A flexurally resistant polypropylene sheet and its preparation method

Abstract

This invention relates to the field of sheet processing technology, specifically proposing a flexurally resistant polypropylene sheet and its preparation method. The flexurally resistant polypropylene sheet comprises an upper polypropylene layer, an intermediate polypropylene layer, and a lower polypropylene layer. Both sides of the intermediate polypropylene layer have rectangularly arranged columnar protrusions. A fiber felt layer is laminated to both sides of the intermediate polypropylene layer. The surface of the fiber felt layer above the intermediate polypropylene layer is laminated with the upper polypropylene layer, and the surface of the fiber felt layer below the intermediate polypropylene layer is laminated with the lower polypropylene layer. The rectangular array of columnar protrusions on both sides of the intermediate polypropylene layer increases the contact area between the intermediate polypropylene layer and the upper and lower polypropylene layers, improving the rigidity of the sheet. The columnar protrusions mechanically interlock with the fiber felt layer and the outer polypropylene layer, enhancing interlayer bonding. Simultaneously, the groove structure effectively disperses external loads and reduces stress concentration.

Description

Technical Field

[0001] This invention relates to the field of sheet processing technology, and in particular to a flexurally resistant polypropylene sheet and its preparation method. Background Technology

[0002] Polypropylene (PP), a lightweight and chemically resistant thermoplastic, is widely used in packaging, automotive, construction, and electronics industries. However, polypropylene sheets have certain limitations in terms of mechanical properties, especially in flexural strength and impact resistance, making it difficult to meet the requirements for high strength and lightweight.

[0003] To improve the mechanical properties of polypropylene sheets, existing technologies mainly optimize the process through fiber reinforcement, multilayer composite structures, and geometric design. For example, some existing technologies add short or long fibers to the polypropylene matrix to enhance the overall performance of the sheet by utilizing the tensile strength of the fibers. However, these methods are prone to problems such as uneven fiber dispersion and insufficient interfacial bonding. Using polypropylene layers of different densities for reinforcement can improve the impact strength, but the interfacial bonding of this multilayer structure is relatively low, making it difficult to achieve directional reinforcement. Some solutions improve mechanical properties by designing specific geometric structures, such as ribs and grooves, on the surface or inside the sheet. However, these solutions cannot break through the material's performance limits, resulting in limited flexural strength.

[0004] Therefore, improving the flexural strength of polypropylene sheets while maintaining their good overall mechanical properties has become one of the urgent technical problems to be solved. Summary of the Invention

[0005] In view of this, the present invention proposes a more structurally sound flexurally resistant polypropylene sheet and its preparation method.

[0006] The technical solution of the present invention is implemented as follows: The present invention provides a flexurally resistant polypropylene sheet, comprising an upper polypropylene layer, an intermediate polypropylene layer, and a lower polypropylene layer. Both sides of the intermediate polypropylene layer are provided with columnar protrusions arranged in a rectangular array. Both sides of the intermediate polypropylene layer are laminated with fiber felt layers. The surface of the fiber felt layer on the upper side of the intermediate polypropylene layer is laminated with the upper polypropylene layer, and the surface of the fiber felt layer on the lower side of the intermediate polyethylene layer is laminated with the lower polypropylene layer.

[0007] The addition of fiber felt layers can improve interfacial bonding, and the high tensile strength of fibers can significantly improve the flexural strength of the board.

[0008] In some embodiments, grooves are formed between adjacent rows of columnar protrusions. The grooves include transverse grooves and vertical grooves, and both the transverse grooves and vertical grooves above the fiber felt layer are filled with glass fiber bundles.

[0009] In some embodiments, the glass fiber bundle has a single filament diameter of 10-15 μm and its surface is treated with a silane coupling agent.

[0010] In some embodiments, the height of the columnar protrusion is 1 / 3 to 1 / 2 of the thickness of the intermediate polypropylene layer.

