Title of Invention	PROCESS FOR THE MODIFICATION OF BIODEGRADABLE POLYMERS
Abstract	Process for the modification of a polymer or copolymer having the following general structure for one or more of the repeating units (1) wherein n is an integer, m is an integer in the range 0 to 6, and R is selected from hydrogen, substituted or unsubstituted C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 aralkyl, and C7-C20 alkaryl, which groups may include linear or branched alkyl moieties, the optional one or more substituents being selected from the group consisting of hydroxy, alkoxy, linear or branched alk(en)yl, aryloxy, halogen, carboxyhc acid, ester, carboxy, nitnle, and amido groups, which process involves contacting the polymer or copolymer with a cyclic organic peroxide under conditions whereby at least some of said peroxide is decomposed This process results in a (co)polymer with a high degree of branching but free of gel formation

Title of Invention

PROCESS FOR THE MODIFICATION OF BIODEGRADABLE POLYMERS

Abstract

Process for the modification of a polymer or copolymer having the following general structure for one or more of the repeating units (1) wherein n is an integer, m is an integer in the range 0 to 6, and R is selected from hydrogen, substituted or unsubstituted C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 aralkyl, and C7-C20 alkaryl, which groups may include linear or branched alkyl moieties, the optional one or more substituents being selected from the group consisting of hydroxy, alkoxy, linear or branched alk(en)yl, aryloxy, halogen, carboxyhc acid, ester, carboxy, nitnle, and amido groups, which process involves contacting the polymer or copolymer with a cyclic organic peroxide under conditions whereby at least some of said peroxide is decomposed This process results in a (co)polymer with a high degree of branching but free of gel formation

