A biodegradable PLA coating material and coating products based thereon

Abstract

The present invention discloses a biodegradable PLA coating material and coated products based thereon. The material comprises a polylactic acid resin (PLA) to which grafted, coated cellulose nanocrystals are added as a modifier. The biodegradable PLA coating material formulation provided by the present invention utilizes two-dimensional modified cellulose nanocrystals that are oriented within PLA molecules, reinforcing and toughening the PLA with a high degree of orientation. Furthermore, the acetylated cellulose nanocrystals effectively alleviate the agglomeration and phase separation issues of nanocrystal powder within the PLA resin, effectively avoiding the degradation loss associated with toughening PLA with other elastomers. This material permanently improves the mechanical strength and impact strength of the PLA blend, imparting the same biodegradability and light transmittance as PLA, and enhancing the added value and performance of biodegradable PLA products.

Description

Technical Field

[0001] The present invention relates to the field of preparation of biodegradable materials, in particular to a biodegradable PLA coating material and a biodegradable coating prepared therefrom. Background Art

[0002] In recent years, along with the development of the laminated paper market, the market size of food-grade laminated paper has also continued to expand. In recent years, under the influence of multiple factors, the laminated paper industry has entered a stage of optimization and upgrading.

[0003] PLA is a biodegradable material with excellent safety performance. The PLA coating layer has strong adhesion and glossiness. PLA coated paper has the water and oil resistance properties of PE coated paper. However, pure polylactic acid resin (PLA) is brittle and generally requires a lower weight and higher mechanical properties. It cannot be directly coated. Therefore, PBS or PBAT needs to be introduced to increase the tensile modulus and increase the toughness of the film, or a plasticizer needs to be introduced. However, the introduction of PBS or PBAT will result in failure to meet the precipitation standard, and due to the high density of PBS and PBAT themselves, the weight after coating will exceed 22g / m 2 , and the weight of PE after lamination is 10g / m 2 The difference is more than double, which not only increases costs but also brings disadvantages such as poor gloss, transparency, and mechanical properties. Most of the plasticizers currently introduced are petroleum-based plasticizers, which lead to the risk of precipitation. The film cannot come into direct contact with food and cannot be used for coated paper cups and coated paper lunch boxes. Summary of the Invention

[0004] To address the aforementioned issues with the existing technology, the present invention provides a biodegradable PLA coating material. This material is enhanced and modified by adding non-toxic and harmless grafted cellulose nanocrystals to PLA, resulting in a coating material with improved performance. This invention aims to ensure the full biodegradability, safety, and environmental friendliness of the PLA material, making it safe for food contact, while also simplifying the process and meeting industrial requirements for carbon emission reduction.

[0005] To achieve the purpose, the present invention adopts the following technical solutions:

[0006] A biodegradable PLA coating material comprises the following raw materials in parts by weight: 88.5 to 94.6 parts of PLA resin, 0.3 to 1 part of lubricant, 5 to 10 parts of grafted coated cellulose nanocrystals, and 0.1 to 0.5 parts of antioxidant.

[0007] Furthermore, the preparation method of the grafted coated cellulose nanocrystals comprises the following steps:

[0008] S1. Add cellulose nanocrystals CNC into a reactor, then add xylene and citric acid, heat to 120-140°C, stir for 6-8 hours, and cool to room temperature to obtain intermediate A;

[0009] S2. Add acetic anhydride and aminosulfonic acid to the intermediate A obtained in step S1, raise the temperature to 55-70° C. and stir for 3-6 hours to obtain intermediate B;

[0010] S3, removing xylene from the intermediate B obtained in step S2 at a temperature of 105 to 130° C. and a pressure of -0.4 to -0.6 MPa for 4 to 6 hours to obtain pretreated CNC;

[0011] S4. The pretreated CNC is mixed with PLA resin, zinc stearate, and antioxidant 1076, and stirred uniformly at a speed of 300-500 r / min at room temperature for 3-6 minutes. The resulting mixture is extruded into pellets through a twin-screw extruder at an extruder temperature of 120-195° C. and an extruder speed of 350-400 rpm, and then dried at 55-60° C. for 4-6 hours to obtain grafted cellulose nanocrystals.

