CN115320198A

CN115320198A - Lightweight and environment-friendly polypropylene-based composite material capable of replacing glass fiber for automobile

Info

Publication number: CN115320198A
Application number: CN202210950909.8A
Authority: CN
Inventors: 杨莉; 徐珍珍; 马翔; 邹梨花; 王凯; 张海超
Original assignee: Anhui Polytechnic University
Current assignee: Anhui Polytechnic University
Priority date: 2022-08-09
Filing date: 2022-08-09
Publication date: 2022-11-11

Abstract

The invention discloses a light-weight environment-friendly polypropylene-based composite material capable of replacing glass fiber for an automobile, belonging to the technical field of composite materials. The composite material is formed by compounding wet-process non-woven fabric and a polypropylene film; the wet-process non-woven fabric is formed by mixing hemp fibers, glass fibers and polypropylene fibers, wherein the mass ratio of the hemp fibers to the glass fibers is (2-8) to (8-2). The composite material is prepared into a preformed body by a wet non-woven process, and the wettability of polypropylene to the preformed body material is improved by means of mixing and self-reinforcing, so that the mechanical property of the composite material is improved.

Description

Light-weight and environment-friendly polypropylene-based composite material capable of replacing glass fiber for automobile

Technical Field

The invention belongs to the technical field of composite materials, and particularly relates to a light-weight environment-friendly polypropylene-based composite material capable of replacing glass fiber for an automobile.

Background

In recent years, with the development of pollution-free green composite materials and the realization of the goal of replacing polymer materials in commercial applications, etc., the research on biodegradable composite materials has been significantly increased. The natural resources as reinforcements are the subject of numerous studies aimed at developing various natural composites. Because the plant fiber has low cost, low density, good mechanical property, strong biodegradability and sustainable development potential, the plant fiber is applied more and more as a polymer reinforced material. In thermoplastic matrix composites, recyclability and energy recovery by incineration as well as mechanical properties are superior to glass fiber reinforced materials.

Research and development of fiber reinforced composite materials contribute to development of lightweight automobiles. With the development of science and technology, more and more non-metallic materials with the advantages of light weight, corrosion resistance, easy molding and the like are used in automobiles. Particularly, after the demands for weight reduction of automobiles, recycling of wastes, and reduction of fuel consumption of automobiles are made, the manufacturing technology of plastic instead of steel is more and more emphasized, particularly, the development and utilization of thermoplastic composite materials. The composite material matrix used by the traditional automobile is usually a thermosetting material, and the waste parts and leftover materials of the material are usually treated by burying or burning, so that the environment is polluted, and the waste of raw materials is caused. Wangchunhong et al uses hemp powder and polylactic acid to compound and prepare a completely degradable composite material for automotive interior. The results show that: when the mass fraction of the hemp powder is 30 percent and the grain diameter of the hemp powder is 40 meshes, the tensile strength, the bending strength, the tensile modulus and the bending modulus of the composite material are all the maximum. The results of tests on the glass fiber reinforced polypropylene composite material prepared by forming crystal grains with different lengths by glass fibers show that the glass fibers are seriously broken after injection molding, and the impact strength of the composite material is increased along with the increase of the length of the glass fibers.

Although scholars at home and abroad carry out a great deal of research on the hybrid technology of the hybrid composite material, the research on the performance characteristics of the hemp/glass fiber hybrid composite material is less.

Disclosure of Invention

Aiming at the technical problems in the prior art, the invention aims to provide a lightweight and environment-friendly polypropylene-based composite material for automobiles, which can replace glass fiber.

In order to achieve the purpose, the invention provides the following technical scheme:

the polypropylene-based composite material for the automobile is light in weight and environment-friendly and can replace glass fiber, and is formed by compounding wet-process non-woven fabric and a polypropylene film;

the wet-process non-woven fabric is formed by mixing hemp fibers, glass fibers and polypropylene fibers, wherein the mass ratio of the hemp fibers to the glass fibers is (2-8) to (8-2).

Further, the glass fiber is alkali-free glass fiber, and the fiber length is 3mm.

