GB2069401A

GB2069401A - A method of producing shaped bodies

Info

Publication number: GB2069401A
Application number: GB8103271A
Authority: GB
Original assignee: Chemiefaser Lenzing AG
Current assignee: Lenzing AG
Priority date: 1980-02-14
Filing date: 1981-02-03
Publication date: 1981-08-26
Also published as: GB2069401B; DE3102587A1; IT1170700B; IT8147759A0; FR2475979A1

Abstract

A method of producing shaped bodies of plastics bonded lignocellulose components includes the steps of suspending the lignocellulose components and the thermoplastics in an aqueous medium, dewatering the suspension, shaping the mixture and drying the shaped bodies. Polyolefin particles are used as thermoplastics for the formation of the suspension and the shaped bodies formed are subjected to a thermal aftertreatment in which the polyolefin particles melt together into a matrix that increases the strength of the shaped bodies. The drying and thermal aftertreatment may be effected in one step or else in two steps.

Description

SPECIFICATION Improvements in or relating to a method of producing shaped bodies The invention relates to a method of producing shaped bodies, in particular insulation boards, of plastics bonded lignocellulose components by suspending the lignocellulose components and the thermoplastic plastics material in an aqueous medium, dewatering the suspension, shaping the mixture and drying the shaped bodies.

On the building sector various materials are known as heat-insulating structual elements, such as e.g. magnesite bonded wood wool, porous wood fibre plates, foamed plastics of polystyrene, polyurethane or polyolefins, mineral wool or cork, which are mostly used in the form of boards with a single layer, but also as multi-layer composite material.

For achieving a good heat insulation, light structural elements with a high content of air and a fine pore structure are desired. Nevertheless, these boards have to have a sufficient strength in order to ensure their utilisation as self-supporting or tread-proof structural elements. It appears advantageous that such a structural element be workable, such as sawable, cuttable, nailable and screwable, by simple and conventional tools. When using them for external construction, no dissolution, no substantial reduction in strength and no substantial swelling with respect to the thickness of the boards must occur under humid and wet conditions. Furthermore, a water absorption as low as possible is desired for preserving the heat-insulating properties.

Lignocellulose-containing structural elements are known, as described in Austrian patents Nos.

343,881 and 334,068, as e.g. wood-chip boards which, by dry or semi-humid methods with an admixture of 5 to 15% by weight of binders, such as phenol resins or urea resins, are moulded and compressed in presses, and cured in a subsequent heat process over several hours. Due to the moulding pressures applied, which are in a range of 50 bar, densities of the shaped bodies in a range of about 0.7 to 1.0 g/cm3 will result, the boards thus containing only slight volume portions of air and being only little suited for heat insulation.

Contrary to wood-chip boards, with which the strength is achieved by admixing binders, the textural strength of wood-fibre boards, which are dewatered and shaped in a wet process from an aqueous suspension of processed lignocellulose-containing substances similar to the manufacture of paper and, if desired, are aftertreated in a subseqently arranged steam press, basically results from the physical and intermolecular binding forces of the wood fibres as well as the contents of wood. There are also known methods in which binders are added, in small amounts though, in order to obtain higher strengths. Furthermore a method is known from Austrian patent No. 338,499 of adding plastics monomers, in particular acrylates, to the wood fibres and completely polymerising the same by energyrich p-radiation, a certain gain in strength thus being feasible.

Departing from the known prior art, according to which it is possible to produce of lignocellulosecontaining substances either dense and strong boards with a low heat insulating capacity, or porous light boards with a high heat insulating capacity and a low strength, the present invention has as its object to provide a method by which it is possible to produce articles that combine the qualities of a low density and thus a high heat insulating capacity with high strengths.

The invention is based on the knowledge that, when using meltable polymer thermoplastics as binders for the lignocellulose components, a skeleton or matrix can form which causes a high increase in the strength and stiffness of the shaped bodies produced.

The invention, with a method of the initially defined kind, thus consists in using polyolefin particles as thermoplastics for the formation of a suspension and subjecting the shaped bodies formed to a thermal aftertreatment, whereing the polyolefin particles melt together to form a matrix that increases the strength of the shaped bodies.

In this manner shaped bodies are formed in which the plastics binder is comprised of polyolefins, in particular polyethylene and polypropylene, and is present in the form of a solidified melt as a matrix or skeleton penetrating the lignocellulose components.

As lignocellulose components cellulose (pulp), ground bark waste, waste paper, cellulose waste, such as rejects, saw dust, wood pulp, and mixtures thereof may be used. The content of solids in the aqueous suspension formed of the lignocellulose components and the thermoplastics is to be in a range of 0.1 to 20% by weight, in particular of between 0.5 and 5% by weight.

