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

Abstract

The invention discloses a polypropylene-based automobile composite material which is light in weight and environmentally friendly and can replace glass fiber, and belongs to the technical field of composite materials. The composite material is composed of wet-laid non-woven fabric and polypropylene film; the wet-laid non-woven fabric is composed of hemp fiber, glass fiber and polypropylene fiber, wherein the mass ratio of hemp fiber to glass fiber is: (2‑8): (8‑2). The composite material uses a wet non-woven process to prepare a preform, and uses hybrid and self-reinforcing means to improve the wettability of polypropylene to the preform material, thereby improving the mechanical properties of the composite material.

Description

A lightweight, environmentally friendly polypropylene-based automotive composite material that can replace glass fibers

technical field

The invention belongs to the technical field of composite materials, and in particular relates to a lightweight, environmentally friendly polypropylene-based composite material for automobiles that can replace glass fibers.

Background technique

In recent years, research on biodegradable composites has increased significantly with the development of non-polluting green composites and the realization of goals such as replacing polymeric materials in commercial applications. Natural resources as reinforcements are the subject of numerous studies aimed at developing various natural composite materials. Due to the low cost, low density, good mechanical properties, strong biodegradability, and sustainable development potential of plant fibers, plant fibers are increasingly used as polymer reinforcement materials. In thermoplastic matrix composites, recyclability and energy recovery via incineration as well as mechanical properties are superior to glass fiber reinforced materials.

The research and development of fiber-reinforced composite materials has contributed to the development of automobile lightweight. With the development of science and technology, more and more non-metallic materials with the advantages of light weight, corrosion resistance and easy molding are used in automobiles. Especially after putting forward the requirements of automobile lightweight, waste recycling and reducing automobile fuel consumption, the manufacturing technology of plastic instead of steel has attracted more and more attention, especially for the development and utilization of thermoplastic composite materials. The composite material matrix used in traditional automobiles is usually a thermosetting material. The waste parts and scraps of this material are often disposed of by landfill or incineration, which not only pollutes the environment, but also leads to waste of raw materials. Wang Chunhong and others prepared a fully degradable composite material for automotive interiors by compounding hemp powder and polylactic acid. The results show that: when the mass fraction of hemp powder is 30% and the particle size of hemp powder is 40 mesh, the tensile strength, flexural strength, tensile modulus and flexural modulus of the composite material are all maximum. There are also relevant personnel who have tested glass fiber reinforced polypropylene composite materials prepared by glass fibers forming grains of different lengths. The results show that the glass fibers are severely broken after injection molding, and the impact strength of the composite material increases with the increase of glass fiber length.

Although scholars at home and abroad have done a lot of research on the hybrid technology of hybrid composites, there are still few studies on the performance characteristics of hemp/glass fiber hybrid composites.

Contents of the invention

Aiming at the technical problems existing in the prior art, the present invention aims to provide a lightweight, environmentally friendly polypropylene-based automotive composite material that can replace glass fiber. The composite material preform is prepared by non-woven, and the hybrid and self-reinforcement methods are used to improve the wetting performance of the polypropylene film on the preform material, thereby improving the mechanical properties of the composite material.

To achieve the above object, the present invention proposes the following technical solutions:

A lightweight, environmentally friendly polypropylene-based automotive composite material that can replace glass fibers. The composite material is composed of wet-laid nonwoven fabric and polypropylene film;

The wet-laid nonwoven fabric is formed by mixing hemp fibers, glass fibers and polypropylene fibers, wherein the mass ratio of hemp fibers to glass fibers is (2-8):(8-2).

Further, the glass fibers are alkali-free glass fibers with a fiber length of 3mm.

Further, in terms of mass percentage, the total amount of the hemp fiber and glass fiber accounts for 20wt%, and the total amount of the polypropylene fiber and polypropylene film accounts for 80wt%; wherein, the polypropylene fiber and polypropylene The mass ratio of the film is 4:1.

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

Further, the fiber length of the hemp fiber is 3 mm.

