WO2021244625A1

WO2021244625A1 - Wet-lap preservation

Info

Publication number: WO2021244625A1
Application number: PCT/CN2021/098257
Authority: WO
Inventors: Marko Kolari; Karoliina MARKKULA; Li Yan; Suhua WU
Original assignee: Kemira Oyj; Kemira (Asia) Co., Ltd.
Priority date: 2020-06-04
Filing date: 2021-06-04
Publication date: 2021-12-09
Also published as: KR20230019193A; WO2021243656A1; CN116034193A

Abstract

A method for preparing wet-lap wherein a combination of an inhibitor of amylase activity and a biocide are incorporated into the wet-lap. The wet-lap produced according to the method exhibits a reduced loss of fibre strength during storage.

Description

WET-LAP PRESERVATION

Field of the Invention

The present invention relates to a method of preparing wet-lap from a source of recycled cellulose fibres, wet-lap comprising an inhibitor of amylase activity and a biocide, a use of wet-lap in a method of making paper or board, and a use of an inhibitor of amylase activity and a biocide in preserving fibre strength in wet-lap.

Background of the Invention

Materials comprising recycled cellulose fibre (RCF) are commonly used as a raw material for paper or board manufacturing.

Paper or board manufacturing using RCF involves the following conventional principal stages:

1) Stock preparation

Material comprising RCF is dispersed in water (usually process water collected from previous paper manufacturing runs) to form a fibre stock or pulp having a high water content of about 98 to 99 wt. %. Mechanical agitation facilitates dispersion of the RCF in water. Large contaminants (for example, large pieces of textiles and plastics) are removed from the pulp using a “ragger” , and remaining undesirable elements are removed from the pulp by passing the pulp through a series of screens. Fillers, binders, pigments and strengthening agents may be incorporated into the pulp to impart desirable properties to the end-product.

2) Forming

The pulp is deposited onto a wire mesh and dewatered whereby the fibres become aligned to form a thin sheet of raw paper or paper web. The water content of the paper web is typically reduced to 75 and 80 wt. %.

3) Pressing

The paper web is usually passed through a series of nip rollers which removes much of the remaining water. The pressure from the rollers compresses the fibres so they intertwine to form a dense, smooth sheet. The water content of the paper sheet is typically between 45 and 55 wt. %. The water collected during forming and pressing of the paper (process water) is usually re-used in diluting the RCF in step 1) to form the fibre stock.

4) Drying

The pressed paper sheet may be subjected to an initial drying step and starch may be incorporated onto the surface of the paper to enhance stiffness prior to a final drying step. Drying reduces the water content of the paper to about 5 to 10 wt. %.

Old corrugated container board (OCC) is used a source of RCF for paper or board manufacturing. OCC can contain a plurality of impurities such as plastics, sand, glass, organic residuals and other waste material. Thus, OCC is classified in many countries as a waste product, and restrictions on its transportation and importation may exist which would not apply to raw material products. For example, forthcoming legislation in China will prohibit the import of all solid waste, including OCC. Consequently, the paper manufacturing industry has developed new processes to convert OCC into sheets of pulp comprising RCF. This is termed wet-lap, which has a reduced level of contaminants, and is classified as a raw material which can be imported into China in the form of bales for subsequent processing into paper or board according to the conventional steps 1) to 4) described above.

The time taken between production of wet-lap to the actual use of the wet-lap in paper manufacturing, including storage and transport time, may be as long as two months. It has been found that wet-lap produced according to current processes has high levels of microbial contamination, including bacteria and fungi. The temperature and humidity that may be observed during storage and transport of wet-lap are favourable for microbial growth. The degradation of RCF by microorganisms in wet-lap leads to an undesirable loss of fibre strength in the wet-lap, with downstream, negative consequences on the quality of paper or board manufactured from the wet-lap.

Microbial growth in paper and board manufacturing processes is a widespread problem. Microorganisms may affect the quality of the end product and/or the running of the paper machine. Attempts have been made to control microbial growth, and in particular, the application of biocides has been investigated.

A specific application of biocides is the control of starch degradation in process waters of the paper industry. Starch is a widely used additive in paper making to impart properties such as improved strength and printing properties of the end product. Starch may be incorporated into paper at various stages of the paper making process, including incorporation into process waters, incorporation into wet pulp, and/or incorporation as a coating before drying. Starch is also present in raw material comprising RCF. Not all of the starch (added or originally present in the raw material) is retained or bound by paper fibres, and during dewatering or drying steps, excess, unbound starch is removed in the collected process water for subsequent cycles of paper making. Starch is composed of two types of polysaccharides, amylose and amylopectin. Amylose is linear and composed of D-glucose residues linked by α- (1→4) bonds. Amylopectin is branched and composed of D-glucose residues linked by α- (1→4) bonds and α- (1→6) bonds. Amylase is an enzyme that catalyses degradation of starch. It is produced by many microorganisms, including fungi and bacteria. Amylase enzymes are divided into three groups: α-, β-and γ-amylases. All amylase enzymes hydrolyse α- (1→4) bonds. β-amylase can hydrolyse only the second a-l, 4-glycosidic bond in a polysaccharide chain, yielding two glucose units (maltose) as a degradation product whilst α-amylase can attack any α- (1→4) bonds in the starch molecule, yielding single glucose units. Thus, α-amylase is often faster-acting than β-amylase. γ-amylase cleaves the last α-1, 4 glycosidic bond at the non-reducing end of amylose and amylopectin, as well as α-1, 6 glycosidic bonds in amylopectin, yielding single glucose units. γ-amylase is most efficient in acidic environments.

Process waters in paper machines often contain microorganisms which produce free amylase enzymes that degrade starch and cause loss of functionality of added or residual starch. This may have a negative impact on paper quality, and/or may force manufacturers to increase the amounts of starch added during paper manufacturing, thus creating unwanted additional costs.

WO 2013/045638 describes the use of zinc ions in combination with a biocide to prevent or reduce starch degradation in starch-containing process waters from pulp, paper or board production processes. Specifically, when fibre-containing process water with added starch is incubated up to 24 hours, a significant amount of starch is lost through microbial degradation. The starch loss is inhibited when zinc ions for amylase control and a biocide are incorporated into the fibre-containing process water.

Attempts have been made to incorporate existing biocides into wet-lap to control microbial growth over the long time periods required (i.e. two to three months) . However, these attempts have proven unsuccessful and the incorporation of biocides is not sufficient to prevent loss of fibre strength in wet-lap.

Therefore, it is an object of the invention to provide an improved process for producing wet-lap which allows storage of the wet-lap over long periods of time, with a reduced loss of fibre strength.

Summary of the Invention

Accordingly, in a first aspect, the present invention provides a method of preparing wet-lap comprising:

i) suspending a source of recycled cellulose fibres in water to form a fibre stock, and

ii) dewatering the fibre stock to form wet-lap;

wherein the fibre stock comprises starch, and

wherein the method further comprises treating one or more of the cellulose fibres, fibre stock and wet-lap with an inhibitor of amylase activity and a biocide.

In a second aspect, the present invention provides wet-lap produced by the above method.

The treatment of one or more of the cellulose fibres, fibre stock and wet-lap with an inhibitor of amylase activity and a biocide during the method of preparing wet-lap results in incorporation of the inhibitor of amylase activity and the biocide into the wet-lap.

In a third aspect, the present invention provides wet-lap comprising an amylase inhibitor and a biocide.

In a fourth aspect, the present invention provides a method of making paper or board using the wet-lap defined above, wherein the method comprises:

i) suspending the wet-lap in process water obtained from pulp, paper or board production to form a fibre stock;

ii) passing the fibre stock through a paper machine to form paper or board.

In a fifth aspect, the present invention provides a use of an inhibitor of amylase activity and a biocide in preserving fibre strength in wet-lap.

Preferred features of all aspects of the present invention are defined in the dependent claims.

The present inventors have unexpectedly found that incorporation of both an amylase inhibitor and a biocide into wet-lap during the manufacturing process effectively provides long-term preservation effects and inhibits loss of fibre strength.

Detailed Description of the Invention

Method of preparing wet-lap and wet-lap obtained by the method

In one aspect, the present invention provides a method of preparing wet-lap comprising:

ii) dewatering the fibre stock to form wet-lap;

wherein the fibre stock comprises starch, and

The present invention further provides wet-lap prepared according to the method described herein.

The term “comprising” or “comprises” as used herein denotes the inclusion of at least the features following the term, and does not exclude the inclusion of other features which have not been explicitly mentioned. The term may also denote an entity which consists of features following the term.

