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Файл:The bases of special methods of biomass processing into prospective materials. Tutorial
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compounds as in this case material is not supposed to go through a thin
opening.
Foaming. Porous insulation materials are manufactured using the
foaming method. Porous structure of plastic is obtained as a result of liquid
or viscous-flow compositions foaming. This process takes place under the
influence of gases that bleed while chemical reaction between components
or decomposition of special additives (porophores) occurring while heating.
Foaming is also performed mechanically by mixing the polymer
composition with foam and jetting (dissolving) gas and light volatile
substances in a polymer (cellular polystyrene manufacturing).
Hot shaping. Hot shaping is processing of heated sheet, film and tube
parisons in order to give them a more complicated form and obtain finished
products. A force that is required for molding is created mechanically,
hydraulically, pneumatically, using vacuum or by a combination of two
methods. Hot shaping is implemented in production of components of
collecting systems, Plexiglas covers. Vacuum-molding of heated sheets is
used for details of sanitary installations made of high-impact polystyrene
and vinyl polymers.
Extrusion molding. Extrusion is mixing of mass in a heated screw
extruder (extruder) with the further forcing through a block breaker plate to
form a granulated semi-finished product.
From batch hopper granules of thermoplastic polymer enter the press
where they soften while being heated. After that material is taken by a
screw conveyer to the head of the machine where it is pushed through a die
orifice with the section corresponding product profile.
Straight-through extrusion is used to produce tubes and trim
moldings like grab rails, floor moldings, films, bars, etc.
There are two absolutely different schemes of obtaining extrusiontype products from thermoplastic WPC:
– two-step-process (compounding + extrusion);
– one-step-process (direct extrusion).
Wood-polymeric compound is made of initial ingredients in twostage-process. In the process of preparation (hot-cold extruder, compound
extruder or agglomerator) undesirable humidity lessen till the level that is
lower than 1 % of residual moisture. It facilitates through wood and plastic
mixing as well as moistening and invasion of shavings into plastic.
This leads to increasing of breakdown voltage indexes and
considerable improvement of impact elasticity of profiles (with coefficient
from 2 to 3) in the process of two-step processing in comparison with one-
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step process. Moreover, profile extruding machine can be used in case of
low humidity (less than 1 %) with rated output. When shavings from wood
working wastes are used their humidity is up to 8 % that can cause up to
50 % loss of rated output. Direct labor efficiency variances are not
considered due to unavoidable problems in retracting shavings and further
deviations are not considered as well. As a result there is no necessity in
constant regulating and optimization of extrusion parameters.
For example, flour dried in a special machine and resin are directed
to a weighing batcher and enter a blender where they are thoroughly mixed
in hot condition with necessary additives. Obtained mixture is granulated
and chilled in a cooler. The following compound is used for extrusion of
structural products. Granulated material is fed into an extruder, heated to a
plastic state and pressed through extrusion nozzle. Structural extrusion is
calibrated, sawed and put on a draw table. Wood-polymer compound is
used for molding and press work.
In case of direct extrusion the ingredients are directed into extruder.
In this case wood flour is drawn from a batcher to a dryer where it is dried
till its humidity is less than 1 % and is moved into a storage-hopper. Then
flour and additives are taken to a weighing batcher, and after that into an
extruder. Prepared mixture is taken to extruder storage container with the
help of conveyer. Resin, coloring agents and lubricating agent are put into
the extruder where final mixing, heating and extrusion take place. Then
cooling and calibration and cut of the obtained profile occur.
Pressure of melted mixture in an extruder cylinder is usually from
5 MPa to 30. It depends on mixture composition, extruder’s construction,
form of extruded profile and velocity of efflux of hot melt.
Extruding rating of WPC varies from 1 to 5 m per minute.
2.4.4. Fields of application
The most typical fields of application of products manufactured at the
present time from the wood-polymer composites on a commercial scale are
the following:
– building elements (floors, balustrades, door and window profiles,
siding and accessories, fence, roofing);
– structural elements (walkways, piers, marine pilings, bulkheads,
railings, rail parts, anti-noise barriers, formwork for concrete work);
– car parts (interior panels, doors and roof lining, covers on the spare
wheel box, overhead shelves, trucks floors, seat backs);
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– industrial and consumer applications (garden design, pallets,
containers, equipment for sports and children’s playgrounds, park benches,
tables, trash containers, furniture and its components).