The present invention also provides a method for preparing a lightweight, environmentally friendly polypropylene-based automotive composite material that can replace glass fibers, comprising the following steps:

Weigh raw materials by mass, add dispersant and water to the mixture of hemp fiber and glass fiber, stir at a speed of 1400r/min for 5 minutes, then adjust the speed to 600r/min, add polypropylene fiber to the mixture, and stir until fiber entanglement occurs (When it is found that there is fiber entanglement on the stirring rod, stop the agitator, and pick the entangled fiber back into the slurry with a glass rod) After adjusting the rotating speed to 1400r/min, stir for 10min to make a wet fiber slurry; The pulp is prepared into a hemp/glass fiber/polypropylene fiber hybrid nonwoven fabric through a wet-laid process, and then dried and pumped into a composite material reinforcement;

The polypropylene film is laid on the upper and lower surfaces of the composite material reinforcement to obtain a lightweight, environmentally friendly polypropylene-based composite material for automobiles that can replace glass fibers.

Further, in terms of mass percentage, the total amount of the hemp fiber and glass fiber accounts for 20wt%, and the total amount of the polypropylene fiber and polypropylene film accounts for 80wt%; wherein, the polypropylene fiber and polypropylene The mass ratio of the film is 4:1.

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

Further, the dosage ratio of the water and the dispersant is 500mL:0.1g, and the dispersant is a polyacrylamide dispersant. In order to improve the dispersibility of fibers in water, a dispersant is added in the preparation of the fiber suspension slurry. The dispersant can make the fibers have good dispersibility in water, maintain uniform distribution in the suspension slurry, and increase the hygroscopicity of the fibers. Make the fibers swell in water, and make the fibers have a certain bonding strength in the wet state after being formed into a web. In order to improve the wettability of polypropylene film to fibers, polypropylene fibers are added to wet-laid nonwovens.

The invention also provides the application of a lightweight, environmentally friendly polypropylene-based automotive composite material that can replace glass fibers in the field of automotive materials.

Compared with prior art, the beneficial effect of the present invention is:

The present invention adopts the wet nonwoven process to prepare the hemp/glass fiber nonwoven preform, and in order to improve the wettability of the polypropylene film to the preform fabric, a hybrid method is adopted to combine a certain quality of polypropylene fiber with hemp fiber, glass Preforms were prepared by mixing fibers, and hemp/glass fiber reinforced polypropylene composites with different mixing ratios were prepared by compression molding. The tensile properties, flexural properties and impact properties of hemp/glass fiber hybrid reinforced polypropylene matrix composites were tested, and it was found that when the mass ratio of hemp fiber to glass fiber was 3:7, the tensile properties and flexural properties of the composite material were the best. Good; the impact performance of the composite is best when the mass ratio of hemp fiber to glass fiber is 1:1.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required in the embodiments. Obviously, the accompanying drawings in the following description are only some of the present invention. Embodiments, for those of ordinary skill in the art, other drawings can also be obtained based on these drawings without any creative effort.

Fig. 1 is a schematic diagram of the operation process of embodiment 1;

Fig. 2 is the tensile strength histogram of the different composite materials that embodiment 1 prepares;

Fig. 3 is the tensile strength displacement curve figure of the different composite materials that embodiment 1 prepares;

Fig. 4 is the stress-strain curve of the different composite materials that embodiment 1 prepares;

Fig. 5 is the schematic diagram of the maximum bending stress position of different composite materials prepared in Example 1;

Fig. 6 is the bending strength of the different composite materials prepared by embodiment 1;

Fig. 7 is the impact strength of different composite materials prepared in Example 1.

Detailed ways

Various exemplary embodiments of the present invention will now be described in detail. The detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features and embodiments of the present invention.

It should be understood that the terminology described in the present invention is only used to describe specific embodiments, and is not used to limit the present invention. In addition, regarding the numerical ranges in the present invention, it should be understood that each intermediate value between the upper limit and the lower limit of the range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated value 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 from 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 the 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 to disclose and describe the methods and/or materials in connection with which the documents are described. In case of conflict with any incorporated document, the contents of this specification control.

It will be apparent to those skilled in the art that various modifications and changes can be made in the specific embodiments of the present invention described herein without departing from the scope or spirit of the present invention. Other embodiments will be apparent to the skilled person from the description of the present invention. The specification and examples in this application are exemplary only.

As used herein, "comprising", "comprising", "having", "comprising" and so on are all open terms, meaning including but not limited to.

