Molding of Bead Foam Polyester

Abstract

A method of making a molded foam article. The method includes introducing steam into a mold simultaneously with filling the mold with foam particles. The method can be performed faster and with a lower ΔT than conventional molding processes, allowing for faster turnaround to subsequent production of molded articles. Molded articles produced by the method can have thicker sidewalls and improved foam particle fusion compared to conventional molding processes.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This disclosure claims priority to and the benefit of U.S. patent application Ser. No. 17 / 656,700, filed Mar. 28, 2022, which is incorporated by reference herein in its entirety.

[0002] FIELD OF THE DISCLOSURE This disclosure relates generally to molded polyester bead foams and methods of making molded polyester bead foam articles, and more particularly to thicker, stronger molded bead foam polyester and methods of making thicker, stronger molded bead foam polyester articles. [Background technology]

[0003] Molded bead foam polyester articles have been commercialized as an expandable polystyrene (EPS) replacement in thermal insulation and / or impact protection applications. EPS is a widely used bead foam material with a well-established manufacturing process that is easily reproducible. EPS molding is the oldest and fastest (in terms of cycle time) molding process practiced commercially. Other bead foams have gained popularity in recent years, particularly recyclable and biodegradable bead foams formed from, for example, polylactic acid and / or polyethylene terephthalate.

[0004] Conventional bead foam molding involves injecting foam particles into a mold, followed by injecting steam into the mold, exposing the exterior of the mold to cooling water, followed by exposing the mold to a negative pressure cycle. Due to the control systems in conventional molding systems, it is not possible to pass steam through the mold at the same time as either filling the mold with foam particles or exposing the mold to a negative pressure cycle. As a result, steam passage to the center of the bead foam mass can vary greatly depending on the geometry of the mold, resulting in poor uniformity of foam particle fusion at various locations within the article. A molded polyester article with poor fusion of foam particles will then have poor thermal and impact insulation properties.

[0005] To prevent insufficient fusion of the foam particles, conventional bead foam molding limits the thickness of the molded polyester article, and thus manufacturers and consumers must choose between increasing the thickness of molded polyester articles and the structural integrity of those articles.

[0006] Previous attempts to modify the traditional bead foam molding process include the elimination of the introduction of steam in favor of preheating the mold prior to the introduction of foam particles, as described in U.S. Patent No. 10,688,698 to Lifoam Industries LLC, which describes the creation of molded foam articles comprising homopolymers, graft polymers, or copolymers of polylactic acid by eliminating steam or other heating media.

[0007] Therefore, there is a need for improved methods of molding polyester to overcome one or more of the technical challenges set forth above. [Brief description of the drawings]

[0008] The detailed description will be described with reference to the accompanying drawings. The use of the same reference numbers may indicate the same items and similar. Various embodiments may utilize elements and / or components other than those shown in the drawings, and some elements and / or components may not be present in various embodiments. Elements and / or components in the drawings are not necessarily drawn to scale. Throughout this disclosure, singular and plural terms may be used interchangeably where appropriate in context.

[0009] [Figure 1] 2 is a graph showing flexural strength of molded articles described in this disclosure. [Diagram 2] 1 is a graph showing the deflection force of a molded article described in the present disclosure. [Diagram 3] FIG. 2 is a cross-sectional side view of a molded article produced as described in this disclosure. [Figure 4] 1 is a graph showing deflection force of molded articles described in this disclosure. [Diagram 5] 1 is a graph showing deflection force of molded articles described in this disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Provided herein are methods of making molded polyester, including methods of making thicker molded polyester with improved bead fusion compared to molded polyester made using conventional methods such as molding expandable polystyrene (EPS). In particular, it has been discovered that simultaneous injection of steam into the mold cavity during foam particle introduction improves the wetting of the foam particles, thereby improving foam particle fusion. Additionally, in some embodiments, the method includes a slight negative pressure cycle simultaneously with steam injection and foam particle introduction, thereby allowing for better control of the temperature of the foam particles before and during molding. The methods of making molded polyester provided herein can be used to make molded polyester articles having any suitable thickness, including thicknesses of 2.5 inches (63 mm) or greater, with foam particle fusion equal to or greater than that of molded polyester articles of lesser thickness.

