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Файл:The bases of special methods of biomass processing into prospective materials. Tutorial
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01
0
mm
mm
W
n
−
−
=
, (16)
where m0 – mass of the weighing cup, g;
m1 – mass of the cup with a specimen in a completely dry state, g;
mn – mass of the cup with a specimen weighed after n days from the
initial placing of the specimen in the desiccator, g.
The final experimental result is the average value of water absorption
determinations of all tested specimens for each conditioning period. The water
absorption index is taken as the maximum rate of moisture of the wood
seasoned before the end of water absorption tests but not less than 30 days.
Determination of modulus of elasticity in compression
The specimens are made in the form of square-section bars sized
30х30х60 mm. The directions of compressive load in relation to the annual
rings of wood are shown in fig. 2.9.
Fig. 2.9. Directions of compressive load
The width and thickness of each specimen are measured in the
middle with an accuracy of 0.1 mm. The strain gauges are symmetrically
fixed about the center of the cross section on the two opposite sides of the
working part of each specimen to measure the strain. To determine the
modulus of elasticity in compression along (parallel) the grain the specimen
is placed on the holder of the testing machine so that the load compressing
the specimen is directed along to the grain. To determine the modulus of
elasticity in compression across (perpendicular to) the grain the specimen is
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placed on the holder of the testing machine so that the load compressing the
610−
=
lbh
Pl
E
2
21
lll+
=
1
l
2
l
specimen is directed across the grain.
The test is carried out at ambient temperature of (20 ± 2) 0C and
relative humidity of (60 ± 5) %.
Determination of modulus of elasticity in compression parallel the grain.
Each specimen is subjected to loading six-fold: first to 5.000 H
(lower limit), then up to 20.000 N (upper limit). After each load to the
upper limit the specimen is unloaded to 2.000 N. The average rate of
specimen loading is 17030 N/s.
Determination of modulus of elasticity in compression perpendicular
to the grain in the radial and tangential directions.
Each specimen is subjected to loading six-fold: first to 1.000 H
(lower limit), then up to 3.000 N (upper limit). After each load to the upper
limit the specimen is unloaded to 500 N. The average rate of specimen
loading is 150 ± 30 N/s.
Strain gauges indications corresponding to the upper and lower limits
of loading are measured with an accuracy of 0.5 scale division.
Modulus of elasticity in compression parallel and perpendicular to
the grain in the radial and tangential directions E expressed in MPa is
calculated by the formula:
, (17)
whereP– the load increment from the lower to the upper limits of loading
in the radial and tangential directions, N;
b – width of the specimen, m;
h – thickness of the specimen, m;
l – base of the strain gauge, m;
l– average value of the absolute strain, m.
, (18)
where
– the average (arithmetic mean) of the last three readings for the
left strain gauge, m;
– the average (arithmetic mean) of the last three readings for the
right strain gauge, m.
The results are rounded off in compression: along the grain – up to
100 MPa; across the grain – up to 10 MPa. The final result is the average
value (arithmetic mean) of all parallel determinations.
72
3. TECHNOLOGY OF DEEP PROCESSING OF BIOMASS
Type of flour
The main application
120, 160
Production of light-colored
phenoplasts
140, 180
Production of phenoplasts,
industrial explosives, polymer
composites and building materials
200
Production of alkyd linoleum,
building materials, starch
production
250
Production of industrial explosives
Т
Production of titanium dioxide
pigment
560, 1250
Production of filter elements and
catalysts
3.1. Technology for production and use of wood flour
3.1.1. The main properties of wood flour
Wood flour is typically defined as shredded wood; with a particle
size of less than 1.2 mm. Color of wood flour depends on wood species and
can range from light straw to dark brown. Particles of wood flour have
random irregular shapes. On the one hand this is due to the peculiarities of
the structure of wood, and on the other – the fact that fragmentation of the
particles in the working parts of the mill is the result of random multi
effects – compression, displacement, shock and collision, etc. A specific
fraction of wood flour in the supply depends on the method of grinding and
classification of particles (centrifugal, sieve, etc.). GOST (national
standard) 16361-87 specifies the following types of wood flour (Table 3.1).
Table 3.1
Type of wood flour
The standard does not provide the direct requirements of the particle
size of flour. Humidity standard is 8 %. Some applications may require
73
different moisture content. For example, when used in the manufacture of
thermoplastic WPC moisture of flour should be less than 1 %.
