WO2015142158A1

WO2015142158A1 - Bio-based resole type phenolic resin adhesive

Info

Publication number: WO2015142158A1
Application number: PCT/MY2015/000015
Authority: WO
Inventors: Binti Zakaria SARANI; Chin Hua CHIA; Roslan RASIDI
Original assignee: Universiti Kebangsaan Malaysia
Priority date: 2014-03-18
Filing date: 2015-03-13
Publication date: 2015-09-24
Also published as: MY191695A

Abstract

A method of preparing a bio-based resol-type phenolic resin adhesive includes the steps of providing a lignocellulosic biomass, drying the lignocellulosic biomass to produce a lignocellulosic biomass material, mixing the lignocellulosic biomass material, and a reactive substance in presence of a catalyst to form a viscous liquefaction mixture, dissolving the liquefaction mixture in a diluting agent to dilute the viscous liquefaction mixture, dissolving solution in an alkaline medium, reacting the solution with a linking molecule at a set temperature in the alkaline medium to form a liquefied resole type biomass resin, and cooling the liquefied resole type resin at room temperature to recover the resol-type biomass resin adhesive.

Description

Title: Bio-based Resole Type Phenolic Resin Adhesive

Technical Field:

Embodiments of the present invention generally relate to preparation of phenolic resins, and more particularly, to bio-based resole type resin and method of preparation of resol-type resins such as those employed in the manufacture of wood adhesives.

Background Art:

In the current scenario especially in the manufacturing industry the cost of raw materials used in several manufacturing processes has increased tremendously over the years. Particularly, in the wood products industry chemicals derived from petroleum and natural gas are utilized as bonding agents. The application of bonding agents enables the use of smaller trees, wood chips, fibers and mill residues to produce various products that meet the consumer needs. As the quality of harvested timber declines due to the shrinking commercial forest land base, the future of wood utilization will require an even higher dependence on bonding agents or resins to convert the limited timber resources into viable products. In view of the environmental strains caused by fossil fuels and chemicals and their inherent vulnerable and limited supply, the efforts to identify other available resources for bonding raw materials have accelerated in the last few decades.

Resins are most commonly applied in composite wood panel manufacture.

"Resin" is a generic term used to describe both natural and synthetic glues which derive their adhesive properties from their inherent ability to polymerize in a consistent and predictable fashion. The vast majority of modern industrial resins available is synthetic, and is normally derived from petroleum feedstocks. Two of the most important classes of synthetic resins, in terms of production volume and total sales are phenol formaldehyde (P/F) and urea formaldehyde (U/F) resins. In both cases, the principal market application is for use as a glue binder in man-made wood products.

Phenol-formaldehyde resins are polymers prepared by reacting phenol with aldehyde in the presence of acid or base. Under acidic conditions and with an excess molar ratio of phenolic component an essentially linear low-degree-of-polymerization "prepolymer" is formed. This material is known as a novolak. Polymerization can be continued to an infusible solid through the addition of sufficient aldehyde. The completely polymerized material, often referred to as cured or hardened, is usually used in pressed products. Novolak prepolymers are usually not water soluble. However, under sufficiently basic conditions the novolak may form a salt and become water soluble. Under basic conditions aldehyde can be added to the mixture and a base catalyzed polymerization performed at elevated temperatures.

The base-catalyzed phenolic resins are classified as resol-type phenolic resins.

A typical resol is made by reacting phenol with an excess of formaldehyde, in the presence of a base such as ammonia, to produce a mixture of methylol phenols which condense on heating to yield low-molecular weight prepolymers, or resols. This material is usually water soluble because of salt formation in the basic solution. No additional aldehyde is required for continued polymerization to an infusible water insoluble product. On heating of the resols at elevated temperature under basic, neutral, or slightly acidic conditions, a high molecular weight network structure of phenolic rings is produced, linked by methylene groups, and typically retaining residual methylol groups. Resol prepolymers are the phenolic resins usually used for wood adhesives. They are preferred over novolaks for numerous reasons. No additional aldehyde is required in the process as the resol adhesive is a single component entity. Moreover, the most common phenolic-type resin for wood adhesives is phenol-formaldehyde resol resin. Resorcinol-formaldehyde cold-setting adhesives are of the novolak-type, but without an acidic catalyst due to their high reactivity. These cold-setting adhesives are two component systems requiring aldehyde addition to the novolak prepoiymer immediately before use; otherwise there is no means of controlling the polymerization to an infusible product.

However, Phenol is petroleum derived, i.e., it is a petrochemical. Moreover, using petroleum feedstocks based materials in the manufacturing processes increase the product cost. To overcome the cost price in the competitive market raw materials derived from renewable resources or alternative resources will be highly advantageous. Renewable resources are the most promising in this field and much research and development have been devoted in this area. An increase in demand for environmentally friendly products, together with the ambiguity of the variable and volatile petrochemical market, has encouraged the development of raw materials from renewable and/or inexpensive sources. For example, a biomass derived phenolic material which is readily available to the forest products industry, and which is presently under-utilized, would be an ideal substitute for petrochemical derived phenol. Moreover, the costs associated with formaldehyde production have increased and there is a need in the art for alternative materials for use as wood adhesives and binders. One alternative for phenol that has been considered are lignins which have been recovered from wood, wood residues, bark, bagasse and other biomass via industrial or experimental processes. Natural lignin is the polymer which occurs in nature and lignin holds wood and bark fibres together and gives wood its strength and phenol formaldehyde resins are structurally very similar. Lignin is a random network polymer with a variety of linkages, based on phenyl propane units. There are number of publications describing the use of various lignin sulfonates, by-products of the sulfite pulping industry, although many other types of lignin are also mentioned. This information is comprehensively covered by H. H. Nimz in "Lignin-Based Wood Adhesives", a chapter in "Wood Adhesives: Chemistry and Technology" edited by A. Pizzi, Marcel Dekker, Inc. publisher (1983). Lignin and pyrolysis oil have been successfully used to directly replace phenol in phenolic resin synthesis, but the substitution ratio is generally less than 30-50% due to the much lower reactivity of lignin compared with pure phenol as disclosed in Van der Klashorst, 1989; Cetin and Ozmen, 2002.

