JP3295717B2 - Processable poly (hydroxy acid) - Google Patents

Description

The present invention relates to poly (hydroxy acid) compositions having high melt strength and processability. In particular, the invention relates to the use of these compositions in the production of films.

Biodegradable polymers and biopolymers constitute a group of substances that are being continuously developed. Among these are poly (hydroxy acids), which are polymers whose monomers can have both carboxyl and hydroxyl groups. Examples of such polymers include polylactic acid (polylactide, PLA), poly (hydroxybutyrate), polyglycolide, and poly (ε-caprolactone). Polylactide or polylactic acid, which is best produced from lactic acid dimer, lactide, has already been used for several years for medical or sustained release of drugs such as sutures, degradable bone and nails. The molecular weight of the polymers in these applications is typically very high, and the polymers are purified by dissolution and precipitation before processing, with low thermal degradation. The high price of the polymer and its in-process pyrolysis have limited its use in bulky applications such as packaging. The manufacture or handling of such polymers by methods such as those used for medical applications is not economically beneficial.

Polylactic acid can be directly produced by a polycondensation reaction that is typical in producing polyester. However, the highest molecular weights are achieved by ring-opening polymerization of lactide. Polylactide is a thermoplastic polyester with properties similar to many conventional polymers. The problem, however, was that these polymers were difficult to process and, for example, the production of blown films was not possible.

Non-medical uses of polylactide have also been of particular interest in recent years. Biodegradable compostable materials are being sought for packaging applications, either sanitary products, agricultural films and paper coatings or free films. The reason for this was the objective regarding the use of natural products instead of fossil raw materials and the good mechanical and barrier properties of polylactides, for example, comparable to starch-based thermoplastics.

Polylactide is a thermoplastic polyester similar to many conventional polymers. However, there is the problem that the polymer decomposes during processing and the molecular weight is significantly reduced. As a result, the useful life of the end product and, in part, these mechanical properties are degraded. In the case of conventional polymers, the use of stabilizers can eliminate these problems. The purpose of the use of stabilizers is to keep the molecular weight as constant as possible after the polymerization and especially during processing. Changes in molecular weight can be monitored, for example, by melt viscosity.

Conventional stabilizers that can be used with aromatic polyesters have no effect on lactic acid polymers. According to DE-A-4102170, boric acid used for stabilizing poly (hydroxybutyrate) does not work with lactic acid polymers.

Reliable experiments with various stabilizers have been published. In JP-A-68-008614, polylactic acid is γ
Stabilized with a lactone compound such as -butyrolactone or α-acetal-γ-butyrolactone. JP-A-68-002949 describes that an isocyanate is added to improve the heat resistance of a lactic acid polymer. These methods have been tried, but have yielded poor results.

Attempts to make processed films from pure polylactide,
Not successful. Some films were made by blending with other polymers or from copolymers.

In German Patent Application No. 4300420, a blend of polylactide and another aliphatic polyester, preferably polycaprolactone, is obtained. The polymer is mixed in solution, granulated, and the granules are treated for a long time at a temperature just prior to melting to achieve transesterification.

PCT Publication No. 92/04493 discloses a polylactide composition having a large amount of lactide or lactide oligomer as a plasticizer for flexibility.

In PCT Publication No. 94/07941, melt stable polylactide compositions are obtained which are said to be suitable for films. The lactide and moisture content of the residue should be very low and the exact amount of meso-lactide should be used for the polymerization. Several "films" were made in Example 2 by extrusion of a thick sheet. The thickness of the test product was between 1 and 13 mm. Test bars were used in all other examples. Even according to this patent application it is most preferred to use a polylactide blend, for example with polycaprolactone.

Polylactides or copolymers have been produced into free-standing films by casting from solution or by compression, as already indicated in very old patent publications. For example, there are U.S. Pat. Nos. 2,703,316 and 4,045,418.

Many attempts have been made for film production,
Large-scale production based on the economical conventional large-scale blown film process for making thin stretched films has not been possible due to the low or missing polymer melt strength. It is obvious. When films are obtained in several ways, these films are brittle and have a very high breaking value unless many plasticizers are added or blended with other polymer components. Has low elongation.

