Patent Application
20130004759
The present invention relates to an item produced via injection molding and comprising:
The invention further relates to processes for producing the abovementioned items.
Filled biodegradable polymer mixtures which comprise a flexible polymer such as an aliphatic-aromatic polyester (PBAT), and a rigid polymer, such as polylactic acid (PLA), are known from U.S. Pat. No. 6,573,340 and WO 2005/063883. However, injection-molded items produced therefrom are not always entirely satisfactory in terms of heat distortion resistance, stress-strain performance (modulus of elasticity), and biodegradability.
DE 198 57 067 discloses monofilaments which comprise polybutylene succinate (PBS), polylactic acid, and talc. Said polymer mixtures have insufficient biodegradability for numerous injection-molding applications.
An objective of the present invention was therefore to provide injection-molded items, or items produced via thermoforming, which do not have the abovementioned disadvantages. A particular objective was to provide a sufficiently rigid plastic with heat resistance sufficient for applications in the hot food and drinks sector. Biodegradability rate should moreover be sufficiently high for certification to ISO 17088 and/or EN 13432 and/or ASTM D6400 for an item with wall thicknesses of from 50 μm to 2 mm.
Surprisingly, an item produced via injection molding and comprising:
Components i to iii are in particular responsible for the interesting property profile of the item. Component i guarantees high heat resistance together with good biodegradability, component ii provides the necessary rigidity and moreover improves biodegradability through a supplementary degradation mechanism. The mineral filler iii) improves mechanical properties, such as modulus of elasticity, and heat distortion resistance, and in particular in the case of chalk, promotes biodegradability.
A more detailed description of the invention appears below.
The aliphatic polyesters i suitable for the invention have been described in more detail in WO 2010/034711, which is expressly incorporated herein by way of reference.
Polyesters i are generally composed of the following:
The copolyesters described are preferably synthesized in a direct polycondensation reaction of the individual components. The dicarboxylic acid derivatives here are reacted together with the diol in the presence of a transesterification catalyst directly to give the high-molecular-weight polycondensate. On the other hand, it is also possible to obtain the polyester via transesterification of polybutylene succinate (PBS) with C8-C20 dicarboxylic acids in the presence of diol. Catalysts used usually comprise zinc catalysts, aluminum catalysts, and in particular titanium catalysts. An advantage of titanium catalysts, such as tetra(isopropyl) orthotitanate and in particular tetraisobutoxy titanate (TBOT) over the tin catalysts, antimony catalysts, cobalt catalysts, and lead catalysts often used in the literature, for example tin dioctanoate, is that any residual amounts of the catalyst or downstream product from the catalyst that remain within the product are less toxic. This is a particularly important factor in biodegradable polyesters because they pass into the environment by way of example in the form of composting bags or mulch films.
A mixture of the dicarboxylic acids is generally first heated in the presence of an excess of diol together with the catalyst to an internal temperature of from 170 to 230° C. within a period of about 60-180 min, and resultant water is removed by distillation. The melt of the resultant prepolyester is then usually condensed at an internal temperature of from 200 to 250° C. within the period of from 3 to 6 hours at reduced pressure while the diol liberated is removed by distillation until the desired viscosity has been achieved with intrinsic viscosity (IV) from 50 to 450 mL/g and preferably from 95 to 200 mL/g.
The copolymers of the invention can also be produced by the processes described in WO 96/15173 and EP-A 488 617. It has proven advantageous to begin by reacting components a to c to give a prepolyester with IV from 50 to 100 mL/g, preferably from 60 to 80 mL/g, and then to react this with chain extenders d, for example with diisocyanates or with epoxy-containing polymethacrylates, in a chain extension reaction to give a polyester with IV from 50 to 450 mL/g, preferably from 95 to 200 mL/g.
Acid component a used comprises from 90 to 99.5 mol %, based on acid components a and b, preferably from 91 to 99 mol %, and with particular preference from 92 to 98 mol %, of succinic acid. Succinic acid is accessible by a petrochemical route, or else preferably from renewable raw materials, for example as described in PCT/EP2008/006714. PCT/EP2008/006714 discloses a biotechnological process for producing succinic acid and 1,4-butanediol starting from various carbohydrates and using microorganisms from the Pasteurellaceae family.
The amount used of acid component b is from 0.5 to 10 mol %, preferably from 1 to 9 mol %, and with particular preference from 2 to 8 mol %, based on acid components a and b.
