A method for preparing a high biomass content polylactic acid composite material suitable for injection molding.

Abstract

This invention relates to the field of polylactic acid (PLA) technology and discloses a method for preparing a high-biomass-content PLA composite material suitable for injection molding. The composite material consists of 40-50 parts PLA, 50-60 parts amination-modified biomass fiber, and 5-10 parts epoxidized vegetable oil. The raw materials are melt-blended to obtain granules suitable for injection molding. However, the processing method is not limited to injection molding; compression molding, blow molding, and thermoforming are also possible. The biomass fibers include bamboo fiber, wood fiber, straw fiber, and other plant fibers. The epoxidized vegetable oil includes epoxidized soybean oil, epoxidized castor oil, and other plant-derived epoxidized vegetable oils. The composite material produced by this invention contains more than 50% biomass fiber but can be used for injection molding. Simultaneously, the composite material exhibits good mechanical strength, with a tensile strength exceeding 35.6 MPa and a flexural strength exceeding 74.5 MPa. This can promote the application of low-cost, high-biomass-fiber-content PLA composite materials in injection molding.

Description

Technical Field

[0001] This invention belongs to the field of biodegradable polymer materials and material molding, specifically relating to a method for preparing a polylactic acid composite material with high biomass content that can be used for injection molding. Background Technology

[0002] Polylactic acid (PLA) is a biodegradable polymer material obtained through chemical synthesis using lactic acid as the main raw material. In recent years, with the continuous development of the "plastic restriction order," PLA has become the main biodegradable product to replace petroleum-based plastics, and has broad prospects in many aspects such as catering packaging, takeaway tableware, agricultural tools, home decoration, clothing and footwear.

[0003] One of the main factors limiting the large-scale use of polylactic acid (PLA) is its high price, which is 3-5 times that of similar petroleum-based plastics. To reduce the cost of using PLA, low-cost fillers need to be added to lower the cost of composite materials. The addition of biomass fibers to create biomass PLA composites has been extensively studied, but PLA has a low melt viscosity. When the biomass content exceeds 30% of the total mass, its molding and processing methods become limited, making injection molding difficult. Authorization notice number CN 106147173 B discloses a high-toughness PLA wood-plastic composite, but due to the excessively high content of modified plant fibers, hot pressing was chosen. However, the cost of PLA composites with added plant fibers remains too high. While ensuring the mechanical strength of the composite, it is hoped that the biomass fiber content can be increased to over 50% to further reduce the cost of the composite. Summary of the Invention

[0004] In order to obtain high-performance, low-cost, environmentally friendly and biodegradable biomass polylactic acid-based composite materials, the present invention aims to provide a method for preparing high biomass content polylactic acid composite materials that can be used for injection molding.

[0005] The technical solution of this invention:

[0006] A high-performance, low-cost, simple and environmentally friendly polylactic acid composite material is characterized by being composed of 40-50 parts polylactic acid, 50-60 parts amination-modified biomass fiber, and 5-10 parts epoxidized vegetable oil. The raw materials are melt-blended to obtain granules that can be used for molding and processing.

[0007] As a preferred embodiment, the preparation method of the amination-modified biomass fiber is as follows:

[0008] 200g of biomass was added to 1500ml of distilled water, followed by 2.5g of 2,2,6,6-tetramethylpiperidin-1-oxy (TEMPO), 25g of sodium bromide, and 225ml of 9% (v / v) sodium hypochlorite solution. The mixture was stirred at room temperature for 6 hours, maintaining the pH at 8.5, then washed and dried to obtain oxidized biomass fiber. 200g of the dried oxidized biomass fiber was then added to 1500ml of distilled water, followed by 11.2g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC), 8.1g of N-hydroxysuccinimide (NHS), and 5ml of amination agent. The mixture was reacted at 40℃ for 5 hours, then washed and dried to obtain amination-treated biomass fiber.

[0009] Preferably, the amination modifier to be added in the preparation method of the amination-modified biomass is characterized by using one or more amine compounds, such as diethylenetriamine, tetraethylenetriamine, etc.