The invention utilizes a compression molding method to prepare polypropylene-based composite materials for automobiles. The polypropylene film and the prepared composite material reinforcement are laminated in a sandwich lay-up manner, and polypropylene is respectively laid on the surface layer and the middle layer of the hybrid nonwoven fabric. The film is laminated and compounded in the mold to obtain a lightweight, environmentally friendly polypropylene automotive composite material that can replace glass fibers in whole or in part.

A lightweight, environmentally friendly polypropylene-based automotive composite material that can replace glass fibers. The composite material is composed of wet-laid nonwoven fabric and polypropylene film;

The wet-laid nonwoven fabric is formed by mixing hemp fibers, glass fibers and polypropylene fibers, wherein the mass ratio of hemp fibers to glass fibers is (6-20):(6-20). More preferred are 3:7 and 1:1.

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

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

In some preferred embodiments, in terms of mass percentage, the total amount of the hemp fiber and the glass fiber accounts for 20wt%, and the total amount of the polypropylene fiber and the polypropylene film accounts for 80wt%; wherein, the polypropylene The mass ratio of fiber and polypropylene film is 4:1.

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

In some preferred embodiments, the fiber length of the hemp fiber is 3 mm.

The present invention also provides a method for preparing a lightweight, environmentally friendly polypropylene-based automotive composite material that can replace glass fibers, comprising the following steps:

Weigh raw materials by mass, add dispersant and water to the mixture of hemp fiber and glass fiber, stir at a speed of 1400r/min for 5 minutes, then adjust the speed to 600r/min, add polypropylene fiber to the mixture, and stir until fiber entanglement occurs (When it is found that there is fiber entanglement on the stirring rod, stop the agitator, and pick the entangled fiber back into the slurry with a glass rod) After adjusting the rotating speed to 1400r/min, stir for 10min to make a wet fiber slurry; The pulp is prepared into a hemp/glass fiber/polypropylene fiber hybrid nonwoven fabric through a wet-laid process, and then dried and pumped into a composite material reinforcement;

The polypropylene film is laid on the upper layer, the lower layer and the middle layer of the composite material reinforcement to obtain a lightweight, environmentally friendly polypropylene-based composite material for automobiles that can replace glass fibers.

In some preferred embodiments, in terms of mass percentage, the total amount of the hemp fiber and the glass fiber accounts for 20wt%, and the total amount of the polypropylene fiber and the polypropylene film accounts for 80wt%; wherein, the polypropylene The mass ratio of fiber and polypropylene film is 4:1.

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

In some preferred embodiments, the dosage ratio of the water and the dispersant is 500mL:0.1g, and the dispersant is a polyacrylamide dispersant. In order to improve the dispersibility of fibers in water, a dispersant is added in the preparation of the fiber suspension slurry. The dispersant can make the fibers have good dispersibility in water, maintain uniform distribution in the suspension slurry, and increase the hygroscopicity of the fibers. Make the fibers swell in water, and make the fibers have a certain bonding strength in the wet state after being formed into a web. In order to improve the wettability of the resin to the fibers, polypropylene fibers are added to the wet-laid nonwovens.

The invention also provides the application of a lightweight, environmentally friendly polypropylene-based automotive composite material that can replace glass fibers in the field of automotive materials.

Non-woven fabrics are also called non-woven fabrics, which belong to the textile industry category, and the English name is "nonwovens". It is a fabric that does not need to be spun. It just orients or randomly arranges short fibers or filaments to form a fiber network structure, which is then strengthened by mechanical, thermal bonding or chemical methods. The non-woven fabric in the national standard GB/T5709-1997 refers to: a sheet, net or felt made of oriented or randomly arranged fibers rubbed, bonded or bonded, excluding paper, machine, knitted, tufted and wet scratch felt. Put simply: instead of yarns that interweave and weave together, it's made of fibers that are bonded together. Nonwovens have broken through the traditional textile principles, and have the characteristics of short process, fast production speed, high output, low cost, wide application, and wide source of raw materials.

During wet-laid technology, a large amount of water is used as a medium to obtain a homogeneous fiber suspension and fiber web after dewatering. Wet-laid nonwovens have the following advantages: the internal fibers of the net formed under water flow conditions are three-dimensionally distributed, with good uniformity; the fibers are arranged in an orderly manner; and they have a large pore structure. However, fiber webs are usually loose due to the low bond strength between fibers. Therefore, the present invention processes the wet-laid nonwoven support to overcome these disadvantages and improve mechanical properties.

