Insulation for Structural Insulated Panels

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The instant application is a continuation-in-part (CIP) of co-pending application Ser. No. 18/447,487 filed Aug. 10, 2023. All disclosure of the parent application is incorporated at least by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is in the technical field of modular prefabricated structural components and relates more particularly to structural insulated panels (SIPS), and to filler materials and binders.

2. Description of Related Art

Modular and prefabricated components for use in developing structures for residences and commercial buildings are notoriously well known in the art. In a particular circumstance, insulated panels, such as prefabricated panels insulated with polymer foam of various sorts, are well known and are referred to as F-SIPS. It is also well known that creation and production of the polymer insulating materials for F-SIPS is not carbon neutral. It is desirable in the present circumstance of global warming to reduce carbon emissions to a minimum, and a significant quantity of carbon is released into the atmosphere in the thermal and chemical procedures producing polymer foam.

What is clearly needed in the art is apparatus and process for providing insulation that does not release carbon into the atmosphere and even sequesters it. Plants capture carbon through photosynthesis and straw is a proven plant-based insulation material as it is produced in harvesting crops that bind carbon. Straw-insulated structural panels, termed hereafter S-SIPS and the procedures of growing additional straw crops and processing same into insulation for prefabricated structural panels can make a significant difference in carbon emissions.

A well-known issue in insulating structural panels is in preparing the insulative material, such as straw, and in how the prepared material may be placed in panels and how binding may be done.

BRIEF SUMMARY OF THE INVENTION

In one embodiment of the invention a method for insulating a building panel is provided, comprising chopping plant matter into pieces having a specific size range; mixing gluten with warm water, forming a slurry, adding a catalyst that precipitates cross-linking to the gluten slurry, mixing the chopped plant matter with the gluten slurry having been mixed with the catalyst, and adding the plant matter mixed with the gluten slurry to one or more volumes in a structural frame.

In one embodiment the method further comprises introducing one or both of heat and airflow after the plant matter mixed with the gluten slurry is added to one or more volumes in the structural frame. Also, in one embodiment the method selecting the plant matter from one of or a mixture of wheat, rice, barley or oat straw. In one embodiment the method comprises chopping the plant matter into pieces of a size range from one-eighth to two inches inclusive. In one embodiment the method comprises selecting the catalyst as an enzyme. And in one embodiment the enzyme is transglutaminase.

In an alternate aspect of the invention an insulated building panel is provided, comprising one or more volumes for insulating material, insulating material in at least one of the one or more volumes, the material comprising plant matter chopped into pieces of a specific size range, mixed with a gluten slurry formed with warm water, with an added catalyst that precipitates cross-linking.

In one embodiment the building panel is subject to heat and airflow. Also, in one embodiment the plant matter is one of or a mixture of wheat, rice, barley or oat straw. Also, in one embodiment the plant matter is in pieces in a size range from one-eighth to two inches inclusive. In one embodiment the catalyst is an enzyme, and in one embodiment the enzyme is transglutaminase.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a perspective view of a straw insulated structural panel in an embodiment of the present invention.

FIG. 2A is a perspective view of a sturdy support plate supporting a frame for a building panel in an embodiment of the invention.

FIG. 2B illustrates the frame of FIG. 2A filled with chopped straw

FIG. 2C illustrates a rectangular section of fabric hardware netting of the width and length of the frame of FIG. 2B.

FIG. 3A is a perspective view of a mold in an embodiment of the invention.

FIG. 3B is a perspective view of a ram to fit in the mold of FIG. 3A.

DETAILED DESCRIPTION OF THE INVENTION

An important object of the present invention is to provide building panels that minimize heat transfer across the panels and do so by incorporating insulative material in the panels that derive from plant material, which binds carbon. In embodiments of the present invention building panels are provided that limit heat transfer through the panels by features of construction of the panels, and also by incorporating insulative material that is straw from various sources, treated with a binder to old the straw together, as is needed to have panels that may be stored, shipped and manipulated in building procedures.

