Low dielectric composite material suitable for microwave degumming of silk and its preparation method

Abstract

This invention provides a low-dielectric-performance composite material suitable for microwave degumming of silk and its preparation method. The low-dielectric-performance composite material is composed of surface-modified mica, ultra-high molecular weight polyethylene (UHMWPE) chopped fibers, and polyethylene resin. The polyethylene resin is composed of linear low-density polyethylene (LDPE) and high-density polyethylene (HDPE). The preparation method includes: heating and melting the polyethylene resin to obtain resin melt A, and injecting it into a heating container with surface-modified mica, stirring to obtain resin melt B, and injecting it into an impregnation tank; passing UHMWPE long fibers through the impregnation tank containing resin melt B, curing them in air, and then cutting them to obtain chopped fiber prepreg; and molding the chopped fiber prepreg to obtain the low-dielectric-performance composite material. The low-dielectric-performance composite material provided by this invention has a low dielectric constant and low dielectric loss, good thermal conductivity, and is suitable for use in microwave degumming of silk.

Description

Technical Field

[0001] This invention relates to the field of composite material technology, and specifically to a method for preparing a low-dielectric-performance composite material suitable for microwave degumming of silk. Background Technology

[0002] Silk is a protein fiber with a pleasing luster, a soft feel, and excellent moisture absorption and breathability, and has long been used as a high-end textile raw material in the textile industry. Silk is mainly composed of fibroin and sericin. Fibroin accounts for about 75% of the total content, while sericin accounts for about 25%. Due to the significant differences in structural properties between fibroin and sericin, the presence of sericin in raw silk fibers (raw silk) woven into fabrics or other silk products affects the luster, feel, texture, and subsequent processing quality of the textile products. Therefore, in the textile industry, most of the sericin in raw silk or raw silk fabric must be removed. This process is called degumming (also known as refining), which separates the fibroin fibers from the sericin protein.

[0003] Silk fibroin is a water-insoluble fibrous protein, while sericin is a hot-water-soluble globular protein. Common degumming methods rely on the difference in water solubility between the two, using chemical reagents containing acids, alkalis, soaps, synthetic detergents, or enzymes to dissolve the sericin in a degumming bath. Conventional chemical degumming not only consumes a large amount of energy but also releases large quantities of wastewater containing sericin and chemicals, placing significant pressure on the environment. Furthermore, as a byproduct of raw silk degumming, sericin possesses excellent moisturizing properties, biological activity, and pharmacological effects. Recovering sericin from silk degumming processes can reduce water pollution and provide valuable raw materials for the food, pharmaceutical, and cosmetic industries. However, the sericin produced in existing degumming (refining) processes contains a large amount of the chemical auxiliaries used in degumming and is generally treated as waste, increasing the environmental burden and wasting this valuable natural protein resource.

[0004] Therefore, silk industry workers have been committed to developing clean and environmentally friendly degumming processes and have made some research progress. Examples include degumming via electrolytic water, infrared heating, supercritical CO2 fluid, and calcium hydroxide. However, some of these degumming methods still suffer from being uneconomical or having complex processes for directly recovering sericin. Therefore, it is necessary to continuously explore new processing technologies to truly achieve green processing of silk degumming.

[0005] Currently, research has been conducted on using microwaves for silk degumming. Microwaves are a clean, high-frequency electromagnetic wave energy source, characterized by high efficiency, uniform heating, and high penetration. However, the degumming temperature is around 100℃. While ceramic containers are relatively heat-resistant, they have high dielectric constants and dielectric losses, and due to the high adhesiveness of sericin, it easily adheres to the container walls. A high dielectric constant and dielectric loss in the microwave container affects the efficiency and energy consumption of silk degumming, and sericin adhesion further impacts the efficiency and effectiveness of degumming. Although low-polarity polymer materials have lower dielectric constants and are less prone to sericin adhesion, their thermal conductivity is often low. Because the container is located within a fixed microwave cavity, continuous microwave degumming can easily lead to localized overheating, causing safety issues. These factors affect the practical application of microwave silk degumming. Summary of the Invention

