GB2265150A

GB2265150A - Composition containing sub-divided straw or other agricultural fibres

Info

Publication number: GB2265150A
Application number: GB9205380A
Authority: GB
Inventors: Brian Harmer
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-03-12
Filing date: 1992-03-12
Publication date: 1993-09-22
Also published as: GB9205380D0

Abstract

A composition, an agglomerate thereof as well as formed articles produced by compressing and setting or curing such composition or agglomerate are provided. The composition comprises at least 50% and preferably from 70 to 90% by weight of a subdivided straw (as defined in the specification) which has a particle size of from 0,5mm to 3,0mm. The subdivided straw is mixed with from 10 to 30% by weight synthetic resin or bonding agent; from 0 to 40% by weight fillers and preferably from 1 to 5% by weight of a styrene compound and from 0,5% to 3% by weight of a mould release agent. A formed article preferably has a specific gravity of from 1,1 to 1,5. The composition may additionally comprise lignin from peat or dried wood dust in an amount of up to 10% wt. The synthetic resin may be a two-stage phenolic resin containing hexamine as a crosslinker. The release agent may be zinc stearate.

Description

COMP08ITION OF MATTER CONTAINING SUBDIVIDED STRAW OR OTHER AGRICULTURAL FIBRE8" FIELD OF THE INVENTION THIS INVENTION relates to a composition of matter which contains, as a substantial part thereof, subdivided straw and/or bagasse or other fibrous vegetable matter, and which may be moulded or otherwise formed into useful sheets thereof. Alternatively, and preferably, the composition of matter may be moulded directly into shaped components, for example, furniture components, pal lets, packaging components, building components such as window frames or floor tiles, etc.

Still more particularly, but not exclusively, the invention relates to an agglomerate of such a composition of matter which facilitates the handling and moulding thereof.

It is to be understood that the term "straw" as used in this specification is intended to include the stalks of grasses, grain products such as barley, wheat, rice and, indeed, even maize stalks as well as other vegetable products such as bagasse, cocoa and coffee husks, all of which have a generally very low bulk specific gravity in view of the inclusion of large quantities of air or other gases in the structure of the stalk or the like.

BACKGROUND TO THE INVENTION In general, the most widely used vegetable fibres are those of wood which can be used in many different forms. In one form the wood is subdivided into a multitude of chips which are then pressed together with synthetic resin or a bonding agent to form a sheet material commonly known as "chipboard". Other boards having their origin in timber are known as "composition boards" and such composition is also sometimes pressed into other structural shapes as may be required.

However, wood is extremely costly and becoming more scarce.

Various attempts have been made to employ other fibrous vegetable materials such as straw (as above defined) with varying degrees of success, depending on the product to be produced. Thus, straw has been employed to produce lightweight acoustic ceiling panels with great success, but without strength. However, there is an enormous amount of such fibrous vegetable material which has not been employed usefully due largely to its extremely low specific gravity and the inclusion of a large amount of air or other gaseous content in the material. The reason for this is, applicant believes, appreciable difficulty in compressing such material in a mould or other forming apparatus to an extent where a sufficiently high density is attained to provide strong, reasonably dense products.

It is accordingly, one object of this invention to provide a useful composition of matter which includes, at least as a substantial part thereof, subdivided straw (as herein defined).

It is, another object of this invention to provide a partially or wholly compressed agglomerate of such a composition of matter which can more easily be used as a feed material to a moulding or other forming apparatus.

SCiMMARY OF THE INVENTION In accordance with this invention there is provided a composition of matter comprising (i) at least 50% by weight of subdivided straw (as herein defined) wherein the straw is subdivided to a state in which at least 90% of the straw particles have a size from 0,5mm to 3,Omm and, (ii) from 10% to 308 by weight of a synthetic resin or other bonding agent.

Further features of the invention provide for the composition to include (iii) from 0% to 40% by weight of fillers, or a mixture of fines and particles of longer lengths, a lignin in the form of refined low moisture peat, other materials of the same plastic make-up as the resin or bonding agent, (iv) from 1% to 5% by weight of a styrene compound; and, (v) from 0,5% to 3% by weight of a suitable release agent such as zinc stearate.

The invention also provides an agglomerate of a composition of matter as above defined. Preferably, the agglomerated elements have a density greater than the bulk density of the composition of matter before agglomeration.

The invention still further provides a formed article made by compressing and curing or setting a composition of matter as above defined, or an agglomerate thereof.

DETAILED DESCRIPTION OF THE INVENTION It is preferred that the synthetic resin or bonding agent be a two-stage phenolic resin containing hexamine as a cross-linking agent.

A preferred composition comprises from about 70% to 90% by weight of subdivided straw, from 1% to 5% by weight of styrene monomer, and from 0,5% to 3% by weight of zinc stearate, and up to 10% lignin from peat or dried wood dust.

Also it is preferred that the straw be subdivided to a state in which 100% thereof has a particle size of from 0,5mm to 3,0mm and preferably 100% have a size of less than 2,0mm with a moisture content of from 5% to 12% by weight.

It has been found that the styrene tends to migrate to the surface of a moulded article produced from such a composition of matter and provides a very much improved surface appearance than in the absence of such styrene.