Bulk density of wood flour depends on many factors (moisture,
particle size and shape, wood species) and ranges within 100 – 220 kg/m3;
standard values for the types of flour 120 – 180, 100 – 140 kg/m3.
The wood in the production of wood flour is practically not exposed
to chemical transformations. Therefore, the chemical composition of wood
flour content corresponds with the original wood, and wood flour can be
considered completely natural material.
Wood flour has a pronounced sorption properties, as well as
thixotropic qualities (greasy, but it does not leak).
Wood flour ignites in air at temperatures above 200 0C.
Auto-ignition temperature of aerosol is 430 0C.
The lower explosive limit concentration of wood flour aerosol is 11.2
g/m3. It largely depends on its dispersion, ash and moisture. Wet or oiled
wood flour, like sawdust, rags, grain is capable of spontaneous combustion.
GOST (national standard) 16361-87 also establishes requirements for
the ash content, the presence of impurities, acidity, wood flour, and some
other requirements.
Wood flour absorbs moisture easily, so the supply is packaged into
dense paper or plastic bags, including «big bags», plastic containers
(buckets, barrels, containers). Foreign flour and products based on it,
especially for retail sale, often have an artistic colorful packaging. Small
packages are combined into a transport position on wooden pallets and
transported in covered transport. For example, about 20 tons of flour packed
in sacks can be placed into a standard car, and a standard 40-foot container
can hold about 16 tons of wood flour. So do not assume that the wood flour
is difficult to transport over long distances. Another thing is that flour is a
cheap product, but it is only an advantage rather than disadvantage. For
regular shipments of flour in bulk special cars – flour transports can be
used. If necessary, wood flour can be sealed by briquetting or pelletizing.
3.1.2. Technology of production
The technological process of wood flour production consists of the
following operations:
1) Preparation of raw materials: acceptance and storage of raw
material (sawdust, chips, flake), sorting it to remove the bark and large
inclusions, crushing lump of waste.
74
2) Mechanical grinding of raw materials in the raw product to the
relative alignment of the particle size.
3) Drying of the crude product to obtain the desired moisture content
of flour and ensure the most favorable grinding regime.
4) Chopping of dry material to obtain the desired product fineness.
5) Product sorting grinding – extracting of wood flour of required
types.
6) Packaging of wood flour, which includes packing of flour sacks,
their sewing and storage.
3.1.3. Fields of application
Currently, wood flour is widely used in various industries in our
country and abroad. There is no world’s industrial statistics for wood flour,
but according to experts – there are millions of tons. Fields of application of
wood flour, and production are increasing rapidly.
Wood flour can be used as:
– component in the manufacture of titanium dioxide pigment;
– additive for coating welding electrodes (electrode cellulose);
– additive for ceramic kiln and brick;
– additive in porous abrasive products;
– additive in plaster and finishing mixes (drying mixes, solutions,
pastes), concrete, fillers, etc.);
– additive in concrete and gypsum boards, concrete and composite
pavements;
– additive in adhesives based on natural and synthetic glues;
– filler for natural and synthetic linoleum and linkrust;
– basis for moulded powder and moulded plastic and compounds
based on thermosetting resins (phenoplasts, etc.);
– addition to the compounds based on epoxy, polyester resins, etc.;
– basis for xylolith (wood composite material with magnesium
binder);
– basis for wood-thermoplastic polymer composites (WPC);
– part and the raw material for various explosives;
– filler in the manufacture of adhesives mastics and sealants
(flooring, roofing, etc.);
– basis for the filters and filter media;
– additive in the manufacture of steel and ferroalloys;
– additive in molding compounds for the manufacture of molds;
75
– additive in drilling fluids and grouting materials used in oil
production;
– raw materials for production of sorbents including for removal of
oil pollution from roads, water, etc.;
– raw material for activated carbon production;
– cleaning agent in the manufacture of leather and fur;
– mild abrasive, polishing and cleaning agent in metal, for example,
in the manufacture of hardware and bearings, accessories, etc. (tumbling);
– underground lifter to improve the structure of heavy soils poor in
plant cultivation (along with the chalk and limestone, etc.);
– base substrates for mushroom cultivation industry;
– the basis for the manufacture of items for keeping pets (sorbent
litter);
– feed additive in some compound animal feedstuffs;
– means for smoking fish and meat;
– raw material for producing the active extracts and extracts of wood
(oak, fir, juniper, etc.).
