JP3608007B2 - Decomposition accelerator - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an improved polylactic acid composition and a decomposition accelerator used for molded articles thereof.
[0002]
[Prior art]
Polymers that are biodegradable or decompose in the natural environment have attracted attention from the standpoint of environmental protection. In particular, polylactic acid is expected to be the most practical because it uses agricultural products as raw materials and is excellent in polymer melt moldability, product heat resistance and strength.
[0003]
However, unmodified polylactic acid has a problem that its degradation rate is relatively slow because of its high crystallinity and rigid molecular structure.
[0004]
Generally, degradable polymers having different degradation rates and lifetimes are required depending on purposes and applications. However, the conventional polylactic acid has a slow degradation rate as described above, and it is desired to have a faster degradation rate depending on the application.
[0005]
[Problems to be solved by the invention]
It is known that polylactic acid is copolymerized with a second component to lower its crystallinity and increase its degradability. However, the copolymerization method has a problem that the melting point is lowered together with the crystallinity and the heat resistance and solvent resistance of the molded product are lowered. Although it is conceivable to lower the crystallinity by mixing the second component, few effective additives are known that control the degradation rate while suppressing deterioration of the physical properties of polylactic acid.
[0006]
An object of the present invention is to provide a novel composition capable of enhancing and controlling the degradability while minimizing deterioration of physical properties of polylactic acid.
[0007]
[Means and Actions for Solving the Problems]
The object of the present invention is a polyester (B) having a sulfone group content of 0.1% by weight or more and a melting point of 200 ° C. or less, so that the sulfone groups occupy 0.01% or more of the total weight, and lactic acid This is achieved by a decomposition accelerator added so that the weight ratio of the polymer (A) containing as a main component is 50% or more. In the present invention, the polymer (A) containing lactic acid as a main component includes poly L-lactic acid, poly D-lactic acid, poly L / D-lactic acid copolymer, and compounds that form ester bonds to them. Copolymerized so as to have a ratio of 50% or less by weight. Examples of ester bond-forming compounds (polymerization raw materials) include hydroxyalkyl or arylcarboxylic acids such as glycolic acid, hydroxybutylcarboxylic acid, and hydroxybenzoic acid, lactones such as glycolide, propiolactone, butyrolactone, valerolactone, and caprolactone Diols and dicarboxylic acids.
[0008]
Examples of the diol include aliphatic diols having about 2 to 20 carbon atoms such as ethylene glycol, propanediol, butanediol, hexanediol, octanediol, decanediol, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, poly Examples include oligomers and polymers of polyalkylene ethers (polyalkylene oxides) such as butylene glycol and copolymers thereof. Examples of dicarboxylic acids include aliphatic dicarboxylic acids having about 4 to 20 carbon atoms, such as succinic acid, adipic acid, sebacic acid, decanedicarboxylic acid, phthalic acid, isophthalic acid, sulfoisophthalic acid, and metal salts thereof (Na, K). And aromatic dicarboxylic acids such as terephthalic acid and naphthalenedicarboxylic acid.
[0009]
The copolymerization of these copolymer components with polylactic acid may be random copolymerization or block copolymerization. However, block copolymerization is often preferred for performing the desired modification without significantly impairing crystallinity and heat resistance, and is particularly suitable for the present invention.
[0010]
In the present invention, the polymer (A) containing lactic acid as a main component is the base material of the composition of the present invention, and a polylactic acid homopolymer and a copolymerized polylactic acid obtained by copolymerizing polylactic acid with other components. Include. The main purpose of the copolymerization is (1) moderately lowering the crystallinity and melting point, lowering the polymerization temperature and molding temperature, and preventing the deterioration of the polymer in those processes. (2) polyester for promoting degradation rate (B ), To facilitate mixing, and to prevent white turbidity of the mixture caused by insufficient affinity, and (3) to plasticize polylactic acid to increase flexibility and impact resistance. The melting point of poly L-lactic acid homopolymer (endothermic peak of DSC curve) is 175 to 180 ° C, but in order to meet the above purpose, the melting point of the copolymer is preferably 120 ° C to 170 ° C, and 130 to 165 ° C. Is particularly preferred. Such modification by copolymerization of polylactic acid is carried out by copolymerizing at least one second component to 50% by weight or less, particularly 1 to 30%, most often 2 to 20%.
