WO1999010293A1

WO1999010293A1 - Bonded products and processes for their manufacture

Info

Publication number: WO1999010293A1
Application number: PCT/GB1998/002474
Authority: WO
Inventors: Dennis Jones; Jeremy Tomkinson
Original assignee: Bangor University
Current assignee: Bangor University
Priority date: 1997-08-22
Filing date: 1998-08-24
Publication date: 1999-03-04
Anticipated expiration: 2000-02-22
Also published as: AU8869198A

Abstract

This invention relates to bonded products and processes for their manufacture, more particularly it relates to bonded products or composites formed by compacting particulate material in the presence of a bonding agent, produced in situ, which is a reaction product of cashew nut shell liquid (CNSL), and to processes of forming such composites using a reaction product of CNSL as a bonding agent.

Description

Bonded products and processes for their manufacture. This invention relates to bonded products and processes for their manufacture. The invention relates more particularly to bonded products (or composites) formed by compacting particulate material in the presence of a bonding agent based on cashew nut shell liquid (CNSL), and to processes of forming such composites using a reaction product of CNSL as a bonding agent.

Typical composites formed by compacting particles in the presence of a bonding agent include such products as chemically resistant bricks, grinding wheels, slate composites, coal briquettes, and products made by compressing wood particles.

CNSL is extracted from the mesocarp of the cashew nut obtained from the cashew nut tree, Anacardium Occidentale Linn. The extraction process includes a heating process which results in the chemical modification of one of the major components of the liquid. The material obtained consists of a mixture of components containing a phenolic hydroxyl group and an unsaturated side chain. CNSL thus produced is sometimes referred to as technical CNSL and can vary in composition as a result of many factors e.g. its country of origin. Brazil and India are the main producers.

The use, and treatment, of both natural and technical CNSL has been the subject of considerable investigation and a substantial body of prior art exists in the patent literature dating back to the 1920's. We are aware of the following relating to the use of acids to polymerise natural, or raw, CNSL.

UK-A-481960, (Harvel Corporation) describes the treatment of raw CNSL to thicken or give body thereto. This is done by polymerising raw CNSL with about 15 to 65 of its volume of concentrated sulphuric acid, e.g 100 parts by weight of raw CNSL and a solution of 5.4 parts of concentrated sulphuric acid in about 15 parts of water are emulsified and heated to about 300°F to 375°F for 30 to 45 minutes to produce a body which may vary in appearance from very heavy cold molasses to a ropy sticky mass. Longer reaction times of 8 to 15 hours are used to obtain material with rubberlike properties suitable for compounding with rubber. US-A-2067919, in the name of the same applicants, states that the lower limit using sulphuric acid is one part by volume to 100 parts by volume of CNSL, and the upper limit is about 6 parts by volume of sulphuric acid to 100 parts by volume of CNSL.

UK-A-259959, (Mortimer Thomas Harvey) discloses the treatment of raw CNSL to reduce the iodine number of the oil. This is done by oxidising the oil under acid conditions, e.g one example is given of reacting one part of raw CNSL with one part nitric acid and one part water. The use of sulphuric acid with an oxidising agent such as manganese dioxide is suggested, but no examples of the reaction are given. The products are said to be gums which can be dissolved in solvents such as naptha, to make a coating which dries quickly.

U -A-536800 (Harvel Research Corporation) describes the conversion of CNSL to a dry hard and infusible state for use in frictional elements such as clutch facings. This material is produced by reacting paraformaldehyde or hexamethylene tetramine with polymerised CNSL. The CNSL may be polymerised using sulphuric acid by the method described in UK-A-481960.

