Biodegradable polymer materials

Abstract

This specification provides various bio-based biodegradable materials, films, packaging materials, and methods for producing the same. For example, these components may include materials that use polyvinyl alcohol (PVA) as a base and contain lactic acid (LA) in the form of polylactic acid (PLA). In this regard, various PVA-based copolymers are synthesized in which PLA oligomers are grafted as a result of synthesis from LA. The result is a PVA-g-PLA copolymer, which is different from a blend of PVA and PLA.

Description

Technical Field

[0001] This application relates to biobased biodegradable polymer materials such as biodegradable packaging for food and a method for producing the same.

Background Art

[0002] Packaging materials are used to contain and protect various articles during storage and transportation. Conventionally, various materials such as cardboard, plastics, metals, and glass have been used for packaging. However, many packaging materials are discarded in landfill sites after use. Non-renewable resources such as petroleum have been used in the production of conventional non-biodegradable plastics. Plastic-based packaging may be desirable because of its low cost, but packaging materials containing such plastics can remain in the environment for a long time after disposal.

[0003] There is an increasing demand for using renewable resources and / or materials that are more easily decomposed in the environment for the production of packaging materials. For example, polylactic acid (PLA) is a biobased biodegradable polymer formed from lactic acid (LA) and can be used for packaging. However, PLA is often brittle and has a high glass transition temperature and melting point. In other words, although PLA is biobased and biodegradable, it may not be suitable for certain types of packaging because it cannot provide the required physical and chemical properties, etc.

[0004] For example, PLA may not be suitable for food packaging depending on the moisture content, pH, shelf life, and other attributes of the food and the requirements of the packaging. However, since PLA is a renewable material and has biodegradability, it may be desirable to combine it with other components to form food packaging. From this perspective, it may be desirable to provide a biobased biodegradable material containing PLA that can be used as packaging for seasonings such as ketchup.

[0005] Polyvinyl alcohol (PVA) is a synthetic polymer material used in a wide range of applications, including medical and pharmaceutical uses, due to its biocompatibility. However, PVA films can sometimes have drawbacks such as brittleness, low elongation at break, poor water resistance, and poor processability.

[0006] Blends of PVA and PLA have also been used to improve material performance. However, these blended forms may still not provide the performance and functionality suitable for certain applications, such as food packaging. [Overview of the project]

[0007] This specification provides various bio-based biodegradable materials, films, packaging materials, and methods for producing the same. For example, these components may include polyvinyl alcohol (PVA)-based materials containing lactic acid (LA) in the form of polylactic acid (PLA). In this regard, various PVA-based copolymers are synthesized in which PLA oligomers are grafted as a result of synthesis from LA. The result is a PVA-g-PLA copolymer, which is different from a blend of PVA and PLA.

[0008] The amounts of constituent elements and reactants can be adjusted to provide the desired performance in the resulting material and packaging. Similarly, the parameters of the reaction and process can also be adjusted to achieve the desired performance and functionality.

[0009] For example, the ratio of polyvinyl alcohol to lactic acid (PVA:LA ratio), the amount of catalyst, the total amount of water used as a solvent, and the synthesis time and temperature can be adjusted individually or in combination as needed. For instance, the ratio of PVA to PLA may range from approximately 1:1 to approximately 1:4. The synthesis time can also be varied from approximately 5 hours to approximately 7 hours to achieve the desired function.

[0010] The copolymer may be further crosslinked. For example, crosslinking can be performed using crosslinking agents such as citric acid or succinic acid. Furthermore, crosslinking of the copolymer can be accelerated as desired using high temperatures, ultraviolet irradiation, etc.

[0011] This material can be combined with other materials to form films. Similarly, by forming this material into a polymer film and then bonding or coating it with other films, desired properties can be obtained.

[0012] The resulting material is a bio-based copolymer possessing desirable transparent film properties, high flexibility, and high cohesive strength. The obtained material can be easily sealed into a sachet by welding under simple laboratory conditions.

[0013] These and other aspects can be more easily understood from the following description. [Brief explanation of the drawing]

[0014] [Figure 1] This is a differential scanning calorimetry (DSC) plot of copolymer 12 before drying. [Figure 2] This is a DSC plot of copolymer 12 after drying at 80°C for 100 minutes. [Figure 3] This is a DSC plot of copolymer 13 before drying. [Figure 4] This is a DSC plot of copolymer 13 after drying at 80°C for 100 minutes. [Figure 5] This is a DSC plot of copolymer 14 after drying at 80°C for 100 minutes. [Figure 6] This is a DSC plot of copolymer 15 after drying at 80°C for 100 minutes. [Figure 7] This is a plot of the molecular weight distribution of copolymer 6. [Figure 8] This is a DSC plot of copolymer 6. [Figure 9] This is a DSC plot of copolymer 6. [Figure 10]DSC plot of copolymer 6. [Figure 11] DSC plot of copolymer 6. [Figure 12] FTIR plot of copolymer 6. [Figure 13] TGA plot of copolymer 6. [Figure 14] DSC plot of an additional sample of copolymer 6. [Figure 15A] Plot and distribution of sample A. [Figure 15B] Plot and distribution of sample A. [Figure 15C] Plot and distribution of sample A. [Figure 16A] [[ID=)24]]Plot and distribution of sample B. [Figure 16B] Plot and distribution of sample B. [Figure 16C] Plot and distribution of sample B. [Figure 17A] Plot and distribution of sample C. [Figure 17B] Plot and distribution of sample C. [Figure 17C] Plot and distribution of sample C. [Figure 18A] Plot of XPS analysis. [Figure 18B] Plot of XPS analysis. [[ID=)47]]<) [Figure 18C] Plot of XPS analysis. [Figure 19] Graph of CO2 and O2 content changes of copolymer 6. [Figure 20] Graph of CO2 and O2 content changes of sample soil standard. <0000!07> [Figure 21] Table of characteristics of various copolymer materials.