During the material preparation process, short fibers (usually <30mm) are dispersed in water, and a dispersant is added to ensure that the fibers are evenly dispersed. Continuous web formation is 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 strainer. The deposition of fibers on the screen is controlled by the filtration resistance of the web formed in the process. The cohesion of the fiber web is the result of friction (entanglement) between fibers or chemical bonding through adhesives.

In the present invention, heating and pressing the fiber web with a hot press is a suitable method for strengthening the wet-laid nonwoven fabric. It allows low-melt fibers to melt, flow and spread in the web. After cooling, the fibers bond together and the web is strengthened to form a hot-pressed nonwoven scaffold. During this process, the melted fibers not only serve as adhesives to bond and protect other fibers, but also reduce the pore size of the nonwoven. The technology has a fast production rate, no waste water, exhaust gas, and solid waste, and is suitable for the reinforcement of thin nonwovens, which is a promising method for fabric scaffold manufacturing. The bonding strength of wet-laid nonwovens can be improved by hot pressing, thereby improving their mechanical properties. In addition, this method can reduce the pore size of wet-laid nonwovens and reduce their porosity.

Hemp can be roughly divided into: flax, jute, kenaf, hemp, apocynum, wound hemp and abaca.

Cannabis in hemp is also called hemp and hemp. Because of the presence of cannabidiol, there are very few pests during growth and placement. The surface of hemp single fiber is rough, with longitudinal gaps and holes and transverse branches, without natural turning. The cross-section of cannabis has a variety of shapes mixed, such as triangle, oblong, waist and so on. The fineness and length of the single fiber of hemp are equivalent to that of flax, so it also needs to be spun with craft fiber. It is known from experience that hemp fiber and its products are softer and less itchy, which is related to the softness of the interfiber gum and the fiber itself. The hemp fiber has a middle cavity, which is connected with the cracks and pores distributed on the surface of the fiber, which is the main reason for its excellent capillary effect, high adsorption and moisture absorption and perspiration performance. Hemp fiber also has certain anti-mildew and bactericidal functions.

Test material and instrument of the present invention:

1. Experimental raw materials:

E-glass fiber: 3mm, Shanghai Chenqi Chemical Technology Co., Ltd.;

Hemp fiber: provided by Shenyang Beijiang Hemp Industry Development Co., Ltd.;

Polypropylene fiber: provided by Changshu Changjiang Chemical Fiber Co., Ltd., the fiber length is 3mm, and the linear density is 1.67dtex;

Polypropylene masterbatch: model ST868M, Taiwan Li Changrong Chemical Industry Company;

Polyacrylamide dispersant: MW3 million, anionic, Sinopharm Chemical Reagent Co., Ltd.

2. Experimental equipment:

12-inch slicer: FY0002 type, Fengye Trading Co., Ltd., Jiangcheng District, Yangjiang City;

Hot press: YLJ-HP300 type, Hefei Kejing Material Technology Co., Ltd.;

Desktop band saw machine: MBS240/E type, German PROXXON company;

Metallographic sample grinding and polishing machine: Jinan Fengzhi Testing Instrument Co., Ltd.;

Computer-controlled electronic universal testing machine: WDW20 type, Jinan Tianchen Testing Machine Manufacturing Co., Ltd.;

Digital display simply supported beam impact testing machine: XJJ-50S type, Jinan Hengsi Shengda Instrument Co., Ltd.;

High-definition CCD measuring microscope: GP-300C, Kunshan Gaopin Precision Instrument Co., Ltd.;

Electronic balance: HZK-FA210S type, Huazhi (Fujian) Electronic Technology Co., Ltd.;

Water circulation sheet copying machine: AT-CP-202111180, Jinan Zhuobang Test Instrument Co., Ltd.;

Super thermostat: Model 501A, Shanghai Experimental Instrument Factory Co., Ltd.;

Electric stirrer: D2025W type, Shanghai Meiyingpu Instrument Manufacturing Co., Ltd.;

Glass rod, acid-free paper, 50cm ruler, tin foil, vernier caliper.

