Since the 1950s, 8.3 billion tonnes (Bt) of virgin plastics have been produced, of which about 5 Bt have accumulated as waste in natural environments, posing severe threats to the entire ecosystem. With the total amount of petrochemical-based plastics produced by 2050 predicted to be 33 billion tons, compared to 0.28 billion tons in 2012 (I. Campbell and M.-Y. Lin et. al., Annu. Rev. Mater. Res. 2023, 53), the need for sustainable bio-based alternatives to traditional petroleum derived plastics is evident.
The chemical stability of common plastics makes them attractive for numerous applications, but is also responsible for slow degradation rates, which allow them to permeate the environment (X. Zhang, et al., Chem. Rev. 2018, 118, 839). During the long degradation timeframes, plastics are fragmented into microplastics that can seep into food and water systems at all levels of the food chain, causing health hazards throughout the environment (C. M. Rochman, et al. Nature, 2013, 494, 169).
Current bioplastics such as polylactic acid (PLA) and poly(hydrozyalkanoate) (PHA), have the potential to reduce petroleum dependency and plastic pollution. However, scalability challenges and economic feasibility limit the range of applications for these bioplastics. Other bioplastics suffer from similar issues. For example, thermoplastic starch has a relatively low strength of less than 6 MPa (K. M. Dang, et al., Carbohydr. Polym 2020, 242, 116392). Lingocellulosic polymers provide materials with a higher strength than thermoplastic starch, but the extraction of cellulose from biomass involves multi-step processes and harsh chemicals, and therefore does not address the ongoing environmental concerns of plastic production and use (G. Tedeschi, et. Al., Biomacromolecules, 2020, 21, 910).
Microalgae holds interest as a potential source for bioplastics, as microalgae capture around 1.8 kg CO2 per kg of dry biomass, providing an ecological advantage over fuel-derived polymers. For comparison, the global warming potential of 1 kg of high-density polyethylene pellets was reported to be 1.9 kg CO2 by PlasticsEurope, while polypropylene was reported to have a GWP of 2.0 kg CO2. In 2019, a cradle-to-gate study showed the GWP of Corbion PLA pellets to be 0.501 kg CO2 per kg of PLA. However, as of yet, microalgae have not yielded promising results as heated compression of Arthrospira platensis (spirulina) and Chlorella vulgaris (chlorella) show poor tensile strengths of 5.7 and 3.0 MPa, respectively (M. A. Zeller, et al., J. Appl. Polym. Sci. 2013, 130, 3263).
In an effort to overcome the drawbacks of biodegradable plastics, recent studies have attempted to introduce biologically based materials as fillers in common plastic matrices, thus minimizing the use of non-renewable materials. However, the poor bonding between plant-based biomatters and common plastics often leads to mechanical weakening of the produced bioplastics. Further, the heavy use of chemical additives and multi-step processing necessary to circumvent these bonding obstacles has rendered the manufacturability of this filler-based strategy challenging.
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Various implementations described herein relate to bioplastics and methods of manufacturing bioplastics from biomatter. The mechanical and physical properties of the bioplastics may be varied depending on composition and manufacturing conditions. In some examples the bioplastics may be made of a single biomatter source such as spirulina. In other aspects, the bioplastics may be made of a combination of biomatter sources such as spirulina and sorbitol. In other aspects, biomatter may be used with a filler or as a filler with existing plastics.
In particular embodiments, the biomatter may be used without extraction or chemical modification. In other embodiments, the biomatter may be pre-treated prior to self-bonding. In some examples the bioplastics are backyard compostables, losing their mass at a rate comparable to other backyard compostables such as fruits or plant matter. In some examples the bioplastics may also be biodegradable, in that they can be metabolized by microorganisms present in the environment that the bioplastics are disposed of. Microorganism degradation entails metabolic conversion of the carbon in bioplastics to gases (CO2 and or CO2+CH4) over time. In some aspects, the compostable products as described here may degrade at rates similar to food waste of the same surface area.
Biomatter may be obtained from any number of sources including algal, and non-algal biomatter. Exemplary algal biomatter sources include Arthrospira sp. (aka. spirulina); Chlorella sp. (subspecies: vulgaris); Ulva sp. (subspecies: expansa, lactuca, etc.); Saccharina latissima (sugar kelp); agarophyton; sargassum; Gracilaria parvispora; Halymenia hawaiiana; and Caulerpa lentillifera. Exemplary non-algal biomatter sources include proteins (including gluten, lactalbumin, bovine serum albumin BSA); lignin; cellulose (including bacterial cellulose fibers, nanocellulose, cellulose nanocrystals, cellulose nanofibers, alpha cellulose, carboxymethylcellulose); hemicellulose (including xylan, glucomannan); other carbohydrates (including starch, isomalt, sucrose); powdered wood from Douglas fir; agai; coffee beans; dragon fruit; matcha powder. The biomatter may include monomers, polymers, cells, tissues, or dissociated cells or tissues from a biological organism.
