Plastic hollow plate and manufacturing method

Abstract

The invention discloses a plastic hollow plate and a manufacturing method thereof, the plastic hollow plate comprises the following components by weight: 30%-60% of a polypropylene matrix and 40%-70% of phosphogypsum powder, and polypropylene provides thermoplastic formability and toughness. The preparation method specifically comprises the following steps: 1) pretreating ardealite; 2) melt blending granulation; (3) forming a hollow plate; and 4) post-processing. The ardealite hollow plate has the advantages that the ardealite filling amount is increased, meanwhile, the bending strength and impact strength of a traditional hollow plate are improved, and the performance is improved by 20% or above compared with that of a traditional hollow plate with the same filling amount; the moisture content of the pretreated phosphogypsum is less than 6%, so that bubbles in the processing process are avoided, and the interface bonding strength is improved; the comprehensive utilization rate of industrial byproduct phosphogypsum is improved, and the production cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer composite materials, and in particular to a polypropylene (PP)-based plastic hollow board using phosphogypsum (PG) as a filler reinforcement and a manufacturing method thereof, and is particularly suitable for the field of packaging materials. Background Art

[0002] Plastic hollow boards are widely used in logistics packaging, building partitions and other fields due to their light weight, strong impact resistance and recyclability. Currently, most commercially available hollow boards use inorganic fillers such as calcium carbonate and talc to fill the polypropylene matrix, but they have the following problems:

[0003] The filling amount of traditional fillers (such as calcium carbonate) in polypropylene usually does not exceed 50%. Excessive filling will lead to a significant increase in the brittleness of the material and a decrease in strength. Existing plastic hollow boards are made using industrial by-product phosphogypsum as a filler. However, phosphogypsum has problems such as high moisture content, large impurity content, coarse particles, and difficulty in removing free water. The resulting plastic hollow boards have unsatisfactory bending and impact strength, and are therefore not suitable for direct use in polymer composite materials.

[0004] Therefore, there is an urgent need to develop a plastic hollow board manufacturing technology that has high filling content, high strength and resource-recyclable phosphogypsum. Summary of the Invention

[0005] The object of the present invention is to provide a plastic hollow board and a manufacturing method thereof to solve the problems raised in the above background technology.

[0006] To solve the above technical problems, the present invention provides a technical solution: a plastic hollow board, which includes the following components in parts by weight: 30-60 parts of polypropylene matrix and 40-70 parts of phosphogypsum powder, wherein the polypropylene provides thermoplastic formability and toughness.

[0007] As a preferred embodiment, the phosphogypsum powder is pretreated phosphogypsum powder, the moisture content of the pretreated phosphogypsum powder is less than 6%, and the particle size is 800-1000 mesh. The pretreated phosphogypsum powder is dried and subjected to ultrafine grinding process to achieve high dispersibility and low hygroscopicity, and forms a "rigid particle-flexible matrix" composite structure with polypropylene.

[0008] As a preferred solution, the amount of the pretreated phosphogypsum powder is 50-70 parts, and the amount of polypropylene is 30-50 parts.

[0009] As a preferred solution, the amount of the pretreated phosphogypsum powder is 60 parts, and the amount of polypropylene is 40 parts.

[0010] A method for manufacturing a plastic hollow board specifically comprises the following steps:

[0011] 1) Pretreatment of phosphogypsum: Phosphogypsum with a total moisture content of 18% is pre-dried in a hammer airflow dryer to remove 13% of free water, reducing the moisture content to below 6%. The dried phosphogypsum is then ground to 800-1000 mesh using a vertical mill to obtain dry ultrafine phosphogypsum powder.

[0012] 2) melt blending and granulation: the phosphogypsum powder obtained in step 1) and polypropylene are pre-mixed in a high-speed mixer at a mass ratio of 40%-70%:60%-30%, and then melt blended in a twin-screw granulator at 180-220° C., extruded and granulated to produce PP / PG composite particles;

[0013] 3) Hollow board molding: PP / PG composite particles are extruded through a plastic hollow board production line. After shaping, cooling, and pulling, a plastic hollow board with a length of 1.8m or 2.3m is produced.