Further, according to the mass percentage, the total amount of the hemp fibers and the glass fibers accounts for 20wt%, and the total amount of the polypropylene fibers and the polypropylene film accounts for 80wt%; wherein the mass ratio of the polypropylene fiber to the polypropylene film is 4.

Further, the polypropylene fiber has a fiber length of 3mm and a linear density of 1.67dtex.

Further, the hemp fibers have a fiber length of 3mm.

The invention also provides a preparation method of the polypropylene-based composite material for automobiles, which is light in weight and environment-friendly and can replace glass fiber, and the preparation method comprises the following steps:

weighing raw materials according to the mass, adding a dispersing agent and water into a mixture of hemp fibers and glass fibers, stirring at a rotating speed of 1400r/min for 5min, then adjusting the rotating speed to 600r/min, adding polypropylene fibers into the mixture, stirring until a fiber winding phenomenon occurs (when a fiber winding phenomenon is found on a stirring rod, stopping a stirrer, and picking the wound fibers back into a slurry by using a glass rod), then adjusting the rotating speed to 1400r/min, and stirring for 10min to prepare wet-process fiber slurry; then preparing the fiber pulp into hemp/glass fiber/polypropylene fiber hybrid non-woven fabric through a wet-laid process, and drying and pumping the non-woven fabric into a composite material reinforcement;

the polypropylene films are paved on the upper surface and the lower surface of the composite material reinforcement, and the polypropylene-based automobile composite material which is light in weight, environment-friendly and capable of replacing glass fiber is obtained.

Further, the solid-to-liquid ratio of the total amount of the hemp fibers, the glass fibers and the polypropylene fibers to water is (0.01-0.05): 1.

Further, the using ratio of the water to the dispersant is 500mL and 0.1g, and the dispersant is a polyacrylamide dispersant. In order to improve the dispersibility of the fibers in water, a dispersing agent is added in the preparation of the fiber suspension pulp, the dispersing agent can ensure that the fibers have good dispersibility in water, can keep uniform distribution in the suspension pulp, increases the hygroscopicity of the fibers, ensures that the fibers generate swelling in water, and ensures that the fibers have certain bonding strength in a wet state after web formation. In order to improve the wettability of the polypropylene film to the fibers, the polypropylene fibers are added into the wet-process non-woven fabric.

The invention also provides application of the polypropylene-based automobile composite material which is light in weight and environment-friendly and can replace glass fiber in the field of automobile materials.

Compared with the prior art, the invention has the beneficial effects that:

the invention adopts a wet non-woven process to prepare the hemp/glass fiber non-woven preformed body, adopts a mixing mode to mix the polypropylene fiber with certain mass, the hemp fiber and the glass fiber to prepare the preformed body in order to improve the wettability of the polypropylene film to the fabric of the preformed body, and utilizes a compression molding mode to prepare the hemp/glass fiber reinforced polypropylene composite material with different mixing ratios. The hemp/glass fiber hybrid reinforced polypropylene-based composite material is tested for tensile property, bending property and impact property, and the tensile property and bending property of the composite material are best when the mass ratio of hemp fiber to glass fiber is 3; when the mass ratio of the hemp fibers to the glass fibers is 1.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.

FIG. 1 is a schematic flow chart of the operation of example 1;

FIG. 2 is a bar graph of tensile strength of various composites prepared in example 1;

FIG. 3 is a graph of tensile strength versus displacement for various composites prepared in example 1;

FIG. 4 is a stress-strain curve of various composites prepared in example 1;

FIG. 5 is a schematic representation of the location of maximum bending stress for different composites prepared in example 1;

FIG. 6 is a graph of the flexural strength of various composites prepared in example 1;

FIG. 7 is a graph of the impact strength of various composites prepared in example 1.

Detailed Description

Reference will now be made in detail to various exemplary embodiments of the invention, the detailed description should not be construed as limiting the invention but as a more detailed description of certain aspects, features and embodiments of the invention.

It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In addition, for numerical ranges in the present disclosure, it is understood that each intervening value, to the upper and lower limit of that range, is also specifically disclosed. Every smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in a stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference herein for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.

