Note: Descriptions are shown in the official language in which they were submitted.
CA 02249273 1998-09-21
Shaped body made of impregnated wood
The invention relates to a shaped body made of impregnated solid
wood. Since ancient times, wood has been impregnated with various
substances, mainly as protection against fungi and insects, for reducing the
5 water absorption or improving the swelling behaviour, for example with tar
oil (for wood plaster), paraffin and waxes, or with mixtures of montan wax
and synthetic resin solutions (alkyd resins), but the problem of removing the
solvent (e.g. trichloroethylene) from the impregnated solid wood persists.
For the production of bearing discs, wood was also impregnated with
10 lubricating oil.
This is better achieved, in particular for dimensional stabilization and
an increase in the hardness with water-soluble phenol/formaldehyde or
urea/formaldehyde resins; however, these generally only delay but do not
suppress the swelling and on the other hand result in a reduction in the
15 tensile strength. They are therefore used as a rule only in the case of
veneers, which are then optionally further processed as moulded laminated
materials. In addition, the combination of wood with urea/formaldehyde
resin, as well as with other plastics, leads to thermosetting materials which,
after shaping and subsequent crosslinking, can no longer be
20 thermoplastically shaped, and are no longer biodegradable and can therefore
present a disposal problem.
The impregnation of veneers with dye and polyethylene glycol or
polypropylene glycol and with an aqueous solution of starch,
polyvinylpyrrolidone or polyvinyl acetate for the production of coloured
25 laminates produced by bonding together individual veneers (JP-A54-117004
or JP-A55-034931), as well as the impregnation of only the cut edge of
wood before the veneer peeling process for edge strengthening, once again
with aqueous solutions of starch, gelatin, polyvinyl acetate, sodium alginate,
polyvinylpyrrolidone, resol, melamine or urea resin, monomers, such as
30 acrylic or methacrylic esters, styrene, vinyl acetate, acrylamide or
acrylonitrile, etc. (JP-A54-026317), has also been disclosed.
Finally, the impregnation of wood or porous mineral materials with an
aqueous polyvinyl acetate solution in vacuo and subsequent application of
CA 02249273 1998-09-21
slightly superatmospheric pressure has also been disclosed, optionally wax
and/or biocides being added (FR-A2505187) .
Other publications, too, are concerned with the impregnation of wood
parts with nonbiodegradable, polymerizable or crosslinking synthetic resins
5 or linseed oil, frequently from solutions, with the stated disadvantages;
these include in particular DE-A1-3942136, FR-A-2647388, JP-A-6071614,
JP-54 057 732, W094/11167, US-A-1991752, SU-A1-1701521, JP-A-
1174401, SU-A- 1288063 and NL-A-23392.
However, all these methods for the production of impregnated shaped
10 wood bodies have the disadvantage that the removal of the solvents used
(including water) on the one hand is time-consuming and energy-
consumptive and on the other hand leaves behind a shaped body which is
porous - even if to a lesser extent than previously.
It is therefore the object of the invention to provide an impregnated,
15 biodegradable shaped solid wood body whose pores are very substantially
filled but which is relatively light and can be produced without special
finishing, and overcomes the disadvantages of the conventional
combinations of wood and plastics with respect to porosity, biodegradability
and thermoplasticity. This object is surprisingly achieved for the first time,
20 according to the invention, by the combination of the features mentioned in
the characterizing clause of Claim 1. Particularly advantageous further
developments of the invention are described in the characterizing clauses of
the dependent Claims.
The natural resin used is in particular a monomer from the group
25 consisting of tall resin, dammar, copal; but also balsam resin or tall oil; as
oil, in particular blown (preoxidized) linseed oil or wood oil, optionally with
the addition of a drying agent (siccative); as fatty ester, in particular one
which is obtained when tall oil is worked up to give tall resin.
