Patent Publication Number: US-2018030654-A1

Title: Agricultural Fibre-Based Paper

Description:
The present invention relates to agricultural fibre-based paper, such as straw paper, in particular a lamination or specialty paper, such as décor paper, that is suitable for printing and/or impregnating for lamination and/or coating and use in laminated and/or coated products. 
     Lamination is the technique of manufacturing a material in multiple layers so that the composite material achieves improved strength, stability, sound insulation, appearance or other properties from the use of differing materials. A laminate is usually permanently assembled by heat, pressure, welding, or adhesives. 
     A laminate consists of a single or multiple layers, each having its own distinct function. The base is most often particle- or fibreboards, then some layers of absorbent kraft paper. The last layers are a decor paper covered with an overlay. The lamination papers are covered with an inert resin, often melamine, which is cured to form a hard composite with the structure of paper. 
     Lamination paper is a paper used for laminates, normally on particle or fibreboards, giving a good-looking and resistant surface typically for use in interior design as decoration panels, flooring, doors and furniture, such as book cases, shelves, table tops and chairs, and flooring. 
     Décor paper is the most critical of the lamination papers as it gives the visual appearance of the laminate. Traditionally, décor paper is composed of pulp, pigments and fillers. The pulp is typically derived from soft woods wood such as spruce, recycled papers or other post-consumer fibres and is blended from a range of different fibre cut lengths and mixes. The paper is then sized and this uses different coatings to alter the ink and water repellence of the paper. Décor paper has a grammage in the range of 50-150 g/m 2 . 
     There are different types of décor paper, such as high and low pressure laminate paper (“HPL”/“LPL”) (also referred to as “unicolour”), print base paper (“PBP”), balance paper and pre-impregnated paper and other papers. 
     High pressure laminate (HPL) is the direct descendent of the original plastic laminate and is considered to be one of the most durable decorative surface materials. It is available with special performance properties including chemical, fire and wear resistance. 
     HPL is produced by saturating multiple layers of kraft paper with phenolic resin. A layer of printed décor paper is placed on top of the kraft paper before pressing. The resulting sandwich is fused together under heat and pressure (more than 1,000 PSI). Because phenolic and melamine resins are thermoset plastics, the curing process transforms the resin into plastic by a cross linking process that converts the paper sheets into a single, rigid laminated sheet. Thermosetting creates strong, irreversible bonds that contribute to HPL&#39;s durability. 
     HPL and LPL paper is sold almost exclusively to laminators, who impregnate the papers with melamine resin and then laminate them with high temperature and high pressure. The weight of HPL paper is typically 80-120 grams while LPL paper usually has a weight of about 80 grams. 
     PBP is sold mainly to printers, who print the decor paper for panel and laminate flooring producers. The core competence of the printers is in design, i.e. in creating different decorative prints decor such as wood, stone or coloured patterns. The paper weight of PBP is 70 grams or lower. 
     Pre-impregnated décor paper is sold to printers and is impregnated by the décor paper manufacturer in the decor paper machine. The weight of pre-impregnated decor paper is 60 grams or less. 
     In further processing stages, décor paper is often printed by the decor paper producers&#39; customers with decors such as wood, stone or coloured patterns (more than 50% of decor paper is printed). In further stages, both printed and non-printed décor paper is impregnated with melamine resin (pre-impregnated paper needs a lacquered surface instead). After impregnation, the resulting intermediate product is laminated onto a wood-based substrate such as medium density fibreboards (“MDF”) or particleboard. Pre-impregnated décor paper is not laminated, but glued onto the wood-based substrate. 
     Use of field crop fibre or agricultural residues instead of wood fibre in paper and board manufacturing is advocated as being more sustainable. Not only is there enough straw to meet much of North America&#39;s book, magazine, catalogue and copy paper needs, but agricultural-based paper is a guaranteed way to reduce the stress of paper production on old growth and endangered forests. Furthermore, some agricultural residue pulps take less time to cook than wood pulps which, in turn, means agricultural-based paper uses less energy, less water and fewer chemicals. In addition, pulp made from wheat and flax straw has half the ecological footprint of pulp made from forests. 