Lignin is one of the most abundant, renewable natural products on earth and technically lignins are produced in tremendous quantities every year as a byproduct of the pulping process. Malaysia produces an abundant supply of palm-press fibres and oil palm empty fruit bunches (EFB) which are regarded as wastes and have not been utilized satisfactorily. Therefore, the utilization of lignin from oil palm empty fruit bunch has such advantages as an inexpensive raw material and environmentally friendly thereby realizing the comprehensive utilization of the highly additive value of the lignin. There remains a need in the art for preparing bio-based resole type resin. Moreover, the prior art does not disclose methods directed at producing a cost effective method to prepare bio-based resole type resin.

It is an object of the invention to overcome disadvantages of the prior art. The above object is met by the combinations of features of the main claims, the sub-claims disclose further advantageous embodiments of the present invention.

Disclosure of the Invention:

Embodiments of the present invention aim to provide a method for preparing a resol-type biomass resin adhesive which includes the steps of providing a lignocellulosic biomass, drying the lignocellulosic biomass to produce a lignocellulosic biomass material, mixing the lignocellulosic biomass material with a reactive substance in presence of a catalyst to form a viscous liquefaction mixture. The liquefaction mixture is dissolved in a diluting agent to dilute the viscous liquefaction mixture. In subsequent steps, the liquefaction mixture is filtrated to remove non-soluble materials and obtain a residue and a solution containing a soluble part of the liquefaction mixture. The recovered solution is contained in the organic solvent, and the solution is dissolved in an alkaline medium. In addition, the solution is reacted with a linking molecule at a set temperature ranging from about 65°C to 85°C in the alkaline medium to form a liquefied resole type biomass resin and the liquefied resole type resin is cooled at room temperature to recover the resol-type biomass resin adhesive.

In accordance with an embodiment of the present invention, the set temperature is about 65°C for about 60 minutes while reacting the solution with the linking molecule and subsequently increasing the temperature to about 85°C for about another 60 minutes to form the liquefied resole type biomass resin.

In accordance with an embodiment of the present invention, the diluting agent is an organic solvent.

In accordance with an embodiment of the present invention, the lignocellulosic biomass is selected from a group including an oil type empty fruit bunch (EFB) fiber, kenaf fiber, a hardwood feedstock, a softwood feedstock, and an annual fibre feedstock. Particularly, the reactive substance is a liquefying reagent and the liquefying reagent is selected from a group consisting of a phenol, phenol derivatives and condensates of phenol.

Embodiments of the present invention further aim to provide a resole type biomass resin adhesive composition which includes a product obtained by drying a lignocellulosic biomass to produce a lignocellulosic biomass material, mixing the lignocellulosic biomass material, and a reactive substance in presence of a catalyst to form a viscous liquefaction mixture, dissolving the liquefaction mixture in a diluting agent to dilute the viscous liquefaction mixture and wherein the diluting agent is an organic solvent, recovering the solution contained in the organic solvent, dissolving the solution in an alkaline medium, and reacting the solution with a linking molecule at a set temperature ranging from about 65°C to 85°C in the alkaline medium to form a liquefied resole type biomass resin and cooling the liquefied resole type resin at room temperature to recover the resol-type biomass resin adhesive.

In yet another embodiment of the present invention, aim is to provide a wood product prepared using the adhesive compositions as defined above. Preferably, the wood product is selected from the group consisting of laminated wood, plywood, particle board, high density particle board, oriented strand board, medium density fiber board, hardboard or wafer board. Furthermore, the wood product prepared using the adhesive composition of this invention is used for exterior, interior or both interior and exterior applications.

While the invention is described herein by way of example using several embodiments and illustrative drawings, those skilled in the art will recognize that the invention is not limited to the embodiments of drawing or drawings described, and are not intended to represent the scale of the various components. Further, some components that may form a part of the invention may not be illustrated in certain figures, for ease of illustration, and such omissions do not limit the embodiments outlined in any way. It should be understood that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the invention is to cover all modification, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description or the claims. As used throughout this application, the word "may" is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words "include," "including," and "includes" mean including, but not limited to. Further, the words "a" or "an" mean "at least one" and the word "plurality" means one or more, unless otherwise mentioned. Description of Drawings and Best Mode for Carrying Out the Invention:

So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. For example, the method of isolating lignin using the herein disclosed solvent extraction process should not vary substantially with the original source of the lignin material, nor should the use of such isolated lignin vary substantially in the preparation of resol resins for adhesives. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

These and other features, benefits and advantages of the present invention will become apparent by reference to the following text figures, with like reference numbers referring to like structures across the views, wherein:

FIG.1 illustrates SEM images of the native and liquefied residue for EFB at different ratio of phenol/EFB (P/E), in accordance with an embodiment of the present invention;

FIG.2 illustrates a wood-to-wood adhesive bonds specimen dimensions, in accordance with an embodiment of the present invention;

FIG.3 illustrates a Fourier transform infrared absorption spectrum for commercial phenolic resin and synthesized phenolic resin at different weight ratio, in accordance with an embodiment of the present invention; FIG.4 illustrates Thermogravimetric Analysis (TGA) weight lose curves for the phenolic resin produced at different weight ratio, in accordance with an embodiment of the present invention;

FIG.5A illustrates a Dynamic Mechanical Analysis (DMA) cure profile of the liquefied PF resin at F/L_EFB weight ratio PF 1.8 at storage modulus development at 2°C/min, in accordance with an embodiment of the present invention;

FIG.5B illustrates the DMA cure profile of the liquefied PF resin at F/L_EFB weight ratio PF 1.8 at vitrification temperature dependence on ramp rates, in accordance with an embodiment of the present invention; and

FIG.6 illustrates shear strength of plywood bonded with resol-type adhesive from liquefied EFB at different weight ratio of F/LEFB, in accordance with an embodiment of the present invention;

Embodiments of the present invention aim to provide a method for preparing a resol-type biomass resin adhesive as an alternative to reduce the consumption of petroleum-based phenol by using the phenolic derivatives from lignin in EFB fibres.