Mode for Carrying Out the Invention

[0015] First, unless otherwise specified, all percentages and ratios in this specification are based on weight. Furthermore, it should be noted that the materials described herein relate to copolymers, etc., with PVA as the base material and LA grafted onto the PVA material. This is different from blends of PVA and LA or PLA. The preparation methods, properties, and performance differ from those of blends, as will be described in more detail below.

[0016] This specification provides various biodegradable films, materials, laminates, packaging, and methods for producing them. These components can be considered bio-based and can be used to form polymers, copolymers, etc., in the form of polymer films. Similarly, these materials can also be used to form pellets, which are used to form polymer films in industrial processing and packaging systems.

[0017] The materials described herein are generally obtained by synthesizing PVA-based copolymers grafted with polylactic acid (PLA) oligomers as a result of synthesis from lactic acid, thereby forming PVA-g-PLA. In other words, PVA-g-PLA copolymers can be prepared in which the PLA chain is initiated by initiating the polymerization of lactic acid on the PVA backbone. These polymerizations can be achieved using various catalysts as described below.

[0018] By forming PVA-g-PLA, it is possible to reduce the solubility of the resulting material, improve its mechanical properties, and enhance its barrier properties. By bio-combining the two materials, the shortcomings of conventional PVA and PLA or LA blends can be improved.

[0019] For example, PVA-g-PLA materials exhibit varying levels of water solubility depending on the manufacturing conditions and components of the synthesis and polymer blend. These materials exhibit high mechanical strength and have a wide range of mechanical properties, from hard and brittle to those similar to thermoplastic elastomers, depending on the manufacturing conditions and components of the synthesis and polymer blend. Furthermore, the hydrophilicity of the copolymer can be obtained to various degrees, as solubility can be controlled depending on the synthesis conditions and the ratio of raw materials used.

[0020] The PVA-g-PLA materials described herein have many applications because copolymers can be formed to have a variety of properties and functional performance. These materials are bio-based and can be biodegradable, making them particularly suitable as alternatives to other non-biodegradable plastics and similar materials. For example, the materials described herein can be used as packaging for various foods with different moisture content, pH, oxygen sensitivity, etc. In this regard, PVA-g-PLA materials can be used with condiments such as ketchup. Other exemplary condiments include mayonnaise, mustard, relish, ponzu sauce, oil, vinegar, tartar sauce, frying sauce, soy sauce, and the like.

[0021] Biodegradable ketchup packaging presents challenges stemming from the moisture content and pH of the ketchup ingredients, which must be balanced with the solubility and biodegradability of the packaging material. The material must be able to contain ketchup and be biodegradable and / or water-soluble.

[0022] Similarly, packaging materials must also provide adequate barrier properties. For example, packaging materials must offer appropriate water vapor and oxygen permeability. Packaging materials are also required to provide an appropriate shelf life.

[0023] The components used to form the PVA-g-PLA material are not particularly limited. Generally, the components include, but are not limited to, PVA, LA, any filler, crosslinking agents, etc.

[0024] The PVA material used can be supplied in any form and in various quantities to obtain the desired properties. For example, PVA may initially be supplied in bead form and mixed with a solvent, or it may be supplied in solution form. PVA can be prepared at concentrations from about 10% to about 60%, or it may be supplied directly in solid form with the solvent during synthesis.

[0025] In some forms, aqueous PVA solutions can contain 0-10% water, although other amounts may be used. Under laboratory-scale processing conditions, primarily due to the high viscosity of the solution and the ability to achieve proper mixing and homogenization, concentrations of 20-25% in PVA aqueous solutions were easily achieved. While higher water content reduces the viscosity of the mixture and facilitates mixing, excess water also acts as a catalyst deactivator, reducing the degree of grafting and the length of the grafted chains. With appropriate equipment, it is believed that the water content of PVA racemates can be reduced to 50%, and even to anhydrous reactions.

[0026] LA used to form PLA in graft copolymers can also be provided in various forms and concentrations. For example, LA can be initially supplied in solid form and mixed with a solvent such as water, or it can be supplied in a pre-diluted form. LA can be supplied at concentrations from about 25% to about 100%, or it can be supplied directly in solid form with a solvent during synthesis.

[0027] PVA and LA can be supplied in varying amounts to obtain different performance and properties of the resulting PVA-g-PLA material. For example, the ratio of PVA to LA can be varied from about 1:1 to about 1:4. In addition, or alternatively, the ratio may be about 1:2 to about 1:3.

[0028] The PVA-g-PLA material may, but is not limited to, contain other components such as fillers, coatings, stabilizers, polyhydroxyalkanoates, polycaprolactones, and other biopolymers. For example, fillers can be used to improve barrier properties or enhance water resistance. These fillers include, but are not limited to, alkyl ketene dimers (AKD) and tomato peel materials.

