As we all know, when it comes to the safety of fiber materials (natural fibers, rayon, synthetic fibers) and their raw materials, they cannot simply stay in the direct safety of people, but also consider the earth ecosystem in which we live. Safety, that is, the suppression and reduction of the global environmental load. In recent years, the global warming gas that has become a problem has been increasing, affecting the global environment. Therefore, it is not only from the local point of view on the safety of people and the natural environment, but also from the perspective of the entire global environment in terms of time and space.

In addition, fiber products use a variety of chemicals (solvents, coagulants, oils, antibacterials, weathering agents, fire retardants, antifoulants, dyes, finishing agents) in their manufacturing and processing. And energy, these chemicals must also be considered from the same point of view, and the energy used should also be considered as energy-saving from the viewpoint of environmental load reduction.

Synthetic fiber polylactic acid fiber and its raw materials not only have safety to humans and the natural environment. In addition, it also has inherent antibacterial properties, fire resistance, and weather resistance without adding any harmful chemicals.

1. Evaluation of environmental load

In comparison with conventional fiber materials, the environmental load of polylactic acid fibers was evaluated objectively and quantitatively using life cycle evaluation (LCA). That is, the carbon dioxide emissions from the collection of the raw materials of the polylactic acid through the lactic acid fermentation, the polymerization, the fiberization (manufacturing and processing), and the waste treatment after use (that is, from the cradle to the cemetery) are quantitatively evaluated.

Equivalent to the collection of raw materials from polylactic acid (seeding, fertilizing and spreading the corn, harvesting), carbon dioxide emissions per ton of resin produced by starch preparation, saccharification, and lactic acid fermentation to produce polylactic acid resin (sliced) , published by the American Nature Works. Secondly, the amount of carbon dioxide emitted from the fiber slicing process by melt spinning from the resin chips, there is no official data on the existing synthetic fibers, but generally the proportion in the whole process is very low, especially polylactic acid, especially high energy. There is no big difference (same) between the materials. Finally, consider the amount of carbon dioxide emitted during combustion or re-recycling (biooxidation in biodegradation, also converted to carbon dioxide), where emissions can be theoretically predicted from chemical structures.

Each of these values according to the material together, the conventional viscose rayon fiber is a regenerated cellulose 14680CO ₂ Kg / t, typical of synthetic polyester fibers 6443 CO ₂ Kg / t, and polylactic acid fibers only However, 3650 CO ₂ Kg/t has significant environmental load characteristics (Table 1). Cellulose viscose is a biodegradable fiber derived from plants. The raw material itself does not contain one drop of petroleum. However, since a large amount of energy (petroleum) is used in the production and processing of fibrillation, carbon dioxide above the petroleum system is released. In addition, companies that have withdrawn from the company in recent years have continued to export chemical substances that are harmful to humans and the environment in addition to carbon dioxide.

Table 1 Environmental impact and combustion characteristics of lactic acid fiber and other fiber materials

Note: The CO2 emission data of viscose fiber is based on the data of viscose film cellophane produced by the same viscose method. The heat of combustion of viscose fiber is wood data.

2, polylactic acid and its constituent monomer lactic acid safety

2.1 Basic characteristics and safety of lactic acid

Since polylactic acid is decomposed in the human body and in the natural environment during use or after use, it is finally decomposed into lactic acid as a constituent unit thereof, so it is first necessary to understand lactic acid and its safety.

Humans learned to use fermented food preservation technology in the process of changing lifestyles from hunting life to farming and animal husbandry about 10,000 years ago. Lactic acid is a natural organic compound that has been coexisting with humans for a long time. However, it was first discovered as lactic acid in the second half of the 18th century.

The Swedish chemist Carl Wilhelm Scheele (1742–1786) fermented the milk in 1780, analyzed the acid obtained, and found a new organic acid different from acetic acid, etc., named lactic acid. Then, in 1839, lactic acid was synthesized by fermentation for the first time using carbohydrate as a raw material.

Lactic acid is a colorless viscous liquid, and most of the products produced by fermentation are accompanied by a weak fermentation odor. Lactic acid is a strong organic acid, the specific gravity is 1.22, and the melting point of L-lactic acid and D-lactic acid is 52.8 ° C (the melting point of DL-lactic acid is 16.8 ° C), and the boiling point is 125 to 140 ° C. Lactic acid has a mild and refreshing sour taste and is used as various food additives (sour flavoring agents, pH adjusters, food preservatives, fermentation assistants, softeners) without changing the original taste.

