JP2016529375A - Biodegradable polymer composition with improved impact resistance - Google Patents

Abstract

The present invention relates to a biodegradable polymer composition with improved impact resistance, in which a large particle size impact modifier is dispersed in a continuous phase of the biodegradable polymer. This impact modifier has a core-shell type structure and the average particle size may exceed 250 nm. The composition with improved impact resistance has good impact resistance and low haze. The biodegradable polymer is preferably polylactic acid or polyhydroxybutyric acid. The composition comprises 30-99.9 weight percent degradable polymer and 0.1-15 weight percent of one or more impact modifiers.

Description

  The present invention relates to a biodegradable polymer composition having improved impact resistance, in which an impact modifier having a large particle size is dispersed in a continuous phase of the biodegradable polymer. This impact modifier has a core-shell structure and has an average particle size greater than 250 nm. The composition with improved impact resistance has good impact resistance and low haze.

  With increasing global interest in plastic waste, which has never been reduced, biodegradable polymers for daily use have gained much attention. One of the most attractive candidates is a biodegradable polymer based on polylactic acid (PLA) that can be easily produced from reclaimed agricultural resources such as corn. Recent developments in the economical production of this polymer from agricultural resources have accelerated the entry of this polymer into the biodegradable plastics daily necessities market.

  The use of linear acrylic copolymers as processing aids in blends with biopolymers such as polylactic acid has been disclosed (US Patent Publication No. 2007/0179218). The linear acrylic copolymer disclosed here does not give sufficient impact resistance. It is possible that additives such as impact modifiers can be used in the polylactic acid composition.

  One problem with many biodegradable polymers, such as polylactic acid, is that the polymer alone has a very brittle nature. This property makes the impact resistance of the finished article very low, which is much lower than required for proper product performance. It is known that impact modifiers such as methyl methacrylate-butadiene-styrene (MBS) and acrylic core-shell or block copolymers improve the impact properties of blends of PVC and polycarbonate.

  PCT / US Patent Application No. 07 / 84,502 describes block copolymers and core-shell polymers for use in biodegradable polymers. This application does not mention anything about the granularity.

  WO 2008/051443 pamphlet describes a transparent polylactic acid resin having improved impact resistance. This resin has been improved with a core-shell impact modifier having a bimodal distribution and the overall number average particle size of the particles and aggregates is less than 210 nanometers.

  Surprisingly, it is possible to use core-shell impact modifiers with a number average particle size greater than 250 in biodegradable plastics, still achieving very good impact resistance and low haze. It was found that

The present invention
a) 30-99.9 weight percent of one or more biodegradable polymers;
b) 0 to 69.9 weight percent of one or more biopolymers; and c) 0.1 to 15 weight percent of one or more core-shell impact modifiers, the impact resistance improvement. The present invention relates to a biodegradable polymer composition in which the number average particle size of the agent exceeds 250 nm.

  The biodegradable polymer composition may be transparent or translucent and preferably has a haze of less than 15.

  The biodegradable polymer of the present invention may be a single type of biodegradable polymer or a mixture of biodegradable polymers. Some examples of biodegradable polymers useful in the present invention include, but are not limited to, polylactic acid and polyhydroxybutyric acid. The biodegradable composition includes 30 to 99.9 weight percent of one or more biodegradable polymers.

  Preferred polylactic acid and polyhydroxybutyric acid may be normal or low molecular weight.

  In addition to biodegradable polymers, other biopolymers such as, but not limited to, starch, cellulose, polysaccharides may also be present. Additional biopolymers such as, but not limited to, polycaprolactam, polyamide 11, and aliphatic or aromatic polyesters may also be present. This other biopolymer may be present in the composition from 0 to 69.9 weight percent.

  One or more impact modifiers may be used from 0.1 to 15 weight percent of the composition.

  This impact modifier is a core / shell impact modifier. Core-shell (multi-layer) impact modifiers include hard (rubber or elastomer) cores and hard shells, hard cores covered with a soft elastomer layer, and other core-shell forms of hard shells well known in the art. Can have. The rubber layer is composed of a polymer having a low glass transition temperature (Tg) and includes, but is not limited to, butyl acrylate (BA), ethyl hexyl acrylate (EHA), butadiene (BD), butyl acrylate / styrene, and There are many other combinations. Preferably, the core is an all-acrylic homopolymer or copolymer. It has been found that the use of an acrylic core results in a lower haze of the biodegradable polymer composition than the diene core polymer.