[0014] 4) Post-processing: According to the needs, the hollow board is cut into molds, hot-melt welded, and surface printed to make packaging boxes of different specifications.

[0015] As a preferred solution, in step 2), the melt blending temperature is 190-210° C., the screw speed is 200-400 rpm, and the mixing time is 5-10 minutes.

[0016] As a preferred solution, the extrusion molding temperature in step 3) is 200-230° C., and the die pressure is 8-15 MPa.

[0017] The advantages of the present invention are: the filling amount of phosphogypsum is increased, and the bending strength and impact strength of the traditional hollow board are improved at the same time, and the performance is improved by more than 20% compared with the traditional hollow board with the same filling amount; the moisture content of the phosphogypsum after pretreatment is less than 6%, which avoids the generation of bubbles during the processing and improves the interface bonding strength; the comprehensive utilization rate of industrial by-product phosphogypsum is improved, and the production cost is reduced. DETAILED DESCRIPTION

[0018] The present invention is described below with reference to specific embodiments, which are not intended to limit the present invention.

[0019] Example 1

[0020] Formula: PP 40 parts, pretreated phosphogypsum 60 parts

[0021] Process flow:

[0022] 1. Pretreatment: Put the phosphogypsum with a moisture content of 18% into the HJG-15 hammer airflow dryer, set the temperature to 140℃, the wind speed to 8m / s, and dry it to a moisture content of 5.8%;

[0023] 2. Grinding: Use LM1900K vertical mill, control the grinding disc speed at 60 rpm, and grind to a particle size of D50 = 45 μm (about 325 mesh);

[0024] 3. Melt blending: pre-mix in SHR-500A high-speed mixer for 5 minutes, transfer to SHJ-72 twin-screw granulator, set zone 1 at 190°C, zone 2 at 210°C, zone 3 at 205°C, screw speed at 300 rpm, and mixing time for 8 minutes;

[0025] 4. Extrusion molding: SJSZ-80 hollow board production line, die head temperature 220℃, pressure 12MPa, pulling speed 1.5m / min, to produce 1.8m×1.2m hollow board.

[0026] Example 2

[0027] Formula: PP 50 parts, pretreated phosphogypsum 50 parts

[0028] Process adjustment: the mixing temperature of the twin-screw granulator is 200° C., the screw speed is 250 rpm, the die pressure is 10 MPa, and the rest is the same as in Example 1.

[0029] Example 3

[0030] Formula: PP 30 parts, pretreated phosphogypsum 70 parts

[0031] Process adjustment: grinding particle size D50 = 80 μm (about 200 mesh), twin-screw mixing temperature 215°C, die head pressure 15 MPa, and pulling speed 1.2 m / min.

[0032] Comparative experiment

[0033] Control group 1 (commercially available product)

[0034] A certain brand of calcium carbonate filled PP hollow board (filling amount 50%), bending strength 22MPa, impact strength 4.5kJ / m 2 .

[0035] Control group 2 (comparative example)

[0036] Using untreated phosphogypsum (water content 15%, particle size 50 mesh) to fill 60%, PP 40%, bubbles appear on the surface of the board under the same process, bending strength 18MPa, impact strength 3.8kJ / m 2 .

[0037] Test results

[0038] Group Filling amount Flexural strength (MPa) <![CDATA[Impact strength (kJ / m 2 )]]> Example 1 60％ 32.5 6.2 Control group 1 50％ 22.0 4.5 Control group 2 60％ 18.0 3.8

[0039] How it works

[0040] 1. Pretreatment enhances interface bonding: Ultrafine phosphogypsum powder forms a strong bonding interface with polypropylene molecular chains through surface hydroxyl groups and van der Waals forces and mechanical interlocking.

[0041] Pretreatment significantly improves the interfacial bonding between phosphogypsum powder and the polypropylene matrix by regulating the surface chemical properties and micromorphology of the phosphogypsum powder. The specific mechanism is as follows:

[0042] Surface hydroxyl activation:

[0043] After drying, free water is removed from phosphogypsum (CaSO4·2H2O) (water content <6%), exposing hydroxyl (-OH) groups on its surface. The polarity of hydroxyl groups creates a dipole-induced dipole interaction (Debye force) with polypropylene molecular chains during melt blending, enhancing physical adsorption.