[0006] To address the problems in existing technologies, this invention provides a low-dielectric-performance composite material suitable for microwave silk degumming and its preparation method. This invention uses surface-modified mica and ultra-high molecular weight polyethylene chopped fibers as reinforcing materials, and a mixture of low-density linear polyethylene and high-density polyethylene as the matrix to prepare the low-dielectric-performance composite material. This low-dielectric-performance composite material possesses low surface energy, low dielectric constant, and low dielectric loss, and also exhibits good thermal conductivity, preventing overheating of the container, making it suitable for use in microwave silk degumming.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A low-dielectric-performance composite material suitable for microwave degumming of silk, wherein the low-dielectric-performance composite material is composed of surface-modified mica, ultra-high molecular weight polyethylene chopped fibers, and polyethylene resin; wherein the polyethylene resin is composed of linear low-density polyethylene and high-density polyethylene.

[0009] Polyethylene resin possesses ultra-low dielectric constant and low dielectric loss due to its unique structure, which lacks polar groups in its molecules. High-density polyethylene (HDPE) exhibits good toughness, chemical resistance, and good flowability, and can be processed through various molding methods such as extrusion, injection molding, and compression molding. It also has a relatively high operating temperature. Linear low-density polyethylene (LDPE) resin, on the other hand, has an even lower dielectric constant. Blending the two in a certain proportion can fully leverage their respective advantages.

[0010] However, since polyethylene resin has a low thermal conductivity, adding mica can improve the thermal conductivity and reduce heat accumulation during microwave heating. Simultaneously, the addition of ultra-high molecular weight polyethylene chopped fibers allows for better dispersion of mica within the resin matrix and enhances the mechanical properties of the composite material.

[0011] Preferably, in the polyethylene resin, the mass ratio of linear low-density polyethylene to high-density polyethylene is 1:1~3.

[0012] Preferably, the mass ratio of the surface-modified mica, ultra-high molecular weight polyethylene chopped fibers, and polyethylene resin is 1:0.5~1:4~10. In this invention, if the proportion of polyethylene resin is too low, it will affect the dielectric constant; if the proportion is too high, it will affect the thermal conductivity.

[0013] Preferably, the preparation method of the surface-modified mica includes the following steps: placing mica in isopropanol, treating it with microwave-ultrasound combination at 50~60℃ for 30~90 min, then adding 0.5%~1% of the mica mass of surface treatment agent, treating it with ultrasound at 50~60℃ for 3~5 h, and then filtering and drying to obtain surface-modified mica; the surface treatment agent is one or more of hexadecyltrimethylammonium bromide and aliphatic amine salt.

[0014] Preferably, the mass-to-volume ratio of mica to isopropanol is 1 g: 15~25 mL.

[0015] Preferably, the length of the chopped ultra-high molecular weight polyethylene (UHMWPE) fibers is 2.5~4.5 mm. The chopped UHMWPE fibers are formed by cutting long UHMWPE fibers during the preparation of low-dielectric composite materials. These chopped fibers can effectively disperse mica, increase the mechanical properties of the composite material, improve the service temperature of the composite material, and facilitate molding. If the chopped fibers are too short, the mechanical reinforcement effect is poor; if they are too long, it will affect the processing performance, and the surface of the molded product is prone to fuzziness.

[0016] Preferably, the low-dielectric-performance composite material is tested using the resonant cavity method at a frequency of 1 MHz, exhibiting a dielectric constant of 2.00~2.15, a dielectric loss ≤0.0007, and a thermal conductivity of 0.6~0.9 W / (m²). 2 ·k).

[0017] This invention provides a method for preparing a low-dielectric-performance composite material suitable for microwave degumming of silk, comprising the following steps:

[0018] S1: Linear low-density polyethylene and high-density polyethylene are mixed in a mixer to obtain polyethylene resin;

[0019] S2: Heat and melt polyethylene resin to obtain resin melt A; inject resin melt A and surface-modified mica into a heating container, stir, and obtain resin melt B containing mica; inject resin melt B into an impregnation tank equipped with a heating device.