[0011] In some embodiments, the angle between the transverse grooves on both sides of the intermediate polypropylene layer is 45°.

[0012] In some embodiments, the fiber felt is glass fiber felt, and the weight of the glass fiber felt is 100-200 g / m². 2 .

[0013] In some embodiments, the upper and lower polypropylene layers are both high-density polypropylene with a density of 0.91-0.93 g / cm3 and a melt index of 10-20 g / 10 min, while the middle polypropylene layer is low-density polypropylene with a density of 0.89-0.91 g / cm3 and a melt index of 15-25 g / 10 min.

[0014] The density gradient design improves rigidity and enhances flexural strength, while the middle layer uses low-density polypropylene to provide toughness and impact resistance.

[0015] Secondly, the present invention also provides a method for preparing the above-mentioned flexurally resistant polypropylene sheet, comprising the following steps:

[0016] (1) A pp-g-MAH solution is uniformly coated on both sides of the intermediate polypropylene layer. The solvent is xylene and the concentration is 5wt%.

[0017] (2) The fiber felt is attached to the surface of the intermediate layer and compacted by a mold. The mold temperature is 120-140 degrees Celsius and the pressure is 0.5-1 MPa.

[0018] (3) After preheating the intermediate polypropylene with fiber felt to 100-120℃, it is fed into a co-extruder. Through a T-die, the molten high-density polypropylene is evenly covered on both sides of the intermediate polypropylene layer. After calendering and cooling, the flexurally resistant polypropylene sheet is obtained.

[0019] In some embodiments, the calendering cooling temperature is 30-50°C, and the calendering cooling rate is 1-2 m / min.

[0020] In other embodiments, the present invention also provides a method for preparing the above-mentioned flexurally resistant polypropylene sheet, comprising the following steps:

[0021] (1) A pp-g-MAH solution is uniformly coated on both sides of the intermediate polypropylene layer. The solvent is xylene and the concentration is 5wt%.

[0022] (2) The fiber felt is attached to the surface of the intermediate layer and compacted by a mold. The mold temperature is 120-140℃ and the pressure is 0.5-1MPa.

[0023] (3) Embed the glass fiber bundle into the groove and heat it with a hot air gun at a temperature of 200-220℃ to melt and bond the glass fiber bundle to the inner wall of the groove.

[0024] (4) After preheating the intermediate polypropylene with fiber felt to 100-120℃, it is fed into a co-extruder (feeding section 190℃, compression section 205℃, homogenization section 215℃, die head 215℃). Through the T-die, the molten high-density polypropylene is evenly covered on both sides of the intermediate polypropylene layer. It is calendered and cooled at 50℃ and 1m / min to obtain flexurally resistant polypropylene sheet.

[0025] The present invention has the following advantages over the prior art:

[0026] This invention features a rectangular array of columnar protrusions on both sides of the intermediate polypropylene layer. This structure increases the contact area between the intermediate polypropylene layer and the upper and lower polypropylene layers, improving the rigidity of the sheet. The columnar protrusions mechanically interlock with the fiber felt layer and the outer polypropylene layer, enhancing interlayer bonding. Simultaneously, the groove structure effectively disperses external loads and reduces stress concentration. Furthermore, in some further structural designs, glass fiber bundles are embedded within the grooves to form a network structure, providing directional tensile strength. This fiber network also prevents crack propagation and improves toughness. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is an isometric view of the flexural strength polypropylene sheet of the present invention;

[0029] Figure 2 This is an exploded view of the flexural strength polypropylene sheet of the present invention.

[0030] In the diagram: 1-Upper polypropylene, 2-Middle polypropylene, 3-Lower polypropylene, 4-Fiber felt layer, 5-Glass fiber bundle, 22-Horizontal groove, 23-Vertical groove. Detailed Implementation

[0031] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0032] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0033] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of this invention pertain. If any definition stated in this section is contrary to or otherwise inconsistent with a definition stated in a patent, patent application, published patent application, or other publication incorporated herein by reference, the definitions listed here shall prevail over those incorporated herein by reference.

