Preparation method of degradable polylactic acid packaging box

Abstract

The invention relates to the technical field of packaging boxes, and particularly discloses a preparation method of a degradable polylactic acid packaging box. The method comprises the following steps: firstly coating the surface of graphene oxide with a 3-hydroxybutyrate and 4-hydroxybutyrate copolymer, and then grafting maleic anhydride to obtain a modified graphene filler; blending the modified graphene filler with polylactic acid and a 3-hydroxybutyrate and 4-hydroxybutyrate copolymer according to a specific ratio, performing extrusion granulation, and pressing into sheets; and after the sheet is preheated, the sheet is heated to the hot-pressing temperature, hot-pressed, cooled and shaped, and the packaging box is obtained. The packaging box is excellent in toughness, has high ductility, can be rapidly formed at the hot pressing temperature, and is high in yield.

Description

Technical Field

[0001] The present invention relates to the technical field of packaging boxes, and more specifically, to a method for preparing a degradable polylactic acid packaging box. Background Art

[0002] Polylactic acid, also known as polylactide, is a thermoplastic aliphatic polyester with excellent biodegradability and biocompatibility. It is safe and non-toxic and can be applied to the field of food packaging, with great development potential. In terms of mechanical properties, the tensile strength of polylactic acid is generally 45MPa~70MPa, and the elongation at break is only 3%~10%; in terms of thermal properties, the melting point of polylactic acid is 170℃~180℃, and the glass transition temperature is as low as 53℃. At the same time, it can be seen from the molecular structure that the molecular chain segments of polylactic acid contain a large number of ester bonds. In the presence of water molecules, the ester bonds are prone to hydrolysis reactions, resulting in breakage, which accelerates the degradation of polylactic acid. Therefore, polylactic acid itself has poor heat resistance, poor toughness, and poor hydrolysis stability. During the hot pressing process, polylactic acid sheets are prone to uneven softening, and local stretching of polylactic acid sheets is difficult, which leads to local breakage of polylactic acid packaging boxes, and the yield rate of polylactic acid packaging boxes is low. Summary of the invention

[0003] In order to solve the problem of low production yield of polylactic acid packaging boxes, the present application provides a method for preparing a degradable polylactic acid packaging box.

[0004] The present application provides a method for preparing a degradable polylactic acid packaging box, which adopts the following technical solution: A method for preparing a degradable polylactic acid packaging box comprises the following steps: Prefabricated modified filler: 3-hydroxybutyrate and 4-hydroxybutyrate copolymer and graphene oxide are mixed in a weight ratio of (1.68-2.12):1, heated to 70-90°C, and kept warm for reaction for 0.5-1h to obtain an intermediate; maleic anhydride and an initiator are prepared into a modified liquid, and the modified liquid is added to the intermediate, wherein maleic anhydride and graphene oxide are added in a weight ratio of (0.35-0.70):1, and the modified liquid and the intermediate are ultrasonically dispersed, and after dispersion, placed at 80-100°C, kept warm for reaction for 20-40min, swelled for 10-15h, and microwave irradiated after swelling is completed, reacted for 10-15min, to obtain a modified graphene filler; Mixing and granulation: polylactic acid, 3-hydroxybutyrate and 4-hydroxybutyrate copolymer, and modified graphene filler are blended, wherein the weight ratio of polylactic acid, 3-hydroxybutyrate and 4-hydroxybutyrate copolymer, and modified graphene filler is 1:(1.884-1.968):(0.22-0.66), extrusion granulation, heating and hot pressing to obtain a sheet; Molding process: put the sheet into the mold for preheating, preheat to 100-150℃, keep warm for 10-20min, raise the temperature to 180-200℃ after preheating, hot press molding, cool and shape to get the packaging box.

[0005] Furthermore, in the step of prefabricating the modified filler, the weight ratio of the copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate, maleic anhydride and graphene oxide is (1.86-1.94):(0.5-0.6):1.

[0006] Furthermore, in the step of prefabricating the modified filler, the molar fraction of 4-hydroxybutyrate in the copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate is 20 to 35%.

[0007] Furthermore, in the step of prefabricating the modified filler, maleic anhydride is dissolved in xylene, and the concentration of maleic anhydride in the modified solution is 5 to 10 wt %.

[0008] Furthermore, in the step of prefabricating the modified filler, the sheet diameter D of the graphene oxide is 50 =100nm, D 90 =300nm.

[0009] Furthermore, in the step of prefabricating the modified filler, the intensity of microwave irradiation is 350-400W.

[0010] Furthermore, in the mixing and granulation step, the weight average molecular weight of the polylactic acid is 10,800 to 16,000.

[0011] Furthermore, in the mixing and granulation step, the weight ratio of polylactic acid, 3-hydroxybutyrate and 4-hydroxybutyrate copolymer, and modified graphene filler is 1:(1.9-1.92):(0.44-0.55).

