RU2014217C1 - Method of manufacturing tiles from plant raw material - Google Patents

Abstract

FIELD: production of tiles. SUBSTANCE: method involves providing cotton stems used as raw material; grinding cotton stems while effectuating moistening up to 40-70 % humidity of absolutely dry raw material mass; drying at 95-105 C to 17-19% humidity; forming mat and providing hot pressing at 150-170 C and at pressure of 2.5-3.5 MPa; abrupt cooling under above mentioned pressure to 120-130 C with cooling rate during the first 4.5-5 min. within the range of 4-5 C; with subsequent smooth cooling up to 25-30 C; providing smooth decreasing of pressure. EFFECT: high quality of tiles and wider operational capabilities. 2 cl, 1 tbl

Description

 The invention relates to the woodworking industry, and in particular to methods for producing plates and other pressed materials from plant materials by the dry method.

A known method of manufacturing chipboards. (See ed. St. USSR N 1579.782, class B 27 N 3/02, 3/04, BI N 27 July 23, 90). According to this method, wood particles, previously crushed, with a moisture content of 6%, are treated with a binder based on polyisocyanates and a release agent, mixed and a carpet is formed. The carpet is then placed into a cold press and operate degassing and hot pressing at a temperature of 200-230 ^{° C,} pressure 2.8-3.0 MPa, for 6 minutes.

 The disadvantage of the described method is environmental pollution due to the evaporation of the binder during hot pressing, water pollution from raw materials of containers from the binder, as well as the release of insufficiently environmentally friendly products containing polyisocyanites and anti-adhesives.

There is also a known method of producing plates from plant materials. With this method of producing plates from plant material, which is used as rice straw or pine sawdust, it is crushed, the temperature is brought to 157-167 ^о С for steam of rice straw and 180-250 ^о С for sawdust and humidity to 10 -12%. The resulting mass is modified with ammonia in an amount of 3% of the mass of absolutely dry fiber and form a carpet. Then, the hot pressing at a temperature of 170-180 ^{° C} to 200-220 rice straw and sawdust ^C. and a specific pressure of respectively 70 kgf / cm ² and 50 kgf / cm ² for 2 minutes and 1 minute, respectively.

 When implementing the above method of obtaining plates from plant materials, environmental pollution occurs when the feedstock is modified with water vapor and ammonia.

There is also a known method of manufacturing a dry-formed fibreboard, which is the closest analogue. (See ed. St. N 1516357, class B 27 N 3/04, BI N 39, 10.23.89). The above method involves the processing of plant materials with steam, then it is crushed on a refiner, phenol-formaldehyde resin is introduced and dried to a moisture content of 6-8%. Thereafter, the molding of the carpet, after which cold prepressing subjected to hot pressing at a temperature of 190 ^C, a pressure of 5.5 MPa for 6 minutes.

 The disadvantage of this method is the prototype is also environmental pollution due to the release of free formaldehyde during hot pressing, water pollution from washing containers from a binder, the release of environmentally dirty products with the presence of formaldehyde elements. In addition, when using this and other methods, valuable wood species are consumed.

When implementing the proposed method for the manufacture of plates from plant materials, the technical result is achieved:
- due to the disposal of cotton waste, resource-saving of valuable raw materials and the expansion of the arsenal of substances used in the manufacture of plates are ensured. For the manufacture of plates, cotton stalks (guzopai) are used, and not wood;
- Improvement of the ecological situation is ensured through the use of cotton stalks that were not previously used in the production, but clogged agricultural fields (land) with extracts leached from cotton stalks (when rotting). In addition, the proposed method is carried out without the use of any binder, which is one of the main factors that have a harmful effect both on the environment and on manufactured products — plates — in the manufacture of plates. The plates obtained by this method are non-toxic.

 An additional technical result is to simplify the process and reduce the cost of plates by eliminating the operation of introducing a binder.

The achievement of the specified technical result is ensured by the fact that the method of manufacturing plates from plant materials includes grinding the stalks of cotton, according to the invention, with moistening up to 40-70% of the mass of absolutely dry (a.c.) Raw materials. Drying of the raw materials is carried out, in accordance with the invention, at a temperature of 95-105 ^about C to a moisture content of 17-19%. After the formation of the carpet, hot pressing, according to the invention, is carried out at a temperature of 150-170 ^about C and a pressure of 2.5-3.5 MPa. The novelty of the method consists also in that not reducing the pressure plate is quenched to a temperature of ^about 120-130 C, and further cooling is performed gradually to 25-30 ^{° C,} after which the start smoothly without abrupt discontinuity to lower the pressure. Abrupt cooling is carried out in the first 4.5-5 minutes at a cooling rate of 4-5 ^° C per minute.

 The proposed method for the manufacture of plates from plant materials was developed at the inventive step and does not follow explicitly from the prior art. The authors used an effect that is unexpected, manifested as a result of applying a series of techniques in the pressing process.

 Wood and plant raw materials (cotton stalks) used in the technology consist of three main components: cellulose, lignin and hemicelluloses. Depending on the type of raw material, the percentage ratio of these components is different, but the physical meaning of the processes that occur during pressing is the same.

. Это достигается на первой стадии прессования, путем поднятия давления (сжатие ковра между нагревательными плитами) до 2,5-3,5 МПа. Одновременно с этим идет подъем температуры до 165^оС.Cellulose is a natural polymer belonging to the class of hetero-chain polymers in a hydrated (moistened state) easily forms intermolecular bonds, for this it is only necessary to bring the chains closer to a distance of 1-1.5

. This is achieved at the first stage of pressing, by raising the pressure (compression of the carpet between the heating plates) to 2.5-3.5 MPa. At the same time, there is a rise in temperature to 165 ^about C.

