WO2014184057A1 - Process for production of polymer powders - Google Patents

Process for production of polymer powders Download PDF

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Publication number
WO2014184057A1
WO2014184057A1 PCT/EP2014/059224 EP2014059224W WO2014184057A1 WO 2014184057 A1 WO2014184057 A1 WO 2014184057A1 EP 2014059224 W EP2014059224 W EP 2014059224W WO 2014184057 A1 WO2014184057 A1 WO 2014184057A1
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weight
polymer
monomer
powder according
polymer powder
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PCT/EP2014/059224
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French (fr)
Inventor
Jordan Thomas KOPPING
Uwe Hartnagel
Volker SPRENGER
Stefan Dahmen
Simone Schillo
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Basf Se
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L67/00—Compositions of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Compositions of derivatives of such polymers
    • C08L67/04—Polyesters derived from hydroxycarboxylic acids, e.g. lactones
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F257/00—Macromolecular compounds obtained by polymerising monomers on to polymers of aromatic monomers as defined in group C08F12/00
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F2/00—Processes of polymerisation
    • C08F2/12—Polymerisation in non-solvents
    • C08F2/16—Aqueous medium
    • C08F2/22—Emulsion polymerisation
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L51/00—Compositions of graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Compositions of derivatives of such polymers
    • C08L51/06—Compositions of graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Compositions of derivatives of such polymers grafted on to homopolymers or copolymers of aliphatic hydrocarbons containing only one carbon-to-carbon double bond

Definitions

  • the present invention relates to a polymer powder with improved powder properties, and to its use as impact modifier for polylactic acid.
  • the polymer powder comprises
  • poly(lactic acid) polymers are becoming of increasing interest because of their preparation from renewable resource materials and their ability to biodegrading under certain composting conditions to regenerate carbon dioxide. Such materials are specifically beneficial in packaging applications; however, PLA is a brittle polymer and in many applications the PLA requires an additive to improve the mechanical properties. Such modification additives, for example impact modifiers, act to increase the fracture resistance of the plastic and in turn make the material more pliable and less brittle.
  • Common impact modifiers include core/shell polymer particles to improve these materials properties, where a soft rubber core absorbs energy from an impact to prevent cracking and material failure, while the exterior shell acts to compatibilize the polymer particles with the PLA matrix.
  • the common impact modifiers require relatively high additive loading of 3-5% to achieve moderate improvement of impact strength.
  • the problem herein lies twofold: first is the restrictions for classification of PLA biodegradability limit the amount of "non-degradable” and secondly the higher loading levels required to achieve good impact strength significantly reduce the transparency of the PLA.
  • Impact modifiers and rheology modifiers are rubber particles and can be core /shell morphology with efforts to match the shell refractive index with PLA
  • Rheology modifiers are described as typically medium molecular weight uncrosslinked polymers which have specific chemical groups to increase the molecular weight and branching of PLA in the melt.
  • the use of glycidyl methacrlate is describe as a functional monomer, in conjunction with other non functional monomers such as styrene, methylmethacrylate etc., to make a polymer with a MW in the range of 1000 -6000 g/mol.
  • the synthesis is seen in patent US6552144.
  • the use of these polymers as rheology modifiers does not show any improvement on the impact resistance of the PLA material (WO2006002372A2, US 2007/0179218A1 ).
  • WO2008063988 and EP1785453 disclose a crosslinked impact modifier particle with an additional copolymer in a PLA matrix.
  • the impact modifier and copolymer descriptions do not define any acrylic acid or epoxide (glycidyl) functional groups.
  • Object of the present invention was to develop a high performance product which could be used at much lower loading levels to achieve high impact strength and sample transparency.
  • the invention achieves the object via a Polymer powder comprising
  • the impact modifier is composed of emulsion polymer particles which have a core-shell structure, where the shell is composed of a hard polymer and the core is composed of a soft, cross- linked rubber polymer.
  • Impact modifiers of this type are usually produced via a multistage free-radical emulsion polymerization process.
  • the resultant modifier dispersion is converted into powder form via spray drying or via precipitation and subsequent drying of the coagulate, and is mixed with pulverulent polylactic acid (PLA), component (i), and component (iii) and, if appropriate, with conventional additives.
  • PVA pulverulent polylactic acid
  • the impact modifier, component (ii) is a polymer powder from an aqueous polymer dispersion, which comprises obtaining the aqueous dispersion of the polymer particles II via free-radical- initiated aqueous emulsion polymerization of at least one ethylenically unsaturated monomer C in the presence of dispersely distributed polymer particles I, where a) the polymer of the at least one unsaturated monomer C has a glass transition temperature > 60°C, b) the dispersely distributed polymer particles I are obtained via free-radical-initiated aqueous emulsion polymerization of a monomer mixture I, composed of from 98.0 to 99.9% by weight of at least one ethylenically unsaturated monomer A whose polymer has a glass transition temperature ⁇ - 20°C, and
  • the powder is produced from the aqueous dispersion of polymer particles II i. via spray drying, optionally in the presence of from 0.1 to 15% by weight of at least one antiblocking agent, based on the total weight of polymer particles II, and subsequent comminution of the crude powder by means of mechanically and/or pneumat- ically induced shear forces, or
  • the invention also provides PLA compositions comprising the polymer powder produced by the inventive process, and provides moldings produced using the resultant PLA compositions.
  • the average particle diameter of the polymer particles II is in the range from 100 to 500 nm, preferably from 220 to 320 nm.
  • the graft copolymers of the inventive chemical constitution are known per se.
  • the core of the particles is composed of a crosslinked emulsion polymer (polymer I) with a glass transition temperature ⁇ -20°C.
  • the shell is composed of a polymer of the at least one monomer C.
  • the content of the graft shell is from 25 to 0.1 % by weight, preferably from 20 to 10% by weight. It comprises from 90 to 100% by weight of the ethylenically unsaturated monomer C.
  • the monomer C are Ci-C4-alkyl methacrylates, Ci-Cs-alkyl acrylates, vinyl chloride, styrene, or acrylonitrile, or mixtures of these.
  • the monomer C used particularly preferably comprises methyl methacrylate.
  • copolymerizable ethylenically unsaturated monomers may also be added to the monomers C, where the total amounts of monomer C and of the eth- ylenically unsaturated monomer give a total of 100% by weight.
  • the graft copolymers comprise from 75 to 99.9% by weight, preferably from 80 to 90% by weight, of a soft graft core composed of a crosslinked rubber composed of the monomers A and B (polymer I).
  • the monomers A have been selected from the group of the Ci-Cs-alkyl acry- lates, preferably butyl acrylate, 2-ethylhexyl acrylate, or from mixtures of these.
  • other copolymerizable ethylenically unsaturated monomers may also be added to the monomers A.
  • the content of monomer A is from 95 to 100% by weight, where the total amounts of monomer A and of the ethylenically unsaturated monomer give a total of 100% by weight.
  • the monomers B act as crosslinking agents and their amounts used are from 0.1 to 2.0% by weight.
  • the monomers B are compounds having crosslinking action and having at least two non-conjugated vinyl groups, examples being allyl methacrylate, butanediol methacrylate, or dihydrodicyclopentadienyl acrylate.
