US3663673A - Process for making a bagasse pith composite structure - Google Patents

Abstract

THE PROCESS FOR THE MANUFACTURE OF A COMPOSITE FIBERBOARD STRUCTURE FROM PITH AND FIBROUS PORTIONS OF BAGASSE WHICH COMPRISES FORMING A FELTED MAT OF BAGASSE PITH, FINES AND COARSE FIBERS THE FINES BEING DISTRIBUTED ON THE SURFACES, THEREAFTER APPLYING A RESIN TO THE SURFACE AND APPLYING HEAT AND PRESSURE TO CURE THE COMPOSITE BOARD.

Description

United States Patent 3,663,673 PROCESS FOR MAKING A BAGASSE PITH COMPOSITE STRUCTURE Jose A. Rionda, Beverly Hills, Jamaica, assignor to Esso Research and Engineering Company No Drawing. Original application May 22, 1967, Ser. No. 640,391. Divided and this application Oct. 1, 1969, Ser. No. 870,985

Int. Cl. D21b 1/08 US. Cl. 264-113 3 Claims ABSTRACT OF THE DISCLOSURE The process for the manufacture of a composite fiberboard structure from pith and fibrous portions of bagasse which comprises forming a felted mat of bagasse pith, fines and coarse fibers the fines being distributed on the surfaces, thereafter applying a resin to the surface and applying heat and pressure to cure the composite board.

The present application is a division of Ser. No. 640,391 filed May 22, 1967 entitled, Bagasse Pith Compositions and Structures, inventor Jose A. Rionda.

The present invention relates to the formation of compositions and structural boards of superior surface quality from bagasse, a milled fibrous by-product of a sugar cane mill. It contemplates the extraction or removal of parenchyma from the fibrous portions of the bagasse, the formation of compositions by admixture of the parenchyma with thermosetting binder resins, and the use of the compositions as molding compounds, or compounds especially suitable for formation of laminae. It contemplates, in particular, structures formed by use of this type of laminae, particularly when the laminae is reapplied as a surface coating or layer upon structural boards composed, in whole or in part, of the fibrous portions of the bagasse. It contemplates, especially, the formation of core structures from fibrous portions of the bagasse or other lignocellulosic materials, or both, wherein the core is covered with bagasse pith resin compositions, and pressed.

Bagasse, a by-product of sugar manufacture, is the dried, crushed residue of the sugar can stalk. It consists principally of fibrous components and parenchyma, generally (and hereinafter) referred to as pith. The fibrous components include the rind fiber and the fibre-vascular bundles or cells from which the juice has been extracted. The fibrous components, especially the fibro-vascular fiber bundles or shives are united or bonded together with the pith, though some of the pith is found in the bagasse in loose powder form.

The pith is a nonorganized, nonfibrous, pulpy substance. Its chemical nature, light cellular structure and high surface area, relative to its mass, make it a highly reactive and absorbent material of limited commercial utility. It is, in fact, most often a waste product.

In prior art processes, the pith, which constitutes a major proportion of the bagasse, is separated via chemical or mechanical means from the fibrous materials as completely as possible, and then discarded. This has been considered necessary to provide a raw material suitable for the formation of structural boards or finished products of optimum structure and qualityviz., optimum for machine operation, product quality and low chemical cost per ton of pulp produced. In the separation, large quantities of the fibrovascular fiber are also unavoidably removed along with the pith, and generally discarded therewith. This represents additional waste and, though bagasse is variable in composition, the waste can range above about 50 percent based on the initial Weight of the bagasse.

The surface qualities which can be developed from bagasse fiber in conventional processes can be varied to some extent depending upon the processing or extent of preparation of the fibrous materials remaining after separation of the pith, i.e., the conventional reject fraction of the bagasse. Thus, after removal of the pith, relatively coarse fibers are left behind. On the one hand, the coarse fibers can be formed into a mat and processed into a board of homogeneous structure, the surface quality of which is rather coarse. On the other hand, a portion of the coarse fibers can be further ground and this relatively fine fiber reapplied upon the coarse fiber as a surface layer. The surface of the structure can be sanded, buffed, and then sealed, to provide a surface sufliciently smooth for some commercial applications. Nevertheless, the surface quality is deficient in many respects and leaves much to be desired. Moreover, to provide even relatively smooth surfaces requires considerable processing steps which, inter alia, adds to the cost of the finished products.

