CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application Serial Nos. 62/467,320, filed on March 6, 2017, 62/503,401, filed on May 9, 2017, and 62/573,207, filed on October 17, 2017, the disclosures of which are incorporated herein in their entireties by reference.

BACKGROUND

Field of the Invention

The present disclosure relates to a novel sampling container such as a centrifuge tube, and methods of making and using the same.

Description of the Related Art

A centrifuge is an apparatus that causes an object to rotate around a fixed axis, thereby applying a force perpendicular to the axis of spin. When the centrifuge operates, more dense particles and substances move radially outward on account of centripetal acceleration, and less dense particles and substances move radially inward. In a centrifuge that employs one or more sample tubes, radial acceleration causes denser particles to settle to the bottom of a given sample tube while lower density substances rise to the top of said sample tube.

In the petroleum industry, centrifuges are used for multiple applications, including for use to measure sediment and water in crude oil and petroleum products. Centrifuge tubes for these applications are almost invariably made from glass. Since glass products are highly susceptible to breakage or shattering during handling and centrifugation, substantial efforts have been made to increase the shatter-resistance of the glass used to make the centrifuge tubes. These efforts have been focused primarily on increasing the strength and stability of the glass centrifuge tubes, which has led to a steady increase in the wall thickness of glass centrifuge tubes designed for petroleum industry applications. The use of thick-walled glass centrifuge tubes introduces a myriad of other potential problems, such as increased weight and cost of each centrifuge tube and other problems. Moreover, thick-walled glass centrifuge tubes are still susceptible to breakage, and thus while somewhat shatter-resistant, are certainly not shatterproof.

Thus, there is a great need in the petroleum industry and other industries for a centrifuge tube that overcomes the challenges associated with the development, manufacture, and use of shatter-resistant glass centrifuge tubes for various applications.

SUMMARY

A container suitable for obtaining information from a sample containing materials such as, but not limited to, crude oil, petroleum products, petrochemicals, fractions thereof, and impurities therein is disclosed herein. The container preferably comprises a tube and more preferably a centrifuge tube. It has been found that a centrifuge tube comprising one or more polymers that render the centrifuge tube substantially transparent; substantially chemically inert to degradation by crude oil and petroleum products; substantially thermally stable; substantially rigid when subjected to conditions such as elevated temperatures, centrifugal forces, or the combination thereof; and substantially shatter-resistant provides superior performance for sediment and water measurement in crude oil and petroleum products than centrifuge tubes that do not satisfy one or more of these criteria. It has also been found that one or more polymers selected from the group consisting of polymers in the polysulfone family, more preferably selected from the group consisting of polysulfone (PSU) and polyphenylsulfone (PPSU), and most preferably polyphenylsulfone meet the unique criteria set forth above and result in an improved product compared to those currently used in industry.

Accordingly, a container useful for obtaining information from samples comprising one or more polymers is provided, wherein the container is substantially transparent; substantially chemically inert to degradation by crude oil and petroleum products; substantially thermally stable; substantially rigid when subjected to conditions such as elevated temperatures, centrifugal forces, or the combination thereof; and substantially shatter-resistant.

A method of obtaining information from a sample containing materials such as, but not limited to, crude oil, petroleum products, petrochemicals, fractions thereof, and impurities therein is also disclosed herein. The method comprises the steps of (1) introducing the sample into a container, (2) applying a force to the container to generate at least two layers within the container, and (3) obtaining information from at least one of the at least two layers, wherein the container is substantially transparent; substantially chemically inert to degradation by crude oil and petroleum products; substantially thermally stable; substantially rigid when subjected to conditions such as elevated temperatures, centrifugal forces, or the combination thereof; and substantially shatter-resistant.