     As explained in WO 00/25998, the use of agricultural residue or “straw” in the production of composite panels is known. The first development of these composite panels used wheat straw and was originally formulated in Europe more than thirty years ago. 
     The early developments of such products typically used wheat straw as a filler. In the manufacture of cereal grain straw particleboard, an isocyanate resin is conventionally used to fuse the particles together. The advent of MDI (diphenylmethane diisocyanate) resin technology, for example, has allowed the use of a 100% cereal grain straw particleboard. 
     WO 02/081160 describes methods of processing straw to obtain fibres useful for board or panel production such as medium density fibreboard (“MDF”) and particleboard that use urea-formaldehyde (UF) and melamine urea formaldehyde (MUF) as alternative resins. 
     Thus, agricultural fibres are known to be suitable for use in the manufacture of boards that are used in laminated products. However, the resins used in the manufacture of the board and the need for the fibres to be of a length and arrangement to allow impregnation with resin means that it is not possible to print directly onto the finished surface with sufficient clarity to be acceptable for decorative purposes. As a result, a printable décor paper is adhered to the top surface. 
     WO 2013/044347 provides an example of a method of manufacturing paper from a non-wood fibre source that has a finish suitable for use as photocopy paper, toilet paper, tissue paper, paper towels, wrapping paper, box board, photo paper, coloured paper, commercial printer-grade paper (for use in book and periodical printing and publishing), writing paper, stationery, sack paper and paper board. 
     These papers all require a long fibre content for strength and stiffness, freeness for the rate of drainage of water, and smoothness, brightness and opacity for printing surface quality. Such qualities make the paper unable to take up and absorb resin for lamination. 
     Because of the printable surface required by décor paper and the inability of printable décor paper to be impregnated with resin, it is not possible to adhere a décor paper to lamination paper using a typical lamination process. As a result, décor paper is usually adhered to lamination paper using adhesive or high temperature and pressure. Over time, the adhesive dries resulting in the décor paper becoming unstuck. This gives an unsightly article which besets the laminate industry, particularly in the field of furniture. 
     It is against this background that the present invention has been devised. Specifically, it has been appreciated that there is a need for a non-wood based lamination, décor or packaging paper that is suitable for resin impregnation and that has a printable surface. 
     Accordingly, the present invention encompasses a decor or lamination paper for lamination, wherein the paper has a furnish in which the fibre portion comprises between 1% and 100% non-wood pulp. 
     A decor paper, decorative lamination paper or lamination paper is generally understood in the art to be the top sheet of paper used in decorative laminates. In the present invention, the paper is a technical paper that needs to be both printable and able to absorb types of resin and other coatings to give it a resilience that is essential for lamination. 
     A furnish is defined as the mixture of fibrous and non-fibrous materials, such as fillers, sizing and dyes, in a water suspension from which paper is made. In other words, a furnish is the mixture of paper-making ingredients, including cellulose fibres, ready for use in a paper machine to produce a designated grade of paper. Pulp provides the fibrous material to a furnish and is produced either mechanically or chemically from fibrous cellulose raw material. 
     In one embodiment, the fibre portion of the furnish may comprise 50% to 100% non-wood pulp, preferably 75% to 100% non-wood pulp. 
     Ideally, the non-wood pulp is derived from plant materials, particularly the stalks of one or more families of short-rotation plant materials grown under cultivation. Examples of plant materials include cereal straw, perennial grasses, reeds and bamboo. Generally wood (including hardwoods, softwoods, and coppiced wood) is not included in this definition. 
