Preparation method of degradable high-strength polylactic acid-based composite material

Abstract

The application relates to the technical field of polylactic acid, and discloses a preparation method of high-strength and degradable polylactic acid composite materials. The preparation method is as follows: firstly, wood powder is treated by using cellulase; then polylactic acid, cellulase modified wood powder and a compatilizer are blended according to a certain proportion; and finally, the composite material is prepared through reactive extrusion. The bending strength and tensile strength of the polylactic acid composite material are respectively increased by 21.45% and 28.85% after modification. The method uses a safe and simple two-step process, reduces the polylactic acid consumption by 20%-30%, makes the cost low, and the tensile and bending properties exceed those of polylactic acid, especially the bending modulus is increased by 43.96% compared with pure polylactic acid. The method provides a high-strength, simple preparation process and low-cost method for the polylactic acid composite material, and widens the application of polylactic acid.

Description

Technical Field

[0001] This invention belongs to the field of biodegradable polymer materials and food materials, specifically relating to a method for preparing polylactic acid / wood fiber composite materials with low cost, high mechanical properties and simple process. Background Technology

[0002] Polylactic acid (PLA) is a high-molecular polymer prepared from lactic acid obtained by fermentation of corn, rice, etc. Due to its good biocompatibility, biodegradability, renewability, and non-toxicity and non-irritation to the human body, it is used as a substitute for traditional non-degradable materials and is widely used in medical, pharmaceutical, agricultural, packaging, and clothing industries, with broad industrial prospects.

[0003] Although polylactic acid (PLA) is a crystallizable, renewable, and biodegradable material, its mechanical properties are limited due to numerous side reactions during production, making it difficult to further increase its molecular weight. This hinders the production of high-performance PLA and limits its wider application and promotion. To address this, some researchers have explored ways to reduce PLA costs by blending or copolymerizing inexpensive wood fibers with PLA. Application CN202211222401.2 discloses a method for blending high-density polyethylene, PLA, PLA-grafted polyethylene compatibilizer, and wood flour to obtain a self-compensating modified polyethylene wood-plastic composite material; however, its mechanical properties do not meet the requirements. Application CN202111048117.3 discloses a biodegradable, high-performance modified particle PLA-based composite material and its preparation method; however, its cost is high. Summary of the Invention

[0004] To obtain high-strength, low-cost, environmentally friendly, and biodegradable polylactic acid (PLA)-based composite materials, the present invention aims to provide a high-strength, low-cost, simple-process, and environmentally friendly PLA material and its preparation method. It is hoped that this invention will address the shortcomings of existing technologies.

[0005] The technical solution of this invention:

[0006] A high-strength, biodegradable polylactic acid composite material is characterized by: firstly treating wood flour with cellulase to obtain cellulase-modified wood flour; then, producing the composite material by reactive extrusion through a certain proportion of polylactic acid, cellulase-modified wood flour, and a compatibilizer.

[0007] Preferably, the method for preparing the cellulase-modified wood flour is as follows:

[0008] Take 130g of wood flour and add it to a 1000mL beaker, then add distilled water to the 1000mL mark. Soak the mixture for 12 hours, then add 4g of cellulose and adjust the pH to 5-6 with a few drops of glacial acetic acid. Place the mixture in a 50℃ constant temperature water bath and stir for 1-2 hours. Let it stand until the wood flour precipitates, then discard the supernatant. Wash with water, let it stand, and discard the supernatant again. Repeat this washing process 3-5 times. Dry at 80℃ for 2-3 hours to obtain cellulase-modified wood flour.

[0009] Preferably, the cellulase treatment time is inversely proportional to the activity. For example, the cellulase activity is 100,000-200,000 u / g, wherein the wood flour is treated for 1-2 hours.

[0010] Preferably, the compatibilizer includes one or more of 2,2'-(1,3-phenylene)-dioxazoline, polymerized carbodiimide, and 2,2'-bis(2-oxazoline).

[0011] Preferably, the polylactic acid can be L-polylactic acid, D-polylactic acid, or a mixture thereof.

[0012] Preferably, the wood flour can be one or more of wood flour, straw flour, and rice husk flour.

[0013] Preferably, the polylactic acid-based composite material is composed of 70-80 parts polylactic acid, 20-30 parts cellulase-modified wood flour, and 1-3 parts compatibilizer.

[0014] Preferably, the high-strength biodegradable polylactic acid composite material includes the following steps:

[0015] (1) Dry polylactic acid and wood flour in an oven to remove excess moisture.

[0016] (2) Weigh out polylactic acid, wood flour and compatibilizer by weight and add them to the mixer to mix evenly. Then, extrude them in a twin-screw extruder at 170°C in each zone to form a sheet.

[0017] The beneficial effects of this invention are as follows:

[0018] (1) The tensile strength, flexural strength, elongation at break and impact strength of the obtained composite material are greatly improved, and the mechanical properties are excellent, especially the tensile strength and flexural strength.

[0019] (2) The resulting composite material has low cost, which greatly reduces the amount of polylactic acid used, thus making the cost low;

[0020] (3) The preparation process of the obtained composite material is simple, safe and environmentally friendly, avoiding the pollution and cumbersome process caused by organic reagent modification. Detailed Implementation

[0021] Polylactic acid: Model 4032D (NatureWorks Ingeo PLA, USA), density 1.24 g / cm³ 3 The price is 31.5 yuan / kg (25kg per bag).

