Neck-in prediction method for polylactide resins

Abstract

The present invention provides a method for predicting or evaluating the neck-in properties of a film manufactured from a polylactide resin. This method is simple, highly predictive, and can replace measurement methods, and it allows for the prior determination of film properties for new structures.

Description

Technical Field

[0001] Cross-reference of related applications This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0175672 filed on December 6, 2023, and all the contents disclosed in the documents of the Korean patent application are included as part of this specification.

[0002] The present invention relates to a method for predicting Neck-in of a polylactic acid resin.

Background Art

[0003] Polylactic acid (PLA) is a plant-derived resin obtained from plants such as corn, has biodegradable properties, and has attracted attention as an excellent environmentally friendly material. Different from conventional petroleum-based resins such as polystyrene resin, polyvinyl chloride resin, and polyethylene, polylactic acid has effects such as preventing depletion of petroleum resources and suppressing carbon dioxide emissions, so it can reduce environmental pollution, which is a disadvantage of petroleum-based plastic products. Therefore, as the environmental pollution problem caused by waste plastics and the like emerges as a social problem, efforts are being made to expand the application range of polylactic acid to product fields where general plastics (petroleum-based resins) have been used, such as food packaging materials and containers, and electronic product cases.

[0004] However, since the polylactic acid resin has low melt strength and melt elasticity due to its structural characteristics, the molding process stability decreases during film production. In particular, when the production speed is increased to improve productivity, the Neck-in phenomenon increases, and there is a limit to reducing the film thickness in consideration of processability. In addition, there is a disadvantage that Edge Weave becomes intense in the molding process, and the width and thickness deviation of the produced film becomes intense.

[0005] To address the aforementioned shortcomings, many attempts have been made to develop new polylactide resins with a branched structure to improve chain entanglements. One such attempt involves adding epoxy branching agents to the polylactide resin to improve melt strength. This is because the branched structure is mainly formed by the reaction between the carboxyl groups and epoxy groups at the end groups of the polylactide resin. Therefore, the reactivity varies considerably depending on the acid value (influence of end groups due to additives, initiators, etc.) and purity (D content) of the polylactide resin. Consequently, the tendency towards branching is diverse, and it is not easy to determine whether it is possible to improve neck-in while ensuring processing stability with a certain level of physical properties until the actual product is evaluated.

[0006] Therefore, the present invention relates to a method for predicting or evaluating the neck-in properties of a film manufactured from polylactide resin in a simple and highly accurate manner, thereby replacing measurement methods and enabling the prior determination of film properties for new structures. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] This invention provides a method for predicting the neck-in state of polylactide resins. [Means for solving the problem]

[0008] To solve the above problems, the present invention provides a neck-in prediction method for polylactide resins, comprising the following steps: 1) Step 1: Measuring the following physical properties A and B for each of the multiple polylactide resins; -Physical property A: Tanδ (at 0.4 rad / s) -Physical property B:η”(at 0.3 rad / s) 2) A step of measuring the Neck-in value (N) for the plurality of polylactide resins (step 2); and 3) Step 3: Deriving a Neck-in prediction formula for polylactide resin by performing regression analysis on the Neck-in value (N) based on the measured values ​​of physical properties A and B.

[0009] As used in this invention, the term "polylactide resin" is defined as encompassing monopolymers or copolymers containing the following repeating units. [ka]

[0010] The polylactide resin can be manufactured by a step of forming the repeating units by ring-opening polymerization of lactide monomers, and the polymer after such ring-opening polymerization and the formation of the repeating units steps can be referred to as the "polylactide resin".

[0011] In this context, "lactide monomer" can be defined as follows. Normally, lactide is divided into L-lactide (composed of L-lactic acid), D-lactide (composed of D-lactic acid), and meso-lactide (composed of one L-form and one D-form). Furthermore, a mixture of L-lactide and D-lactide in a 50:50 ratio is called D,L-lactide or rac-lactide. It is known that when polymerization proceeds using only L-lactide or D-lactide with high optical purity, L- or D-polylactide (PLLA or PDLA) with very high stereoregularity is obtained. Such polylactides are known to have a faster crystallization rate and higher crystallinity compared to polylactides with lower optical purity. However, in this specification, "lactide monomer" is defined as encompassing all forms of lactide, regardless of the differences in properties between each form and the polylactide resin formed from them.