     A significant advantage of the paper and furnish of the present invention lies in the use of non-wood pulps whose inherent physical attributes can be used to reduce the processing costs associated with conventional papermaking without compromising quality. Particularly useful attributes are a high unrefined tensile strength combined with a lower unrefined drainage rate. Expressed in another way, the furnish provides a paper with a greater tensile strength for a given freeness (a measure of drainage). Freeness is the ability of a pulp and water mixture to release or retain water on a paper machine. 
     The use of agrifibre or plant material pulp in paper has largely been avoided because of perceived quality and operational issues, with drainage being one of the most significant. Yet, in the decorative overlay and laminating paper market, wood pulps must be heavily refined to impart the desired properties. For example, when aspen pulp is refined to the same tensile strength, smoothness and porosity as unrefined wheat straw, the aspen pulp has a freeness that is lower than that of wheat, meaning that aspen should be more drainage-limited that wheat at that point in the papermaking process. It is the pulp properties that are found in unrefined plant fibres that are harnessed in the present invention. 
     The plant material may be derived from crop residue from the production of cereals, legumes, sugar, bamboo, reeds and perennial grasses, bast plants and/or leaf fibres. 
     Suitable plants include but are by no means limited to flax, hemp, oats (including water oats), rye, wheat (bread, Durum, macaroni, spelt, Einkorn, Emmer, Kamut), barley, jute, kenaf, rice (wild, Canada, Indian), cotton, corn, maize, alfalfa, millet, sugar cane, sorghum, triticale, Job&#39;s Tears,  Eragrostis, Digitaria, Phalaris, Agave sisalana, Musa textilis , perennial grasses, perennial plants and combinations thereof, bamboo, as well as other crop residues that traditionally are sent to landfills/incinerators or ploughed back under the field. Pseudocereals may also be used, such as amaranth, Love-lies-bleeding, Prince-of-Wales-feather, Breadnut, buckwheat, chia, cockscomb, kañiwa, pitseed goosefoot, quinoa and wattleseed (also called acacia seed). 
     One type of plant fibre is cereal straw which comprises straw collected from cereal grain crops and includes but is not limited to wheat, oats, barley, rice and rye. 
     A suitable furnish comprises a blend of sugarcane bagasse and wheat straw pulp. Preferably, the wheat straw pulp is unrefined. Alternatively or in addition, the sugarcane bagasse pulp is refined. 
     In a further embodiment, the furnish further comprises a bonding agent. A bonding agent is typically a resin and may be synthetic, plant-based or bio-based. A suitable resin is a thermosetting resin selected from the group consisting of: melamine, polyurethanes, acrylics (including acrylic acid, methacrylic acid, polymethyl acrylate and polymethyl methacrylate), epoxy resins, phenolic resins (including urea-formaldehyde), polyester resins and mixtures thereof. 
     The papers of the invention may be used for High Pressure Lamination (HPL) and Continuous Pressure Lamination (CPL). Decor papers for HPL process require a complete saturation by pure melamine formaldehyde (MF) resin evenly absorbed in the core and are glued on wood based panels or directly used as compact panels. Suitable uses include worktops, water resistant panels, furniture for reception counters or laboratories, window sills and outdoor cladding. 
     The papers of the invention may also be used for Low Pressure Lamination (LPL). The most frequent application of such papers is as decorative surfaces for furniture, doors and laminate flooring. 
     Preferably the lamination and decor paper of the present invention has a grammage of about 50-150 g/m 2 . 
     The paper of the present invention is envisioned for use to upgrade the surface of wood-based panels or articles that provide an excellent surface for decorative printing and resin saturation for use in the production of laminate flooring, interior and exterior architectural panels including decoration panels and doors, and furniture, such as book cases, shelves, table tops and chairs. The paper may also be used as a luxury paper for packaging, such as for use in the manufacture of laminated paper bags. 
     The manufacture of paper from pulp begins with “slushing” which turns the pulp into an aqueous slurry that allowed fibres to be dispersed. The paper is then treated by mechanical refining. During this process, clusters of fibres are brushed out and cut to a more uniform length, thereby further increasing their surface area and improving their adhesion. 
