Note: Descriptions are shown in the official language in which they were submitted.
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Background of the Invention:
Field of the Invention:
The present invention relates to a method for
manufacturing a lignin for continuous carbon fiber
spinning by heat-fusion process, employing lignin as
a starting material, which is contained in woody material
in an amount of about 20 to 30 %.
Nowadays comprehensive studies are being made
on separation or modification of cellulose, hemicellulose
and lignin from woody resources for the purpose of
utilizing such materials as food, forage, and chemical
industrial starting materials. In certain fields,
development for industrialization is going on. In the
field of pulping technology, new organic solvent digestion
processes are extensively studied, where an alcohol,
a phenol, acetic acid, or the like are used as the
digesting agent. However, success of these new
technologies depends upon the accomplishment of effective
utilization of lignin.
Description of the Related Arts:
One technology of converting lignin to
industrial materials of high added value relates to
manufacture of carbon fiber therefrom.
One prior art regarding lignin carbon fiber
relates to lignin-poval type carbon fiber proposed by
Professor Ohtani of Gumma University on 1963: See Japanese
Patent Publications No. 15727/1966, and No. 26356/1967.
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This process is characterized by drawing out thread from
a spinning solution prepared by heating and dissolving
lignin (of industrial grade) and polyvinyl alcohol in
a highly concentrated aqueous NaOH solution. This process
was ousted by PAN type and pitch type carbon fiber
because of the cost and the properties. After 20 years
therefrom, the present inventors proposed a process for
manufacturing lignin for continuous spinning by
hydrogenolysis, and heating lignin obtained by digestion
and explosion-disintegration of wood, as well as a
process of carbon fiber therefrom: See Japanese Laid-Open
Patent Application No. 110922/1987. The carbon fiber
of the former of the above processes has disadvantages
such that the manufacturing cost is high because of
the wet spinning process and of high temperature
treatment at 1400C or higher for vaporizing-off of
sodium, and that the product is significantly low in
strength characteristics. The latter of the above
processes is now under study for industrialization.
20- This process involves the problems of high capital cost
resulting from high energy consumption and use of pressure
vessels in hydrogenolysis in the spinning-lignin
preparation process, and further of low yield of the
carbon fiber.
Summary of the Invention:
The present invention has been accomplished
from the aforementioned view point, and provides a method
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for manufacturing lignin for carbon fiber spinning
which process makes it feasible to manufacture
carbon fiber of high added value in high yield and
economically from lignin separated from woody
resources as mentioned above.
In accordance with the present
invention, there is provided a method of
manufacturing a lignin for carbon fiber spinning,
which comprises subjecting a phenolated lignin
deriving from woody material to heat treatment in
a non-oxidizing atmosphere.
Preferably, the phenolated lignin is
prepared by phenolation of lignin dissolved out
from the woody material by delignification. The
phenolated lignin can also be prepared by
digestion of the woody material with a phenolic
substance.
Detailed Description of the Invention:
In this invention, the lignin derived
from woody materials includes lignins exhausted
from or produced as a by-product in paper plants
or pulp plants using woody materials as a raw
material; and lignins produced as a by-product in
a new separation process such as a boiling
process, explosive disintegration, and organic
solvent digestion, or in a new pulping technology.
In this invention, the lignin is phenolated, and
subjected to heat treatment in non-oxidizing
atmosphere to prepare lignin material for
spinning, and subsequently it is spun, made
infusible, and carbonized to produce carbon fiber.
The gist of the present invention is to
heat the lignin and phenolic solvent to reflux at
its boiling point to produce phenolated lignin
having thermal
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fluidity, and to continue further heating in a reaction
vessel in a non-oxidizlng atmosphere to complete heat
tretment, thus producing lignin for spinning.
The phenolation may be conducted by heating
the mixture of the above-mentioned lignin with a phenol
in presence of or absence of catalyst such as an acidic
organic catalyst as an accelerator. The phenols useful
for the phenolation includes pure substance such as
phenol, cresole as well as mixtures of phenolic substances
like quaiacol such as creosote, and methyl creosole and
xylenol. The catalyst useful for accelerating phenolation
includes organic acidic catalysts such as p-toluene
sulfonic acid, sulfonyl chloride, amide salts and
hydroxyamine salts thereof.
The heat treatment for densification may be
conducted by heating a phenolated lignin in a
non-oxidizing atmosphere. The non-oxidizing atmosphere
may be prepared with nitrogen stream under reduced
pressure. The pressure reduction is preferable in many
cases and the heat treatment mainly for increased
viscosity or densification in the present invention is
conducted under a reduced pressure of several tens of
mmHg, or preferably of 10 mmHg or less, and the solvent
is easily recovered. The heating is conducted at a
temperature and for a lapse of time sufficient to
polycondensation of phenolated lignin for viscosity
increase of the solution. Generally, heating is
preferably conducted to such a degree that the spinning
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temperature of l50C or more is attained. For example,
heat treatment in a temperature range of from 180 to
300C for 30 minutes to 6 hours is preferable.
The lignin for spinning prepared as mentioned
above may be continuously spun by conventional heat-fusion
process.
This fiber is made infusible by heating in
the air at a constant rate of temperature elevation.