  The preferred glass transition temperature (Tg) of the elastomer layer should be less than 25 ° C. The elastomer or rubber layer is usually crosslinked with a polyfunctional monomer to enhance energy absorption. Suitable cross-linking monomers for use as cross-linking agents for core / shell impact modifiers are well known to those skilled in the art and are usually of approximately the same degree of reactivity that can be copolymerized with existing monounsaturated monomers. Is a monomer having an ethylenic polyfunctional group. Examples include, but are not limited to, divinylbenzene, di- and trimethacrylate and acrylate glycols, triol triacrylate, methacrylate, and allyl methacrylate. Graft monomers may also be used to improve impact modifier interlayer grafting and matrix / modifier particle grafting. The graft monomer may be any multifunctional crosslinking monomer.

  In the case of multilayer impact modifiers having a soft core, the core is in the range of 30-95 weight percent of the impact modifier and the outer shell is in the range of 15-70 weight percent. The crosslinking agent of the elastomer layer is in the range of 0 to 5.0%. The synthesis of core-shell impact modifiers is well known in the art, for example, US Pat. No. 3,793,402, US Pat. No. 3,808,180, US Pat. , 971,835, and U.S. Pat. No. 3,671,610, which are hereby incorporated by reference. The refractive index of the modifier particles and / or the matrix polymer can be matched to each other using copolymerizable monomers having different refractive indices. Preferred monomers include, but are not limited to, styrene, alphamethylstyrene, and vinylidene fluoride monomers having an ethylenically unsaturated group.

  Other impact modifiers other than the core / shell type can also be used in the present invention if very high transparency and clarity may not be required. For example, butadiene rubber may be added to the acrylic matrix in order to achieve a high ballistic resistance property.

  In a preferred embodiment, the core-shell polymer is 80-90% acrylic core and the shell is 75-100% by weight methyl methacrylate, 0-20 weight percent butyl acrylate, and 0-25 weight ethyl acrylate. Consists of percent. The acrylic core is preferably selected from butyl acrylate homopolymer and ethylhexyl acrylate homopolymer or butyl acrylate and ethylhexyl acrylate copolymer (any monomer ratio).

  In one embodiment, the acrylic copolymer impact modifier may be 1,3-diene (also a copolymer with a vinyl aromatic compound) or an alkyl acrylate having an alkyl group with 4 or more carbons. An acrylate-based copolymer having a core-shell type polymer having a rubbery core, the shell is grafted onto the core, and a vinyl aromatic compound (for example, styrene), alkyl methacrylate (with 1 alkyl group) ˜4 carbons), alkyl acrylate (alkyl group has 1 to 4 carbons), acrylonitrile, and other monomers.

  A preferred acrylic resin-type core / shell polymer has a core of 0 to 100% by weight of butyl acrylate, 0 to 100% of 2-ethylhexyl acrylate, and 0 to 35% of butadiene. And a shell composed of 75 to 100 weight percent methyl methacrylate, 0 to 20 weight percent butyl acrylate, and 0 to 25 weight percent ethyl acrylate.

  The core-shell impact modifier of the present invention is a particle having a number average particle size of more than 250 nm, preferably 250 to 400 nm, and most preferably 280 to 330 nm. The core-shell impact modifier may be blended in two or more sizes or chemical compositions, but the overall number of impact modifier particles exceeds 250 nm. The particle size can be measured under normal operating conditions using a NiComp 380 dynamic light scattering particle size distribution analyzer. The mean particle size of a Gaussian distribution weighted by intensity can be shown.

  Preferably, the impact modifier of the biodegradable polymer composition of the present invention comprises, consists essentially of impact modifier particles having a number average particle size as described herein, or These are pellets or powders composed solely of these.

  The impact modifier pellets of the present invention comprise a shaped small mass that can have any shape, including but not limited to circular, spherical, cylindrical, etc. It is not something.