UK-A-742286 British Resin Products is directed to an improved method of polymerising CNSL by using a phenolic sulphonic acid devoid of ethylenic unsaturation, by which is meant a phenolic compound containing a sulphonic acid group attached to the aromatic nucleus which does not contain any ethlenically unsaturated hydrocarbon groups attached thereto. It is acknowledged that it has previously been proposed to polymerise CNSL by the action of heat using, as a polymerisation catalyst, either a strong mineral acid or hydrochloric acid, or an alkyl ester such as diethyl sulphate. It is pointed out in UK-A-742286 that the mineral acids have been found to be somewhat deficient because they are only slightly miscible with CNSL, and consequently have produced local reactions resulting in non-homogenous compositions. Attempts to overcome this deficiency were made by using alcohol solutions of sulphuric acid, but this also proved unsatisfactory. The material produced by the use of phenol sulphonic acids is used for the formation of solid, infusible products by further reaction with an agent containing a reactive methylene group.

US-A-2754283 discloses the use of sulphonic acids to polymerise CNSL. In all cases CNSL is mixed with the sulphonic acid so as to form a solution which is then heated until the viscosity has increased at least four-fold. The product from this heating step can then be further reacted with an aldehyde so as to convert it into a substantially infusible resin. There is no disclosure of the addition of sulphonic acids in the presence of water nor of the production of a binder precursor capable of being added to a substrate by spraying.

The use of polymerised CNSL to form composite materials by moulding under pressure a dry moulding composition, comprising a solid CNSL resin polymer, a chemically resistant filler, and an aldehyde or aldehyde yielding substance is disclosed in UK-A-664169 (British Resin Products). The filler is carbon or graphite which may be mixed with one or more of silica flour, quartz, barytes, fused alumina, asbestos, brick dust, pumice, bentonite, kaolin and titanium dioxide. This method requires the prior reaction of CNSL to a polymerised form.

According to a first aspect of the present invention there is provided a process for forming a bonded product in which the particles to be bonded are mixed with CNSL and an acid to form a uniform mixture, and the mixture is then compacted under pressure in a mould.

According to a further aspect of the present invention there is provided a process for forming a bonded product in which the particles to be bonded are mixed with CNSL, water and an acid to form a uniform mixture, and the mixture is then compacted under pressure in a mould.

We have now surprisingly found, and this forms the basis of the present invention, that we can form composite materials by moulding under pressure, using a process in which there is no need to pre-polymerise CNSL to use it to form a binder. The particles to be bonded may simply be mixed with CNSL, which may be natural or technical CNSL, and an acid capable of polymerising CNSL, and the mixture pressed to obtain a product with satisfactory properties.

The method of the invention may be used to produce bonded products comprising 70 to 98%, preferably 80 to 98%, even more preferably 90 to 98% by weight of the bonded particulate material.

Particles which can be used to form the bonded products of the invention include those derived from carbonaceous materials such as coal or coke, mineral materials such as slate, and synthetic and natural materials used as abrasives. The invention is also applicable to the manufacture of pressed products from wood particles.

The addition of water assists in obtaining a satisfactory product. The presence of water, as well as assisting in obtaining uniform mixing, is also believed to assist in the wetting of the particles during polymerisation, thus ensuring good inter particle bonding

The CNSL reaction with an acid is related to the pKa value of the acid and to the concentration of double bonds relative to a fully saturated side chain. CNSL can contain up to three double bonds in the side chain. It is believed these double bonds react with acids to generate reactive carbocationic intermediates which in turn react with further double bonds in adjacent molecules, further increasing the production of carbocatioiis. This propagation spreads quickly through the matrix giving a resilient cross linked polymer which acts as a bonding agent.

In most cases, any acid may be used which achieves a satisfactory bonding. We prefer to use acids with a pKa in the range +3 to -9, and of acids in this range we prefer to use sulphuric acid at a concentration of about 98% although any concentration can be used which causes the CNSL to polymerise with a exothermic reaction. Other acids that can be used include other mineral acids e.g. phosphoric acid, with a pKa of +2, and organic crystalline acids, e.g. p-toluene sulphonic acid, with a pKa of -6. We have found that in the case of wood particles, satisfactory performance is best obtained by using an organic crystalline acid such as p-toluene sulphonic acid, which can be added as a solid so that the acid only becomes effective under particular operating parameters.

The amount of acid (expressed as the acid as such) is preferably at least 0.2 parts by weight per part by weight of CNSL. Good results will be obtained with higher acid to CNSL ratios.