Another important issue is melt stability. It is well known that polylactide decomposes at high temperatures during melt processing. While most of the mechanical properties are kept above a certain limiting molecular weight, the viscosity drops drastically and also
This makes inflation of these polymers impossible. Melt-stable compounds are discussed only in PCT Patent Application Publication No. 94/07941, already mentioned above, but even here the melt strength is not sufficient for the inflated process. The melt stability in this specification is the sum of many different factors, and there is a need for precisely defined polymer compounds.

According to the invention, it has surprisingly been found that polylactic acid can be stabilized by adding various peroxides to the mixture during processing or in a separate step. The addition of peroxide can reduce chain breakage,
That is, the decrease in molecular weight can be delayed. The stabilizing effect of the peroxide can also be seen from the melt viscosity values, which decrease considerably later during processing than without peroxide due to the peroxide addition.
The effect of peroxide can be several-fold. Catalyst deactivation and end group capping appear to be possible mechanisms. Crosslinking can be ignored. This is because no gel formation is observed. The theoretical background of peroxide action is outside the scope of the present invention.

Furthermore, it is an object of the present invention to achieve a polylactide composition having good melt strength and elongation.
A further object is to achieve a composition having sufficient melt strength to form a film by conventional methods, such as the blown method.

In the stabilization according to the present invention, a large number of commercially available organic peroxy compounds can be used. Particularly suitable are peroxy compounds, from which the acids are formed as decomposition products. It is clear that this acid radical stabilizes the hydroxyl end groups of the polymer.
In addition, peroxides acting as stabilizers are short,
It is preferably characterized by a half-life of less than 10 seconds, but more preferably less than 5 seconds. Available examples of suitable peroxides include dilauroyl peroxide (half-life at 200 ° C., 0.057 seconds), tert-butylperoxy-diethyl acetate (0.452 seconds), t-butylperoxy-2.
-Includes ethyl hexanonate (0.278 sec), tert-butyl peroxy-isobutyrate (0.463 sec) and tert-butyl peroxyacetate (3.9 sec), tert-butyl peroxybenzoate (4.47 sec) and dibenzoyl peroxide (0.742 sec) It is. The last two mentioned proved to be particularly good. The above are only a few examples of working peroxides, and it is understood that other peroxides that work in a corresponding manner are also within the scope of the present invention.

The amount of peroxide used is preferably from 0.01 to 3% by weight. The most preferred amount depends on the peroxy compound.

Surprisingly, it has been found that stabilizing polylactide with certain peroxides results in very high post-stabilization melt temperatures and elongations. Elongation rate is 150 ~ 300
%. This allows for a polylactide inflation process using conventional commercial inflation equipment. This film can also be stretched effectively.

The polylactide used can be produced from L-, D- or D, L-lactide or a blend thereof by any polymerization method. Copolymers or polymer blends can also be used, but are not required for use performance in the present invention. In particular, it is preferable to use poly-L-lactide. The polymer according to the present invention has a molecular weight of about 20,000 to 400,000, preferably 40,000.
It has a 000-200,000 weight average molecular weight (Mw). This is 1
Refers to a number average molecular weight (Mn) of from 0,000 to 200,000, preferably from 10,000 to 100,000.

Polylactide films can be easily finished for different purposes by adding small amounts of conventional plasticizers, pigments, fillers and the like.

Generally suitable plasticizers include di- or tricarboxylic esters, epoxide oils or esters, polymeric polyesters, aliphatic diesters, alkyl ether mono- or diesters and glycerin esters.
It is a commercially available plasticizer. Blends of these plasticizers can also be used. If a plasticizer is used, an appropriate amount
0.5 to 30% by weight.

Fillers include calcium carbonate, kaolin, mica,
All conventional inorganic or organic fillers can be used, such as talc, silicon oxide, zeolites, glass fibers or spheres, starch or sawdust. Suitable amounts of filler can be from 0.5 to 50% by weight, depending on the end product.

