JP5164423B2 - Lignophenol-polylactic acid complex - Google Patents

Description

  The present invention relates to a lignophenol-polylactic acid complex. More specifically, the present invention relates to a composite of lignophenol and polylactic acid obtained by phenol derivatization of lignin, which is a constituent component of wood.

  The development of materials using renewable resources such as plant materials is a highly social research theme that should be urgently started from the viewpoint of building a recycling-oriented society. If we can replace plastics made mainly from petroleum with bio-based polymers made from renewable raw materials, we will realize “carbon neutral” that does not increase carbon dioxide in the atmosphere in the life cycle, Can contribute to prevention.

  Lignocellulosic materials, which are forest resources, are composed of hydrophilic carbohydrates such as cellulose and hemicellulose and hydrophobic lignins (polyphenols), which have an interpenetrating polymer network (IPN) structure in the cell wall and are complicated. They are entangled to form a complex. The lignocellulosic material is given utility as various materials according to the structure of such a composite. However, lignin has been difficult to use industrially due to its structural complexity and chemical stability. Therefore, paying attention to the function of lignin as a composite constituent material, a technique for extracting a lignocellulose-based material in the form of a lignophenol derivative has been developed (Patent Documents 1 and 2 and Non-Patent Documents 1 and 2).

  Lignophenol derivatives generally have a molecular weight of about several thousand, and have the disadvantages that, by themselves, the moldability is poor and their shape cannot be maintained, so their use has been limited. It has only been reported that a lignophenol hybrid material capable of maintaining the film shape can be obtained by mixing a lignophenol derivative and a silane coupling agent (Patent Document 3).

  On the other hand, polylactic acid obtained by polymerization of lactide or lactic acid is a polyester composed of renewable resources. Polylactic acid is a crystalline thermoplastic polymer having a tensile strength equivalent to that of polyethylene (PE) and transparency equivalent to that of polyethylene terephthalate (PET). In addition, the calorie burned when polylactic acid is burned is as small as about 1/3 of PE, polypropylene (PP), etc., hardly hurts the incinerator, and no harmful gas is generated. Furthermore, since the raw material of polylactic acid is a plant-derived renewable resource, an increase in carbon dioxide when incinerated is unlikely to be an environmental burden. Therefore, it is friendly to the global environment. In particular, there is a high interest in polylactic acid produced from corn.

Due to the above-mentioned advantages, research and development of polylactic acid production methods and application uses have been actively carried out in recent years, and diversification of uses and accompanying increase in production volume are expected. For example, pharmaceutical materials (such as sutures), agricultural materials (sheets, films, etc.), food packaging materials (food packaging films, sheets, bags, etc.), other packaging materials (clothing, daily miscellaneous goods packaging sheets) , Film, bag, etc.) are expected. However, polylactic acid, which is thermoplastic, has a drawback of poor workability when used in various applications such as resin raw materials and paints because of its high crystallinity and high melting point.
WO99 / 14223 pamphlet JP 2003-268116 A JP 2006-342270 A M. Funaoka, Polymer International, 47, 277, 1998 Y. Nagamatsu and M. Funaoka, Green Chemistry, 5, 595, 2003 AS Karikari et al., Biomacromolecules, 6, 2866, 2005 Y. Ikada et al., Macromolecules, 20, 904, 1987

  The object of the present invention is to develop new uses of lignophenol and polylactic acid, which are plant-derived resources.

  It is known that lactide, which is a cyclic dimer of lactic acid, can graft a polylactic acid chain from a primary hydroxyl group by using a tin catalyst (Non-patent Document 3). The present invention focuses on the primary hydroxyl group of lignophenol and finds that a complex of lignophenol and polylactic acid (lignophenol-polylactic acid complex) can be obtained by initiating ring-opening polymerization of lactide. Based on that.

  The present invention provides a lignophenol-polylactic acid complex having at least three branched chains composed of polylactic acid in the molecule.

  In one embodiment, the lignophenol-polylactic acid complex is obtained by a step of ring-opening polymerization of lactide using lignophenol having at least three hydroxyl groups in the molecule as an initiator.

  In one embodiment, the lactide is in the L form.