In one embodiment, the lignocellulosic biomass is selected from a group including an oil type empty fruit bunch (EFB) fiber, kenaf fiber, a hardwood feedstock, a softwood feedstock, an annual fibre feedstock and combinations thereof which may be utilized in the present invention. Particularly, the method of preparing the resol-type biomass resin adhesive includes the steps of utilizing a lignocellulosic biomass. Then, the lignocellulosic biomass material is mixed with a reactive substance in presence of a catalyst to form a viscous liquefaction mixture. Particularly, the reactive substance is a liquefying reagent and the liquefying reagent is selected from a group consisting of a phenol, phenol derivatives and condensates of phenol. The catalyst used is sulfuric acid and the sulfuric acid is used in quantity of about 1 % to about 5% based on weight of the reactive substance.

In one embodiment of the present invention, liquefaction process includes varying a weight ratio of the phenol to the lignocellulosic biomass. Particularly, the weight ratio of the phenol to the lignocellulosic biomass is selected from a weight ratio of about 2:1 to about 3:1. Moreover, different ratios of phenol/EFB (2:1 , 2.5:1 , and 3:1 ) are selected to investigate in the liquefaction process.

In one embodiment of the present invention, the liquefaction process is performed at a temperature of about 150°C for about 120 minutes in an oil bath. Subsequently, the liquefaction mixture is dissolved in a diluting agent to dilute the viscous liquefaction mixture. Particularly, the diluting agent is an organic solvent and the organic solvent in the present invention is methanol.

In the subsequent steps, the liquefaction mixture is filtrated to remove non- soluble materials and a residue is obtained along with a solution containing a soluble part of the liquefaction mixture.

In the preferred embodiment of the present invention, the present method is followed by resinification with the addition of linking molecule in alkaline condition. Particularly, the linking molecule is an aldehyde source and the aldehyde source is selected from a group consisting of formaldehyde, paraformaldehyde, hexamethylenetetramine, acetaldehyde, furfural or a combination thereof. The liquefied EFB mixture solution is then resinified in different amount of the linking molecule. In addition, the solution is reacted with a cross linking molecule at a set temperature ranging from about 65°C to 85°C in the alkaline medium to form the liquefied resole type biomass resin. After that, the liquefied resole type resin is cooled at room temperature to recover the resol-type biomass resin adhesive. The obtained result illustrated that more than 95% of empty fruit bunch (EFB) is liquefied at 150°C by using sulphuric acid as catalyst.

In one embodiment of the present invention, the set temperature is about 65°C for about 60 minutes while reacting the solution with formaldehyde and the method further includes subsequently increasing temperature to about 85°C for about another 60 minutes to form the liquefied resole type biomass resin.

In one embodiment of the present invention, reaction of the solution with the linking molecule is carried out at a plurality of different weight ratios of formaldehyde to liquefied lignocellulosic biomass composition at about pH 9. Particularly, different weight ratios of formaldehyde to liquefied lignocellulosic biomass in the reaction is selected from a range of about 1.8 to about 2.2. Particularly, the different weight ratios of formaldehyde to liquefied lignocellulosic biomass are 1.8, 2.0, and 2.2.

In one embodiment of the present invention, the reaction of the solution with the formaldehyde in the alkaline medium is carried out in an alkaline medium produced by a metal hydroxide selected from a group consisting of sodium hydroxide, potassium hydroxide and calcium hydroxide and carried out in conjunction with a phenolic component, in order to form the resole type resin. Particularly, the resol-type phenolic resin is synthesized from empty fruit bunch (EFB) fibers via liquefaction technique in the presence of phenol and sulphuric acid.

In one embodiment of the present invention, the method further includes drying the residue for performing at least one calculation. Particularly, the at least one calculation includes determining percentage of unreacted lignocellulosic biomass in the liquefaction process. Further, the percentage of unreacted empty fruit bunch (EFB) fibers (R) is calculated by using following equation:

%R = (W_r / W_o) x 100 % (1)

where W₀ is the initial oven-dried empty fruit bunch (EFB) fibers (g) and W_r is the oven-dried weight of the solid residue (g) after filtration.

