A PROCESS FOR DE-INKING PAPER PULP

Abstract: The de-inking of paper pulp is rendered more efficient and capable of producing a high quality recycled paper for printing purposes by the addition of surfactants having a chemical character similar to surfactants naturally present in the pulp. The surfactants may be in the form of hemicellulose which include polysaccharides and a small proportion of side-chain carboxyl groups. Methods for the manufacture of artificial surfactants similar to the surfactants present in the pulp are described, such as surfactants being copolymers made for example from vinyl acetate and acrylic or maleic acid, the conversion being completed by transesterification with methanol in the presence of sodium methoxide.

Description: A PROCESS FOR DE-INKING PAPER PULP. This invention relates to ■ a process for de-inking paper pulp and to materials used in the process. With the continued depletion of world supplies of raw materials and consequent increased costs, general interest in recycling paper has increased substantially of recent years. While the problem of de-inking the pulp is not particularly acute where the recycled product is to be used for packaging and other non-print applications, where the recycled product involves subsequent printing, efficient de-inking becomes essential. Two de-inking processes currently in use employ aqueous alkaline suspensions of paper fibre as the feedstock, and one process involving use of large quantities of water is only practicable where large quantities of fresh water are readily available. ■ The other process involves flotation. The basic flotation process is simple and merely calls for disintegration of the waste paper in a dilute alkaline solution of a sodium soap. The resultant pulp is generally diluted to a consistency of about one percent solids and calcium ions are then added to insolubilize the sodium soap. This mixture is stirred and aerated so that the calcium soap particles, together with the ink, are carried to the surface of the liquid by the air bubbles and the floating scum or foam is then removed by any suitable conventional means. Consideration in more detail of the flotation process indicates that the following requirements must be met: 1. The action of pulping the waste material must detach the ink particles from the fibres and since inks are held to paper by purely physical forces the mechanical pulping action is generally adequate to have this effect and can be enhanced by surfactants. 2. The detached ink particles must be emulsified to a sufficient extent to prevent redeposition on the fibres but at the same time, the emulsions produced must not be so stable that carrier particles required to raise the ink particles to the surface have difficulty in attracting the ink from the emulsions. 3. The carrier itself must have the required affinit for the ink and be suitable for rapid transport t the surface of the pulp by the air and the carrie and ink must form a foam or scum at the surface. 4. The foam must have characteristics suited to efficient mechanical removal in particular it should not incorporate significant quantities of fibres, since otherwise the overall efficiency will be reduced. Flotation de-inking as currently used in practice, indicates that the complex processes are finely balanced and unsatisfactory results can easily occur if any imbalance occurs in these processes. It has been found th the level of calcium ions which it is necessary to add to the pulp much exceeds that required to insolubilize the sodium soap and it is also found that the addition of synthetic anionic and non-anionic surfactants in addition to the added sodium soaps serve to reduce the speed with which the carrier particles can transport the ink to the surface foam. Also the production of foam is dependant upon the pH value and a minimum level of 8-8.5 is generally needed for satisfactory results. The fact that the addition of any synthetic surfactants is not helpful to the efficient de-inking process is anomalous because the soap is present in an insolubilized form and cannot therefore play its normal roles, It is therefore to be concluded that the surfactants required for efficient de-inking are present in the pulp itself and the invention is based on the addition to the pulp of synthetic surfactants having a character and composition generally similar to the surfactants naturally present, According to the present invention there is provided a process for de-inking paper pulp comprising the addition to the pulp of a surfactant having a character and composition generally similar to surfactants naturally present in the