CA1115908A

CA1115908A - Process for manufacture of thermoformable panels

Info

Publication number: CA1115908A
Application number: CA290,625A
Authority: CA
Inventors: Georges J. Cloetens; Leonard F. Divens
Original assignee: P R B SA
Current assignee: P R B SA
Priority date: 1976-11-11
Filing date: 1977-11-10
Publication date: 1982-01-12
Also published as: EG12869A; AT364863B; FI64174C; CH624971A5; BE860113A; JPS5360958A; FI64174B; ZA776333B; NO773823L; DE2749499A1; SE7712711L; FR2370576A1; FI773251A; IT1087438B; FR2370576B1; LU76172A1; GB1592805A; BR7707572A; NL7712468A; ATA795677A

Abstract

ABSTRACT
Process for the manufacture of thermoformable panels or boards from ligno-cellulose fibres emanating e.g. to the extent of 20 - 100% from recycled paper wherein in order to improve filterability, avoid pollution problems and ensure a product of high quality, at least one fraction of fibres is grafted, with an olefinic monomer in the presence of a redox catalytic system at a pH value of below 4, this operation being carried out in a suspension of fibres in water.
This process is used i.e. for the production of moulded articles such as car door liners.

Description

7~e~ o~
PROCESS FOR MANUFACTURE OF.~ P~NELS
~he present invention relates to a process enabling thermoformable panels also called boards to be manufactured from a raw material consisting of modified ligno-cellulose fibres.
It also extends to panels which can be produced in this manner and to thermo-moulded products which can be made from the said panels.
The principle of manufacturing panels from a ligno-cellulose fibre base by the wet, semi-wet or dry method is well known. The addition of plastic materials, particularly resins of the phenolic type, to the pulp used for manufacturing the panel is likewise already known.
The nature of the raw materials i.e. the chemical compo-sition and the dimension of -the fibres may involve production difficulties when preparing panels thereof. The separation of lS the water from the pulp, an operation which is preferably per-formed by filtration and which is necessary for the manufacture of the panel and which should be completed in a fairly short space of time, is one of the essential factors in the economy of the process. The filterability, which can be expressed as the speed at which the water is eliminated from a mass of pulp by filtering in the panel manufacturing plant, may be modified by the various additives provided in the course of the prepara-ticn of the pulp, and usually most of the additives do not modify the filterability in a favourable direction.
In one particular sector inadequate filterability charac-teristics manifest themselves to a particularly marked degree.
It has been found that the Eilterability becomes worse with an increasing content of lingo-cellulose base fibres made of non-refined material, such fibres consisting mainly of recuperation 3~ fibres, such as ol~ paper or raw vegetal fibres.

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A further drawback caused by the addition of additi~es and particularly of phenolic resins to the pulp is the resulting serious pollution oE the water, mainly from the phenolic compounds and salts.

In the Swiss Patent 378,665 it is said i.e. that the pulp produced from a stock containin~ 20% of old paper results n such poor filterability characteristics that productivity is considerably reduced. Said patent proposes a mechanical treat-ment which is however limited to old paper ~reated by a dry method and which does not reduce the pollution of water due to the presence of the conventional additives.

The object of the invention is thus to provide a process for manufacturing thermoformable panels from a ligno-cellulose base made of non-refined material by a semi-wet method permitting to avoid the above mentioned drawbacks.
The invention provides a process for treating an aqueous suspension of ligno-cellulose fibres with an olefinic monomer from the group consisting of styrene, methyl methacrylate, and methyl acrylate for use in the manufacture of thermoformable panels said process comprising the steps of partially grafting said monomer onto at least a fraction of the fibres and partially homopalymerizing said monomer in the presence of a catalytic redox Fe/H2O2 system at a p~l of below 4 said fibres having a Canadian ~reeness value deter-mined by the Scandinavian Standard Method SC~N 21:65 lower than 500 prior to said grafting and homopolymerizing steps.
The invention also provides in a process for the manuEacture oE thermoformable panels from ligno-cellulose fibres including the steps of treating an aqueous suspension oE said fibres within an olefinic monomer from the group consisting of styrene, methyl methacrylate and methyl acrylate, filtering the treated fibres, drying the filtered fibres down to an average pressure of about 3~

