Patent Application
20190232522
The present specification relates to in-plane isotropic products derived from cellulosic filament based compositions that are binderless (i.e. substantially free of binders); and methods for producing these products by compression molding.
As described by Hua et al (US20110277947A1; US20130017394A1), when wood pulp fibers are suitably refined, to peel the fibers into cellulose filaments, the resulting filaments have no lumen and are considerably thinner than the parent fibers while maintaining much of their length. The unique morphology of these cellulose filaments increase their flexibility and promote their entanglement. Furthermore, these filaments have a higher surface area when compared to the parent fiber which exposes more hydroxyl groups per given weight. Higher amounts of surface hydroxyl groups in turn lead to increased hydrogen bonding density. When an aqueous suspension of these cellulose filaments was used in compression molding process under high temperature, the dewatering and drying times were in the order of several hours. Furthermore, the resulting products were non uniform and dimensionally unstable.
Production of fibrillated cellulose pulp, microfibrillated cellulose and nanofibrillated cellulose are made by applying either mechanical or chemical energy to conventional pulp which in turn liberates fibrils of cellulose that are much narrower than original pulp fibers, providing access to much more hydrogen bond sites than in the original material. Advantageous use of these hydrogen bonds to produce solid products without pressing has been reported (U.S. Pat. No. 6,379,594B1 and WO2011/138604 A1).
As early as 1997, DOpfner et al (CA 2,237,942) described the forming and molding of work pieces from aqueous cellulose microfiber pulp without the addition of bonding or filler material or use of external pressure. The cellulosic material was produced from hemp or other sources of cellulose. The manufacture of this microfiber material and the formation of binderless work pieces in stamping molds, but without pressure, were also described by DOpfner et al in a second patent (U.S. Pat. No. 6,379,594 B1).
In 2011, Dean and Hurding (WO2011/138604 A1, US20130101763) patented various products using fiber and fiber pulps where the microfiber acted as a self-bonding agent or microfibrous matrix capable of holding conventional fiber pulps, plastics, or fillers. US20130101763 A1 refers to the fabrication of microfiber pulp, and that other fibrillated cellulose fibers such as macro-, micro-, and nanofiber pulp can also be used. The self-binding nature of the microfiber was thought to mean that compatibilizers and polymeric matrices, typically required for composites, were not required in the fabrication of the cellulosic binderless pieces.
The end products made by Dean and Hurding were described according to their final density as either high or medium density products. Products were composed of 1-80% micro fiber with addition of 1-20% of conventional cellulosic fibers that were made from wood, grasses, straws or reeds. The range of end products made from these fiber self-binding systems included finishing boards or panels used for structural or finishing purposes in the construction industry. High density products of 1-1.5 g/cm3 and medium density products of 0.5-0.9 g/cm3 could be made with panel thicknesses varying from 1 to 25 mm. Dean and Hurding (US20130101763 A1) claimed that the addition of up to 35% of inorganic fillers such as calcium carbonate, talc or clay could increase the final product density to greater than 1.5 g/cm3. The products could be colored or brightened with the addition of mineral or synthetic colors, aluminum sulfate mordant or optical brighteners. The fabrication of larger 3D heating briquettes was described that had low flare with high calorific values. Metal salts to color the resulting flame emitted from briquettes could also be added. In other cases, the fiber binderless system, acting as matrix as stated by Dean and Hurding (US20130101763 A1), could hold from 1-49% of oil or bio-based plastic particles such as polypropylene.
Although Dean and Hurding (WO2011/138604 A1) describe the types and proportions of pulp fiber used, the shaping of a work piece, and the removal of water with the use of external pressure prior to drying, no detailed methods of work piece molding process were described. Furthermore, the combination of microfibers and conventional cellulosic fibers was always cited in the embodiments of Dean and Hurding (WO2011/138604 A1), most probably to accelerate the dewatering before and during the final drying. The microfiber content in the end work piece products never exceeded 80% by weight, as detailed by Dean and Hurding (WO2011/138604 A1).
Lee and Hunt (US20130199743A1) describe wet forming and compression molding processes to make binderless cellulosic fiber based panels and boards by using relatively low quality fibers, wood particles, such as saw dust and other natural wood components like lignin. Dewatering through vacuum and compression molding was accelerated through the addition of wood particles of larger dimensions than the pulp fibers.
