CA1087825A

CA1087825A - Hot pressing lignocellulosic material mixed with a binding agent

Info

Publication number: CA1087825A
Application number: CA248,351A
Authority: CA
Inventors: Alan M. Wooler
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1975-03-12
Filing date: 1976-03-12
Publication date: 1980-10-21
Also published as: DK147599C; FR2303661B1; IE42654B1; FI760651A; SE418271B; DK107376A; FI64621B; CH619975A5; NL7602614A; AU1195776A; LU74550A1; DE2610552B2; IT1058409B; NO147525C; NO147525B; FR2303661A1; DK147599B; ZA761527B; DE2610552A1; GB1523601A

Abstract

ABSTRACT OF THE DISCLOSURE
A process for manufacturing sheets or moulded bodies which comprises hot pressing of a mass of ligno-cellulosic material mixed with a binding agent comprising an aqueous emulsion of an organic isocyanate.

Description

'7JS~S
rrhis invention relates to a process for manufacturing sheets or moulded bodies.
Composite boards and flat sheets or moulded bodies and the like are commonly prepared hy hot pressing of a mass of wood chips, wood fibres or other lignocellulosic material mixed with binding agents, particularly solutions of urea-formaldehyde or phenol-formaldehyde resins. Pressing tempera-tures are usually about 150 to 220C otherwi~e adequate adhesion does not occur in an acceptable time even at the high pressures ~20 to 70 kilograms force per square centimetre ~gf/cm2~) -which are normally used.
It is known to use isocyanate solutions as binding agents for chipboard in place of the urea-formal.dehyde or phenol-ormaldehyde resins.
`~ According to the present invention a process for manufacturing sheets of moulded bodies comprises hot , pressing of a mass of lignocellulosic material mixed with a binding agent comprising an aqueous emulsion of an organic polyisocyanate.
; 20 Lignocellulosic material which can be used in the ~ .
' process includes wood chips, wood fibres, shavings, wood wool, cork and bark, sawdust and like waste products from the . .
woodworking industry, and/or fibres from other natural , products which are lignocellulosic, for example, bagasse, ,` straw, flaz residues and dried rushes, reeds and grasses.
,~ Additionally, there may be mixed together with the lignocellu~
~.
losic materials inorganic flake or fibrous material e.g.
glass fibre, mica or asbestos.
"
Organic polyisocyanates include di-isocyanates, particularly aromatic di-isocyanates, and isocyanates of ' :-,.i "~:
.,

2 -: ..
~'~
. .. .
'"''" ~k :-37~5 : higher functionality.
Examples of organic polyisocyanates which may be used in the process of the invention include aliphatic isocyanates such as hexamethylene diisocyanake, aromatic isocyanates such as m- and p- phenylene diisocyanate, tolylene -2,4- and 2 r 6-diisocyanates, diphenylmethane-4,4'~diisocyanate, chlorophenylene-2,4-diisocyanate, naphthylene-1,5-diisocyanate, ~;
. diphenylene-4,4'-diisocyanate, 4,4'-diisocyanate-3,3'-dimethyl-diphenyl, 3-methyldiphenylmethane-4,4'-diisocyanate and ~ 10 diphenyl ether diisocyanate, cycloaliphatic diisocyanates such :.~ as cyclohexane-2,4- and 2,3-diisocyanakes, l-methyl cyclohexyl - -2,4- and 2,6-diisocyanates and mixtues thereof and bis-(isocyanatocyclohexyl-)methane and tri-isocyanates such as . 2,4,6-triisocyanatotoluene and 2,4,4'-triisocyanatodiphenylether.
. Mixtures of isocyanates may be used, ~or example a mixture of tolylene diisocyanate isomers such as the commercially available mixtures of 2,4- and 2,6-isomers and ~ also the mixture of di- and higher poly-isocyanates produced by phosgenation of aniline/formaldehyde condensates. Such :. 20 mi.xtures are~well-known in the art and include the crude i phosgenation products containing mixtures of methylene bridged polyphenyl polyisocyanates, including diisocyanate, triisocyanate and higher polyisocyanates together with any phosgenation ~ by-products.