“Recycled cellulose fibres” (RCF) as used herein refers to fibres comprising cellulose which are found in, or have been obtained from, paper or board recovered for recycling into new paper products. Common sources of recycled cellulose fibres include, but are not limited to, waste paper and board, and old corrugated container board (OCC) . A preferred source of RCF is OCC. In a preferred embodiment, the source (s) of cellulose fibres used to produce wet-lap comprises only recycled cellulose fibres. In other embodiments, a blend of recycled fibres and virgin fibres (i.e. fresh material comprising cellulose fibres) may be used as the starting material for the production of wet-lap.

The term “wet-lap” as used herein refers to material comprising RCF which has been processed into a fibre stock (or pulp) , typically subjected to a decontamination process to remove at least some large contaminants from the fibre stock, and further subjected to water removal from the fibre stock (dewatering) , to form sheets.

Wet-lap is physically and chemically distinct from paper or board made by conventional processes, and is typically transported and/or stored for subsequent use as a raw material to make paper or board. Notably, wet-lap sheets are more robust, more rigid and thicker than paper or board, and unlike paper or board, have an uneven, rough surface. Additionally, the fibre stock used to produce wet-lap does not undergo the same decontamination process that is carried out during paper or board manufacturing and therefore, wet-lap has a higher level of impurities than paper or board. Furthermore, typically, wet-lap is not subjected to the chemical processing that is carried out during conventional paper or board manufacturing to improve the efficiency of the paper or board manufacturing process and to impart desirable properties to the paper or board ultimately produced. (Such chemical processes include, for example, defoaming, stickies control, retention, sizing and strengthening. )

Wet-lap typically has a solid content of from about 30 wt. %to about 70 wt. %by total weight of the wet-lap. Preferably, the solid content of wet-lap is from about 40 wt. %to about 60 wt. %or from about 45 wt. %to about 55 wt. %by total weight of the wet-lap. Most preferably, the solid content of wet-lap is about 50 wt. %by total weight of the wet-lap.

In order to form the fibre stock, the source of RCF is suspended or dispersed in water. This may be done in a large vessel such as a pulper which provides mechanical agitation or a blending action to separate fibres in the source of RCF. High temperatures of about 25℃ to about 40℃may improve pulping efficiency. The solid content of the fibre stock may vary from 1 wt. %to about 30 wt. %or be as low as 1 wt. %to 2 wt. %by total weight of the fibre stock. In some embodiments, the solid content may be higher than 2 wt. %, for example from about 2 wt. %to about 30 wt. %, from about 2 wt. %to about 10 wt. %, or from about 2 wt. %to about 5 wt. %by total weight of the fibre stock.

Some sources of RCF, particularly, OCC, contain contaminants such as inks, glue, clays, dirt, plastics, glass and metals. Contaminants may be removed by means of coarse and fine screens, centrifugal cleaners, and dispersion or refining units that promote disintegration of large contaminant particles. Typically, only large contaminants are removed for wet-lap manufacturing. The amount of contaminants that is acceptable for paper or board manufacture depends upon the type of paper or board that will be produced. Removal of smaller contaminants is typically completed after transport and storage, at the stage of paper or board manufacture. Unlike conventional paper or board manufacturing processes, additional chemicals for decontamination (other than the biocide and inhibitor of amylase activity as described herein) or for modifying fibre properties are preferably not incorporated into the fibre stock when manufacturing wet-lap. Sources of RCF may further comprise microorganisms such as bacteria and fungi which contributes to loss of fibre strength in the wet-lap during storage and transport.

The water used to form the fibre stock is preferably recycled process water for reasons of economy and environment. Process water is typically water that has been collected from previous wet-lap production cycles. Fresh water, or a blend of fresh water and process water from either paper manufacturing or other industrial processes may be used as an alternative. Whilst process water is favourable from an economical and environmental standpoint, it has the disadvantage that it is often contaminated by microorganisms such as bacteria and fungi which further contributes to loss of fibre strength in the wet-lap during storage and transport. The water, and particularly process water, used to form the fibre stock may contain bacteria in amount greater than 1 x 10 ⁵ CFU/ml. Typically, observed bacterial concentrations in the water may be greater than 1 x 10 ⁶ CFU/ml, 1 x 10 ⁷ CFU/ml, 1 x 10 ⁸ CFU/ml, or 1 x 10 ⁹ CFU/ml. Other contaminants such as fibre particles, ink particles, and dyes may also be present.

Typically, RCF includes starch. This starch originates predominantly from the surface coating that is applied prior to the final drying step during paper or board making, and/or from starch that is added during the initial stock formation. As not all added starch is retained by cellulose fibres, excess, unbound starch may be removed in process waters during dewatering steps. Therefore, the fibre stock prepared in the methods of the present invention typically also comprises dissolved starch.

In the dewatering step, water is removed from the fibre stock so as to form dense sheets of wet-lap in which the cellulose fibres are in a compressed state. Dewatering is typically achieved by the use of a press, preferably a twin wire press. In one embodiment, the fibre stock which preferably has a solid content of about 2 wt. %to about 5 wt. %, and more preferably, about 4 wt. %to about 5 wt. %, by total weight of the stock, is pumped under pressure into a headbox of a twin wire press, prior to being distributed evenly between two wires of the twin wire press. Within the press, the fibre stock may be subjected to dewatering by gravity and/or by passing through a dehydration filter plate to increase the solid content of the fibre stock, preferably to about 10 to 12 wt. %by total weight of the fibre stock. Further dewatering may occur within the press by passing the fibre stock through a series of rolls under pressure to achieve a further increase in solid content of up to about 70 wt. %, about 60 wt. %, or about 50 wt. %by total weight of the fibre stock. A screw press may be used instead of a twin press to achieve dewatering. A screw press typically compresses the paper sheet against a screen or filter and accomplishes dewatering by continuous gravitational drainage. A twin press is generally preferred over a screw press due to reduced power consumption and maintenance costs, and improved output consistency. Centrifugation may also be used to remove water from the fibre stock and/or paper sheet to form wet-lap.

The sheets of wet-lap formed from dewatering may subsequently be introduced into a sheet-cutting machine for cutting to a customized size, prior to stacking the cut sheets evenly in a layboy system. Finally, a baling machine may be used to further compress and tie the stacked wet-lap sheets to form bales that are suitable for transport and storage. Wet-lap may also be cut into loose chips which are subsequently bagged for transport.

In the methods of the present invention, one or more of the recycled cellulose fibres, fibre stock and wet-lap are treated with an inhibitor of amylase activity and a biocide. The inventors have unexpectedly found that the inhibitor of amylase activity and biocide act synergistically to prevent or diminish the reduction in cellulose fibre strength that is otherwise observed with untreated controls.

The treatment is such that the inhibitor of amylase activity and biocide are incorporated into, and retained in, the wet-lap. Preferably, the inhibitor of amylase activity and biocide remain active during storage of the wet-lap for periods up to one day, one week, two weeks, one month, two months or three months.

By “treatment” it is meant that the inhibitor of amylase activity and biocide are brought into contact with one or more of the RCF, fibre stock and wet-lap. The treatment may be continuous, intermittent or carried out once. The inhibitor of amylase activity and biocide may be provided as individual aqueous solutions or combined into a single aqueous solution. Alternatively, one of the inhibitor of amylase activity and biocide may be a solid that is dissolved in an aqueous solution of the other of the inhibitor of amylase activity and biocide. The method by which the inhibitor of amylase activity and biocide are brought into contact with one or more of the RCF, fibre stock and wet-lap is not particularly restricted. For example, the source of RCF and/or wet-lap may be sprayed with the amylase inhibitor. Spraying may occur during or after the dewatering step, for example, when the solid content of the fibre stock has been increased to at least 20 wt. %, 30 wt. %, 40wt. %, 50 wt. %, 60 wt. %or 70 wt. %. by total weight of the fibre stock. The biocide is generally not applied as a spray since it may be a safety risk for workers near wet-lap machinery. Alternatively, the source of RCF and/or wet lap may be coated with aqueous solutions of the amylase inhibitor and biocide. The amylase inhibitor and biocide may also be dissolved or dispersed in the water used to form the fibre stock, or added directly to the suspension of cellulose fibres in water or to the fibre stock.