A method of making the disclosed container is also disclosed herein. The method comprises: (1) heating at least one polymer selected from the group consisting of the polysulfone family, (2) extruding the heated polymer to generate an extruded polymer, (3) introducing the extruded polymer into a mold having the shape of the container, and (4) removing the mold from the extruded polymer contained within the mold to generate a polymer container, wherein the polymer container is substantially transparent; substantially chemically inert to degradation by crude oil and petroleum products; substantially thermally stable; substantially rigid when subjected to conditions such as elevated temperatures, centrifugal forces, or the combination thereof; and substantially shatter-resistant.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates an embodiment of the centrifuge tube disclosed herein.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

A container that may be used to measure sediment and water content and other properties of samples comprising crude oil, petroleum products, petrochemicals, fractions thereof, and impurities therein is disclosed herein. The disclosed container comprises one or more polymers that render the container substantially transparent; substantially chemically inert to degradation by crude oil and petroleum products; substantially thermally stable; substantially rigid when subjected to conditions such as elevated temperatures, centrifugal forces, or the combination thereof; and substantially shatter-resistant.

The preferred container is a solid, rigid receptacle with at least one closed end and one open end, and is capable of containing a sample such as a liquid, liquid-solids mixture, or another sample capable of being separated or otherwise partitioned by centrifugal forces. The open end of the container may be configured to be securely closed using a cap or other seal. The container preferably comprises a tube with one closed end and one open end, although the container does not need to be tubular and can be configured in other cross-sectional shapes as may be suitable for use in various applications. The container, whether a tube or another configuration, may be the same diameter across its entire length or may include differing cross- sectional diameters or other dimensions. Preferably, the container comprises a centrifuge tube, wherein the centrifuge tube may have an approximately uniform diameter across its entire length or may have an approximately uniform diameter across a part of its length and terminate with a conical tip at the end of the tube opposing the open end. A centrifuge tube that has an approximately uniform diameter across a part of its length and terminates with a conical tip at the end of the tube opposing the open end may be particularly suitable to receive more dense materials or precipitate separated during centrifugation.

It has been found that centrifuge tubes suitable for use with materials used in the petroleum industry for sediment and water measurement applications and other property measurements will fail or undoubtedly be less effective unless they are substantially: (1) transparent; (2) chemically inert to degradation by crude oil and petroleum products; (3) thermally stable; (4) rigid when subjected to conditions such as elevated temperatures, centrifugal forces, or the combination thereof; and (5) shatter-resistant; as those terms are defined herein. Preferably, at least two of these properties will be satisfied in conjunction with one another. More preferably, at least three of these properties will be satisfied in conjunction with one another. Even more preferably, at least four of these properties will be satisfied in conjunction with one another. Most preferably, all five of these properties will be satisfied in conjunction with the remaining properties. Thus, in the most preferred embodiments, a centrifuge tube will remain substantially transparent, substantially chemically inert to degradation, substantially stable, substantially rigid, and substantially shatter-resistant, particularly when exposed to crude oil, petroleum products, petrochemicals, fractions thereof, and/or impurities therein at elevated temperatures and centrifugal forces simultaneously.

The disclosed centrifuge tube is substantially transparent so that the amount of sediment and water in a sample may be determined visually or using another suitable technique for optical measurement after centrifugation. In some embodiments, centrifugation may cause a sample to substantially separate into a precipitate and a supernatant liquid within the centrifuge tube. In other embodiments, no precipitate will be present. As used herein, the term supernatant liquid refers to any liquid in the centrifuge tube after centrifugation, regardless of whether a precipitate is also present. In some embodiments, the supernatant liquid comprises at least two immiscible liquids, and the supernatant liquid is substantially separated into layers of immiscible liquids. In other embodiments, the supernatant liquid forms an emulsion or is otherwise not separated into multiple layers. A substantially transparent centrifuge tube will allow visual determination of the location of the interface between the precipitate and the supernatant liquid when a precipitate is present or allow visual determination of the interface between immiscible layers of liquids within the supernatant liquid if any such layers are present.