It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the present disclosure without departing from the scope or spirit of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification. The specification and examples are exemplary only.

As used herein, the terms "comprising," "including," "having," "containing," and the like are open-ended terms that mean including, but not limited to.

The invention utilizes the mould pressing forming method to prepare the polypropylene-based composite material for the automobile, the polypropylene film and the prepared composite material reinforcement are layered in a sandwich layering mode, the polypropylene film is respectively paved on the surface layer and the middle layer of the hybrid non-woven fabric, and the polypropylene film is layered and compounded in a mould, thus obtaining the light and environment-friendly polypropylene composite material for the automobile, which can completely or partially replace glass fiber.

the wet-process non-woven fabric is formed by mixing hemp fibers, glass fibers and polypropylene fibers, wherein the mass ratio of the hemp fibers to the glass fibers is (6-20) to (6-20). More preferably 3.

In some preferred embodiments, polypropylene fibers are also included in the composite.

In some preferred embodiments, the glass fibers are alkali-free glass fibers having a fiber length of 3mm.

In some preferred embodiments, the total amount of hemp fibers and glass fibers is 20wt% and the total amount of polypropylene fibers and polypropylene film is 80wt%, based on mass percentage; wherein the mass ratio of the polypropylene fiber to the polypropylene film is 4.

In some preferred embodiments, the polypropylene fibers have a fiber length of 3mm and a linear density of 1.67dtex.

In some preferred embodiments, the hemp fibers have a fiber length of 3mm.

the polypropylene films are laid on the upper layer, the lower layer and the middle layer of the composite material reinforcement, and the polypropylene-based automobile composite material which is light in weight, environment-friendly and capable of replacing glass fiber is obtained.

In some preferred embodiments, the solid-to-liquid ratio of the total amount of hemp fibers, glass fibers, and polypropylene fibers to water is (0.01-0.05): 1.

In some preferred embodiments, the ratio of water to dispersant is 500ml. In order to improve the dispersibility of the fibers in water, a dispersing agent is added in the preparation of the fiber suspension pulp, the dispersing agent can ensure that the fibers have good dispersibility in water, can keep uniform distribution in the suspension pulp, increases the hygroscopicity of the fibers, ensures that the fibers generate swelling in water, and ensures that the fibers and the fibers have certain bonding strength in a wet state after web formation. In order to improve the wettability of the resin to the fibers, the polypropylene fibers are added into the wet-process non-woven fabric.

The invention also provides application of the polypropylene-based automobile composite material which is light in weight, environment-friendly and capable of replacing glass fiber in the field of automobile materials.

Non-woven fabrics, also called non-woven fabrics, belong to the textile industry, and have the name of "nonwovens". It is a fabric that does not require spinning. It is simply an arrangement of short fibers or filaments, either oriented or randomly, to form a fibrous network, which is then reinforced by mechanical, thermal bonding or chemical means. The non-woven fabric in the national standard GB/T5709-1997 refers to: sheets, nets or felts made of oriented or randomly arranged fibres rubbed, bonded or bonded, excluding paper, machine, knitted, tufted and wet-flex felts. Briefly: it is not composed of yarns that are interwoven and woven together, but rather is composed of fibers that are bonded together. The non-woven fabric breaks through the traditional spinning principle and has the characteristics of short process, high production speed, high yield, low cost, wide application, wide raw material source and the like.

In wet technology processes, large amounts of water are used as a medium, and a uniform fibre suspension and fibre web is obtained after dewatering. The wet-laid nonwoven fabric has the following advantages: the internal fibers of the net formed under the condition of water flow are distributed in three dimensions, and the uniformity is good; the fibers are arranged orderly; has a larger pore structure. However, due to the low bond strength between the fibers, the web is typically loose. Therefore, the present invention processes the wet-laid nonwoven fabric support to overcome these disadvantages and improve mechanical properties.

During the stock preparation, short fibers (typically <30 mm) are dispersed in water and a dispersant is added to ensure uniform fiber dispersion. Continuous web formation can be achieved by depositing the fibers on an inclined screen. The water is then evenly sucked out of the machine through a suction box located below the screen. The deposition of the fibers on the screen is controlled by the filtration resistance of the web formed in the process. Wherein the bonding force of the web is the result of fiber-to-fiber friction (entanglement) or chemical bonding by a binder.