Treatment of the RCF, fibre stock and wet-lap may encompass bringing the amylase inhibitor and biocide into contact with one or more of these materials simultaneously or in succession. Thus, the amylase inhibitor may be brought into contact with one or more of the RCF, fibre stock and wet-lap before the biocide or after the biocide, or at the same time as the biocide. It is also envisaged that the inhibitor of amylase activity and biocide may be used separately to treat one or more of the RCF, fibre stock and wet-lap. Thus for example, in one embodiment, the RCF may be treated with an inhibitor of amylase activity but no biocide, and the fibre stock may be treated with a biocide without any inhibitor of amylase activity. In another embodiment, the fibre stock may be treated with an inhibitor of amylase activity but no biocide, and both the RCF and wet-lap may be treated with biocide, but no inhibitor of amylase activity. In a further embodiment, the fibre stock may be treated with both an inhibitor of amylase activity and a biocide, and the wet-lap may additionally be treated with the biocide. It is also possible to add one component continuously and the other component intermittently. Various permutations and combinations of treatment are thus encompassed by the invention. What is required is that the treatment results in incorporation of the inhibitor of amylase activity and biocide into the final wet-lap.

The inhibitor of amylase activity is any compound or agent which acts upon one or more of α-, β-, and γ-amylase, resulting in a reduction in their activity, and consequent reduction in the rate at which starch is degraded. Inhibitors may bind to the active site of an amylase enzyme (competitive inhibitor) or to a site distal to the active site such that the amylase has a reduced affinity for its starch substrate (non-competitive inhibitor) .

A preferred inhibitor of amylase activity comprises zinc ions. In one embodiment, zinc ions are derived from an inorganic zinc salt. In another embodiment, zinc ions are derived from organic zinc salt. Preferably, an inorganic zinc salt is used as it does not introduce carbon to the wet-lap manufacturing process which would be usable by microbes. In addition, as inorganic salts are not strongly acidic or alkaline, they do not have any direct effect on the pH. Zinc has been found to be compatible with the wet-lap manufacturing processes and it has been shown to be effective in concentrations that are not harmful for the environment. Furthermore, zinc ions are generally regarded as safe even in applications for human consumption (U.S: Food & Drug Administration; GRAS Substances Database (SCOGS) ) . In addition, zinc is an inexpensive raw material.

Preferably, the zinc ion source is selected from ZnBr ₂, ZnCl ₂ , ZnF ₂, Zn , ZnO, Zn (OH) ₂, ZnS, ZnSe, ZnTe, Zn ₃N ₂, Zn ₃P ₂, Zn ₃As, Zn ₃Sb ₂, ZnO ₂ , ZnH ₂, , ZnCO ₃, Zn (NO ₃) ₂, Zn (ClO ₃) ₂, ZnSO ₄, Zn ₃ (PO ₄) ₂, ZnMoO ₄, ZnCrO ₄, Zn (AsO ₂₎ ₂, Zn (AsO ₄) ₂, Zn (O ₂CCH ₃) ₂, zinc metal, and a combination thereof. Preferred zinc salts are ZnCl ₂, ZnBr ₂, and ZnSO ₄ and other salts having high solubility in aqueous solutions such as process water.

Other amylase inhibitors for use in the present invention include natural (organic) amylase inhibitors which are found in, and may be isolated from, the seeds of plants such as cereal grains and legumes.

The biocide is any agent which inhibits the growth and/or viability of microorganisms, including bacteria and fungi. The biocide may be effective against one of bacteria and fungi, or both. Preferably, the biocide is effective against both bacteria and fungi. The biocidal action may result through physicochemical interaction with microbial target structures (for example, cell membranes) , specific reactions with biological molecules, or disturbance of selected metabolic or energetic processes.

Numerous biocides are known in the paper manufacturing industry and are suitable for use in the methods of the present invention. The biocide may comprise a non-oxidizing biocide or an oxidizing biocide.

Non-oxidizing biocides may include 2, 2-Dibromo-3-nitrilopropionamide (DBNPA) , 2-Bromo-2-nitropropane-1, 3-diol (Bronopol) , 2-Bromo-2-nitro-propan-1-ol (BNP) , 2, 2-Dibromo-2-cyano-N- (3-hydroxypropyl) acetamide, 2, 2-Dibromomalonamide, 1, 2-Dibromo-2, 4-dicyanobutane (DCB) , Bis (trichloromethyl) sulfone, 2-Bromo-2-nitrostyrene (BNS) , Didecyl-dimethylammonium chlorine (DDAC) , Benzalkonium chloride (ADBAC) and other quaternary ammonium compounds, 3-Iodopropynyl-N-butylcarbamate (IPBC) , Methyl and Dimethyl-thiocarbamates and their salts, 5-Chloro-2-methyl-4-isothiazolin-3-one (CMIT) , 2-Methyl-4-isothiazolin-3-one (MIT) , 2-n-Octyl-4-isothiazolin-3-one (OIT) , 4, 5-Dichloro-2- (n-octyl) -3 (2H) -isothiazolone (DCOIT) , 4, 5-Dichloro-1, 2-dithiol-3-one, 1, 2-Benzisothiazolin-3-one (BIT) , 2- (Thiocyanomethylthio) benzthiazole (TCMBT) , 2-Methyl-1, 2-benzisothiazolin-3 (2H) -one (MBIT) , Tetrakis hydroxymethyl phosphonium sulfate (THPS) , Tetrahydro-3, 5-dimethyl-2H-1, 3, 5-thiadiazine-2-thione (Dazomet) , Methylene bisthiocyanate (MBT) ; Ortho-phenylphenol (OPP) and its salts; Glutaraldehyde; Ortho-phthaldehyde (OPA) , Guanidines and biguanidines, N-dodecylamine or n-dodecylguanidine, dodecylamine salt or dodecylguanidine salt such as dodecylguanidine hydrochloride, Bis- (3-aminopropyl) dodecylamine, Pyrithiones, Triazines such as Hexahydro-1, 3, 5-trimethyl-1, 3, 5-triazine, 3- [ (4-Methylphenyl) sulfonyl] -2-propenenitrile, 3-Phenylsulphonyl-2-propenenitrile, 3- [ (4-trifluormethylphenyl) sulphonyl] -2-propenenitrile, 3- [ (2, 4, 6-trimethylphenyl) sulphonyl] -2-propenenitrile, 3- (4-methoxyphenyl) sulphonyl-2-propenenitrile, 3- [ (4-methylphenyl) sulphonyl] prop-2-enamide, any isomers thereof, and any combination thereof. A preferred non-oxidizing biocide is a thiazoline compound such as 4, 5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) or 2-n-Octyl-4-isothiazolin-3-one (OIT) .

Oxidizing biocides may include an oxidant selected from: chlorine, alkali and alkaline earth hypochlorite salts, hypochlorous acid, bromine, alkali and alkaline earth hypobromite salts, hypobromous acid, chlorine dioxide, ozone, hydrogen peroxide, peroxy compounds such as performic acid, peracetic acid, percarbonate or persulfate, halogenated hydantoins such as monohalodimethylhydantoins, dihalodimethylhydantoins, perhalogenated hydantoins, mono-chloramines, monobromamines, dihaloamines, trihaloamines, urea reacted with an oxidant, the oxidant being for example, alkali and alkaline earth hypochlorite salts or alkali and alkaline earth hypobromite salts, ammonium salts such as ammonium bromide, ammonium sulfate or ammonium carbamate reacted with an oxidant, the oxidant preferably being alkali and alkaline earth hypochlorite salts or alkali and alkaline earth hypobromite salts, and any combination thereof. Particularly suitable oxidizing biocides may include ammonium salts reacted with an oxidant, for example, ammonium bromide, ammonium sulfate or ammonium carbamate, or any other ammonium salt which is reacted with an oxidant such as hypochlorite. Preferred oxidizing biocides are selected from alkali and alkaline earth hypochlorite salts.

According to the present invention, it has been found that loss of strength in fibres and products produced from wet-lap correlates well with degradation of starch in the wet-lap during storage. Without wishing to be bound by theory, it is believed that microorganisms, particularly bacteria which are present in wet-lap, produce free amylase which degrades starch in the wet-lap into smaller units of glucose or maltose. The microorganisms may originate from the water (particularly, process water) which is used to form the fibre stock and/or from the source of recycled cellulose fibres. Whilst starch itself cannot be used as an energy source or cannot be metabolised by microorganisms, starch degradation products such as glucose are easily assimilated by the microorganisms, resulting in significant growth of the microbial populations over extended time periods during wet-lap storage and transportation. The starch degradation products further activate cell signalling pathways, resulting in increased amylase production by the microorganisms, and further starch degradation and assimilation of degradation products. Once the starch in wet-lap becomes depleted, microorganisms present in the wet-lap seek an alternative energy source and produce cellulase which degrades cellulose in the cellulose fibres to glucose. This glucose is used by microorganisms as a new energy source in the absence of starch. The degradation of cellulose fibres in wet-lap leads to a loss in fibre strength which is undesirable for future use of the wet-lap in paper or board making.

