Preparation method of high-biomass-content polylactic acid composite material capable of being used for injection molding

Abstract

The invention relates to the technical field of polylactic acid, and discloses a preparation method of a high-biomass-content polylactic acid composite material capable of being used for injection molding. The raw materials of the composite material comprise 40-50 parts of polylactic acid, 50-60 parts of amination modified biomass fibers and 5-10 parts of epoxy vegetable oil, the raw materials are subjected to melt blending to prepare granules which can be used for injection molding processing, but the processing method is not limited to an injection molding mode, but also can be used for modes such as mold pressing, blow molding and plastic uptake. The biomass fibers comprise bamboo fibers, wood fibers, straw fibers and other plant fibers. The epoxidized vegetable oil comprises epoxidized soybean oil, epoxidized castor oil and other epoxidized vegetable oil derived from plants. The content of biomass fibers in the composite material prepared by the invention exceeds 50%, but the composite material can be used for injection molding of the composite material. Meanwhile, the composite material has good mechanical strength, the tensile strength is higher than 35.6 MPa, and the bending strength is higher than 74.5 MPa. The polylactic acid composite material with low cost and high biomass fiber content can be promoted to be applied to the aspect of injection molding processing.

Description

Technical Field

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

[0002] Polylactic acid is a biodegradable polymer material obtained through chemical synthesis with lactic acid as the main raw material. In recent years, with the continuous development of the "plastic ban", polylactic acid has become the main biodegradable product to replace petroleum-based plastics, and has broad prospects in catering packaging, take-out tableware, agricultural tools, home decoration, clothing and shoes, etc.

[0003] However, one of the main factors limiting the large-scale use of polylactic acid is the high price of polylactic acid, which is 3-5 times the price of similar petroleum-based plastics. In order to reduce the cost of polylactic acid during use, it is necessary to add low-cost fillers to reduce the cost of composite materials. Adding biomass fibers to make biomass polylactic acid composites has been widely studied, but the melt viscosity of polylactic acid is low. When the biomass content exceeds 30% of the total mass, its molding and processing method will be limited, and it is difficult to use injection molding to process and mold. Authorization announcement number CN 106147173 B discloses a high-toughness polylactic acid wood-plastic composite material, but due to the high content of modified plant fibers, hot pressing molding is selected. However, the cost of polylactic acid composite materials after adding plant fibers is still too high. While ensuring the mechanical strength of the composite material, it is hoped that the biomass fiber content will be increased to more than 50% to ensure that the cost of the composite material is further reduced. Summary of the invention

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

[0005] The technical solution of the present invention: A polylactic acid composite material with high performance, low cost, simple process and environmental protection, characterized in that: 40-50 parts of polylactic acid, 50-60 parts of aminated modified biomass fiber and 5-10 parts of epoxidized vegetable oil are prepared by melt blending the raw materials to obtain pellets that can be used for molding processing.

[0006] Preferably, the preparation method of the aminated modified biomass fiber is as follows: Take 200g of biomass, add 1500ml of distilled water, then add 2.5g of 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO), 25g of sodium bromide and 225ml of 9% sodium hypochlorite solution. Stir at room temperature for 6h, keep the pH at 8.5, wash and dry to obtain oxidized biomass fiber. Take 200g of dried oxidized biomass fiber, add 1500ml of distilled water, then add 11.2g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC), 8.1g of N-hydroxysuccinimide (NHS) and 5ml of aminating agent, react at 40°C for 5h, wash and dry to obtain aminated biomass fiber.

[0007] Preferably, the amination modifier to be added in the preparation method of the amination-modified biomass is characterized in that one or more amine compounds are used, such as diethylenetriamine, tetraethylenetriamine and other amine compounds.

[0008] Preferably, the biomass fiber can be one or more of plant biomass such as bamboo fiber, wood fiber, hemp fiber, etc.

[0009] Preferably, the epoxidized vegetable oil may be one or more of epoxidized modified vegetable oils from plants such as epoxidized soybean oil and epoxidized castor oil.

[0010] Preferably, a method for preparing a polylactic acid composite material with a high biomass content that can be used for injection molding comprises the following steps:

[0011] (1) PLA, aminated modified biomass fiber, and epoxy vegetable oil are placed in an oven to dry and remove excess water. (2) Weighing by weight: polylactic acid, aminated modified biomass fiber, and epoxy vegetable oil are added to a mixer and mixed evenly, and then extruded and granulated in a twin-screw extruder at 170-190° C. in each zone to obtain pellets. The pellets are then processed by injection molding or other molding methods to obtain molded products.

[0012] Preferably, the pellets can be formed by injection molding, but other plastic molding methods such as blow molding, compression molding, vacuum forming, etc. can also be selected.

[0013] The beneficial effects of the present invention are:

[0014] (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.

[0015] (2) The mechanical strength of the high biomass content polylactic acid composite material that can be used for injection molding, such as tensile strength and flexural strength, still maintains a certain value and can be used as a material. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 : Infrared spectra of bamboo fiber and aminated bamboo fiber.