  According to the present invention, a complex of lignophenol, which is a plant-derived material, and polylactic acid (ie, lignophenol-polylactic acid complex) is provided. This composite is used as a modifier of polylactic acid, and can reduce the crystallinity of polylactic acid and improve toughness. It also has the effect of plasticizing polylactic acid. Furthermore, this complex can also be used as a compatibilizer between polylactic acid and other polymers. In addition, since the raw materials of this complex are all derived from plants, an increase in carbon dioxide is less likely to be an environmental burden and is friendly to the global environment.

(Lignophenol)
In this specification, lignophenol refers to a compound in which phenol or a phenol derivative is added to lignin.

  Below, the partial structural formula of an example of lignophenol which can be used for this invention is shown.

  The molecular weight of lignophenol is not particularly limited. In view of physical properties, the molecular weight is preferably 500 or more, and more preferably 1000 or more. In view of ease of handling, the molecular weight is preferably 100,000 or less, and more preferably 10,000 or less.

(Method for producing lignophenol)
Lignophenol can be obtained by adding a phenol derivative to lignin.

  The lignin used for the production of lignophenol is not particularly limited. Purified lignin may be used, but more conveniently, lignin present in any lignocellulosic material can be used. Examples of lignocellulosic materials include woody parts of plants (for example, wood) or processed products thereof (for example, paper).

  When using wood, the kind of the tree is not particularly limited. It may be a conifer or a broad-leaved tree. Various herbaceous plants such as rice, corn, and sugarcane can also be used as raw materials for lignocellulosic materials.

  The lignocellulosic material may be a lignocellulosic material waste or scrap, and feed or agricultural waste made of lignocellulosic material may also be used. The lignocellulosic material can be used regardless of the form such as powder or chip. The powder form is convenient for efficiently producing lignophenol from lignocellulosic material.

  A phenol derivative refers to a monovalent phenol derivative, a divalent phenol derivative, or a trivalent phenol derivative.

  The monovalent phenol derivative refers to a compound having a substituent on the benzene ring of phenol or phenol. Specific examples include phenol and cresol.

  The divalent phenol derivative refers to a divalent phenol or a compound having a substituent on its benzene ring. Specific examples include catechol, resorcinol, hydroquinone and the like.

  The trivalent phenol derivative refers to a trivalent phenol or a compound having a substituent on its benzene ring. Specific examples include phloroglucinol, hydroxyhydroquinone, pyrogallol and the like.

  Of the monovalent, divalent, and trivalent phenol derivatives, monovalent phenol derivatives are preferred. Cresol is more preferred.

  The cresol may be o-cresol, m-cresol, or p-cresol. Most preferred is p-cresol.

  The number of substituents on the benzene ring in the phenol derivative can be arbitrarily selected. 1-3 are preferable, 1-2 are more preferable, and 1 is more preferable.

  Any substituent on the benzene ring in the phenol derivative can be used. Preferably, it is an alkyl group. This alkyl group may be linear or branched. This alkyl group preferably has 1 to 5 carbon atoms, more preferably 1 to 3 carbon atoms, and still more preferably 1.

  When a phenol derivative is reacted with a lignocellulosic material, the lignin in the lignocellulosic material is grafted with the phenol derivative, and the phenol derivative is exclusively at the side chain α position (benzyl position) of the phenylpropane unit, which is the basic lignin skeleton. Lignophenol into which is introduced is obtained.

  Since lignocellulosic materials generally contain a large amount of components other than lignin, the products of lignocellulosic materials treated with phenol derivatives usually contain a large amount of compounds other than lignophenol. For this reason, lignophenol with high purity can be obtained by removing these impurities.

  As a specific method for producing lignophenol, various conventionally known methods can be used. The lignophenol produced by the known method can be used in the present invention.

  For example, as a first specific method, a lignocellulosic material is treated with a phenol derivative, concentrated acid is added to obtain a two-phase product, and a lignophenol is obtained from the phenol derivative phase of the upper phase (that is, the organic phase). There is a method of recovering (see Patent Document 1). In this case, as described in FIG. 4 of Patent Document 1, if necessary, excess ethyl ether is added to the upper phase (organic phase) of the two phases obtained by adding concentrated acid. Separated into a lysate and an insoluble matter, acetone was added to the resulting insoluble matter to separate it into a lysate and an insoluble matter, and excess ethyl ether was added to the lysate to separate it into a lysate and an insoluble matter By recovering the insoluble matter, purified lignophenol can be obtained.