According to the invention it has been found that there is a high proportion of anaerobic bacteria in wet-lap bales. These bacteria, rather than fungi, are thought to be responsible for cellulase production and degradation of the cellulose fibres.

Using an amylase inhibitor alone in the absence of a biocide has proven unsatisfactory in inhibiting the loss of fibre strength in wet-lap over incubation periods of up to several weeks perhaps due to continued amylase production by viable microbes. It was hypothesised that using a biocide to destroy the microorganisms in wet-lap would reduce amylase production and starch degradation, thereby preventing any depletion of starch, and consequently any breakdown of cellulose by fungi. It was further considered that fungi present in wet-lap bales would contribute significantly to breakdown of cellulose. However, using a biocide alone in the absence of an amylase inhibitor has also unexpectedly proven unsatisfactory in inhibiting the loss of fibre strength in wet-lap over incubation periods of up to several weeks. It is believed that free amylase produced by microorganisms remains in wet-lap for a significant period of time even after the microorganism population has been reduced, thus leading to starch degradation and depletion, and cellulase production by the remaining bacterial and fungal cells. It is further believed that the primary cause of cellulase production is anaerobic bacteria rather than fungi. The combination of an inhibitor of amylase activity and a biocide provides a two-pronged approach in inhibiting cellulose degradation and loss of fibre strength in wet-lap.

Accordingly, the present invention further provides a use of an inhibitor of amylase activity and a biocide to preserve fibre strength in wet-lap. The wet-lap, inhibitor of amylase activity and biocide may be as defined herein.

The amount of amylase inhibitor and biocide to be used in the methods of the present invention may be dependent upon the microbial levels and amount of starch present in the water used to form the fibre stock, and in the source of cellulose fibres.

In some embodiments, the inhibitor of amylase activity can be incorporated into the source of RCF, fibre stock and/or wet-lap in amount of from about 1 to about 1000 ppm, or from about 1 to about 500 ppm, or from about 1 to about 100 ppm, or from about 1 to about 50 ppm, or from about 5 to about 100 ppm, or from about 5 to about 50 ppm, or from about 5 to about 20 ppm, or from about 5 to about 10 ppm, based on the weight of the active ingredient of the inhibitor of amylase activity relative to the weight of water in the RCF, fibre stock and/or wet-lap. (For the purposes of the specification, unless otherwise stated, a concentration of 1 ppm refers to 1mg of active ingredient in 1kg of water. ) Thus, if the inhibitor of amylase activity is a source comprising zinc ions, then the aforementioned amounts are based on the weight of the Zn ions.

In some embodiments, the oxidizing biocide can be incorporated into the source of RCF, fibre stock and/or wet-lap in amount of from about 0.1 to about 100 ppm, or from about 0.1 to about 50 ppm, or from about 0.1 to about 15 ppm, or from about 0.5 to 10 ppm, based on the active ingredient content of the oxidizing biocide relative to the weight of water in the source of RCF, fibre stock and/or wet-lap. In embodiments where the oxidizing biocide contains chlorine, the active ingredient is understood to be total active chlorine.

In some embodiments, the non-oxidizing biocide can be incorporated into the source of RCF, fibre stock and/or wet-lap in amount of from about 0.1 to 1000 ppm, or from about 1 to about 100 ppm, or from about 2 to about 50 ppm, or from about 2 to about 20 ppm, or from about 2 to about 15 ppm, or from about 5 to about 15 ppm, based on the active ingredient content of the non-oxidizing biocide relative to the weight of water in the source of RCF, fibre stock and/or wet-lap.

In the methods of the present invention, the inhibitor of amylase activity and the oxidizing biocide may be used a weight ratio of from about 1 : 1 to 100 : 1, based on the weight of the active components. In a preferred embodiment, the inhibitor of amylase activity and the biocide are present in a ratio of from about 1 : 10 to 100 : 1, preferably from about 1 : 5 to 20 : 1, and more preferably, from about 1 : 2 to 5 : 1, based on the weight of the active components. The inhibitor of amylase activity and the non-oxidizing biocide may be used in a ratio of about 1 : 10 to 10 : 1, based on the weight of the active components In a preferred embodiment, the inhibitor of amylase activity and the non-oxidizing biocide are present in a ratio of from about 1 : 20 to 20 : 1, preferably from about 1 : 10 to 10 : 1, and more preferably from about 1 : 5 to 5 : 1, based on the weight of the active components.

The fibres of the wet-lap produced according to methods of the present invention may have a zero-span breaking strength index of about 90 to about 120 N·m/g, or about 100 N·m/g as measured according to TAPPI standard T 231 cm-96 (using Z-Span Tester (Model: 2400, PULMAC) . Testing is conducted in a dry state by following standard conditions specified in T402 sp-98. The zero-span breaking strength index of the fibres may depend on the number of rounds of recycling the RCF have undergone prior to their processing into the wet-lap. Successive rounds of recycling may weaken fibre strength of the resulting wet-lap. However, wet-lap produced in accordance with the invention exhibits a reduced loss of fibre strength when stored over time, as compared to wet-lap produced by methods which do not involve treatment with an inhibitor of amylase activity and a biocide. In some embodiments, the wet-lap maintains at least 50%, at least 60%, at least 70%, at least 80%or at least 90%of its fibre strength, as quantified by zero-span breaking strength index measured using the methods described above, after one week of storage at a temperature of 20℃ to 40℃ and at a humidity of 80%to 100%. In some embodiments, the wet-lap maintains at least 50%, at least 60%, at least 70%, at least 80%or at least 90%of its fibre strength, as quantified by zero-span breaking strength index measured using the methods described above, after two weeks of storage at a temperature of 20℃ to 40℃and at a humidity of 80%to 100%. In some embodiments, the wet-lap maintains at least 50%, at least 60%, at least 70%, at least 80%or at least 90%of its fibre strength, as quantified by zero-span breaking strength index measured using the methods described above, after six weeks of storage at a temperature of 20℃ to 40℃ and at a humidity of 80%to 100%. In other embodiments, the wet-lap maintains at least 50%, at least 60%, at least 70%, at least 80%or at least 90%of its fibre strength, as quantified by zero-span breaking strength index measured using the methods described above, for at least one, two, three or six weeks of storage in a substantially constant environment. By “substantially constant” , it is meant that at least the temperature and humidity is maintained within about 5%of the original values at time zero (i.e. at the start of the storage) . In another aspect, the present invention provides a wet-lap which has a bacterial concentration of less than 1 x 10 ⁹, less than 1 x 10 ⁸ or less than 1 x 10 ⁷ CFU/g wet-lap. The bacterial concentration may be an anaerobic bacterial concentration. The wet-lap may alternatively or additionally have a fungal concentration of less than 1 x 10 ⁷, less than 1 x 10 ⁶, or less than 1 x 10 ⁵ CFU/g wet-lap. The wet-lap may have an anaerobic bacterial content of less than 25%, less than 20%, less than 15%or less than 10%of the overall bacteria, based on quantitative PCR. Preferably, the wet-lap is produced according to the methods described herein. The above microbial counts may be observed in wet-lap which has been stored at a temperature of 20℃ to 40℃ and at a humidity of 80%to 100%, for at least one, two, three or six weeks.

Paper or board manufacturing

In a further aspect of the invention, the wet-lap described herein is used as a raw material in a process of paper or board manufacturing. In the process of paper of board manufacturing, the wet-lap is re-suspended in water, preferably process water, to form a fibre stock. Other sources of fibres may be incorporated into the fibre stock. These include virgin fibres such as wood fibres and/or other sources of recycled fibres.

As described above, during wet-lap manufacturing according to the present invention, typically only large contaminants are removed. Therefore, when using the wet-lap as a source of pulp for paper or board manufacturing, the remainder of the contaminants need to be removed to the extent required by the grade of paper or board to be produced from the pulp. Smaller contaminants may be removed by further screening and/or centrifugation processes. Additional of chemicals may also facilitate the decontamination process. For example, surfactants may be used to remove ink from the cellulose fibres and bleaching agents may be used to remove colour.

Further chemicals may also be introduced into the fibre stock to improve the efficiency of the paper or board manufacturing process (performance chemicals) , and to modify or enhance the properties of the paper or board eventually produced (functional chemicals) . Performance chemicals may include defoamers which reduce foaming and hence improve paper machine runnability, stickies control agents which prevent deposit formation by sticky hydrophobic materials originating from glues and tapes, and further biocides which reduce microbial contamination and associated slime formation. Functional chemicals may include fillers to enhance the aesthetic and physical properties of the paper or board produced, retention aids to promote the binding of fillers and fine materials to the cellulose fibres, strengthening agents to impart durability, and sizing agents to impart water-resistance and maintain writing quality and printability.

