GB1599215A

GB1599215A - Process for making a building board

Info

Publication number: GB1599215A
Application number: GB4117/78A
Authority: GB
Original assignee: London & Malaga Board Co Ltd
Current assignee: London & Malaga Board Co Ltd
Priority date: 1978-05-26
Filing date: 1978-05-26
Publication date: 1981-09-30
Also published as: PH15740A

Description

(54) PROCESS FOR MAKING A BUILDING BOARD (71) We, LONDON & MALAGA BOARD COMPANY LIMITED, a British Company of 200 Brent Street, Hendon, London NW4 1BH, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a process for the production of a building board from coconut husks.

Substantial quantities of coconut husks are available as by-products of the processing of coconuts; however, industrial use of this by-product material is extremely limited and large quantities are, as a result, either wasted or used unprofitably. The husks include fibres of varying length and thickness and also a powdery substance. Although some attempts are made to recover the longer fibres from the discarded coconut husks, for the manufacture of yarn, rope, brooms. mats and mattress stuffing, the majority of coconut husk material produced is unused and is discarded as waste.

We have now discovered a process for producing dimensionally controlled building boards from coconut husks, the resulting material being useful for a variety of constructional and insulation purposes and being comparable in strength with, or stronger than, conventional chipboard. It can also be varied to compare with conventional wood-based hardboard insulation board, or a cork-like material (when the powdery constituent is used without the. fibres).

Thus, the present invention provides a process for producing a building board from coconut husk material in which all or part of said coconut husk material is mixed with water without any additional binder, and without any intervening de-watering action the soaked coconut husk material is subjected to pressure and to a temperature greater than 100"C to form the husk material into a desired shape.

The process of the present invention has the substantial advantage that it requires only hot pressing of the husks admixed with water and that it is not necessary for an additional binder to be incorporated.

The moisture content of coconut husks from ripe nuts will vary somewhat, depending upon their origin and the conditions under which they are stored. However, in general, the equilibrium moisture content of discarded coconut husks will vary from 8 to 17 per cent by weight with a value of 12.8 + 0.9 per cent bemg common. It is normally best that the coconut husks should be comminuted or reduced prior to use. The comminution may be achieved using a high speed mill fitted with a perforated screen; a very open screen may be used to produce comparatively coarse comminution and low density insulation board, whilst a finer screen may be used for shorter fibres and a medium density, closely bonded material suitable for constructional use.

For use in the process of the present invention, it is preferable that the water content should be greater than 20 per cent by weight (including the moisture already in the coconut husks) this being ensured, if necessary, by the addition of water. A water content of less than 20% will, however. give a satisfactory low density board. Preferably the water content at pressing may be from 30 to 75 per cent by weight, and more preferably from 30 to 50 per cent by weight. To achieve a water content higher than that of the coconut husks available the husks may simply be thoroughly mixed with water or, better still, allowed to stand in water until absorption is complete (generally about 24 hours); alternatively, they may be steamed for a long enough period to take up the required water.

After adjusting the water content of the reduced coconut husks (if necessary), they are subjected to pressure, at a temperature greater than 100"C. The temperature is preferably from 1300 to 165"C an; the pressure is preferably at least 200 p.s.i.g., more preferably from 250 to 2000 p.s.i.g. and most preferably from 450 to 650 p.s.i.g. Provided, however, that suitable equipment is employed, pressures substantially higher than 2000 p.s.i.g. may be used with success and, indeed, more firmly bonded boards are often obtained at higher pressures.Temperatures above 165"C tend to char the surface of the board and, accordingly, if such higher temperatures are to be used, the time for which the board is maintained at elevated temperature should be reduced, e.g. by employing higher pressure.

The period for which the moistened and reduced coconut husks are subjected to pressure will depend upon the origin and nature of the husks, the temperature, the desired moisture content before pressing and water resistance properties. Of course, if pressing moisture contents towards the upper region of the preferred range are employed, in order to reduce the water content of the final product to an acceptable level, it will be necessary to use a higher temperature and/or a longer time.