10 to 100 bars and a-t a temperatuxe of between 160 degrees and 220 degrees C. to form a panel, the improvement in said treating step comprising partially grafting said monomer onto at least a fraction of said fibres and partially homopolymeriziny said monomer, in the presence of a catalytic redox Fe/H2O2 system at a pH below 4, said fibres having a Canadian Freeness value determined by the Scandinavian Standard Method SCAN 21:65 lower than 500, prior to said grafting and homopolymerizing steps.
The operation of filtering, drying and forming the panels is carried out in the conventional manner for the production of thermoformable panels. It is found that the mass of fibres is remarkably easy to filter after the grafting treatment accordiny to the invention.
During the grafting, a fraction of the monomer undergoes homopolymerization. This homopolymeric fraction does not deter-iorate the quality of the product and is maintained in the mass ,~1 from which the water i5 separated by filtra-tion.
The water separated by filtration is l~rgely free of pollution and can be recycled direct a number of times without the need for any treatment.
The process is suitable for all types of ligno-cellulose fibre but is particularly advantageous when applied to raw mater-ials consisting of recuperated fibres, especially recycled paper, such as old newspapers and raw vegetal fibres such as bamboo, bagasse, cane-trash etc.
Under the specified grafting conditions i.e. a-t a pH
of below 4 and in the presence of a redox catalytic system, a relatively great part of the monomers will undergo a homopolym-erization but also a gxafting which takes place partially on the cellulose (polysaccharide) and on the lignin will occur. The choice of the pH and of the catalytic system which is used will allow an optimal distribution of the polymer which is fixed on the fibers i.e. which is gra~ted on the cellulose and the lignin and of the polymer which is only deposited on the fibres as a homopolymer in order to achieve a good cohesion of the fibres with each other. It seems that the grafted polymer ensures a good adhesion of said homopolymer on the fibres while the presence of the homopolymer on the fibres results in a good bondiny of the fibre.s with each other when the product undergoes thermoforming.
Furthermore, as it is well known in the chemistry of polymers, the mean molecular weight oE the polymer is of ~reat importance for the mechanical properties oE the product. The above operative conditions are critical for achieving satis-factory properties of the product to be thermoformed~
The polymerization conditions have thus to be strictly ~.

followed. It has been observed that when the pH is higher than 4, only the use of specially treated or refined fibres will allow satisfactory qualities.
Under the above conditions the resulting product com-prises 0,5-20% of graft polymers i~e. 0-10% graft cellulose and 0-10~ graft lignin as well as 10-30% homopolymer~ The products are not sticking.
The most interesting monomers, in view of the necessity of using inexpensive reagents, are styrene, methyl methacrylate and methyl acrylate. Other monomers, such as acrylonitrile and ethyl acrylate, many nevertheless prove equally suitable~
When operating under pressure vinylic monomers such as vinyl chloride or vinylidene chloride may also be used. These reagents are interesting for the flame-retardant characteristics of the products thus formed.
The other chemical and physical conditions for perfor-ming the grafting depending upon the nature of the selected monomer are conventional and are described in French patent

2,276,423, British patent 1,011,431, U.S. Patents 3,330,686 and

3,533,725 and German published application DT OS 1,546!468.
The catalytic system to which preference is given, both by reason of its efficacity and owing to its low cost, is the redox Fe/H2O2 system.
When using recycled paper as the cellulose base under-going grafting, the pulp will always contain a sufficient amount of iron.
Usually when using the redox system Fe/F~2O2 the iron content to the total weight of suspension and the liquid should be at least 0.0001 - 0.01%. The H2O2 content should be 0.0001 The total amount of fibers to the total weight of sus-pension and liquid should be 0.5-8%.
The ratio between the monomers and the ligno-cellulose base should preferably be 5-40%, especially 9~30%. The upper limit stipulated is mainly due to economic considerations and to the desirability of preserving the fibrous character of the product, and also, of course, to the ractivit~ of the monomer, which influences the quantity of monomer grafted or homopoly-merized.
The best results are obtained from styrene, with values of 15-20%, and for methyl methacrylate, with values of 25-30~.
The grafting is usually performed at a temperature of the order of 10-100C, preferably 30-70C, and particularly 50-60C.
After filtration, the dried mass having a wet content which is preferably lower than 1% is pressed for a short time (0.5 - 2 minutes) at a mean pressure of about 10-100 bars, pre-ferably 30-80 bars and a temperature of 160-220C.
It is also possible to use a mixture of fibres treated in accordance with the invention with conventional fibres i.e.
refined and/or non-refined fibres which have not been grafted, the presence of the graft i.bres of the invention improving greatly the filerability characteristics of the final product.
By the process of the invention it is possible to achieve "Canadian Freeness" values according to the Scandinavian Standard Method SC~N-C19:65 (correspnding to the Canadian Standard Method CPPA C 1:62) highex than 500, starting from a CF value lower than 500~
The process to which the invention relates provides thermo-formable panels to be produced from raw materials having CE values lower than 500 emanating to the extent of 20-100~ from non "~ , ~s~

