AU677651B2

AU677651B2 - Board and manufacture thereof

Info

Publication number: AU677651B2
Application number: AU65145/94A
Authority: AU
Inventors: Lars-Ake Lindstrum; Aron Mikaelsson; Thomas Olofsson; Christer Safstrom
Original assignee: Sunds Defibrator Industries AB
Current assignee: Valmet AB
Priority date: 1993-05-19
Filing date: 1994-03-01
Publication date: 1997-05-01
Anticipated expiration: 2014-03-01
Also published as: FI955571A; KR960701731A; WO1994026487A1; CZ299495A3; FI955571A0; PL174283B1; TW261567B; ZA941236B; JPH08510186A; IL108739A0; NO954661D0; SE502663C2; CN1123533A; NO954661L; SE9301735D0; CA2162396A1; SE9301735L; BR9406538A; HUT78030A; NZ263890A

Description

WO 94/26487 PCT/SE94/00164 Board and manufacture thereof This invention relates to board of lignocellulosecontaining material in the form of particles or fibers such aJ particle board and fiberboard. The invention also relates to a method of manufacturing such board.

Board of this type is manufactured by disintegrating the lignocellulose-containing material to particles or fibers.

This disintegrated material is then dried, glued and formed to a mat. Thereby glueing can be performed prior to or after the drying. The finished board is then produced by final drying of the mat by hot pressing for hardening the glue so that a finished board is formed.

Examples of this type of board are particle board and MDF (Medium Density Fiberboard). Particle board is made of material, which is disintegrated to coarse particles while fiberboard is made of material, which is disintegrated by defibering, i.e. to more or less exposed fibers.

The strength of the board is determined by the binding of the particles or fibers to each other. The strength of dry-formed glued board is determined by the glue addition, in that the hardened glue binds the particles or fibers together.

As binding agent at the manufacture of glued board normally urea-formaldehyde glue is used, which is admixed to the disintegrated material. The amount of glue can be up to 6% or more. The glue is relatively expensive, and, therefore, it is desired to minimize the glue addition. A smaller glue amount, however, deteriorates the strength of the finished board. In view thereof, glue addition has to be optimized.

The present invention renders it possible to improve the strength of the aforesaid types of board. Alternatively, the glue addition can be reduced while maintaining the strength of the board.

According to the invention, the lignin at least in the surface layer of the particles or fibers is modified chemically prior to the final drying, so that an increase in binding reactivity is obtained by introducing hydrophilic groups, and so that the softening temperature of the lignin is lowered. The chemical modification of the lignin can be brought I WO 94/26487 PCTISE94/00164 2 about by chemicals, for example sulphonation or ozone treatment, or in some other way.

The invention is described in greater detail in the following, with reference to some embodiments thereof.

At the manufacture of fiberboard according to the dry method, by starting with raw material of chips, the chips are disintegrated by defibering in a defibering apparatus in one or more steps. After the disintegration, glueing, drying, forming and hot pressing are carried out. Alternatively, drying can take place prior to glueing. At hot pressing, a temperature of 100-115°C is tried to be obtained at the centre of the board for glueing systems based on urea-formaldehyde.

At this method, chemicals reacting with the lignin are added to the material before the hot pressing. The chemical treatment, for example sulphonation, modifies the lignin chemically so that an increased binding reactivity is obtained by the introduction of hydrophilic groups. The softening temperature of the lignin also is lowered at the same time. As examples of such chemicals known per se can be mentioned Na 2

SO

3 and NaHSO 3 The chemicals can be added after the final defibering of the material, during or prior to the defibering.

It can be suitable to add the chemicals in direct connection to the defibering in a disc refiner, for example in the inlet, the centre or further outward to the periphery of the discs. At defibering in two or more steps, the chemicals should be added immediately before or during the second or last defibering step. Other chemical dosing points can be in the blow line after the refiner, in connection with the drying or at the preheating before the defibering.

At the manufacture of particle board, the raw material in the form of chips is disintegrated to particles.

The particles are dried, glued and formed to a web, which is hot pressed to a finished board. As in the case of fiberboard manufacture, hardenable glue based on urea-formaldehyde normally is used. Chemicals reacting with the lignin are added also in this case prior to the hot pressing. The chemical treatment has the same object and can be the same as at the manufacture of fiberboard. The chemicals can be added after the WO 94/26487 PCT/SE9400164 3 final disintegration of the material, during or before the disintegration, preferably immediately before the disintegration, so that the chemical reaction in the lignin takes place during the disintegration and subsequent drying.