The heating and pressing of the web by the heated press is a suitable method of reinforcing wet-laid nonwovens in the present invention. It allows the low melting fibers to melt, flow and diffuse through the web. After cooling, the fibers are bonded together and the web is reinforced to form a hot-pressed nonwoven scaffold. In this process, the melted fibers not only act as a binder to bind and protect other fibers, but also reduce the pore size of the nonwoven. The technology has high production speed, no waste water, waste gas and solid waste, is suitable for reinforcing thin non-woven fabric, and is a promising method for manufacturing the fabric support. The bond strength of the wet laid nonwoven fabric can be increased by hot pressing to improve its mechanical properties. In addition, the method can reduce the pore size and porosity of the wet-laid nonwoven fabric.

Hemp is roughly classified into: flax, jute, kenaf, hemp, kendir, kenaf and abaca.

Among the hemp, hemp is also called as hemp and hemp. Due to the presence of the hemp polyphenol, there are few insect pests during growth and placement. The hemp single fiber has rough surface, longitudinal slits, holes and transverse branches, and has no natural turning. The cross section of hemp has various forms, such as triangle, long circle, oval, etc. The hemp single fiber has the same fineness and length as flax, so the technical fiber spinning is also needed. It is known from experience that hemp fibres and products are softer and less scratchy, which is related to the softness of the inter-fibre gums and the fibres themselves. Hemp fibers have a central cavity, which is connected with cracks and pores distributed on the surface of the fibers, and are the main reasons for the excellent capillary effect, high adsorbability and moisture absorption and sweat releasing performance of the hemp fibers. The hemp fiber also has certain functions of resisting mildew and sterilizing.

The test materials and instruments of the invention:

1. experiment raw materials:

alkali-free glass fiber: 3mm, shanghai minister and Start chemical technology Co., ltd;

hemp fiber: shenyang North Jiangma industry development Co., ltd;

polypropylene fiber: the fiber length is 3mm and the linear density is 1.67dtex, which are provided by Changjiang chemical fiber company Limited in Henry City;

polypropylene master batch: model ST868M, taiwan li longrong chemical industries;

polyacrylamide dispersant: MW300 million, anionic, national drug group chemical agents, inc.

2. An experimental instrument:

12 inch slicer: model FY0002, yangjiang river, fengye trading Limited in Jiangchan district;

hot press: YLJ-HP300 type, available from Synfeiki Technique Co., ltd;

a table band saw machine: MBS240/E, PROXXON, germany;

grinding and polishing machine for metallographic specimen: denn peak testing instruments ltd;

microcomputer control electronic universal tester: WDW20, junanchen testing machine manufacturing ltd;

digital display simply supported beam impact tester: XJJ-50S, hengsi Shengda instruments Inc. of Jinan;

high definition CCD measurement microscope: GP-300C, kunshan high-quality precision instruments, inc.;

an electronic balance: HZK-FA210S, huazhi (Fujian) electronic technology, inc.;

a water circulation sheet making machine: AT-CP-202111180, zongnan Zong testing instruments, inc.;

a super-thermostat: model 501A, shanghai laboratory instruments ltd;

an electric stirrer: model D2025W, shanghai meipu instruments manufacturing ltd;

glass rod, acid-free paper, 50cm straight ruler, tinfoil and vernier caliper.

Example 1

A preparation method of a polypropylene-based composite material for automobiles, which is light in weight and environment-friendly and can replace glass fiber, comprises the following steps:

1) Raw material treatment: cutting the hemp fibers, the glass fibers and the polypropylene fibers into fibers with the fiber length of 3mm by using a slicer (a cutter);

2) According to the mass percentage, the total amount of the hemp fibers and the glass fibers accounts for 20wt%, and the total amount of the polypropylene fibers and the polypropylene film accounts for 80wt%; wherein the mass ratio of the polypropylene fiber to the polypropylene film is 4.