Preferably the amount of water present in the process of the invention (including water from the acid, any moisture in the particulate material to be bound, and, if necessary, added water) does not exceed 30% by weight and is more preferably in the range 0% to 10% by weight.

Using sulphuric acid at a concentration of 97.5%, we prefer to operate so that the ratio of acid to CNSL, by weight, is not less than 0.5 to 1 , preferably a ratio of acid to CNSL of 1 to 1; good results will be obtained up to a ratio of acid to CNSL of 2.5 to 1 by weight. Under these conditions, the water content of the whole mix, if present, should be kept at less than 10%, as we find that as the water content increases above 10%, it is necessary to increase the quantity of acid present to compensate for the dilution of the acid. It will be seen that the quantity of acid used in forming composites to cause the CNSL to polymerise, is very much greater than that used in the prior art for the production of CNSL polymers using acids in so called catalytic amounts.

We have found that small amounts of a compound having an active methylene group such as formaldehyde or a formaldehyde yielding substance, can be beneficial in ensuring effective initial bonding in the matrix, particularly when acids other than sulphuric acid are used. The addition of such materials is also believed to assist in avoiding any problems arising from variation in the composition of the technical CNSL from source to source. Typically the amount of the compound having an active methylene group is 5 to 40%, more preferably 15 to 20%, by weight of the CNSL.

It is usually beneficial to add formaldehyde, or a formaldehyde yielding substance, such as paraformaldehyde or hexamethylenetetramine. We have found, for example, when using sulphuric acid (97.5% concentration), that amounts up to a ratio of about one part by weight of formaldehyde to five parts by weight of CNSL, can be used to give an increased green strength on removal from pressing, although on standing products made without formaldehyde can achieve the same strength. The material with an active methylene group such as formaldehyde is not added so as to form the primary bonds of the polymerised matrix, but so as to provide additional extra cross linking bonding, which assists in stabilising the matrix. In manufacturing slate composites via routes which use as the acid sulphuric acid, as opposed to acids of a lower pKa, we prefer to avoid adding formaldehyde to the mixture as it can cause problems in that when formaldehyde is present we sometimes obtain a proportion of dry granular material which is impossible to incorporate into a pressed product.

The quantity of bonding agent (polymerised CNSL) in the final product, and hence the amount of CNSL added relative to the total content of any particular product, is related to the void volume available between the particles when compaction has taken place, and also to the need to ensure adequate bonding. We have found that in most cases, the use of 2 to 30%>, more preferably 5 to 15% by weight (e.g. about 6% by weight) of bonding agent will give a satisfactory product. Larger amounts can be used but it is desirable from a cost point of view to limit the amount of CNSL used.

Other additives which assist in producing a satisfactory product may be present, such as release agents. We have found that stearates, such as calcium stearate, give good release from the mould with the products of the present invention.

Satisfactory pressures for compacting the products of the invention fall in the range 500 to 1200 psi, and we have found for most products we can operate at a pressure of 1000 psi. The reaction of CNSL with, for example, sulphuric acid is exothermic, and pressing at pressures of the order of a 1000 psi produces a strong composite within seconds. When acids other than sulphuric acid are used we prefer to operate at elevated temperatures.

The time for which the mixture should be held under pressure so as to ensure adequate bonding is easily determined by experiment. We have found, using sulphuric acid, that as little as one second can produce satisfactory products. Although, as indicated above, the reactivity of CNSL can vary, we have been able to operate satisfactorily pressing composites based on carbonaceous particles with CNSL from different sources, while only varying the time over the range from one second to 60 seconds. Heating may be required using some materials, along with longer times to produce products acceptable in the market place, e.g when forming slate composites with p-toluene sulphonic acid, pressing may be carried out for as long as ten minutes at a temperature of 180 C in the presence of formaldehyde.