Preferred polyisocyanates to be used in the present ~ invention are those wherein the isocyanate .is an aromatic . diisocyanate or polyisocyanate of higher functionality in particular crude mixtures of methylene bridged polyphenyl ~-. polyisocyanates are well known in the art and have the ` 30 gneric formula:

- 3 :~

, , . .. ~ . . :

[~Lc~2~ c~2~3 NCO n-l NCO -~ ;

where n is one or more and in the case of the crude mixtues represents an average of more than one. They are prepared by phosgenation of corresponding mixtures of palyamines obtained by condensation of aniline and formaldehyde. For :
convenience, crude mixtures of methylene bridged polyphenyl -~
polyisocyanates containing diisocyanate, triisocyanate and higher functionality polyisocyanates are referred to herein~
~ ~ ~rnT
a ~er as 1~ .
Especially preferred organic isocyanates which ~; 10 can be used in the invention include isocyanate-ended pre-polymers made by reaction of an excess of a diisocyanate or higher functionality polyisocyanate wi~h a hydroxyl-ended polyester or hydroxyl-ended polyether and products obtained by reacting an excess of diisocyanate or higher functionality polyisocyanate with a monomeric polyol or mixture of mon~meric , 1 .- ~ polyols such as ethylene glycol, trimethylol propane or butane-diol. Of particular value, however, because of their slower ;~
reaction with water, a desideratum hereinater discusqed, are isocyanate-ended prepolymers prepared using hydrophobic polyols such as castor oil.
One class of isocyanate-ended prepolymers which may be used are the isocyanate-ended prepolymers of diphenylmethane-4-

4'-diisocyanate (MDI).
The aqueous emulsion of organic polyisocyanate used in the process of the invention may advantageously contain .. j , ,.

! 4 , ~
.~ ' .

7~3Z5 a non-ionic surEace active agent devoid of hydroxy, amino and carboxylic acid groups, in particular condensates of ethylene oxide molecules which are devoid of chain-end hydroxy, amino or carboxylic acid groups. These include for example condensates of ethylene oxide with alkyl phenols, long chain alcohols or amides, wherein in each case the end-hydroxy group is for example etherified or esterifiea.
of particular value are the reaction products of diisocyanates and higher functionality polyisocyanates with monoalkyl ethers of polyethylene glycols. These particular , ~
surface active agents or emulsifying agents have the formula:

RO(C~I2CH2O)nCONHX
wherein R is an alkyl group of from l to 4 carb~n atoms, n is an integer such that the compound contains an average of at ; least 5-oxy ethylene groups and X is the residue o a di or polyisocyanate and contains at least one free isocyanate group. Examples of R include ethyl, propyl and hutyl, preferably methyl. There must be sufficient oxyethylene groups (CH2CH2O) present in the surface active urethane that there is an average of at least 5 such groups per molecule. It is preferred that n represents an average of from 5 to 120 and especially from 10 to 25.
, The group X is the residue which would remain after '~ one isocyanate group had been removed. The group X may be the residue of any diisocyanate or higher polyisocyanate and for example if the diisocyanate is a tolylene diisocyanate the residue X will be ~ CH
i I ' ~; NCO
,. ,. ~
'j: .,l :
~,!