[0020] S3: Pass ultra-high molecular weight polyethylene long fibers with a twist of 200~600T / m through an impregnation tank containing resin melt B to obtain ultra-high molecular weight polyethylene long fibers with resin melt B adhering to the surface. After curing in air, they are cut into short pieces with a length of 2.5~4.5 mm to obtain short fiber prepreg.

[0021] S4: The short-cut fiber prepreg is molded to obtain the low dielectric composite material.

[0022] In step S3, ultra-high molecular weight polyethylene (UHMWPE) long fibers with a twist of 200~600 T / m are used. This is mainly because UHMWPE fibers have low surface energy, and twisting is done to increase surface roughness, which facilitates the adhesion of mica-containing resin melt. If the twist is too low, the number of coils per unit length is small, affecting the adhesion effect. If the twist is too high, the fibers are prone to generating excessive centrifugal force due to untwisting during cutting, causing the adhered resin to fall off.

[0023] Preferably, in step S3, the ultra-high molecular weight polyethylene long fibers are passed through an impregnation tank containing resin melt at a speed of 0.5~15 m / min.

[0024] Preferably, in step S4, the chopped fiber prepreg is shaped using a twin-screw extrusion process or a hot pressing process.

[0025] The beneficial effects of this invention are:

[0026] 1. The low-dielectric-performance composite material product prepared by this invention is suitable for containers used in microwave degumming of silk. On one hand, it leverages the low dielectric constant and low dielectric loss of the mixture of low-density linear polyethylene and high-density polyethylene to reduce energy loss during microwave degumming of silk, and the low surface energy of polyethylene reduces sericin adhesion. On the other hand, introducing surface-modified mica into the matrix not only increases the thermal conductivity of the composite material but also raises the deformation temperature of the matrix, reducing overheating of the container during microwave degumming of silk. Furthermore, the introduction of ultra-high molecular weight polyethylene fibers increases the mechanical properties of the composite material without affecting the dielectric constant; in particular, the molecular structure of ultra-high molecular weight polyethylene fibers is consistent with the molecular structure of the polyethylene matrix, exhibiting good interfacial compatibility.

[0027] 2. The present invention uses twisted ultra-high molecular weight polyethylene fibers to increase the adhesion of resin containing mica particles to the fibers. The method of preparing short fiber prepreg by bonding long fibers with resin containing mica particles can increase the dispersion of mica particles and ultra-high molecular weight polyethylene short fibers in the matrix and the molding and processability of the composite material, thereby optimizing the performance of the composite material. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the preparation process of the short-cut fiber prepreg of the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1:

[0032] A low-dielectric-performance composite material suitable for microwave degumming of silk is composed of surface-modified mica, ultra-high molecular weight polyethylene (UHMWPE) chopped fibers, and polyethylene resin. The polyethylene resin is composed of linear low-density polyethylene (LDPE) and high-density polyethylene (HDPE). In the polyethylene resin, the mass ratio of LLDPE to HDPE is 1:1; the mass ratio of surface-modified mica, UHMWPE chopped fibers, and polyethylene resin is 1:0.5:10.

[0033] This embodiment applies to the preparation method of low dielectric composite materials for microwave degumming of silk, and includes the following steps:

[0034] S1: Place 10g of mica into a container containing 200mL of isopropanol, cover the container, place it in an ultrasonic-microwave combined reactor, and treat it with microwave-ultrasound combination at 60℃ for 30min. Then add 1% of the mica mass of hexadecyltrimethylammonium bromide, and treat it with ultrasound at 60℃ for 4h. After filtration and drying, surface-modified mica is obtained.

[0035] S2: After mixing 50g of linear low-density polyethylene and 50g of high-density polyethylene in a mixer, polyethylene resin is obtained.

[0036] S3: Place 100g of polyethylene resin in a heating container and heat it to melt it to obtain resin melt A; simultaneously and slowly inject 100g of resin melt A and 10g of surface-modified mica into a heating container with a stirring function. After stirring, resin melt B containing mica is obtained. Resin melt B is then injected into an impregnation tank with a heating device.

[0037] S4: Pass ultra-high molecular weight polyethylene long fibers with a twist of 400T / m through an impregnation tank containing resin melt B at a speed of 15m / min, and after curing in air, ultra-high molecular weight polyethylene fibers with resin melt B adhering to the surface are obtained, and cut into lengths of about 3mm to obtain short fiber prepreg.

