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Файл:The bases of special methods of biomass processing into prospective materials. Tutorial
.pdf
Procedure.
1. Make specimens of plastics from cellulose containing wood
particles of different fractions in laboratory.
The sequence of a specimen making process:
– select portions of hardwood and softwood aggregate to make a
specimen with fractional size 0.5 mm;
– moisten the portion of the aggregate up to 20 % humidity;
– fill the aggregate in the mold, mold by cold perform method at a
pressure of 1 MPa to make a transportable briquette;
– produce hot pressing of the briquette at a working pressure of
5 MPa; press plates temperature 180 0C with continuous cooling to 18–
25 0C, while maintaining the working pressure;
– normalize the quality of the resulting specimens under normal
conditions for 1 day;
– cut out boards for specimens.
2. Test physical and mechanical properties of the resulting plastics in
accordance with standard methods for wood boards: strength is tested in
accordance with GOST 10635-88 «Particle boards. Methods for
determining ultimate strength and modulus of elasticity in bending»,
physical properties are tested in accordance with GOST 10634-88 «Wood
particle boards. Methods of determination of physical properties».
2.1. Determination of strength and modulus of elasticity in bending.
Preparing specimens for testing
The specimens should be in the form of rectangular parallelepiped
with thickness equal to the board thickness. It should be 50 mm wide, its
length should be 10–15-fold of thickness plus 50 mm. One half of the
specimens are cut off along the testing board, the other half is cut off across
the board. The thickness of the specimen is measured at the center of the
transverse.
The length of the specimen is measured by its longitudinal axis, the
width is measured by its transverse axis.
Testing
The distance between the centers of support is 10–15-fold of the
specimen thickness. The specimen is put on the supports of the testing
machine marks so that the longitudinal axis of the specimen is
perpendicular to the axes of the supports, and the transverse axis is at the
same vertical plane with the vertical axis of the knife blade.
51
In the experiment one half of the specimens with the same orientation
2
23bhH
Fl
=
( )
( )
12
3
12
3
4 SSbh
FFl
E
−
−
=
are put face up and the other half is put face down on the test device
supports.
To determine the flexural strength the specimen is loaded at a
constant speed up to destruction and the maximum load is recorded with an
accuracy1 %. Time from start of loading to failure of the specimen should
be 60 ± 20 s.
To determine the flexural modulus the specimen is loaded at a knife
moving speed 1–2 mm/min up to 1/3 of the breaking load. At least eight
readings of the specimen deflection are taken at regular intervals of load
increment.
The deflection is measured in the plane of loading up to 0.01 mm.
The measuring device sensor should not be affected by local crushing of the
specimen.
The results of load increment and deflection are plotted in a straightline graph, making average value spread from the linear law.
Processing results
The flexural strength of the specimen σ (MPa) is calculated using the
formula below:
, (3)
where F – loading force acting on the specimen at the moment of
destruction, Н;
l – the supports span of the testing machine, mm;
b – the width of the specimen, mm;
h – the thickness of the specimen, mm.
The result is rounded up to the first decimal place.
The flexural modulus of the specimen Е (MPa) is calculated using
the formula below:
, (4)
where l – the supports span of the testing machine, mm;
b – the width of the specimen, mm; h – the thickness of the specimen,
mm;
F2-F1 – the fixed (2-3 intervals) load increment, Н;
S2-S1 – the deflection increment corresponding to the fixed load
increment determined according to the graph up to 0.1 mm.
52
The result is rounded up to a whole number.
w
%100
1
12
−
=
m
mm
w
The result of testing a board is the arithmetic mean from the test
results of all specimens taken from this same board. These values are
expressed accurate to one decimal place and to a whole number
respectively.
2.2. Determination of physical properties: water absorption and
thickness swelling.
The specimens are weighed with an error not exceeding 0.1 %
maximum in half an hour after conditioning. The thickness of the specimen
depending on its size is measured:
(25х25) mm – at one point in the center of the face;
(100х100) mm – at four points.
The specimens are placed into a can with water at a temperature of
20 ± 1 0С. They should not be in contact with each other and with the bottom
and side walls of the can. The specimens should be kept at (20 ± 2) mm
below the water surface. The specimens with (100х100) mm size are placed
in an upright position. The exposure time of the specimens in water should
be:
– h±5 min for the specimens with (25х25) mm size;
– h±15 min for the specimens with (100х100) mm size.
The sequential test is allowed for 2 and 24 h, but the second time the
specimens immerse into water no later than in 10 min. After exposure the
specimens are taken from water.
To determine the thickness swelling the surface of the specimens is
dried of water drops with filter paper.
To determine the water absorption the specimens with (100х100) mm
size each are placed individually in a horizontal position between two
sheets of filter paper and piled. The specimens with (25х25) mm size are
laid in rows between sheets of filter paper. The load is put on the specimens
for 30 s. Then the load and filter paper are removed. The specimens are
weighed for the second time. The thickness is measured no later than 10
min after taking the specimens from water.