Although we do not wish to be limited by any theory, it is believed that the heat-pressure treatment in the process of the invention causes curing of water-soluble resins naturally present in the coconut husks to form a cured thermosetting resin; since we have found that coconut husks having too low a moisture content do not produce well-bonded fibre boards, it is believed that the water may participate in the curing reaction.

As mentioned above, the reduced coconut husks comprise fibres, which may be up to 10 mm long, mixed with a brown powder (which is believed to be the source of resins which act as binding agents in the process of the present invention). In connection with board manufacture we have found that, other conditions being equal, the lower the pressure employed, the lower the density of the board produced.

If the fibrous content of the husks is separated and discarded, the residual brown powder may be subjected to heat and pressure, at the moisture contents stipulated for this invention to produce an insulating material resembling cork.

It is an advantage of the process of the present invention that it may be operated continuously or semi-continuously. The accompanying drawing shows diagrammatically a side sectional view of one form of apparatus suitable for carrying out the process of the invention in an essentially continuous manner.

Coconut husks are reduced to the desired size in a high speed mill (not shown) and then, if necessary, conditioned to a moisture content greater than 20% by weight. The reduced, moistened husks are then fed along a feed passage 1 to be metered onto a continuously circulating endless screen 2. While on the screen 2 the moist husks may pass over an optional suction box 3 to withdraw excess moisture, and then the husks material passes between upper and lower spaced pressing/metering rolls 4, 5 where the thickness of the matrix of fibres on the screen 2 is reduced to a uniform value. Thus from the pressing/metering rolls 4, 5 the matrix passes rightwardly as a relatively loosely compressed mattress of uniform thickness as far as a knife 6 which cuts off a given length of the matrix to form a sheet to be pressed in a multi-daylight platen press 7.

Each sheet cut off by the knife 6 is placed on a respective support screen 8 which is conveyed to the press 7. Once all the daylights of press 7 are occupied the press is closed and the various support screens and the sheets thereon are pressed at a temperature sufficient to ensure that, after a not too long dwell time in the press, the sheets taken from the press will be dimensionally stable.

From the press 7, the sheets are removed and then advanced along the direction of arrow 9 to any subsequent finishing stations for treatment steps such as further heat treatment or humidity condltioning, if these treatments are necessary.

The press 7 is heated by the application of steam to ensure a pressing temperature of at least 100"C.

The use of the suction box 3 will not normally be required unless very high moisture contents are used. Generally, as the use of a water content high up in the range 70% to 80% prior to arrival of the husks will require subsequent removal of the moisture either before, during or after pressing and since it has been found that a quite acceptable board will result without the use of such high moisture contents, it is envisaged that the actual moisture content after soaking or other moistening will be low enough to allow the box 3 to be dispensed with.

The length of the finished board will, of course, depend on the frequency of operation of the knife 6 and will be subject to a maximum value dictated by the dimensions of the press 7. The density of the board will depend upon both the pressure exerted by the press 7 and the gap between rolls 4 and 5. The thickness of the finished boards will depend upon the pressure in the press 7.

The process of the invention, used to produce a board of hardboard-like appearance but exhibiting the superior mechanical properties expected of chipboard will now be further illustrated with reference to the following Examples. In all cases, the coconut husks originated in Central America and had an equilibrium moisture content of about 13 per cent. In Examples 1 to 4 pressure was applied by an hydraulic ram Apex bench press with 6 x 6 inch electrically heated platens.

Example 1 40 grams of reduced coconut husks (13 per cent moisture content upon intake) were weighed into a screw-topped bottle. 10 grams of tap water were then slowly added with shaking, after which the bottle was capped and placed on shaking rolls. Initially, fine dust in the coconut husks attracted the water and caused caking on the sides of the bottle and formation of balls from the dust. These balls were broken up and the mix homogenised by mixing with a spatula and then rolling for a further 48 hours. The moistened mass thus obtained has a moisture content of 30.4 per cent by weight.