[0012] Furthermore, in the mixing and granulation step, the particle size D of the modified graphene filler is 50 =500nm, D 90 =1200nm.

[0013] Furthermore, in the molding process, the preheating treatment is performed in stages, firstly the temperature is raised to 100° C., and the temperature is kept for preheating for 10 minutes, and then the temperature is raised to 150° C., and the temperature is kept for preheating for 5 minutes.

[0014] This application has at least the following advantages: First, in this application, the steps of prefabricating modified fillers, mixing granulation and molding are carried out in sequence to produce a hard packaging box with a high yield rate. The packaging box has excellent toughness, resistance to water and oily solvents, and excellent heat resistance; the specific principles are as follows: In the step of prefabricating modified fillers, 3-hydroxybutyrate and 4-hydroxybutyrate copolymers and maleic anhydride are sequentially grafted on the surface of graphene fillers to obtain modified graphene fillers; the surface of graphene oxide contains active functional groups such as carboxyl, hydroxyl, and epoxy groups, and the chain segments of 3-hydroxybutyrate and 4-hydroxybutyrate copolymers contain functional groups such as hydroxyl and ester groups. The 3-hydroxybutyrate and 4-hydroxybutyrate copolymers can be combined on the surface of graphene oxide by forming ester groups or by hydrogen bonds, intermolecular forces, etc.; the 3-hydroxybutyrate and 4-hydroxybutyrate copolymers are further grafted and modified with maleic anhydride, and the double bonds of maleic anhydride are opened under the action of initiators such as dibenzoyl peroxide and connected to the chain segments of the 3-hydroxybutyrate and 4-hydroxybutyrate copolymers, so that the surface of graphene oxide is rich in active groups such as hydroxyl and anhydride; In the mixing and granulation step, modified graphene filler, polylactic acid and 3-hydroxybutyrate and 4-hydroxybutyrate copolymer are selected for blending and granulation. The surface of the modified graphene filler is rich in acid anhydride. The modified graphene filler can be used as both a thermal conductive material and a compatibility modifier. The polylactic acid chain segment contains carboxyl and hydroxyl groups, which can enhance the compatibility with the 3-hydroxybutyrate and 4-hydroxybutyrate copolymer under the action of acid anhydride. After blending, the 3-hydroxybutyrate and 4-hydroxybutyrate copolymer and a small amount of 3-hydroxybutyrate and 4-hydroxybutyrate copolymer macromolecular chain segments on the surface of the modified graphene filler reduce the polylactic acid crystal regularity, the macromolecular chain segments are easy to move, and the toughness of the sheet is improved. During the molding process, since the sheet is rich in graphene oxide, which has good thermal conductivity, the sheet is preheated in the hot press, and the heat is quickly transferred to the sheet. The temperature of the sheet rises evenly, and then rises to the predetermined pressing temperature. The sheet melts to form a continuous matrix material, and the sheet can be quickly hot-pressed and finally cooled and shaped. The packaging box has a high yield rate.

[0015] Second, the modified graphene filler is attached to the surface of the packaging box, and a micro-nano structure is formed on the surface of the packaging box. The micro-nano structure gives the packaging box good hydrophobicity, and it is difficult for water, oil and other solvents to penetrate the surface of the packaging box. The ester group in the packaging box is not easy to decompose, and the packaging box has good hydrolysis resistance and solvent resistance.

[0016] Third, the modified graphene filler in the packaging box has good heat dissipation performance, and the heat dissipation effect of the packaging box is relatively excellent; at the same time, hydrogen bonds are formed between maleic anhydride, polylactic acid, 3-hydroxybutyrate and 4-hydroxybutyrate copolymers in the packaging box, and the cross-linking density of the packaging box is increased. Without reducing the toughness of the packaging box, the glass transition temperature of the packaging box is high; under the action of modified graphene and maleic anhydride, the heat resistance of the packaging box is excellent, and the packaging box can withstand high temperatures above 105°C without deformation.

[0017] Fourth, in the molding process, the segmented preheating operation can shorten the molding time of the sheet at high temperature, which can reduce the possibility of degradation of polylactic acid, 3-hydroxybutyrate and 4-hydroxybutyrate copolymer, thereby further reducing the possibility of damage to the packaging box during the molding process. DETAILED DESCRIPTION

[0018] Unless otherwise specified, the sources of raw materials involved in the following preparation examples, embodiments and comparative examples are as follows: Polylactic acid: Product number: 001, weight average molecular weight is 9000, intrinsic viscosity is 0.15dL / g; Product number: 002, weight average molecular weight is 10800, viscosity is 0.162dL / g; Product number: 003, weight average molecular weight is 16000, viscosity is 0.185dL / g; Product number: 004, weight average molecular weight is 30000, viscosity is 0.28dL / g; Maleic anhydride: analytical grade; 3-Hydroxybutyrate and 4-Hydroxybutyrate Copolymer: Customized product; Product No. 1: The mole fraction of 4-hydroxybutyrate is 20%, and the weight average molecular weight is 15,000; Product No. 2: The mole fraction of 4-hydroxybutyrate is 30%, and the weight average molecular weight is 18,600; Product No. 3: The mole fraction of 4-hydroxybutyrate is 35%, and the weight average molecular weight is 20,800; Product No. 4: The mole fraction of 4-hydroxybutyrate is 7% and the weight average molecular weight is 11,500; Graphene oxide: Item No. A#, sheet diameter D 50 =15μm, D 90 =30μm; Item No. B#, sheet diameter D 50 =100nm, D 90 =300nm; Item No. C#, sheet diameter D 50 =10nm, D 90 =30nm.

