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Answers to the Quickies
distillation (bp. 78 °C). Even more favorable
is supercritical carbon dioxide (T c = 31 °C,
p c = 74 bar), which evaporates gaseous after
decompression.
6. Wood turpentine oil is obtained by steam
distillation or extraction of chopped spruce
roots. Due to the great effort involved, this
method is becoming less and less important.
Gum turpentine oil results from the balm
of the spruce, which is isolated by scratching the tree bark. Sulfate turpentine oil is
produced by the sulfate process of cellulose
production.
7. Important acyclic monoterpene hydrocarbons are, e.g. myrcene and ocimen; important acyclic monoterpenols are, e.g. linalool,
geraniol, nerol and citronellol.
8. In turpentine oils, α- and β-pinene are
the two main components. They belong
to the bicyclic monoterpenes which have
a four-membered and a six-membered
ring. The C=C double bond in α-pinene is
endocyclic (i.e. in the ring); in β-pinene it is
exocyclic (i.e. outside the ring).
9. Isomerization and hydration of camphene, a
bicyclic monoterpene with a five-membered
and a six-membered ring, leads to borneol,
which is converted into camphor by further
oxidation. The powder, which smells like
eucalyptus, is used to produce celluloid,
applied as plasticiser for cellulose esters or
as a moth repellent.
10. Important acyclic sesquiterpenes include
farnesenes, nerolidol and α-sinensal. Examples of cyclic sesquiterpenes are zingiberene,
abscisic acid, humulol and taurine. Important diterpenes are the alltransretinol and
abietic acid.
Answers to 7 Chap. 13
1. The fastest way is 1 H-NMR spectroscopy,
which allows to distinguish the cis- and
trans-configurations.
2. Alternatives to hevea brasiliensis are the rubber tree (ficus elastica), the climbing plant
Landolphia owariensis, the guayule shrub
(from desert areas of Mexico and the southern USA) and the Russian or Caucasian
dandelion. The 50 cm high Guayule shrub,
which can be harvested by machine, stores
rubber in its wooden parts and contains up
to 20% natural rubber. The Caucasian dandelion carries rubber in its roots. It is currently being cultivated as part of a European
joint research project to increase yields. The
industrial partner Continental Reifen AG is
planning application tests with the products.
3. The hevea trees must be planted with
sufficient distance in between. As a result,
usually only up to 400 trees grow on one
hectare, each delivering up to 5 kg of natural
rubber per year. The annual yield is thus
approx. 2 tonnes of rubber per hectare. This
yield can be slightly increased by strong
fertilization. But the problem is that the
latex from all trees has to be collected “by
hand”, i.e. no mechanical harvesting can take
place. One collector can handle up to 500
taps a day. The latex must be brought to the
collection station as quickly as possible so
that no chemical changes already occur.
4. During centrifugation in specially designed
machines, at speeds of up to 6000 rpm, the
lighter natural rubber is separated from the
heavier residue by centrifugal force. In this
way, enrichment to 60% can be achieved in
one step. In order to remove the secondary
components, especially the proteins, as completely as possible, the second centrifugation
can be carried out after dilution with water.
Thus, a high purity of the concentrated latex
is achieved.
5. Creaming is very time-consuming (several
days to weeks). Evaporation requires a lot
of energy and all secondary components
remain in the concentrate.
6. The smoked sheet RSS3 is yellow to brownish
due to smoking; the pale crepe is white to
light yellow in color.
7. In the mechanical treatment of natural
rubber in kneaders, the maximum working
temperature reaches 80 °C, which particularly breaks down the long polymer chains.
The result is a product with unimodal
molecular weight distribution. During
thermal-oxidative degradation, the temperature is increased to more than 120 °C:
Chain degradation takes place statistically
over the entire bimodal molecular weight
distribution.
8. In the tire press, temperatures of up to
200 °C and pressures of up to 22 bar are
Answers to the Quickies
distillation (bp. 78 °C). Even more favorable
is supercritical carbon dioxide (T c = 31 °C,
p c = 74 bar), which evaporates gaseous after
decompression.
6. Wood turpentine oil is obtained by steam
distillation or extraction of chopped spruce
roots. Due to the great effort involved, this
method is becoming less and less important.
Gum turpentine oil results from the balm
of the spruce, which is isolated by scratching the tree bark. Sulfate turpentine oil is
produced by the sulfate process of cellulose
production.
7. Important acyclic monoterpene hydrocarbons are, e.g. myrcene and ocimen; important acyclic monoterpenols are, e.g. linalool,
geraniol, nerol and citronellol.
8. In turpentine oils, α- and β-pinene are
the two main components. They belong
to the bicyclic monoterpenes which have
a four-membered and a six-membered
ring. The C=C double bond in α-pinene is
endocyclic (i.e. in the ring); in β-pinene it is
exocyclic (i.e. outside the ring).
9. Isomerization and hydration of camphene, a
bicyclic monoterpene with a five-membered
and a six-membered ring, leads to borneol,
which is converted into camphor by further
oxidation. The powder, which smells like
eucalyptus, is used to produce celluloid,
applied as plasticiser for cellulose esters or
as a moth repellent.
10. Important acyclic sesquiterpenes include
farnesenes, nerolidol and α-sinensal. Examples of cyclic sesquiterpenes are zingiberene,
abscisic acid, humulol and taurine. Important diterpenes are the alltransretinol and
abietic acid.
Answers to 7 Chap. 13
1. The fastest way is 1 H-NMR spectroscopy,
which allows to distinguish the cis- and
trans-configurations.
2. Alternatives to hevea brasiliensis are the rubber tree (ficus elastica), the climbing plant
Landolphia owariensis, the guayule shrub
(from desert areas of Mexico and the southern USA) and the Russian or Caucasian
dandelion. The 50 cm high Guayule shrub,
which can be harvested by machine, stores
rubber in its wooden parts and contains up
to 20% natural rubber. The Caucasian dandelion carries rubber in its roots. It is currently being cultivated as part of a European
joint research project to increase yields. The
industrial partner Continental Reifen AG is
planning application tests with the products.
3. The hevea trees must be planted with
sufficient distance in between. As a result,
usually only up to 400 trees grow on one
hectare, each delivering up to 5 kg of natural
rubber per year. The annual yield is thus
approx. 2 tonnes of rubber per hectare. This
yield can be slightly increased by strong
fertilization. But the problem is that the
latex from all trees has to be collected “by
hand”, i.e. no mechanical harvesting can take
place. One collector can handle up to 500
taps a day. The latex must be brought to the
collection station as quickly as possible so
that no chemical changes already occur.
4. During centrifugation in specially designed
machines, at speeds of up to 6000 rpm, the
lighter natural rubber is separated from the
heavier residue by centrifugal force. In this
way, enrichment to 60% can be achieved in
one step. In order to remove the secondary
components, especially the proteins, as completely as possible, the second centrifugation
can be carried out after dilution with water.
Thus, a high purity of the concentrated latex
is achieved.
5. Creaming is very time-consuming (several
days to weeks). Evaporation requires a lot
of energy and all secondary components
remain in the concentrate.
6. The smoked sheet RSS3 is yellow to brownish
due to smoking; the pale crepe is white to
light yellow in color.
7. In the mechanical treatment of natural
rubber in kneaders, the maximum working
temperature reaches 80 °C, which particularly breaks down the long polymer chains.
The result is a product with unimodal
molecular weight distribution. During
thermal-oxidative degradation, the temperature is increased to more than 120 °C:
Chain degradation takes place statistically
over the entire bimodal molecular weight
distribution.
8. In the tire press, temperatures of up to
200 °C and pressures of up to 22 bar are