The fibre stock is subsequently passed through a paper machine to form paper or board. Paper machines are very commonly used in the paper industry and readily available. Typically, a paper machine comprises the following operational sections: a forming section comprising a wire mesh for forming a sheet from the fibre stock; a press section for dewatering the sheet to form a dewatered sheet; a dryer section for drying the dewatered sheet to form a dried sheet; and optionally, a calender section for smoothening the dried sheet.

The unexpected reduction in loss of fibre strength that is observed in the wet-lap of the present invention is advantageous when the wet-lap is further processed to make paper or board. In particular, the strength of the paper or board end product is improved. This in turn reduces the amount of additives such as starch that need to be incorporated into the paper or board, and costs associated with the manufacturing process.

The description further provides the following embodiments:

Clauses

1. A method of preparing wet-lap comprising:

ii) dewatering the fibre stock to form wet-lap;

wherein the fibre stock comprises starch, and

wherein the method further comprises treating one or more of the recycled cellulose fibres, fibre stock and wet-lap with an inhibitor of amylase activity and a biocide.

2. The method of clause 1, wherein the water is process water obtained from pulp, paper or board production.

3. The method of clause 1, wherein the amylase inhibitor comprises a source of zinc ions.

4. The method of clause 3, wherein the zinc ions are derived from an inorganic or organic zinc salt, preferably an inorganic zinc salt.

5. The method of claim 3 or claim 4, wherein the source of zinc ions is selected from: ZnBr ₂, ZnCl ₂, ZnF, Znl ₂, ZnO, Zn (OH) ₂, ZnS, ZnSe, ZnTe, Zn ₃N ₂, Zn ₃P ₂, Zn ₃As ₂, Zn ₃Sb ₂, ZnO ₂, ZnH ₂, ZnCO ₃, Zn (NO ₃) ₂, Zn (C1O ₃) ₂, ZnS0 ₄, Zn ₃ (PO ₄) ₂, ZnMoO ₄, ZnCrO ₄, Zn (AsO ₂) ₂, Zn (AsO4) ₂, Zn (O ₂CCH ₃) ₂) , zinc metal, and a combination thereof.

6. The method of any preceding clause, wherein the biocide comprises a non-oxidizing biocide or an oxidizing biocide.

7. The method of clause 6, wherein the non-oxidizing biocide is selected from: 2, 2-Dibromo-3-nitrilopropionamide (DBNPA) , 2-Bromo-2-nitropropane-1, 3-diol (Bronopol) , 2-Bromo-2-nitro-propan-1-ol (BNP) , 2, 2-Dibromo-2-cyano-N- (3-hydroxypropyl) acetamide, 2, 2-Dibromomalonamide, 1, 2-Dibromo-2, 4-dicyanobutane (DCB) , Bis (trichloromethyl) sulfone, 2-Bromo-2-nitrostyrene (BNS) , Didecyl-dimethylammonium chlorine (DDAC) , Benzalkonium chloride (ADBAC) , 3-Iodopropynyl-N-butylcarbamate (IPBC) , Methyl and Dimethyl-thiocarbamates and their salts, 5-Chloro-2-methyl-4-isothiazolin-3-one (CMIT) , 2-Methyl-4-isothiazolin-3-one (MIT) , 2-n-Octyl-4-isothiazolin-3-one (OIT) , 4, 5-Dichloro-2- (n-octyl) -3 (2H) -isothiazolone (DCOIT) , 4, 5-Dichloro-1, 2-dithiol-3-one, 1, 2-Benzisothiazolin-3-one (BIT) , 2- (Thiocyanomethylthio) benzthiazole (TCMBT) , 2-Methyl-1, 2-benzisothiazolin-3 (2H) -one (MBIT) , Tetrakis hydroxymethyl phosphonium sulfate (THPS) , Tetrahydro-3, 5-dimethyl-2H-1, 3, 5-thiadiazine-2-thione (Dazomet) , Methylene bisthiocyanate (MBT) ; Ortho-phenylphenol (OPP) and its salts; Glutaraldehyde; Ortho-phthaldehyde (OPA) , Guanidines and biguanidines, N-dodecylamine or n-dodecylguanidine, dodecylamine salt or dodecylguanidine salt, preferably dodecylguanidine hydrochloride, Bis- (3-aminopropyl) dodecylamine, Pyrithiones, Triazines, preferably, Hexahydro-1, 3, 5-trimethyl-1, 3, 5-triazine, 3- [ (4-Methylphenyl) sulfonyl] -2-propenenitrile, 3-Phenylsulphonyl-2-propenenitrile, 3- [ (4-trifluormethylphenyl) sulphonyl] -2-propenenitrile, 3- [ (2, 4, 6-trimethylphenyl) sulphonyl] -2-propenenitrile, 3- (4-methoxyphenyl) sulphonyl-2-propenenitrile, 3- [ (4-methylphenyl) sulphonyl] prop-2-enamide, isomers thereof, and any combination thereof.

8. The method of clause 7, wherein the non-oxidizing biocide is 4, 5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) or 2-n-Octyl-4-isothiazolin-3-one (OIT) .

9. The method of clause 6, wherein the oxidizing biocide is selected from: chlorine, alkali and alkaline earth hypochlorite salts, hypochlorous acid, bromine, alkali and alkaline earth hypobromite salts, hypobromous acid, chlorine dioxide, ozone, hydrogen peroxide, peroxy compound, preferably, performic acid, peracetic acid, percarbonate or persulfate, halogenated hydantoins, preferably monohalodimethylhydantoins, dihalodimethylhydantoins, perhalogenated hydantoins, monochloramines, monobromamines, dihaloamines, trihaloamines, urea reacted with an oxidant, the oxidant selected from alkali and alkaline earth hypochlorite salts or alkali and alkaline earth hypobromite salts, ammonium salts, preferably ammonium bromide, ammonium sulfate or ammonium carbamate reacted with an oxidant, the oxidant selected from alkali and alkaline earth hypochlorite salts or alkali and alkaline earth hypobromite salts, and any combination thereof..

10. The method of any preceding clause, wherein the source of cellulose fibres comprises one or more of old corrugated containers (OCC) , packaging board and paper.

11. The method of any preceding clause, wherein the wet-lap comprises from about 30 wt.%to about 70 wt. %solids.

12. The method of clause 10, wherein the wet-lap comprises from about 40 wt. %to about 60 wt. %solids.

13. The method of clause 12, where the wet-lap comprises about 50 wt. %solids.

14. The method of any preceding clause, wherein the fiber stock comprises from about 1 wt.%to about 20 wt. %solids.

15. The method of any preceding clause, wherein the fiber stock comprises from about 2 wt.%to about 5 wt. %solids.

16. The method of any preceding clause, wherein the inhibitor of amylase activity and biocide are added to the water prior to suspension of the source of cellulose fibres.

17. The method of any preceding clause, wherein the inhibitor of amylase activity and biocide are added to the water after suspension of the source of cellulose fibres.

18. The method of any preceding clause, wherein the inhibitor of amylase activity and biocide are added to the source of cellulose fibres prior to suspension in water.

19. The method of any preceding clause, wherein the wet-lap is sprayed with an inhibitor of amylase activity.

20. The method of any preceding clause, wherein the dewatering is carried out by passing the fibre stock over a wire mesh in a forming process.

21. The method of any preceding clause, wherein dewatering is carried out by pressing action.

22. The method of clause 21, wherein dewatering is carried out using a twin-press machine.

23. The method of clause 21, wherein dewatering is carried out using a screw press.

24. The method of clause 21, wherein dewatering is carried out by centrifugation.

25. The method of any preceding clause, wherein the fibre stock is passed through one or more screens prior to dewatering to remove contaminants.

26. The method of clause 25, wherein the contaminants comprise plastic.

27. The method of any preceding clause, wherein the water comprises microorganisms.

28. The method of clause 27, wherein the microorganisms comprise bacteria and fungi.

29. The method of clause 27 or clause 28, wherein the amount of bacteria in the water is greater than 1 x 10 ⁵ CFU/ml.

30. The method of any preceding clause, wherein the inhibitor of amylase activity is incorporated into one or more of the recycled cellulose fibres, fibre stock and wet-lap in an amount of about 5 to about 100 ppm based on the weight of the inhibitor of amylase activity, relative to the weight of water in the recycled cellulose fibres, fibre stock or wet-lap.

