BG4500U1 - Environmentally sustainable three-layer hempcrete slab with adhesive compound of synthetic and natural binders - Google Patents

Abstract

The present utility model relates to a three-layer hempcrete slab with two face layers and one intermediate layer interposed between the two face layers. Said three-layer hempcrete slab contains hemp particles and fibers of short hemp stalks and includes a dispersed phase and a matrix phase, wherein the dispersed phase includes hemp particles amounting to 70 – 95 weight percent (wt. %) of the total dispersed phase as well as short hemp stalks amounting to 5 – 30 wt. % of the total dispersed phase. The matrix phase includes binders with an adhesive phase which includes one or more of the following: urea-formaldehyde resin with molar ratio 1.0 to 1.2, melamine formaldehyde resin with molar ratio 1.1 to 1.6, lignosulfonate (sulphite lignin) or polymethylene diphenyl diisocyanate, and one or more improvers selected among the following: ammonium hydrogen sulphite, paraffin and amino-polyphosphate. In a preferred embodiment, the face layers of the three-layer slab according to the present utility model contain hemp particles and fibers of short hemp stalks with the following dimensions: length from 10 to 15 mm, width from 2 to 8 mm and thickness from 0.1 to 0.5 mm. In a preferred embodiment, the intermediate layer of the three-layer slab according to the present utility model contains hemp particles and fibres of short hemp stalks, wherein the dimensions of the particles are as follows: length 20 to 40 mm, width 2 to 5 mm and thickness 0.3 to 0.8 mm. The utility model enables the production of environmentally sustainable three-layer hemcrete slabs which leads to a reduction of the use (and accordingly felling) of timber by replacing it with residual agricultural lignocellulosic material, namely hemp stalks. Furthermore, the present utility model enables the utilization of a by-product from the pulp and paper industry, namely lignosulfonate (sulphite lignin). The entirety of these factors together with the physical and mechanical parameters achieved with the utility model result in an improved product with improved lifecycle combined with a reduced carbon footprint of the production process due to the use of a ready-made product, namely lignosulfonate, as well as to a decrease of the amount of energy used for during the drying stage. The use of drying agents is also reduced.

Description

Field of technique

The present utility model relates to the field of processing hemp particles and short fibers from hemp stems for the purpose of applying industrial hemp in construction. In particular, the utility model relates to a hemp padder plate and a method of manufacturing the same.

Prior art

Hemp, as a building material, is heat-insulating, fire-resistant and ecological. As a result, hemp fiber used as a building element can significantly reduce CO2 emissions in the construction sector.

Hemp also behaves very well in relation to moisture. As an insulating material, it absorbs water from the air and thus regulates the humidity inside the premises. This property has a positive effect on the inhabitants and prevents the appearance of mold. In buildings insulated with hemp, the appearance of mold is extremely rare. This natural insulation is associated with higher investment costs, but they are returned due to the large energy savings - about 70%.

A utility model BG 4395 U1 is known where a hemp pazder plate is disclosed for the utilization of agricultural waste from hemp particles and short fibers, with the aim of providing a substitute for the traditionally used wood materials. In particular, the board is indicated to include the binder in an amount relative to dry mass ranging from 8% to 14% depending on the strength and purpose of the board. The adhesive composition of the plate consists of 90% urea formaldehyde resin (CFC) and 10% melamine formaldehyde resin (MFS). As a water-repellent substance, a paraffin emulsion was used, in which the paraffin content relative to the absolutely dry particles was 0.5%, and the emulsion was introduced at a concentration of 50%.

Thus, the task of the present utility model is to create an ecological board comprising a hemp pad with improved environmental and other field-relevant performance. It is important for the useful model to achieve an economic effect with the technical solution from the object of the present application.

Technical nature of the utility model

The present utility model relates to a three-layer hemp pazder plate, wherein two face and one intermediate layer are provided. The intermediate layer constitutes according to the present utility model from 50 to 70% of the total thickness of the three-layer plate, and the face layers comprise from 30 to 50% of the total thickness of the three-layer plate.

The substantially three-layer hemp padder plate according to the utility model includes a hemp padder representing a dispersed phase which is made up of

1) hemp particles - 70 ^ 95% of the total dispersed phase;

2) short fibers from hemp stems - 5 ^ 30% of the total dispersed phase.

Further, the three-layer hemp padder plate according to the utility model includes two face layers of hemp padder and an intermediate padder layer located therebetween, wherein:

3) the sizes of the particles of the face layer are preferable - length from 10 to 15 mm; width from 2 to 8 mm; thickness from 0.1 to 0.5 mm;

4) the sizes of the particles for the intermediate layer are preferably - length from 20 to 40 mm; width from 2 to 5 mm; thickness from 0.3 to 0.8 mm.