  The impact modifier pellets may be formed using melt processing methods such as extrusion or other techniques. When melt processing is used to form the pellets, the pellets can be obtained by extrusion. For example, a melt processing method such as extrusion using a single or twin screw extruder is performed, or co-kneading extrusion using a reciprocating screw such as a Buss kneader and a Banbury mixer. By carrying out, an impact resistance improver in the form of pellets can be obtained. The final pellet can be formed using a strand method or other pelletizing means.

  The processing temperature can be controlled by controlling the temperature of each barrel zone (end, center and start) of the extruder, the temperature range being about 150-460 ° F, preferably about 200. It can be from about F to 450F, more preferably from about 300 to 400F.

  Preferably, the extruder can be operated at a rotational speed of about 140-300 RPM, preferably about 150-250 RPM and a feed rate / extrusion rate of about 10 Kg / hour.

  Preferably, the pelletization process is such that the final pellet has the desired size, shape, composition, and molecular weight while minimizing shear heating (low shear force) and minimizing the temperature of the impact modifier. The pellets are formed so as to have. For example, the size and / or shape of the impact modifier pellet is substantially the same as the size and / or shape of the biodegradable polymer pellet that can be mixed with the impact modifier pellet as described herein. Can be matched.

  Alternatively, the pellets can be cold pressed.

  When the impact modifiers are in powder form, problems may arise when they are used in some applications such as injection molding where powder agglomeration and / or undesired plug formation may occur. . Feeding the powder to the equipment is difficult and can increase costs, but these problems are avoided by making the impact modifier into pellets.

  Another advantage of pelletizing the impact modifier is that it allows easy and simple processing without causing component separation. For example, can impact resistance improver pelletization allow bag mixing or tumbler mixing with other pelletized products to reduce separation of individual components? Or it may not even separate at all, and the components will not settle. In addition, pelletization can substantially reduce or even completely eliminate the dusting and potential problems associated with dusting that can occur with the use of powders.

  Furthermore, by using pellets of impact modifiers, the production of the biodegradable polymer composition of the present invention can be made at a lower production cost and with higher efficiency (due to less processing equipment required). ), The final product can be made more uniform and can be handled with higher handling.

  The impact modifier of the present invention can be a powder comprising, consisting essentially of, or consisting solely of impact modifier particles having a number average particle size as described herein. . The impact modifier powder can be formed by spray drying or agglomeration.

  The biodegradable polymer composition of the present invention comprises 30 to 99.9 weight percent biodegradable polymer, 0 to 69.9 weight percent other biopolymer, and 0.1 to 15 acrylic copolymer. May include weight percent. The components may be mixed before processing or may be combined during one or more processing steps such as melt kneading operations. This may be performed by, for example, a single screw extruder, a twin screw extruder, a Buss kneader, a two-roll mill, or a stirring blade kneading. Any mixing operation that uniformly disperses the acrylic-methacrylic copolymer in the biodegradable polymer is allowed. The formation of the blend is not limited to one-step formation. It is also envisioned that after forming a masterbatch containing 15-99% acrylic-methacrylic copolymer in 1-85% carrier polymer, the final blend is obtained by adding the biodegradable polymer. This carrier polymer may be, but is not limited to, polylactic acid, acrylic-methacrylic copolymer, and methacrylic homopolymer.

  In addition to a total of up to 100 percent biodegradable polymer, biopolymer, and impact modifier, the composition of the present invention may further include various additives, but is not limited thereto. These include, but are not limited to, heat stabilizers, internal and external lubricants, other impact modifiers, processing aids, melt strength addenda, fillers, and pigments.

  It has been found that the impact resistance properties of the composition of the present invention are significantly improved over the case of polylactic acid alone. This core-shell polymer impact modifier has excellent impact resistance while still imparting low haze.

  Biodegradable polymer compositions with improved impact resistance may vary from approximately transparent or translucent to opaque depending on the composition and degree of improvement in impact resistance. In one embodiment, the biodegradable polymer with improved impact resistance has a haze level measured by ASTM 1003-00 of less than 15 percent, preferably less than 12 percent.

  The compositions of the present invention can be processed using any known method, including but not limited to injection molding, extrusion molding, calendar molding, blow molding, foaming, and thermoforming. . Useful articles that can be made using the biodegradable composition include, but are not limited to, packaging materials, films, and bottles. Those skilled in the art will be able to infer various other useful articles and methods for forming these articles based on the disclosures and examples herein.