paper. Experimental work shows that using identical flotation techniques, different papers used in the pulps will give substantially different efficiencies of de-inking. For example, papers based on unbleached sulphite pulp from integrated production facilities were much more easily de- inked than those derived from market sulphite, sulphate or mechanical pulps. It was- found that alkaline extracts of integrated sulphite pulps improved the efficiency of de- inking to a marked extent. Experiments showed that the required- surfactant material was soluble in alkaline but relatively insoluble in acid situations. Further experimental work shows that an extract of the sulphite-insoluble hemicellulose fraction of wood contained the active ingredient. The hemicellulose fraction is a mixture of polysaccharides based mainly on xylose and a small proportion of side-chain carboxyl groups. This hemicellulose is soluble in alkaline but insoluble in acid and is therefore found only, in pulps prepared under acid conditions. . It follows from this experimental work that the sodium soap merely acts as a carrier when insolubilized with calcium and the stabilization of the ink particle emulsion and the surfactant foam is effected by calcium salts of the hemicellulose fraction. Hence, in order to obtain the best results it is necessary to use alkaline solutions in order to dissolve the hemicellulose and to use a relatively high level * of calcium ions in-order- to form the -calcium salts of the hemicellulose compound. With regard to the use of synthetic foaming agents added to the flotation process, those currently used for - A Γ OMPI - - . example fatty alchohol ethoxylates, have the disadvantage that they hinder efficient surface removal of ink and more¬ over, lead to high " fibre losses due to the collection of fibre in the foam structure under the conditions of use, In contrast, naturally-occurring foaming agents found in sulphite pulps produce stable foams and do not, in general, induce foam collection of. fibre. These natural foaming agents are believed to be xylanpolymers containing methylated glucuronic acid side-chains but the quantity available in the natural pulp is not always adequate and/or cannot readily be controlled. The added material intended both as a surfactant and as a foaming agent should resemble natural hemicelluloses as far as possible and thus contain a high proportion of hydroxyl and a low proportion of carboxyl groups in a linear polymeric structure. * One suitable co-polymer is made from vinyl acetate and acrylic or maleic acid and the co-polymer is made by removing acetate residues by transesterification with methanol in the presence of sodium methoxide (made by adding sodium to methanol) . It is found that such co-polymers have specific properties necessary for foaming at high calcium levels (say 250 p.p.m) in alkaline solutions. The manufacture of synthetic co-polymers suitable for carrying out the process in accordance with the invention will now be described. 50 gm. of vinyl acetate monomer was dissolved in 100 ml. of toluene and subsequently hydroxy-propyl methacrylate and maleic acid or acrylic acid were added to the solution to form a co-polymer from the three monomers, Azo-bis-iso- butyronitrile (hereinafter referred to as "AZBN") was used as an initiator for the co-polymerization. In the quanti¬ ties used 0.3 gm. was sufficient. As an alternative benzoyl peroxide could be used but gave slightly less good results. The solution was then heated under reflux for three hours after which period it had become more viscous. After allowing the-solution to cool to some-extent-,-petroleum ether (60-80° fraction, approximately 200 ml.) was then added. — The mixture-was then stirred by hand,, .and the. polymer separated out as a gel. The liquid was decanted off and discarded. Approximately 250 ml. of methanol was then added and the gel dissolved by heating and stirring. When all the polymer had dissolved, a small amount, of sodium methoxide was added. The solution was then heated under reflux for half an hour, at the end of which time the polymer had precipitated. The polymer was then filtered off. At this stage, the polymer was swollen due to methanol trapped in the structure. After drying in an oven overnight, the polymer had shrunk to a very small fraction of its original volume. It was then crushed to powder. In some of the preparations, deviations were made from this general method: in the first process, for example, the acid was added at the start, but in some preparations, it was added in a solvent dropwise throughout the reaction. When the intermediate product was reluctant to dissolve in