The primary objective of the present invention is to obviate these and other prior art deficiencies while providing new and useful compositions made from the pith, or the conventional reject portion of the bagasse. In particular, this invention contemplates extraction or removal of the pith from the bagasse, and use of the pith to form molding compositions, or composiitons useful for impregnation and bonding with fibrous components, or useful as laminae. More particularly, it is an object to provide structures formed from this type of pith composition, especially structures wherein the compositions are employed as laminae. It is an even more particular object to provide structures wherein the laminae is reapplied as surface coatings or layers upon structural boards composed in whole or in part of the fibrous portions of bagasse. Even more particularly, it is an object to provide structures formed from a fibrous core of the bagasse or other lignocellulosic materials, or both, and the core is covered with bagasse pith resin compositions, and pressed. It is a further object to provide such structures which have superior surface characteristics.

These and other objects are achieved in accordance with the present invention which contemplates the formation of new and novel compositions by extraction and removal of pith (or pith and fines) from bagasse, and admixture of the pith with thermosetting resins. The pith is extracted and separated from the whole bagasse by known chemical or mechanical means, preferably the latter, admixed with the desired amount of thermosetting resin, or resins, and then deliquefied to form a moist powder.

In a preferred embodiment, pith-resin compositions as moist powders are applied upon or spread over the surfaces of board structures, particularly fiber board structures, pressed and cured to form tenacious high quality surfaces. In particularly preferred embodiments, the pithresin compositions are utilized as surface layers on fibrous core structures, constituted in whole or in part of bagasse or other lignocellulosic fibers, or mixtures thereof. In an especially preferred embodiment, the pith-resin compositions are reapplied upon fibrous bagasse board structures, and then pressed and cured to form surfaces admirably suitable for embossing in a hot press, for finishing with stains, paints and lacquers or printing. In accordance therewith, essentially the whole bagasse can be used in forming board structures having superior face qualities.

The pith-resin compositions can be applied to a wide variety of structural boarsd, e.g., hardboard, fiberboard or particleboard, of essentially any density. The compositions can be used as core impregnants, but preferably they are used as surface layers. In the formation of bagasse boards for structural or nonstructural applications, the compositions can be applied as a face upon a relatively loose or highly compacted core fiber to provide a finished structure of low, medium or high density.

Bagasse fiber has thus been shown to be an extremely versatile boardmaking material. Boards can be conveniently produced which range, e.g., in low to high density from about 18 pounds per cubic foot to about 62 pounds per cubic foot and in thicknesses from about one-eighth inch to about 2 inches-all from essentially the same basic fiber. The surface appearance of such boards can be greatly improved by application of pith-resin compositions, and with minimal or no processing, as described.

Boards can be made with pith-resin compositions and fibers, especially bagasse fibers. Preferred articles of manufacture are those made from fibers, especially bagasse fibers, by mat felting techniques. Pursuant to such methods, articles are formed wherein the coarser fibers lie at the core or intermediate the surface layers or faces of the mats or finished boards. The pith and finer fibers lie substantially at the faces of the mats or finished boards. The outstanding face characteristics of the pith-resin compositions can, of course, be developed only when the compositions are exposed for visual appearance.

The methods of forming mats for production of conventional board structures are such that classification of the pith, fines and coarse fractions is effected, the finer particles being distributed to the faces of a mat or structure, while the coarser particles are distributed to the core of the structure. In any construction using conventional classification techniques, it is extremely difiicult to form mats from the pith and fibers without some classification taking place. It is also true that both the pith and fibers, and the fines and coarse fractions, will take up resin. The fines fractions, however, will take up considerably more of the applied resin than will the coarser fractions. In general, the pith and fines, distributed to the faces, will absorb about twice as much of the applied resin as the coarser fractions. In general, a pith-resin composition surface, or face, should range from at least about 0.010 inch in thickness, and more preferably at least about 0.020 inch in thickness, to prevent exposure of the underside layer. More optimum thicknesses, however, range at least from about 0.05 inch and greater. In typical board constructions, the sum-total of the face or surface layer ranges about five to about fifty percent, and preferably from about fifteen to about forty percent, of the total weight of the board structure. Structures having surface layers ranging from about fifteen to about twenty-five percent of the total weight of board structures are found most satisfactory for a wide variety of applications.