Full Text	PROCESS FOR THE MODIFICATION OF BIODEGRADABLE POLYMERS The present invention relates to a process for the modification of a polymer or copolymer having the following general structure for one or more of the repeating units wherein n is an integer, m is an integer in the range 0 to 6, and R is selected from hydrogen, substituted or unsubstituted C1-C20 alkyi, C3-C20 cycloalkyl, C6-C2o aryl, C7-C2o aralkyl, and C7-C20 alkaryl, which groups may include linear or branched alkyl moieties, the optional one or more substituents being selected from the group consisting of hydroxy, alkoxy, iinear or branched alk(en)yl, aryloxy, halogen, carboxylic acid, ester, carboxy, nitnle, and amido groups These polymers are generally biodegradable, meaning that they can degrade by the action of naturally occurring microorganisms such as bacteria, fungi, and algae The commercial potential of these (co)polymers is very high, especially due to their biodegradabihty and/or natural renewability compared to petrochemically-denved polymers However, processing of these (co)polymers into commercially attractive products has been hindered by difficulties, such as their poor melt strength during melt processing Several pnor art documents disclose processes for the modification of such (co)polymers in order to solve these difficulties US 6,096,810 discloses the modificaoon of polyhydroxyalkanoates which may have the general structure shown above using free radical initiators, such as organic peroxides The peroxides disclosed in this document are all Iinear in nature and include 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane and butyl-4,4-di(tert-butylperoxy)valerate WO 95/18169 discloses the modification of poly(hydroxy acids) such as polylactic acid by reactive extrusion of the polymer with an organic peroxide Organic peroxides disclosed in this document are dilauroyl peroxide, tert-butylperoxy-diethylacetate, tert-butylperoxy-2-ethylhexanoate, tert-butyl-peroxyisobutyrate, tert-butylperoxyacetate, tert-butylperoxybenzoate, and dibenzoyl peroxide, which are all of linear nature Also US 5,594,095 discloses the modification of polylactic acid with linear organic peroxides such as 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane and dicumyl peroxide The polymers modified according to these prior art processes either result in only a minor degree of branching or suffer from gel formation, due to cross-linking Gel formation results in the occurrence of "fish eyes" in transparent films or coatings or in particulates in mouldings, which is evidently undesired Surprisingly, it has now been found that if acyclic organic peroxide is used to modify the (co)polymer, (co)polymers can be prepared which combine a high degree of branching with the absence of gel formation The present invention therefore relates to a process for the modification of a (co)polymer according to the above general structure for one or more of its repeating units, which involves contacting the (co)polymer with a cyclic organic peroxide under conditions whereby at least some of said peroxide is decomposed In addition, high molecular weight distributions of the (co)polymer can be obtained, thereby improving its melt strength A further advantage of the process of the present invention is that, unlike the peroxides used in the prior art, the cyclic organic peroxides used in the process of the present invention do not release t-butanol as decomposition product This absence of t-butanol - which, due to its toxicological properties, is undesired in (co)polymers for food-related applications - allows the modified (co)polymers according to the invention to be used in applications involving food contact The (co)polymers to be modified using the process according to the invention have the following general structure for one or more of the repeating units wherein n is an integer, m is an integer in the range 0 to 6, and R is selected from hydrogen substituted or unsubstituted C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 aralkyl, and C7-C20 alkaryl, which groups may include linear or branched alkyl moieties, the optional one or more substituents being selected from the group consisting of hydroxy, alkoxy, linear or branched alk(en)yl, aryloxy, halogen, carboxyfic aad, ester, carboxy, nitnle, and amido groups Preferably, all of the repeating units in the (co)polymer satisfy the general structure shown above, although not all of these repeating units need to be the same For instance, copolymers can be used in which part of the repeating units have a structure wherein m=1 and R=ethyl, while another part of the repeating units have a structure wherein m=1 and R=methyl Examples of suitable (co)polymers include polylactic acid (PLA, m=0, R=methyl in the above structure), poly(3-hydroxybutyrate) (m=1, R=methyl), polyglycolic acid (m=0 R=H), polyhydroxy-butyrate-covalerate (m=1, R=ethyl), and poly(e-caprolactone) (m=4, R=H) The (co)polymer according to the above structure can be modified in the process of the invention individually or while present in a blend with one or more other (co)polymers or materials Suitable other (co)polymers are polyacrylates and polymethacrytales, copolymers like Ecoflex® (a copolymer of 1,4-butanediol and terephthahc acid/adipmic acid), starch or starch-derived polymers, cellulose or cellulose-derived polymers, and other natural (co)polymers Cyclic organic peroxides are defined as organic molecules having a cyclic moiety and wherein the cyclic moiety contains a peroxide group Cyclic organic peroxides that are suitable for use in the process of the present invention include cyclic ketone peroxides and 1,2,4-tnoxepanes Also mixtures of one or more cyclic organic peroxides or mixtures of one or more cyclic organic peroxides with one or more non-cyclic organic peroxides may be used As shown in the Examples below, the use of 1,2,4-tnoxepanes even increases the melt flow index of the resulting (co)polymer This means that the melt processing properties of the resulting (co)polymer are improved, which is of importance if the polymer is to be processed by extrusion coating, fibre spinning, or injection moulding Preferred cyclic ketone peroxides are selected from the peroxides presented by formulae l-lll wherein RrR6 are independently selected from the group consisting of hydrogen, C1-C20 alkyl, C3-C2o cycloalkyl, C6-C2o aryl, C7-C2o aralkyl, and C7-C20 alkaryl, which groups may include linear or branched alkyl moieties, and each of Ri-R6 may optionally be substituted with one or more groups selected from hydroxy, alkoxy, linear or branched alkyl, aryloxy, ester, carboxy nitnle, and amido Preferably, the cyclic ketone peroxides consist of oxygen, carbon, and hydrogen atoms More preferably, the cyclic ketone peroxide is derived from linear, branched or cyclic C3-C13 ketones, most preferably C3-C7 ketones or C4-C20 diketones, most preferably C4-C7 diketones The use of ketones leads to the formation of the cyclic ketone peroxides of formulae I and II, while the use of diketones leads to the formation of the cyclic ketone peroxides of formula III Examples of suitable cyclic ketone peroxides for use in the process of the present invention include the peroxides derived from acetone, acetyl acetone, methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl butyl ketone, methyl isobutyl ketone, methyl amyl ketone, methyl isoamyl ketone, methyl hexyl ketone, methyl heptyl ketone, diethyl ketone, ethyl propyl ketone, ethyl amyl ketone, methyl octyl ketone, methyl nonyl ketone, cyclopentanone, cyclohexanone, 2-methylcyclohexanone, 3,3,5-tnmethyl cyclohexanone, and mixtures thereof Cyclic ketone peroxides can be produced as described in WO 96/03397 wherein R1, R2, R3 are independently selected from hydrogen and a substituted or unsubstituted hydrocarbyl group and wherein optionally two of the group of R1, R2, and R3 are linked to form a ring structure Preferred 1,2,4-tnoxepanes are those wherein R1"3 are independently selected from the group consisting of hydrogen and substituted or unsubstituted C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 aralkyl, and C7-C20 alkaryl, which groups may include linear or branched alkyl moieties, while two of the groups R1"3 may be connected to form a (substituted) cycloalkyl ring, the optional one or more substituents on each of R1-R3 being selected from the group consisting of hydroxy, alkoxy, linear or branched alk(en)yl, aryloxy, halogen, carboxyhc acid, ester, carboxy, nitnle, and amido Preferably, R1 and R3 are selected from lower alkyl groups, more preferably Ci-C6 alkyl groups, such as methyl, ethyl, and isopropyl, methyl and ethyl being most preferred R2 is preferably selected from