The expression C8-C20 dicarboxylic acids b in particular means terephthalic acid, suberic acid, azelaic acid, sebacic acid, brassylic acid and/or arachidonic acid. Preference is given to suberic acid, azelaic acid, sebacic acid and/or brassylic acid. The abovementioned acids, inclusive of terephthalic acid, are accessible from renewable raw materials. By way of example, sebacic acid is accessible from castor oil. Polyesters of this type feature excellent biodegradation performance [reference: Polym. Degr. Stab. 2004, 85, 855-863].
The dicarboxylic acids a and b can be used either in the form of free acid or in the form of ester-forming derivatives. Particular ester-forming derivatives that may be mentioned are the di-C1- to C6-alkyl ester, such as dimethyl, diethyl, di-n-propyl, diisopropyl, di-n-butyl, diisobutyl, di-tert-butyl, di-n-pentyl, diisopentyl, or di-n-hexyl ester. Anhydrides of the dicarboxylic acids can also be used.
The dicarboxylic acids or ester-forming derivatives thereof can be used individually or in the form of a mixture here.
The diols 1,3-propanediol and 1,4-butanediol are also accessible from renewable raw materials. It is also possible to use a mixture of the two diols. 1,4-Butanediol is preferred as diol because of the higher melting points and the better crystallization of the resultant copolymer.
At the start of the polymerization reaction, the ratio of the diol (component c) to the acids (components a and b) is generally adjusted so that the ratio of diol to diacids is from 1.0 to 2.5:1 and preferably from 1.3 to 2.2:1. Excess amounts of diol are drawn off during the polymerization reaction so that the ratio obtained at the end of the polymerization reaction is approximately equimolar. The expression approximately equimolar means a diol/diacids ratio of from 0.90 to 1.10.
Use is generally made of from 0 to 1% by weight, preferably from 0.01 to 0.9% by weight, and with particular preference from 0.1 to 0.8% by weight, based on the total weight of components a to b, of a crosslinking agent d and/or chain extender d′ selected from the group consisting of: a polyfunctional isocyanate, isocyanurate, oxazoline, carboxylic anhydride, such as maleic anhydride, epoxide (in particular an epoxy-containing poly(meth)acrylate), an at least trihydric alcohol, or an at least one tribasic carboxylic acid. Chain extenders d′ used can comprise polyfunctional, and in particular difunctional, isocyanates, isocyanurates, oxazolines, or epoxides.
Chain extenders and alcohols or carboxylic acid derivatives having at least three functional groups can also be considered to be crosslinking agents. Particularly preferred compounds have from three to six functional groups. Examples that may be mentioned are: tartaric acid, citric acid, malic acid, trimesic acid, trimellitic acid, trimellitic anhydride, pyromellitic acid, and pyromellitic dianhydride; trimethylolpropane, trimethylolethane; pentaerythritol, polyethertriols, and glycerol. Preference is given to polyols, such as trimethylolpropane, pentaerythritol, and in particular glycerol. By using components d it is possible to construct pseudoplastic biodegradable polyesters. The rheological behavior of the melts improves; the biodegradable polyesters have better processability, for example better drawability to give films via melt solidification. The compounds d have a shear-thinning effect, i.e. they make the polymer more pseudoplastic. Viscosity decreases under load.
It is generally advisable to add the crosslinking (at least trifunctional) compounds to the polymerization reaction at a relatively early juncture.
Examples of suitable bifunctional chain extenders are tolylene 2,4-diisocyanate, tolylene 2,6-diisocyanate, diphenylmethane 2,2′-diisocyanate, diphenylmethane 2,4′-diisocyanate, diphenylmethane 4,4′-diisocyanate, naphthylene 1,5-diisocyanate, and xylylene diisocyanate, hexamethylene 1,6-diisocyanate, isophorone diisocyanate, and methylenebis(4-isocyanatocyclohexane). Particular preference is given to isophorone diisocyanate and in particular hexamethylene 1,6-diisocyanate.
The number-average molar mass (Mn) of the polyesters i is generally in the range from 8000 to 100 000 g/mol, in particular in the range from 8000 to 50 000 g/mol, and their weight-average molar mass (Mw) is generally from 10 000 to 300 000 g/mol, preferably from 10 000 to 120 000 g/mol, and their Mw/Mn ratio is generally from 1 to 6, preferably from 2 to 4. Intrinsic viscosities from 30 to 450 g/mL, preferably from 50 to 200 g/mL (measured in o-dichlorobenzene/phenol (ratio by weight 50/50)). Melting point is in the range from 85 to 130, preferably in the range from 95 to 120° C.
The rigid component ii is polylactic acid (PLA).