In accordance with one aspect, there is provided a method of hot press compression molding an in-plane isotropic product comprising providing a cellulosic filament substantially free of a binder; providing an inorganic filler comprising an average particle size of less than or equal to 5 μm; mixing the cellulosic filament and the filler to produce a suspension; transferring the suspension to a preforming jig to produce a mat in the jig; and compression molding the mat to produce the in-plane isotropic product.
In accordance with another aspect, there is provided the method herein described, wherein the mat is further pressed to produce a preform and the preform is compression molded to produce the in-plane isotropic product.
In accordance with another aspect, there is provided the method herein described, wherein the suspension is 5 to 10 wt % solids.
In accordance with another aspect, there is provided the method herein described, wherein the preform is a consistency of 30 to 55 wt % solids.
In accordance with another aspect, there is provided the method herein described, wherein the inorganic filler for example are selected from the group consisting of CaCO3, Mg(OH)2, Al(OH)3, Al2O3, B2O6Zn3 or combinations thereof.
In accordance with another aspect, there is provided the method herein described, wherein the average particle size of the filler is less than 3 μm.
In accordance with another aspect, there is provided the method herein described, wherein the average particle size of the filler is between 1 and 3 μm.
In accordance with another aspect, there is provided the method herein described, wherein the compression molding is at ambient temperature and 250 psi to prepare a preform.
In accordance with another aspect, there is provided the method herein described, wherein the compression molding is done at an incremental increases in temperature of up to 150° C. and incremental increases in pressure of up to 1000 psi.
In accordance with another aspect, there is provided the method herein described, wherein the filler is 10 to 20% of the weight of the cellulose filament.
In accordance with another aspect, there is provided an in-plane isotropic product comprising a cellulosic filament substantially free of a binder; a filler comprising an average particle size of less than or equal to 5 μm.
In accordance with another aspect, there is provided the product herein described, wherein the filler is like CaCO3, Mg(OH)2, Al(OH)3, Al2O3, B2O6Zn3 or combinations thereof.
In accordance with another aspect, there is provided the product herein described, wherein the average particle size of the inorganic filler is less than 3 μm.
In accordance with another aspect, there is provided the product herein described, wherein the average particle size of the inorganic filler is between 1 and 3 μm.
In accordance with another aspect, there is provided the product herein described, wherein the product comprising 20% by weight of inorganic filler has a density in the range of 1.25 to 1.56 g/cm3.
In accordance with another aspect, there is provided the product herein described, wherein the product comprising 20% by weight of filler has a tensile strength superior to that of the non-filled product and greater than 50 MPa.
In accordance with another aspect, there is provided the product herein described, wherein the product comprising 20% by weight of filler has a flexural strength superior to that of the non-filled product and greater than 80 MPa.
In accordance with another aspect, there is provided the product herein described, wherein the product comprising 20% by weight of filler has an impact strength superior to that of the non-filled product and greater than 8 kJ/m2.
The cellulose filament based compounds described herein relate to and are suitable for accelerated dewatering compression molding, in a preferred embodiment by hot press compression molding. Final products are in-plane isotropic and binderless with enhanced surface uniformity, dimensional stability and mechanical properties. Also described herein are methods of compression molding of aqueous suspension of pure cellulose filaments or cellulose filament based compositions to produce in-plane isotropic binderless products with two dimensions such as flat panels or simple three dimensions such as fluted panels.
The method described herein for producing binderless and in-plane isotropic products from pure cellulose filaments or cellulose fibrils homogenously dispersed with inorganic fillers in a water suspensions, includes a first step of uniformly preforming the suspensions and then compression molded under high temperature to dryness. A variety of geometries, sizes, and surface finishes can be made. The present description further illustrates the parameters and mold design required for the compression molding of dimensionally stable products.
The method to accelerate dewatering and drying of the cellulose filament or fibril suspensions and products described herein relates to the addition of inorganic fillers to the suspension prior to the preforming stage. Added functionalities may also be given to the final product depending on the choice of inorganic fillers used. In other embodiments, addition of lower density fillers such as inorganic hollow microspheres might be selected for lowering the final binderless product density. Furthermore, expandable polymeric beads can also be added for further lightweight binderless products.
The products described herein are unique in terms of: 1) the used cellulosic material compositions are pure cellulose filaments, produced as described by Hua et al (US20130017394A1), without any addition of conventional cellulosic fibers or wood particles; 2) a high temperature compression molding process is described to accelerate dewatering and consolidation of cellulose filaments; and 3) the addition of inorganic fillers to accelerate the dewatering rate.