Using an electronic balance of HZK-FA210S type and acid-free paper to weigh hemp fibers and glass fibers in a certain proportion, pouring the hemp fibers and the glass fibers into a stainless steel barrel (the specific proportion is shown in table 1), then adding water and a dispersing agent (polyacrylamide) into the stainless steel barrel to control the solid-to-liquid ratio of the total amount of the hemp fibers, the glass fibers and the polypropylene fibers to be 0.01, the using ratio of the water to the dispersing agent to be 500mL; after being evenly stirred, the mixture is poured into an AT-CP-202111180 type water circulation sheet making machine to be made into hemp/glass fiber/polypropylene fiber hybrid non-woven fabric, and then the non-woven fabric is put into a drying oven to be dried and then is cut into the non-woven fabric with the size of length multiplied by width: a17.5 cm x 17.5cm hemp/glass fiber/polypropylene fiber hybrid nonwoven fabric is shown in FIG. 1.

3) The polypropylene master batch was hot-pressed into a 1mm thick film using a YLJ-HP300 type hot press and tinfoil, and then cut into pieces with dimensions length x width: 17.5cm x 17.5cm membranes;

4) Laminating the polypropylene film and the hemp/glass fiber/polypropylene fiber hybrid non-woven fabric prepared in the step 2) in a mould by using a YLJ-HP300 type hot press in a compression molding mode, wherein the size of the mould is 18cm multiplied by 4mm, the laminating sequence is the polypropylene film-wet non-woven fabric-polypropylene film, 3 layers of the polypropylene film are finally paved, and 2 layers of the hemp/glass fiber/polypropylene fiber hybrid non-woven fabric are pressed for 30min at the temperature of 180 ℃ under the pressure of 4MPa to obtain the lightweight and environment-friendly polypropylene-based automobile composite material capable of replacing the glass fiber.

TABLE 1

Test examples

1. Tensile Property test

The implementation standard is ASTMD3039/D3039M-08. The composite material prepared in example 1 was cut out into samples meeting the tensile properties test standards using an MBS240/E type saw blade machine, and the sample size was length × width: 18mm by 20mm. Measuring the thickness of the sample by using a vernier caliper, recording the thickness, marking the sample, adhering four carbon plate reinforcing sheets at two ends of a tensile experimental sample by using glue, keeping the clamping distance at 13.8mm, putting the tensile experimental sample into a WDW20 microcomputer control electronic universal testing machine, setting the speed to be 2mm/min before the tensile starts, and storing and recording related data after the tensile finishes. Three sets of valid data were measured for each hemp to glass fiber ratio. Finally, the tensile strength of each group was calculated and averaged, and the results are shown in fig. 2. The tensile strength calculation formula is as follows:

in the formula F ^tu -tensile strength, MPa;

p ^max -maximum pull, N;

a-actual cross-sectional area of the specimen, mm, measured before the test ² 。

Fig. 2 is a bar graph of tensile strength for various composites prepared in example 1. From fig. 2, it can be seen that the tensile strength of the composites using wet laid nonwovens was significantly greater than that of the control group, with a maximum increase of approximately 3 times and a minimum increase of approximately 2 times, where the sample with the greatest tensile strength was a composite with a hemp to glass fiber mass ratio of 7. Composites made using wet laid nonwovens have such a high tensile strength because the wet laid nonwovens used for the preform allow for better cohesion and entanglement between the fibers, resulting in a composite having a tensile strength greater than that of a material made only of glass fibers.

The tensile strength of the composite material prepared by the glass fiber/polypropylene fiber is greater than that of the composite material prepared by the hemp fiber/polypropylene fiber. Because the tensile strength of the glass fiber is greater than that of the hemp fiber, wherein the tensile strength of the glass fiber is 2400MPa, and the tensile strength of the hemp fiber is 550-900MPa.