Particularly the lignocellulosic biomass, hardwood feedstocks include Acacia; Afzelia; Synsepalum duloificum; Albizia; Alder (e.g. Alnus glutinosa, Alnus rubra); Applewood; Arbutus; Ash (e.g. F. nigra, F. quadrangulata, F. excelsior, F. pennsylvanica lanceolata, F. latifolia, F. profunda, F. americana); Aspen (e.g. P. grandidentata, P. tremula, P. tremuloides); Australian Red Cedar (Toona ciliata); Ayna (Distemonanthus benthamianus); Balsa (Ochroma pyramidale); Basswood (e.g. T. americana, T. heterophylla); Beech (e.g. F. sylvatica, F. grandifolia); Birch; (e.g. Betula populifolia, B. nigra, B. papyrifera, B. lenta, B. alleghaniensis/B. lutea, B. pendula, B. pubescens); Blackbean; Blackwood; Bocote; Boxelder; Boxwood; Brazilwood; Bubinga; Buckeye (e.g. Aesculus hippocastanum, Aesculus glabra, Aesculus flava/Aesculus octandra); Butternut; Catalpa; Cherry (e.g. Prunus serotina, Prunus pennsylvanica, Prunus avium); Crabwood; Chestnut; Coachwood; Cocobolo; Corkwood; Cottonwood (e.g. Populus balsamifera, Populus deltoides, Populus sargentii, Populus heterophylla); Cucumbertree; Dogwood (e.g. Cornus florida, Cornus nuttallii); Ebony (e.g. Diospyros kurzii, Diospyros melanida, Diospyros crassiflord); Elm (e.g. Ulmus americana, Ulmus procera, Ulmus thomasii, Ulmus rubra, Ulmus glabra); Eucalyptus; Greenheart; Grenadilla; Gum (e.g. Nyssa sylvatica, Eucalyptus globulus, Liquidambar styraciflua, Nyssa aquatica); Hickory (e.g. Carya alba, Carya glabra, Carya ovata, Carya laciniosa); Hornbeam; Hophornbeam; Ipe; Iroko; Ironwood (e.g. Bangkirai, Carpinus caroliniana, Casuarina equisetifolia, Choricbangarpia subargentea, Copaifera spp., Eusideroxylon zwageri, Guajacum officinale, Guajacum sanctum, Hopea odorata, Ipe, Krugiodendron ferreum, Lyonothamnus lyonii (L. floribundus), Mesua ferrea, Olea spp., Olneya tesota, Ostrya virginiana, Parrotia persica, Tabebuia serratifolia); Jacaranda; Jotoba; Lacewood; Laurel; Limba; Lignum vitae; Locust (e.g. Robinia pseudacacia, Gleditsia triacanthos); Mahogany; Maple (e.g. Acer saccharum, Acer nigrum, Acer negundo, Acer rubrum, Acer saccharinum, Acer pseudoplatanus); Meranti; Mpingo; Oak (e.g. Quercus macrocarpa, Quercus alba, Quercus stellata, Quercus bicolor, Quercus virginiana, Quercus michauxii, Quercus prinus, Quercus muhlenbergii, Quercus chrysolepis, Quercus lyrata, Quercus robur, Quercus petraea, Quercus rubra, Quercus velutina, Quercus laurifolia, Quercus falcata, Quercus nigra, Quercus phellos, Quercus texana); Obeche; Okoume; Oregon Myrtle; California Bay Laurel; Pear; Poplar (e.g. P. balsamifera, P. nigra, Hybrid Poplar {Populus x canadensis)); Ramin; Red cedar; Rosewood; Sal; Sandalwood; Sassafras; Satinwood; Silky Oak; Silver Wattle; Snakewood; Sourwood; Spanish cedar; American sycamore; Teak; Walnut (e.g. Juglans nigra, Juglans regia); Willow (e.g. Salix nigra, Salix alba); Yellow poplar (Liriodendron tulipifera); Bamboo; Palmwood; and combinations/ hybrids thereof.

For example, hardwood feedstocks for the present invention may be selected from Acacia, Aspen, Beech, Eucalyptus, Maple, Birch, Gum, Oak, Poplar, and combinations/hybrids thereof. The hardwood feedstocks for the present invention may be selected from Populus spp. (e.g. Populus tremuloides), Eucalyptus spp. (e.g. Eucalyptus globulus), Acacia spp. (e.g. Acacia dealbata), and combinations/hybrids thereof.

Softwood feedstocks include Araucaria (e.g. A. cunninghamii, A. angustifolia, A. araucana); softwood Cedar (e.g. Juniperus virginiana, Thuja plicata. Thuja occidentalis, Chamaecyparis thyoides Callitropsis nootkatensis); Cypress (e.g. Chamaecyparis, Cupressus Taxodium, Cupressus arizonica, Taxodium distichum, Chamaecyparis obtusa, Chamaecyparis lawsoniana, Cupressus semperviren); Rocky Mountain Douglas fir; European Yew; Fir (e.g. Abies balsamea, Abies alba, Abies procera, Abies amabilis); Hemlock (e.g. Tsuga canadensis, Tsuga mertensiana, Tsuga heterophylla); Kauri; Kaya; Larch (e.g. Larix decidua, Larix kaempferi, Larix laricina, Larix occidentalis); Pine (e.g. Pinus nigra, Pinus bandana, Pinus contorta, Pinus radiata, Pinus ponderosa, Pinus resinosa, Pinus sylvestris, Pinus strobus, Pinus monticola, Pinus lambertiana, Pinus taeda, Pinus palustris, Pinus rigida, Pinus echinata); Redwood; Rimu; Spruce (e.g. Picea abies, Picea mariana, Picea rubens, Picea sitchensis, Picea glauca); Sugi; and combinations/hybrids thereof.

For example, softwood feedstocks which may be used herein include cedar; fir; pine; spruce; and combinations/hybrids thereof. The softwood feedstocks for the present invention may be selected from loblolly pine (Pinus taeda), radiata pine, jack pine, spruce (e.g., white, interior, black), Douglas fir, Pinus silvestris, Picea abies, and combinations/hybrids thereof. The softwood feedstocks for the present invention may be selected from pine (e.g. Pinus radiata, Pinus taeda); spruce; and combinations/hybrids thereof. Annual fibre feedstocks include biomass derived from annual plants, plants which complete their growth in one growing season and therefore must be planted yearly. Examples of annual fibres include: kenaf, flax, cereal straw (wheat, barley, oats), sugarcane bagasse, rice straw, corn stover, corn cobs, hemp, fruit pulp, alfalfa grass, esparto grass, switchgrass, palm fibre/residue, miscanthus, giant reed, and combinations/hybrids thereof. Industrial residues like corn cobs, fruit peals, seeds, etc. may also be considered annual fibres since they are commonly derived from annual fibre biomass such as edible crops and fruits. For example, the annual fibre feedstock may be selected from wheat straw, corn stover, corn cobs, sugar cane bagasse, and combinations/hybrids thereof.

Resins prepared using the present method may be used for a variety of purposes including, but not limited to, the preparation of wood products, for example, laminated wood, plywood, particle board, high density particle board, oriented strand board, medium density fibre board, hardboard, or wafer board.

The above description is not intended to limit the claimed invention in any manner, furthermore, the discussed combination of features might not be absolutely necessary for the inventive solution.

The present invention will be further illustrated in the following examples. However it is to be understood that these examples are for illustrative purposes only, and should not be used to limit the scope of the present invention in any manner. EXAMPLES

Materials

EFB fibres and commercial phenolic resin are utilized in the present invention. Industrial grade phenol, analytical grade sulfuric acid (98%), methanol, formaldehyde (37%) and NaOH are used in the present method. All chemicals are used without purification.

