FR2549768A1 - METHOD FOR MANUFACTURING COMPOSITE PRODUCTS FROM LIGNOCELLULOSIC MATERIALS AND PRODUCTS THUS OBTAINED - Google Patents

Abstract

COMPOSITE PRODUCTS ARE OBTAINED FROM LIGNOCELLULOSIC MATERIALS CONTAINING SUGARS (BAGASSE, SORGHUM, CORN, SUNFLOWER, FLAX), USING THE RESIDUAL SUGARS AS AGGLOMERANT AND REINFORCING AGENT. A LIGNOCELLULOSIC MATERIAL CONTAINING SUGAR, FRAGMENTED, ALONE OR MIXED WITH OTHER LIGNOCELLULOSIC MATERIALS, WITHOUT AGGLUTINANTS OR AGGLOMERANTS, IS MOLDED AT A TEMPERATURE OF AT LEAST 180C UNDER PRESSURE AND DURATION SUFFICIENT TO UNIT THE MATERIAL INTO A COMPOSITE PRODUCT. THE FREE SUGARS OF LIGNOCELLULOSIC MATERIALS PLAY THE ROLE OF THERMOSETTING AGGLUTINANT AND PRODUCE AN EFFECT AT THE TIME OF AGGLOMERATION AND REINFORCEMENT. THE COMPOSITE PRODUCTS OBTAINED HAVE A HIGH MECHANICAL RESISTANCE AND EXCELLENT DIMENSIONAL STABILITY.

Description

Process for manufacturing composite products from materials

  lignocellulosic and products thus obtained. The present invention relates to the manufacture of composite products from bagasse, sorghum stalks, corn stalks, sunflower stems, stems

  flax and other lignocellulosic materials, especially non-woody plants, containing sugars, carbohydrates or saccharides soluble in water and easy to extract.

  More particularly, the invention relates to

  such composite products and their method of manufacture, without the addition of agglutinants or agglomerants.

  This production is carried out according to the invention using the sugars, carbohydrates or saccharides free to

  both as agglomerating agents and as reinforcing agents with application of heat.

  In the conventional manufacture of bagasse panels, binders are used, especially thermosetting synthetic resins such as phenol-formaldehyde and urea-formaldehyde resins. The more expensive phenol-formaldehyde resins being used for Conventional binder resins account for a large part of the total cost of composite materials. It is therefore economically attractive to manufacture composite products without the use of expensive binder resins. In addition, a binderless manufacturing system simplifies the manufacturing process. reduces the cost of production by eliminating the operation and the mixing equipment. It is therefore easy to see the advantage, both from an economic and a technological point of view, of using a process without

  binder for the manufacture of composite products.

  In the traditional method of manufacturing bagasse panels, the removal of the marrow and residual free sugars is essential if we want to obtain good quality panels The marrow, compared to the true fiber, is a very short cell, Thin-walled, and contains a higher proportion of sugars, but does not contribute to the strength of the end product. Being fluffy, it absorbs an excessive amount of binder resin, especially when liquid resin is used. a sponge and absorbs water, swelling excessively if it is incorporated into the composite bagasse panels. Besides, the bagasse normally contains 2 to 6% of residual sugars, the exact number depending on the variety of the cane, its maturity, the harvesting process and finally the yield of the grinding plant. The residual sugars of the bagasse, if they are not eliminated before the treatment, can These sugars may not be chemically compatible with the conventional binder resins used in the production of bagasse panels and hamper agglomeration, which confers poor resistance to If residual sugars are not chemically modified or burned during hot pressing, they may ferment when the bagasse board is exposed to moisture, resulting in an unpleasant odor and ultimately chemical and biological degradation. What abridges

  the service life of the bagasse board.

  Therefore, marrow and sugar removal operations are necessary to produce satisfactory products with Gold bagasse, these operations not only increase

  the cost of manufacturing, but also complicate the process.

  It has been found, in contrast to the conventional method, that bagasse composite products such as building panels, furniture panels, reconstituted wood and soft products can be produced without the use of binder resin or removal of marrow and residual sugars. The sugars, carbohydrates or saccharides provide not only the binder but also the reinforcing element of the lignocellulosic materials, so that a composite product having a good resistance is obtained.

  mechanical and excellent dimensional stability.

  The process of the invention essentially uses a fragmented mass of bagasse or other lignocellulosic material, particularly non-ligneous plants, containing a high proportion of free sugars. The fragmented mass is first dried to a low humidity, This mass can be used alone or mixed with other lignocellulosic or non-lignocellulosic materials. The mass is molded without binding resins at a temperature of at least 180.degree. sufficient pressure to unite the material into a molded product and for a time sufficient for the development and curing of the binder in situ, the residual sugars being transformed into an insoluble and infusible polymeric substance which is highly resistant to

  boiling water and acid hydrolysis.