The moist mass was spread to a thickness of 0.25 inch into a thin collapsible aluminium foil box laid on a nickel-plated pressing plate to form a carpet of length 4 inch and width 3.5 inch. A second similar pressing plate was placed on top of the foil box and the carpet was then placed between the platens and the press, which had been preheated to 1200C. Two tons pressure were applied on the ram and then the moulding was vented to allow steam to escape. During this application of pressure, the temperature had been slowly increased to 1600C. Maintaining the temperature of the platens at 1600C a pressure of 4 tons (603 p.s.i.) was then applied to the platens for 20 minutes. The compressed sample was then removed at 1600C.

The pressed fibre board was approximately 0.05 inch thick and had vein markings on both surfaces. Although the board was dry and non-cohesive around its periphery, it had a dark coloured cohesive resin patch in the centre.

Example 2 Reduced coconut husks were adjusted to a moisture content of 30.4 per cent by weight, as described in Example 1. A carpet of thickness 1 inch, length 4.5 inch and width 3 inch was placed in the press described in Example 1, whose platens were maintained at 1600C. A pressure of 2 tons was applied and then the pressing was vented, to allow steam to escape.

A pressure of 3 tons (500 p.s.i.) was then applied to the sample for 15 minutes at 1600C. The pressed fibre board was removed hot. The board had a thickness of approximately 0.05 inch. Around the edges of the board, it retained the original colour of coconut husks and was partially non-cohesive. A dark-coloured glazed resin patch extended essentially along the entire length but not entirely across the width; there was substantially better bonding in this patch.

Example 3 Reduced coconut husks were adjusted to a moisture content of 30.4 per cent by weight as described in Example 1. These were then formed into a carpet of thickness 2 inch, length 5 inch, and width 2.5 inch, and treated as described in Example 2. The board obtained had a thickness of 0.10 inch and was otherwise similar to the product of Example 2.

Example 4 35 grams of reduced coconut husks (13 per cent moisture) and 77 grams of water were mixed in the manner described in Example 1, to produce a moistened mass having a moisture content of about 73 per cent by weight. This was formed into a carpet of thickness 2 inch, length 5 inch, and width 2.5 inch. This carpet was then pressed as described in Example 2. Except at the extreme edges, the board produced had a dark-coloured resinous glazing on both faces and the binding of the coconut fibre was superior to that of Examples 1 to 3. The rigidity of the board was good and the board had a thickness of approximately 0.1 inch.

In the following Examples, a Finney hydraulic press with high pressure steam heated platens and a 10 x 8 x 5 inch mould bolster having one plain force plate and one vented force plate was used. The vented force plate consisted of an aluminium plate fitting the bolster, drilled over its entire face with approxmately 0.10 diameter holes spaced at 0.5 inch centres. A second, smaller steel plate, channelled with grooves, was placed on the perforated aluminium plate so that the grooves lined up with the holes.

Example 5 200 grams of reduced coconut husks (13 per cent moisture) were supported in a mesh cage above water in an industrial pressure cooker. The mass was steamed for 35 minutes, until 60 grams of water had been taken up. Some dust settled from the coconut husks through the mesh cage. The moisture content of the mass after steaming was approximately 35 per cent by weight. The mould bolster described above was preheated empty using a steam pressure on the platens of 120 p.s.i.g. A carpet of the steamed coconut husks was spread evenly in the mould, the vented force late was placed on top, and the mould was replaced in the press. A pressure of 10 tons (280 p.s.i. on the sample) was then applied, whilst the mould was heated at 160 - 1700C for 20 minutes.At the end of this time the sample was cooled by water cooling the platens for 45 minutes, whilst maintaining the sample under 10 tons pressure, until cold.

The board produced was approximately 0.2 inch thick and had a weight of 183 grams and a density approximately 43.5 Ibs/cu ft.

The colour of the board was that of coconut husks on the face adjacent the vented force plate and was darker on the other face with a much darker patch near the centre. The board had comparatively poor cohesion and a low breaking strength.

Example 6 250 grams of reduced coconut husks (13 per cent moisture) were mixed with 550 grams of water to produce a mix having a water content of approximately 73 per cent by weight.