[0017] Figure 2 : Injection molding pictures of samples of Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0018] Figure 3 : The tensile strength of the samples of Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0019] Figure 4 : The bending strength of the samples of Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3. DETAILED DESCRIPTION

[0020] Embodiment 1:

[0021] Take 200g of bamboo fiber and add 1500ml of distilled water, then add 2.5g of 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO), 25g of sodium bromide and 225ml of 9% sodium hypochlorite solution. Stir at room temperature for 6h, keep the pH at 8.5, then wash and dry to obtain oxidized bamboo fiber. Take 200g of dried oxidized bamboo fiber and add 1500ml of distilled water, then add 11.2g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC), 8.1g of N-hydroxysuccinimide (NHS) and 5ml of triethylenediamine, react at 40°C for 5h, then wash and dry to obtain aminated bamboo fiber.

[0022] 40 parts of polylactic acid, 60 parts of aminated modified bamboo fiber and 5 parts of epoxy soybean oil were mixed evenly in a mixer, and then extruded and granulated at 180°C in each zone in a twin-screw extruder to obtain pellets. The pellets were processed by injection molding or other molding methods to obtain pellets, and melted at 190°C for 4 minutes and 30 seconds in a micro injection molding machine to obtain products.

[0023] Embodiment 2:

[0024] Take 200g of bamboo fiber and add 1500ml of distilled water, then add 2.5g of 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO), 25g of sodium bromide and 225ml of 9% sodium hypochlorite solution. Stir at room temperature for 6h, keep the pH at 8.5, then wash and dry to obtain oxidized bamboo fiber. Take 200g of dried oxidized bamboo fiber and add 1500ml of distilled water, then add 11.2g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC), 8.1g of N-hydroxysuccinimide (NHS) and 5ml of triethylenediamine, react at 40°C for 5h, then wash and dry to obtain aminated bamboo fiber.

[0025] 40 parts of polylactic acid, 60 parts of aminated modified bamboo fiber, and 10 parts of epoxy 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 pellets. The pellets were processed by injection molding or 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 products.

[0026] Comparative Example 1

[0027] Pure polylactic acid was injection molded in a micro injection molding machine at 180°C for 3 min 30 s to obtain a product.

[0028] Comparative Example 2

[0029] 40 parts of polylactic acid and 60 parts of 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 pellets. The pellets were processed by injection molding or other molding methods to obtain pellets, and then injection molded in a micro injection molding machine at 190°C for 4min30s and 5min30s to obtain products.

[0030] Comparative Example 3

[0031] 40 parts of polylactic acid, 60 parts of bamboo fiber and 5 parts of epoxy soybean oil were mixed evenly in a mixer, and then extruded and granulated at 180°C in each zone in a twin-screw extruder to obtain pellets. The pellets were processed by injection molding or 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 products.

[0032] Comparative Example 4

[0033] 40 parts of polylactic acid, 60 parts of bamboo fiber and 10 parts of epoxy 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 pellets. The pellets were processed by injection molding or 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 products.

[0034] The infrared spectrum of aminated bamboo fiber is as follows: Figure 1 As shown in the figure. The pictures of different samples after injection molding are as follows Figure 2 The tensile strength results of the samples are shown in Figure 3 The bending strength results of the samples are shown in Figure 4 As shown, the test methods for mechanical properties are based on GB / T 1040-2006 (determination of tensile properties of plastics) and GB / T9341-2008 (determination of bending properties of plastics) standard methods.

[0035] from Figure 1 The infrared spectra of bamboo fiber before and after amination show that 1559cm -1 The stretching vibration peak of NH bond appeared at , indicating that the aminated bamboo fiber was successfully prepared.

[0036] from Figure 2 It can be seen that even after heating for 4 min 30 s, the comparative example 2 still cannot be completely injected to obtain a sample, while both examples 1 and 2 can obtain complete samples by injection molding.

[0037] from Figure 2 and Figure 3 It can be seen that the tensile and bending properties of the embodiment are improved to a certain extent compared with those with bamboo fiber added, indicating that the aminated biomass can react with the epoxidized vegetable oil.

[0038] This patent invents a method for preparing a high-biomass content polylactic acid composite material that can be used for injection molding, which has the advantages of low cost, high mechanical strength, and multiple processability.

Claims

1. A method for preparing a polylactic acid composite material with a high biomass content that can be used for injection molding, characterized in that: The raw materials are melt-blended with 40-50 parts of polylactic acid, 50-60 parts of aminated modified biomass fibers and 5-10 parts of epoxy vegetable oil to obtain pellets which can be used for molding processing. The method for preparing the polylactic acid composite material with high biomass content comprises the following steps: treating biomass with an amination modifier to obtain aminated biomass fibers; The aminated biomass fiber, polylactic acid and epoxy vegetable oil are melt-blended and then extruded and granulated to obtain pellets; The pellets are injection molded to obtain a biomass polylactic acid composite product.

2. The aminated biomass according to claim 1 is modified by amination of oxidized biomass fibers using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC), N-hydroxysuccinimide (NHS) and an aqueous solution of an aminated modifier.

3. The aminated modifier to be added in the preparation method of aminated modified biomass fiber according to claim 1 is characterized in that: One or more amine compounds are used, such as diethylenetriamine, tetraethylenetriamine and the like.

4. The addition content of the aminated modified biomass according to claim 1, characterized in that: The total added content of the aminated modified biomass exceeds 50% of the total mass.

5. Add epoxidized vegetable oil according to claim 1, characterized in that, The epoxidized vegetable oil used is one or more of epoxidized modified vegetable oils from plants, such as epoxidized soybean oil and epoxidized castor oil.

6. According to the claim 1, it is characterized in that It can be used for injection molding, but the processing method is not limited to injection molding, it can also be used for molding methods such as compression molding, blow molding, and vacuum forming.

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