Phenoplast production. One of the major consumers of wood flour
(about 60 % of total production) is the production of phenoplasts intended
for manufacturing of industrial products with high mechanical strength,
electrical insulation, which can be used at high temperatures, humidity,
voltage and high frequency currents. Phenolic products are used to
manufacture low-current electronic equipment, parts of automobile and
tractor electrical products with high moisture and chemical resistance.
Despite the fact that phenoplasts have long been known, they remain the
most common and cheapest types of plastics. The production of phenoplasts
is growing steadily. The extension of phenoplasts application is due to the
development of advanced methods of processing them into products –
injection molding, injection and die casting. Wood flour in comparison with
mineral fillers determines the best characteristics of phenoplasts strength,
electrical resistance, etc.
Fig. 3.1. shows the most common technological scheme of
phenoplasts production by means of roller method. From the measuring
hopper wood flour enters the drum mixer 2. The resin is crushed in a
hammer mill with air classifier is and fed into the same mixer.
Hexamethylenalnine and other additives also enter here. After stirring for
20–30 min, the mixture through a hopper 3 will continuously yield to rolls 4
with a temperature of 70–130 0C for the thermal plasticization. When
rolling the resin melts and impregnates all components of the mixture.
76
Rolled material is pre-crushed in a crusher gear 5 and is ground in a
Wood flour
Additives
Resin
Moulding
Рowder for mixing and
packaging
hammer mill 6 with an air classifier. Through a cyclone and the filter
moulding powder is fed into the hopper, mixed in the mixer, after which it
is packaged in a container by the packaging machine.
Fig. 3.1. Scheme of production phenoplasts by means of a roller:
1, 3 – hopper; 2 – drum mixer; 4 – rolls; 5 – toothed crusher; 6 – mill
In the production of phenoplasts wood flour types140, 180, and F,
top and 1st class softwood are used. The quality of the press powder is
greatly influenced by the adsorption capacity of wood flour, i.e., the ability
to absorb resin and additives, which is determined by the dispersion and
structure of the flour, its species composition. Significant admixture of
colored particles (bark) in wood flour impede the production of phenoplasts
of light colors and decrease their electrical properties due to different
chemical composition of bark and wood. Therefore, 2nd class wood flour is
not used in the production of foams. The use of wood flour of only conifer
group is mainly due to higher rates of mechanical strength and dielectric
properties. Moulding powders derived from flour type 140 have better
mechanical strength and appearance than those made on the basis of a
larger type of flour 180.
Production of titanium dioxide pigment. In recent years, due to a
sharp increase in the production of pigment titanium dioxide - the main
white pigment-base in paint industry, the demand for wood flour grade T
(about 20 % of total production) has increased greatly. Wood flour in the
production of pigment titanium dioxide by sulfuric acid method according
77
to GOST (national standard) 9808-75 is used as filter material in drum
Metatitanic
acid
Suspension of metatitanic acid
Wood flour
Water
Suspensi
on of
wood
flour
Нydrolysis acid
filters at two stages of the process: during filtration (cleaning) of «black
solutions» of titanium sulfate and filtering the suspension of metatitanic
acids after hydrolysis and bleaching.
Drum filter works as follows (fig. 3.2.a). During the precoating the
wood flour slurry enters the trough 1. Drum 2-coated with polypropylene
mesh, is set into rotation, vacuum is switched on and for 1 h a layer of
wood flour with thickness of 50–100 mm is built up on the surface of the
drum. When the layer reaches the desired thickness, knife 3 is set so that it
cuts the roughness of the layer. The filter is ready to work.
Fig. 3.2. The use of wood flour in the production of titanium dioxide:
a – scheme of the filter:1 – tray; 2 – drum; 3 – knife;
b – scheme of precoating and filtering of metatitanic acid:
1 – mixer 2 – tank, 3 – vacuum cooling; 4 – hydraulic gate with a mixer; 5 – filter;
When cleaning the titanium sulfate solution on the surface of the
filter slurry is deposited on a layer of wood flour, and transparent solution
6 – vacuum boiler; 7 – mixer
78
of salts of titanium and other metals enters the drum through a layer of
flour. After each rotation of the drum a layer of flour is cut with a knife, and
the surface of the filter is updated. A slice with flour slurry is removed. The
working time of the filter is 13–14 hours. The quality control of filtering is
carried out according to the transparency of the solution. As soon as cloudy
solution begins to flow, the remainder of the layer is cut and a new layer is
precoated. The thickness of the discharged layer depends on the quality of
wood flour. When filtering metatitanic acid the filter tray is filled with its
suspension. During one revolution of the drum a blade moves by 0.1–0.2
mm, cutting off a layer of wood flour along with the settled part of the
alluvial metatitanic acid. Filtration is carried out as long as the layer
thickness is reduced to 10–12 mm (about 40 h), after which the filter is
recharged.