It is preferable to use polylactic acid with the following property profile:
Examples of preferred polylactic acids are NatureWorks® Ingeo 6201 D, 6202 D, 6251 D, 3051 D, and in particular 3051 D or 3251 D, and also crystalline polylactic acids from NatureWorks.
The percentage proportion by weight used of the polylactic acid ii, based on components i and ii, is from 15 to 50%, preferably from 15 to 45%, and with particular preference from 20 to 40%. It is preferable here that the polylactic acid ii forms the dispersed phase and that the polyester i forms the continuous phase or is part of a co-continuous phase. Polymer mixtures with polyester i in the continuous phase or as part of a co-continuous phase have higher heat distortion resistance than polymer mixtures in which polylactic acid ii forms the continuous phase.
The amount used of at least one mineral filler selected from the group consisting of: chalk, graphite, gypsum, conductive carbon black, iron oxide, calcium chloride, dolomite, kaolin, silicon dioxide (quartz), sodium carbonate, titanium dioxide, silicate, wollastonite, mica, montmorillonites, talc powder, and mineral fibers is generally from 10 to 50% by weight, in particular from 10 to 40%, and particularly preferably from 10 to 35%, based on the total weight of components i to iv.
Interestingly, it has been found that addition of chalk can achieve a further improvement in the biodegradability of the items. The chalk is essential as filler in the mixtures of the invention. The amount of chalk added is preferably from 5 to 35% by weight, with preference from 8 to 30% by weight, with particular preference from 10 to 20% by weight, based on the total weight of components i to iv. Talc powder in turn can provide greater effectiveness in terms of increasing modulus of elasticity and improving heat distortion resistance. The combination of chalk and talc powder is particularly preferred as filler.
Mixtures of talc powder and chalk have proven particularly advantageous. A mixing ratio that has proven advantageous here is from 1:5 to 5:1, preferably from 1:3 to 3:1, and in particular from 1:2 to 1:1.
For the purposes of the present invention, a substance or substance mixture complies with the “biodegradable” feature if the percentage degree of biodegradation of said substance or the substance mixture to DIN EN 13432 is at least 90% after 180 days.
Biodegradbility generally leads to decomposition of the polyesters or polyester mixtures in an appropriate and demonstrable period of time. The degradation can take place by an enzymatic, hydrolytic, or oxidative route, and/or via exposure to electromagnetic radiation, such as UV radiation, and can mostly be brought about predominantly via exposure to microorganisms, such as bacteria, yeasts, fungi, and algae. Biodegradability can be quantified by way of example by mixing polyester with compost and storing it for a particular period. By way of example, in DIN EN 13432 (with reference to ISO 14855), CO2-free air is passed through ripened compost during the composting process, and the compost is subjected to a defined temperature profile. Biodegradability here is defined as a percentage degree of biodegradation, by taking the ratio of the net amount of CO2 released from the specimen (after subtraction of the amount of CO2 released by the compost without specimen) to the maximum amount of CO2 that can be released from the specimen (calculated from the carbon content of the specimen). Biodegradable polyesters or biodegradable polyester mixtures generally exhibit clear signs of degradation after just a few days of composting, examples being fungal growth, cracking, and perforation.
Other methods of determining biodegradability are described by way of example in ASTM D5338 and ASTM D6400-4.
Injection molding involves a shaping process which is very frequently used in plastics processing. Injection molding can produce large numbers of directly usable moldings extremely cost-effectively. In simplified terms, the process functions as follows: the respective thermoplastic material (“molding composition”) is melted in an injection-molding machine composed of a heatable cylinder in which a screw rotates, and is injected into a metal mold. The cavity of the mold determines the shape and the surface structure of the finished part. It is now possible to produce parts weighing from significantly below one gram up to double-digit kilograms.
Injection molding can produce consumer articles with high precision quickly and cost-effectively. The nature of the surface of the respective component here can be selected by the designers with almost no restriction. A wide variety of surface structures can be produced, from smooth surfaces for optical applications to graining for regions that are pleasant to touch, through to patterns or engraved effects.
Cost-effectiveness reasons make the injection molding process particularly suitable for producing relatively large numbers of units, since the costs for the injection mold themselves represent a considerable proportion of the capital investment required. Even in the case of simple molds, the purchase cost is not recouped until several thousand parts have been produced.
Particularly suitable materials for injection molding are polymer mixtures of components i to iv with MVR (190° C., 2.16 kg) to ISO 1133 of from 10 to 100 cm3/10 min, preferably from 10 to 80 cm3/10 min and in particular from 25 to 60 cm3/10 min. Materials which have proven suitable in these polymer mixtures are moreover in particularly linear or only slightly branched polyesters which comprise from 0 to 0.1% by weight, based on components a to c, of a branching agent.