Example 1

A method for preparing a lightweight, environmentally friendly polypropylene-based automotive composite material that can replace glass fibers, the steps are as follows:

1) Raw material processing: use slicer (cutter) to cut hemp fiber, glass fiber and polypropylene fiber into fibers with a fiber length of 3mm;

2) According to mass percentage, the total amount of the hemp fiber and the glass fiber accounts for 20wt%, and the total amount of the polypropylene fiber and the polypropylene film accounts for 80wt%; wherein, the mass of the polypropylene fiber and the polypropylene film The ratio is 4:1.

Use the HZK-FA210S model electronic balance and acid-free paper to weigh a certain proportion of hemp fiber and glass fiber and pour it into the stainless steel bucket (see Table 1 for the specific ratio), then add water and dispersant (polyacrylamide) to the stainless steel bucket to control The solid-to-liquid ratio of the total amount of hemp fiber, glass fiber and polypropylene fiber to water is 0.01:1, and the consumption ratio of water and dispersant is 500mL:0.1g, then the stainless steel bucket is fixed in the 501A type super thermostat, and then Use the D2025W type electric stirrer to stir, adjust the rotating speed to 600r/min after stirring for 5 minutes with the rotating speed of 1400r/min, then weigh a certain amount of polypropylene fiber (as shown in Table 1) and slowly add it to the stainless steel bucket, and stir until Fiber entanglement occurs (when fiber entanglement is found on the stirring rod, stop the agitator and pick the entangled fiber back into the slurry with a glass rod), adjust the speed to 1400r/min, stir for 10min, and make a wet fiber slurry ; After stirring evenly, pour it into the AT-CP-202111180 water circulation sheet-making machine to make a hemp/glass fiber/polypropylene fiber hybrid non-woven fabric, then put it into an oven for drying, and cut it into sizes after drying. Length × width: 17.5cm × 17.5cm hemp/glass fiber/polypropylene fiber hybrid nonwoven fabric, the operation flow diagram is shown in Figure 1.

3) Use a YLJ-HP300 hot press and tin foil to heat-press the polypropylene masterbatch into a film with a thickness of 1mm, and then cut it into a film with a size of length×width: 17.5cm×17.5cm;

4) Using a YLJ-HP300 hot press machine, the polypropylene film and the hemp/glass fiber/polypropylene fiber hybrid nonwoven fabric prepared in step 2) are laminated in a mold by compression molding, and the mold size is 18cm×18cm ×4mm, the layering sequence is polypropylene film-wet-laid nonwoven fabric-polypropylene film, finally laying 3 layers of polypropylene film, 2 layers of hemp/glass fiber/polypropylene fiber hybrid nonwoven fabric, under the pressure of 4MPa, temperature Press at 180°C for 30 minutes to obtain a lightweight, environmentally friendly polypropylene-based composite material for automobiles that can replace glass fibers.

Table 1

Test case

1. Tensile performance test

The implementation standard is ASTMD3039/D3039M-08. Use the MBS240/E type saw blade to cut out the composite material made in Example 1 to meet the tensile performance test standard, and the sample size is length×width: 18mm×20mm. Use a vernier caliper to measure the thickness of the sample, record it, and label the sample, and then glue four carbon plate reinforcements on both ends of the tensile test sample, keep the clamping distance at 13.8mm, and then put it into the WDW20 microcomputer control In the electronic universal testing machine, the speed should be set to 2mm/min before the stretching starts, and the relevant data should be saved and recorded after the stretching is over. Three sets of valid data were measured for each hemp fiber and glass fiber ratio. Finally, the tensile strength of each group was calculated, and the average value was taken, and the results are shown in Figure 2. The formula for calculating tensile strength is as follows:

In the formula, F ^{tu ——tensile} strength, MPa;

p ^max —— maximum pulling force, N;

A——the actual cross-sectional area of the sample measured before the test, mm ² .

Fig. 2 is the histogram of the tensile strength of different composite materials prepared in Example 1. As can be seen from Fig. 2, the tensile strength of the composite materials using wet nonwovens is significantly greater than that of the control group, with a maximum increase of nearly 3 times, the minimum increased by nearly 2 times, and the sample with the largest tensile strength is a composite material with a mass ratio of hemp fiber to glass fiber of 7:3. The reason why the wet-laid nonwoven composite material has such a large tensile strength is that the preform is wet-laid nonwoven, so that the fibers can be better entangled and entangled, so that the tensile strength of the composite material is improved. The tensile strength is greater than that of materials made only of glass fibers.