hydrogen, methyl, ethyl, iso-propyl, iso-butyl, tert-butyl, amyl, iso-amyl, cyclohexyl, phenyl, CH3C(0)CH2-, C2H5OC(0)CH2-, HOC(CH3)2CH2-, and wherein R4 is independently selected from any of the group of compounds given for R1"3 Another preferred 1,2 4-tnoxepane is The (co)polymer and the cyclic organic peroxide may be brought into contact in various ways, depending on the particular object of the modification process The peroxide may be mixed with a melt, a solid (as powder, flake, pellet, film, or sheet), or a solution of the (co)polymer To accomplish homogeneous mixing of the (co)polymer and the peroxide, a conventional mixing apparatus may be used, such as a kneader, an internal mixer, or an extruder Should mixing be a problem for a particular material because of its high melting point, for example, the (co)polymer can first be modified on its surface while in the solid state and subsequently melted and mixed Alternatively, the (co)polymer may first be dissolved in a solvent and the reaction with the peroxide can then be carried out in solution The moment at which the peroxide and the (co)polymer are brought into contact with each other and the moment at which the peroxide is to react with the (co)polymer can be chosen independently of the other usual processing steps, including the introduction of additives, shaping, etc For instance, the (co)poiymer may be modified before additives are introduced into the (co)polymer or after the introduction of additives More importantly, it is possible to accomplish the present (co)polymer modification during a (co)polymer shaping step such as extrusion, extrusion coating, compression moulding, thermoformmg, foaming, film blowing, blow moulding, injection moulding, or injection stretch blow molding The present polymer modification process is most preferably carried out in an extrusion apparatus The amount of peroxide used in the process of the present invention should be such as to be effective to achieve significant modification of the (co)polymer Preferably at least 0 005 wt%, more preferably at least 0 01 wt%, and most j preferably at least 0 05 wt% of cyclic organic peroxide is used, based on the weight of (co)poiymer The amount of cyclic organic peroxide, based on the weight of (co)polymer, preferably is below 10 wt%, more preferably below 5 wt%, and most preferably below 1 wt% Suitable conditions under which at least some of the peroxide is decomposed are temperatures of preferably at least 180°C, more preferably at least 190°C, more preferably still at least 200°C, even more preferably at least 215°C, and most preferably at least 220°C The temperature applied during the process of the invention preferably is not higher than 260°C, more preferably not higher than 250°C, more preferably still not higher than 240°C, even more preferably not higher than 230°C, and most preferably not higher than 225°C After modification, the (co)polymer is cooled and/or devolatized using standard techniques in the polymerization industry The processing time, i e the time period ranging from the moment of contacting the peroxide and the (co)polymer to the moment of cooling or devolatizing the modified (co)polymer preferably is at least 5 seconds, more preferably at least 10 seconds, and most preferably at least 15 seconds The processing time preferably is not more than 15 minutes, more preferably not more than 10 minutes, more preferably still not more than 5 minutes, even more preferably not more than 60 seconds, and most preferably not more than 45 seconds Both the desired processing time and the desired temperature depend on the manner in which the peroxide and the (co)polymer are contacted with each other According to one embodiment of the invention, the cyclic organic peroxide is injected into a melt of the (co)polymer, for instance in an extruder Using this procedure, the processing time preferably ranges from 5-60 seconds, more preferably 5-45 seconds The temperature of the (co)polymer melt at the moment of injection preferably is in the range of 200-240°C, more preferably 215-230°C, and most preferably 220-225°C According to another embodiment, the (co)polymer and the cyclic organic peroxide are pre-mixed and then introduced into the mixing apparatus - e g a kneader, an internal mixer, or, preferably, an extruder This embodiment may require processing times of up to 15 minutes or more, preferably up to 10 minutes, more preferably up to 5 minutes The desired temperature of the mixture while present in the mixing apparatus will depend on its residence time therein The longer the residence time, the lower the temperature may be During modification, the (co)polymer may also contain additives Preferred additives are catalyst quenchers and slip and antiblocking agents such as fatty amides If desired, also stabilizers such as inhibitors of oxidative, thermal, or ultraviolet degradation, lubricants, extender oils, pH controlling substances such as calcium carbonate, release agents, colorants, reinforcing or non-reinforcing fillers such as silica, clay, chalk, carbon black, and fibrous materials such as glass fibres, natural fibres, wood-derived materials, nucleating agents, plasticizers, and accelerators, may be present The modified (co)polymer according to the present invention can be used in various applications, such as extruded or blown films, coatings for packaging, in particular for coating paper or board, foamed or moulded articles such as bottles, beakers, or trays, for instance foamed trays for microwavabie or ovenable food products, clam shells or other thermoformed articles, or injection-moulded trays FIGURES Figure 1 shows the viscosity as a function of the angular frequency for an unmodified polylactic acid (PLA) and for polylactic acid modified according to the present invention using Tngonox® 301 (Tx 301) and Tngonox® 311 (Tx 311) Figure 2 shows measurement of the storage modulus (G') and the loss modulus (G") in an oscillatory frequency sweep of the unmodified polymer and the modified polymers of Example 4 Figure 3 shows the low-shear viscosities of the unmodified polymer and the modified polymers of Example 4 EXAMPLES Methods Melt Flow Index The melt-flow index (MFI) was measured with a Gottfert® Melt indexer Model MP-D according to DIN 53735/ASTM 1238 (190°C, 21 6 N load) The MFI is expressed in g/10 mm Molecular weight characterization and branching The molecular weight of the modified (co)polymer was determined using a size- exclusion chromatography (SEC)-system consisting of a Pump Knauer HPLC-pump K501 Eluent 1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) Flow 0 6 ml/mm Injection Spark Holland Triathlon autosamples, 50 ul Concentration about 2 mg/ml Solvent 1,1,1,3,3,3-Hexafluoroisopropanol Column 2x PSS PFG linear XL 7u, 300 x 8 mm Detection Rl Waters 410 Differential Refractometer DP Viscotek Viscometer detector H502 LS Viscotek RALLS detector The molecular weights of the samples, i e the number-average (Mn), weight-average (Mw), and z-average (Mz) molecular weights, were calculated from Light Scattering (LS) detection The dispersity (D) was calculated as Mw/Mn The Intrinsic Viscosity (IV) was determined in the viscometer detector From the Mark-Houwink plots, the branching number (Bn, i e the average number of branches per molecule) and the frequency (k, i e the branching per 100 monomenc units) were calculated according to the theory of Zimm and Stockmayer, J Chem Phys 17 (1949) 1301 The structure factor z for randomly branched polymers was taken as 0 75 Measurement of the gel fraction Prior to the analysis, the samples were dried overnight in a circulation oven at 50°C Procedure 1 gram of sample and 50 ml of dichloromethane were added to a 50 ml crimp cap vial and the vial was capped The vial was shaken for at least 10 hours at room temperature A filter paper (Schleicher & Schuell No 597, 45 mm) was washed with 5 ml of dichoromethane (DCM) using a Buchner funnel, a filtering conical flask, and a water aspirator to provide suction for speeding up the filtration process The cleaned filter paper was placed on a petri dish, dried for 1 hour at 130°C, and cooled to room temperature in a desiccator The petri dish, including the dried filter paper, was weighed Next, a vacuum was applied to the Buchner funnel and the sample solution was poured into the funnel The filter paper including the residue was placed in the petri dish again, dried for 2 hours at 130°C, and cooled to room temperature in a desiccator The petri dish including the dried filter paper and the residue was weighed again and the weight of the residue was calculated The gel content is defined as the weight of the residue, relative to the initial weight of the sample (1 gram) A gel fraction of less than 0 2 wt% indicates the absence of gel formation Low-shear viscosity measurement Rheology measurements at low shear were performed at 180°C using a AR2000 Shear Dynamic Rheometer (TA Instruments) with the following specifications Torque range CS 0 1 jiN m to 200mN m Speed range CS 1E-8 to 300 rad/s Inertia ~15μ.Nm2 Frequency range 1 2 E-7 to 100 Hz Step change in speed Step change in strain Step change in stress Measurement of volatiies Volatiles in the modified polymer samples were determined by GC static head space analysis using a Hewlett Packard HP5890 series 2 GC, a Combi-Pal (CTC Analytics, Switzerland) auto-injector capable of standard liquid injection and static headspace injection, and LabSystems' Atlas 2000 as the data system The following conditions were used Column Fused silica, 25 m x 0 32 mm ID, coated with CP-Sil 5 CB, film thickness 5 urn, ex Chrompack Carrier gas Helium, methane retention time 62 sec at 40°C Injector Split -temperature 150°C - split flow 20 ml/mm Detector Flame Ionization Detector - temperature 320°C - detector sensitivity Range = 2 Oven temperature Initial 40°C for 3 mm Rate 1 5°C/min to 80 °C Rate 2 12°C/min Final 300°C for 1 mm Injection volume Headspace (gas) 1 0 ml 1 gram of polymer sample was heated for 1 hour at 140°C in a 20 ml crimp cap vial 1 ml of the headspace from the vial was then injected onto the GC column Example 1 Polylactic acid (PLA) granules (HM1010, ex Hycail, MFI = 59 g/10 mm) were added to a W&P ZSK30 extruder (L/D=36) using a Retsch vibrating gutter placed on a KTRON 1 balance for measuring throughput The screw speed of the extruder was 200 rpm, the screw length 1,150 mm The following temperature profile was used in the extruder 200 - 240 - 240 - 240 - 240 - 240°C Pure peroxide was injected to the polylactic acid melt at a screw length of 439 mm Vacuum degassing was started at a screw length of 895 mm Injection of peroxide was performed using a Knauer (Separations) 10 ml dosing pump with pressure readout and high-pressure restriction The dosing head was cooled with water Three cyclic organic peroxides were used Tngonox® 301 (3,6,9-tnethyl-3,6,9-trimethyl-1,4,7-triperoxononane ex Akzo Nobel) Tngonox® 311 (3,3,5,7,7-pentamethyl-1,2,4-tnoxepane, ex Akzo Nobel) and MEK-TP (3-ethyl-3,5,7,7~tetramethyl-1,2,4-tnoxepane) Tugonox® 101 (2, 5-dimethyl-2, 5-di (tert-butylperoxy) hexane, ex Akzo Nobel) Tngonox® 117 (Tert-butylperoxy 2-ethylhexyl caibonate, ex Akzo Nobel) Tugonox® 17 (Butyl-4, 4-di (tert-butylperoxy)valerate, ex Akzo Nobel) Tngonox® C (Tert-butylperoxybenzoate, ex Akzo Nobel) The peroxides were used in two quantities 0 25 wt% and 0 50 wt%, based on polylactic acid The MFI, the molecular weight distnbution, the branching number and fiequency, and the gel fiaction of the resulting modified polylactic acid were determined according to the piocedures explained above The results are presented in Tables 1 and 2 (wheiein "Tx" stands foi Tngonox®) These tables show that the use of a cyclic organic peroxide according to the present invention combines the absence of gel formation with broadening of the molecular weight distribution and increased branching In addition, Tngonox® 311 was able to increase the melt flow of the polymer Example 2 Example 1 was repeated, except that the polylactic acid used was commercial grade ex NatureWorks (MFI=8 2 g/10 mm), the temperature profile in the extruder was 220/220/220/220/220/220°C, and the peroxides tested were Tngonox® 301, Tngonox® 311, Tngonox® 101, mixtures of these peroxides (both 0 25 wt%), and MEK-TP The results are shown in Tables 3 and 4 These tables again show that the use of a cyclic organic peroxide according to the present invention combines the absence of gel formation with broadening of the molecular weight distribution and increased branching In addition, the volatiles generated by decomposition of the peroxide and remaining in the polylactic acid even after devolatization in the extruder were detected according to the method described above The results are shown in This data shows that by using the cyclic organic peroxides according to the invention the amount of volatiles remaining in the polymer, and in particular the amount of acetone and tert-butanol, is significantly lower than upon use of a linear peroxide Further, the low-shear viscosities of the unmodified polymer and the polymer modified with 0 5 wt% Tngonox® 301 and Tngonox® 311 were measured The result is plotted in Figure 1, which shows that the process according to the invention leads to polymer with an increased low-shear viscosity, indicating increased chain entanglement by long-chain branching Example 3 Example 2 was repeated, except that the temperature profile in the extruder was 210/210/210/210/210/210°C The results are shown in Tables 6 and 7 These Tables confirm that the use of a cyclic organic peroxide according to the present invention combines the absence of gel formation with broadening of the molecular weight distribution and increased branching Example 4 Example 2 was repeated, except that a different polylactic acid grade ex NatureWorks (MFI=13 8 g/10min) was used The peroxide tested was Tngonox® 301, at higher concentrations (up to 1 0 wt%) \| The results are shown in Table 8 The gel fraction was measured for all samples, indicating the absence of gel formation The results from Table 8 indicate the introduction of long-chain branches, leading to an increase in Mw and an enhanced Mz, which provides increased melt elasticity to the polymer The increase in melt elasticity of the modified polymers was confirmed by measurement of the storage modulus (G') and the loss modulus (G") in an osciHatory frequency sweep The result is plotted in Figure 2 The storage modulus (G') increases at higher wt% Tngonox® 301, indicating enhancement of the melt elasticity Further, the low-shear viscosities of the unmodified polymei and the modified polymeis weie measured The result is plotted in Figure 3, which shows that the process according to the invention leads to polymer with an increased zeio- shear viscosity (as a result of highei Mw) and "shear thinning" behavior (as a result of higher Mz/Mw, also lefeired to as polydispeisity), next to the enhanced melt elasticity These properties aie enhanced further with incieasing wt% of Tngonox® 301 We Claim: 1 Piocess foi the modification of a polymer or copolymer having the following general structure for one 01 more of the repeating units wherein n is an integer, m is an integer in the range 0 to 6, and R is selected from hydrogen, substituted or unsubstituted C1-C20 alkyl, C3-C20 cycloalkyl, C6-C2o aryl, C7-C20 arylalkyl, and C7-C20 alkylaryl, which groups may include linear or branched alkyl moieties, the optional one or more substituents being selected from the group consisting of hydroxy, alkoxy, linear or branched alk(en)yl, aryloxy, halogen, carboxylic acid, ester, carboxy, nitnle, and amido groups, which process involves contacting the polymer or copolymer with a cyclic organic peioxide at a temperatuie in the range 180-260°C 2 The process as claimed in claim 1 wherein the polymer or copolymer and the cyclic peroxide are contacted at a temperature in the range 200-240°C 3 The process as claimed in any one of the preceding claims wherein the cyclic peroxide is injected into a melt of the polymer or copolymei 4 The process as claimed in any of the preceding claims wherein the cyclic peroxide is selected from the group of cyclic ketone peroxides and 1,2,4-trioxepanes 5 The process as claimed in any one of the preceding claims wherein the polymer is polylactic acid 6 The process as claimed in any one of the preceding claims wherein the (co)polymer is present in a blend with one or more other (co)polymers or materials ABSTRACT "PROCESS FOR THE MODIFICATION OF BIODEGRADABLE POLYMERS" Process for the modification of a polymer or copolymer having the following general structure for one or more of the repeating units (1) wherein n is an integer, m is an integer in the range 0 to 6, and R is selected from hydrogen, substituted or unsubstituted C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 aralkyl, and C7-C20 alkaryl, which groups may include linear or branched alkyl moieties, the optional one or more substituents being selected from the group consisting of hydroxy, alkoxy, linear or branched alk(en)yl, aryloxy, halogen, carboxyhc acid, ester, carboxy, nitnle, and amido groups, which process involves contacting the polymer or copolymer with a cyclic organic peroxide under conditions whereby at least some of said peroxide is decomposed This process results in a (co)polymer with a high degree of branching but free of gel formation