     To reduce porosity and develop equivalent tensile strength to non-wood pulps, wood pulps must be heavily refined, which requires an additional processing step (i.e. a refiner) that consumes a significant amount of electricity. Refining or beating of chemical pulps is the mechanical treatment and modification of fibres so that they may be formed into paper or board of the desired properties. It is one of the most important unit operations when preparing papermaking fibres for high-quality papers or paperboards. The method consists of a series bars which provide a brushing and compressive action on the pulp fibres and may be carried out on a small or laboratory scale in a PFI mill or Valley Beater. 
     The main target of refining is to improve the bonding ability of fibres so that they form strong and smooth paper sheet with good printing properties. Sometimes the purpose is to shorten too long fibres for a good sheet formation or to develop other pulp properties such as absorbency, porosity, or optical properties specifically for a given paper grade. 
     Once refined, the drainage behaviour of wood pulps approaches that of non-wood pulps, effectively negating any perceived disadvantage associated with the poor drainage of non-wood pulps. 
     However, the present invention uses the drainage behaviour of non-refined non-wood pulps, thus providing a method that results in the use of significantly less energy than that which is typically associated with paper making. 
     Thus, the present invention also encompasses a method for making a non-wood paper, wherein the method comprises forming a slurry of bleached or unbleached unrefined non-wood pulp, blending the slurry with chemical or mineral additives, and passing the slurry into a paper-making machine. 
     It may be necessary to include wood pulp to the slurry. In which case, the method further comprises blending the slurry of unrefined non-wood pulp with a slurry of refined wood pulp. It may also be advantageous to include a slurry of refined non-wood pulp. Such blends enable properties, such as strength and porosity, of the final paper to be selected. 
     The inclusion of unrefined non-wood pulp enables significant savings on energy usage, such that it should be possible to refine the slurry of non-wood pulp using less than 50 kWh/ODMT (Kilowatt-hours per oven-dry metric tonne). 
     It will be appreciated that the unrefined non-wood pulp is produced by a chemical pulping method. This is because a mechanical pulp requires refining using energy in the order of 1000-2000 kWh/ODMT. 
     It has been found that when sugarcane bagasse is included in the non-wood slurry, refining of the bagasse enables the production of a paper that is suitable for use as a décor or lamination paper. However, it has been found that the amount of refining required for sugarcane bagasse is still considerably less than that which is required to refine wood pulps to the same freeness, tensile strength, surface and optical properties. 
     It will be appreciated that the slurry of refined wood pulp may comprise any wood pulp. For example, the use of a softwood pulp has been found to be particularly suitable for a décor or lamination paper. 
     It will be appreciated that any non-wood source may be used. The use of plant material and agrifibres as described herein above is an example only. In particular, it will be appreciated that use of local and regionally grown agrifibres and plant materials is preferred, with the composition of the furnish changing according to each region in the world. 
     Sizing is the process of coating the fibres and filling the pores of the paper to give it some degree of water or ink repellence. This may be carried out at the refining stage, by the addition of rosin, aluminium sulphate, starch or water-glass. 
     Fillers, dyes and other additives are also added at this stage to improve the strength and quality of the paper. Fillers increase opacity and give a better printing surface. For example, the method may further comprise the addition of ash to the slurry. 
     While the present invention has been described for lamination and speciality papers, such as décor paper, it will be appreciated that the papers described herein may also be suitable for use as packaging paper. A particularly suitable example is coated paper for use in luxury packaging. Packaging paper constitutes the largest portion of packaging material, even more than glass, metal or plastic. It is multi-purpose, clean and flexible. Types of packaging paper include corrugated cardboard, kraft paper for paper bags, classic brown packaging paper and coated papers for luxury packaging. They perform important functions in merchandise management: protection from damage during transport and storage, as information carriers or purely for image enhancement. 
     The present invention will now be described by way of non-limiting examples. 
    