While biomatter may be obtained from any number of sources, algal biomatter, specifically spirulina, is used in particular embodiments. Spirulina is a multicellular, filamentous cyanobacteria with a rapid growth rate in a variety of aquatic environments (Mathiot, C. et al. Microalgae starch-based bioplastics: Screening of ten strains and plasticization of unfractionated microalgae by extrusion. Carbohydrate Polymers 208, 142-151 (2019)). The environmental resilience of algae including spirulina allows for it to be grown close to fabrication facilities, reducing the need for transportation. Further, microalgae may serve as a carbon sink, decreasing the carbon footprint of the manufactured bioplastics. As shown in
In various examples, the mechanical and physical properties of biomatter plastics, including spirulina bioplastics, may be altered by combining the biomatter with one or more matrix materials such as proteins (including gluten, lactalbumin, bovine serum albumin (BSA)); lignin; cellulose (including bacterial cellulose fibers, nanocellulose, cellulose nanocrystals, cellulose nanofibers, alpha cellulose, carboxymethylcellulose); hemicellulose (including xylan, glucomannan); and other carbohydrates (including starch, isomalt, sucrose). In various examples, biomatter plastics including spirulina bioplastics may be combined with fillers such as small (e.g., low molecular weight) sugars/carbohydrates (e.g., oligomers consisting of 3-10 monosaccharide units such as polyols like sorbitol, mannitol, glycerol, xylitol); lipids/fatty acids (including stearic acid, oleic acid, linoleic acid, palmitic acid, caprylic acid, lauric acid), carboxylic acids (e.g., monocarboxylic acids (formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, palmitoleic acid, oleic acid, linoleic acid, linolenic acid, or arachidonic acid) or a dicarboxylic acid (e.g., oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassylic acid, thapsic acid, or japanic acid), nanoclays (e.g., montmorillonite, halloysite), nanocellulose, and diatoms. Additional materials that may be combined with the algal materials included viscosity modifiers such as small (low molecular weight) sugars/carbohydrates (polyols like sorbitol, mannitol, glycerol), and lipids/fatty acids (including stearic acid, oleic acid, linoleic acid, palmitic acid, caprylic acid, lauric acid, palm oil) as well as components that enhance electrical conductivity such as graphene, carbon nanotubes (CNTs), carbon fibers, graphite or the magnetic properties of the compositions such as iron oxide particles.
Various bioplastics described herein may additionally be combined with commercial polymers such as polylactic acid (PLA); polybutylene adipate terephthalate (PBAT); polyhydroxyalkanoates (PHAs including copolymers such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate)); Polybutylene succinate (PBS); polyethylene; polypropylene; polystyrene; polycarbonate; and maleic anhydride. In some aspects, the polymers may be biodegradable polymers such as poly(lactic acid) (PLA), polybutylene adipate terephthalate (PBAT), polyethylene oxide (PEO), polycaprolactone (PCL), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), lignin, pine gum, BSA, gluten, casein, lactoglobulin, and/or lysozyme.
The various additives may include 0-99.99 wt % of the composition. In some aspects, the additives may include 0-30 wt % of the composition, including 0%, 10%, 30%, 40%, 45% or fractions thereof. In other aspects, the biomatter may comprise 50% of the bioplastic. The various additives to the biomatter compositions may alter one or more properties of the bioplastic in comparison to pure biomatter bioplastics. For example, a plasticizer such as sorbitol, glycerol, mannitol, xylitol, water, may increase the flexural strength of the bioplastic. In other aspects, the plasticizer may increase the tensile strength of the bioplastic. In some aspects, the plasticizer may increase the facture strain of the bioplastic.
Example biomatter plastics described herein may be used in a variety of consumer and industrial products. In some aspects, the bioplastics described herein may be used as plastic substitutes in a variety of consumer and industrial uses. For example, such bioplastics may be useful in the manufacture of computer peripherals, circuit bords, braille boards, packaging including food packaging, furniture, panels, doors, tarps, household decorative articles, trash bags, toys, fibers, filaments, packaging, foams, medical device packaging, and medical testing devices. In some aspects, the bioplastics described herein may be freeze dried or combined with a blowing agent to form foams.
Various implementations of the present disclosure are directed to improvements in the technological field of bioplastics. Prior bioplastics suffer from issues such as poor tensile strength or toxic production and extraction practices. Earlier bioplastics additionally require high temperature industrial composting facilities to break down and therefore are not readily compostable. In implementations of the present disclosure, algal materials are used to produce strong and stiff backyard-compostable bioplastics.
