A method for preparing a foamed wood plastic composite

Abstract

The application discloses a preparation method of foamed wood plastic composite material, and relates to a preparation method of foamed composite material.The application aims at solving the problems of large density and poor sound absorption and heat insulation performance of the existing traditional wood plastic composite material.The method comprises the following steps: firstly, fiber pretreatment;secondly, high-speed mixing;thirdly, melting, extrusion and pelletizing;fourthly, water content control;and fifthly, extrusion foaming.The application is used for the preparation of the foamed wood plastic composite material.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for preparing a foamed composite material. BACKGROUND

[0002] Wood plastic composite material is a new type of composite material which uses wood or other lignocellulosic materials as filling or reinforcing material and thermoplastic polymer as matrix, and is made by extrusion, molding or injection forming process. Compared with traditional wood materials, wood plastic composite material has the advantages of water resistance, corrosion resistance, aging resistance, insect resistance, good dimensional stability, etc., and can be recycled and reused, which is conducive to alleviating the shortage of wood resources and solving the problem of plastic pollution. At present, it has been applied to automotive interior panels, building decoration, freight pallets, outdoor tables and chairs, packaging materials, sleepers, furniture and military industry, and is a green environmental protection material with great development prospects.

[0003] However, the currently commercially used wood plastic composite material generally has the defects of large density (≥1.0 g / cm³) and poor heat insulation and sound absorption performance (thermal conductivity coefficient ≥0.3 W / m·K), which greatly limits the application of wood plastic composite material in the fields of lightweight and heat insulation and sound absorption. SUMMARY

[0004] The present application aims to solve the problems of large density and poor heat insulation and sound absorption performance of existing traditional wood plastic composite material, and further provides a method for preparing a foamed wood plastic composite material.

[0005] A method for preparing a foamed wood plastic composite material, which is carried out according to the following steps:

[0006] I. Fiber pretreatment:

[0007] The wood fiber powder is pretreated to obtain pretreated wood fiber powder;

[0008] II. High-speed mixing:

[0009] 10-80 parts by mass of pretreated wood fiber powder, 10-80 parts by mass of thermoplastic, 3-5 parts by mass of compatibilizer and 1-2 parts by mass of lubricant are weighed, and then mixed uniformly in a high-speed mixer to obtain mixed raw materials;

[0010] III. Melting, extrusion and granulation:

[0011] The mixed raw materials are melted and extruded into strands by using a twin-screw extruder, and finally cooled and granulated to obtain wood plastic composite granules;

[0012] IV. Moisture content control:

[0013] The wood-plastic mixed granules are subjected to moisture content regulation until the equilibrium moisture content is 1% to 10%, to obtain the wood-plastic mixed granules after moisture content regulation;

[0014] V. Extrusion foaming:

[0015] The wood-plastic mixed granules after moisture content regulation are extruded by using a screw extruder, and then are shaped by a two-stage conical die, and finally are subjected to cooling, cutting and balancing in sequence, to obtain the foamed wood-plastic composite material.

[0016] The wood-plastic composite material has the following advantages:

[0017] (1) The wood-plastic composite material is prepared by using the moisture absorption of wood fiber in the wood-plastic component as the driving force, and using the water absorbed by the fiber as the in-situ foaming agent. In the high-temperature and high-pressure environment of the screw, the release of water vapor pressure at the die of the screw extruder leads to the formation of wood-plastic foam pores. The two-stage conical die limits foaming, which is conducive to the stable and continuous preparation of the foamed material and avoids material spraying or molding difficulty caused by sudden pressure change of the cylinder. Compared with the traditional chemical foaming, the method avoids the use of various chemical foaming agents and does not produce harmful gases such as carbon monoxide and ammonia, so it is a green and efficient wood-plastic foaming technology that meets the green building material standard.

[0018] (2) By introducing water vapor as a green foaming agent, the foamed wood-plastic composite material prepared by the method has a density of 0.31 g / cm 3 ~0.78 g / cm 3 , meets the mechanical properties of the wood-plastic composite material, and has uniform material and high surface quality, and can be continuously and stably extruded.