Full Text

PROCESS FOR THE MODIFICATION OF BIODEGRADABLE POLYMERS
The present invention relates to a process for the modification of a polymer or copolymer having the following general structure for one or more of the repeating units
wherein n is an integer, m is an integer in the range 0 to 6, and R is selected from hydrogen, substituted or unsubstituted C1-C20 alkyi, C3-C20 cycloalkyl, C6-C2o aryl, C7-C2o aralkyl, and C7-C20 alkaryl, which groups may include linear or branched alkyl moieties, the optional one or more substituents being selected from the group consisting of hydroxy, alkoxy, iinear or branched alk(en)yl, aryloxy, halogen, carboxylic acid, ester, carboxy, nitnle, and amido groups These polymers are generally biodegradable, meaning that they can degrade by the action of naturally occurring microorganisms such as bacteria, fungi, and algae
The commercial potential of these (co)polymers is very high, especially due to their biodegradabihty and/or natural renewability compared to petrochemically-denved polymers However, processing of these (co)polymers into commercially attractive products has been hindered by difficulties, such as their poor melt strength during melt processing Several pnor art documents disclose processes for the modification of such (co)polymers in order to solve these difficulties
US 6,096,810 discloses the modificaoon of polyhydroxyalkanoates which may have the general structure shown above using free radical initiators, such as organic peroxides The peroxides disclosed in this document are all Iinear in

nature and include 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane and butyl-4,4-di(tert-butylperoxy)valerate
WO 95/18169 discloses the modification of poly(hydroxy acids) such as polylactic acid by reactive extrusion of the polymer with an organic peroxide Organic peroxides disclosed in this document are dilauroyl peroxide, tert-butylperoxy-diethylacetate, tert-butylperoxy-2-ethylhexanoate, tert-butyl-peroxyisobutyrate, tert-butylperoxyacetate, tert-butylperoxybenzoate, and dibenzoyl peroxide, which are all of linear nature
Also US 5,594,095 discloses the modification of polylactic acid with linear organic peroxides such as 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane and dicumyl peroxide
The polymers modified according to these prior art processes either result in only a minor degree of branching or suffer from gel formation, due to cross-linking Gel formation results in the occurrence of "fish eyes" in transparent films or coatings or in particulates in mouldings, which is evidently undesired
Surprisingly, it has now been found that if acyclic organic peroxide is used to modify the (co)polymer, (co)polymers can be prepared which combine a high degree of branching with the absence of gel formation
The present invention therefore relates to a process for the modification of a (co)polymer according to the above general structure for one or more of its repeating units, which involves contacting the (co)polymer with a cyclic organic peroxide under conditions whereby at least some of said peroxide is decomposed
In addition, high molecular weight distributions of the (co)polymer can be obtained, thereby improving its melt strength

A further advantage of the process of the present invention is that, unlike the peroxides used in the prior art, the cyclic organic peroxides used in the process of the present invention do not release t-butanol as decomposition product This absence of t-butanol - which, due to its toxicological properties, is undesired in (co)polymers for food-related applications - allows the modified (co)polymers according to the invention to be used in applications involving food contact
The (co)polymers to be modified using the process according to the invention have the following general structure for one or more of the repeating units

wherein n is an integer, m is an integer in the range 0 to 6, and R is selected from hydrogen substituted or unsubstituted C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 aralkyl, and C7-C20 alkaryl, which groups may include linear or branched alkyl moieties, the optional one or more substituents being selected from the group consisting of hydroxy, alkoxy, linear or branched alk(en)yl, aryloxy, halogen, carboxyfic aad, ester, carboxy, nitnle, and amido groups Preferably, all of the repeating units in the (co)polymer satisfy the general structure shown above, although not all of these repeating units need to be the same For instance, copolymers can be used in which part of the repeating units have a structure wherein m=1 and R=ethyl, while another part of the repeating units have a structure wherein m=1 and R=methyl
Examples of suitable (co)polymers include polylactic acid (PLA, m=0, R=methyl in the above structure), poly(3-hydroxybutyrate) (m=1, R=methyl), polyglycolic acid (m=0 R=H), polyhydroxy-butyrate-covalerate (m=1, R=ethyl), and poly(e-caprolactone) (m=4, R=H)
The (co)polymer according to the above structure can be modified in the process of the invention individually or while present in a blend with one or more

other (co)polymers or materials Suitable other (co)polymers are polyacrylates and polymethacrytales, copolymers like Ecoflex® (a copolymer of 1,4-butanediol and terephthahc acid/adipmic acid), starch or starch-derived polymers, cellulose or cellulose-derived polymers, and other natural (co)polymers
Cyclic organic peroxides are defined as organic molecules having a cyclic moiety and wherein the cyclic moiety contains a peroxide group Cyclic organic peroxides that are suitable for use in the process of the present invention include cyclic ketone peroxides and 1,2,4-tnoxepanes Also mixtures of one or more cyclic organic peroxides or mixtures of one or more cyclic organic peroxides with one or more non-cyclic organic peroxides may be used As shown in the Examples below, the use of 1,2,4-tnoxepanes even increases the melt flow index of the resulting (co)polymer This means that the melt processing properties of the resulting (co)polymer are improved, which is of importance if the polymer is to be processed by extrusion coating, fibre spinning, or injection moulding
Preferred cyclic ketone peroxides are selected from the peroxides presented by formulae l-lll

wherein RrR6 are independently selected from the group consisting of hydrogen, C1-C20 alkyl, C3-C2o cycloalkyl, C6-C2o aryl, C7-C2o aralkyl, and C7-C20 alkaryl, which groups may include linear or branched alkyl moieties, and each of Ri-R6 may optionally be substituted with one or more groups selected from hydroxy, alkoxy, linear or branched alkyl, aryloxy, ester, carboxy nitnle, and