Fig. 2.1. Structure of consumption of WPCs in Europe:
56 % – car industry;
30 % – constructing;
10 % – production of furniture;
4 % – the rest
According to the reports, the scope of application of the WPC is
constantly expanding. Extrusion is used in the production of flower pots,
cosmetic pencils, measuring tools, pens, tools handles, panels for
bathrooms, office accessories, cases for musical instruments, decorative
boxes, etc. We must assume that with the creating capacities and improved
technology, extruded and molded thermoplastic on the WPC binder will
soon be applied in other areas of technology – agricultural and general
engineering, shipbuilding, etc. It is important to note that the production
once started with products for outdoor use, in recent years tends to develop
interior spaces (floors, panels, doors, furniture, etc.). Not far off is a
composite house – with all its structures, exterior and interior decoration.
2.5. Technology testing
2.5.1. Technology for producing the composite materials
based on wood particles and gypsum
Objectives: to make specimens from wood particles and gypsum in
laboratory; to learn the effect of preparation parameters, component ratios
on physical and mechanical properties of resulting products.
43
Materials and reagents. Softwood and hardwood particles in the
form of chips and sawdust. The binder is gypsum.
Equipment. Apparatus for testing ignitability.
Procedure.
1. Test physical and mechanical properties of the resulting specimens
in accordance with standard methods.
1.1. Determination of strength and modulus of elasticity in bending.
Similarly to the procedure described in the laboratory work № 1.
1.2. Determination of density. Similarly to the procedure described in
the laboratory work № 1.
1.3. Determination of ignitability. In accordance with GOST
30402-96 “Building materials. Ignitability test method”.
Preparing specimens for testing
15 specimens are made in the shape of a square with sides of 165 mm
and the deviation of minus 5 mm. The thickness of the specimens should
not exceed 70 mm. Before testing the specimens are conditioned to achieve
a constant weight at a temperature of 23 ± 2 0C and a relative humidity of
50 ± 5 %. The constant weight is achieved if in two successive weightings
at intervals of 24 h the difference in mass of the specimens is less than
0.1 % of initial weight.
Testing
The apparatus for testing ignitability is illustrated in fig. 2.2.
The apparatus consists of the following parts:
– supporting base;
– mobile platform;
– source of radiant heat flux (radiation panel;
– ignition system (the auxiliary fixed burner, the moving burner with
mechanized and manual transfer system).
The auxiliary equipment includes: the specimen holder, the shielding
plate, the holder with a specimen simulator, the system controlling the flow
of gas-air mixture, the control and recording devices, the heat flow meter,
the time recorder. The apparatus must be equipped with a protective screen
and hoods.
The testing specimen is wrapped in a sheet of aluminum foil
(nominal thickness is 0.2 mm) with a hole (140 mm diameter) in its center.
The testing specimen is placed in the holder, set the holder on a mobile
platform and regulate the balance bob. Then the holder with the testing
specimen is replaced by the holder with a specimen simulator. The moving
burner is set to its original position, the gas flow rate is adjusted
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(19–20 ml/min) and the air flow rate is 160–180 ml/min. The flame length
in the auxiliary burner is approximately 15 mm. Then the power is turned
on.
Fig. 2.2.The apparatus for testing ignitability:
1 —the radiation panel with heating element; 2 – the moving burner;
3 — the auxiliary fixed burner; 4 — power cable of the heating element;
5— the cam with stroke limiter for manual control of a moving burner;
6 – the cam for automatic control of a moving burner; 7 —the belt; 8 – the plug for
connecting a moving burner to the fuel supply system; 9— the mounting plate for
the ignition system and a system of moving burner; 10 —the protective plate;
11 – vertical support; 12 — vertical guide; 13 — the mobile platform for the
sample; 14 – the supporting base; 15 — manual control; 16 – the balance bob;
17 — the motor drive
The calibrated magnitude of the thermoelectric power corresponding
to the surface heat flux (SHF) 30 kg/m2 is defined in the thermoelectric
converter. After reaching this magnitude of the thermo power, the apparatus
is working in this mode for at least 5 min. The magnitude of the fixed
thermoelectric power in the converter must not differ from the calibrated
one more than 1 %. The shielding plate is placed on the protective plate.