According to a preferred embodiment of the invention, the polyolefin particles are used in the form of cut, ground or fibrilated substances, preferably in the form of comminuted film threads, fibres or flaked fibrides. Advantageously, the polyolefin particles are used in an amount of 10 to 80% by weight, preferably 20 to 60% by weight, based on the total content of solids in the shaped bodies. If the plastics content were chosen to be smaller than 10% by weight, practically no intensifying properties would be achieved with the heat treatment, since the plastics material can no longer form a coherent skeleton having a supporting function. Higher portions of plastics material than those mentioned, only negligibly improve the strength qualities, but cause an undersiredly dense structure, thus reducing the heatinsulating properties.

Suitably, flame-inhibiting additives, hydrophobicity-inducing additivies, or such increasing the rotting resistance are added. The shaped bodies produced according to the invention have a considerably lower density than the conventional ones; i.e. a density of less than 0.5 g/cm3, preferably of between 0.2 and 0.25 g/cm3. According to a preferred embodiment, the dewatering and moulding take place without applying a moulding pressure, under normal pressure or negative pressure.

An advantage of the wet method according to the invention consists in that the suspension can be brought into a very homogenous form.

The method of the invention is carried out in detail in a manner that, after the formation of the aqueous suspension of the lignocellulose particles and the polyolefin particles, preferably polyethylene and polypropylene particles, the suspension is placed onto a dewatering screen or wire, as is common in the paper and pulp industry, and dewatered afterwards.

The dewatering possibly is to be carried out without applying high moulding pressures by using gravity as well as by applying a vacuum. Thereby the prerequisites of a low density in the end product are created.

The moist pulp webs with such a treatment have a content of dry substance of between 30 and 50% by weight, strengths of 5 to 100 mm, preferably 10 to 50 mm, and plane surfaces.

The following method steps comprise shaping -- with boards size-cutting-, subsequent drying, and a thermal aftertreatment for melting together the plastics particles.

These method steps can be carried out continuously in line or discontinuously. When producing insulation boards, the preshaped moist pulp web at first may be cut into sizes. Drying and thermal aftertreatment take place in two steps, the shaped bodies being subjected to the influence of hot air, hot steam, infrared radiation or short-wave radiation, at temperatures of between 95 and 1 200C in the first step, and at temperatures of above the crystallite melting temperature of the polyolefin particles used in the second step. According to another embodiment drying and thermal aftertreatment are effected in one step, the shaped bodies being subjected to the influence of hot air or hot steam at temperatures of between 950 and 3000 C, preferably of between 1 60 and 2400 C.

The pre-shaped moist pulp web in this case is continuously heated, preferably by overheated steam, so that the melting process of the plastics portions is initiated already simultaneously with the drying process. Size-cutting in this case follows upon the thermal treatment. This mode of operation has the advantage that the melting process with the skeleton formation is effected already during considerably shorter dwell times. The size-cut product may still contain up to 50% by weight of moisture, and afterwards may be subjected to drying by air until the moisture equilibrium has been reached.

The invention will now be explained in more detail by way of the following examples: Example 1 For the production of insulation boards having a thickness of 10 mm and a plastics content of 20% by weight, beech-cellulose and polyethylene fibrides were transformed into an aqueous suspension having a solid content of 1.2% by weight. The suspension was dewatered on a sheet forming screen by the influence of gravity and by applying a vacuum, so as to form boards having a solid content of about 30% by weight. The wet boards, delimited by two parallel screens according to a moulding pressure of 0.002 bar, were put into a vacuum drying chamber and dried at a surrounding temperature of 1 000C during 120 minutes.Thereafter, the boards were subjected to a 25-minute heat treatment at 1 8O0C in a second vacuum drying chamber, so that the temperature in the centre of the boards had risen to 1620C.

The finished boards were examined for their thicknesses, densities, flexural-tensile strengths, as well as thickness swelling after 2 hours of storage in water, and their relative water absorption, the mean values being indicated in Table 1.

TABLE 1:

Polyethylene content, % by weight 20 Cellulose content, % by weight 80 Thickness, mm 10 Density, g/cm3 0.21 Flexural-tensile strength, N/mm2 3.2 Thickness swelling, % 2.2 Water absorption, % by weight 42.2 As can be seen from Table 1, the boards produced according to the invention exhibit very good properties with regard to strength, thickness swelling and water absorption. In addition, they are very easy to work on, e.g. with sawing they show a straight and smooth cut.

EXAMPLE 2 For the production of insulation boards having a thickness of 1 8 mm and a plastics content of 1 1% by weight, cellulose waste, socalled rejects, and polyethylene fibrides were transformed into an aqueous suspension with a solid content of 2.5% by weight. The suspension was dewatered on a sheet forming screen, as described in Example 1. The wet boards were put into a vacuum drying chamber, as described in Example 1, and dried at a temperature of 1400C for 420 minutes, and the plastics portion was melted together.

