DE102007054549A1 - Producing natural fiber plastic composite material by drying the natural material such as hemp and/or wood in the form of fiber, shred or flour, crushing the wood raw materials and then compounding with a plastic melt and/or additives - Google Patents

Abstract

The method for the production of natural fiber plastic composite material for the production of different products, comprises drying the natural material such as hemp, hay, flax, straw and rice husks and/or wood in the form of fiber, splinter, shred or flour, crushing the wood raw materials and then compounding with a plastic melt and/or additives for the natural fiber plastic composite material. The wood raw materials, solid or liquid plastic and if necessary additives are mixed through kneading and simultaneous pressing in a closed system in a discontinuous production process. The method for the production of natural fiber plastic composite material for the production of different products, comprises drying the natural material such as hemp, hay, flax, straw and rice husks and/or wood in the form of fiber, splinter, shred or flour, crushing the wood raw materials and then compounding with a plastic melt and/or additives for the natural fiber plastic composite material. The wood raw materials, solid or liquid plastic and if necessary additives are mixed through kneading and simultaneous pressing in a closed system in a discontinuous production process. The wood raw materials are crushed during the mixing process and water contained in the wood raw material is evaporated through heat energy produced during kneading and pressing process through friction. The surface of the wood raw materials is activated through a further introduction of frictional warmth and/or its reaction capability is increased. The plastic is melted by the frictional heat and the wood raw material is compounded with the plastic melt or with a supplied plastic melt and/or if necessary with additives for a homogeneous natural fiber plastic composite material. The plastic is processed in the form of granulates, cubes or powder. The additive is bonding agent, ultraviolet protective additives and color pigments. An independent claim is included for a device for the production of natural fiber plastic composite material.

Description

The The invention relates to a method and an apparatus for the production of natural fiber-plastic composites, using natural materials such as hemp, hay, flax, straw and rice husks, and especially wood in the form of fibers, shavings, chips or dried flour, crushed the wood pulp and with a Plastic melt and as needed with one or more additives to a natural fiber-plastic composite material is compounded to produce different products.

Natural fiber-plastic composites (WPC) are thermoplastically processable materials based on Natural fibers, in particular wood fibers, synthetic polymers and Biopolymers and additives. The polymers include polyethylene (PE), polypropylene (PP) and polyvinylchloride (PVC) as well as bioplastics on the basis of strength and Lignin with a melting or processing temperature below 200 ° C, because temperatures above 200 ° C too damage of wood components lignin and hemicelluloses. The mentioned synthetic ones Include polymers to the group of cheap ones Standard plastics; other plastics such as acrylonitrile-butadiene-styrene copolymers (ABS-plastics) are currently not used mainly for cost reasons. Next The polymers mentioned are still thermoplastically processable Thermosets in small quantities for the production of natural fiber-plastic composites used.

to Production of WPC materials, additives are essential even if they usually only account for 2 to 4% of needed for WPC production Make up components.

The main functions of additives can be summarized as follows:
Improvement of mechanical properties: Adhesion promoters such as maleic anhydride for better bonding between wood and plastic matrix as well as calcium carbonate, talc and mica for improved flexural strength, heat stability and reduced creep.

improvement the compoundability and the flow behavior of the raw materials and lubricants.

conservation the chemical stability during the Manufacture and use.

pigments and light or UV stabilizers to the optical properties influence or maintain.

UV stabilizers, and fungicides, um - just in high wood filled WPC materials - the durability of the material.

fire retardant Additives for fire protection.

One For example, typical WPC product is an extruded profile Wood flour, polyethylene or polypropylene and the aforementioned additives, the used for laying on a terrace or for an outside staircase.

Compared to solid wood products and usual wood materials WPC materials have the advantages of a free formability and the greater moisture resistance and the associated good weather resistance without aftertreatment on. These advantages are higher Compared to production costs.

Compared to synthetic Plastics, WPC materials have the advantages of lower production costs due to the high wood content of 60 to 90% and the resulting independence of the rising oil prices, a haptic perceptibility, a natural appearance as well as improved technical properties such as a higher rigidity and a significantly lower thermal expansion coefficient.