[0019] (3) By introducing water vapor as a foaming agent through balancing treatment, the foaming agent is uniformly mixed with the material, the foaming process is more controllable, and the problems of poor pore uniformity and low foaming ratio caused by uneven mixing of the foaming agent in the traditional chemical foaming are avoided.

[0020] (4) The wood-plastic foamed material prepared by the method has a dense surface layer providing mechanical support, and an internal wood fiber-mediated porous foam structure, which realizes good performance of weight reduction, heat insulation and sound absorption. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a structure diagram of the two-stage conical die of the application, ① is a first die heating zone, ② is a first expansion zone, ③ is a second die heating zone, ④ is a second expansion zone, and ⑤ is a cooling and shaping zone.

[0022] Figure 2 is a scanning electron micrograph of the foamed wood-plastic composite material prepared in Example 1.

[0023] Figure 3A physical photo of the foamed wood-plastic composite material prepared in Example 1;

[0024] Figure 4 A physical photo of the foamed wood-plastic composite material prepared in Example 1 and the wood-plastic composite material prepared in Comparative Example 1;

[0025] Figure 5 Sound absorption test results of the foamed wood-plastic composite material prepared in Example 1 and the wood-plastic composite material prepared in Comparative Example 1. DETAILED DESCRIPTION

[0026] Detailed Implementation I: A preparation method of the foamed wood-plastic composite material in this implementation is performed according to the following steps:

[0027] I. Fiber pretreatment:

[0028] The wood fiber powder is pretreated to obtain pretreated wood fiber powder;

[0029] II. High-speed mixing:

[0030] 10-80 parts by mass of the pretreated wood fiber powder, 10-80 parts by mass of the thermoplastic, 3-5 parts by mass of the compatibilizer, and 1-2 parts by mass of the lubricant are weighed and then mixed uniformly in a high-speed mixer to obtain mixed raw materials;

[0031] III. Melting, extrusion, and pelletizing:

[0032] The mixed raw materials are melted and extruded into strands by using a twin-screw extruder, and finally cooled and pelletized to obtain wood-plastic mixed pellets;

[0033] IV. Moisture content control:

[0034] The wood-plastic mixed pellets are subjected to moisture content control until the equilibrium moisture content is 1-10% to obtain wood-plastic mixed pellets with controlled moisture content;

[0035] V. Extrusion foaming:

[0036] The wood-plastic mixed pellets with controlled moisture content are extruded by using a screw extruder, then shaped by a two-stage conical die, and finally cooled, cut, and balanced in sequence to obtain the foamed wood-plastic composite material.

[0037] Figure 1It is a structure schematic view of the two-stage conical die of the application, ① is a die heating area, ② is an expansion area, ③ is a die heating area, ④ is an expansion area, and ⑤ is a cooling and shaping area. The design adopts a two-stage expansion method, which has three main purposes: 1. To enhance the stability of the continuous extrusion of wood-plastic composite foam, the two-stage restriction reduces the material spraying and cutting caused by gas expansion, and enhances the stability; 2. Through multi-stage die temperature control, the nucleation and growth of wood-plastic composite foam are realized, and the foam shrinkage and collapse caused by rapid cooling are avoided; 3. Through the die, the expansion ratio of wood-plastic foam can be adjusted to obtain foamed wood-plastic composite materials with the required strength and cell diameter.

[0038] The beneficial effects of the embodiment are:

[0039] (1) The embodiment uses the hygroscopicity of wood fibers in wood-plastic components as the driving force, and uses the water absorbed by the fibers as the in-situ foaming agent. In the high-temperature and high-pressure environment of the screw, the release of water vapor pressure at the die of the screw extruder causes the formation of wood-plastic cells. And through the two-stage conical die, the foaming is limited, which is conducive to the stable and continuous preparation of the foaming material, and avoids the material spraying or molding difficulty caused by sudden change of barrel pressure. Compared with traditional chemical foaming, this method avoids the use of various chemical foaming agents and does not produce harmful gases such as carbon monoxide and ammonia, which is a green and efficient wood-plastic foaming technology that meets the green building material standard.