An outstanding property of pith-resin faced boards is the surface which is developed. This surface is sufficiently smooth, uniform, and light colored to provide a neutral background for virtually any type of finishing procedure. Prefinishing operations can range from no treatment at all to technically simple, minimal or low-cost techniques such as staining the board surface with a water-base stain, to more sophisticated techniques such as lacquering, embossing, and grain printing. Prefinishing techniques can be provided in the pressing operation itself, e.g., stain can be added to the resin used for the face layers, and the use of high resin levels in the surface layer can produce hard surfaces which can be brought to a condition of high gloss by simple buffing techniques. Embossing and grain printing the board surfaces in hot presses is quite feasible. These techniques and others provide a wide variety of high quality surface finishes without need for additional processing of the board.

For example, in interior application, i.e., wall paneling or furniture components, these types of pith-resin faced boards are not only adequate, but highly suited, by virtue of the exceptional surface quality and adaptability to finishing techniques. The pith-resin face can even be employed to develop a hardboard type of surface when applied on a medium density board. Thin boards, i.e., boards of three-sixteenth inch with density in the range of about 32 to about 50 pounds per cubic foot are thus suitable for many applications as traditional hardboards.

4 Other boards suitable as medium density boards are those ranging, e.g., one-half, five-eights, and three-quarters inch in thickness, with densities between about 34 to about 45 pounds per cubic foot. The pith-resin faced board structures can also be adapted to the manufacture of alkali resistant boards, e.g., concrete form boards.

In forming the pith-resin compositions, the amount of resin applied to or admixed with the extracted pith depends to some extent upon the chemical nature and atfinity of the pith for the particular resin. It also depends upon the particular use to be made of the finished compositions. In general, from about five to about fifty percent resin is mixed with the pith, based on the weight relationship of dry pith to dry resin solids. Preferably from about 10 weight percent to about 30 weight percent resin is applied for most structural applications. Generally higher concentrations of resin, in relation to the pith, are used in the formation of high gloss hard surfaces. The surfaces of boards formed with about 20 percent and higher resins thus have harder surfaces, are more glossy and smooth in in appearance, and have higher resistance to alkali. Such boards also have high resistance to abrasion and water absorption. Nonetheless, surface coatings, e.g., print, paint and lacquers, can be readily applied. Boards formed with lesser resin concentrations are most highly suitable for inside applications.

The pith-resin compositions are formed by spraying or by admixture of solutions or dispersions of the resin with the pith, followed by partial or complete removal of the liquid. It is generally necessary to partially deliquefy or dry the resultant composition by removing the liquid without curing the resin. Preferably, this is accomplished by quick partial deliquefication or drying at a temperature below the curing temperature of the resin. The maximum temperature to be used, and time of drying, thus depends upon the nature of the resin.

In most instances it is preferable to admix, spray or otherwise incorporate the pith and resin by addition of the resin to the pith, whether wet or dry, as a slurry or solution. Generally, from about 15 percent to about 50 percent, and preferably from about 20 percent to about 40 percent, resin is dispersed in a liquid, e.g., water, based on the total weight of the liquid solids system formed. A sufficient amount of the liquid is then removed to form, preferably, moist powder.

Essentially any thermosetting resin, plastic or plasticlike substance which will heat soften and fiow to adhere to and bind the pith and which, subsequently, can be cured or hardened, and permanently set, by application of sufficient heat can be used in this invention. Preferably, the thermosetting resin to be used is one having a viscosity, at 25 C., ranging from about 40 to about 1000 centipoises when the total solids content of the resin solution or slurry is about fifty percent. The specific gravity of the slurry or solution should range between about 1.0 and 1.2 and the pH between about 7.5 and '10. Illustrative of the more preferred thermosetting resins are phenol-aldehyde resins, particularly phenol-formaldehyde and urea-formaldehyde resins whether used alone or with catalytic materials to aid in the curing.

The following illustrative examples bring out the more salient features of the invention. These show extraction of pith, the formation of pith-resin compositions, and development of board structures from the whole bagasse. The pith, as pith-resin compositions, is used to improve the face quality of bagasse articleboards. Particleboards so formed are compared with bagasse particle board formed by conventional processing techniques.