  More specifically, a liquid phenol derivative (cresol or the like) is infiltrated into a lignocellulosic material such as wood flour, lignin is solvated with the phenol derivative, and then concentrated acid (as an example 72 % Sulfuric acid) is added and mixed to dissolve the cellulose component. According to this method, a phenol derivative obtained by solvating lignin and a concentrated acid dissolving a cellulose component form a two-phase separation system. Lignin solvated with a phenol derivative contacts the acid only at the interface where the phenol derivative phase contacts the concentrated acid phase. Therefore, the cation at the side chain α-position (benzyl position), which is a highly reactive site of the lignin basic structural unit generated by contact with the acid, is attacked simultaneously by the phenol derivative. As a result, a phenol derivative is introduced into the benzyl position by a C—C bond, and the benzyl aryl ether bond is cleaved to reduce the molecular weight. Thus, lignophenol in which the lignin is reduced in molecular weight and the phenol derivative is introduced at the benzyl position of the basic structural unit is produced in the phenol derivative phase. Next, by extracting lignophenol from this phenol derivative phase, lignophenol can be obtained as part of a collection of low molecular weight lignins that have been reduced in molecular weight by cleavage of the benzyl aryl ether bond in the lignin. . It is known that some phenol derivatives are introduced into the benzyl position through the phenolic hydroxyl group.

  Extraction of lignophenol from the phenol derivative phase can be performed, for example, by the following method. First, a precipitate (insoluble matter) obtained by adding a phenol derivative phase to a large excess of ethyl ether is collected and dissolved in acetone. Acetone-insoluble matter is removed by centrifugation, and the acetone-soluble part is concentrated. The acetone soluble part is dropped into a large excess of ethyl ether, and the precipitate is collected. After the solvent is distilled off from this precipitate, it is dried in a desiccator containing phosphorus pentoxide to obtain lignophenol. The crude lignophenol can also be obtained by simply removing the phenol derivative phase by distillation under reduced pressure. Moreover, an acetone soluble part can also be used for a secondary derivatization process as a lignophenol solution as it is.

  The second specific method is as shown in FIG. Specifically, first, a lignocellulosic material is infiltrated with a solvent (for example, ethanol or acetone) in which a solid or liquid phenol derivative is dissolved, and then the solvent is distilled off (phenol derivative adsorption step). . Next, a concentrated acid is added to the lignocellulosic material to dissolve the cellulose component. As a result, as in the first method, the lignin in the state solvated with the phenol derivative is attacked by the phenol derivative at the high reaction site (side chain α-position) of the lignin generated by contact with concentrated acid. A phenol derivative is introduced. In addition, the benzyl aryl ether bond is cleaved to lower the molecular weight of lignin. The properties of the lignophenol obtained are the same as those obtained by the first method. Next, lignophenol is extracted with a liquid phenol derivative. Extraction of lignophenol from the phenol derivative phase can also be performed in the same manner as in the first method. Alternatively, the entire reaction solution after the concentrated acid treatment is poured into excess water, insoluble matters are collected by centrifugation, dialyzed, and dried. Acenolic alcohol is added to the resulting dried product to extract lignophenol. Furthermore, this soluble part is dripped at excess ethyl ether etc. similarly to the 1st method, and lignophenol is obtained as a deposit.

  Also in this method, the acetone soluble part can be used as a lignophenol solution for the secondary derivatization treatment.

  In these two types of methods, the second method, especially the latter, that is, the method of extracting and separating lignophenol with acetone or alcohol, is economical because the amount of phenol derivative used is small. is there. Moreover, since this method can process many lignocellulosic materials with a small amount of a phenol derivative, it is suitable for mass synthesis of lignophenol.

  A third specific method is to add a phenol derivative to lignin, add an acid, add excess water to separate a soluble part and an insoluble substance, dry the insoluble substance, and provide an antioxidant and an alkaline aqueous solution. Is added, and then solid-liquid separation (for example, centrifugation) is performed to obtain lignophenol (Patent Document 2).

  The lignophenol obtained by any of the above-described methods usually has at least three hydroxyl groups in the molecule and can be used in the present invention.

(Lactide)
The polylactic acid constituting the branched chain in the star-shaped branched chain, which is one feature of the lignophenol-polylactic acid complex of the present invention, is synthesized, for example, by ring-opening polymerization of lactide using lignophenol as an initiator.

