Abstract:
An organic agent for enhancing opacity in paper, paperboard or pulp comprises a hydrolase or an oxido-reductase; this enzymatic opacifying agent overcomes drawbacks associated with traditional organic and inorganic opacifying agents but also serves to provide increased strength and reduced porosity in paper and paperboard.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to a composition for use in making paper, pulp or paperboard; and a process of making paper, pulp or paperboard employing the composition, especially to add opacity to the paper, pulp or paperboard and a paper, pulp or paperboard produced using the composition.  
       BACKGROUND OF THE INVENTION  
       [0002]     In paper and paperboard manufacture, sheet formation is generally obtained on wire webs in a wet end from pulp slurry and is followed by the gradual removal of moisture in a press section and drier section. A calender section follows the drier section with the purpose of obtaining a desired finish, for example, smoothness, thickness or gloss.  
         [0003]     Despite the real advantages of using mechanical action to impart certain characteristics to the sheet, these advantages are limited. Complementary solutions for improving even further certain paper or paperboard characteristics can be applied internally in the wet end or externally with size-presses or coaters when these are available. These solutions are related to the use of fillers and functional additives.  
         [0004]     Fillers are generally white pigments that can be divided into two major categories: 
    a) regular fillers having wide application and cost lower than that of cellulosic fiber, e.g. kaolin clay, ground calcium carbonate and precipitated calcium carbonate;     b) specialized fillers having usually lower volume applications and costs sometimes comparable with or even higher than cellulosic fiber; Some examples are: anatase titanium dioxide, rutile titanium dioxide, composite pigments, e.g. clay and titanium dioxide, PSS (precipitated synthetic silica—silica oxides and precipitated silicate—aluminum silicate), talc (industrial grade hydrated magnesium silicate), aluminum trihydrate, calcium sulfate, natural or precipitated barium sulfate, zinc oxide, zinc sulfur—surface treatments only, Satin White (calcium sulfo-aluminate complex)—surface treatments only, urea formaldehyde resin (organic pigment), plastic pigments (empty or full spheres)—surface treatments only.    
 
         [0007]     The advantages brought by fillers in paper or paperboard manufacture are mostly related to cost reductions, except with some of the specialized fillers, especially titanium dioxide. The process disadvantages are however important and concern mostly wire, felt, doctor blade, refiners abrasion, machine deposits increase, increased linting dust, breaks related to sheet strength decrease and filler retention difficulties requiring retention program solutions.  
         [0008]     On the other hand, the functional advantages, with respect to final product characteristics, brought by fillers are also important: optical properties, i.e. brightness and opacity, improvement, improved printability, better sheet formation, increased smoothness and improved dimensional stability. The functional disadvantages are mostly related to increased two sidedness, reduced rigidity, increased linting and decreased sheet strength.  
         [0009]     Improving the paper or paperboard characteristics beyond the mechanical limits of a paper or paperboard machine often requires the use of fillers for their functional advantages and the use of functional additives for even better results.  
         [0010]     Examples of functional additives which can improve the sheet characteristics are dyes and optical brighteners, coating polymers, wet and dry strength resins, sizing agents, fluorocarbons, traditional organic opacifying agents and other specialty additives, while process additives that improve the production process include biocides, deposit-control agents, felt conditioners and cleaners, defoamers, and effluent treatments.  
         [0011]     Traditional organic opacifying agents are important functional additives used to improve the sheet characteristics obtained with mechanical means and with filler use. Resistance to water penetration, better printing characteristics, increased opacity brightness and whiteness, increased bulk and caliper, better formation, have been investigated and often obtained. Some process improvements related to reduced abrasion and cost reduction have also been noticed in some cases.  
         [0012]     The following examples illustrate some of the traditional organic opacifiers:  
         [0013]     U.S. Pat. Nos. 5,296,024 and 5,292,363 disclose a composition for enhancing opaqueness in papermaking comprising the reaction product of a fatty acid and a diamine.  
         [0014]     Different US patents related to U.S. Pat. No. 5,296,024 indicate that the resulting amide of the diamine, which forms the cationic softener base, is the fatty acid monoamide or the diamide or a mixture thereof.  
         [0015]     U.S. Pat. No. 5,488,139 describes an opacifier which is a reaction product of an alkanol amine and a dimerized acid, wherein the diamine (aminoethylethanol amine) is preferred, in this Patent, the principal reactant with the amine is a dimerized acid.  
         [0016]     Despite the clear advantages traditional opacifiers bring to papermaking, functional limitations on their use related especially to paper sheet strength and porosity have been noticed in mill conditions.  
         [0017]     A particular category of chemical additives with both funtional and process applications are enzymes, which are proteins with catalytic properties.  
         [0018]     The use of enzymes is ecologically interesting, and such enzymes can generally be applied anywere in the paper, paperboard or even pulp production. The following examples illustrate some of the present mill or laboratory applications for enzymes: 
        Xylanases—for prebleaching and bleaching pulps, especially Kraft.     Pectinases and xylanases—for debarking.     Laccases, proteases—for mechanical pulp refining     Cellulases and xylanases—for chemical pulp refining     Cellulases—for recycled pulp refining     Cellulases—for KAPPA number reduction in Kraft cooking     Xylanases—for brightness reversion     Cellulases, amylases, xylanases, lipases—for deinking     Cellulases—for tissue softness     Laccases—for mechanical pulp strength     Manganese peroxidases—for chemical pulp strength     Cellulases—for chemical fibre Tinting reduction     Laccases—for increased chemical fibre bulk     Cellulases and xylanases—for increased chemical fibre flexibility     Cellulases—for reduced porosity and increased fibrilation of chemical fibres     Cellulases and amylases—for increased drainage     Esterases—for stickies reduction     Amylases, proteases, levan hydrolase—for paper machine cleaning     Acetyl esterase, pectinases—for mechanical pulp white water treatments     Peroxidases, laccases, catalases—for effluent treatments     Pectinases for cationic demand reduction in peroxide bleached mechanical pulp        
 
