Preparation method of light-weight PP carbon fiber composite board

Abstract

The application provides a preparation method of a lightweight PP carbon fiber composite board and relates to the technical field of composite material preparation, taking carbon fiber / PP hybrid fiber needle punched felt as an intermediate, and preparing a composite board through laminated hot pressing molding, so as to solve the technical problems of carbon fiber easy to agglomerate, complex interface treatment, complicated board preparation process and high board density in the prior art, realize the preparation of a lightweight board with a density lower than 1 g / cm3, a simple process and recycling, and make the mechanical properties of the board be flexibly regulated through the number of laminations.

Description

Technical Field

[0001] This invention relates to the field of composite material preparation technology, and in particular to a method for preparing a lightweight PP carbon fiber composite plate. Background Technology

[0002] Lightweighting is a common pursuit in many fields, including automotive parts, rail transit interiors, building formwork, logistics pallets, and packaging materials. Reducing material weight not only reduces transportation energy consumption and improves load-bearing efficiency but also lowers installation and usage costs, making it an important indicator for material selection. Traditional metal materials have high density, are prone to corrosion, and have high processing costs; wood consumes forest resources, is prone to moisture absorption and deformation, and has unstable performance; the density of glass fiber reinforced composite boards is generally between 1.5 and 2.0 g / cm³, offering limited lightweighting effects; moreover, most of these composite boards use thermosetting resins such as epoxy resin as the matrix, which cannot be melted and reprocessed after molding, resulting in poor recyclability and failing to meet the development trend of green manufacturing.

[0003] Polypropylene (PP) is one of the most widely produced and used general-purpose thermoplastics. With a density of only about 0.90 g / cm³, it is low in cost, chemically resistant, and has good processability, making it a natural matrix candidate for lightweight sheets. Carbon fiber possesses extremely high specific strength and specific modulus, making it the most ideal lightweight reinforcing fiber. However, existing methods for preparing carbon fiber reinforced thermoplastic composite sheets have three prominent problems: First, the smooth surface and strong chemical inertness of carbon fibers result in poor interfacial compatibility with the non-polar PP matrix, typically requiring expensive interfacial modification methods such as sizing agents and maleic anhydride grafting onto PP, increasing cost and process complexity. Second, if chopped carbon fibers are directly dispersed using melt blending, agglomeration is highly likely, and uneven dispersion significantly affects the performance uniformity and stability of large-size sheets. Third, mainstream processes such as prepreg and impregnation have long chain lengths, high energy consumption, and low production efficiency, making it difficult to manufacture large-format sheets at low cost.

[0004] Needle-punched nonwoven fabric manufacturing relies on repeated punctures by needles to entangle fibers, forming a three-dimensional entangled structure. This is a low-cost fiber forming method suitable for large-scale continuous production. If carbon fibers and PP fibers are first mixed and needle-punched into a felt, using the felt as an intermediate, the problem of carbon fiber agglomeration during melt blending can be bypassed, allowing the carbon fibers to be evenly distributed within the felt. Then, through lamination and hot pressing, the PP fibers in the felt melt in situ to become the matrix, impregnating and bonding the carbon fibers, without the need for any external resins, resulting in a simple process route. However, current technologies lack mature methods for preparing lightweight sheets using this route, with a density below 1 g / cm³ and properties controllable through process parameters.

[0005] Therefore, there is an urgent need in this field for a method to prepare lightweight PP carbon fiber composite boards that is simple in process, low in cost, has uniform carbon fiber dispersion, controllable board density and performance, and is recyclable and reprocessable. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention proposes a PP carbon fiber composite board that combines lightweight and high strength.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing a lightweight PP carbon fiber composite board, characterized by comprising the following steps: Mixing and opening: Carbon fiber and PP polypropylene fiber are mixed at a mass ratio of 30:70 and opened evenly; short carbon fiber with a length of 5 cm is used to achieve a balance between reinforcement effect and dispersion processability. Needle-punching felt: The mixed fibers are fed into a needle punching machine and repeatedly punctured by needles to make the fibers entangle with each other, thus producing carbon fiber / PP mixed needle-punched felt; the three-dimensional entanglement structure of the felt body makes the carbon fibers uniformly dispersed and prevents agglomeration. Lamination and hot pressing: 4 to 12 layers of mixed needle-punched felt are stacked in a mold, heated to about 190°C and hot pressed; the PP fibers in the felt melt in situ to become the matrix, impregnating and covering the carbon fibers, and adjacent felt layers are melted and bonded together as a whole. After holding the pressure and cooling, the mold is removed to obtain a lightweight PP carbon fiber composite board. Post-processing: Cutting, machining, and sample making of the boards according to usage requirements.