    
     EXAMPLE 1 
     In 2004, a study sponsored by Alberta Agriculture Research Institute (AARI) explored the behaviour of wood and non-wood chemical pulp properties during the refining process. Table 1 shows the results from unrefined pulps of spruce, aspen, Eucalyptus and wheat. The wheat pulp for this study was a commercial pulp sourced from China. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                   Euca - 
                   
               
               
                 Analysis 
                 Unit 
                 Spruce 
                 Aspen 
                 
                   lyptus 
                 
                 Wheat 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 PFI, TAPPI †   
                 revs 
                 0 
                 0 
                 0 
                 0 
               
               
                 C.S. Freeness 
                 mLs 
                 631 
                 487 
                 500 
                 483 
               
               
                 Bulk 
                 cc/g 
                 1.72 
                 1.71 
                 1.98 
                 1.59 
               
               
                 Tear index 
                 mN · m 2 /g 
                 25.8 
                 2.7 
                 2.8 
                 3.5 
               
               
                 Burst index 
                 kPa · m 2 /g 
                 2.96 
                 0.72 
                 0.68 
                 2.41 
               
               
                 Tensile index 
                 N · m/g 
                 37.3 
                 20.7 
                 20.7 
                 51.4 
               
               
                 Stretch 
                 % 
                 3.20 
                 0.94 
                 1.15 
                 2.12 
               
               
                 Tensile Energy 
                 J/m 2   
                 51.9 
                 7.5 
                 9.3 
                 44.5 
               
               
                 Absorption 
               
               
                 Roughness OR 
                 SCCM 
                 228 
                 181 
                 243 
                 143 
               
               
                 Smoothness* 
               
               
                 Air permeability OR 
                 SCCM 
                 1675 
                 1781 
                 2376 
                 115 
               
               
                 porosity* 
               
               
                   
               
               
                   † TAPPI—Technical Association of the Pulp and Paper Industry 
               
               
                 *Bendtsen surface roughness and air permeability tests were used. 
               
            
           
         
       
     
     Table 2 shows data from the same study comparing refined pulps of spruce, aspen, Eucalyptus and wheat. Again, Bendtsen surface roughness and air permeability tests were used. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                   
                   Euca - 
                   
               
               
                 Analysis 
                 Unit 
                 Spruce 
                 Aspen 
                 
                   lyptus 
                 
                 Wheat 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 PFI, TAPPI 
                 revs 
                 9,138 
                 9,019 
                 10,000 
                 1,000 
               
               
                 C.S. 
                 mLs 
                 265 
                 265 
                 265 
                 269 
               
               
                 Freeness 
               
               
                 Bulk 
                 cc/g 
                 1.32 
                 1.48 
                 1.67 
                 1.49 
               
               
                 Tear index 
                 mN · m 2 /g 
                 10.3 
                 7.1 
                 8.1 
                 3.3 
               
               
                 Burst index 
                 kPa · m 2 /g 
                 8.63 
                 2.52 
                 2.88 
                 3.50 
               
               
                 Tensile 
                 N · m/g 
                 105.1 
                 47.0 
                 50.9 
                 65.6 
               
               
                 index 
               
               
                 Stretch 
                 % 
                 4.29 
                 3.15 
                 3.27 
                 2.99 
               
               
                 Tensile 
                 J/m 2   
                 179.7 
                 66.3 
                 70.4 
                 79.5 
               
               
                 Energy 
               
               
                 Absorption 
               
               
                 Roughness* 
                 SCCM 
                 64 
                 77 
                 107 
                 56 
               
               
                 Air perme- 
                 SCCM 
                 34 
                 202 
                 685 
                 29 
               
               
                 ability* 
               
               
                   
               
               
                 *Bendtsen surface roughness and air permeability tests were used. 
               
            
           
         
       
     
     The data shows that the wheat furnish required much less refining energy than wood-based furnishes to achieve the same freeness. In addition, the wheat furnish had a lower tear strength than wood furnishes, but the tensile, burst, and tensile energy absorption (TEA) properties of the wheat furnish were superior to refined hardwoods (Eucalyptus, Aspen). 
     EXAMPLE 2 
     The aim of this experiment was to compare the properties of unrefined wheat against unrefined and refined sugarcane bagasse as a function of refining extent. Sugarcane bagasse pulp was refined in a laboratory “PFI mill” in accordance with standard TAPPI test methods. 
     It is to be understood that the wheat straw pulp sourced for this study was inferior to that used in the AARI study. In this example, the sugarcane bagasse pulp was either unrefined or refined at 100 or 5500 PFI revolutions. The wheat straw was unrefined. 
     The resulting papers were analysed and the results are set out in Table 3. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Analysis 
                 Unit 
                 Wheat Straw 
                 Sugarcane Bagasse 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 PFI, TAPPI 
                 revs 
                 0 
                 0 
                 100 
                 5500 
               