Fig. 3.2.b shows a schematic diagram of precoating of wood flour
and filtering of metatitanic acid in a vacuum drum filter. When precoating
layer on the filter of the wood flour hopper 2 enters the mixer 1, in which an
aqueous suspension (shown by dotted line) containing a suspension of
wood flour (1–2 %).is prepared. In the process of filtering the suspension of
metatitanic acid from vacuum-cooler 3 via hydraulic valve with a mixer 4,
is fed into the filter 5. The filtrate (hydrolysis acid) through a vacuum –
boiler 6 and hydraulic seal is sent for recycling, and paste from the filter
goes to the mixer 7. Wood flour, entered in the metatitanic acid is
consumed during the subsequent rolling in a rotary kiln.
Production of titanium dioxide pigment imposes certain requirements
for wood flour:
– minimum content of fine particles (less than 63 μm) which are not
precoated in the layer and are carried away with the water and also prevent
the filtration;
– minimum content of large particles (250 μm), since they are not
precoated on the filter, and when cut with a knife are pulled out and the
damage the layer. Therefore, the fibrous shape of the flour particles is
undesirable;
– minimum ash content and the content of metallomagnetic
impurities, since during the ignition ash and impurities remain in the
titanium dioxide, giving it gray and reddish colour.
Wood flour of type T of high class and 1st class of softwood satisfies
these requirements.
In the production of alkyd linoleum according to GOST (national
standard) 19247-73 wood flour is part of the song as one of the major
79
components. Alkyd linoleum is roll material produced in the form of solid
fabrics up to 2.1 m wide and 2.5 to 5.0 mm thick, as well as in the form of
strips and carpets. Linoleum mass is a mixture of binder (alkyd), fillers
(wood and cork flour, asbestos, talc, etc.) and colors (mummy, minium).
Homogeneous mass, resulted from a sequential mixing in faucets and
mixers, is drummed and fed to the calender rollers, where it is applied to the
fabric. Then the band is primed, dried and trimmed. The composition of
linoleum mass consists 16–25 % of wood flour. In the manufacture of
linoleum flour of types 140 and 180 of all sorts and groups is used.
Wood flour of types 560 and 1250 of all sorts and groups is used for
the production of replacement filter elements of fine filters for fuel and
diesel engines oil.
The same types of flour are used in the production of macroporous
granular corundum used in the manufacture of catalysts in the production of
ammonia, methanol, technical hydrogen, and protective gas atmospheres on
the nitrogen industry plants. Wood flour is used as an additive, after the
burnout of which the pores of set value are formed.
Wood flour of types 140, 180, 250 and 400 of all sorts and groups is
used in the production of industrial explosives. It is a scavenger, which
reduces the detonation velocity to the desired value as well as the amount of
heat and combustion temperature, which protects them from the explosion
during transporting and shaking.
Wood flour of types 180 and 250 is used in foundries. It gives the
compliance to the dry forms and increases their permeability. Flour in the
amount of 3–4 %, is part of the mold for the products of IV–V class
complexity.
Wood flour is used as filler adhesives: it improves operational
performance, durability and other properties of the adhesive joint. Also it
saves costly synthetic resin. The composition of adhesives is 6–25 % of
flour. In resorcinic adhesives FR-100, FGF-50 and DF-12 etc., widely used
for bonding wood in the manufacture of laminated constructions, wood
flour of types 140, 180 and 250 of all sorts and groups is used as filler.
Recently, wood flour is used in agriculture in the seed coating,
mainly of sugar beet, as it allows mechanizing the process of cultivation.
Pelleting which is carried out at the seed plants is the running in the seeds to
give them a spherical shape with a diameter 3.5–5.5 mm. Wood flour of
type 180 of deciduous and mixed groups is used as filler.
Currently, interest in the production of wood flour is stimulated by
the development of new directions for its use – the production of wood-
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