A process for the delignification of chips of vegetable matter by pretreating the chips to obtain at least 64 percent by weight refined vegetable matter, and delignifying the refine vegetable matter with chlorine dioxide. A pulp produced in high yield by the process which refines easier, dries more readily on a paper machine, exhibits higher on-machine filler retention, and possesses greater strength than conventionally bleached kraft pulp made from the same wood mixture. A paper produced from said pulp which has higher tensile, tear, burst, fold, pick and delamination strengths and greater brightness stability that paper produced from conventionally bleached kraft pulp made from the same wood mixture. A process of delignifying lignocellulosic vegetable matter wherein the vegetable matter is pretreated to obtain a refined vegetable matter which is thereafter delignified by reacting it in at least two stages with chlorine dioxide, each successive stage using less chlorine dioxide than the preceding stage and the total chlorine dioxide used being from about 1% to about 15% based upon the dry weight of the vegetable matter, and wherein the vegetable matter is extracted between successive chlorine dioxide stages with a caustic material, pulp produced from said process and paper prepared from said pulp.
|
24. A process for the delignification of wood chips comprising, in combination, the steps of:
(a) pretreating said chips to obtain a refined vegetable matter in a yield of about 64% to about 100% by weight, based upon the dry weight of said chips; (b) delignifying said refined vegetable matter by reacting it in three stages with preformed chlorine dioxide, each successive stage using less chlorine dioxide than its preceding stage, and the total chlorine dioxide used being from about 2% to about 13% based upon said dry weight; and (c) extracting said vegetable matter after the first two of the three chlorine dioxide stages with a water solution of caustic material at a temperature of from about 50°C. to about 75°C; wherein said caustic material is an alkali metal hydroxide, alkali metal carbonate, ammonium hydroxide or ammonia gas.
1. A process for the delignification of lignocellulosic vegetable matter comprising, in combination, the steps of:
(a) pretreating said vegetable matter to obtain a refined vegetable matter in a yield of about 64% to about 100% by weight, based upon the dry weight of said vegetable matter, (b) delignifying reacting said refined vegetable matter by reacting it in at least two stages with at least about 2% to about 15% preformed chlorine dioxide , each successive stage using less chlorine dioxide than its preceding stage, and the total chlorine dioxide used being from about 1% to about 15% based upon said dry weight; and (c) treating extracting said vegetable matter between successive chlorine dioxide stages with a water-soluble caustic material at a temperature of from about 50° C. to about 75° C; wherein said water soluble material is an alkali metal hydroxide, alkali metal carbonate, ammonium hydroxide or ammonia gas; and (d) reacting said vegetable matter with chlorine dioxide.
14. A process for the delignification of vegetable matter comprising, in combination, the steps of:
(a) pretreating said vegetable matter to obtain a refined vegetable matter in a yield of about 64% to about 95% by weight, based upon the dry weight of said vegetable matter, said pretreating comprising, in combination, the steps of: (i) prepulping prepared vegetable matter chips by kraft, nitric acid, bisulfite, or neutral sulfite process, (ii) refining said prepulped vegetable matter, (iii) washing said prepulped vegetable matter; (b) reacting said refined vegetable matter with from about 2% to about 7% chlorine dioxide, based upon the total weight of dry fibrous material fed to said pretreating step until all of said chlorine dioxide is substantially consumed; (c) water washing said reacted vegetable matter; (d) treating said washed vegetable matter with an aqueous solution of sodium hydroxide for at least about one-half hour at a temperature of from about 50°C to about 75°C; (e) water washing said treated vegetable matter; (f) reacting said washed vegetable matter with about one-half the amount of chlorine dioxide used in step (b) at a temperature of from about 40°C to about 60°C for about 30 minutes to about 4 hours; (g) water washing said reacted vegetable matter; (h) treating said washed vegetable matter with sodium hydroxide in aqueous solution for at least about one-half hour at a temperature of from about 50°C to about 75°C; (i) water washing said caustic treated vegetable matter; (j) reacting said washed vegetable matter with about one-half the amount of chlorine dioxide used in step (f) for a period of from about 2 hours to about 6 hours at a temperature of from about 40°C to about 80°C; and (k) water washing said reacted vegetable matter.
2. The process of
3. The process of
6. The process of
7. The process of
(i) prepulping prepared vegetable matter chips by a kraft, nitric acid, bisulfite, or neutral sulfite process; (ii) refining said prepulped vegetable matter; (ii) washing said prepulped vegetable matter; and (iv) dewatering said prepulped vegetable matter.
8. The process of
9. The process of
10. The process of
11. The process of
12. The process of
13. The process of
15. The process of
16. The process of
17. The process of
18. The process of
20. A paper prepared from the pulp of
21. A paper made predominantly from softwood pulp produced by the process of
22. A paper made prodominantly from hardwood pulp produced by the process of
23. The process of
chlorine dioxide reaction stages. 25. The process of
26. The process of
27. The process of
28. The process of
29. A pulp produced by the process of
30. A paper prepared from the pulp of
|
|||||||||||||||||||||||||||||||||||||||||||||||||
Vegetable materials such as wood, reed, bamboo, cane and the like which are or can be used for the preparation of fibrous materials are composed of several basic parts. In general, fibrous vegetable matter is made up of about 15 to 30 percent lignins and extractives, such as resins and the like, with the remainder of the about 70 to 80 percent being carbohydrates. The carbohydrate portion of the fibrous vegetable matter is about 10 to 30 percent hemicellulose with the remainder being cellulose, and the cellulose portion of the carbohydrate is about 45 to 55 percent alpha cellulose and about 5 percent other celluloses, all percentages being expressed on a wood basis.
As is well known, one of the first steps in conventionally converting fibrous vegetable materials to fibers for use in the preparation of paper or paper-like materials is a pulping process. The primary goal of the process is to remove most of the lignins from the fibrous vegetable material and separate the remaining carbohydrate fibers into individual fibers. In all known pulping processes, such as kraft, sulfite and others, when efforts are made to remove substantially all of the lignin from the vegetable fiber mass, a major part of the hemicellulose is lost, and the remaining cellulose and hemicellulose fibers are chemically and/or mechanically damaged. This results in a significant loss of yield and a major reduction in strength of paper or paper-like products due to fiber damage. For example, in a kraft pulping process, the normal yield known in the art is about 45 percent by weight. But, if only the lignins and extractives were removed from the fibrous vegetable material, the yield obtained would be 70-80 percent.
This invention is directed toward a new and novel pulping process and the pulp and paper products resulting therefrom. The pulping process removes substantially only lignins and extractives from fibrous vegetable materials and leaves the cellulose and hemicellulose part of the material substantially undamaged, thereby resulting in pulp and paper products having new and unusual properties and exceptionally high strengths. Since the pulping process is reasonably selective and substantially only the lignins and extractives are removed, yields are exceptionally high and in the 55 to 85 percent range. The pulping process includes a basic sequential unit of a chlorine dioxide treatment, caustic extraction and a chlorine dioxide treatment, and this basic unit is preceded by a chemical or mechanical pretreatment of prepared vegetable fiber chips. Each step of the basic sequential unit is followed by a water washing, which may be with process liquids obtained elsewhere in the process, as by countercurrent washing which has attendant conservation advantages.
A more preferred embodiment of the process is one including a chemical and/or mechanical pretreatment of prepared vegetable fiber chips followed by the sequential processing of the pretreated chips in a chlorine dioxide treatment, a caustic extraction, a chlorine dioxide treatment, a caustic extraction and a final chlorine dioxide treatment. A water washing or its equivalent follows each chlorine dioxide treatment and each caustic extraction.
An even more preferred embodiment of the process is one in which the water wash for the final chlorine dioxide treatment is used as the water wash for the preceding caustic extraction and so on countercurrently to the flow of fiber material through the process to the first water wash following the first chlorine dioxide treatment; from this point the wash water may then be sent to waste or treated for recovery of chemicals contained therein.