The most important machine for the production of WPC materials is the extruder, which is widely used in the plastics industry. Extruders are used for the mixing of wood, plastic and additives as well as for the actual production of WPC parts. Accordingly, one can divide the WPC manufacturing process in two stages:
Stage 1, compounding: production of WPC material from the components wood, plastic and additives. Here are roughly divided three lines: conical, counter-rotating twin-screw extruder and parallel, co-rotating twin-screw extruder and heating-cooling mixer.
Stage 2, Production: Production of WPC parts from WPC material. The most common processes are extrusion and injection molding, but thermal pressing processes are also possible, which at present play virtually no role, but which may become increasingly important in the future.

Under WPC compounding is the mixing of plastic and wood and additives to a homogeneous mass. The process of compounding forms the first stage of a WPC manufacturing process.

For the production of WPC materials today, the extrusion process is used in the first place, in the opposite double-screw extruders with a conical shape and parallel, co-rotating twin-screw extruder are used.

Conical shaped, opposing Twin-screw extruders are particularly suitable for direct extrusion of linear profiles as the most important product group for WPC materials so far. These twin screw extruders are characterized by a compact design, low speeds and short residence times of the material in the extruder, whereby the thermal stress and the risk of damage to the wood material low fail. However, these extruders have a poor mixing effect.

Of the Twin-screw extruder with two parallel, co-rotating Snails is the classic extruder for the processing of bulk plastics like polypropylene, when using these plastics with fillers like talc and additives must be mixed. In the production of WPC materials, such extruders especially for compounding and subsequent WPC granule production used. If a direct extrusion or direct injection molding is required, must on the synchronous twin-screw extruder for pressure build-up a single-screw extruder, standard in plastics processing is, or follow a pump.

advantages the co-rotating twin-screw extruder are the good mixing effect and the production speed. A disadvantage of this extruder is the longer one Residence time of the material in the extruder, through which a longer thermal Influence on the wood materials takes place.

Finally will for compounding of wood raw material, plastic and additives to a homogeneous material, a heating-cooling mixing method used. Object of the working according to this method heating-cooling mixer, especially for the processing of PVC plastics is used, it is plastics, fillers such as wood, stabilizers, adhesion promoters, lubricants, pigments and to distribute further modifiers homogeneously and these Mix in one as possible Dust-free, dry and free-flowing condition to convict. there be in the heating-cooling mixer the plastic and the components are mixed for 5 to 10 minutes and simultaneously at 110 to 130 ° C heated. This binds the components to the plastic particles. at At this temperature, the resulting compound tends to be pressed. To avoid this, the mix is removed from the heating mixer a cooling mixer deflated and cooled in this to about 40 ° C.

Fresh beaten wood can have a moisture content of over 100% to have. In order to use it for the production of WPC materials, must the wood to be pre-dried. Depending on the particular extruder design can be worked with different damp wood. In any case should the moisture content be below 12%, some extruder designs even require values below 0.5%.

Basically one possible low moisture content, since moisture compounding interferes with plastics and must be removed in the process. Since the predrying but with considerable cost, there is a tradeoff between Technology and economy to find.

The above-described extrusion process for the production of wood-plastic composites according to the prior art has the following disadvantages:
The most important requirement in the production of WPC materials is the combination of hydrophilic and hydrophobic properties of the two material components wood raw material and plastic in a solid composite, so that the water absorption - one of the most important characteristics - can be kept at a low level.

all Extruders have in common that they work continuously. The Dwell time of the material is thus limited by the length of the extruder and ultimately determines the quality of the produced next to the energy input Material that is influenced by the use of chemical additives can.

The Mixing of the material components along the way is however not always given in the necessary quality, so that such phenomena Aglumorate, segregation and different orientations of Structures occur.

Farther is the total homogeneity of the material is not always constant; in an extruder become materials mixed only in cross-section, the mass is then conveyed forward. If not properly dosed when feeding with material components and the material is transported is excluded, that this can be subsequently improved.

