Wood plastic composite material

Abstract

The invention relates to a wood-plastic composite for structural components of transport pallets that can be mutually pinned, having a matrix that is foamed with the aid of an auxiliary agent, wood fiber and an adhesion promoter. In order to produce such a wood-plastic composite, to enable transport pallets having a wood-like appearance to be produced cost-effectively and to be a reliable replacement for the currently used softwood materials at least in terms of weight and mechanical strength properties, the invention proposes that the matrix comprising a long-chain branched polyolefin has a mass fraction of 30-95% of the wood-plastic composite, the wood fiber has a mass fraction of 5-50% of the wood-plastic composite and the adhesion promoter has a mass fraction of up to 10% of the wood-plastic composite, wherein the composite density is less than 0.3 g / cm 3 .

Description

TECHNICAL FIELD

[0001] The invention relates to a wood-plastic composite material for structural components of transport pallets (or also called stack boards) which can be nailed to each other, having a matrix foamed with the aid of a blowing agent (Triebmittel), wood fiber and an adhesion promoter (or also called coupling agent).

[0002] In the context of sustainable development and increasing resource efficiency, it is necessary to produce transport pallets according to the Europool standard, the material of which is at least comparable to the previously used cork material in terms of weight, mechanical strength properties, manufacturing and processing properties and cost efficiency, or preferably superior to the cork material, and has a certain wood appearance for reasons of customer acceptance. Furthermore, in order to ensure an economic production process of the transport pallets, the respective structural components must be able to be nailed to each other, in particular using compressed air or compressed head nails, in order to prevent damage to the parts and to enable reliable functioning of the transport pallets. PRIOR ART

[0003] For example, a wood-plastic composite material, so-called wood-polymer composite (WPC) (WO2002088233A1), is known from the prior art, which comprises a high-density polyethylene (PE-HD) matrix and wood fibers foamed by a blowing agent based on carbon dioxide. However, due to its relatively brittle properties and relatively low fatigue strength, this wood-plastic composite material is not suitable as a structural component of the above-mentioned transport pallets, in particular because this wood-plastic composite material is prone to cracking due to the nails. SUMMARY

[0004] The technical problem addressed by the invention is therefore to provide a wood-plastic composite material which enables the production of transport pallets with a wood-like appearance in a cost-effective manner and which is at least a reliable alternative to the hitherto used cork material in terms of weight and mechanical strength properties.

[0005] The proposed technical problem is solved by the invention in that in the wood-plastic composite material, the proportion by mass of the matrix comprising a long-chain branched polyolefin is 30-95%, the proportion by mass of the wood fibers is 5-50%, and preferably the proportion by mass of the adhesion promoter based on maleic anhydride is up to 10%, wherein the composite material has a density of less than 0.3 g / cm 3 .

[0006] Wood fibers, preferably wood fibers having a particle size of 70 to 150 pm, would in principle counteract the formation of a uniform foam structure, since the wood fibers have the potential to pierce and thus destroy any foam cavities. Thus, a higher mass fraction of wood up to 50% which would favor an attractive wood appearance is not readily achievable. Surprisingly, however, a uniform foam structure can be formed even at high mass contents of wood up to 50% using long-chain branched polyolefins. Due to the strain hardening effect promoted by the long-chain branching of the polyolefins occurring during processing, a low composite density and relatively high strength values can be achieved. The strain hardening effect can be demonstrated, for example, by uniaxial strain rheometry, in which an increase in viscosity can be identified by the strain load. In the context of the present application, long-chain branching is understood to mean that at least 10% of the side chains of the polyolefin have a chain length of at least 6 carbon atoms. Preferably, the polyolefin is a low-density polyethylene (PE-LD or LDPE) or a polypropylene. When the density is less than 0.2 g / cm 3 , preferably less than 0.1 g / cm 3 , the wood-plastic composite according to the application is used as a structural component for transport pallets, resulting in particularly advantageous properties and high cost efficiency. Furthermore, the wood-plastic composite of the application can have an elastic modulus of 500 to 1000 megapascals, determined by ISO-178 flexural test at a test speed of 1 millimeter per second, and a flexural strength of at least 7 megapascals. Thus, the structural components made of the wood-plastic composite of the application are suitable for enduring the loads usually imposed on transport pallets for a long time. Furthermore, the wood-plastic composite has sufficient ductility, so that any structural component can be easily nailed together with compressed air or a compression head, so that no dangerous cracks in the foam structure are produced and no splinters are formed.

