A method for improving the dispersibility in the process of preparing biodegradable plastic masterbatch from dry starch

Abstract

This invention belongs to the field of biodegradable plastics technology and relates to a method for improving the dispersibility of dry starch in the preparation of biodegradable plastic masterbatch. Edible oil is added to dry starch with a moisture content of less than 6%, and the mixture is stirred in a high-speed mixer. PLA or PBTA granules are then added and the mixture is stirred further in a high-speed mixer. Finally, the mixture is extruded and granulated to obtain a homogeneous biodegradable plastic masterbatch. The addition of edible oil as a dispersant allows for direct mixing with PLA or PBTA, simplifying the processing, overcoming starch agglomeration, and enabling the starch addition to reach 70%, thus reducing the amount of PLA or PBTA used and lowering material costs. There is no issue of plasticizer precipitation, and the tensile strength, tear strength, elongation, and impact toughness of the product are significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of biodegradable plastics technology and relates to a method for improving the dispersibility of dry starch in the preparation of biodegradable plastic masterbatch. Background Technology

[0002] With increasing environmental awareness and stricter national environmental policies, the plastics industry is increasingly requiring the use of biodegradable plastics for packaging materials such as supermarket plastic bags and takeout containers. Currently, the most common biodegradable plastics on the market are polylactic acid (PLA) and diacid and diol copolyester (PBAT). These two materials are expensive, and their inherent properties result in poor processing performance. Therefore, in practical applications, a large proportion of fillers is often added to improve their performance and reduce the raw material cost of biodegradable plastic masterbatches. Currently, the most commonly used filler for PLA and PBAT is calcium carbonate, but calcium carbonate is an inorganic substance and is difficult to biodegrade naturally. Starch is a more ideal filler for PLA and PBAT, and much research currently focuses on its use in biodegradable plastics. Currently, there are several technical obstacles to applying starch in biodegradable plastics: First, the properties of starch itself result in poor plasticity and difficulty in molding, lacking the mechanical and performance characteristics of traditional plastics. Second, when starch is added to plastic masterbatches as a filler, approximately 30% glycerol needs to be added, and the subsequent precipitation of glycerol increases the viscosity of the masterbatch, affecting subsequent processing and use. Third, commercial starches currently have a high water content, generally around 13%. When commercial starch is added to biodegradable plastic masterbatches, the water will slowly precipitate over time, and the retrogradation of starch will cause biodegradable plastic products to become brittle and their mechanical properties to decline. Patent application number 2021114585542 describes the preparation process of low-moisture dry starch. Plastic masterbatches prepared from dry starch can solve the problem of "brittleness over time" in starch-based plastic products. However, researchers have found that during processing, when dry starch combines with PABT, an agglomeration phenomenon occurs. These agglomerated particles can prevent subsequent processing, reduce the uniformity of the final product's internal structure, and render the product unusable. Currently, there are no literature or patent reports on solving this problem that occurs during the processing of dry starch and PABT alloys. Summary of the Invention

[0003] This invention addresses the problem of "agglomeration" of dry starch during use by proposing a method to improve the dispersibility of dry starch in PBAT plastic.

[0004] To achieve the above objectives, the present invention is implemented using the following technical solution:

[0005] A method for improving the dispersibility of dry starch in PBAT plastic includes the following steps:

[0006] (1) First, mix the bio-oil and PBAT granules evenly in a mixer;

[0007] (2) Add the dry starch to the mixer and continue mixing until a mixture is obtained;

[0008] (3) Add the mixture to a plastic processing machine for melting and processing to obtain a starch and PBAT alloy with uniform structure.

[0009] The dry starch accounts for 10-70% of the alloy mass, and the bio-oil accounts for 2-10% of the dry starch mass.

[0010] Preferably, the bio-oil is one or a combination of plant oils and their modified oils, animal oils and their modified oils.

[0011] Preferably, the dry starch is obtained by the following process: taking semi-wet starch with a moisture content of 15-30%wt from the wet milling starch processing step, or

[0012] Water is mixed with commercially available starch to obtain semi-wet starch with a moisture content of 15-30%wt. After being puffed in an extruder, starch puffed body is obtained. Then, the starch puffed body is dried and pulverized to obtain dry starch with a moisture content of less than 6%.

[0013] Preferably, the dry starch content accounts for 50-70% of the weight of the masterbatch.

[0014] The basic principle of this invention is as follows:

[0015] First, it solves the technical problems encountered in the use of dried starch, reducing or even eliminating the "agglomeration" phenomenon. Furthermore, during the formation of the PBAT alloy, the "agglomeration" phenomenon worsens with increasing dried starch content. When the dried starch content is less than 10% of the alloy mass, this phenomenon almost does not occur; however, when the dried starch content exceeds 70% of the alloy mass, the dried starch almost completely fills the alloy's structure, making the "agglomeration" phenomenon less noticeable. Therefore, this invention requires a dried starch content of 10-70%.

[0016] Secondly, adding bio-oil to the PBAT alloy as a dispersant maintains or even improves the biodegradability of the PBAT plastic. Furthermore, the amount of bio-oil added cannot be too high. If it exceeds 10% of the added dry starch mass, noticeable oil stains will appear on the surface of the starch and PBAT alloy, affecting its use. If the amount added is too low, such as below 2%, it will not effectively disperse the dry starch. Therefore, the requirement for the amount of bio-oil added in this invention is 2-10% of the dry starch mass.