For the purposes of the invention, the polymers, natural resins, oils or
30 fatty esters chosen should be in particular those which are liquid at the
loading temperature and preferably do not attack the wood. Substances
which have a relatively low viscosity below the temperature at which the
wood is attacked are particularly preferred. A person skilled in the art will
CA 02249273 1998-09-21
choose a mixture of impregnating agents and any additives such that a solid
wood part to be impregnated reaches the desired degree of penetration
within an appropriate time depending on its porosity - optionally with the
use of a vacuum and/or pressure. For the purposes of the invention,
5 "attack" is to be understood as meaning any undesired change in the
properties, in particular discoloration; decomposition by chemical reaction, in
particular in the case of extreme changes in the pH; swelling or shrinkage
(where undesired); pore formation, etc. It is self-evident that some
thermoplastic materials according to the invention may be suitable for
10 impregnating specific wood types but not for others. For example, slight
discolorations may still be acceptable in the case of darker woods; certain
woods may be more insensitive than others to certain pH changes, etc.
In recent years, as a result of the discussion of the environment, a
quantity of various biodegradable materials based on natural substances,
15 including fossil sources, have been developed, among which many even
exhibit hydrophilic character and, like many natural substances and in
particular wood are capable of absorbing and releasing water. These
materials contain certain percentages of water, depending on the relative
ambient humidity, and are therefore more suitable for combination than
20 plastic in the conventional sense. Their hydrophilic character also facilitates
the penetration into the wood matrix, the properties of wood not being
completely masked but merely supplemented.
The following substances may be mentioned as examples of
biodegradable polymers: polyhydroxybutyric acids, polycaprolactones,
25 polylactic acids, polyesters based on diols and dicarboxylic acids,
polyamides, polyesterurethanes, chemically modified natural polymers, such
as, for example, cellulose acetates.
Further additives, for example various fats, oils, waxes, as well as
lignin or alcohols, in particular to [sic] the natural resins, oils or fatty esters
30 are used for producing specific properties in the completely impregnated
shaped solid wood bodies, without substantially limiting the thermoplasticity
or biodegradability. In particular, hardened or modified, animal and vegetable
fats, for example hydrogenated vegetable fats, epoxidized oils, wool fat,
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tallow as well as salts of various fatty acids, such as, for example, stearic
acid, behenic acid, lauric acid, etc., may also be used.
Finally, various salts, such as, for example, phosphates, borates,
sulphates, chlorides and silicates, may also be concomitantly used by
5 introducing them with the melt into the wood structure. They have a
positive effect on the reduction of the swelling and shrinkage behaviour, but
also have flame-retardant and/or fungicidal activity.
Glycerol, too, is used as a "solvent", plasticizer or humectant; alkali
metal and alkaline earth metal resinates act as drying agent, but also as
10 wetting agents and emulsifiers and thus promote the penetration of the
resins into the wood.
Some of the resins are preferably used in combination with wax
and/or a drying oil, which are or become hard or solid and even brittle at
room temperature but soften at higher temperatures and then preferably
15 have a significant viscosity gradient so that loading can still take place at temperatures at which wood is not attacked at all or is only slightly
attacked. The brittleness of some of the stated substances is compensated
by the fine distribution in the wood matrix.
The viscosity of the impregnating composition at the loading
20 temperature should be less than 20 dPas, expediently less than 10 dPas (the
viscosity of glycerol at room temperature), in particular less than 1 dPas
(water has 0.01 dPas at room temperature). While the pores in solid wood
are of the order of magnitude of a few,um, the resins or polymers according
to the invention have a size of a few nm. The smaller the molecules, the
25 more rapidly and more deeply do they penetrate into the wood. The largest -
in particular polymeric- particles will penetrate only into the uppermost
layers of the surface at the respective treatment temperature in the
respective treatment time; however, it is exactly this which gives rise to the
advantage that the surface properties of the shaped body according to the
30 invention - in particular with regard to hardness and visual appearance (e.g. polishability) - are improved without impairing the thermoplastic
mouldability. Moreover, the diffusion of the smaller molecules from the
interior at elevated temperature is effectively prevented.
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Preferably used waxes are natural ones, such as, for example,
Carnauba wax, bees' wax or montan wax. Waxes have even more
advantageous processing conditions, such as a generally lower melting point
and an even sharper viscosity gradient with increasing temperature. The
combination of wax and resin exhibits good processing properties and end
product properties since the unpleasant property of economical balsam
resin, i.e. being tacky at room temperature is compensated by the use of
waxes. On the other hand, waxes alone tend to sweat at slightly elevated
temperatures of use, which in turn is suppressed by the natural resins
10 present in the mixture.