amido
Preferably, the cyclic ketone peroxides consist of oxygen, carbon, and hydrogen atoms More preferably, the cyclic ketone peroxide is derived from linear, branched or cyclic C3-C13 ketones, most preferably C3-C7 ketones or C4-C20 diketones, most preferably C4-C7 diketones The use of ketones leads to the formation of the cyclic ketone peroxides of formulae I and II, while the use of diketones leads to the formation of the cyclic ketone peroxides of formula III Examples of suitable cyclic ketone peroxides for use in the process of the present invention include the peroxides derived from acetone, acetyl acetone, methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl butyl ketone, methyl isobutyl ketone, methyl amyl ketone, methyl isoamyl ketone, methyl hexyl ketone, methyl heptyl ketone, diethyl ketone, ethyl propyl ketone, ethyl amyl ketone, methyl octyl ketone, methyl nonyl ketone, cyclopentanone, cyclohexanone, 2-methylcyclohexanone, 3,3,5-tnmethyl cyclohexanone, and mixtures thereof Cyclic ketone peroxides can be produced as described in WO 96/03397

wherein R1, R2, R3 are independently selected from hydrogen and a substituted or unsubstituted hydrocarbyl group and wherein optionally two of the group of R1, R2, and R3 are linked to form a ring structure
Preferred 1,2,4-tnoxepanes are those wherein R1"3 are independently selected from the group consisting of hydrogen and substituted or unsubstituted C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 aralkyl, and C7-C20 alkaryl, which groups may include linear or branched alkyl moieties, while two of the groups R1"3 may be connected to form a (substituted) cycloalkyl ring, the optional one or more substituents on each of R1-R3 being selected from the group consisting of

hydroxy, alkoxy, linear or branched alk(en)yl, aryloxy, halogen, carboxyhc acid, ester, carboxy, nitnle, and amido
Preferably, R1 and R3 are selected from lower alkyl groups, more preferably Ci-C6 alkyl groups, such as methyl, ethyl, and isopropyl, methyl and ethyl being most preferred R2 is preferably selected from hydrogen, methyl, ethyl, iso-propyl, iso-butyl, tert-butyl, amyl, iso-amyl, cyclohexyl, phenyl, CH3C(0)CH2-, C2H5OC(0)CH2-, HOC(CH3)2CH2-, and

wherein R4 is independently selected from any of the group of compounds given for R1"3 Another preferred 1,2 4-tnoxepane is

The (co)polymer and the cyclic organic peroxide may be brought into contact in various ways, depending on the particular object of the modification process The peroxide may be mixed with a melt, a solid (as powder, flake, pellet, film, or sheet), or a solution of the (co)polymer
To accomplish homogeneous mixing of the (co)polymer and the peroxide, a conventional mixing apparatus may be used, such as a kneader, an internal mixer, or an extruder Should mixing be a problem for a particular material because of its high melting point, for example, the (co)polymer can first be modified on its surface while in the solid state and subsequently melted and mixed Alternatively, the (co)polymer may first be dissolved in a solvent and the reaction with the peroxide can then be carried out in solution The moment at which the peroxide and the (co)polymer are brought into contact with each other and the moment at which the peroxide is to react with the (co)polymer can be chosen independently of the other usual processing steps,

including the introduction of additives, shaping, etc For instance, the (co)poiymer may be modified before additives are introduced into the (co)polymer or after the introduction of additives More importantly, it is possible to accomplish the present (co)polymer modification during a (co)polymer shaping step such as extrusion, extrusion coating, compression moulding, thermoformmg, foaming, film blowing, blow moulding, injection moulding, or injection stretch blow molding The present polymer modification process is most preferably carried out in an extrusion apparatus
The amount of peroxide used in the process of the present invention should be such as to be effective to achieve significant modification of the (co)polymer Preferably at least 0 005 wt%, more preferably at least 0 01 wt%, and most j preferably at least 0 05 wt% of cyclic organic peroxide is used, based on the weight of (co)poiymer The amount of cyclic organic peroxide, based on the weight of (co)polymer, preferably is below 10 wt%, more preferably below 5 wt%, and most preferably below 1 wt%
Suitable conditions under which at least some of the peroxide is decomposed are temperatures of preferably at least 180°C, more preferably at least 190°C, more preferably still at least 200°C, even more preferably at least 215°C, and most preferably at least 220°C The temperature applied during the process of the invention preferably is not higher than 260°C, more preferably not higher than 250°C, more preferably still not higher than 240°C, even more preferably not higher than 230°C, and most preferably not higher than 225°C
After modification, the (co)polymer is cooled and/or devolatized using standard techniques in the polymerization industry
The processing time, i e the time period ranging from the moment of contacting the peroxide and the (co)polymer to the moment of cooling or devolatizing the modified (co)polymer preferably is at least 5 seconds, more preferably at least 10 seconds, and most preferably at least 15 seconds The processing time

preferably is not more than 15 minutes, more preferably not more than 10 minutes, more preferably still not more than 5 minutes, even more preferably not more than 60 seconds, and most preferably not more than 45 seconds
Both the desired processing time and the desired temperature depend on the manner in which the peroxide and the (co)polymer are contacted with each other According to one embodiment of the invention, the cyclic organic peroxide is injected into a melt of the (co)polymer, for instance in an extruder Using this procedure, the processing time preferably ranges from 5-60 seconds, more preferably 5-45 seconds The temperature of the (co)polymer melt at the moment of injection preferably is in the range of 200-240°C, more preferably 215-230°C, and most preferably 220-225°C
According to another embodiment, the (co)polymer and the cyclic organic peroxide are pre-mixed and then introduced into the mixing apparatus - e g a kneader, an internal mixer, or, preferably, an extruder This embodiment may require processing times of up to 15 minutes or more, preferably up to 10 minutes, more preferably up to 5 minutes The desired temperature of the mixture while present in the mixing apparatus will depend on its residence time therein The longer the residence time, the lower the temperature may be
During modification, the (co)polymer may also contain additives Preferred additives are catalyst quenchers and slip and antiblocking agents such as fatty amides If desired, also stabilizers such as inhibitors of oxidative, thermal, or ultraviolet degradation, lubricants, extender oils, pH controlling substances such as calcium carbonate, release agents, colorants, reinforcing or non-reinforcing fillers such as silica, clay, chalk, carbon black, and fibrous materials such as glass fibres, natural fibres, wood-derived materials, nucleating agents, plasticizers, and accelerators, may be present
The modified (co)polymer according to the present invention can be used in various applications, such as extruded or blown films, coatings for packaging, in particular for coating paper or board, foamed or moulded articles such as

