Patent Application
20240052574
This disclosure relates generally to single-use commodities and, in particular, relates to compostable single-use commodities suitable with improved mechanical strength.
Single-use commodities, such as disposable cutlery, cups for condiments, plates, bowls, and the like, are traditionally formed from plastic derived from petroleum. However, the nature of single-use plastic articles used for “food on the go” is that the articles are readily disposed of and normally include some amount of food particles or contamination. Recycling such articles can be resource intensive because the food particles must be removed in advance of recycling. Thus, forming single-use plastic articles that are compostable can significantly impact the amount of waste production attributed to “food on the go.”
Recent studies have shown that waste food in trash is the largest preventable contributor to green house gas production in United States. The trash waste produces methane gas as it degrades in the anaerobic environment. The most sustainable endpoint for all waste food and contaminated single-use plastic is disposal in a home or industrial compost facility, which converts the waste to nutrient rich compost, carbon dioxide, and water. This provides a complete loop for organic matter.
At present, the compostable plastic technology is limited to starch, cellulose acetate, polyhydroxy butyrate, polyhydroxy alkonate, polylactic acid, polyvinyl alcohol, polycaprolactam, poly(butylene succinate), poly(butyl-adipate terephthalate) as building blocks for compostable resins. Even though all of these plastics are biodegradable and compostable at a thin layer, they fail to pass home compost or industrial compost certification as the article gets thicker. Thus, conventional compostable cutlery is either thick enough to withstand normal use but incapable of home composting, or too thin for comfortable use but capable of home composting.
Further, some of the above-mentioned polymers have low flex modulus resulting in a cutlery or single use plastic being too flexible for use.
Accordingly, improved compostable resins for single-use commodities are needed for overcoming one or more of the technical challenges described above.
Compostable resin formulations are provided herein including a compostable polymeric resin, starch, a compatibilizer, a mineral filler such as calcium carbonate, and titanium dioxide. In particular, it has been unexpectedly discovered that incorporating starch into a compostable polymeric resin formulation improves compostability but has no detrimental effect on the resin's ability to be molded, the inclusion of a compatibilizer and calcium carbonate substantially increases stiffness without affecting compostability, and the inclusion of titanium dioxide stabilizes the color of the resulting article.
Throughout this disclosure, various aspects are presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosure. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.
As used herein, the term “about” with reference to dimensions refers to the dimension plus or minus 10%.
Compostable Polymeric Resin Formulations
Compostable resin formulations are disclosed herein. In some embodiments, the compostable resin formulation includes a compostable polymeric resin, starch, a biodegradable compatibilizer, a mineral filler, and titanium dioxide. In some embodiments, the compostable polymeric resin includes a biopolyester. In some embodiments, the compostable polymeric resin includes cellulose acetate. In some embodiments, the compatibilizer includes polyvinyl alcohol, polyvinyl acetate, partially hydrolyzed polyvinyl acetate, or polycaprolactam. In some embodiments, the mineral filler includes calcium carbonate.
In some embodiments, the compostable resin is suitable for molding. It has been unexpectedly discovered that incorporation of starch and/or calcium carbonate into the compostable resin for the purpose of increasing strength has no detrimental effect on the ability to mold the resin into single-use commodities.
Cellulose acetate resin formulated with food grade plasticizer has recently become available from Celanese Corporation and Eastman Chemical Company. This plastic resin can be extruded and injection molded. An advantage of this material is that, when molded into an article such as cutlery, it passes home and industrial compost at thicknesses of less than 14-20 mil (355-500 microns). This resin is more flexible than polystyrene but exhibits excellent impact strength. However, the flexural strength is generally too low for commodities such as cutlery.
Combining this resin with small amounts of mineral filler, such as calcium carbonate, both enhances the stiffness and maintains the resin's ability to be molded and retain toughness despite addition of calcium carbonate filler. Furthermore, higher loading of calcium carbonate in combination with compostable polymeric resins also enhanced biodegradation rate, enabling a standard cutlery with a thickness of 60 mil (1524 microns) to pass home compostability standards.
Conventional compostable cutlery typically has a brown or dark brown color as a result of the starch included in the formulation. Attempts to add colorants to the formulation normally results in discoloration after using the cutlery. It has been unexpectedly discovered that including titanium dioxide in the formulation stabilizes the color of the cutlery and prevents discoloration during use.
PLA-based cutlery at a 60 mil thickness passes industrial compostability (ASTM D6400) testing. However, passing home compostable standards with 60 mil thickness is challenging. Although there is a polyhydroxyalkonate (PHA) based cutlery with awarded certification, this certification was awarded to a cutlery having a thickness of 30 mil. There is also a starch based cutlery claiming to pass home compostability, but it has no certification. There is no readily available article having a thickness suitable for use as cutlery that may be successfully composted at home without foaming. Previous attempts to use PHA and starch-based cutlery which may have passed home compostability standard are not functional as they suffer from low stiffness and unable to function like polystyrene based cutlery. For example, cutting a piece of chicken or scooping out ice cream is challenging and results in utensil overly deforming.
The inventive formulation is useful for cutlery, sauce cups, cup lids, plates, bowls, and other single use applications where the pieces are contaminated with food or pieces are too small to recycle. Unlike currently available compostable formulations, the inventive formulation is lower cost and may be produced using standard extrusion and molding equipment.
Cellulose acetate is commercially available from Eastman Chemical Company and Celanese Corporation and has a very high flexural modulus. A resin was formed by compounding this cellulose acetate with a plasticizer in a twin-screw compounder. To this resin, calcium carbonate (an inorganic filler), thermoplastic starch, polyvinylalcohol, polyhydroxyalkonate (optional), and titanium dioxide was added and well-mixed using the twin-screw compounder. The resulting compound was molded on a conventional injection molding machine using molds designed for polystyrene.