- 5 -, .
. ~.~ -,, ~

8~

The group X preferably contains an isocyanate group.
Isocyanates from which the group X can be derived include the di- and poly-isocyanates listed above.
Such surface active urethanes may be manufactured ~`
by reacting an alcohol of the formula RO(CH2CH2O)nH with an isocyanate having at least two isocyanate groups, there being used at least one molar proportion of isocyanate for each molar proportion of the alchol. Preferably an excess of the isocyanate is used.
The reaction may be carried out by adding the alcohol to the isocyanate with stirring until clear and allowing the reaction to proceed, at room temperature. The reaction may - be accelerated by heating at temperatures up to 100C.
- In order to obtain the emulsions used in the present invention, the above type of surface active agent may be prepared in situ in the isocyanate. Thus if it is desired to produce an emulsion of an isocyanate of the formual ~; X(NCO)2 a small amount of the polyathenoxy alchol RO(CH2CH2O) H
may be added to a large excess of the isocyanate X(NCO)2 and ~` 20 the emulsifying agent formed in situ in the isocyanate.
In the cases where the polyisocyanate is a prepolymer, . .
formation of the prepolymer and an in situ surfactant may be carried out simultaneously or as two separate steps and the prepolymer/surfactant then mixed with water to give the emulsified prepolymer. Emulsification is facilitated by initially mixing the prepolymer/surfactant with about one quarter of its own weight of water and then diluting with more water as required.
Thus when the polyisocyanate present in the emulsion is to be one of the class of preferred prepolymers mentioned ,, -:
~ - 6 - ~
: . ;
~ .
.~ .
' ~ "' `;'~`.
: :.
.~ , .

~L~)8~ 5 hereinbefore, namely a prepolymer of MDI, the emulsion of the pre~lvmer mav he macle by an~ of the following three mehtods:
1. Reaction of the MDI with the required amount of polyol to give the prepolymer followed by reaction with - a small amount of the polyethenoxy alcohol CH30~CH2CH20)nH
~ followed by emulsification by agitation with water.
-~ 2. Reaction of the MDI with the required small ::
, amount of the polyethenoxy alcohol CH30(CH2CH~O)nH f~llowed by reaction with the amount of polyol required to give the - prepolymer followed by emulsification.
3. Reaction of the MDI with the required amounts of polyol and polyethenoxy alcohol simultaneously followed by ;
emulsification in water.
. In the above three methods the preparation of the surfactant is carried out in situ in the polyisocyanate, , the surfactant being of the general formula RO(CH2CH20)nX
'. where X is the residue of the isocyanate and R is an alkyl . t ~: group of from 1 -to 4 carbon atoms.
Preferred surfactants are those derived from ~: - polyethenoxy compound RO(CH2CH20)nH wherein R is methyl and n is an average of from 10 to 25. Typical examples of the polyethenaxy compounds are methoxypolyethylene glycols of molecular weight of 300 to 1000.
.. The surfactant can of course be prepared separately and a small amount dissolved in the prepolymer-forming mixture ' or in the preformed prepolymer.
Formatlon of the prepolymers can be carried out by .. 30 any of the known methods, i.e. by heating the compvnents _ : ,;
:::. ., :~ - 7 - ~
. . .
,~,.`' ' . .

, .
.: , . . . .

o~ z~ ::

together or b~ allowing them to r~act an ambien-t temperature ~;
optionallv in the pre~ence of catalys~s.
The emulsions of the prepolymers prepared by the methods described above are oil-in-water emulsions.
A further type of sur~ace active agent which may ~ be utilised is that which has the ~eneral f~rmula:
', :
.. 1 ~
/CoO (cH2cH20) R - X - NHCOCH ~ :~
.` ~COO (CH2CH20) nRl ~ ' ,. :
wherein X is the residue of an organic isocyanate, Rl is an alkyl group of from 1 to 4 carbon atoms, n and m are inkegers ~ `~
such ~hat m ~ n is at least 10 and R which is only present when X represents the residue of a diisocyanate or a higher ,, functionality polyisocyanate, is an isocyanate group or a group of the formula:
; .
;` COO(CH2OEI2O)mR
NHCOCH
COO (CH2CH20) nRl ` ~ ''' ' ~ ' ;~ ~ Rl is preferably methyl and the sum of m and n is preferably between 20 and 80.
When X represents the residue of a monoisocyanate ;~
the group R is absent.
X may for example be the residue of any of the ~;~
isocyanates listed earlier in this specification.
These surface active agents or emulsifiers may be ;~
made by reaction of an isocyanate with a bis(alkoxy polyethenoxy) ~ ester of malonic ~cid, and may if desired be prepared in situ -~ ~ in the ~socyanate.

,-1 ' ~ ,.: `'`, :! ~ `: ' . .

- ~0~ 325 re~erred emulsions for use in the present invention are those in which fro~ 99 parts to 25 parts by weight of water are associated with from 1 part to 75 parts by weight o~ organic polyisocyanate, (especially those in which 75 to 50 parts by weight of water are associated with 25 to ~ 50 parts by weight of organic isocyanate) and which contain : also a stabilising amount of a non-ionic surface active agent ; devoid of hydroxy, amino and carboxylic acid groups. A
: preferred amount of the surface active agent is from 5 parts to ~, 10 1.5 parts by weight based on 100 parts by weight of the isocyanate.
The emulsions can be prepared by conventional methods, preferably by mixing the emulsifying agent with the organic polyisocyanate and mixing this mixture with water.
` Alternatively in some cases the non-ionic surface active '. agent can be prepared in situ in the polyisocyanate, mixed ,.6 with water and the whole agitated to obtain the desired emulsion.
"~' To carry out the pxocess of the invention the `,. lignocellulosic material is mixed,with the binding agent, ', desirably by~spraying it finely with the aqueous emulsion so b' 20 as to produce good coverage. It has been found that aqueous .
.,. emulsions of the organic polyisocyanates are of sufficiently . . .
low viscosity to be sprayed at strengths of up to 65~, , whereas the solutions of ure~-formaldehyde and phenol-, formaldehyde resins normally used in manufacture of chipboard ,. and like materials are not normally sprayable at strengths ~, above 40~. Thus the invention provides a means of operation ~ in which less water is present,than has hitherto been possible, ,, so that less water needs to be expelled during the hot pressing ;''. stage or subsequent conditioning. Alternatively1 the ligno- :

0 cellulosic material neeed not be dried to the hitherto normal ,~, extent before mixing with the binding agent. The use of warm ;~, ' ,~ ' ~'.

7~5 water and/or organic polyisocyanate may faci.litate emulsification and spraying.
It has further been found that the hot pressing stage in the process of the invention can be effectively operated at temperatures below 100C (e.g. at 90 to 95C) instead of the usual 150 to 220C used with urea-formaldehyde and phenol-formaldehyde resins. The use of such lower tempera-tures saves energy, reduces environmental discomfort, and eliminates fumes. It is also advantageous because it avoids ~` 10 the disruptive influence of steam pressures generated internally within sheets or moulded articles made at the higher temperatures, particularly important in the manufacture of laminates having ~` impermeable facings. Improved consolidation can therefore be obtained during the pressing stage because it is no longer necessary to leave sufficient permeability for steam to escape.
The more conventional higher temperatures may of ' course still be used and may in fact be desirable in certain :
circumstances, since they give rise to shorter curing times and tend to promote improved release of the chipboard from . 20 the press platens. This latter consideration may be of ~,. .
importance where unfaced sheets are to be produced. ~
,~ In a preferred from therefore the invention provides ~`
a process for manufacturing sheets or moulded bodies which .:", comprises spraying lignocellulosic material with an aqueous ~' emulsion of an organic polyisocyanate, desirably an ;;~
; isocyanate-ended prepolymer of a crude mixture of methylene bridged polyphenyl polyisocyanates, said aqueous emulsion ~ ~
containing a stabilising proportion of non-ionic surface ~ ~;
; ~ agent devo~d of hydroxy, amino and carboxylic acid groups and having 75 to 50 parts be weight of water associated with ` -- 1 0 -- , ."

.- . .
,........................................................................... .