However, there is a saying that "if fatigue is accumulation of lactic acid". For example, post-exercise fatigue is thought to be “lactate in blood and muscle.” Lactic acid is an old waste or fatigue substance of exercise. This may be said because the concentration of lactic acid in muscles and blood rises after strenuous exercise. However, in fact, high-efficiency energy for fatigue recovery should consider the metabolic production of lactic acid, and it is actually confirmed that if it is 30 to 50 minutes, it will return to the original level. Needless to say, lactic acid is an important energy source for life activities, and is easily converted to energy compared to sugar and fat, and because it is chemically stable, L-sodium lactate is utilized as an electrolyte for infusion and peritoneal dialysis.

As a monomer unit of polylactic acid, lactic acid CH ₃ C*H(OH)COOH, because the atoms and molecules bonded on the carbon atom are 4 and different (H, CH ₃ , OH, COOH), carbon in this case The atom is called asymetric carboon, and there are two different forms of molecules in the three-dimensional structure. However, since natural organisms including humans usually synthesize L-lactic acid, there is a concern that D-lactic acid is toxic. Indeed, D-lactic acid cannot be metabolized in the usual metabolic pathway of L-lactic acid. If it is ingested in a large amount, it will increase the acidity in the blood and become a cause of acidemia.

However, it is known that after about three months after the production in our body, D-lactic acid is converted into L-lactase lactate racemase. Moreover, D-lactic acid can be neutralized and discharged in any form. This is very clear, and since there is no such question in subsequent research, it is now equivalent to L-lactic acid.

By the way, the acute toxicity (LD ₅₀ ) of D-lactic acid was 4.875 g/kg in laboratory mice and 3.73 g/kg in normal mice. In 1973, L-lactic acid, D-lactic acid and DL-lactic acid were all in WTO. The range of daily intake limits was removed. In fact, lactic acid which has been produced in Japan from the 1970s to 1980s and has been used as a food additive is a racemic variant synthesized by a chemical synthesis method (equal amount of a mixture containing D-lactic acid and L-lactic acid). Currently, fermented L-lactic acid used as an additive also contains 1% to 5% of D-lactic acid. However, the United Nations' FAO/WHO Joint Food Additives Special Committee has advised that “D-lactic acid and DL-lactic acid should not be used in food for infants and young children” because they cannot metabolize D-lactic acid in children (less than half a year after birth).

2.2 Polylactic acid safety

The polylactic acid is a crystalline aliphatic polyester having a melting point of 160 to 180 ° C and a glass transition temperature of about 60 ° C. Polylactic acid is excellent in moldability in various biodegradable plastics, and can be subjected to melt extrusion molding represented by fibers, nonwoven fabrics, and films to injection molding, spray molding, and foam molding. Further, since the film and the fiber are subjected to directional crystallization accompanying the drawing and heat treatment operations, improvement in mechanical properties and thermal properties has been sought. Further, various shapes can be imparted from the film for forming, the nonwoven fabric, and the laminate of the paper by heat setting (vacuum, pressure forming) and heat compression molding.

Polylactic acid is a hydrophobic crystalline polymer composed of an aliphatic polyester. As long as it is left for a long time without being exposed to high temperature and high humidity (50° C. or higher and relative humidity 85% or more), it hardly causes hydrolysis and is stable. of. In addition, it is suitable for use as a general food container including oily foods because of its oil resistance, water resistance and volatility. Further, microorganisms and enzymes which decompose high-molecular-weight polylactic acid are extremely rare in nature, and even as a fermented food container, there is a texture which can be safely used for a certain period of time.

In fact, it is considered to be basically lactic acid, lactic acid oligomer, (lactic acid linear dimer, trimer, tetramer, etc.) and lactide when it is used as a food container or a packaging material. (cyclic dimer of lactic acid), these are lactic acid (usually containing about 20% of oligomers) in food hygiene laws widely used as food additives. Lactic acid oligomers and lactide are rapidly hydrolyzed into lactic acid in food or digestive organs.

Polylactic acid is a constituent unit of natural organic compound lactic acid which is also present in living organisms, and is excellent in safety and food hygiene among various biodegradable plastics or bioplastics. Further, unlike polylactic acid, which is different from biodegradable plastics, polylactic acid does not easily produce microorganisms and molds on the surface of the material, and there is no eating according to the test using mice and cockroaches.

Next, regarding the current state of the world in the use of polylactic acid for food containers and packaging materials, and the status of certification. In Europe, the EEC Directive (Directive 90/128/EEC) issued in 1990 is the basic content, and if the monomer is safe, the polymer is a good monolithic position. According to the toxicity test that has been carried out, there is a list of permitted free imports of monomers and additives that are registered even if used. Lactic acid was posted on the list of permitted free imports in the 96/11/EC, which was subsequently amended. In response to these EU directives, domestic laws in European countries have been reorganized.