[0008] Fiber ratio design: 30% carbon fiber provides reinforcement, while 70% PP fiber serves as both the entanglement carrier for needle-punched felt and the matrix source for the hot-pressed board, balancing the processability of the felt and the reinforcement effect.

[0009] The function of needle-punched felt: carbon fibers are fixed in the felt in a random orientation and three-dimensional dispersion state, which fundamentally avoids the agglomeration problem in melt blending; needle-punched felt can be produced continuously in large format, which is suitable for manufacturing large-size plates.

[0010] Hot pressing mechanism: The hot pressing temperature is 190℃, which is higher than the melting point of PP (about 165℃), the pressure is 15MPa, and the holding time is 5 minutes. The PP fibers are fully melted and flowed while the carbon fibers are not damaged. The pressure makes the board denser and controls the porosity. The density of the board is stable at 0.876~0.984 g / cm³.

[0011] The role of layer number control: The layer number can be selected between 4 and 12 layers (even number of layers). With different layer numbers, the thickness of the board, fiber volume content and density will change accordingly, so as to realize the performance classification from light load board to load-bearing board.

[0012] Needle punching process parameters (needle punching density, needle depth, etc.) and the surface density of needle punched felt; needle punching density 15-25 needles / cm², needle depth 10-16 mm, surface density 150-300 g / m².

[0013] PP fiber specifications (fineness, melting point grade) and carbon fiber specifications (grade, tow specifications): fineness 30-60 microns, melting point 165℃, carbon fiber T700 is recycled.

[0014] Target thickness of the board and thickness of each layer of needle-punched felt: Target thickness of the board is 10-25mm; thickness of each layer of needle-punched felt is 5-10mm.

[0015] Specific standards and conditions for performance testing (sample size, tensile rate, impact test method standards): Type IIa; tensile rate 5 mm / min; pendulum impact. The board obtained by the above method is an integrated board structure of multi-layer needle-punched felt fused together by hot pressing: short carbon fibers with a length of 5 cm are randomly oriented and dispersed in the PP matrix, and there is no obvious interface after the adjacent felt layers are fused together; the density of the board is 0.876~0.984 g / cm³, which is lower than the density of water and can float on the water surface.

[0016] This invention utilizes carbon fiber / PP hybrid fiber needled felt as an intermediate, and then prepares composite boards through lamination and hot pressing. This addresses the technical problems of existing technologies, such as easy agglomeration of carbon fibers, complex interface treatment, cumbersome board manufacturing processes, and high board density. It achieves the preparation of lightweight boards with a density below 1 g / cm³, simple processing, and recyclability, and allows for flexible control of the board's mechanical properties through the number of layers. The desired effect of this invention is to simultaneously achieve both lightweighting and reinforcement benefits using the shortest process route without relying on expensive fiber surface treatments and complex impregnation processes.

[0017] Compared with the prior art, the present invention has the following advantages: 1. Lightweight: The density of the board is 0.876~0.984 g / cm³, which is lower than that of water and significantly lower than that of glass fiber reinforced composite board (1.5~2.0 g / cm³) and metal materials; 2. Simple process and low cost: Only "mixing and opening - needle punching into felt - lamination and hot pressing" is required to form a board. PP fibers are melted in situ to become the matrix, without the need for external resin or impregnation process; 3. Uniform carbon fiber dispersion: The three-dimensional entanglement of needle-punched felt overcomes the problem of easy agglomeration of carbon fibers in melt blending, resulting in uniform and stable performance of the sheet material. 4. Performance is flexibly adjustable with the number of layers: the tensile strength of 10-layer and 12-layer boards reaches 62.6 and 61.3 MPa respectively, which is much higher than that of 4-8 layer boards (10.6-12.9 MPa), and the impact strength is also increased to 10-15 kJ / m². 5. Recyclable and environmentally friendly: It is a fully thermoplastic system that can be reprocessed into new shapes after being crushed and hot-pressed. Attached Figure Description

[0018] Figure 1This is a SEM image of the internal structure of a lightweight PP carbon fiber composite board. Detailed Implementation

[0019] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings to further illustrate the technical solutions of the present invention. However, the present invention is not limited to these embodiments.