The centrifuge tube may also be labeled with volumetric graduations on its exterior surface. Since the disclosed centrifuge tube is substantially transparent, a user can visually observe and measure the sediment and water in a sample using the volumetric graduations on the exterior of the centrifuge tube.

When determining the amount of sediment and water in crude oil, petroleum products, petrochemicals, fractions thereof, and impurities therein, after centrifugation a sample will generally separate into a precipitate comprising sediment and a supernatant liquid comprising a water layer and a hydrocarbon layer that is immiscible with and less dense than the water layer. After centrifugation, the precipitate will be located at the bottom of the centrifuge and the hydrocarbon layer will be located above the water layer within the supernatant liquid, on account of the lower density of the hydrocarbon layer. Use of a substantially transparent centrifuge tube will allow visual determination of the interface between the water layer and the precipitate and will also allow visual determination of the interface between the water layer and the hydrocarbon layer. Thus the amount of sediment and water in a sample may be visually determined and may be quantified using volumetric graduations on the centrifuge tube if present. It is also understood that, in certain circumstances, the supernatant liquid comprising one or more hydrocarbons and water may not fully partition and there may thus be no visually distinguishable interface between a hydrocarbon layer and a water layer within the supernatant liquid.

The centrifuge tube may preferably be sufficiently transparent so as to have a transmittance above 50 percent, more preferably a transmittance above 65 percent, and most preferably a transmittance above 80 percent.

The disclosed centrifuge tube is substantially chemically inert to degradation by crude oil and petroleum products, including crude oil, kerosene, mineral spirits, Stoddard solvent, Varsol, and other petroleum products, petrochemicals, fractions thereof, and impurities therein. Chemical degradation of the centrifuge tube may lead to reduced mechanical strength that may result in mechanical failure, may lead to possible contamination of samples by byproducts of chemical degradation processes, and may also lead to other potentially deleterious consequences. In preferred embodiments, the centrifuge tube is substantially chemically inert to degradation by a test solvent where the testing is carried out according to the test conditions set forth in Woishnis, et al. Chemical Resistance of Specialty Thermoplastics, 2012, Elsevier Inc., 876-903 (hereinafter "Woishnis, et al").

Chemical degradation of a centrifuge tube comprising one or more polymers may be caused by disruption of the order of individual polymer chains that is introduced during the manufacture of the centrifuge tube by increasing the stress on the individual polymer chains. When the stress passes a given limit, evidence of chemical degradation may be observed visually. Visual indications of chemical degradation include but are not limited to crazing, hazing, cloudiness, and discoloration.

Crude oil and other petroleum products may sometimes contain sufficiently high percentages of solids and other materials, such as paraffinic waxes, asphaltenes, and other substances that can solidify or become sufficiently viscous at room temperature so as to impede or disrupt the formation of layers during the centrifuging step. For this and other reasons, these samples may be heated prior to or during the centrifuging step so as to help ensure that sample separation can take place in the centrifuge.

The disclosed centrifuge tube is substantially thermally stable, so that it does not appreciably expand or contract or otherwise physically deform when processing samples that must be heated for proper analysis. Any expansion or contraction of less than 100 will not be considered appreciable. Accurate volumetric measurements, such as sediment and water measurements for crude oil samples or other volumetric measurements related to the separation of liquids from solids or other liquids in samples such as crude oil, petroleum products, petrochemicals, fractions thereof, and impurities therein, require minimal thermal expansion. If a centrifuge tube exhibits appreciable thermal expansion, there may be discrepancies in volumetric measurements of the contents of the centrifuge tube at different temperatures. Therefore, in preferred embodiments, the centrifuge tube comprises one or more polymers with a coefficient of thermal expansion that is less than 100 at both 25 degrees Celcius and 70 degrees Celcius, more preferably a coefficient of thermal expansion that is less than 85 at both 25 degrees Celcius and 70 degrees Celcius, even more preferably a coefficient of thermal expansion that is less than 70 at both 25 degrees Celcius and 70 degrees Celcius, and most preferably a coefficient of thermal expansion that is less than 50 at both 25 degrees Celcius and 70 degrees Celcius for best results.