Biomatter plastics as described herein may be manufactured to have various degrees of strength, toughness, flexibility, flammability, and composability depending on the requirements of the end product. For example, furniture may require different strengths, toughness, flexibility, and compostability than food packaging. Further, the mechanical and physical properties of biomatter plastics may be altered though the use of various additives and fillers. For example, as shown in
Such biomatter plastics may be formed using a variety of different techniques including, compression molding, extrusion, injection molding, and 3D printing. In some aspects, the biomatter may be pretreated prior to fabrication. For example, it may be ground, sonicated, baked, humidified, and/or freeze-dried. As shown in
As shown in the SEM images at
In some aspects, various features such as strength, toughness, brittleness, appearance, density, chemical bonding, and compostability of a bioplastic may be manipulated by changing one or more of pre-processing, temperature, time, or pressing force. Such manipulation may allow for bioplastics to have different properties suitable for different end products.
Changes in pre-processing, temperature, time, and pressing force may be altered individually or in combination and may confer different properties on the physical and mechanical properties of the resulting bioplastics. For example, alterations in temperature alter the strength of bioplastics even if the pressure and time are constant as shown for spirulina alone in
The effect of combinations of changes to temperature, pressure and time can also alter a number of different properties of spirulina-based bioplastics including strength, density, elasticity, and toughness. As shown in
While not wishing to be bound by any particular limitations, it is theorized that specific temperature/pressure/time ratios may unexpectedly change the state of the bioplastics. For example, in some aspects, increasing the temperature of fabrication may enable the transition of a biomatter from a loosely bonded mass of cells to an amorphous uniform matrix. As shown in the SEM photographs in
The change in state may result in a smoother surface in the final product as described in Example II, below. Further, variations in pressure resulted in differences in infrared spectroscopy imaging as shown in
The unexpected self-bonding of spirulina powder allows for the creation of strong, flexible, backyard compostable bioplastics with mechanical properties ranging from 1.2-25.5 MPa for flexural strength, 0.35-3.1 GPa for flexural modulus for example 1 to 3.5 GPa, 0.63%-1.14% for strain to break, and 0.01-0.14 MJ m−3 for work to fracture. Example bioplastics contemplated herein may have one or more mechanical properties in these ranges or subsets thereof. For comparison, PLA has a strength of 21-60 MPa and stiffness of 0.35-3.5 GPa (A. Z. Naser, I. Deiab, B. M. Darras, RSC Adv. 2021, 11, 17151.). TPS has a strength below 6 MPa and stiffness less than 1 GPa (K. M. Dang, R. Yoksan, E. Pollet, L. Avérous, Carbohydr. Polym. 2020, 242, 116392; Y. Zhang, C. Rempel, Q. Liu, Crit. Rev. Food Sci. Nutr. 2014, 54, 1353). Unexpectedly, the spirulina based products described herein have improved mechanical properties in view of previously reported spirulina bioplastics, which were reported to have a strength of 3.0 MPa and stiffness of 249 MPa (Zeller et al., J. Appl. Polym. Sci., 2013, 130, 5).
As shown in
Along with bioplastics made of biomatter alone, in some implementations, the biomatter may be combined with one or more matrix materials such as proteins (including gluten, lactalbumin, BSA); lignin; cellulose (including bacterial cellulose fibers, nanocellulose, cellulose nanocrystals, cellulose nanofibers, alpha cellulose, carboxymethylcellulose); hemicellulose (including xylan, glucomannan); and other carbohydrates (including starch, isomalt, sucrose). In various examples, fillers such as small (low molecular weight) sugars/carbohydrates (polyols like sorbitol, mannitol, glycerol); Lipids/fatty acids (including stearic acid, oleic acid, linoleic acid, palmitic acid, caprylic acid, lauric acid), nanoclays (montmorillonite, halloysite), nanocellulose, and diatoms. Additional materials that may be combined with the algal materials included viscosity modifiers such as small (low molecular weight) sugars/carbohydrates (polyols like sorbitol, mannitol, glycerol), and lipids/fatty acids (including stearic acid, oleic acid, linoleic acid, palmitic acid, caprylic acid, lauric acid, palm oil) as well as components that enhance electrical conductivity such as graphene, CNTs, carbon fibers, graphite or the magnetic properties of the compositions such as iron oxide particles.
The bioplastics described herein may additionally be combined with commercial polymer such as PLA; PBAT; PHAs including copolymers such as Poly(3-hydroxybutyrate-co-3-hydroxyvalerate; PBS; polyethylene; polypropylene; polystyrene; polycarbonate; and maleic anhydride.