As stated above, the chemical treatment, preferably sulphonation, has the object to chemically modify the lignin at least in the surface layer of the particles or fibers, partly by introducing hydrophilic groups so that an increased binding reactivity is obtained in the lignin, and partly by lowering the softening temperature of the lignin. The chemically modified surface layer should have a thickness of about 1pm where the lowering of the softening temperature shall be at least 100C.

At sulphonation, the lignin should be so sulphonated that a sulphur distribution over the entire cross-section of the particles or fibers is obtained, but where the sulphur content is concentrated to a surface layer of the particles or fibers. Thus, the sulphur content in a 2pm thick surface layer should be at least 50% higher than the average sulphur content in the remaining parts of the particles or fibers. Further, the sulphur content in a 1pm thick surface layer should be at least twice as high as the average sulphur content in the remaining parts of the particles or fibers.

At the final pressing of the board the temperature is increased above the hardening temperature of the glue in the entire board in order to ensure throughhardening of the board.

The lowest temperature in the board at hot pressing, thus, must exceed the hardening temperature required.

Therefore, the softening temperature of the lignin in the surface layer of the particles or fibers shall be lowered to a temperature below the lowest temperature in the board at hot pressing. As a result of the lowered softening tempr-.ature, the soft lignin layer in the surface of the particles or fibers is pressed out in the point of contact with adjacent particles or fibers, whereby the size of the contact surfaces increases, the glue is utilized more effectively and improved strength properties are obtained, especially in transverse direction of the board.

WO 94/26487 PCT/SE94/00164 4 The increase in binding reactivity of the lignin by the introduction of hydrophilic groups further implies, that the lignin can form hydrogen bindings more easily. Thereby the binding forces per surface unit increase, and the strength of the board is increased additionally.

Chemical modification of the lignin in the innner portions of the particles or fibers should be avoided in order to maintain their dimensional stability. Low dosing of sulphite, therefore, is of advantage. Low dosing yields substantially sulphonation of the primary wall and secondary wall of the fiber. At higher dosing, the sulphur distribution correlates well with the lignin uistribution in the cell wall.

Against this background, sulphur for the sulphonation shall be added in an amount of at maximum 13 kg sulphur, preferably at maximum 6 kg sulphur, per ton of lignocellulose-containing material.

In order to achieve the desired chemical modification of the lignin in the surface layer of the particles or fibers, the chemicals should be added at or after the disintegration of the material. The dosing of chemicals, the reaction time and temperature conditions must be accurately controlled. By sulphonating the lignin selectively in the surface layer of the particles or fibers, the modification of the lignin is achieved at lower dosings, and large parts of the interior of the particles or fibers will be unaffected by the sulphonation, so that these parts remain stiff and dimensional stable, which is of advantage for the strength of the board. Thereby the lignocellulosic material in the form of particles or fibers is partially sulphonated so that the organically combined sulphur exceeds the native sulphur content of the lignocellulose material but is lower than Preferably the combined sulphur content is 0.04-0.2%. The sulphur is substantially combined with the lignin of the lignocellulose material in the form of sulphonic acid groups.

WO 94/26487 PCT/SE94/00164 EXAMPLE 1 Raw material in the form of chips from European beech was preheated to 175 0 C, and an Na 2

SO

3 solution was added.

Thereafter disintegration of the material was carried out in a defibering apparatus. The charged amount of sulphite (Na 2

SO

3 corresponded to 10 kg/ton chips (2.5 kg sulphur/ton chips). A reference charge without chemical addition was also made.

The softening temperature of the lignin in the reference charge was about 125 0 C, while the lignin softening temperature of the charge treated with chemical was lowered to about 100°C in the surface layer of the fiber material.

In the blow line after the defibering apparatus a urea-formaldehyde glue (UF-glue) was added. The charged amount for material treated with sulphite was corresponded by 8% UFglue, counted on dry fiber material and for the reference material 13% UF-glue, counted on dry fiber material. Thereafter the two material charges were dried to a dry matter content of about 90% and dry-formed to mats. These fiber mats were prepressed with a pressure of 1.5 MPa and hot pressed to board for 6 minutes at 170 0 C. The temperature at the centre of the board at the end of hot pressing was measured to be between 115 and 120°C, i.e. lower than the softening temperature of the lignin in the reference charge but higher than the softening temperature of the lignin in the charge treated with sulphite.