[0012] Furthermore, in the preparation method of the grafted coated cellulose nanocrystals: the mass ratio of xylene to CNC is 10:1, the added amount of citric acid is 5 to 20 wt% of the mass of CNC, the added amount of acetic anhydride is 30 to 50 wt% of the mass of citric acid, the added amount of sulfamic acid is 1 to 2 wt% of the mass of acetic anhydride, the added amount of CNC is 20 to 50 wt% of the mass of PLA, the added amount of zinc stearate is 0.2 to 0.8 wt% of the mass of PLA, and the added amount of antioxidant 1076 is 0.2 to 0.5 wt% of the mass of PLA.

[0013] Furthermore, the PLA resin is of blown film grade, with a melt index of 3 to 5 g / 10 min (190° C., 2.16 kg).

[0014] Most preferably, the raw materials of the biodegradable PLA coating material are composed of 91.5 parts by weight of PLA resin, 10 parts of grafted coated cellulose nanocrystals, 0.2 parts of antioxidant 1076, and 0.3 parts of lubricant stearic acid.

[0015] The biodegradable coating material of the present invention can be processed into the desired coating product by the following method: the raw materials are weighed according to the proportion and added to a high-speed mixer for thorough mixing, the resulting mixture is sent to a twin-screw extruder for extrusion and granulation, then transported to a dryer for repeated drying, and then sent to a coating machine for coating and film formation (paper drawing → coating → longitudinal stretching → cooling → winding), so as to obtain a biodegradable coating product of a certain thickness.

[0016] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0017] 1. The biodegradable coating material provided by this invention comprises a polylactic acid resin (PLA) with grafted, coated nanofiber crystals added as a reinforcing and toughening modifier. During subsequent high-temperature twin-screw extrusion granulation (extrusion temperature 165-210°C), the acetylated cellulose nanocrystals are evenly dispersed and oriented within the PLA, reinforcing and toughening the PLA with a high degree of orientation. This system exhibits high melt strength, resulting in films with enhanced strength, tear resistance, and heat sealing properties when stretched longitudinally by the coating machine. This permanently improves the bond strength between PLA and fiber paper, as well as the mechanical and impact strength of the PLA blend, enhancing the safety of biodegradable film products.

[0018] 2. The modifier used in the present invention is a non-toxic and harmless grafted cellulose nanocrystal. By acidifying and then acetylating the cellulose nanocrystals, the problems of high surface energy and easy agglomeration of the cellulose nanocrystals are solved. No toxic solvents are introduced and no precipitation occurs. The product does not have residues of xylene, toluene, heavy metals, etc., is more environmentally friendly, and the products made can come into contact with food.

[0019] 3. The grafted coated cellulose nanocrystals of the present invention do not affect the degradation rate, effectively avoiding the problem of degradation rate loss after toughening PLA with other elastomers. It also does not affect its size, directly avoiding damage to the transparency and gloss of PLA, and improving the high added value and performance of biodegradable PLA products.

[0020] 4. The biodegradable coating material of the present invention is green and environmentally friendly, can be in contact with food safely, and can be widely used in the fields of paper cups, hotel supplies, takeaway supplies, snacks and fast food supplies.

[0021] 5. The preparation process of the biodegradable coating material of the present invention is simple and is expected to be industrialized. Its promotion and application will bring great economic and social benefits.

[0022] 6. The present invention adds grafted coated cellulose nanocrystals to PLA. After lamination, the resulting modified material has excellent longitudinal tensile strength, elongation at break, and heat sealing. The elongation at break increases from 5% (without grafted cellulose nanocrystals) to 16%. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a TEM image of pure cellulose nanocrystals used in Example 1 of the present invention.

[0024] Figure 2 This is an SEM image of the grafted and coated cellulose nanocrystals obtained in Example 1 of the present invention.