[0011]
In the present invention, the polyester (B) having a sulfone group content of 0.1% by weight or more and a melting point of 200 ° C. or less increases and controls the decomposition rate of the composition. ). The feature of the decomposition accelerator (B) is that it has a sulfone group. The sulfone group may be used as it is, but in many cases, a salt neutralized with an alkali metal (Na, K, Li, etc.) is widely used, and the decomposition promoting effect is high and preferable. Salts such as silver, copper, and zinc have antibacterial action and can be applied to medical and hygiene fields. Although the mechanism of action for promoting the degradation of the sulfone group is not clear, (1) the crystallinity of the polylactic acid is reduced by the shape effect of the sulfone group, and (2) the hydrolysis of the polylactic acid by the water absorbed by the water absorption of the sulfone group And two of the acceleration of biodegradation.
[0012]
The higher the sulfone group content of the decomposition accelerator (B), the more remarkable the decomposition promotion action. The sulfone group content of the decomposition accelerator (B) needs to be 0.1% by weight or more, preferably 0.3% or more, and particularly preferably 0.5 to 15%. Here, the content rate of the sulfone group is calculated with the sulfone group as SO ₃ and the molecular weight of 80. For example, when S (sulfur, atomic weight 32) in the decomposition accelerator is quantified and it is 1% by weight, the sulfone group content is multiplied by 80/32 = 2.5 to be 2.5%. calculate.
[0013]
In order to introduce a sulfone group into the decomposition accelerator (B), an ester bond-forming compound having a sulfone group, for example, 5-sulfoisophthalic acid or / and a metal salt thereof may be used as a polymerization raw material. Similarly, bishydroxyethylsulfoisophthalic acid (metal salt) that is a derivative thereof and a product obtained by adding an alkylene oxide such as ethylene oxide and / or propylene oxide to the hydroxyl group thereof are also useful. The melting point of the decomposition accelerator (B) needs to be 200 ° C. or less, preferably 180 ° C. or less, and 170 ° C. from the standpoint of melt mixing with the polymer (A) containing lactic acid as a main component, melt molding and the like. The following are most preferred. In the case of an amorphous substance, the melting point of the crystal is not observed, but the melting point is the temperature at which the crystallizing or flow starts sufficiently.
[0014]
Sulfone groups tend to increase the melting point when present at high density. For example, polyethylene sulfoisophthalic acid (sodium salt) has a high sulfone group content of about 24%, but has a melting point of 200 ° C. or higher and is not suitable for the present invention. In order to lower the melting point, a glycol having a long molecular chain (for example, having 4 or more carbon atoms, particularly 6 or more) is used, or other (low melting point) polyester polymerization components such as succinic acid, adipic acid, sebacic acid, What is necessary is just to dilute a sulfone group by making decanedicarboxylic acid etc. react (polymerization or copolymerization). Similarly, low melting point polyesters such as polylactic acid such as polylactic acid, polyglycolic acid, polyhydroxybutyrate, polylactone such as polycaprolactone, polyethylene adipate, polyethylene sebacate, polybutylene succinate, polybutylene adipate, poly Decomposition accelerators having a melting point of 200 ° C. or less by copolymerization of polymers or / and oligomers such as polyalkylene alkylates such as butylene sebacate, polyhexane succinate, polyhexane adipate, and polyhexane sebacate with sulfone group-containing compounds ( B) can be obtained. Similarly, polyalkylene ethers such as polyethylene glycol, polypropylene glycol, polybutylene ether and copolymers thereof, and polymers and oligomers of polyalkylene carbonates such as polyhexane carbonate can also be decomposed with a low melting point in combination with a component having a sulfonic group. An accelerator can be obtained. For example, polymers such as polyalkylene oxide (ether) and polyalkylene carbonate and oligomers having a low polymerization degree, for example, those having a molecular weight of 1,000 or less, particularly 500 or less, can be combined with an aliphatic dicarboxylic acid to obtain a low melting point polyester. In addition, by introducing sulfoisophthalic acid into the molecular chain as a copolymerization component, a low-melting polyester having an arbitrary sulfone group content can be easily obtained.