Another preferred embodiment of the process involves the chemical pretreatment of prepared vegetable fiber chips followed sequentially by a chlorine dioxide treatment, a caustic extraction, a chlorine dioxide treatment, a caustic extraction and a final chlorine dioxide treatment with countercurrent water washing and extraction after each treatment; the most preferred chemical pretreatment is a neutral sulfite pretreatment at a specified concentration of chemicals and cooking cycle.
The pulp produced by the process of the present invention has a higher degree of polymerization, a higher hemicellulose content, a higher carboxyl content, and a lower carbonyl content than conventionally bleached kraft pulp from the same wood mixture. In addition, it requires less energy to refine than a conventionally bleached kraft pulp from the same wood mixture. Also, laboratory handsheets prepared from the pulp have superior tensile strength and tear strength when compared to sheets of conventionally bleached kraft pulp from the same wood mixture.
The above pulp properties relate directly to paper made from the pulp. Such paper has higher tensile, tear, burst, fold, pick, and delamination strengths.
In the drawing, FIGS. 1 and 3 are block diagrams and FIGS. 4 to 13 are graphs. FIG. 1 describes the basic process of this invention. FIG. 2 shows a more preferred embodiment of the process of this invention, and FIG. 3 discloses a highly preferred chemical pretreatment step for the process of this invention. FIG. 4 compares yield of pretreated material with caustic utilized in each stage. FIG. 5 compares G.E. brightness with caustic utilized in each stage. FIG. 6 compares percent rejects with caustic utilized. FIG. 7 shows final yield compared with pretreatment yield. FIG. 8 compares chlorine dioxide consumption with pretreatment yield. FIG. 9 shows a comparison of freeness with beating time. FIG. 10 compares Schopper fold with effect of cation treatment. FIG. 11 provides a comparison of MIT fold with Schopper fold. FIG. 12 relates to Schopper fold to days of aging, and, FIG. 13 relates Schopper fold to years of aging.
Referring now to FIG. 1, fiber chips of any fibrous vegetable matter are fed first to a pretreatment step 10 which may be either mechanical, chemical or a combination thereof. Following pretreatment, the pretreated chips are then fed to a first chlorine dioxide treatment 11 where they are contacted with chlorine dioxide in either aqueous solution or as a gas. Following this, the chlorine dioxide treated material is washed with water 12 to return the mixture to substantially neutral pH; following washing, the washed chlorine dioxide treated material is subjected to caustic extraction 13 for a period of about one-half to one hour. The extracted material is washed again with water to return to substantially neutral pH, as indicated at 14, and to remove the water soluble materials produced in the extraction step. Then this second washed, extracted fibrous material is subjected to a second chlorine dioxide treatment 15, either aqueous or gaseous, and the second chlorine dioxide treated material is water washed, 16, to produce a pulp in high yield with good brightness. Yields from this basic process range from about 55 to about 85 percent at a G.E. color brightness (TAPPI Standard T 217m-48) of approximately 80 to 90.
Referring now to FIG. 2, a more preferred embodiment of the invention is shown. Prepared vegetable fiber chips are fed to a pretreatment step 20 where they are subjected to a chemical, mechanical or a combined chemical-mechanical pretreatment to make the lignin and extractives more readily available for removal. Following the pretreatment step, the pretreated material is subjected sequentially to a chlorine dioxide treatment 21, water washing 22, caustic extraction 23, water washing 24, chlorine dioxide treatment 25, water washing 26, caustic extraction 27, water washing 28, chlorine dioxide treatment 29, and water washing 30.
In a more preferred embodiment, fresh water is fed only to the last water washing 30 by line 40 and then circulated countercurrently to the flow of the material through the process as indicated by line 41 to the next to last water washing step 28, and from there as indicated by line 42 to the next preceding water washing step 26, then by line 43 to water washing step 24, and from that wash to the first water washing 22 as indicated by line 44, and then to waste or chemical recovery as indicated by line 45. It is clear, of course, that fresh or make-up water may be added to any one of the water washing steps as indicated by lines 46, 47, 48, 49 and that water may be sent to waste or chemical recovery from any or all of the water washing steps as indicated by lines 50, 51, 52 and 53.
Chlorine dioxide, either in aqueous solution or in gaseous form, may be fed to each of the chlorine dioxide steps as indicated by lines 60, 61 and 62 and an aqueous solution of caustic may be fed to each of the caustic extraction steps as indicated by lines 63 and 64. The novel pulp of this invention is recovered from the process, as indicated at 70, in a high yield of about 55 to about 85 percent and at a G.E. brightness of approximately 80 to 90.
A more preferred embodiment of the invention is a five stage process that comprises the sequential steps of chlorine dioxide treatment, caustic extraction, chlorine dioxide treatment, caustic extraction, and chlorine dioxide treatment, with a water wash between each step, and having first chlorine dioxide treatment preceded by chemical or a chemical-mechanical pretreatment.
Referring now to FIG. 3, a block diagram of a preferred chemical-mechanical pretreatment is shown. Prepared vegetable fiber chips are fed to a chemical treatment step 70 where a prepulping treatment is given. This prepulping treatment may be in the nature of a weak pulping to a high yield by a kraft, nitric acid, neutral sulfite process, or other. In the pre-pulping treatment, the fiber chips are prepulped to a yield at least greater than 64 percent by weight based upon the dry weight of the chips of the vegetable matter. Following the chemical treatment, the prepulped material is refined in step 71, washed in step 72, then dewatered as indicated at 73 to prepare a combined chemically-mechanically pretreated material ready for processing in the first chlorine dioxide treatment as indicated at 21 in FIG. 2.
The novel process of this invention is suitable for preparing a novel pulp and paper product from any fibrous vegetable matter containing lignin. As is necessary with all pulping processes, the vegetable matter should have extraneous materials removed before being subjected to the process. For example, in the case of wood, it must be debarked in a prior operation. In the following description, wood will be referred to as the fibrous vegetable material; however, it should be understood that the process of the invention is applicable to all fibrous vegetable materials.
Debarked wood, either hard or soft, may be converted into chips by a Carthage multiknife chipper or other equivalent apparatus. The chips should be approximately 15 to 75 millimeters in length, 10 to 40 millimeters in width and have a thickness of 0.5 to 20 millimeters. When chemical or chemical-mechanical pretreatment is used it is preferred that chips have an approximate length and width as described and that the thickness be from about 2 to about 5 millimeters. Following chipping, prepared chips are then subjected to the pretreatment step.
The pretreatment step can be either mechanical, chemical or a combination of chemical and mechanical. In mechanical pretreatment, the vegetable fiber chips are subjected to a shredding, refining, or flaking operation, such as is well known in the art, by a Pallman knife ring flaker, which by slicing reduces conventionally sized chips to thin flakes while maintaining chip length and width, or a standard disc refiner, or the equivalent. As is also known, the chips may be subjected to water or steam treatment prior to flaking or refining, either under vacuum or pressure, and following either flaking or refining the resulting fibers or fiber bundles should be as small as possible without significant damage to the fibers. The optimum size depends upon the flaking or refining equipment employed. When chemical pretreatment is used, the vegetable fiber chips are subjected to a chemical treatment followed by a refining operation and then a water washing. The chemical pretreatment results in a yield of at least about 64 percent or greater and may be a mild prepulping by a neutral sulfite, nitric acid, kraft or other known pulping process (e.g., bisulfite, acid sulfite, cold soda, soda, sodium xylene sulfonate, polysulfide). A more preferred chemical pretreatment is a mild neutral sulfite prepulping under particular conditions of chemical concentrations; the heating and cooking cycles are carbohydrate preservation.