In addition, the disclosed centrifuge tube is substantially rigid when exposed to elevated temperatures, such that the tube does not deform when exposed to elevated temperatures and thereby introduce unacceptable measurement errors into sediment and water measurements, or into other measurements related to the separation of liquids from solids or other liquids in samples such as crude oil, petroleum products, petrochemicals, fractions thereof, and impurities therein. When the glass transition temperature of a polymeric material is exceeded, the material may lose its mechanical rigidity and may deform when exposed to forces such as centrifugal forces. For materials that do not have a defined glass transition temperature, measurement of mechanical strength may be an alternative way of measuring rigidity that correlates directly to the preferred ranges for glass transition temperatures. In preferred embodiments, the centrifuge tube comprises one or more polymers with a glass transition temperature above approximately 70 degrees Celcius, more preferably above approximately 120 degrees Celcius, even more preferably above approximately 160 degrees Celcius, and most preferably above approximately 210 degrees Celcius for best results.

In addition to the effect of exceeding the glass transition temperature on the rigidity of a centrifuge tube comprising polymeric materials, the amount of force exerted upon the centrifuge tube also may affect its rigidity. The disclosed centrifuge tube is substantially rigid when exposed to centrifugal forces, such that the tube does not deform during centrifugation and thereby introduce unacceptable measurement errors into sediment and water measurements, or into other measurements related to the separation of liquids from solids or other liquids in samples such as crude oil, petroleum products, petrochemicals, fractions thereof, and impurities therein. In preferred embodiments, the centrifuge tube is substantially rigid when exposed to a relative centrifugal force (RCF) of 500, more preferably an RCF of 750, even more preferably an RCF of 900, and most preferably an RCF of 1000 for best results.

The disclosed centrifuge tube is substantially shatter-resistant to prevent breakage or other damage during handling and use. If a centrifuge tube breaks or is damaged during handling or use, one or more deleterious consequences may result, including but not limited to sample contamination, safety concerns for the centrifuge operator and others, and increased costs of testing. The centrifuge tube is preferably shatter-resistant when dropped from a height of 1 m onto a concrete surface comprising Portland cement, more preferably shatter-resistant when dropped from a height of 3 m onto a concrete surface comprising Portland cement, even more preferably shatter-resistant when dropped from a height of 5 m onto a concrete surface comprising Portland cement, and most preferably shatter-resistant when dropped from a height of 8 m onto a concrete surface comprising Portland cement for best results.

The disclosed container comprises one or more polymers that generally meet the unique criteria defined above. Preferably, the one or more polymers have at least one member selected from the group consisting of polymers in the polysulfone family. The polysulfone family comprises thermoplastic polymers comprising at least one monomer comprising a sulfone moiety, including polysulfone (PSU), polyethersulfone (PESU), and polyphenyl sulfone (PPSU). More preferably, the one or more polymers have at least one member selected from the group consisting of polysulfone (PSU) and polyphenylsulfone (PPSU). Even more preferably, the one or more polymers comprise polyphenylsulfone (PPSU) for best results.

It has been found that polyphenylsulfone (PPSU) may be more chemically inert to certain test samples, such as test samples containing higher percentages of aromatics with 25 or fewer carbon atoms per molecule, such as benzene, toluene, and xylene. Polyphenylsulfone (PPSU) is particularly preferred over other members of the polysulfone family where a test sample comprises more than 10 volume percent aromatic hydrocarbons with 25 or fewer carbon atoms per molecule, more preferred where a test sample comprises more than 15 volume percent aromatic hydrocarbons with 25 or fewer carbon atoms per molecule, and particularly preferred where a test sample comprises more than 20 volume percent aromatic hydrocarbons with 25 or fewer carbon atoms per molecule.