The water absorption of the specimen
expressed in % is
calculated using the formula below:
53
, (5)
where m1 – the mass of the specimen before immersion into water, g;
w
t
%100
1
12
−
=
t
tt
t
w
№ of
the
specimen
The
aggregate
Fraction,
mm
Stren
gth,
MPa
Thickness
swellling, %
Volume
swellling,
%
Water
absorption, %
The
mass
loss
during
combustion, %
1
Birch
2
Pine
3
Annual
m2 – the mass of the specimen after immersion into water, g.
The result is rounded up to the first decimal place.
The thickness swelling of the specimen
expressed in % is
calculated using the formula below:
, (6)
where t1 – the thickness of the specimen before water immersion, mm;
t2 – the thickness of the specimen after it has been taken off the
water, mm.
The result is rounded up to the first decimal place.
The result of testing a board is the arithmetic mean from the test
results of all specimens taken from this same board. These values are
expressed accurate to one decimal place.
The results of the research are presented in the form of the table.
2.5.4. Technology for producing the wood-polymer composite (WPCs)
by extrusion
Objectives: to conduct experimental study on the preparation and
determination WPCs physical and mechanical properties by extrusion
Materials and reagents: wood sawdust, wood flour, thermoplastics,
antioxidant.
54
Equipment:
– testing sieve;
– laboratory oven;
– scales with an accuracy of 0.1;
– calendering machine;
– extruder;
– liquid thermostat with an accuracy of temperature control ± 1.0
0
С;
– desiccator;
– cans from glass or enameled steel;
– ruler;
– distilled water.
Procedure.
Make specimens of WPCs in laboratory.
The sequence of the specimen making process:
1) Preparation of the components: dry wood particles to moisture
content of less than 1 % and fractionate by size. Part of the aggregate is
milled to the size of wood flour.
2) Dosing. The following ratio between wood flour and
thermoplastics is used: 80/20, 70/30, 60/40.
Fig. 2.5. Schematic diagram of the rolling machine:
1 – wood particles, 2 – polypropylene, 3 –rolls
3) Mixing of the components takes place in the rolling machine. The
result is semi-finished WPCs suitable for loading into the extruder.
4) Extrusion. The resulting semi-finished WPCs are sent into a
single-screw extruder. First, the cylinder is heated to the specified
temperature then the screw is started. Each polymer has its own temperature
in accordance with reference data. The temperature for each polymer is
55
selected in accordance with reference data. The melting temperature of
polypropylene is known to be about 175 0С.
The single-screw extruder is used to produce WPCs (fig. 2.6). The
components of WPCs are poured into the hopper. Loading of inter turn
space under the hopper bin takes place in the screw length segment that
equals to (1–1.5) D. The beads are forced forward due to the difference of
friction force of the polymer on the inner surface of the cylinder and the
surface of the screw. The polymer adjacent to the surface of the cylinder
begins to melt. Since the depth of screw cut decreases as the material flows,
the resulting pressure makes the cork be tightly pressed to the hot cylinder
wall where the polymer melts.
Fig. 2.6. Scheme of horizontal single-screw extruder:1 – drive motor;
2 – extruder head; 3– heater barrel; 4 – barrel ; 5 – screw; 6 – hopper;
7 – axiallager; 8 – extruder gear ; 9 – tachometer; 10 – voltage regulator;
11 – multimeter for measuring temperature; 12 – die; 13 – ammeter;
14 – voltmeter
2. Test physical and mechanical properties of the resulting plastics in
accordance with standard methods: density is tested in accordance with
GOST 15139-69 «Plastics. Methods for the determination of density (mass
density)», strength is tested in accordance with GOST 25.602-80 «Design
calculation and strength tests. Methods of mechanical testing of polymeric
56
composite materials. Test for compression properties at normal, elevated
and low temperatures», GOST 25.601-80 «Design calculation and strength
tests. Methods of mechanical testing of polymeric composite materials. Test
for tensile properties on plane specimens at normal, elevated and low
temperatures», GOST 25.604-82 «Design calculation and strength tests.
Methods of mechanical testing of polymeric composite materials. Test for
bending properties at normal, elevated and low temperatures», GOST 465080 «Plastics. Methods for the determination of water absorption».
2.1. Determination of compressive strength.
Similarly to the procedure described in the laboratory work № 6.
2.2. Determination of water absorption.
Similarly to the procedure described in the laboratory work № 7.
2.3. Determination of WPCs bending properties.
Preparing the specimens for testing.