[0038] S5: The short-cut fiber prepreg is molded using a hot pressing process (temperature 132℃, pressure 5MPa, time 30min) to obtain the low dielectric composite material.

[0039] Example 2:

[0040] A low-dielectric-performance composite material suitable for microwave degumming of silk is composed of surface-modified mica, ultra-high molecular weight polyethylene (UHMWPE) chopped fibers, and polyethylene resin. The polyethylene resin is composed of linear low-density polyethylene (LDPE) and high-density polyethylene (HDPE). In the polyethylene resin, the mass ratio of LLDPE to HDPE is 1:1.5; the mass ratio of surface-modified mica, UHMWPE chopped fibers, and polyethylene resin is 1:0.8:5.

[0041] This embodiment applies to the preparation method of low dielectric composite materials for microwave degumming of silk, and includes the following steps:

[0042] S1: Place 10g of mica into a container containing 150mL of isopropanol, cover the container, place it in a microwave-ultrasound combined reactor, and treat it with microwave-ultrasound combination at 50℃ for 90min. Then add 0.5% of the mica mass of hexadecyltrimethylammonium bromide, and treat it with ultrasound at 50℃ for 5h. After filtration and drying, surface-modified mica is obtained.

[0043] S2: 20g of linear low-density polyethylene and 30g of high-density polyethylene are mixed in a mixer to obtain polyethylene resin;

[0044] S3: Place 50g of polyethylene resin in a heating container and heat it to melt it to obtain resin melt A; simultaneously and slowly inject 50g of resin melt A and 10g of surface-modified mica into a heating container with a stirring function. After stirring, resin melt B containing mica is obtained. Resin melt B is then injected into an impregnation tank with a heating device.

[0045] S4: Pass ultra-high molecular weight polyethylene long fibers with a twist of 600T / m through an impregnation tank containing resin melt B at a speed of 5m / min, and after curing in air, ultra-high molecular weight polyethylene long fibers with resin melt B adhering to the surface are obtained, and then cut into lengths of about 3mm to obtain short fiber prepreg.

[0046] S5: The short-cut fiber prepreg is molded using a hot pressing process (temperature 132℃, pressure 5MPa, time 30min) to obtain the low dielectric composite material.

[0047] Example 3:

[0048] A low-dielectric-performance composite material suitable for microwave degumming of silk is composed of surface-modified mica, ultra-high molecular weight polyethylene (UHMWPE) chopped fibers, and polyethylene resin. The polyethylene resin is composed of linear low-density polyethylene (LDPE) and high-density polyethylene (HDPE). The mass ratio of LLDPE to HDPE in the polyethylene resin is 1:3; the mass ratio of the surface-modified mica, UHMWPE chopped fibers, and polyethylene resin is 1:1:4.

[0049] This embodiment applies to the preparation method of low dielectric composite materials for microwave degumming of silk, and includes the following steps:

[0050] S1: Place 10g of mica into a container containing 250mL of isopropanol, cover the container, place it in an ultrasonic-microwave combined reactor, and treat it with microwave-ultrasound combination at 60℃ for 60min. Then add 1% of the mica mass of hexadecyltrimethylammonium bromide, and treat it with ultrasound at 50℃ for 5h. After filtration and drying, surface-modified mica is obtained.

[0051] S2: 10 g of linear low-density polyethylene and 30 g of high-density polyethylene are mixed in a mixer to obtain polyethylene resin;

[0052] S3: Place 40 g of polyethylene resin A in a heating container and heat it to melt to obtain resin melt A; simultaneously and slowly inject 40 g of resin melt A and 10 g of surface-modified mica into a heating container with a stirring function. After stirring, resin melt B containing mica is obtained. Resin melt B is then injected into an impregnation tank with a heating device.

[0053] S4: Pass ultra-high molecular weight polyethylene long fibers with a twist of 200T / m through an impregnation tank containing resin melt at a speed of 0.5 m / min, and after curing in air, ultra-high molecular weight polyethylene long fibers with resin melt B adhering to the surface are obtained, and then cut into lengths of about 4 mm to obtain short fiber prepreg.