Example 1
A blend of 95 and 93.5% polylactic acid containing 5 and 7.5% by weight of an acrylic-methacrylic copolymer impact modifier was formed by melt extrusion using a twin screw extruder. The processing temperature and melting temperature during extrusion was maintained above the melting point of polylactic acid (> 152 ° C.) to ensure that the melt was homogeneous. The extrudate was formed into sheets (17-22 mils) using a three roll stack and a take-up device. The haze of the sheet was measured using a Colormeter, and the dart drop impact resistance was measured using a Gardner impact tester equipped with a 2 lb impactor having a hemispherical head. The observed data is shown in Table 1 below.

Example 2-Pelletization of impact modifier using an intermeshing co-rotating twin screw extruder Pellet pellets from an acrylic-methacrylic impact modifier using the following equipment Formed: the same with an air-coolable temperature control band heater with two vent ports equipped with an inner meshing screw with an L / D (length / diameter) ratio of 40/1 Directional rotating twin screw. For this twin screw, a commercially available 27 mm twin screw designed to operate at 260 RPM and a feed rate / extrusion rate of 10 kg / hour was used.

  The temperature profile of the barrel when performing the pelletization process is such that 1/3 of the barrel (starting end) is set to about 455 ° C., 1/3 of the barrel central is heated to about 437 ° C., and the termination zone (feed (Including the zone) was controlled to be heated to about 410 ° C. The temperature profile of the barrel can be adjusted depending on the type and type of extruder and the feed rate.

  A water bath and strand pelletizer were placed downstream of the twin screw. The pelletizer cutting speed was adjusted based on the desired length of the pellet.

Claims (13)

a) 30-99.9 weight percent of one or more biodegradable polymers;
a biodegradable polymer composition comprising b) 0-69.9 weight percent of one or more biopolymers, and c) 0.1-15 weight percent of one or more core-shell impact modifiers. A biodegradable polymer, wherein the impact modifier is a pellet comprising particles having a number average particle size greater than 250 nm and the haze of the composition measured by ASTM 1003-00 is less than 15 percent Composition. a) 30-99.9 weight percent of one or more biodegradable polymers;
a biodegradable polymer composition comprising b) 0-69.9 weight percent of one or more biopolymers, and c) 0.1-15 weight percent of one or more core-shell impact modifiers. A biodegradable polymer, wherein the impact modifier is a powder comprising particles having a number average particle size greater than 250 nm and the haze of the composition measured by ASTM 1003-00 is less than 15 percent Composition.   The biodegradable polymer composition according to claim 1, wherein the biodegradable polymer is polylactic acid, polyhydroxybutyric acid, or a mixture thereof.   The biodegradable polymer composition according to claim 1, wherein the impact modifier has a number average particle size of more than 250 nm to 400 nm.   The biodegradable polymer composition according to claim 1, wherein the impact modifier has a number average particle size of 280 to 330 nm.   The biodegradable polymer composition according to claim 3, wherein the polylactic acid has a weight average molecular weight of 10,000 to 3,000,000 g / mol.   The biodegradable polymer composition according to claim 1, wherein the core-shell impact modifier is a blend of two or more copolymers.   The biodegradable polymer composition of claim 1, wherein the biopolymer comprises one or more polymers selected from the group consisting of starch, cellulose, polysaccharides, aliphatic or aromatic polyesters, and polycaprolactone.   The biodegradable polymer composition according to claim 1, wherein the core-shell type impact resistance improver is a pure acrylic core / shell type polymer.   The biodegradable polymer composition according to claim 1, wherein the core of the core-shell type impact modifier includes one or more monomer units selected from the group consisting of butyl acrylate and ethylhexyl acrylate.   The biodegradable polymer composition according to claim 1, wherein the core of the core-shell type impact modifier is polybutyl acrylate.   The biodegradable polymer composition of claim 1, wherein the biopolymer comprises one or more of starch, cellulose, and polycaprolactone.   The core of the core / shell impact modifier comprises 75-100% by weight methyl methacrylate, 0-20% by weight butyl acrylate, and 0-25% by weight ethyl acrylate, The biodegradable polymer composition according to claim 1, wherein the core of the impact modifier comprises one or more monomer units selected from the group consisting of butyl acrylate and ethyl hexyl acrylate.