To determine the maximum bending stress, the modulus of elasticity
and the dependence of the deflection on load when loading a specimen up
to destruction the specimen in the form of a strip of rectangular cross
section is used. The specimens are cut or shaped of the panels in the
direction of the principal axes of the material orthotropy. In accordance
with GOST 2789-73 the specimens should have a smooth flat surface no
rougher than Rа = 20 uM without blistering, chipping, cracks, delamination
and other defects visible to the naked eye. The specimens are conditioned
before the test in accordance with GOST 12423-66, if special conditioning
is not listed in the normative and technical documentation for composite
materials. The process from the end of preparation of molded specimens or
composite material that they are cut from to their testing including time for
conditioning should take not less than 16 hours. Numbering the specimens
is carried out with paint with a soft pencil before the test. The thickness of
the specimen is measured with accuracy up to 0.05 mm. The width is
measured in three places of its test portion with accuracy up to 0.10 mm.
The arithmetic mean values of thickness and width of the specimen are
determined. The results are recorded in the test report.
Testing
The test at normal temperature is carried out in a room or enclosed
space at temperature and relative air humidity specified in technical
documentation for the testing material. If there are no specifications, the test
is carried out at one of the standard atmospheres in accordance with GOST
12423-66.
57
The test at elevated and low temperature is carried out in specially
и
n
F
wbhFl
=
3
3
и
п
4
F
provided heat chambers and cryochambers. The test temperature and its
permissible variations are determined in accordance with specifications or
standards for the material. Otherwise they are determined in accordance
with GOST 14359-69.
Testing at elevated and low temperature the time required for a
complete heating or cooling of the specimen before the test should be
specified in the regulatory and technical documentation on the test material.
If there are no specifications, the specimen is exposed at the given
temperature at least for 20 min for 1 mm of its thickness.
The specimen is set with its wide side on the supports of the testing
machine. The upper surface of the specimen comes in contact with the
heated loading tip. The fit of the specimen to the supports of the tip surface
is determined. The rate of loading tip displacement is determined according
to the specifications of the material. If there are no specifications the rate
equals 5–20 mm/min. While determining the modulus of elasticity the
specimen is loaded with a given constant speed. Deflection values and
corresponding load are recorded. If the diagram deviates from the linear one
the test is stopped. The specimen is unloaded. While determining the
dependence of the deflection on load the specimen is loaded with a given
constant speed. The deflection and the load are continuously recorded up to
destruction of the specimen. While determining the tensile strength the
maximum load that precedes the destruction of the specimen is recorded.
While determining the modulus of elasticity the specimen can be
loaded stepwise or continuously up to the load that does not exceed 50 % of
destructive one. Under continuous loading deflection and load are recorded
automatically. In the case of a step loading deflection measurements are
performed at each load value. The number of steps should be at least four.
The recommended value is 5–10% of the maximum load before to the
destruction of the specimen.
Processing results
The modulus of elasticity in transverse bending
expressed in
MPa is calculated using the formula below:
, (7)
58
where
F
w
F
wbh
Fcl
=
3
2
и
4
3
F
2
max
F5,1
bh
l
=
№ of the
specimen
The
aggregate
Fraction,
mm
Density,
kg/m
3
Compressive
strength,
MPa
Flexural
strength,
MPa
Water
absorption, mg
– increment of load, МН;
l –support span, mm;
b, h – width and height of the specimen, mm;
– increment of deflection in the middle of the specimen
corresponding to load change of
, mm.
The modulus of elasticity in pure bending Еи expressed in MPa is
calculated using the formula below:
. (8)
Tensile strength in transverse bending expressed in MPa is
calculated using the formula below:
, (9)
where F
– maximum load when at the moment of the specimen
max
destruction, МН.
2. Present the results of the research in the form of the table:
2.5.5. Technology for producing the wood-polymer composite
by casting process
Objectives: to conduct experimental studies on the preparation and
determination WPCs physical and mechanical properties by casting method.
Materials and reagents:
– wood sawdust;
– wood meal of various grades and species;
– thermoplastics;
– antioxidant.
59
Equipment:
Thermoplastics, %
Wood sawdust, %
40
60
30
70
20
80
Thermoplastics, %
Wood meal, %
40
60
30
70
20
80
– testing sieve;
– laboratory oven;
– scales with an accuracy of 0.1;
– rolling machine;
– casting machine;
– liquid thermostat with an accuracy of temperature control ± 1.0
– desiccators;
– сans from glass and enameled steel;
– ruler;
– distilled water;
– phosphorus pentoxide or other dryers.
Procedure.
Prepare specimens of WPCs in laboratory.
The sequence of the specimen preparation process:
1) Preparation of the components: drying of wood meal and sawdust
to a moisture content of less than 1 %.
2) Weighing components. The components ratio is presented in Table
2.4 and 2.5.
0
C;
Table2.4
Table2.5
3) Calendering. The ingredients are put into the machine one by one:
polyethylene, then wood meal with additives. The mixing process takes
about 10 min. The result is a tape, semi-finished WPCs.
60
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