[0054] S5: The short-cut fiber prepreg is molded using a hot pressing process (temperature 132 ℃, pressure 5 MPa, time 30 min) to obtain the low dielectric composite material.

[0055] Performance testing:

[0056] The dielectric constant and dielectric loss of the low dielectric composite materials prepared by the methods in Examples 1-3 were tested at a frequency of 1 MHz, and the thermal conductivity was also tested.

[0057] Table 1 Performance Test Results Data

[0058] Dielectric constant Dielectric loss <![CDATA[Thermal conductivity / W / (m 2 ·k)]]> Example 1 2.00 0.0006 0.60 Example 2 2.11 0.0007 0.85 Example 3 2.15 0.0007 0.90

[0059] As shown in Table 1, the low-dielectric composite materials prepared by the methods in Examples 1-3 all possess dielectric constants and low dielectric losses, as well as excellent thermal conductivity. Therefore, the low-dielectric composite material products obtained by the method of this invention can be used to manufacture containers for microwave degumming of silk.

[0060] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low dielectric property composite material suitable for microwave degumming of silk, characterized in that, The low dielectric property composite material is composed of surface modified mica, ultra-high molecular weight polyethylene short fibers and polyethylene resin; The mass ratio of the linear low density polyethylene and the high density polyethylene in the polyethylene resin is 1:1-3; the mass ratio of the surface modified mica, the ultra-high molecular weight polyethylene short fibers and the polyethylene resin is 1:0.5-1:4-10; The preparation method of the low dielectric property composite material suitable for microwave silk degumming comprises the following steps: S1: mixing linear low density polyethylene and high density polyethylene in a mixing machine to obtain polyethylene resin; S2: heating and melting the polyethylene resin to obtain resin melt A; injecting the resin melt A and surface modified mica into a heated container, stirring to obtain mica-containing resin melt B, and injecting the resin melt B into an impregnation tank with a heating device; S3: passing ultra-high molecular weight polyethylene long fibers with a twist of 200-600 T / m through the impregnation tank containing the resin melt B to obtain ultra-high molecular weight polyethylene long fibers with surface-adhered resin melt B, cutting the short fibers into short fibers pre-impregnated material with a length of 2.5-4.5 mm after solidification in air, and obtaining the short fibers pre-impregnated material; S4: performing molding treatment on the short fibers pre-impregnated material to obtain the low dielectric property composite material.

2. The low dielectric property composite material suitable for microwave degumming of silk as claimed in claim 1, wherein, The preparation method of the surface modified mica comprises the following steps: placing mica in isopropanol, microwave-ultrasonic combined treatment at 50-60℃ for 30-90min, then adding 0.5%-1% of surface treatment agent based on the mass of the mica, ultrasonic treatment at 50-60℃ for 3-5h, and then filtering and drying to obtain surface modified mica; the surface treatment agent is one or more of cetyltrimethylammonium bromide and fatty amine salt.

3. The low dielectric property composite material suitable for microwave degumming of silk as claimed in claim 2, wherein, The mass-volume ratio of the mica and isopropanol is 1g:15-25mL.

4. The low dielectric property composite material suitable for microwave degumming of silk as claimed in claim 1, wherein, The length of the ultra-high molecular weight polyethylene short fibers is 2.5-4.5mm.

5. The low dielectric property composite material suitable for microwave degumming of silk as claimed in claim 1, wherein, The low dielectric property composite material is tested by using a resonance cavity method under the condition that the frequency is 1M, the dielectric constant is 2.00-2.15, the dielectric loss is less than or equal to 0.0007, and the thermal conductivity is 0.6-0.9 W / (m 2 ·k).

6. The low dielectric property composite material suitable for microwave degumming of silk as claimed in claim 1, wherein, In step S3, the ultra-high molecular weight polyethylene long fibers pass through the impregnation tank containing the resin melt at a speed of 0.5-15m / min.

7. The low dielectric property composite material suitable for microwave degumming of silk as claimed in claim 1, wherein, In step S4, the short fibers pre-impregnated material is molded by using a double screw extrusion process or a hot pressing process.

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