  • the ratio by weight of the polymer I to monomer C is more than 90% by weight to less than 10% by weight, preferably more than 93% by weight to less than 7% by weight, particularly preferably more than or equal to 97% by weight to less than or equal to 3% by weight, where the total amounts give a total of 100% by weight. It has been found that impact-resistance efficiency passes through an optimum in the inventive range.
  • the graft polymers are usually prepared via emulsion polymerization in two stages, first polymerizing the monomers A + B to give the crosslinked polyacrylate rubber, and then, in its presence, polymerizing the monomers C.
  • the initiators used may comprise water-soluble thermally decomposing initiators or redox systems.
  • thermally decomposing initiators examples include sodium peroxodisulfate, potassium peroxodisulfate, or ammonium peroxodisulfate.
  • Exam- pies of redox systems which may be used are hydroperoxides in combination with reducing agents.
  • the emulsion polymerization process may use conventional emulsifiers, such as: alkyl, aryl, alkanyl, Cio-Ci3-alkyl derivatives of benzenesulfonic acid, or the corresponding sulfates, or polyether sulfates, ethoxylated fatty acids, ethoxylated fatty esters, ethoxylated fatty alcohols, ethoxylated fatty amines, ethoxylated fatty amides, ethoxylated fatty-alkylphenols, or organo- phosphoric acids.
  • the emulsion polymerization process takes place at from 10 to 100°C.
  • the graft copolymer can have a bi- or multimodal particle size distribution.
  • It can comprise at least two types of graft rubber which have the same chemical constitution but whose average particle diameters differ by at least 30 nm, preferably by at least 50 nm.
  • the content here of the type of graft rubber with the greatest average particle diameter is at least 15%, preferably at least 20% and in particular at least 25%, based on the entire graft copolymer. Its average particle diameter is preferably in the range from 200 to 500 nm, in particular from 250 to 350 nm.
  • the content of the type of graft rubber with the smallest average particle diameter is at least 5%, preferably at least 8%, and in particular at least 12%, based on the entire graft polymer.
  • Its average particle diameter is preferably in the range from 50 to 250 nm, in particular from 80 to 200 nm.
  • other types of graft rubber Yi, Y2, Y3, etc. may be present, their average particle diameters being between those of the types X and Z of graft rubber.
  • Multimodal particle size distributions can be obtained via various methods: a targeted particle size distribution can even be produced via synthesis parameters during the emulsion polymerization process. It is also possible to mix monomodal dispersions produced via emulsion polymerization after the synthesis process, or to mix appropriate powders after the dispersions have been dried. Graft rubbers with comparatively narrow, defined particle size distribution are advantageously prepared via the "seed latex" method.
  • the seed latex is the aqueous emulsion of a polymer of the monomers C, preferably a homopolymer of styrene, of methyl methacrylate, of a Ci-Cs-alkyl acrylate, or is a copolymer of these monomers.
  • the average particle diameter of the polymer is preferably from 10 to 50 nm.
  • the emulsion of the monomers A + B is carried out in the presence of the initial charge of the seed latex, whose solids amount to from 0.01 to 7% by weight, preferably from 0.1 to 5% by weight, of the monomers.
  • the average particle diameter of the graft rubber then depends on the amount of solid used as initial charge: if the amount of solid is high, either the amount of seed latex or its concentration can be used as control factors.
  • the fine-particle graft copolymer obtained during polymerization of the monomers C in the presence of the polyacrylate rubber composed of the monomers A + B is dried, and amounts of from 0,5 to 10% by weight of the pulverulent impact modifier are mixed with PLA powder and with conventional additives, e.g. fillers, stabilizers, and processing aids, and are processed by conventional methods to give high-impact-resistance PLA moldings.
  • conventional additives e.g. fillers, stabilizers, and processing aids
  • polymer particles II of the impact modifier are blended, prior to the spray-drying process, with polymer particles III obtained via free-radical-initiated aqueous emulsion polymerization of at least one ethylenically unsaturated monomer D, these having a glass transition temperature > 50°C (monomers D).
  • Examples of the monomers D are Ci-Cs-alkyl acrylates, Ci-C4-alkyl methacrylates, styrene, ac- rylonitrile, methacrylic acid, acrylic acid, or compounds having crosslinking action and having at least two non-conjugated vinyl groups, or mixtures of these.
  • other copolymer- izable ethylenically unsaturated monomers may also be added to the monomers D, where the total amounts of monomer D and of the ethylenically unsaturated monomer give a total of 100% by weight.
  • the average particle diameter of the polymer particles III is from 50 to 300 nm, preferably from 70 to 170 nm.
  • the content is greater than 5% by weight and smaller than 30% by weight, based on the amount of polymer particles II.
  • Examples of the other copolymerizable ethylenically unsaturated monomers which may also be added to the monomers A, C and D are acrylic acid, methacrylic acid, ethylacrylic acid, allyla- cetic acid, crotonic acid, vinylacetic acid, maleic half-esters, such as monomethyl maleate, their mixtures or their alkali metal and ammonium salts, linear 1 -olefins, branched-chain 1 -olefins or cyclic olefins, e.g.
  • oligoole- fins prepared via metallocene catalysis and having a terminal double bond, e.g.
  • oligopropene oligohexene, and oligooctadecene
  • methyl vinyl ether ethyl vinyl ether, propyl vinyl ether, isobutyl vinyl ether, 2-ethylhexyl vinyl ether, vinyl cyclohexyl ether, vinyl 4-hydroxybutyl ether, decyl vinyl ether, dodecyl vinyl ether, octadecyl vinyl ether, 2- (diethylamino)ethyl vinyl ether, 2-(di-n-butylamino)ethyl vinyl ether, methyldiglycol vinyl ether, and also the corresponding allyl ethers and their mixtures.
  • Acrylamides and alkyl-substituted acrylamides e.g. acrylamide, methacrylamide, N-tert- butylacrylamide, N-methyl(meth)acrylamide.
  • Monomers containing sulfo groups e.g. allylsulfonic acid, methallylsulfonic acid, styrenesul- fonate, vinylsulfonic acid, allyloxybenzenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, their corresponding alkali metal or ammonium salts, and mixtures of these.
  • Alkylaminoalkyl (meth)acrylates or alkylaminoalkyl(meth)acrylamides or their quaternization products e.g. 2-(N,N-dimethylamino)ethyl (meth)acrylate, 3-(N,N-dimethylamino)propyl (meth)acrylate, 2-(N,N,N-trimethylammonium)ethyl (meth)acrylate chloride, 2- dimethylaminoethyl (meth)acrylamide, 3-dimethylaminopropyl(meth)acrylamide, 3- trimethylammoniumpropyl(meth)acrylamide chloride.
  • Vinyl and allyl esters of C1-C30 monocarboxylic acids e.g. vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, vinyl 2-ethylhexanoate, vinyl nonanoate, vinyl decanoate, vinyl pivalate, vinyl palmitate, vinyl stearate, vinyl laurate.
  • N-Vinylformamide N-vinyl-N-methylformamide, styrene, a-methylstyrene, 3-methylstyrene, butadiene, N-vinylpyrrolidone, N-vinylimidazole, 1 -vinyl-2-methylimidazole, 1 -vinyl-2- methylimidazoline, N-vinylcaprolactam, acrylonitrile, methacrylonitrile, allyl alcohol, 2- vinylpyridine, 4-vinylpyridine, diallyldimethylammonium chloride, vinylidene chloride, vinyl chlo- ride, acrolein, methacrolein, and vinylcarbazole, and mixtures of these.
