AU688126B2 - Structural and insulative materials and products - Google Patents

Description

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AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: Actual Inventor: Address of Service: Invention Title: KENNETH LINDSAY PAGDEN Kenneth Lindsay PAGDEN SHELSTON WATERS MARGARET STREET SYDNEY NSW 2000 STRUCTURAL AND INSULATIVE MATERIALS AND

PRODUCTS

Details of Original Application No. 68923/94 dated 4th August, 1994 The following statement is a full description of this invention, including the best method of performing it known to me:- -2- The present invention relates to moulded structural and insulative products, and more particularly to such products formed from waste rice hulls.

Each year in Australia and around the world, the processing of rice for human consumption involves the removal of millions of tonnes of rice husks or "hulls". These hulls are difficult to dispose of, since they are essentially waterproof and are particularly resistant to biodegradation. Furthermore, their relatively high silicic acid content prevents their use as cattle fodder. Even rodents and insects will not eat them.

One means of disposal is to incinerate the hulls at high temperature, which substantially reduces their volume. However, this method is relatively energy 0 inefficient, expensive, and has undesirable effects on the environment in terms of atmospheric pollution.

Some attempts have also been made to use waste rice hulls constructively. They *0 .have, for example, been used as insulation in building cavities and other applications.

However, this use is severely limited by the lack of structural integrity of the raw 15 product.

In an attempt to address this problem, the rice hulls have also been mixed with various binding agents. For example, it has been known, although not commonly, to employ a binding agent curable by RF (Radio Frequency) radiation in order to consolidate the individual rice hulls. However, this has also been found to be an expensive process which is not cost effective on a commercial scale. Moreover, to date, the end products from this and other similar techniques have been excessively weak and prone to "crumbling". More particularly, they have lacked the requisite structural integrity for use as a self-supporting structural or insulative material, which has substantially limited their applicability in many potential fields of use.

L II_~ I -3- It is an object of the present invention to overcome, or at least substantially ameliorate, one ore more of these disadvantages of the prior art.

Accordingly, in a first aspect the invention provides a method for producing a stable structural or insulative product from rice hulls, said method including the steps of: adding a binding agent including a phenolic resin to rice hulls; and curing said binding agent; such that said binding agent binds said rice hulls into a stable structural mass.

Preferably, the method further includes the steps of: mixing said rice hulls with said binding agent; pouring the resultant mixture into a mould cavity; applying pressure to the mixture within the mould cavity; and *555 "curing said binding agent under conditions of increased heat to produce a stable structural product in the shape of the mould cavity.

15 In an alternative embodiment, rather than moulding, the resultant mixture may be oe .i extruded under conditions of increased pressure and subsequently cured.

Desirably, the rice hulls are shredded before mixing with the phenolic resin.

In one preferred method, the rice hulls are mixed with phenolic resin in a ratio of approximately 5:1 by mass, although different ratios may be used depending upon the desired characteristics of the final product.

Desirably, the phenolic resin used is Potassium Hydroxide based with up to around 60 solids. Alternatively, a Sodium Hydroxide based phenolic resin may be used, incorporating up to about 40 solids.

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-4- The curing temperature may be between 500 and around 200'C and is preferably between 1000 and around 150'. Most preferably, the curing temperature is about 1301C.

The curing pressure is preferably between 2 and around 80 pounds per square inch. More preferably, the curing pressure is between 15 and around 50 pounds per square inch, and most preferably around 40 pounds per square inch.

In one particularly preferred embodiment, the mould is defined at least partially by a layer of sheet metal designed to form a permanent outer layer of a composite structural product after curing. This configuration is particularly suitable for o..I constructing pallets or insulating panels, since the composite product is rendered Vlso.

extremely durable by the outer layer of sheet metal.

In some circumstances, it is desirable that the mixture includes some ground rice hull. Alternatively, whole or shredded rice hull may be replaced entirely with ground o00* rice hull.

oe ri In other embodiments, additives such as polyvinyl acetate or fortified urea *o 15 formaldehyde may form part of the binding agent for specific purposes. Furthermore, other agents may be added to the binding agent to modify the fire, water, weather or rodent resistance of the cured products.

In a second aspect, the invention provides a stable stnrmctural product formed substantially from rice hull, in accordance with the method defined above.

Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic view of a production line for producing a stable structural or insulative product from rice hulls according to the invention; ~I C- Figure 2 is a schematic view of an alternative production line for producing a stable structural product according to the invention.