refined fibres e.g. from recycled paper, in an economical manner and with a quality comparable to that of panels obtained from refined materials. They can be used for the production of moulded articles such as inner liners of car doors.
The invention will be described ln greater detail by means of the following examples 7 given solely by way` of illu-stration and without any intention of limiting the invention thereto. The percentages in these examples, unless stated to the contrary, are percentages by weightO
Example 1 The purpose of this example is to enable a comparison to be made between the pulps obtained in the conventional manner and those to which the invention relates.
A suspension with ~% of fibrous substances of varying origin in water was prepared and then heated to 50-60C. Re-agents consisting of 0.1% FeSO4 and 1% H2O2 at 100% were added to the pulp and the monomer was then introduced. The reaction was completed after one hour, the results being given in attached Table I.
Example 2 The proportion of grafted polymer in accordance with different parameters was studied on the laboratory scale.
10 g of cellulose (whitened kraft paper or newspaper) was introdttced into an Erlemeyer flask of 500 ml with 250 ml oE
water. This was then given an addition of 5 ml FeC13, 0.1 M
and 5 ml of H2O~ at 3%.
It was found that even in the presence of lignin, graft-ing is obtained, although in this case a considerable proportion of homopolymer may form.
The yield of the monomer was in each case close to 100%.

.

The results of the test are given in attached Table II. The percentage of homopolymer is determined by extraction with dichloro-ethane or benzene.
Example 3 Various further operative factors were studied.
In a 2-litre reactor, fitted with a cover and an agita tor, 1.5 litres of water and 30 g of cellulose to be grafted were introduced, this latter having been crushed beforehand.
The required quantity of FeIII was then added in the form of a solution of 0.1 M FeCl3 and H2O2 at 3% (10% by volume).
On the completion of the reaction the filtering and dry-ing is effected.
The percentage of homoplymer is determined by extraction by means of dichloro ethane or benzene.
The accompanying Table III provides the result obtained in grafting methyl methacrylate onto newpaper.
Example 4 The influence of the process on different raw materials during grafting with methyl methacrylate was studied by treating 60 g oE product in a 2-litre reactor. The initiator used was the FeSO4/H2O2 system, the pH value being adjusted with H2SO4 and the temperature being 60, the reaction taking 60 minutes.
The results appear in the attached Table IV.
Example 5 A comparati~e test similar to the above was performed, this time with styrene. The results are given in attached Table V.
Example 6 The effect of mixtures of monomers was likewise studied, by grafting them onto 60 g of newspaper in a 2-litre reactor.

The results are shown in attached table VI.
Example 7 Compositions containing the graft polymer prepared by using styrene as monomer under the reaction condition stated 5 for example 1 and containing 8% of graft styrene and 16% of styrene homopolymer together with non grafted fibres have been prepared.
Their properties compared to those of a 100% non grafted fiber preparation are shown in Table VII.

. . _ .
Table I
. . . -- . _ . _ _ _ ConventionalStyreneNoM~A~

Rraft 50 Wood fibres 20 Newspaper 15 80 70 Phenolia resins 15 Polystyrene 20 Polymethyl methacrylate 30 Tensile strength: N/mm40 39 40 : Absorption of moisture 20after 24 hrs. 27 20 30 Bending modulus: N/mm4500 6500 7000 Ultimate bending2 s-trength: N/mm 70 80 86 Compressive stren~th:
N/mm 45 50 55 .:

Table II

Cellulose Kraft Newspaper ___ . _ _ .
g~ cellulose 10 1010 10 10 10 Monomer MMA MA MM~ + MA
g. monomer 20 10 10 10 8 6 Temperature 50 20 50 20 50 20 Time 60' 60'60'60' 60' 60 % homopolymer 14 22 41 39 20 25 % polymer graf-ted 48 22 3 5 20 12 MMA = methyl methacrylate MA = methyl acrylate ., Table III
. _ _ _ _ _ _ _ Ml Fe 46 8 12 16 3216 16 I6 Ml H2O2 1616 16 16 16 164 8 12 Temperature 30 a-t beyinning. 60 at end.
Time 60l homopolymer 2 9 13 23 26 31 32 27 31 pol~mer grafted 0 32 3, 21 19 13 14 18 14 f~ L5i~
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Table V (styrene) . __ CelluloseRaw kraft Mechanical Newspapers Eucalyptus pulp .