  • the graft shell comprises methylmethacrylate and acrylic acid.
  • the amount of acrylic acid comprises 0.1 - 5 weight% of total monomer content.
  • Component i) preferably comprises polylactic acid with the following property profile:
  • melt volume rate of from 0.5 to 15 ml/10 minutes, preferably from 1 to 9 ml/10 minutes, particularly preferably from 2 to 8 ml/10 minutes (MVR at 190°C using 2.16 kg to ISO 1 133)
  • polylactic acids examples include the following from NatureWorks® : Ingeo® 2002 D, 4032 D, 4042 D and 4043 D, 8251 D, 3251 D.
  • Polylactic acids that have proven particularly advantageous for producing the expandable pelletized material of the invention have MVR of from 5 to 8 ml/10 minutes to ISO 1 133 [190°C/2.16 kg].
  • Polylactic acids which are particularly suitable have the abovementioned MVR range and/or have a low-temperature-crystallization onset temperature in the range from 80°C to 125°C, preferably from 90°C to 1 15°C, and particularly preferably from 95°C to 105°C, measured by means of DSC (differential scanning calorimetry) at a heating rate of 20K/min (measurement range from -60°C to 220°C; Mettler DSC 30 using a TC15/TA controller, Mettler-Toledo AG).
  • DSC differential scanning calorimetry
  • Epoxides are in particular a copolymer which is based on styrene, acrylate, and/or methacrylate, and which contains epoxy groups.
  • the units bearing epoxy groups are preferably glycidyl (meth)acrylates.
  • Copolymers that have proven advantageous have a proportion of glycidyl methacrylate greater than 20% by weight, particularly preferably greater than 30% by weight, and with particular preference greater than 50% by weight, based on the copolymer.
  • the epoxide equivalent weight (EEW) in these polymers is preferably from 150 to
  • the average molecular weight (weight average) Mw of the polymers is preferably from 2000 to 25 000, in particular from 3000 to 8000.
  • the average molecular weight (number average) M n of the polymers is preferably from 400 to 6000, in particular from 1000 to 4000.
  • Polydispersity (Q) is generally from 1 .5 to 5. Copolymers of the abovementioned type containing epoxy groups are marketed by way of example by BASF Resins B.V. as Joncryl ® ADR. Joncryl ® ADR 4368 is particularly suitable as chain extender.
  • Antioxidants may be added to the dispersion prior to the spray-drying process.
  • the form in which the antioxidants are admixed with the polymer dispersion is that of pellets, of pulverulent solid, or preferably of dispersion. Addition of antioxidants is described by way of example in EP 44 159 and EP 751 175. A particular purpose of adding antioxidants is to avoid spontaneous heating and spontaneous ignition of the spray-dried product during storage and transport.
  • Preferred antioxidants are those selected from the substance class of the sterically hindered al- kylphenols or of their condensates. Possible antioxidants can be found in Plastics Additives Handbook, 5th ed., Kunststoff 2000, 1 -139, Hanser Verlag.
  • Antiblocking agents are moreover added to the dispersion during the spray-drying process.
  • the amounts added of the antiblocking agent are from 0.1 to 15% by weight, preferably from 3 to 8% by weight.
  • hydrophobicized antiblocking agents are used.
  • the antiblocking agents are fine-particle powders, for example composed of calcium carbonate, talc, or silicas.
  • hydrophobicized antiblocking agents are calcium carbonate coated with fatty acids or with fatty alcohols, for example stearic acid or palmitic acid, or silicas chemically modified via surface treatment with reactive silanes, for example with chlorosilanes or with hexamethyldisilazane. It is preferable to use stearic acid-coated calcium carbonate.
  • the primary particle size of the antiblocking agents is preferably smaller than 100 nm.
  • Any of the mills known to the person skilled in the art for fine milling can be used to apply shear to the powder obtained from the spray-drying process and to comminute the same. These are cutting mills, impact mills, such as rotor-impact mills or jet-impact mills, roller mills, such as rolling mills, roll mills, or grinding rolls, mills comprising grinding materials, e.g. bore mills, rod mills, autogenous mills, planetary mills, vibratory mills, centrifugal mills, or stirrer mills, and also mill- ing driers. Comminution machinery is described in Ullmann's Encyclopedia of Industrial Chemistry, 6th ed.
  • Solids contents were generally determined by drying a defined amount of the aqueous polymer dispersion (about 5 g) at 140°C in a drying cabinet to constant weight. In each case two separate measurements were carried out. The value stated in each of the examples is the average value from the two measurement results.
  • the average particle diameter of the copolymer particles was generally determined via dynamic light scattering on an aqueous dispersion of strength of from 0.005 to 0.01 % by weight at 23°C by means of an Autosizer IIC from Malvern Instruments, England. The stated value is the average diameter from cumulative evaluation (cumulant z-average) of the autocorrelation function measured (ISO standard 13321 ).
  • a mixture composed of 213.2 g deionized water and 2.91 g of a 33 % by weight aqueous polymer latex (prepared by free-radical-initiated-polymerization of styrene) with a weight-average particle diameter Dw50 of 30nm was heated to 80 °C under nitrogen in a 2 I polymerization reactor with blade stirrer and heating/cooling equipment.
  • a 7 % by weight solution of sodium peroxodisulfate was added at 80 °C. After 5 min, feed 1 and 2 were started. Feed 1 was added in uniformly over 2 h and feed 2 was added in over the course of 3 h 45 min.
  • Feed 1 was an aqueous emulsion comprised of:
  • Feed 2 consisted of 19.28 g of a 7 % by weight solution of sodium peroxodisulfate.
  • feed 3 was started and added in over the course of 1 h.
  • Feed 3 was an aqueous emulsion comprised of:
  • a mixture composed of 213.2 g deionized water and 5.64 g of a 33 % by weight aqueous polymer latex (prepared by free-radical-initiated-polymerization of styrene) with a weight-average particle diameter Dw50 of 30nm was heated to 80 °C under nitrogen in a 2 I polymerization re- actor with blade stirrer and heating/cooling equipment.
  • 6.55 g of a 7 % by weight solution of sodium peroxodisulfate was added at 80 °C. After 5 min, feed 1 and 2 were started. Feed 1 was added in uniformly over 2 h and feed 2 was added in over the course of 3 h 45 min.
  • Feed 1 was an aqueous emulsion comprised of:
  • Feed 2 consisted of 19.18 g of a 7 % by weight solution of sodium peroxodisulfate.
  • feed 3 was started and added in over the course of 1 h.
  • Feed 3 was an aqueous emulsion comprised of:
  • a mixture composed of 213.2 g deionized water and 5.64 g of a 33 % by weight aqueous polymer latex (prepared by free-radical-initiated-polymerization of styrene) with a weight-average particle diameter Dw50 of 30nm was heated to 80 °C under nitrogen in a 2 I polymerization reactor with blade stirrer and heating/cooling equipment.
