Abstract:
A selective immobilized enzyme bioadditive retention aid comprising an enzyme chemically bound to a particulate inorganic support, said enzyme having a binding site selectively linkable to an organic polymeric fibrous material component of a pulp. The invention provides an improved process of paper manufacture and the novel paper making additives of use therein.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to paper making processes and additives of use therein.  
       BACKGROUND OF THE INVENTION  
       [0002]     Modern papers are a sophisticated blend of fibers, fillers and polymers wherein during manufacture synthetic retention aids are required to enhance the deposition of fillers and fines onto the fibers before sheet formation. Without retention aids, most of the fillers and some of the fines pass through the sheet and remain in the white water. Poor retention lowers product quality and paper-machine efficiency, and wastes raw material. Loss of fines is especially significant in thermomechanical and chemi-thermomechanical pulping processes, which produce a significant quantity of fines in suspension.  
         [0003]     Typical retention aids include high molecular weight organic polymers, with either positive, negative or net neutral charges. Cationic polymers are frequently employed to bind with cellulosic fibres, which naturally possess a negative charge. Unfortunately, conventional “effective” retention aids cause everything to stick to everything else. Fillers form large aggregates instead of uniformly depositing onto fibers and unwanted fiber-fiber flocculation gives poor sheet formation. A fundamental problem is that retention aid adsorption is not selective in that fines, fillers and fibers compete for the retention additives.  
         [0004]     Pulp and Paper Canada, 81, 54, 1980—R. H. Pelton, L. H. Allen, and H. M. Nugent and TAPPI J, 68, 91, 1985—R. H. Pelton describe the use of high molecular weight organic polymers as retention aids for pulp systems, and compare the effects of charge on retention aid effectiveness.  
         [0005]     “Pulp and Paper: Chemistry and Chemical Technology, Vol 2”, Chap 8, T. N. Kershaw, ed., John Wiley and Sons, New York, 1981—J. P. Casey describes the impact of the loss of cellulosic fines on paper properties, the justification for the need for retention aids for effective paper formation and the economic impact of fine fiber loss.  
         [0006]     “Handbook for Pulp and Paper Technologies”, Chap 15, CPPA/TAPPI joint textbook committee, 1982—G. A. Smook describes, in a general way, the role of retention aids in papermaking in that they facilitate the aggregation of fibers and fine materials of cellulosic fines or fillers, which are often less than about 5 microns.  
         [0007]     J. Wood Chem. Technol., 9, 407, 1989—S. Roy, M. Desrochers, and L. Jurasek describes the use of proteins as potential retention aids, including lysozyme, trypsinogen, myoglobin, carbonic anhydrase and protease. Proteins were chosen based on their charge characteristics, without any consideration of their ability to bind chemically to the materials in a papermaking suspension, i.e., the expected mechanism of action for these proteins was essentially equivalent to that observed with high molecular weight polymers currently used in industry. However, the results suggested that, in addition to electrostatic interactions, some other form of binding was probably also occurring. The isoelectric point of the proteins had a significant effect on binding, suggesting that most of the binding was based on electrostatic interactions.  
         [0008]     U.S. Pat. No. 5,998,183, issued Dec. 7, 1999—G. N. Le Fevre and B. A. Saville, describes the immobilization of enzymes, and means to ensure that enzyme activity is retained and maximized. The teachings of the processes for making immobilized enzymes described in U.S. Pat. No. 5,998,183 is incorporated herein by reference.  
       SUMMARY OF THE INVENTION  
       [0009]     It is an object of the present invention to provide an improved process of paper manufacture and novel paper making additives of use therein.  
         [0010]     Generally, the invention provides processes of preparing selective paper making additives by immobilizing enzymes, for example, cellulase/cellulose binding domain (CBD) onto a clay/kaolinite support, and/or by co-immobilizing cellulase/(CBD) and α-amylase onto a clay/kaolinite support. The cellulase/CBD moiety selectively binds to cellulose in a papermaking suspension, while amylase will bind to starch. The product obtained is therefore highly selective, possessing specific recognition sites for starch and cellulose. Furthermore, the immobilization support (clay/kaolinite) is a commonly used filler within paper.  
         [0011]     Accordingly, in one aspect, the invention provides a selective immobilized enzyme bioadditive retention aid comprising an enzyme chemically bound to a particulate inorganic support, said enzyme having a protein recognition site selectively linkable to an organic polymeric fibrous material component of a pulp.  
         [0012]     Preferably, the enzyme having the protein recognition site is selected from the group consisting of cellulase, a cellulose binding domain, amylase, mannanase and xylanase.  
         [0013]     The particulate support is preferably a paper-making acceptable filler or coating material, such as a paper-making acceptable clay and most preferably, kaolinite.  