[0012] On the other hand, each of the aforementioned polylactide resins has a weight-average molecular weight of 70,000 to 400,000. Preferably, the polylactide resin according to the present invention has a weight-average molecular weight of 80,000 or more, 90,000 or more, or 100,000 or more; or 300,000 or less, 250,000 or less, or 200,000 or less.

[0013] Furthermore, the number-average molecular weight of the plurality of polylactide resins is 50,000 to 100,000. Preferably, the polylactide resin according to the present invention has a number-average molecular weight of 55,000 or more, or 60,000 or more; or 90,000 or less, 85,000 or less, or 80,000 or less.

[0014] Furthermore, each of the aforementioned polylactide resins may contain additional additives. Examples of such additives include polylactide oligomers and compatibilizers. For example, some polylactide resins may contain other components besides the polylactide resin, and some may contain additives. It is also possible to predict how the additives used will affect the neck-in properties by using the same polylactide resin and only changing the type and amount of additives.

[0015] The present invention relates to a method for easily and accurately predicting or evaluating the neck-in properties of a film made from such a polylactide resin. For this purpose, the present invention measures the rheological properties A and B of the polylactide resin.

[0016] The aforementioned physical property A is Tan delta, and the tan delta value for each vibration interval can be confirmed by measuring the rheological physical property. The specific measurement method for this is embodied in the following example. In the low vibration range (0.3~0.4 rad / s), when compared with the measured Neck-in within the processing conditions, there is a correlation in which Neck-in decreases as Tan delta decreases.

[0017] The aforementioned physical property B is η'', and the results of η' and η'' for each vibration interval can be confirmed by measuring the rheological properties, and can be obtained by showing a Cole-Cole plot. The specific measurement method related to this is embodied in the following example. In the low vibration range (0.3~0.4 rad / s), when compared with the measured Neck-in within the processing conditions, there was a correlation in which Neck-in decreased as η'' increased.

[0018] Therefore, by measuring physical properties A and B for multiple polylactide resins (Step 1), measuring the Neck-in value (N) for the multiple polylactide resins (Step 2), and performing regression analysis on the Neck-in value (N) based on the measured physical properties A and B, a Neck-in prediction formula for the polylactide resin can be derived. On the other hand, the method for measuring the measured value of Neck-in is exemplified in the following example.

[0019] The aforementioned multiple polylactide resins refer to at least two or more types of polylactide resins, and it is preferable to have a large number of types, taking into account the correlation coefficient of the prediction formula. Preferably, the aforementioned multiple polylactide resins are 5 or more types, 6 or more types, 7 or more types, 8 or more types, 9 or more types, or 10 or more types, and 50 or fewer types, 40 or fewer types, 30 or fewer types, or 20 or fewer types of polylactide resins. Preferably, the Neck-in prediction formula for the polylactide resin is as shown in Equation 1 below: [Formula 1] N = (0.077*A) - (0.085*B) + 27.69

[0020] In the above formula 1, A represents Tanδ (at 0.4 rad / s), and B represents η'' (at 0.3 rad / s).

[0021] As shown in the examples described later, the prediction formula obtained by the present invention showed a high correlation with the measured values, and the difference between the values ​​calculated using the obtained prediction formula and the measured values ​​was very small. Therefore, the present invention makes it possible to predict film properties easily and with high accuracy without actually manufacturing a film. [Effect of the Invention]

[0022] As described above, the present invention is a method for predicting or evaluating the Neck-in property of a film to be produced from a polylactic acid resin. By this method, it is possible to replace the actual measurement method with a simple and highly predictive method, and to pre-judge the film physical properties for a new structure. [Brief Description of the Drawings]

[0023] [Figure 1] It is a figure showing the result of mapping two factors measured in Experimental Example 1. [Figure 2] It is a figure showing the method for obtaining the Neck-in prediction formula in Experimental Example 1. [Modes for Carrying Out the Invention]

[0024] Hereinafter, embodiments of the present invention will be described in more detail with reference to the following examples. However, the following examples are merely illustrative of the embodiments of the present invention, and the content of the present invention is not limited by the following examples.