the methanol, a chain terminator, such as dodecyl mercaptan or iso-propyl alcohol, was added at the start of the reaction to keep the molecular weight of the polymer comparatively low. For the same purpose 2 ml. of concentrated sodium hydroxide solution were used instead of -the methoxide in the latter stage in some examples, and in others, it was necessary to add a little petroleum ether (60° - 80° fraction) to precipitate the final product. In one example, a little glacial acetic acid and a little water were needed to throw the product .out. Pure poly (vinyl alcohol) , was also prepared so that its properties in the flotation de-inking system could be compared with the co-polymers. The polymers prepared were characterised by the . following two methods: a) By infra-red spect ' roscopy: the polymer was dissolved in water and a film cast on a silver chloride plate. The water was evaporated in an oven. The spectrum was run on a Perkin-Elmer 157 grating infra-red spectrometer. b) A weighed amount of each polymer was dissolved in 250 ml. of methanol and the solution was titrated with standardised potassium or sodium hydroxide, using phenolphthalein as indicator. The percent¬ age by weight of acid monomer in the polymer was then calculated from this titration. These two tests were also performed on a sample of the intermediate which was taken before the methanol was added. In accordance with the general preparation methods referred to, the following synthetic polymers were made: Example 1 Reactants: 50gm. vinyl acetate, 30gm. hydroxy- propyl methacrylate, 5gm maleic acid, 20ml. iso-propanol. Solvent: 100ml toluene. Initiator: 0.3gm. AZBN. The reactants were heated at 85°C under reflux for three hours. Theisolation of the intermediate and the methanolysis were then performed and the product was precipitated by the addition of petroleum ether. Yield 21gm. Acid content of intermediate: 15.1% and of the product: 6.2%, Example 2 Reactants: 50gm. vinyl acetate, 30gm. of hydroxy propyl methacrylate 6.9gm. of acrylic acid, 20ml. of iso- propyl alcohol. Solvent: 100ml. of toluene. Initiator: 0.3gm. of AXBN. This mixture was heated at 86 C under reflux for 2 hours. The general method was then followed and petroleum ether was used to precipitate the product. Yield 30gm. Acid content of intermediate: 19.2% ' of product: 13.7%. Exam le 3 Reactants: 50gm. of vinyl acetate, 30gm of hydroxy-propyl methacrylate, 2gm. of acrylic acid, 20ml. of iso-propyl alcohol. Solvent: 100ml. of toluene. Initiator: 0.3gm. of AZBN. The reactants were heated under reflux at 83 C for two hours. . The product prepared by the general method proved difficult " to " extracT; " : "" oή adding toluene and petroleum ether still no product was precipitated. A little glacial acetic acid and a little water were added and the product separated slowly with stirring. ' Yield 5.6gm. Acid content of intermediate-: 9.6%, of product: 9.7%,. Example 4 Reactants: 50gm. of vinyl acetate, 30gm. of hydroxypropyl methacrylate, 5gm. of maleic acid, J.0gm, of trichloroacetic acid. Solvent: 100ml. of toluene. Initiator 0.3gm. AZBN. These were heated under reflux at 90°C for two hours. The product was then prepared as in the general method. Yield 6gm. Acid content of product: 10.6% Example 5 Reactants: 50gm. of vinyl acetate, 25gm. of methyl acetate, then 0.15gm. of maleic acid dissolved in 25gm. more of methyl acetate added dropwise. Initiator: 0.3gm of AZBN. The mixture was heated under reflux for one hour while the acid was added, and the heating was continued for a further hour. Approx. 20ml_ methanol and 1ml. of 40% sodium hydroxide solution were then added. The mixture was heated under reflux for 30 minutes, at the end of which time the product had precipitated out. This was filtered and washed with acetone before being dried in an oven. Yield 6.7gm. Acid content of product: 2.0%, Example 6 Reactants: 50gm. of vinyl acetate, 25gm. of methyl acetate, Initiator: 0.3gm. of AZBN. These reactants were heated under reflux for four hours. During the first two hours the following were run in dropwise: 25mg. of methyl acetate, 0.15gm. of maleic acid, 0,2gm of AZBN, After-four-hours approximately 20 ml. of methanol, and l-2ml. 40% sodium hydroxide solution were added. This produced a considerable amount of heat and some of the solution blew out of the top of the condenser. The solution was cooled in an ice bath before heating under reflux for 30 minutes. . . .. . _ _ Yield 6gm. Acid content of product 2.1%. Example 7 Reactants: 50gm. of vinyl acetate, 25gm. of methyl acetate and then O.lgm.