The for the Verbund necessary conditions are therefore determined by the chemical Aids such as adhesion promoters, linked to the thermal as well achieved the mechanical energy supply. An energy application is at such processes at about 200 W / kg, so that the production the WPC material is correspondingly expensive.

Of the Raw material wood must not exceed a moisture content of 15%, because this makes the water leakage significantly more difficult. This means that the wood raw material must be pre-dried, which additional Production costs due to the required heat energy for the drying process arise.

Of the to be processed wood fiber raw material must have a certain maximum length, because there is no fiber shredding during the compounding process instead, due to the extruder design.

Farther are the poorly controllable in such continuous processes Dwell time of the material along the transport path and a very difficult litigation always given. this leads to to have such properties as water absorption, strength and impact strength only conditionally meet the required requirements.

Of the Invention is based on the object, a method and an apparatus for the production of natural fiber-plastic composites, in particular wood fiber-plastic composites to develop, facing each other the known materials of this kind by improved quality and lower Distinguish manufacturing costs.

These The object is achieved by the manufacturing method having the features of the claim 1 and working according to this method device according to claim 5th

The under claims contain advantageous and expedient developments of the method and the device.

The inventive method and working by this method device used as a kneader is formed, characterized by the advantages listed below By: By using the frictional heat generated by the kneading and Pressing process when compounding the natural material, in particular of the wood raw material, the plastic and the additives to a homogeneous Wood-plastic composite is produced, to vaporize the Water from the wood raw material, to activate the surface of the wood Holzrohstoffs and to increase the reactivity of the Wood material and melting the plastic component can the energy input of 200 W / kg in conventional compounding be significantly increased to up to 2 to 10 kW / kg. by virtue of of high energy input the processing times shortened become, so that a cheapening of the manufacturing costs reached becomes. Furthermore, can through the use of frictional heat Processed wood pulp with a water content of over 15%, whereby the manufacturing costs for WPC material due to the cost of pre-drying of the wood material continue to sink. The discontinuous course of the Compounding the WPC materials in a kneader allows a exact adjustment of the processing times of the material depending on material quality and an exact temperature control, the processing of polymers such as polyamide and polystyrene having a melting point above 200 ° C allows. This can be completely new WPC materials are produced, which are produced by the known compounding methods, mainly the extrusion process and the injection molding process, can not be made. The compounding of wood raw material, plastic and additives through a controllable kneading and pressing operation, in a closed System expires, guaranteed to a homogeneous wood-plastic composite a consistently good material quality and allows a reaction-related chemical processing in addition to pure compounding by individual Reagents either directly or with a time delay in the compounding process supplied Be such, that any chemical reactions in a given order expire and desired Material properties can be achieved. The combined kneading and pressing in a closed system under utilization the frictional heat guaranteed optimal mixability of the processed materials and prevents agglomeration of the materials resulting in a damage lead the WPC material can, and also ensures that the quality of the wood raw material due to the fiber length, the moisture content and the composition of the wood material is determined to have little effect on the compounding process and the quality of the composite material produced Has. After all enable the new compounding process and the process according to this method Kneader the production of wood-plastic composite materials with improved mechanical properties, namely the bending strength and impact strength, an elevated one Thermal stability and a reduced creep behavior.

The inventive method for the production of natural fiber-plastic composite materials, in particular of wood-plastic composite materials, dried in the wood raw material in the form of fibers, shavings, chips or flour, the wood pulp crushed and with a plastic melt and, if necessary, with one or more additives is compounded to a wood-plastic composite material for the production of different products, is characterized in that in a discontinuous production process, the wood raw material, in particular wood fiber, solid or liquid plastic and optionally one or more Additives are mixed by kneading and simultaneous pressing in a closed system, wherein the wood pulp is crushed during the mixing process and is evaporated by the heat energy generated during the kneading and pressing process by friction, the water contained in the wood raw material and then by another introduction of frictional heat the surface the wood raw material is activated and its reactivity is increased, and when using solid plastic, this is melted by the frictional heat and the wood raw material with the generated by the frictional heat plastic melt or with a supplied plastic melt and optionally with one or more additives to a homogeneous wood-plastic Compound compounded.