This process for infusibleness may be carried out
according to a conventional method, for example, by
starting at 80C and completing at 200C. The fiber
thus made infusible is generally carbonized by elevation
of the temperature at a rate of 200C per hour up to
800C in nitrogen stream.
The present invention provides lignin for
spinning with a high yield of 80 % or more which is twice
or more times that of the conventional method conducted
by the pres$nt inventors. The yield of the carbon fiber
as the final product is about 30 ~, which is higher than
not only the conventional method but also pitch type
carbon fiber.
Description of the Preferred Embodiments:
The present invention is explained below by
referring to examples. This invention, however, is not
limited by these examples.
Raw material
The lignin material was obtained from white
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birch wood by boiling with saturated steam of 15 kg/cm
(guage pressure) for 10 minutes, disintegration by means
of a refiner, removal of hemicellulose by extraction
with water, and extraction with methanol.
Example l:
10 grams of the above-described lignin material
was made to react with an equal amount of phenol in an
glass flask equipped with a stirrer and a cooler for
3 to 5 hours at the boiling temperature (180C) of phenol.
p-Toluence sulfonic acid was added at the
reaction in an amount of 2 % relative to the lignin.
After the reaction, the reaction vessel was evacuated
(to approximately 10 mmHg), and the heat treatment was
conducted (for further 3 to 5 hours) at the same
temperature for recovery of the unreacted phenol and
for densification. Lumpy solid matter was thus obtained
by the treatment.
Table 1 shows the yield of the lignin for
spinning thus prepared, spinning characteristics thereof
in continuous spinning according to conventional
heat-fusion process, and heat stability of the spun fiber.
The spinning characteristics was evaluated by spinning
speed within which continuous spinning is feasible.
The heat stability was evaluated by occurrence of
fusion-bonding between fibers.
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Table 1
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Heat Treatment
Exper- Condition Yield Spinning Heat
No. (~) istics Stability
Temper- Time
(C) (Hours)
1 180 3 100.3 +++ _
2 180 4 96.8 +++
3 180 5 93.8 + ++
In the Table:
Yields are shown in percentage by weight of lignin,
The symbol "+" means feasibility of spinning at
the rate of 100 m per minute for one +, and the
number of the symbol is the multiple thereof,
Thermal stability is represented by the symbols
as below:
- : Fusion-bonding occurs between fibers,
+ : Slight fusion-bonding is observed between
fibers,
++ : No fusion-bonding was observed.
As shown in Table 1, the yields of lignin for
spinning were not less than 90 % in all Examples, which
are twice or more that of the conventional process
(Japanese Laid-Open Patent Application No. 110922/1987).
All samples could be spun at a spinning rate of 100 m
per minute or more in the thermal fusion process. The
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thermal s~ability of fiber was inclined to depend on
the length of the neat treatment time: the fiber spun
after 3 hours of heat treatment became fused during the
thermal stabilization treatment, while the fibers from
the lignin for spinning obtained by 4 hours or 5 hours
of the treatment could be made infusible by heating up
to 200C with temperature elevation rate of 6C per hour.
By changing the heat treatment conditions,
it is possible to substantially change the time required
by the thermal stabilization treatment. For example,
the fibers prepared by spinning the phenolated lignin
- heated at 300C for 30 minutes under reduced pressure
can be made infusible by heating up to 250C with a
heating rate of 10C/minute.
The lignin for spinning which had been made
infusible in Experiment 2 was carbonized by elevating
the temperature at a rate of 100C per hour up to 1000C
in nitrogen;stream in a firing furnace. Table 2 shows
the properties of the resulting carbon fiber.
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Table 2: Properties of Li~nin Carbon ~iber
Fiber Breadth 21.4 + 5.44 ~m
Tensile Strength 52.8 + 11.6 kg/mm
Elongation 1.06 + 0.18 %
Elasticity Modulus 4.99 + 0.63 t/mm
The yield of this carbon fiber was about 30 %.
Table 3 shows the yield in each steps from lignin
to carbon fiber in comparison with that of conventional
method.
Table 3: Yields in Manufacturing Steps and of Carbon Fiber
Hydrogenolysis Method of ,
Method Present Invention
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Sample Preparation Step 0.4 0.9
20 Spinning Step 0.8 0.8
Heat Stabilization Step 1.0 1.0
Carbonization Step 0.5 0.4
Yield of Carbon Fiber (%) 16 28.8
From Table 3, it is understood that the present
invention provides carbon fiber in a high yield.
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Example 2:
The above-mentioned raw material and the equal
amount of creosote were made to react in an autoclave
under agitation at 300C for one hour. Then the reaction
liquor was transferred into a glass vessel and heated
under a reduced pressure to remove and recover the
unreacted creosote and to prepare phenolated lignin.
No catalyst was added in this Example.
The resulting phenolated lignin was densified
by heating at 250C for 15 minutes under a reduced
pressure (the pressure being the same as in Example 1)
to prepare lignin for spinning.
The yield was 85.5 %.
The spinning characteristics in the heat fusion
method, and the stability of the fiber were tested in
the same manner as in Example 1 to find that it was as
excellent as the product of Example 1 for use as the
starting material for carbon fiber.
In the above examples, the lignin extracted
from the woody material is used as the starting material.
However, the woody material can directly be treated with
a phenolic substance to obtain the phenolated lignin
for further heat treatment. In this case also similar
results can be obtained.
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