  • 6.55 g of a 7 % by weight solution of sodium peroxodisulfate was added at 80 °C. After 5 min, feed 1 and 2 were started. Feed 1 was added in uniformly over 2 h and feed 2 was added in over the course of 3 h 45 min.
  • Feed 1 was an aqueous emulsion comprised of:
  • Feed 2 consisted of 19.18 g of a 7 % by weight solution of sodium peroxodisulfate.
  • feed 3 was started and added in over the course of 1 h.
  • Feed 3 was an aqueous emulsion comprised of:
  • a polymer dispersion according to inventive example 1 was isolated and dried in a drying oven with circulating air at 22 °C until constant weight was obtained. The film was cut into small fragments and ground to a find powder using a rotary grinding with a 2 mm sieve.
  • a dryblend consisting of dry powder dispersion, poly(lactic acid) granulate, and Joncryl ® ADR-4368 was made and used for extrusion samples. Typical concentration of impact modifier polymer powder was 5 weight %, typical concentration for Joncryl ® ADR-4368 was 0.25 weight %. Before extrusion the dryblend was placed in a 50 °C vacuum oven overnight.
  • a dryblend mixture comprised of:
  • the dryblend mixture was then extruded on a twin screw extruder with a processing temperature gradient from 120 °C to 175 °C.
  • the extrudiate was cooled and subsequently pelletized.
  • the dried pelletized material was dried in a 50 °C vacuum oven to less than 0.1 % moisture content and processed by injection molding (nozzle temperature 180 °C) and pressed into a 30 °C mold to produce test specimens.
  • Charpy specimens were molded to conform to Charpy method EN ISO 179-1 e U. Impact resistance was measured using a pendulum impact tester with the nominal value of energy of 4 J provided by the pendulum. 5 samples were tested and an average value for impact strength was obtained.
  • Example 1 Example 1 mple 2 n-butyl acrylate 79.6 % 79.6 % 79.4 % allylmethacrylate 0.4 % 0.4 % 0.6 % isobutylmethacrylate 0% 0% 15.75 % methylmethacrylate 18.75 % 19.50 % 0%

Abstract

The present invention relates to a polymer powder with improved powder properties, and to its use as impact modifier for polylactic acid. The polymer powder comprises (i) 90.0-99.5 weight%, in particular from 95.0-99.0, of polylactic acid (ii) 0.5-10.0 weight%, in particular from 1.0-5.0 of an impact modifier and (iii) from 0,1 to 2% by weight, in particular from 0,1 to 1% by weight based on the total weight of components (i) to (iii), of a copolymer which comprises epoxy groups and which is based on styrene, acrylate, and/or methacrylate.

Description

Process for production of polymer powders
Description The present invention relates to a polymer powder with improved powder properties, and to its use as impact modifier for polylactic acid.
The polymer powder comprises
(i) 90.0-99.5 weight% , in particular from 95.0-99.0, of polylactic acid
(ii) 0.5-10.0 weight%, in particular from 1.0-5.0 of an impact modifier and
(iii) from 0,1 to 2% by weight, in particular from 0,1 to 1 % by weight based on the total weight of components (i) to (iii), of a copolymer which comprises epoxy groups and which is based on styrene, acrylate, and/or methacrylate. Poly(lactic acid) polymers are becoming of increasing interest because of their preparation from renewable resource materials and their ability to biodegrading under certain composting conditions to regenerate carbon dioxide. Such materials are specifically beneficial in packaging applications; however, PLA is a brittle polymer and in many applications the PLA requires an additive to improve the mechanical properties. Such modification additives, for example impact modifiers, act to increase the fracture resistance of the plastic and in turn make the material more pliable and less brittle.
Common impact modifiers include core/shell polymer particles to improve these materials properties, where a soft rubber core absorbs energy from an impact to prevent cracking and material failure, while the exterior shell acts to compatibilize the polymer particles with the PLA matrix.
The common impact modifiers require relatively high additive loading of 3-5% to achieve moderate improvement of impact strength. The problem herein lies twofold: first is the restrictions for classification of PLA biodegradability limit the amount of "non-degradable" and secondly the higher loading levels required to achieve good impact strength significantly reduce the transparency of the PLA.
Two separate fields of modifiers for PLA are described in the prior art. Impact modifiers and rheology modifiers. As previously discussed impact modifiers are rubber particles and can be core /shell morphology with efforts to match the shell refractive index with PLA
(WO2005/085352, WO2008/051443, WO2008/063988, EP2011/066348) in order to achieve low haze.
Additionally functional groups on the surface of the impact modifier particle have been de- scribed which serve to react with the carboxylic acid end groups in PLA in order to improve the particle interface - PLA matrix chemical incorporation (WO2008/036335).
Rheology modifiers are described as typically medium molecular weight uncrosslinked polymers which have specific chemical groups to increase the molecular weight and branching of PLA in the melt. The use of glycidyl methacrlate is describe as a functional monomer, in conjunction with other non functional monomers such as styrene, methylmethacrylate etc., to make a polymer with a MW in the range of 1000 -6000 g/mol. The synthesis is seen in patent US6552144. The use of these polymers as rheology modifiers does not show any improvement on the impact resistance of the PLA material (WO2006002372A2, US 2007/0179218A1 ).
WO2008063988 and EP1785453 disclose a crosslinked impact modifier particle with an additional copolymer in a PLA matrix. However, the impact modifier and copolymer descriptions do not define any acrylic acid or epoxide (glycidyl) functional groups. Object of the present invention was to develop a high performance product which could be used at much lower loading levels to achieve high impact strength and sample transparency.
The invention achieves the object via a Polymer powder comprising
(i) 90.0-99.5 weight% , in particular from 95.0-99.0, of polylactic acid
(ii) 0.5-10.0 weight%, in particular from 1.0-5.0 of an impact modifier and
(iii) from 0,1 to 2% by weight, in particular from 0,1 to 1 % by weight based on the total weight of components (i) to (iii), of a copolymer which comprises epoxy groups and which is based on styrene, acrylate, and/or methacrylate.
The impact modifier is composed of emulsion polymer particles which have a core-shell structure, where the shell is composed of a hard polymer and the core is composed of a soft, cross- linked rubber polymer.
Impact modifiers of this type are usually produced via a multistage free-radical emulsion polymerization process.
The resultant modifier dispersion is converted into powder form via spray drying or via precipitation and subsequent drying of the coagulate, and is mixed with pulverulent polylactic acid (PLA), component (i), and component (iii) and, if appropriate, with conventional additives.
It was an object of the present invention to improve the properties of an impact modifier powder with a high proportion of core by weight and with high impact-resistance efficiency.