               
                 C.S. Freeness 
                 mLs 
                 264 
                 501 
                 481 
                 264 
               
               
                 Basis weight, 
                 g/m 2   
                 65.70 
                 65.63 
                 66.92 
                 65.86 
               
               
                 conditioned 
               
               
                 Bulk 
                 cc/g 
                 1.31 
                 1.64 
                 1.47 
                 1.33 
               
               
                 Caliper 
                 ml 
                 3.40 
                 4.23 
                 3.86 
                 3.44 
               
               
                 Burst index 
                 kPa · m 2 /g 
                 2.27 
                 2.10 
                 2.58 
                 3.62 
               
               
                 Tear index 
                 mN · m 2 /g 
                 2.56 
                 6.15 
                 6.14 
                 5.97 
               
               
                 Tensile index 
                 N · m/g 
                 44.4 
                 38.5 
                 44.8 
                 58.9 
               
               
                 Tensile 
                 km 
                 4.53 
                 3.92 
                 4.57 
                 6.01 
               
               
                 Stretch 
                 % 
                 1.84 
                 2.17 
                 2.39 
                 3.16 
               
               
                 Tensile Energy 
                 J/m 2   
                 37.9 
                 38.9 
                 51.4 
                 89.3 
               
               
                 Absorption 
               
               
                 Smoothness* 
                 SCCM 
                 620 
                 1984 
                 1669 
                 952 
               
               
                 Porosity* 
                 SCCM 
                 223 
                 2997 
                 1750 
                 245 
               
               
                 Brightness, ISO †   
                 % 
                 71.2 
                 42.4 
                 41.6 
                 39.6 
               
               
                 Opacity, ISO 
                 % 
                 85.8 
                 93.2 
                 92.0 
                 88.8 
               
               
                   
               
               
                 *Sheffield smoothness and porosity (0.75″ orifice) tests were used. 
               
               
                   † ISO refers to the standard method used to test brightness which is that published by the International Standards Organisation. 
               
            
           
         
       
     
     EXAMPLE 3 
     Analysis of the non-wood fibre pulps in Example 2 was used to inform the creation of two blends of non-wood fibres. 
     In particular, the experiment allowed the comparison of paper made from pure unrefined wheat with pure sugarcane refined at 100 PFI revolutions and blends of unrefined wheat and sugarcane refined at 100 PFI revolutions. 
     Analysis of the resulting papers is set out in Table 4. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                   
                   
                   
                   
                 60%  
                 70%  
                   
               
               
                   
                   
                   
                   
                 Sugarcane  
                 Sugarcane  
                   
               
               
                   
                   
                   
                 Sugar  
                 Bagasse +  
                 Bagasse +  
                   
               
               
                   
                   
                 Wheat  
                 Cane  
                 40%  
                 30%  
                 Refined  
               
               
                 Analysis 
                 Unit 
                 Straw 
                 Bagasse 
                 Wheat straw 
                 Wheat straw 
                 wood 
               
               
                   
               
             
            
               
                 % sugarcane 
                   
                 0.1% 
                 100.0% 
                 60.0% 
                 70.0% 
                 0% 
               
               
                 C.S. Freeness 
                 mLs 
                 264 
                 481 
                 384 
                 418 
                 N/A 
               
               
                 Basis weight, conditioned 
                 g/m 2   
                 65.70 
                 66.92 
                 65.81 
                 67.39 
                 62.63 
               
               
                 Bulk  
                 cc/g 
                 1.31 
                 1.47 
                 1.39 
                 1.44 
                 1.18 
               