The addition of a mineral filler such as calcium carbonate advantageously enables a combination of beneficial features such as stiffness, color, water-fast color, impact, feel and home compo stability. The further addition of a compatabilizer such as polyvinyl alcohol further enhances stiffness when paired with the mineral filler. Some exemplary formulations are displayed in Table 1.
The impact property for the injection molded forks was tested using a simple method where a fork held at the end is swung 16 inches at a solid surface such as a frame of injection molding machine or lab countertop and noting if the article cracks or survives. Nearly 100 percent of cutlery produced using crystal polystyrene fails and so did formulations F1 and F2. Meanwhile, those formulations that included polyvinyl alcohol and calcium carbonate were toughened and had increased stiffness.
As displayed in Table 1, the inventive formulation that includes each of the cellulose acetate, thermoplastic starch, polyvinyl alcohol, calcium carbonate, and titanium dioxide produced a compostable cutlery with superior impact resistance and stiffness with color stability.
When the above formulations were immersed in 65° C. hot water for 2 minutes, the formulations without TiO2 showed noticeable and potentially objectionable color change. TiO2 resolved this issue where no discernable color change was observed.
Cutlery were formed using the same materials as those used in Example 1, but with the relative ratio of TPS and cellulose acetate fixed to 1:5. Compatibilizer PVA level was fixed to 3 wt % while two of the formulations contained TiO2 and the other two did not. For each formulation, a plastic fork was injection molded and mounted in an Instron® material testing equipment. The force required to deflect the overall fork by 2 mm was measured and recorded Table 2 below lists the formulation vs. force
The force required for deflecting a fork by 2 mm is a good proxy for flex modulus. A higher measured force correlates to a stiffer fork.
Traditionally, the addition of inorganic fillers such as talc, calcium carbonate, to plastics is known to result in enhancement of stiffness. However, in most cases the stiffness results in brittleness. In the inventive formulations, the high impact properties above persist even with the addition of inorganic fillers.
Combining immiscible polymers in a compounding operation often results in stiffness decrease and increase in brittleness. It has been further unexpectedly discovered that the addition of polyvinyl alcohol and cellulose acetate seems to have yielded superior mixing.
Overall, this formulation has enabled the formation of disposable cutlery which is stiffer, maintains flexibility and impact properties, while increasing the compostability thickness limit. The higher stiffness further reduces cutlery thickness without impacting performance. A further benefit where less organic material is used in production of useful cutlery.
Various cutlery were formed as described herein having the standard cutlery design referred to as “HD size” cutlery. The cutlery in this example were forks. The cutlery formulations are listed in Table 3.
Each formulation was blended/compounded together using a twin-screw extruder equipped with two vents and three kneading sections, then injection molded at 460° F. Various mechanical tests were performed and compared against polystyrene (PS) and polyhydroxyalkonate (PHA), two commonly used materials in commercial cutlery. The tests were performed in an Instron® material testing equipment equipped with a 500 N load cell, with the samples clamped into the test fixture so that the loading anvil is perpendicular to the longitudinal axis of the cutlery. Each sample was first pretested with a strain rate of 12.7 mm/min until a load measurement of 0.50 N was observed, and then the Instron® AutoBalance feature was used to hold the 0.50 N load for 1 second. After pretesting, vertical testing was performed by subjecting the sample to a strain rate of 35.40 mm/min until the end of the test. Horizontal testing was performed with the same parameters but with the force applied to the face of the cutlery (i.e., the tines of the fork). The end of the test was marked by either breakage of the sample as measured by a change in force with 40% sensitivity, or by a compressive displacement of 25.40 mm.
For each test, the trim mean was determined by discarding the highest and lowest values and averaging the remaining measurements. The weight was measured to four significant figures and reported to three significant figures. The dimensions and test results are displayed in Table 4.
Of the seven measured, only sample SBCA3 displayed any discoloration. All other samples, including PS and PHA, displayed no discoloration. Furthermore, although Kuraray Poval™ 5-88 was used in these samples, which is an 86.5%-89% hydrolyzed polyvinyl acetate (i.e., both polyvinyl acetate and polyvinyl alcohol are present), other levels of hydrolysis such as 60% or 95% could be used.
As shown in Table 4, the compostable cutlery of the present invention have an average max force significantly greater than PHA, which is the most common resin used for compostable cutlery. In fact, the compostable cutlery of the present invention has an average max force closer to that of polystyrene. Predictably, the average compressive displacement at max force is greater than polystyrene, indicating greater flexibility, but the displacement is less than PHA for all but one of the compostable samples.
Although the disclosure often refers to “cutlery,” it is to be understood that the decision to recite “cutlery,” to the exclusion of other single-use plastic commodities, is in the interest of brevity only. Any suitable single-use plastic commodity may be formed from the compositions described herein.
While the disclosure has been described with reference to a number of embodiments, it will be understood by those skilled in the art that the disclosure is not limited to such embodiments. Rather, the disclosure can be modified to incorporate any number of variations, alterations, substitutions, or equivalent arrangements not described herein, but which are commensurate with the spirt and scope of the disclosure. Conditional language used herein, such as “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, generally is intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements or functional capabilities. Additionally, while various embodiments of the disclosure have been described, it is to be understood that aspects of the disclosure may include only some of the described embodiments. Accordingly, the disclosure it not to be seen as limited by the foregoing described, but is only limited by the scope of the appended claims.
This application claims priority to U.S. Provisional Patent Application No. 63/371,306, filed Aug. 12, 2022, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63371306 | Aug 2022 | US |