  The fragmentation of the raw material is very useful because the particles, lamellae or strands facilitate and improve the shaping and molding operation. In addition, the fragmentation minimizes the presence of epidermal material from the plant stem. thin outer layer

  epidermis, which is normally cuticular material, is impermeable to water and clumping.

  In a binderless system, fine particles usually give better products, mainly because of the uniform and close union between them, which gives a strong bond and a tight and uniform texture. On the contrary, the conventional process can not Economically, use fine particles because these require a greater amount of expensive synthetic binder resin. The invention provides, for the manufacture of composite products, use of extremely fine particles when they are mixed with other lignocellulosic materials. not containing sugars Fine particles

  essentially play the same role as a powder binder resin in the conventional process.

  The beneficial effect of the use of bagasse and other lignocellulosic materials, particularly non-woody sugars-containing plants, can be attributed to the sugars and soluble materials in the water which they contain, which melt during the course of time. In addition, the sugars and water-soluble materials which have penetrated the cell wall of the lignocellulosic tissues are also transformed and hardened to a cross-linked rigid substance. The molded products therefore have excellent mechanical strength, dimensional stability and resistance to boiling water and acid hydrolysis, and all the better as the subjects

  lignocellulosics contain a higher proportion of sugars and water-soluble matter.

  The chemical reactions that come into play in the agglomeration system of the invention have not been fully elucidated. It is known that acids and bases break down sugar into low molecular weight compounds, the sugar molecule water If a weak acid or even pure water is reacted with sugar at 130.degree. C. and under pressure, about 20% is formed.

  It is also possible, under similar conditions, to form other intermediates and furfural derivatives from carbon hydrates. These derivatives are very reactive and can also polymerize and transform to produce substances at high temperature. Thus, the hardened binder thus produced is very resistant to boiling water and acid hydrolysis.

  It is believed that all or some of the above-mentioned reactions may be involved in the agglomeration process of the invention. It is further believed that the high temperature chemical conversion of sugars and water-soluble materials is irreversible chemical and physical change and is essential to the invention It is believed that the polymerized reinforcing and clumping material of the invention contains a carbohydrate dehydration product derived from

  furan consisting essentially of hydroxymethylfurfural.

  It has been found that the physical and mechanical properties of the bagasse panels produced by the process of the invention are comparable to or superior to those of conventional bagasse panels produced with expensive synthetic binder resins.

  The embodiment of the invention is described in detail in the following examples.

EXAMPLE 1

  Dried bagasse containing 3.8% moisture from a conventional sugarcane mill was used. It contained 7.2% by weight of water-soluble materials, of which 4.7% was sugars. in the form of glucose, found by the so-called CCA-11 method of the Swedish cellulose industry A further study indicated that

  bagasse contained, by weight, about 70% true fiber and 30% marrow.

  The bagasse was milled with a hammer mill to obtain two fractions. The particles passing through a so-called "Tyler 16 mesh" screen with a mesh of 0.991 mm opening were used for the outer layers and the refusal was used. As the core material for a three-layer mat, the weight ratio outer layers / core on oven-dried material was 1 This mat was hot pressed for 12 minutes at 235 ° C with a pressure of 2.8 M Pa to obtain a panel of 500 x 500 x 11.1 mm density 0.72 During hot pressing, it was observed that a certain amount of material other than moisture evaporated in the form of Steam

  The weight loss of the mat 35 was 8.4%, a figure well above the humidity

  initial loss of 3.8% of the mat Additional weight loss indicates a significant chemical reaction at high temperatures The final analysis indicated that only 0.7% of reducing sugar remained in the finished panel. that we do not

  found in a trade bagasse board.

  The bending tests gave a dry tensile strength of 16.3 M Pa and a dry modulus of elasticity of 3.8 G Pa. 8.6 M Pa For the determination of the wet flexural strength, the specimens were immersed for two hours in boiling water and tested in a cold wet state. The immersion in water test Boiling 15 is required by the Canadian standard "ICAN 3-0188-2 M 78" for poplar particleboard for outdoor use. Minimum Canadian requirements for dry tensile strength and tensile strength Wet condition is 14 and 7 M Pa, respectively. In summary, the bagasse board has met all Canadian standards for composite wood panels.

outdoor use.

EXAMPLE 2

  Sugar cane bark was produced by a separating machine that separates the soft inner marrow containing the sugar from the hard outer layer or bark of the stem of the cane.

  Sugar The bark bagasse contained 28.6% water-soluble material and 17.3% reducing sugars, the sugars not having been extracted therefrom.