FIG. 1 is a perspective view of a straw insulated structural panel 100 in an embodiment of the present invention, from a viewpoint within a building, such that the front surface of the structure in FIG. 1 faces into the building and the back surface is to the outside. Panel 100 in this embodiment has a rectangular frame 101 that has a cap beam 102 and a base beam 103. In one embodiment the cap beam and the base beam are both 2×6 lumber, having a width of 5.5 inches. In alternative embodiments the cap beam and the base beam may be wider, such as 2×8, and in some embodiments may be other than lumber, such as a combination of wood pulp and synthetic materials covered with a synthetic shell, similar to decking materials. In one embodiment W is four feet and H is eight feet, and in another the dimensions are four by ten feet. The overall dimensions are determined in some cases by standard sizes for structural panels, but these dimensions are not limiting to the scope of the invention.

Frame 101 has, in this example, three vertical studs 104, 105 and 106 that, in this example, are 2×4 lumber, 3.5 inches in width. In other embodiments the studs may be other than lumber, such as a combination of wood pulp and synthetic materials covered with a synthetic shell, similar to decking materials. Studs 104 and 106 form partial outer edges of frame 101 and the rear edge of studs 104 and 106 are even with the rear edge of cap and base beams 102 and 103. Vertical stud 105, however, has an inner edge that is even with the forward edge of cap and base beams 102 and 103. The lesser depth of the three studs, and the staggering of the studs, minimizes thermal bridging through the structure. A vertical strip 110 is added along the forward edge of vertical studs 104 and 106 to even out the overall size of the building panel, and this strip does not contact the vertical studs.

Structural panel 100 has a structural sheathing panel 107 covering the rear of frame 101. The structural sheathing panel may be one-quarter, one half, or three quarters thickness plywood in alternative embodiments. In alternative embodiments the sheathing panel may be other than plywood, such as, for example, weatherboard or fiberboard. The sheathing panel has in some embodiments an additional weather barrier 113, preferably of a biodegradable material. Vertical strips of wood 112, in some embodiments 1×2 inch, is added on the back side to provide a rainscreen as a space between the sheathing and siding, allowing moisture to evaporate.

In this example a series of cross pieces 109, spanning the width of the building panel on the forward side, and spaced apart vertically, act as chase strips to provide space for electrical wiring. These strips may be 1×2 inch lumber, or in some cases 1×4.

The internal volumes of the building panel, for the full depth of the frame, are filled with an especially prepared straw material 111. Straw material 111 in one embodiment is prepared from dried straw that has been chopped in a chopping machine to individual strands that may vary between one-half inch to about 1 inch in length. The individual strands may vary within a predetermined range in length. The type of straw may vary. The original straw may be wheat, rice, barley or oat straw depending on a number of factors, such as, for example, availability and cost. In some embodiments a mixture of different types of straw may be used.

Although the panels described above have staggered studs, that is, the cap and base beams may be greater in depth than the studs, to minimize conductive heat transfer through the panel, in some embodiments the cap and base beams and the studs may be of equal depth.

FIG. 2A is a perspective view of a sturdy support plate 201 supporting a frame 101 for a building panel in an embodiment of the invention. In FIG. 2A frame 101 has structural sheathing 107 attached, but not the rainscreen strips on the back or the chase strips on the front. In this circumstance frame 101 presents two side-by-side volumes 202 and 203 upward.

In one embodiment of a method to apply the insulation material into the open frame, dried straw is fed through the chopping machine and blown or poured after chopping into the side-by-side volumes of the panel frame. FIG. 2B illustrates frame 101 filled with chopped straw. FIG. 2C illustrates a rectangular section of a natural fiber fabric netting of the width and length of frame 101. In one embodiment after the frame volumes are filled with chopped straw, netting 204 is placed over the frame and stapled or nailed to the edges of the cap beam, base beam, and studs to retain the chopped straw in the frame. Once netting 204 is attached, the chase strips and rainscreen strips may also be attached, and the building panel is finished.

In an alternative method the chopped straw may be treated with an additive binder and formed into the volumes of the frame while the binder has yet to cure. In some embodiments the binder may be nanocellulose or sugar or starch-based material. Natural waxes may also be used as binders. After filling the frame the binder material may harden by a chemical or a physical process and cause the chopped straw to form a semi-solid form. In some cases the binder may be liquid at a temperature at application and may gel on cooling. There are a wide variety of materials that might be used as a binder. Some are polymeric. Other chemical fillers may be used as well. Naturally derived admixtures are preferably used. In some circumstances chopped straw with a binder may be used and a fabric netting or screen may be employed as well.