  In the present invention, lactide refers to a cyclic diester obtained by dehydration condensation of two molecules of lactic acid. Therefore, it is a renewable resource. In the present invention, commercially available lactide can be used.

  Lactide has optical isomers. Lactic acid constituting lactide is obtained, for example, by lactic acid fermentation. In many cases, only L-form is obtained by fermentation of lactic acid bacteria. However, some microorganisms (eg, Lactobacillus lactis, Lactobacillus bulgaricus, Leuconostoc cremoris) produce D-form. By mixing several types of microorganisms including such microorganisms and subjecting them to fermentation, DL-form (racemic) lactic acid can be obtained, and DL-form lactide can be obtained by dehydration condensation. Alternatively, L-lactic acid can be racemized by a microorganism producing lactate racemase to produce DL lactic acid, followed by dehydration condensation to obtain DL lactide.

(Lignophenol-polylactic acid complex)
The lignophenol-polylactic acid complex of the present invention is a star-shaped branched polymer having at least three branched chains (that is, polylactic acid chains or lactic acid oligomer chains) containing lactic acid as a structural unit. Specifically, as schematically shown below, the carboxy terminus of polylactic acid is ester-bonded to each hydroxyl group of lignophenol having at least three hydroxyl groups in the molecule.

  The physical and chemical properties of the lignophenol-polylactic acid complex of the present invention vary depending on the ratio of lignophenol and polylactic acid chain. In general, the greater the proportion of polylactic acid chains, that is, the longer the polylactic acid chains, the greater the molecular weight. Lignophenol is insoluble in chloroform, but lignophenol-polylactic acid complex is soluble in chloroform. However, when the molecular weight increases, it becomes difficult to dissolve in acetone, dimethylformamide (DMF), and tetrahydrofuran (THF) in which lignophenol is soluble. Moreover, the glass transition temperature (Tg) decreases as the molecular weight of the lignophenol-polylactic acid complex increases.

  Such a lignophenol-polylactic acid complex is useful as a modifier for polylactic acid. For example, the crystallinity and toughness of polylactic acid can be reduced.

(Synthesis method of lignophenol-polylactic acid complex)
The method for synthesizing the lignophenol-polylactic acid complex of the present invention is not particularly limited. Preferably, the lignophenol-polylactic acid complex of the present invention is obtained by a step of ring-opening polymerization of lactide using lignophenol having at least three hydroxyl groups in the molecule as an initiator. Specifically, a polylactic acid chain obtained by ring-opening polymerization of lactide starting from lignophenol is prepared by placing lignophenol and lactide in a sufficiently dried container, adding a catalyst, and heating and stirring under an inert gas. The lignophenol-polylactic acid complex can be synthesized.

  The charging ratio of lignophenol and lactide is a mass ratio (lignophenol (LP) / lactide (LA)), preferably 1 / 0.5 to 1/50, more preferably 1/1 to 1/10. . When the ratio of lactide (LA) is larger than 50, the polylactic acid chain that is a branched chain becomes longer and the characteristics as polylactic acid are likely to appear. That is, the crystallinity increases and the melting point rises, so that it becomes difficult to function as a polylactic acid modifier. From the viewpoint of the physical properties of the resulting lignophenol-polylactic acid complex as a polylactic acid modifier, the charging ratio of lignophenol and lactide is more preferably 1/1 to 1/3.

  The lactide used for the synthesis may be any of L-form, DL-form, and D-form. When the obtained lignophenol-polylactic acid complex is added to polylactic acid, L-form is preferred in that the crystallinity of polylactic acid can be greatly reduced.

Examples of the catalyst for ring-opening polymerization of lactide include those usually used by those skilled in the art. Specifically, porphyrin aluminum complex, (n-C ₄ H ₉ O) ₄ Al ₂ O ₂ Zn, double metal cyanide complex, tin dichloride (SnCl ₂ ), tin 2-ethylhexanoate, tin octylate ( SnOct ₂ ), diethyl zinc-water or diethyl cadmium, aluminum triisopropoxide, titanium tetrabutoxide, zirconium tetrapropoxide, tributyltin methoxide, tetraphenyltin, lead oxide, zinc stearate, bismuth 2-ethylhexanoate, potassium Examples include alcoholates, antimony fluoride catalysts, and industrially stannous octanoate catalysts. From the viewpoint of yield, tin dichloride (SnCl ₂ ), tin 2-ethylhexanoate, and tin octylate (SnOct ₂ ) are particularly preferable. Although the usage-amount of a catalyst is not specifically limited, About 0.0001-5 mass parts is suitable with respect to a total of 100 mass parts of lignophenol and lactide, and about 0.05-1 mass part is preferable.