[0007] If the mass fraction of wood fibers is 20 to 40%, preferably 25 to 35%, in particular 30%, and the mass fraction of the adhesion promoter is 1 to 5%, preferably 2 to 4%, in particular 3%, a favorable combination of low density, sufficient strength and ductility and an attractive wood appearance can be achieved.

[0008] In order to achieve a composite density of less than 0.1 g / cm 3In order to further improve the mechanical properties in this case, it can be provided that the matrix is a polymer blend of a polyolefin and at least one thermoplastic polymer, wherein the mass fraction of the at least one thermoplastic polymer is 5-50% of the polymer blend, wherein the melting temperature of the at least one thermoplastic polymer is 20-70°C, preferably about 30°C, higher than the processing temperature of the polyolefin and / or the glass transition temperature is 40°C lower than the processing temperature of the polyolefin. Due to the strain hardening effect which occurs during processing as a result of the long-chain branching, the mechanical properties are further improved in accordance with these features, wherein the melt flow rate is still sufficient overall to meet the advantageous processing conditions.

[0009] It is proposed in this regard that the at least one thermoplastic polymer is a thermoplastic polycondensate. Preferably, the polycondensate can be a polyamide and / or a thermoplastic polyester. Particularly preferred polycondensates can be polyamide 6, polycarbonate, polyethylene terephthalate and / or polybutylene terephthalate.

[0010] The application also relates to a method for producing a wood-plastic composite according to the application by means of a two-stage screw extrusion process. Here, in a first step, the matrix melt, the wood fiber and the preferably maleic anhydride-based adhesion promoter are first mixed to form a composite melt. Then, in a second step, the composite melt is homogenized and extruded at a melt temperature of 170°C to 200°C and a mass flow of 5 to 15 kg / h, wherein the aid is introduced into the composite melt by means of a gas dispensing device upstream of the extruder mixing zone. The steps of producing the composite melt and introducing the aid can also be carried out in one process step. The extruder mixing zone is the extruder section which is assigned to any mixing components of the extruder screw. Thus, the aid is introduced into the melt in the extruder section which is located upstream of the mixing components in the conveying direction with reference to the longitudinal axis.

[0011] The wood-plastic composite according to the application is suitable as a material for structural components for transport pallets, the dimensions and design of which can comply with the Europool standard. In order to produce a transport pallet, the respective structural components made of the wood-plastic composite according to the application are at least partially nailed together, in particular using compressed air or a compression head.

[0012] Method for carrying out the application

[0013] Example 1:

[0014] The wood-plastic composite according to the application comprises a long-chain branched polypropylene (WB 140 HMS) in a mass fraction of 67% as a matrix, wood fiber (Lignocel C120) in a mass fraction of 30% and an adhesion promoter (Scona TPPP 8112) in a mass fraction of 3%.

[0015] For example, for the production of a wood-plastic composite, a single-screw extruder (diameter 50 mm) is used, which is equipped with a core progressive screw with an additional mixing element. The melt is loaded with the auxiliary gas carbon dioxide by means of a gas dispensing station, wherein the auxiliary gas is introduced into the melt before the mixing element with reference to the conveying direction. The mass temperature along the screw is set in the range from 175 °C to 195 °C, and the mass throughput or mass flow is approximately 10 kg / h. The extrudate is extruded through a profile nozzle and then cooled and stripped.