Straw might in some embodiments be long strand. In other embodiments the straw may be chopped to specific parameters that denote both a gradient and proportion of straw fiber sizes, for example from roughly 12″ in length down to roughly 1/32 inches in length. The chapped straw may be cleaned to remove small straw particles by graded screening and by moving air over the straw to remove fines and dust. In some cases a binder may be heated before being added to straw particles, and in some processes the straw particles may be heated without a binder. In some processes industrial agricultural machinery may be used in the processing of straw.

An important feature of the processing a straw with or without a binder is to create a straw matrix with a microstructure that significantly improves upon the thermal performance of unprocessed straw.

In yet another alternative method as illustrated in FIG. 3A a mold 301 is constructed with an internal volume of a width D1 and length D2 equal to the internal dimensions of frame 101 between the cap and base beams and studs 104 and 105. A depth D3 of the mold is greater than the depth of the frame 101, perhaps in some cases as much as twice or more. FIG. 3B illustrates a ram 303 of width D1 and length D2 trimmed to fit into mold 301. In practice straw is chopped and mixed with a binder material and mold 301 is filled to the top (depth D3) with the treated chopped straw. Ram 303 is placed over the chopped straw in the mold and urged downward by forces F. The treated chopped straw in mold 301 is compressed until the thickness of the mass of straw in the mold is the depth of frame 101, that is, the width of 2×6 lumber. The chopped straw in the mold is held at the compressed thickness until the binder cures, and the ram may be removed. The mold may then be disassembled or upturned to remove the compressed straw, which, by virtue of the cured binder, may form a semi-rigid, self-supporting block. In some cases reinforcement such as one or more wooden rods laid lengthwise in the mold may be included to help the released straw block to maintain the shape.

In practice straw blocks may be manufactured as described above and stored until needed in the manufacture of building panels according to embodiments of the invention.

Such straw blocks may be moved and stored between plywood panels. Building panels are constructed up to the point of adding the rainscreen strips and the chase strips, and straw blocks manufactured as described above may be placed into the side-by-side volumes in the frames of the panels, then the rainscreen strips and chase strips may be added to complete the panels. In this example the chase strips may be enough restraint to hold the straw blocks in place.

There may be in embodiments of the invention a variety of methods and processes employed. In assembly of structural panels in embodiments of the invention traditional, that is conventional, framing methods of nailing and screwing in a factory setting may be practiced. Assembly line methods may also be used with automated machines.

Processes to be performed either manually or by machines may include:

• • Moving material from stacks to be processed
  • Cutting material to size
  • Nailing/screwing framing together
  • Nailing/screwing sheathing onto framing
  • Handling panels (flipping over, standing upright, etc.)
  • Moving panel down the assembly line to different stations
  • Adding straw to cavity
  • Sandwiching the panel between temporary rigid plates to resist bulging forces during insulation densification, vertically filling with straw, removing plates

Processes in straw installation may include:

• • Compressing horizontal layers with a hydraulic or pneumatic press.
  • Compressing vertical layers with a hydraulic or pneumatic press
  • Blowing insulation matrix into panel volumes
  • Filling the panel and using vibratory consolidation either via an internal vibrating tamper (similar to concrete) or external vibration of the panel

Straw installation density is likely to be in the range of 6 pcf-14 pcf.

In one embodiment of the invention the binder is of choice is specifically a protein: gluten. There are other biobased protein binders such as, for example corn zein, soy protein, whey, and casein, to name just a few. These are the most readily available and also the most studied. In alternative embodiments of the invention one or another of these alternative protein binders may well be used. Generally speaking, relative to protein binders, proteins have a unique structural form which enables a wide range of functional properties, in particular a high intermolecular binding potential. Proteins generally unfold and dissociate in subunits when treated with heat, acid, base and/or various solvents. Once unfolded, protein chains may interact through hydrogen, ionic, hydrophobic and covalent bonding. Bonding formation is affected by the degree of denaturation and the nature and concentration of amino acids able to form those bonds.

Utilizing a protein material as a binder generally involves denaturing the protein, and then facilitating crosslinking of a protein network within the matrix material. Additives that facilitate protein unfolding and subsequent crosslinking vary from protein to protein and depend upon the properties desired. This is particularly true in the case of gluten.

Solvents useful to prepare protein film-forming solutions are generally based on water, alcohol or mixture of water and alcohol or a mixture of other solvents. Most commonly, after mixing and application, solvent removal is generally achieved by hot air or a combination of techniques as it may lead to a differential protein structuring and therefore variable protein film properties.