  Although it does not specifically limit as an inert gas, For example, nitrogen gas and argon gas are mentioned.

  The polymerization reaction can be performed at room temperature, but is heated as necessary. Preferably it heats in the range of 100 to 180 degreeC, More preferably, it heats to 120 to 160 degreeC. If it is less than 100 degreeC, since reaction rate becomes small, it is unpreferable. On the other hand, at a temperature higher than 180 ° C., there are disadvantages such as an increase in decomposition rate and vaporization of low molecular weight substances.

(Modification of polylactic acid by lignophenol-polylactic acid composite)
By adding the lignophenol-polylactic acid composite of the present invention to polylactic acid as a modifier, the crystallinity of polylactic acid can be reduced and the toughness can be improved.

  When the lignophenol-polylactic acid complex of the present invention is added to polylactic acid, for example, these are dissolved in a solvent such as chloroform and mixed, and then placed in a mold and dried to obtain a polylactic acid molded product. .

  The amount of lignophenol-polylactic acid complex added to polylactic acid varies depending on the properties of the complex. For example, when a complex having a charge mass ratio of lignophenol (LP) / polylactic acid (LA) = 1/2 is added, the amount of the complex added is 1 to 1 with respect to the total mass of polylactic acid and the complex. 20% by mass, preferably 5 to 15% by mass. If the added amount of the lignophenol-polylactic acid complex is more than 20% by mass, the polylactic acid and the complex are phase-separated and the physical properties of the polylactic acid are deteriorated. When the added amount of the lignophenol-polylactic acid complex is less than 1% by mass, the effect as a modifier is hardly exhibited. Moreover, in the charged mass ratio of the lignophenol-polylactic acid complex, the complex having a high ratio of lignophenol exhibits an effect similar to that obtained when lignophenol alone is added because its molecular weight is close to the molecular weight of lignophenol, On the other hand, since a complex having a high lactide ratio is close to the properties of polylactic acid, it is difficult to exhibit an effect as a modifier of polylactic acid.

(Example 1: Synthesis of lignophenol-polylactic acid complex)
Lignophenol (provided by Prof. Masamitsu Kajioka, Faculty of Bioresources, Mie University) and L-lactide (Tokyo Chemical Industry Co., Ltd.) are mixed at an arbitrary mass ratio (lignophenol (LP) / L-lactide (LA)) and octyl Using 1% by mass of tin oxide (Wako Pure Chemical Industries, Ltd.) based on the total amount, the mixture was heated at 130 ° C. for 24 hours under an argon atmosphere to obtain a lignophenol-polylactic acid complex.

  Size exclusion chromatography (SEC) was performed on lignophenol alone and the resulting lignophenol-polylactic acid complex.

The SEC measurement conditions are as follows:
Column: TSK-gel (α-3000, α-M) (manufactured by Tosoh Corporation)
Degasser: SD-8022 (manufactured by Tosoh Corporation)
Pump: DP-8020 (manufactured by Tosoh Corporation)
Detector: UV-8020 (manufactured by Tosoh Corporation), RI-8020 (manufactured by Tosoh Corporation)
Column oven: CO-8020 (manufactured by Tosoh Corporation)
Autosampler: AS-8020 (manufactured by Tosoh Corporation)
Standard substance: Polystyrene Eluent: Dimethylformamide (DMF) (LP / LA = 1/20 was not dissolved in DMF, so chloroform was used as the eluent)
Flow rate: 1.0 mL / min Temperature: 60 ° C

  The results are shown in FIG. The numbers in the figure represent the charge mass ratio of lignophenol (LP) / L-lactide (LA) (hereinafter sometimes referred to as the charge ratio). Compared to lignophenol alone, the molecular weight of the resulting complex is increased, so it is considered that polylactic acid is conjugated to lignophenol. In addition, it was found that by increasing the lactide charge ratio, the elution time in SEC was accelerated and the molecular weight was increased. As will be described below, purification yields were calculated for complexes with a charge ratio of 1/1, 1/2, and 1/3, where homopolymer formation was small. As the polylactic acid chain increased, the purification yield tended to decrease.