In the United States, according to the FFDCA (Federal Food and Drug Cosmetics Act) application as an indirect food additive, among the five types of applications permitted by law, except for Nature Works, which is a self-declaration of safety by GRAS (Generally Recognized As Safe) It is also certified as FCN (Food Contact Nortification) No. 178 (temperature zone sequence: B to H). The sequence B is in the field of boiling water injection temperature boiling at 100 ° C for 30 minutes, and shows the potential as a food filter material such as a tea bag, which is remarkable.

In Japan, polylactic acid was passed by the Ministry of Health and Welfare Notice No. 370 (Revised in Showa 57: The Notice No. 20), which was established in the 34th year of the Showa Food and Environmental Hygiene Law. There is no legal problem. In addition, polylactic acid is registered in the list of permitted free imports of the Health and Welfare Association (JOHSPA), which is a more stringent industry group's independent standard, and then additional applications are required for additives.

3, environmental low load type high functional fiber - polylactic acid fiber

In general, chemical fibers are often added with various additives (antibacterial agents, weathering agents, fire retardants, flame retardants, etc.) in order to impart high functionality as fibers. However, in addition to the increased cost due to the addition of additives, the safety of these additives has also been questioned. Often, these additives are mostly substances that are substantially harmful to humans and the natural environment, and are now only used in low concentration ranges where no harmfulness is found. However, even if the safety is guaranteed during temporary use, the possibility of surface aging cannot be denied when the waste is disposed after use.

Ideally, these additives are not added, and it is best that the materials themselves have these high functionality. In fact, the polylactic acid fiber raw material is derived from plants, and in addition to being a completely biodegradable environmentally low-load material, it has been found to have excellent antibacterial properties, fire resistance, and weather resistance without adding any additives. It can be said that polylactic acid fiber can be regarded as a high-performance fiber having excellent functional literacy.

3.1 Antibacterial (static bacteria)

According to the new standard for antibacterial and deodorant processing of fiber products using Staphylococcus aures ATCC6538P, polylactic acid fiber (Taramark: Unijika trademark) was evaluated and found to be much higher than the qualified value (static) The bacteriostatic activity value and the bactericidal activity value of the bacterium activity value of 2.2 or more. After 10 washes in advance, or by mixing half of other fibers such as natural cotton, the antibacterial activity can be maintained substantially. The antibacterial action of polylactic acid is not only the above-mentioned Staphylococcus aureus as a standard strain, but also Gram-negative bacilli such as Escherichia coli and Pseudomonas aeruginosa.

It is estimated that this is due to the static action of a substance containing a very small amount of lactic acid or oligomer in polylactic acid. That is to say, since a very small amount of lactic acid in the material leaches a part of the surface of the material, the surface of the material is kept weakly alkaline as in the human skin, preventing the adhesion and reproduction of microorganisms such as bacteria and mold. In general, biodegradable plastics tend to be more susceptible to epidemics than conventional plastics, with the exception of polylactic acid, which is safe and hygienic as a living/sanitary material, food/medical material, or agriculture, forestry, and horticultural materials. The above is suitable. In fact, from the purchase of bath polylactic acid fiber (Termak) towel, long-term consumer feedback, compared with the traditional product (nylon fiber), it is difficult to bring fragrance.

Regarding the antibacterial property of the polylactic acid fiber, the selection of the raw material polylactic acid resin and the spinning conditions were mainly carried out, and the influence of the spinning oil agent, the influence of the weaving and knitting processing oil agent, and the dyeing and finishing agent were not found. The situation of impact needs to be clarified separately.

3.2 Fire resistance

The oxygen resistance index (LOI value) of the polylactic acid fiber or the spunbonded nonwoven fabric was evaluated by the flammability test according to JIS K 7201, and the results showed that the polylactic acid fiber was 23 to 24 (polyester fiber: 20 to 21), and the polymerization was carried out. The lactic acid spunbonded nonwoven fabric is more surprising, showing 28 to 30 close to the aramid fiber, and was found to have excellent fireproof properties. In addition, the burning test (horizontal method) from ASTM E1354 and the US Federal Automotive Safety Specification FMVSS 302 also shows that the polylactic acid fiber has a good fire extinguishing property after being ignited, and the amount of gas generated during combustion is also less than that of the polyester fiber. This characteristic is an inherent characteristic of polylactic acid fiber and its spunbonded nonwoven fabric material, and no harmful halogen or phosphorus-based disaster-preventing and flame retardant is added.