In addition, the three-layer hemp pazder plate according to the utility model also includes a matrix phase that is made up of binders (synthetic and natural) in an amount of 4 to 20% relative to the total mass of the absolutely dry hemp particles and short fibers.

Essentially, the three-layer hemp pazder plate according to the utility model contains hemp particles and short fibers from hemp stems and consists of a dispersed and matrix phase, wherein the dispersed phase includes hemp particles - 70 ^ 95 wt. % of the total dispersed phase and short fibers from hemp stems - 5 ^ 30 wt. % of the total dispersed phase, and the matrix phase includes an adhesive phase comprising one or more of urea formaldehyde resin (CFC) in a molar ratio of 1.0 to 1.2; melamine formaldehyde resin (MFS), with a molar ratio of 1.1 to 1.6; Lignosulfonate (sulfite lignin) or polymethylene diphenyl diisocyanate; and one or more enhancers selected from ammonium hydrogen sulfite, paraffin, and amino polyphosphate.

In a preferred embodiment of the three-layer plate according to the utility model, the urea-formaldehyde resin, with a molar ratio of 1.0 to 1.2 is present in an amount of 70 × 90 wt. % of the adhesive phase. To the urea formaldehyde resin is added 1 to 3% relative to the dry resin, ammonium sulfate. Ammonium sulfate acts as a catalyst for the polymerization process, through polycondensation of the resin.

In a further preferred embodiment of the three-layer plate according to the utility model, the melamine formaldehyde resin, with a molar ratio of 1.1 to 1.6 is present in an amount of 10^20 wt. % of adhesive phase;

In a further preferred embodiment of the three-layer plate according to the utility model, the lignosulfonate (sulfite lignin) is present in an amount of 10^30 wt. % of adhesive phase;

In a further preferred embodiment of the three-layer plate according to the utility model, the polymethylene diphenyl diisocyanate is present in an amount of 10^20 wt. % of the adhesive phase.

In a further preferred embodiment of the three-layer plate according to the utility model, ammonium hydrogen sulphite, as a scavenger of free formaldehyde, is present in an amount of 1 ^ 3 wt. % compared to absolutely dry synthetic resins (urea formaldehyde and melamine formaldehyde resins).

In a further preferred embodiment of the three-layer plate according to the utility model, the paraffin, as a water-repellent additive, is present in an amount of 0.5 × 1.0 wt. % relative to absolutely dry hemp particles and fibers. The paraffin is introduced in the form of an emulsion with a concentration preferably of 50%.

In a further preferred embodiment of the three-layer plate, according to the utility model, the amino polyphosphate, as a flame retardant, is present in an amount of 15 ^ 20 wt. % of matrix phase.

The present utility model also provides a method of manufacturing a three-layer hemp pad as defined above, which includes the following manufacturing steps.

1) Hemp stalks are prepared, by means of guillotine scissors, into cutlets with a length of 10 ^ 50 mm;

2) The resulting cuttings are crushed into particles (with short fibers included in their composition) by means of rotor-centrifugal mills;

3) The particles are separated into those for the face and intermediate layer by means of flat sieve sorting machines;

4) If there is a shortage of particles for the face layers, or if very large particles are present, they are subjected to secondary crushing by means of counter-selector mills. Secondary crushed particles are returned for re-sorting;

5) Drying of the particles to a humidity of 1 to 5%, by means of belt dryers;

6) Bonding of the particles to face layers of the plate, by means of mixers with continuous action;

7) Bonding of the particles for an intermediate layer of the plate, by means of mixers with continuous action;

8) Forming a hemp pazder carpet using a bulking machine with 3 to 4 bulking heads - 2 bulking heads for the lower and upper face layer of the plate, respectively; and from 1 to 2 pouring heads for the intermediate layer of the slab;

9) Pre-pressing (cold pressing) of the carpet, using a belt press with a maximum specific pressure of up to 4.0 MPa;

10) Format cutting of the carpet using circular saws;

11) Hot pressing by using multi-stage presses with tact action; temperature of the press surfaces from 140 to 200°C, pressing duration from 15 s/mm to 60 s/mm; Three-stage hot pressing mode - first stage at pressure up to 6 MPa and duration up to 30% of the entire cycle; second stage at pressure up to 2 MPa and duration up to 30% of the entire cycle; third stage at pressure up to 0.8 MPa and duration up to 40% of the entire cycle;

12) Acclimatization of the slabs when using racks (suns) with a circular cross-section, forming the floors by means of discontinuous supports driven clockwise or counter-clockwise;

13) Second degree of acclimatization by forming figures with plates in buffer storage;

14) Calibrating the thickness and reducing the roughness of the plates by means of wide-band double-sided grinding machines;

15) Format cutting of the plates by means of circular machines;

16) Surface refinement of the plates, including one of the following operations: lamination, veneering, varnishing, priming and painting, lamination, perforation, milling;

17) Packaging and storage of finished products.