[0019] Example 1

[0020] A method for preparing a degradable polylactic acid packaging box is carried out according to the following steps: Take a copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate, the molar fraction of the copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate is 20%, the weight average molecular weight is 15,000, and the same copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate is used in the subsequent prefabricated modified filler and mixed granulation steps; take graphene oxide, the sheet diameter of graphene oxide is D 50 =100nm, D 90 =300nm; take polylactic acid, the weight average molecular weight of polylactic acid is 10,800; Prefabricated modified filler: 3-hydroxybutyrate and 4-hydroxybutyrate copolymer and graphene oxide were added in a weight ratio of 1.68:1, put into a reactor, heated to 70° C., and kept warm for 1 hour to obtain an intermediate; Add maleic anhydride and initiator dibenzoyl peroxide into xylene, stir and blend, and form a modified solution, wherein the weight ratio of maleic anhydride to graphene oxide is 0.35:1, the concentration of maleic anhydride in the modified solution is 5wt%, and the concentration of dibenzoyl peroxide in the modified solution is 0.015wt%; Add the modified liquid to the intermediate, perform ultrasonic dispersion, the ultrasonic power is 150W, the ultrasonic time is 30min, the temperature is raised to 80°C after the ultrasonic treatment, the temperature is kept for 40min, the reaction is swollen for 10h after the reaction is completed, and microwave irradiation is performed after the swelling is completed, the irradiation intensity is 350W, and the irradiation is performed for 15min to obtain a modified graphene filler; the modified graphene filler is screened to control the particle size D of the modified graphene filler 50 =500nm, D 90 =1200nm; Mixing and granulation: Put polylactic acid, 3-hydroxybutyrate and 4-hydroxybutyrate copolymer, and modified graphene filler into a twin-screw mixer according to a weight ratio of 1:0.884:0.22, and the twin-screw mixer performs extrusion granulation, and the extruded particles are heated to 180° C. and hot-pressed to obtain a sheet; The sheet is placed in an oven for curing and is ready for use; Forming process: The sheet is placed in a hot press for preheating to 100°C, kept warm for 20 minutes, and then heated to 180°C, hot-pressed at a moving speed of 1 cm / s, cooled and shaped to obtain a packaging box.

[0021] Example 2

[0022] A method for preparing a degradable polylactic acid packaging box is carried out according to the following steps: Take a copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate, the molar fraction of the copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate is 20%, the weight average molecular weight is 15,000, and the same copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate is used in the subsequent prefabricated modified filler and mixed granulation steps; take graphene oxide, the sheet diameter of graphene oxide is D 50 =100nm, D 90 =300nm; take polylactic acid, the weight average molecular weight of polylactic acid is 10,800; Prefabricated modified filler: 3-hydroxybutyrate and 4-hydroxybutyrate copolymer and graphene oxide were added in a weight ratio of 1.86:1, put into a reactor, heated to 80° C., and kept warm for 0.75 h to obtain an intermediate; Adding maleic anhydride and an initiator dibenzoyl peroxide into xylene, stirring and blending to form a modified solution, wherein the weight ratio of maleic anhydride to graphene oxide is 0.5:1, the concentration of maleic anhydride in the modified solution is 8wt%, and the concentration of dibenzoyl peroxide in the modified solution is 0.02wt%; Add the modified liquid to the intermediate, perform ultrasonic dispersion, the ultrasonic power is 200W, the ultrasonic time is 30min, the temperature is raised to 90°C after the ultrasonic is finished, the temperature is kept for reaction for 30min, the reaction is swollen for 12h after the reaction is finished, microwave irradiation is performed after the swelling is completed, the irradiation intensity is 350W, and after irradiation for 15min, a modified graphene filler is obtained; the modified graphene filler is screened to control the particle size D of the modified graphene filler 50 =500nm, D 90 =1200nm; Mixing and granulation: Put polylactic acid, 3-hydroxybutyrate and 4-hydroxybutyrate copolymer, and modified graphene filler into a twin-screw mixer according to a weight ratio of 1:0.884:0.22, and the twin-screw mixer performs extrusion granulation, and the extruded particles are heated to 180° C. and hot-pressed to obtain a sheet; The sheet is placed in an oven for curing and is ready for use; Forming process: The sheet is placed in a hot press for preheating to 100°C, kept warm for 20 minutes, and then heated to 180°C, hot-pressed at a moving speed of 1 cm / s, cooled and shaped to obtain a packaging box.