In some embodiments, the centrifuge tube may comprise a polysulfone copolymer or a polyphenylsulfone copolymer.

In other embodiments, the one or more polymers in the polysulfone family may be impregnated with glass fibers.

A method of gathering information from a sample containing materials such as, but not limited to, crude oil, petroleum products, petrochemicals, fractions thereof, and impurities therein is also disclosed herein. The method comprises the steps of (1) introducing the sample into a container, (2) applying a force to the container to generate at least two layers within the container, and (3) obtaining information from at least one of the at least two layers, wherein the container is substantially transparent; substantially chemically inert to degradation by crude oil and petroleum products; substantially thermally stable; substantially rigid when subjected to conditions such as elevated temperatures, centrifugal forces, or the combination thereof; and substantially shatter-resistant.

The container is the apparatus for partially, substantially, or fully enclosing the sample to which force will be applied. The container may preferably be enclosed in a protective sleeve to prevent scratching or other damage caused by contact between the container and the instrument used to apply force to the container. When the container is a centrifuge tube subjected to a force using a centrifuge, the protective sleeve may prevent scratching or other damage caused by contact between the centrifuge tube and the metal surface of the centrifuge tube holder or preheating element. The protective sleeve may preferably be made from nylon such as an anti-static nylon. The protective sleeve may be configured to securely contain a desired centrifuge tube. The protective sleeve may further include a double-sided adhesive on its exterior surface to allow the protective sleeve to be secured to the metal surface of the centrifuge tube holder or preheating element.

The present disclosure contemplates measuring samples that may include crude oil, petroleum products, petrochemicals, syncrude, tar sands, shale oil, solids, water, naphthenic and other associated acids, fractions thereof, and impurities therein. The feedstock may be heterogeneous or homogenous. The chemical composition of a sample may include, but is not limited to, paraffins, naphthenes, aromatics, sulfur-containing structures, nitrogen-containing structures, asphaltenes, and the like generally found in petroleum crude, petroleum products, petrochemicals, fractions thereof, and impurities therein. In some embodiments, the sample may comprise up to 0.2 volume percent aromatic hydrocarbons with 25 or fewer carbon atoms per molecule. In other embodiments, the sample may comprise as much as 0.6, 1.0, or 2.0 volume percent aromatic hydrocarbons with 25 or fewer carbon atoms per molecule. In less common embodiments, the sample may comprise as much as 5, 10, or 20 volume percent aromatic hydrocarbons with 25 or fewer carbon atoms per molecule.

The force that is applied is generally centripetal force applied via a centrifuge but may alternatively comprise other forces applied to separate composite materials by their relative densities. The method generally separates the sample into at least two layers. One layer is generally a precipitate while at least one other layer is generally a supernatant liquid comprising one or more hydrocarbons. The precipitate often comprises one or more sediments. In some embodiments, no precipitate is present. The supernatant liquid may comprise discrete water and hydrocarbon layers that may be substantially immiscible with one another or the water and hydrocarbon layers may not partition and may exist as a single layer. The water layer may be water or may alternatively be an aqueous solution of water soluble compounds in water, with or without water insoluble compounds suspended therein. In some embodiments, the water layer may be an emulsion of water insoluble compounds suspended in water or an aqueous solution.

A method of making the disclosed container is also disclosed herein. The method comprises: (1) heating at least one polymer selected from the group consisting of the polysulfone family, (2) extruding the heated polymer to generate an extruded polymer, (3) introducing the extruded polymer into a mold having the shape of the container, and (4) removing the mold from the extruded polymer contained within the mold to generate a polymer container, wherein the polymer container is substantially transparent; substantially chemically inert to degradation by crude oil and petroleum products; substantially thermally stable; substantially rigid when subjected to conditions such as elevated temperatures, centrifugal forces, or the combination thereof; and substantially shatter-resistant.