Figure 3 is a perspective view of a roadside marker formed by the method of the invention; Figure 4 is a perspective view of a modular building block formed by the method of the invention; Figure 5 is a perspective view of a composite pallet formed by the method of the invention.

Figure 6 is a perspective view of an agricultural drainage pipe formed by the 10 method of the invention; Figure 7 is a perspective cut-away view of a load bearing structural member formed by the method of the invention, and incorporating an internal strengthening member; and ooaei Figure 8 is a weight bearing disc formed by the method of the invention for use as a building block.

Figure 9 is a building panel formed by the method of the invention.

Referring to Figure 1, rice hulls (not shown) are initially mixed with a phenolic resin in a mixing chamber 1, which in a preferred embodiment includes a ribbon mixer.

The preferred phenolic resins are Sodium Hydroxide based (with up to 40% total solids) and Potassium Hydroxide based (with up to 60% total solids). The resultant mixture is used to fill a mould 2, which is then moved to a main press 3.

The press 3 compresses the mixture into the mould. Pressures of between 2 and pounds per square inch have been tested and proved most effective, with the preferred -6pressure being around 40 psi. Even higher pressures may be used where a very hard and strong end product is desired.

The mould and compressed mixture are then passed through a curing oven 4.

The curing temperatures may be between 500 and 2000 depending on the proportions of resin and hull, and the desired residual moisture levels. For most applications, however, the most effective curing temperature has been found to be around 130'C.

In an alternative form of the invention, the rice hull and phenolic resin mixture is prepared as before. However, instead of being formed in a closed mould, the mixture is *9" extruded through an open extrusion die into a product of substantially constant cross- 10 section throughout its length. The extrudate may then be cut into appropriate lengths either before or after curing.

Also, ground rice hull may be used to either supplement or even replace the whole or shredded rice hull, depending upon the desired characteristics of the finished .:.oo product.

The following are some examples of methods of employing the invention in the manufacture of a variety of structural and insulative products.

ExampleI Ten kilograms of rice hulls and two kilograms of a phenolic resin based adhesive were mixed together thoroughly using a ribbon mixer. The resultant mixture was transferred to a mould, subjected to a pressure of 40 psi and then cured at a temperature of 130 0 C for one hour. The resultant product was a strong, rigid board with a high degree of structural integrity and good insulating properties.

As shown in Figure 3, the mixture may be moulded into "posts" about 1 metre in length. The cured posts may then be painted with a polyurethane based reflective paint, -7for use as a roadside markers. This particular embodiment is of great commercial significance, since such posts in the past have been made of wood or galvanised steel, both of which are relatively expensive to produce and are wasteful of valuable natural resources.

This method may also be used to form other moulded structural products, such as modular building blocks (see Figure 4).

Example 2 IReferring now to Figure 5, a mould incorporating downwardly extending ridges was fabricated from sheet metal, leaving the upper surface open to the atmosphere. This 10 mould was then filled with a mixture similar to that used in the first example and cured under similar temperature and pressure conditions. During the compression step, the mould may be supported in a cavity having a complementary profile, thereby preventing "distortion of the sheet metal. The result was a relatively cheap, lightweight, and weather resistant structural pallet formed by a composite of a lower sheet metal skin and a 15 structural filling formed from bonded rice hulls.

Durable structural building panels with excellent insulative properties, ideal for use in the construction of cool rooms and the like, have also been formed using this technique. Such panels may include additional sheet metal covering to entirely encapsulate the cured mass.

Example 3 In yet another embodiment, the product of the invention was used to insulate the inner walls of bui.ng structures, such as sheds for the housing of poultry and livestock for example. The surfaces to be insulated were first sprayed with a cross linking adhesive to provide a suitable base. A mixture comprising rice hulls, a phenolic resin -8and a curing catalyst was then sprayed over the pre-prepared surfaces and allowed to cure in situ. The result was a relatively cheap and effective insulating layer formed on the inner walls of the structure. Alternatively, the mixture may be pressed onto the prepared surface using suitable forming tools, and may also be moulded into textures which improve the acoustics or aesthetics of the interior of the structure.

Example 4 Hollow areas may also be insulated using the method of the present invention.

go For this application, the rice hulls and a binding agent including phenolic resin were

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mixed together, without the necessary curing agents. This mixture was then blown into the hollow areas to be filled using compressed air. Finally, a curing agent in gaseous ~form was passed through the mixture, thereby allowing it to cure in situ in the desired shape. This method is useful for insulating, for example, the side panels of refrigerators.

-A particularly desirable curing agent for this application is methyl formate.

