charged into the high speed mixer for mixing at 900 rpm, at 30 degree C for 3 min.

Example 12

Preparation of stabilized lactic acid polymers by adding peroxide _r phosphite antioxidant, propionate antioxidant , epoxy matrix agent, carbodiimide matrix agent and inorganic additives

Example 2 above except that after step (v) , an additional step of Master Batch (MB) preparation 5 as described above was conducted.

The lactic acid polymer was then extruded and pelletized similarly to steps (iii) to (v) as described above except that the corresponding temperatures within the extruder from zone 1 to zone 6 were 70 degree C_r 120 degree C, 130 degree C, 130 degree C, 120 degree C, 110 degree C. The die temperature was set at 120 degree C and the melt temperature was set at 130 degree C. The extruder was preheated and the motor speed was set at 15 Hz and the feeding speed was set at 15 Hz.

In step (vi) , 4020 g of the treated and dried lactic acid polymer, followed by a mixture of 352 g MB5 and 40 g

(1.0 wt%) N, N' -dicyclohexylcarbodiimide (DCC) were charged into the high speed mixer for mixing at 900 rpm, at 30 degree C for 3 min.

Example 13

Preparation of stabilized lactic acid polymers by adding peroxide, phosphite antioxidant, propionate antioxidant, epoxy matrix agent, carbodiimide matrix agent and inorganic additives

Example 2 above except that after step (v) , an additional step of Master Batch (MB) preparation 6 as described above was conducted.

The lactic acid polymer was then extruded and pelletized similarly to steps (iii) to (v) as described above except that the corresponding temperatures within the extruder from zone 1 to zone 6 were 70 degree C, 120 degree C, 130 degree C, 130 degree C, 120 degree C, 110 degree; C. The die temperature was set at 120 degree C and the melt temperature was set at 130 degree C. The extruder was preheated and the motor speed was set at 15 Hz and the feeding speed was set at 15 Hz.

In step (vi) , 4024 g of the treated and dried lactic acid polymer, followed by a mixture of 347 g MBβ, 16 g

(0.4 wt%) pentaerythritolyl tetrakis 3- (3, 5-di-t-butyl-4- hydroxyphenyl) propionate / tris (2, 4-di-t-butylphenyl) phosphite ("1010/168 (1/1)", Shanghai KumhoSunny Plasties Co., Ltd, China) and 4 g (0. lwt%) ADR 4385 (epoxy matrix agent) were charged into the high speed mixer for mixing at 900 rpm, at 30 degree C for 3 min.

Example 14

Preparation of stabilized lactic acid polymers by adding peroxide, phosphite antioxidant _r epoxy matrix agent and a biodegrade polyester

Example 2 above except that in step (iii) , the corresponding temperatures within the extruder from zone 1 to zone 6 were 100 degree C, 180 degree C, 190 degree C,

180 degree C, 170 degree C, 170 degree C. The die temperature was set at 160 degree C and the melt temperature was set at 170 degree C. The extruder was preheated and the motor speed was set at 20 Hz and the feeding speed was set at 15 Hz.

In step (vi) , 4024 g of the treated and dried lactic acid polymer, followed by a mixture of 800 g (20.0 wt%)

Ecoflex® FBX 7011 (BASF, United States of America) , 32 g

(0.8 wt%) octadecyl-3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate and 80 g (2.0 wt%) N, N' -dicyclohexyl carbodiimide were charged into the high speed mixer for mixing at 900 rpm, at 30 degree C for 3 min. The lactic acid polymer was then extruded and pelletized in accordance with steps (iii) to (v) as described above.

Example 15 (Comparative Example)

Preparation of stabilized lactic acid polymers by adding phosphite antioxidant and epoxy matrix agent

The stabilized lactic acid polymer was prepared according to the steps as described below. (A) 5 kg lactic acid polymer was charged into a high speed mixer.

(B) 20 g (i.e. 0.4 wt% of lactic acid polymer) tris (nonylphenyl) phosphate (TNPP) antioxidant and 25 g (i.e. 0.5 wt% of lactic acid polymer) ADR 4385 (epoxy matrix agent) were charged into the same high speed mixer for mixing with the lactic acid polymer at a speed of 900rpm for 3 min, at 30 degree C.

(C) All the materials were added into the hopper of a co- rotating extruder (SHJ-36, Nanjing Jieya Extrusion Equipment CO., LTD, China) . The temperature setting within the extruder was divided into six zones. The corresponding temperatures from zone 1 to zone 6 were 120 degree C, 190 degree C, 200 degree C, 190 degree C, 180 degree C, 170 degree C. The die temperature was set at 160 degree C and the melt temperature was set at 180 degree C. The extruder was preheated and the motor speed was set at 20 Hz and the feeding speed was set at 15 Hz.