 At this temperature, lignin and amorphous sugars - hemicelluloses contained in wood raw materials up to 15 to 30% are softened.

Lignin - a natural polymer product belonging to the class of polyphenols pronounced thermoplastic having a softening point of 130-160 ° ^C.

Adsorption moisture has a plasticizing effect on lignin, i.e. in its presence, lignin begins to pass into a viscous-fluid state at a temperature of about 90 ^about C.

 When softened, lignin becomes sticky and prone to autoadhesion. This is due to an increase in the contact area, as well as mutual diffusion of the chains as a result of an increase in their mobility at a temperature above the transition temperature from the glassy to viscous flow state.

Thus, we have crystalline cellulose skeleton which at a pressure of 3.5 MPa and a temperature of 165 ^{° C} gives a rigid structure, and the moist amorphous lignin - hemicellulose matrix which is softened by heat and goes into a flowable state and then diffused into the crystalline framework cellulose .

 As tests have shown, rapid cooling of this system leads to an increase in the strength of the polymer composition.

 The physics and chemistry of this process are quite complex, because each of the listed components cannot be expressed by an unambiguous chemical formula.

 However, from a physical point of view, the ongoing internal processes in the carpet can be explained to some extent. The unexpected effect of hardening the structure of the plate is manifested as a result of correctly selected sequence of operations and technological modes of moistening, compression, as well as heating and cooling.

 The proposed technology for the manufacture of plates from plant materials is not complicated and can be feasible industrially.

 In this case, the hydraulic press mainly uses an oil coolant with the possibility of pumping hot or cold oil into it during the pressing process.

 The possibility of implementing the proposed method for the manufacture of plates from plant materials is confirmed by the act of testing experimental plates obtained in laboratory conditions according to the technology developed by the authors.

 A distinctive feature of the method of manufacturing plates from plant waste is that plant materials, crushed to a certain fraction and geometry of sizes, are not dried, as is customary in traditional technology, but rather moistened to a moisture content of 17-19%. A necessary condition is that all particles, without exception, have the same humidity. This is achieved by the following method: first, the raw material is moistened to excess moisture, and then, by drying in a "fluidized bed" is brought to the desired humidity.

 Then, the carpet formed from these particles is pressed in a hot hydraulic press.

 The required strength of the plates is achieved by the special pressing mode described in examples 1, 2, 3, 4, 5, 6, 7.

PRI me R 1. Fiber boards from plant materials, namely cotton stems, are made as follows: Wood or plant particles ground to a certain fraction (particles must be sieved through a No. 1 sieve), moistened to a moisture content of 50%, then dried in fluidized bed to a moisture content of 17%, form a fibrous carpet on the frame and pressed at a temperature of 165 ^about C. The pressing cycle is as follows:
1 phase of pressing R _beats = 3.5 MPa
T _{heating plate} = 165 ^about With
presses. = 60 s.

2 phase pressing R _beats = 3.5 MPa
_NP T = 120 ^C.
cooling = 300 s
3 phase pressing R _beats - smoothly
reduced to 0
T _np - smoothly
reduced to 20 ^about
= 15-20 minutes

 The pressed plates are cut from 4 sides and tested according to GOST 4598-86.

 PRI me R 2. Similar to example 1, wherein the wood particles are first moistened to 30%, then dried to a moisture content of 8%.

 PRI me R 3. Similar to example 2, but the wood particles are first moistened to a moisture content of 60%, and then dried to a moisture content of 30%.

PRI me R 4. Similar to example 1, and the pressing temperature of the plates on the 1st phase is 140 ^about With on 2 and 3 phase is the same as in example 1.

EXAMPLE EXAMPLE 5 As in example 4, but the temperature of the pressing plates on one phase is 200 ^{° C,} 2 phase - 165 ^{° C,} Phase 3 - 35 min.

 PRI me R 6. Similar to example 1, but the pressing pressure in the 1st phase is 1.4 MPa, in the 2nd phase - 1.4 MPa, the 3rd phase is a smooth pressure relief.

PRI me R 7. Similar to example 1, however, the cooling time in the 2nd phase of pressing from 165 ^about C to 120 ^about C is 600 s.

PRI me R 8. (prototype). Fibrous slabs are made from pulverized pulp, the pulp is treated with steam, then phenol-formaldehyde resin is introduced and dried to 8% moisture. The molded carpet is first subjected to a cold preform, then hot pressed at 190 ^{° C,} a pressure of 5.5 MPa for 6 minutes.

 The test results of the physico-mechanical properties of the obtained plate samples are presented in the table.

 Thus, the invention allows to obtain a material with a strength property exceeding the data of the prototype, and hydrophobic not inferior to the prototype, but without the use of a binder, which reduces the toxicity of the plates and improves the environmental cleanliness of the production and the environment.

 The ecological purity of the obtained slab samples is confirmed by the conclusion of the Inst. Erisman.

Claims (2)

1. METHOD FOR PRODUCING PLATES FROM VEGETABLE RAW MATERIALS, including grinding of raw materials, moistening them, drying, forming a carpet, hot pressing and holding them in a press under pressure, characterized in that the grinding of raw materials produces up to 40 - 70% moisture content from the mass of absolutely dry raw materials, drying is carried out at 95 - 105 ^o C to a moisture content of 17 - 19%, and the carpet is pressed at 150 - 170 ^o C and 2.5 - 3.5 MPa, then it is rapidly cooled to 120 - 130 ^o C, further cooling is carried out smoothly to 25 - 30 ^o C, then gradually reduce the pressure.  2. The method according to claim 1, characterized in that the quenching is carried out for 4.5 to 5 minutes at a speed of 4 to 5 deg / min.

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