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

By comparing the tensile strength of the designed composites with hybrid properties in the form of wet-laid nonwoven structure, it is found that the tensile strength of the hybrid composites increases with the increase of the proportion of glass fibers, and the hybrid composites The growth rate of tensile strength also increases accordingly. The tensile strength of the hybrid composite prepared when the mass ratio of hemp fiber to glass fiber is 7:3 is 20.52% higher than that of the composite material prepared by mixing hemp fiber/polypropylene fiber; the mass ratio of hemp fiber to glass fiber is The tensile strength of the hybrid composite prepared at 7:3 is 11.48% higher than that of the hybrid composite prepared at the mass ratio of hemp fiber to glass fiber at 1:1. The reason for the analysis is that the tensile strength of glass fiber itself is greater than that of hemp fiber, so as the proportion of glass fiber in the composite increases and the proportion of hemp fiber decreases, the tensile strength of the hybrid composite increases and the growth rate improve.

In addition, when the mass ratio of hemp fiber to glass fiber in the hybrid composite is 7:3, the tensile strength is the largest. Because in the wet non-woven process, the hemp fiber is fully stirred by the stirrer in the water suspension, so that the hydroxyl groups on the fiber surface combine with each other to form hydrogen bonds, and the tensile strength is enhanced to a certain extent. The contact is closer and the force is greater, so the tensile strength of the hybrid composite prepared when the mass ratio of hemp fiber to glass fiber is 7:3 is the largest. But the tensile strength of hemp fiber is less than that of glass fiber, so the tensile strength of hemp composite material adopting wet nonwoven is less than that of glass fiber composite material adopting wet nonwoven.

FIG. 3 is a graph of tensile strength displacement curves of different composite materials prepared in Example 1. FIG. It can be seen from Figure 3 that the elongation at break of hybrid composites is significantly greater than that of the control group, because the force between fibers increases after wet nonwovens are used, making the elongation at break higher than that of short-fiber glass. The elongation at break of the fiber is large.

By comparing the composite samples whose reinforcements are all pure fibers, the elongation at break of the hemp fiber/polypropylene fiber composite is the largest, because the breaking strength and elongation at break of hemp fiber are higher than those of ramie and flax, and the elongation of ramie and flax is higher than that of ramie and flax. The elongation at break is 2-4%, while the elongation at break of glass fiber is ≤4%.

Figure 4 is the stress-strain curves of different composite materials prepared in Example 1. It can be seen from Figure 4 that the tensile modulus of the hybrid composite material is significantly greater than that of the control group. The reason for this phenomenon is that there is not much force between the fibers in the composite material made of short-fiber glass fibers and polypropylene film, but more force between the fibers and the matrix, while the reinforcement The wet-laid non-woven composite material not only realizes the perfect combination between the matrix and the fibers, but also fully demonstrates the force between the fibers.

2. Three-point bending performance test

The implementation standard is ASTMD7264/D7264M-07. Use the MBS240/E type saw blade to cut the composite material plate made in Example 1 into a sample that meets the three-point bending performance test standard, and the sample size is length×width: 80mm×10mm. Then use a vernier caliper to measure the thickness of the sample, record it, and label the sample. According to the length of the sample, adjust the distance between the lower indenters to a reasonable position according to the standard requirements, and adjust the position of the beam of the testing machine so that the upper indenter drops to the next level. Press the middle of the head. Adjust the position of the lower pressure head (to ensure that the relative position of the pressure heads on both sides remains unchanged), so that the upper pressure head is located in the middle of the two lower pressure heads. Adjust the position of the beam of the testing machine so that the upper indenter is far away from the lower indenter, place the sample flat on the lower indenter, and adjust the position of the sample visually so that its axis is perpendicular to the width direction of the lower indenter, and the midpoint is just below the upper indenter . The bending schematic diagram is shown in Figure 5, then put the sample in, adjust the position of the beam of the testing machine so that the upper indenter is just in contact with the sample, the pre-pressure is about 5N, then reset to zero, set the bending speed to 2mm/min, and start the experiment.