• acrylic acid and 25gm, methyl acetate. These- dded dropwise over the first three hours. Initiator: 0.3gm. AZBN. The mixture was heated under reflux for four hours before being cooled in an ice-bath. 200ml. of methanol and 2ml. of 40% sodium hydroxide solution, were added. The mixture was then heated to reflux for half an hour, the product was precipitated and was filtered and dried. Yield 4.6gm. Acid content of product: 1.9%. Example 8 Reactants: 50gm. of vinyl acetate, 25gm. of ' methanol, 25gm. of methyl acetate, then 0.2gm acrylic acid and 25gm methanol 25gm dropwise. Initiator: AZBN (O.lgm at start, then two additions, each of O.lgm., after one hour as for product 7. Yield: 7gm. Acid content of product: 2.1%. Example 9 Reactants: 50gm. of vinyl acetate. Solvent: 100ml of methyl acetate. Initiator: AZBN 0.3gm. These reactants were heated under reflux for four hours. Af er two hours, 0.3gm. of AZBN and 20ml. of toluene were added. The solution was then cooled somewhat, and approximately 250ml. of petroleum ether were added with stirring. The liquid was decanted off and discarded. 300ml of methanol was added with heating and stirring to dissolve the polymer. After adding some methoxide the solution was heated under reflux for half an hour. The product was filtered and dried in the usual way. Yield 10.5gm. Use of the examples set out above for de-inking news¬ print will now be described in relation to the general method employed. The first stage was to pulp the sample of newsprint : this was performed..in a standard pulp evaluation disinte¬ grator. 2 litres, 40 -45 C of warm water, 0.7gm. of the polymer, l.Ogm. of sodium hydroxide and 4.0gm, of sodium metasilicate were added to the pulper. The mixture was -- RE OMP ,, WIP then stirred for .a count of 500 on a counter fitted to the pulper to ensure that the polymer had dissolved; each unit on the counter- " -i-s-equivalent- to 25 revolutions~of-,the-stirrer -shaft - 50 revolutions per second. 2ml. of 100 volume hydrogen peroxide solution was then added. The solution was further agitated. 2g___. of- cal-Gium- chloride was- hen.-added with stirring. 70gm. of newsprint was added, the counter was set at 3,000 and the disintegrator started. The contents of the pulper were checked after 100 on the counter, to see if there had been any separation of ink from the pulp. During this process, 1.5gm. of tallow soap was dissolved in 200-300ml. of water on a stirrer/hot plate. 2.0gm. of. calcium chloride and l.Ogm. of sodium hydroxide were placed in a bucket with some hot water to dissolve them. The contents of the pulper were again checked and then transferred to the bucket. The pulper was rinsed with hot water, which was added to the contents of the bucket. The latter was then made up to the volume of the flotation tank with cold water. The flotation tank was a cylindrical cell of * 7.5 litres capacity, constructed of stainless steel, which incorporated a multi-pored base bubbler attached to a pressurised air supply, and an overhead stirrer with a butterfly blade system. The soap solution was placed in the flotation tank and the pulp transferred to it. The air flow was adjusted to a rate of 0.95 litres/min. and the stirrer motor was switched on, running at a rate of approximately 1,200 revolutions/min. The froth was removed by manual scraping with a palette knife from the top of the tank for 20 minutes. The froth removed was checked to see: a) the extent of fibre removal and b) whether the ink was being removed as large or small particles, or not at all. -£ TREA r OMPI fa IPO «* ^ 8J.AT1^ The de-inked pulp was then formed into handsheets: a sample of 1,500ml. was taken out of the flotation tank (through the tap on the side) . The water was then drained off in a 60-mesh sieve and the resultant pulp was then thickened, most of the remaining water being pressed out. The pulp was then re-diluted to 1,500ml. The diluted pulp was then made into three handsheets, each of 500ml. using a filter tank and a press. In each case, some water was run into the filter tank and 500ml. of pulp were poured in at the same time. The tank was then emptied, leaving a film of paper on the mesh. Two sheets of blotting paper and then a 7" diameter metal disc were placed on top of this. Then using a heavy, metal roller, the sheet was rolled seven times. The blotters plus sample were placed on t_2 press for the first pressing: two blotters were placed on the press, then the two blotters plus sample (sar.pia facing upwards), and then a 6" diameter metal plate. This was repeated for the second and third samples, and then a further two blotters were placed on top. The first pressing lasted for four minutes, then the samples were prepared for the second pressing: all the blotters used in the first pressing were discarded and the- metal plate and sample were removed together in each case. For the second pressing, each sample plus metal plate was placed on top of two blotters (.sample upwards) on the press. Two blotters were placed on top of all and the second pressing (two minutes) was performed. The samples were then left to dry overnight. A number of points were monitored throughout the whole flotation de-inking process. At the pulping stage, the state of the pulp in the pulper was checked twice, after 100 on the counter and at the end, to see how clean the pulp was and if the ink had separated at that stage. During the transfer from pulper to flotation tank, it was noted whether any ink had stuck to the sides of the bucket-. BADORJGlNALf . -≤ OgM The state of the foam in the tank was also noted, i.e. whether the bubbles were large or small (heavy or light foam) " , whether the ink was remove'd " as ' laϊge O ' small particles, how much fibre was being removed. This was ' checked by putting a sample of foam on to a blotter. " The " finished handsheets " were examined ~ both visually- and spectrophotometrically. Reflectance values at 457nm. were obtained using a 90 incident beam against a standard of barium sulphate. The rougher side of the handsheet (the non-wire side) was used for this measurement. A reflectance value of about 50 was considered very poor, and a value of 56 or more was very good. The method outlined above and the tests applied were carried out with each Example hereinbefore described. The results are conveniently summarized in the following table for each example: OMPI Differences Contents of Fc>-_--_____g in Handsheets from general pulper tank (Reflectance Example 1 Trial 1 No polymer Clean (after Small, light Fair (50.6) added 100 on the • bubbles slow counter), some to form, some ink stuck to . fibre, not all sides of the ink removed. bucket at the end of trial. Trial 2 None Slight separ¬ Inky foam, Fair (51.2) ation of ink. slightly quick¬ er to. orm than trial 1. Mst ink seemed to be taken out, extra lgm. NaOH impro¬ ved foaming. Trial 3 Extra 0.5gm. Slight separ¬ Good foaming, Quite good NaOH in flo¬ ation of ink. largish, light (54.4) tation. bubbles, quite quick to form, little fibre loss. Ink taken out quite quick¬ ly. Trial 4 1.5gm. NaOH in Slight separ¬ Good foaming, Good (56.3) each stage ation of ink largish, light at 100 on the bubbles, ink counter, clea¬ came off quick¬ ner at end of ly, foam quicker trial. to form than in trial 3. Little fibre loss. Trial 5 60gm. news¬ Inky scum at Large, heavy Quite good print, 15m. top after 100 bubbles quick (53.9) magazines, no on the count¬ to form; good polymer used. er, same at foaming. Con¬ 1.5gm.NaOH in end, some ink siderable ink, each stage stuck to sides but little of container. fibre taken out. O Differences Contents of Foaming in Handsheets frcm general .pulper tank (Reflectance) Trial 6 As Trial 5, Considerable 1-fore foam Quite good but with inky scum than trial 5 (55.0) polymer separated. quicker form¬ ation of same type of foam. Most ink re¬ moved by 15 minutes. Trial 7 1.5gm. NaOH in Inky scum on Very good Good (56.4) flotation stagei.top after 100 foaπing, large Soap added in on the count¬ heavy bubbles, pulper. er, ink par¬ most of the ink ticles separ¬ removed by 10 ated at the minutes, very end of the little fibre trial. removed. Trial 8 No polymer, Considerable Again good Quite Good soap was inky scum fθ-__ning, most (53.3) placed in pul¬ after 100 on ink removed by per. 1.5gm. the counter, 15 minutes, NaOH in each but only foaming slower . stage. traces of ink and less than at end. trial 7. Little fibre loss. Trial 9 No peroxide, Inky scum sep¬ Comparable to Fair (49.9) soap in pulper arated out. trial 8. 1.5gm. NaOH in each stage. Trial 10 Aged w/o news¬ Clean Good foaming, Fair (52.2) print used; small bubbles 1.5g_rtNaOH in removed con¬ each stg. siderable ink at start but little at end. S ne fibre removed. Trial 11 0.15gm * - polymer Reasonably Quite good Quite good used; 1.5gm clean foaming, quite (52.7) NaOH in each a lot of ink stage. but little fibre removed. Differences Contents of Foaming in Handsheets from general pulper tank (Reflectanc EXAMPLE 2 Trial 1 No polymer .Slightly inky Not very good; Fair (52.0) used. 1.5g___. scum separa¬ seemed to re¬ NaOH in pul¬ ted. move,little ink. ping stage. Sane fibre re¬ moved. Trial 2 1.5gm. NaOH Slight foam¬ More foam than Good (54.5) in pulping ing on top trial 1, did stage not seem to re¬ move a lot of ink. Some fibre loss. Trial 3 None Slight inky Not very good Fair (52.3) scum separated some ink re¬ moved as small particles, little fibre removed. Trial 4 4gn. CaCl2 in Reasonably Not very great. Quite good flotation clean. Some ink re¬ (53.3) stage moved at first, little at end of trial. Some fibre loss. Trial 5 4gm. CaCl^ and Reasonably Quite good foam¬ Good (55.6) 1.5gm. NaOH in clean, a ing and ink re¬ flotation little foam. moval. Some stage fibre removed. Trial 6 6gm. CaCl ? and Reasonably Good foaming. Good (56.8) 2gn. NaOH in clean Good removal flotation stage of ink as fine particles. Little fibre removal. EXAMPLE 3 Trial 1 No polymer Quite clean Quite good foam¬ Good (55.4) used. 1.5gm. ing, but not good NaOH in removal of ink. stage. Some fibre re¬ moved. Differences Contents of Foaming in Handsheets from general pulper tank (Reflectance) Trial 2 0.7gπ_. inter¬ Much the same Very light foam Quite good mediate used as trial 1. but ink seemed to (52.7) - 1.5g_-i. NaOH - be removed. Pulp in each stage. at end of trial was grey. Little fibre loss. Trial 3 1.5gm. NaOH Slight foam Negligible. 3g_n. Fair (51.2) - in each stage at top. CaCl- and lgm. NaOH added then foaming quite good but light, seemed to remove ink quite well. Some fibre loss. EXAMPLE 4 Trial 1 1.5gm. NaOH Reasonably Poor, unstable Good (55.1) used in each clean after and slow to form stage. 0.7gm. 100 on the foam. Some fibre intermediate counter; removed. Little used. large part¬ ink being removed icles of ink towards the end separated at of trial. the end of trial. Trial 2 1.5gm. NaOH in Quite clean Rather poor foam¬ Quite good each stage. ing - slow to (54.7) form and unstable. Considerable ink removed at start still re oviiig at end. Little fibre loss. Trial 3 Also 2.1g_n. Some ink par¬ Very poor, 2gm. Fair (51.5) polymer in ticles separ- NaOH + 8gm. CaCL, —flotation .ted f-fter 100 added then foameα stage. 2gm. on the counter; very well, but NaOH in reasonably did not seem to each stage clean at end. remove much ink. Little fibre loss. EA CT OMPI *& ' Differences Contents of Foaming in Handsheets frail general pulper tank (Reflectanc EXAMPLE 5 Trial 1 0.25gm. polymer Some foam at Very good; con¬ Quite good used. 1.5gpι top. siderable foam (54.2) NaOH in each and seemed to stage. remove ink well. Seme fibre loss. Foam became wet towards end. Trial 2 1.5gm. NaOH More foam at Much the same as Good (55.6) in each stage. top than • trial 1 but trial 1. seemed to remove ink more effic¬ iently; foaming better near end. Trial 3 1.5gm. NaOH Considerable Quite good, ink Quite good in each foam cn top removed as fine (53.4) stage. at end. particles. Ink still caning off at end. Some fibre removed. EXAMPLE 6 Trial 1 Soap in pul¬ light foam Excellent. Ink Good (54.8) per. 1.5gm. on top. removal clean NaOH in each and finely stage. divided. Ink finished coming off after about 10 minutes. Trial 2 As trial 1, Some ink Foam-free par¬ Excellent but no CaCl 2 particles ticulate scum. (60.2) added. separating 4gm. CaC -, towards end. added: tnen foam generation still much ligh¬ ter than trial 1. Ink still highly particulate. - R _ O Differences Contents of Foaming in Handsheets from general pulper tank (Reflectance) Trial 3 Soap in pul¬ Some partic¬ Poor: all the Very good per. 0.5gpι. les of ink ink came off in (56.2) CaCl2 in pul¬ separated. about 10 minutes per; none in Ink separa¬ after 6gm. CaCl^ flotation ted on dilu¬ added then quite stage. tion. good foaming. Time taken 15 minutes. Trial 4 As trial 3, Much the same Poor: all the Very good but 0.75g_n. as trial 3. ink came off in (57.1) CaCl 2 used. about 5 minutes after 6gm. CaCl 2 added then quite good foaming. Time taken 10 minutes. Trial 5 As trial 3, Much the same Much the same Very good but l.Og . as trial 3. as trial 4. (56.7) CaCl ? used. EXAMPLE 7 - Trial 1 l.Ogm. CaCl Inky scum Very light white Good (54.4) used, in each separated. foam - did not stage, soap Coarse inky seem to take much in pulper. scum on dilu¬ ink out. tion. Trial 2 1.5gm. NaOH in Inky scum on Quite good, took Poor (50.2) each stage top after 100. ink out quite At end quite well as fine par¬ clean. ticles. Some fibre removed. EXAMPLE 8 Trial 1 1.5gm. NaOH Considerable Good, ink Fair (52.9) in each inky scum removed as fine stage. after- 100 on particles, sane the counter, fibre loss. little less at end ink being removed of trial. but still good foaming at end of trial. Page 17a to follow - 17/1- It should be noted that the reflectance of a handsheet is only one measure of its appearance; it may be more or less speckled or off-colour and as a result the reflectance may not measure the appearance exactly. Page 18 to follow O The products prepared before that of Example 1 were stages in developing a linear