The strength of the board thus manufactured was tested. The results obtained were as follows: Reference Sulphite-treated Property charge charge Bending strength, MPa 39.5 39.0 Internal bond strength MPa 1.8 1.9 UF-glue content, 13.0 The result shows that equivalent strengths for the board was obtained although the glue content in the board .ith lowered lignin softening temperature was considerably lower.

This confirms the technical effect referred to above.

I,

WO 94/26487 PCT/SE94/00164 6 EXAMPLE 2 Raw material in the form of chips from spruce was preheated to 1700C, and an Na 2

SO

3 solution was added. The material was thereafter defibered in a defibering apparatus.

The charged amount of sulphite corresponded to 15 and, respectively, 22 kg/ton chips (3.8 and, respectively 5.6 sulphur/ton chips).

A reference charge without chemical addition was also made. No glue addition was made at this test.

The softening temperature of the lignin in the reference charge was about 1250C, while the lignin softening temperature of the charge treated with chemical was lowered to below 100°C in the surface layer of the fiber material.

After defibering the fiber material was dried to a dry matter content of about 90% and dryformed to mats. These mats were pre-pressed with a pressure of 1.5 MPa and hot pressed to board for 6 minutes at 1700C. The temperature at the centre of the board at the end of hot pressing was measured to be between 115 and 120 0 C, i.e. lower than the softening temperature of the lignin in the reference charge but higher than the softening temperature of the lignin in the charge treated with sulphite.

The strength of the board thus manufactured was tested. The re-ults obtained were as follows: Property Reference Sulphite 15 kqlton Sulphite 22 kq/ton Bending strength MPa 5.8 9.0 12.6 Modulus of elasticity MPa 785 1599 1796 The result shows a substantial difference between the properties of the board treated with chemical and of the reference board. The strengths show the effect of increased binding reactivity and increased binding area, which verifies the technical effect of the invention.

The tion, of course, is not restricted to the embodiments described, but can be varied within the scope of the invention idea.

i w

Claims

1. Dry-formed and hot pressed board of lignocellulose- containing material in the form of particles or fibers, c h ar a c t e r i z e d i n t ha t the lignocellulose material is partially sulphonated so that the organically combined sulphur exceeds the native sulphur content of the lignocellulose material but is lower than 0.4%.

2. Board as defined in aim 1, c h ar a c t e r i z e d i n that the organically combined sulphur content is 0.04-0.2%.

3. Board as defined in claim 1-2, c h ar a c t e r i z e d i n that the sulphur is substantially combined with the lignin of the lignocellulose material in the form of sulphonic acid groups.

4. Board as defined in any one of claims 1-3, c h a r a c t e r i z e d i n that the combined sulphur is concentrated to a surface layer of the particles or fibers so that the sulphur content in a 2pm thick surface layer is considerably higher, preferably at least 50% higher, than the average sulphur content in the remaining part of the particles or fibers.

5. Board as defined in claim 4, c h a r a c t e r i z e d i n that the sulphur content in a 1pm thick surface layer is at least twice as high as the average sulphur content in the remaining part of the particles or fibers.

6. A method of manufacturing board of lignocellulose- containing material, where the material is disintegrated to particles or fibers, dried, glued prior to or after the drying, formed to a mat and finally dried by hot pressing to a finished board, ch a r a c t e r i z e d in that prior to the final drying the lignin at least in the surface layer of the particles or fibers is modified chemically, so that an increased binding reactivity is obtained by introducing hydrophilic groups and so that the softening temperature of the lignin is lowered to a temperature below the lowest temperature required in the board for hardening the glue at the hot pressing. I-

7. A method as defined in claim 6, c h a r a c t e r i z e d i n that the lignin is modified chemically by the addition of chemicals reacting with the lignin.

8. A method as defined in claim 7, c h a r a c t e r i z e d i n that the lignin is modified chemically by sulphonation.

9. A method as defined in any one of claims 6-8, c h a r a c t e r i z e d i n that the softening temperature of the lignin is lowered by at least 10°C in a surface layer of about 1pm thickness on the particles or fibers. A method as defined in claim 8, c h a r a c t e r i z e d i n that the lignin is sulphonated so that a sulphur distribution across the entire cross-section of the particles or fibers is obtained.