[0029] Furthermore, the PVA-g-PLA material may be modified with other materials such as crosslinking agents. By adjusting the degree of crosslinking of the PVA copolymer, the barrier properties and other characteristics of the PVA-g-PLA material can be modified. For example, citric acid, succinic acid, high temperature, ultraviolet irradiation, or combinations thereof can be used. Crosslinking is promoted by unreacted PVA hydroxyl groups. This process itself reduces the solubility of the copolymer. In one form, a sample crosslinked with citric acid did not dissolve in water but swelled significantly into a hydrogel structure. On the other hand, the copolymer crosslinked with succinic acid was highly crosslinked, did not dissolve in water, and did not swell strongly.

[0030] In some forms, the crosslinking agent is a bifunctional or polyfunctional compound containing at least two carbonyl groups (-COOH) in its structure, such as an organic carboxylic acid or an aminodioic acid (-NH2). Since PVA is the main component of the copolymer, crosslinking can also be performed using certain salts containing polyvalent ions, such as sodium tetraborate. Typically, the crosslinking agent is used up to a maximum of 2%. The more crosslinking agent is used, the lower the flexibility becomes, but the stronger the material becomes. Generally, as the degree of crosslinking increases, solubility and biodegradability decrease.

[0031] Coating agents can also be used to modify the properties and functions of PVA-g-PLA materials, particularly when used for food packaging. Such coating agents include, but are not limited to, beeswax, acrylics, and other biopolymers. Similarly, PVA-g-PLA materials can be laminated with other materials, with PVA-g-PLA forming the inner layer, outer layer, and / or intermediate layer. Furthermore, multiple layers of PVA-g-PLA materials can be used individually or in combination with other layers. Examples of other layers include, but are not limited to, ethylcellulose, soy protein, and other biopolymers.

[0032] PVA-g-PLA material can be prepared in various thicknesses as desired. PVA-g-PLA material can also be supplied in solid form, such as pellets. This solid form can then be processed through processes such as extrusion molding to form films, packaging, etc. Typically, PVA-g-PLA material is formed into films and further processed for use, for example, in food packaging. For instance, such films can be formed into sachets for storing and distributing condiments like ketchup.

[0033] PVA-g-PLA materials can be provided to have various properties and performance characteristics. For example, PVA-g-PLA can have various molecular weights, glass transition temperatures, and so on.

[0034] Generally, PVA-g-PLA materials are synthesized using PVA copolymers grafted with PLA oligomers as a result of synthesis from lactic acid. PVA is combined with LA in the presence of a catalyst and / or under conditions of sufficient temperature and time to graft LA onto the PLA backbone. After the reaction, the material can be dried in the form of solid pellets, films, etc.

[0035] Various catalysts can be used in various amounts. For example, Sn salts such as Sn(Oct)2 and SnCl2, Zn salts such as ZnCl2, and combinations thereof can be used as catalysts. The amount of catalyst can also be varied. For example, 1 to 1.5% by weight of Sn(Oct)2 may be used. Small amounts of catalyst can be rapidly deactivated by water contained in the reaction mixture and may be produced as reaction byproducts. To reduce the amount of catalyst used, the reaction may be carried out in a smaller amount of solvent, or H2O may need to be removed by vacuum during the reaction.

[0036] However, in addition to changing the composition and components of the PVA-g-PLA material, the synthesis methods and processes for preparing the material can also be modified to achieve different properties and performance. In fact, synthesis parameters can have a significant impact on the development of materials with desired properties. Indeed, materials obtained under different conditions exhibited water solubility, but the degree of water solubility varied depending on both the conditions and the synthesis components. The materials also exhibited high mechanical strength and, depending on the components and processing conditions, showed a wide range of mechanical properties, from hard and brittle to those similar to thermoplastic elastomers. Similarly, the hydrophilicity of the copolymer can be controlled depending on the synthesis conditions and the ratio of components used.

[0037] As is evident from the examples below, the ratio of poly(vinyl alcohol) to lactic acid (PVA:LA ratio) can affect the properties of the PVA-g-PLA material. Similarly, the amount of catalyst and the total amount of water used as a solvent can also affect the properties and performance. Synthesis time and temperature also change the properties and performance of the resulting PVA-g-PLA material.

[0038] The presence and amount of crosslinking agents, i.e., citric acid or other crosslinking agents, can also affect the synthesis and the resulting properties. Firstly, they alter the pH of the reaction medium, and secondly, they facilitate the crosslinking process, in which chemical reactions between polymer chains form bonds and connect them to a network. The resulting network density then affects the resulting material properties, such as solubility, mechanical strength and stiffness, and hardness.

[0039] The reaction temperature can also be changed. While the reaction temperature may vary, the minimum reaction temperature is 100°C. Below this temperature, lactic acid will not be effectively grafted onto the PVA surface.

[0040] The amount of water used as a solvent during synthesis under laboratory conditions can also be varied. For example, in some forms, the ratio of water to PVA is approximately 4:1 by weight. Lower water content may lead to more efficient synthesis, but under laboratory conditions, the high viscosity necessitates adding a solvent to reduce this value.

[0041] Reaction time and conditions can also be modified. Reaction or synthesis times of approximately 4 to 10 hours are commonly used and can be altered to achieve various performance and properties. One range of reaction time is 5 to 7 hours. Shorter times result in lower effectiveness, insufficient conversion from lactic acid to oligo-PLA, wasted reagents, and undesirable properties. Times exceeding 12 hours can cause hydrothermal decomposition of the copolymer under test conditions, leading to partial degradation of the copolymer and deterioration of its properties. In some cases, even when the synthesis time was tripled, i.e., 24 hours instead of 7 hours, no significant improvement was observed in mechanical properties, transparency, or the degree of lactic acid grafting into PVA.

