NL8302960A - METHOD FOR MANUFACTURING COMPOSITE PRODUCTS FROM LIGNOCELLULOSE MATERIAL - Google Patents

Description

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Method of manufacturing composite products. from lignocellulosic material.

The invention relates to the manufacture of composite products. from sugarcane tampas, sorghum stalks, corn stalks, sunflower stalks, flax stalks and other lignocellulosic materials, in particular from non-woody plants, containing sugars, carbohydrates or saccharides, which are water-soluble and easily extracted.

The invention particularly relates to the production of composite products from sugary lignocellulosic material, such as sugar cane tampas, sorghum stalks, corn stalks, sunflower stems, flax stalks, etc. without the addition of adhesive binders. This is achieved by using the free sugars, carbohydrates or saccharides using heat both as a binder and as an enhancer.

In the ordinary manufacture of panels from sugarcane tampas, traditionally synthetic thermosetting Hind resins, such as phenol-formaldehyde and urea-formaldehyde, have been used, the more expensive phenol-formaldehyde being used for weather resistant products. Ordinary bonding resins contribute greatly to the total material cost of composite products. It is economically attractive to produce composite products without the use of expensive binding resins. In addition, a binderless manufacturing system 25 simplifies the manufacturing process and reduces production costs because mixing operation and equipment are unnecessary. The use of a binder-free process in the manufacture of composite products is therefore desirable for both economic and technical reasons.

^ ^ c. * - 2 -. In the usual manufacture of. ampas panels is essential to remove kernel and residual free sugars for good quality panels. The kernel, compared to real fiber, is a very short and thin-walled cell and contains a greater amount of sugars, but does not impart strength to the final product. Because it is fluffy, the wick absorbs binding resin, especially when liquid resin is used. Pit also acts as a sponge and will absorb water under excessive swelling if not removed from the composite panel products of ampas 10. Ampas also normally contains 2 to 6% residual sugars, depending on the reed variety, its ripeness, method of harvesting and finally the effectiveness of the sugar mill. The residual sugars in ampas, if not removed for processing or reduced to a minimum of 15, can cause board manufacturing and subsequent use problems. Sugars may be chemically incompatible with the bonding resins commonly used in ampasboard production and may interfere with bonding leading to poor strength. If the residual sugars are not chemically modified or consumed during hot pressing, they can begin to ferment when the ampashoard is exposed to humid conditions, causing an unpleasant odor and leading to chemical and biodegradation. This gives an essential shortening of. the life of the used 25 ampas board.

Consequently, seeds and sugar must be removed if satisfactory products are to be made from sugar cane tampas. These operations not only increase manufacturing costs, but complicate the process.

In contrast to the conventional method, it has been found that composite ampas products such as building board, furniture board. fiberboard and molded articles can be manufactured without the use of binding resin and the removal of kernel and residual sugars. Sugars, carbohydrates or saccharides give not only the binder, but also the reinforcing element in the lignocellulose materials, resulting in a composite product with good strength properties and attractive spatial, stability.

In principle, the method of the invention uses a comminuted mass of ampas or other lignocellulosic material containing large amounts of free sugars, in particular from non-woody plants. The comminuted mass is first dried to a low moisture content, preferably 2-8%, based on oven dry weight. This mass can optionally be combined with other lignocellulose or non-ligocellulosic material. The mass is press-molded without any addition of bonding resin at a temperature of at least 180 ° C and a pressure sufficient to process the material into a compression-molded product for a sufficiently long time for the development and thermosetting of the bond in situ to be converted. residual sugars in an insoluble and infusible polymeric material, which is highly resistant to boiling water and acid hydrolysis.

Crushing the starting materials is particularly useful because individual particles, flakes or strands facilitate and promote formation. Further crushing also reduces and minimizes the presence of epidemic material from the plant stems. The thin outer layer of epidermis, which normally consists of epidermis material, is impermeable to water and adhesive. In a binderless system, finer particles usually give better products, mainly of an even and tight interconnection of individual particles, resulting in a tightly bound, dense and even texture. Conventional method 30, on the other hand, is economically incapable of using finer particles, because finer particles require larger amounts of expensive synthetic bonding resin. In the present invention, it is preferable to use extremely fine particles in combination with other sugar-free lignocellulose materials at the manufacture of composite products.

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The beneficial effect of the use of sugarcane tampas and other sugar-containing ligno llulose materials of non-woody plants in particular can be attributed to the sugars contained therein and water-soluble substances which flow and polymerize during the hot molding treatment and Bind lignocellulosic material in situ. Furthermore, the sugars and water-soluble substances permeated through the cell wall of lignocellulosic tissues are converted and heat-cured into a cross-linked rigid substance which acts as an enhancer throughout the compression molded body. Thus, the compression molded articles have excellent strength properties, spatial stability and boiling water resistance and acid hydrolysis.

These results are best obtained when the ligno-15 cellulosic materials contain a large amount of sugar and water-soluble substances.

