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Chapter 7 · From Wood to Pulp - Cellulose
7
5 Today, paper production is carried out
on a large industrial scale with fully
automatic paper machines that are
up to 10 m wide and 200 m long. The
subsequent “coating” with binders and
pigments gives the paper a smooth
surface. During “finishing”, the desired
sizes are finally cut.
5 An important secondary product of
cellulose is regenerated cellulose. For
this purpose, the cellulose is swollen
in caustic soda solution to form alkali
cellulose, which is then converted
with carbon disulfide CS 2 into soluble
cellulose xanthogenate. This solution
is injected into a bath consisting of
sulfuric acid and sulfates and regenerated
cellulose precipitates and is spun into
filaments (viscose rayon). The CS 2 is
released and can be recycled. However,
the formation of sodium sulfate in
stoichiometric quantities as a by-product
is disadvantageous.
5 If the xanthogenate solution is passed
through wide, thin slit nozzles into the
precipitation bath, a transparent film,
cellophane is formed, to which glycerol
is added as plasticizer. It is used for
packaging, e.g. for food.
5 An alternative to the xanthogenate
process is the Lyocell process.
The cellulose is dissolved in
N-methylmorpholine-N-oxide (NMMO)
and then precipitated again as Tencel
fiber. This fiber has a good adsorption
behavior and is used in the manufacture
of sportswear and workwear.
5 Other important derivatives of cellulose are
its esters with organic or inorganic acids.
The most important representatives are
cellulose acetates, which are processed
into fibers and films, and cellulose nitrates.
If cellulose nitrate is mixed with camphor,
the celluloid, which was formerly used as a
film carrier, is formed.
5 Cellulose ether are also important.
Methyl chloride and ethyl chloride form
methylcellulose (MC) and ethylcellulose
(EC). The reaction with chloroacetic acid
produces carboxymethylcellulose (CMC),
which is used as a graying inhibitor in
Hydroxyethyl cellulose is preferably used as:
5 Viscosity improver in latex paints
5 Additive in mortars and concrete mixes
5 Additive for sausage casings
5 Protective colloid during PVC emulsion
polymerization.
Ethylcellulose (EC) is produced from alkali cellulose and ethyl chloride and hydroxypropyl cellulose (HPC) with propylene oxide, respectively.
Both cellulose ether are only of minor importance (. Fig. 7.18) and are also used in construction chemicals, adhesives and pharmaceuticals.
Summary (Take-Home Messages)
5 Cellulose is a polysaccharide, in which
the glucose monomer units are linked to
each other by a β-1,4-glycosidicbond. The
cellulose chains intermolecularly interact
with each other by hydrogen bonds and
partially form crystalline regions.
5 The main source of cellulose is wood, in
which cellulose has a proportion of up to
50%. Hemicelluloses and lignin are also
found in wood. Worldwide, 3.4 billion
tons of wood are harvested annually.
5 In the sulfate process (or “Kraft
process”), wood is processed under
basic conditions. The digestion solution
consists of caustic soda and sodium
sulfide. The sulfur losses are compensated
by sodium sulfate, after which the
process is named. The by-product is black
liquor in which the lignin components
are dissolved. Worldwide, 80% of the
cellulose is produced by the sulfate
process.
5 In the sulfite process, wood is
decomposed in the acidic to neutral pH
range with the addition of hydrogen
sulfite solutions. Since no hydrogen
sulfide is formed, the process is much
more environmentally friendly. However,
it can only be used for wood species low
in resin and silicic acid, such as pines.
5 Paper consists of cellulose, mechanically
crushed wood and other fillers and
additives. Increasingly, recycled waste
paper that has previously been deinked is
also being added to paper production.
Chapter 7 · From Wood to Pulp - Cellulose
7
5 Today, paper production is carried out
on a large industrial scale with fully
automatic paper machines that are
up to 10 m wide and 200 m long. The
subsequent “coating” with binders and
pigments gives the paper a smooth
surface. During “finishing”, the desired
sizes are finally cut.
5 An important secondary product of
cellulose is regenerated cellulose. For
this purpose, the cellulose is swollen
in caustic soda solution to form alkali
cellulose, which is then converted
with carbon disulfide CS 2 into soluble
cellulose xanthogenate. This solution
is injected into a bath consisting of
sulfuric acid and sulfates and regenerated
cellulose precipitates and is spun into
filaments (viscose rayon). The CS 2 is
released and can be recycled. However,
the formation of sodium sulfate in
stoichiometric quantities as a by-product
is disadvantageous.
5 If the xanthogenate solution is passed
through wide, thin slit nozzles into the
precipitation bath, a transparent film,
cellophane is formed, to which glycerol
is added as plasticizer. It is used for
packaging, e.g. for food.
5 An alternative to the xanthogenate
process is the Lyocell process.
The cellulose is dissolved in
N-methylmorpholine-N-oxide (NMMO)
and then precipitated again as Tencel
fiber. This fiber has a good adsorption
behavior and is used in the manufacture
of sportswear and workwear.
5 Other important derivatives of cellulose are
its esters with organic or inorganic acids.
The most important representatives are
cellulose acetates, which are processed
into fibers and films, and cellulose nitrates.
If cellulose nitrate is mixed with camphor,
the celluloid, which was formerly used as a
film carrier, is formed.
5 Cellulose ether are also important.
Methyl chloride and ethyl chloride form
methylcellulose (MC) and ethylcellulose
(EC). The reaction with chloroacetic acid
produces carboxymethylcellulose (CMC),
which is used as a graying inhibitor in
Hydroxyethyl cellulose is preferably used as:
5 Viscosity improver in latex paints
5 Additive in mortars and concrete mixes
5 Additive for sausage casings
5 Protective colloid during PVC emulsion
polymerization.
Ethylcellulose (EC) is produced from alkali cellulose and ethyl chloride and hydroxypropyl cellulose (HPC) with propylene oxide, respectively.
Both cellulose ether are only of minor importance (. Fig. 7.18) and are also used in construction chemicals, adhesives and pharmaceuticals.
Summary (Take-Home Messages)
5 Cellulose is a polysaccharide, in which
the glucose monomer units are linked to
each other by a β-1,4-glycosidicbond. The
cellulose chains intermolecularly interact
with each other by hydrogen bonds and
partially form crystalline regions.
5 The main source of cellulose is wood, in
which cellulose has a proportion of up to
50%. Hemicelluloses and lignin are also
found in wood. Worldwide, 3.4 billion
tons of wood are harvested annually.
5 In the sulfate process (or “Kraft
process”), wood is processed under
basic conditions. The digestion solution
consists of caustic soda and sodium
sulfide. The sulfur losses are compensated
by sodium sulfate, after which the
process is named. The by-product is black
liquor in which the lignin components
are dissolved. Worldwide, 80% of the
cellulose is produced by the sulfate
process.
5 In the sulfite process, wood is
decomposed in the acidic to neutral pH
range with the addition of hydrogen
sulfite solutions. Since no hydrogen
sulfide is formed, the process is much
more environmentally friendly. However,
it can only be used for wood species low
in resin and silicic acid, such as pines.
5 Paper consists of cellulose, mechanically
crushed wood and other fillers and
additives. Increasingly, recycled waste
paper that has previously been deinked is
also being added to paper production.