         [0040]     In the prior art, WO95/27825 discloses a preparation process for increasing the content of inorganic fillers while maintaining or increasing the Scott internal bond strength, by addition of a cellulase type enzyme. Increasing the content of inorganic fillers is known in the art to be needed for particular applications; inorganic fillers function as opacifiers.  
         [0041]     Increasing the level of inorganic fillers for the majority of specific paper grades very often equates into one or more of the following disadvantages: 
        Increased paper machine blades abrasion     Increased paper machine press rolls wear     Increased paper machine inorganic deposits and breaks     Increased chemical costs in papermaking (e.g. when TiO 2  is used)     Increased printer equipment abrasion        
 
         [0047]     All these reasons justify the use of traditional organic opacifiers rather than inorganic filleras as opacifiers.  
         [0048]     In the prior art. it was known that increasing the levels of inorganic fillers favors opacity increase, but also results in decrease in strength.  
       SUMMARY OF THE INVENTION  
       [0049]     Surprisingly, while investigating porosity increase enzymatic applications, it has now been discovered that some enzymes also improve opacity without the drawbacks associated with traditional organic opacifiers. The handsheets made with enzyme treated fibres were often less porous, with increased tensile strength as compared with the untreated controls; and were much less porous, and exhibited much higher tensile strength as compared with the traditional organic opacifier treated handsheets.  
         [0050]     In this invention, the opacity obtained with enzymes as opacifying agents was higher or similar to that obtained with traditional organic opacifiers while porosity and strength properties were clearly improved.  
         [0051]     Although the prior art such as WO95/27825 shows that a cellulase can increase an internal bond strength of paper, the particular features of the present invention are absent from prior art. The prior art contains no showing that enzymes increase sheet opacity without an increase in the content of opacifying inorganic fillers.  
         [0052]     The enzymes which function as organic opacifying agents may be added during the course of paper and paperboard manufacturing processes; and can also be used in the pulp manufacture stage.  
         [0053]     It is an object of the present invention to provide an agent that adds opacity to paper, paperboard or pulp to which it is added.  
         [0054]     It is another object of the present invention to provide an agent for adding to a pulp slurry of cellulosic fibers to enhance opacity without adversely affecting other properties.  
         [0055]     It is another object of the invention to provide a method of enhancing opacity in a paper composition such as paper, paperboard or papermaking pulp.  
         [0056]     It is yet another object of the invention to provide a process of producing paper or paperboard of enhanced opacity.  
         [0057]     It is still another object of the invention to provide a papermaking stock, which stock may be formed into a paper or paperboard of enhanced opacity.  
         [0058]     It is yet another object of this invention to provide an opacified paper composition, for example a paper, paperboard or papermaking pulp of enhanced opacity.  
         [0059]     It is a specific object of the present invention to provide a process wherein an organic opacifying agent is added to recycled, deinked or virgin pulp of cellulosic fibers to form a paper, paperboard or pulp having desirable physical characteristics.  
         [0060]     Still another specific object of the present invention is to provide a process for adding a composition to pulp slurry of cellulosic fibers in a papermaking process that results in a paper, paperboard or pulp having enhanced opacity.  
         [0061]     Another specific object of the present invention is to provide a paper, paperboard, pulp or pulp slurry having the desirable characteristic of enhanced opacity.  
         [0062]     In accordance with the invention, there is provided in a method of enhancing opacity in a paper composition, in which an organic opacifying agent is incorporated in the paper composition, the improvement wherein the organic opacifying agent comprises an enzyme selected from the group consisting of hydrolases and oxidoreductases.  
         [0063]     In accordance with another aspect of the invention, there is provided an opacifying agent for use in enhancing opacity in a paper composition selected from paper, paperboard and papermaking pulp, comprising an enzyme selected from the group consisting of hydrolases and oxidoreductases.  
         [0064]     In accordance with still another aspect of the invention, there is provided a papermaking stock comprising: pulp slurry of papermaking fibers and an organic opacifying agent in an aqueous vehicle; said organic opacifying agent comprising an enzyme selected from hydrolases and oxidoreductases.  
         [0065]     In accordance with yet another aspect of the invention, there is provided an opacified paper composition comprising papermaking fibers and an organic opacifying agent, wherein said organic opacifying agent comprises an enzyme selected from the group consisting of hydrolases and oxidoreductases.  
         [0066]     In accordance with yet another aspect of the invention, there is provided a process of producing paper or paperboard of enhanced opacity comprising: i) providing a pulp slurry of papermaking fibers, ii) adding an organic opacifying agent to said slurry, and iii) forming paper or paperboard from said slurry, wherein said organic opacifying agent comprises an enzyme selected from hydrolases and oxidoreductases.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0067]     The invention employs an organic opacifying agent which avoids disadvantages associated with traditional inorganic opacifying agents while providing superior physical properties as compared with prior organic opacifying agents.  
         [0068]     The organic opacifying agents of the invention comprise a hydrolase or an oxidoreductase enzyme. A preferred hydrolase is a cellulose (E.C.3.2.1.4); a preferred oxidoreductase is laccase (E.C.1.10.3.2).  
         [0069]     Hydrolases are enzymes that catalyse the hydrolysis of a chemical bond, whereby a molecule is cleaved into two parts by the addition of a molecule of water. The catalysed reaction would have the following form: 
 
A-B+H 2 O→A-OH+B-H 
 
         [0070]     The chemical bonds cleaved in this way by hydrolysis include C—O, C—N and C—C bonds or in the case of organophosphorous hydrolases even P—O, P—F and P—S bonds.  
         [0071]     As shown indirectly in the pulp and paper enzymatic applications example list hereinbefore, hydrolases are a class of enzymes that benefit from the presence of an extremely large group of substrates available for enzymatic action, for example cellulose, hemicelluloses and many others, in conjunction with the presence of water in large quantities in the pulp, paper and paperboard processes.  
         [0072]     Cellulases, in particular hydrolyse cellulose, which is an unbranched glucose polymer composed of 1,4 glucose units linked by β-1,4-glycosidic bonds, and is the main component of pulp, by cleaving the β-1,4-glycosidic bonds. Hydrolases which are cellulolytic enzymes can be classified into three major types: 
    1.0 ENDOGLUCANASES, hydrolyzing randomly the polymeric chain (EC 3.2.1.4)     2.0 EXOGLUCANASES, hydrolyzing the ends of the chain: 
        2.1.1 Cellobiohydrolases, eliberating cellobiose—the glucose dimer (EC 3.2.1.91) 
            Cellobiohydrolases I: hydrolyzing the reducing end     Cellobiohydrolases II: hydrolyzing the non-reducing end     2.1.2 Glucanhydrolases, eliberating directly glucose (EC 3.2.1.74)    
           
        3.0 β-GLUCOSIDASES or cellobiases, acting on cellobiose or soluble cellodextrins (EC 3.2.1.21).    
 