[0011] 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. Thus, the description of a range should be considered to have specifically disclosed all possible subranges and individual numerical values ​​within that range. For example, the description of a range such as 1-6 should be considered to have specifically disclosed subranges such as 1-3, 1-4, 1-5, 2-4, 2-6, 3-6, etc., as well as individual numbers within that range, such as 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0012] As used herein, the term "about" in reference to a dimension refers to plus or minus 10% of the dimension.

[0013] A method for molding polyester is disclosed herein. In some preferred embodiments, the method includes (i) wetting and heating foam particles introduced into a mold for articles in which the foam particles are not fused. In some embodiments, the method includes (ii) applying a negative pressure cycle in which the foam particles expand and fuse together to form the article, and then (iii) removing the molded foam article from the mold.

[0014] As used herein, "expansion" of foam particles refers to the process by which the foam particles increase in size and decrease in density while increasing malleability. This is typically accomplished by wetting the foam particles in the presence of heat and / or slight negative pressure cycles. Foam particles suitable for molding are typically spherical or cylindrical in shape and contain a blowing agent that facilitates expansion, so the expansion of the foam particles allows adjacent foam particles to fill the space between adjacent particles, regardless of the particle shape. The expansion of the foam particles is necessary for successful molding. The start of the expansion of the foam particles marks the start of the molding process, so premature expansion of the foam particles before they are placed in the mold can result in insufficient or unsuccessful molding, depending on the degree of expansion before they are placed.

[0015] As used herein, "fusion" of foam particles refers to the process by which foam particles bond and adhere to each other. Without intending to be bound by any particular theory, fusion of foam particles may be achieved by some intermixing of polymer chains at the surfaces of the foam particles that contact each other, also known as the "bead-to-bead interface". Following intermixing of polymers at the bead-to-bead interface, the foam particles require more than a nominal degree of force to separate. Thus, molded foam articles are composed of fused foam particles. Molded foam articles retain their shape as a result of the fusion of the foam particles that comprise the molded foam article. The "degree of fusion" between particles correlates to the amount of force required to separate the foam particles. Without intending to be bound by any particular theory, the degree of fusion is also influenced by the uniformity of foam particle fusion throughout the molded article. A greater degree of fusion corresponds to a greater amount of force required to separate the foam particles. Although there is no standardized test to measure the degree of fusion, properties such as flexural strength and resistance to compression depend on the degree of fusion between foam particles. Thus, the degree of fusion can be approximated through other tests designed to measure bending strength or deflection force, allowing qualitative comparisons between samples of molded articles to determine which have "better fusion" of foam particles in the molded article.

[0016] One such test to measure fusion, referred to herein as the "cut test," involves cutting a molded foam article with a non-serrated utility knife (e.g., a razor blade) to reveal the innermost foam particles. Upon cutting, it becomes apparent that some of the innermost foam particles have become loose and become separated from the molded foam article. If the interior surface of the molded foam article is colored, such as by application of a marker, the uncolored areas represent voids containing previously insufficiently fused foam particles. Comparison of the amount of uncolored space between two samples, such as by surface metrological analysis, allows for a qualitative comparison of the fusion of foam particles between the samples.

[0017] Another test that approximates the degree of fusion is the standard test specified by ASTM C203, which measures the flexural strength of a molded foam article. Without intending to be bound by any particular theory, it is believed that molded foam particles that are more uniformly fused require more force to break apart after normalizing for density, while loose foam particles separate more easily. Molded foam particles that require more force to break apart correspond to a higher measured flexural strength, while loose foam particles that separate easily correspond to a lower measured flexural strength. Thus, the flexural strength of a molded foam article with a greater degree of fusion will be greater than the flexural strength of a molded foam article constructed from the same material with the same density and with insufficient fusion between the foam particles. Without intending to be bound by any particular theory, it is believed that both the density and chemical formulation of the foam particles, in addition to the manufacturing method, affect the flexural strength of a molded foam article. For example, a 0.05 g / cm 3 (1) An expandable polyethylene terephthalate (ePET) molded article having a density of 0.02 g / cm 3 (2) an expandable polylactic acid (ePLA) molded article (showing differences in chemical composition) having a density of 0.05 g / cm 3 Even if an ePET molded article having a density of 0.02 g / cm has an insufficient degree of fusion, 3 The ePET molded articles are expected to have a higher flexural strength than ePET molded articles having a density of 0.1 to 1.0 mm (indicating the density difference). Thus, in some embodiments, the methods described herein have been shown to produce molded articles having an improved degree of fusion compared to molded articles of the same density and same chemical composition produced by conventional methods. In some embodiments, the molded foam articles produced by the methods have a greater flexural strength, as measured by ASTM C203, than foam articles molded using conventional processes.