[0044] Formula Support: Van der Waals Strength

[0045]

[0046] (A is the Hamaker constant, C is the surface polarity coefficient, and d is the spacing). After pretreatment, the surface polarity coefficient C increases by 20%-30%.

[0047] Mechanical interlocking effect:

[0048] Grinding phosphogypsum particles in a vertical mill (such as the LM1900K) forms an irregular flaky structure with nanoscale cracks at the edges. Molten polypropylene (viscosity 0.1-0.3 Pa·s) infiltrates these cracks under shear force, forming a "hook-like" interlocking structure upon cooling. This increases the interfacial peel strength to 8-10 MPa (compared to 3-4 MPa in the untreated group).

[0049] Thermodynamic compatibility optimization:

[0050] After pretreatment, the surface energy of phosphogypsum is 45mJ / m 2 Reduced to 38mJ / m 2 (Contact angle test), and polypropylene (30mJ / m 2 ) difference is reduced, wettability is improved (contact angle θ is reduced from 85° to 65°), and interface defects are reduced.

[0051] Experimental verification

[0052] DSC test: After pretreatment, the crystallinity of the composite material increased to 65%. Phosphogypsum served as a heterogeneous nucleation point, promoting the densification of polypropylene spherulites (spherulite size <10μm).

[0053] 2. Gradient temperature control: During melt blending, the low temperature zone (190°C) prevents thermal decomposition of phosphogypsum, while the high temperature zone (210°C) promotes the diffusion of polypropylene molecular chains;

[0054] Scientific Mechanism

[0055] Melt blending uses zoned temperature control (190°C low temperature zone → 210°C high temperature zone) to achieve the dual goals of thermal stability protection and molecular chain diffusion enhancement:

[0056] Low temperature zone (190℃):

[0057] The thermal decomposition temperature of phosphogypsum is greater than 220°C, and 190°C can avoid its dehydration and decomposition (CaSO4·2H2O→CaSO4+2H2O↑) and prevent bubble formation (bubble rate <0.5%).

[0058] At the same time, polypropylene is in the initial melting stage at this temperature (melt index MFI = 15-20 g / 10 min), with a high viscosity (about 500 Pa·s), and initially wraps the phosphogypsum particles.

[0059] High temperature zone (210℃):

[0060] The mobility of polypropylene molecular chains is enhanced (viscosity is reduced to 100-200 Pa·s), and the diffusion coefficient is increased to 10- 11 m 2 / s (3 times higher than that at 190℃), promoting the penetration of molecular chains into the cracks on the surface of phosphogypsum, forming a more uniform interface bonding layer (thickness of about 0.5-1μm).

[0061] Process parameter optimization

[0062] Temperature gradient design: Zone 1 190°C (plasticization), Zone 2 210°C (diffusion), Zone 3 205°C (equilibrium);

[0063] Screw shear field: at 300rpm, the shear rate reaches 500-800s -1 , ensuring uniform dispersion (particle size distribution D90<100μm).

[0064] Effect comparison

[0065] Single high temperature (220℃) process: phosphogypsum is partially decomposed and the impact strength of the board decreases by 15%;

[0066] Single low-temperature (180°C) process: Polypropylene diffusion is insufficient and the interface bonding strength is reduced by 30%.

[0067] 3. Pressure-induced orientation: The high pressure (8-15MPa) of the die head orients the phosphogypsum particles along the extrusion direction, thereby improving the longitudinal strength of the board.

[0068] Scientific Mechanism

[0069] The high pressure (8-15MPa) at the die head causes the phosphogypsum particles to be oriented along the extrusion direction through shear flow field and stretching flow, forming a reinforcing fiber effect:

[0070] Shear-induced orientation:

[0071] In the die flow channel, the melt experiences a high shear rate (γ·=10 3 -10 4 s -1 ), the flaky phosphogypsum particles rotate under the action of shear force, and the direction of the long axis is consistent with the flow direction (orientation degree > 70%).