[0035] Unless otherwise specified, the methods used in the following embodiments are conventional methods. Unless otherwise specified, the materials, reagents, and instruments used are conventional materials, reagents, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0036] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1 to 5” is disclosed, the described range should be interpreted as including ranges “1 to 4”, “1 to 3”, “1 to 2”, “1 to 2 and 4 to 5”, “1 to 3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range. In this specification and claims, range definitions may be combined and / or interchanged, unless otherwise stated, these ranges include all subranges contained therein.

[0037] like Figure 1 As shown, combined Figure 2 The flexural strength polypropylene sheet of the present invention comprises: an upper polypropylene layer 1, an intermediate polypropylene layer 2, and a lower polypropylene layer 3. Both sides of the intermediate polypropylene layer 2 are provided with columnar protrusions 21 arranged in a rectangular array. Both sides of the intermediate polypropylene layer 2 are laminated with fiber felt layers 4. The surface of the fiber felt layer 4 on the upper side of the intermediate polypropylene layer 2 is laminated with the upper polypropylene layer 1, and the surface of the fiber felt layer 4 on the lower side of the intermediate polypropylene layer 2 is laminated with the lower polypropylene layer 3.

[0038] The flexural strength polypropylene sheet provided in the above embodiment is based on a multi-layer structure design, with integrated columnar protrusions 21 on the surface of the middle polypropylene layer 2. These columnar protrusions 21 form a mortise and tenon-like structure, which improves the composite structural strength between the middle polypropylene layer 2, the upper polypropylene layer 1, and the lower polypropylene layer 3. Moreover, these columnar protrusions 21 can more effectively disperse stress when the sheet is subjected to bending, reduce local deformation of the sheet, and thus improve the overall flexural strength.

[0039] Secondly, to address the inherent brittleness of polypropylene, a fiber felt layer 4 is placed between adjacent polypropylene layers. This fiber felt layer 4 provides additional strength and toughness. The addition of the fiber felt layer 4 improves the impact resistance of the sheet, reduces crack initiation and propagation, thereby enhancing the flexural strength of the sheet. Furthermore, the fiber felt layer 4 provides a micro-riveting structure between layers, further refining stress dispersion and reducing localized minor deformations or cracks in the sheet, further improving flexural strength.

[0040] In some embodiments, grooves are formed between adjacent rows of columnar protrusions 21, the grooves including transverse grooves 22 and vertical grooves 23, and glass fiber bundles 5 are filled in both the transverse grooves 22 and the vertical grooves 23 located above the fiber felt layer 4.

[0041] In the above embodiments, filling the grooves formed between the columnar protrusions 21 with glass fiber bundles can further increase the rigidity and stability of the plate. The columnar protrusions 21 provide additional support points, while the glass fiber bundles 5 in the grooves can withstand more shear and tensile forces. This structural design is similar to a truss structure, which can effectively improve the flexural strength of the plate. The distribution of glass fiber bundles in the transverse grooves 22 and vertical grooves 23 can provide multi-directional reinforcement. This multi-directional fiber reinforcement can more effectively disperse stress and improve the flexural strength of the plate in different directions.

[0042] In some embodiments, the glass fiber bundle 5 has a single filament diameter of 10-15 μm and its surface is treated with a silane coupling agent.

[0043] The glass fiber bundles contain monofilaments with diameters ranging from 10-15 μm, classifying them as medium-sized fibers. Fibers of this diameter maintain a certain strength while also exhibiting good flexibility and high specific strength. This fiber size effectively disperses stress, improving the overall flexural strength of the sheet. Silane coupling agent treatment improves the interfacial bonding between the glass fiber and the polypropylene matrix. The silane coupling agent reduces the contact angle of the glass fiber surface, increasing its wettability and making it easier for the matrix to bond with the glass fiber. This chemical bonding significantly improves the mechanical strength and stability of the composite material. The silane coupling agent-treated glass fiber surface generates active functional groups, which can chemically react with the polypropylene matrix to form chemical bonds, enhancing the interfacial adhesion strength.