The finished boards were examined for their thicknesses, densities, flexural-tensile strengths, as well as thickness swelling after 2 hours of storage in water, and their relative water absorption, the mean values being indicated in Table 2.

TABLE 2:

Polyethylene content, % by weight 11 Content of rejects, % by weight 89 Thickness, mm 18 Density, g/cm3 0.23 Flexural-tensile strength, N/mm2 1.8 Thickness swelling, % 5.6 Water absorption, % by weight 191 As can be seen from Table 2, the boards produced according to the invention also exhibit very good properties with regard to strength, thickness swelling and water absorption.

EXAMPLE 3 For the production of insulation boards having a thickness of 9 mm and a plastics content of 40% by weight, cellulose waste, socalled rejects, and polyethylene fibrides were transformed into an aqueous suspension with a solid content of 1.2% by weight. The suspension was dewatered on a sheet forming screen, as described in Example 1. The wet boards, delimited by two parallel screens according to a moulding pressure of 0.007 bar, were put into a chamber, overheated steam streaming therethrough perpendicularly to the board surfaces. A steam amount of 217 kg/h.m2 and a steam temperature of 2200C were chosen so that the temperature in the board centre had risen to 2180C after a treatment time of 32 minutes.

Material testings were performed at the finished boards, their mean values being indicated in Table 3.

TABLE 3:

I Polyethylene content, % by weight 40 Content of rejects, % by weight 60 Thickness, mm 9 Density, g/cm3 0.24 Flexural-tensile strength, N/mm2 2.2 Thickness swelling, % 4.9 Water absorption, % by weight 27.6 EXAMPLE4 For the production of insulation boards having a thickness of 10 mm and a plastics content of 20%, cellulose waste, socalled rejects, and sawdust, at a weight ratio of 3:1, together with polyethylene fibrides, were transformed into an aqueous suspension with a solid content of 1.2% by weight.The suspension was dewatered on a sheet forming screen, as described in Example 1. The wet boards were treated with hot steam under the same conditions as described in Example 3, so that, after a period of treatment of 68 minutes, the temperature in the centre of the boards had risen to 21 60C.

Measurements were carried out at the finished boards as described in Example 1 , the mean values being indicated in Table 4.

TABLE 4:

Content of rejects9 % by weight 60 Content of sawdustt % by weight 20 Content of polyethylene fibrides, % by weight 20 Thickness, mm 10 Density, g/cm3 0.23 Flexural-tensile strength, N/mm2 1.6 Thickness swelling1 % 7.7 Water absorption, % by weight 29.3 EXAMPLE 5 For the production of insulation boards having a thickness of 10 mm and a plastics content of 30% by weight, cellulose waste, socalled rejects, and waste paper at a ratio of 4:3, together with polyethylene fibrides and ground polyethylene waste sheets at a weight ratio of 1::2, were transformed into an aqueous suspension with a solid content of 1.2% by weight. The suspension was dewatered on a sheet forming screen, as described in Example 1. The wet boards, delimited by two parallel screens according to a moulding pressure of 0.001 bar, were put into a drying chamber with recycle of air and dried at an air temperature of 1 600C during 30 minutes, and the plastics portion was melted together.

Measurements were carried out at the finished boards as described in Example 1, the mean values being indicated in Table 5.

TABLE 5:

Content of rejects, % by weight 40 Content of waste paper, % by weight 30 Content of polyethylene fibrides, % by weight 10 Content of polyethylene waste, % by weight 20 Thickness, mm 10 Density, g/cm3 0.25 Flexural-tensile strength, N/mm2 L 1.8 Thickness swelling, % 4.0 Water absorption, % by weight 24.3 EXAMPLE 6 For the production of insulation boards having a thickness of 1 5 mm and a plastics content of 30% by weight, cellulose waste, socalled rejects, and ground bark waste at a weight ratio of 4: :3, together with polyethylene fibrides and monoaxially drawn fibrilated and cut polyethylene sheets at a weight ratio of 1:2, were transformed into an aqueous suspension with a solid content of 1.8% by weight. The suspension was dewatered on a sheet forming screen, as described in Example 1. The wet boards, delimited by two parallel screens according to a moulding pressure of 0.007 bar, were put into a chamber, hot air streaming therethrough perpendicularly to the surfaces of the boards. Therein, an air amount of 72 Nm3/h.m2 and an air temperature of 2000C were adjusted so that the temperature had risen to 1 840C after a period of treatment of 52 minutes.

Measurements were carried out at the finished boards as described in Example 1, the mean values being indicated in table 6.