[0017] Furthermore, an unconventional method of adding bio-oil to starch is employed: the problem this invention aims to solve is the "agglomeration" phenomenon that occurs during the processing of dry starch. However, the bio-oil is first mixed with the PBAT plastic matrix and then mixed with the dry starch. This is significant because it can better improve the dispersibility of the dry starch and the dispersibility of the bio-oil in the dry starch.

[0018] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0019] 1. Applying bio-oil as a dispersant for dry starch in biodegradable plastics.

[0020] 2. With the participation of bio-oil, the material uniformity of the resulting dry starch and PBAT plastic alloy is significantly improved.

[0021] 3. No plasticizers such as glycerin are needed during the use of dry starch, so there is no problem of plasticizer precipitation. This avoids the impact of plasticizers on the masterbatch, and the tensile strength, tear strength, elongation and impact toughness of the final product are significantly improved.

[0022] 4. Dry starch and PBAT alloy products do not exhibit the phenomenon of "becoming brittle over time," and the product's shelf life and usage period are significantly extended. Attached Figure Description

[0023] Figure 1 The dry starch and PBAT alloy is obtained by first mixing soybean oil with PBAT and then mixing it with dry starch.

[0024] Figure 2 It is a dry starch and PBAT alloy obtained by mixing only dry starch and PBAT.

[0025] Figure 3 The dry starch-PBAT alloy is obtained by first mixing soybean oil with starch, and then mixing it with PBAT. Detailed Implementation

[0026] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described below with reference to specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0027] Numerous specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways than those described herein, and therefore the invention is not limited to the specific embodiments disclosed in the following specification.

[0028] Example 1

[0029] This embodiment provides a process for preparing a starch-PBAT alloy. 350g of PBAT plastic and 7.5g of soybean oil are weighed and added to a high-speed mixer, where they are mixed for 5 minutes. Then, 150g of dry starch with a moisture content of 1% (the specific preparation process of the dry starch is described in patent application number 2021114585542) is weighed and added to the high-speed mixer, and mixed for another 10 minutes. The mixture is then fed into a single-screw extruder for extrusion. The single-screw extruder parameters are set as follows: speed 15 r / min, three heating zones, and heating temperatures of 60℃ / 140℃ / 145℃. This yields a starch-PBAT alloy with a uniform structure (see [link to relevant documentation]). Figure 1 ).

[0030] Example 2

[0031] In this embodiment, soybean oil is replaced with epoxidized soybean oil, and the other conditions are the same as in Example 1.

[0032] Example 3

[0033] Set the heating temperature of the high-speed mixer to 80℃. Weigh 350g of PBAT plastic and 7.5g of lard, add them to the high-speed mixer and mix for 10 minutes. Then weigh 150g of dry starch with a moisture content of 1% (the specific preparation process of the dry starch is described in patent application number 2021114585542) and add it to the high-speed mixer, continuing to mix for 10 minutes. Add the mixture to a single-screw extruder for extrusion. Set the single-screw extruder parameters as follows: speed 15r / min, three heating zones, heating temperatures of 60℃ / 140℃ / 145℃. This will yield a uniformly structured starch-PBAT alloy.

[0034] Comparative Example 1

[0035] Weigh 350g of PBAT plastic and 150g of dry starch with a moisture content of 1% (see patent application number 2021114585542 for the specific preparation process). Place both into a high-speed mixer and mix for 10 minutes. Add the mixture to a single-screw extruder for extrusion. The single-screw extruder parameters are set as follows: speed 15 r / min, three heating zones, and heating temperatures of 60℃ / 140℃ / 145℃. The resulting starch and PBAT alloy will show clearly visible granular starch clumps (see...). Figure 2 ).

[0036] Comparative Example 2

[0037] Weigh 150g of dry starch with a moisture content of 1% (see patent application number 2021114585542 for the specific preparation process) and 7.5g of soybean oil, and mix them in a high-speed mixer for 10 minutes; weigh 350g of PBAT plastic, put it into the high-speed mixer, and mix for another 10 minutes. Add the mixture to a single-screw extruder for extrusion. The single-screw extruder parameters are set as follows: speed 15 r / min, three heating zones, heating temperatures of 60℃ / 140℃ / 145℃. The resulting starch and PBAT alloy exhibit extremely uneven microstructure (see...). Figure 3 ).

[0038] Unless otherwise specified, this invention employs conventional operations in the production process of biodegradable plastics.

[0039] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for improving the dispersibility of dry starch in PBAT plastic, characterized in that, Includes the following steps: The bio-oil and PBAT granules are mixed evenly in a mixer; Add the dry starch to the mixer and continue mixing until homogeneous to obtain the mixture; The mixture is added to a plastic processing machine for melt processing to obtain a starch and PBAT alloy with a uniform structure; The dry starch accounts for 10-70% of the alloy mass, and the bio-oil accounts for 2-10% of the dry starch mass. The moisture content of the dry starch is less than 6%; The bio-oil is one or more of the following: plant oils and their modified oils, animal oils and their modified oils.

2. The method for improving the dispersibility of dry starch in PBAT plastic according to claim 1, characterized in that, Dry starch is produced using the following process: semi-wet starch with a moisture content of 15-30% wt is obtained from the wet milling starch processing step, or... Mixing water with commercially available starch yields semi-wet starch with a moisture content of 15-30%wt. After being expanded in an extruder, starch extrusion is obtained. Then, the starch extrusion is dried and pulverized to obtain dry starch with a moisture content of less than 6%.

3. The method for improving the dispersibility of dry starch in PBAT plastic according to claim 1, characterized in that, The amount of dry starch added should be 50-70% of the weight of the mixture.

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