[0044] In some embodiments, the height of the columnar protrusion 21 is 1 / 3 to 1 / 2 of the thickness of the intermediate polypropylene layer 2.

[0045] In the above embodiments, the columnar protrusions 21 serve as an internal support structure of the sheet, and the ratio of their height to the thickness of the intermediate polypropylene layer directly affects the rigidity of the sheet. When the height of the columnar protrusions 21 accounts for 1 / 3 to 1 / 2 of the thickness of the intermediate layer, the rigidity of the sheet can be effectively improved without significantly increasing its weight, thereby enhancing its flexural strength. The columnar protrusions 21 can act as stress concentration points, dispersing the force applied to the sheet and reducing local stress concentration, thus reducing the risk of the sheet breaking under stress. This design helps to evenly distribute stress and improve the overall flexural strength of the sheet. The composite structure of the columnar protrusions and the fiber felt layer can enhance the bonding force between the layers of the polypropylene sheet. This structure is similar to a truss, which can effectively transfer stress between different layers, improving the overall structural stability and flexural strength.

[0046] In some embodiments, the angle between the transverse grooves 22 located on both sides of the intermediate polypropylene layer 2 is 45°.

[0047] In the above embodiments, the columnar protrusions 21 on both sides of the intermediate polypropylene 2 are arranged in different directions, which can change the arrangement direction of the corresponding glass fiber bundles 5. Therefore, the stress dispersion effect of the board can be achieved in more directions, thereby achieving a better flexural strength.

[0048] In some embodiments, the fiber felt 4 is a glass fiber felt, and the weight of the glass fiber felt is 100-200 g / m². 2 .

[0049] The weight used is 100-200g / m 2 Fiberglass felt can effectively improve the flexural strength of boards without significantly increasing their weight, thereby improving material utilization and economic benefits.

[0050] In some embodiments, both the upper polypropylene layer 1 and the lower polypropylene layer 3 are high-density polypropylene with a density of 0.91-0.93 g / cm³. 3 The melt index is 10-20 g / 10 min, and the intermediate layer polypropylene 2 is low-density polypropylene with a density of 0.89-0.91 g / cm³. 3 Melt index 15-25g / 10min.

[0051] In the above embodiments, high-density polypropylene exhibits higher strength and rigidity, while low-density polypropylene provides better impact resistance and flexibility. This combination of materials with different densities can improve the impact resistance of the sheet while maintaining its overall strength, thereby reducing the initiation and propagation of cracks under bending forces and improving flexural strength. The polypropylene layers of different densities may also exhibit better adhesion because their differences in flowability in the molten state can promote interpenetration and bonding of the interlayer materials, thus improving the overall stability and flexural strength of the sheet.

[0052] To further illustrate the flexural resistance of the polypropylene sheet of this application, the following examples and comparative examples are provided:

[0053] Example 1

[0054] This embodiment provides a method for preparing a flexurally resistant polypropylene board having columnar protrusions 21 and a fiber felt layer 4, but without glass fiber bundles 5.

[0055] Step 1: Apply polypropylene (density 0.90 g / cm³) to the intermediate layer. 3 The two sides of the sample (melt index 20g / 10min, thickness 3mm, columnar protrusion height 1mm, diameter 1mm, spacing 5mm) are uniformly coated with pp-g-MAH solution, the solvent is xylene, concentration is 5wt%;

[0056] Step 2: Apply glass fiber felt (100g / m²) 2It is bonded to the surface of the intermediate layer and compacted by a mold at a temperature of 130℃ and a pressure of 1MPa.