         [0080]     As shown indirectly in the pulp and paper enzymatic applications example list, oxidoreductases are a second class of enzymes that benefit from the presence of an extremely large group of substrates available for enzymatic action, for example lignin, cellulose, hemicelluloses and many others, in the pulp, paper and paperboard processes.  
         [0081]     Oxidoreductases are enzymes that catalyse the transfer of electrons from one molecule (oxidant or hydrogen donor or electron donor) to another molecule (reductant or hydrogen acceptor or electron acceptor). The catalyzed reation would have the following form: 
 
A − +B→A+B − 
 
         [0082]     Laccases in particular (EC 1.10.3.2), surprisingly catalyse the oxidation of a large number of different substrates, while enzymes in general, for example cellulases, are usually substrate specific. Phenolic lignin units, lignin is an aromatic heteropolymer of phenyl-propanoid units, many phenolic compounds (diphenols, polyphenols, different substituted phenols), diamines, aromatic amines, benzenethiols and some inorganics (e.g. iodine) are oxidised directly with molecular oxygen as final electron acceptor through laccase action, the oxygen being reduced to water.  
         [0083]     Besides the presence of molecular oxygen, laccases may require organic mediators which are sometimes already present in the pulp slurry.  
         [0084]     Suitable mediators, by way of example, are 2-2′azinobis(3-ethylbenzthiazoline-6-sulfonate); ABTS 1-hydroxybenzotriazole; HBT N-acetyl-N-phenylhydroxylamine or NHA violuric acid or VIO N-hydroxybenzotriazole or NHB methyl 3,5-dimethoxy-4-hydroxybenzoate; methyl syringate potassium octacyanomolybtate; 1-phenyl-3-methyl-pyrazolone sodium; 1-phenyl-3methyl-4-methylamino-pyrazolone-5-N(4)-methanesulfonate; PPNa 1-(3′sufophenyl)-3-methylpyrazolone-5); and SPP N-hydroxyphthalimide as well as numerous phenoxazines and phenotiazines.  
         [0085]     The laccase active site contains four copper atoms. In a reported mechanism, the separate type 1 copper atom extracts one electron from the substrate, while the other copper atoms (one type 2 and two type 3) grouped in a trinuclear cluster receive the electron through presumably a conserved Hys-Cys-His tripeptide. Once the complete reduction in the trinuclear center takes place it is followed by the molecular oxygen reduction.  
         [0086]     The organic opacifying agent of this invention is usually added to bleached wood pulp or recycled paper pulp.  
         [0087]     The organic opacifying agent of this invention can be added alone or in conjunction with sizing agents, brighteners and other opacifying agents or any other functional or process additives.  
         [0088]     The organic opacifying agent of this invention can be added to any pulp slurry, deinked or recycled pulp.  
         [0089]     The amount of the opacifying agent and the other components added to the pulp slurry depends on the type of pulp slurry to which the opacying agent is added.  
         [0090]     The opacifying agent of this invention provides an increase in opacity to the paper, paperboard or pulp and provides an improved strength and porosity.  
         [0091]     The opacifying agent may be employed in conjunction with a surfactant and stabilizing agents  
         [0092]     Even though the opacying agent can be applied as a powder, typically it is dispersed in water for addition to the pulp slurry and typically is added in an amount of 0.00002% to 2%, preferably 0.0002% to 0.2%, catalytic protein by weight, based on the oven dry weight of the pulp fibers.  
         [0093]     The dispersion in water typically contains 0.1 to 30%, and preferably about 1-10%, by weight of the catalytic protein.  