To demonstrate the preferred conditions of temperature and applied alkali to be used in the caustic extraction stages of the chlorine dioxide-extraction sequence, a pretreated wood such as produced in Example X was delignified using the following four-stage sequence.
First chlorine dioxide stage:
5% chlorine dioxide (wood basis), 10% consistency, one hour;
First extraction stage:
12% consistency; temperature and sodium hydroxide applied to be optimized;
Second chlorine dioxide stage:
2.5% chlorine dioxide (wood basis), 10% consistency, one hour at 65° C.;
Second extraction stage:
Same conditions as used in first extraction stage.
Water wash was employed after each of the above. The resulting pulps were analyzed for yield, G.E. brightness (TAPPI Standard T 217m-48), and screen rejects (amount retained on a 0.006-inch laboratory vibratory flat screen). The results for two extraction temperatures (20° and 65°C) and an applied alkali ranging from one to six percent (pulp basis) are shown in the drawing in FIG. 4 (yield), FIG. 5 (brightness), and FIG. 6 (rejects).
FIGS. 4 and 5 show that yield losses and brightness are relatively little affected by temperature. However, while yield loss is approximately proportional to alkali applied, there is little advantage in either brightness increase or rejects reduction in using more than about 4 percent sodium hydroxide at 12 percent consistency. Therefore, to conserve yield while achieving maximum brightness and minimum rejects, about 4 percent applied caustic is employed at 12 percent consistency. FIG. 6 clearly shows that a higher temperature (65°C) is advantageous in reducing rejects. Since this does not adversely affect yield, preferred temperature conditions for extraction are above ambient, in the vicinity of 65°C
To show the preferred range of sodium base neutral sulfite pretreatment yield, a series of sodium base neutral sulfite pretreatments was carried out. In all cases, sufficient (and constant between runs) liquid impregnation of the southern hardwood chips was allowed before the pretreatment temperature was raised to its maximum of 335° F. Following the chemical pretreatment, the hardwood materials were refined in an eight-inch laboratory disc refiner and thoroughly washed. The materials were then pulped and bleached to 80 G.E. brightness (TAPPI Standard T 217m-48) by the preferred five-stage chlorine dioxide-caustic extraction sequence, using the total amounts of chlorine dioxide corresponding to the level of pretreatment yield involved and shown in Example IX. The pretreatment yield range covered was 61 percent to 86 percent.
The yield data, strength data of standard laboratory handsheets, and some data on the degree of polymerization (D.P.) of the final bleached pulp is summarized in the following table.
| __________________________________________________________________________ |
| At 600/300 degrees Canadian |
| Neutral sulfite |
| Final Standard Freeness |
| pretreatment |
| yield, |
| yield, percent |
| percent of |
| Percent |
| Percent |
| Percent |
| of wood wood DP1 |
| tensile2 |
| burst3 |
| tear4 |
| __________________________________________________________________________ |
| 61 53 1,680 |
| 46/78 78/150 |
| --/160 |
| 62 53 50/83 98/152 |
| --/165 |
| 63 54 56/78 100/152 |
| --/174 |
| 70 57 2,000 |
| 61/85 105/160 |
| --/173 |
| 71 57 70/89 115/159 |
| ---175 |
| 86 65 2,100 |
| 55/90 96/178 |
| --/176 |
| __________________________________________________________________________ |
| 1 DP (polymerization) estimated from Cuene viscosity measurement |
| performed according to TAPPI Standard T 230 su-66 (pipet method). |
| 2 |
| Lbs. to rupture 1 inch wide strip |
| Lbs. per 3,000 sq. ft. |
| 3 |
| P.s.i. to rupture 1.2 inch disc |
| Lbs. per 3,000 sq. ft. |
| 4 |
| Grams of force to tear 137.6 cm. |
| Lbs. per 3,000 sq. ft. |
It is evident from these data that there is a trend toward increasing (all) strength properties as pretreatment yield is increased. Also, it is evident that this increase generally is most pronounced over the yield range of 61 to 70 percent, and then a reasonably constant, high strength level is maintained with further yield increases.
This same trend is borne out by the degree of polymerization (DP) data. As bleached yield decreases (other things remaining constant), a pulp contains less low-DP hemicellulose and (proportionately) more high-DP cellulose. Therefore, if there were no undesirable chemical degradation occurring, a steady increase in DP would be expected as pretreatment yield decreases. Actually, just the opposite occurs, showing that the chemical pretreatment (particularly in the pretreatment yield range below 70%) is having a chemically degrading effect on the retained pulp carbohydrates.
From both the test results and the measurements of pulp DP or molecular length, it is apprent that maximum pulp strengths are favored at higher chemical pretreatment yields. Further, this effect is most pronounced at the low end of the pretreatment yield scale, and suggests that the preferred conditions would involve pretreatment yields above approximately 64 percent.
An upper limit on pretreatment yield is fixed by considering the pretreatment yield-final bleached yield-chlorine dioxide consumption relationships. FIG. 8 shows the pretreatment yield-chlorine dioxide consumption relationship for neutral sulfite pretreatment, with the no-chemical pretreatment point corresponding to 100 percent pretreatment yield. In reality, the neutral sulfite line is followed until a pretreatment yield of 95 percent is approached; at this point the consumption rises rapidly from this line and passes through the no-chemical pretreatment point. Thus, at pretreatment yields above 95 percent, a disproportionately large amount of chlorine dioxide is consumed. This is, of course, very undesirable.
FIG. 7 shows a parallel behavior for bleached yields. At pretreatment yields above about 95 percent, the bleached yield actually decreases to the point corresponding to mechanical pretreatment only. Since maximum yield is desirable, this decrease is undesirable.
Further reason for maintaining pretreatment yield below 95 percent is found in Example IX, in which it is shown that 100 percent pretreatment yield produces inferior paper strength properties as compared with papers in the below 95 percent pretreatment yield range.
To demonstrate the preferred conditions for the sodium base neutral sulfite pretreatment, it is shown below that proper pretreatment liquor impregnation of the chips prior to heating is necessary to maximize handsheet strength and minimize fiber bundle or shive content. It is also shown that proper ratio of pretreatment chemicals is necessary to provide maximum strength and ease of pulping and bleaching with the subsequent chlorine dioxide-caustic sequence.
Runs were made using two extremes of liquor impregnation prior to chemical pretreatment, and with a range of ratios of sodium sulfite to sodium carbonate in the pretreatment liquor. In all cases sufficient pretreatment chemical was applied so that the final liquor pH was above 7. If allowed to drop below this value, a weak pulp resulted. The raw material was a southern hardwood chip mixture. Following chemical pretreatment, the materials produced were refined under constant conditions in a laboratory eight-inch disc refiner, thoroughly water washed, and subjected to the five-stage chlorine dioxide-caustic sequence for pulping and bleaching to 80 G.E. brightness (TAPPI Standard T 217m-48). The total chlorine dioxide required to achieve this brightness was determined together with standard handsheet physical tests on the bleached pulp.