         [0014]     The fibrous material is preferably selected from cellulose, hemi-cellulose, xylan, mannan and lignan.  
         [0015]     In a preferred aspect the retention aid has a dual functionality in containing the protein recognition sites of cellulase and amylase.  
         [0016]     In a further aspect, the invention provides a method of preparing a paper sheet from a pulp comprising an organic polymeric fibrous material, said method comprising treating said pulp with a retention aid to assist in enhancing the deposition of said fines onto said fibers to produce a resultant pulp and forming said paper sheet from said pulp; the improvement wherein said retention aid comprises an enzyme chemically bound to a particulate inorganic support, said enzyme having a protein recognition site selectively linkable to an organic polymeric fibrous material component of said pulp.  
         [0017]     The pulp may be a slurry comprising significant volumes of water, or in an alternative embodiment, be in the form of a damp sheet of paper-forming components, wherein the process comprises coating one or both sides of the sheet with a retention aid according to the invention.  
         [0018]     In preferred embodiments for coating a sheet, starch fines in admixture with an amylase-containing retention aid according to the invention with, optionally, also a immobilized cellulase is used.  
         [0019]     In a yet further aspect, the invention provides a paper sheet comprising fibers, fines, a filler and a retention aid wherein said retention aid is a an enzyme chemically bound to a particulate inorganic support, said enzyme having a protein recognition site selectively linkable to an organic polymeric fibrous material component of a pulp. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     In order that the invention may be better understood, preferred embodiments will now be described by way of example only with reference to the accompanying drawings, wherein  
         [0021]      FIG. 1  is a graph showing immobilized enzyme activity for different loadings of a clay;  
         [0022]      FIG. 2  represents scanning election microscope images of clay on cotton fibers;  
         [0023]      FIG. 3  is a graph showing the production of xylo-oligosaccharides with time using xylanase immobilized on kaolinite; and  
         [0024]      FIG. 4  is a diagrammatic sketch of a dynamic drainage jar apparatus. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0025]     Use of the process of the invention for starch coatings is described herein.  
         [0026]      FIG. 4  shows generally as  10 , a dynamic drainage jar apparatus used to compare absorption/retention values in several experiments using particulate clay supports.  
         [0027]     Apparatus  10  is a right-vertical cylindrical glass vessel  12 , which holds the pulp slurry under test, fitted with a wire mesh  14  at a lower part  16 . Lower part  16  has a conical bottom  18  having a drainage spout  20 , located within a recepticle  22 . Vessel  12  has a paddle-stirrer  24 .  
         [0028]     Use of the DDJ apparatus is exemplified under Example 3, hereinafter.  
         [0029]     Starch coatings (“sizes”) are typically utilized to fill in gaps or voids on the surface of the sheet. These coatings may be administered on a size press, or by tub sizing. In the former operation, the rollers (or nip) are flooded with starch solution, which is then delivered and attached to the paper by absorption as it passes between the rollers. The process must be carefully controlled to avoid non-uniform distribution of the sizing agent onto the paper stock. In particular, the paper machine may need to run at relatively low or moderate speeds to ensure proper attachment of the solids in the sizing solution. In a tub sizing operation, the sheet passes through a shallow tub or bath that contains the starch solution; excess solution is subsequently removed by passing the sheet through a set of rollers.  
         [0030]     In either type of process, the objective is to achieve a uniform coating of the sizing agent onto the paper. Selective or controlled deposition of starch onto the underlying cellulosic component of the paper will improve sheet formation and coating uniformity. The additives described herein, which promote selective binding between paper constituents and starch therefore improves deposition of starch coatings onto paper.  
         [0031]     Enzymes were immobilized onto clay/kaolinite, through a cross-linking process, adapting an existing immobilization technology, in accordance with aforesaid U.S. Pat. No. 5,998,183, to α-amylase, cellulase, and the cellulose-binding domain (CBD) of cellulase. The effectiveness of the intelligent paper additive was established through adsorption studies, followed by examination of fibers using scanning electron microscopy. Measurements of the activity of the soluble and immobilized enzyme provided additional evidence regarding the effectiveness of the immobilization procedure.  
       EXAMPLES  
     Example 1  
     Experiments with Cellulase Immobilized on Kaolinite  
       [0032]     For a variety of different immobilization conditions, measurements of the activity of soluble cellulase before and after immobilization were conducted, based on the production of reducing sugars. The activity of the immobilized enzyme was affected by the duration of immobilization, and the relative concentration of cellulase to clay. For the support modification step, which takes place over 1.5 to 10 hours, with glutaraldehyde, the concentration typically ranged between 1 and 4% (v/v). For the immobilization step, the modified support was incubated in enzyme solution, comprised of raw enzyme solution diluted either 5, 10, or 20 fold, to establish the effect of protein concentration on the immobilization process. The activity of the immobilized enzyme for some different loadings of clay and immobilization conditions is shown in  FIG. 1 . These data indicate that cellulase is attached to clay, and that this configuration recognizes the cellulose in the solution, establishing that cellulose and clay can be attached in this manner.  