The container may be made using an injection molding process such as the injection molding process for making a centrifuge tube described below. For example, polyphenylsulfone pellets may be dried according to drying parameters in a pre-processing step to remove any trace water in the pellets. The drying parameters may be any suitable temperature and drying time for removing trace water. The drying parameters may preferably be a temperature between approximately 250 and 400 degrees Fahrenheit, more preferably approximately 300 degrees Fahrenheit, and a drying time of between approximately 3 and 5 hours, more preferably approximately 4 hours. The pellets may then be placed in an injection molding apparatus comprising an extruder and a mold. The pellets may be melted by the extruder and then fed into the mold at high temperature and pressure. The melted polymer may be injected into the mold during an injection period, wherein the injection period may preferably be between approximately 3 and 8 seconds and more preferably be approximately 5.5 seconds. The mold may be held for a setting period, wherein the setting period may preferably be between approximately 20 and 30 seconds and more preferably be approximately 25 seconds.

By way of example, the centrifuge tube may be made using an injection molding apparatus, wherein the injection molding apparatus may be operated according to the parameters shown in Table 1.

TABLE 1

The polyphenylsulfone pellets used in the above example were obtained from Dongguan Jiate Plastics Co., Ltd. (JT-PPSU-5000).

The parameters specified above to make centrifuge tubes using an injection molding process are merely illustrative, and one or more parameters may be varied without departing from the scope and spirit of the disclosed method.

In some preferred embodiments, the centrifuge tube may be coated with one or more coatings. The one or more coatings may preferably be applied as spray coatings. In some highly preferred embodiments, the one or more coatings may be one or more coatings selected from the group consisting of a polyurethane coating and a spar urethane coating, and even more preferably a spar urethane coating. In some preferred embodiments, two spray coatings may be applied to the centrifuge tubes. The two spray coatings may be applied with a time delay between application of each coating, and the two spray coatings may be the same or different.

For example, a spar urethane coating manufactured by Varathane was applied to centrifuge tubes as two spray coatings. The time delay between application of the two coatings was 1 h, and the coatings were cured at room temperature for 24 h. The coated centrifuge tubes were visually unaffected when heated to 200 degrees Fahrenheit for 12 h or when submerged in Varsol for 24 h.

In some preferred embodiments, an optical finish may be applied to the mold used to make the injection molded centrifuge tube to increase transparency of the tube. The Society of Plastic Industry (SPI) defines optical finishes according to the type of finish, including diamond buff polish to generate a glossy surface, paper polish to generate a non-glossy surface, stone polish to generate a rough surface, and dry blash polish to generate a very rough surface. The SPI diamond buff polishes include SPI Finish A-l (Grade #3, 6000 Grit Diamond Buff), SPI Finish A-2 (Grade #6, 3000 Grit Diamond Buff), and SPI Finish A-3 (Grade #15, 1200 Grit Diamond Buff). The optical finish may preferably be applied to the mold using one or more polishing steps to apply a finish selected from the group consisting of SPI Finish A-l, SPI Finish A-2, and SPI Finish A-3, more preferably applied using one or more polishing steps to apply an SPI Finish A-2.

The container may alternatively be made using an injection blow molding or extrusion blow molding process. In some embodiments, an optical finish may be applied to the mold used to make the container as described above and according to the preferred parameters described above. In some embodiments, one or more spray coatings may be applied to the container as described above and according to the preferred parameters described above.