[0025] Figure 3 This is a SEM image of a coating film processed using the biodegradable coating material of Comparative Example 1 of the present invention.

[0026] Figure 4 This is a SEM image of a coating film processed using the biodegradable coating material of Example 2 of the present invention. DETAILED DESCRIPTION

[0027] The present invention is described in detail below through examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention. Those skilled in the art may make some non-essential improvements and adjustments based on the above contents of the present invention, which still fall within the scope of protection of the present invention.

[0028] The polylactic acid resin used in the following examples is FY804 produced by Anhui Fengyuan Futailai Lactic Acid Co., Ltd., with a melt index of 4-5 g / 10 min (190° C., 2.16 kg).

[0029] Example 1

[0030] In this example, grafted cellulose nanocrystals were prepared according to the following steps, which served as the modifier used in subsequent examples:

[0031] S1, 10 kg cellulose nanocrystals CNC (diameter 4-10 nm, length 50-500 nm) (TEM image as shown Figure 1 The reaction mixture was added with 100 kg of xylene and 1 kg of citric acid, and the mixture was heated to 140° C. and stirred for 6 h. The mixture was cooled to room temperature to obtain intermediate A.

[0032] S2. Add 0.3 kg of acetic anhydride and 0.004 kg of aminosulfonic acid to the intermediate A obtained in step S1, raise the temperature to 70° C. and stir for 3 h to obtain intermediate B.

[0033] S3, the intermediate B obtained in step S2 was removed from xylene at a temperature of 105°C and a pressure of -0.4 MPa for 4 hours to obtain pretreated CNC, the SEM image of which is shown as follows: Figure 2 shown.

[0034] S4. The pretreated CNC was mixed with 34 kg of PLA resin, 0.08 kg of zinc stearate, and 0.08 kg of antioxidant 1076, and stirred uniformly at a speed of 500 r / min at room temperature for 3 min. The resulting mixture was extruded into pellets through a twin-screw extruder at an extruder temperature of 120-195 ° C and an extruder speed of 350 rpm, and then dried at 60 ° C for 4 hours to obtain grafted coated cellulose nanocrystals.

[0035] Example 2

[0036] The raw materials of the biodegradable PLA coating material of this embodiment are composed of 91.5 parts of PLA resin, 5 parts of grafted coated cellulose nanocrystals, 0.2 parts of antioxidant 1076, and 0.3 parts of lubricant stearic acid.

[0037] Example 3

[0038] The raw materials of the biodegradable PLA coating material of this embodiment are composed of 91.5 parts of PLA resin, 8 parts of grafted coated nanofiber crystals, 0.2 parts of antioxidant 1076, and 0.3 parts of lubricant stearic acid.

[0039] Example 4

[0040] The raw materials of the biodegradable PLA coating material of this embodiment are composed of 91.5 parts of PLA resin, 10 parts of grafted coated nanofiber crystals, 0.2 parts of antioxidant 1076, and 0.3 parts of lubricant stearic acid.

[0041] Comparative Example 1

[0042] The raw materials of the biodegradable PLA coating material of this comparative example are composed of 91.5 parts of PLA resin, 5 parts of pure cellulose nanocrystals, 0.2 parts of antioxidant 1076, and 0.3 parts of lubricant stearic acid.

[0043] In order to test the performance of the biodegradable coated materials in Examples 2 to 4 and Comparative Example 1, they were processed into fully biodegradable coated paper according to the following method: the raw materials were weighed according to the ratio and added to a high-speed mixer for thorough mixing (speed of 500 r / min, time of 6 min), the resulting mixture was sent to a twin-screw extruder for extrusion granulation (temperature 165-210 ° C, speed of 330 r / min), and then transported to a dryer for repeated drying, and then sent to a coating machine for coating (paper drawing → coating → longitudinal stretching → cooling → winding) to obtain a biodegradable coated product of a certain thickness, 18-18.4 g / m 2 .