The mould of the Finney hydraulic press was preheated for 45 minutes under a steam pressure of 120 p.s.i.g. The mix was spread evenly in the mould and the vented force plate fitted on top. The mix was then pressed under 18 tons (504 p.s.i.) for 20 minutes at 160-164"C. Maintaining the pressure, the mix was then cooled for 45 minutes to room temperature.

The board obtained had a thickness of approximately 0.17 inch. One of the faces of the board, the face adjacent the vented force plate, had an appearance similar to hardboard whilst the other was covered with a black, semi-matt resinous glaze. There was good bonding of the fibre. The rigidity of the board was comparable with that of 0.25 inch hardboard. The weight of the board as removed from the mould was 218 grams and the density was approximately 61 Ibs/cu ft.

Example 7 400 grams of reduced coconut husks (13 per cent moisture) were blended with 600 grams of water to produce a mix having a moisture content of approximately 65 per cent by weight.

Meanwhile the mould of the Finney hydraulic press was preheated in the press for 45 minutes under a steam pressure of 120 p.s.i.g. The mix was spread in the mould with the vented force plate in the bottom of the mould and a polyester cloth separator was placed over the face of the force plate. The mix was then subjected to a pressure of 20 tons (560 p.s.i.) for 15 minutes at a temperature of 160-170"C. The moulded board was cooled in the mould with water for 15 minutes and then left under pressure to cool overnight. The board which had a thickness of about 0.28 inch was very similar in appearance to that of Example 6. The fibre in the board was well consolidated and bound and the board had a high rigidity on ageing. The board as taken from the mould weighed 440 grams and had a density of approximately 77 Ibs/cu ft.

Example 8 400 grams of reduced coconut husks (13 per cent moisture) and 200 grams of water were blended to form a mix having a water content of approximately 42 per cent by weight. This mix was then compressed under the conditions described in Example 7 to produce a board having a thickness at its centre of 0.265-0.314 inch. The weight of the board on removal from the mould was 448 grams and it had a density of approximately 77 Ibs/cu ft. On cutting the board with a band saw it was noted that the board was hard throughout.

Examples 9, 10 and 11 The procedure described in Example 8 was repeated exactly, to produce three boards of very similar appearance and properties to that of Example 8. The boards were each weighed on removal from the mould and then left at ambient temperature and humidity for 17 days after which they were weighed again. The results are shown in the following Table 1.

TABLE 1 Example Weight of Board No.

From Mould After 17 days 9 390 g 369.5 g 10 421 g 367.5 g 11 419 g 367.2 g It will be seen that each sample had lost weight and that the weight of each was reduced below the initial weight of the reduced coconut husks.

The ability of several of the boards to absorb water was determined by cutting 2 x 1 inch samples from the boards, accurately weighing them, steeping them in water and then determining the weight at intervals. The results obtained are shown in Table 2.

TABLE 2 Example Weight of board (grams) after Total water No. uptake (%) 0 hours 1 hour 120 hours 168 hours 5 5.5008 - 9.0642 9.0929 65.3 6 3.8421 - 6.7235 6.7928 76.8 7 12.2414 13.70 15.2211 15.3758 25.6 (~12%) 8 12.0490 - 14.7177 14.8283 23.1 Although all the boards became softer, none broke up in the water.

The densities and bending strengths of boards produced in Examples 7 and 8 were determined and are shown in the following Table 3.

TABLE 3 Example Bending Density No. Strength (MN/m2) (kg/m3) 7 21.6 1000 8 17.7 990 In each case the values of bending strength and density exceeded the minimum required by the relevant British Standard.

WHAT WE CLAIM IS: 1. A process for producing a building board from coconut husk material in which all or part of said coconut husk material is mixed with water without any additional binder, and without any intervening de-watering action the soaked coconut husk material is subjected to pressure and to a temperature greater than 100"C to form the husk material into a desired shape.

2. A process according to claim 1, wherein the water content of the coconut husk material, before heating and pressing is greater than 20% by weight.