[0016] The composite density of the wood-plastic composite is 0.06 g / cm 3 At room temperature and a test speed of 1 mm / s, the modulus of elasticity is determined to be 800 MPa by means of the ISO 178 flexural test. The obtained flexural strength is 16 MPa.

[0017] Example 2:

[0018] The wood-plastic composite according to the application comprises a polymer blend in a mass fraction of 67% as a matrix, wood fiber (Lignocel C120) in a mass fraction of 30% and an adhesion promoter (Scona TPPE5002GALL) in a mass fraction of 3%. The polymer blend itself comprises low-density polyethylene (PE-LD recyclate) in a mass fraction of 70% of the polymer blend and polyamide 6 in a mass fraction of 30% of the polymer blend. The melting temperature of the polyamide 6 is 215 °C.

[0019] The production can be carried out analogously to Example 1. Thus, the melting temperature of the polyamide 6 used is 20 °C to 40 °C higher than the processing temperature, which is in the range from 175 °C to 195 °C.

[0020] The composite density of the wood-plastic composite is 0.08 g / cm 3 At room temperature and a test speed of 1 mm / s, the modulus of elasticity is determined to be 620 MPa by means of the ISO 178 flexural test. The obtained flexural strength is 7 MPa.

Claims

1. A wood-plastic composite material for interlocking structural members of a transport pallet, comprising a matrix foamed with additives, wood flour fibers, and an adhesion promoter, characterized in that, The matrix containing long-chain branched polyolefins accounts for 30-95% of the mass of the wood-plastic composite, wood flour fiber accounts for 5-50% of the mass, and the admixture accounts for up to 10% of the mass. The composite material density is less than 0.3 g / cm³. 3 The long-chain branched polyolefin refers to a polyolefin in which at least 10% of the side chains have a chain length of at least 6 carbon atoms.

2. The wood-plastic composite material according to claim 1, characterized in that, Long-chain branched polyolefins are polyethylene or polypropylene.

3. The wood-plastic composite material according to claim 1, characterized in that, The elastic modulus is 500 to 1000 MPa.

4. The wood-plastic composite material according to claim 1 or 2, characterized in that, The mass fraction of wood flour fiber is 20-40%, and the mass fraction of the admixture is 1-5%.

5. The wood-plastic composite material according to claim 1, characterized in that, The matrix is ​​a polymer blend of a polyolefin and at least one thermoplastic polymer, wherein the at least one thermoplastic polymer accounts for 5-50% of the polymer blend by mass, and wherein the melting temperature of the at least one thermoplastic polymer is 20-70°C higher than the processing temperature of the polyolefin, and / or the glass transition temperature is 40°C lower than the processing temperature of the polyolefin.

6. The wood-plastic composite material according to claim 5, characterized in that, At least one thermoplastic polymer is a thermoplastic condensation polymer.

7. The wood-plastic composite material according to claim 6, characterized in that, The condensation polymer is polyamide and / or thermoplastic polyester.

8. The wood-plastic composite material according to claim 6 or 7, characterized in that, The condensation polymer is polyamide 6, polycarbonate, polyethylene terephthalate and / or polybutylene terephthalate.

9. A method for manufacturing the wood-plastic composite material according to any one of the preceding claims by a two-stage screw extrusion process, characterized in that, In the first step, the matrix melt, wood flour fiber, and additives are first mixed into a composite melt. Then, in the second step, the composite melt is homogenized and extruded at a melt temperature of 170°C to 200°C and a mass flow rate of 5 to 15 kg / h. Before the mixing zone of the extruder, additives are fed into the composite melt via a gas delivery device. The long-chain branched polyolefin refers to a polyolefin in which at least 10% of the side chains have a chain length of at least 6 carbon atoms.

10. A transport pallet having structural members made of a wood-plastic composite material according to any one of claims 1 to 8, characterized in that, The structural members are at least partially nailed together.