bottles, beakers, or trays, for instance foamed trays for microwavabie or ovenable food products, clam shells or other thermoformed articles, or injection-moulded trays
FIGURES
Figure 1 shows the viscosity as a function of the angular frequency for an
unmodified polylactic acid (PLA) and for polylactic acid modified according to
the present invention using Tngonox® 301 (Tx 301) and Tngonox® 311 (Tx
311)
Figure 2 shows measurement of the storage modulus (G') and the loss modulus
(G") in an oscillatory frequency sweep of the unmodified polymer and the
modified polymers of Example 4
Figure 3 shows the low-shear viscosities of the unmodified polymer and the
modified polymers of Example 4
EXAMPLES
Methods
Melt Flow Index
The melt-flow index (MFI) was measured with a Gottfert® Melt indexer Model
MP-D according to DIN 53735/ASTM 1238 (190°C, 21 6 N load) The MFI is
expressed in g/10 mm
Molecular weight characterization and branching
The molecular weight of the modified (co)polymer was determined using a size-
exclusion chromatography (SEC)-system consisting of a
Pump Knauer HPLC-pump K501
Eluent 1,1,1,3,3,3-Hexafluoroisopropanol (HFIP)
Flow 0 6 ml/mm
Injection Spark Holland Triathlon autosamples, 50 ul
Concentration about 2 mg/ml
Solvent 1,1,1,3,3,3-Hexafluoroisopropanol

Column 2x PSS PFG linear XL 7u, 300 x 8 mm
Detection Rl Waters 410 Differential Refractometer
DP Viscotek Viscometer detector H502
LS Viscotek RALLS detector
The molecular weights of the samples, i e the number-average (Mn), weight-average (Mw), and z-average (Mz) molecular weights, were calculated from Light Scattering (LS) detection The dispersity (D) was calculated as Mw/Mn The Intrinsic Viscosity (IV) was determined in the viscometer detector From the Mark-Houwink plots, the branching number (Bn, i e the average number of branches per molecule) and the frequency (k, i e the branching per 100 monomenc units) were calculated according to the theory of Zimm and Stockmayer, J Chem Phys 17 (1949) 1301 The structure factor z for randomly branched polymers was taken as 0 75
Measurement of the gel fraction
Prior to the analysis, the samples were dried overnight in a circulation oven at
50°C
Procedure 1 gram of sample and 50 ml of dichloromethane were added to a 50
ml crimp cap vial and the vial was capped The vial was shaken for at least 10
hours at room temperature
A filter paper (Schleicher & Schuell No 597, 45 mm) was washed with 5 ml of
dichoromethane (DCM) using a Buchner funnel, a filtering conical flask, and a
water aspirator to provide suction for speeding up the filtration process
The cleaned filter paper was placed on a petri dish, dried for 1 hour at 130°C,
and cooled to room temperature in a desiccator The petri dish, including the
dried filter paper, was weighed
Next, a vacuum was applied to the Buchner funnel and the sample solution was
poured into the funnel The filter paper including the residue was placed in the
petri dish again, dried for 2 hours at 130°C, and cooled to room temperature in
a desiccator The petri dish including the dried filter paper and the residue was
weighed again and the weight of the residue was calculated

The gel content is defined as the weight of the residue, relative to the initial weight of the sample (1 gram) A gel fraction of less than 0 2 wt% indicates the absence of gel formation
Low-shear viscosity measurement
Rheology measurements at low shear were performed at 180°C using a
AR2000 Shear Dynamic Rheometer (TA Instruments) with the following
specifications
Torque range CS 0 1 jiN m to 200mN m
Speed range CS 1E-8 to 300 rad/s
Inertia ~15μ.Nm2
Frequency range 1 2 E-7 to 100 Hz
Step change in speed Step change in strain Step change in stress Measurement of volatiies
Volatiles in the modified polymer samples were determined by GC static head
space analysis using a Hewlett Packard HP5890 series 2 GC, a Combi-Pal
(CTC Analytics, Switzerland) auto-injector capable of standard liquid injection
and static headspace injection, and LabSystems' Atlas 2000 as the data
system
The following conditions were used
Column Fused silica, 25 m x 0 32 mm ID, coated with CP-Sil 5
CB,
film thickness 5 urn, ex Chrompack
Carrier gas Helium, methane retention time 62 sec at 40°C
Injector Split
-temperature 150°C
- split flow 20 ml/mm

Detector Flame Ionization Detector
- temperature 320°C
- detector sensitivity Range = 2
Oven temperature Initial 40°C for 3 mm
Rate 1 5°C/min to 80 °C
Rate 2 12°C/min
Final 300°C for 1 mm Injection volume Headspace (gas) 1 0 ml
1 gram of polymer sample was heated for 1 hour at 140°C in a 20 ml crimp cap vial 1 ml of the headspace from the vial was then injected onto the GC column
Example 1
Polylactic acid (PLA) granules (HM1010, ex Hycail, MFI = 59 g/10 mm) were
added to a W&P ZSK30 extruder (L/D=36) using a Retsch vibrating gutter
placed on a KTRON 1 balance for measuring throughput The screw speed of
the extruder was 200 rpm, the screw length 1,150 mm
The following temperature profile was used in the extruder
200 - 240 - 240 - 240 - 240 - 240°C
Pure peroxide was injected to the polylactic acid melt at a screw length of 439 mm Vacuum degassing was started at a screw length of 895 mm Injection of peroxide was performed using a Knauer (Separations) 10 ml dosing pump with pressure readout and high-pressure restriction The dosing head was cooled with water
Three cyclic organic peroxides were used
Tngonox® 301 (3,6,9-tnethyl-3,6,9-trimethyl-1,4,7-triperoxononane ex Akzo
Nobel)
Tngonox® 311 (3,3,5,7,7-pentamethyl-1,2,4-tnoxepane, ex Akzo Nobel) and
MEK-TP (3-ethyl-3,5,7,7~tetramethyl-1,2,4-tnoxepane)

