Method for producing a lignocellulose plastic composite material

Abstract

A method for producing a lignocellulose plastic composite material, in particular a simpler and more cost-effective option for producing lignocellulose plastic composite materials. Thermoplastic particles and a mixture of water and lignocellulose-containing particles are supplied to a refiner, and the lignocellulose-containing particles are reduced to fibers in the refiner. The thermoplastic particles are supplied to the refiner in a melted or fused state, or are melted or fused in the refiner, so that the melted or fused thermoplastic particles and the lignocellulose-containing particles that are reduced to fibers form material composite particles in the refiner.

Claims

1. A method for producing a lignocellulose-plastic composite material, wherein thermoplastic particles and a mixture of water and lignocellulose-containing particles are fed to a refiner, and the lignocelluslose containing particles are reduced to fibers in the refiner, and wherein the thermoplastic particles melted or pre-melted only in the refiner so that the melted or pre-melted thermoplastic particles and the lignocellulose-containing particles that have been reduced to fibers than material composite particles in the refiner, and wherein the thermal energy required to melt or partially melt the thermoplastic particles is generated exclusively by (a) shearing energy in the refiner, (b) heating the refiner by electric heating or (c) by a combination of shearing energy in the refiner and heating the refiner by electric heating.

2. The method according to claim 1, wherein the thermoplastic particles and the mixture of water and lignocellulose-containing particles are fed to the refiner jointly or separately.

3. The method according to claim 2, wherein an aqueous suspension of lignocellulose-containing particles and thermoplastic particles is fed to the refiner, and the thermoplastic particles are melted or pre-melted in the refiner, and the lignocellulose-containing particles are reduced to fibers so that the melted or pre-melted thermoplastic particles and the lignocellulose-containing particles that have been reduced to fibers form material composite particles in the refiner.

4. The method according to claim 1, wherein the temperature in the refiner is at or above the glass transition temperature of the thermoplastic particles.

5. The method according to claim 1, wherein the refiner is a disk refiner with grinding disks.

6. The method according to claim 5, wherein a supply of thermoplastic particles and the mixture of water and lignocellulose-containing particles take place centrally through a grinding disk, and material composite particles are discharged radially or tangentially with respect to the grinding disks.

7. The method according to claim 1, wherein the lignocellulose-containing particles are wood particles or lignin-free cellulose fibers (CTMP) or wood pulp.

8. The method according to claim 1, wherein the thermoplastic particles in the particle comprise polyethylene (PE), polypropylene (PP), acrylonitrile-butadiene-styrene (ABS), polyamide (PA) [nylon], polylactate, polymethyl methacrylate (PMMA), polycarbonate (PC), polyethylene terephthalate (PET), polystyrene (PS), polyether ether ketone (PEEK), thermoplastic starch (TPS) or polyvinyl chloride (PVC) or a mixture thereof.

9. The method according to claim 1, wherein the wood particles are wood shavings, wood chips, wood fibers or sawdust.

10. The method according to claim 1, wherein the thermoplastic particles and the mixture of water and lignocellulose-containing particles are fed to the refiner jointly.

Description

(1) The invention is explained in greater detail below on the basis of the accompanying figures and exemplary embodiments merely for illustrations purposes.

(2) FIG. 1 shows a schematic diagram of a preferred embodiment of a device for carrying out the method according to the invention.

(3) FIG. 2 shows a schematic diagram of another preferred embodiment of a device for carrying out the method according to the invention.

(4) FIG. 1 shows schematically the design of an experimental refiner used in the exemplary embodiment 1 (see below). The refiner 1 is a disk refiner with two grinding disks 2, 3, which form a milling gap 5 in a housing 4. The first grinding disk (stator grinding disk) 2 is stationary, while the second grinding disk (rotor grinding disk) 3 rotates around the axle 10, as indicated by the arrow. A screw conveyor 6 is arranged in the hollow axle 11 of the stator grinding disk 2, such that the material to be milled can be introduced centrally into the milling gap 5. The material to be milled can be charged to the conveyor screw 6 through a hopper 7. The housing 4 has a line 8 on its top side, through which steam can be introduced into the interior of the housing 4. An outlet 9 is provided at the bottom of the housing 4, through which the finished product can be removed from the housing 4.

(5) FIG. 2 shows schematically the design of a refiner, such as that used in exemplary embodiment 2. The refiner 1 differs essentially in that a cooker 12 has been used instead of a hopper 7.

EXEMPLARY EMBODIMENT 1

(6) For the experiments described below, a low-density polyethylene (LDPE) and spruce sawdust have been used for wet compounding according to the invention. A mixing ratio of 60% spruce shavings and 40% LDPE (amounts by weight) was used for this purpose. Before reducing these components to fibers in the refiner, the sawdust was precooked in a so-called paddle reactor for 6 minutes at 170 C. In doing so, 10 L of water were added to 5 kg shavings. The middle lamella of the wood fibers was softened due to such a hydrothermal pretreatment, so that the modulus of elasticity drops, and the reduction of the particles to fiber in the refiner is facilitated. In an industrial production process, such as MDF production, the precooking of the chips and the subsequent reduction to fibers are carried out in a continuous process, such that from the cooker to the refiner is a closed pressure system at temperatures of 170 C. to 200 C. at 6 to 12 bar. However, the experimental refiner used here was an open system, in which temperatures of 100 C. could be implemented. Immediately after precooking the chips, the weighed polymer in granular form was manually undermixed into the softened shavings and sent to the refiner without further treatment (screening, pressing or the like).