As shown in
To fabricate example biomatter plastics described herein, the components for the bioplastics may be combined using methods known to those of ordinary skill in the art. In some aspects, the components may be combined using dry powder mixing, in which the components are combined using any mixer generally known to one of ordinary skill in the art, or wet solution blending, in which water is added to the dry components and probe sonication or planetary mixing is used to homogenize the mixture. In some aspects, one or more of the components are pre-treated, for example using sonication and/or freeze drying.
The combined components are then subjected to a thermoforming step using compression molding, a heated extruder, a hot-press, injection molding, or any device that can apply pressure and heat to the mixtures. In some aspects, the processing temperatures may be between 60-200° C. The pressing forces between 1-150 N/mm2. The time in which the pressure and temperature is applied may be 0.5-30 minutes. For example, the time may be 5 minutes, the temperature between 120 and 160° C. and the pressing force 7 kN. For some bioplastics with additives, the operating conditions for the extruder range from: 65 to 140° C. and 10-50 rpm or fractions thereof. Bioplastics with additives can also be formed a hot-press operating between 60 and 175° C. and 1-50 kN (corresponding to a force per unit area of the sample of around 2-100 N/mm2). Further examples of combinations of bioplastics may be found at least in Examples III to VI as well as throughout the application. Exemplary embodiments of bioplastics and the manufacturing methods are shown in Table 1.
Spirulina
Spirulina
Spirulina
Chlorella
vulgaris
Saccharina
latissima
Ulva
Spirulina
Chlorella
Spirulina
Chlorella
Spirulina
Chlorella
Spirulina
Spirulina
Chlorella
Spirulina
Chlorella
Spirulina
Chlorella
Spirulina
Chlorella
Spirulina
Chlorella
Spirulina
Chlorella
Spirulina
Chlorella
SEM imaging provides some insight into the unexpected self-bonding along with the change in mechanical properties of spirulina bioplastics and composite spirulina bioplastics. While the self-bonding of spirulina appears to come from molecules within the spirulina cells, the sorbitol-plasticization of spirulina appears to come from the melting of sorbitol. Sorbitol has a melting temperature of around 90° C. When the sorbitol is heated and pressed along with the spirulina, the sorbitol melts and in some aspects the sorbitol may diffuse in the spirulina matrix and react with the spirulina polymers. The amount of sorbitol in the spirulina composite created according to the methods described herein provides different materials with different properties than the self-bonded spirulina, and may make stronger and tougher samples if combined with the method of self-bonding used for the pure spirulina samples as described herein. Combinations of spirulina with additional compositions such as nanoclay and cellulose also alters the strength and toughness of exemplary resulting bioplastics as shown in
The combination of spirulina with other matrices and plasticizers may also alter the flammability of such bioplastics. As shown in
Various bioplastics described herein may also be reusable. In some aspects, the bioplastics may be ground at the end of their initial life cycle and re-formed as described above. As shown at
Various bioplastics described herein may also be backyard compostable (Law, K. L., Narayan, R. Reducing environmental plastic pollution by designing polymer materials for managed end-of-life. Nat Rev Mater 7, 104-116 (2022). doi.org/10.10381s41578-021-00382-0). As used herein, backyard compostable means biodegradable at rates similar to food waste of the same surface area. Biodegradable plastics are plastics that are completely metabolized by microorganisms in an end-of-life (disposal) system, as measured by the microbial conversion of plastic carbon to CO2 (or CO2+CH4) as a function of time.
Decelerating degradation kinetics may be calculated using Equation 1 as follows:
dα/dt=k(1−α)n (1)
where α=Δm/m0 corresponds to the degree of conversion with Δm the mass variation and m0 the initial mass of the buried sample,
As shown in
In order that various implementations described herein may be more fully understood, the following examples are set forth. Those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the disclosure. Further, it should be understood that these examples are for illustrative purposes only and are not to be construed as limiting the scope of this disclosure in any manner.
Spirulina algae cells were procured from Nuts.com as Organic Spirulina. An aqueous suspension of the as-received spirulina cells in a 1:10 w/w concentration was sonicated for 20 min using Fisher Scientific Model 505 probe sonicator, on an ice bath. As shown at
The powder was then subjected to a compression molding process on a TMAX-SYP-600 hot press from TMAXCN, using custom-made stainless-steel molds. These molds were loaded with 1 g of spirulina per sample to produce beams with lengths and widths of approximately 60 and 8 mm, respectively. Samples were curved at the ends with radii of approximately 3.5 mm.
After production, each sample was labeled and placed in a desiccation chamber for 24 hours. Once a specimen had reached at least 24 hours of desiccation, their thicknesses, widths, and masses were measured and the samples were subjected to additional analysis via imaging and mechanical testing.