Linseed oil and wood oil are liquid even at room temperature prior to
"drying"(curing by polymerization), the viscosity decreasing further with
increasing temperature. A linseed oil having a viscosity of 90 dPas at room
temperature exhibits a viscosity drop to 15 dPas when the temperature is
15 increased by only 30~C. This low viscosity in combination with the small
molecular size - since it is also initially a monomer - considerably supports
the impregnation process. The combination of such an oil with resin permits
the production of virtually linoleum-like shaped bodies in a natural wood
matrix.
For the catalytic acceleration of the polymerization reaction (drying) of
the oils used, so-called metal soaps based on one or more metals (in
combination), in particular cobalt, zinc and manganese resinates,
octanoates, linoleates and naphthenates, are used as drying agents. What
was surprising in the case of the combination of biodegradable
25 thermoplastics, some of them hydrophilic, and wood, a hydrophilic
thermosetting plastic, was that it leads to products, shaped articles or
materials in which the characteristic properties of wood, in particular with
regard to the water absorption and release, biodegradability and mechanical
properties, which are known to be excellent, are not lost. The wood
30 additionally acquired the properties of thermoplasticity, improved surface
and, in specific cases, faster biodegradability; completely novel fields of use
have thus been opened up for such shaped articles.
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The swelling and shrinkage of wood is a property which substantially
limits its use in many cases, and is reduced by at least 50% by the process
according to the invention. Consequently, the expensive measures during
processing, for example repeated glueing, tongue-and-groove joints and
provision of expansion joints, are reduced.
The higher the temperatures chosen for impregnation of the solid
wood parts, the better the vacuum which can be applied before the
impregnation or the higher the air, gas or steam pressure which can be
applied during or after the impregnation, the faster and more complete is the
10 penetration of the thermoplastic materials into the wood matrix.
For the production of the shaped bodies, various types of wood may
be used. Whether hard or soft wood or very thin-walled or thick wood parts
are employed depends predominantly on the requirements of the end
products. For example, eucalyptus and poplar wood, as fast-growing
15 plantation timbers, are used predominantly for pulp production or as energy
sources. Their rapid growth results in only a low total hardness and surface
hardness. As a result of the treatment according to the invention, these
woods can however also be used for high-quality applications, for example
in the floor and window sector, and therefore replace more expensive high-
20 quality natural timbers which are in increasingly short supply.
A good example of the improvement of the durability of wood is also
the beech, which can be easily laden with the melts described and achieves
a substantial improvement in durability, stability and also resistance to
mlcroorganlsms.
Wood is by nature only very slightly thermoplastic. The shaped bodies
according to the invention on the other hand can be subjected to
conventional techniques of thermoplastic forming, such as embossing,
pressing, bending and shaping, just as easily as the conventional plastics
parts. This thermoplastic forming takes place substantially without
30 destruction of the material wood structure, so that in certain cases the
wood grain is even completely retained.
The properties of the shaped solid wood bodies according to the
invention can be varied within wide limits by the choice of the type and
CA 02249273 1998-09-21
amount of material and any additives and of the process parameters, such
as temperature and pressure. Said properties include, for example, the rate
of biodegradation, which can even be slowed down compared with wood by
the use of slowly degradable substances, such as, for example, cellulose
5 acetate. However, the density of the shaped articles, too, can be changed
within a wide range. This ranges from very low loading of light wood
(density 0.2 t/m3) to a fully laden wood matrix with about 1.5 t/m3. A
frequently desired effect, especially in the case of soft wood parts, is the
dramatic increase in the surface hardness by the incorporation of a material
10 according to the invention into the wood matrix, so that, by their very
nature, soft woods are also suitable for high-quality floors.
To counteract the disadvantage of the easy flammability of the wood
parts laden with resins, waxes and possibly oils, flame retardants, such as,
for example, ammonia phosphate and zinc borate, may be added to the
15 loading melt, it being possible to use glycerol as a solubilizer.