[0057] Step 3: After preheating the intermediate polypropylene with laminated glass fiber felt to 120°C, feed it into a co-extruder and pass it through a T-die to extrude molten high-density polypropylene (density 0.92 g / cm³). 3 A melt index of 15 g / 10 min is evenly applied to both sides of the intermediate polypropylene layer, and then calendered, cooled, and shaped to obtain a flexurally resistant polypropylene sheet.

[0058] Example 2

[0059] This embodiment provides a method for preparing a flexurally resistant polypropylene board having columnar protrusions 21, a fiber felt layer 4, and glass fiber bundles 5.

[0060] Step 1: Apply polypropylene (density 0.90 g / cm³) to the intermediate layer. 3 The two sides of the sample (melt index 20g / 10min, thickness 3mm, columnar protrusion height 1mm, diameter 1mm, spacing 5mm) are uniformly coated with pp-g-MAH solution, the solvent is xylene, concentration is 5wt%;

[0061] Step 2: Apply glass fiber felt (100g / m²) 2 It is bonded to the surface of the intermediate layer and compacted by a mold at a temperature of 130℃ and a pressure of 1MPa.

[0062] Step 3: Embed the glass fiber bundle (with a single filament diameter of 12μm and a surface treated with silane coupling agent) into the groove, and heat it with a hot air gun at a temperature of 220℃ to melt and bond the glass fiber bundle to the inner wall of the groove.

[0063] Step 4: After preheating the intermediate polypropylene with the laminated glass fiber felt to 120°C, feed it into a co-extruder and pass it through a T-die to extrude molten high-density polypropylene (density 0.92 g / cm³). 3 A melt index of 15 g / 10 min is evenly applied to both sides of the intermediate polypropylene layer, and then calendered, cooled, and shaped to obtain a flexurally resistant polypropylene sheet.

[0064] Comparative Example 1

[0065] This comparative example provides a method for preparing a flexurally resistant polypropylene board having columnar protrusions 21 but lacking a fiber felt layer 4 and glass fiber bundles 5.

[0066] Intermediate polypropylene (density 0.90 g / cm³) 3The high-density polypropylene (HDPP) with a melt index of 20 g / 10 min, a thickness of 3 mm, and columnar protrusions of 1 mm height and 1 mm diameter spaced 5 mm apart, is preheated to 120°C and fed into a co-extruder. The molten HDPP (density 0.92 g / cm³) is then extruded through a T-die. 3 A melt index of 15 g / 10 min is evenly applied to both sides of the intermediate polypropylene layer, and then calendered, cooled, and shaped to obtain a flexurally resistant polypropylene sheet.

[0067] Comparative Example 2

[0068] This comparative example provides a method for preparing a flexurally resistant polypropylene board having columnar protrusions 21, a fiber felt layer 4, and glass fiber bundles 5, wherein the structural design of the fiber felt layer is different from that in Example 1.

[0069] Step 1: Embed the glass fiber bundle (single filament diameter of 12μm, surface treated with silane coupling agent) into the groove, and heat it with a hot air gun at a temperature of 220℃ to melt and bond the glass fiber bundle to the inner wall of the groove.

[0070] Step 2: Apply polypropylene (density 0.90 g / cm³) to the intermediate layer. 3 The two sides of the sample (melt index 20g / 10min, thickness 3mm, columnar protrusion height 1mm, diameter 1mm, spacing 5mm) are uniformly coated with pp-g-MAH solution, the solvent is xylene, concentration is 5wt%;

[0071] Step 3: Apply glass fiber felt (100g / m²) 2 It is bonded to the surface of the intermediate layer and compacted by a mold at a temperature of 130℃ and a pressure of 1MPa.