[0010] Preferably, the biomass fiber can be one or more plant biomass such as bamboo fiber, wood fiber, and hemp fiber.

[0011] Preferably, the epoxidized vegetable oil may be one or more of the following: epoxidized vegetable oil derived from plants, such as epoxidized soybean oil and epoxidized castor oil.

[0012] Preferably, a method for preparing a high biomass content polylactic acid composite material suitable for injection molding includes the following steps:

[0013] (1) Place polylactic acid, amination-modified biomass fiber and epoxy vegetable oil in an oven to dry and remove excess moisture.

[0014] (2) Weigh out polylactic acid, amination-modified biomass fiber, and epoxy vegetable oil by weight and add them to a mixer to mix evenly. Then, extrude and granulate the mixture in a twin-screw extruder at 170-190℃ in each zone to obtain granules. The granules are then processed by injection molding and other molding methods to obtain molded products.

[0015] Preferably, the granules can be formed by injection molding, but other plastic molding methods such as blow molding, compression molding, vacuum forming, etc., can also be selected.

[0016] The beneficial effects of this invention are as follows:

[0017] (1) The biomass content in the composite material is higher than 50%, which greatly reduces the cost while the molding and processing methods are not restricted.

[0018] (2) High biomass content polylactic acid composite materials that can be used for injection molding still maintain certain values ​​of mechanical strength such as tensile strength and flexural strength, and can be used as materials. Attached Figure Description

[0019] Figure 1 Infrared spectra of bamboo fiber and aminated bamboo fiber.

[0020] Figure 2 Injection molding images of samples from Examples 1, 2, 1, 2, and 3.

[0021] Figure 3 Tensile strength of samples from Examples 1, 2, 1, 2, and 3.

[0022] Figure 4 Bending strength of samples from Examples 1, 2, 1, 2, and 3. Detailed Implementation

[0023] Example 1:

[0024] 200g of bamboo fiber was added to 1500ml of distilled water, followed by 2.5g of 2,2,6,6-tetramethylpiperidin-1-oxy (TEMPO), 25g of sodium bromide, and 225ml of 9% sodium hypochlorite solution. The mixture was stirred at room temperature for 6 hours, maintaining the pH at 8.5, and then washed and dried to obtain oxidized bamboo fiber. 200g of the dried oxidized bamboo fiber was then added to 1500ml of distilled water, followed by 11.2g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC), 8.1g of N-hydroxysuccinimide (NHS), and 5ml of triethylenediamine. The mixture was reacted at 40℃ for 5 hours, followed by washing and drying to obtain aminated bamboo fiber.

[0025] 40 parts polylactic acid, 60 parts ammoniated modified bamboo fiber, and 5 parts epoxidized soybean oil were mixed evenly in a mixer, and then extruded and granulated in a twin-screw extruder at 180°C in each zone to obtain granules. The granules were then processed by injection molding and other molding methods to obtain pellets, and then melted at 190°C for 4 min 30 s in a micro injection molding machine to obtain the finished product.

[0026] Example 2:

[0027] 200g of bamboo fiber was added to 1500ml of distilled water, followed by 2.5g of 2,2,6,6-tetramethylpiperidin-1-oxy (TEMPO), 25g of sodium bromide, and 225ml of 9% sodium hypochlorite solution. The mixture was stirred at room temperature for 6 hours, maintaining the pH at 8.5, and then washed and dried to obtain oxidized bamboo fiber. 200g of the dried oxidized bamboo fiber was then added to 1500ml of distilled water, followed by 11.2g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC), 8.1g of N-hydroxysuccinimide (NHS), and 5ml of triethylenediamine. The mixture was reacted at 40℃ for 5 hours, followed by washing and drying to obtain aminated bamboo fiber.