[0015]
From the standpoint of suppressing deterioration of physical properties of the mixture, a polymer (A) containing lactic acid as a main component (hereinafter sometimes referred to as “matrix polymer (A)”) and a decomposition accelerator (B) as an additive. Preferably have a high mutual affinity. The higher this mutual affinity is, the easier and more uniform the composition can be mixed, and the better the transparency, mechanical properties such as strength, elongation and impact strength. Affinity (miscibility, compatibility, adhesiveness) between the base polymer (A) and the degradation accelerator (B) can be increased by having the same (same) or similar components in both. . For example, if the decomposition accelerator (B) is a block copolymer having a polylactic acid segment (block) in the molecular chain, the affinity with the base material (A) is high. In general, an aliphatic polyester whose molecular structure (for example, the number of atoms between ester bonds in the main chain) is close to that of polylactic acid (the difference in the number of atoms is 4 or less, particularly 2 or less) has an affinity for the base polymer (A). Is expensive. Here, the segment refers to one part of the molecular chain of the polymer.
[0016]
Moreover, when the base polymer (A) is a copolymer, the affinity between the copolymer component and the decomposition accelerator (B) can be increased by using a common or approximate component. For example, if a block copolymer of polylactic acid and polybutylene adipate is used as the base polymer (A) and a block copolymer polyester having a polybutylene adipate segment is used as the decomposition accelerator (B), the affinity between the two is high.
[0017]
Here, even when the polybutylene adipate segment in the decomposition accelerator is replaced with polyethylene sebacate, the molecular structures of both are highly similar and their mutual affinity is high. Thus, the decomposition accelerator (B) has a component (constituent unit or segment) that is common or close to the polylactic acid or / and the copolymer component as the main component of the base polymer (A) in the molecule. From the viewpoint of the affinity between the two, it is particularly preferable.
[0018]
The greater the amount of the sulfone group in the decomposition accelerator (B), the stronger the decomposition promoting action. In order to obtain a practically sufficient sulfone group content, for example, in order to make the sulfone group content 1% or 5%, one sulfone group per molecular weight of about 8,000 or one sulfone group per molecular weight of about 1,600 What is necessary is just to design a molecule to introduce. For example, sulfoisophthalic acid (Na salt) or its ester (methyl ester, ethylene glycol ester, etc.) and polyalkylene glycol (polyethylene glycol etc.) having a hydroxyl group at both ends and a molecular weight of about 600, or polyalkylene alkylate (polybutylene) Polyester having a sulfone group content of about 10% is obtained by condensation (formation of ester bond) with polyalkylene carbonate (such as polyhexane carbonate) or adipate.
[0019]
The degradability of the mixture composed of the base polymer (A) and the degradation accelerator (B) is higher as the weight fraction of the sulfone group relative to the whole composition is larger. In order to show a sufficient decomposition accelerating action, the weight ratio of the sulfone group to the whole composition needs to be at least 0.01%, preferably 0.05% or more, and most widely used is about 0.1% to 5%. It is done. The mixing ratio (weight ratio) of the decomposition accelerator (B) to the entire composition is 50% or less, but may be appropriately mixed so that the amount of the sulfone group in the entire composition falls within the above range. For example, if 10% of a decomposition accelerator having a sulfone group content of 5% is mixed, the sulfone group content of the entire composition is about 0.5%. The effect of promoting the decomposition of is fairly clearly exhibited, and, for example, it can be easily obtained that exhibits, for example, 1.5 times or more, especially 2 times or more of the case where no sulfone group is contained. The mixing ratio of the decomposition accelerator (B) may be arbitrarily selected depending on the purpose within a range of 50% or less, for example, 1 to 40%, particularly 3 to 30% is often used, and 5 to 20% is the widest. Used.
[0020]
The molecular weight of the decomposition accelerator (B) is not particularly limited, but is somewhat large, for example, 1,000 or more, particularly 3,000 or more, preferably 5,000 or more, and in many cases 10,000 to 200,000. The one of the degree is widely used.