         [0094]     The opacifying agent of the invention is more efficient and more effective even at lower concentration than traditional organic opacifying agents.  
         [0095]     The opacifying agent of the invention provides improved opacity to the treated paper, paperboard or pulp.  
         [0096]     A particular advantage of the present invention is that for a given amount of inorganic filler, if present, in the paper, paperboard or pulp, which filler may or may not have opacifying properties, the opacity is enhanced by the organic, enzymatic opacifying agent. More especially, it is not necessary to use an inorganic opacifying agent and it is not necessary to increase the content of an inorganic filler having opacifying properties in order to increase the opacity, and which increase in content would result in loss of strength. The organic, enzymatic opacifying agent of the invention not only enhances the opacity but also increases the strength and lowers the porosity.  
         [0097]     An inorganic filler is not required in order to provide opacity when employing the organic opacity agent of the invention; and the invention contemplates paper compositions containing the opacifying agent of the invention and being free of inorganic filler, although inorganic fillers may be included in the paper composition for the traditional purpose of reducing the pulp content, without their necessity to provide an opacifying function.  
         [0098]     The invention is further illustrated by reference to the Examples.  
       EXAMPLES  
     Example 1  
       [0099]     Laboratory opacity, brightness, porosity and tensile strength testing were performed with the following materials and methods:  
         [0000]     Pulp Preparation:  
         [0100]     Water deionized at pH 7.0  
         [0101]     Furnish: 400 g a.d. pulp: 10% deinked market pulp (40 g), 25% Softwood Kraft (100 g a.d.), 65% Hardwood Kraft (260 g a.d.).  
         [0000]     Additives:  
         [0000]     Traditional organic opacifier (amide of fatty acid and diamine), Trizym DEO (trademark for a cellulase of Tri-Tex), PCC (without dispersant), TiO 2  (anatase), anionic PAM retention aid  
         [0000]     Apparatus for Pulp Preparation:  
         [0102]     Beater with controlled bedplate (Pile Valley Iron Works)  
         [0103]     British disintegrator  
         [0104]     Canadian standard freeness tester  
         [0105]     150 microns mesh  
         [0106]     Hotplate (Termolyne Cimarec 2™)  
         [0107]     pH meter (VWR scientific model 8000)  
         [0108]     Thermometer (Fisherbrand)  
         [0109]     Caframo stirrer RZR50™ 
         [0110]     1000 ml beaker  
         [0111]     In all trials (control/amide of fatty acid and diamine/cellulase) the pulp treatments were made as described below: 
    1) In a first stage refining was performed for the entire 400 g a.d. of pulp according to TAPPI T 200 om-85 to a freeness of 300 ml CSF. Following the refining, pulp consistency was adjusted to 3% by filtration through a 150 micron mesh.     2) In the second stage 30 g a.d./trial of fibre (1000 g pulp) were heated and maintained at 55° C. for 20 minutes with opacifier additions or with no opacifier additions (control) in a 1000 ml beaker on the hotplate, while stirring at 300 rpm. The opacifier additions were made at 0.2% as is/a.d. fibre for Trizym DEO (trademark for a cellulase of Tri-Tex) and at 0.2% dry/a.d. fibre for the traditional organic opacifier (amide of fatty acid and diamine)     3) In the third stage 15% PCC (4.5 g dry) and 15% TiO 2  (4.5 g dry) addition was followed by 10 minutes of stirring while maintaining 55° C. pulp temperature.     4) In the fourth stage the heating was stopped and the pulp was diluted to 1% with the addition of 2000 g deionized room temperature water, followed by 0.1% (0.03 g dry) anionic PAM addition and 2 minutes stirring at 200 rpm.    
 