[0042] Drying time and temperature can also affect performance. For example, drying time and / or temperature can affect the stiffness of the synthesized material and its resistance to tensile and tearing during mechanical testing. Drying temperature can also vary. For example, in some forms, the drying temperature may be around 80°C. Drying time can also vary. However, typically the minimum time is 6 hours, as at lower temperatures, water and unreacted lactic acid in the copolymer do not evaporate effectively. High temperatures above 100°C and times exceeding 16 hours can cause material degradation, i.e., yellowing and increased brittleness of the material.

[0043] The materials described herein have been shown to be effective in preventing moisture loss (less than 3%) of filled ketchup within one week (RH=50%~90%, sealed in a desiccator). The sachets showed adequate moisture resistance (weight loss = 16%, 1 month) in low humidity storage tests (RH approximately 20~40%, open). Overall, bio-based solutions may be suitable as an environmentally friendly packaging option for ketchup.

[0044] Various examples were prepared and tested to compare the effects of starting materials, manufacturing methods, and other variables related to the material.

[0045] (Example 1)

[0046] The laboratory equipment used for PVA-g-PLA synthesis included a magnetic stirrer with heating function, an oil bath, a flask with a thermometer, a condenser, and an excess solvent receiver. The reagents used to carry out the reaction included poly(vinyl alcohol) (PVA), 80% lactate, tin(II) octanoate as a catalyst, and distilled water. Gelatin was also used in some of the reactions.

[0047] To produce the polymer blend, a predetermined amount of PVA was dissolved in distilled water and heated in an oil bath while vigorously stirring on a magnetic stirrer to prepare solution A. A predetermined amount of gelatin was dissolved in distilled water and prepared in an oil bath while maintaining constant stirring to prepare solution B. The two resulting solutions were combined and stirred while gradually increasing the temperature. After homogenization, the solution was poured into a large crystallization dish lined with a PTFE sheet and placed in an oven to evaporate the water.

[0048] (Example 2)

[0049] A laboratory composition was prepared with the following component amounts. 40 g of PVA, 100 g of H2O, and 87.5 g of 80% lactic acid solution were weighed into a 500 ml flask. A stirring bar was added, and the mixture was heated and stirred on a magnetic stirrer under reflux condenser until the reaction solution was homogeneous at at least 85°C (approximately 1 hour). Then, the Sn(Oct)2 catalyst was added. Next, the mixture was heated to 100 ± 5°C while maintaining vigorous stirring. After reaching the target temperature, the reaction was continued for another 2 hours. Then, the citric acid solution was added, and the reaction was continued for another 5 hours. The rotation of the magnetic stirrer was adjusted as needed, paying attention to the high viscosity of the reaction mixture. After the process was completed, the reaction mixture was poured in a thin film into a cuvette lined with PTFE film to prevent excessive adhesion. The poured film was left for 16 hours to evaporate the solvent, and then dried in an 80°C laboratory dryer for 12 hours.

[0050] (Example 3)

[0051] Overview of reaction parameters for various blend and copolymer synthesis

[0052] Various blends of PVA and gelatin were prepared, and the resulting materials were evaluated. The quantities of materials and processing / reaction times are summarized in Table 1 below.

[0053] [Table 1]

[0054] Blend B_1 was prepared according to the procedure shown in Table 1 above. The blend was poured into a Petri dish and left in an oven at 40°C for 24 hours to evaporate the solvent. Blend B_1 consists of PVA and gelatin. A transparent film with high mechanical strength and extremely soluble in water was obtained. In thicker samples, the evaporation time was longer, resulting in the precipitation of two phases and a decrease in transparency. The processing conditions are as shown in Table 1.

[0055] Blend B_2 was prepared in the same manner as B_1, then mixed for a further 30 minutes, and the temperature was gradually increased from 55°C to 70°C. After this, 1 g of citric acid dissolved in 30 ml of water was added. The mixture was heated at 50°C for 30 minutes. Then, it was poured into a crystallization dish lined with PTFE film and dried in an oven at 40°C for 24 hours to evaporate the moisture. The next day, the product was sieved at 130°C for 1 hour. The resulting product was hard and rigid and softened upon contact with moisture. Blend B_2 was less soluble than B_1.

[0056] Blend B_3 was prepared as the copolymer blend PVA-g-PLA, and both were poured together and mixed at 100°C for 30 minutes. The solution was then poured into a large container lined with PTFE film and dried in an oven at 40°C for 24 hours to evaporate the moisture. The resulting polymer material was flexible and had a texture similar to tomato peel.

[0057] (Example 4)

[0058] Various PVA-g-PLA copolymers were prepared according to the instructions described above. The amounts of each component and the various processing and reaction times are shown in Table 2 below.

[0059] [Table 2]

[0060] Copolymer 1 presented difficulties in homogenizing the mixture at low temperatures due to its excessive viscosity. The synthesis was undesirable, and PLA separated as a separate phase. The resulting product was yellow, suggesting it may be partially decomposed.

[0061] Copolymer 2 was pre-homogenized before catalyst addition. Due to the large amount of solvent, the resulting product was more homogeneous and transparent.

[0062] Copolymer 3 was initially homogenized at 80°C for 1 hour before catalyst addition. After synthesis, the hot solution was poured onto a PTFE film to form a copolymer film, and then the solvent was evaporated in a 40°C oven for 24 hours.

[0063] Copolymer 4 was initially homogenized at 80°C for 1 hour before catalyst addition. After synthesis, the hot solution was poured onto a PTFE film to form a copolymer film, and then the solvent was evaporated in a 40°C oven for 24 hours.