[0025] <0000​​PLA oligomers were prepared using pentaerythritol (PT) as an initiator. Specifically, lactide and PT were added to a 500 mL reactor in a molar ratio of 100:1, totaling 75 g each. After adding Sn(Oct)2 catalyst (0.075 g), the reaction was carried out at 180°C for 5 hours to produce the oligomers. To replace the hydroxyl terminal groups of the produced oligomers with carboxyl groups (COOH), the number of moles was calculated using the amount of lactide added (g) and the number-average molecular weight (g / mol) of the produced oligomers. The total number of hydroxyl terminal groups of the produced oligomers was calculated considering the number of terminal groups (4) in the initiator (PT). Next, succinic anhydride (SA) in an amount equivalent to 2 equivalents to the total hydroxyl terminal groups of the oligomers was added in a one-pot reaction, and the reaction proceeded for an additional 3 hours. After the reaction was complete, the PLA oligomers prepared in a CHCl3 / MeOH solvent system were precipitated / separated to remove unreacted SA and remaining impurities. The final product was obtained by vacuum drying at 45°C for 12 hours and named "PT-SA".

[0026] The weight-average molecular weight of the PLA oligomer "PT-SA" manufactured as described above was measured. Specifically, the weight-average molecular weight (Mw) was measured using a GPC (Gel Permeation Chromatography) apparatus, and the specific measurement conditions were as follows. The weight-average molecular weight measured was approximately 40,000. - Column: PLgel Mixed Ex2 - Solvent: THF -Flow rate: 0.7mL / min -Sample concentration: 3.0 mg / mL -Injection volume: 100μl - Column temperature: 40°C -Detector:Waters 2414 RID -Standard: PS (Polystyrene)

[0027] Example: Production of polylactide resin The components listed in Table 1 below were subjected to reaction extrusion using a 19Ψ extruder (BA-19, Bautek).

[0028] Specifically, 1 kg of polylactide resin (Anhui BBCA Biochemical & Futerro PLA Corp, FY201; FY202; FY212; FY601; FY801) was mixed with the components listed in Table 1 below (epoxy compatibilizer (Joncryl ADR 4468) or PT-SA), extruded at a screw rotation speed of 200 rpm, and the maximum temperature was adjusted (190-230°C) to obtain PLA pellets. The number-average molecular weight and weight-average molecular weight of the obtained PLA pellets were measured as follows, and these are shown in Table 1.

[0029] - Column: PL mixed Bx2 - Solvent: THF -Flow rate: 1.0ml / min -Sample concentration: 1.5 mg / ml -Injection volume: 100μl - Column temperature: 40°C -Detector:Waters 2414 RID -Standard: PS (Polystyrene) [Table 1]

[0030] In addition, the following four types of polylactide resins were used in the following experiments. #9: NW 4032D (NatureWorks) #10:FY601(Anhui BBCA Biochemical&Futerro PLA Corp) #11:FY604(Anhui BBCA Biochemical&Futerro PLA Corp.) #12:FY801(Anhui BBCA Biochemical&Futerro PLA Corp)

[0031] Experimental Example 1 1) Neck-in measurement of polylactide resin The obtained pellets were vacuum-dried at 85°C for more than 4 hours, and a PLA film was manufactured by T-die extrusion molding (Eurotech benchtop monolayer cast film apparatus, ScrewΨ17.5mm, T-die width120mm).

[0032] The neck-in value was measured using film width (X) manufactured under identical conditions: calendar speed of 3.0 M / m and haul-off speed of 4.5 M / m. The results are shown in Table 2 below.