         [0116]     Handsheet preparation for optical testing was made with a slight modification of TAPPI T 218 om-83 without a dispersion stage, with conditioning (without preconditioning) according to TAPPI T 402 om-88 for 5 hours at 23° C. and 51% RH. The modification aimed at improved monitoring of the effect of fines and white water recirculation on opacity, concerned reusing three times the white water resulting from sheet formation and retaining for testing only each fourth sheet.  
         [0117]     Handsheet preparation for physical testing was made with a slight modification of TAPPI T 205 om-83, with conditioning (without preconditioning) according to TAPPI T 402 om-88 for 5 hours at 23° C. and 51% RH. The second modification aimed at improved monitoring of the effect of fines and white water recirculation on porosity, concerned reusing three times the white water resulting from sheet formation and retaining for testing only each fourth sheet.  
         [0118]     Handsheet printing opacity (ISO standard 2471) and ISO brightness testing were made in the conditioning temperature and humidity conditions after 5 hours from the handsheet preparation on a Technibrite Micro TB-1C™.  
         [0119]     Handsheet tensile strength (TAPPI T 220 om-88 and TAPPI T 494 om-88) and the air resistance of paper (TAPPI T 460 om-88) were tested in the conditioning temperature and humidity conditions after 5 hours from the handsheet preparation with a MC TEC vertical tensile tester and a UEC-1012—A densometer tester.  
                                                                                     ISO   ISO   Densometer   Tensile       Trial       Brightness   Opacity   sec/100 ml   Strength       nr.       %   %   air   kN/m                                1   Control   86.50   80.69   63   4.8       2   amide of   86.88   81.58   55   4.4           fatty acid           and diamine       3   cellulase   86.91   82.71   121   5.4                  
 