Films can be formed from the polylactide compositions of the present invention by the blown method, which is one of the greatest benefits of the present invention. In addition, cast films or sheets can, of course, also be formed, but these do not usually have a high demand on materials. The thickness of the blown or cast film can be adjusted according to the final product by using different molecular weight polymers and by varying the amount of peroxide and also by adding appropriate plasticizers and / or fillers. It can be easily finished.

The purpose of the use of the film is for all conventional uses of the film, and in particular for those wishing to minimize the amount of waste and to treat it, for example by composting. Such applications are, for example, various packaging materials such as pouches, films, bags, sanitary products such as diapers, and agricultural films.

Sheets formed from polylactide can be processed into various packaging trays or lids, or shallow agricultural containers or flower pots.

Many different types of products can be made from the polymer compositions of the present invention. One such application is
It is called a twist film, which means a wrap used, for example, for a candy, which wraps around an object and twists both ends to close the package. This twist remains closed and does not open before use by the consumer. Not many polymers have good torsional properties. One of the best torsion materials is cellophane.

It is also characteristic of the film or sheet formed from the polymer composition of the present invention that it can be easily sealed by either heat sealing or high frequency sealing. Various printing inks, even when soluble in water, adhere very well to the film.

 The following examples illustrate the invention in more detail.

In Examples 1-3, two different poly (L-lactic acids) were used and their weight average molecular weights Mw were 16
The number average molecular weight Mn was about 70,000 and 60,000 g / mol, respectively. Therefore,
The molecular weight ratio Mw / Mn was about 2.3. Polymer is nested
Manufactured in Oy and used as such in experiments. The following peroxides: A. dibenzoyl peroxide (Fluka), half-life 0.742
Second B. di-tert-butyl peroxide (Akzo), half-life
20.5 seconds C. dicumyl peroxide (Akzo), half-life 14.7 seconds D. tert-butyl peroxybenzoate (Akzo),
A half-life of 4.47 seconds was used for stabilization in the experiment.

All peroxides were commercial products and were used as such.

In another example, 11
Polylactides with molecular weights (Mw) of 5,000, 130,000, and 145,000 were used.

The molecular weight is determined by GPC using a polystyrene standard.
(Gel permeation chromatograph) It measured with the apparatus. DSC
(Differential scanning calorimetry) is measured by Perkin Elmer DS
Performed on C7 and METTLER DSC-30S equipment. The sample weight in these measurements was 10 mg. The heating and cooling rates were 10 ° C./min and the measurement was for two cycles. Thermogravimetric analysis (TGA) was performed using a Mettler TG50 instrument. The size of the sample during the measurement was 10 mg, the sample was heated to 500 ° C under a nitrogen atmosphere, and the heating rate was 10 ° C / min. The gel content of the polymer was determined by the method of ASTM D2765 using chloroform as solvent.

Example 1 Films Stabilization of polylactic acid was investigated using a Brabender mixer (Plasticorder® PL2000), thereby directly monitoring the melt viscosity of the compound from the machine torque. I could do it. 40 g of polylactide having a Mw of 160,000 was mixed with 0 to 3% of dibenzoyl peroxide (A) at 180 ° C. for 5 minutes. Assuming all peroxide had reacted, the DSC measurement did not show any out-of-range peaks. Polymer samples were pressed between PET films for 15 seconds at a pressure of 200 bar and a temperature of 180 ° C. After molding, the film was rapidly cooled to room temperature. The thickness of the film was 250-300 μm. The film was dissolved in chloroform and no gel was visually detectable.

The amount of peroxide added affected the melt viscosity, as can be seen from FIG. Add peroxide to 0-0.
With the addition of 5 wt%, the melt viscosity increased, but the difference was small between the 0.5 wt% and 3.0 wt% additions. Without peroxide, the melt viscosity decreased rapidly during processing.