The spirulina powder as prepared in Example I was subjected to a compression molding process on a TMAX-SYP-600 hot press from TMAXCN, using custom-made stainless-steel molds. The temperature, pressure, and time of pressing was varied among different samples. Temperatures ranging from 60 to 160° C. were increased 20° C. in a step-wise fashion while pressing forces of 2, 7, 20, and 35 kN were used. The duration of the hot-pressing process was measured starting when pressing force was achieved. The samples that were tested in compression had a cube geometry (length of 25.4 mm for each side) and were prepared using an aluminum square tube with an inner edge length of 1 inch. The hot press conditions for those samples were set to 140° C., 7 kN, and 10 min, although extra time was allowed for packing the powder down in steps to avoid exceeding the stroke of the hot press piston.
One set of samples was subjected to pressing time, t, between 0 and 1800 s (30 min) under fixed temperature and pressing force conditions of T=120° C. and F=7 kN and the samples were tested for stress/strain as a function of time as shown in
σ*(t)=σ0+(σp−σ0)(1−exp−t/τ) (2)
According to this fit, the strength increases from σt=0=8.8 MPa up to a plateau value of approximately σp=20.9 MPa with a characteristic time constant τ=15.4 s. At pressing times below 60 s (≈4τ), the strength is significantly lower than the plateau strength and the data exhibit higher standard deviations than at longer pressing times. Below this threshold, the pressing time is not sufficient to facilitate the formation of a bonded uniform spirulina matrix.
A second set of samples used a fixed pressing time of the conservative value of 300 s (20τ, dotted line in
As shown in the heat-map of
Compressive strength was measured at 76.1±3.9 MPa in the axial direction (with respect to the hot pressing direction), and 70.2±2.9 MPa in the transverse direction (7.7% difference). While not wishing to be bound to any particular limitations, this small but statistically significant difference (p-value 0.04) is attributed to the fact that during the fabrication process, the compaction and binding of the bioplastics are naturally enhanced along the hot-pressing direction before a continuous matrix is formed. Interestingly, compression tests reveal a nearly isotropic behavior.
As shown in
At the lowest (in this example) pressing force of 2 kN there was a significant jump in flexural strength as the temperature increases from 100 to 120° C. (from 2.75±0.90 to 15.54±1.78 MPa), at which point a plateau is reached in strength (
Similarly, there was a substantial increase in elastic modulus (from 0.68±0.19 to 2.04±0.47 GPa) at the lowest (tested) pressure force of 2 kN as the temperature increased from 100 to 120° C., which was maintained for the 140° C. and was slightly reduced (to 1.69±0.23 GPa) at 160° C. as shown in
The AGS-X (10 kN) test frame, made by Shimadzu Scientific Instruments in Columbia, MD, USA, was used in a three-point bending configuration to test elastic modulus. All samples were tested at a 0.5% strain rate. The stress on a sample in three-point bending is calculated using Equation 3:
where σf is the flexural stress at the outer surface at the midspan of the beam, F is the load at a point on the load-displacement curve, L is the support span of the test setup, b is the width of the specimen, and d is the depth of the specimen. The support span for these tests were either 40 mm or 20 mm. Full specimens were tested at the 40 mm span length, with the sample breaking in half. Each half was then tested on the 20 mm support span. There was no significant difference observed in the mechanical properties between testing the full specimens and the half specimens, so the procedure was deemed adequate. Three specimens were produced for each trial, giving nine samples total for each trial, when including the number of half-specimens tested on the 20 mm span. The bending modulus follows the trend for strength as shown in
The significant increase-plateau-decrease trend of the elastic modulus was only observed to that extent at the minimum pressure conditions (2 kN) indicating that at this low pressure condition a temperature of 120-140° C. is required for the samples to reach the maximum elastic modulus. At lower temperatures the loose packing results in non-well-bonded bioplastics as shown in
Nanoindentation was used to calculate a reduced modulus to characterize the stiffness in accordance with Equation 4.
E
r=1/β√π/2S/√(A_p(h_c)) (4)
Er is the reduced Young's modulus, β is a geometrical constant for the specific type of indenter, S is the stiffness as measured by the slope of the load-displacement curve at the point of unloading, and Ap(hc) is a fitting polynomial specific to the type of indenter being used. For these tests, a Berkovich tip was used. The reduced modulus was used in this study to confirm the trends of flexural modulus produced by the three-point bend testing. The nanoindentation machine used for this experiment was an FT-MTA03 produced my Femto Tools.
Density was plotted versus temperature and pressing force to examine any relationships between the three variables, as shown in
The last part of the density analysis was analyzing the density vs the strength of the materials.