[0021]
As described above, the decomposition rate of the composition increases as the sulfone group content of the decomposition accelerator increases and the mixing ratio of the decomposition accelerator in the composition increases. Furthermore, when using a copolymer as a base polymer (A), there exists a tendency for a decomposition rate to become large, so that the weight ratio of a copolymerization component is high. By appropriately selecting and adjusting these factors related to the degradation rate, it is possible to obtain a composition having a very wide variety of degradability depending on the purpose and application.
[0022]
In addition to the base polymer (A) and the decomposition accelerator (B), a secondary additive (C) can be mixed as necessary. Examples of secondary additives include stabilizers, antioxidants, ultraviolet absorbers, colorants, pigments, various inorganic compound particles, fillers, lubricants, antistatic agents, mold release agents, water repellents, hydrophilic agents. , Antibacterial agents, fragrances, foaming agents, plasticizers, and other well-known organic and inorganic additives and fillers.
[0023]
In many cases, the base polymer (A) and the decomposition accelerator (B) are mixed after the polymerization of the base polymer (A) or after the end of the polymerization step. This is because when the decomposition accelerator (B) is mixed with the polymerization raw material or added during the polymerization, they react with each other to cause copolymerization or decomposition, and the target composition may not be obtained. Since the reaction between the two may slightly occur during mixing by the melting method, the time for melt mixing is as short as possible, for example, preferably within 20 minutes, particularly preferably within 10 minutes, Most preferably within 5 minutes. In order to prevent the reaction between the two, at least one of the terminal functional groups, that is, a hydroxyl group or a carboxyl group, is preferably reacted with a monofunctional compound and blocked.
[0024]
Mixing of the base polymer (A) and the decomposition accelerator (B) may be a melting method or a solvent method, but the melting method is preferable because of its high efficiency. That is, the decomposition accelerator can be melt-mixed at the end of the melt polymerization of the base polymer, before molding, or during the molding process. Any mixing method may be used, but a single- or multi-shaft mixer, an extruder, a kneader, a gear pump, or other mechanical stirring, and a static mixer that repeats flow division and combination in multiple stages by a guide device. Is preferable because it can be continuous and has high efficiency.
[0025]
【Example】
In the following examples, “parts”, “%” and the like are “parts by weight” and “% by weight” unless otherwise specified. [Example 1]
Bishydroxyethylsulfoisophthalic acid sodium salt and bishydroxyethyladipic acid are mixed at a molar ratio of 1/2, and 400 ppm of antimony trioxide fine particles are added as a polymerization catalyst. Next, after adding a random copolymer of polybutylene adipate / polyhexane adipate having a hydroxyl group at both ends and a molecular weight of 3,000 (copolymerization molar ratio 1/1) to 60% of the total, The mixture was reacted and heated at 240 ° C. and a pressure of 0.7 Torr for 2 hours to obtain a polyester P1 having a sulfone group. The polymer P1 (decomposition accelerator) has a sulfone group content of about 5.0%, a molecular weight of 18,000, and is amorphous, so the melting point is not clear, but it flows at 160 ° C.
[0026]
Addition of 0.2% of polymerization catalyst tin octylate, 0.05% of antioxidant Ciba Geigy Irganox 1010, 0.05% of titanium oxide particles 0.05mm in diameter to L-lactide with optical purity 99% or more Two-flight type (oval) that continuously mixes and reacts under nitrogen gas at 150 ° C for an average of about 7 minutes in a mixed-feeding machine with twin-screws meshing with each other and then meshing with the screws meshing with each other The mixture was stirred and polymerized in a twin-screw kneader / extruder having a large number of mixing elements at 190 ° C. for 3 minutes on average in a nitrogen stream. Further, from the final vent hole, the polymer P1 melted was supplied and mixed so as to be 10% of the reaction system, and then extruded from the die, cooled in the water, solidified, and cut to obtain a chip C1. Chip C1 was subjected to centrifugal dehydration and air drying, then heated in nitrogen at 120 ° C. for 12 hours, and further heated at 140 ° C. for 4 hours to obtain chip C2.