Prior to the method described herein, there was no hot press compression molding method for the production of cellulose filament-based products reported. Methods for making such products are described herein.
The cellulose filaments used and described herein are those of Hua et al (US20130017394A1); having the following properties; their thin width of approximately 30 to 100 nm and low thickness of approximately 50 nm and their high length of up to millimeters. These characteristics increase their flexibility, specific surface area, promote entanglements, and enhance hydrogen bonding density.
Binderless is defined herein as substantially free of any binders that would be understood to bind the cellulose filaments described herein together. Binders are understood to include but are not limited to any bio-based such as starch and latex; and oil based polymeric matrix known as thermoplastic such as polypropylene, nylon, and poly-lactic acid (PLA) or thermoset resins such as polyester, vinyl ester, epoxy, polyurethane; formaldehyde based binders such as urea formaldehyde, polymeric diphenyl methane diisocyanate (pMDI); or synthetic fibres such as polyester, polypropylene and nylon and polypropylene; or adhesives such as polyvinyl acetate and polyvinyl alcohol.
In-plane isotropic is defined herein as having identical properties in all in-plane directions/or axes. The cellulose filaments are randomly oriented in compression molded products; this being distinct from natural wood and engineered wood products (i.e. plywoods, cross-laminated timber) and have varying properties in different in-plane directions/axes.
As in prior art references (US 2013/0199743 A1 and US 2013/0017394 A1), the ability of cellulose filaments to form an isotropic solid block material by a simple ambient air drying over a period of weeks of an aqueous suspension has been noticed by the refiner operators and demonstrated in the laboratory. The air dried isotropic solid was found to have impressive properties, namely its specific gravity of 1.5 g/cm3, equal to that of pure cellulose, its hardness, and its distinguish fire resistance with respect to other cellulosic materials.
This present description illustrates methods and equipment that produce cellulose filament based products in an industrially viable compression molding process under high temperature. This process accelerates dewatering, drying and consolidation of the cellulose filament products, is flexible in that it allows application of different temperature and pressure cycles. By changing the temperature and pressure cycles, compression molding process gives the manufacturer added ways to control the mechanical properties, dimensional stability, and surface quality of the molded products.
The flow chart in
The formulation embodiments described herein are prepared by compounding aqueous suspensions of cellulose filament and inorganic fillers. This aqueous compounding is a very critical step required to convey uniformity and in-plane isotropic properties to the final products.
The embodiments described herein are prepared using pure cellulose filament pulp which was manufactured in pilot scale at 30% consistency as described by Hua et al (US20130017394A1). A medium to high consistency laboratory pulper was used to attain uniform aqueous suspensions of cellulose filaments within 10 min at 800 rpm. A 10% consistency based on dry weight was used for aqueous compound cellulose filament with inorganic fillers. The 10% dry consistency was suitable to optimize the dispersion and the entanglement of the cellulose filaments while minimizing the air entrapment within the aqueous suspensions. Low compound consistency and the addition of inorganic fillers both contribute to limiting the defects in the cellulose filament based products as well as improving their uniformity.
Other means of mixing can be used such as industrial compounders, blenders, mixers or pulpers. It is preferable to keep the compounding consistency at or below 10% for the benefits explained above. In one embodiment the suspension consistency is 5 to 30% solids, where in a preferred embodiment the suspension consistency is 5-15% solids, and in a particularly preferred embodiment the suspension consistency is 5-10 solids. Even though a lower consistency will improve the suspension and product uniformity, excessive dilution should be avoided in order to minimize the time and the dimensions of the tools required for the dewatering phases. More particularly, the level of dilution affects the volume of the compounder and the height of the jig required for dewatering the suspension into the desired preform. Dilution is nevertheless essential to minimize the defects, reduce the standard deviation of the measured physico-mechanical properties and dimensional stability of the final products.
Inorganic fillers are widely used in different industries such as paper making, coating, polymer reinforced composites, etc. In prior paper making art, Laleg et al (WO/2012/040830) and Dorris et al (US20160102018) have shown that cellulose filaments have the ability of retaining up to 92% by weight of inorganic fillers within their network to form highly filled papers and boards.
Inorganic fillers are typically used in composites to lower cost, increase stiffness and sometimes to increase fire resistance (aluminum tri-hydroxide). Also disclosed herein is a novel use for the inorganic fillers in compression molding. In compression molding of cellulose filaments, a defined amount of inorganic fillers are added during the compounding of aqueous suspension to accelerate drying and to improve the uniformity of the final product. Furthermore, the addition of inorganic fillers uniquely improves the dimensional stability and the surface quality of the compression molded products.