               
                 Caliper 
                 ml 
                 3.40 
                 3.86 
                 3.61 
                 3.82 
                 2.91 
               
               
                 Burst index 
                 kPa · m 2 /g 
                 2.27 
                 2.58 
                 2.34 
                 2.30 
                 1.17 
               
               
                 Tear index 
                 mN · m 2 /g 
                 2.56 
                 6.14 
                 4.86 
                 5.09 
                 4.025 
               
               
                 Tensile index 
                 N · m/g 
                 44.4 
                 44.8 
                 45.6 
                 43.7 
                 30.45 
               
               
                 Tensile 
                 km 
                 4.53 
                 4.57 
                 4.65 
                 4.46 
                 N/A 
               
               
                 Stretch 
                 % 
                 1.84 
                 2.39 
                 2.21 
                 2.19 
                 4.44 
               
               
                 Tensile Energy Absorption 
                 J/m 2   
                 37.9 
                 51.4 
                 47.7 
                 46.6 
                 30.45 
               
               
                 Smoothness †   
                 SCCM 
                 620 
                 1669 
                 1142 
                 1339 
                 627 
               
               
                 Porosity †   
                 SCCM 
                 223 
                 1750 
                 644 
                 972 
                 1316 
               
            
           
           
               
            
               
                 Optical Properties: 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Brightness, ISO 
                 % 
                 71.2 
                 41.6 
                 50.4 
                 48.4 
                 86.8 
               
               
                 Opacity, ISO 
                 % 
                 85.8 
                 92.0 
                 91.5 
                 91.7 
                 96.05 
               
               
                   
               
               
                 * Sugarcane Bagasse pulp was refined at 100 PFI revolutions. Wheat straw pulp was unrefined 
               
               
                   † Sheffield smoothness and porosity (0.75″ orifice) tests were used. 
               
            
           
         
       
     
     Sugarcane bagasse clearly increases bulk, tear strength, tensile energy absorption, roughness and porosity. 
     Based on strength and porosity, a blend of 70% sugarcane bagasse and 30% wheat straw was used for further experiments. 
     EXAMPLE 4 
     This experiment illustrates the impact of adding Northern bleached softwood kraft (NBSK) pulp (60-70% Pine, 25-33% Spruce and 5% Fir) to a blend of 70% refined sugarcane bagasse pulp and 30% unrefined wheat straw pulp on the resulting calliper (thickness), smoothness and porosity of the blended sheet. Due to its high fibre length and low fibre coarseness, NBSK is one of the most commonly used pulps in the paper industry for increasing paper strength. 
     The NBSK pulp was refined at 1000 PFI revolutions before addition to the wheat straw/sugarcane bagasse blend. As with Example 3, the wheat straw pulp was unrefined and the sugarcane bagasse pulp was refined at 100 PFI revolutions. 
     Analysis of the resulting sheets is set out in Table 5. 
     
       
         
           
               
               
             
               
                   
                 TABLE 5 
               
             
            
               
                   
                   
               
               
                   
                 70% sugarcane bagasse/30% wheat straw 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 0% 
                 5% 
                 10% 
                 20% 
               
               
                   
                   
                 refined 
                 refined 
                 refined 
                 refined 
               
               
                 Analysis 
                 Unit 
                 NBSK 
                 NBSK 
                 NBSK 
                 NBSK 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 C.S. Freeness 
                 mLs 
                 418 
                 435 
                 457 
                 528 
               
               
                 Caliper 
                 ml 
                 3.82 
                 3.66 
                 3.67 
                 3.62 
               
               
                 Smoothness †   
                 SCCM 
                 1339 
                 1177 
                 1250 
                 1444 
               
               
                 Porosity †   
                 SCCM 
                 972 
                 780 
                 952 
                 1252 
               
               
                   
               
               
                 * Sugarcane Bagasse pulp was refined at 100 PFI revolutions. Wheat straw pulp was unrefined. 
               
               
                   † Sheffield smoothness and porosity (0.75″ orifice) tests were used. 
               