By comparing the tensile strength of the composite material designed with the hybrid reinforcement in the form of a wet laid non-woven structure, it was found that the tensile strength of the hybrid composite increased with increasing proportion of glass fiber, and the rate of increase in tensile strength of the hybrid composite increased. Wherein the tensile strength of the hybrid composite material prepared when the mass ratio of the hemp fiber to the glass fiber is 7% is increased by 20.52% compared with the tensile strength of the composite material prepared by mixing the hemp fiber and the polypropylene fiber; the tensile strength of the hybrid composite prepared with the mass ratio of hemp fiber to glass fiber of 7 was increased by 11.48% over the tensile strength of the hybrid composite prepared with the mass ratio of hemp fiber to glass fiber of 1. The reason for the analysis is that the tensile strength of the glass fibers is inherently greater than that of the hemp fibers, so that as the proportion of the glass fibers in the composite material increases, the proportion of the hemp fibers decreases, the tensile strength of the hybrid composite material increases, and the growth rate increases.

In addition, when the mass ratio of hemp fibers to glass fibers in the hybrid composite material is 7. In the wet-process non-weaving process, the hemp fibers are fully stirred by the stirrer in the water suspension, so that hydroxyl groups on the surfaces of the fibers are combined with each other to form hydrogen bonds, the tensile strength is enhanced to a certain extent, and after hot pressing, the fibers are in closer contact and have larger acting force, so that the hybrid composite material prepared when the mass ratio of the hemp fibers to the glass fibers is 7. However, the tensile strength of hemp fibers is less than that of glass fibers, so that the tensile strength of hemp composites using wet-laid nonwovens is less than that of glass fiber composites which are also wet-laid nonwovens.

FIG. 3 is a graph of the tensile strength shift for different composites prepared in example 1. As can be seen from fig. 3, the elongation at break of the hybrid composite was significantly greater than that of the control because the force between the fibers increased after the wet-laid nonwoven, making the elongation at break greater than that of the chopped glass fibers.

By comparing the composite material samples of which the reinforcing bodies are all pure fibers, the breaking elongation of the hemp fiber/polypropylene fiber composite material is the largest, because the breaking strength and the breaking elongation of the hemp fiber are higher than those of ramie and flax, the breaking elongation of the ramie and the flax is 2-4%, and the breaking elongation of the glass fiber is less than or equal to 4%.

Fig. 4 is a stress-strain curve of various composites prepared in example 1, and it can be seen from fig. 4 that the tensile modulus of the hybrid composites are all significantly greater than the tensile modulus of the control. The phenomenon occurs because there is not too much acting force between the short fiber glass fiber and the fiber in the composite material pressed by the polypropylene film, and more is acting force between the fiber and the matrix, and the reinforcement adopts the wet-method non-woven composite material, which not only realizes perfect combination between the matrix and the fiber, but also fully displays the acting force between the fibers.

2. Three point bending performance test

The implementation standard is ASTMD7264/D7264M-07. The composite material sheet prepared in example 1 was cut out into samples meeting the three-point bending property test standard using an MBS240/E type saw blade machine, the sample size being length × width: 80mm by 10mm. And measuring the thickness of the sample by using a vernier caliper, recording the thickness, marking the sample, adjusting the distance between the lower pressure heads to a reasonable position according to the standard requirement according to the length of the sample, and adjusting the position of a cross beam of the testing machine to enable the upper pressure head to descend to the middle of the lower pressure heads. And adjusting the position of the lower pressing head (ensuring the relative positions of the pressing heads on the two sides to be unchanged) to ensure that the upper pressing head is positioned between the two lower pressing heads. And adjusting the position of a crossbeam of the testing machine to enable the upper pressure head to be far away from the lower pressure head, flatly placing the sample on the lower pressure head, and visually adjusting the position of the sample to enable the axis of the sample to be perpendicular to the width direction of the lower pressure head and enable the midpoint of the sample to be right below the upper pressure head. The bending schematic diagram is shown in fig. 5, then a sample is put in, the position of a cross beam of the testing machine is adjusted, so that the upper pressure head just contacts with the sample, the pre-pressure is about 5N, then zero clearing is carried out, the bending speed is set to be 2mm/min, and the experiment is started.

