AU671534B2 - A process for producing composite particle boards from rice husks - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT 99 9 9.

9*99 Name of Applicant: Actual Inventor: NATIONAL RESEARCH

CORPORATION

DEVELOPMENT

GEORGE, Joseph Address for Service: CULLEN

CO.,

Patent Trade Mark Attorneys, 240 Queen Street, Brisbane, Qld. 4000, Australia.

Invention Title: A PROCESS FOR PRODUCING COMPOSITE PARTICLE BOARDS FROM RICE HUSKS The following statement is a full description of this invention, including the best method of performing it known to us: FIELD OF INVENTION This invention relates to a process for producing composite particle boards from rice husk and composite boards produced therefrom.

PRIOR ART It is known in the art to produce particle board from agro-wastes using phenolic resins. Such a known process envisages the step of blending rice husk with a phenolic resin containing a substantial quantity of water. Due to the presence of water, the blend is subjected to the step of drying for removal of the excess moisture content during or after the resin is coated on the rice husk or furni'sh.

The furnish is then hot pressed to form particle boards.

Several disadvantages are associated with the use of 15 such a known phenolic resin. One such disadvantage is that a drying operation results in a precuring of the resin, thereby diminishing its adhesive strength and resulting in poor quality particle boards. Moreover, since rice husk is a material of low bulk density, handling of the resin coated husk or furnish for drying is not convenient. Another disadvantage is that of the control of the moisture content of the furnish.

It is generally known that the furnish should have a moisture content, but which simultaneously should not be substantial in quantity as an excess of moisture could result in the formation of blisters or steam pockets in the formed boards.

a Thus, as rice husk itself contains moisture, the use of the known resin containing substantial quantities of water results in a furnish having a high moisture content, which is detrimental to the formation of the board. Furthermore, even if the furnish is subjected to the step of drying, it is difficult to control the correct content of moisture in the furnish.

OBJECTS OF THE INVENTION An object of this invention is to propose an improved 0 process for the production of composite particle boards from rice husk and composite boards produced therefrom.

Another object of this invention is to propose a process for the production of composite particle boards from rice hus]k which no longer requires the step of drying of the furnish.

Still another object of this invention is to propose a process for the production of composite particle boards from rice husk which no longer is attended with the disadvantage of formation of steam pockets or blisters.

DESCRIPTION OF THE INVENTION According to this invention there is provided a process for producing composite particle boards from rice husk which comprises in blending cleaned and split rice husk with a substantially free moisture 2 resin to form a furnish, said resin comprising a condensation product of cashew nut shell liquid and/or cardanol with phenol, paraformaldehyde and an alkaline catalyst, spreading the furnish to form a layer, subjecting the furnish layer to the step of hot pressing and subseauent cooling to form the board.

It is generally known that rice husk is of a so::boat shape. It has now been found that such a rice 10 husk is not receptive to a uniform coating of resin.

Thus, in accordance with this invention, rice husk is first subjected to the step of splitting to provide a surface more receptive to resin. Such a step of splitting is important, as in the absence S* 15 thereof, the bulk density of rice husk would be low and, consequentially, the thickness of furnished mat would be high, and that when such a furnished mat is subjected to the step of pressing, the edges of the mat would tend to spread. As the density in the spread portion would be lower than the main body portion of the board, the spread portion would need to be trimmed and, thereby, resulting in a lo s of material, The split rice husk is subjected to the step of cleaning and grading by any known method for removal of dust and other extraneous matter.

3 One of the concepts of the present invention resides in the use of a substantially moisture free resin so that, firstly, the moisture content of the furnish can be controlled and, secondly, the step of drying of the furnish is avoided. The ;tep cf control on the moisture content of the furnish is important, as the presence of a correct moisture content provides a board without blisters and steam pockets.

1" The furnish should contain a moisture content of 6 to 15% based on dry weight, and preferably between 8 to 12%. Simultaneously, rice husk itself contains a moisture content, which normally is in the proximity of 8 to 12%. Thus, prior to the step of blending with resin, the moisture content of rice husk is determined and only, if reauired, water is added to the blend so that the furnish contains the required moisture content of 6 to S"and preferably 8 to 12%.

The upper and lower limits of the moisture content contained in the furnish is dependant on the thickness of the board. If the board is thin, for example 6mm, the moisture content can then be upto 15%. However, if the board has a thickness of, for example, 25 mm a moisture content of the lower value of 6% is preferred.