Tugonox® 101 (2, 5-dimethyl-2, 5-di (tert-butylperoxy) hexane, ex Akzo Nobel) Tngonox® 117 (Tert-butylperoxy 2-ethylhexyl caibonate, ex Akzo Nobel) Tugonox® 17 (Butyl-4, 4-di (tert-butylperoxy)valerate, ex Akzo Nobel) Tngonox® C (Tert-butylperoxybenzoate, ex Akzo Nobel)
The peroxides were used in two quantities 0 25 wt% and 0 50 wt%, based on polylactic acid
The MFI, the molecular weight distnbution, the branching number and fiequency, and the gel fiaction of the resulting modified polylactic acid were determined according to the piocedures explained above The results are presented in Tables 1 and 2 (wheiein "Tx" stands foi Tngonox®)

These tables show that the use of a cyclic organic peroxide according to the present invention combines the absence of gel formation with broadening of the molecular weight distribution and increased branching In addition, Tngonox® 311 was able to increase the melt flow of the polymer
Example 2
Example 1 was repeated, except that the polylactic acid used was commercial
grade ex NatureWorks (MFI=8 2 g/10 mm), the temperature profile in the
extruder was 220/220/220/220/220/220°C, and the peroxides tested were
Tngonox® 301, Tngonox® 311, Tngonox® 101, mixtures of these peroxides
(both 0 25 wt%), and MEK-TP
The results are shown in Tables 3 and 4

These tables again show that the use of a cyclic organic peroxide according to the present invention combines the absence of gel formation with broadening of the molecular weight distribution and increased branching
In addition, the volatiles generated by decomposition of the peroxide and remaining in the polylactic acid even after devolatization in the extruder were detected according to the method described above The results are shown in

This data shows that by using the cyclic organic peroxides according to the invention the amount of volatiles remaining in the polymer, and in particular the amount of acetone and tert-butanol, is significantly lower than upon use of a linear peroxide
Further, the low-shear viscosities of the unmodified polymer and the polymer modified with 0 5 wt% Tngonox® 301 and Tngonox® 311 were measured The result is plotted in Figure 1, which shows that the process according to the invention leads to polymer with an increased low-shear viscosity, indicating increased chain entanglement by long-chain branching
Example 3
Example 2 was repeated, except that the temperature profile in the extruder
was 210/210/210/210/210/210°C
The results are shown in Tables 6 and 7

These Tables confirm that the use of a cyclic organic peroxide according to the present invention combines the absence of gel formation with broadening of the molecular weight distribution and increased branching
Example 4
Example 2 was repeated, except that a different polylactic acid grade ex NatureWorks (MFI=13 8 g/10min) was used The peroxide tested was Tngonox® 301, at higher concentrations (up to 1 0 wt%) | The results are shown in Table 8

The gel fraction was measured for all samples, indicating the absence of gel formation
The results from Table 8 indicate the introduction of long-chain branches, leading to an increase in Mw and an enhanced Mz, which provides increased melt elasticity to the polymer
The increase in melt elasticity of the modified polymers was confirmed by measurement of the storage modulus (G') and the loss modulus (G") in an osciHatory frequency sweep The result is plotted in Figure 2 The storage modulus (G') increases at higher wt% Tngonox® 301, indicating enhancement of the melt elasticity

Further, the low-shear viscosities of the unmodified polymei and the modified polymeis weie measured The result is plotted in Figure 3, which shows that the process according to the invention leads to polymer with an increased zeio- shear viscosity (as a result of highei Mw) and "shear thinning" behavior (as a result of higher Mz/Mw, also lefeired to as polydispeisity), next to the enhanced melt elasticity These properties aie enhanced further with incieasing wt% of Tngonox® 301

We Claim:
1 Piocess foi the modification of a polymer or copolymer having the following
general structure for one 01 more of the repeating units

wherein n is an integer, m is an integer in the range 0 to 6, and R is selected from hydrogen, substituted or unsubstituted C1-C20 alkyl, C3-C20 cycloalkyl, C6-C2o aryl, C7-C20 arylalkyl, and C7-C20 alkylaryl, which groups may include linear or branched alkyl moieties, the optional one or more substituents being selected from the group consisting of hydroxy, alkoxy, linear or branched alk(en)yl, aryloxy, halogen, carboxylic acid, ester, carboxy, nitnle, and amido groups, which process involves contacting the polymer or copolymer with a cyclic organic peioxide at a temperatuie in the range 180-260°C
2 The process as claimed in claim 1 wherein the polymer or copolymer and the cyclic peroxide are contacted at a temperature in the range 200-240°C
3 The process as claimed in any one of the preceding claims wherein the cyclic peroxide is injected into a melt of the polymer or copolymei
4 The process as claimed in any of the preceding claims wherein the cyclic peroxide is selected from the group of cyclic ketone peroxides and 1,2,4-trioxepanes
5 The process as claimed in any one of the preceding claims wherein the polymer is polylactic acid

6 The process as claimed in any one of the preceding claims wherein the
(co)polymer is present in a blend with one or more other (co)polymers or materials

ABSTRACT

"PROCESS FOR THE MODIFICATION OF BIODEGRADABLE POLYMERS"
Process for the modification of a polymer or copolymer having the following general structure for one or more of the repeating units (1) wherein n is an integer, m is an integer in the range 0 to 6, and R is selected from hydrogen, substituted or unsubstituted C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 aralkyl, and C7-C20 alkaryl, which groups may include linear or branched alkyl moieties, the optional one or more substituents being selected from the group consisting of hydroxy, alkoxy, linear or branched alk(en)yl, aryloxy, halogen, carboxyhc acid, ester, carboxy, nitnle, and amido groups, which process involves contacting the polymer or copolymer with a cyclic organic peroxide under conditions whereby at least some of said peroxide is decomposed This process results in a (co)polymer with a high degree of branching but free of gel formation

PROCESS FOR THE MODIFICATION OF BIODEGRADABLE POLYMERS

Documents:

Inventors:

PCT Conventions: