Method of preparing an exfoliated vermiculite for the manufacture of finished product

A method of preparing particles of an exfoliated vermiculite for the manufacture of a finished product, such as a particle board, includes the steps of, if necessary, chemically modifying the vermiculite by impregnating the vermiculite with a suitable anhydride in a non-aqueous solvent; if necessary, applying to the particles of vermiculite an adhesion promoter to promote the adherence of a resin to the surfaces of the particles of vermiculite; and resinating the particles of vermiculite either with a thermoplastic resin which has been surface modified by irradiation or by fluorination, or by an isocyanate thermosetting resin, or by a dry powder novolac thermosetting resin; and if necessary removing any solvent present.

BACKGROUND OF THE INVENTION 
This invention relates to a method of preparing particles of an exfoliated 
vermiculite for the manufacture of a finished product and to a method of 
making a finished product from the particles of exfoliated vermiculite. 
SUMMARY OF THE INVENTION 
According to a first aspect of the invention there is provided a method of 
preparing particles of an exfoliated vermiculite for the manufacture of a 
finished product which method includes the steps of: 
(a) if necessary chemically modifying the vermiculite by impregnating the 
vermiculite with an impregnating composition comprising a dicarboxylic 
anhydride or a tricarboxylic anhydride dissolved in a suitable non-aqueous 
solvent; 
(b) if necessary applying to the particles an adhesion promoter to promote 
the adherence of a resin to the surfaces of the particles of vermiculite; 
(c) resinating the particles of vermiculite by either: 
(i) applying to the particles a thermoplastic resin in dry powder form, so 
that after the application of the adhesion promoter, the thermoplastic 
resin adheres to the surfaces of the particles of vermiculite, the 
thermoplastic resin having been surface modified by irradiation or by 
fluorination; or 
(ii) including in the impregnating composition of step (a) an isocyanate 
thermosetting resin dissolved in a suitable compatible solvent; or 
(iii) applying to the particles a dry powder novolac thermosetting resin 
and if necessary a catalyst therefor so that after the application of the 
adhesion promoter, the dry powder novolac thermosetting resin adheres to 
the surfaces of the particles of vermiculite; and 
(d) if necessary after step (c), removing any solvent present. 
In a first alternative, the method includes the steps of: 
(a) chemically modifying the vermiculite by impregnating the vermiculite 
with an impregnating composition comprising a dicarboxylic anhydride or a 
tricarboxylic anhydride dissolved in a suitable non-aqueous solvent; 
(c) (ii) resinating the particles of vermiculite by including in the 
impregnating composition of step (a) an isocyanate thermosetting resin 
dissolved in a suitable compatible solvent; and 
(d) after step (c) (ii), removing the solvent. 
In this case, no adhesion promoter is necessary. 
The dicarboxylic anhydride may be selected from the group consisting of 
maleic anhydride, phthalic anhydride, succinic anhydride and 
tetrahydrophthalic anhydride, and the tricarboxylic anhydride may be 
trimellitic anhydride. Suitable solvents include methyl acetate, ethyl 
acetate, methylethyl ketone, benzene, trichloroethylene and 
dichloromethane, preferably dichloromethane. 
The impregnating composition preferably contains from 0,25% to 20% 
inclusive, more preferably from 0,25% to 10% inclusive of the anhydride by 
weight of the impregnating composition. 
As the vermiculite preferably takes up from 20% to 250% inclusive, more 
preferably from 30% to 150% inclusive of the impregnating composition by 
weight of the vermiculite before removal of the solvent, after removal of 
the solvent the amount of the anhydride in the vermiculite thus ranges 
from 0,05% to 50% inclusive by weight of the vermiculite. 
The solvent for the isocyanate resin is preferably the same as the solvent 
for the impregnating composition, but may be a different compatible 
solvent. 
The impregnating composition preferably contains the isocyanate 
thermosetting resin in an amount of from 0,25% to 50% inclusive of the 
isocyanate thermosetting resin by weight of the impregnating composition. 
In a second alternative, the method includes the steps of: 
(b) applying to the particles an adhesion promoter to promote the adherence 
of a resin to the surfaces of the particles of vermiculite; 
(c) (i) applying to the particles a thermoplastic resin in dry powder form, 
so that after the application of the adhesion promoter, the thermoplastic 
adheres to the surfaces of the particles of vermiculite, the thermosetting 
resin having been surface modified by irradiation or by fluorination; and 
(d) if necessary after step (c), removing any solvent present. 
Step (c) (i) may precede or follow step (b). 
In this case, no chemical modification of the vermiculite is required. The 
adhesion promoter may be applied with or without a solvent therefor. 
The adhesion promoter is preferably selected from the group consisting of 
convertible resins such as petroleum resins, hydrocarbon resins and 
coumarone indene resins; thermoplastic rubbers; styrene butadiene resins; 
styrene acrylate resins; chlorinated rubbers; phenolic resins; solvent 
soluble thermoplastic resins such as polystyrene or polyvinyl chloride; 
lignocellulosic derived gums or rosins; solvent swellable celluloses such 
as methylhydroxypropylcellulose; phenol formaldehyde novolac resins; 
urethane elastomers; resinous tackifiers; bitumen; coal tar; asphalt and 
pitch; if necessary dissolved in a suitable non-aqueous solvent such as 
those listed above for the anhydrides. 
In the second alternative, the adhesion promoter may be one used in the 
water phase, such as those selected from the group comprising water 
soluble, dispersible or miscible polymers, which are stable to 
electrolytes with film forming temperatures between minus 15.degree. C. 
and 40.degree. C., including polyvinyl alcohol, polyurethanes, olefins, 
acrylate vinyl esters, polyvinyl halides, chloroprene copolymers, and 
dispersions of styrene butadiene rubber, butadiene vinyl acetate 
copolymers and polyacrylic acid esters, acrylics and the acrylic pressure 
sensitives. 
The adhesion promoter is preferably applied to the particles in an amount 
of from 0,1% to 25% inclusive of the adhesion promoter by weight of the 
particles of vermiculite. 
The thermoplastic resin preferably comprises an irradiated cross-linkable 
thermoplastic resin in dry powder form, preferably finely divided dry 
powder form, which resin has been subjected to gamma irradiation whilst in 
dry powder form, the resin being selected from the group consisting of 
polyvinyl chloride, linear low density polyethylene, low density 
polyethylene and high density polyethylene, or a thermoplastic resin in 
dry powder form, preferably finely divided dry powder form, which has been 
fluorinated, the resin being selected from the group consisting of 
polyvinyl chloride, polyethylene and polypropylene. 
In step (c) (i), the particles of vermiculite are resinated with from 1% to 
500% inclusive of the thermoplastic resin by weight of the vermiculite. 
Where the particles of vermiculite are destined for an extrusion or 
injection moulding process, then the particles are preferably resinated 
with from 50% to 500% inclusive of the thermoplastic resin by weight of 
the vermiculite. However, where the particles are destined for a 
compression moulding process, e.g. the manufacture of a particle board, 
then the particles are preferably resinated with from 2% to 50% inclusive 
of the thermoplastic resin by weight of the vermiculite. 
As a further alternative, the adhesion promoter may be applied to the 
particles of thermoplastic resin before step (c) (i). 
In a third alternative, the method includes the steps of: 
(b) applying to the particles an adhesion promoter which comprises a 
solvent which wets the particles of vermiculite and which causes adherence 
of a resin to the surfaces of the particles of vermiculite; 
(c) (iii) applying to the particles a dry powder novolac thermosetting 
resin and if necessary a catalyst therefor so that after the application 
of the adhesion promoter, the dry powder novolac thermosetting resin 
adheres to the surfaces of the particles of vermiculite; and 
(d) after step (c) removing the solvent. 
Step (c) (iii) may precede or follow step (b). 
The solvent may be selected from the group consisting of water or 
dichloromethane. 
There may also be incorporated with the vermiculite particles suitable 
reinforcing fibres. 
In addition, the particles of vermiculite may be mixed with a suitable 
amount of cryogenically ground crumb rubber particles, such as those 
recovered from automobile tires, in the range of particle sizes from 0,25 
to 3 mm inclusive, to improve the resilience, shock resistance, nail 
holding ability and flexibility of the finished product made therefrom. 
According to a second aspect of the invention there is provided a process 
of making an article from particles of an exfoliated vermiculite treated 
by steps (a), (b), (c) and (d) above, which process includes the step of: 
(1) compressing the particles of vermiculite with heating in a suitable 
press or mould to allow the resin present to polymerise to form the 
article. 
For example, the particles of vermiculite may be compressed and heated in a 
suitable press or mould at temperatures between 120.degree. C. and 
250.degree. C. inclusive, preferably from 130.degree. C. to 220.degree. C. 
inclusive, and pressures of from 2 to 70 kg/cm.sup.2 inclusive. 
The article may be for example a particle board. 
According to a third aspect of the invention, there is provided a process 
of making a particle board from particles of an exfoliated vermiculite 
treated by steps (a), (b), (c) and (d) above, which process includes the 
steps of: 
(i) impregnating a sheet or sheets of a lignocellulosic material with a 
composition comprising a thermosetting resin, an extending liquid for the 
thermosetting resin and where necessary a catalyst for the thermosetting 
resin; 
(ii) recovering the extending liquid; 
(iii) placing on one or both sides of a layer of the particles of 
vermiculite, the impregnated sheet or sheets of lignocellulosic material 
to form a composite; and 
(iv) compressing the composite with heating in a suitable press to allow 
the resin present to polymerise, and to allow the thermosetting resin in 
the impregnated sheet or sheets to polymerise and to bond, and all to set 
to form the particle board. 
Again, for example, the composite may be compressed and heated in a 
suitable press at temperatures between 120.degree. C. and 250.degree. C. 
inclusive, preferably from 130.degree. C. to 200.degree. C. inclusive, and 
at pressures of from 2 to 70 kg/cm.sup.2 inclusive. 
According to a fourth aspect of the invention there is provided a process 
of making an article from particles of an exfoliated vermiculite treated 
by steps (a), (b), (c) and (d) above, which process includes the step of: 
(I) subjecting the particles of vermiculite to an extrusion or injection 
moulding process with heating to allow the resin present to polymerise to 
form the article. 
DESCRIPTION OF EMBODIMENTS 
The first aspect of the invention is a method of preparing particles of a 
exfoliated vermiculite for the manufacture of a finished product. 
Vermiculite is the geological name for a group of hydrated lamina minerals 
which are aluminium iron magnesium silicates resembling muscovite, i.e. 
mica or the clays, and which when subjected to heat, exfoliate as a 
function of the inter lamina generation of steam. The material is inert, 
chemically pure, non carcinogenic, free of asbestos, non corrosive, non 
combustible, non allergenic, odourless and harmless if swallowed. It has a 
melting point of 1 315.degree. C., and a sinter temperature of 1 
260.degree. C. It has a thermal conductivity of K=0,062 to 0,065 
w/m.degree.C. It is used in particle sizes of from a screen analysis of 98 
to 100% passing a 200 micron screen, through to a screen analysis of 90 to 
98% retained on a 3 000 micron screen, with a bulk density of from 50 to 
75 g/liter to 90 to 130 g/liter respectively. Typical suitable grades are 
MDX, SFX, FNX or Micron by Micronised Products Ltd. which is a subsidiary 
of Palabora Mining Company, South Africa. 
In the first alternative of the invention, the vermiculite is chemically 
modified by impregnating the vermiculite with an impregnating composition 
comprising a dicarboxylic anhydride such as maleic anhydride, phthalic 
anhydride, succinic anhydride, or tetrahydrophthalic anhydride, or a 
tricarboxylic anhydride such as trimellitic anhydride, dissolved in a 
suitable solvent. 
The choice of solvent is dictated by its suitability including toxicity, 
ease of handling, boiling point and evaporative rate, which in turn affect 
its ease of recovery from the vermiculite after impregnation, its 
inertness and therefore absence of interference chemically, flammability 
and danger of explosion, its solvency thereby propagating the infusion and 
intimate wetting of the vermiculite and finally its ease of recovery by 
absorption in activated carbon followed by steam purging and distillation, 
or condensation and refrigeration or membrane or sieve technologies. 
Examples of suitable solvents are methyl acetate, ethyl acetate, 
methylethyl ketone, benzene, trichloroethylene and dichloromethane. 
Dichloromethane is the preferred solvent, because it is non flammable, has 
a boiling point of approximately 39.degree. Centigrade and is relatively 
inert, and meets the other requirements of the process. In addition 
dichloromethane has the propensity to absorb water as a solute forming a 
98% azeotrope and thus further propagating the latency of the isocyanates 
which react with hydroxyl containing compounds, notably water, to produce 
urethanes. The high evaporative rate of dichloromethane also propagates 
the more rapid evaporation of residual water. 
The impregnating composition includes an isocyanate thermosetting resin 
dissolved in a suitable compatible solvent. 
Isocyanates are compounds containing the group--N.dbd.C.dbd.O and are 
characterised by the general formula: 
EQU R(NCO).sub.x. 
wherein x is variable and denotes the number of NCO groups and R denotes a 
prepolymer group. 
Examples of these isocyanates are those containing an (NCO) content 
percentage preferably exceeding 20%, more preferably exceeding 30%. These 
isocyanates promote latency or reduced reactivity and provide the maximum 
capacity for hydroxyl bonding. Examples are Desmadur VKS or Desmadur VK by 
Bayer, which are solvent free mixtures of aromatic polyisocyanates such as 
diphenyl methane-4,4 di-isocyanate and polymeric matter. These and similar 
are typically referred to as MDIs in the industry. A further description 
used is a di-isocyanato-diphenyl methane, further examples being Suprasec 
DNR-5005, which is a polymeric MDI, or Suprasec 2020 which is a monomeric 
MDI with available NCO percentages of 30,7% and 29% and which are 
polymeric MDI with standard functionality and monomeric MDI respectively. 
The Suprasec resins are supplied by ICI. A further example of a crude MDI 
is Voronate M 229 by Dow Chemical Company. 
Further suitable di-isocyanates are the toluene di-isocyanates with the 
alternative names tolylene di-isocyanate or toluylene di-isocyanate with 
the abbreviation TDI, such as Desmadur L75 by Bayer. 
The solvent may be any suitable solvent and is preferably dichloromethane, 
the isocyanate thermosetting resin being dissolved in the dichloromethane 
at a concentration of from 0,25% to 50% by weight, more preferably at a 
concentration of from 1 to 10% by weight of the impregnating composition. 
Vermiculite being a natural alumino silicate, has layers of linked 
aluminium silicate tetrahedra, combined with layers of magnesium hydroxide 
and aluminium hydroxide. It is to hydroxyl groups in the clay lattice that 
the isocyanate groups and anhydrides cross-link, catalysed by the presence 
of the metallic hydroxides. It has been found, for example, that an 
exfoliated vermiculite board of a density of 0,4, bound with only 2% and 
0,6% by weight on the vermiculite of "Supersec 5005" (ICI) MDI and maleic 
anhydride respectively has remarkable cohesive strength. Given the surface 
area of the fine exfoliated vermiculites, this would appear to 
substantiate the binder mechanism. 
After the treatment of the vermiculite with the isocyanate thermosetting 
resin in the solvent, the solvent is recovered for reuse. The isocyanate 
thermosetting resin is left on and in the vermiculite in a latent 
condition ready for subsequent polymerisation when subjected to the 
appropriate condistions of heat and pressure. 
The vermiculite may be impregnated with the impregnating composition by 
immersion, or by spraying, following which the solvent may be recovered 
for reuse. 
A second alternative of the method of the invention is to apply to the 
particles an adhesion promoter to promote the adherence of a thermoplastic 
resin to the surfaces of the particles of vermiculite. 
The adhesion promoter may be applied with or without a solvent therefor, 
and in any suitable manner such as for example by spraying or the like. 
The adhesion promoter is preferably selected from the group consisting of: 
convertible resins such as petroleum resins, hydrocarbon resins and 
coumarone indene resins. The petroleum resin, for example, may be derived 
from cracked oil C9 unsaturated monomers. The hydrocarbon resin may be an 
alkylated hydrocarbon resin or a hydroxy modified hydrocarbon resin; 
thermoplastic rubbers, e.g. Kraton D 1102CS by Shell; 
styrene butadiene resins; 
styrene acrylate resins; 
chlorinated rubbers; 
phenolic resins; 
solvent soluble thermoplastic resins such as polystyrene or polyvinyl 
chloride; 
lignocellulosic derived gums or rosins; 
solvent swellable celluloses such as methylhydroxypropylcellulose, e.g. 
Culminal MHPC 2000S by Hercules Corporation; 
phenol formaldehyde novolac resins, e.g. Plyophen 602N or Varcum 3337 by 
PRP Resins Division of Sentrachem Ltd; 
bitumen, e.g. hard bitumen Mexphalte H80/90 by Shell; coal tar, asphalt or 
pitch; 
urethane elastomers; 
resinous tackifiers, e.g. Oulutac 20GPR by Forchem OY; 
if necessary dissolved in a suitable non-aqueous solvent such as those 
listed for the anhydrides, preferably dichloromethane. 
The adhesion promoter is applied to the particles in an amount of from 0,1% 
to 25% inclusive of the adhesion promoter by weight of the particles of 
vermiculite. 
Either before or after application of the adhesion promoter there is 
applied to the particles a thermoplastic resin preferably in finally 
divided dry powder form, so that after the application of the adhesion 
promoter the thermoplastic resin adheres to the surfaces of the particles 
of vermiculite, the thermoplastic resin having been surface modified by 
irradiation or by fluorination. 
Thus the thermoplastic resin may be mixed with the dry particles of 
vermiculite before application of the adhesion promoter. Then, when the 
adhesion promoter is applied, the thermoplastic resin adheres to the 
surfaces of the particles of vermiculite. 
Alternatively, the thermoplastic resin may be applied to the particles of 
vermiculite after application of the adhesion promoter. 
The thermoplastic resin may be an irradiated cross-linkable thermoplastic 
resin in dry powder form, preferably finely divided dry powder form, which 
resin has been subjected to gamma irradiation whilst in dry powder form, 
the resin being selected from the group consisting of polyvinyl chloride, 
linear low density polyethylene, low density polyethylene and high density 
polyethylene. 
The dry powder thermoplastic resin may, for example, be a polyvinyl 
chloride, or a linear low density polyethylene, low density polyethylene 
or a high density polyethylene, which resin has been subjected to gamma 
irradiation at various absorbed dosages, typically in the range of from 5 
to 30 kGy, preferably from 8 to 25 kGy, and preferably in oxygen or in an 
oxygenated atmosphere, irradiation being carried out at a typical dose 
rate of 1,38 Gy per second. It is to be noted that excessive dosing can 
result in the polymer being degraded. 
The process of preirradiating these feed stock resins in fine particle size 
in bags is practical and relatively inexpensive. Further, radiation 
induced chemical changes in the chemical structure of the resins lead to 
remarkable physical changes in the resins, amongst which are improved 
cohesive strength and adhesion on conversion, when such radiation induced 
chemical changes occur before the conversion of the resins. Irradiation 
has a marked influence on the morphological characteristics of the 
resulting resins and their associated physical properties when used as 
binders in vermiculite composites. Radiation induced cross-linking takes 
place predominantly in the amorphous phase of the resins and results in an 
enhancement of the crystalline content of the final thermoplastic resins 
and which are induced to behave in a thermosetting manner, through the 
presence of irradiation induced grafting of reactive groups. 
After the dry powder irradiated thermoplastic resin has adhered to the 
surface of the vermiculite any solvent used may be recovered for re-use, 
or otherwise removed. This leaves the vermiculite with a resinated surface 
which is dry and effectively in a latent condition, ready for processing 
to form a finished product. 
The level of dry powder resination of the vermiculite is from 1% to 500% 
inclusive on a weight basis, depending upon the end application of the 
resulting product, but is more usually in the range of from 2% to 50% 
inclusive on a weight basis for a compression moulding process, e.g. for 
composite boards and in the range of from 50% to 500% inclusive on a 
weight basis for extruded and injection moulded products. 
In addition, these irradiated thermoplastic resins in finely divided dry 
powder form may be ground with pigments and suitable extenders such as 
carbonates, talcs or kaolins, and laid up as a dry outer horizon or as a 
pre-pigmented film on one or both outer surfaces of a vermiculite core 
during the manufacture of a board, so providing for decorative surfaces. 
The thermoplastic resin may also be a thermoplastic resin in dry powder 
form, preferably in finely divided dry powder form, which has been 
fluorinated, the resin being selected from the group consisting of 
polyvinylchloride, polyethylene and polypropylene. 
The resin in finely divided powder form or in very high aspect ratio fibre 
form, or in thin flake form, is treated with fluorine gas, which because 
it is such a strong oxidising agent may be diluted with another gas up to 
99% by volume. The resin particles may be first subjected to a vacuum 
before the introduction of the fluorine gas which may be diluted with 
nitrogen or oxygen or other gas, and under pressure. After sufficient 
period of contact the fluorine is once again removed and purged by vacuum 
in order to reduce the free fluorine level to the order of 0,1 parts per 
million in the entrained air, or lower. 
The thermoplastic resin is selected from the group consisting of polyvinyl 
chloride, polyethylene or polypropylene, polypropylene being the 
preferable polymer, which has been fluorinated and which adheres to the 
surface of the vermiculite. 
Fluorination induced chemical changes in the chemical structure of the 
resins leads to physical changes in the resins, amongst which are improved 
cohesive strength and adhesion on conversion when such fluorination 
induced chemical changes occur before the conversion of the resin. 
Fluorination has an influence on the morphological characteristics of the 
resins and their associated physical properties when used as binders in 
vermiculite composites in which they may be induced to behave in a 
thermosetting rather than a purely thermoplastic manner, through the 
presence of fluorination induced grafting of reactive groups. 
After the dry powder, fibre or flake of fluorinated thermoplastic resin has 
adhered to the surface of the vermiculite, any solvent used may be 
recovered for re-use or otherwise removed. This leaves the vermiculite 
with a resinated surface which is dry and which is effectively in a latent 
condition, because the activation of the fluorinated binder resin is only 
achieved on subjection to the necessary conditions of temperature and 
pressure as is described hereinafter. 
The level of resination of the vermiculite is from 1% to 500% inclusive on 
a weight basis depending upon the end application of the resulting 
product, but is more usually in the range of from 2 to 50% inclusive on a 
weight basis, for a compression moulding process, e.g. for composite 
boards and in the range of from 50% to 500% inclusive on a weight basis 
for extruded and injection moulded products. 
In addition, these fluorinated thermoplastic resins in finely divided dry 
powder or flake or fibre form, or in film form may be pre-pigmented for 
laying up as a dry outer horizon or as a pre-pigmented film on one or both 
outer surfaces of the vermiculite composite core, during the manufacture 
of a board, so providing for decorative surfaces. In addition outer 
laminating films may be used which in themselves are laminates, the inner 
laminate only having been fluorinated. 
As a further alternative, the adhesion promoter may be applied to the 
particles of thermoplastic resin before step (c) (i). 
The resination of the particles is designed to bind the particles to one 
another to form a composite product or an extruded product or the like. 
A third alternative of the method of the invention is to apply to the 
particles an adhesion promoter which is a solvent, to promote the 
adherence of a dry powder novolac resin to the surfaces of the particles 
of vermiculite. Again the adhesion promoter may be applied before or after 
application of the dry powder novolac resin to the particles of 
vermiculite. 
Thus the novolac resin may be mixed with the dry particles of vermiculite 
before application of the adhesion promoter. Then, when the adhesion 
promotor is applied, the novolac resin adheres to the surfaces of the 
particles of vermiculite. 
Alternatively, the novolac resin may be applied to the particles of 
vermiculite after application of the adhesion promoter. 
The solvent may be selected from water and dichloromethane. 
A novolac resin is a resin based upon phenol and formaldehyde and any of 
the variations and modified forms of such a resin, where the molar ratio 
of phenol to formaldehyde exceeds parity. The novolac resin may contain a 
catalyst, which on decomposition with heat gives rise to a source of 
formaldehyde, inducing the condensation of the polymer to form a three 
dimensional stable network with minimal shrinkage and which is hard, 
strong and insoluble. The resin is used in finely divided powder form and 
has the property of commencing to flow at approximately 100.degree. to 
130.degree. C., generally around 110.degree. C., followed by the 
decomposition of the catalyst, for example, hexamethylene tetramine. 
Example of suitable novolac resins are Schenectady Corporation of South 
Africa codes 6240 or 3174, or Plyophen 24-700 and Plyophen 602N or Varcum 
3337 of PRP Resins Division of Sentrachem Ltd of South Africa. 
After the dry powder novolac thermosetting resin has adhered to the surface 
of the vermiculite, the solvent adhesion promoter may be recovered for 
reuse or otherwise removed. This leaves the vermiculite with a resinated 
surface which is dry and in a latent condition, ready for processing to 
form a finished product. 
In addition, the particles of vermiculite may be mixed with a suitable 
amount of cryogenically ground crumb rubber particles, such as those 
recovered from automobile tires, in the range of particle sizes from 0,25 
mm to 3 mm, to improve the resilience, shock resistance, nail holding 
ability and flexibility of the finished product made therefrom. 
Examples of the invention will now be given.

EXAMPLE 1 
There is formed an impregnation mixture comprising a 1% phthalic anhydride 
and a 3% Suprasec 5005 MDI (by ICI) solution in dichloromethane. 
Exfoliated vermiculite particles are impregnated with the impregnation 
mixture so that the particles absorb up to 150% of the impregnation 
mixture, after drainage. 
Thereafter the solvent, dichloromethane, is recaptured for reuse. 
The treated particles are placed between the platens of a press and pressed 
into a board at a temperature of about 210.degree. C. for about 5 minutes 
to produce a particle board having a density of 0,34 g/cm.sup.3. 
EXAMPLE 2 
There is formed an impregnation mixture comprising 10 kg of 
dichloromethane, 400 g of methanol, 40 g of Culminal MHPC 2000S by 
Hercules Corporation. The impregnation mixture is left to stand for not 
less than 40 minutes to allow the cellulose to swell. 
Exfoliated vermiculite particles are impregnated with the impregnation 
mixture and are thereafter drained. 
The treated vermiculite particles are then mixed with 12% by weight of a 
linear low density irradiated polyethylene of 300 mesh particle size, 
which has been irradiated at an absorbed dose of 16 kGy, so that the 
polyethylene particles adhere to the vermiculite particles. 
Thereafter, the solvent, dichloromethane is recaptured for reuse. 
The particles are pressed between the platens of a press at about 
220.degree. C. for about 6 minutes to produce a board having a density of 
0,93 g/cm.sup.3. 
EXAMPLE 3 
There is formed an impregnation mixture comprising a 1% solution of maleic 
anhydride in dichloromethane. 
Exfoliated vermiculite particles are sprayed with the impregnation mixture 
so that the impregnation mixture is absorbed. 
While the vermiculite particles are still damp, 10% by weight of the 
vermiculite of Varcum 3337 novolac resin at an average particle size of 
250 mesh, is added to the vermiculite particles and the particles are 
mixed so that the novolac resin particles adhere to the vermiculite 
particles. 
Thereafter the solvent, dichloromethane, is recaptured for reuse. 
The particles are pressed between the platens of a press at about 
190.degree. C. for about 4 minutes to produce a board having a thickness 
of 12 mm and a density of 0,6 g/cm.sup.3. 
The second aspect of the invention is a process of making a article from 
particles of an exfoliated vermiculite treated by steps (a), (b), (c) and 
(d) above, which process includes the step of compressing the particles of 
vermiculite with heating in a suitable press or mould to allow the resin 
present to polymerise to form the article. 
For example the particles of the vermiculite may be compressed and heated 
in a suitable press at temperatures between 120.degree. C. and 250.degree. 
C., preferably in the range of from 150.degree. C. to 220.degree. C., and 
at pressures of from 2 to 70 kg/cm.sup.2, preferably about 18 to 30 
kg/cm.sup.2. 
The third aspect of the invention is the process described above but for 
making a particle board from particles of an exfoliated vermiculite, which 
is modified by the inclusion in the particle board of one or more sheets 
of a lignocellulosic material impregnated with a particular composition. 
In this way, the impregnated sheet or sheets of lignocellulosic material 
are incorporated into one or both the outer horizons of the particle board 
thereby providing a stressed skin composite with a surface to which 
finishes can be applied. 
The sheet or sheets of a lignocellulosic material may be sheets of paper, 
preferably kraft paper, pulp in sheet form, wood veneer, or sheets of any 
other suitable lignocellulosic material. 
The sheet or sheets of lignocellulosic material are impregnated with a 
composition comprising a thermosetting resin, an extending liquid for the 
thermosetting resin, and where necessary a catalyst for the thermosetting 
resin. 
Examples of suitable compositions for impregnation are disclosed in South 
African Patent No 90/2260 to Plascon Technologies (Proprietary) Limited 
and are set out in more detail below. 
It is desirable that the thermosetting resin has an extended pot life, i.e. 
the period of time during which no significant viscosity change occurs in 
the resin mix. A pot life of at least fourteen to twenty five weeks is 
desirable. This may be achieved by suitable selection of thermosetting 
resin and the extending liquid and where present the catalyst. The 
thermosetting resin may also be kept at a low temperature, for example 
below 10.degree. C. to extend the pot life. 
The extending liquid has other important functions which are to provide 
variability as to the weight of resin to be impregnated into the sheets, 
to control resin viscosity, not to interfere with polymerisation, to be 
easily recovered from the impregnated material and to be easily handled 
without danger of toxicity, explosion or fire. 
The thermosetting resin may be a phenolic resin (phenol formaldehyde resole 
resin), preferably a liquid phenolic resin, which can be polymerised at 
room or elevated temperatures. Examples of suitable phenolic resins 
include Celobond J 2027 L, J 2018, J 20/1096 L and J 20/1081 L from 
British Petroleum Company Plc, which may be catalysed with a catalyst such 
as Phencat 10 or more preferably latent catalyst Phencat P.R.P 382 from 
British Petroleum Plc. A phenol furfuryl resin catalysed with 
hexamethylenetetramine, or a blend of a phenolic resin with melamine 
formaldehyde or urea formaldehyde resins are also choices. 
Suitable extending liquids for use with phenolic resins may be either 
solvents for the resin or low viscosity diluents, and may be either 
reactive or non reactive. Typical examples include water, C1 to C4 
alcohols such as methanol or ethanol, higher carbon alcohols such as 
furfuryl alcohol, acetone or methyl ethyl ketone, or blends between them. 
Other particularly suitable thermosetting resins are the MDI and TDI 
isocyanates which may be used without polyol or usual cross-linking 
components, because they link with the hydroxyl groups in the cellulose 
and hemicellulose of the lignocellulosic sheets of materials. An example 
of a suitable polyurethane pre-cursor of this type is Desmodur VK or 
Desmodur VKS by Bayer. 
Suitable extending liquids for use with isocyanates are the halogenated 
hydrocarbons such as dichloromethane or trichloroethylene, or ethyl 
acetate. No catalyst is necessary. 
Another type of thermosetting resin which may be used are the liquid room 
temperature curing acrylic and methacrylic acid esters and methyl 
methacrylates, typically catalysed with benzoyl peroxide powders. Further 
types are the urea formaldehydes, melamine formaldehyde resins, catalysed 
either with acids or alkalis, and which may have been internally 
plasticised with glycols. 
The composition may also include other components such as an inhibitor, an 
accelerator or a surfactant, a fire retardant or a plasticiser. 
There are two particularly preferred compositions for the use in this 
invention. These compositions are preferred because they have optimum pot 
life, they provide for suitable levels of impregnation of the resin into 
the sheet materials to be impregnated, they provide for easy 
polymerisation of the thermosetting resin once impregnated, and the 
extending liquid is easily recovered. 
The first preferred liquid composition comprises a phenolic resin, 30% to 
400% by weight of the phenolic resin of an extending liquid which is 
chosen from a C1 to C4 alcohol, preferably methanol, which imposes 
latency, but which may have blended with it another solvent to increase 
evaporative rate, and a catalyst for the phenolic resin, such as Phencat 
10 or a latent catalyst such as P.R.P 382 BY British Petroleum Plc or its 
equivalent. 
The second preferred liquid composition comprises an isocyanate, preferably 
a MDI or TDI isocyanate, in which no catalyst inclusion is necessary, 20% 
to 350% by weight of the resin of an extending liquid which is selected 
from dichoromethane, trichloroethylene, ethyl acetate, methyl acetate or 
other suitable extending liquids, preferably dichloromethane, and an 
anhydride. The methyl or ethyl isocyanates esterify with the hydroxyl 
groups in the cellulose and hemi-cellulose molecules of the pulp or paper 
or wood veneer or other natural fibre or lignocellulosic material and in 
themselves form polyurea polymer structures imposing good mechanical 
properties on the material treated. 
The sheets of lignocellulosic materials may be impregnated with the liquid 
composition in any suitable manner. Immersion or impregnation by 
vacuum/pressure/vacuum impregnation in a suitable pressure cylinder or 
examples. Thereafter the impregnated sheets are passed to the next step of 
the process. 
In the next step of the process, the extending liquid present in the 
impregnated sheets is recovered for re-use by evaporation and subsequent 
recondensation, or absorption. 
In the next step of the process, the impregnated sheets of lignocellulosic 
material are positioned either at the bottom or top or on both bottom and 
top of a layer of the vermiculite particles to form a composite and the 
composite is then pressed under suitable conditions of temperature and 
pressure between the platens of a press, on either a continuous or 
discontinuous basis, whereupon the thermosetting resin in the impregnated 
sheets is polymerised, the resin in the vermiculite polymerises, and all 
set to form the particle board with the outer impregnated sheets firmly 
adhered to the core of the composite. These lend themselves to powder 
coating immediately the board exits the press and is at the requisite 
temperature. 
After steps (a) to (d) of the methods described above, the particles of an 
exfoliated vermiculite so treated may be made up into a particle board or 
other article by compressing the particles of vermiculite with heating in 
a suitable press or mould. It has been found that the particles of 
vermiculite may be further treated before they are compressed in a press 
or mould, by wetting of the particles of vermiculite with a solution of a 
natural latex or thermoplastic rubber or other tacky or sticky soluble 
compound, and then evaporating off the solvent, which may be water in the 
case of natural latex, or an acrylic pressure sensitive adhesive. 
The result of this is that the particles of the vermiculite, either in the 
outer horizon or optionally throughout the depth thereof, are stuck 
together by the thermoplastic rubber or other tacky or sticky compound, to 
provide a flexible sheet. This flexible sheet may then be compressed with 
heating in a suitable press or mould as is described above. 
The thermoplastic rubber may be any of those listed above, and the solvent 
may be any suitable solvent such as dichloromethane. Alternatively a 
natural latex in water may be used. 
The solution of the thermoplastic rubber or other sticky or tacky compound 
may be applied to the particles of the vermiculite by spraying. Thereafter 
the particles may be subjected to a moderate pressure, before or after 
removal of the solvent. 
The advantage of the product produced by this step is that the flexible 
sheet may be placed in a press or mould which has a shaped surface, for 
example a corrugated or curved surface, without particle displacement 
which would result in undue thickness variations in the final product. 
When the flexible sheet is pressed at appropriate temperatures and 
pressures, it first conforms to shape of the press or mould, is then 
compressed and then the irreversible binding takes place to form a 
suitably shaped component. The resulting component is water resistant, has 
good mechanical properties, retains its shape, has no binder related toxic 
volatiles and is cost effective. 
The fourth aspect of the invention is a process of making an article from 
particles of an exfoliated vermiculite treated by steps (a), (b), (c) and 
(d) above, by conventional extrusion or injection moulding techniques. 
The treated particles of vermiculite may also be combined with a suitable 
amount of lignocellulosic particles or with reinforcing fibres such as 
glass fibre or synthetic organic fibres, before manufacture of the 
finished product. 
The various methods disclosed above and the products produced by these 
methods have various advantages which are set out below: 
1 After the chemical treatment and resination of the particles, and the 
recovery of the solvent for re-use, the particles are in the latent 
condition allowing the pressing operation in making up the board to be 
carried out at a different place and at a different time. This allows for 
discontinuous production and results in the further advantage of 
minimising capital investment costs per unit of product produced, as well 
as greater marketing flexibility, i.e. selling the pre-manufactured board 
or the beneficiated vermiculite only for board pressing by the customer. 
2 The avoidance of binder related toxic volatiles, the minimisation of 
bulking on contact with water, the imposition of good mechanical 
properties and of good surface integrity are achieved. 
3 The entire composite is pressed from dry constituents which allows for a 
much wider choice of specification such as outer horizon make up, internal 
binder combinations and percentage levels, core constituent additives such 
as fibres or outer laminate choice, and product shape and forming method.