The processed plastics are polymers, in particular polyethylene, Polypropylene and polyvinyl chloride, melt processable Thermosets, bioplastics based on starch and lignin, as well as refractory Plastics such as polyamide, acrylonitrile-butadiene-styrene copolymers and polycarbonate.

Of the Plastic supplied in solid state in the compounding process which is melted in the process, the form of granules, roll the dice or powder.

When Additives are preferably used adhesion promoters, UV protection additives and color pigments.

The kneader operating according to the above-described method for the production of wood-plastic composite materials is described below with reference to the schematic 1a to 1d illustrating the kneader in four successive stages of a work cycle:
The kneader 1 has a cylindrical housing 2 that is a mixing chamber 3 has, in the upper area 3a one in the direction of the housing longitudinal axis 4-4 displaceable cylindrical plunger 5 for compacting the materials to be processed and for conveying the materials to the lower area 3b the mixing chamber 3 is arranged in the two counter-rotating rotors 6 . 7 are installed.

The rotors 6 . 7 form a compression nip 8th for crushing into the kneader housing 2 filled wood raw material, for mixing the wood raw material, in solid or liquid state in the kneader housing 2 introduced plastic and one or more in the kneader housing 2 and additives for generating frictional heat by a compression and mixing process to evaporate the water contained in the wood raw material, to activate the surface and increase the reactivity of the wood raw material and to melt the solid state in the kneader 2 introduced plastic. The housing 2 of the kneader 1 has a closable filling opening 9 for the materials to be processed in the upper area 3a the mixing chamber 3 and a closable emptying opening 10 for the compounded wood-plastic composite in the case back 11 on.

Conveniently, the insertion opening serves 12 of the kneader housing 2 for the plunger 5 in the out of the case 2 extended piston position 5a as a filling opening.

In a modified embodiment of the kneader 1 are one or more filling openings 9 in the upper area 3a the mixing chamber 3 of the kneader housing 2 in its wall 13 arranged.

The rotors 6 . 7 of the kneader 1 are designed as impellers.

In modification of the above-described kneader, the kneader housing 2 and the plunger 5 have a rectangular or square shape.

In the in 1a shown first operating stage of a working cycle of the kneader 1 be over the filling hole 9 of the kneader housing 2 passing through the insertion opening 12 of the kneader housing 2 for the plunger 5 in the out of the kneader housing 2 extended position 5a of the plunger 5 is formed, wood raw materials, plastic and one or more additives at room temperature in the kneader housing 2 filled.

Thereafter, in the second operating stage according to 1a by commissioning the rotors 6 . 7 and pressing the material components by ancestors of the plunger 5 in the direction of arrow a in the lower area 3b the mixing chamber 3 of the kneader 1 initiated the kneading and pressing process, in which the fibers or chips of the wood pulp crushed, the wood material dried by the frictional heat generated in the kneading and pressing process, activated by further introduction of frictional heat after completion of the drying process, the surface of the wood pulp and its reactivity is increased in that the plastic material supplied in the form of small particles is melted and the various material components are homogeneously mixed.

Subsequently, in the third operating stage according to 1c after retraction of the plunger 5 in the direction of arrow b in the upper area 3a the mixing chamber 3 chemical additives via lateral filling openings 9 or injectors in the housing wall 13 of the kneader 1 in the upper area 3a the mixing chamber 3 are initiated in this, the chemical reactions of the material components to achieve certain properties such as increasing the bending strength and reducing the creep of the composite material to be produced, and the material components are mixed ready.

Finally, in the in 1d illustrated fourth operating stage of the work cycle of the kneader 1 the plunger 5 in the direction of arrow a in the lower area 3b the mixing chamber 3 advanced, such that the mixture through the through the plunger 5 and the rotors 6 . 7 compounded pressing and mixing process to form a homogeneous wood-plastic composite, which after completion of a working cycle of the kneader 1 over the opened discharge opening 10 in the ground 11 of the kneader housing 2 discharged and immediately thereafter in a warm state, for example, an extruder for further processing to a profile or a cutting and cooling device for producing a granulate for later production of different products is supplied.