[0027]
The weight average molecular weight of the chip C2 is 188,000, the sulfone group content is 0.5%, and the residual monomer (lactide) is 0.1%.
[0028]
Chip C2 was melted with a screw extruder at 210 ° C., spun from an orifice with a hole diameter of 0.2 mm and a temperature of 200 ° C., cooled and oiled in air, and wound at a speed of 800 m / min. The film was drawn at 3.9 times and heat-treated at 110 ° C. under tension to obtain a drawn yarn Y1 of 150 denier / 48 filaments. Yarn Y1 has a strength of 4.3 g / d and an elongation of 31.2%.
[0029]
For comparison, an unmodified polylactic acid obtained in substantially the same manner as the polymer C2 except that the polymer P1 was not added at the end of the polymerization of L-lactide was obtained. The drawn yarn obtained by heat treatment is designated Y2. Yarn Y2 has a strength of 4.5 g / d and an elongation of 28.3%.
[0030]
The deterioration test was performed by burying the yarns Y1 and Y2 in the soil. That is, the yarn is aligned and fixed to a metal frame, a sample is taken out every month, and the strength of the yarn is measured. The time during which the intensity is ½ of the initial value is defined as the half-life. The half-life of the yarn Y1 of the present invention is 3.3 months, which is less than half the half-life of 7.4 months of the yarn Y2 of the comparative example, and the effect of the polymer P1 as a degradation accelerator is clear.
[0031]
[Example 2]
95 parts of L-lactide having an optical purity of 99% or more, 5 parts of polybutylene adipate / polyhexane adipate having a molecular weight of 20,000 at both ends and a molecular weight of 20,000, and a copolymer (molar ratio 1/1) are melt mixed. The chips C1 and C2 were polymerized in the same manner, and 5% and 10% of the polymer P1 of Example 1 were mixed at the end of polymerization to obtain chips C3 and C4, respectively. For comparison, a chip obtained in the same manner as the chip C3 but without adding the polymer P1 is referred to as C5.
[0032]
Y3, Y4, and Y5 are yarns obtained by melt spinning and drawing using the chips C3, C4, and C5 in the same manner as the yarn Y1 of Example 1, respectively. For these yarns, the half-life when buried in the soil was determined in the same manner as in Example 1. The half-life of the yarn Y3 according to the present invention is 3.5 months, the half-life of the yarn Y4 is 2.1 months, both of which are considerably shorter than the half-life of 6.0 months of the comparative yarn Y5, and the degradation accelerator P1 The effect of is obvious. Yarns Y3 and Y4 were superior to the yarn Y1 of Example 1 in transparency and gloss, because the base polymer and the decomposition accelerator have the same components, and their mutual affinity is high.
[0033]
【The invention's effect】
According to the present invention, it is possible to effectively increase the degradation rate of polylactic acid having a slow degradation rate. That is, the degradation rate of polylactic acid or a modified product thereof can be controlled fairly freely and over a wide range by adjusting the composition and addition amount of the degradation accelerator according to the purpose and application. Furthermore, by increasing the affinity of the polymer mainly composed of lactic acid, which is the base polymer, and the decomposition accelerator, problems such as white turbidity and strength deterioration due to mixing of both can be reduced.
[0034]
Moreover, the decomposition accelerator having a sulfone group of the present invention also acts as a plasticizer for the base polymer, and improves the flexibility and impact resistance of the molded product. Similarly, the sulfone group, particularly its metal salt, has a high affinity for basic dyes, and the fibers, films and other molded articles according to the present invention can be dyed with basic dyes. Yes.
[0035]
The composition containing the decomposition accelerator according to the present invention can be used for fibers, knitted fabrics, woven fabrics, nonwoven fabrics, paper, ropes, nets, sheets, films, foams, packaging materials, plates, bars, tubes, various parts and other molded products. It can be preferably used.

Claims (2)

It is made of polyester (B) having a sulfone group content of 0.1% by weight or more and a melting point of 200 ° C. or less. A decomposition accelerator added so that the weight ratio of the polymer (A) is 50% or more. The degradation accelerator according to claim 1, wherein the polyester (B) has 5-sulfoisophthalic acid or / and a derivative thereof as a constituent component.