TABLE 6:

Content of rejects, % by weight 40 Bark content, % by weight 30 Content of polyethylene fibrides, % by weight 10 Content of polyethylene fibrils, % by weight 20 Thickness, mm 15 Density, g/cm3 0.25 Flexural-tensile strength, M/mm2 1.5 Thickness swelling, % 5.1 Water absorption, % by weight 33.4 EXAMPLE 7 For the production of insulation boards having a thickness of 10 mm and a plastics content of 30% by weight, beech cellulose and wood pulp at a weight ratio of 3::4, together with poiyethylene fibrides and ground polypropylene fibres at a weight ratio of 1:2, were transformed into an aqueous suspension with a solid content of 1.2% by weight. The suspension was dewatered on a sheet forming screen, as described in Example 1. The wet boards were dried in a vacuum drying chamber as described in Example 1, and were subjected to a 45-minute heat treatment at 2000C in a second vacuum drying chamber so that the temperature in the centre of the boards had risen to 1890C.

Measurements were carried out at the finished boards as described in Example 1 , the mean values being indicated in Table 7.

TABLE 7:

Cellulose content, % by weight 30 Content of wood pulp, % by weight 40 Content of polyethylene fibrides, % by weight 10 Content of polypropylene fibres, % by weight 20 Thickness, mm 10 Density, g/cm3 0.22 Flexural-tensile strength, N/mm2 2.8 Thickness swelling, % 3.5 Water absorption, % by weight 30.8 EXAMPLE 8 For the production of insulation boards having a thickness of 10 mm and a plastics content of 40% by weight, cellulose waste, socalled rejects, together with polyethylene fibrides and an agglomerate prepared of polyethylene and polypropylene mixed-wastes by mechanical and thermal compression, at a weight ratio of 1:3, were transformed into an aqueous suspension with a solid content of 1.2% by weight. The suspension was dewatered on a sheet forming screen, as described in Example 1. The wet boards were dried in a vacuum drying chamber as described in Example 1, and were subjected to a 48minute heat treatment at 2000C in a second vacuum drying chamber so that the temperature in the centre of the boards had risen to 1 800 C.

Measurements were carried out at the finished boards as described in Example 1, the mean values being indicated in Table 8.

TABLE 8:

i Content of rejects, % by weight 60 Content of polyethylene fibrides, % by weight 10 Content of polyethylene-polypropylene agglomerate, % by weight 30 Thickness, mm 10 Density, g/cm3 0.25 Flexural-tensile strength, N/mm2 1.7 Thickness swelling, % 5.2 Water absorption, % by weight 48.9

Claims

1. A method of producing shaped bodies, in particular insulation boards, of plastics bonded lignocellulose components, which method comprises suspending the lignocellulose components and the thermoplastic plastics in an aqueous medium, dewatering the suspension, shaping the mixture and drying the shaped bodies, and wherein polyolefin particles are used as thermoplastics material for the formation of said suspension and the shaped bodies formed are subjected to a thermal aftertreatment in which said polyolefin particles melt together into a matrix that increases the strength of the shaped bodies.

2. A method according to claim 1, wherein dewatering and shaping are effected without applying a moulding pressure, at normal pressure or negative pressure.

3. A method according to claim 1, wherein the polyolefin particles are used in the form of cut, ground or fibrilated substances, preferably in the form of comminuted film threads, fibres or flaked fibrides.

4. A method according to claims 1 to 3, wherein the polyolefin particles are used in an amount of 10 to 80% by weight, preferably 20 to 60% by weight, based on the total solid content of the shaped bodies.

5. A method according to any one of claims 1 to 4, wherein flame-inhibiting additives, hydrophobicity-inducing additives, or additives increasing the rotting resistance, are added to the suspension.

6. A method according to any one of claims 1 to 5, wherein drying and thermal aftertreatment are effected in one step, the shaped bodies being subjected to the influence of hot air or hot steam at temperatures of between 95 and 3000 C, preferably 1 60 and 2400c.

7. A method according to any one of claims 1 to 5, wherein drying and thermal aftertreatment are effected in two steps, the shaped bodies being subjected to the influence of hot air, hot steam, infrared radiation or shortwave radiation, at temperatures of between 95 and 12000 in the first step, and at a temperature of above the crystallite melting temperature of the polyolefin particles used in the second step.

8. Shaped bodies produced according to any one of claims 1 to 7, having a content of lignocellulose components and plastics as binders, wherein said plastics binder comprises polyolefins, in particular polyethylene and polypropylene, and is present in the form of a solidified melt as a matix or skeleton penetrating the lignocellulose components.

9. Shaped bodies according to claim 8, wherein their densities are below 0.5 g/cm3, preferably 0.20 to 0.25 g/cm3.

10. A method substantially as hereinbefore described with reference to the accompanying examples.

11. Shaped bodies substantially as hereinbefore described with reference to the accompanying examples.