The impact modifier, component (ii) is a polymer powder from an aqueous polymer dispersion, which comprises obtaining the aqueous dispersion of the polymer particles II via free-radical- initiated aqueous emulsion polymerization of at least one ethylenically unsaturated monomer C in the presence of dispersely distributed polymer particles I, where a) the polymer of the at least one unsaturated monomer C has a glass transition temperature > 60°C, b) the dispersely distributed polymer particles I are obtained via free-radical-initiated aqueous emulsion polymerization of a monomer mixture I, composed of from 98.0 to 99.9% by weight of at least one ethylenically unsaturated monomer A whose polymer has a glass transition temperature < - 20°C, and
from 0.1 to 2.0% by weight of at least one compound (monomer B) having cross- linking action and having at least two non-conjugated vinyl groups, c) the quantitative ratio of monomer mixture I to monomer C is > 90% by weight: < 10% by weight, where the total amounts of monomer mixture I and monomer C give a total of 100% by weight, d) the powder is produced from the aqueous dispersion of polymer particles II i. via spray drying, optionally in the presence of from 0.1 to 15% by weight of at least one antiblocking agent, based on the total weight of polymer particles II, and subsequent comminution of the crude powder by means of mechanically and/or pneumat- ically induced shear forces, or
ii. via mechanical and/or pneumatic grinder drying optionally in the presence of from 0.1 to 15% by weight of at least one antiblocking agent, based on the total amount of polymer particles II. Preferably the spray drying is performed the presence of from 0.1 to 15% by weight of an antiblocking agent.
The invention also provides PLA compositions comprising the polymer powder produced by the inventive process, and provides moldings produced using the resultant PLA compositions.
The average particle diameter of the polymer particles II is in the range from 100 to 500 nm, preferably from 220 to 320 nm.
The graft copolymers of the inventive chemical constitution are known per se.
The core of the particles is composed of a crosslinked emulsion polymer (polymer I) with a glass transition temperature < -20°C. The shell is composed of a polymer of the at least one monomer C. The content of the graft shell is from 25 to 0.1 % by weight, preferably from 20 to 10% by weight. It comprises from 90 to 100% by weight of the ethylenically unsaturated monomer C. Examples of the monomer C are Ci-C4-alkyl methacrylates, Ci-Cs-alkyl acrylates, vinyl chloride, styrene, or acrylonitrile, or mixtures of these. The monomer C used particularly preferably comprises methyl methacrylate. Alongside this, other copolymerizable ethylenically unsaturated monomers may also be added to the monomers C, where the total amounts of monomer C and of the eth- ylenically unsaturated monomer give a total of 100% by weight.
The graft copolymers comprise from 75 to 99.9% by weight, preferably from 80 to 90% by weight, of a soft graft core composed of a crosslinked rubber composed of the monomers A and B (polymer I).
By way of example, the monomers A have been selected from the group of the Ci-Cs-alkyl acry- lates, preferably butyl acrylate, 2-ethylhexyl acrylate, or from mixtures of these. Alongside the- se, other copolymerizable ethylenically unsaturated monomers may also be added to the monomers A. The content of monomer A is from 95 to 100% by weight, where the total amounts of monomer A and of the ethylenically unsaturated monomer give a total of 100% by weight.
The monomers B act as crosslinking agents and their amounts used are from 0.1 to 2.0% by weight. The monomers B are compounds having crosslinking action and having at least two non-conjugated vinyl groups, examples being allyl methacrylate, butanediol methacrylate, or dihydrodicyclopentadienyl acrylate.
The ratio by weight of the polymer I to monomer C is more than 90% by weight to less than 10% by weight, preferably more than 93% by weight to less than 7% by weight, particularly preferably more than or equal to 97% by weight to less than or equal to 3% by weight, where the total amounts give a total of 100% by weight. It has been found that impact-resistance efficiency passes through an optimum in the inventive range. The graft polymers are usually prepared via emulsion polymerization in two stages, first polymerizing the monomers A + B to give the crosslinked polyacrylate rubber, and then, in its presence, polymerizing the monomers C. The initiators used may comprise water-soluble thermally decomposing initiators or redox systems. Examples of suitable thermally decomposing initiators are sodium peroxodisulfate, potassium peroxodisulfate, or ammonium peroxodisulfate. Exam- pies of redox systems which may be used are hydroperoxides in combination with reducing agents. The emulsion polymerization process may use conventional emulsifiers, such as: alkyl, aryl, alkanyl, Cio-Ci3-alkyl derivatives of benzenesulfonic acid, or the corresponding sulfates, or polyether sulfates, ethoxylated fatty acids, ethoxylated fatty esters, ethoxylated fatty alcohols, ethoxylated fatty amines, ethoxylated fatty amides, ethoxylated fatty-alkylphenols, or organo- phosphoric acids. The emulsion polymerization process takes place at from 10 to 100°C. It can be conducted either as a batch process or else in the form of a feed process, including a procedure involving stages or gradients. Preference is given to the feed procedure in which one portion of the polymerization mixture is used as initial charge and heated to polymerization temperature, and incipient polymerization is carried out and then the rest of the polymerization mixture is added, usually by way of two or more separate feeds, of which one or more comprise the monomers in pure or emulsified form, continuously, in stages, or with imposition of a concentration gradient while maintaining the polymerization process. According to the invention, the graft copolymer can have a bi- or multimodal particle size distribution. It can comprise at least two types of graft rubber which have the same chemical constitution but whose average particle diameters differ by at least 30 nm, preferably by at least 50 nm. The content here of the type of graft rubber with the greatest average particle diameter is at least 15%, preferably at least 20% and in particular at least 25%, based on the entire graft copolymer. Its average particle diameter is preferably in the range from 200 to 500 nm, in particular from 250 to 350 nm. The content of the type of graft rubber with the smallest average particle diameter is at least 5%, preferably at least 8%, and in particular at least 12%, based on the entire graft polymer. Its average particle diameter is preferably in the range from 50 to 250 nm, in particular from 80 to 200 nm. Alongside these, other types of graft rubber Yi, Y2, Y3, etc., may be present, their average particle diameters being between those of the types X and Z of graft rubber.
Multimodal particle size distributions can be obtained via various methods: a targeted particle size distribution can even be produced via synthesis parameters during the emulsion polymerization process. It is also possible to mix monomodal dispersions produced via emulsion polymerization after the synthesis process, or to mix appropriate powders after the dispersions have been dried. Graft rubbers with comparatively narrow, defined particle size distribution are advantageously prepared via the "seed latex" method. The seed latex is the aqueous emulsion of a polymer of the monomers C, preferably a homopolymer of styrene, of methyl methacrylate, of a Ci-Cs-alkyl acrylate, or is a copolymer of these monomers. The average particle diameter of the polymer is preferably from 10 to 50 nm. In this method, the emulsion of the monomers A + B is carried out in the presence of the initial charge of the seed latex, whose solids amount to from 0.01 to 7% by weight, preferably from 0.1 to 5% by weight, of the monomers. The average particle diameter of the graft rubber then depends on the amount of solid used as initial charge: if the amount of solid is high, either the amount of seed latex or its concentration can be used as control factors. The fine-particle graft copolymer obtained during polymerization of the monomers C in the presence of the polyacrylate rubber composed of the monomers A + B is dried, and amounts of from 0,5 to 10% by weight of the pulverulent impact modifier are mixed with PLA powder and with conventional additives, e.g. fillers, stabilizers, and processing aids, and are processed by conventional methods to give high-impact-resistance PLA moldings.
Another possibility is that the polymer particles II of the impact modifier are blended, prior to the spray-drying process, with polymer particles III obtained via free-radical-initiated aqueous emulsion polymerization of at least one ethylenically unsaturated monomer D, these having a glass transition temperature > 50°C (monomers D).