Liquefaction Process of the EFB fibers

The empty fruit bunch (EFB) fibers in the first stage are dried in an oven at about 105°C for 24 hours. Then, the process of liquefaction is carried out by varying the weight ratio of phenol to EFB (P/E) (2:1 , 2.5:1 , and 3:1) in the presence of sulfuric acid (3% based on phenol weight) as a catalyst. Particularly, the liquefaction process is carried out at 150°C for 120 min in an oil bath. After that, the liquefied mixture is dissolved with 400 ml methanol to dilute the viscous mixture and then subsequently filtrated with filter paper (Whatman No. 1). Later, the residue is dried in an oven at 105°C for 24 hours to determine the percentage of unreacted EFB fibres in the liquefaction process.

Determination of unliquefied EFB residue

The percentage of unliquefied EFB fibres residue, methanol-insoluble residue (R) is calculated by using following equation:

%R = (Wr / Wo) x 100 % (1 )

where Wo is the initial oven-dried EFB (g) and Wr is the oven-dried weight of the solid residue (g) after filtration of the liquefied mixture.

Resinification Process of the EFB fibers

Resinification was continued by using the liquefied mixture that produced from the previous liquefaction process. During the resinification process, 10g of liquefied EFB (LEFB) mixture is resinified with different molar ratios between formaldehyde and liquefied EFB (L_EFB) mixture, which are 1 .8, 2.0, and 2.2 under alkaline condition. Alkaline condition in the reaction is controlled by two steps addition of NaOH. The first addition of NaOH (0.5 g) is to neutralize the acid catalyst added during the liquefaction process and the second addition of NaOH (4.5g) is to maintain the reaction in alkaline condition. This reaction was carried out for 120 min. The temperature was set at 65°C for the first 60 min and then it was increased to 85°C for another 60 min after the second addition of NaOH solution. After the reaction is completed, liquefied PF resin produced is cooled to room temperature and characterized.

Effect of Phenol to EFB ratio in the liquefaction process

Table 1 below illustrates the effect of phenol/EFB (P/E) ratio on the unreacted EFB fibers produced at a constant reaction temperature of about 150 °C.

Table 1 : Effect of residue (%) at different phenol/EFB ratio

Ratio Phenol/EFB Residue

[wt/wt] [%]

2:1 35.35

2.5:1 19.3

3:1 3.02 Ratio of phenol to lignocellulosic materials influences the residue produced after the liquefaction process. As illustrated in Table 1 the amount of unreacted EFB fibres decreases when the ratio of P/E is increased. The values in Table 1 shows the effect of phenol/EFB (P/E) ratio on the residue produced at a constant reaction temperature 150 ^°C and the amount of catalyst (H2S04) is 3%. The amount of residue is decreased when the ratio of P/E increased. For examples, when the ratio is increased from 2 to 2.5, 16 % reduction on the residue is observed and another 16% reduction as the ratio increase to 3. The amount of residue produced is highest at ratio 2:1 due to insufficient liquefying reagent and the recondensation reaction tends to occur. Particularly, at higher phenol content, greater amount of phenol penetrates into the reaction sites in the EFB and consequently the amount of unreacted EFB fibers are reduced.

Scanning Electron Microscope

FIG.1 illustrates SEM images of the native and liquefied residue for EFB at different ratio of phenol/EFB (P/E), in accordance with an embodiment of the present invention. The surface of the EFB fibers in the SEM image appears rough. Moreover, the silica on the EFB fiber is clearly visible in the image. When EFB fiber undergoes liquefaction at ratio 2:1 , the silica on the surface is slightly removed. Furthermore, as the P/E ratio is increased from 2.5:1 to 3:1 , all the silica visible on the EFB fiber are totally eliminated. Particularly, the elimination of the silica on the surface of the fiber leads to the chemical penetration across the grain of the fiber and hence causes the fiber bundles to start separating into individual fibers.

Characterizations of the PF resin

The physical properties of the produced PF resins from the liquefied EFB are illustrated in Table 2. Table 2: The physical properties of the produced PF resin

PH Solid content (%) Viscosity (cP)

PF 1.8 9.43 49.50 193.3

PF 2.0 9.59 50.28 311.5

PF 2.2 9.75 50.46 441.7

Com. PF 1 1.16 64.37 200.0

As illustrated in table 2 the pH value of the PF resin is lower as compared to the commercial PF resin. This may attribute to the presence of residual H₂S0₄, which is used as a catalyst during the liquefaction process and has reduced the pH of the resinification mixture. The solid content for each PF resin produced is almost similar, but slightly lower than that of the commercial PF resin, which may probably due to the existence of urea in the commercial PF resin. Meanwhile, the viscosity of the liquefied PF resins is higher as compared to the commercial PF resin. The results show that the amount of formaldehyde used in the reaction has influenced the viscosity of liquefied PF resin tremendously. Besides, higher formaldehyde content might result in the increase of viscosity for each resin produced because higher content of formaldehyde tends to speed up the polymerization process.

FTIR Analysis

FIG.3 illustrates a Fourier transform infrared absorption spectrum for commercial phenolic resin and synthesized phenolic resin at different weight ratio of F/LEFB (PF 1.8, PF 2.0 and PF 2.2), in accordance with an embodiment of the present invention. The IR absorbance bands obtained from the liquefied PF resins are identical to the commercial PF resin, as summarized in Table 3 below.