The critical experimental conditions, together with the indicated results, are shown below. Runs 1 and 2, at equal pretreatment yield, show the effect of variations in applied chemicals.
| __________________________________________________________________________ |
| Pretreatment liquor Percent |
| Percent |
| Percent |
| Sodium chlorine |
| Std. |
| Pretreatment sodium |
| sodium |
| sulfite/ dioxide |
| percent |
| Handsheet properties at |
| 600° |
| impreg. time |
| Max. pre- |
| sulfite |
| carbonate |
| sodium |
| Pre- required |
| chlorine |
| CSF/300°CSF5 |
| before max. |
| treatment |
| wood |
| wood carbonate |
| treatment |
| wood dioxide |
| Tensile,2 |
| Burst,3 |
| Tear,4 |
| Run |
| temp., min. |
| temp., °F. |
| basis |
| basis |
| ratio yield basis |
| required1 |
| percent |
| percent |
| percent |
| __________________________________________________________________________ |
| 1 120 335 24 5 4.8 74 6.0 6.2 56/76 89/133 |
| 175/136 |
| 2 120 335 12 10 1.2 73 6.3 6.0 55/82 93/165 |
| 208/152 |
| 3 120 335 12 10 1.2 86 8.0 8.5 55/90 96/178 |
| 208/176 |
| 4 120 335 9 9 1.0 84 10.1 8.1 49/71 78/132 |
| 156/128 |
| 5 30 345 14.2 |
| 5.2 2.7 85 8.3 8.3 35/74 62/135 |
| 210/175 |
| __________________________________________________________________________ |
| 1 Values taken from the chlorine dioxide consumption-pretreatment |
| yield curve, Example IX, FIG. 8. |
| 2 TAPPI Standard T404 ts-66.? |
| 3 TAPPI Standard T403 ts-63.? |
| 4 TAPPI Standard T414 ts-65. |
| 5 Canadian Standard Freeness, TAPPI Standard T227 m-58. |
While pulping chemical (chlorine dioxide) consumption is constant, a significant increase in pulp handsheet strengths results when the sulfite/carbonate ratio is reduced from about five to slightly more than one.
Runs 3 and 4 show the effect of still further reduction in this base ratio from 1.2 to 1∅ A very significant decrease in pulp handsheet strengths results, along with a large increase (about 25 percent based on the normal chemical application) in chlorine dioxide consumption. Thus, while optimum conditions exist at a sulfite/carbonate ratio of slightly above unit, it is critical that this ratio not be allowed to drop below about 1.2 because of detrimental effects on both pulp physical properties and pulping chemical consumption.
Runs 1, 3 and 5 show the importance of adequate pretreatment liquor impregnation of the chipped raw material. Since the chemical ratio of Run 5 is intermediate between those of Runs 1 and 3, the observed marked decrease in handsheet physical properties is attributable to the lack of adequate chip impregnation. Optimum impregnation conditions depend upon the type (wood species) and chip dimensions of the raw material. Sufficient pretreatment chemical must be added to maintain the pH at 7 or above during the pretreatment.
The ratio of sodium sulfite to sodium carbonate applied should be held in the vicinity of about 1.5 for highest pulp strength. Higher values result in reduced strengths; values below about 1.2 give weaker pulps and increased pulping chemical (chlorine dioxide) consumption.
Adequate pretreatment liquor penetration into the raw material must be achieved, or strength properties suffer and shive content increases. Optimum conditions depend upon raw material structure and particle dimensions.
To demonstrate the extent to which chlorine can be substituted for chlorine dioxide in the present pulping-bleaching sequence, and because of potential economics, the desirabilty of substituting other selective delignifying agents for at least a portion of this chlorine dioxide was investigated.
In general, with equivalent additions of bleaching chemicals, a higher bleached brightness is obtained using mixtures than with either chlorine or chlorine dioxide alone when bleaching kraft pulps. However, since the starting material with a bleachable kraft pulp is much different from the neutral sulfite-pretreated material presently under consideration, and since the desired action with chlorine and chlorine dioxide additions to conventional kraft pulp is largely one of bleaching (initial pulp lignin contents of perhaps two percent), while the chlorine dioxide in the present case is used to remove a large quantity of chemically different lignin (pretreated pulp lignin content approximately fifteen percent) as well as to bleach, prior art results are not directly translatable to the present invention.
Since some systems for chlorine dioxide generation result in the simultaneous generation of chlorine, and since efficient use of this chlorine is essential to sound chlorine dioxide generation economics, runs were made to determine the feasibility of substituting chlorine for chlorine dioxide at various points in the pulping sequence. Sodium base neutral sulfite pretreated southern hardwood chips were mechanically refined in a laboratory disc refiner and thoroughly water washed prior to the pulping-bleaching sequence. In one run all chlorine was substituted for the normally used chlorine dioxide. The chemical application and results in terms of pulp pentosan content, brightness, screen rejects (amount retained on a laboratory vibratory flat screen using a 0.008-inch cut screen) and handsheet brightness are summarized below:
| __________________________________________________________________________ |
| Pulping |
| chemical |
| Neutral applied, |
| sulfite percent (wood |
| pretreat- basis) Final pulp |
| ment Pulping |
| equivalent |
| G.E. Final pulp |
| Final pulp |
| Screening |
| yield, |
| sequence |
| chlorine |
| bright- |
| pentosans,3 |
| viscosity,4 |
| rejects, |
| Case |
| percent |
| used1 |
| dioxide ness2 |
| percent |
| DP percent |
| __________________________________________________________________________ |
| 1 88 DEDED 8.8 86 19.8 2,310 0.4 |
| 2 88 CECEC 8.8 69 8.1 1,290 25 |
| __________________________________________________________________________ |
| 1 D=chlorine dioxide, C=chlorine, E=caustic extraction. |
| 2 TAPPI Standard T217 m-48. |
| 3 Measure of amount of hemicellulose, TAPPI Standard T19 m-50. |
| 4 TAPPI Standard T230 su-66: DP is degree of polymerization. |
It is apparent from the extremely low brightness, low pentosan content, low DP, and high screen rejects that chlorine cannot be substituted for all chlorine dioxide.
Next a series of runs was conducted in which all and half of the chlorine dioxide normally applied in the first stage (equivalent oxidizing basis) was substituted by chlorine. The raw material again was a neutral sulfite pretreated southern hardwood chip mixture, mechanically refined in an eight-inch laboratory disc refiner; the pretreatment yield was 85 percent. The conditions employed, together with the brightness and strength results of handsheets prepared from the final pulps, are shown below:
| __________________________________________________________________________ |
| First First stage |
| stage all |
| 1/2 chlorine |
| First |
| chlorine |
| plus 1/2 chlo- |
| stage all |
| dioxide |
| rine dioxide |
| chlorine |
| __________________________________________________________________________ |
| Percent chlorine dioxide in 1st stage |
| (wood basis) 4.7 2.35 0 |
| Percent chlorine in 1st stage (wood |
| basis) 0 6.15 12.3 |
| Percent sodium hydroxide in each of |
| the 1st and 2d extraction stages |
| 8 8 8 |
| Percent chlorine dioxide in 2d chlorine |
| dioxide stage (wood basis) |
| 2.4 2.4 2.4 |
| Percent chlorine dioxide in 3d chlorine |
| dioxide stage (wood basis) |
| 1.2 1.2 1.2 |
| G.E. bleached brightness1 |
| 80.6 78.5 66.2 |
| Shives No No Yes |
| Percent tensile strength2 : |
| 600°C.S.F.4 59 59 43 |
| 300°C.S.F. 85 78 69 |
| Percent bursting strength3 : |
| 600°C.S.F. 102 102 58 |
| 300°C.S.F. 148 148 128 |
| __________________________________________________________________________ |
| 1 TAPPI Standard T217 m-48. |
| 2 TAPPI Standard T404 ts-66. |
| 3 TAPPI Standard T403 ts-63. |
| 4 TAPPI Standard T227 m-58. |
From the above results it was concluded that there is to synergistic effect of chlorine-chlorine dioxide mixtures, as has been reported in the art for such mixtures when bleaching kraft pulps; brightness is somewhat lowered by 50 percent chlorine substitution (oxidizing equivalent basis), and is very significantly harmed by use of all chlorine in the first stage of the pulping sequence; substitution of all chlorine in the first stage results in unbleached, undefibered shives or fiber bundles; and strength properties are not greatly affected by the half-substitution case, but are very significantly reduced when all chlorine is used in the first stage.
While the use of chlorine in any proportion in the present invention offers no advantages in terms of pulp quality, certain amounts of chlorine can be used in the initial chlorine dioxide stage without adverse effects. The upper limit to chlorine substitution is about 25 to 30 percent of the total chlorine dioxide requirement on an equivalent oxidant basis; this maximum corresponds to a weight proportion of about 50 percent chlorine and 50 percent chlorine dioxide.