~'71 3~S

25 to 50 parts by weight oE the organic polyisocyanate, optionally drying at 20 to 40 C to remove a portion of the water and hot pressing the sprayed lignified raw material at a temperature below 200C, and especially below 100C, particulary 90-95C, to effect cohesion.
By this means strongly bonded sheets or moulded bodies are obtainable economically.
In practice, there will inevitably be periods of delay between the stages of preparing the emulsion, spraying the lignocellulosic material and hot pressing the sprayed material, and delays also arising from clearing processing faults and making operational adjustments. Desirably the!
reaction between the isocyanate and water of the emulsion will be sufficiently slow so that a delay o, say, two hours between preparing the emulsion and hot pressing can be tolerated. The reaction rate can be slowed down to provide an emulsion having an acceptable working life by using less surface active agent or by using a less efficient agent but either of these courses adversely influences the stability of the binder and distrlbution of the isocyanate over the lignocellulosic material in addition to causing spraying i difficulties. It is preferable therefore to slow down the reaction rate by using an isocyanate-ended prepolymer derived from a hydrophobic polyol~ as already men-tioned, and/or by including in the emulsion an inert hydrophobic diluent which . .
may also provide benefits in terms of improving the water - repellent nature of the resultant chipboard and assisting release of the chipboard from the press platens. Suitable ; diluents are fatty hydrocarbons, aromatic and aliphatic, and esters, optionally containing a halogen substituent. As ' :

, . `: ' `''' . '' ~. .. .. . . ..

examples we mention, mineral oil and slack wax (impure paraffin wax), didodecyl phthalate, -tris-~-chlorpropylphosphate and, in particular, chlorinated paraffin waxes. These diluents, which are not reactive towards isocyanate groups, may be added during the preparation of the prepol~ner or just prior to emulsification.

320 g of wood chips were dried to a moistura content of 6%. They were placed in an open mixer bowl and whilst -being tumbled bonding agent flùid was sprayed in by means of a simple hand operated spray, the amount applied being controlled by reference to the loss in weight. Agitation of the sprayed chips was continued for 1 minute after which they were sprinkled evenly over the area of 18 cm x 18 am in a mould box. The mass was then compressed manually as much as possible after fitting a similar sized upper plate thus producing a loosely `~
., - consolidated mat of chips about 43-5 cm thick. The mat was transferred on to release treated metal plates and placed in ;~
a hydraulic press where it was cdmpressed using a pressure of 50 kgf/cm2 between platens at 90-95C for 5 minutes. A
clearance plate of 1.4 cm was used to restrict the den~ity to about 0.7 SG. After removal the boards were conditioned to obtain the water content at about 10~ and physical testing was , carried out on the representative 15 cm x 15 cm central regioon of the resultant pieces of board.
A comparison was made of emulsifiable MDI and ,~
I emulsiflable MDI prepolymer from i MDI 100 :1 :
Oxypropylated glycerol MW 1000 30 " 30 Methoxy polyethylene glycol (Methoxy PEG) MW 65010 ,' :

"
.~ , ... .
~:, ;

~o~ s Each was emulsified by mixing with half its weight of water followed by its own weigh-t of water to thus produce emulsions with 40~ "solids" content.
40 g of these emulsions were used in spraying onto 320 g batches of wood chips as described above.
The boards both displayed good cure at removal from the press and at this temperature there was produced no visible ~- steam or fumes and no serlling was observed when removed from the press.
A similar pair of tests was made using half quantities ::
; of the emulsions to give only 2~% solids as bonding agent on i the weight of chips.
Physical properties by tests described in BS 1811 part 2 were as follows:
EMDI = emulsifiable MDI
:
EMDIPP = emulsifiable MDI prepolymer ,.' ..;,.
. .
~' ' ;', .
. ' `.

,. .

'} :