1

compounder

2

Housing of 1

3

Mixing chamber of 2

3a

upper area of 3

3b

lower area of 3

4-4

Longitudinal axis of 2

5

plunger

5a

extended position of 5

6

rotor

7

rotor

8th

Compression nip of 6 . 7

9

Filling opening of 2 in 3a

10

Emptying opening of 2 in 11

11

Caseback of 2

12

Sliding opening of 2 For 5

13

Wall of 2

a, b

Lifting movement of 5

Claims (11)

Process for the production of natural fiber-plastic composites, in which natural materials such as hemp, hay, flax, straw and rice husks and especially dried wood in the form of fibers, shavings, chips or flour, the wood pulp crushed and with a plastic melt and as needed with one or more additives to a natural fiber-plastic composite material for the production of different products is compounded, characterized in that in a batch production process, the natural material, in particular the wood raw material, solid or liquid plastic and optionally one or more additives by kneading and simultaneous pressing in be mixed with a closed system, wherein the wood pulp is crushed during the mixing process and by the heat energy generated during the kneading and pressing process by friction, first the water contained in the wood raw material is evaporated and then by another E In the presence of solid plastic this is melted by the frictional heat and the wood pulp with the plastic melt generated by the frictional heat or with a supplied plastic melt and optionally with one or more additives to one homogeneous natural fiber-plastic composite material is compounded. Method according to claim 1, characterized by Processing of polymers, especially of polyethylene, polypropylene and polyvinyl chloride, thermoplastically processable thermosets, Bioplastics based on starch and lignin as well as on refractory Plastics such as polyamide, acrylonitrile-butadiene-styrene copolymers and polycarbonate. Method according to claims 1 and 2, characterized by the processing of plastics in the form of granules, cubes or Powder. The method of claim 1 to 3, characterized by the processing of additives such as adhesion promoters, UV protection additives and Color pigments. Device for carrying out the method according to claims 1 to 4, characterized in that it comprises a kneader ( 1 ) comprises a housing ( 2 ), which has a mixing chamber ( 3 ), in the upper area ( 3a ) in the direction of the housing longitudinal axis (4-4) displaceable plunger ( 5 ) for compacting the materials to be processed and for conveying the materials into the lower area ( 3b ) of the mixing chamber ( 3 ) is arranged in the at least two counter-rotating rotors ( 6 . 7 ), which have a compression gap ( 8th ) form for crushing into the kneader housing ( 2 ), mixing the wood raw material, the solid or liquid state in the kneader housing ( 2 ) introduced plastic and one or more in the kneader housing ( 2 ) and for generating frictional heat by a compression and mixing process to evaporate the water contained in the wood raw material, to activate the surface and increase the reactivity of the wood raw material and to melt in the solid state in the kneader housing ( 2 ) Plastic, and that the housing ( 2 ) of the kneader ( 1 ) at least one closable filling opening ( 9 ) for the materials to be processed at the top ( 3a ) of the mixing chamber ( 3 ) and a closable emptying opening ( 10 ) for the compounded wood-plastic composite material in the housing bottom ( 11 ) having. Apparatus according to claim 5, characterized in that the insertion opening ( 12 ) of the kneader housing ( 2 ) for the plunger ( 5 ) in from the housing ( 2 ) extended piston position ( 5a ) serves as a filling opening. Apparatus according to claim 5, characterized by at least one in the upper area ( 3a ) of the mixing chamber ( 3 ) of the kneader housing ( 2 ) in its wall ( 13 ) arranged filling opening ( 9 ). Apparatus according to claim 5, characterized by at least one in the upper area ( 3a ) of the mixing chamber ( 3 ) of the kneader housing ( 2 ) in its wall ( 13 ) arranged mixing nozzle. Device according to one of claims 5 to 8, characterized in that kneader housing ( 2 ) and plunger ( 5 ) have a cylindrical shape. Device according to one of claims 5 to 8, characterized by a rectangular or square shape of the kneader housing ( 2 ) and the plunger ( 5 ). Device according to one of claims 5 to 10, characterized by a design of the rotors ( 6 . 7 ) as impellers.