  Furthermore, purification by reprecipitation was examined for the lignophenol-polylactic acid complex having a charge ratio of LP / LA of 1/2. As a result of examining good and poor solvents, when reprecipitation was performed using acetone as a good solvent and toluene as a poor solvent, the peaks considered to be homopolymers and lactides around 17 to 19 minutes and around 20 minutes Disappeared and became almost a single peak as shown in FIG. FIG. 2 shows the RI peak before and after reprecipitation and the peak at the UV detector 310 nm. When the peak area ratio was measured, the peak areas of the homopolymer and lactide were 1% or less of the target lignophenol-polylactic acid complex.

(Example 2: Physical property confirmation of lignophenol-polylactic acid complex)
(1) Solvent resistance In order to confirm the solvent resistance of the lignophenol-polylactic acid complex, the solubility in an organic solvent was examined. The solvents used are chloroform, acetone, DMF, and tetrahydrofuran (THF). The results are shown in Table 2.

  Lignophenol alone did not dissolve in chloroform, but any lignophenol-polylactic acid complex dissolved in chloroform. It was also found that lignophenol alone dissolved in acetone, DMF, and THF, but it became insoluble in these solvents when the molecular weight was increased as in the case of a composite with a charge ratio of 1/10 and 1/20.

(2) Differential scanning calorimetry (DSC)
Next, in order to measure the thermal properties of the lignophenol-polylactic acid complex, differential scanning calorimetry (DSC) was performed using EXSTAR6000 (manufactured by Seiko Instruments). The measurement was performed in a nitrogen atmosphere using 1 to 5 mg of sample. Since the thermal history is reflected in the first measurement, the thermal history is erased by once raising the temperature to 200 ° C. to melt the sample and holding it for 10 minutes. Then, after cooling to −50 ° C. at 10 ° C./min and holding for 10 minutes, the peak when the temperature was raised at 10 ° C./min was measured. Table 3 shows the measurement results.

  As the molecular weight of the lignophenol-polylactic acid complex increased, the glass transition temperature (Tg) decreased. Moreover, since a clear melting peak could not be confirmed, it is considered that the crystallinity disappeared and an amorphous composite was obtained.

(3) Differential thermogravimetric measurement (TG / DTA)
Further, the lignophenol-polylactic acid complex was subjected to differential thermogravimetric measurement (TG / DTA) using SSC / 5200 (manufactured by Seiko Instruments). The measurement was performed using a sample of 1 to 5 mg in a nitrogen atmosphere at a heating rate of 5.0 ° C./min. The results are shown in FIG. The pyrolysis point was defined as the temperature at which the weight was reduced by 3% by weight compared to the initial weight.

  The formation of the lignophenol-polylactic acid complex improved the thermal decomposition temperature compared to lignophenol alone.

(Example 3: Modification of polylactic acid with lignophenol-polylactic acid complex-1)
(1) Production of polylactic acid sheet containing lignophenol-polylactic acid composite Lignophenol-polylactic acid composite and polylactic acid prepared at various LP / LA feed ratios were mixed in the proportions shown in Table 5 below. 1 g thereof was dissolved in 6 mL of chloroform. This solution was poured onto a glass plate and made uniform with an applicator having a thickness of 200 μm. After drying at room temperature for 12 hours, it was taken out from the glass plate and then further dried under reduced pressure for 1 day. Finally, the sheet was obtained by heating and drying at 70 ° C., which is higher than the glass transition temperature (Tg) of polylactic acid, for 2 hours. The obtained sheet | seat became thickness of 50-100 micrometers.

(2) Crystallinity The problem that polylactic acid is hard and brittle is considered to be due to the high crystallinity of polylactic acid. Therefore, the degree of crystallinity of the polylactic acid sheet containing the lignophenol-polylactic acid complex was determined from the melting enthalpy at the time of melting measured by DSC. The melting enthalpy when polylactic acid was completely crystallized was 93.6 J / g, and the melting enthalpy of each sheet was determined in comparison with this. The results are shown in Table 5.