[0033] Neck-in evaluation: ((T-die width)-(film width)) / 2=(120-X) / 2 [Table 2]

[0034] 2) Calculation of the Neck-in prediction formula for polylactide resin Using a TA Instruments ARES-G2 rheometer (Strain-Controlled Type), rheological properties were evaluated using a 25mm diameter parallel plate with a geometry reference at 1mm intervals. PLA samples were packed to the aforementioned geometry size and measured. An appropriate strain was set for each sample by amplitude sweeping at the initial measurement temperature of 210°C. Based on the set strain (5-10%), amplitude sweeps from 0.1 rad / s to 500 rad / s were performed at the same measurement temperature of 210°C. From these results, the following two factors were derived.

[0035] (i) Tan Delta Rheological measurements allowed us to confirm the tan delta values ​​for each vibration interval. In the low vibration range (0.3-0.4 rad / s) that reflects structural (LCB) effects, when compared with the results of neck-in tests within the processing conditions, there was a correlation where neck-in decreased as tan delta decreased.

[0036] (ii)η” Using the same measurement method, we were able to confirm the results for η' and η'' in each vibration interval and present a Cole-Cole Plot. Within the Cole-Cole Plot, η'' showed a tendency to increase due to structural changes (LCB) in PLA. In the low vibration range (0.3-0.4 rad / s) that reflects the structural (LCB) effect, when compared with the neck-in test results within the processing conditions, there was a correlation where neck-in decreased as η'' increased.

[0037] The two significant factors mentioned above each showed a high correlation with Neck-in, and mapping between the significant factors was possible, as shown in Figure 1.

[0038] The two significant factors mentioned above showed a high correlation with Neck-in, and based on this, it is possible to predict Neck-in using rheological factors. The data is summarized in Table 3 below, and a prediction equation between the factors can be constructed using a linear regression model as shown in Figure 2. The correlation coefficient between the prediction equation and Neck-in was 0.82. [Table 3] Neck-in (prediction formula) = 0.077 * A - 0.085 * B + 27.69 In the above formula, A is Tan delta (at 0.4 rad / s) B is η” (at 0.3 rad / s)

[0039] Experimental Example 2 To evaluate the prediction formula obtained in Experimental Example 1, a polylactide resin composition was prepared using the same method as the sample preparation method for #7, but with 0.5 phr of Joncryl ADR 4468. Its weight-average molecular weight and number-average molecular weight were 162,102 and 76,588, respectively.

[0040] For the polylactide resin composition, Tan delta and η'' were measured in the same manner as in Example 1, and were measured as 21.5255 and 16.431, respectively. These values ​​were substituted into the prediction formula obtained in Experimental Example 1 to predict the Neck-in value as shown below.

[0041] Neck-in=0.077*(21.5255)-0.085*(16.431) +27.69 =27.95

[0042] For the polylactide resin composition, the Neck-in measurement value was determined in the same manner as in Example 1, and the result was 27.5, which was confirmed to be almost identical to the value obtained by the prediction formula.

Claims

1. 1) Step 1: Measuring the following physical properties A and B for each of the multiple polylactide resins; - Physical property A: Tanδ (at 0.4 rad / s) - Physical property B: η'' (at 0.3 rad / s) 2) A step of measuring the Neck-in value (N) for the plurality of polylactide resins (step 2); and 3) Step 3 includes a step of deriving a Neck-in prediction formula for polylactide resin by performing regression analysis on the Neck-in value (N) based on the measured values ​​of physical properties A and B. Neck-in prediction method for polylactide resins.

2. The Neck-in prediction formula for the polylactide resin is given by the following equation 1: The prediction method according to claim 1: [Formula 1] N=(0.077*A)-(0.085*B)+27.69 In the above formula 1, A represents Tanδ (at 0.4 rad / s), B stands for η'' (at 0.3 rad / s).

3. The aforementioned polylactide resins each have a weight-average molecular weight of 70,000 to 400,000. The prediction method according to claim 1.

4. The number-average molecular weight of the aforementioned plurality of polylactide resins is 50,000 to 100,000. The prediction method according to claim 1.

5. Some of the aforementioned polylactide resins additionally contain additives. The prediction method according to claim 1.

6. The aforementioned polylactide resins number 10 to 20 types. The prediction method according to claim 1.

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