[0023] Example 3

[0024] A method for preparing a degradable polylactic acid packaging box is carried out according to the following steps: Take a copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate, the molar fraction of the copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate is 20%, the weight average molecular weight is 15,000, and the same copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate is used in the subsequent prefabricated modified filler and mixed granulation steps; take graphene oxide, the sheet diameter of graphene oxide is D 50 =100nm, D 90 =300nm; take polylactic acid, the weight average molecular weight of polylactic acid is 10,800; Prefabricated modified filler: 3-hydroxybutyrate and 4-hydroxybutyrate copolymer and graphene oxide were added in a weight ratio of 1.94:1, put into a reactor, heated to 90° C., and kept warm for 0.5 h to obtain an intermediate; Add maleic anhydride and initiator dibenzoyl peroxide into xylene, stir and blend, and form a modified solution, wherein the weight ratio of maleic anhydride to graphene oxide is 0.6:1, the concentration of maleic anhydride in the modified solution is 10wt%, and the concentration of dibenzoyl peroxide in the modified solution is 0.025wt%; Add the modified liquid to the intermediate, perform ultrasonic dispersion, the ultrasonic power is 250W, the ultrasonic time is 30min, the temperature is raised to 100°C after the ultrasonic treatment, the temperature is kept for 20min, the reaction is swollen for 15h after the reaction is completed, microwave irradiation is performed after the swelling is completed, the irradiation intensity is 400W, and the irradiation is performed for 10min to obtain a modified graphene filler; the modified graphene filler is screened to control the particle size D of the modified graphene filler 50 =15μm, D 90 =30μm; Mixing and granulation: Put polylactic acid, 3-hydroxybutyrate and 4-hydroxybutyrate copolymer, and modified graphene filler into a twin-screw mixer according to a weight ratio of 1:0.884:0.22, and the twin-screw mixer performs extrusion granulation, and the extruded particles are heated to 180° C. and hot-pressed to obtain a sheet; The sheet is placed in an oven for curing and is ready for use; Forming process: The sheet is placed in a hot press for preheating to 100°C, kept warm for 20 minutes, and then heated to 180°C, hot-pressed at a moving speed of 1 cm / s, cooled and shaped to obtain a packaging box.

[0025] Example 4

[0026] A method for preparing a degradable polylactic acid packaging box is carried out according to the following steps: Take a copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate, the molar fraction of the copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate is 20%, the weight average molecular weight is 15,000, and the same copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate is used in the subsequent prefabricated modified filler and mixed granulation steps; take graphene oxide, the sheet diameter of graphene oxide is D 50 =100nm, D 90 =300nm; take polylactic acid, the weight average molecular weight of polylactic acid is 10,800; Prefabricated modified filler: 3-hydroxybutyrate and 4-hydroxybutyrate copolymer and graphene oxide are added in a weight ratio of 1.2.12:1, put into a reactor, heat to 90°C, and keep the temperature for 0.5h to obtain an intermediate; Adding maleic anhydride and an initiator dibenzoyl peroxide into xylene, stirring and blending to form a modified solution, wherein the weight ratio of maleic anhydride to graphene oxide is 0.7:1, the concentration of maleic anhydride in the modified solution is 10wt%, and the concentration of dibenzoyl peroxide in the modified solution is 0.03wt%; Add the modified liquid to the intermediate, perform ultrasonic dispersion, the ultrasonic power is 300W, the ultrasonic time is 30min, the temperature is raised to 100°C after the ultrasonic treatment, the temperature is kept for 20min, the reaction is swollen for 15h after the reaction is completed, microwave irradiation is performed after the swelling is completed, the irradiation intensity is 400W, and the irradiation is performed for 10min to obtain a modified graphene filler; the modified graphene filler is screened to control the particle size D of the modified graphene filler 50 =15μm, D 90 =30μm; Mixing and granulation: Put polylactic acid, 3-hydroxybutyrate and 4-hydroxybutyrate copolymer, and modified graphene filler into a twin-screw mixer according to a weight ratio of 1:0.884:0.22, and the twin-screw mixer performs extrusion granulation, and the extruded particles are heated to 180° C. and hot-pressed to obtain a sheet; The sheet is placed in an oven for curing and is ready for use; Forming process: The sheet is placed in a hot press for preheating to 100°C, kept warm for 20 minutes, and then heated to 180°C, hot-pressed at a moving speed of 1 cm / s, cooled and shaped to obtain a packaging box.