Examples of the monomers D are Ci-Cs-alkyl acrylates, Ci-C4-alkyl methacrylates, styrene, ac- rylonitrile, methacrylic acid, acrylic acid, or compounds having crosslinking action and having at least two non-conjugated vinyl groups, or mixtures of these. Alongside these, other copolymer- izable ethylenically unsaturated monomers may also be added to the monomers D, where the total amounts of monomer D and of the ethylenically unsaturated monomer give a total of 100% by weight.
The average particle diameter of the polymer particles III is from 50 to 300 nm, preferably from 70 to 170 nm. The content is greater than 5% by weight and smaller than 30% by weight, based on the amount of polymer particles II.
Examples of the other copolymerizable ethylenically unsaturated monomers which may also be added to the monomers A, C and D are acrylic acid, methacrylic acid, ethylacrylic acid, allyla- cetic acid, crotonic acid, vinylacetic acid, maleic half-esters, such as monomethyl maleate, their mixtures or their alkali metal and ammonium salts, linear 1 -olefins, branched-chain 1 -olefins or cyclic olefins, e.g. ethene, propene, butene, isobutene, pentene, cyclopentene, hexene, cyclo- hexene, octene, 2,4,4-trimethyl-1 -pentene, if appropriate mixed with 2,4,4-trimethyl-2-pentene, Cs-C-io olefin, 1 -dodecene, C12-C14 olefin, octadecene, 1 -eicosene (C20), C20-C24 olefin; oligoole- fins prepared via metallocene catalysis and having a terminal double bond, e.g. oligopropene, oligohexene, and oligooctadecene; olefins prepared via cationic polymerization and having high content of a-olefin, e.g. polyisobutene.
Vinyl and allyl alkyl ethers having from 1 to 40 carbon atoms in the alkyl radical, where the alkyl radical can also bear other substituents, such as a hydroxy group, an amino group, or a dialkyl- amino group, or may bear one or more alkoxylate groups, e.g. methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, isobutyl vinyl ether, 2-ethylhexyl vinyl ether, vinyl cyclohexyl ether, vinyl 4-hydroxybutyl ether, decyl vinyl ether, dodecyl vinyl ether, octadecyl vinyl ether, 2- (diethylamino)ethyl vinyl ether, 2-(di-n-butylamino)ethyl vinyl ether, methyldiglycol vinyl ether, and also the corresponding allyl ethers and their mixtures.
Acrylamides and alkyl-substituted acrylamides, e.g. acrylamide, methacrylamide, N-tert- butylacrylamide, N-methyl(meth)acrylamide. Monomers containing sulfo groups, e.g. allylsulfonic acid, methallylsulfonic acid, styrenesul- fonate, vinylsulfonic acid, allyloxybenzenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, their corresponding alkali metal or ammonium salts, and mixtures of these.
Ci-Ce-alkyl esters or Ci-C4-hydroxyalkyl esters of acrylic acid, methacrylic acid, or maleic acid, or esters of C1-C18 alcohols alkoxylated with from 2 to 50 mol of ethylene oxide, of propylene oxide, of butylene oxide, or of mixtures of these, with acrylic acid, methacrylic acid, or maleic acid, e.g. methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl
(meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, hydroxy- ethyl (meth)acrylate, hydroxypropyl (meth)acrylate, 1 ,4-butanediol monoacrylate, dibutyl male- ate, ethyldiglycol acrylate, methylpolyglycol acrylate (1 1 EO), (meth)acrylic esters of C13/C15 oxo alcohol reacted with 3, 5, 7, 10, or 30 mol of ethylene oxide and, respectively, their mixtures.
Alkylaminoalkyl (meth)acrylates or alkylaminoalkyl(meth)acrylamides or their quaternization products, e.g. 2-(N,N-dimethylamino)ethyl (meth)acrylate, 3-(N,N-dimethylamino)propyl (meth)acrylate, 2-(N,N,N-trimethylammonium)ethyl (meth)acrylate chloride, 2- dimethylaminoethyl (meth)acrylamide, 3-dimethylaminopropyl(meth)acrylamide, 3- trimethylammoniumpropyl(meth)acrylamide chloride. Vinyl and allyl esters of C1-C30 monocarboxylic acids, e.g. vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, vinyl 2-ethylhexanoate, vinyl nonanoate, vinyl decanoate, vinyl pivalate, vinyl palmitate, vinyl stearate, vinyl laurate.
Other monomers which may be mentioned are:
N-Vinylformamide, N-vinyl-N-methylformamide, styrene, a-methylstyrene, 3-methylstyrene, butadiene, N-vinylpyrrolidone, N-vinylimidazole, 1 -vinyl-2-methylimidazole, 1 -vinyl-2- methylimidazoline, N-vinylcaprolactam, acrylonitrile, methacrylonitrile, allyl alcohol, 2- vinylpyridine, 4-vinylpyridine, diallyldimethylammonium chloride, vinylidene chloride, vinyl chlo- ride, acrolein, methacrolein, and vinylcarbazole, and mixtures of these.
Preferably, the graft shell comprises methylmethacrylate and acrylic acid. The amount of acrylic acid comprises 0.1 - 5 weight% of total monomer content. Component i) preferably comprises polylactic acid with the following property profile:
• melt volume rate of from 0.5 to 15 ml/10 minutes, preferably from 1 to 9 ml/10 minutes, particularly preferably from 2 to 8 ml/10 minutes (MVR at 190°C using 2.16 kg to ISO 1 133)
· melting point below 180°C
• glass transition temperature (Tg) above 40°C
• water content smaller than 1000 ppm
• residual monomer content (lactide) smaller than 0.3%
• molecular weight greater than 50 000 daltons.
Examples of preferred polylactic acids are the following from NatureWorks® : Ingeo® 2002 D, 4032 D, 4042 D and 4043 D, 8251 D, 3251 D. Polylactic acids that have proven particularly advantageous for producing the expandable pelletized material of the invention have MVR of from 5 to 8 ml/10 minutes to ISO 1 133 [190°C/2.16 kg].
Polylactic acids which are particularly suitable have the abovementioned MVR range and/or have a low-temperature-crystallization onset temperature in the range from 80°C to 125°C, preferably from 90°C to 1 15°C, and particularly preferably from 95°C to 105°C, measured by means of DSC (differential scanning calorimetry) at a heating rate of 20K/min (measurement range from -60°C to 220°C; Mettler DSC 30 using a TC15/TA controller, Mettler-Toledo AG).
Component iii) is described in more detail below. Epoxides are in particular a copolymer which is based on styrene, acrylate, and/or methacrylate, and which contains epoxy groups. The units bearing epoxy groups are preferably glycidyl (meth)acrylates. Copolymers that have proven advantageous have a proportion of glycidyl methacrylate greater than 20% by weight, particularly preferably greater than 30% by weight, and with particular preference greater than 50% by weight, based on the copolymer. The epoxide equivalent weight (EEW) in these polymers is preferably from 150 to
3000 g/equivalent and with particular preference from 200 to 500 g/equivalent. The average molecular weight (weight average) Mw of the polymers is preferably from 2000 to 25 000, in particular from 3000 to 8000. The average molecular weight (number average) Mn of the polymers is preferably from 400 to 6000, in particular from 1000 to 4000. Polydispersity (Q) is generally from 1 .5 to 5. Copolymers of the abovementioned type containing epoxy groups are marketed by way of example by BASF Resins B.V. as Joncryl® ADR. Joncryl® ADR 4368 is particularly suitable as chain extender.