[0020] Take short carbon fibers with a length of 5 cm and PP polypropylene fibers, mix them at a mass ratio of 30:70 and open them evenly. The mixed fibers are needle-punched into felt to produce carbon fiber / PP hybrid needle-punched felt; The needle-punched felt was stacked in the mold in 4, 6, 8, 10 and 12 layers respectively, numbered A4 to A12; heated to about 190℃ and hot-pressed under pressure, and demolded after holding pressure and cooling to obtain five kinds of composite boards; The sheet material was machined into dumbbell-shaped tensile specimens, and the tensile strength was tested on a computer-controlled electronic universal testing machine. Density, impact strength, and oxygen index were also tested. All specimens were black, and carbon fiber pull-out was visible at the fracture surface, indicating that the load was effectively transferred to the carbon fibers.

[0021] The measured performance data is shown in the table below:

[0022] The table above compares five indicators horizontally using the number of layers as a variable, reflecting the influence of the number of layers on the overall performance of the board.

[0023] Results Analysis Density: The densities of the five types of boards range from 0.876 to 0.984 g / cm³, all of which are lower than the density of water and can float on the water surface; as the number of layers increases, the overall density of the boards tends to increase, but the lightweight characteristics remain.

[0024] Tensile strength: 10.6–12.9 MPa for 4–8 layer sheets, jumping to 62.6 MPa with 10 layers, and 61.3 MPa for 12 layer sheets, approximately five times that of lower layer sheets. This is due to the significant improvement in carbon fiber network connectivity and sheet density. SEM images of its internal structure are shown below. Figure 1 As shown, the carbon fiber begins to bear the main load.

[0025] Impact strength: A12 board has the highest impact strength, reaching 15 kJ / m², while A10 board has 10 kJ / m², which is significantly better than 6-layer and 8-layer boards (5.1 and 4.0 kJ / m², respectively). High-layer boards have a more complete fiber network and stronger energy absorption capacity.

[0026] Oxygen index: The oxygen index of each board ranges from 17.7 to 19.2, which is within the normal combustion performance range of polypropylene-based composite materials.

[0027] In summary, 10 to 12 layers is the optimal implementation method for this approach: it achieves a significant increase in tensile strength and improved impact performance while maintaining lightweight properties.

[0028] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A method for preparing a lightweight PP carbon fiber composite board, characterized in that, Includes the following steps: 1) Mixing and opening: Mix carbon fiber and PP polypropylene fiber at a mass ratio of 30:70 and open evenly; use short carbon fiber with a length of 3-5cm to achieve a balance between reinforcement effect and dispersion processability. 2) Needle-punched felt: The mixed fibers are fed into a needle punching machine and repeatedly punctured by needles to make the fibers entangle with each other, thus producing carbon fiber / PP mixed needle-punched felt; the three-dimensional entanglement structure of the felt makes the carbon fibers uniformly dispersed and prevents agglomeration; 3) Lamination and hot pressing: Multiple layers of mixed needle-punched felt are stacked in a mold and hot pressed; PP fibers in the felt are melted in situ to become the matrix, impregnated and coated with carbon fibers, and adjacent felt layers are melted and bonded together as a whole. After holding pressure and cooling, the mold is removed to obtain a lightweight PP carbon fiber composite board. 4) Post-processing: Cutting, machining and sample making of the boards according to the usage requirements.

2. The method for preparing a lightweight PP carbon fiber composite board according to claim 1, characterized in that, In step 3), the hot pressing temperature is 190℃.

3. The method for preparing a lightweight PP carbon fiber composite board according to claim 1, characterized in that, In step 3), the number of layers of mixed needle-punched felt is 4 to 12.

4. The method for preparing a lightweight PP carbon fiber composite board according to claim 1, characterized in that, In step 2), the needle punching process parameters (needle punching density, needle depth, etc.) and the surface density of the needle punching felt are as follows: needle punching density 15-25 needles / cm², needle depth 10-16 mm, and surface density 150-300 g / m².

5. The method for preparing a lightweight PP carbon fiber composite board according to claim 1, characterized in that, The target thickness of a single-layer lightweight PP carbon fiber composite board is 10-25mm; the thickness of each layer of needle-punched felt is 5-10mm.

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