[0027] Embodiment 5-7 A method for preparing a degradable polylactic acid packaging box, which differs from Example 3 in that, in the mixing and granulation step, the weight ratios of polylactic acid, 3-hydroxybutyrate and 4-hydroxybutyrate copolymer, and modified graphene filler are different, as follows: In Example 5, the weight ratio of polylactic acid, 3-hydroxybutyrate and 4-hydroxybutyrate copolymer, and modified graphene filler is 1:1.9:0.44; In Example 6, the weight ratio of polylactic acid, 3-hydroxybutyrate and 4-hydroxybutyrate copolymer, and modified graphene filler is 1:1.92:0.55; In Example 7, the weight ratio of polylactic acid, 3-hydroxybutyrate and 4-hydroxybutyrate copolymer, and modified graphene filler is 1:1.968:0.66.

[0028] Embodiment 8-9 A method for preparing a degradable polylactic acid packaging box, which differs from Example 6 in that the sheet diameter of the graphene oxide filler is different, as follows: In Example 8, the sheet diameter D of graphene oxide is 50 =10nm, D 90 =30nm, the obtained modified graphene filler particle size D 90 =300nm; In Example 9, the sheet diameter D of graphene oxide is 50 =15μm, D 90 =30μm, the obtained modified graphene filler particle size D 90 >20μm.

[0029] Example 10

[0030] A method for preparing a degradable polylactic acid packaging box, which differs from Example 6 in that the specific operations of the molding process are different: the sheet is placed in a hot press for preheating, and the preheating treatment is divided into sections and treatments, first heated to 100°C, kept warm for 10 minutes, then heated to 150°C, kept warm for 5 minutes, and after the preheating treatment, heated to 180°C, hot-pressed at a moving speed of 1 cm / s, cooled and shaped to obtain a packaging box.

[0031] Examples 11-16 A method for preparing a degradable polylactic acid packaging box, which differs from Example 10 in that the selection of polylactic acid and the selection of a copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate are different, as follows: In Example 11, the weight average molecular weight of polylactic acid is 16,000, the viscosity is 0.185 dL / g, the molar fraction of 4-hydroxybutyrate in the copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate is 20%, and the weight average molecular weight is 15,000; In Example 12, the weight average molecular weight of the polylactic acid is 30,000, the viscosity is 0.28 dL / g, the molar fraction of 4-hydroxybutyrate in the copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate is 20%, and the weight average molecular weight is 15,000; In Example 13, the weight average molecular weight of the polylactic acid is 9,000, the intrinsic viscosity is 0.15 dL / g, the molar fraction of 4-hydroxybutyrate in the copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate is 20%, and the weight average molecular weight is 15,000; In Example 14, the weight average molecular weight of polylactic acid is 16,000, the viscosity is 0.185 dL / g, the molar fraction of 3-hydroxybutyrate and 4-hydroxybutyrate is 30%, and the weight average molecular weight is 18,600; In Example 15, the weight average molecular weight of the polylactic acid is 16,000, the viscosity is 0.185 dL / g, the molar fraction of 3-hydroxybutyrate and 4-hydroxybutyrate is 35%, and the weight average molecular weight is 20,800; In Example 16, the weight average molecular weight of the polylactic acid is 16,000, the viscosity is 0.185 dL / g, the molar fraction of 3-hydroxybutyrate and 4-hydroxybutyrate is 7%, and the weight average molecular weight is 11,500.

[0032] Comparative Example Comparative Example 1 A method for preparing a degradable polylactic acid packaging box is carried out according to the following steps: Take 3-hydroxybutyrate and 4-hydroxybutyrate copolymer, the mole fraction of 3-hydroxybutyrate and 4-hydroxybutyrate copolymer is 20%, and the weight average molecular weight is 15,000; take graphene oxide, the sheet diameter of graphene oxide is D 50 =100nm, D 90 =300nm; take polylactic acid, the weight average molecular weight of polylactic acid is 10,800; Mixing and granulation: Put polylactic acid, 3-hydroxybutyrate and 4-hydroxybutyrate copolymer, and graphene oxide filler into a twin-screw mixer according to a weight ratio of 1:0.884:0.22, and the twin-screw mixer performs extrusion granulation, and the extruded particles are heated to 180° C. and hot-pressed to obtain a sheet; The sheet is placed in an oven for curing and is ready for use; Forming process: The sheet is placed in a hot press for preheating to 100°C, kept warm for 20 minutes, and then heated to 180°C, hot-pressed at a moving speed of 1 cm / s, cooled and shaped to obtain a packaging box.