In addition to speeding up the drying during the hot press compression molding and the improvement of the dimensional stability of the molded cellulose filament binderless products,
In addition to the calcium carbonate and magnesium hydroxide, other inorganic fillers, such as aluminum hydroxide, aluminum oxide, and zinc borate (technical light, Sigma-Aldrich 14470), were also successfully tested to reduce the drying time during compression molding process. In addition to changes in mean particle size of the filler, changes in filler particle shape could also affect the drying rate and final properties of the cellulose filament products made by compression molding. Combinations of different filler types, shape and mean particle size could change drying rate and product characteristics but also may have a synergistic effect on drying and physico-mechanical properties of the compression molded products. Note that other types of inorganic fillers could also be used to improve drying rate but also to add functionality such as color, brightness, magnetism, conductivity, fire resistance, hardness, impact resistance, bullet proofing, acoustic insulation, dimensional stability and surface properties such as smoothness. In other embodiments, addition of lower density fillers such as inorganic hollow microspheres might be selected for lowering the final binderless product density. Expandable polymeric beads can also be added for further lightweight binderless products.
As the inorganic fillers are less hydrophilic than the cellulose filaments, they tend to dry faster than the surrounding cellulose filaments when exposed to hot pressing during compression molding. One of the potential mechanisms for this accelerated drying may involve this dryness differential that will drive the water and the vapor from the cellulose filament toward the closest inorganic particle, and so on. Thus, the inorganic filler particles act by creating a path for water and vapor evacuation during the hot pressing and drying.
Preform, Molding and Drying
The cellulose filaments based suspensions with inorganic fillers are dewatered in specially designed jig to generate the desired preform.
As per the embodiments described herein, the pre-forming may be conducted at room temperature or at temperatures below 100° C. The applied pressure was set at 250 psi.
As illustrated in
In a hot press molding process, the press platen temperatures and the pressure subjected on the preform are controlled and cycled to optimize the drying time and usually to maximize the molded part properties. Table 1 shows different compression molding and drying cycles. For example, in the cycle 3, the temperature is kept constant at 110° C. for the first 10 minutes and then increased and maintained at a maximum of 150° C. for 15 minutes. After the maintenance period, the temperature is gradually decreased to the initial starting temperature of 110° C. Simultaneously, the pressure rises by three step increments to reach 250 psi after 10 minutes, 500 psi after 15 minutes and a maximum of 1000 psi after 17 minutes. The pressure is then kept constant for 23 minutes before it is released to atmospheric pressure for a complete cycle time of 45 minutes.
The drying and molding cycle will have an impact on hydrogen bonding density as well as the whole consolidation quality, and thus the mechanical properties. This is illustrated in
Other means of drying could eventually be considered such as oven drying, microwave, radio frequency, all of which could be assisted with a vacuum system. Freeze drying might also be considered for lightweight cellulose filaments based products.
A variety of different surface finishes can be produced either from the mold used, from an insert embedded in the mold or by mechanical action or cutting of the cellulose filament molded product.
Contrary to wood that have oriented fibers or engineered wood products that have oriented particles, the cellulose filaments are randomly oriented in compression molded products.
In accordance with this present disclosure, Table 2 shows comprehensive comparison of CF-based panel properties with respect to commercial wood fibre based panel, both binderless and hot press molded. As clearly shown, CF-based molded products can address different market needs, that actual sustainable commercial binderless products cannot, where higher overall performance is required.
The method described herein produces binderless products from cellulose filament compositions from aqueous suspension more quickly and in an industrially viable manner by forming a hot press compression molding.
Addition of inorganic fillers such as calcium carbonate of smaller mean particle size in the cellulose filament compound to control drying rate during the hot press compression molding process has surprisingly improved dimensional stability and strength properties of the molded product. Cellulose filament preforms with or without inorganic fillers or organic additives for subsequent hot press compression molding or ambient air dried process are also disclosed.
Although hot press compression molding, mainly through the addition of inorganic fillers, seems like an industrially viable process, the ambient air dried products have superior features that may justify their longer production times. With their unique water and fire resistance, and marble-like features, these air dried products from cellulose filaments could be used in different markets. Furthermore, a combination of compression molding with a final air dried step may provide characteristics that near the air dried products.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CA2017/051101 | 9/19/2017 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62396402 | Sep 2016 | US |