Performance Tests:
The molecular weights Mn and Mw of the semiaromatic polyesters were determined by means of SEC to DIN 55672-1: eluent hexafluoroisopropanol (HFIP)+0.05% by weight of potassium trifluoroacetate; narrowly distributed polymethyl methacrylate standards were used for calibration.
Intrinsic viscosities were determined to DIN 53728 part 3, Jan. 3, 1985, Capillary viscometry. An M-II micro-Ubbelohde viscometer was used. The solvent used comprised a phenol/o-dichlorobenzene mixture in a ratio by weight of 50/50.
Modulus of elasticity was determined by means of a tensile test on pressed films of thickness about 420 μm to ISO 527-3: 2003.
Charpy impact resistance was determined to ISO 179-2/1eU:1997. The test specimen (80 mm×10 mm×4 mm) in the form of a horizontal bar supported close to its ends is subjected to a single pendulum impact, the impact line being in the middle between the two test-specimen supports, and a high, nominally constant bending velocity (2.9 or 3.8 m/s) is used (on the specimen).
HDT-B heat distortion resistance was determined to ISO 75-2:2004. A standard test specimen is subjected to three-point bending under constant load, thus producing a flexural stress (HDT/B 0.45 MPa) as stated in the relevant part of said international standard. The temperature is increased at uniform rate (120 K/h), and the temperature value measured is that at which a defined standard deflection is achieved, corresponding to the defined increase in flexural strain (0.2%).
The degradation rates of the biodegradable polyester mixtures and of the mixtures produced for comparison were determined as follows:
Films were produced from the biodegradable polyester mixtures and from the mixtures produced for comparison, in each case via pressing at 190° C. and with thickness of 400 μm. In each case, these foils were cut into rectangular pieces with edge lengths of 2×5 cm. The weight of said film pieces was determined. The film pieces were heated to 58° C. in an oven in a plastics container containing moistened compost, for a period of four weeks. At weekly intervals the residual weight of each piece of film was measured. On the assumption that biodegradation can be considered in these instances to be purely a surface process, the gradient of the resultant weight reduction (biodegradation rate) was determined by calculating the difference between the weight measured after taking of a sample and the mass of the film before the start of the test, less the average total weight reduction that occurred up to the taking of the preceding specimen. The mass reduction obtained was also standardized for surface area (in cm2) and also for time between taking of current and previous specimen (in d).
The degradation rates determined were based on the degradation rate of PBS (=100%).
Starting Materials
Polyester i:
a) Polylbutylene succinate (Comparative System)
First, butanediol (93.7 g, 130 mol %), succinic acid (94.5 g, 100 mol %), and 0.2 g of glycerol (0.1% by weight) were heated to 200° C. in the presence of tetrabutyl orthotitanate TBOT (0.2 g), and the resultant water was removed by distillation during a period of 30 min. This prepolyester was then reacted at reduced pressure (<5 mbar) to give the high-molecular-weight polyester. For this, 1,4-butanediol was removed by distillation up to a temperature of 250° C. The IV of the resultant polyester was 171 mL/g.
b) Polybutylene succinate-co-suberate (succinic acid:suberic acid=90:10)
Butanediol (85.0 g, 130 mol %), succinic acid (77.1 g, 90 mol %), and suberic acid (12.6 g, 10 mol %), and 0.18 g of glycerol (0.1% by weight) were first heated to 200° C. in the presence of TBOT (0.2 g). The melt was kept at this temperature during a period of 80 min. 1,4-Butanediol was then removed by distillation at reduced pressure (<5 mbar) and at a maximum internal temperature of 250° C. The polyester was decanted and analyzed after cooling. The intrinsic viscosity of the resultant polyester was 170 mL/g.
c) Polybutylene succinate-co-sebacate (succinic acid:sebacic acid=95:5)
Butanediol (89.0 g, 130 mol %), succinic acid (85.3 g, 95 mol %), and sebacic acid (7.7 g, 5 mol %), and 0.14 g of glycerol (0.1% by weight) were first heated to 200° C. in the presence of TBOT (0.2 g). The melt was kept at this temperature during a period of 80 min. 1,4-Butanediol was then removed by distillation at reduced pressure (<5 mbar) and at a maximum internal temperature of 250° C. The polyester was decanted and analyzed after cooling. The intrinsic viscosity of the resultant polyester was 214 mL/g.