  By adding the lignophenol-polylactic acid complex to polylactic acid, it was confirmed that the crystallinity was lowered as compared with polylactic acid. In particular, it was found that by adding a lignophenol-polylactic acid complex having an LP / LA charge ratio of 1/2, the crystallinity of polylactic acid is greatly reduced. This is considered to be due to the fact that the molecular weight of the lignophenol-polylactic acid complex having a charging ratio of 1/1 is close to the molecular weight of lignophenol, so that the crystallinity is hardly lowered as in the case of adding lignophenol alone. . Further, since the lignophenol-polylactic acid complex having a charging ratio of 1/3 is closer to the properties of polylactic acid, it is considered that the crystallinity is hardly lowered as in the case of polylactic acid alone.

  About glass transition temperature (Tg) and melting | fusing point (Tm), compared with the sheet | seat of polylactic acid alone, there is almost no fall also in the polylactic acid sheet containing a lignophenol-polylactic acid complex, and heat resistance similar to polylactic acid It was found that it retains sex.

(3) Transparency Transparency was examined for a polylactic acid sheet produced by adding 5% by mass of a lignophenol-polylactic acid complex having an LP / LA charge ratio of 1/2 with the lowest crystallinity. Sheets made of polylactic acid alone are transparent. On the other hand, since lignophenol itself is colored light pink, the polylactic acid sheet containing the lignophenol-polylactic acid complex was colored light brown. When the mark placed on the desk was covered with this sheet, it could be clearly confirmed visually and the transparency was maintained.

(Example 4: Modification of polylactic acid by lignophenol-polylactic acid complex-2)
A uniaxial extension test was performed on polylactic acid containing a lignophenol-polylactic acid complex having an LP / LA charge ratio of ½ with the lowest crystallinity. The uniaxial extension test was performed on a test piece having dimensions of H40 mm × W5 mm × D50 to 100 mm using EZ Graph (manufactured by Shimadzu Corporation) with a crosshead speed of 5 mm / min and a distance between grippers of 10 mm. The results are shown in FIG.

  By adding 5% by mass of the lignophenol-polylactic acid composite with respect to the total mass of the polylactic acid and the composite, the toughness of polylactic acid was most improved. However, it has also been found that the toughness decreases when added in an amount of more than 5 mass%. This is because, in general, in the case of a crystalline resin, if the amount of the plasticizer is increased, bleeding tends to occur on the surface. Therefore, for the lignophenol-polylactic acid composite, the toughness is increased. It is thought that the trend has decreased.

  Next, lignophenol alone, a lignophenol-polylactic acid complex having a charging ratio of 1/1 or 1/3, whose crystallinity did not decrease so much, was prepared by adding 5% by mass with respect to polylactic acid. A uniaxial extension test was performed on the polylactic acid sheet. The results are shown in FIGS.

  As shown in FIG. 5, when lignophenol alone was added to polylactic acid, lignophenol did not mix well with polylactic acid, and both stress and toughness decreased. On the other hand, as shown in FIG. 6, when the lignophenol-polylactic acid complex is added, the toughness is not limited even if the LP / LA is a complex having a charging ratio of 1/1 to 1/3. Improvement was seen.

(Example 5: Synthesis of lignophenol-polylactic acid complex using D- or DL-lactide)
A lignophenol-polylactic acid complex having a charge ratio of lignophenol / lactide (LP / LA) of 1/2 was synthesized using D- or DL-lactide (Tokyo Chemical Industry Co., Ltd.). The synthesis conditions were the same as in Example 1 above. Each obtained lignophenol-polylactic acid complex was subjected to size exclusion chromatography (SEC) and differential scanning calorimetry (DSC). The measurement conditions for SEC and DSC are the same as those in Examples 1 and 2, respectively. The results are shown in Table 7. For comparison, the results of lignophenol-polylactic acid complex using L-lactide are also shown.

  As can be seen from Table 7, a lignophenol-polylactic acid complex having almost the same molecular weight as that obtained when the L-form was used also when the DL-form and D-form lactide were used. The glass transition temperature (Tg) of the lignophenol-polylactic acid complex using D-form lactide was slightly lowered. In addition, no lignophenol-polylactic acid complex showed a melting peak, and a lignophenol-polylactic acid complex having no crystallinity was obtained.