[0033] Comparative Example 2 A method for preparing a degradable polylactic acid packaging box is carried out according to the following steps: Take a copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate, the molar fraction of the copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate is 20%, the weight average molecular weight is 15,000, and the same copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate is used in the subsequent prefabricated modified filler and mixed granulation steps; take graphene oxide, the sheet diameter of graphene oxide is D 50 =100nm, D 90 =300nm; take polylactic acid, the weight average molecular weight of polylactic acid is 10,800; Prefabricated modified filler: Add maleic anhydride and initiator dibenzoyl peroxide into xylene, stir and blend to form a modified liquid, wherein the weight ratio of maleic anhydride to graphene oxide is 0.35:1, the concentration of maleic anhydride in the modified liquid is 5wt%, and the concentration of dibenzoyl peroxide in the modified liquid is 0.015wt%; Adding a modifying liquid to the graphene oxide filler, performing ultrasonic dispersion, the ultrasonic power is 150 W, the ultrasonic time is 30 min, the temperature is raised to 80° C. after the ultrasonication, the temperature is kept for 40 min, the reaction is swollen for 10 h after the reaction is completed, and microwave irradiation is performed after the swelling is completed, the irradiation intensity is 350 W, and after irradiation for 15 min, a modified graphene filler is obtained; the modified graphene filler is screened; Mixing and granulation: Put polylactic acid, 3-hydroxybutyrate and 4-hydroxybutyrate copolymer, and modified graphene filler into a twin-screw mixer according to a weight ratio of 1:0.884:0.22, and the twin-screw mixer performs extrusion granulation, and the extruded particles are heated to 180° C. and hot-pressed to obtain a sheet; The sheet is placed in an oven for curing and is ready for use; Forming process: The sheet is placed in a hot press for preheating to 100°C, kept warm for 20 minutes, and then heated to 180°C, hot-pressed at a moving speed of 1 cm / s, cooled and shaped to obtain a packaging box.

[0034] Comparative Example 3 A method for preparing a degradable polylactic acid packaging box is carried out according to the following steps: Take a copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate, the molar fraction of the copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate is 20%, the weight average molecular weight is 15,000, and the same copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate is used in the subsequent prefabricated modified filler and mixed granulation steps; take graphene oxide, the sheet diameter of graphene oxide is D 50 =100nm, D 90 =300nm; take polylactic acid, the weight average molecular weight of polylactic acid is 10,800; Prefabricating modified filler: adding 3-hydroxybutyrate and 4-hydroxybutyrate copolymer and graphene oxide in a weight ratio of 1.68:1, putting into a reactor, heating to 70° C., keeping the temperature for 1 hour, and obtaining modified graphene filler; Mixing and granulation: Put polylactic acid, 3-hydroxybutyrate and 4-hydroxybutyrate copolymer, and modified graphene filler into a twin-screw mixer according to a weight ratio of 1:0.884:0.22, and the twin-screw mixer performs extrusion granulation, and the extruded particles are heated to 180° C. and hot-pressed to obtain a sheet; The sheet is placed in an oven for curing and is ready for use; Forming process: The sheet is placed in a hot press for preheating to 100°C, kept warm for 20 minutes, and then heated to 180°C, hot-pressed at a moving speed of 1 cm / s, cooled and shaped to obtain a packaging box.

[0035] Comparative Example 4 A method for preparing a degradable polylactic acid packaging box is carried out according to the following steps: Take a copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate, the molar fraction of the copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate is 20%, the weight average molecular weight is 15,000, and the same copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate is used in the subsequent prefabricated modified filler and mixed granulation steps; take graphene oxide, the sheet diameter of graphene oxide is D 50 =100nm, D 90 =300nm; take polylactic acid, the weight average molecular weight of polylactic acid is 10,800; Prefabricated modified filler: 3-hydroxybutyrate and 4-hydroxybutyrate copolymer and graphene oxide were added in a weight ratio of 1.68:1, put into a reactor, heated to 70° C., and kept warm for 1 hour to obtain an intermediate; Add maleic anhydride and initiator dibenzoyl peroxide into xylene, stir and blend, and form a modified solution, wherein the weight ratio of maleic anhydride to graphene oxide is 0.35:1, the concentration of maleic anhydride in the modified solution is 5wt%, and the concentration of dibenzoyl peroxide in the modified solution is 0.015wt%; Adding a modifying liquid to the intermediate, performing ultrasonic dispersion, the ultrasonic power is 150 W, the ultrasonic time is 30 min, the temperature is raised to 80° C. after the ultrasonic is finished, the temperature is kept for reaction for 40 min, the reaction is swollen for 10 h, and microwave irradiation is performed after the swelling is completed, the irradiation intensity is 350 W, and after irradiation for 15 min, a modified graphene filler is obtained; the modified graphene filler is screened; Mixing and granulation: Put polylactic acid and modified graphene filler into a twin-screw mixer at a weight ratio of 1:0.22, and perform extrusion granulation in the twin-screw mixer. Heat the extruded particles to 180° C. and perform hot pressing to obtain a sheet. The sheet is placed in an oven for curing and is ready for use; Forming process: The sheet is placed in a hot press for preheating to 100°C, kept warm for 20 minutes, and then heated to 180°C, hot-pressed at a moving speed of 1 cm / s, cooled and shaped to obtain a packaging box.