The chemical reactions involved in the binding system of the present invention have not been fully elucidated. It is well known that sugar is degraded by both acids and alkalis into low molecular weight compounds with loss of water from the sugar molecule. If a weakly acidic or even pure water reacts with sugar at a temperature of 130-17 ° C and under pressure, about 20% hydroxymethylfurfural is produced. Other intermediates and furfural derivatives can also be produced from carbohydrates under similar conditions. These derivatives are highly reactive and can further polymerize at elevated temperature and convert to insoluble and infusible cross-linked materials. The thermoset bond thus formed is highly resistant to boiling water and acid hydrolysis.

It is believed that all or some of the above reactions may be involved in the bonding and forming process of the present invention. Furthermore, it is believed that chemical conversion of sugars and water-soluble substances at elevated temperature is an irreversible chemical and chemical. Yf \ r \ λ λ -1> ~ v -.J ww ” * - 5 - is a change and is essential to the present invention. The polymerized binder and builder of the present invention is believed to contain a furan dehydration product of the carbohydrate consisting essentially of hydroxymethylfurfural.

It has been found that the physical and mechanical properties of sugarcane tampasboard made according to the present invention are at least comparable to or better than the properties of known ampas boards made with the expensive synthetic bonding resins used hitherto.

The following examples illustrate the invention.

Example I

a

Dried sugarcane tampas with a moisture content of 3.8% were obtained from a regular sugar mill. It contained 7.2% by weight of water-soluble substances, of which 4.7% were reducing sugars (as glucose), as determined by Swedish Cellulose Industry method CCA-11. Further investigation revealed that the ampas contained about 70% by weight of real fiber and 30% by weight of kernel.

The ampas was treated in a hammer mill to obtain two fractions of particles. Particles that passed a 1 mm mesh sieve were used for the surface layer and particles larger than 1 mm were used as the core material for a three-layer fleece. The surface area and core ratio at dry oven weight was 1 to 1. From this web 30, a board of 500 x 500 x 11.1 mm was pressed hot for 12 minutes at a temperature of 235 ° C and a pressure of 2.8 MPa. a specific gravity of 0.72. During this hot pressing, it was noted that a certain amount of material other than the moisture evaporated in the form of steam and various vapors. The fleece weight loss was 8.4%, much more than the 1 - A ~ -1 Λ

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- 6 - original moisture content of 3.8%. The additional weight loss indicated the rigorous chemical reaction at elevated temperatures. Final analysis confirmed that only 0.7% reducing sugar was left in the final board. This was much less than was found in a normal ampas board.

Tensile strength tests gave a dry MOR (tear modulus) of 16.3 MPa and a dry MOE (elastic modulus) of 3.8 Gpa. The wet MOR was 8.6 Mpa. The wet flexural strength was obtained by dipping the samples in boiling water for 2 hours and then testing them wet and cold. The boiling test is required by Can-3-0188-2M78 for weatherproof poplar waffle board as standard. The Canadian minimum standards for dry and wet MOR are 14 and 7 Mpa, respectively. In short, the 15 ampas board complied with all Canadian composite wood panel standards specified for weatherproof application.

Example II

20

Sugarcane shells were produced by a sugarcane separator, which separates the internal sugar-containing soft kernel from the hard outer layer or shell of the sugarcane stem. The peeling ash contained 28.6% water-soluble substances and 17.3% reducing sugars, because sugars were not extracted from them.

The peeling ash was chopped into strands 1.5 to 3.2 mm wide and thick and contained about 5% moisture.

The strands varied in length from 15 to 300 mm. and were oriented in one direction to be compression molded into a composite slat of 30 x 50 x 2650 mm and a specific gravity of 0.65. The compression molding temperature was 225 ° C at a pressure of 3.4 Mpa for 30 minutes. Flexural strength tests gave a dry MOR of 31.6 Mpa and a wet MOR of 18.6 Mpa.

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Example III

. Fresh sugarcane shells obtained from a sugarcane separating machine were treated in boiling water for several times to remove sugars. Three batches of peel were subjected to boiling for 5, 10 and 30 minutes, respectively, and a fourth batch was not boiled but included in the experiment as a control. After. boiling, the shells were dried to a moisture content of 8% and then treated in a hammer mill to a fraction with a particle size of ± 0.8 mm. Chemical analysis indicated that the resulting residual sugars were inversely proportional to the length of the boiling period. She also revealed a close linear relationship between water-soluble substances and reducing sugars. The following Table A gives the results of the cooking treatment.

TABLE A. Sugar content of four batches of peel, which have been treated in boiling water.

Charge Treatment Extracted Reducing number (cooking) soluble Sugar _CS) * CO * 25 1 none 24.4 15.2 2 5 min 16.0 11.2 3 10 min 12.3 10.2 4 _30 min 5.4. 3.7 * Oven dry weight content of peeling fibers. 30

Each batch of shells was used to make six plates of 500 x 500 x 11.1 mm and a specific gravity of about 0.70 using three different pressing temperatures (180, 210 and 240 * 0, two 35 different pressing times (10 and 20 minutes) and a pressing pressure of JQ -C. * * VV - * 9 * - 8 - 3.4 Mpa. The moisture content in the surface layer (particle size less than 0.8 mm) was approximately 9. , 0% and in the core (particle size more than 0.8 mm) 3.0%: The surface area and core ratio of the oven-dry weight of the web was 1 to 1. Test results 5 to 48 plates are shown in the following Table B .