d) Polybutylene succinate-co-sebacate (succinic acid:sebacic acid=90:10)
Butanediol (87.5 g, 130 mol %), succinic acid (79.4 g, 90 mol %), and sebacic acid (15.1 g, 10 mol %), and 0.19 g of glycerol (0.1% by weight) were first heated to 200° C. in the presence of TBOT (0.2 g). The melt was kept at this temperature during a period of 80 min. 1,4-Butanediol was then removed by distillation at reduced pressure (<5 mbar) and at a maximum internal temperature of 250° C. The polyester was decanted and analyzed after cooling. The intrinsic viscosity of the resultant polyester was 252 mL/g.
e) Polybutylene succinate-co-azelate (succinic acid:azelaic acid=90:10)
Butanediol (92.0 g, 130 mol %), succinic acid (83.4 g, 90 mol %), and azelaic acid (14.8 g, 10 mol %), and 0.19 g of glycerol (0.1% by weight) were first heated to 200° C. in the presence of TBOT (0.2 g). The melt was kept at this temperature during a period of 80 min. 1,4-Butanediol was then removed by distillation at reduced pressure (<5 mbar) and at a maximum internal temperature of 250° C. The polyester was decanted and analyzed after cooling. The intrinsic viscosity of the resultant polyester was 214 mL/g.
f) Polybutylene succinate-co-brassylate (succinic acid:brassylic acid=90:10)
Butanediol (85 g, 130 mol %), succinic acid (77.1 g, 90 mol %), and brassylic acid (18.1 g, 10 mol %), and 0.17 g of glycerol (0.1% by weight) were first heated to 200° C. in the presence of TBOT (0.2 g). The melt was kept at this temperature during a period of 80 min. 1,4-Butanediol was then removed by distillation at reduced pressure (<5 mbar) and at a maximum internal temperature of 250° C. The polyester was decanted and analyzed after cooling. The intrinsic viscosity of the resultant polyester was 160 mL/g.
g) Polybutylene succinate-co-terephthalate (succinic acid:terephthalic acid=90:10)
Butanediol (90.8 g, 130 mol %), succinic acid (82.4 g, 90 mol %), and dimethyl terephthalate (15.0 g, 10 mol %), and 0.18 g of glycerol (0.1% by weight) were first heated to 200° C. in the presence of TBOT (0.2 g). The melt was kept at this temperature during a period of 80 min. 1,4-Butanediol was then removed by distillation at reduced pressure (<5 mbar) and at a maximum internal temperature of 250° C. The polyester was decanted and analyzed after cooling. The intrinsic viscosity of the resultant polyester was 172 mL/g.
To determine biodegradability, a molding press was used to produce films of thickness about 420 μm.
Polylactic acid ii-1: 4043D from NatureWorks
Mineral Fillers
iii-1: chalk from Omya
iii-1: talc powder from Mondominerals
General Specification (GS1)
Polymer blends COMP1 and COMP2 were produced by a corotating twin-screw extruder from Coperion. The screw diameter was 26 mm, and the L/D ratio of the extruder was 40. The extrusion temperature was from 150° C. to 240° C. The polymer was charged at room temperature to zone 0. For inventive examples 3 to 5, the same extruder was used with the same production conditions. The fillers were fed by hot feed to zone 4. The subsequent zones 5 and 6 served for dispersion. The material was devolatilized in zones 7 and 8 and zone 9 served for discharge.
The test specimens used were produced by injection molding at melt temperatures of from 150 to 200° C. and at a mold temperature from room temperature to 60° C. The tests used standard test specimens as specified in ISO 20753. Disintegration rates were determined on plaques of dimensions 60×60×1 mm3.
The relative disintegration rate of various polyester/PLA blends was studied by incubating each of 30 moldings (plaques, 60×60×1 mm3) in compost for 12 weeks. After incubation, the amounts of plastics residues remaining in the material that does not pass through the sieve were compared and used to determine the relative disintegration rate, and are listed in Table 3.
aModulus of elasticity to ISO 527-3: 2003
bCharpy impact resistance to ISO 179-2/1eU: 1997
cHDT-B to ISO 75-2: 2004
The results listed in Table 4 show that the moldings produced from the mixtures 4 and 5 of the invention exhibit a very advantageous combination of mechanical properties (high modulus of elasticity) and thermal properties (good heat distortion resistance).
At the same time, the results in Table 5 show an improved degradation rate for the mixtures of the invention.
| Number | Date | Country | |
|---|---|---|---|
| 61502891 | Jun 2011 | US |