(D) The sheets extruded from the extruder die were passed through cooling water, and then pelletized. (E) The pellets were dried in a rotational vacuum drier (Twin Cone, Wenzhou Feilong M&EEngineering CO., LTD, China) according to the method as mentioned above. During drying, the temperature did not exceed 85 degree C. After drying, the moisture content of lactic acid polymer was below 500 parts-per-million by weight.

(F) No other additive was added in this Example, as shown in Table 2 below.

(G) The properties of the lactic acid polymers thus obtained were measured according to above mentioned methods. The results were tabulated in Table 3 below.

(H) The data in relation to the reduced viscosity and acid number of the stabilized lactic acid polymer obtained under different treating conditions (as described above) were tabulated in Tables 4, 5 and 6 below.

Table 1 Weight percentage of additives added for stabilizing lactic acid polymers (Examples 1 to 7)

Table 2 Weight percentage of additives added for stabilizing lactic acid polymers (Examples 8 to 14)

Table 3 Pxoperties of stabilized lactic acid polymers

(Examples 1 to 15)

Table 4 Reduced Viscosity and Acid Number data of stabilized lactic acid polymer with processing time

RV 2.17 1.77 1.48 1.06

15 165

AN 3. 40 3. 57 3. 76 4. 06

*Note: RV refers to Reduced Viscosity (dL/g) ; AN refers to Acid Number (mgKOH/g) .

Table 5 Hydrolysis stability of stabilized lactic acid polymer under water treatment

*Note: RV refers to Reduced Viscosity (dL/g) ; AN refers to Acid Number (mgKOH/g)

Table 6 Hydrolysis stability of stabilized lactic acid polymer under buffer solution treatment

*Note: RV refers to Reduced Viscosity (dL/g); AN refers to

Acid Number (mgKOH/g) The results as tabulated above indicate that the addition of an organic peroxide in combination with at least one stabilizing agent helps to improve the stability .of the lactic acid polymer.

This is apparent from the results as tabulated in

Table 5. Taking for example, a comparison between the relative viscosity and acid number for the lactic acid polymers obtained from Examples 1, 5 and 15 after undergoing 5 hours of water treatment.

In Example 1, the lactic acid polymer was stabilized by the addition of the organic peroxide only. Stabilizing agent was added. It is noted that the relative viscosity decreases by about 65% and the acid number increases by more than 400%.

In Example 15, the lactic acid polymer was stabilized by the addition of two stabilizing agents, namely an antioxidant and an epoxy matrix agent. Organic peroxide was not added. It is noted that the relative viscosity decreases by about 70% and the acid number increases by more than 300%.

On the other hand, in Example 5, the lactic acid polymer was stabilized by the addition of organic peroxide as well as stabilizing agents such as antioxidant, epoxy matrix agent, carbodiimide matrix agent, inorganic additive and other degradable polymer. It is noted that the relative viscosity decreases by only 6% and the acid number increases by only 110%. Applications

It will be appreciated that the disclosed method results in the formation of melt-stable and hydrolysis resistant hydroxy acid polymer, such as poly (lactic acid) . It will be appreciated that organic peroxide is added to deactivate the catalyst that used for polymerization of the hydroxy acid polymer, as well as to act as a coupling agent for coupling the de-polymerized hydroxy acid polymers together again. It will be further appreciated that stabilizing agent not only acts as a coupling agent, but also is also capable of neutralizing acid by-products, and/or removing the water by-products.

Advantageously, when the stabilizing agent is used in combination with the organic peroxide, the stability of the hydroxy acid polymer can be effectively improved and the degree of degradation of the hydroxy acid polymer can be greatly reduced.

It will be appreciated that the average molecular weight of the hydroxy acid polymer obtained is at least about 25,000, or at least about 50,000.

It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims .

Claims

1. A method for stabilizing hydroxy acid polymer comprising the steps of: (a) adding an organic peroxide to a hydroxy acid polymer melt composition containing catalyst that catalyses the polymerization reaction to form the hydroxy acid polymer; and

2. The method of claim 1, wherein said organic peroxide is added in an amount in the range of 0.01 wt% to 1 wt% of the total hydroxy acid polymer.

3. The method of claim 2, wherein said organic peroxide is added in an amount in the range of 0.05 wt% to 0.2 wt% of the total hydroxy acid polymer.

4. The method of claim 1, wherein said organic peroxide is selected from the group consisting of lauroyl peroxide, alkylperoxy-alkylacetate, alkylperoxy-acetate, alkylperoxy-carobylate, alkylperoxy-alkylhexanote, alkylperoxy-butyrate, alkylperoxy-benzoate .

5. The method of claim 1, wherein said organic peroxide is selected from the group consisting of dilauroyl peroxide, tert-butylperoxy-diethylacetate, tert- butylperoxy-2-ethylhexanote, tert-butylperoxyisobutyrate, tert-butylperoxyacetate, tert-butylperoxybenzoate and dibenzoylperoxide, di-tert-butyl peroxide, dicumyl peroxide.