Table 3: Functional groups and observed wave numbers for commercial phenolic resins compared to the synthesized PF

Commercial PF Synthesized PF

Functional Group

[cm^"1] [cm ¹]

3300 3301 OH

Out of phase stretching vibration of -CH₂-

2850 2877

alkane

1620 1626 C = C aromatic ring

1470 1482 Methylene bridges, para-para

1446 1447 Methylene bridges, ortho-ortho

1266

1202 1223 Asymmetric stretch of phenolic C-C-OH

1155 1153 C-0 stretch

1051 1 108 Dimethylene ether C-0 stretch

O-H deformation stretch in hydroxymethyl

1010 1009

groups

964 981 1 ,2,4-trisubstituted benzene ring

882 884 1 ,2,4,6 - tetrasubstituted benzene ring

,2 - disubstituted benzene ring

755

1 ,2,6 - trisubstituted benzene ring The IR band at approximately 1447 cm^"1 is assigned to the methylene bridges in the ortho-ortho position, while the small absorbance band at 1482 cm^"1 is assigned to the methylene bridges in the para-para position. The intensity of these bands increased when the F/L_EFB weight ratio is increased, suggesting the greater cross linking degree at higher formaldehyde concentration. It has been proposed that, there are two types of condensation reactions that occur during resinification, i.e., condensation reaction between hydroxymethyl groups themselves forming dimethylene ether and with the hydrogen in phenol free position to produce methylene bridges. In the present invention, the second reaction become dominant which can be seen in the spectra where the peak for the methylene bridges increased, while no changes occur to the dimethylene ether peak at 1 108 cm^"1 and 1153 cm^"1.

Characterizations

The FTIR spectra are recorded on a Perkin-Elmer FTIR-ATR spectrometer with a resolution of 1 cm^"1. An attenuated total reflection (ATR) is used to determine the functional group of the PF resin produced. Thermogravimetric analysis (TGA) is carried out using Mettler-Toledo (SDTA 851 e) thermal analyzer. Approximately 15 mg of PF resin is placed in a 30 μΙ aluminum crucible and subjected to TGA in a nitrogen atmosphere at a heating rate of 10 °C/min from 25 to 600 °C. DMA measurements are conducted on Perkin-Elmer DMA 8000. Wood name strips with dimensions of 50 mm * 10 mm x 0.7 mm are oven-dried at 105°C for 24 h and stored in a desiccator over blue silica gel to control the relative humidity around 10 - 15 % until used. Samples are prepared immediately before the tests. The amount of resin loaded is approximately 120 - 130 mg for each sample. All scans were tested under dual cantilever mode at various ramp rates from 2 to 5°C/min with fixed frequency and displacement which is 1 Hz and 0.05 mm respectively. The degree of mechanical cure (β) is calculated by using equation (2): where £ is the storage modulus at vitrification.

β^— E _vjt— E min / max~ E _mj_n (2)

Shear Strength

FIG. 2 illustrates a wood-to-wood adhesive bonds specimen dimensions, in accordance with an embodiment of the present invention. Shorea sp. plywood is used as wood testing panel. The sample is cut into strips (90 mm * 25.4 mm χ 2.5 mm), as illustrated in Fig. 2. The symbol "a" denotes cut up but not beyond the adhesive line, symbol "b" denotes width of saw cut, symbol "c" denotes adhesive lines and symbol "^F" denotes force.

The samples are conditioned at 23±1°C for at least seven days before used. After that, the liquefied PF adhesive produced is spread on one side of the sample at amount of 0.035 g/cm² (on solid basis) in an area of 25.4 mm ^χ 90 mm. Then, the adhesives coated veneer sample is overlapped with an uncoated veneer with the length direction parallel to the wood grain. The resulting two layered panel is then clamped with G- clamp for three days and followed by conditioning at temperature of 23±1 °C at a relative humidity of 50 % either for seven days, or until they attain a constant mass, whichever is the longer period. The evaluation of bonding strength is carried out according to Japanese Industrial Standard (JIS K-6852) using a Universal Testing Machine (Testometric M500-50CT) until failure at a force of 9.7 MPa of shear area per minute (approximately 1.3 mm/min crosshead speed).

Thermal analysis

FIG. 4 illustrates Thermogravimetric Analysis (TGA) weight lose curves for the phenolic resin produced at different weight ratio, in accordance with an embodiment of the present invention. Particularly, FIG. 4 curves obtained through the TGA analysis (Thermogravimetric Analysis) of the liquefied PF resins illustrates there are three main thermal decomposition regions. The first decomposition occurred from 80 to 150°C, indicates removal of low molecular weight components, such as water, free phenol, and formaldehyde. The second decomposition is between 150 and 350°C which can be attributed to the release of carbon monoxide, carbon dioxide, and methylene, suggesting the elimination of carbonyl, diphenyl ether and hydroxymethyl groups due to the cleavage of methylene bridge. As the temperature increases, the ratio of the concentration of diphenyl ether link structure of phenol increases. The structure of the diphenyl ether link form an intermediate structure generated for phenolic resins during the process of thermal degradation. The third decomposition from 350 to 600°C is due to thermal pyrolysis of methylene bridges in ortho-ortho and para-para position. After the curing process, phenolic resin structures contain mainly methylene bridged phenolic units. Further, the cross linking networks begin to break with increase in temperature during the heating process.

Dynamic Mechanical Analysis (DMA)

FIG. 5A illustrates a Dynamic Mechanical Analysis (DMA) cure profile of the liquefied PF resin at F/L_EFB weight ratio PF 1.8 at storage modulus development at 2°C/min and FIG. 5B illustrates the DMA cure profile of the liquefied PF resin at F/LEFB weight ratio PF 1.8 at vitrification temperature dependence on ramp rates, in accordance with an embodiment of the present invention. The cure profile illustrates the representative changes for E' and tan 6^" with temperature for wood bonded with PF 1.8 at 2°C/min. The process of heating is started from a room temperature to about 180°C. Subsequently, three phenomenas are observed on the £' curve. The first phenomenon occurs at lower temperature where the £' curve decreases which can be attributed to thermal softening of uncured wood-resin system. During the application of PF resin on the surface of the wood, the water from the resin is absorbed into the wood and causes the adhesive layer becoming semi-solid at low temperatures.