EXAMPLES Whole green bagasse is processed in a hammer mill and a disc mill to provide fibers which are then sprayed with a twenty-five percent aqueous solution of phenol-formaldehyde-resin to impregnate or coat essentially all of the fiber with the resin. Mats are then formed using a B'achre Bison air felting machine which classifies the fibers into fine and coarse fractions. These fractions are simul taneously classified and formed into a mat such that the fines are on the outermost surface of each face, and the coarse fibers form the core of the board. Thus, this mat form gives bound coarse fractions in which the outermost layers contain the largest proportion of pith and fines. The coarse fiber fractions which form the coreof the boards have about one-half as much resin as on the fines at the faces.

In several applications, sufficient of a phenol-formaldehyde resin is applied to form faces of different resin content. Three typical constructions thus have, respectively, 32 percent, 16 percent, and 8 percent of the board weight as the fines fraction applied to the faces of the boards. Each is hot pressed to cure the resin and to form finished structural boards as discussed below.

A board made with 32 percent fines applied as faces is pressed at a low press temperature-viz, for 8 minutes at 300 F. This board has a good quality surface, and sanding of the surface is unnecessary to provide a smooth surface. The relatively short press cycle achieved at this low temperature is also advantageous and is apparently the result of the steam-shock effect of moisture being driven from the face layers.

A second board is made with 16 percent fines applied as faces. This board, pressed at 350 F., shows about the same level of surface softness as the board made with 32 percent fines.

A third board is made with 8 percent fines applied as faces. In this construction the board is pressed at 350 F. for suflicient time to cure the board. When the faces of this board are sanded, the sanding is extended just deep enough to provide a fairly glossy surface.

In general, both a high moisture content and a fairly high proportion of material are needed in the face layers to gain press time for the steam-shock effect and to protect the surface against dry-out. Reasonable press times can be obtained at relatively low press temperatures. For a board that is to be sanded, a press temperature of the order of from about 300 F. to about 350 F. is probably 6 ing the amount of material picked from the surface by the pressure-sensitive adhesive of the tape. It is found that the pith faces on unsanded boards is highly pick resistant, and almost equal in this respect to certain conventionally hardboard.

Specimens of boards boiled for 4 hours, oven dried, and conditioned show a thickness increase of about 35 percent and a corresponding drop in density from 42 pounds per cubic foot to 31 pounds per cubic foot. There is no indication that the pith surface is unduly softened by exposure to boiling water, and the boil test proves to be most effective in detecting undercure. The residual bending strength ofthe material after boiling and drying is about 70 percent of the original strength.

Water absorption measurements show that the pith faced boards are unsurpassed as compared with boards made with plain bagasse fiber. The 24 hour water absorption is 6.7 percent while the 24-hour thickness swell is 4.5 percent (washed fiber).

The advantage gained by using the reject fraction of bagasse on the faces of boards lies primarily in the excellent surface quality which can be developed with this material. This surface quality is at its highest in the unsanded board pressed at low temperatures. The surface quality of the sanded boards depends to some extent on the depth to which the board is sanded.

Compared to certain commercial boards, the surface qualities of the pith-faced boards range from superior to greatly superior, even for unsanded boards. Exposure to water produces much less surface roughening than in certain commercial boards.

A board pressed at low temperatures without sanding can even be classed as a paint grade" board in that it takes a uniform coat of spray paint without the need for prime or sealer coats.

The following table is illustrative and provides a summary of the physical properties obtained for the 32 percent pith-faced boards sanded and unsanded. These are contrasted with a three-layer board made without pith and with 6 percent resin throughout. All values are corrected to 42 pounds density.

1,000 cycle abrasion thick- 24-hours, Screw holding Surface ness, (percent) M.O.R. LB. soundness loss (p.s.i.) (p.s.i.) Edge Face (p.s.i.) (inch) W.A. T.S.

Pith-faced sanded 3, 800 78 250 275 203 009 7. 8 4. 2 Pith-faced unsanded 4, 280 75 250 275 175 006 6. 7 4. 5 Plain fiber sanded- 3,770 89 250 270 208 .009 12.0 4.2

No'rE.M.O.R.=Modu lus of rupture, or the maximum fiexual stress developed in the outermost fibers of the board at the; time of rupture in simple bending;

stress perpendicular to the surface,

on a Taber abraser;

"10 screw inserted to a depth of 0.6; the board (measured perpendicular to board surface);

LB. (p.s.i.)=Internal bond, or the maximum tensile Screw holding=The maximum screw holding capacity of the board. Surface soundness=The tensile strength of the outer surface of Abrasion th1ckness=Loss in inches after 1,000 cycles W.A.=Water absorption: The water absorbed by the board after a submersion test;

I.S.=Thlckness Swell: The percentage increase in board thickness after a 24hour water submersion test.

suitable. For unsanded boards, the need to provide harder faces requires the use of temperatures of the order of from about 250 F. to about 300 F., and perhaps one or two minutes additional press time.