[0036] Performance Testing

[0037] The packaging boxes prepared in Examples 1-16 and Comparative Examples 1-4 were randomly sampled, each example or comparative example being a batch, 20 boxes were sampled from each batch, and the following tests were performed on the samples sampled from each batch: 1. Yield rate: Count the number of defective products in each batch of 10,000 packaging boxes. Products that have at least one of the following conditions are considered defective: the packaging box has holes or damage; the wall thickness of the packaging box is uneven; the color of the packaging box is uneven, and the color depth is uneven; the packaging box does not conform to the target shape of the mold; the packaging box has local deformation, scratches, stains and other problems; Yield rate = number of defective products / total number × 100%.

[0038] 2. Tensile strength and elongation at break: Cut out specimens from the packaging box samples, and use GF-HV2000A-C6W computer servo universal testing machine to test the tensile strength and elongation at break of the specimens according to the test standard GB / T 1040.1-2018; record the test data of the specimens and calculate the mean of each batch of specimens.

[0039] 3. Drop resistance: According to the test standard GB / T 4857.5-1992, put a 1kg weight into the packaging box, raise it to 3m, release it, repeat 5 times, observe whether the packaging box is damaged, count the damage, record the damaged area, and use the average value as the drop resistance test data; the larger the damaged area, the worse the drop resistance.

[0040] 4. Solvent resistance: Soak the packaging box in an ethanol aqueous solution with an ethanol concentration of 55wt%, observe its immersion state, and record the time it takes for the packaging box to soften and degrade. The shorter the time, the worse the solvent resistance of the material.

[0041] 5. Heat resistance: Place the packaging box in a high and low temperature test chamber, gradually increase the temperature at a rate of 1°C / min until the packaging box softens or deforms, and record the highest tolerable temperature of the packaging box. The higher the tolerable temperature, the better the heat resistance.

[0042] 6. Heavy metal content and harmful substance limit test: According to the test standard GB 4806.7-2023, if the heavy metal content is ≤1mg / kg and the total migration of aromatic primary amines is lower than the detection limit of 0.01mg / kg, the physical and chemical indicators are qualified.

[0043] Table 1. Performance test data of polylactic acid packaging boxes of Examples 1-16 and Comparative Examples 1-4

[0044] Examples 1-16 and Comparative Examples 1-4 all passed the heavy metal content and harmful substance limit tests, indicating that the packaging box prepared by the preparation method of the present application is safe and non-toxic and meets the standards for contact use with food packaging.

[0045] According to the test data, we can see that: First, Example 1 and Comparative Example 1 form a single comparison. In Comparative Example 1, only graphene oxide filler is added, but the active functional groups on the surface of the graphene oxide filler are relatively few, and the compatibility with polylactic acid and 3-hydroxybutyrate and 4-hydroxybutyrate copolymer is relatively poor. The graphene oxide filler is easy to agglomerate, and stress concentration points appear. In addition, the sheet is heated unevenly during the molding process. The molten sheet cannot be fully extended during the hot pressing process. The sheet breaks at some positions during the deformation process, resulting in the packaging box being broken and the yield rate being reduced.

[0046] Second, Example 1 and Comparative Example 2 form a single comparison. The surface of the modified graphene filler used in Comparative Example 2 is modified by only using maleic anhydride to modify graphene oxide. The surface of the graphene oxide sheet lacks the coating of the macromolecular chain segments of the 3-hydroxybutyrate and 4-hydroxybutyrate copolymer. Although maleic anhydride helps to promote the compatibility of graphene oxide, the size of the modified graphene filler is small, and it is difficult to form a micro-nano structure on the surface of the packaging box, thereby failing to form a super-hydrophobic bionic structure. The hydrophobic performance of the packaging box is significantly reduced, and the hydrolysis resistance of the packaging box is reduced.

[0047] Third, Example 1 and Comparative Example 3 form a single comparison. In Comparative Example 3, only 3-hydroxybutyrate and 4-hydroxybutyrate copolymers are grafted onto the surface of graphene oxide, and the compatibility between the modified graphene filler and polylactic acid is limitedly improved. The formed sheet is still prone to stress concentration points. The sheet is unevenly heated during the molding process and is difficult to fully soften and mold. It is easy to break during the stretching process, which leads to a decrease in the yield rate of the packaging box.

[0048] Fourth, Example 1 and Comparative Example 4 form a single comparison. In Comparative Example 4, only modified graphene filler is added as a modifier. Due to the lack of the toughening effect of the copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate, even at a lower modified graphene filler dosage, the sheet is difficult to fully stretch and is prone to breakage, resulting in a reduced yield rate of the packaging box.

[0049] Fifth, Examples 1-4 form a single comparison, and the only difference is that the parameters of the prefabricated modified filler step are different. According to the test data in Table 1, it can be seen that the 3-hydroxybutyrate and 4-hydroxybutyrate copolymer and maleic anhydride are controlled within a moderate proportion range, and the 3-hydroxybutyrate and 4-hydroxybutyrate copolymer is better coated on the surface of graphene oxide. At the same time, the grafting rate of maleic anhydride is moderate. Under the premise of not affecting the toughness and yield rate of the packaging box, the cross-linking strength inside the packaging box is increased, and the tensile strength is improved.