[0040] (2) By introducing water vapor as a green foaming agent, the foamed wood-plastic composite material prepared by the embodiment has a density of 0.31 g / cm 3 ~0.78g / cm 3 , and the material is uniform in quality and has a high surface quality, which can be continuously and stably extruded.

[0041] (3) By balancing the introduction of water vapor as a foaming agent, the foaming agent is uniformly mixed with the material, and the foaming process is more controllable, avoiding the problems of poor cell uniformity and low foaming ratio caused by uneven mixing of traditional chemical foaming agents.

[0042] (4) The wood-plastic foaming material prepared by the embodiment provides mechanical support for the surface dense layer, and forms a porous foam structure mediated by wood fibers inside, achieving good performance of weight reduction, heat insulation and sound absorption synergy.

[0043] Embodiment two: the difference between this embodiment and embodiment one is that the pretreatment in step one is one or a combination of several of the following: alkali treatment, supercritical fluid treatment, steam explosion, microwave treatment, plasma modification and silane grafting modification; the alkali treatment is specifically carried out by the following steps: immersing the wood fiber powder in a NaOH solution with a mass percentage of 5% to 10%, soaking for 2 to 4 hours, then washing to neutral and drying. The rest is the same as embodiment one.

[0044] Embodiment three: the difference between this embodiment and one of embodiment one or two is that the wood fiber powder in step one is one or a combination of several of the following: wood powder, rice husk powder, bamboo powder, straw powder, fruit shell powder, bagasse and hemp fiber; the mesh number of the wood fiber powder is 10 to 300. The rest is the same as embodiment one or two.

[0045] Embodiment four: the difference between this embodiment and one of embodiment one to three is that the thermoplastic plastic in step two is one or a combination of several of the following: polyethylene, polypropylene, polystyrene, polyvinyl chloride, polylactic acid and polybutylene adipate terephthalate. The rest is the same as embodiment one to three.

[0046] Embodiment five: the difference between this embodiment and one of embodiment one to four is that the compatibilizer in step two is a maleic anhydride grafted polymer. The rest is the same as embodiment one to four.

[0047] Embodiment six: the difference between this embodiment and one of embodiment one to five is that the lubricant in step two is one or a combination of several of the following: polyethylene wax, stearic acid, zinc stearate and calcium stearate. The rest is the same as embodiment one to five.

[0048] Embodiment seven: the difference between this embodiment and one of embodiment one to six is that the mixing in step two is specifically carried out by the following steps: mixing uniformly in a high-speed mixer under the condition of a rotation speed of 100 to 300 r / min for 3 to 5 min, then mixing at a low speed for 5 to 7 min under the condition of a rotation speed of 500 to 1000 r / min to obtain the mixed raw materials. The rest is the same as embodiment one to six.

[0049] Eighth Embodiment: The difference between this embodiment and any one of the first to seventh embodiments is that in step three, the temperature of each section of the twin-screw extruder is set from the feeding section to the head section as follows: the temperature of the first section is 130-140°C, the temperature of the second section is 140-150°C, the temperature of the third section is 150-160°C, the temperature of the fourth section is 160-170°C, the temperature of the fifth section is 160-170°C, the temperature of the sixth section is 160-170°C, and the temperature of the seventh section is 150-160°C, and then the mixed raw materials are melted and extruded into strands under the condition that the screw speed is 30-70 r / min, and finally the strands are cooled and cut into particles with a particle size of 2-8 mm. The other steps are the same as those in the first to seventh embodiments.

[0050] Ninth Embodiment: The difference between this embodiment and any one of the first to eighth embodiments is that in step four, the moisture content of the wood-plastic mixed particles is controlled under the condition that the temperature is 30-60°C and the humidity is 30-100%, until the equilibrium moisture content is 1-10%. The other steps are the same as those in the first to eighth embodiments.