[0022] 2,2'-(1,3-phenylene)-dioxazoline: Hubei Peizi Pharmaceutical Technology Co., Ltd., price is 400 yuan / kg (25kg per pack).

[0023] Cellulase: Shandong Longket Enzyme Products Co., Ltd., the activity of cellulase is 100,000-200,000 u / g.

[0024] Example 1

[0025] 70 parts of polylactic acid, 30 parts of cellulase-modified wood flour, and 1 part of 2,2'-(1,3-phenylene)-dioxazoline compatibilizer were added to a mixer and mixed evenly. The mixture was then extruded in a twin-screw extruder at 170°C in each zone to obtain a polylactic acid-based composite material.

[0026] Example 2

[0027] 80 parts of polylactic acid, 20 parts of cellulase-modified wood flour, and 1 part of 2,2'-(1,3-phenylene)-dioxazoline compatibilizer were added to a mixer and mixed evenly. The mixture was then extruded in a twin-screw extruder at 170°C in each zone to obtain a polylactic acid-based composite material.

[0028] Example 3

[0029] 80 parts of polylactic acid, 20 parts of cellulase-modified wood flour, and 1.5 parts of compatibilizer were added to a mixer and mixed evenly. The mixture was then extruded in a twin-screw extruder at 170°C in each zone to obtain a polylactic acid-based composite material.

[0030] Example 4

[0031] 80 parts of polylactic acid, 20 parts of cellulase, wood flour, and 1.5 parts of poly2,2'-(1,3-phenylene)-dioxazoline carbodiimide compatibilizer were added to a mixer and mixed evenly. The mixture was then extruded in a twin-screw extruder at 170°C in each zone to obtain a polylactic acid-based composite material.

[0032] Comparative Example 1

[0033] 80 parts polylactic acid and 20 parts wood flour were added to a mixer and mixed evenly. The mixture was then extruded in a twin-screw extruder at 170°C in each zone to obtain a polylactic acid-based composite material.

[0034] Comparative Example 2

[0035] 70 parts polylactic acid and 30 parts wood flour were added to a mixer and mixed evenly. The mixture was then extruded in a twin-screw extruder at 170°C in each zone to obtain a polylactic acid-based composite material.

[0036] Comparative Example 3

[0037] 80 parts of polylactic acid, 20 parts of wood flour, and 1 part of 2,2'-(1,3-phenylene)-dioxazoline compatibilizer were added to a mixer and mixed evenly. The mixture was then extruded in a twin-screw extruder at 170°C in each zone to obtain a polylactic acid-based composite material.

[0038] The mechanical property test results are shown in Table 1. The mechanical property test methods adopted are GBT1843-2008 (Determination of impact strength of simply supported beam of plastic), GB / T 1040-2006 (Determination of tensile properties of plastic) and GB / T9341-2008 (Determination of bending properties of plastic).

[0039] Table 1. Mechanical properties of polylactic acid, Examples 1-4 and Comparative Examples 1-2.

[0040]

[0041] Table 1 shows that the composite material of the present invention has good mechanical properties. Compared with Comparative Example 1, all properties of the example are improved, but the tensile strength, flexural strength and flexural modulus are significantly improved, which shows the effectiveness of cellulase modification and 2,2'-(1,3-phenylene)-dioxazoline modification.

[0042] Based on 1 kg of material, Example 1, Example 2 and polylactic acid were selected for cost comparison of 1 kg, and the costs are shown in Table 2.

[0043] Table 2 Cost budget for Example 1

[0044] Polylactic acid wood flour compatibilizer Cellulase Total cost Price / kg 33.4 2.9 400 99 Dosage required / gram 693.1 297 9.9 12 Total / Yuan 23.5 0.86 3.96 1.19 29.16

[0045] Table 3. Cost budget for Example 2.

[0046]

[0047]

[0048] As can be seen from Tables 2 and 3, when comparing Examples 1 and 2 with polylactic acid, it was found that the cost of Examples 1 and 2 was reduced by RMB 4.24 and RMB 1.22, respectively.

[0049] Considering both mechanical properties and cost, this invention offers advantages such as low cost, good mechanical properties, and a simple modification process. Furthermore, its overall mechanical properties are better than those of polylactic acid (PLA), while maintaining lower cost.

Claims

1. A method for preparing a biodegradable polylactic acid-based composite material, characterized in that, First, wood flour is treated with cellulase to obtain cellulase-modified wood flour. Then, 70-80 parts by weight of polylactic acid, 20-30 parts by weight of cellulase-modified wood flour and 1-3 parts by weight of compatibilizer 2,2'-(1,3-phenylene)-dioxazoline are blended and extruded through a twin-screw extruder at 170°C in each zone to obtain polylactic acid-based composite material. The specific method for cellulase-modified wood flour is as follows: Take 130g of wood flour and add it to a 1000mL beaker, then add distilled water to the 1000mL mark, then soak the resulting mixture for 12 hours, then add 4g of cellulase and add glacial acetic acid to adjust the pH to 5-6, then place the resulting mixture in a constant temperature water bath at 50℃, stir for 1-2 hours, let it stand, and after the wood flour precipitates, pour off the supernatant, then add water to wash, let it stand, pour off the supernatant again, wash 3-5 times, and dry at 80℃ for 2-3 hours to dry. The resulting wood flour is cellulase-modified wood flour. The activity of the cellulase is 100,000~200,000 u / g.

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