', .`

:. ,,:, ~-1~78~7~3Z5 ~ ,__.
:- P4 Ln ~D 1~) U) N CO 1~ 1~ ~ Il-) H O ~ ) O ~ ~i 0 ~ ~i t~ O O
:~ N ,1 ~ D N t` N ~
1~ ~_ _ ___~ ~
H Ul Ci) a ,~ o ~ d:' ~ N 1` ~D ~ ) ~i ~1 ~r o co o 1-. ~ o 11~ ~ ~; o o ~ ~ r~ ,~ ~ U~
o~o r` a~ ~r :, ls) _ ._ ~ _ _~ _ __._. ,, ,: LS~ r~
~ r~ u~ ~co ~ co a~ d' . ~ r~
:: 1-1 (~ ~) C~N O co ~) O 1` U~ r~i O O
:~ r` , 1 1~ 0Ir~ , N r-l ~Y
_ _ . ~ ~ . - . , ~ :, . H
,' ~ Lr) ~ ~1 ~D ~ ~ ~r-l CO U~ l~
: :. I:~i . ~ ~ . ~ .. . o Iv ''.
.: O d' ~ ~ OCS~ ~OO ~ ~r ~/ o o oP Ll~ t~ r-l ~9 ~ . : '.
~`; ~ ~D ,_1 O, N : .
i~ ~ ~1 ' ' ' ~,~ ~ . _ _. . ': ~
~'. ..
.`.~ o~ o~ oP oP d~: oP
,, ~ a) : `
.. ~n ~a .
,. td ~ .
5~ A N ,::
O (1~ a) o (dO . ~`1 1 :; ~ a) ~.q ~ .~I E~ ' i.-.
rl ~ r1 1~ E~ : .
"" U~ , ~ ~ ~':', ,~ ~ o~ : :
,'. ~ ~ ~ ~ ~ :: :.
.; ~ ~ ~ ~ ~ ~ ~ l : :
O t~l ~ U~ ~ Q) 1~ ~ ~ . :~ ,.
,,., -rl ~ 'r~ 'r~ ~ 'r~S-l ~1 ~ :
~: ~ (L~ aJ ~q) a) ~1: ~ O Z
E ~ u~ K ::
_~ J ':'~
,~,, .,,,~: ~
.. O 1~ ~
,i.~ . ~ ~ ~ ~ ~
' ' I E~ ~ ~ ~ ~ u~ . ~
.~ ~ ~ ~ a) .:: ~ ~ . N .,~ ~
,., 5-1~ 0~ ~ l ':
.. O ~ rl Ql U~
O ~ O 51 '~' -'I u~ o ~ r-l "'I .~ ~ ~ .,~ ~ a~ :' .
~ ~r~ 5~ ~ r~
:; u~ U u~ a~ ~ ~ ~:
,; 1~ r~ -1 .IJ (U ~: ..
: ~, _ ,. ~ ~ :æ _ _ _ . . _ . .
:,i .
.
1 4 - .
.'. ~
., :

~ Q 8~7~ ~ 5 - 'rhe stability of the emulsion was such that it co~ld be used fo~ up to ~ hour a-t ~0-22C and it was possible to ohtain fully satisfactory board even when the freshly sprayed chips were kept at 20-22C for 1 hour before being compressed into board.
By the inclusion of a catalyst in the emulsion it is possible to accelerate the cure thus permitting either a shoEter cycle at 90-95 C or operati:on at a lower temperature e.g. by including 1~ dimethyl hexadecylamine on the weight of ~MDIPP into the emulsion the stability was reduced so that it had to be sprayed within 2 minutes, and the sprayed chips had to be pressed within S minutes but the board was cured ~` in 3 minutes at 95C or in 5 minutes at 70C.
Improvement in the water resistance may be expected ... .
~ by inclusion of supplementary water repellants on similar ., ~ .
lines to the systems already used wlth the conventional ur~a-formaldehyde phenol-ormaldehyde bonded chipboard. .

. EXAMPLE 2 Four emulsifiable MDI prepolymers (i) to (iv) made:by mixing together MDI (100 parts), methoxy P.E.G. MW 650 .

(10 parts)and the following polyols~

: oxypropylated glycerol, OH value 160 (30 parts) in (i) ,:~; . .
oxypropylated glycerol, OH value 540 (9parts) in (ii) l' a polyester, OH value 540, derived from adipic :
.: acid diethylene glycol and glycerol (9 parts) in (iii), and :~ castor oil, OH value 160 (30 parts) in (iv), .: .
were emulsified with water in the weight ration of 1:1. ..