       Example 2  
       [0120]     Laboratory opacity, brightness, porosity and tensile strength testing were performed with the following materials and methods:  
         [0000]     Pulp Preparation:  
         [0121]     Water deionized at pH 7.0  
         [0122]     Furnish: 400 g a.d. pulp: 10% deinked market pulp (40 g), 10% Aspen BCTMP (40 g) 25% Softwood Kraft (100 g a.d.), 55% Hardwood Kraft (220 g a.d.).  
         [0000]     Additives:  
         [0123]     Traditional organic opacifier (amide of fatty acid and diamine), Trizym DLC (trademark for a laccase of Tri-Tex), PCC (without dispersant), TiO 2  (anatase), anionic PAM retention aid  
         [0000]     Apparatus for Pulp Preparation:  
         [0124]     Beater with controlled bedplate (Pile Valley Iron Works)  
         [0125]     British disintegrator  
         [0126]     Canadian standard freeness tester  
         [0127]     150 microns mesh  
         [0128]     Hotplate (Termolyne Cimarec 2™)  
         [0129]     pH meter (VWR scientific model 8000)  
         [0130]     Thermometer (Fisherbrand)  
         [0131]     Caframo stirrer RZR50™ 
         [0132]     1000 ml beaker  
         [0133]     In all trials (control/amide of fatty acid and diamine/laccase) the pulp treatments were made as described below: 
    5) In a first stage refining was performed for the entire 400 g a.d. of pulp according to TAPPI T 200 om-85 to a freeness of 300 ml CSF. Following the refining, pulp consistency was adjusted to 3% by filtration through a 150 micron mesh.     6) In the second stage 30 g a.d./trial of fibre (1000 g pulp) were heated and maintained at 55° C. for 20 minutes with opacifier additions or with no opacifier additions (control) in a 1000 ml beaker on the hotplate, while stirring at 300 rpm. The opacifier additions were made at 0.2% as is/a.d. fibre for Trizym DLC (trademark for a laccase of Tri-Tex) and at 0.2% dry/a.d. fibre for the traditional organic opacifier (amide of fatty acid and diamine)     7). In the third stage 15% PCC (4.5 g dry) and 15% TiO 2  (4.5 g dry) addition was followed by 10 minutes of stirring while maintaining 55° C. pulp temperature.     8) In the fourth stage the heating was stopped and the pulp was diluted to 1% with the addition of 2000 g deionized room temperature water, followed by 0.1% (0.03 g dry) anionic PAM addition and 2 minutes stirring at 200 rpm.    
 
         [0138]     Handsheet preparation for optical testing was made with a slight modification of TAPPI T 218 om-83 without a dispersion stage, with conditioning (without preconditioning) according to TAPPI T 402 om-88 for 5 hours at 23° C. and 51% RH. The modification aimed at improved monitoring of the effect of fines and white water recirculation on opacity, concerned reusing three times the white water resulting from sheet formation and retaining for testing only each fourth sheet.  
         [0139]     Handsheet preparation for physical testing was made with a slight modification of TAPPI T 205 om-83, with conditioning (without preconditioning) according to TAPPI T 402 om-88 for 5 hours at 23° C. and 51% RH. The second modification aimed at improved monitoring of the effect of fines and white water recirculation on porosity, concerned reusing three times the white water resulting from sheet formation and retaining for testing only each fourth sheet.  
         [0140]     Handsheet printing opacity (ISO standard 2471) and ISO brightness testing were made in the conditioning temperature and humidity conditions after 5 hours from the handsheet preparation on a Technibrite Micro TB-1C™.  
         [0141]     Handsheet tensile strength (TAPPI T 220 om-88 and TAPPI T 494 om-88) and the air resistance of paper (TAPPI T 460 om-88) were tested in the conditioning temperature and humidity conditions after 5 hours from the handsheet preparation with a MC TEC vertical tensile tester and a UEC-1012—A densometer tester.  
                                                           ISO   ISO   Densometer   Tensile       Trial       Brightness   Opacity   sec/100 ml   Strength       nr.       %   %   air   kN/m                   1   Control   86.11   80.51   52   4.3       2   amide of   86.48   81.38   45   4.0           fatty acid           and diamine       3   laccase   86.53   81.59   57   5.1