Centrifuge tubes comprising polyphenylsulfone (PPSU) and made using the injection molding process described in the above example were tested for thermal stability when exposed to petroleum products. Centrifuge tubes were exposed to kerosene and Varsol to determine whether any changes would be observed in the overall length of the tubes or for volumetric measurement of individual graduations on the tubes. The height of the empty centrifuge tubes were measured prior to exposure to any petroleum products. The volumes corresponding to each graduation on each centrifuge tube were then verified using verification procedures set forth by the American Petroleum Institute. See American Petroleum Institute, Manual of Petroleum Measurement Standards, 2013, ch. 10, section 4 (hereinafter "API Chapter 10.4"). Each centrifuge tube was then filled with kerosene or Varsol and pre-heated to 200 degrees Fahrenheit. The tubes were centrifuged at 200 degrees Fahrenheit for 2 hours at a maximum RPM corresponding to a relative centrifugal force (RCF) of approximately 1000. These conditions are significantly more rigorous than those required by API Chapter 10.4. The kerosene or Varsol was then removed from the centrifuge tubes, and the centrifuge tubes were subsequently cleaned. The volumes corresponding to each graduation on each centrifuge tube were then reverified using verification procedures set forth in API Chapter 10.4, and the heights of the empty centrifuge tubes were remeasured. As shown in Table 2, the tube heights before and after centrifugation were consistent within 0.015%, which was within the measurement error. As shown in Table 3, the volumetric verifications for each graduation were well within allowable tolerances.

TABLE 2

TABLE 3

Centrifuge tubes were also subjected to repeated exposure to kerosene or Varsol to measure thermal stability after repeated use. The height of an empty centrifuge tube was measured prior to exposure to any petroleum products. The centrifuge tube was then filled with kerosene or Varsol. The tube was then centrifuged at 160 degrees Fahrenheit for 5 minutes at a maximum RPM corresponding to a relative centrifugal force (RCF) of approximately 1000. The height of the tube was then remeasured after centrifugation. This process was repeated 100 times. After 100 iterations using both kerosene and Varsol, the heights of the centrifuge tubes did not change appreciably and the tubes were transparent without any indication of chemical degradation.

Centrifuge tubes made from polymers in the polysulfone family were compared for chemical inertness. Centrifuge tubes were made from polyphenylsulfone (PPSU) as described above. Centrifuge tubes were also made from polysulfone (PSU) using the same injection molding procedures described above. Each PPSU centrifuge tube and PSU centrifuge tube was filled with a test solvent and heated to 150 degrees Fahrenheit. The centrifuge tubes were heated continuously until visual indications of chemical degradation appeared, such as crazing, hazing, cloudiness, or discoloration. Where no visual indication of chemical degradation was observed after one week, the centrifuge tubes were deemed chemically inert under the test conditions. The test solvents used were a mixture of aliphatic and aromatic hydrocarbons, or alternatively exclusively aromatic hydrocarbons. In particular, the test solvents were a mixture of xylenes and kerosene or pure xylenes. The test results are shown in Table 4.

TABLE 4

As shown in Table 4, PPSU centrifuge tubes are significantly more chemically inert to xylenes than PSU centrifuge tubes. These results suggest that PSU centrifuge tubes are likely significantly less chemically resistant to high concentrations of aromatic hydrocarbons and thus are less suitable for use in testing of crude oil or petroleum product samples that include a high percentage of aromatic hydrocarbons.

Centrifuge tubes made using the using the injection molding process described in the above example were tested for shatter resistance using a gravity drop procedure. Glass centrifuge tubes were used as a reference. 100 mL centrifuge tubes were filled with water. Polymer centrifuge tubes were closed with a threaded screw cap, and glass centrifuge tubes were closed with a rubber stopper. The centrifuge tubes were dropped from a pre-defined height, defined as the distance between the bottom of the centrifuge tube and the impact surface, onto a concrete surface comprising Portland cement. Both glass centrifuge tubes and polymer centrifuge tubes were undamaged when dropped from a height of 0.3 m. Glass centrifuge tubes were damaged, as indicated by cracking, chipping, or shattering, when dropped from all heights from between 0.6 m and 9.1 m, whereas polymer centrifuge tubes were undamaged when dropped from all heights below at least 9.1 m. The gravity drop tests were carried out at thirty different heights between about 0.3 m and 9.1 m. The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention disclosed herein. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

All references cited herein are expressly incorporated by reference.