The bending test process continues to load until the sample breaks or the compressive force value drops by more than 25%, and the test ends. Raise the flat knitting machine of the testing machine, take out the sample, save and record the data, collect the remains of the sample, and store it in a ziplock bag. The ziplock bag should be clearly marked to distinguish each sample. For the fracture mode of the sample, judge according to the requirements of ASTM D7264/D7264M-07. Determine whether the fracture mode of the sample meets the standard requirements, and make a clear mark on the test report. If an unacceptable failure mode occurs in a relatively high proportion (50%) of a group of specimens, the data for that group of tests is questionable and should be repeated. Three groups of valid data were measured for each hemp glass fiber ratio, and finally the bending strength of each group was calculated and the average value was taken. The formula for calculating the bending strength is as follows:

In the formula, σ——stress on the outer surface of the mid-span, MPa;

P - force, N;

L——support span, mm;

b——beam width, mm;

h—thickness of the beam, mm.

Note: The maximum stress of three-point simply supported bending occurs at the mid-span position, and the surface stress at the mid-span is the maximum bending stress (see Figure 5).

Fig. 6 is the flexural strength of different composite materials prepared in Example 1. It can be seen from Figure 6 that the flexural strength of the hybrid composites is significantly greater than that of the control group, with a maximum increase of nearly 1 times and a minimum increase of nearly 50% in flexural strength. The sample with the largest flexural strength is the mass ratio of hemp fiber to glass fiber 7:3 composite material. The reason why the hybrid composite material with this ratio has such a large bending strength is that the preform is wet-laid non-woven, which enables better cohesion and entanglement between the fibers, so that the tensile strength of the hybrid composite material made Greater flexural strength than fiberglass material.

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

By comparing the flexural strength of the composites designed with hybrid properties in the form of wet-laid nonwoven reinforcements, it was found that the flexural strength of the hybrid composites increased with the increase in the proportion of glass fibers. Moreover, the growth rate of flexural strength of hybrid composites increases. Among them, the bending strength of the hybrid composite material with a mass ratio of hemp fiber to glass fiber of 7:3 is 40.47% higher than that of the hemp fiber/polypropylene fiber composite material, and the bending strength of the hybrid composite material with a mass ratio of hemp fiber to glass fiber of 7:3 Compared with the hemp fiber and glass fiber mass ratio of 1:1 hybrid composite material bending strength increased by 17.64%. Because the bending strength of glass fiber itself is greater than that of hemp fiber, as the proportion of glass fiber in the composite increases and the proportion of hemp fiber decreases, the bending strength of the hybrid composite increases and the growth rate increases.

In addition, when the mass ratio of hemp fiber to glass fiber in the hybrid composite is 7:3, the bending strength is the largest. Because in the wet non-woven process, the hemp fiber is fully stirred by the stirrer in the water suspension, so that the hydroxyl groups on the fiber surface combine with each other to form hydrogen bonds, and the tensile strength is enhanced to a certain extent. The contact is closer and the force is greater, so the bending strength of the hybrid composite with the mass ratio of hemp fiber to glass fiber is 7:3 is the largest.

3. Impact performance test

According to the ASTMD6110 test, use the MBS240/E type saw blade to cut out a sample that meets the impact performance test standard from the composite material plate made in Example 1. The size of the sample sample is length × width: 80mm × 15mm. The vernier caliper measures the thickness of the sample and records the label. During the test, the impact velocity is 3.8m/s, the energy of the pendulum is 7.5J, and the elevation angle is 160°. Three sets of effective data are measured for each hemp glass fiber ratio, and finally the impact strength of each set is calculated and the average value is taken. The formula for calculating the impact strength is as follows:

Energy unit in the formula: J;

Thickness unit: mm;

Width unit: mm;

Impact strength unit: Kg-cm/cm Meaning: The ratio of the energy absorbed by the sample during the impact failure process to the original cross-sectional area.

The origin of 1002: Because 1 joule = 10.2Kg cm, it is necessary to convert the energy unit from Kg. When divided by the area, it needs to be enlarged by 100 times. Therefore, 10.2Kg·cm×100 is 1002.

Figure 7 shows the impact strength of different composite materials prepared in Example 1. It can be seen from Figure 7 that the impact strength of the reinforcement using wet-laid nonwoven composite materials is significantly greater than that of the control group, with a maximum increase of nearly 2 times and a minimum increase of The sample with the highest impact strength is a hybrid composite with a mass ratio of hemp fiber to glass fiber of 1:1. The reason why the hybrid composite material has such a large impact strength is that the preform is wet-laid non-woven, so that the fibers can be better entangled and entangled, so that the impact strength of the hybrid composite material is higher than that of glass fiber. / Polypropylene fiber composite material has high impact strength.