The specimen simulator is replaced by the testing specimen. The moving
burner mechanism is turned on. The shielding plate is removed. The time
recorder is started.
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All these operations should not take more than 15 s. The specimen
testing is stopped when the specimen ignites or after 15 min. The shielding
plate is placed on the protective plate again. The time recorder and the
moving burner mechanism are stopped. Then the holder with the testing
specimen is replaced by the holder with a specimen simulator on the mobile
platform. The shielding plate is removed. The magnitude of the surface heat
flux is 20 kW/m2 if the specimen ignited in the previous test. Otherwise the
magnitude of the surface heat flux is 40 kW/m2 and the test is repeated. If
the ignition occurred at the surface heat flux of 20 kW/m2, the SHF
magnitude is reduced to 10 kW/m
2
and the operations are repeated.
If there is no ignition at SHF of 40 kW/m2, the SHF magnitude is set
at 50 kW/m2 and the test is repeated. After determining two SHF
magnitudes (with and without ignition), the SHF magnitude (without
ignition) is increased by 5 kW/m2 and the operations are repeated for three
specimens. If there is ignition at10 kW/m2, testing at SHF of 5 kW/m2
should be carried out. Depending on the testing results the SHF magnitude
is increased or reduced by 5 kW/m2. The operations are repeated for two
specimens. The time of ignition for all testing specimens should be
recorded as well as the other additional observations: the place and the time
of ignition; process of the specimen destruction because of the thermal
radiation and flame; melting, swelling, separation, cracking or shrinkage.
2.5.2. Technology for producing the composite materials
based on wood particles and Sorel cement
Objectives: to make specimens from wood particles and Sorel cement
in the laboratory; to learn the effect of preparation parameters, component
ratios on physical and mechanical properties of resulting products.
Materials and reagents. Softwood and hardwood particles in the
form of chips and sawdust. The binder is magnesium cement (Sorel
cement).
Equipment. Apparatus for determining the specific heat capacity.
Procedure.
2. Test physical and mechanical properties of the resulting specimens
in accordance with standard methods.
2.1. Determination of strength and modulus of elasticity in bending.
Similarly to the procedure described in the laboratory work № 1.
2.2. Determination of density. Similarly to the procedure described
in the laboratory work № 1.
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2.3. Determination of ignitability. Similarly to the procedure
described in the laboratory work № 2.
2.4. Determination of specific heat capacity. In accordance with the
GOST 23250-78 “Building materials. Method of specific heat
determination”.
Preparing the specimens for testing
The test material is dried to a constant weight. The drying
temperature is determined by the type of material and should not cause
destructive changes in it. The material is milled to particles with size not
exceeding 5 mm. The dried material is poured into the capsule and
compacted into four layers tamping by hand. The mass of the specimen is
adjusted to the nearest 0.001 g by the mass difference between filled and
empty capsules. The mass of the specimen must be at least 5 g.
Testing
The apparatus for determining the specific heat capacity is illustrated
in fig. 2.3.
Fig. 2.3. The apparatus for determining the specific heat capacity:
1 – the calorimeter; 2 –the electric heating apparatus;
3 – the capsule with the specimen; 4 – the magnetic stirrer; 5 – the stirring bar;
6 – the magnetic stirrer stand; 7 – Beckman thermometer; 8 – the thermocouple;
9 – the thermos with cold junctions of the thermocouple; 10 – the top cover of the
electric heating apparatus; 11 – the bottom cover of the electric heating apparatus;
12 – the cover of the calorimeter; 13 –the cover of the thermos
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To determine the specific heat capacity the capsule with the sample
and the thermocouple attached to the thermoelectric power meter is
suspended with a nylon thread in the center of the electric heating
apparatus. The electric heating apparatus is turned on by setting the voltage
at which the temperature chosen for the experiment is maintained. The
temperature of the electric heating apparatus depends on the testing
material. It should not cause destructive changes in tested specimen. To
ensure the required accuracy the calorimeter should be heated up for at least
1 0C. It means that the temperature of heating the capsule with the specimen
(the minimum mass of the specimen is 5 g) should be at least 50 0C above
the temperature of the calorimeter.