As the temperature increases, the E' curve further decreased to reach £' plateau. At this stage, gelation which the incipient formation of an infinite network of cross linked polymer molecules occurs. A single peak is observed in the tan δ curve, the gelation is defined by the temperature corresponding to the onset of increase in E. After gelation process, the second phenomenon occurs which is the resin curing process where the E' curve increases dramatically and the advent of vitrification peak in the tan δ curve. At this stage, the covalent cross linked network attains the glass state where the glass transition temperature of the polymer reached the oven cure temperature. With increasing temperature, the £' curve increase to the point where E' point reaches a maximum and after that decreased due to thermal softening of cured wood-resin system. The degree of mechanical cure which is obtained by using equation (2), gelation and vitrification temperature for PF resin at different weight ratio of F/L_EFB and different ramp rates are summarized in Table 4 below.

Table 4: Vitrification, gelation and degree of mechanical cure at different ramp rates and different F/LEFB weight ratio

Heating Vitrification Gelation

C vit max f min β at

Sample rates Temperature Temperature

(GPa) (GPa) (GPa) vitrification

(°C) (°C) (°C)

2 1 12 14.69 104 19.44 13.93 0.13

3 120 13.61 107 19.30 12.58 0.15

PF 1 .8

4 124 13.47 1 16 19.54 12.38 0.15

5 128 12.70 1 19 16.49 .92 0.17

PF 2.0 108 13.49 103 18.10 13.15 0.07 3 116 12.25 108 17.19 .57 0.12

4 121 13.24 113 19.44 12.29 0.13

5 125 13.78 117 18.76 12.94 0.14

2 109 21.65 03 31.17 20.76 0.08

3 120 22.74 108 35.10 21.32 0.10

PF 2.2

4 122 21.34 115 33.60 19.78 0.1 1

5 125 13.34 119 19.45 12.56 0.11

It is observed that the vitrification and gelation temperature is decreased as the ramp rates reduced from 5 - 2°C/min. However, the vitrification and gelation temperature occurred earlier and at low temperature as the F/L_EFB weight ratio increased but are not significant from PF 2.0 to PF 2.2. Meanwhile, the degree of mechanical cure found to be decreased for both cases which are different ramp rates and different F/L_EFB weight ratio. Increasing of the F/L_EFB weight ratio influences the degree of cross linking and affects the concentration of methylol groups which mean, the amount of methylene and ether bridges increases in the resin rigid structure. The faster the reaction of liquefied EFB/phenolic monomers with formaldehyde, the higher reactivity of the PF produced, the earlier and at lower temperature the entanglement or cross linking network occurs. Adhesives shear strength test results

FIG. 6 illustrates shear strength of plywood bonded with resol-type adhesive from liquefied EFB at different weight ratio of F/LEFB, in accordance with an embodiment of the present invention. It is observed that the specimens bonded with commercial PF resin provides the highest shear strength value of 2.93 MPa, while the shear strength of the liquefied PF resin is increased from 1 .70 to 2.53 MPa as the weight ratio of F/L_EFB increased from 1 .8 to 2.2. The percentage difference of shear strength between liquefied PF resin and commercial PF resin is about 13.65 %. Nevertheless, the shear strength for all liquefied PF resins surpassed the minimum strength as specified in JIS K-6852 (Standard for the tension shear strength of the resol-type adhesive), 1.18 MPa. There are many factors that influence the shear strength of the adhesive, including the formaldehyde to phenol (F/P) molar ratio and the viscosity of the adhesive. By altering the F/P molar ratio, it affects the cross linking rate or curing reaction. At higher F/P molar ratio, the cross linking rate increase because there are high amounts of phenolic components which having functional groups more than 3. Meanwhile, as for the viscosity, several aspects are affected such as wetting, flow and penetration of the adhesive. With a lower viscosity, the adhesive flow better and wet more surface, but again have a tendency to over-penetrate into the wood specimens. As shown in Table 2 the increase of the F/LEFB weight ratio results in the increase of the adhesive viscosity, and which further increases the shear strength.

Therefore, the present invention provides a method of preparing a resol-type biomass resin adhesive. In the resinification process, the functional group observed in the FTIR spectrum from the phenolic resins prepared is similar as those of commercial one from literature value. The presence of the methylene bridges at the formation of ortho-ortho and para-para links compared to the literature values confirmed the phenolic resin produced is similar to the commercial phenolic resins. From the TGA results, weight lose curve for the resin occurs in three temperature region. In this result, we noticed that the methylene bridges in ortho-ortho position and para-para position decomposed in the third region. These results proved that the phenolic resin structure which is mainly methylene bridged phenolic units is stable against thermal and this phenolic cross linking network can only be break at high temperature. Consequently, thermogravimetric results suggested that both resins EFB based and commercial resins possessed identical thermal properties. Particularly, the IR spectra confirmed that the phenolic structure of the produced PF resin is similar to commercial PF resin. Moreover, the resin adhesive of the present invention can be applied in the manufacture of composite panel products such as particleboard, fibreboard [medium density fibreboard (MDF), high density fibreboard (HDF)], oriented strand board (OSB) and plywood.

While an illustrative embodiment of the present has been shown in the drawings and described in considerable detail, it should be understood that there is no intention to limit the invention to the specific form disclosed. On the contrary the intention is to cover all modifications, alternative constructions, equivalents and uses falling within the spirit and scope of the invention as expressed in the appended claims.

Claims

1. A method of preparing a resol-type biomass resin adhesive comprising:

providing a lignocellulosic biomass;

drying said lignocellulosic biomass to produce a lignocellulosic biomass material; mixing said lignocellulosic biomass material, and a reactive substance in presence of a catalyst to form a viscous liquefaction mixture;

dissolving said liquefaction mixture in a diluting agent to dilute said viscous liquefaction mixture, wherein said diluting agent is an organic solvent;

filtrating said liquefaction mixture to remove non-soluble materials and obtain a residue and a solution containing a soluble part of said liquefaction mixture;

recovering said solution contained in said organic solvent;

dissolving said solution in an alkaline medium;

reacting said solution with a linking molecule at a set temperature ranging from about 65°C to 85°C in said alkaline medium to form a liquefied resole type biomass resin; and

cooling said liquefied resole type resin at room temperature to recover said resol- type biomass resin adhesive.