Examples of implementation of the utility model

The following example shows the production of a three-layer plate according to the utility model, where the components are in a specific weight ratio/quantity:

Three-layer hemp pazder plates with a density of 650 kg.m ^-3 and a thickness of 16 mm were obtained. The ratio of the intermediate to the face layers of the plates are 65% to 35%. The dispersed phase of the plates is made up of 94% hemp particles and 6% short fibers. The hemp seed has an initial moisture content of 6%.

The total content of binders is 12% relative to the absolutely dry lignocellulosic mass (hemp particles and short fibers). The matrix phase is composed of: 70 wt. % urea-formaldehyde resin with a molar ratio of 1.0; 15 wt. % melamine formaldehyde resin with a molar ratio of 1.5; 10 wt. % ammonium lignosulfonate; and 5 wt. % polymethylene diphenyl diisocyanate (pMDI). To: the urea formaldehyde resin was added 1.5 wt. % (relative to the absolutely dry: resin) ammonium sulfate. Ammonium hydrogen sulphite was used as a formaldehyde scavenger in an amount of 2 wt. % compared to absolutely dry synthetic resins (urea formaldehyde and melamine formaldehyde resins). As a water-repellent substance, paraffin was used in a content of 0.8 wt. % relative to the absolutely dry lignocellulosic mass. Binders and water repellants are introduced into the lignocellulosic mass (hemp particles and short fibers) in the form of solutions/suspensions with a concentration of 50%. The total time to apply and mix the enhancers and hemp paste is 2 min and 40 s.

The hot pressing was carried out at a temperature of the press tops of 170°C and at a pressing factor of 30 s.mm ^-1 . The hot pressing mode used is three-stage as follows: I stage - pressure 3.0 MPa and duration 20% of the entire cycle; II stage - pressure 1.4 MPa and duration 20% of the entire cycle; III stage - pressure 0.6 MPa and duration 40% of the entire cycle.

The obtained results establish the following surprisingly high performance figures for the three-layer hemp pazder plates according to the utility model

Water absorption in 24 hours - from 52.6%;

Swelling in thickness for 24 hours - 14.1%;

Bending strength - 18.4 N.mm ^-2 ;

Modulus of elasticity in bending - from 2520 N.mm ^-2 ;

Transverse tensile strength - from 0.91 N.mm ^-2 ;

Screw retention perpendicular to the wide side of the plate - from 92.7 N.mm ^-1 ;

Screw retention perpendicular to the edge of the plate - from 62.3 N.mm ^-1 ;

Content of free formaldehyde - 1.1 mg/100 g of absolute dry matter (ecological boards with emission class Super E ₀ /0.5 CARB 2).

Advantages of eco-friendly three-layer hemp pazder boards and method of their preparation

With the present utility model, ecological three-layer hemp pazder boards and a method of their production are provided, which lead to a reduction in the consumption (respectively, felling) of wood raw material due to the use of residual agricultural lignocellulosic material - hemp stems. In addition, the useful model ensures the use of a secondary product from the production of the pulp and paper industry - lignosulfonate (sulfite lignin). Due to the lower moisture content of the hemp stalks compared to the wood raw material, it is suggested to use a belt dryer for drying, rather than the energy-intensive drum dryers. All this complex of factors leads to a reduction in the carbon footprint of production due to the use of an already ready product - lignosulfonate and a reduction in energy costs during drying. The consumption of drying agent is also reduced.

From the point of view of consumers, the offered three-layer boards made of hemp pazder represent an ecological product with formaldehyde emissions of the Super E _o class, that is, formaldehyde emissions comparable to those of natural wood.

Claims (1)

A three-layer board of hemp pazder, formed in two face layers and placed between them an intermediate layer containing hemp particles and short fibers from hemp stems and including a dispersed phase and a matrix phase, characterized in that the dispersed phase includes hemp particles - 70 - 95 wt. . % of the total dispersed phase and short fibers from hemp stems - 5 - 30 wt. % of the total dispersed phase, and the matrix phase includes, as binders, an adhesive phase comprising one or more of urea-formaldehyde resin, with a molar ratio of 1.0 to 1.2; melamine formaldehyde resin, with a molar ratio of 1.1 to 1.6; lignosulfonate (sulfite lignin) or polymethylene diphenyl diisocyanate; and one or more enhancers selected from ammonium hydrogen sulfite, paraffin, and aminopolyphosphate