31. The method of any preceding clause, wherein the inhibitor of amylase activity is incorporated into one or more of the recycled cellulose fibres, fibre stock and wet-lap in an amount of about 5 to about 20 ppm based on the weight of the inhibitor of amylase activity, relative to the weight of water in the recycled cellulose fibres, fibre stock or wet-lap.

32. The method of any preceding clause, wherein the biocide is incorporated into one or more of the recycled cellulose fibres, fibre stock and wet-lap in an amount of about 1 to about 100 ppm based on the weight of the inhibitor of amylase activity, relative to the weight of water in the recycled cellulose fibres, fibre stock or wet-lap.

33. The method of any preceding clause, wherein the biocide is incorporated into one or more of the recycled cellulose fibres, fibre stock and wet-lap in an amount of about 2 to about 15 ppm based on the weight of the inhibitor of amylase activity, relative to the weight of water in the recycled cellulose fibres, fibre stock or wet-lap.

34. The method of any preceding clause, wherein the wet-lap has a zero-span breaking strength index of about 90 to about 120 N·m/g, as measured according to TAPPI standard T 231 cm-96.

35. The method of clause 34, wherein the wet-lap has a zero-span breaking strength index of about 100N·m/g, as measured according to TAPPI standard T 231 cm-96.

36. Wet-lap produced according to the method of any preceding clause.

37. Wet-lap comprising an inhibitor of amylase activity and a biocide.

38. The wet-lap of clause 36 or clause 37, wherein the amylase inhibitor comprises a source of zinc ions.

39. The wet-lap of clause 38, wherein the zinc ions are derived from an inorganic or organic zinc salt, preferably an inorganic zinc salt.

40. The wet-lap of clause 38 or clause 39, wherein the source of zinc ions is selected from: ZnBr ₂, ZnCl ₂, ZnF, Znl ₂, ZnO, Zn (OH) ₂, ZnS, ZnSe, ZnTe, Zn ₃N ₂, Zn ₃P ₂, Zn ₃As ₂, Zn ₃Sb ₂, ZnO ₂, ZnH ₂, , ZnCO ₃, Zn (NO ₃) ₂, Zn (C1O ₃) ₂, ZnSO ₄, Zn ₃ (PO ₄) ₂, ZnMoO ₄, ZnCrO ₄, Zn (AsO ₂) ₂, Zn (AsO4) ₂, Zn (O ₂CCH ₃) ₂) , zinc metal, and a combination thereof.

41. The wet-lap of any of clause 36 to 40, wherein the biocide comprises a non-oxidizing biocide or an oxidizing biocide.

42. The wet-lap clause 41, wherein the non-oxidizing biocide is selected from: 2, 2-Dibromo-3-nitrilopropionamide (DBNPA) , 2-Bromo-2-nitropropane-1, 3-diol (Bronopol) , 2-Bromo-2-nitro-propan-1-ol (BNP) , 2, 2-Dibromo-2-cyano-N- (3-hydroxypropyl) acetamide, 2, 2-Dibromomalonamide, 1, 2-Dibromo-2, 4-dicyanobutane (DCB) , Bis (trichloromethyl) sulfone, 2-Bromo-2-nitrostyrene (BNS) , Didecyl-dimethylammonium chlorine (DDAC) , Benzalkonium chloride (ADBAC) , 3-Iodopropynyl-N-butylcarbamate (IPBC) , Methyl and Dimethyl-thiocarbamates and their salts, 5-Chloro-2-methyl-4-isothiazolin-3-one (CMIT) , 2-Methyl-4-isothiazolin-3-one (MIT) , 2-n-Octyl-4-isothiazolin-3-one (OIT) , 4, 5-Dichloro-2- (n-octyl) -3 (2H) -isothiazolone (DCOIT) , 4, 5-Dichloro-1, 2-dithiol-3-one, 1, 2-Benzisothiazolin-3-one (BIT) , 2- (Thiocyanomethylthio) benzthiazole (TCMBT) , 2-Methyl-1, 2-benzisothiazolin-3 (2H) -one (MBIT) , Tetrakis hydroxymethyl phosphonium sulfate (THPS) , Tetrahydro-3, 5-dimethyl-2H-1, 3, 5-thiadiazine-2-thione (Dazomet) , Methylene bisthiocyanate (MBT) ; Ortho-phenylphenol (OPP) and its salts; Glutaraldehyde; Ortho-phthaldehyde (OPA) , Guanidines and biguanidines, N-dodecylamine or n-dodecylguanidine, dodecylamine salt or dodecylguanidine salt, preferably dodecylguanidine hydrochloride, Bis- (3-aminopropyl) dodecylamine, Pyrithiones, Triazines, preferably, Hexahydro-1, 3, 5-trimethyl-1, 3, 5-triazine, 3- [ (4-Methylphenyl) sulfonyl] -2-propenenitrile, 3-Phenylsulphonyl-2-propenenitrile, 3- [ (4-trifluormethylphenyl) sulphonyl] -2-propenenitrile, 3- [ (2, 4, 6-trimethylphenyl) sulphonyl] -2-propenenitrile, 3- (4-methoxyphenyl) sulphonyl-2-propenenitrile, 3- [ (4-methylphenyl) sulphonyl] prop-2-enamide, isomers thereof, and any combination thereof.

43. The wet-lap of clause 41, wherein the oxidizing biocide is selected from: chlorine, alkali and alkaline earth hypochlorite salts, hypochlorous acid, bromine, alkali and alkaline earth hypobromite salts, hypobromous acid, chlorine dioxide, ozone, hydrogen peroxide, peroxy compound, preferably, performic acid, peracetic acid, percarbonate or persulfate, halogenated hydantoins, preferably monohalodimethylhydantoins, dihalodimethylhydantoins, perhalogenated hydantoins, monochloramines, monobromamines, dihaloamines, trihaloamines, urea reacted with an oxidant, the oxidant selected from alkali and alkaline earth hypochlorite salts or alkali and alkaline earth hypobromite salts, ammonium salts, preferably ammonium bromide, ammonium sulfate or ammonium carbamate reacted with an oxidant, the oxidant selected from alkali and alkaline earth hypochlorite salts or alkali and alkaline earth hypobromite salts, and any combination thereof.

44. The wet-lap of any of clauses 36 to 43, wherein the wet-lap comprises water, and wherein the inhibitor of amylase activity is present in an amount of about 5 to about 100 ppm based on the weight the inhibitor of amylase activity, relative to the weight of water in the wet-lap.

45. The wet-lap of clause 44, wherein the inhibitor of amylase activity is present in an amount of about 5 to about 20 ppm based on the weight the inhibitor of amylase activity, relative to the weight of water in the wet-lap.

46. The wet-lap of any of clauses 36 to 45, wherein the wet-lap comprises water, and wherein the biocide is present in an amount of about 1 to about 100 ppm based on the weight of the biocide, relative to the weight of the water in the wet-lap.

47. The wet-lap of clause 46, wherein the biocide is present in an amount of about 2 to about 15 ppm based on the weight of the biocide, relative to the weight of the water in the wet-lap.

48. The wet-lap of any of clauses 36 to 47, wherein the wet-lap has a zero-span breaking strength index of about 90 to about 120 N·m/g, as measured according to TAPPI standard T 231 cm-96.

49. The method of clause 48, wherein the wet-lap has a zero-span breaking strength index of about 100N·m/g, as measured according to TAPPI standard T 231 cm-96.

50. The wet-lap of any of clauses 36 to 49, wherein the wet-lap comprises from about 30 wt.%to about 70 wt. %solids.

51. The wet-lap of clause 50, wherein the wet-lap comprises from about 40 wt. %to about 60 wt. %solids.

52. The wet-lap of clause 51, where the wet-lap comprises about 50 wt. %solids.

53. The wet-lap of any of clauses 36 to 52, wherein the wet-lap is produced from old corrugated container board (OCC) .

54. The wet-lap of any of clauses 36 to 53, wherein the wet-lap is provided in a bale.

55. The wet-lap of any of clauses 36 to 54, which has been stored at a temperature of 20℃ to 40℃, at a humidity of 80%to 100%for a period of at least two weeks.

56. The wet-lap of clause 55, which has been stored for a period of at least six weeks.

57. The wet-lap of any of clauses 36 to 56, wherein the amount of aerobic bacteria present in the wet-lap is less than 1 x 10 ⁹, less than 1 x 10 ⁸, or less than 1 x 10 ⁷ CFU/g wet-lap.

58. The wet-lap of any of clauses 36 to 57, wherein the amount of fungi present in the wet-lap is less than 1 x 10 ⁷, less than 1 x 10 ⁶, or less than 1 x 10 ⁵ CFU/g wet-lap.