The NCO content of each emulsion was determined . after 2 hours at 22C using the standard method of adding :~

. excess di-n-butylamine to a 40~ aqueous emulsion followed by ~-~` 3Q back titration with hydrochloric acid. The loss of activity .

.
, - :
. ~

108'7BZ5 The loss of activity of each emulsion was as follows:
emulsion derived from (i) - 55 ~: (ii) " " (iii) - ~4~
" " " (iv) ~ 17%
These results show that the more hydrophobic is the polyol used in the preparation of the prepolymer, the greater is the working life of the emulsion. ~:
~:~ Further, the loss of activity of emulsions derived 10 from 7 parts o:~ an emulsifiable prepolymer and 12 parts of water and the corresponding emulsions incorporating a ::
chlorinated para~fin wax diluent, "Cereclor S45" (Registered .
Trade Mark) was as :~ollows:
Castor oil prepolymer - 27.3 " " " ~ 4 parts "Cereclor S45" - 18.9% :`:
.
Prepolymer from hydrogenated castor oil - 22.9%
.~'! " 1l 11 1l n ~ 4 parts "Cereclor S45" - 13.7%
Prepolymer from oxypropylated glycerol (OH value 540) - 30.4%
4 Parts . "Cereclor S45" - 17.2% - ~ .
. "
20 " " " " " ~ 7 parts . "Cereclor S45" - 13.~%
These results show that by including a parafin ;; wax in an aqueous emulsion of a prepolymer the working li:Ee o:~ the emulsion is extended.
. ' EXAMPLE 3 ,' A prepolymer was prepared by mixing together: :
100 parts MDI
~ 30 parts Castor oil (first pressing) OH 160, and ~ -:; 10 paxts Methoxy PEG MW 650, ~:~;1 heating at 80C overnight, and then cooling. Two emulsions ~:
(a) and ~b~ :were prepared by mixing together: ~ ~

:i :
::. - 16 -,':, ~ .

2~
(a) 4 parts of the abovP castor oil prepolymer and 10 parts of water; and (b) 6 parts of a mixture of the a~ove castor oil prepolymer (4 parts) and "Cereclor S45" (2 parts), and 10 parts of water.
Two chipboard samples were then prepared by taking 102 parts of wood chips containing 2~ moisture and spraying separately whilst tumbling with the above emulsions which were sufficiently fulid to give good atomisation. Each batch of treated chips , was sprinkled into a frame laid on a still plate to form a ` cake which after removal of the frame was covered with an ; aluminium plate, both metal plates having been treated with a wax based release agent. The cakes were compressed in a hydraulic press with platens at 175C using a pressure of 135 Kg/cm2. A distance plate was fitted to limit the compression `
to 19 mm and the amount of treated chips was chosen to give a final chipboard desnity of about 680 Kg/m3. The time of pressing was 4 3/4 minutes and when pressure was released the ~, adhesions of the board using ~he "Cereclor S45" in the binder ;
was better than that of the blank (a), which showed some :. ~
tendency for sticking especially in the case of the steel plate.
., , The boards were allowed to cool and condition and were subsequently tested. The results were as fo~llows~:
, ........................................................................ . .

= b Density Kg/m 704 713 ,Water swell 2 hours ~ 23.0 18.0 " " 24 hours ~ 26.0 21.6 ~;

German V20 test KN/m2 703 822 V100 test KN/m l57 190 , .

7~

A batch of the same type wood chips with 2%
moisture was sprayed with an emulsion prepared ~rom `~.

6 parts of a mixture of castor oil prepolymer used in Example 3 (4 parts) and "Cereclor S45" (a pa~ts), and 6 parts of water and subsequently 5 parts of 20% slack wax emulsion were sprayed on and the treated chips then sprinkled and processed as before.
The cooled conditioned board was tested, the results being ~ .
: as follows~
,~ ' ' Density 690 ~`
Water swell 2 hrs % 13.5 ~ :
" " 24 hrs % 22.0 -.
" 2 V20 KN/m 790 : " .

.~.;;
,,~

~, ..
. .