In an aqueous alcohol solution, gluten can be cross-linked using several methods, including chemical cross-linkers, enzymes, and thermal treatment. These approaches create covalent bonds that alter the protein's structure, which typically increase strength and resistance to water.

Chemical cross-linking incorporates chemical agents to form new bonds between the functional groups of the gluten proteins. Water-soluble carbodiimides, such as 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide HCl (EDC), can form cross-links by coupling carboxyl groups with amino groups on the gluten proteins. The efficiency of this reaction is dependent on pH, with a neutral pH (5-7) favoring intermolecular cross-linking. Addition of N-hydroxysuccinimide (NHS) can also enhance the cross-linking process. Dialdehydes like glutaraldehyde can react with amino groups on the gluten proteins to form strong, covalent bonds. Isophorone diisocyanate may be used to cross-link gluten proteins dissolved in ethanol, significantly improving the resulting material's mechanical strength.

Enzymes may also be used to precipitate cross-linking gluten, particularly in food applications, and may also be used in an alcohol-based solution. The enzyme Transglutaminase catalyzes formation of new bonds between the amino acid lysine and glutamine residues, creating strong, intermolecular bonds. Further, enzymes like sulfhydryl oxidase, laccase, and glucose oxidase promote formation of disulfide bonds (S—S) by oxidizing free sulfhydryl (thiol) groups (SH) on cysteine amino acids. They can also cause other reactions, such as the formation of dityrosine bonds.

In addition to the above, thermal treatment at relatively high temperature may induce cross-linking, especially with addition of other agents like alkali.

Heating an aqueous alcohol solution of gluten can cause the proteins to denature and unfold, exposing hydrophobic groups and sulfhydryl groups. This circumstance promotes formation of new disulfide bonds and other aggregates through hydrophobic interactions. Increasing pH (such as by adding alkali) can lower the temperature required for heat-induced aggregation and strengthen the gluten network.

When working with gluten in aqueous alcohol, only the alcohol-soluble gliadin proteins and reduced glutenin subunits may be fully dissolved. The overall extent and mechanism of cross-linking will depend in part on the ratio of water to alcohol. Increasing concentration of ethanol in the solution can inhibit some types of heat-induced cross-linking, as it affects the protein's conformation and solvent interactions.

A Specific process in the present invention comprises firstly preparing the straw. The straw may be any one of a number of plant-based fibers as described above, such as wheat, rice, barley or oat straw. Other types of plant-based fiber may also be used.

The straw is chopped to an optimal length range and proportion of different fiber lengths, ranging primarily from 2 inches down to ⅛ inch in length. Dust and microparticles may removed if necessary, depending on the batch of straw. In some embodiments a micro-abrasion process may be applied to the surface of the fiber to increase receptivity to binder.

To prepare the binder, gluten within a target protein content range is mixed with warm water. The temperature range may vary. The mixing is accomplished with a blending apparatus converting the gluten material into an aqueous slurry. Soon after preparing the slurry a catalyst or cross-linking agent is added. There are many candidates, such as certain enzymes like Transglutaminase. This enzyme creates strong, covalent bonds that cross-link gluten proteins. Glucose Oxidase operates by catalyzing formation of hydrogen peroxide, creating new disulfide bonds between gluten proteins. Several other enzymes may also be used also cross-link gluten proteins. These include Lactase which cross-links ferulic acid and tyrosine residues on proteins, Peroxidase, similar to glucose oxidase, which uses hydrogen peroxide to form cross-links, Lipoxygenase, which oxidizes lipids, which in turn causes the oxidation of proteins and the formation of cross-links, Ascorbic Acid, which promotes formation of disulfide bonds, which strengthens the gluten network.

After preparation as described above, the binder with the catalyst of cross-linking agent is added to the chopped fiber and mixed, and the chopped fiber with activated gluten binder is added to whatever framed structure meany to be insulated by the fiber matrix. This process is, of course, time sensitive, as taking too much time may result in a bonded fiber not malleable enough to add to the framed structure. Finally, heat and airflow is incorporated in encouraging the bonded fiber matrix to solidify, that is, set.

The skilled person will understand that the order and timing of steps in the process may be varied somewhat in practice. Further, the skilled person will be aware that the embodiments described above, both methods and apparatus, are entirely exemplary, and are not limiting to the scope of the invention. There are a wide range of variations that might be made within the scope of the invention, which is limited only by the claims.