As indicated above, the particulate material to be bonded may be coal and as such the invention may be applied to the production of coal briquettes. Such briquettes as produced in accordance with the invention are of satisfactory strength, appearance and good burning characteristics. Coal used for forming briquettes will usually have a particle size ranging from 0.01 mm to 15 mm. A typical distribution is:

Particle size / mm Percentage / g

>5 0.9

>2 17.7

>1.4 13.2

>1.0 10.9

>0.6 22.6

>0.3 15.8

>0.18 16.2

>0.09 2.6

<0.09 0.1

In the case where the particulate material in slate, the particle size distribution of the slate will vary according to the source but a typical distribution is:

Particle size μm Percentage by mass

> 106 47.0

75 - 106 5.0

45 - 75 30.5

< 45 17.5

In the case of slate composites, we find that because of the large surface capacity of the slate particle, it is necessary to use larger amounts of CNSL and acid than with, for example, coal particles; and in this case, the addition of water makes little difference to the production of a satisfactory slate composite. It is also possible, in forming slate composites, to increase the amount of acid to so high a level that dry granular materials are formed, which cannot be incorporated into a pressed product. However, this upper limit of acid, which will vary with the size distribution of the slate particles used, is easily determined by simple experimentation.

The invention also includes composites formed by compacting particles together in the presence of a binder, in which the binder is a reaction product of CNSL with an acid, the reaction product being formed in situ during the production of the composite, and composites in which a compound with an active methylene group such as formaldehyde is present during the formation of the binder.

The invention also includes slate composites which have been prepared by compacting slate particles selected from slate grains and slate powder, or mixtures thereof, in the presence of a binder which is a reaction product of CNSL and an acid, the reaction product being formed in situ during the production of the composite.

The invention also includes slate composites which have been prepared by compacting slate particles selected from the group consisting of slate grains and slate powder, or mixtures thereof, and a binder precursor mixture at elevated temperature, the binder precursor mixture containing CNSL, an organic crystalline acid, a material containing an active methylene group, and water.

Our invention also includes a bonded wood particle board which has been prepared by pressing a mixture of particulate wood and a binder precursor mixture at an elevated temperature, the binder precursor mixture containing CNSL, an organic crystalline acid, a material containing an active methylene group and water.

We prefer to add the mixture containing CNSL to the particulated wood by spraying. The material containing an active methylene group can be formaldehyde, and when formaldehyde is used it is preferably added as hexamethylene tetramine. We have found that aromatic sulphonic acids are organic crystalline acids which remain substantially undissolved for a period of days in CNSL, until the temperature is raised to greater than 120°C. A readily available aromatic sulphonic acid which has been found satisfactory for manufacturing both wood and slate composites is p-toluene sulphonic acid.

The following examples in which all parts are parts by weight illustrates but does not limit the invention.

Example 1

133 parts of coal with a particle size distribution as given above were placed in a stainless steel mixer with 12 parts of CNSL (supplied by Marlin Chemicals as Technical CNSL). Sufficient water was added to ensure that the total water content, including the water content of the coal, was 15 parts, along with 7 parts of a mould release agent: calcium stearate. The contents of the mixer were mixed until a homogeneous mix was obtained, when 8 parts of sulphuric acid (97.5 % concentration) were added, and mixing continued until the sulphuric acid had all been incorporated into the mixture. The mixture was then transferred without any further delay to a series of conventional briquetting moulds in which it was pressed to form the compacted product or briquettes of the invention. Pressing was carried out for 4 seconds at 1000 psi. The briquettes on removal from the moulds had a good appearance and could be handled and transferred to store without damage. The briquettes had an acceptable performance when used as a fuel.

Example 2 to 30

The following examples illustrate the production of briquettes at varying compositions and pressing times. Test briquettes were made on a laboratory scale in a Kenwood Major Batch Blender and the pressing carried out in a single daylight press with a single ram. None of the test briquettes produced from mixtures with the compositions given in Table 1 failed a drop test . The drop test is a drop of 1.5 metres onto a brick flooring surface, and the briquettes fail if they fall apart on impact. Testing is carried out within one minute of the briquette being removed from the press. It was found that if the quantity of CNSL fell below 5 parts there was an increased risk of the test briquette disintegrating despite attempts to modify the formulation and pressing conditions.