[0028] 40 parts polylactic acid, 60 parts ammoniated modified bamboo fiber, and 10 parts epoxidized soybean oil were mixed evenly in a mixer, and then extruded and granulated in a twin-screw extruder at 180°C in each zone to obtain granules. The granules were then processed by injection molding and other molding methods to obtain pellets, and then injection molded in a micro injection molding machine at 180°C for 3 minutes and 30 seconds to obtain finished products.

[0029] Comparative Example 1

[0030] The product is obtained by injection molding pure polylactic acid at 180℃ for 3 minutes and 30 seconds in a micro injection molding machine.

[0031] Comparative Example 2

[0032] 40 parts polylactic acid and 60 parts bamboo fiber were mixed evenly in a mixer, and then extruded and granulated in a twin-screw extruder at 180°C in each zone to obtain granules. The granules were then processed by injection molding and other molding methods to obtain finished products.

[0033] Comparative Example 3

[0034] 40 parts polylactic acid, 60 parts bamboo fiber, and 5 parts epoxidized soybean oil were mixed evenly in a mixer, and then extruded and granulated in a twin-screw extruder at 180°C in each zone to obtain granules. The granules were then processed by injection molding and other molding methods to obtain finished products.

[0035] Comparative Example 4

[0036] 40 parts polylactic acid, 60 parts bamboo fiber, and 10 parts epoxidized soybean oil were mixed evenly in a mixer, and then extruded and granulated in a twin-screw extruder at 180°C in each zone to obtain granules. The granules were then processed by injection molding and other molding methods to obtain finished products by injection molding at 180°C for 3 minutes and 30 seconds in a micro injection molding machine.

[0037] Infrared spectra of amination-modified bamboo fiber as follows Figure 1 As shown. Images of different samples molded using injection molding methods are shown below. Figure 2 As shown. The tensile strength results of the sample are as follows. Figure 3 As shown, the bending strength results of the sample are as follows: Figure 4 As shown, the mechanical properties were tested using the standard methods of GB / T 1040-2006 (Determination of tensile properties of plastics) and GB / T9341-2008 (Determination of flexural properties of plastics).

[0038] from Figure 1 A comparison of the infrared spectra of bamboo fibers before and after amination shows that at 1559 cm⁻¹... -1 The appearance of the stretching vibration peak of the NH bond indicates that the amination of bamboo fiber was successfully prepared.

[0039] from Figure 2 It can be seen that even after heating for 4 minutes and 30 seconds, Comparative Example 2 still could not be completely injection molded to obtain a sample, while Examples 1 and 2 could both obtain complete samples through injection molding.

[0040] from Figure 2 and Figure 3 It can be seen that the embodiment shows a certain improvement in tensile and bending properties compared to the one with added bamboo fiber, indicating that amination biomass can react with epoxidized vegetable oil.

[0041] This patent invention discloses a method for preparing polylactic acid composite materials with high biomass content that can be used for injection molding, which has advantages such as low cost, high mechanical strength, and various processability.

Claims

1. A method for preparing a high biomass content polylactic acid composite material suitable for injection molding, characterized in that: 200g of bamboo fiber was added to 1500ml of distilled water, followed by 2.5g of 2,2,6,6-tetramethylpiperidin-1-oxy, 25g of sodium bromide, and 225ml of 9% sodium hypochlorite solution. The mixture was stirred at room temperature for 6 hours, maintaining the pH at 8.5, and then washed and dried to obtain oxidized bamboo fiber. 200g of dried oxidized bamboo fiber was added to 1500ml of distilled water, followed by 11.2g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, 8.1g of N-hydroxysuccinimide, and 5ml of triethylenediamine. The mixture was reacted at 40℃ for 5 hours, followed by washing and drying to obtain aminated bamboo fiber. 40 parts polylactic acid, 60 parts ammoniated modified bamboo fiber, and 5 parts epoxidized soybean oil were mixed evenly in a mixer, and then extruded and granulated in a twin-screw extruder at 180°C in each zone to obtain granules. The granules were then melted at 190°C for 4 min 30 s in a micro injection molding machine to obtain the finished product.

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