59. A method of making paper or board using the wet-lap of any of clauses 36 to 58, wherein the method comprises:

ii) passing the fibre stock through a paper machine to form paper or board.

60. Use of an amylase inhibitor and a biocide in preserving fibre strength in wet-lap.

Example 1

A fibre stock was prepared from old corrugated container board, and treated with a source of zinc ions in an amount of 6.3 ppm (relative to the weight of water) in combination with 4, 5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) in an amount of 4.4 ppm (relative to the weight of water) . The fibre stock was then pressed and dehydrated into wet-lap cakes having a solid content of 50 wt. %and stored at 35℃ with high humidity conditions for a period of six weeks. The zero-span breaking strength index of the wet-lap (an indicator of fibre strength) was measured prior to storage, and after two weeks, four weeks, six weeks, and eight weeks of storage according to TAPPI standard T231 cm-96 as described above. The starch content was also measured at the same time points by absorbance spectroscopy.

In order to conduct the absorbance measurements, the wet-lap cake (approximately 25 g) was soaked in 1l tap water for 30 minutes and disintegrated to form a pulp using a laboratory disintegrator at 3000 rpm for 10 min. Approximately 30 g of pulp was filtered under gravity using a funnel lined with black ribbon filter paper. The filtrate was collected and 3 ml of this was suspended into 1.3 ml 1wt. %HCl and 5.7 ml H ₂O to form a test sample. An absorbance spectrophotometer (HACH DR 900, program 275#) was calibrated to zero with the suspension solution above, at a wavelength of 610 nm. 0.4 ml iodine reagent (7.5 g/l KI and 5 g/l I ₂) was added to the test sample and the absorbance measured after 30 seconds.

The results are provided in Tables 1a, 1b, 2a and 2b below.

Table 1a –Fibre strength

Table 1b –Reduction in fibre strength

Table 2a –Starch Content

Table 2b –Reduction in starch content

The results above illustrate that the combined use of zinc and DCOIT in the method of wet-lap preparation significantly reduces the loss of fibre strength in wet-lap that is otherwise observed with no treatment up to a period of at least six weeks. The combined treatment further reduces the loss in starch content that is otherwise observed with no treatment up to a period of at least six weeks.

These data suggest that maintaining starch levels in wet-lap by using a combination of an inhibitor of amylase and a biocide, results in reduced cellulose degradation and associated loss of fibre strength.

Example 2

Bacterial counts in wet-lap produced according to the process described in Example 1 were further conducted using standard methods. The results are shown in Table 3 below.

Table 3 –Bacterial counts in wet-lap

The results above illustrate that treatment with DCOIT significantly reduces the level of aerobic bacteria in the wet-lap in the presence of a zinc amylase inhibitor compared to the untreated control, across all time-points tested.

Example 3

A fibre stock was prepared from old package boxes to a pulp consistency of approximately 5 wt. %and a starch content of approximately 4.6 Abs/g. The fibre was treated with a source of zinc ions in an amount of 6.4 ppm (relative to the weight of water) in combination with a biocide. The biocide was added to the fibre stock and the identity and dosage amount is set out below. The fibre stock was then pressed and dehydrated into wet-lap cakes having a solid content of 50 wt. %and sprayed with 1 ml of zinc ion source on each of the two major surfaces. The cakes were stored at 35℃ with high humidity conditions for a period of eight weeks. The zero-span breaking strength index of the wet-lap (an indicator of intrinsic fibre strength) was measured at the times set out below using the methodology as described in Example 1. Bacterial counts were also measured.

The results are provided in Tables 4a, 4b and 4c below.

Table 4a –Biocide

Biocide
4, 5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT)
2-n-Octyl-4-isothiazolin-3-one (OIT)
Didecyl-dimethylammonium chlorine (DDAC)

Table 4b –Reduction in zero-span breaking strength index at week 8 relative to week 0

	Percentage reduction
Control (OIT –6.4 ppm)	17.4
Zn + OIT (4.3 ppm)	11.1
Control (DDAC –39.1 ppm)	28.4
Zn + DDAC (26.6 ppm)	23.7

Table 4c –Bacterial counts in wet-lap

	Aerobic count (CFU/g wet-lap)
	Week 8
Control (No treatment)	2.4E+08
DCOIT	6.53E+06
Zn + DCOIT	4.08E+05
OIT	1.58E+08
Zn + OIT	7.95E+07
Zn + DDAC	1.21E+08

The results above illustrate that treatment with zinc and biocide reduces long-term zero span breaking strength loss in wet-lap as compared with treatment with biocide alone. This effect correlates to some extent with the level of aerobic bacteria in the wet-lap at the same time point. Bacterial counts in Table 4c are lower in wet-lap treated with biocide in the presence of zinc amylase inhibitor as compared to either untreated control or treatment with biocide alone.

Inhibition of starch degradation was also observed in the Zn + DCOIT and Zn + OIT treated wet-lap samples (data not shown) .

Example 4

A fibre stock was prepared from a mixture of recycled cardboard sources to a pulp consistency of approximately 5 wt. %and a starch content of approximately 4.94 Abs/g. The fibre was treated with a source of zinc ions in an amount of 7.4 ppm (relative to the weight of water) in combination with a biocide. The biocide was added to the fibre stock and the dosage amount is set out below. The fibre stock was then processed to produce wet-lap cakes as set out in Example 3. 30%of the zinc source was added to the fibre stock with the biocide and 70%was sprayed on the surfaces of the wet-lap cakes. Starch was measured using the methodology as described in Example 1. Strength parameters were determined as described below.

The results are provided in Tables 5a, 5b, 5c and 5d below.

Table 5a –Reduction in starch content

These results show that starch degradation is inhibited in wet-lap treated with both Zn and biocide as compared with biocide alone.

Bursting strength, ring compression strength (RCT) and short-span tensile strength (SCT) were measured using standard methodology using Lorentzen & Wettre apparatus. Bursting strength was measured according to ISO 2759: 2014. RCT was measured according to ISO 12192: 2011. SCT was measured according to ISO 9895: 2008.

Table 5b –Reduction in bursting strength

These results show that reduction in bursting strength is inhibited in wet-lap treated with both Zn and biocide as compared with biocide alone.

Table 5c –Reduction in ring compression strength

These results show that reduction in ring compression strength is inhibited in wet-lap treated with both Zn and biocide as compared with biocide alone.

Table 5d –Reduction in short-span tensile strength

These results show that reduction in short-span tensile strength is inhibited in wet-lap treated with both Zn and biocide as compared with biocide alone.

It was also found that there was a correlation between bursting strength, ring compression strength and short-span tensile strength; and also between bursting strength, short-span tensile strength and starch content reduction (data not shown) . Taken together, these results indicate that use of a biocide to inhibit microorganism growth will in turn inhibit starch loss and loss of fibre strength when used in the presence of a zinc amylase inhibitor.

Example 5

This example relates to a study of the microorganism profile in wet-lap and the effect of a combination of Zn and biocide on the microorganism profile.

It has been common to believe that the main cause of fibre strength degradation in wet-lap is the presence of fungi. Fungi can produce cellulases which degrade cellulose fibres. The surface of wet-lap cakes and bales show fungal growth, for example in the form of clearly visible white dots, patches or coatings. In the examples above. Some of the wet-lap cakes displayed these signs of fungal growth.

DNA based analysis was performed using quantitative polymerase chain reaction (qPCR) and next generation sequencing (NGS) according to standard methods. qPCR weas used to determine total fungal count and total bacterial count. NGS was used to determine bacterial community composition.

Samples were taken from various spots in the interior of two different wet-lap bales (1a-1e and 2a –2e) . The results are provided in Tables 6a and 6b below.

Table 6a –Bacterial and fungal densities (qPCR)

Sample	Total Bacterial (cells/g)	Total Fungi (cells/g)
WL-1a	1.11E+08	1.10E+05
WL-1b	4.77E+07	ND
WL-1c	1.13E+08	6.23E+04
WL-1d	7.27E+07	1.33E+04
WL-1e	6.10E+07	ND
WL-2a	1.12E+08	ND
WL-2b	2.88E+08	3.24E+05
WL-2c	6.88E+08	5.82E+05
WL-2d	2.58E+08	7.64E+04
WL-2e	4.84E+08	5.20E+05

These results indicate that wet-lap bales contain at least three orders of magnitude fewer fungi than bacteria. This finding is consistent with microbial counts taken from untreated wet-lap cakes. This suggests that bacteria are primarily responsible for fibre degradation, rather than fungi.