mg Fe 8 28 56 28 28 168 ml H22 3% 15 15 15 30 30 30 pH 3 3 3 3,2 3,2 3,1 Tensile strength2 N/mm 14 16 19 21 21 Bending modulus 2 N/mm 4200 Ultimate bendin~
strength N/mm 45 Moisture 2 hrs ~ 41 32 11 9 9 24 hrs * 97 86 25 19 19 % resin 0 9 10,5 25 30 30 % homopolymer 10,5 6,7 10,514,8 % cellulose grafted _ 1,7 1,3 1,9 % lignin grafted - 16,618,2 13,3 ._ _ Table VI (mixture of monomers) ml styrene 20 20 15 15 15 ml MMA - - 5 5 5 ml Fe 0.1 M 10 5 0 1 2,5 ml H22 3% 30 30 30 30 30 pH 3 3,2 3,1 3,3 3,2 Tensile streng~h N/mm 38 30 12 23 Moisture 24 hrs * 22 25 28 23 % resin 22 18,4 3 21 22,3 % homopolymer16,2 11 6,6 10 % polymer grafted 5,8 7,4 14,4 12,3 Table VII (mixture of fibres) Graft polymer 25 75 25 75 Shredded wood 100 75 25 Kraft 75 ~5 Tensile strength 16 14,8 34 12 28 Moisture 2 hrs* 20 10 7 21 13 24 hrs* 50 30 16 71 25

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for treating an aqueous suspension of ligno-celluose fibres with an olefinic monomer from the group consisting of styrene, methyl methacrylate, and methyl acrylate for use in the manufacture of thermoformable panels said process comprising the steps of partially grafting said monomer onto at least a fraction of the fibres and partially homopolymerizing said monomer in the presence of a catalytic redox Fe/H2O2 system at a pH of below 4 said fibres having a Canadian Freeness value determined by the Scandinavian Standard Method SCAN 21:65 lower than 500 prior to said grafting and homopolymerizing steps.

2. Process in accordance with Claim 1, wherein 0.00001 to 0.01% of Fe and 0.00001 to 0.1% of H2O2 by weight in relation to the total weight of the suspension and of the liquid are used for grafting

3. Process in accordance with Claim 1, characterized by the fact that the monomers are used in a proportion of 5-40% in relation to the ligno-cellulose base.

4. Process in accordance with Claim 1, characterized by the fact that the monomers are used in a proportion of 9-30% in relation to the ligno-cellulose base.

5. Process in accordance with Claim 1, characterized by the fact that the grafting is effected at a temperature of the order of 10-l00°C.

6. Process in accordance with Claim 1, characterized by the fact that the grafting is effected at a temperature of the order of 30-70°C.

7. Process in accordance with Claim 1, characterized by the fact that the grafting is effected at a temperature of the order of 50-60°.

8. Process in accordance with Claim 1, characterized by the production, in relation to the ligno-cellulose mass, of 0.5 to 20%
by weight of grafted products, at the rate of 0 to 10% of grafted cellulose and 0 to 10% of grafted lignin and 10 to 30% of homopolymer.

9. process in accordance with Claim 1, wherein fibres which did not undergo a grafting operation are mixed with fibres which have been treated by the grafting process.

10. In a process for the manufacture of thermoformable panels from ligno-cellulose fibres including the steps of treating an aqueous suspension of said fibres within an olefinic monomer from the group consisting of styrene, methyl methacrylate and methyl acrylate, filtering the treated fibres, drying the filtered fibres down to an average pressure of about 10 to 100 bars and at a temperature of between 160 degrees and 220 degrees C. to form a panel, the improvement in said treating step comprising partially grafting said monomer onto at least a fraction of said fibres and partially homopolymerizing said monomer, in the presence of a catalytic redox Fe/H2O2 system at a pH below 4, said fibres having a Canadian Freeness value determined by the Scandinavian Standard Method SCAN 21:65 lower than 500, prior to said grafting and homopolymeriz-ing steps.