            
           
         
       
     
     The data show a role for refined softwood in papermaking (superior tear, tensile, burst, Tensile Energy Absorption) compared to hardwoods and non-woods. 
     It will be appreciated that other non-wood pulps may be sourced to offset softwood use as reinforcement, particularly of tear strength. Pulps from bamboo, cotton and bast fibre crops such as flax and hemp are specifically known for their tear strength. 
     EXAMPLE 5 
     In this experiment, precipitated calcium carbonate (PCC) was added to the blend of Example 4 containing 10% refined NBSK. PCC (Socal® NR2, Solvay Chemicals) was added as a mineral filler to increase brightness and opacity. 
     Table 6 sets out the analysis of the resulting paper sheets. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 6 
               
             
            
               
                   
                   
               
               
                   
                 0% 
                 25% 
                 50% 
                 50% 
               
               
                   
                 PCC 
                 PCC* 
                 PCC* 
                 PCC †   
               
            
           
           
               
               
               
            
               
                   
                   
                 10% refined NBSK 
               
               
                 Analysis 
                 Unit 
                 70% Sugarcane Bagasse/30% Wheat straw 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Caliper 
                 mils 
                 3.67 
                 3.79 
                 4.10 
                 3.71 
               
               
                 Bulk 
                 cc/g 
                 — 
                 — 
                 1.52 
                 1.53 
               
               
                 Burst index 
                 kPa · m 2 /g 
                 — 
                 — 
                 1.20 
                 0.92 
               
               
                 Tear index 
                 mN · m 2 /g 
                 — 
                 — 
                 5.29 
                 4.21 
               
               
                 Tensile index 
                 N · m/g 
                 — 
                 — 
                 25.1 
                 20.7 
               
               
                 Stretch 
                 % 
                 — 
                 — 
                 2.11 
                 1.57 
               
               
                 Tensile Energy 
                 J/m 2   
                 — 
                 — 
                 24.5 
                 14.4 
               
               
                 Absorption 
               
               
                 Smoothness ‡   
                 SCCM 
                 1250 
                 1475 
                 1527 
                 1442 
               
               
                 Porosity ‡   
                 SCCM 
                 952 
                 2069 
                 2336 
                 2382 
               
            
           
           
               
            
               
                 Optical Properties: 
               
            
           
           
               
               
               
               
               
               
            
               
                 Brightness, ISO 
                 % 
                   
                 — 
                 61.2 
                 65.3 
               
               
                 Opacity, ISO 
                 % 
                   
                 — 
                 96.0 
                 95.8 
               
            
           
           
               
            
               
                 Analytical: 
               
            
           
           
               
               
               
               
               
               
            
               
                 Ash @ 525 C. 
                 % 
                 0 
                 12.8 
                 20.5 
                 28.0 
               
               
                   
               
               
                 *10% refined NBSK at 1000 revolutions + 90% [70% Sugarcane Bagasse (refined at 100 PFI revolutions)/30% Wheat straw soda AQ pulp (unrefined)] 
               
               
                   † 10% refined NBSK at 9300 revolutions + 90% [70% Sugarcane Bagasse (refined at 100 PFI revolutions)/30% Wheat straw soda AQ pulp (unrefined)] 
               
               
                   ‡ Sheffield smoothness and porosity (0.75″ orifice) tests were used. 
               
            
           
         
       
     
     As can be seen, porosity increased dramatically and suggests that tensile strength may be increased by additional refining of the sugarcane bagasse portion of the furnish. 
     It will be appreciated that parameters and blends may be changed to produce a paper having specific properties. For example, burst, tensile, stretch and Tensile Energy Absorption properties could all be improved with additional refining of sugarcane bagasse, by adding 20% heavily-refined NBSK and sourcing a better wheat pulp. 
     Further optimisation of wet end sizing and retention chemistry, as well as soft calendaring of the sheet, will improve these properties. This type of optimisation is best performed on a paper machine, where the impact of paper machine white water recirculation may be taken into account.