The bending test process is continuously loaded until the test sample is broken or the compression force value is reduced by more than 25 percent, and the test is finished. And lifting the flat knitting machine of the testing machine, taking out the samples, storing the recorded data, collecting the remains of the samples, and storing the remains of the samples by using the self-sealing bags, wherein clear marks are required to be made on the self-sealing bags to distinguish each sample. For the sample fracture mode, judgment was made according to the requirements of ASTM D7264/D7264M-07. And judging whether the fracture mode of the sample meets the standard requirements or not, and making clear identification on a test report. If an unacceptable failure mode occurs in a higher proportion (50%) of a set of samples, the set of test data is questionable and needs to be redone. Three groups of effective data are measured according to the proportion of each hemp glass fiber, and finally, the bending strength of each group is calculated and an average value is obtained. The bending strength calculation formula is as follows:

wherein σ -midspan outer surface stress, MPa;

p-force, N;

l-support span, mm;

b-width of beam, mm;

h-thickness of the beam, mm.

Note: the three-point simple-support bending maximum stress occurs at the mid-span position, and the mid-span surface stress is the maximum bending stress (see fig. 5).

FIG. 6 is a graph of the flexural strength of various composites prepared in example 1. As can be seen from fig. 6, the bending strength of the hybrid composite was significantly greater than that of the control group, with a maximum increase of approximately 1-fold and a minimum increase of approximately 50% bending strength, wherein the sample with the highest bending strength was a composite with a mass ratio of hemp fiber to glass fiber of 7. The hybrid composite material with the proportion has the large bending strength because the preformed body adopts wet-process non-woven to enable the fibers to be better cohered and entangled, so that the tensile strength of the prepared hybrid composite material is larger than the bending strength of a glass fiber material.

The bending strength of the glass fiber/polypropylene fiber composite material group is greater than that of the hemp fiber/polypropylene fiber composite material. Because the bending strength of the glass fibers is greater than that of the hemp fibers.

By comparing the flexural strength of a composite designed with the hybrid reinforcement in the form of a wet laid non-woven structure, it was found that the flexural strength of the hybrid composite increased with increasing glass fiber fraction. And the hybrid composite material increases in the rate of increase in flexural strength. Wherein the bending strength of the hybrid composite material with the mass ratio of the hemp fiber to the glass fiber being 7 is increased by 40.47% compared with the bending strength of the hemp fiber/polypropylene fiber composite material, and the bending strength of the hybrid composite material with the mass ratio of the hemp fiber to the glass fiber being 7. Since the bending strength of the glass fibers is inherently greater than that of the hemp fibers, the proportion of the hemp fibers decreases with an increase in the proportion of the glass fibers in the composite material, the bending strength of the hybrid composite material increases, and the growth rate increases.

In addition, when the mass ratio of the hemp fibers to the glass fibers in the hybrid composite material is 7. In the wet-process non-weaving process, hemp fibers are fully stirred by a stirrer in water suspension, so that hydroxyl groups on the surfaces of the fibers are combined with each other to form hydrogen bonds, the tensile strength is enhanced to a certain extent, and after hot pressing, the fibers are contacted more tightly and the acting force is larger, so that the bending strength of the hybrid composite material with the hemp fiber-glass fiber mass ratio of 7.

3. Impact testing

The composite material sheet produced in example 1 was cut out into samples meeting the impact strength test standards according to the astm d6110 test using a MBS240/E type saw blade machine, and the sample size of the sample was length × width: 80mm 15mm, the thickness of the sample is measured by a vernier caliper before the test, and the mark is recorded, when in the test, the impact speed is 3.8m/s, the pendulum energy is 7.5J, and the elevation angle is 160 degrees. Three groups of effective data are measured according to the proportion of each hemp glass fiber, and finally, the impact strength of each group is calculated and the average value is taken. The impact strength calculation formula is as follows:

energy units in formula (la): j;

thickness unit: mm;

width unit: mm;

impact strength unit: kg-cm/cm means: the ratio of the energy absorbed by the sample during impact failure to the original cross-sectional area.

The calendar of 1002: for 1 joule =10.2Kg · cm, the energy unit needs to be converted from kg.m to Kg-cm, i.e. 10.2Kg-cm, for the thickness and width units are mm, the unit needs to be converted to cm, and for the calculation divided by the area, it needs to be expanded by 100 times. Therefore, 10.2 Kg. Cm. Times.100 was 1002.