[0051] Tenth Embodiment: The difference between this embodiment and any one of the first to ninth embodiments is that in step five, the temperature of each section of the screw extruder is set from the feeding section to the head section as follows: the temperature of the first section is 140-150°C, the temperature of the second section is 150-160°C, the temperature of the third section is 150-160°C, and the temperature of the fourth section is 160-170°C, and then the wood-plastic mixed particles with controlled moisture content are extruded under the condition that the screw speed is 30-70 r / min; the inner chamber of the two-section conical die in step five is in the shape of a tower, and the inner chamber is divided into a die heating zone one, an expansion zone one, a die heating zone two, an expansion zone two, and a cooling and shaping zone from the inlet to the outlet; the expansion zone one and the expansion zone two are trapezoidal chambers, and the die heating zone one, the die heating zone two, and the cooling and shaping zone are rectangular chambers; the upper and lower spacing of the die heating zone one is K1, the width is M1, and the length is L1; the upper and lower spacing of the die heating zone two is K2, the width is M2, and the length is L2; the upper and lower spacing of the cooling and shaping zone is K3, the width is M3, and the length is L3; the length of the expansion zone one is L4; the length of the expansion zone two is L5; K1=2-4 mm, 1:1K1:K2<1:4, and 1:2K1:K3<1:6; L1=30-80 mm, L2=30-60 mm, L3=30-60 mm, L4=30-60 mm, and L5=30-60 mm; M1:M2=1:(1-3), and M2:M3=1:(1-3); the temperature of the die heating zone one is 150-190°C, and the temperature of the die heating zone two is 80-120°C; the cooling in step five is water tank cooling or air cooling. The other steps are the same as those in the first to ninth embodiments.

[0052] The beneficial effects of the present application are verified by the following examples:

[0053] Example 1:

[0054] A preparation method of foamed wood-plastic composite material is carried out by the following steps:

[0055] I. Fiber pretreatment:

[0056] The wood fiber powder is immersed in a 5% NaOH solution by mass fraction, soaked for 4h, then washed to neutral and dried to obtain pretreated wood fiber powder;

[0057] The wood fiber powder is poplar powder; the wood fiber powder has a mesh size of 60 mesh;

[0058] II. High-speed mixing:

[0059] 60 parts of pretreated wood fiber powder, 33 parts of thermoplastic, 5 parts of compatibilizer and 2 parts of lubricant are weighed by mass fraction, then placed in a high-speed mixer, mixed at a speed of 100r / min for 5min, then mixed at a speed of 800r / min for 5min to obtain mixed raw materials;

[0060] The thermoplastic is high-density polyethylene;

[0061] The compatibilizer is maleic anhydride grafted polyethylene;

[0062] The lubricant is a mixture of polyethylene wax and stearic acid in a mass ratio of 1:1;

[0063] III. Melting, extrusion and granulation:

[0064] The temperature of each section of the double-screw extruder is set from the feeding section to the die head in the order of zone 1 temperature 140℃, zone 2 temperature 150℃, zone 3 temperature 160℃, zone 4 temperature 170℃, zone 5 temperature 170℃, zone 6 temperature 170℃ and zone 7 temperature 150℃, then the mixed raw materials are melted and extruded into strands under the condition of screw speed 50rpm, and finally cooled and granulated to a particle size of 5mm to obtain wood-plastic mixed granules;

[0065] IV. Moisture content control:

[0066] The wood-plastic mixed granules are subjected to moisture content control under the conditions of temperature 30℃ and humidity 70% until the equilibrium moisture content is 6% to obtain wood-plastic mixed granules after moisture content control;

[0067] V. Extrusion foaming:

[0068] The temperature of each section of the single screw extruder is set, from the feeding section to the head, as follows: the temperature of the first section is 150℃, the temperature of the second section is 160℃, the temperature of the third section is 160℃, and the temperature of the fourth section is 170℃, then the wood-plastic mixed granules after the moisture content control are extruded under the condition that the screw rotation speed is 30r / min, then the wood-plastic mixed granules are shaped through a two-stage conical die, and finally the wood-plastic foamed composite material is obtained after cooling, cutting and balancing in sequence.