°15 A mixture similar to that used in Example 1 was prepared. The mixture was extruded under pressure of about 60 pounds per square inch, cured at about 130 degrees Celsius and then cut into approximately 1 metre lengths to form highway posts similar to those in Example 1. The extrusion process may also be used to form, for example, continuous tubular lengths of agricultural drainage pipe (Figure or modular building blocks which may be cut to size before or after curing (Figure 4).

The extrusion process may also be modified so the rice hull and resin mixture is extruded around one or more internal support members 6, such as a steel beam of Ushaped cross-section (Figure These reinforcing members add to the overall strength of the product.

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-9- Referring to Figure 8, a load bearing disc of 200 mm diameter and 100 mm height was formed from a mixture of rice hulls and phenolic resin in a ratio of 5:1. The mixture was cured in the mould for around 120 minutes at 150 Celsius and about 60 psi.

The cured disc was capable of withstanding a 60 tonne mass during a 2 day sea voyage, demonstrating the very high strength of the product formed by the invention.

General Comments *fee The synergistic combination of rice hulls and phenolic resin, when used in 4 accordance with the method of the present invention, provides a diverse range of cost 0@ l0 effective products, having unexpected structural integrity substantially greater than the moulded or extruded products of the prior art. Further, the products of the method have good acoustic insulation properties, and relatively high resistance to fire, water and rodent damage. At the same time, the invention addresses the problems previously .:o.oi encountered in disposing of waste rice hull. For these reasons, the present invention 15 provides a commercially significant advance over the prior art.

Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims (11)

1. 2. A method for producing a stable structural product according to claim 1, further o**e including the steps of: mixing said rice hulls with said binding agent; SO 10 pouring the resultant mixture into a mould cavity; 3 .".applying pressure to the mixture within the mould cavity; and io 5 curing said binding agent under conditions of increased heat to produce a stable structural product in the shape of the mould cavity.
2. 3. A method for producing a stable structural product according to claim 1 or claim 15 2 wherein said binding agent is cured by a curing agent containing methyl formate.
3. 4. A method for producing a stable structural product according to any one of the preceding claims, wherein said rice hulls are mixed with said phenolic resin in a ratio of approximately 5:1 by mass. A method for producing a stable structural product according to any one of the preceding claims, wherein a fibrous reinforcing material is added to said rice hulls and said binding agent before curing.
4. 6. A method for producing a stable structural product according to any one of claims 2 to 5 wherein said increased temperature is in the range of 80 to around 150 degrees Celsius. I, II
5. 7. A method for producing a stable structural product according to claim 6 wherein said increased temperature is about 130 degrees Celsius.
6. 8. A method for producing a stable structural product according to any one of claims 2 to 7 wherein said pressure is between 2 and about 75 PSI.
7. 9. A method for producing a stable structural product according to claim 8 wherein said increased pressure is about 40 PSI. A. t.ethod for producing a stable structural product according to any one of the preceding claims, further including the step of applying a polyurethane coating to the cured product.
8. 11. A method for producing a stable structural product according to any one of the preceding claims, wherein said mould is defined by a layer of sheet metal, and wherein said mould is designed to permanently form an outer layer of a composite stable structural product after curing. S" 12. A method for producing a stable structural product according to claim 11 wherein 15 said mould is configured for use as a pallet. p.
9. 13. A method for a producing a stable structural product according to any one of the preceding claims, wherein said binding agent further includes polyvinyl acetate or melamine fortified urea formaldehyde. 14 A method for producing a stable structural product according to any one of the preceding claims, further including the step of adding modifying agents to said binding agent to modify the fire, water, weather or rodent resistance of the cured product. A stable structural product formed according to the method defined in any one of the preceding claims. I 12-
10. 16. A method for producing a stable structural product substantially as herein described with reference to figure 1 of the accompanying drawings.
11. 17. A stable structural product substantially as herein described with reference to any one of figures 2 to 7 of the accompanying drawings. DATEDthis 26th Day of October, 1995 KENNETH LINDSAY PAGDEN Attorney: STUART M. SMITH Fellow Institute of Patent Attorneys of Australia of SHELSTON WATERS *0.o o 0 S e Il I ABSTRACT A method for producing stable structural or insulative products, including the steps of mixing a binding agent including phenolic resin to rice hulls and then curing the binding agent. The result is a stable structural product with good insulative and acoustic properties. In the preferred embodiment, the mixture is compressed within a mould cavity and then cured under conditions of increased heat. This in turn increases the strength and stability of the end product. C too* S C S 0 I