The toughness of the specimens was similarly plotted against temperature and pressure in
As shown in the SEM images of
As shown in
and 140° C. (3271 cm−1). Shifts in the O—H peak indicate changes in hydrogen bonding.[43] The slight shift for the 60° C. pressed spirulina, for which significant protein conformational transformation does not occur, may indicate an increase in intermolecular hydrogen bonding that is unrelated to the formation of beta sheets. Therefore, this result suggests that the samples formed at the low-temperature condition are held together via intermolecular hydrogen bonding between the different biopolymers present in the spirulina cell walls and protoplasm, which are typically rich in surface hydroxyl groups (T. Lafarga, J. M. Fernández-Sevilla, C. González-Löpez, F. G. Acién-Fernández, Food Res. Int. 2020, 137, 109356; D. G. Bortolini, G. M. Maciel, I. d. A. A. Fernandes, A. C. Pedro, F. T. V. Rubio, I. G. Brancod, C. W. I. Haminiuk, Food Chem. 2022, 5, 100134). Other types of intermolecular interactions such as biopolymer chain entanglement and Van der Waals interactions may also contribute to the bonding of the samples pressed at lower temperatures. The more significant redshift of the O—H bond in the absorption spectrum of the sample pressed at 140° C. indicates more intermolecular hydrogen bonding in that sample. In this case, increased intermolecular hydrogen bonding can be attributed to both enhanced hydrogen bonding between biopolymers in the spirulina and the transition from α-helices (intramolecular connections) to β-sheets (intermolecular connections).
The samples were additionally examined using Fourier Transform Infrared (IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Fourier transform infrared spectroscopy (FTIR) was performed using a Thermo Scientific Nicolet iS10 FTIR in ATR mode. Spectra were obtained with a resolution of 2 cm−1 and 128 scans. Scans were performed between 400 and 4000 cm−1. Spectra were vector normalized and distributed vertically for ease of comparison. Peak identification was performed using the scipy.signal.find_peaks function in Python. All XPS spectra were taken on a Kratos Axis-Ultra DLD spectrometer. This instrument has a monochromatized Al Kα X-ray and a low energy electron flood gun for charge neutralization. X-ray spot size for these acquisitions was on the order of 700×300 μm. Pressure in the analytical chamber during spectral acquisition was less than 5×10-9 Torr. Pass energy for survey and detailed spectra (composition) was 80 eV. Pass energy for the high resolution spectra was 20 eV. The take-off angle (the angle between the sample normal and the input axis of the energy analyzer) was 0° (0 degree take-off angle 100 Å sampling depth). CasaXPS was used to peak fit the high-resolution spectra. For the high-resolution spectra, a Shirley background was used and all binding energies were referenced to the C 1s C—C bonds at 285.0 eV.
The deconvolution of the collected XPS spectra as shown at
While not wishing to be bound by any particular limitations, it is theorized that heat and pressure facilitate reactions of the C═O and C—O bonds at chain ends and pendant sites which result in the increased amount of C—C bonds measured in the spectra of hot-pressed samples. Therefore, distinct changes in the covalent bond makeup of the spirulina samples upon hot pressing in addition to the hydrogen bonding suggested by the IR spectra was observed. The data collectively suggest that the processing of spirulina powder with heat and pressure leads to changes in covalent bonding and enhances the secondary interactions between the biopolymers within the biomatter in addition to causing conformational changes (β-sheet formation) in the protein matrix. These changes together support the measured increases in the mechanical properties as the biomatter is processed at higher temperatures. The presence of PHA in spirulina may also contribute to the bonding of the bioplastics, but because of PHA's relatively low concentration and high melting point its contributions are likely minimal compared to those of the other biopolymers discussed above (S. S. Costa, et al. Algal Res. 2018, 33, 231).
Thermogravimetric analysis was conducted to examine the thermal stability of the bioplastics. The thermogravimetric analysis (TGA) was performed on a Discovery TGA 550, from TA Instruments. Samples of 13±4 mg of each material were subjected to heating from room temperature to 1000° C. at a heating rate of 10° C. min−1 in a nitrogen gas flow of 25 μL min−1. Differential Scanning calorimetry (DSC) was done on a Discovery 2500 DSC from TA Instruments, in hermetically sealed TZero aluminum pans. Each specimen went through two heating and cooling cycles each, at rates of 10° C. min−1, with isothermal holds of 1 min between each cycle, from −75 to 200° C.
Analysis was conducted on unpressed, powdered spirulina and a pressed, well plasticized sample. As shown in
Spirulina algae cells were procured from Nuts.com as Organic Spirulina. Nanoclay was Montmorillonite K 10 procured from Sigma Aldrich. An aqueous suspension of the as-received spirulina cells in a 1:10 w/w concentration was sonicated for 20 min using Fisher Scientific Model 505 probe sonicator, on an ice bath. After sonication, the dissociated biomatter suspension was freeze-dried using a Freezone lyophilizer from Labcono Corp. The pre-sonicated and freeze-dried dissociated spirulina powder was then mixed with the nanoclay powder using an Analog Vortex Mixer from VWR. The premixed powders were then subjected to a compression molding process on a TMAX-SYP-600 hot press from TMAXCN, using custom-made stainless-steel molds. These molds were loaded with 1 g of spirulina per sample to produce beams with lengths and widths of approximately 60 and 8 mm, respectively. Samples were curved at the ends with radii of approximately 3.5 mm.