Example 2. Tape A polylactide having a Mw of 140,000 was mixed with the peroxides AD. The peroxide was dissolved in a small amount of cyclohexane before addition. However, when peroxide A was used, toluene was used as the solvent because A was insoluble in cyclohexane. The solvent was evaporated from the polymer before processing. All experiments were performed under a stream of nitrogen. The experimental batch size was 40 g of polylactic acid. The samples were then processed to tape on a Brabender Plasticoder® PL E651 single screw extruder. Zone temperature is 190 ℃, 200 ℃, 200
C., the nozzle temperature was 200.degree. The rotation speed of the screw was 50 rpm. The residence time of the extruder was about 1.5 minutes.

The molecular weight Mw of the unstabilized reference sample of polylactide dropped during processing to at least one third of its initial value. Mw / Mn dropped from an initial value of 2.3 to about 1.9. D
According to the SC analysis, the reference sample had a glass transition temperature of about 50 ° C. Tg, the melting point Tm of about 170 ° C., and about 50% crystallinity C _r. According to thermogravimetric analysis, the decomposition temperature (T _D ) was about 30
3 ° C. Table 1 shows the molecular weights using different peroxides and Table 2 shows the DSC / TGA of the corresponding experiment.
The measurement results are shown. The results in Table 1 show that peroxides B and C did not achieve the desired stabilizing effect, whereas peroxides A and D reduced the molecular weight only slightly.

Example 3 Gel formation Possible cross-linking of polylactide was investigated by measuring the gel content of the polymer after peroxide treatment.
Polylactide was blended with various amounts of dibenzoyl peroxide in the manner of Example 1. Gel content is AS
As measured by TM D2765, chloroform was used instead of xylene. No gel formation was observed when the peroxide content was 0.25% by weight or less, and gel formation was low even when the peroxide content was less than 3% by weight. When the results were further examined on a particle size analyzer Malvern 2600c, the amount of very small particles was noticeable at low peroxide contents, and the amount of large particles increased with increasing peroxide content. The results are shown in Table 3.

Example 4 Melting Properties of Stabilized Polylactide Poly-L-lactide (PLLA) was stabilized by the method described in the previous example, that is, the polymer was treated with dibenzoyl peroxide (fluca, half-life 0.742 seconds). 180 for 5 minutes
The mixture was melt mixed at ℃. The equipment used to measure the melting properties
Getfelted extruder with screw diameter 30mm and length 20D, equipped with melt pump and capillary die, L
/ D = 100/3. The take-off device is a Gttfert Rheotens for uniaxial elongation of the polymer melt.
Rheotens) testing machine. The polymer melt strand was gripped between two co-rotating wheels and stretched at a constant speed or constant acceleration until the strand broke. In this experiment, a constant acceleration was used. The tensile force used to stretch the polymer melt was recorded as a function of stretched strand speed.

The extruder temperature profile was 160-180-180-180 and the melt pump and die temperatures were 180 ° C. Die pressure was adjusted by the melt pump rpm to avoid melt fracture of the polymer strand. Table 4 shows the tensile strength of the melt at various speeds. Comparing the stabilized polylactide with the unstabilized polylactide, and
It was also compared to a film grade low density polyethylene with a melt index of 4.5.

These results indicate that 0.5% peroxide stabilized polylactide is comparable to film grade polyethylene.

Example 5 Melt Strength Properties of Stabilized Polylactide Blown films of various grades of polylactide were produced on a Brabender extruder with a screw diameter of 19 mm and a length of 25D. Extruder has a diameter of 25mm and 1.0m
A blown film die with a m die gap was provided. The extruder temperature profile was set at 170-180-190 ° C and at the die at 190 ° C. The screw speed was set at 30 rpm. The expansion ratio was 2: 1. Film thickness of 10
The size was changed from μm to 150 μm, and adjusted by the speed of the unloading device.

Subsequent to the extrusion process, a visual inspection of the foam stability corresponding to the melt strength and elasticity of the extruded polymer, which is the main criterion for a suitable blown process, was performed. The steady state extrusion was held for 1 hour.

Table 5 shows the film extrusion properties of stabilized and unstabilized polylactides of various molecular weights. Blown films cannot be formed from unstabilized polylactide. These results show that the appropriate amount of stabilizer is higher for polylactides with lower molecular weights to form a suitable blown film.