-. , ~ -- 1 8 .: . ':
., . ~, . ~ .

. .
's'~
~ ::
. .. .

,, ~' `
: ......................................................................... .

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a process for the manufacture of sheets and moulded bodies by hot pressing a mass of lignocellulosic material mixed with a binding agent, the improvement which comprises employing as said binding agent an oil in water emulsion of an organic isocyanate comprising (a) 99 to 25 parts by weight of water;
(b) 1 to 75 parts by weight of an organic isocyanate selected from the group consisting of aliphatic polyisocyanates, aromatic polyisocyanates and isocyanate-terminated prepolymers, made by reacting together an organic polyisocyanate and a polyol in amount such that there is an excess of isocyanate groups to isocyanate-reactive groups present; and (c) a stabilising amount of a non-ionic surface active agent devoid of isocyanate-reactive groups.

2. A process as claimed in Claim 1 wherein the organic isocyanate is a crude mixture of methylene bridged polyphenyl polyisocyanates containing diisocyanates, triisocyanates and higher functionality polyisocyanates.

3. A process as claimed in Claim 1 wherein the organic isocyanate is an isocyanate-ended prepolymer derived from a crude mixture of methylene bridged polyphenyl polyisocyanates containing diisocyanates, triisocyanates and higher functionality polyiso-cyanates.

4. A process as claimed in Claim 1 wherein the organic isocyanate is an isocyanate-ended prepolymer prepared using a hydrophobic polyol.

5. A process as claimed in Claim 4 wherein the hydro-phobic polyol is castor oil.

6. A process as claimed in Claim 1 wherein the surface active agent has the formula:
RO(CH2CH2O)nCONHX
in which R is an alkyl group of from 1 to 4 carbon atoms, n is an integer such that the compound contains an average of from 5 to 120 oxyethylene groups and X is the residue of a di or polyisocyanate and contains at least one free isocyanate group.

7. A process as claimed in Claim 6 wherein R is methyl.

8. A process as claimed in Claim 6 wherein n re-presents an average of from 10 to 25.

9. A process as claimed in Claim 1 wherein the emulsions are those in which from 75 to 50 parts by weight of water are associated with from 25 to 50 parts by weight of organic isocyanate and which contains a stabilising amount of a non-ionic surface active agent devoid of hydroxy, amino and carboxylic acid groups.

10. A process as claimed in Claim 1 wherein the amount of surface active agent used is from 5 parts to 15 parts by weight based on 100 parts by weight of the organic isocyanate.

11. A process for manufacturing sheets or moulded bodies which comprises spraying lignocellulosic material with an aqueous emulsion of an organic polyisocyanate, said aqueous emulsion containing a stabilising proportion of a non-ionic surface active agent devoid of hydroxy, amino and carboxylic acid groups and having 75 to 50 parts by weight of water as-sociated with 25 to 50 parts by weight of an organic isocyanate selected from the group consisting of aliphatic polyisocyanates, aromatic polyisocyanates and isocyanate-terminated prepolymers, made by reacting together an organic polyisocyanate and a polyol in amount such that there is an excess of isocyanate groups to isocyanate-reactive groups present; and hot pressing the sprayed lignified raw material at a temperature below 200°C.

12. A process as claimed in Claim 11 wherein the organic polyisocyanate is an isocyanate-ended prepolymer of a crude mixture of methylene bridged polyphenyl polyisocyanates.

13. A process as claimed in Claim 11 wherein the sprayed lignified raw material is hot pressed at a temperature below 100°C.

14. A process as claimed in Claim 11 wherein the sprayed lignified raw material is hot pressed at a temperature of from 90 to 95°C.

15. A process as claimed in Claim 11 wherein there is included in the emulsion an inert hydrophobic diluent,

16. A process as claimed in Claim 15 wherein the hydrophobic diluent is a chlorinated paraffin wax,

17. A process as claimed in Claim 11 wherein the sprayed lignocellulosic material is dried at 20 to 40°C to remove a portion of the water prior to being hot pressed.