Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1998-10-13
2002-02-12
Yao, Sam Chuan (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C264S109000, C162S023000, C162S026000, C162S097000, C162S099000, C162S225000
Reexamination Certificate
active
06346165
ABSTRACT:
FIELD OF INVENTION
This invention relates to the production of lignocellulosic fibres and formation of composite materials therefrom. It particularly relates to the production of such fibres and bonding with synthetic binders into composite materials.
BACKGROUND OF THE INVENTION
There is considerable pressure on the world's fibre resource. World-wide economic growth and development have created needs for converted forest products. While global fibre production systems are capable of meeting these overall demands there are some serious local and regional fibre shortages and resource management conflicts.
Many developing countries do not possess adequate forest reserves to cover their needs for fuelwood, industrial wood, sawn wood, and wood-based composition panels. However, many of these countries do have relatively large quantities of lignocellulosic materials available in the form of agricultural residues from annual crops. Annual plant fibres like cereal straw and the like are difficult to bond using conventional adhesives such as UF resins, PF-resins and PMDI binders.
The present invention is related, therefore, to a method of improving the bondability of lignocellulosic materials from annual plant fibres such as cereal straw by synthetic binders.
Composite materials such as particleboards, medium and high density fibreboards are mainly made from wood using binders such as acid curing amino-formaldehyde resins, alkaline curing phenol-formaldehyde resins, as well as polyisocyanate adhesives. Medium density fibreboards are fibreboards prepared using a dry technique as follows: Wood is subjected to thermomechanical pulping at a temperature of about 160 to 180° C., then mixed with the resin and dried. Thereafter mats are formed from the fibres and pressed to form fibreboards. Particleboards, on the other hand, can be prepared from chips which are mixed with resins and the glued particles are spread to mats and pressed at high temperature to particleboards.
Recently, interest has been developed on using agricultural residues like wheat and rice straw and sunflower as a starting material for particleboards and medium density fibreboards. The main difficulty in using annual plant residues such as straw as a raw material for composites, is their poor bondability particularly using urea-formaldehyde resins. The reason for this is probably the specific morphological structure of the straw, where the waxy and silica layer encirculating the straw stem inhibit sufficient direct contact between the binder and the straw fibres. Other types of adhesives for example polymeric isocyanates have been tried. However, the mechanical strength as well as the water resistance of the boards made from straw and isocyanates are much lower than those made from wood using the same bonding conditions.
Therefore, it was the main aim of the invention to find a practical method to improve the bondability of annual plant residues towards bonding agents in general and particularly towards acid curing aminoplastic resins and also polyisocyanate binders.
While fibrous/particulate ligno/cellulosic materials have been treated by water/steam treatments with simultaneous or subsequent high shear treatment, use of lower temperatures has only been in the context of treatments for the manufacture of paper or similar materials and there has been no suggestion that this treatment when applied to lignocellulosic materials in the context of producing composites would enhance the fibrous or particulate material for forming into composite material. The process of the invention is also to be distinguished from producing composite materials from lignocellulosic materials in which there is an initial treatment at high temperature of at least 150° C., usually 150° C. to 170° C. followed by defibration.
Thus many treatments have been described in the literature to improve the bondability of lignocellulosic materials in both particle and fibre form with synthetic resins. D. H. GARDNER and T. J. ELDER: (Bonding surface activated hardwood flakeboard with phenol-formaldehyde resin —Holzforschung 44(3): 201-206, 1990) added hydrogen peroxide, nitric acid or sodium hydroxide to enhance bonding characteristics of flakes using phenol-formaldehyde resins as a binder. Dimensional stability and internal bond strength were significantly reduced and it was shown that the chemicals did not change the wood surface, but rather they reacted with the resin.
J. McLAUGHLAN and C. R. ANDERSEN: (In-Line fibre pretreatments for dry process medium density fibreboard: Initial Investigations—Paper presented at the Symposium Pacific Rim Bio-Based Composites, Rotorua, New Zealand 9-13 Nov. 1992, Symposium Proceedings, page 91-99, 1992) tried many treatments to enhance the bondability of fibres towards bonding with urea-formaldehyde resins for the production of medium density fibreboards. The treatments include exposure to wet and dry heat, compression with heat and heat in combination with chemicals. The chemicals include 1% and 10% addition of aluminum sulphate, which is used in the hard board manufacture to control the pH value of the stock and 1% and 10% chromium trioxide. Almost all the treatments resulted in boards with reduced properties compared to the control.
SIMON AND L. PAZNER): (Activated self-bonding of wood and agricultural residues—Holzforschung 48: 82-90, 1994) investigated the influence of the hemicellulose content of the self-bonding behaviour of different raw materials including annual plants and concluded that there is a straightforward relation between the hemicellulose content in the raw materials and the bonding strength of composites prepared therefrom. According to this work hemicelluloses do have adhesive properties, however, bonds created using hemicellulose adhesives have almost no wet strength.
In a recent publication LIAN ZHENGTIAN and HAO BINGYE: (Technology of rice-straw particleboards bonded by Urea-formaldehyde resin modified by isocyanate—Paper presented at the Symposium Pacific Rim Bio-Based Composites, Rotorua, New Zealand 9-13 Nov. 1992 Symposium Proceedings, page 295-301, 1992) mentioned that slight improvement of bondability of straw can be achieved by destroying the waxy layers encircling the stem of straw, however, the bondability was still very poor and the boards made still could not meet the requirements of common standards.
In DE-A-36 09 506 is described a modified standard dry process for the production of MDF in which UF resin is injected after treatment of wood particles with overheated steam and separation of steam from the treated fibres. The treatment of the fibres is by a conventional disc refiner.
In US-A-3 843 431 composite panels are produced from fibres prepared using as starting material scraps, shavings, sawdust. The raw material is blended with water and ground with the use of a double-disc attrition mill.
In WO-A-93 25358 MDF is produced according to the standard dry process involving wood chips pre-treated prior to defibration. The pre-treatment procedure involves the impregnation of raw material with Na
2
SO
3
/NaHSO
3
, and heating at a temperature between 150-200° C.
The aim of the present invention to develop a method for the treatment of annual plant fibres, so that their bondability to synthetic resins is significantly improved and the production of composite panels with properties that meet the requirements of common standards is effected.
SUMMARY OF THE INVENTION
It has been discovered that thermal treatment of straw or other annual plant fibres with water or steam at temperatures between 40-120° C., and preferably between 60 -100° C. accompanied by or followed by defibration of the fibres using high shear forces destroys the morphological structure of the straw and increases tremendously its affinity towards bonding.
According to the invention, therefore, there is provided a method for producing composite materials wherein a lignocellulosic material which is an annual plant fibre residue is subjected to treatment with water or steam at 40° to 120° C. and simultaneously or subseque
Markessini Efthalia Vergopoulou
Mouratidis Pavlos
Rigal Luc
Roffael Edmone
Ladas & Parry
Marlit Ltd.
Yao Sam Chuan
LandOfFree
Method for production of lignocellulosic composite materials does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for production of lignocellulosic composite materials, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for production of lignocellulosic composite materials will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2982984