[0044] The tensile strength, elongation at break and sealing strength of the laminated papers obtained in Examples 2 to 4 and Comparative Example 1 were tested according to GB / T 1040.2-2006. The results are shown in Table 1.

[0045] Table 1

[0046]

[0047] As can be seen from Table 1, the biodegradable PLA coated paper with the addition of the modifier in Examples 2 to 4 has good breaking strength and elongation at break, improved heat sealing, high transparency and decomposition rate retention, and low total migration amount, which meets the food contact safety requirements and can meet the use requirements of PLA coated paper materials for paper cups, takeout supplies, and snack and fast food supplies.

[0048] Figure 3 This is a SEM image of the coating made from the biodegradable coating material of Comparative Example 1 of the present invention. Figure 4 This is an SEM image of the coating made using the biodegradable coating material of Example 2 of the present invention. By comparison, it can be seen that the addition of grafted and coated cellulose nanocrystals significantly improves the compatibility of PLA.

[0049] The foregoing description shows preferred embodiments of the present invention. As stated above, it should be understood that the present invention is not limited to the forms of experimentation performed herein and should not be construed as excluding other embodiments. Rather, it is open to various combinations, modifications, and environments, and is capable of being modified within the scope of the invention described herein by utilizing the techniques of the related art. Modifications and variations made by those skilled in the art without departing from the scope of the present invention are intended to be within the scope of the appended claims.

Claims

1. A biodegradable PLA coating material, characterized by: The raw materials of the biodegradable PLA coating material are composed of 88.5 to 94.6 parts of PLA resin, 0.3 to 1 part of lubricant, 5 to 10 parts of grafted coated cellulose nanocrystals, and 0.1 to 0.5 parts of antioxidant. The preparation method of the grafted coated cellulose nanocrystals comprises the following steps: S1. Add cellulose nanocrystals CNC into a reactor, then add xylene and citric acid, heat to 120-140°C, stir for 6-8 hours, and cool to room temperature to obtain intermediate A; S2. Add acetic anhydride and aminosulfonic acid to the intermediate A obtained in step S1, raise the temperature to 55-70° C. and stir for 3-6 hours to obtain intermediate B; S3, removing xylene from the intermediate B obtained in step S2 at a temperature of 105 to 130° C. and a pressure of -0.4 to -0.6 MPa for 4 to 6 hours to obtain pretreated CNC; S4. The pretreated CNC is mixed with PLA resin, zinc stearate, and antioxidant 1076, and stirred uniformly at a speed of 300-500 r / min at room temperature for 3-6 minutes. The resulting mixture is extruded into granules through a twin-screw extruder at an extruder temperature of 120-195° C. and an extruder speed of 350-400 rpm, and then dried at 55-60° C. for 4-6 hours to obtain grafted coated cellulose nanocrystals.

2. The biodegradable PLA coating material according to claim 1, characterized in that: The mass ratio of xylene to CNC is 10:1, the added amount of citric acid is 5-20wt% of the mass of CNC, the added amount of acetic anhydride is 30-50wt% of the mass of citric acid, the added amount of sulfamic acid is 1-2wt% of the mass of acetic anhydride, the added amount of CNC is 20-50wt% of the mass of PLA, the added amount of zinc stearate is 0.2-0.8wt% of the mass of PLA, and the added amount of antioxidant 1076 is 0.2-0.5wt% of the mass of PLA.

3. The biodegradable PLA coating material according to claim 1, characterized in that: The PLA resin is of blown film grade, and has a melt index of 3-5 g / 10 min at 190° C. and a load of 2.16 kg.

4. The biodegradable PLA coating material according to claim 1, characterized in that: The raw materials of the biodegradable PLA coating material are composed of 91.5 parts of PLA resin, 10 parts of grafted coated cellulose nanocrystals, 0.2 parts of antioxidant 1076, and 0.3 parts of lubricant stearic acid.

5. A coated product made from the biodegradable PLA coating material according to any one of claims 1 to 4.

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