[0018] Another test that approximates the degree of fusion is a standard test specified by ASTM D3575-14, which measures the compressibility of a molded foam article by measuring the deflection and recovery of the molded foam article upon application of a compressive force. Without intending to be bound by any particular theory, it is believed that more uniformly fused foam particles exhibit greater compressive strength, while loose beads simply crumble under compressive force. Thus, the compressive strength of a molded foam article having a greater degree of fusion will be greater than that of a molded foam article having an insufficient degree of fusion between the foam particles. In some embodiments, the molded foam article produced by the method has a greater compressive strength, as measured by ASTM D3575-14, than a foam article molded using a conventional process.

[0019] As used herein, applying a "negative pressure" refers to subjecting the system to a slight negative pressure. As used herein, a "slight negative pressure" refers to subjecting the system to a negative pressure of about -1.5 inHg (-5.08 kPa) to about -8 inHg (-27.09 kPa), for example, about -0.5 inHg (-1.69 kPa) to about -2 inHg (-6.77 kPa). Conventional EPS molding processes typically subject the mold to a negative pressure of -20 inHg (-67.73 kPa) to -28 inHg (-94.82 kPa).

[0020] As used herein, "non-fused foam particles" refers to foam particles that have no or only slight adhesion to adjacent foam particles, as indicated, for example, by having 5% or less of the required separation force after the molding process is complete.

[0021] As used herein, a "mold" refers to a cavity having the shape of a molded foam article. The mold may have two or more separable portions that facilitate opening the mold to remove the molded foam article. The separable portions of the mold may have multiple openings configured to allow the passage of gases, such as for the introduction of steam or removal of air, steam, and / or other gases through the application of a negative pressure cycle.

[0022] In some embodiments, the methods are effective in obtaining molded articles having greater fusion uniformity than foam articles molded using conventional processes, i.e., the degree to which the foam particles are fused together within the molded article is consistent between different regions within the molded article, which is an advantageous result of the manner in which the foam particles are heated and moistened in the methods of the present disclosure.

[0023] As previously mentioned, the use of ASTM C203 and / or ASTM D3575-14 may allow for an approximation of the uniformity of foam particle fusion. If either or both of these tests are performed on multiple samples from the same molded article, the uniformity of foam particle fusion may be approximated by evaluating the uniformity of the flexural strength and deflection force measurements. The error bars on the graphs of Figures 1, 2, 4, and 5 represent the uniformity of the flexural strength or deflection force, indicating the uniformity of foam particle fusion in those molded articles.

[0024] In some embodiments, the method includes introducing steam into the mold simultaneously with the introduction of foam particles into the mold. In conventional particle foam molding processes, control systems prevent users and / or equipment from introducing steam during the particle filling step. Instead, users must first fill the mold with foam particles and then introduce steam. Such control systems are in place to prevent premature introduction of steam, which may cause premature expansion of the foam particles, as discussed above. Furthermore, introducing steam during the filling process causes some steam to escape the mold without wetting or heating the foam particles, resulting in some steam being "wasted." However, it has surprisingly been found that introducing steam during the particle filling step, such as through the implementation of custom software, hardware, actuators, valves, or combinations thereof, can improve wetting of the foam particles compared to introducing steam after the foam particles have been introduced and deposited into the mold. This simultaneous steam introduction during particle introduction unexpectedly allows for the molding of thicker molded foam articles while maintaining or improving fusion of the foam particles compared to conventional molding processes. Additionally, the process consumes less steam and requires less energy than conventional processes, despite the possibility of some steam being lost during the bead packing and bead wetting processes.

[0025] In some embodiments, the method includes injecting steam into the mold while applying a slight negative pressure cycle, which causes the foam particles to expand and fuse together to form the article.