[0072] Pressure-velocity coupling effect:

[0073] Under high pressure (12 MPa), the velocity gradient increases when the melt passes through the die, and the particles are further arranged under the influence of extensional flow (orientation factor f = 0.6-0.8, calculated by: θ is the angle between the long axis of the particle and the flow direction).

[0074] Mechanical enhancement effect

[0075] Longitudinal bending strength: The oriented structure transfers stress along the long axis of the particle, with a longitudinal strength of 35MPa (only 25MPa in the transverse direction);

[0076] Anisotropy control: By adjusting the die pressure (8MPa→15MPa), the orientation degree (60%→85%) can be controlled to meet different load-bearing requirements.

[0077] Process parameter correlation

[0078] Pressure-pulling speed matching: When the pressure is 12MPa, the pulling speed is 1.5m / min to ensure that the melt is fully oriented and has no turbulence;

[0079] Die temperature: 220℃, the viscosity of polypropylene is moderate, and the particle rebound is avoided (elastic modulus decreases by 20%).

[0080] Three principles work together:

[0081] Pretreatment solves interface compatibility issues; gradient temperature control balances thermal stability and dispersibility; high-pressure orientation achieves structural strengthening.

[0082] Ultimately, the phosphogypsum filling volume exceeded 60%, the strength was increased by more than 20%, and the production cost was reduced by 30% (compared to the traditional calcium carbonate filling process).

[0083] Industrial Applications

[0084] The hollow board produced according to Example 1 can be made into a logistics turnover box with a load-bearing capacity of 50 kg after die cutting (such as QC-1200 cutting machine), hot melt welding (temperature 180°C), and UV printing. The overall cost is 40% lower than that of pure PP boxes, and the waterproofness is 90% higher than that of cardboard boxes.

[0085] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A plastic hollow board, characterized in that: The invention comprises the following components in parts by weight: 30% to 60% of a polypropylene matrix and 40% to 70% of phosphogypsum powder.

2. A plastic hollow board according to claim 1, characterized in that: The phosphogypsum powder is pretreated phosphogypsum powder, the moisture content of the pretreated phosphogypsum powder is lower than 6%, the particle size is 800-1000 mesh, and the phosphogypsum powder is industrial by-product phosphogypsum that has been processed by drying and grinding processes.

3. The plastic hollow board according to claim 1, characterized in that: The mixing amount of the pretreated phosphogypsum powder is 50% to 70%, and the mixing amount of the polypropylene is 30% to 50%.

4. The plastic hollow board according to claim 1, characterized in that: The mixing amount of the pretreated phosphogypsum powder is 60%, and the mixing amount of the polypropylene is 40%.

5. A method for manufacturing a plastic hollow board, characterized in that: The specific steps include: 1) Pretreatment of phosphogypsum: Phosphogypsum with a total moisture content of 18% is pre-dried in a hammer airflow dryer to remove 13% of free water, reducing the moisture content to below 6%. The dried phosphogypsum is then ground to 800-1000 mesh using a vertical mill to obtain dry ultrafine phosphogypsum powder. 2) melt blending and granulation: the phosphogypsum powder obtained in step 1) and polypropylene are pre-mixed in a high-speed mixer at a mass ratio of 40%-70%:60%-30%, and then melt blended in a twin-screw granulator at 180-220° C., extruded and granulated to produce PP / PG composite particles; 3) Hollow board molding: PP / PG composite particles are extruded through a plastic hollow board production line. After shaping, cooling, and pulling, a plastic hollow board with a length of 1.8m or 2.3m is produced. 4) Post-processing: According to the needs, the hollow board is cut into molds, hot-melt welded, and surface printed to make packaging boxes of different specifications.

6. The method for manufacturing a plastic hollow board according to claim 5, characterized in that: In the step 2), the melt blending temperature is 190-210° C., the screw speed is 200-400 rpm, and the mixing time is 5-10 minutes.

7. The method for manufacturing a plastic hollow board according to claim 5, characterized in that: The extrusion molding temperature in step 3) is 200-230° C., and the die pressure is 8-15 MPa.

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