[0064] Copolymer 5 was initially homogenized at 80°C for 1 hour before catalyst addition. 2.5 hours after the start of the process, a solution of 0.3 g of pulverized tomato peel dispersed in 15 ml of water was added. The reaction was then carried out at 100°C for 2.5 hours. After synthesis, the hot solution was poured onto a PTFE film to form a copolymer film, and the solvent was then evaporated in a 40°C oven for 24 hours.

[0065] Copolymer 6 forms a transparent, uniform film. Immediately after drying, the material hardens until it reaches equilibrium by absorbing some moisture from the environment. After that, it becomes more flexible and possesses satisfactory mechanical properties. The product is soluble in water. It is characterized by good barrier properties, high flexibility, and acceptable strength. The surface is slightly sticky. The copolymer showed biodegradation within one month. Copolymer 6 had lower viscosity, was easier to mix, and had a smoother consistency than copolymer 7. When a catalyst was added to copolymer 6 and grafting occurred, the viscosity increased.

[0066] Initial mechanical properties of copolymer 6 after 24 hours of adjustment at 23°C and 50% humidity: average strength at 100% elongation 0.746±0.107 [MPa], average strength at 200% elongation 1.29±0.19 [MPa], average stress at maximum command force 1.54±0.08 [MPa], average elongation at maximum command force 215.2±37.7 [%].

[0067] Initial mechanical properties of copolymer 6 after 24 hours of adjustment at 30°C and 80% humidity: average strength at 100% elongation 0.628±0.067 [MPa], average strength at 200% elongation 0.984±0.107 [MPa], average stress at maximum command force 1.28±0.14 [MPa], average elongation at maximum command force 286.2±0.6 [%].

[0068] (Example 5)

[0069] Additional copolymers were prepared in the same manner as described in Example 4 above. The composition and processing conditions are summarized in Table 3 below.

[0070] [Table 3]

[0071] Copolymer 7 contains mechanically ground tomato peel, which was added to copolymer 6. 4 g of ground tomato peel (4% by weight relative to PVA+LA) was added to copolymer 7. The tomato peel was added to the reaction 2.5 hours after the start of the reaction, dispersed in 25 ml of water. The resulting product exhibits good mechanical strength, an orange color, and an odor characteristic of processed tomatoes. The film is not completely transparent due to the throughout dispersion of ground tomato peel. The dispersibility of this additive is good and uniform, even in areas with flat surfaces.

[0072] Copolymer 8 was prepared by changing the PVA:LA ratio and synthesis time. The ratio of poly(vinyl alcohol) to lactic acid in the copolymer structure was tested at 2:3. Furthermore, the drying time and drying temperature were also changed. Under these drying conditions, the product becomes harder. It exhibits greater mechanical resistance to tensile and fracture. The resulting film remains homogeneous, transparent, and soluble in water. It is assumed that drying at high temperatures causes more water and unreacted lactic acid to evaporate from the product. It is also assumed that further copolymerization reactions may proceed during drying, increasing the oligomeric chain length of lactic acid. Under these conditions, no significant thermal oxidative decomposition of the material occurs, and only slight thermal crosslinking reactions may occur.

[0073] Copolymer 9 was prepared by changing the PVA:LA ratio and synthesis time. The PVA:LA ratio was 3:7, and the synthesis time was 24 hours. The catalyst content was 1.5% by weight. Similar observations were obtained as with copolymer 8. However, the dried product had lower mechanical durability, absorbed moisture from the environment more quickly and in greater quantities, and had a more viscous surface.

[0074] In some configurations, the process temperature in the flask may be around 100°C for the copolymerization process, but to perform polycondensation of PLA with PVA, the solution needs to be divided into 140-160°C sections. In some configurations, a PVA-to-LA ratio of 3 / 7, excess lactic acid, and a synthesis time of 24 hours were used to obtain the highest possible degree of grafting and the longest possible PLA chains in the copolymer structure. In some configurations, a higher amount of lactic acid in the reaction mixture resulted in a lower viscosity of the solution. However, the degree of reactivity of lactic acid in PLA and the residue of unreacted monomers can reduce the yield and make the removal of unreacted materials difficult.

[0075] Copolymer 10 was prepared with the same PVA and LA ratios as copolymer 9. However, the amount of catalyst was reduced to 1% by weight, and the synthesis time was altered. Synthesis took 7 hours, but this did not result in any noticeable improvement in mechanical properties, transparency, or the degree of lactic acid grafting onto the PVA surface. The reduction in the amount of catalyst resulted in a decrease in the amount of PLA in the copolymer structure.

[0076] Copolymer 11 was synthesized with a PVA:LA ratio of 4:7, while the synthesis time was the same as for copolymer 10. The catalyst used was Sn(Oct)2, in an amount of 1.5% by weight. The amount of water added as solvent was four times the weight of PVA. The obtained results showed better properties than copolymer 10, but were inferior to the example synthesized in 5-7 hours. This is presumed to be because, after the active molecule was deactivated during the reaction, chain growth ceased, resulting in partial hydrolysis of the ester bonds present in the structure.

[0077] (Example 6)

[0078] Further variations of copolymer were prepared. The composition and processing conditions are summarized in Table 4 below.