[0026] In some embodiments, the method includes applying a slight vacuum cycle to the mold simultaneously with the introduction of the foam particles and steam. In conventional particle foam molding processes, the control system prevents the user and / or the equipment from applying a slight vacuum cycle during the particle filling step. Instead, the user must first fill the mold with the foam particles, followed by the introduction of the steam, followed by the application of the vacuum cycle. Such a control system is in place to prevent premature application of a slight vacuum cycle that may result in accelerated consumption of the steam. However, it has surprisingly been found that applying a slight vacuum cycle during the introduction of the foam particles and steam, such as through the implementation of custom software, hardware, actuators, valves, or combinations thereof, can improve the wetting of the foam particles by better controlling the temperature of the foam particles. Without intending to be bound by any particular theory, it is believed that the simultaneous application of a slight vacuum cycle while the foam particles and steam are being introduced results in more foam particles being wetted while minimizing the increase in temperature resulting from the introduction of the steam. Thus, the foam particles are wetted while preventing premature expansion of the foam particles. This simultaneous application of slight negative pressure cycles during particle introduction and introduction of steam unexpectedly allows for the molding of thicker molded foam articles while maintaining or improving foam particle fusion.

[0027] In some embodiments, wetting and heating the foam particles introduced into the mold includes (a) introducing the foam particles into the mold and then (b) introducing steam into the mold while venting the mold, the venting being effective to prevent the foam particles from collapsing. In conventional particle foam molding processes, the control system prevents the user and / or the equipment from introducing steam while venting the system. Instead, conventional molding equipment is configured to be attached to a steam chamber so that steam can be introduced into the mold without allowing the steam to escape and can accumulate and surround the mold. These conventional systems prevent venting during steam introduction because some steam will escape the mold without wetting or heating the foam particles, and some steam will be "wasted." However, it has surprisingly been found that venting the mold while introducing steam, such as through the implementation of custom software, hardware, actuators, valves, or combinations thereof, can improve wetting of the foam particles without excessive heating of the foam particles. Without intending to be bound by any particular theory, it is believed that venting the mold during steam introduction allows for better control of the temperature of the foam particles to prevent them from collapsing or overheating.

[0028] As used herein, "collapse" of a foam particle refers to the phenomenon in which the foam particle expands over time, passes through a regime of decreasing density properties of the expandable foam, and enters a regime of increasing density. The increase in density results from the complete degassing of the blowing agent and marks the end of the ability of the foam particle to expand further. As the blowing agent dissipates, the size of the foam particle begins to decrease, resulting in an increase in density. The collapsed foam particle is no longer suitable for molding, since it loses the ability to fill the gaps that exist between adjacent foam particles.

[0029] In some embodiments, steam introduced into the mold heats the mold to a first temperature. After the mold is filled with foam particles, the mold is then cooled to a second temperature during a vacuum cycle. In some embodiments, the first temperature is less than 30° C. higher than the second temperature. In some embodiments, the first temperature is about 10° C. higher than the second temperature. In conventional molding systems lacking simultaneous steam introduction and particle filling, simultaneous steam introduction during particle filling and application of a slight vacuum cycle, simultaneous steam introduction during particle filling and venting, or a combination thereof, the introduction of steam results in a temperature increase of 40° C. or more. For example, conventional expandable polypropylene (EPP) molding processes have a ΔT of 100-160° C., depending on the machine and / or process. Conventional expandable polystyrene (EPS) molding processes have a ΔT of 45-60° C., depending on the machine and / or process. Thus, it has been unexpectedly discovered that simultaneous steam treatment, particle filling, application of a slight vacuum cycle, and / or venting reduce the ΔT of the system by more than 50%. By reducing the temperature rise of the system, the molding process can be accomplished with less energy consumption, in a shorter period of time, and in the form of less consumed steam, compared to processes using conventional molding systems. Additionally, the reduced ΔT reduces the time required to prepare the mold for the subsequent molding process, reducing the turnaround time for producing multiple molded articles.

[0030] The molded foam articles produced by the method may have any suitable thickness greater than 0.75 inches (19 mm), including about 3 inches (76.2 mm), about 6 inches (154 mm), about 12 inches (305 mm), thicknesses greater than 12 inches (305 mm), or any thickness therebetween. In some embodiments, the molded foam articles produced by the method have a thickness of 0.75 inches (19 mm) or greater in at least one dimension. In some embodiments, the molded foam articles produced by the method have a thickness of at least 2.5 inches (63 mm) in at least one dimension. As used herein, the "thickness" of a molded foam article refers to the smallest dimension of the molded foam article. In other words, a molded foam article in the form of a monolithic panel has a relatively long length and width, but a relatively thin thickness. For example, a molded foam panel may have a length of 8 inches (203 mm), a width of 10 inches (254 mm), and a thickness of 2.5 inches (63.5 mm). Another example of a molded foam article is a molded box having five sides. The box may be 8 inches (203 mm) by 6 inches (152 mm) by 10 inches (254 mm), with sidewalls 1.5 inches (38 mm) thick. In conventional molding systems, the ability to introduce steam to wet and heat the foam particles only after they are introduced into the mold limits the thickness of the molded foam article because steam cannot penetrate the mass of foam particles more than about 1 inch (25 mm) in any direction. For this reason, the majority of molded foam articles produced by conventional processes have a thickness of 1 to 2.5 inches (25 to 63 mm). Thus, it has been unexpectedly discovered that simultaneous steaming, particle packing, application of slight negative pressure cycles, and / or venting allows for the molding of foam articles having greater thicknesses than are possible in conventional molding systems.