Surface tests are made on these boards-viz, surface I.B., abrasion resistance, pick resistance, and photographic comparison of surface uniformity, both before and after exposure to Water.

The surface photography shows that the board made with the pith faces is substantially superior to various boards of commerce, both before and after wetting. The surface I.B. test shows that the unsanded pith face is at least 80 percent as strong as a board made from pure fiber (sanded).

Abrasion tests show that the pure pith face of an unsanded board is more abrasion-resistant than a pure fiber face.

The pick resistance of the face is assessed by applying Scotch Tape to the surface, peeling it off, and estimat- It is apparent that this invention is subject to various modifications and changes Without departing its spirit and scope. In the formation of pith-resin compositions, e.g., the pith or pith-fiber fines fraction or portion is first classified or separated from the whole bagasse, and then admixed with a liquid within which the desired resin, or resins, is dispersed or dissolved.

In separation of the pith from bagasse fiber, the pith is preferably torn loose and then separated from the bagasse by mechanical means. The whole ba-gasse is, e.g., shredded, while wet or dry, by beating within a hammer mill or by tearing the fibers to the desired size by use of rotating discs. The pith can also be separated from the bagasse by acetic acid degradation (by fermentation, natural or cultured) followed by mechanical, hydraulic or pneumatic separation. The loose pith, in wet or dry form, is then sprayed or admixed with solutions or slurries of the desired thermosetting resins, or mixture of resins. The whole slurry is then dried, partially or completely, without curing at relatively low temperature and low pressure, or combination of both, to remove the liquid, this leaving the composition as a moist powdery mass.

The pith compositions can subsequently be used for a wide variety of applications. The compositions can be made to fluidize, plasticize, and subsequently harden in a thermohydrosetting fashion under certain sequential combinations of moisture content, temperature, pressure, pH, time, and the like. The compositions can be made to react and partially copolymerize with monomeric thermosetting resins, e.g., methylol-phenol or dimethylolurea, and the like, by the formation of methylene crosslinkages with the cellulose components. These reactions can be sequentially combined, preferably simultaneously, so that their effects are cumulative and face finishes can be obtained which are embossable so that textured finishes simulating wood grain can be molded directly on the fiberboard or felt surfaces. Slight modifications to equipment and processes presently known to the art permit in situ application of required functional conditions.

Having described the invention, what is claimed is:

1. A process for making a composite structure from the pith and fibrous portions of bagasse comprising the steps of:

forming a felted mat by classifying bagasse pith and fibers into fine and coarse fractions, the fines being distributed to the outermost surface of each face, while the coarse fibers are distributed to the center of the mat to form a core,

simultaneously applying a thermosetting resin upon the fibers in an amount sufficient to provide a pith-resin composition having from about to about 50% resin based on the total weight of pith and resin, said resin being selected from the class consisting of phenolvformaldehyde and urea-formaldehyde 5 resins and having a viscosity at C. in the range of from about to about 1000 centipoises when the total solid content of the resin solution is about and then applying sufiicient heat and pressure upon the 10 mat to cure the resin and to cause the composition to flow and adhere to the surface.

2. The process of claim 1 wherein said resin is added in amounts sufiicient to provide a pith resin composition containing from about 10% to about 30% resin.

15 3. The process of claim 1 wherein the pith and fiber comprises substantially whole bagasse.

References Cited UNITED STATES PATENTS 1,955,411 4/1934 Darrah l62l88 1,996,343 4/1935 Miss 162129 2,080,021 5/1937 Devereux 162--188 2,336,628 12/1943 Muench 162188 2 2,918,398 12/1959' Dorland et a1 162-129 5 3,113,065 12/1963 Newton et-al 162164 'ROBERT F. BURNETT, Primary Examiner L. C. KOECKERT, Assistant Examiner U.S. Cl. X.R.