To demonstrate the advantages of using sodium base neutral sulfite (sodium sulfite and sodium carbonate) chemical pretreatment in preference to either nitric acid or ammonia base neutral sulfite, these three pretreatment combinations were evaluated.
The three chemical-mechanical pretreatments were achieved using the chemical conditions shown below using mixed southern hardwood chips as raw material. In all cases, the chemical pretreatment was followed by refining in a laboratory eight-inch disc refiner, thorough washing, and pulping and bleaching using the chlorine dioxide-caustic-chlorine dioxide-caustic-chlorine dioxide treatment sequence. Conditions and results are in the table below.
It is apparent that nitric acid pretreatment results in both lower bleached yield and lower handsheet strength, indicating excessive carbohydrate degradation during this pretreatment. Sodium base neutral sulfite produces a stronger pulp than ammonia base pretreatment. Also, with the ammonia base pretreatment it is more difficult to delignify and bleach, and the pulp contains somewhat more shives and fiber bundles.
From this comparison, it is apparent that either of the neutral sulfite bases gives a better pretreatment than does nitric acid. Also, sodium base is superior to ammonia base neutral sulfite, other factors not considered. The ammonia base does give a very acceptable, high yield bleached pulp, and where factors such as pollution considerations are controlling, the ammonia base is exceptionally attractive.
| __________________________________________________________________________ |
| Sulfite, |
| Carbonate, Percent |
| percent |
| percent chlorine At 300° Canadian |
| 1 |
| equivalent |
| equivalent |
| Percent |
| Pre- Standard |
| Freeness5 |
| sodium |
| sodium |
| nitric |
| treatment |
| dioxide |
| Bleached |
| G.E. |
| sulfite |
| carbonate |
| acid yield, |
| (wood |
| yield, |
| bright- |
| Tensile,3 |
| Burst,4 |
| Tear,5 |
| Pretreatment Chemical1 |
| (on wood) |
| (on wood) |
| (on wood) |
| percent |
| basis) |
| percent |
| ness2 |
| percent |
| percent |
| percent |
| __________________________________________________________________________ |
| Sodium base neutral |
| sulfite 12 10 -- 73 6.0 58 80 82 152 165 |
| Ammonia base neutral |
| sulfite 13.2 11.1 -- 72 6.0 58 80 73 143 148 |
| Nitric acid 25 73 6.1 54 80 70 121 112 |
| __________________________________________________________________________ |
| 1 The neutral sulfite pretreatment cycle for both sodium and ammonia |
| base involved 30 min. to and 60 min. at 273°F. plus 30 min. to and |
| 120 min. at 335°F. |
| 2 TAPPI Standard T217 m-48. |
| 3 TAPPI Standard T404 ts-66. |
| 4 TAPPI Standard T403 ts-63. |
| 5 TAPPI Standard T414 ts-65. |
| 6 TAPPI Standard T227 m-58. |
To demonstrate the advantages of using a neutral sulfite pretreatment in preference to a high-yield kraft pretreatment or an entirely mechanical pretreatment, the following runs were made.
The raw material was a mixture of southern hardwood chips (approximately one-third oak, one-third yellow poplar, and one-third gum). In the case of the chemical pretreatments (kraft and neutral sulfite), sufficient time for liquor impregnation was allowed prior to heating to maximum temperature. The chemically pretreated material (and the hardwood chips following presteaming in the case of mechanical pretreatment only) was then refined in an eight-inch laboratory disc refiner to give a starting material for the chlorine dioxide pulping/bleaching sequence. Pretreatment was analyzed through the following: ##EQU2##
Selectivity of various chemical pretreatment yields was determined as follows:
| Pretreatment |
| S (pretreat- |
| Pretreatment yield ment only) |
| ______________________________________ |
| 60 0.38 |
| Sodium base neutral sulfite |
| 70 0.43 |
| 80 0.47 |
| 90 0.52 |
| 60 0.39 |
| Kraft 70 0.32 |
| 80 0.24 |
| ______________________________________ |
The above table shows that, for a high-yield pulping process, the neutral sulfite pretreatment offers the greatest selectivity and therefore the greatest potential for final bleached or semibleached pulp yield. As the pretreatment yield approaches that normally achieved during the pulping portion of a pulp-bleach sequence, the selectivities approach each other.
By pulping and bleaching this pretreated material to 80 G.E. brightness (TAPPI Standard T217m-48) using the chlorine dioxide-caustic-chlorine dioxide-caustic-chlorine dioxide treatment sequence, the selectivities shown below are obtained:
| ______________________________________ |
| Final |
| bleached Overall |
| yield, selec- |
| Pretreatment percent tivity, S |
| ______________________________________ |
| 50 0.46 |
| Sodium base neutral sulfite |
| 55 0.53 |
| 60 0.61 |
| 65 0.69 |
| 50 0.53 |
| 55 0.54 |
| Kraft 60 0.56 |
| 65 0.58 |
| Mechanical only 63 0.64 |
| ______________________________________ |
Again, it is apparent that at the higher bleached yields (above 55 percent), the neutral sulfite pretreatment is more selective than kraft.
Since the chlorine dioxide pulping sequence itself is quite selective, use of a mechanical pretreatment only, followed by the chlorine dioxide sequence, might be expected to give a very high selectivity value. However, the data show that a high-yield neutral sulfite pretreatment followed by the chlorine dioxide sequence is more selective than the no-pretreatment case.
These results are shown graphically in FIG. 7. For any given pretreatment yield, the neutral sulfite pretreatment gives a significantly higher final bleached yield, indicating its increased selectivity. The mechanically pretreated case (shown at 100 percent pretreatment yield) lies far below the extrapolated chemical pretreatment cases, indicating the relatively low degree of selectivity achieved.
The relatively lower selectivity of kraft pretreatment suggests more lignin remaining at any given pretreatment yield, and therefore a higher pulping chemical (chlorine dioxide) requirement. The table below shows this to be true. Thus, neutral sulfite pretreatment gives a higher bleached yield and lower chlorine dioxide consumption than does kraft pretreatment; chlorine dioxide savings up to 24 percent are possible at higher pretreatment yields.
| ______________________________________ |
| Chlorine |
| Pretreat- dioxide |
| ment consumption Chlorine |
| yield, (percent of dioxide |
| Pretreatment |
| percent wood) savings1 |
| ______________________________________ |
| Kraft 50 1.8 |
| Neutral sulfite |
| 50 1.7 6 |
| Kraft 60 4.2 17 |
| Neutral sulfite |
| 60 3.6 |
| Kraft 70 6.6 20 |
| Neutral sulfite |
| 70 5.5 |
| Kraft 80 9.0 23 |
| Neutral sulfite |
| 80 7.3 |
| Kraft 90 11.4 24 |
| Neutral sulfite |
| 90 9.2 |
| Mechanical only |
| 100 14.0 -- |
| ______________________________________ |
| 1 Neutral sulfite vs. kraft (percent of neutral sulfite-chlorine |
| dioxide requirement). |
These results, as well as the relatively high consumption of chlorine dioxide by the mechanical pretreatment case, are also shown graphically by FIG. 8 of the drawings.
From these comparisons, it is clear that the sodium base neutral sulfite pretreatment gives higher bleached yield and lower pulping chemical (chlorine dioxide) cost than does kraft. Also, pure mechanical pretreatment yields higher chlorine dioxide consumption and lower yield than extrapolated neutral sulfite data. From yield and chemical economy standpoints, neutral sulfite is preferred over these two alternates.