2. The method as claimed in Claim 1 , wherein said set temperature is about 65°C for about 60 minutes while reacting said solution with said linking molecule and said method further comprises subsequently increasing temperature to about 85°C for about another 60 minutes to form said liquefied resole type biomass resin.

3. The method as claimed in Claim 1 , wherein said method further comprises drying said residue for performing at least one calculation.

4. The method as claimed in Claim 1 , wherein said method further comprises drying said lignocellulosic biomass at about 105°C for about 24 hours.

5. The method as claimed in Claim 1 , wherein said liquefaction process comprises varying a weight ratio of said reactive substance to said lignocellulosic biomass.

6. The method as claimed in Claim 5, wherein said weight ratio of said reactive substance to said lignocellulosic biomass is from about 2:1 to about 3:1.

7. The method as claimed in Claim 5, wherein said liquefaction process is performed at a temperature of about 150°C for about 120 minutes in an oil bath.

8. The method as claimed in Claim 1 , wherein reaction of said solution with said linking molecule is carried out at a plurality of different weight ratios of formaldehyde to liquefied lignocellulosic biomass composition at about pH 9.

9. The method as claimed in Claim 8, wherein said plurality of different weight ratios of formaldehyde to liquefied lignocellulosic biomass in said reaction is selected from a range of about 1.8 to about 2.2.

10. The method as claimed in Claim 3, wherein said at least one calculation comprises determining percentage of unreacted lignocellulosic biomass in said liquefaction process.

11. The method as claimed in Claim , wherein said linking molecule is an aldehyde source and said aldehyde source is selected from a group consisting of formaldehyde, paraformaldehyde, hexamethylenetetramine, acetaldehyde, furfural or a combination thereof.

12. The method as claimed in claim 11 , wherein said reaction of said solution with said formaldehyde in said alkaline medium is carried out in an alkaline medium produced by a metal hydroxide selected from a group consisting of sodium hydroxide, potassium hydroxide and calcium hydroxide and carried out in conjunction with a phenolic component, in order to form a resole type resin.

13. The method as claimed in Claim 1 , wherein said solution is dissolved in said organic solvent in an amount of about 400 ml and said catalyst is sulfuric acid.

14. The method as claimed in Claim 1, wherein said organic solvent is methanol.

15. The method as claimed in Claim 1 , wherein said lignocellulosic biomass is selected from a group comprising an oil type empty fruit bunch (EFB) fiber, kenaf fiber, a hardwood feedstock, a softwood feedstock, and an annual fibre feedstock and said reactive substance is a liquefying reagent and said liquefying reagent is selected from a group consisting of a phenol, phenol derivatives and condensates of phenol.

16. The method as claimed in Claim 13, wherein said sulfuric acid is used in quantity of 3% based on weight of said reactive substance.

17. A resole type biomass resin adhesive composition which comprises a product obtained by drying a lignocellulosic biomass to produce a lignocellulosic biomass material, mixing said lignocellulosic biomass material, and a reactive substance in presence of a catalyst to form a viscous liquefaction mixture, dissolving said liquefaction mixture in a diluting agent to dilute said viscous liquefaction mixture and wherein said diluting agent is an organic solvent, filtrating said liquefaction mixture to remove non- soluble materials and obtain a residue and a solution containing a soluble part of said liquefaction mixture, recovering said solution contained in said organic solvent, dissolving said solution in an alkaline medium, and reacting said solution with a linking molecule at a set temperature ranging from about 65°C to 85°C in said alkaline medium to form a liquefied resole type biomass resin and cooling said liquefied resole type resin at room temperature to recover said resol-type biomass resin adhesive.

18. The biomass resin composition as claimed in Claim 17, wherein said set temperature is about 65°C for about 60 minutes while reacting said solution with said linking molecule and said set temperature is subsequently increased to about 85°C for about another 60 minutes to form said liquefied resole type biomass resin and said reactive substance is at least one compound selected from a group consisting of phenols, and phenol derivatives.

19. The biomass resin composition as claimed in Claim 17, wherein said liquefaction process comprises varying a weight ratio of said reactive substance to said lignocellulosic biomass and said weight ratio of said reactive substance to said lignocellulosic biomass is from about 2:1 to about 3:1.

20. The biomass resin composition as claimed in Claim 17, wherein reaction of said solution with said linking molecule is carried out at a plurality of different weight ratios of formaldehyde to liquefied lignocellulosic biomass composition at about pH 9 and said plurality of different weight ratios of formaldehyde to liquefied lignocellulosic biomass in said reaction is selected from a range of about 1.8 to about 2.2.

21. The biomass resin composition as claimed in Claim 17, wherein said linking molecule is an aldehyde source and said aldehyde source is selected from a group consisting of formaldehyde, paraformaldehyde, hexamethylenetetramine, acetaldehyde, furfural or a combinations thereof and said reaction of said solution with said formaldehyde in said alkaline medium is carried out in an alkaline medium produced by a metal hydroxide selected from a group consisting of sodium hydroxide, potassium hydroxide and calcium hydroxide.

22. The biomass resin composition as claimed in Claim 17, wherein said solution is dissolved in said organic solvent in an amount of about 400 ml and said organic solvent is methanol, and said catalyst is sulfuric acid.

23. The biomass resin composition as claimed in Claim 22, wherein said sulfuric acid is used in quantity of 3% based on weight of said reactive substance.

24. The biomass resin composition as claimed in Claim 17, wherein said lignocellulosic biomass is selected from a group comprising an oil type empty fruit bunch (EFB) fiber, kenaf fiber, a hardwood feedstock, a softwood feedstock, and an annual fibre feedstock and said reactive substance is a liquefying reagent and said liquefying reagent is selected from a group consisting of a phenol, phenol derivatives and condensates of phenol.

25. An industrial product prepared using said biomass resin adhesive composition of claim 17.

26. The product of claim 25, wherein said industrial resin product is selected from the group consisting of laminated wood, plywood, particle board, high density particle board, oriented strand board, medium density fiber board, hardboard or wafer board, mouldings, linings, insulation, foundry resins, asphalt, concrete, brake linings, and grit binder.