[0079] [Table 4]

[0080] Copolymer 12 was prepared based on copolymer 10. However, the influence of citric acid (CA), a crosslinking agent, on the copolymer's properties and the effect of environmental acidification on the equilibrium shift of the graft reaction were confirmed. Two hours after the start of the reaction, 13.3 g (10 wt% of PVA + LA) of citric acid solution dissolved in 25 ml of water was added to change the pH of the reaction medium to promote equilibrium shift and partially crosslink the copolymer. The resulting material had the highest ester and carbonyl group content in its structure to date, indicating the highest concentration of LA bonds in the copolymer structure. This was determined by FTIR spectroscopy. However, the resulting product exhibited significant surface tackiness after drying.

[0081] Copolymer 13 was prepared based on the composition tested for copolymer 11. However, as with copolymer 12, citric acid was used to crosslink the hydroxyl groups in PVA that did not react during the grafting reaction. Two hours after the start of the reaction, 11 g (10 wt% of PVA + LA) of citric acid solution dissolved in 25 ml of water was added. Similar results were obtained as with copolymer 12. However, due to the large amount of catalyst added, the resulting film appeared to lose its tackiness after drying.

[0082] Copolymer 14 was prepared with the same composition as copolymer 10. However, succinic acid, which has an even lower pH than citric acid (used in copolymer 12), was used as the crosslinking agent. After initial homogenization, a copolymerization reaction was carried out for 2 hours under catalyst addition, and then a succinic acid solution dissolved in 25 ml of water and heated to 60°C was added. The resulting product was a transparent film with high flexibility and high cohesive strength. The surface was slightly sticky.

[0083] Copolymer 15 was prepared with the same composition as copolymers 11 and 13. In this example, succinic acid was used as the crosslinking agent. Although there were slight differences in the grafting of lactic acid onto poly(vinyl alcohol) due to the high PVA-to-LA ratio and the large amount of catalyst added, the surface tackiness was eliminated. The resulting product was less flexible than copolymer 14 and showed higher resistance to elongation and fracture in tensile tests. The addition of succinic acid slightly reduced the transparency of the product (making it slightly milky white).

[0084] (Example 7)

[0085] Preparation of a bonded film made of PVA-g-PLA copolymer and ethyl cellulose. Copolymer 6 was thermally bonded with ethyl cellulose, and the two films were physically bonded by heating. In this example, the PVA-g-PLA copolymer was synthesized, and then the hot film was poured onto a Teflon foil. After pouring, modified ethyl cellulose was placed on the surface and smoothed. The laminated film was dried in a laboratory dryer at 80°C for 12 hours. The bond was permanent, but a large number of bubbles formed at the joint. This is presumed to be due to the difficulty of evaporating moisture.

[0086] (Example 8)

[0087] As an alternative composite material, an attempt was made using a copolymer of hydroxypropyl methylcellulose (HPMC g PLA) grafted with polylactic acid (PLA) in a 1:9 ratio. HPMC was used as a bio-adhesive for bonding with the other polymer. It is a viscous liquid with viscosity and color similar to honey. It exhibits certain adhesive properties and should have high affinity for both materials being bonded due to its similar chemical properties (presence of hydroxyl groups and similar viscosity). Next, the composite material was placed in a laboratory dryer at 80°C for 4 hours. The bond was durable, with few bubbles, and the material partially dissolved where the excess HPMC g PLA copolymer remained as an adhesive.

[0088] Elongation tests were conducted on the various samples mentioned above. The test results are shown in Table 5 below.

[0089] [Table 5]

[0090] The behavior of the materials is briefly compared and discussed. For copolymer 8, the material behavior was somewhat non-uniform. For copolymer 9, it was more non-uniform. For copolymer 10, the sample was sticky and the strain gauge (i.e., extensometer) chuck slipped on the sample, resulting in the most uncertain measurements. Copolymer 10 differed the most from the others and exhibited the most non-uniform behavior during testing. Copolymer 11 was the most stable sample during measurement and exhibited the most uniform behavior during the tensile test. Copolymer 13 exhibited somewhat non-uniform behavior.

[0091] Thermal analysis using differential scanning calorimetry (DSC) was also performed on various copolymer samples. The phase transition temperature ranges of copolymers 12-15 were obtained using a differential scanning calorimetry (DSC) (METTLER TOLEDO DSC analyzer, TA 2920, TA INSTRUMENTS). 5-6 mg of the sample was placed in a 40 μl aluminum pan and heated at a rate of 10 °C / min in the range of 20-200 °C. Before measurement, the film was dried at 80 °C for 100 minutes. Comparative thermograms of copolymers 12 and 13 before drying are also shown. The results are shown in Figures 1-6.

[0092] The glass transition temperatures (Tg) of copolymers 12-15 after drying at 80°C for 100 minutes are shown in Table 6 below.

[0093] [Table 6]

[0094] All copolymers exhibited a glass transition temperature. The glass transition temperatures of copolymers 12 and 13 were approximately 17–18°C (start), and those of copolymers 14 and 15 were approximately 29–31°C (start). Despite drying the copolymers before DSC measurement, desorption of moisture present in the film was observed on the thermogram (a broad peak from 60–190°C). This desorption of moisture may have introduced some error in the measurement of the glass transition temperature.

[0095] Thermograms of copolymers 12 and 13 before drying showed that water desorption was dominant. Therefore, these results may contain large errors and are not included in Table 6.

[0096] Additional tests were conducted on several copolymers. These tests included water vapor transmission rate (WVTR), oxygen transmission rate (OTR), tensile strength, and puncture strength. The results are shown in Tables 7 and 8, where copolymer 6 in Table 7 corresponds to LODZ-1 in Table 8.