11. A method as defined in claim c h a r a c t e r i z e d i n that the lignin is sulphonated so that the sulphur content in a 2pm thick surface 0:00.0 layer is at least 50% higher than the average sulphur content in the remaining part of the particles or fibers.

12. A method as defined in any one of claims 8-11, c h a r a c t e r i z e d i n that sulphonation of the lignin is made by addition of chemicals containing sulphur in an amount of at maximum 13 kg, preferably at maximum 6 kg sulphur per ton of lignocellulose-containing material. S13. A method as defined in claim 7, c h a r a c t e r i z e d i n that the lignin is modified chemically by ozone treatment.

14. A method as defined in claim 7, c h a r a c t e r i z e d i n that the chemicals are added after the final disintegration of the material. A method as defined in claim 7, c h a r a c t e ri z e d i n that the chemicals are added prior to or during the disintegration.

16. A method as defined in any one of claims 6-15, ch a r a c t e r i z e d i n that the disintegration comprises defibering of the material in one or several steps. I- INTERNATIONAL SEARCH REPORT International application No. PCT/SE 94/00164 A. CLASSIFICATION OF SUBJECT MATTER IPC5: B27N 1/00 According to International Patent Classification (IPC) or to both national classification and IPC B. FIELDS SEARCHED Minimum documentation searched (classification system followed by classification symbols) B27N Documentation searched other than minimum documentation to the extent that such documents are included in the fields searched SE,DK,FI,NO classes as above Electronic data base consulted during the international search (name of data base and, where practicable, search terms used) DIALOG: ALLSCIENCE C. DOCUMENTS CONSIDERED TO BE RELEVANT Category* Citation of document, with indication, where appropriate, of the relevant passages Relevant to claim No. X DD, A, 205382 (PECINA, HEINZ ET AL), 6,8,9,15,16 28 December 1983 (28.12.83), page 4, claims 1,2 A 1,7,10-13,17 X DD, Al, 242193 (TECHNISCHE UNIVERSITAT DRESDEN), 6,8,9,16 21 January 1987 (21.01.87) A 1,7,10-13, 15,17 Further documents are listed in the continuation of Box C. E See patent family annex. Special categories of cited documents later document published after the international filing date or priority date and not in conflict with the application but cited to understand document defining the general state of the art which is not considered the principle or theory underlying the invention to be of particular relevance erier document but published on or after the international filing date document of particular relevance: the claimed invention cantt be considered novel or cannot be considered to involve an inventive document which may throw doubts on priority claim(s) or which is step when the document is taken alone cited to establish the publication date of another citation or other special reason (as specified) document of particular relevance: the claimed invention cannot be document referring to an oral disclosure, use, exhibition or other considered to involve an inventive step when the document is means combined with one or more other such documents, such combination IP" document published prior to the international filing date but later than being obvious to a person skilled in the art the priority date claimed document member of the same patent family Date of the actual completion of the international search Date of mailing of the international search report 26 -08- 1994 19 August 1994 Name and mailing address of the ISA/ Authorized officer Swedish Patent Office Box 5055, S-102 42 STOCKHOLM Olov Jensdn Facsimile No. +46 8 666 02 86 Telephone No. +46 8 782 25 00 Form PCT/ISA/210 (second sheet) (July 1992) I 1 a INTERNATIONAL SEARCH REPORT International application No. PCT/SE 94/00164 C (Continuation). DOCUMENTS CONSIDERED TO BE RELEVANT Category* Citation of document, with indication, where appropriate, of the relevant passages Re'evant to claim No. A Dialog Information Services, File 240, 280525, 6,8,14 Paperchem no. 51-00525, Kibblewhite, R.P. et al: "Effects of ozone on the fiber characteristics of high-temperature thermomechanical pulp" TAPPI/CPPA Intern. Mech. Pulping Conf. (Toronto):

293-301 (June 11-14, 1979) I Form PCT/ISA/21C) (continuation of second sheet) (July 1992) INTERNATIONAL SEARCH RL±PORT Internatonal application No. Information on patent family members 0/79 C/E9/06 Patent document Publication Patent family Publication cited in search report Id ate Imember(s) date DO-A- 205382 28/12/83 NONE D0-Al- 242193 21/01/87 N4ONE Form PCr/ISA/210 (patent family annex) (July 1992)