(7) For melting or partial melting of the polymer in refiner 1, the refiner 1 here was heated with steam (temperature T approx. 100 C.) through line 8 and preheated (see FIG. 1). Because of the open system, the preheating of the refiner 1 by steam was possible only up to a temperature of approx. 100 C. Further input of energy that causes melting or partial melting of the polymer was introduced into the system by shear energy generated by reduction of the chips and shavings to fibers and also reducing the polymer granules to fibers. The refiner 1 was steam-treated continuously during this reduction to fibers.

(8) The grinding disk spacing and thus the thickness of the milling gap 5 were set at 0.5 mm for the wet compounding and reduction to fibers. After turning on the refiner 1 and the screw conveyor unit, the material was sent to the milling unit through the funnel 7, reduced to fibers and discharged through the outlet 9 by centrifugal forces at the lower end of the refiner housing 4. The dwell time of the material in the refiner was 10 seconds from input of the material into the funnel until discharge of the material 9.

(9) The experimental parameters for the experiment described above are given in Table 1.

(10) TABLE-US-00001 TABLE 1 Experimental parameters for exemplary embodiment 1 Experimental parameter spruce savings and LDPE material mixing ratio (amount by weight) 60% spruce shavings 40% LDPE refiner Sprout-Waldron 12, 3000 min.sup.1 grinding disk spacing 0.1 mm grinding disk model: Andritz R243 throughput approx. 8 kg hydrothermal pretreatment Paddle Reactor Herbst Machinenbau Model: 1203027 T = 170 C. T = 6 min. steam preheating of refiner steam generator: model CD9ST Dino, Bremen 4 bar (max. 8 bar) steam outlet: approx. 100 C.

(11) The prepared wet compound had been drastically reduced to fibers in comparison with the starting material. The polymer was extremely reduced in size in comparison with the starting material and was not discernible with the naked eye. There were visible signs of melted polymer. A subsequent separation of wood and thermoplastic (e.g., by slurrying) was no longer possible.

EXEMPLARY EMBODIMENT 2

(12) Polypropylene (PP) and high-density polyethylene were compounded together with spruce/pine wood chips according to the invention for the experimental procedure described below. The input material moisture of the wood chips was 13%. Table 2 lists the individual experimental parameters as well as the material compositions and specifications. A pressure refiner 1 of the Sprout-Waldron 12 type with an upstream cooker 12 (volume 55 L) was used for this experiment (see FIG. 2). By using a pressurized refiner 1, such as that used in the experimental procedure, it is possible to model industrial conditions over a longer period of time in comparison with Exemplary Embodiment 1.

(13) The material was first mixed by hand with water and then placed in the cooker 12. Before reducing the material to fibers, the materials were heated for up to 10 minutes at 125 C. and 145 C. The disk spacing of the refiner was set at 0.1 mm. After heating the material mixture was transported between the refiner disks by steam pressure (manually controllable), starting from the cooker, and a conveyor screw between the refiner disks, then reduced to fibers there and discharged through centrifugal forces tangentially through a valve opening (10 mm).

(14) Immediately downstream from the flow-through valve, sudden evaporation of the water in the material occurs suddenly, resulting in drying of the material. The wetness of the material immediately downstream from the discharge of the material amounted to 35-40%. The material appeared to have been reduced to fibers to a great extent in comparison with the starting material (chips, granules). The fiber geometry is comparable to that of MDF fibers. The thermoplastic appears to be reduced to fibers and is inseparably bonded to the wooden fibers.

(15) TABLE-US-00002 TABLE 2 Experimental parameters for exemplary embodiment 1. Weight Heating Experiment dry Ratio t & T No.: Material Specific. (kg) (%) (min & C.) 1 spruce/pine chips fraction: 7.70 70 10 min type: Rettenmaier FS 14 2.5-4.0 mm at 125 C. HDPE density: 0.954 g/cm.sup.3 3.3 30 Sabic TC 3054 melting point: 132 C. MFI: 30 g/10 min. 2 spruce/pine chips fraction: 5.5 50 10 min. type: Rettenmaier FS 14 2.5-4.0 mm at 125 C. HDPE density: 0.954 g/cm.sup.3 4.4 50 Sabic TC 3054 melting point: 132 C. MFI: 30 g/10 min. 3 spruce/pine chips fraction: 7.7 70 10 min. type: Rettenmaier FS 14 2.5-4.0 mm at 145 C. PP density: 0.905 g/cm.sup.3 3.3 30 Sabic, PP 575p melting point: 160 C. MFI: 10.5 g/10 min. 4 spruce/pine chips fraction: 5.5 50 10 min. type: Rettenmaier FS 14 2.5-4.0 mm at 145 C. PP density: 0.905 g/cm.sup.3 4.4 50 Sabic, PP 575p melting point: 160 C. MFI: 10.5 g/10 min. Fi = spruce, Ta = pine, Specific. = specification, PP = polypropylene, HDPE = high-density polyethylene. The particle size ranges are given under fraction.