In Table 1 all quantities are in parts by weight, the acid was 97.5% sulphuric acid, the water content of the coal particles was 2%, and the particle size distribution was the typical distribution outlined above. HCHO indicates the quantity of formaldehyde added as paraformaldehyde. The stearate was calcium stearate. The press time is given in seconds.

Table One

Example Coal CNSL Acid HCHO water stearate press time.

2 77.3 7.0 7.0 0 4.7 4.0. 5.0

3 77.3 7.0 7.0 0 4.7 4.0 30.

4 81.1 7.3 7.3 0 0 4.3 10.

5 81.1 7.3 7.3 0 0 4.3 30.

6 81.1 7.3 7.3 0 0 4.3 90.

7 80.2 8.4 7.2 0 0 4.2 60.

8 79.2 7.1 9.5 0 0 4.2 60.

9 74.7 6.7 9.0 0 5.6 3.9 60.

10 76.9 6.9 9.2 0 2.9 4.1 60.

11 75.8 6.8 9.1 1.4 2.8 4.0 60.

12 76.7 6.9 9.2 0.3 2.9 4.0 60.

13 79.6 7.2 9.6 0.6 3.0 0 60.

14 76.4 6.9 9.2 0.6 2.9 4.0 60.

15 83.6 7.5 5.0 0.6 3.1 0 60.

16 81.6 7.4 7.4 0.6 3.0 0 60.

17 82.9 5.0 7.5 1.6 3.0 0 60.

18 85.0 3.8 6.4 1.6 3.2 0 60.

19 78.5 7.1 7.1 1.5 5.9 0 60.

20 75.4 6.8 6.8 1.4 5.7 4.0 60.

21 72.1 6.5 9.7 1.4 6.5 3.8 60.

22 70.6 6.4 1 1.7 1.3 6.4 3.7 60.

23 69.8 6.3 12.6 1.3 7.3 3.7 60.

24 68.4 6.2 14.4 1.3 7.2 3.6 60.

25 76.9 6.9 9.2 0 2.9 4.0 60.

26 79.2 7.1 9.5 0 0 4.2 60.

27 77.3 9.3 9.3 0 0 4.1 60.

_ 28 78.2 8.2 9.4 0 0 4.1 60.

29 77.6 8.2 9.3 0.9 0 4.1 60.

30 78.0 8.2 9.4 0.3 0 4.1 60.

Examples 31 to 34

A series of examples to examine variations in formulation of the binder precursor were carried out. In all cases, no attempt was made to obtain a full cure during pressing; as is the case of many building materials, it is customary to operate processes where materials continue to cure after pressing. If a satisfactory product is produced by overnight curing, it means that the formulation can, if necessary, be cured more rapidly with the application of heat and pressure, as in the case of example 31. Table 2, below, shows the formulations used, in all cases 80g material was pressed at 1000 psi for sixty seconds to form a circular disc with a thickness of one cm. All examples formed products whose green strength was such that they could be transferred from the press onto formers for overnight curing at ambient temperatures. All examples cured fully to give a solid slate discs with adequate strengths. The slate was used as slate powder or slate granules, or a mixture thereof. The acid in all cases was 97.5% sulphuric acid. Formaldehyde may be added as paraformaldehyde, and the stearate release agent is calcium stearate.

Table Two

Example 35

A slate tile was made by compressing, for ten minutes at 180 degrees centigrade, a mixture containing ;

1) 550 g of slate powder/dust

2) 250g slate grains

3) 200g binder mixture.

The binder mixture was made by placing 133.2 g of technical CNSL in a vessel, to which was added 26.6 g of p-toluene sulphonic acid, followed by 13.6 g of paraformaldehyde and then 27 g of water. The materials were thoroughly mixed without any heating or vigorous stirring, but so as to ensure the components were thoroughly mixed together. Once mixing was completed the binder mixture was mixed with the slate dust and grain in a Z-blade mixer, and sufficient mix transferred to the press to form a tile. The tile had a satisfactory strength properties and a good surface appearance.