Table 6b –Anaerobic Clostridia composition of wet-lap (NGS)

Sample	Percentage Clostridia
WL-1a	44.5
WL-1b	38
WL-1c	37.4
WL-1d	28.1
WL-1e	42.8
WL-2a	57
WL-2b	46
WL-2c	29.7
WL-2d	29.4
WL-2e	32.6

The above NGS results showed a bacterial community composition in which the mean Clostridia content was 38.2%for bale 1 and 38.9%for bale 2. These values are high for anaerobic Clostridia bacteria, suggesting that wet-lap bales have a significant anaerobic environment during storage.

The Clostridia class of bacteria is from the phylum Firmicutes and includes the following bacterial genera which were detected by NGS in the wet-lap: Clostridium sensu stricto, Qxobacter, Garciella, Sedimentibacter, Anaerosporobacter, Lachnospiraceae_unclassified, Peptococcaceae_unclassified, Acetanaerobacterium, Caproiciproducens, Ruminococcaceae_unclassified, Ruminococcus 1. These bacteria produce cellulases which will degrade the fibre constituents of pulp. For example, Ruminococcaceae, including Caproiciproducens and Acetanaerobacterium, are strictly anaerobic cellulose degraders. Ruminococcaceae are typically found in the rumen of ruminant animals.

In order to study the effect of zinc and biocides on wet-lap microorganism composition, samples were taken from the wet-lap cakes of Example 4. The results are provided in Tables 6c and 6d below.

Table 6c –Bacterial and fungal densities (qPCR)

	Total bacteria (cells/g)	Total fungi (cells/g)
Control (DCOIT –8.6 ppm)	2.18E+08	below quantification limit
Zn (7.4 ppm) + DCOIT (6.1 ppm)	1.22E+08	below quantification limit

Table 6d –Anaerobic Firmicute composition (NGS)

	Percentage of anaerobic Firmicutes
Untreated wet-lap sample	34.8
DCOIT (8.6 ppm)	17
Zn (7.4 ppm) + DCOIT (6.1 ppm)	9.9

These results show that the proportion of anaerobic Firmicutes such as Clostridia in wet-lap can be reduced when treated with a biocide. They also show that treatment with biocide in the presence of a Zn amylase inhibitor as compared with biocide alone is superior in reducing the proportion of anaerobic bacteria.

Claims

A method of preparing wet-lap comprising:

i) suspending a source of recycled cellulose fibres in water to form a fibre stock, and

ii) dewatering the fibre stock to form wet-lap;

wherein the fibre stock comprises starch, and

wherein the method further comprises treating one or more of the recycled cellulose fibres, fibre stock and wet-lap with an inhibitor of amylase activity and a biocide.
The method of claim 1, wherein the water is process water obtained from pulp, paper or board production.
The method of claim 1 or claim 2, wherein the amylase inhibitor comprises a source of zinc ions.
The method of claim 3, wherein the source of zinc ions is selected from: ZnBr ₂, ZnCl ₂, ZnF, Znl ₂, ZnO, Zn (OH) ₂, ZnS, ZnSe, ZnTe, Zn ₃N ₂, Zn ₃P ₂, Zn ₃As ₂, Zn ₃Sb ₂, ZnO ₂, ZnH ₂, ZnCO ₃, Zn (NO ₃) ₂, Zn (C1O ₃) ₂, ZnS0 ₄, Zn ₃ (PO ₄) ₂, ZnMoO ₄, ZnCrO ₄, Zn (AsO ₂) ₂, Zn (AsO4) ₂, Zn (O ₂CCH ₃) ₂) , zinc metal, and a combination thereof.
The method of any preceding claim, wherein biocide comprises a non-oxidizing biocide selected from: 2, 2-Dibromo-3-nitrilopropionamide (DBNPA) , 2-Bromo-2-nitropropane-1, 3-diol (Bronopol) , 2-Bromo-2-nitro-propan-1-ol (BNP) , 2, 2-Dibromo-2-cyano-N- (3-hydroxypropyl) acetamide, 2, 2-Dibromomalonamide, 1, 2-Dibromo-2, 4-dicyanobutane (DCB) , Bis (trichloromethyl) sulfone, 2-Bromo-2-nitrostyrene (BNS) , Didecyl-dimethylammonium chlorine (DDAC) , Benzalkonium chloride (ADBAC) , 3-Iodopropynyl-N-butylcarbamate (IPBC) , Methyl and Dimethyl-thiocarbamates and their salts, 5-Chloro-2-methyl-4-isothiazolin-3-one (CMIT) , 2-Methyl-4-isothiazolin-3-one (MIT) , 2-n-Octyl-4-isothiazolin-3-one (OIT) , 4, 5-Dichloro-2- (n-octyl) -3 (2H) -isothiazolone (DCOIT) , 4, 5-Dichloro-1, 2-dithiol-3-one, 1, 2-Benzisothiazolin-3-one (BIT) , 2- (Thiocyanomethylthio) benzthiazole (TCMBT) , 2-Methyl-1, 2-benzisothiazolin-3 (2H) -one (MBIT) , Tetrakis hydroxymethyl phosphonium sulfate (THPS) , Tetrahydro-3, 5-dimethyl-2H-1, 3, 5-thiadiazine-2-thione (Dazomet) , Methylene bisthiocyanate (MBT) ; Ortho-phenylphenol (OPP) and its salts; Glutaraldehyde; Ortho-phthaldehyde (OPA) , Guanidines and biguanidines, N-dodecylamine or n-dodecylguanidine, dodecylamine salt or dodecylguanidine salt, preferably dodecylguanidine hydrochloride, Bis- (3-aminopropyl) dodecylamine, Pyrithiones, , Triazines, preferably, Hexahydro-1, 3, 5-trimethyl-1, 3, 5-triazine, 3- [ (4-Methylphenyl) sulfonyl] -2-propenenitrile, 3-Phenylsulphonyl-2-propenenitrile, 3- [ (4-trifluormethylphenyl) sulphonyl] -2-propenenitrile, 3- [ (2, 4, 6-trimethylphenyl) sulphonyl] -2-propenenitrile, 3- (4-methoxyphenyl) sulphonyl-2-propenenitrile, 3- [ (4-methylphenyl) sulphonyl] prop-2-enamide, isomers thereof, and any combination thereof, preferably, wherein the non-oxidizing biocide is 4, 5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) or 2-n-Octyl-4-isothiazolin-3-one (OIT) .
The method of any preceding claim, wherein the wet-lap comprises from about 30 wt. %to about 70 wt. %solids, or from about 40 wt. %to about 60 wt. %solids, or about 50 wt. %solids, and optionally, wherein the fiber stock comprises from about 1 wt. %to about 20 wt. %solids or. from about 2 wt. %to about 5 wt. %solids.
The method of any preceding claim, wherein the wet-lap is sprayed with an inhibitor of amylase activity.
The method of any preceding claim, wherein dewatering is carried out by pressing action, preferably, wherein dewatering is carried out using a twin-press machine, or wherein dewatering is carried out using a screw press, or wherein dewatering is carried out by centrifugation.
The method of any preceding claim, wherein the inhibitor of amylase activity is incorporated into one or more of the recycled cellulose fibres, fibre stock and wet-lap in an amount of about 5 to about 100 ppm, or in an amount of about 5 to about 20 ppm, based on the weight of the inhibitor of amylase activity, relative to the weight of water in the recycled cellulose fibres, fibre stock or wet-lap.
The method of any preceding claim, wherein the biocide is incorporated into one or more of the recycled cellulose fibres, fibre stock and wet-lap in an amount of about 1 to about 100 ppm, or in an amount of about 2 to about 15 ppm, based on the weight of the inhibitor of amylase activity, relative to the weight of water in the recycled cellulose fibres, fibre stock or wet-lap..
The method of any preceding claim, wherein the wet-lap has a zero-span breaking strength index of about 90 to about 120 N·m/g, or about 100N·m/g, as measured according to TAPPI standard T 231 cm-96.
Wet-lap comprising an inhibitor of amylase activity and a biocide, optionally, wherein the wet-lap has been produced according to the method of any preceding claim.
The wet-lap of claim 12, which has been stored at a temperature of 20℃ to 40℃, at a humidity of 80%to 100%for a period of at least two weeks, or for a period of at least six weeks.
The wet-lap of claim 12 or claim 13, wherein the amount of aerobic bacteria present in the wet-lap is less than 1 x 10 ⁹, less than 1 x 10 ⁸, or less than 1 x 10 ⁷ CFU/g wet-lap, and/or the amount of fungi present in the wet-lap is less than 1 x 10 ⁷, less than 1 x 10 ⁶, or less than 1 x 10 ⁵ CFU/g wet-lap.
Use of an amylase inhibitor and a biocide in preserving fibre strength in wet-lap.