polymeric chain with a high proportion of -OH groups and a low proportion of carboxyl groups. It was, of course, important that the inter¬ mediate product in the process should dissolve fairly readily in methanol when stirred and heated. The final product should dissolve in warm water fairly easily and should froth freely in both alkaline and neutral solu¬ tions. The polymers were characterised by their acid numbers, the amount by weight of acid monomer as a percentage in the product, and by their infra-red spectra. In practice the infra-red spectra appeared very much the same in all cases. All the polymers• showed a strong absorbance at a wavelength of about 3500cm " ; this is characteristic of the -OH group. There was a peak in the spectra of the intermediates .which became almost negligible in the spec¬ tra of the final products. This peak (at a wavelength of 1575cm ) did not appear in any of the spectra of the monomers on their own, but it did appear in the pure poly (vinyl alcohol) spectrum. • It could perhaps be attributed to a carboxyl group. One peak definitely attributed to a carboxyl group at a wavelength of 1400cm ) appeared in the spectrum of the intermediate and then appeared much weaker in that of the product. There was a peak at a wavelength of 1727cm which was attributed to an ester carbonyl group, but the intensity was approximately the same in the spectra of the intermediate and the product. Example 1, (acid content 6.2%), had twice the level of hydroxypropyl methacrylate at the start as compared to earlier- Examples-, not..described. ...It was found that a higher sodium hydroxide level in each of the pulping and flotation stages gave a much better paper product. These levels were generally used in the production of all hand¬ sheets. The best results were obtained by trial 7, with 0.7gm. polymer and the soap added in the pulper, which - REXCΓ OMPI ^ * Z. . - - gave very good handsheets with a reflectance of 56.4. The trial was repeated with no peroxide and gave poor handsheets with a reflectance of 49.9. This shows that the peroxide is necessary; but merely adding a large amount of bleach to obtain good handsheets does not give adequate results. Also, if the soap is added to the pul¬ per instead of to the flotation tank, the ink tends to separate in the pulper and sticks to its side and to the bucket during transfer to the flotation tank. Example 2, (acid content 13.7%), was prepared simi¬ larly to Example 1, except that acrylic acid was used instead of maleic acid. This also gave quite good results, but only after the addition of extra calcium chloride in the flotation stage. Example 3, (acid content 9.7%,) , contained a smaller amount of acrylic acid than Example 2. This proved particularly difficult to isolate, and after that it gave a very poor performance as de-inking additive. Example 4 including maleic acid as opposed to acrylic acid, and also some trichloroacetic acid which might become trapped in the polymer structure, was then prepared. De-inking trials were then run with both the product and the intermediate and both gave very poor results.. Models for maleic and acrylic acids when in¬ corporated in a co-polymer are succinic and propionic acids, respectively. pK for propionic acid is 4.87, and for succinic acid pKa (1) is 4.16 and pKa(2) is 5.61. From these values it is seen that the two acids are com¬ parable in acidity with each other. Due to the poor performance of thes"e "high-acid" polymers only a trace of acid was added to the co-polymer of later Examples * Both Examples 5 and 6 had a small amount of maleic acid added as a solution in methyl ace¬ tate from a dropping-funnel. To produce Example 5 the first stage was heated under reflux for two hours whereas this polymerisation lasted four hours in Example 6. Example 5 (acid content 2.0%), produced quite good O fa I results; it was interesting to note that 0,7gm, of additive produced the same amount of ξoa ~ as 0.25gm,, but removed the ink more efficiently, Example 6, (acid content 2.1%), gave excellent results, But it was thought that the calcium level was too high and some trials were performed with different calcium levels. These produced particularly good handsheets; probably the best results so far have come from Example 6. Example 7 and 8 were much the same s Example 5 and 6 but contained small amounts of acrylic acid Cadded dropwise). Neither of these products, though, proved to be as good an additive as Example 6,. Example 7, (acid content 1.9%), did not produce a large amount of foam and little -ink seemed to be removed, though the handsheets were reasonable. ' In the second trial, though foaming