[0072] Step 4: After preheating the intermediate polypropylene with the laminated glass fiber felt to 120°C, feed it into a co-extruder and pass it through a T-die to extrude molten high-density polypropylene (density 0.92 g / cm³). 3 A melt index of 15 g / 10 min is evenly applied to both sides of the intermediate polypropylene layer, and then calendered, cooled, and shaped to obtain a flexurally resistant polypropylene sheet.

[0073] Comparative Example 3

[0074] This comparative example provides a method for preparing a flexurally resistant polypropylene board having a fiber felt layer 4 but lacking columnar protrusions 21 and glass fiber bundles 5.

[0075] Step 1: Apply polypropylene (density 0.90 g / cm³) to the intermediate layer. 3 The two sides of the sample (melt index 20g / 10min, thickness 3mm) are uniformly coated with pp-g-MAH solution, with xylene as the solvent and a concentration of 5wt%.

[0076] Step 2: Apply glass fiber felt (100g / m²)2 It is bonded to the surface of the intermediate layer and compacted by a mold at a temperature of 130℃ and a pressure of 1MPa.

[0077] Step 3: After preheating the intermediate polypropylene with laminated glass fiber felt to 120°C, feed it into a co-extruder and pass it through a T-die to extrude molten high-density polypropylene (density 0.92 g / cm³). 3 A melt index of 15 g / 10 min is evenly applied to both sides of the intermediate polypropylene layer, and then calendered, cooled, and shaped to obtain a flexurally resistant polypropylene sheet.

[0078] The flexural strength polypropylene sheets prepared in the different embodiments and comparative examples were subjected to three-point bending tests, interlaminar peel strength tests, impact strength tests, and fracture morphology analysis, and the results are shown in the table below:

[0079] plan Flexural strength (MPa) Flexural modulus (GPa) Maximum deflection (mm) Performance ranking Example 2 85-95 3.2-3.5 8-10 1 Example 1 70-80 2.8-3.0 6-8 2 Comparative Example 3 60-65 2.5-2.7 5-7 3 Comparative Example 2 60-70 2.5-2.8 5-7 3 Comparative Example 1 50-60 2.0-2.3 4-6 4

[0080] The results above show that Example 2, employing a triple reinforcement mechanism (mechanical interlocking, fiber reinforcement, and stress dispersion) with columnar protrusions, fiber felt, and glass fiber mesh, exhibits the highest flexural strength. Example 1, lacking a glass fiber mesh, relies on the interfacial reinforcement of the fiber felt for its flexural strength, making it weaker than Example 2. Comparative Example 2, with its different fiber felt bonding sequence (first embedding fiber bundles and then bonding the felt), suffers from reduced interfacial bonding strength. Comparative Example 1, lacking fiber reinforcement and relying solely on the columnar protrusion structure, exhibits the worst flexural performance. Comparative Example 3, containing only a fiber felt layer without columnar protrusions or glass fiber bundles, has flexural strength lower than Examples 1-2 but higher than Comparative Example 1 (without fiber reinforcement).

[0081] plan Peel strength (N / mm) Performance ranking Example 2 18-20 1 Example 1 15-17 2 Comparative Example 3 12-14 3 Comparative Example 1 8-10 3 Comparative Example 2 5-7 4

[0082] The results above show that Example 2, which uses PP-g-MAH solution + fiber felt + fiber mesh for fusion bonding, has the strongest interfacial bonding; Comparative Example 2, with a different fiber felt bonding sequence, results in insufficient contact between the fiber bundle and the matrix, leading to the weakest interfacial bonding; Comparative Example 3, where the fiber felt layer has enhanced interfacial bonding through PP-g-MAH solution, has a higher peel strength than Comparative Example 1 (without fiber felt).