According to the above findings, the raw material characteristics and fiber shape of the depolymerized lactic acid fiber (Taramark: Unijika brand) were optimized, and the polylactic acid fiber was successfully obtained by the Japan Disaster Prevention Association. Fire protection product certification. For the cotton wool which is recognized as a pillow, bedding, cloth doll, etc., is a composite short fiber HP8F which has a spontaneous curling property, and has excellent bulkiness and cushioning property due to the discovery of spiral micro-curl. Resilience and fatigue resistance. This product is difficult to expand even when it is fired, and it has a low combustion heat and a small amount of gas generated. It is expected to be used as a decorative material for bedding, households, and vehicles.

3.3 Light and weather resistance

Polylactic acid fiber is an aliphatic polyester and cannot be said to be strong against ultraviolet rays and high-energy radiation. However, compared with the polyester (PET) fiber which is the same polyester, it is not only light-resistant (Fade-Ometer), but also exhibits excellent weather resistance in the weathering test (Sunshine Weather Meter) accompanying rain. These tendencies have also been confirmed in actual outdoor exposure tests including polylactic acid fibers and spunbonded nonwoven fabrics, and are necessary conditions for agricultural and forestry, gardening, civil engineering, and building materials used outdoors.

On the other hand, high-energy radiation such as a gamma line differs depending on the amount of the irradiation line, but it is also decomposed, and it is necessary to pay attention to sterilization for medical supplies and the like. That is to say, the amount of the irradiation line is below 25 kGry, causing a partial crosslinking reaction on the surface of the material, tending to be hydrophobic, and the mechanical strength is slightly deteriorated, and it can be recommended as a condition for gamma sterilization. However, it has also been reported that if 100kGry is reached, the molecular chain will be broken and the mechanical strength will be significantly reduced.

4. Reduced environmental load in polylactic acid fiber processing and management engineering

Polylactic acid fiber has been put to a certain level of practical use, but there are several technical problems (durability, dyeability, ironing resistance, dimensional stability, curl resistance, bending wear resistance, etc.) that must be solved in the future. Most of these problems are basically that the polylactic acid produced in the market now has a melting point decrease and a crystallization rate retardation caused by the arbitrary copolymerization of L-lactic acid and a small amount of D-lactic acid. Regarding the method and empirical data for solving these problems with little increase in cost, it is considered separately.

Here, from the viewpoint of the reduction of the environmental load in the processing and management engineering, it is assumed that the problem of solving the problem is to be considered as two aspects of the development of the material for the clothing material, dyeing property and ironing resistance.

First, since the polylactic acid fiber is hydrolyzed, it cannot be dyed at a high temperature and high pressure of 120 ° C like the polyester (PET) fiber. Since the polylactic acid fiber having a Tg lower than the polyester fiber by 10 ° C or more can be dyed at a lower temperature than the polyester fiber, a disperse dye and a dyeing condition for a polylactic acid fiber which can be dyed at a low temperature (105 ° C) have been established. In addition, for the dyeing and finishing industry with energy multi-consumption structure, low temperature dyeing is also an ideal direction considering energy saving and environmental load reduction.

For example, the polylactic acid fiber environmental protection bag (trademark is kna Ppus) developed by Japan Jinjin Fiber Co., Ltd. and the Fujing County Industrial Technology Center has realized 1 dried persimmon from the traditional colors of Japan... 2 plain colors... milky white, 3 yellow green... green, 4 red vines... purple, 5 red... brown, 6 blue... blue, 7 gray blue... grey The color of the 7 colors changes. The results of the dye fastness test (JIS L 0844 A-2 method) were confirmed to be 4 to 5 grades, and there was no problem such as fading. The product is sold at the domestic and international stores of seven famous countries including Europe and the United States, and is well received by the Smithsonian Museum, the world's largest museum.

Regarding the ironing resistance, it was hardly found that ironing was carried out at 160 ° C in the same manner as the polyester fiber. Originally, similar to dyeability, the fabrics with different thermal properties and mechanical properties of the polyester (PET) fibers were ironed under the same conditions as the polyester fabrics, and lacked their own scientific basis. The polylactic acid fiber should have the best ironing conditions using a lower temperature, as well as the optimum spinning, processing conditions, weaving, knitting, dyeing and finishing conditions suitable for its chemical structure.

5, the conclusion

From the above, the application of polylactic acid and its fiber in the field of general life, clothing, and industrial materials (non-medical fields used in vitro) for commercial mass production of polylactic acid is discussed, and the safety of human and natural environment is discussed. It is known that polylactic acid has been used in a very small amount in the past, and it is used as a medical biodegradable absorbent material (screw fixation screw, suture drug carrier, suture, tissue regeneration foot material, etc.).

Here, the medical polylactic acid resin used and the commercial mass production are basically unchanged, but the manufacturing environment conditions and safety management standards for the materials used in the living body are very strict, and the evaluation of their safety will also be required. In addition, the specified specifications are tested.

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