By the use of crosslinked impact modifier particles with a carboxylic acid shell layer, combined with the epoxy functional copolymer (iii), which are co-extruded in the PLA matrix high impact strength performance is achieved.
Antioxidants may be added to the dispersion prior to the spray-drying process. The form in which the antioxidants are admixed with the polymer dispersion is that of pellets, of pulverulent solid, or preferably of dispersion. Addition of antioxidants is described by way of example in EP 44 159 and EP 751 175. A particular purpose of adding antioxidants is to avoid spontaneous heating and spontaneous ignition of the spray-dried product during storage and transport. Preferred antioxidants are those selected from the substance class of the sterically hindered al- kylphenols or of their condensates. Possible antioxidants can be found in Plastics Additives Handbook, 5th ed., Munich 2000, 1 -139, Hanser Verlag. Antiblocking agents are moreover added to the dispersion during the spray-drying process. The amounts added of the antiblocking agent are from 0.1 to 15% by weight, preferably from 3 to 8% by weight. In one preferred embodiment, hydrophobicized antiblocking agents are used. The antiblocking agents are fine-particle powders, for example composed of calcium carbonate, talc, or silicas. Examples of hydrophobicized antiblocking agents are calcium carbonate coated with fatty acids or with fatty alcohols, for example stearic acid or palmitic acid, or silicas chemically modified via surface treatment with reactive silanes, for example with chlorosilanes or with hexamethyldisilazane. It is preferable to use stearic acid-coated calcium carbonate. The primary particle size of the antiblocking agents is preferably smaller than 100 nm. Any of the mills known to the person skilled in the art for fine milling can be used to apply shear to the powder obtained from the spray-drying process and to comminute the same. These are cutting mills, impact mills, such as rotor-impact mills or jet-impact mills, roller mills, such as rolling mills, roll mills, or grinding rolls, mills comprising grinding materials, e.g. bore mills, rod mills, autogenous mills, planetary mills, vibratory mills, centrifugal mills, or stirrer mills, and also mill- ing driers. Comminution machinery is described in Ullmann's Encyclopedia of Industrial Chemistry, 6th ed. Vol. 1 1 , p. 70 and Vol. 33, pp. 41 -81 . It is preferable to use mills which have sieve classification, and particularly preferred equipment is fine granulators with sieves and fine gran- ulators with rotors (grater-shredders).
Examples
Solids contents were generally determined by drying a defined amount of the aqueous polymer dispersion (about 5 g) at 140°C in a drying cabinet to constant weight. In each case two separate measurements were carried out. The value stated in each of the examples is the average value from the two measurement results.
The average particle diameter of the copolymer particles was generally determined via dynamic light scattering on an aqueous dispersion of strength of from 0.005 to 0.01 % by weight at 23°C by means of an Autosizer IIC from Malvern Instruments, England. The stated value is the average diameter from cumulative evaluation (cumulant z-average) of the autocorrelation function measured (ISO standard 13321 ). Inventive example 1
A mixture composed of 213.2 g deionized water and 2.91 g of a 33 % by weight aqueous polymer latex (prepared by free-radical-initiated-polymerization of styrene) with a weight-average particle diameter Dw50 of 30nm was heated to 80 °C under nitrogen in a 2 I polymerization reactor with blade stirrer and heating/cooling equipment. To this mixture, 6.55 g of a 7 % by weight solution of sodium peroxodisulfate was added at 80 °C. After 5 min, feed 1 and 2 were started. Feed 1 was added in uniformly over 2 h and feed 2 was added in over the course of 3 h 45 min.
Feed 1 was an aqueous emulsion comprised of:
510.4 g of deionized water
2.67 g of Dowfax® 2A1 (45 % by weight solution in water)
32.0 g of a 3% by weight of an aqueous solution of sodium pyrophosphate
477.60 g of n-butyl acrylate
2.40 g of allyl methacrylate Feed 2 consisted of 19.28 g of a 7 % by weight solution of sodium peroxodisulfate.
Once feed 1 had ended, feed 3 was started and added in over the course of 1 h.
Feed 3 was an aqueous emulsion comprised of:
125.59 g of deionized water
1 .33 g of Dowfax® 2A1 (45 % by weight solution in water)
1 12.50 g of methyl methacrylate
6.00 g of acrylic acid
1 .50 g of 2-ethylhexyl thiogycolate Comparative example 1
A mixture composed of 213.2 g deionized water and 5.64 g of a 33 % by weight aqueous polymer latex (prepared by free-radical-initiated-polymerization of styrene) with a weight-average particle diameter Dw50 of 30nm was heated to 80 °C under nitrogen in a 2 I polymerization re- actor with blade stirrer and heating/cooling equipment. To this mixture, 6.55 g of a 7 % by weight solution of sodium peroxodisulfate was added at 80 °C. After 5 min, feed 1 and 2 were started. Feed 1 was added in uniformly over 2 h and feed 2 was added in over the course of 3 h 45 min.
Feed 1 was an aqueous emulsion comprised of:
510 g of deionized water
2.67 g of Dowfax® 2A1 (45 % by weight solution in water)
32.0 g of a 3% by weight of an aqueous solution of sodium pyrophosphate
477.60 g of n-butyl acrylate
2.40 g of allyl methacrylate
Feed 2 consisted of 19.18 g of a 7 % by weight solution of sodium peroxodisulfate.
Once feed 1 had ended, feed 3 was started and added in over the course of 1 h.
Feed 3 was an aqueous emulsion comprised of:
125.59 g of deionized water
1 .33 g of Dowfax® 2A1 (45 % by weight solution in water)
1 15.50 g of methyl methacrylate
0,60 g acrylic acid
1 .50 g 2-ethylhexyl thiogycolate Inventive example 2
A mixture composed of 213.2 g deionized water and 5.64 g of a 33 % by weight aqueous polymer latex (prepared by free-radical-initiated-polymerization of styrene) with a weight-average particle diameter Dw50 of 30nm was heated to 80 °C under nitrogen in a 2 I polymerization reactor with blade stirrer and heating/cooling equipment. To this mixture, 6.55 g of a 7 % by weight solution of sodium peroxodisulfate was added at 80 °C. After 5 min, feed 1 and 2 were started. Feed 1 was added in uniformly over 2 h and feed 2 was added in over the course of 3 h 45 min.
Feed 1 was an aqueous emulsion comprised of:
510 g of deionized water
2.67 g of Dowfax® 2A1 (45 % by weight solution in water)
32.0 g of a 3% by weight of an aqueous solution of sodium pyrophosphate
476.60 g of n-butyl acrylate
3.60 g of allyl methacrylate Feed 2 consisted of 19.18 g of a 7 % by weight solution of sodium peroxodisulfate.
Once feed 1 had ended, feed 3 was started and added in over the course of 1 h.