[0083] plan <![CDATA[Izod impact strength (kJ / m 2 )]]> Performance ranking Example 2 25-28 1 Example 1 18-20 2 Comparative Example 3 15-17 3 Comparative Example 1 10-12 3 Comparative Example 2 8-10 4

[0084] The results above show that in Example 2, the glass fiber mesh significantly inhibited crack propagation, and the low-density intermediate layer absorbed the impact energy; in Comparative Example 2, the interface defects caused rapid crack propagation, resulting in the worst impact performance; in Comparative Example 3, the fiber felt layer provided a certain degree of toughness, and the impact strength was higher than that of Comparative Example 1 (without fiber reinforcement).

[0085] Fracture morphology analysis:

[0086] Example 1: Cracks travel around columnar protrusions and fiber meshes, resulting in a longer propagation path and higher fracture toughness;

[0087] Example 2: The cracks run along the fiber mesh, and the fiber-matrix interface is well bonded (SEM shows that the fiber is wrapped in polypropylene);

[0088] Comparative Example 1: The crack passes directly through the columnar protrusion structure without obvious fiber obstruction;

[0089] Comparative Example 2: Cracks propagate along the interlayer interface, and the fiber felt separates from the matrix;

[0090] Comparative Example 3: The cracks propagate along the fiber felt layer. The fiber-matrix interface is well bonded, but there is no columnar protrusion or fiber mesh to hinder the crack propagation.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A flexurally resistant polypropylene sheet, characterized in that, The material includes an upper polypropylene layer (1), an intermediate polypropylene layer (2), and a lower polypropylene layer (3). The two sides of the intermediate polypropylene layer (2) are provided with columnar protrusions (21) arranged in a rectangular array. The two sides of the intermediate polypropylene layer (2) are coated with fiber felt layers (4). The surface of the fiber felt layer (4) on the upper side of the intermediate polypropylene layer (2) is coated with the upper polypropylene layer (1), and the surface of the fiber felt layer (4) on the lower side of the intermediate polypropylene layer (2) is coated with the lower polypropylene layer (3). The grooves are formed between adjacent rows of columnar protrusions (21). The grooves include horizontal grooves (22) and vertical grooves (23). The horizontal grooves (22) and vertical grooves (23) above the fiber felt layer (4) are filled with glass fiber bundles (5). The height of the columnar protrusions (21) is 1 / 3 to 1 / 2 of the thickness of the intermediate polypropylene layer (2).

2. The flexurally resistant polypropylene sheet as described in claim 1, characterized in that, The glass fiber bundle (5) has a single filament diameter of 10-15 μm and its surface is treated with a silane coupling agent.

3. The flexurally resistant polypropylene sheet as described in claim 1, characterized in that, The fiber felt layer (4) is made of glass fiber felt, and the weight of the glass fiber felt is 100-200g / m. 2 .

4. The flexurally resistant polypropylene sheet as described in claim 1, characterized in that, Both the upper polypropylene layer (1) and the lower polypropylene layer (3) are high-density polypropylene with a density of 0.91-0.93 g / cm³. 3 The melt index is 10-20 g / 10 min, and the intermediate layer polypropylene (2) is low-density polypropylene with a density of 0.89-0.91 g / cm³. 3 Melt index 15-25g / 10min.

5. The method for preparing the flexurally resistant polypropylene sheet according to any one of claims 1-4, characterized in that, The steps include: Step 1: Uniformly coat both sides of the intermediate polypropylene layer with pp-g-MAH solution, using xylene as the solvent and a concentration of 5 wt%. Step 2: Lay the fiber felt onto the surface of the intermediate layer and compact it with a mold. The mold temperature is 120-140℃ and the pressure is 0.5-1MPa. Step 3: Embed the glass fiber bundle into the groove and heat it with a hot air gun at a temperature of 200-220℃ to melt and bond the glass fiber bundle to the inner wall of the groove. Step 4: After preheating the intermediate polypropylene with the fiber felt to 100-120℃, feed it into a co-extruder. Through a T-die, the molten high-density polypropylene is evenly covered on both sides of the intermediate polypropylene layer. Calender, cool and shape to obtain a flexurally resistant polypropylene sheet.

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