A possible procedure would be complete immersion of the wood part
- preferably evacuated beforehand - into the molten material and immediate
application of superatmospheric pressure, which leads substantially more
rapidly to the desired result of complete and uniform distribution of the
20 thermoplastic material in the wood matrix. A further improvement of the
impregnation process can be achieved by predrying the shaped solid wood
bodies, with the result that the liquid material is sucked even into relatively
deep wood layers previously occupied by water molecules.
The shaped pieces thus obtained can be processed in the same way
25 as wood and have the additional property of thermoplastic mouldability,
although they can still be readily disposed of through biodegradability.
A wide field of use is open for the finished, possibly thermoplastically
processible parts. Any number of further examples can be added to the
fields of use such as packaging, furniture construction, flooring, vehicle
30 construction and wood construction, interior finishing and toys.
Example 1:
A 120 mm long, 80 mm wide and 20 mm thick soft wood panel
having a density of 420 kg/m3 is heated to 1 20~C and immersed in a
. CA 02249273 1998-09-21
molten low molecular weight polycaprolactone from Union Carbide, at
150~ C; a vacuum is applied for 15 min. The panel is then removed from the
melt and exposed to a gas pressure of 10 bar in a pressure chamber for 30
min to allow the polymeric, biodegradable material to penetrate into deeper
5 wood layers. The panel can be permanently deformed at 170~C, steam
having a supporting effect.
Example 2:
Tall resin (Sacotan3 85 from Krems Chemie, softening temperature 80
- 85~C) is melted in an open vessel and brought to a temperature of 155~C.
10 Wood parts 250 mm long, 80 mm wide and 15 mm thick are introduced
into this hot resin melt. This introduction is effected in a perforated basket
which separates the individual pieces of wood from one another so that the
total surface of each wood part is surrounded by liquid resin, the wood
parts are kept below the liquid level and removal from the hot resin melt is
15 possible.
After the introduction of the pieces of wood, heating of the wood
parts causes the moisture contained to evaporate and the air contained to
escape. This process lasts for about 15 minutes, while the temperature of
the resin solution is kept at 150~C. The vessel is then closed and a gas
20 pressure of 9 bar is applied, which is intended to introduce the resin into
deep wood layers. After pressure has been applied for 1 hour, it is relieved
and the laden pieces of wood are removed from the still liquid resin
(125~C). The amount of resin absorbed during this treatment can be
determined by differential weighing:
Wood type Weight Weight % of resin, % of resin,
before after based on based on
loading loading in total the weight
in gram gram weight of wood
Ash 136 198 31 46
Birch 259 400 35 54
Oak 152 169 10 11
Pine 266 466 42 75
Spruce 99 119 17 20
Alder 188 368 49 96
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Lime 113 158 28 39
Beech 139 210 34 51
Fir 284 293 3 3
Larch 196 201 2 2
Maple 284 436 34 53
Cherry 361 411 12 14
The resin had become homogeneously distributed in the wood
matrix. The wood could be readily subjected to the classical woodworking
methods. The colour changes due to thermal stress and resin introduction
10 (change of light scattering due to filling of wood cavities) on the wood differ
according to wood type but are detectable in every type of wood. The finally
laden wood part (planed) is still rated as slightly tacky.
When the wood which was dry but still contained about 10% of residual
moisture was introduced into the resin melt, a certain degree of foaming,
15 caused by evaporation of the residual water and expulsion of the excess air,
was observed, said foaming being not dissimilar to a "frying process", in the
food industry. This behaviour can be reduced or completely eliminated if
reduced pressure is applied in the treatment vessel and/or the wood parts are
preheated - preferably before immersion of the wood parts in the resin melt.
20 Example 3:
While retaining the essential experimental conditions according to
Example 2, the wood used was merely preheated to 150~C before being
introduced into the resin melt. On the one hand, this results in predrying of
the wood and, on the other hand, the air contained in the wood has escaped
25 according to the temperature.
The wood pretreated in this manner showed only very little or no
foaming, and the pressure vessel could be closed immediately after
introduction of the wood. The fear that this drying process might reduce the
amount of resin loaded was not confirmed. The loading amounts found were
30 virtually identical to those according to Example 2.