[0097] [Table 7]

[0098] [Table 8]

[0099] As described above, at least some copolymers were cold water soluble and also exhibited desirable decomposability under household composting conditions.

[0100] (Example 9)

[0101] As shown in Figure 7, the molecular weight distribution of copolymer 6 described above is shown. Samples were tested using a VISCOTEK GPC MAX, 2*30CM AGILENT OH60 GPC column with water + 0.2M sodium nitrate as the eluent, at a flow rate of 1.0 ml / min and 40°C. As shown in the figure, the weight-average molecular weight (Mw) was 30,000, the number-average molecular weight (Mn) was 1,200, the Mw / Mn ratio was 25.0, and the Mz ratio was 25. The composition can be adjusted to achieve the desired molecular weight and distribution.

[0102] (Example 10)

[0103] DSC analysis was also performed on sample materials based on copolymer 6. Plots of these results can be seen in Figures 8 to 11. Samples were subjected to heating / cooling / reheating up to 270°C (tx2395) and fresh samples up to 150°C (tx2401). Initial measurements appeared to show stability up to approximately 155°C. The glass transition onset point of the received sample was measured at -51.5°C. The variation in melting points in each received measurement may indicate variation in polymer composition throughout the film. The glass transition onset point after reheating following cooling from 270°C was 72.8°C, and after cooling from 150°C it was -39.0°C.

[0104] (Example 11)

[0105] Additional tests were conducted on the copolymer 6 sample. Fourier transform infrared spectroscopy (FTIR) was performed, and the results are shown in Figure 12. Fourier transform absorption measurements were performed on the polymer composite sample using a THERMO SCIENTIFIC NICOLET 6700 FT-IR spectrophotometer in the spectral range of wavenumber 4000 to 400 cm⁻¹, using absorption mode with a SMART ORBIT ATR diamond attachment and 64 scans, to evaluate the functional group content.

[0106] Thermogravimetric analysis was also performed on copolymer 6. A METTLER TOLEDO TGA / DSC 1 STARE SYSTEM (equipped with a GAS CONTROLLER GC10 (Greifensee, Switzerland)) was used for this study. Measurements were performed by combustion in synthetic air (temperature range: 25-600°C, heating rate: 15°C / min, airflow rate: 50 cm³). 3 The test samples were placed in an alumina crucible ( / min). The results are shown in Figure 13.

[0107] Furthermore, DSC analysis was performed on additional samples of copolymer 6. The temperature range for the PVA-g-PLA phase transition of copolymer 6 was obtained using differential scanning calorimetry (DSC) (METTLER TOLEDO DSC analyzer, TA 2920, TA INSTRUMENTS). 5-6 mg of material sample was placed in a 100 μl aluminum pan and heated from -20 to 300°C at a rate of 10°C / min. The results are shown in Figure 14.

[0108] Gel permeation chromatography was performed on three samples of copolymer 6. Copolymer solutions were prepared at concentrations of 7 g / L and 4 g / L, respectively. The polymers were dissolved in 0.1 M NaNO3 by autoclaving and storage at 50°C for 24 hours. Measurements were performed using a GPC system with triple detectors. A multi-angle scattered light intensity detector (MALLS) (BROOKHAVEN INSTRUMENTS CORPORATION, Brookhaven, New York, USA) and a dual refractive index-viscosity detector (RI / DP) (TESTA ANALYTICAL SOLUTIONS, Berlin, Germany) were used. For all measurements, two SUPREMA LUX LINEAR XL analytical columns (suitable for neutral and anionic polymers) and a SUPREMA LUX SDV analytical pre-column (PSS POLYMER STANDARDS SERVICE GMBH, Mainz, Germany) were used. Chromatographic measurements were performed using 0.1 M NaNO3 as the eluent. The flow rate was 1 ml / min and the temperature was 50°C. Each sample was measured three times. The results for sample A are shown in Figures 15A-C, the results for sample B are shown in Figures 16A-C, and the results for sample C are shown in Figures 17A-C. The molecular weights are shown in Table 9 below.

[0109] [Table 9]

[0110] X-ray photoelectron spectroscopy was also performed on copolymer 6. Chemical analysis was carried out by XPS using a 128-channel collector-equipped X-ray photoelectron spectrometer (OMICRON NANOTECHNOLOGY). XPS measurements were performed under ultra-high vacuum conditions and a pressure of 1.1 × 10⁻⁶. -8 The experiment was conducted at a photoelectron emission level of less than mBar. Photoelectrons were excited by a Mg-Kα source. The X-ray anode was operated at 15 KEV and 300 W. An OMICRON ARGUS hemispherical electron analyzer with a 4 mm aperture was used to analyze the emitted photoelectrons. XPS spectra were analyzed using CASA-XPS software with SHIRLEY background subtraction and a Gauss-Lorentz curve fitting algorithm. The collected spectra were deconvoluted using multiple curves corresponding to various chemical states. The results are shown in Figures 18A-C.

[0111] Respiratory measurement tests were also conducted on copolymer 6. To automatically test the progress of biodegradation, a MICRO-OXYMAX ratio meter was used under conditions simulating an intensive aerobic composting process. The apparatus allowed for simultaneous testing in four chambers, with one chamber containing only soil as a reference sample. The chambers were placed in a temperature-controlled 40°C oil bath. During the test, the amount of CO2 released was measured over 30 days. The results are shown in Figure 19, and the reference soil sample is shown in Figure 20.