From Examples 4 and 5, it is clear that polylactide compositions can be effectively prepared by varying the molecular weight of the polymer and the amount of stabilizer to apply a variety of films from thin to thick films.

Example 6 Physical Properties of Blown Film of Stabilized Polylactide Compared to Unstabilized Polylactide As described above, blown films of unstabilized polylactide are formed due to a lack of melt strength of the polymer. I could not do it. However, it was possible to make blown films of unstabilized blown films by coextrusion. A coextruded film with a layer of polylactide between two layers of polyethylene was formed with the die temperature set at 190 ° C. The polyethylene used was NCPE 4024, a film grade LDPE made from Borealis polymer Oy with a melt index of 4.0. Polylactide film,
Peeled off the polyethylene layer. This is possible because the adhesion between polylactide and polyethylene is relatively low.

The co-extruded film is made from stabilized polylactide,
Of course, it can be formed. This can be a good method in some special cases where a sterile film is needed for special purposes.

The physical properties of the stabilized and unstabilized polylactide films are shown in Table 6.

The high flexibility of films made from stabilized polylactide can be clearly seen from the results.

Example 7. Addition of plasticizer to stabilized polylactide Films formed from stabilized polylactide are already flexible by themselves, but can still be finished by adding more plasticizer to the polymer. Commercially available stabilizers were used in the experiments: Emuldan SHR60, a blend of glycerol monooleate and dioleate (manufactured by Grindstead Products AS, Denmark).

 The film was formed as described in Example 5.

Table 7 shows the stress at peak and the elongation at break.
The results show that the addition of the plasticizer further improves the film properties and, in particular, the properties in the machine and transverse directions are more uniform.

Example 8. Addition of filler to polylactide Various amounts of a commercial filler were added to the stabilized polylactide composition. Fillers and plasticizers can be used simultaneously.

A film was produced by the process described in Example 5.
The results are shown in Table 8. These results show that a small amount of talc gives a very strong and hard film, whereas a large amount of kaolin gives a flexible film, which can be further softened by small amounts of some plasticizers.

Example 9 Twist Properties of Stabilized Polylactide Film For example, if candy is wrapped in individual wraps, the ends are closed by twisting about once and a half. One of the best twisting materials is cellophane, which was used for comparative testing. The twist properties of the polylactide composition according to the invention were very good.

Twist properties were tested on an in-house developed device that wrapped a film around a candy substitute and twisted both ends 1.6 turns. The force required to open the twist with this machine, and the angle at which the twist was opened by itself, were also measured. The results for polylactide and cellophane are shown in Table 9.

Example 10 Sealability and Printability of Polylactide Film The sealability of the film formed in Example 6 was investigated.
The sealing property of this film was good. Heat sealing was performed at 105 ° C. with a sealing time of 0.5 seconds. During sealing, only one seal rod was heated. A high frequency seal was formed at 60 ° C. The seal in both cases was perfect.

The printability of the film was tested and it was found that the film could be printed with both solvent and water based inks without corona treatment. This print had very good adhesion to the film when tested by the tape method.

Example 11: Degradation of polylactide buried in soil Test rods with various levels of stabilizers were used to show that stabilized polylactide as well as unstabilized polylactide may at least biodegrade. It was formed by injection molding. The samples were buried in the soil, removed at regular time intervals, and tested for mechanical properties. From the results summarized in Table 10, all samples could be seen to be embrittled after 6-8 weeks.

Example 12. Decomposition of stabilized polylactide product at constant humidity The test bar of Example 11 was stored under constant conditions of a temperature of 23 ° C and a humidity of 50%. This was done to test the assumption that the first stage of biodegradation was hydrolysis with water. Table 11 shows the mechanical properties. The molecular weight was also measured and the results are shown in Table 12. The results showed that the hydrolysis rate was higher for the stabilized samples than for the non-stabilized ones. This is probably due to a different crystal structure.