[0050] Sixth, Examples 3 and 5-7 form a single contrast, and the only difference is that the ratios of modified graphene filler, polylactic acid, and 3-hydroxybutyrate and 4-hydroxybutyrate copolymers in the mixing and granulation step are different, and the amount of modified graphene filler added should not be too high. The amount of modified graphene filler added is high, the content of maleic anhydride is high, and the cross-linking density of the sheet is significantly increased. The segment movement of the sheet is greatly restricted, which easily leads to the difficulty of segment movement in the subsequent molding and processing steps of the sheet, uneven stretching of the sheet, and reduced yield. When the amount of modified graphene filler added is small, although the sheet is easy to stretch, the heat resistance and hydrolysis resistance of the packaging box are reduced.

[0051] Seventh, Examples 6 and 8-9 form a single comparison. The particle size composition of the modified graphene filler has a significant effect on the solvent resistance of the packaging box. The micro-nano structure on the surface of the packaging box allows a thin air layer to exist when the packaging box is immersed in the solvent, which increases the contact angle between the solvent and the packaging box, making it difficult for the solvent to easily infiltrate the packaging box.

[0052] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0053] Moreover, the above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A method for preparing a degradable polylactic acid packaging box, characterized in that: Prefabricated modified filler: 3-hydroxybutyrate and 4-hydroxybutyrate copolymer and graphene oxide are mixed in a weight ratio of (1.68-2.12):1, heated to 70-90°C, and kept warm for reaction for 0.5-1h to obtain an intermediate; maleic anhydride and an initiator are prepared into a modified liquid, and the modified liquid is added to the intermediate, wherein maleic anhydride and graphene oxide are added in a weight ratio of (0.35-0.70):1, and the modified liquid and the intermediate are ultrasonically dispersed, and after dispersion, placed at 80-100°C, kept warm for reaction for 20-40min, swelled for 10-15h, and microwave irradiated after swelling is completed, reacted for 10-15min, to obtain a modified graphene filler; Mixing and granulation: polylactic acid, 3-hydroxybutyrate and 4-hydroxybutyrate copolymer, and modified graphene filler are blended, wherein the weight ratio of polylactic acid, 3-hydroxybutyrate and 4-hydroxybutyrate copolymer, and modified graphene filler is 1:(1.884-1.968):(0.22-0.66), extrusion granulation, heating and hot pressing to obtain a sheet; Molding process: preheat the sheet to 100-150°C, keep warm for 10-20 minutes, raise the temperature to 180-200°C after preheating, hot press mold, cool and shape to obtain a packaging box.

2. The method for preparing a degradable polylactic acid packaging box according to claim 1, characterized in that: In the step of prefabricating the modified filler, the weight ratio of the copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate, maleic anhydride and graphene oxide is (1.86-1.94):(0.5-0.6):

1.

3. The method for preparing a degradable polylactic acid packaging box according to claim 1, characterized in that: In the step of prefabricating the modified filler, the molar fraction of 4-hydroxybutyrate in the copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate is 20 to 35%.

4. The method for preparing a degradable polylactic acid packaging box according to claim 1, characterized in that: In the step of prefabricating the modified filler, maleic anhydride is dissolved in xylene, and the concentration of maleic anhydride in the modified solution is 5-10 wt %.

5. The method for preparing a degradable polylactic acid packaging box according to claim 1, characterized in that: In the step of prefabricating the modified filler, the sheet diameter D of the graphene oxide is 50 =100nm, D 90 =300nm.

6. The method for preparing a degradable polylactic acid packaging box according to claim 1, characterized in that: In the step of prefabricating the modified filler, the intensity of microwave irradiation is 350-400W.

7. The method for preparing a degradable polylactic acid packaging box according to claim 2, characterized in that: In the mixing and granulation step, the weight average molecular weight of the polylactic acid is 10,800 to 16,000.

8. The method for preparing a degradable polylactic acid packaging box according to claim 2, characterized in that: In the mixing and granulation step, the weight ratio of polylactic acid, 3-hydroxybutyrate and 4-hydroxybutyrate copolymer, and modified graphene filler is 1:(0.9-0.92):(0.44-0.55).

9. The method for preparing a degradable polylactic acid packaging box according to claim 2, characterized in that: In the mixing and granulation step, the particle size D of the modified graphene filler is 50 =500nm, D 50 =1200nm.

10. The method for preparing a degradable polylactic acid packaging box according to claim 1, characterized in that: In the molding process, the preheating treatment is performed in stages, firstly the temperature is raised to 100° C., and the temperature is kept for preheating for 10 minutes, then the temperature is raised to 150° C., and the temperature is kept for preheating for 5 minutes.

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