For consideration of the resultant plup properties, as measured by physical properties of standard handsheets, the table below shows the standard strength properties for neutral sulfite, kraft and mechanically pretreated cases, each pulping and bleaching using the chlorine dioxide-extraction five-stage sequence:
| ______________________________________ |
| Pretreat- |
| Values at 600/300 Canadian |
| ment Standard Freeness5 |
| yield, |
| percent of |
| Tensile, Burst, Tear, |
| Pretreatment |
| wood1 |
| percent2 |
| percent3 |
| percent4 |
| ______________________________________ |
| Sodium base neutral |
| sulfite 85 54/91 96/179 207/180 |
| Kraft 86 43/81 83/180 180/165 |
| Mechanical only |
| 100 55/72 90/133 165/134 |
| ______________________________________ |
| 1 Southern hardwood chips.? |
| 2 TAPPI Standard T404 ts-66. |
| 3 TAPPI Standard T403 ts-63. |
| 4 TAPPI Standard T414 ts-65. |
| 5 TAPPI Standard T227 m-58. |
It is apparent that the kraft pretreatment results in lower tensile and tear than neutral sulfite pretreatment, and that the mechanical pretreatment is also inferior in strength.
Overall, it can be concluded that the sodium base neutral sulfite pretreatment is preferred over either high-yield kraft or mechanical pretreatment, since it results in higher final bleached yield, lower chlorine dioxide consumption, and higher pulp handsheet strengths.
To demonstrate the uniqueness of the sodium base neutral sulfite pretreatment-chlorine dioxide pulping sequence compared to conventional bleaching of neutral sulfite pulps, the strength properties of paper prepared from southern hardwood chips via the process of the present invention were compared with the properties of a bleached pulp prepared by a conventional neutral sulfite pulping step followed by a conventional bleaching sequence of chlorination-caustic extraction-hydrochlorite bleaching, the latter case being typical of present state of the art bleached neutral sulfite pulps. The differences obtained were as follows:
| __________________________________________________________________________ |
| Neutral |
| Conven- |
| sulfite pre- |
| tional |
| treatment- |
| bleached |
| chlorine |
| hardwood |
| dioxide Percent |
| neutral |
| pulping improve- |
| sulfite |
| case ment |
| __________________________________________________________________________ |
| Neutral sulfite (pretreatment |
| yield, percent of wood) |
| ∼60 |
| 80 |
| Final bleached yield, percent of |
| wood 52 62 19 |
| At 300 Canadian Standard |
| Freeness6 |
| Tensile strength, kilometers2 |
| 7.2 9.1 38 |
| Burst, percent3 |
| 98 137 40 |
| Tear, percent4 |
| 110 125 14 |
| M.I.T. fold5 |
| 120 880 630 |
| __________________________________________________________________________ |
| 1 Improvement calculated relative to the conventional case. |
| 2 TAPPI Standard T404 ts-66. |
| 3 TAPPI Standard T403 ts-63. |
| 4 TAPPI Standard T414 ts-65. |
| 5 TAPPI Standard T511. |
| 6 TAPPI Standard T227 m-58. |
From these comparisons, it is very apparent that the present invention produces a pulp of much higher yield, while at the same time giving paper of much higher physical strengths. The difference in folding endurance is particularly noteworthy, since this is the most important paper physical property of most book and publication papers.
To demonstrate the superiority of the sodium base neutral sulfite-chlorine dioxide sequence relative to conventionally bleached kraft pulps, the below tests were conducted. Previous examples have demonstrated the superiority of the product of the sodium base neutral sulfite-chlorine dioxide process relative to conventionally bleached neutral sulfite as well as relative to pretreatment-chlorine dioxide sequence pulps in which the pretreatment is any of the following: mechanical, ammonia-base neutral sulfite, high-yield kraft, and nitric acid.
Using a constant raw material source of mixed southern hardwood chips, pulp samples were prepared using two processes: the sodium base neutral sulfite pretreatment-chlorine dioxide pulping sequence of the present invention and a conventionally pulped and bleached kraft pulp. These pulps were refined to 300 degrees Canadian Standard Freeness (TAPPI Standard T227 m-58) and formed into paper on a small twelve-inch paper machine, so that the results would be more indicative of the properties of machine-made papers. The physical and surface smoothness properties of these two papers are compared in the following tables:
| ______________________________________ |
| Neutral |
| Conven- sulfite- |
| tional chlorine |
| bleached dioxide |
| Physical property tested |
| kraft pulp |
| pulp |
| ______________________________________ |
| Burst, percent1 43.8 91.6 |
| Tear, percent2 MD/CD3 |
| 86/104 124/197 |
| Tensile, percent4 MD/CD |
| 33/14 93/35 |
| Stretch, percent5 MD/CD |
| 1.5/2.6 2.1/3.4 |
| Tensile energy absorption,6 MD/CD |
| 1.65/1.52 4.73/3.56 |
| Fold (M.I.T.),7 MD/CD |
| 27/6 1,019/92 |
| Wax pick, felt/wire8 |
| 6/2 13/6 |
| ______________________________________ |
| 1 TAPPI Standard T403 ts-63. |
| 2 TAPPI Standard T414 ts-65. |
| 3 MD and CD refer to machine direction and cross-machine direction |
| set properties. |
| 4 TAPPI Standard T404 ts-66. |
| 5 TAPPI Standard T457 m-46. |
| 6 TAPPI Standard T494 su-64. |
| 7 TAPPI Standard T-511. |
| 8 TAPPI Standard T-459 su-65. |
| ______________________________________ |
| Gurley2 |
| Bekk3 |
| Sheffield4 |
| Pulp1 porosity smoothness |
| smoothness |
| ______________________________________ |
| Conv. bleached kraft pulp |
| 5 17 276 |
| Neutral sulfite-chlorine |
| dioxide pulp 15 50 194 |
| ______________________________________ |
| 1 Both pulps from the same hardwood mixture. |
| 2 Gurley porosity is the time interval required to pass a constant |
| volume of air through the sheet, thus high values indicate low porosity. |
| 3 Bekk smoothness is the time required to leak a constant volume of |
| air between the sheet and a polished glass surface, thus higher values |
| indicate greater sheet smoothness. |
| 4 Sheffield smoothness is the rate at which air leaks between two |
| rings which are in contact with the sheet. Thus, high values indicate low |
| smoothness. |
It is apparent that the paper made from the neutral sulfite-chlorine dioxide process is greatly superior in the physical properties of burst, tear, tensile, stretch, and M.I.T. fold. The wax pick test shows the new pulp to be very superior in internal bond strength, a property of great importance for papers which are to be printed. The smoothness measurements show the new pulp to be of greater smoothness, which is advantageous for printing papers and various other applications.
The superiority of the new pulp in terms of both handsheet tensile and tear suggests that the new process gives a pulp of very superior fiber strength; if bonding alone were involved, a high tensile would result in a low tear and vice versa. To confirm the superiority of fiber strength, zero-span tensile tests were run on handsheets prepared from the two pulps. These results are shown below:
| Zero-span |
| Pulp: value, percent1 |
| ______________________________________ |
| Conventional bleached kraft |
| 89 |
| Neutral sulfite-chlorine dioxide |
| 150 |
| ______________________________________ |
TAPPI Standard T231 sm-60. Values expressed as percent calculated as: ##EQU3##
Since this test, run on standard sheets of constant basis weight, gives a direct means of comparing fiber strengths, it is concluded that a very unique fiber, having a strength per unit fiber mass of over sixty percent greater than that of a conventionally prepared fiber, is produced by the pulping process of the present invention.
To demonstrate that, in addition to the superior properties of the pulp of the present invention when made into laboratory handsheets or paper on a paper machine, the pulp exhibits certain unique properties related to its processing before and during the papermaking operation, such as great ease of refining, increased ease of drainage during paper formation, ability to retain fillers more efficiently, superior wet web strength on the paper machine, and increased ease of paper machine drying, the following comparisons were made.