  The bark bagasse was cut into strands 1.5 to 3.2 mm in width and thickness which contained about 5% moisture. The strands were 15 to 300 mm in length and were oriented in the same direction to be molded into a composite slat of 30 x 50 x 2650 mm having a density of 0.65 The molding was done at 225 C under a pressure of 3.4 M Pa and lasted 30 minutes The bending tests gave a breaking stress of 31.6

  M Pa in the dry state and 18.6 M Pa in the wet state.

EXAMPLE 3

  Fresh sugarcane peel produced by a separating machine was immersed in boiling water for different times for the removal of sugars Three batches of bark were immersed respectively 5, 10 and minutes and a fourth batch was not immersed and

  After standing in the boiling water, the barks were dried to a moisture of 8% and then milled in a hammer mill and split into two fractions using a "Tyler 20 mesh" sieve.

  The chemical analysis indicated that the residual sugar content was inversely proportional to the increase in the immersion time. It also revealed a strict linear relationship between the water-soluble content and the sugar content. Reducers Table 1 below shows the results of immersion treatment in boiling water. TABLE 1 Sugar content of four batches of bark subjected to immersion in boiling water 35 Matures Duration Materials Sures Immersion batch soluble reductants Extracted% * minute-%

1 O 24.4 15.2

2 5 16.0 11.2

3 10 12.3 10.2

4 30 5.4 3.7

  * Values reported to dried bark fiber in the oven.

  With each batch of bark, six panels of 500 x 500 x 11.1 mm were made having a density of about 0.70 using three pressing temperatures (180, 210 and 240 C), two pressing times ( 10 and 20 minutes) and a final pressure of 3.4 M Pa. The moisture content of the outer layers (sieve rejection) was about 9.0% and that of the material of the core (passing through the sieve) of 3.0% The weight ratio outer layers / core of the mat on oven-dried material was equal to 1 The results of the tests made on the 24 panels are given in

Table 2 below.

  These results show that the properties of the panels improve as the bark content increases. A higher pressing temperature and a longer pressing time also improve the quality of the panels. smooth and a dark brownish color due mainly to the extremely fine particles and the high sugar content and the high humidity of the outer layers of the mat. The dimensional stability of the panels, especially those made with a high sugar content material and the conditions Severe pressing is excellent compared to that of products made by the conventional method. This results from the binding and reinforcing effect of the polymerized sugars.

TABLE 2

  Properties of sugar cane bark panels (thickness 11.1 mm) Pressing conditions Elasticity modulus Lot of bark deatct Bark batch Temperature Time e Dite N flexion (C) ((man) ens (G Pa )

10 0.72 5.01

  No. 1 Control * 9 f 20 0.74 5.12 (15.2% sugars 210 10 0.72 5.06

0.75 5.20

reducing agents) 240 10 0.74 4.85

0.75 5.24

10 0.73 4.91

  No.2 5 minutes immersion 20 0.75 5.00 (11.2% sugars 210 10 0.73 4, 85 reducing agents) 20 OJ, 76 4.81

240 10 0.75 5.01

0.75 5.05

10 0.70 4.75

  No.3 10 minutes immersion 20 0.72 4.72 (10.2% sugars 210 10 0.72 4, 59 reducers) 20 0.73 4.76

240 10 0.73 4.66

0.75 4.91

10 0.70 3.03

  No.4 30 minutes immersion 20 0.72 3.23 (3.7% sugars 210 10 0.73 3, 00 reducers) 20 0.73 2.88

240 10 0.74 3.33

0.75 3.05

  o ru vi 0% TABLE 2 (cont'd 1) Flexural fracture stress Cohesion Resumption Elastic inner bark batch Dry state Condition (K Pa> (%) l (M Pa) wet <M Fa (M Pa)

23.0 5.2 686 23 10.8

  No. 1 Control 22.3 7.7 749 18 9.2 (15.2% sugars 23.2 10.4 658 13 7.1 reducing agents) 23.3 11.5 714 9 3.8, 7 11.0 679 he 1,6

23.5 14.5 735 7 0.7

17.3 3.0 644 27 13.3

  No.2 5 minutes of immersion 19.1 5.4 623 21 11.0 (11.2% of sugars 19.0 8, 3 630 19 8.5 reducers) 18.6 9.1 679 16 3.1 reducing gear>) 19,5 10,8 630 16 3,8

19.2 11.4 602 15 2.7

  18.1 1.9 m 574 29 16.4 No.3 10 minutes immersion 17.6 6.2 630 24 14.5 (10.2% sugars 18.8 7.4 637 19 11.6 reducing agents ) 18.8 7.4 637 19 1 1.6 reducers) 18.7 8.5 602 18 11.8

18.3 9.2 623 16 9.2

0 0.7 266 44 23.5

  No.4 30 minutes of immersion 16.6 2.1 297 38 19.7 (3.7% of sugars 16.4 4, 5 288 36 18.4 reducers) 16.8 5.1 302 25 16.2

, 7.44, 416, 29, 17.1

16.0 7.3 430 22 15.3

1- 'P%; co

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EXAMPLE 4

  This example illustrates the use of bagasse mixed with other lignocellulosic materials for

manufacture of a composite product.