The capsule with the specimen is heated up to the chosen constant
temperature. The temperature of the thermocouple cold junctions in the
thermos is measured with Beckman thermometer with an accuracy of
0.01 0C after heating the capsule. After measuring the thermos temperature
Beckman thermometer is dried with gauze and placed into the calorimeter.
The magnetic stirrer is turned on in 15 min and the recording of the
calorimeter temperature (with 5 min interval) begins with an accuracy of
0.01 0C. The stopwatch measures time. The hot capsule with the specimen
is put into the calorimeter 15 min after the magnetic stirrer has been turned
on. The top cover of the electric heating apparatus should not be lifted. The
calorimeter is closed. The thermocouple is inside the electric heating
apparatus. The axes of the electric heating apparatus and the calorimeter are
combined only at the reset moment. The other time the electric heating
apparatus should be taken aside to prevent thermal interaction with the
calorimeter. The temperature of the calorimeter with the capsule inside is
measured for 20 min with a minute interval. When determining water
equivalent of the calorimeter, the temperature is measured for 10 min. After
the temperature has been measured the capsule with the specimen is dried
with gauze and weighed. If the mass of the capsule with the specimen
increased by more than 0.005 g the experiment is considered invalid.
Processing results
The results of measurements are plotted in a graph of the calorimeter
temperature versus time in the scale: 1 0С corresponds to 100 mm on the Yaxis, 1 min corresponds to 5 mm on the X-axis (fig. 2.4).
The graph shows:
1) The calorimeter temperature when the capsule with the specimen or the
standard material immerse into the calorimeter t0, because temperature
readout of the calorimeter and immersion do not coincide in time;
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2) The temperature of the thermal equilibrium between the capsule with the
( )
( )
ж
ж
pн
M
tC
ttCM
E −
−
−
=
0p
00
t
specimen or the standard material and the calorimeter tp. It is found by
extrapolation to eliminate heat given to the calorimeter by the magnetic
stirrer rod rotating.
Fig. 2.4. The graph of the experiment
Water equivalent Е up to 0.1 g is calculated using the formula
below:
where М0 –the mass of the standard material, g;
С0 – the specific heat capacity of the standard material, kcal / (kg·0С);
tн – temperature of the heated standard material, 0С;
tр – equilibrium temperature of the calorimeter, 0С;
Cж – the specific heat capacity of distilled water equal to 1
kcal/(kg·0C);
t0 – the calorimeter temperature at the moment of the standard
material immersion, 0С;
Мж – mass of the distilled water, g.
The specific heat capacity С up to 0.01 kcal/(kg·0С) is calculated
using the formula below:
, (1)
49
( )
( )
( )
0
0p
t
M
CM
tt
tСЕM
C
kk
pn
жж
−
−
−+
=
, (2)
where tn – temperature of the heated capsule with the specimen, 0С;
Мк – the mass of the capsule, g;
Ск – the specific heat capacity of the capsule material, kcal/(kg 0С);
М0 – the mass of a specimen, g.
The specific heat capacity of the specimen material in the
temperature range is calculated as the arithmetic mean of three
determinations made on this specimen.
The relative error in determining the specific heat capacity by this
method does not exceed 5 %.
2.5.3. Technology for producing
bio-composite materials with natural binding agents
Objectives: to conduct experimental study on the preparation and
determination piezothermoplastics’ physical and mechanical properties.
Materials and reagents. Softwood and hardwood particles. Potable water in
accordance with GOST 2874-82. Filter paper.
Equipment:
– testing sieve, size 0.5 mm;
– dessicator;
– moisture meter;
– molds;
– hobbing press;
– indirect heated mold;
– table saw;
– testing machine;
– balance with accuracy 0.1 %;
– laboratory oven with temperature of 103
0
С;
– a ruler.
Water can with thermostat, ensuring the constant temperature
(20 ± 1) 0С and a device for holding the specimens under water.
Metal, glass or porcelain weighing bottle in accordance with
GOST 25336 - 82.
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