(Example 6: Modification of polylactic acid with lignophenol-polylactic acid complex-3)
A polylactic acid sheet in which 5% by mass of a lignophenol-polylactic acid complex synthesized using L-, D- or DL-lactide at a charging ratio of 1/2 is added to the total mass of polylactic acid and the complex. Was produced in the same manner as (1) in Example 3 above. About these polylactic acid sheets, the crystallinity was measured by DSC. The results are shown in Table 8.

It was found that when the lignophenol-polylactic acid complex synthesized using L-lactide was added to polylactic acid, the crystallinity decreased most. The polymer chains of optically active poly-L lactic acid and poly-D lactic acid form a symmetrical helical structure, and when these are mixed at a ratio of 1: 1, a stereocomplex is formed (Non-patent Document 4). Therefore, when a lignophenol-polylactic acid complex is synthesized using DL-lactide, the crystallinity is considered to decrease if a stereocomplex is formed, but conversely, the crystallinity is increased. This is thought to be because the stereocomplex was not formed because the polylactic acid chain branched from lignophenol was short. Furthermore, if a stereo complex is formed, an increase in melting point is expected. However, since it is almost the same as the melting point of polylactic acid alone (T _m = 169 ° C.), it is considered that a stereo complex is not formed.

(Example 7: Modification of polylactic acid with lignophenol-polylactic acid complex-4)
5% by mass of lignophenol-polylactic acid complex synthesized using L-, D- or DL-lactide at a charge ratio of LP / LA = 1/2 is added to the total mass of polylactic acid and the complex. The polylactic acid sheet thus manufactured was subjected to a uniaxial extension test in the same manner as in Example 4. The results are shown in FIG.

  It was found that the toughness is most improved in the polylactic acid containing the lignophenol-polylactic acid complex synthesized using L-lactide having the lowest crystallinity. When DL-form or D-form lactide was used, a slight modification effect was observed.

  ADVANTAGE OF THE INVENTION According to this invention, the composite_body | complex (lignophenol-polylactic acid composite_body | complex) of lignophenol and polylactic acid which are plant-derived materials is provided. This composite is used as a modifier of polylactic acid, and can reduce the crystallinity of polylactic acid and improve toughness. It also has the effect of plasticizing polylactic acid. Furthermore, this complex can also be used as a compatibilizer between polylactic acid and other polymers. As described above, since the crystallinity is high and the melting point is also high, it is possible to modify the disadvantage of polylactic acid that the workability when used in various applications such as resin raw materials and paints is poor. Therefore, agricultural materials (sheets, films, etc.), food packaging materials (food packaging films, sheets, bags, etc.), medical materials, and other packaging materials (clothing, daily miscellaneous goods packaging sheets, films, bags, etc.) The range of application of polylactic acid to such as can be expanded.

It is a chromatogram which shows the result of the size exclusion chromatography (SEC) about lignophenol independent and various lignophenol-polylactic acid composites. It is the chromatogram of SEC by RI detection before and behind reprecipitation and UV detection about the lignophenol-polylactic acid composite whose charge mass ratio of LP / LA is 1/2. It is a graph which shows the relationship between the temperature by residual thermogravimetry (TG / DTA), and residual weight about a lignophenol-polylactic acid composite_body | complex. It is a tensile stress-strain curve in the uniaxial extension test of the polylactic acid containing the lignophenol-polylactic acid composite whose charging mass ratio is LP / LA = 1/2. It is a tensile stress-strain curve in the uniaxial extension test of the polylactic acid containing the lignophenol-polylactic acid composite whose charging mass ratio is LP / LA = 1/2, and polylactic acid alone. It is a tensile stress-strain curve in the uniaxial extension test of polylactic acid containing the lignophenol-polylactic acid composite of various preparation mass ratios. It is the tensile stress-strain curve in the uniaxial extension test of polylactic acid containing the lignophenol-polylactic acid composite synthesize | combined using L-, D-, or DL-lactide.

Claims (3)

A polylactic acid modifier comprising a lignophenol-polylactic acid complex having at least three branched chains of polylactic acid in the molecule. A method for producing a modifier for polylactic acid according to claim 1, comprising a step of ring-opening polymerization of lactide using lignophenol having at least three hydroxyl groups in the molecule as an initiator. The manufacturing method of Claim 2 whose said lactide is a L-form.

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