These test results clearly show, according to Table B, that the properties of the board improved as the sugar content of the skins increased. Higher press temperature and longer press times also improve board quality. The shell board had a slightly smooth surface and a dark brown color mainly because of the extremely fine particles and a high sugar and moisture content in the surface layer of the fleece. The spatial stability of the shell ampas board, especially in high sugar manufacture and rigorous pressing, was excellent compared to the known products. This is the result of the binding and strengthening effect of polymerized sugars.

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. Example .IV

This example illustrates sugar cane ash in combination with other lignocellulosic materials to form a mixed composite product.

Sugarcane peel ash, containing about 19% reducing sugars, was treated in a hammer mill to a particle size of 0.8 mm. The peel ash splinters were mixed with poplar wood splinters of the same size at a weight ratio of 70:30. A fleece was formed from the mixture, which was hot pressed at 235 ° C for 10 minutes with a pressure of 2.8 MPa to obtain a 500 x 500 x 11.1 mm plate with a specific gravity of 0.72. Static bending tests gave a dry HOR of 18.2 MPa and a wet MOR of 8.1 MPa. The internal bonding test gave a perpendicular tensile strength of 390 kPa.

All test values met the minimum requirements of CAN 3-0188-2M78.

Example V

20

This example shows that similar results can be obtained with other sugar containing 1 ignoce 1 lui o s mate riales.

Sweet sorghum stems, containing about 18% reducing sugars, were made to a moisture content.

of 3% dried and treated in a hammer mill to a particle size of 0.8 mm. A sheet (500 x 500 x 11.1 mm and 0.75 specific gravity) was prepared from this material under the same pressing conditions as in Example IV. Run 30 results gave a dry MOR of 18.5 Mpa, a wet MOR

of 9.2 Mpa and an internal bond strength of 480 kPa.

Corn stalks containing about 12% surfactants or about 7% reducing sugars were dried to 3% moisture and treated in a hammer mill to a particle size of 0.8 mm. From this, a plate (500 x f) n o ft ^ Π W -la - 11 - 500 x 11.1 mm and. 0.82 specific gravity) manufactured under the same pressing conditions as in Example IV. The test results were a dry MOR. of 14.3 Mpa, a wet MOR of 7.4 Mpa and an internal bond strength of 320 Kpa.

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Claims (10)

9 · - r, - 12 - COITCtllS IES. Process for the production of composite products from comminuted sugar-containing lignocellulose materials without the addition of adhesive binders, characterized in that the starting material is separated into particles, fibers, strands and flakes, the comminuted starting material is dried, the dried starting materials are formed into a desired web and presses the formed web under heating at a temperature of 180 ° C or higher and a pressure and time sufficient to process the web into a compression molded article, while the adhesive bond develops in situ and thermosets , by conversion and polymerization of sugars and water-soluble substances into an insoluble and infusible cross-linked material as a binder and builder, which is resistant to boiling water and acid hydrolysis. A method according to claim 1, characterized in that the sugar-containing lignocellulosic materials are sugarcane tampas, sorghum stalks, corn stalks, sunflower stems, flax stalks and other non-woody vegetable sugars and materials containing water solubles. 3. Process according to claim 1, characterized in that the sugars are free sugars, carbohydrates or saccharides, which are soluble in water, are easily extracted and are easily converted and thermoset using heat, to an insoluble and infusible fabric, which can bind and strengthen. 4. Process according to claim 1, characterized in that the sugars and water-soluble substances contained in the lignocellulosic materials are converted at a temperature of 180 ° C or higher and thermoset to an insoluble and infusible cross-linked polymeric material, which both the binding and reinforcing agent in the compression molded front axle ”O s ·» · * f \ 6. ka V - W "" "^ - 13 - throw. A method according to claim 1, characterized in that the hot press molding temperature is 220 ° C or more. amounts. 5 b. Process according to claim 1, characterized in that the sugars and water-soluble substances remaining in the final composite products are greatly reduced by chemical conversion and weight loss during compression molding at a temperature of 180 ° C or higher. Process according to claim 1, characterized in that the sugar-containing lignocellulose material is comminuted and combined to obtain composite products with other lignocellulose or non-lignocellulose material. Process according to claim 1, characterized in that the sugars and water-soluble substances and kernel are partially or not removed before manufacture. 9. Process according to claim 1, characterized in that the lignocellulosic material is comminuted into extremely fine particles or fibers before producing composite products with a high bonding strength, excellent spatial stability and a dense, uniform, smooth and fine texture. 10. A method according to claim 1, characterized in that the composite products are building board, furniture board, fiber board, compressed hearth logs and compression molded articles with a water-resistant bond which is resistant to boiling water and acid hydrolysis. Q * y i «| *> * W V ί, ✓ · ** u ____M