By comparing the composite material samples whose reinforcements are all pure fibers, the impact strength of the hybrid composite material with the mass ratio of hemp fiber to glass fiber is 1:1 is the largest; for the comparison of hybrid composite materials, the mass ratio of hemp fiber to glass fiber is The impact strength of the 1:1 hybrid composite is 27.51% higher than the impact strength of the hemp fiber/polypropylene fiber composite; the mass ratio of hemp fiber to glass fiber is 1:1 The impact strength ratio of the hybrid composite is The impact strength of the 7:3 hybrid composite increased by 49.60%. Because in the wet non-woven process, the hemp fiber is fully stirred by the stirrer in the water suspension, so that the hydroxyl groups on the fiber surface combine with each other to form hydrogen bonds, and the tensile strength is enhanced to a certain extent. The contact is closer and the force is greater, so the impact strength of the hybrid composite material with a mass ratio of hemp fiber to glass fiber of 1:1 is the largest.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention within.

Claims (9)

1. A kind of light weight, environmental protection can replace the polypropylene-based automobile composite material of glass fiber, it is characterized in that, described composite material is to be compounded by wet-laid nonwoven fabric and polypropylene film; The wet-laid nonwoven fabric is formed by mixing hemp fibers, glass fibers and polypropylene fibers, wherein the mass ratio of hemp fibers to glass fibers is (2-8):(8-2). 2. The lightweight, environmentally friendly polypropylene-based automotive composite material that can replace glass fibers according to claim 1, wherein the glass fibers are alkali-free glass fibers, and the fiber length is 3 mm. 3. The lightweight, environmentally friendly polypropylene-based automotive composite material that can replace glass fibers according to claim 1, wherein, in terms of mass percentage, the total amount of the hemp fibers and glass fibers accounts for 20wt%, The total amount of the polypropylene fiber and the polypropylene film accounts for 80wt%; wherein, the mass ratio of the polypropylene fiber and the polypropylene film is 4:1. 4. The lightweight, environmentally friendly polypropylene-based automotive composite material that can replace glass fibers according to claim 3, wherein the polypropylene fibers have a fiber length of 3mm and a linear density of 1.67dtex. 5. The lightweight, environmentally friendly polypropylene-based automotive composite material that can replace glass fibers according to claim 1, wherein the fiber length of the hemp fibers is 3 mm. 6. A method for preparing a lightweight, environmentally friendly polypropylene-based automotive composite material that can replace glass fibers as claimed in any one of claims 1-5, characterized in that it comprises the following steps: Weigh raw materials by mass, add dispersant and water to the mixture of hemp fiber and glass fiber, stir at a speed of 1400r/min for 5 minutes, then adjust the speed to 600r/min, add polypropylene fiber to the mixture, and stir until fiber entanglement occurs Finally, adjust the rotation speed to 1400r/min, stir for 10min, and make a wet-laid fiber slurry; then prepare the fiber slurry into a hemp/glass fiber/polypropylene fiber hybrid nonwoven fabric through a wet-laid process, and then dry and pump it into a Composite reinforcement; The polypropylene film is laid on the upper layer, the lower layer and the middle layer of the composite material reinforcement to obtain a lightweight, environmentally friendly polypropylene-based composite material for automobiles that can replace glass fibers. 7. according to claim 6, the preparation method of the polypropylene-based automobile composite material that is light in weight, environment-friendly and can replace glass fiber is characterized in that, in terms of mass percentage, the total amount of the hemp fiber and glass fiber accounts for 20wt%, the total amount of the polypropylene fiber and the polypropylene film accounts for 80wt%; wherein, the mass ratio of the polypropylene fiber and the polypropylene film is 4:1. 8. the preparation method of the polypropylene-based automotive composite material that is light in weight and environmentally friendly and can replace glass fibers according to claim 6, characterized in that, the dosage ratio of the water and the dispersant is 500mL:0.1g. 9. An application of the lightweight, environmentally friendly polypropylene-based automotive composite material that can replace glass fibers in the field of automotive materials as claimed in any one of claims 1-5.

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