The ease of refining is shown by the data in the table below, as well as in FIG. 9. A comparison is made of the response of pulps to refining in a standard TAPPI beating test. Neutral sulfite-chlorine dioxide pulps are compared to conventional bleached kraft, in one case with the pulps prepared from a southern hardwood chip mixture and in the second case using northern hardwood chips. The slopes of the curves in FIG. 9 indicate that the relative beating rate, new pulp versus kraft, is 3.0 for pulps from the southern woods and 4.2 for pulps from the northern woods. Since the time required to beat a pulp under these standard conditions is directly proportional to the energy required to refine to any given degree, it is apparent that refining energy requirement for the new pulp is only 1/3 to 1/4 that required with kraft.
| ______________________________________ |
| Beating Freeness, |
| time, ml. |
| Wood Process min.1 |
| (C.S.F.)2 |
| ______________________________________ |
| Southern hard- |
| Conventionally bleached |
| 0 650 |
| woods. kraft. |
| Do. Neutral sulfite-chlorine |
| 0 740 |
| dioxide sequence. |
| Do. Conventionally bleached |
| 14 600 |
| kraft. |
| Do. Neutral sulfite-chlorine |
| 8 600 |
| dioxide sequence. |
| Do. Conventionally bleached |
| 25 500 |
| kraft. |
| Do. Neutral sulfite-chlorine |
| 11 500 |
| dioxide sequence. |
| Do. Conventionally bleached |
| 34 400 |
| kraft. |
| Do. Neutral sulfite-chlorine |
| 14 400 |
| dioxide sequence. |
| Do. Conventionally bleached |
| 41 300 |
| kraft. |
| Do. Neutral sulfite-chlorine |
| 15 300 |
| dioxide sequence. |
| Northern hard- |
| Conventionally bleached |
| 0 600 |
| woods. kraft. |
| Do. Neutral sulfite-chlorine |
| 0 600 |
| dioxide sequence. |
| Do. Conventionally bleached |
| 0 600 |
| kraft. |
| Do. Neutral sulfite-chlorine |
| 5 600 |
| dioxide sequence. |
| Do. Conventionally bleached |
| 36 500 |
| kraft. |
| Do. Neutral sulfite-chlorine |
| 10 500 |
| dioxide sequence. |
| Do. Conventionally bleached |
| 59 400 |
| kraft. |
| Do. Neutral sulfite-chlorine |
| 14 400 |
| dioxide sequence. |
| Do. Conventionally bleached |
| 80 300 |
| kraft. |
| Do. Neutral sulfite-chlorine |
| 18 300 |
| dioxide sequence. |
| ______________________________________ |
| 1 Beaten in Vally Beater according to TAPPI Standard T200 ts-66. |
| 2 TAPPI Standard T 227 m-58. |
When making small scale paper machine trials, it was observed that, at a constant freeness of 300 degrees Canadian Standard, only one-half as much vacuum applied to the drainage area of the paper machine wire was required to drain the free water from the neutral sulfite-chlorine dioxide pulp as was required with the corresponding bleached kraft pulp (when in both cases the drainage was forced to occur over a constant distance on the paper machine wire). This illustrates the potential for increased machine speeds with the new pulp.
During these same paper machine trails, filler wa was added to the fiber furnish and the retention of this filler during the sheet forming process was measured. These results, shown below, illustrate the very marked superior retention exhibited by the new pulp compared to conventional bleached kraft. Actually, the effect is even more dramatic than the percent retention numbers indicate, since fifty percent more filler was added in the case of the new pulp. It is well known that percent retention decreases as the applied amount of filler increases, other factors remaining constant.
| __________________________________________________________________________ |
| Filler, percent applied |
| Percent of the filler applied |
| (pulp basis) which was retained |
| Titanium Titanium |
| Pulp Clay |
| dioxide |
| Total |
| Clay |
| dioxide Total |
| __________________________________________________________________________ |
| Conventional bleached kraft |
| 32 8.0 40 8.7 9.6 8.8 |
| Neutral sulfite-chlorine dioxide |
| 43 12 60 19 28 21 |
| __________________________________________________________________________ |
When the wet sheet is lifted from the paper machine wire and passes to the first press, there is a danger of the sheet rupturing while in a wet, tender condition. This tendency for breaks is controlled by the wet web strength of the sheet. On the small paper machine trials, with the machine running under identical conditions, it was observed that the kraft sheet was very prone to frequent breaks, while the new pulp sheet ran trouble free. While these results are not quantitive, they do show the superior wet web strength possessed by this new pulp.
During these same paper machine trials, and with the machine operating at a constant speed, it was observed that only one-half as great a temperature differential was required in the drier section to dry the new pulp sheet as was required with conventional kraft. In other words, the new pulp sheet possessed double the drying rate of the conventional kraft.
The ease of refining, coupled with more rapid drainage, higher wet web strength and ease of drying, all indicate the ability to increase paper production relative to that obtainable with conventional pulp. The greatly increased filler retention characteristics also leads to significantly improved economics, especialy in the case of highly filled sheets.
To demonstrate the chemical uniqueness of the pulp, comparisons of the degree of polymerization and hemicellulose content of various pulps from the same wood mixture were made as follows:
| __________________________________________________________________________ |
| Hemi- |
| Final |
| cellulose, |
| bleached |
| percent |
| Degree of |
| yield, |
| (wood polymeri- |
| Pulping process percent |
| basis) |
| zation |
| __________________________________________________________________________ |
| Conventional kraft-conventional |
| bleach 42.3 7.1 650 |
| Neutral sulfite-chlorine dioxide se- |
| quence 53.0 9.6 1,770 |
| Do. 57.3 10.7 2,000 |
| Do. 65.3 12.9 2,100 |
| __________________________________________________________________________ |
The carboxyl content of the neutral sulfite-chlorine dioxide sequence pulp is at least twice as great as the carboxyl content of conventionally bleached pulps. At the same time, the carbonyl content is only 1/2 to 1/3 as great as the carbonyl content of conventionally bleached pulp from the same wood. The neutral sulfite pretreatment portion of the sequence is necessary to keep the carbonyl content low as is seen by comparison of the data for pulps with and without the neutral sulfite pretreatment.
| ______________________________________ |
| Carbonyl Carboxyl |
| Pulping process number1 |
| number2 |
| ______________________________________ |
| Conventional bleached kraft |
| 0.67 4.9 |
| Mechanical pretreatment-chlorine |
| dioxide sequence 1.2 18.8 |
| Neutral sulfite-chlorine dioxide |
| 0.24 14.2 |
| sequence |
| ______________________________________ |
| 1 TAPPI Standard T215 m-50 |
| 2 TAPPI Standard T237 su-63 |
to demonstrate the effort of pulp chemical properties on brightness stability and ion exchange capacity, two chlorine dioxide-sequence pulps are compared to conventional bleached kraft in the table below. In all cases the raw material was a mixture of sourthern hardwoods. It is apparent that the pulps rank: neutral sulfite> mechanical pretreatment>chlorine dioxide>conventional kraft in terms of brightness stability with kraft being poorest even though it is of intermediate carbonyl content (high percent reversion or high post color number indicates low brightness stability).