[0069] The inner chamber of the two-stage conical die is in a tower type, and the inner chamber is sequentially divided into a first die heating zone, a first expansion zone, a second die heating zone, a second expansion zone and a cooling and shaping zone from the inlet to the outlet; the first expansion zone and the second expansion zone are ladder-shaped chambers, and the first die heating zone, the second die heating zone and the cooling and shaping zone are rectangular chambers; the first die heating zone is provided with an upper and lower spacing K1, a width M1 and a length L1; the second die heating zone is provided with an upper and lower spacing K2, a width M2 and a length L2; the cooling and shaping zone is provided with an upper and lower spacing K3, a width M3 and a length L3; the first expansion zone is provided with a length L4; the second expansion zone is provided with a length L5; K1=4mm, K2=6mm and K3=10mm; L1=60mm, L2=30mm, L3=30mm, L4=30mm and L5=30mm; M1=4mm, M2=6mm and M3=8mm; the temperature of the first die heating zone is 180℃, and the temperature of the second die heating zone is 80℃.

[0070] The cooling is water tank cooling.

[0071] The balancing treatment is specifically moisture content regulation for 48h under the condition that the temperature is 30℃ and the humidity is 70%.

[0072] Example 2: Different from Example 1, the temperature of the first die heating zone is 170℃. The others are the same as Example 1.

[0073] Example 3: Different from Example 1, the temperature of the first die heating zone is 160℃. The others are the same as Example 1.

[0074] Example 4: Different from Example 1, the temperature of the first die heating zone is 150℃. The others are the same as Example 1.

[0075] Comparative Example 1: Different from Example 1, the moisture content regulation in step four is cancelled, the wood-plastic mixed granules obtained in step three are in an absolutely dry state, and the wood-plastic mixed granules are directly subjected to step five to prepare the wood-plastic composite material. The others are the same as Example 1.

[0076] Table 1: Product performance indicators of Examples and Comparative Example 1

[0077]

[0078] Figure 2 The scanning electron micrograph of the foamed wood plastic composite prepared in Example 1. As can be seen from the figure, the cross section of the foamed wood plastic composite is a uniformly distributed cell structure, with an average pore size of 234 μm, and one or more wood fibers are distributed in the center of the cell. This proves that the water absorbed by the wood fiber plays the role of an environmentally friendly blowing agent in the system, and the cell is formed during the process of water changing from liquid to gas, while the wood fiber acts as a carrier for the blowing agent.

[0079] Figure 3 The physical photograph of the foamed wood plastic composite prepared in Example 1. As can be seen from the figure, the foamed wood plastic composite forms a dense and uniform cell in the cross section, and the presence of the cell makes the foamed wood plastic composite have certain heat insulation and sound absorption performance.

[0080] Figure 4 The physical photograph of the foamed wood plastic composite prepared in Example 1 and the wood plastic composite prepared in Comparative Example 1. As can be seen from the figure, Example 1 is a foamed wood plastic composite, which is a clear foam structure with a dense and uniform cell structure on the surface; Comparative Example 1 is a physical photograph of a wood plastic composite without foaming with the same raw material ratio, which is a clear board structure with a smooth and dense surface without obvious pores.

[0081] Figure 5 The sound absorption test results of the foamed wood plastic composite prepared in Example 1 and the wood plastic composite prepared in Comparative Example 1. As can be seen from the figure, the sound absorption coefficient of the example is significantly higher than that of the comparative example, at 3800 Hz, the sound absorption coefficient of Comparative Example 1 is 0.16, while the sound absorption coefficient of Example 1 reaches 0.65, which is 4 times that of the comparative example. Therefore, the foamed wood plastic composite of the present example has excellent sound absorption performance.