After production, each sample was labeled and placed in a desiccation chamber for 24 hours. Once a specimen had reached at least 24 hours of desiccation, their thicknesses, widths, and masses were measured, and the samples were subjected to additional analysis via imaging and mechanical testing.
Spirulina algae cells were procured from Nuts.com as Organic Spirulina. Bacterial Cellulose was produced from a kombucha culture as described in J. L. Fredricks, M. Parker, P. Grandgeorge, A. M. Jimenez, E. Law, M. Nelsen, E. Roumeli, MRS Commun. 2022, 12, 394.
An aqueous suspension of the as-received spirulina cells in a 1:10 w/w concentration was sonicated for 20 min using Fisher Scientific Model 505 probe sonicator, on an ice bath. After sonication, the dissociated biomatter suspension was freeze-dried using a Freezone lyophilizer from Labcono Corp. BC sheets with dimensions of 40 mm by 1 mm were laid along the X-Y plane of the mold, in between pure spirulina powder, creating a layered structure that was hot pressed at 140° C./7 kN. The BC sheets made up 10 wt. % of the biocomposite.
After production, each sample was labeled and placed in a desiccation chamber for 24 hours. Once a specimen had reached at least 24 hours of desiccation, their thicknesses, widths, and masses were measured, and the samples were subjected to additional analysis via imaging and mechanical testing.
Spirulina algae cells were procured from Nuts.com as Organic Spirulina. Sorbitol was purchased from Sigma Aldrich. An aqueous suspension of the as-received spirulina cells in a 1:10 w/w concentration was sonicated for 20 min using Fisher Scientific Model 505 probe sonicator, on an ice bath. After sonication, the dissociated biomatter suspension was freeze-dried using a Freezone lyophilizer from Labcono Corp. The pre-sonicated and freeze-dried dissociated spirulina powder was then mixed with the sorbitol powder were combined at the desired concentrations of 1, 5, 10, and 30 wt. % in sorbitol. The blended powders were then fed through a Scientific Process 11 Twin-Screw Extruder from Thermo Fisher, operating at 40 rpm, with a uniform temperature profile of 90° C., before being hot pressed at 80° C. and 7 kN, for 1 min. Once a homogenous powder was produced by the extruder, the powder was loaded into molds (typical size of the molds 8×60×1 mm3) and pressed at 80° C., 7 kN at sorbitol concentrations from 0% to 30%.
After production, each sample was labeled and placed in a desiccation chamber for 24 hours. Once a specimen had reached at least 24 hours of desiccation, the specimen's thicknesses, widths, and masses were measured, and the samples were subjected to additional analysis via imaging and mechanical testing.
Three-point bend specimens of each bioplastic type were desiccated for 24 h at 23° C., before being tested on an AGS-X test frame from Shimadzu Scientific Instruments. A minimum of nine samples were tested for each composition at a 0.5% per second strain rate and 40 mm gauge length. Compression testing was performed using an Instron 4505 universal test frame with a 5500R upgrade. A 100 kN load cell was used. A minimum of five samples per testing direction were tested at 0.5% per second strain rate.
An AGS-X (10 kN) test frame, made by Shimadzu Scientific Instruments in Columbia, MD, USA, was used in a three-point bending configuration. All samples were tested at a 0.5% strain rate. The stress on a sample in three-point bending is calculated using Equation 3:
where σf is the flexural stress at the outer surface at the midspan of the beam, F is the load at a point on the load-displacement curve, L is the support span of the test setup, b is the width of the specimen, and d is the depth of the specimen. This equation is appropriate for three-point bend specimens with a rectangular cross-section, which was the case with the samples used in this study.