Fig. 7 shows the impact strength of different composite materials prepared in example 1, and it can be seen from fig. 7 that the impact strength of the wet-process non-woven composite material used for the reinforcement is significantly higher than that of the control group, the maximum impact strength is increased by nearly 2 times, the minimum impact strength is increased by nearly 1 time, and the sample with the highest impact strength is a hybrid composite material with the mass ratio of hemp fiber to glass fiber being 1. The hybrid composite material has such high impact strength because the preformed body is made of wet non-woven fabric, so that the fibers can be better cohered and entangled, and the impact strength of the prepared hybrid composite material is higher than that of a glass fiber/polypropylene fiber composite material.

By comparing composite material samples with pure fibers as reinforcing bodies, the hybrid composite material with the mass ratio of hemp fiber to glass fiber being 1; comparing the hybrid composite material, wherein the mass ratio of the hemp fiber to the glass fiber is 1; the mass ratio of the hemp fiber to the glass fiber is 1. In the wet-process non-weaving process, hemp fibers are fully stirred by a stirrer in water suspension, so that hydroxyl groups on the surfaces of the fibers are combined with each other to form hydrogen bonds, the tensile strength is enhanced to a certain extent, and after hot pressing, the fibers are contacted more tightly and the acting force is larger, so that the impact strength of the hybrid composite material with the mass ratio of hemp fibers to glass fibers being 1.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included therein.

Claims

1. The polypropylene-based composite material for the automobile, which is light in weight and environment-friendly and can replace glass fiber, is characterized in that the composite material is formed by compounding wet-process non-woven fabric and a polypropylene film;

2. The lightweight, environmentally friendly glass fiber substitutable polypropylene-based automotive composite material of claim 1, wherein said glass fiber is an alkali-free glass fiber and has a fiber length of 3mm.

3. The lightweight, environmentally friendly glass fiber substitutable polypropylene-based automotive composite material of claim 1, wherein the hemp fibers and glass fibers are present in a total amount of 20wt%, and the polypropylene fibers and polypropylene film are present in a total amount of 80wt%, in terms of mass%; wherein the mass ratio of the polypropylene fiber to the polypropylene film is 4.

4. The lightweight, environmentally friendly glass fiber substitutable polypropylene-based automotive composite material of claim 3, wherein said polypropylene fibers have a fiber length of 3mm and a linear density of 1.67dtex.

5. The lightweight, environmentally friendly glass fiber substitutable polypropylene-based automotive composite material as claimed in claim 1, wherein the hemp fiber has a fiber length of 3mm.

6. A method for preparing a lightweight, environmentally friendly glass fiber substitutable polypropylene-based automotive composite material as claimed in any one of claims 1 to 5, comprising the steps of:

weighing raw materials according to mass, adding a dispersing agent and water into a mixture of hemp fibers and glass fibers, stirring at a rotating speed of 1400r/min for 5min, then adjusting the rotating speed to 600r/min, adding polypropylene fibers into the mixture, stirring until a fiber winding phenomenon occurs, then adjusting the rotating speed to 1400r/min, and stirring for 10min to prepare wet-process fiber pulp; then preparing the fiber pulp into hemp/glass fiber/polypropylene fiber hybrid non-woven fabric through a wet-laid process, and drying and pumping the non-woven fabric into a composite material reinforcement;

7. The method for preparing a lightweight, environmentally friendly glass fiber substitutable polypropylene-based automotive composite material as claimed in claim 6, wherein the hemp fiber and the glass fiber are present in a total amount of 20wt%, and the polypropylene fiber and the polypropylene film are present in a total amount of 80wt%, in terms of mass percentage; wherein the mass ratio of the polypropylene fiber to the polypropylene film is 4.

8. The method for preparing a polypropylene-based automobile composite material which is light in weight and can replace glass fiber in an environment-friendly manner according to claim 6, wherein the usage ratio of the water to the dispersant is 500mL.

9. Use of a lightweight, environmentally friendly glass fiber substitutable polypropylene-based automotive composite material as claimed in any one of claims 1 to 5 in the field of automotive materials.