  Bagasse bark containing about 19% reducing sugars was milled in a hammer mill so as to pass through a so-called "Tyler mesh" screen. The particles obtained were mixed with poplar particles of similar size in the 70:30 weight proportions With the mixture was made a mat that was hot pressed at 235 C with a pressure of 2.8 M Pa for 10 minutes to obtain a panel of 500 x 500 x 11, 1 mm having a density of 0.72 The bending tests gave a breaking stress of 18.2 M Pa in the dry state and 8.1 M Pa in the wet state. perpendicular to the faces) gave

  a break stress of 390 k Pa All test results were better than the minimum requirements of the Canadian standard "CAN 3-0188-2 M 78".

EXAMPLE 5

  This example shows that similar results can be obtained with other materials

  lignocellulosic containing sugars.

  Sweet sorghum stalks containing about 18% reducing sugars were dried to a moisture of 3% and milled with a hammer mill.

  way to pass through a sieve called "Tyler 20 mesh".

  A 500 x 500 x 11.1 mm panel having a density of 0.75 was made with the material obtained under the pressing conditions of Example 4. The tests gave as results a flexural breaking stress of 18.5 M Pa in the dry state and 9.2 M Pa at

  the wet state and a transverse internal cohesion (breaking stress) of 480 k Pa -

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  Corn stalks containing about 12% solids and about 7% reducing sugars were dried to 3% moisture and hammer milled to pass through a "Tyler 20 mesh" screen. panel of 500 x 500 x 11.1 mm having a density of 0.82 was manufactured with the material obtained under the pressing conditions of Example 4. The tests gave as results a bending break stress of 14, 3 M Pa in the dry state and 7.4 M Pa in the wet state and a transverse internal cohesion (stress of

rupture) of 320 k Pa.

Claims (7)

  Process for the production of composite products from lignocellulosic materials containing sugars, fragmented, without the addition of agglutinants, characterized in that it comprises the following phases: division of the raw material into particles, fibers, strands and lamellae, drying the fragmented raw material, forming a mat with the dried raw material and pressing and heating the mat at a temperature of at least 180 C under pressure and for a time sufficient for its consolidation to obtain a molded product, while the binder develops and cures in situ, the sugars and water soluble materials being transformed and polymerizing into an insoluble and infusible crosslinked substance acting as a binder and reinforcing agent which Resists boiling water and acid hydrolysis.   Process according to claim 1, characterized in that the raw material is at least one lignocellulosic material of the group consisting of bagasse, sorghum stalks,   but, sunflower stalks, flax stalks, and other non-woody plants containing sugars and water soluble materials.   3 Process according to claim 1 or 2, characterized in that the sugars used are sugars, carbohydrates or free saccharides which are soluble in water, extraction   easy and easily processed and hardened by the application of heat to an insoluble and infusible substance having an agglomeration and reinforcing power.   4 Process according to one of claims 1   at 3, characterized in that the sugars and the water-soluble materials contained in the lignocellulosic materials are chemically transformed and cured at a temperature of at least 180 ° C into an insoluble and infusible cross-linked polymeric substance.   which provides both the binder and the reinforcing agent of the molded product.   Method according to one of claims 1   at 4, characterized in that the molding temperature   and hot pressing is 220 C or more.   6 Method according to one of claims 1   at 5, characterized in that the proportion of sugars and water soluble materials remaining in the finished composite products is greatly reduced by the chemical conversion and weight loss that take place   during the molding operation at 180 C or more.   Method according to one of claims 1   at 6, characterized in that the lignocellulosic materials containing sugars are fragmented and mixed with other lignocellulosic materials or   non-lignocellulosic to form the raw material processed for the production of composite products.   8 Process according to one of claims 1   7, characterized in that the sugars, the materials   soluble in water and marrow are eliminated at least partially from the raw material before treatment. Process according to one of claims 1   to 8, for obtaining composite products having a high cohesion, excellent dimensional stability and a tight, uniform, smooth and   characterized in that lignocellulosic materials containing sugars are comminuted into extremely fine particles or fibers.   Composite products including building panels, furniture panels, reconstituted wood, densified wood and molded products having a waterproof binder which is resistant to boiling water and   acid hydrolysis, characterized in that they are manufactured by a process according to one of claims 1 to 10.