| __________________________________________________________________________ |
| Aged2 |
| Rever- |
| Post |
| Original1 |
| bright- |
| sion,3 |
| color |
| Pulp identification |
| brightness |
| ness percent |
| number4 |
| __________________________________________________________________________ |
| Conventionally bleached |
| kraft 79.8 74.9 6.1 1.6 4.1 |
| Mechanical pretreatment |
| chlorine dioxide sequence |
| 80.8 77.4 4.2 2.7 |
| Neutral sulfite-chlorine |
| dioxide sequence |
| 80.5 78.6 2.4 .[∅55 1.5 |
| __________________________________________________________________________ |
| 1 Brightness before aging, percent General Electric, TAPPI Standard |
| T217 m-48. |
| 2 Brightness after aging for 4 hours at 105°. |
| 3 Reversion, percent defined as: |
| Brightness before- brightness after |
| 100 × |
| Brightness before |
| 4 Post color number, defined as: |
| 100-percent brightness |
| 100-percent brightness |
| after aging before aging |
| 100 × - |
| 2×(percent brightness |
| 2×(percent brightness |
| after aging) before aging) |
The carboxyl content of the chlorine dioxide sequence pulp is so high that it can behave as an ion exchange material. If this pulp is treated with a salt solution, the resulting pulp will retain the metal atoms. This results in higher ash content and many unique chemical properties. Brightness and opacity as well as brightness stability are strongly affected by the nature of the cation bound to the pulp. The table below shows the effects of trace amounts of zinc, sodium, aluminum, and potassium ions on pulp optical properties. It is apparent that significant changes result, which do not occur when conventional kraft pulp is subjected to similar treatments.
| __________________________________________________________________________ |
| Percent |
| Percent |
| change in |
| change |
| Pulp Cation1 |
| brightness2 |
| in opacity3 |
| __________________________________________________________________________ |
| Kraft conventional bleach |
| Zinc +1 +3 |
| Neutral sulfite-chlorine dioxide |
| do. +2 +14 |
| Kraft conventional bleach |
| Sodium |
| -1 0 |
| Neutral sulfite-chlorine dioxide |
| do. +3 +14 |
| Kraft conventional bleach |
| Aluminum |
| 0 0 |
| Neutral sulfite-chlorine dioxide |
| do. +4.0 +20 |
| Kraft conventional bleach |
| Potassium |
| +1 0 |
| Neutral sulfite-chlorine dioxide |
| do. +5 +9 |
| __________________________________________________________________________ |
| 1 These cations were removed from dilute salt solutions by the ion |
| exchange phenomena of the pulp. |
| 2 TAPPI Standard T217 m-48. |
| 3 TAPPI Standard T425 m-60. |
To demonstrate the durability of the neutral sulfite-chlorine dioxide pulp, fold tests were run on four cation treated neutral sulfite-chlorine dioxide pulps after zero, one, two, three, and seven days of aging at 105°C The results were compared to typical book paper and to a special alkaline treated softwood paper.
It was found that hand sheets made of the neutral sulfite-chlorine dioxide pulp that had been treated with either sodium, lead, or no cations were very durable. Handsheets made from pulp of the present invention treated with alum were less durable although they were more durable that typical rosin alum sized book paper.
The pulp used was produced from a southern hardwood species mixture. The wood mixture was given a neutral sulfite cook, and refined in a high pressure refiner for a 85.5 percent yield. The pulp was then washed and bleached by a five-stage chlorine dioxide-extraction sequence. All chlorine dioxide stages were conducted with gaseous chlorine dioxide. The pulp was tumbled in a 3 gallon polyethylene reactor during the reaction period. A total of 8.4 percent chlorine dioxide (wood basis) was consumed by the pulp. All chlorine dioxide stages were conducted at room temperature without addition of buffer.
The processed pulp was beaten 11 minutes to 300 ml. Canadian Standard Freeness (TAPPI Standard T227 m-58) in a Valley beater. Three cation treated series of handsheets were made and one series was made with just distilled water. The treated handsheets were made by applying 1.2 gram of the salt or base of interest to a slurry containing 12 grams of pulp (oven dry basis). Sufficient slurry was then added to the handsheet mold (using distilled water) to make a standard 1.2 gram handsheet. Cations selected were sodium in the form of sodium hydroxide, lead in the form of lead acetate, aluminum in the form of aluminum sulfate, and the control which was made from distilled water.
Pairs of handsheets from the four groups were aged at 105°C for zero days, one day, two days, three days and seven days. Each handsheet was then cut into four strips and tested to failure in the Schopper fold tester. All strips were, of course, conditioned in the test laboratory prior to testing. The data obtained is presented in the table below and in FIG. 10.
| ______________________________________ |
| Schopper fold values |
| Chemical treatment |
| No |
| Aging, days at |
| chemical Sodium Lead Aluminum |
| 105°C. |
| treatment hydroxide acetate |
| sulfate |
| ______________________________________ |
| Zero 864 643 557 |
| One 675 779 593 391 |
| Two 659 713 505 1 685 |
| Three 535 1 988 |
| 507 128 |
| Seven 406 492 401 89 |
| ______________________________________ |
| 1 These values out of line with other values. |
FIG. 11 develops the relationship between M.I.T. and Schopper folds, based on data on pulp of the present invention tested according to both methods.
From FIG. 12 of the drawings it is evident that typical book paper which has been treated with alum degrades most rapidly. Neutral sulfite-chlorine dioxide pulp which has been exchanged with aluminum ions from alum degrades less rapidly. The neutral sulfite-chlorine dioxide pulp which has been exchanged with sodium is very resistant to fold loss. The last curve represents the behavior of a special long fiber softwood pulp treated with alkali to develope its high degree of permanence. The neutral sulfite-chlorine dioxide pulp with sodium treatment (or no treatment) is almost as durable as the special pulp. Even with alum treatment the neutral sulfite-chlorine dioxide pulp is much more durable than modern book paper.
In FIG. 13 of the drawings the same pulps are compared with respect to their fold durability on the basis of years at standard conditions. The half life (the time in years required to decrease the fold to one half of its original value) of the neutral sulfite-chlorine dioxide pulps is very high compared to conventional book. The half life of the neutral sulfite-chlorine dioxide alum treated pulp is about 18 years. The typical modern book paper has a half life of about 6 years.
From the above data it is concluded that the neutral sulfite-chlorine dioxide pulp of the present invention without special treatment or with lead or sodium treatment is very durable. Alum treated neutral sulfite-chlorine dioxide pulp is less durable than the lead, sodium or no-treatment pulps but is more durable than typical alum treated book paper.
| Patent | Priority | Assignee | Title |
| 5267655, | Aug 14 1990 | Ahlstrom Machinery Oy | Method and apparatus for treating a gas containing aqueous fiber suspension |
| 6752904, | Feb 09 2000 | NOURYON CHEMICALS INTERNATIONAL B V | Process for removal of lignin from lignocellulosic material |
| 7976676, | Dec 18 2006 | International Paper Company | Process of bleaching softwood pulps in a D1 or D2 stage in a presence of a weak base |
| 7976677, | Dec 18 2006 | International Paper Company | Process of bleaching hardwood pulps in a D1 or D2 stage in a presence of a weak base |
| Patent | Priority | Assignee | Title |
| 2882965, | |||
| 3020197, | |||
| 3433702, | |||
| 3501374, | |||
| 3829357, | |||
| CA553,129, |
| Executed on | Assignor | Assignee | Conveyance | Frame | Reel | Doc |
| Jun 28 1974 | Ethyl Corporation | (assignment on the face of the patent) | / |
| Date | Maintenance Fee Events |
| Date | Maintenance Schedule |
| Apr 20 1979 | 4 years fee payment window open |
| Oct 20 1979 | 6 months grace period start (w surcharge) |
| Apr 20 1980 | patent expiry (for year 4) |
| Apr 20 1982 | 2 years to revive unintentionally abandoned end. (for year 4) |
| Apr 20 1983 | 8 years fee payment window open |
| Oct 20 1983 | 6 months grace period start (w surcharge) |
| Apr 20 1984 | patent expiry (for year 8) |
| Apr 20 1986 | 2 years to revive unintentionally abandoned end. (for year 8) |
| Apr 20 1987 | 12 years fee payment window open |
| Oct 20 1987 | 6 months grace period start (w surcharge) |
| Apr 20 1988 | patent expiry (for year 12) |
| Apr 20 1990 | 2 years to revive unintentionally abandoned end. (for year 12) |