As shown in
Differential Scanning calorimetry (DSC) was used to study thermal events that materials undergo during heating and cooling cycles. Sorbitol was studied using a Discovery 2500 DSC from TA Instruments in New Castle, DE, USA. Hermetically sealed TZero aluminum pans were used to hold the sample and as a reference. Two heating and cooling cycles each were done at rates of 10° C./min, with isothermal holds of 1 minute between each cycle. The DSC experiment was run from −75° C. to 200° C. As sorbitol concentration increases, a gradual increase in strength and toughness is observed. The 5 and 10 wt. % sorbitol bioplastics have a 41.4% and 90.5% increased modulus, 45.9% and 136.4% increased strength, and 100% and 300% increased toughness compared to the neat spirulina, as shown in
The mechanical properties of spirulina/sorbitol samples pressed at 80° C./2 kN/1 min with varying concentrations of sorbitol are shown in
As shown in
Pure spirulina bars produced through the compression molding process described in Example I, self-extinguish in less than 1 s, producing a char. As shown in
Spirulina composites also improved the flammability of the resulting bioplastics. Composite bacterial cellulose and spirulina samples were created by mixing blended bacterial cellulose (BC) with water at a 0.8 wt % concentration. Spirulina powder (CS) was mixed in at various concentrations with respect to the amount of water in the slurry. The slurry was then loaded in molds and put in the freezer overnight. The resultant frozen materials were put in a freeze dryer for another night to get the desired rectangular molds.
Samples were prepared using the ratios shown in Table 2:
The samples were then placed above a Bunsen burner such that the tip of the bright blue flame contacted the bottom the specimen during testing. The samples were tested by applying the flame to the hanging edge of the sample for 1 minute, after which the flame was removed. However, if the sample completely burned before 1 minute and the flame source was no longer contacting any portion of the remaining sample, the flame source would be removed earlier. As shown in
Pure spirulina bioplastics were ground into a powder. The powder was subsequently incubated in ambient conditions for 24H before re-pressing under the hot-pressing conditions described above. As shown in
The soil biodegradation study was performed by burying a total of 36 samples with dimensions 5×5×1 mm3 of each material in gardening soil which was regularly watered to keep wet. Every two weeks, a set of four samples was recovered to measure their mass loss after cleaning them in deionized water and drying them in an oven (60° C.), for 48 h to obtain the dry weight. PLA was chosen because it is a commonly used plastic that is considered compostable. A banana peel is a commonly available, purely natural material that degrades on a kitchen counter, let alone buried in soil.
As shown in
where α=Δm/m0 corresponds to the degree of conversion with Δm the mass variation and m0 the initial mass of the buried sample, gives a reasonable fit of our data. A least-square fitting provided values of n=2.89, k=0.29 and n=2.28, k=0.39 for banana and spirulina, respectively, with corresponding root-mean-square error values of 0.013 and 0.028.
1. A method of self-bonding biomatter, the method including:
The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be used for realizing implementations of the disclosure in diverse forms thereof.
This document cites various printed publications, articles, journals, patent documents, and other references. Each one of the references described is incorporated by reference herein in its entirety.
As will be understood by one of ordinary skill in the art, each implementation disclosed herein can comprise, consist essentially of or consist of its particular stated element, step, or component. Thus, the terms “include” or “including” should be interpreted to recite: “comprise, consist of, or consist essentially of.” The transition term “comprise” or “comprises” means has, but is not limited to, and allows for the inclusion of unspecified elements, steps, ingredients, or components, even in major amounts. The transitional phrase “consisting of” excludes any element, step, ingredient or component not specified. The transition phrase “consisting essentially of” limits the scope of the implementation to the specified elements, steps, ingredients or components and to those that do not materially affect the implementation. As used herein, the term “based on” is equivalent to “based at least partly on,” unless otherwise specified.
Unless otherwise indicated, all numbers expressing quantities, properties, conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. When further clarity is required, the term “about” has the meaning reasonably ascribed to it by a person skilled in the art when used in conjunction with a stated numerical value or range, i.e. denoting somewhat more or somewhat less than the stated value or range, to within a range of ±20% of the stated value; ±19% of the stated value; ±18% of the stated value; ±17% of the stated value; ±16% of the stated value; ±15% of the stated value; ±14% of the stated value; ±13% of the stated value; ±12% of the stated value; ±11% of the stated value; ±10% of the stated value; ±9% of the stated value; ±8% of the stated value; ±7% of the stated value; ±6% of the stated value; ±5% of the stated value; ±4% of the stated value; ±3% of the stated value; ±2% of the stated value; or ±1% of the stated value.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
The terms “a,” “an,” “the” and similar referents used in the context of describing implementations (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein is intended merely to better illuminate implementations of the disclosure and does not pose a limitation on the scope of the disclosure. No language in the specification should be construed as indicating any non-claimed element essential to the practice of implementations of the disclosure.
Groupings of alternative elements or implementations disclosed herein are not to be construed as limitations. Each group member may be referred to and claimed individually or in any combination with other members of the group or other elements found herein. It is anticipated that one or more members of a group may be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.
This application claims benefit of U.S. Provisional Patent App. No. 63/373,437, filed on Aug. 24, 2022, which is incorporated by reference herein in its entirety.
Number | Date | Country | |
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63373437 | Aug 2022 | US |