3. A process according to claim 2, wherein said water content is from 30 to 75% by weight.

4. A process according to claim 3, wherein said water content is from 30 to 50% by weight.

5. A process according to any preceding claim wherein said husks are allowed to stand in water until absorption of water is complete.

6. A process according to any one of claims 1 to 4, wherein said husks are steamed for a time long enough to ensure the desired starting water content.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

Examples 9, 10 and 11 The procedure described in Example 8 was repeated exactly, to produce three boards of very similar appearance and properties to that of Example 8. The boards were each weighed on removal from the mould and then left at ambient temperature and humidity for 17 days after which they were weighed again. The results are shown in the following Table 1.

TABLE 1 Example Weight of Board No.

From Mould After 17 days

9 390 g 369.5 g

10 421 g 367.5 g

11 419 g 367.2 g It will be seen that each sample had lost weight and that the weight of each was reduced below the initial weight of the reduced coconut husks.

The ability of several of the boards to absorb water was determined by cutting 2 x 1 inch samples from the boards, accurately weighing them, steeping them in water and then determining the weight at intervals. The results obtained are shown in Table 2.

TABLE 2 Example Weight of board (grams) after Total water No. uptake (%) 0 hours 1 hour 120 hours 168 hours

5 5.5008 - 9.0642 9.0929 65.3

6 3.8421 - 6.7235 6.7928 76.8

7 12.2414 13.70 15.2211 15.3758 25.6 (~12%)

8 12.0490 - 14.7177 14.8283 23.1 Although all the boards became softer, none broke up in the water.

The densities and bending strengths of boards produced in Examples 7 and 8 were determined and are shown in the following Table 3.

TABLE 3 Example Bending Density No. Strength (MN/m2) (kg/m3)

7 21.6 1000

8 17.7 990 In each case the values of bending strength and density exceeded the minimum required by the relevant British Standard.

WHAT WE CLAIM IS: 1. A process for producing a building board from coconut husk material in which all or part of said coconut husk material is mixed with water without any additional binder, and without any intervening de-watering action the soaked coconut husk material is subjected to pressure and to a temperature greater than 100"C to form the husk material into a desired shape.
2. A process according to claim 1, wherein the water content of the coconut husk material, before heating and pressing is greater than 20% by weight.
3. A process according to claim 2, wherein said water content is from 30 to 75% by weight.
4. A process according to claim 3, wherein said water content is from 30 to 50% by weight.
5. A process according to any preceding claim wherein said husks are allowed to stand in water until absorption of water is complete.
6. A process according to any one of claims 1 to 4, wherein said husks are steamed for a time long enough to ensure the desired starting water content.
7. A process according to any one of the preceding claims, wherein an additional binder

is added to the husk material before pressing.
8. A process according to any one of the preceding claims, wherein said coconut husk material is comminuted before use.
9. A process according to any one of claims 1 to 7, wherein the fibrous content of the husk material is separated and discarded and the residual brown powder is subjected to heat and pressure.
10. A process according to any one of claims 1 to 8, wherein said husk material is pressed between a platen and a moisture-pervious screen.
11. A process according to any one of claims 1 to 8, wherein said coconut husk material is pressed between two moisture-pervious screens.
12. A process according to claim 11, wherein several screens are stacked in the press and coconut husk material is placed between the adjacent screens of the stack to enable the simultaneous pressing of several sheets of board material.
13. A process according to any one of the preceding claims, wherein said temperature to which the coconut husk material is subjected is from 1300 to 1650C.
14. A process according to any one of the preceding claims, wherein said pressure to which the coconut husk material is subjected is at least 200 lbs/inch2 gauge.
15. A process according to claim 14, wherein said pressure is from 250 to 2,000 Ibs/inch2 gauge.
16. A process according to claim 15, wherein said pressure is from 450 to 650 lbs/inch2 gauge. A
17. A process for producing a building board substantially as hereinbefore described with reference to Examples 1 to 11.
18. A building board produced from coconut husk material by the process of any one of the preceding claims.