Claims

1. A process for the production of a foamed wood plastic composite, characterized in that It is carried out in the following steps: I. Fiber pretreatment: The wood fiber powder is pretreated to obtain pretreated wood fiber powder; The pretreatment is carried out in the following steps: the wood fiber powder is immersed in a NaOH solution with a mass percentage of 5%~10%, soaked for 2h~4h, then washed to neutral and dried; II. High-speed mixing: 60~80 parts by mass of pretreated wood fiber powder, 10~33 parts by mass of thermoplastic, 3~5 parts by mass of compatibilizer and 1~2 parts by mass of lubricant are weighed, then mixed uniformly in a high-speed mixer to obtain mixed raw materials; III. Melting, extrusion and granulation: The mixed raw materials are melted and extruded into strands by a twin-screw extruder, and finally cooled and granulated to obtain wood-plastic mixed granules; IV. Moisture content control: The moisture content of the wood-plastic mixed granules is controlled until the equilibrium moisture content is 1%~10% to obtain wood-plastic mixed granules with controlled moisture content; V. Extrusion foaming: The wood-plastic mixed granules with controlled moisture content are extruded by a screw extruder, then shaped by a two-stage conical die, and finally cooled, cut and balanced to obtain foamed wood-plastic composite materials; In step V, the temperature of each section of the screw extruder is set from the feeding section to the die head as follows: the temperature of the first section is 140℃~150℃, the temperature of the second section is 150℃~160℃, the temperature of the third section is 150℃~160℃, and the temperature of the fourth section is 160℃~170℃. Then, the wood-plastic mixed granules with controlled moisture content are extruded under the condition that the screw rotation speed is 30r / min~70r / min; In step V, the inner chamber of the two-stage conical die is in the shape of a tower, and the inner chamber is divided into mold heating area one, expansion area one, mold heating area two, expansion area two and cooling and shaping area from the inlet to the outlet. The expansion area one and the expansion area two are ladder-shaped chambers, and the mold heating area one, the mold heating area two and the cooling and shaping area are rectangular chambers. The upper and lower spacing of the mold heating area one is K1, the width is M1, and the length is L1. The upper and lower spacing of the mold heating area two is K2, the width is M2, and the length is L2. The upper and lower spacing of the cooling and shaping area is K3, the width is M3, and the length is L3. The length of the expansion area one is L4, and the length of the expansion area two is L5. K1=2mm~4mm, 1:1 2. The method for preparing a foamed wood-plastic composite material according to claim 1, characterized in that... The wood fiber powder in step one is one or a combination of wood powder, rice husk powder, bamboo powder, straw powder, fruit shell powder, bagasse and hemp fiber; the wood fiber powder has a mesh size of 10 mesh to 300 mesh.

3. The method for preparing a foamed wood-plastic composite material according to claim 1, characterized in that... The thermoplastic plastic in step two is one or a combination of polyethylene, polypropylene, polystyrene, polyvinyl chloride, polylactic acid and polybutylene adipate terephthalate.

4. The method for preparing a foamed wood-plastic composite material according to claim 1, characterized in that... The compatibilizer in step two is a maleic anhydride grafted polymer.

5. The method for preparing a foamed wood-plastic composite material according to claim 1, characterized in that... The lubricant in step two is one or a combination of polyethylene wax, stearic acid, zinc stearate and calcium stearate.

6. The method for preparing a foamed wood-plastic composite material according to claim 1, characterized in that... In step two, the mixture is mixed in a high-speed mixer, specifically at a speed of 100 r / min to 300 r / min for 3 min to 5 min at low speed, and then at a speed of 500 r / min to 1000 r / min for 5 min to 7 min at high speed, to obtain the mixed raw materials.

7. The method for preparing a foamed wood-plastic composite material according to claim 1, characterized in that... In step three, the temperature of each section of the twin-screw extruder is set from the feeding section to the die head as follows: the first section temperature is 130℃ to 140℃, the second section temperature is 140℃ to 150℃, the third section temperature is 150℃ to 160℃, the fourth section temperature is 160℃ to 170℃, the fifth section temperature is 160℃ to 170℃, the sixth section temperature is 160℃ to 170℃, and the seventh section temperature is 150℃ to 160℃, then the mixed raw materials are melted and extruded into strands at a screw speed of 30 r / min to 70 r / min, and finally cooled and cut into particles with a particle size of 2 mm to 8 mm.

8. The method for preparing a foamed wood-plastic composite material according to claim 1, characterized in that... In step four, the moisture content of the wood-plastic mixed particles is adjusted at a temperature of 30℃ to 60℃ and a humidity of 30% to 100% until the equilibrium moisture content is 1% to 10%.

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