[0112] (Example 12)

[0113] The properties of the various copolymers described above were analyzed. These properties include oxygen permeability, water vapor permeability, gauge, average gauge, tensile strength, puncture strength, shelf life, dispersibility, and degradability. These properties were tested according to the methods outlined above and / or standard test methods. Some properties of copolymer 6 are outlined individually in the examples above.

[0114] Various observations have been made regarding the copolymer described above. When lactic acid is added beyond a PVA:LA ratio of 30:70, the tackiness of the copolymer surface increases. This phenomenon is presumed to be due to the fact that not all lactic acid reacts during the synthesis reaction, or that the barrier properties of the product increase, preventing sufficient moisture from being released from the structure during the drying process. Furthermore, as the amount of LA in the structure increases, the mechanical strength of the resulting copolymer tends to decrease, while its flexibility increases. When citric acid is added to the reaction to crosslink the copolymer and change the reaction medium, the viscosity of the reaction mixture increases significantly, but the mechanical strength does not increase; only the flexibility increases.

[0115] The effects of drying and thermal curing on the properties of the starting copolymers were compared among various copolymers. Samples of copolymers 8-13 were dried at 40°C, 60°C, 80°C, and 100°C. The effect of drying time was also examined at time intervals of 2 hours, 6 hours, and 12 hours. Based on the results of the sample tests and observations, the preferred drying and thermal crosslinking time was 12 hours at 80°C. Products prepared by this method showed increased rigidity, higher mechanical strength, lower surface tackiness, still high transparency, and low thermal oxidative degradation.

[0116] It should be understood that transparent thermoplastic materials for packaging can be obtained by synthesizing copolymers based on PVA and LA. The resulting materials are compostable and water-soluble in a controlled manner. The dissolution process of the resulting copolymers can be adjusted by changing the ratio of the substrates and the synthesis parameters.

[0117] By crosslinking copolymers biocompatible, materials can possess excellent physicochemical, mechanical, and optical properties. The degree of crosslinking can be adjusted to control the material's stiffness and strength, and appropriate crosslinking can also control its solubility.

[0118] Materials and manufacturing processes can be modified to achieve the properties required for packaging different products. For example, by changing the materials and processes, the PVA LA copolymer can be made to not exhibit high solubility in ketchup. Similarly, materials can be designed to withstand the transportation of ketchup as specified by the manufacturer.

[0119] The copolymers described herein may be bio-based, and films with high transparency, flexibility, and high cohesive strength can be obtained. The obtained material can be easily sealed into sachets by welding. Depending on the morphology, the surface may be slightly sticky, but this can be controlled by the amount of catalyst added; increasing the amount of catalyst eliminated the stickiness of the film obtained after drying.

[0120] The matters described herein and in the accompanying drawings are provided for illustrative purposes only and are not intended to be limiting. While specific embodiments are shown and described, it will be apparent to those skilled in the art that modifications and alterations are possible without departing from broader aspects of the applicant's contribution. The scope of protection actually sought is intended to be defined by the following claims, based on the prior art and viewed from an appropriate viewpoint.

Claims

1. Poly(vinyl alcohol) (PVA) skeleton, Lactic acid (LA) grafted onto the aforementioned PVA skeleton, A composition containing the following:

2. The composition according to claim 1, wherein the PVA is provided in a ratio (PVA:LA) in the range of about 1:1 to about 1:

4.

3. The composition according to claim 1, further comprising a filler.

4. The composition according to claim 3, wherein the filler is selected from the group consisting of alkyl ketene dimer, tomato peel material, and combinations thereof.

5. The composition according to claim 1, wherein the material is crosslinked.

6. The composition according to claim 1, wherein the material is biodegradable.

7. The composition according to claim 1, wherein the material is in the form of pellets used to form a polymer film.

8. The composition according to claim 1, wherein the material is in the form of a polymer film.

9. The steps include preparing poly(vinyl alcohol) (PVA) material, The steps include preparing a lactic acid (LA)-containing material, The process includes the step of reacting the PVA material with an LA-containing material in the presence of a catalyst to synthesize a PVA skeleton with polylactic acid (PLA) grafted onto the PVA skeleton to form PVA-g-PLA. A method for preparing biodegradable packaging materials.

10. The method according to claim 9, wherein the ratio of the PVA material to the LA-containing material is about 1:1 to 1:

4.

11. The method according to claim 9, wherein the catalyst is provided in an amount of about 1 to about 1.5% by weight.

12. The catalyst is Sn(Oct) ２ SnCl ２ ZnCl ２ The method according to claim 9, comprising at least one of the following: and combinations thereof.

13. The method according to claim 9, wherein the reaction is carried out over a period of about 5 to 7 hours.

14. The method according to claim 9, wherein the reaction is carried out at a temperature of about 80°C to about 100°C.

15. The method according to claim 9, further comprising the step of adding at least one of alkyl ketene dimers, fillers, coating agents, stabilizers, polyhydroxyalkanoates, polycaprolactones, other biopolymers, and combinations thereof.

16. The method according to claim 9, further comprising the step of adding a crosslinking agent.

17. The method according to claim 16, wherein the crosslinking agent comprises at least one of citric acid, succinic acid, and combinations thereof.

18. The method according to claim 9, further comprising the step of crosslinking PVA-g-PLA with at least one of citric acid, succinic acid, ultraviolet irradiation, and combinations thereof.

19. The method according to claim 9, further comprising the step of forming PVA-g-PLA into a film.

20. The method according to claim 19, further comprising the step of combining the film with a second film.

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