Example 4:
To minimize the discoloration of the wood by the thermal stress, a
balsam resin was used, which begins to soften at 60 - 65~C and has a low
viscosity at 115 ~ C. The wood was pretreated for one hour at 115 ~ C and
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was introduced into the resin melt at the same temperature. A very short
loading time of only 15 min, but at a pressure of 15 bar, substantially
reduced the discoloration of the wood. The amount of resin loaded
corresponded substantially to the data of Example 2. However, what was
rather unpleasant was the fact that the resin-laden wood parts are slightly
tacky even at room temperature, which is probably associated with the low
melting point of the balsam resin.
Example 5:
As a negative example from the prior art, the wood parts described
10 in Example 1 were laden under conditions similar to those in Example 1, but
only with Carnauba wax or with a montan wax (melting point: 75~C) from
Schlickum. The melting point was 155 ~ C; the wood was predried for 60
minutes at 130~C; the temperature when the wood was removed was
120 ~ C.
The amount of wax absorbed corresponds approximately to that
which had been found in the case of resin. During heating tests on the wax-
laden pieces of wood, however, an unpleasantly rapid release of the liquid
wax from the wood matrix was observed from about 80~C.
Example 6:
To minimize the remaining disadvantages of the pure wax or pure
resin impregnation of the wood, the two materials were combined with one
another. Surprisingly, waxes and resins can be combined with one another
without limits; they form a common, clear melt which has a common
softening point. They can no longer be separated from one another even by
cooling.
66% of tall resin (Sacotan'~ 85) and 34% of montan wax (Iscoblend~
207 from Schlickum) were melted together and gave a softening
temperature of about 80~ C. The further condition for loading wood with
this combination corresponded to the conditions mentioned in the preceding
Examples. The amount loaded was comparable with the values stated in the
Table of Example 2.
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The laden pieces of wood thus obtained combined the positive
properties of the variants laden only with resin or only with wax. The tacky
impression of wood laden only with resin was sufficiently reduced by the use
of wax; on the other hand, the release of melt from pure wax-laden pieces of
5 wood on increasing the temperature is decisively reduced.
Wood type Brinell Brinell Reduction of
hardness hardness after swelling and
before loading loading shrinkage in %
H Bll( N/mm2) H Bll( N/mm2)
parallel to the fibres
Ash 60 90 50
Pine 40 70 40
Alder 30 75 60
Beech 70 95 70
Spruce 30 55 30
Example 7:
To accelerate the incomplete long-lasting oxidation of the linseed oil,
resins or metal salts of different resin acids and other drying agents are used
for improving the hardness properties. The raw material composition of the
biodegradable material mixture was 70% of linseed oil, 14% of zinc resinate,
15% of rosin and 1 % of cobalt octanoate. Said composition was heated to
150~ C until a clear solution was obtained. The further working conditions
for loading the wood corresponded to the preceding experiments.
The aim of this raw material mixture was to enable the raw materials,
which are used for linoleum production, to penetrate the wood matrix while
still in liquid form or as thermoplastic substances and hence to combine the
properties of wood and linoleum with one another or, so to speak, to enable
the linoleum to form in the wood.
Example 8:
A raw material mixture consisting of 30% of linseed oil, 15% of zinc
resinate, 15% of rosin, 20% of Carnauba wax and 19% of biodegradable
polyester (Skygreen~) and about 0.5% of manganese resinate is heated to
150~C so that a clear but coloured solution forms. The other loading
CA 02249273 1998-09-21
conditions correspond to Example 2. The raw material combination gave end
products having the following properties:
~ Continuous further drying of the linseed oil even when the wood surface
is damaged.
5 ~ The resin and wax content improves the hardness of the wood.
~ The wax content reduces the tack of the linseed oil and of the resin.
~ Owing to its macromolecular structure, the polyester remains
predominantly at the surface of the wood.