well, poor handsheets resulted. Example 8 (acid content 2.1%), gave a good foam but poor handsheets were pro¬ duced. Generally, ink removal was not satisfactory, From the foregoing results it will be apparent that there was a definite improvement in foaming and ink removal'in general when using one of the co-polymers in accordance with the invention in the flotation de-inking process as opposed to using no additive at all. The polymers which performed the best in flotation de-inking as an additive were those with some acid present in the chain, but not too much. The polymers which seemed to work best were those with about 2% of acid by weight in the polymeric chain. v- Of the two acids used in the preparation of the co- polymers it was found that maleic acid containing poly¬ mers gave much better- reaults -than, those,containing acrylic acid. - lEAcT OMPI _ χ WIPO * *

Claims: CLAIMS 1, A process for de-inking paper pulp characterized by addition to the pulp of a, surfactant having a character and composition generally similar to surfactants naturally present in the paper. 2. A process according to claim 1 characterized in that pulp to be de-inked is unbleached sulphite pulp and t added surfactant is of a type soluble in alkaline but relatively insoluble in acid solutions. 3.. A process according to claim 2 characterized in that surfactant is an extract of the sulphite-insoluble hemicellulose fraction of wood pulp. 4. A process according to claim 3 characterized in that cellulose fraction is a mixture of polysaccharides and a minor proportion of side chain carboxyl groups, * 5. A process according to claim 4 characterized in that the polysaccharides are based on xylose. 6. A process according to any one of the claims 3 to 5 characterized in that the process is carried out under alkaline conditions, and a level of calcium ions is present so as to form calcium salts of the hemicellulose, 7. A process according to claim 1 characterized in that the added surfactant is similar in structure to natural hemicellulose and contains a relatively high propor tion of hydroxyl and a relatively low proportion of carboxy groups in a linear polymeric structure, 8. A process according to claim 7 characterized in that the hemicellulose is made from vinyl acetate and acryl acid by removing acetate residues by transesterification wi methanol in the presence of sodium methoxide that the hemicellulose i,s made from vinyl acetate and maleic acid by removing acetate residues by transesterification with methanol in the. presence of sodium methoxide. 10. A process for de-inking paper pulp according to claim 1 characterized in that the pulp is sulphite pulp and the added surfactant is a xylan polymer containing methyl¬ ated glucuronic acid side-chains. 11. A method of manufacturing a synthetic co-polymer suitable for carrying out the process according to any one of the preceding claims, characterized in that the method used involves solution polymerisation. 12. A method of manufacturing a synthetic co-polymer suitable for carrying out the process according to claim 1, said method is characterized by the steps of dissolving a vinyl acetate monomer in toluene, adding hydroxy-propyl methacrylate and maleic or acrylic acid and AZBN as co- polymer initiator, heating the solution thus prepared, adding petroleum ether, adding methanol, followed by sodium methoxide and separating the co-polymer precipitated by the sodium methoxide. 13. A method according to claim 12 characterized by the modification of the initial addition of maleic or acrylic acid in place of subsequent addition thereof. 14. A method according to claim 12 or claim 13 characterized by the addition of dodecyl mercaptan, iso- propyl alcohol or other chain terminator, 15. A method according to claim 12, characterized in that reactants are 50 gm. vinyl acetate, 25 gm, of methyl acetate, 0.3 gm. AZBN, and during the first two hours of heating under reflux 25 gm. of methyl acetate, 0,15 gm. of maleic acid and 0.2 gm, AZBN are added. . process or e- n ng paper pu p su s an a as hereinbefore described. 17. A method * of manufacturing surfactants for us in the de- inking of paper pulp substantially as hereinbefore described in any one of the Examples . 18. Surfactant, when prepared by a method claimed i any one of claims 11 to 15 or claim 17. 19. Paper pulp de- inked by the by the process accor ing to any one of the claims 1 to 9 or 16 , - O .

Inventors: BURSTALL M, COLLINGS C, MATTINGLEY J
Applicants: BURSTALL M, COLLINGS C, MATTINGLEY J, UNIV SURREY, UNIVERSITY OF SURREY
Application year: 1979
Main classification: D21C5
IPC codes: C08B1, C08B37, C08F8, C08F218, C09D9, D21C5