         [0033]     Adsorption studies with the immobilized cellulase (bioadditive) were conducted by incubating the bioadditive in a solution containing cotton (cellulose) fibers. As a control, fibers were also incubated in a suspension of clay alone.  FIG. 2  compares the SEM images of native cotton fibers, cotton fibers exposed to clay only, and cotton fibers incubated in cellulase immobilized onto clay, wherein  
         [0034]     (a) is untreated cotton fiber;  
         [0035]     (b) is cotton fiber incubated in clay suspension;  
         [0036]     is cotton fiber incubated in clay-cellulase complex  
         [0037]     As shown in  FIG. 2 , much more clay is attached to the cotton when the clay is coupled to cellulase than if the cotton is incubated in clay alone. The selective interaction between cellulase and cellulose (cotton) thus facilitates greater deposition of clay.  
       Example 2  
     Experiments with Xylanase Immobilized on Kaolinite  
       [0038]     Kaolinite (clay) was suspended in 200 mL of glutaraldehyde/phosphate buffer (pH 7.5) solution for 2 to 8 hours, then recovered by vacuum filtration. The recovered kaolinite was washed with 600 mL of distilled water, and dried. The dried modified support was incubated for 4 to 24 h in enzyme solution, prepared by diluting raw xylanase, either 5, 10 or 20 fold, with phosphate buffer (pH 7.5). The immobilized enzyme was recovered by vacuum filtration and dried. Activity tests using birchwood xylan confirmed that the xylanase attached to the kaolinite was active ( FIG. 3 ).  
       Example 3  
     Retention Studies  
       [0039]     Adsorption/retention studies were conducted using a dynamic drainage jar (DDJ) apparatus ( FIG. 4 ) to compare retention of unmodified clay, cellulase immobilized on clay (from Example 1), and xylanase immobilized on clay (from Example 2): 
        1. 8.0 g of unbeaten bleached kraft softwood pulp was put in deionized water for 24 hours, and diluted to 2 L with deionized water.     2. The pulp slurry was disintegrated at 15000 revolutions, and then diluted to 4 L with deionized water.     3. 250 mL of pulp slurry was mixed with 200 mL water, put into the DDJ apparatus and mixed at 800 rpm.     4. 0.25 g of filler sample (either unmodified clay or clay modified with enzyme) was suspended in 10 mL of water, then added into the DDJ apparatus and mixed for two minutes.     5. The containers originally containing the pulp solution and the filler solution were rinsed using 40 mL of water, which was then transferred into the DDJ apparatus.     Thus, at the conclusion of steps (1)-(5), the DDJ apparatus contained 500 mL of water, 0.5 g of pulp, and 0.25 g of filler.     6. After the two minutes had elapsed, the DDJ mixer was turned off.     7. 20-30 mL of slurry was drained off the bottom of the DDJ apparatus and discarded. The next 100 mL was collected for filtration analysis, and the rest was drained completely, to collect a fiber cake formed on the screen of the DDJ apparatus.     8. The 100 mL of filtrate collected in step (7) was vacuum filtered using 0.22 micron filter paper. The filter paper was collected after filtration, and dried. The mass of solid collected was determined by comparing the dry mass of the filter paper before and after the filtration step; this information was subsequently used to calculate the first pass retention of pulp and filler on the mesh.     9. Ash/pyrolysis tests were performed on the filter+fibre cake collected during step (7), to determine the relative amount of (non-pyrolyzable) filler versus (pyrolyzable) fibre in the sample.        
 
         [0050]     Table 1 shows that the first-pass retention of filler (clay) was improved by coupling with cellulase or xylanase.  
                                         TABLE 1                                       First pass retention,           Filler   %                                        Clay   2.3           Cellulase-   5.2           modified clay           Xylanase-   13.3           modified clay                      
 
         [0051]     Table 2 also shows that modification of clay with enzymes, particularly xylanase, substantially improves the ash (filler) content of pulp samples retained on the DDJ mesh.  
                           TABLE 2                                   Filler   Filler on Fibre (g/g)                           Clay   0.0128           Cellulase-   0.0096           modified clay           Xylanase-   0.0252           modified clay                      
 
         [0052]     Although this disclosure has described and illustrated certain preferred embodiments of the invention, it is to be understood that the invention is not restricted to those particular embodiments. Rather, the invention includes all embodiments which are functional or mechanical equivalents of the specific embodiments and features that have been described and illustrated.