Feed 3 was an aqueous emulsion comprised of:
125.58 g of deionized water
1 .33 g of Dowfax® 2A1 (45 % by weight solution in water) 94.50 g of isobutyl methacrylate
18.00 g of methyl acrylate
6.00 g of acrylic acid
1 .50 g of 2-ethylhexyl thiogycolate
Determination of impact resistance of PLA
Isolation of polymer:
A polymer dispersion according to inventive example 1 was isolated and dried in a drying oven with circulating air at 22 °C until constant weight was obtained. The film was cut into small fragments and ground to a find powder using a rotary grinding with a 2 mm sieve. A dryblend consisting of dry powder dispersion, poly(lactic acid) granulate, and Joncryl® ADR-4368 was made and used for extrusion samples. Typical concentration of impact modifier polymer powder was 5 weight %, typical concentration for Joncryl® ADR-4368 was 0.25 weight %. Before extrusion the dryblend was placed in a 50 °C vacuum oven overnight.
Extrusion:
A dryblend mixture comprised of:
100 parts PLA granulate (Natureworks PLA grade 4042D
0.025 parts Si02
0.25 parts Joncryl® ADR 4368
Together with 5 parts (based on polymer solids content) of the dried and pulverized dispersion of the inventive example 1 and comparative example 1 , and together with 3 parts (based on polymer solids content) for inventive example 2.
The dryblend mixture was then extruded on a twin screw extruder with a processing temperature gradient from 120 °C to 175 °C. The extrudiate was cooled and subsequently pelletized. The dried pelletized material was dried in a 50 °C vacuum oven to less than 0.1 % moisture content and processed by injection molding (nozzle temperature 180 °C) and pressed into a 30 °C mold to produce test specimens. Charpy specimens were molded to conform to Charpy method EN ISO 179-1 e U. Impact resistance was measured using a pendulum impact tester with the nominal value of energy of 4 J provided by the pendulum. 5 samples were tested and an average value for impact strength was obtained.
Table 1 : Monomer compositions for representative test samples
Inventive ExaComparitive Inventive Exa¬
Monomers
mple 1 Example 1 mple 2 n-butyl acrylate 79.6 % 79.6 % 79.4 % allylmethacrylate 0.4 % 0.4 % 0.6 % isobutylmethacrylate 0% 0% 15.75 % methylmethacrylate 18.75 % 19.50 % 0%
methylacrylate 0% 0% 3.00 % acrylic acid 1 .00 % 0.25 % 1 .00 %
2-ethylhexylthioglycolate 0.25 % 0.25 % 0.25 %
Totals 100% 100% 100%
Table 2: Impact strength results
% Acrylic Charpy
% Impact MoJoncryl®
Acid in Impact
Sample difier in PLA Content %
Shell PolyStrength Matrix by weight
mer Layer (kJ/m2)
Unmodified Poly(lactic
— 0% — 18.89 acid)
Inventive Example 1 5% 0% 1 ,00% 23.51
Inventive Example 1 5% 0.25 % 1 ,00% 34.69
Comparative Example 1 5% 0.25 % 0,25% 22.47
Inventive Example 2 3% 0.15 % 1 ,00% 23.96
Inventive Example 2 3% 0.35 % 1 ,00% 25.21
Inventive Example 2 3% 0.50 % 1 ,00% 30.28

Claims

Patent claims
Polymer powder comprising
(i) 90.0-99.5 weight% , in particular from 95.0-99.0, of polylactic acid
(ii) 0.5-10.0 weight%, in particular from 1.0-5.0 of an impact modifier and
(iii) from 0,1 to 2% by weight, in particular from 0,1 to 1 % by weight based on the total weight of components (i) to (iii), of a copolymer which comprises epoxy groups and which is based on styrene, acrylate, and/or methacrylate.
Polymer powder according to claim 1 , wherein component (ii) is a polymer powder from an aqueous polymer dispersion, which comprises obtaining the aqueous dispersion of the polymer particles II via free-radical-initiated aqueous emulsion polymerization of at least one ethylenically unsaturated monomer C in the presence of dispersely distributed polymer particles I, where
(a) the polymer of the at least one unsaturated monomer C has a glass transition temperature > 60°C,
(b) the dispersely distributed polymer particles I are obtained via free-radical-initiated aqueous emulsion polymerization of a monomer mixture I, composed of from 98.0 to 99.9% by weight of at least one ethylenically unsaturated monomer A whose polymer has a glass transition temperature < - 20°C, and
from 0.1 to 2.0% by weight of at least one compound (monomer B) having cross- linking action and having at least two non-conjugated vinyl groups, the quantitative ratio of monomer mixture I to monomer C is > 90% by weight:
< 10% by weight, where the total amounts of monomer mixture I and monomer C give a total of 100% by weight, the powder is produced from the aqueous dispersion of polymer particles II i. via spray drying, optionally in the presence of from 0.1 to 15% by weight of at least one antiblocking agent, based on the total weight of polymer particles II, and subsequent comminution of the crude powder by means of mechanically and/or pneumatically induced shear forces, or
ii. via mechanical and/or pneumatic grinder drying optionally in the presence of from 0.1 to 15% by weight of at least one antiblocking agent, based on the total amount of polymer particles II. Polymer powder according to claim 2, where the spray drying i. Is performed in the presence of from 0.1 to 15% by weight of an antiblocking agent.
Polymer powder according to any of claims 1 to 3, wherein the the content of the graft shell of component (ii) is from 25 to 0.1 % by weight.
Polymer powder according to any of claims 1 to 3, wherein the the content of the graft shell of component (ii) is from 20 to 10% by weight.
Polymer powder according to any of claims 1 to 3, wherein the content of the graft copolymers of component (ii) comprise from 75 to 99.9% by weight, of a soft graft core composed of a crosslinked rubber composed of the monomers A and B (polymer I). Polymer powder according to any of claims 1 to 3, wherein the content of the graft copolymers of component (ii) comprise from 80 to 90% by weight, of a soft graft core composed of a crosslinked rubber composed of the monomers A and B (polymer I).
Polymer powder according to any of claims 1 to 7, wherein component i) preferably comprises polylactic acid with the following property profile:
• melt volume rate of from 0.5 to 15 ml/10 minutes, preferably from 1 to 9 ml/10 minutes, particularly preferably from 2 to 8 ml/10 minutes (MVR at 190°C using 2.16 kg to ISO 1 133)
melting point below 180°C
glass transition temperature (Tg) above 40°C
• water content smaller than 1000 ppm
residual monomer content (lactide) smaller than 0.3%
molecular weight greater than 50 000 daltons.
Polymer powder according to any of claims 1 to 8, wherein component iii) have a proportion of glycidyl methacrylate greater than 20% by weight, based on the copolymer and wherein the epoxide equivalent weight (EEW) is from 150 to 3000 g/equivalent, the average molecular weight (weight average) Mw of the polymers is from 2000 to 25 000, and the average molecular weight (number average) Mn of the polymers is from 400 to 6000, andpolydispersity (Q) is from 1.5 to 5.
A formed article comprising the polymer powder according to any of claims 1 to 9.
The use of a polymer powder according to any of claims 1 to 9 as an impact modifier for PLA.
PCT/EP2014/059224 2013-05-14 2014-05-06 Process for production of polymer powders WO2014184057A1 (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3781622B1 (en) * 2018-04-20 2022-10-12 Basf Se Adhesive compositions with a gelcontent from crosslinking of keto- or aldehyde groups

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