4 A moisture content of 6 to 15% in the furnish is reauired because when the furnish is subjected to the step of hot pressing, the resin nmlts but does not flow adeauately to wet adjacent particlc Further, to permit a bcnoing of rice husk tc trmi the board, the surfaces of rice husk must act tgacther, and for which a flexibility of rice husk is reouired.

Such a flexibility is imparted through the moisture contained in the furnish.

If the moisture content contained in the furnish is greater than 15%, and as temperatures as high as 170 to 180°C are employed in the step of hot pressing, only'a negligible amount of mcisture is allowed to escape from the edges. Thus, water is entrapped at high temperature during such a step of pressing, which is converted to steam on release or removal of pressure, and which results in the possible formation of blisters. However, if the furnish contains less than 6% of moisture, then the flexibility property is not present and, whereby, the wetting of the rice husk with resin is reduced.

In accordance with this invention, rice husk is blended with 5 to 20% of resin to rhtain a furnish.

If more than 20% of resin is added to rice husk, the process is uneconomical. If the furnish contains less than 5% of resin, the board does not contain enough strength. Preferably, 10 to 12% cf resin is added to rice husk.

The furnish layer is subjected to the step of hot pressing at a temperature of 150 to 200 0

C,

and preferably at a temperature of 170 to 180 0

C.

The pressure aprlied to the furnish layer is to 15 kg/cm 2 and preferably 10 to 12 kg/cm 2 The density of the particle board may very from 400 to 1200 kg/m 3 The board prepared by the process of the present invention may advantageously be used for 0 0 overlaid and/or reinforced composite particle boards. In the instance of a reinforced board, one or more fibrous materials such as coconut fibre, bamboo slivers and wood strips are incorporated in the board.

15 Coconut fibre, bambco and wood used as reinforcement increases the strength of the boards and incorporation of short length or chopped fibre in the rice husx increases the internal bond strength of the boards prepared therewith.

Coconut fibre, bamboo and wood strips may also be used as surface reinforcrements cfr the rice husk particle board. Such surtace reinfrocoments increases the bonding strength and the decorative value of the resulting board.

Rice husk and the reinforcement such as chopped fibre is blended with a coconut shell liauid and/or cardanol-phenol-formaldehyde adhesive resin which is substantially moisture free. This admixture is then spread out evenly to form a layer and then hot pressed to obtain reinforced boards. Alternatively, and in the instance where the reinforcement is in the form of strips and slivers, the reinfcrcement is coated with coconut shell liauid and/or cardanolphenol-formaldehyde resin and then embedded in an even layer of resin coated rice husk furnish and hot pressed to form the reinforced board.

Overlaying is effected on one side or on both sides to provide a compact overlaid finished board.

Known phenolic resin adhesives and resin adhesives compatible with coconut shell liquid and/or cardanolphenol-formaldehyde resin may be used for bonding the overlays to the rice husk. Overlays such as 0* bamboo mats, coconut fibre felt, wood veneer and the like are coated with a coconut shell liquid cardanolphenol-formaldehyde resin or a phenol-formaldehyde adhesiveresin or any other resin compatible wit.h coconut shell liquid and/or cardanol -phenol-tormaldehyde resin. Resin coated rice husk turnish is then spread evenly thereon. Another resin coated overlayino material may be placed over the rice hu.;k turnish layer if overlaying is required on both sides. in each of the overlaying, the layers nfhould have a total moisture ccitent of 6 tc 15%. T1his assembly may then be subjected to hot pressinq.

This invention further relates to a process for preparing an improved adhesive ro~sin suitable for bonding rice husk which comprises in the steps of Ott Iadmixing cashewnut shell liouid and/or cardanol with phenol, heating the said mixture in presence of an alk~aline catalyst, adding para-tormoldehyde to the said reaction mixture while the heating is continued to coanplete the condensation reaction and thereafter cooling the reaction prcduct.

In the preparation of the improved resin according to the invention, the reactants are tak~en according to the proportion set forth below *CNSL/Cardanol 20% to 9N by weight Phenol 10% to aQ~l b~y welight Para tormalIdehyde culVal cnt to I.A to 2 moles of formaldehyde based on the C3tand pheniol. used.

Alkaline catalyst In the ooe 1 to by we ight ot ~.he CNSL, Cardane 1 and pheniol utwod The catalyst is dissolved in 2 tc 101 time.- Its, Weioit (it water before addinq to the corldonoatioi mAIxt tre.

P

The condensation takes place at the temperature range of 50 to 95 0 C. The heating is generi ity continued for a period of 25 to 45 minutes initially.

The second stage of condensation after the addition of a further quantity of phenol is carried out at the temperature range ot 55 to 950C for a period of 30 to 45 minutes to complete the condensation reaction.

The followinq examples are only illustrative 10 and not restrictive on the scope of the invention.

EXAMPLE 1 Kg cleaned riceo husk is blended with 5 Ko of the adhesive resin of the present invention in a muller for 15 mts. 15 Kg of the furnish so 15 formed is taken out and is spread out in an even layer. This is subjected to hot pressing at 170 'C :for 15 minutes to a nominal thickness of 1.2 cm.

The board produced is then cooled and the edges trimmed to a nominal size 1.2 m x 1.2 m x 1.2 cm.

The board prepared accordingly has a specific gravity of 0.70.

EXAMPLE 2- 38 Kg of the furnish prepare according to example 1 is laid out as an even mat and hot pressed at 1701C for 25 minutes, to a nominal thi(ckne ,a of 1.9 cm. The board is cooled and trimmed to a nominal size of 1.8 M x 1.2M x 1.9 CM and has a specific gravity of 0.82.

:9: EXAMPLE 3- Bamboo slivers of about 1 mm thick, about 1!5 MM wide and about 1.4 m to 2 m length are coated with CNSL and/or phenol-tormaldehyde resin which is substantially moisture tree. 50) Kqi. cleaned rice huvsk i.s- blended with 6 Kg. of CNSL and/or carda.ncl-phencl-tcrmaldeh-fyde, resqin subs-tantially free of water. 24 Kqi,t the furnish thus produced is spread out as an. even layer and the resin coated bamboo slivers are placnd over the layer at approximately' 10 cm interva-io both along .and across the length of the furnish layer. Another 2A Kq. of the said furnish is ;rpread ov(t the bamboo slivers in a uniform layer and the aosembly pressed at 175-185 0 C for 30 minutes to a nominal thickness 2.0 cm. The bamboo reinforced composite rice husk board that is formed is cooled and trimmed to a nominal size of 1.8 mn x 1.2 m x 2.0 cm. It has a specific 0000 gravity of 0.85.

E~XAMPL~E 4~ Two bamboo mato of the size 1.5 m x 1.5 m are evenily coated with a CNSE 1 and/or cardan~rol-pheincl-t(rmaldehyde res;ir which is subs-tantially ,isturv tree. 50 Kq rice1 husk is blended with 5.5 Ko. (t the s;aid rve:tin and 1A Eq (it the furnisnh so obtaiined is sproad as,, an even 2 1,layer on one of the s aid resin coated bamboo mats. The other mat is then placed on top of the f urnish layer.

This assembly js then Pressed inl a hot press at 160 to 170 0 C for 20 mts.tc obtain a bamboo mat overlaid composite particle hoard having a nominal thickness of 1 .2 cm.

The board is cooled and trimmed to a nominal size of 1.2 m x 1.2 m x 1.2 cm. This board has a specific gravity of 0.78.

~:.EXAMPLE 15 Kg. phenol 0.,31 kg sodi um hydroxide di ssol ved in 2.35 Kg water, 26.5 Kg CNSL and 1.56 Kg paratormaldehyde are mixed together and heated to 50 to 550C. In about minutes, 8.15 Kc' of faraformaldehyde are added to the above react ion mixtue in 12 approximatley eaual ouantities, *at about 4 mini. intervals each. The heatina is continued during the addition of paraforrnadehyde, 5.9 Kg phenol and 0.15 Kg of sodium hydroxide dissolved in 0.75 Kg water are added to the reaction of mixture, while continuing the heating. The temperature is then raised to around 65 to 70 0 C, and the mixture ja heated for around 410 minutes to complete the condensation. The resinous produICt is then cooled.