The amount of styrene added will depend on the surface appearance required. The styrene forms a skin on the surface which increases water resistance (ie. reduces water penetration). It also increases impact resistance when using other styrene based plastics.

The two-stage phenolic resin is a dry resin and can be easily admixed with the finely subdivided straw and other additives and moulded under pressure with heating to between about 110 C and 160 C.

The zinc stearate has been found to be eminently suitable for use as a release agent to ensure proper release of the moulded articles from a mould.

A composition, as above described, can be mixed dry, preferably followed by agglomerating, particularly by pelletization, and the agglomerated composition, which is somewhat compressed, is, at a chosen later time, compression moulded, either in one or two stages, to form a moulded article having a satisfactorily high specific gravity, in particular a specific gravity in the range of 1,1 to 1,5. The degree of compression of the raw mix will be determined according to the specific gravity required of the final product and dependent on the quantity of the base fibrous material and its natural lignin, cellulose and sugar content.

It has been found that, where a composition of the indicated preferred range is agglomerated by pelletization, the agglomerate elements, such as pellets, have a suitably increased density to render subsequent moulding more easy and they retain this density without the addition of further binders.

However, if the pellets or other agglomerate units tend to break up, and decrease in density, a suitable binder may be added to prevent or diminish these effects.

Whilst the stated two-stage phenolic resin is a solid finely subdivided material, and can be admixed with the finely subdivided straw and other additives by tumbling, for example, any other suitable synthetic resin or bonding agent could be employed and could assume the form of a liquid, a solid dissolved in a liquid carrier which subsequently evaporates, or any other suitable form. It is also envisaged that up to 40% by mass of the composition could be suitable fillers which could also include colouring agents or materials chosen to provide a specific appearance, surface wear and resistance and water resistance.

It will be understood that, by subdividing the straw to the stated size, the air sacs in the actual straw are broken down and formation of the straw material into an agglomerate can be easily achieved to provide a composition of increased specific gravity which is suitable for feeding to a moulding apparatus, such as compression moulding apparatus.

Whilst it is preferred that the composition of matter be agglomerated prior to moulding, this is by no means essential. It may well be desirable, particularly where a two-stage compression moulding technique is employed, to mould the composition directly without agglomeration.

In trials conducted to date using straw of wheat subdivided to 100% from 0,5mm to 2,Omm pieces, employing 20% of the two-stage phenolic resin (in powder form) with hexamine of the type mentioned above; 5% of styrene monomer and 1,o% of zinc stearate, a pelletized agglomerated was produced using a simple pelletizing machine. The agglomerated composition was then used to produce moulded articles at l5OC and at pressures ranging from 0,08 tonnes/cm2 to 0,8 tonnes/cm2 with highly satisfactory results. The formed articles produced had specific gravities from 1,1 to 1,5.

Claims

WHAT WE CLAIM AS NEW AND DESIRE TO SECURE BY LETTERS

PATENT IS:1. A composition of matter comprising: (i) at least 50si; by weight of subdivided straw (as herein defined) wherein the straw is subdivided to a state in which at least 90% of the straw particles have a size from 0,5mm to 3,Omm and, (ii) from 10% to 30% by weight of a synthetic resin or other bonding agent.
2. A composition as claimed in claim 1 in which there is included: (iii) from 0% to 40% by weight of fillers, or a mixture of fines and particles of longer lengths, a lignin in the form of refined low moisture peat, other materials of the same plastic make-up as the resin or bonding agent, (iv) from 1% to 5% by weight of a styrene compound; and, (v) from 0,5% to 3% by weight of a suitable release agent.
3. A composition as claimed in claim 2 which contains from 0,5 to 3% by weight zinc stearate as a release agent.
4. A composition as claimed in claim 1 in which the subdivided straw is present in an amount of from 70 to 90t by weight.
5. A composition as claimed in claim 1 in which there is included lignin from peat or dried wood dust in an amount of up to 10% by weight.
6. A composition as claimed in claim in which 100% of the subdivided straw has a size of from 0,5mm to 3,0mm.
7. A composition as claimed in claim 6 in which 100% of the subdivided straw has a size of from 0,5 to 2,0mm.
8. A composition as claimed in claim 1 in which the moisture content of the straw is from 5 to 12% by weight.
9. A composition as claimed in claim 1 in which the synthetic resin or bonding agent is a two-stage phenolic resin containing hexamine as a cross-linking agent.
10. An agglomerate of a composition of matter as claimed in claim 1.
11. An agglomerate as claimed in claim 10 in which the agglomerate elements have a density greater than the bulk density of the composition of matter before agglomeration thereof.
12 o A formed article made by compressing and setting or curing of a composition of matter or agglomerate as claimed in either of claims 1 or 10.
13. A formed article as claimed in claim 12 in which the specific gravity thereof is between 1,1 and 1,5.
14. A formed article as claimed in claim 13 in which the compression of the composition or agglomerate is effected at a pressure of from 0,08 to 0,8 tonnes/cm2.
15. A formed article as claimed in claim 12 in which curing or setting is effected during compression at a temperature of from llO C to 1600C.