Example 36

300g. of Technical CNSL (as supplied by Marlin Chemicals under the description Technical CNSL) was mixed with 60g of para toluene sulphonic acid, 30g. of hexamethylene tetramine and 60ml of water. This mixture was added to 909.3 g. of softwood chips, (supplied by Kronospan Ltd Chirk UK) sieved to produce particles of 1-5 mm in length with a moisture content of 4%> of dry wood weight. A sample board was made by pressing a quantity of the mix at a pressure of 1000 psi for ten minutes at

180°C. This formed a product with satisfactory strength properties.

Claims

1. A process for forming a bonded product in which particles are mixed with CNSL and an acid to form a uniform mixture, and the mixture is then compacted under pressure in a mould.

2. A process as claimed in claim 1 wherein the acid has a pKa in the range +3 to - 9.

3. A process as claimed in claim 1 or 2 wherein the amount of the acid is at least 0.2 parts by weight per part by weight of CNSL.

4. A process as claimed in any one of claims 1 to 3 wherein the acid is sulphuric acid.

5. A process as claimed in claim 4 wherein the sulphuric acid has a concentration of about 98%.

6. A process as claimed in claim 5 wherein the mixture comprises at least 0.5 parts by weight of sulphuric acid per part by weight of CNSL.

7. A process as claimed in claim 5 wherein the mixture comprises 0.5 to 2.5 parts by weight sulphuric acid per part by weight of CNSL.

8. A process as claimed in claim 7 wherein the mixture comprises about 1 part by weight of sulphuric acid per 1 part by weight of CNSL.

9. A process as claimed in any one of claims 1 to 3 wherein the acid is an organic crystalline acid.

10. A process as claimed in claim 9 wherein the organic crystalline acid is p- toluene sulphonic acid.

11. A process as claimed in any one of claims 1 to 10 wherein the water content of the mixture is 0%> to 10%) by weight.

12. A process as claimed in any one of claims 1 to 11 wherein the mixture incorporates formaldehyde or a formaldehyde yielding substance.

13. A process as claimed in claims 12 whereas the mixture incorporates paraformaldehyde or hexamethylenetetramine.

14. A process as claimed in any one of claims 12 or 13 wherein the mixture incorporates 5 to 40%> by weight of formaldehyde based on the weight of the CNSL.

15. A process as claimed in any one of claims 1 to 14 wherein the bonded product comprises 70 to 98%> by weight of the particulate material.

16. A process as claimed in any one of claims 1 to 15 wherein the particulate material is a carbonaceous material.

17. A process as claimed in claim 16 wherein the carbonaceous material is coal or coke.

18. A process as claimed in any one of claims 1 to 15 wherein the particulate material is a mineral material.

19. A process as claimed in claim 18 wherein the mineral material is slate.

20. A process as claimed in any one of claims 1 to 15 wherein the particulate material is an abrasive.

21. A process as claimed in any one of claims 1 to 20 wherein pressing is effected at a pressure of 500 to 1200 psi.

22. A process as claimed in any one of claims 1 to 21 wherein pressing is effected for 1 second to 60 seconds.

23. Composites formed by compacting particles together in the presence of a binder, in which the binder is a reaction product of CNSL with an acid, the reaction product being formed in situ during the production of the composite.

24. Composites as claimed in claim 23 in which a compound with an active methylene group such as formaldehyde is present during the formation of the binder.

25. Slate composites which have been prepared by compacting slate particles selected from sale grains and slate powder, or mixtures thereof, in the presence of a binder which is a reaction product of CNSL and an acid, the reaction product being formed in situ during the production of the composite.

26. Slate composites which have been prepared by compacting slate particles selected from the group consisting of slate grains and slate powder, or mixtures thereof, and a binder precursor mixture at elevated temperature, the binder precursor mixture containing CNSL, an organic crystalline acid, a material containing an active methylene group, and water.

27. Bonded wood particle board which has been prepared by pressing a mixture of particulate wood and a binder precursor mixture at an elevated temperature, the binder precursor mixture containing CNSL, an organic crystalline acid, a material containing an active methylene group and water.