EXAMPLE 6- Kg phenol, 0.37 1< sodium hydroxide dJi-:;o1ve1d i2.7 Kg water, 13.4 Kg carcionol and 1.5 Kg para forinaldehy~e ar.- mixed together and hicatod to 50 to thi, 11.0 Kg of paraformaldehyde are added in, approximately 11 12 eaual quantities, at 4 mins. intervals while continuing the heating. Subsequently a further Qiuantity of 12.6 Kg phenol and 0.22 Kg sodium hydroxide dissolved in 1.23 Kg water is added to the mixture, and the temperature raised o 65 to 70'C. The heating is continued for 30 minutes to complete the condensation reaction. The product is thereafter cooled.

090 14"

Claims (14)

1. A process for producing composite particle boards from rice husk which comprises in blending cleaned and split rice husk with a substantially free moisture resin to Oas CeLshQnW a. carva foLm a furnishAsaid resin comprising a condensation product of cashew nut shell licuid and/or cardanol with phenol, paraformaldehyde and an )ka4n.4 catalyst, spreading Sthe furnish to form a layer, subjecting the furnish layer to the step of hot pressing and subsequent cooling to form *e* 10 the board.

2. A process as claimed in claim 1 wherein the furnish has a moisture content of 6 to 15%, and preferably 8 to 12%.

3. A process as claimed in claim 1 wherein the rice 15 husk is subjected to the step cf splitting and then blended with said resin. fter

4. A process as claimed in claim 1 wherein rice husk is blended with 5 to 20% of resin to obtain a furnish. A process as claimed in claim 4 wherein rice husk is blended with 10 to 12% of resin to obtain a furnish.

6. A process as claimed in claim 1 wherein the turnish layer is subjected to the step of hot pressing at a temperature of 150 to 200C, and preferably at 170 to 180°C. 13

7. A process as claimed in claim 1 wherein the furnish layer is subjected to the step of hot pressing at a pressure of 5 to 15 Kg/cm 2 and preferably at 10 to 12 Ko/cm 2

8. A process as claimed in claim 1 wherein reinforcements such as coconut, bamboo and wocd in the form of fibers are blended with said husk and resin. A process as claimed in claim 1 wherein reinforcement. such as coconut, bamboo and wood in the form of slivers 10 and strips are coated with a resin and formed into a layer or layers provided on one or both sides of said furnish and that the tctal moisture content being between 6 to

10. A process as claimed in claim 1 wherein the resin is eeoc prepared from a reaction mixture comprising in t:he steps 15 of admixing cashewnut shell liouid and/or cardanol with o 5 part of phenolt heating the mixture in presence of an alkaline catalyst, such as an aqueous solution of sodium hydroxide, adding paraformaldehyde to the said reaction mixture while the heating is continued to complete the condensation reaction and th teafter cooling the reaction product.

11. A process as claimed in claim 10 wherein the remainder of phenol is added to the react ion mixture t;ubseouent to the addition of paraformaldehyde.

12. A process as claimed in claim 10 where in the reaction mixture is initially heated to a temperature range of 50 to 55'C for 2 5 minutes.

13. A process as claimed in claim 11 wherein the reaction mixture is heated to 55 to 95 0 C for a period of 30 minutes after the addition of the further quantity of phenol.

14. A process as claimed in claim 10 wherein 20 to parts of cashewnut shell liouid is admixed with 10 to 80% by wt. of phenol for resin preparation by condensation with paraformaldehyde. process as claimed in claim 10 wherein para- formaldehyde ecuivalent to 1.4 to 2 moles of formaldehyde based on cashwnut shell liauid and/or cardanol and *o 15 15 phenol is addeo tc the reaction mixture.

16. A process as claimed in claim 10 wherein the alkaline catalyst added in eouivalent to 1 to 5% by weiaht ct cashewnut shell liauid cardanol and phenol.

17. A process for producing composite particle boards from rice husk--, substantially as herein described with reference to the Examples. DATED THIS TWENTIETH DAY OF APRIL 1994 NATIONAL RESEARCH DEVELOPMENT CORPORATION Dy their Patent Attorneys CULLEN CO lb ABSTRACT This invention relates to a process for producing composite particle boards from rice husk. The rice husk is leaned and split and then adrlixed with a substantially free moisture resin to form a furnish. The furnish is spread to form a layer which is then subjected to the step of hot pressing and cooling. The resin comprises a condensation product of cashew nut shell liquid and/or cardanol with phenol paraformaldehyde and alkaline catalyst. e e *0 99 S 17