The pieces of wood are tested with respect to their Brinell hardness,
10 perpendicularto the fibre direction, in accordance with DIN EN 10003-1, and
with respect to their flexural strength in accordance with DIN 52186:
Brinell hardness Flexural strength
N/mm2 Increase % N/mm2 Increase %
Pine before 6.5 118
Pine after 11.1 69.5 137 15.4
Alder before 11.9 104
Alder after 32.4 171.0 143 37.7
Beech before 22.8 162
Beech after 42.2 84.7 179 10.8
Ash before 23.9 149
Ash after 38.1 59.4 159 7.0
The laden wood pieces were introduced into a press which contained
embossing plates already preheated to 140~ C. The press was slowly closed
and was kept at a moulding pressure of 50 bar for 2 min. The parts shaped
25 in this manner had a waffle pattern embossed 2 mm deep, with intact,
closed surface and undamaged edges. Pieces of wood thermoplastically
moulded in this manner can be used, for example, as stair covering.
Example 9:
In order further to improve the penetration of the polyester and to
30 ensure the possibility of loading of relatively long pieces of wood too, the
surface of the wood parts of this Example was perforated with very fine
needles to a depth of about 3 mm before their introduction into the molten
raw materials. The treatment conditions, as well as the raw material
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composition, corresponded to the preceding Example. The depth of
penetration of relatively high molecular weight, thermoplastic materials too,
can be accurately controlled by a very fine perforation. The perforation can
be made in such a way that no surface damage is visible microscopically.
5 With this possibility, the "wood loading", can also be carried out for
substantially larger wood dimensions and for timbers which by their very
nature are poorly loadable.
Example 10:
If it is wished to load solid wood completely with thermoplastic
10 materials, the solid parts are evacuated prior to loading; without eliminating
the vacuum, the procedure is effected as in Example 9 by introducing the
melt described there in the evacuated loading vessel. A loading pressure of
9 bar is then maintained for 1 h at 1 50~C, with the result that the melt is
particularly uniformly distributed even in the interior of the shaped body.
15 Example 11:
If it is wished not to load solid wood quantitatively but only to modify
the cell walls in order to influence in particular the swelling and shrinkage
behaviour but not substantially to change the hardness, the following
procedure is adopted:
20 The conditions and the raw material mixture correspond to Example 8. The
still untreated wood introduced into the loading vessel was exposed to an air
pressure of 4 bar for 15 min before introduction of the molten material and
the procedure is then continued without pressure reduction as in Example 8.
The impregnation pressure is set at 15 bar and is maintained for 100 min.
25 As a result of the "prestressing" of the wood parts under pressure, after the pressure has been let down the liquid raw material components, too, are
forced out by the escape of the compressed air, and filling of the wood
cavities is thus prevented. Only the cell walls are laden with the substances.
Subsequent plastic forming of the solid wood parts can thus be carried out
more easily, particularly when only the surface is to be further shaped by
embossing - i.e. by displacement or compaction of specific parts.
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Example 12:
The combination of natural resin, wax and a biodegradable polyester,
for example in the form of a polylactide, is also particularly preferred. The
loading melt consists of 65% of Erkazit 415 (from Kraemer), 25% of
5 IscoBlend 231 (from Schlickum) and 10%
of EcoPLA (from Cargill). The loading conditions correspond to the
preceding Examples. The polylactide is deposited as a cohesive coating over
the wood surface with only a small (2 mm) depth of penetration.
Example 13:
The so-called fixing of the "swollen" wood structure by the
displacement of the water and simultaneous incorporation of thermoplastic
materials in the cell structure of the wood results in substantially reduced
swelling and shrinkage behaviour. The following behaviour is chosen for
achieving this:
Before introduction into the melt, the wood parts are conditioned in such a
way that the so-called fibre saturation point (water content between 12 and
20% by weight of water, depending on the type of wood) is reached. The
melt composition corresponds to Example 9. The melt temperature is 140
degrees Celsius. The wood parts are introduced rapidly into the melt,
without preheating. The pressure vessel is rapidly closed without
considerable amounts of steam being able to escape. A pressure of 6 bar is
then immediately applied. This slightly lower process pressure is chosen
since the wood matrix might be easily deformed (collapsing of wood) by the
presence of considerable amounts of water.
After 120 minutes, the wood is removed with unchanged melt
temperature. On removal, emergence of a considerable amount of the
excess air, but especially of steam, is observed. The swelling and shrinkage
behaviour of all wood types tested (beech, alder, birch, maple) could be
reduced by at least 75% by the simultaneous displacement of the water and
replacement by thermoplastic materials and the fixing of the swell state due
to solidification.