6. The method of claim 1, wherein said stabilizing agent is selected from the group consisting of antioxidants, water scavengers, acid scavengers, inorganic additives and mixtures thereof.

7. The method of claim 6, wherein the acid scavenger is selected from the group consisting of epoxy, oxazoline, carbodiimide, isocyanate and mixtures thereof.

8. The method of claim 6, wherein said water scavenger is selected from the group consisting of isocyanate, carbodiimide, anhydride, acyl chloride, desiccant material and mixtures thereof.

9. The method of claim 8, wherein said desiccant material is selected from the group consisting of carbonate, bicarbonate, alumina, calcium oxide, sodium sulfate, silica gel, zeolite, clay, and mixtures thereof.

10. The method of claim 1, wherein said stabilizing agent comprises biodegradable polyester.

11. The method of claim 10, wherein said biodegradable polyester is selected from the group consisting of polybutylene succinate, polyhydroxyalkanoate, polycaprolactone, poly (vinyl alcohol) and mixtures thereof.

12. The method of claim 1, wherein said adding step (b) is undertaken in an extruder or a mixer.

13. The method of claim 12, wherein said extruder is a co-rotating twin screw extruder or a counter-rotating twin screw extruder.

14. The method of claim 1, wherein said adding step (b) comprises the step of adding at least three stabilizing agents .

15. The method of claim 14, -wherein said at least three stabilizing agents are mixed together prior to adding to said hydroxy acid polymer.

16. The method of claim 14, wherein said at least three stabilizing agents are added directly to said hydroxy acid polymer without first mixing the said stabilizing agents together.

17. The method of claim 1, wherein said adding step (b) is undertaken at the same time as adding step (a) .

18. The method of claim 1, wherein said adding step (b) is undertaken after adding step (a) .

19. A method for stabilizing hydroxy acid polymer, such as polylactic acid (PLA), comprising the steps of:

(a) adding 0.01 wt% to 1 wt% organic peroxide to a hydroxy acid polymer melt composition containing catalyst that catalyses the polymerization reaction to form the hydroxy acid polymer; and (b) adding stabilizing agent to the melt composition to at least partially reduce the rate of depolymerization of the hydroxy acid polymer within said melt composition, the stabilizing agent comprising 0.01 wt% to 5 wt% anti- oxidant, 0.01 wt% to 5 wt% acid scavenger and 0.1 wt% to 10 wt% inorganic additive.

20. A method for stabilizing polylactic acid (PLA) comprising the steps of:

(a) adding 0.01 wt% to 1 wt% organic peroxide to a PLA melt composition containing catalyst that catalyses the polymerization reaction to form the PLA; and

(b) adding stabilizing agent to the melt composition to at least partially reduce the rate of depolymerization of the hydroxy acid polymer within said melt composition, the stabilizing agent being selected from at least one, preferably at least two and more preferably at least three, of the following: (i) 0.01 wt% to 5 wt% anti-oxidant;

(ii) 0.01 wt% to 5 wt% acid scavenger;

(iii) 0.1 wt% to 10 wt% inorganic additive; and

(iv) 0.05 wt% to 10 wt% water scavenger.

21. A hydroxy acid polymer composition comprising an organic peroxide and at least one stabilizing agent, wherein said stabilizing agent is selected to at least partially reduce the rate of depolymerization of the hydroxy acid polymer.

22. The hydroxy acid polymer composition of claim 21, wherein said hydroxy acid polymer has a weight average molecular weight of 25,000 to 350,000.

23. The hydroxy acid polymer composition of claim 22, wherein said hydroxy acid polymer has a weight average molecular weight of 50,000 to 200,000.

24. A hydroxy acid polymer composition comprising 0.01 wt% to 1 wt% organic peroxide and stabilizing agent selected to at least partially reduce ^' the rate of depolymerization of the hydroxy acid polymer, the stabilizing agent being selected from the group consisting of 0.01 wt% to 5 wt% anti-oxidant, 0.01 wt% to 5 wt% acid scavenger and 0.1 wt% to 10 wt% inorganic additive .

25. A polylactic acid (PLA) composition comprising ^■ 0.01 wt% to 1 wt% organic peroxide and stabilizing agent selected to at least partially reduce the rate of depolymerization of the hydroxy acid polymer, the stabilizing agent comprising at least one, preferably at least two and more preferably at least three, of the following:

(i) 0.01 wt% to 5 wt% anti-oxidant; (ii) 0.01 wt% to 5 wt% acid scavenger; (iii) 0.1 wt% to 10 wt% inorganic additive; and (iv) 0.05 wt% to 10 wt% water scavenger.