As can be seen from the above examples, the polylactide compositions with good melting temperatures and the potential for their production have enabled their use in a wide variety of different applications.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Niemi, Maria Finland EFIEN-0250 Helsinki, Minna Kanthinkatu 24 Ar 25 (72) Inventor Johansson, Karl Johan Finland, EFIEN-06100 Porvoo, Wadenströminkya 32 (72) Inventor Mayndel, Kerstin Finland, EFIEN-06100 Porvoo, Ticantier 6 (56) References WO 94/7949 (WO, A1) Sodergard & JH. Nasman, Stabiliza tion of poly (L -lac tide) in the melt, P olymer Degradation and Stability, the UK, ELSEVIER, vol46, p25-30 (58 ) investigated the field (Int.Cl. ^7, DB name) C08G 63 / 00-63/91 C08J 3/24 C08L 67/04

Claims (22)

(57) [Claims] A processable poly (hydroxy acid) composition having a number average molecular weight of at least 10,000, wherein the melt strength and polymer elasticity are achieved by reactive extrusion of the poly (hydroxy acid) with an organic peroxide. A processable poly (hydroxy acid) composition characterized in that: 2. An organic peroxy compound in an amount of 0.05 to 3% by weight is added to the polymer during the melt processing step, the decomposition of which produces one or several acid radicals. Item 4. A processable poly (hydroxy acid) composition according to Item 1. 3. The poly (hydroxy acid) having a number average molecular weight of 1
The processable poly (hydroxy acid) composition according to claim 1 or 2, wherein the composition has a molecular weight of from 0.000 to 200,000. (4) The amount of peroxide is 0.05 to 0.
The processable poly (hydroxy acid) composition according to any one of claims 1 to 3, which is 8% by weight. 5. The peroxide used has a half-life of 200 ° C.
The processable poly (hydroxy acid) composition according to any one of claims 1 to 4, wherein the temperature is less than 10 seconds. 6. The processable poly (hydroxy acid) composition according to claim 1, wherein the peroxide is tert-butylperoxybenzoate or dibenzoyl peroxide. 7. The processable poly (hydroxy acid) composition according to claim 1, wherein the poly (hydroxy acid) is poly-L-lactide. 8. A poly (hydroxy acid) composition according to claim 1, wherein the melt strength and elasticity are suitable for the production of blown films. 9. The poly (hydroxy acid) according to claim 1, wherein the melt strength and elasticity are suitable for producing a cast film or sheet.
Composition. 10. The poly (hydroxy acid) composition according to claim 1, which contains 0.5 to 30% by weight of a plasticizer. 11. The plasticizer is selected from the group consisting of di- and tolucarboxylic esters, epoxy oils and esters, high molecular weight polyesters, aliphatic diesters, alkyl ether mono- and diesters and glycerin esters or mixtures thereof. 11. The poly (hydroxy acid) composition according to claim 10, wherein: 12. The poly (hydroxy acid) composition according to claim 1, which contains from 0.1 to 50% by weight of a filler. 13. The method according to claim 12, wherein the filler is selected from the group consisting of calcium carbonate, kaolin, mica, talc, silicon dioxide, zeolite, glass fibers or spheres, starch or sawdust. Poly (hydroxy acid) compositions. 14. A film or sheet formed from the poly (hydroxy acid) composition according to any one of claims 1 to 13. 15. The film according to claim 14, produced by blown film extrusion. 16. The film or sheet according to claim 14, produced by cast extrusion. 17. A material which can be sealed by heat sealing or high frequency sealing.
The film or sheet according to any one of the above items. 18. The film or sheet according to claim 14, which can be printed with a solvent or a water-based ink. 19. The film or sheet according to claim 14, which has good twisting characteristics. 20. Use of a film according to any one of claims 14 to 19 in packaging materials such as hygiene products such as diapers, agricultural films, bags, pouches, shrink or twist film packaging. Method. 21. A method of using a sheet according to any one of claims 14 to 19 for thermoformed packaging articles such as trays or lids and agricultural products as cultivation trays or flowerpots. 22. The film, sheet and product according to claim 14, which is hydrolyzable and biodegradable.