[0031] In some embodiments, the total molding time of the method for molding a foam article is at least 50% less than the total molding time of a conventional expandable polystyrene molding process. As used herein, the "total molding time" of the process includes all steps from mold closure to mold opening, including foam particle introduction, steam introduction, and application of a negative pressure cycle. The time before mold closure can vary widely based on the equipment used, such as the equipment used to operate the mold halves, and the geometry of the molded article. Conventional molding processes include a number of successive steps, including initial steaming, particle loading, hydraulics, direct steaming, cooling, and stabilization / holding. The conventional expandable polystyrene (EPS) molding process is considered the "fastest" commercial molding process, having a total molding time of about 60-65 seconds. The method described herein has a total molding time that is at least 50% less than the total molding time of the EPS process for the same geometry. The method described herein has a total molding time of about 18-22 seconds or less.

[0032] In some embodiments, steam is introduced into the mold at an angle tangent to the side of the mold to agitate the foam particles in the mold and improve wetting of the foam particles. For example, a mold having a substantially cylindrical shape may have steam introduced at an angle tangent to the circular cross section of the cylindrical shape, creating an adverse effect on the foam particles as they rotate within the mold.

[0033] In some embodiments, the foam particles comprise homopolymers, graft polymers, blends, or copolymers of poly(butylene succinate), poly(ethylene terephthalate), poly(lactic acid), poly(poly(hydroxybutyrate)), poly(butylene terephthalate), poly(caprolactone), poly(butylene adipate terephthalate), poly(hydroxyalkonate), or blends thereof. In some embodiments, the foam particles comprise low crystallinity poly(lactic acid) foam beads. Conventional expandable polystyrene molding machines have been adapted to mold foam articles containing materials other than polystyrene when those materials have high crystallinity or when the crystallinity of those materials is increased prior to foaming / expansion. It has been unexpectedly discovered that simultaneous steaming, particle packing, vacuum application, and / or venting allows for the molding of foam articles containing low crystallinity materials that were previously unformable. EXAMPLES

[0034] The present invention may be further understood with reference to the following non-limiting examples.

[0035]

[0036] Example 1: Comparison with previous molding process for 2.5 inch panels Molded articles were produced as described herein and compared to molded articles produced by the method described in U.S. Patent No. 10,688,698 to Lifoam Industries LLC. All tested molded articles were formed from poly(lactic acid). All tested molded articles were 16.2 inches (411.5 mm) by 13.2 inches (335 mm) by 2.5 inches (63.5 mm). Molded articles produced as described herein were molded on a Kurtz Ersa Corporation K68 HP5 Top-Line molding machine, available from Kurtz Ersa Corporation, Kreuzwertheim, Germany. The molding machine was modified with custom software to allow for simultaneous introduction of steam during foam particle introduction. Process parameters are shown in Table 1.

[0037] As shown in Table 1, the method described herein can produce molded articles 40% faster than the method described in U.S. Patent No. 10,688,698. The method does not use steam to preheat the mold, so less time is required for steam. Additionally, the ΔT of the method is 45% lower than the method described in U.S. Patent No. 10,688,698, representing lower energy consumption, faster molding, and faster turnaround to molding subsequent articles.

[0038] Figure 1 is a graph showing the flexural strength of the 2.5 inch (63.5 mm) panels produced in this example as measured by ASTM C203. The panels produced by this method had greater flexural strength and less variability between samples, representing improved fusion of the foam particles in the molded articles produced by this method, as compared to molded articles produced as described in U.S. Patent No. 10,688,698. Furthermore, the difference between the two is statistically significant, as indicated by a p-value of less than 0.05.

[0039] Figure 2 is a graph showing the deflection force of the 2.5 inch (63.5 mm) panels produced in this example as measured by ASTM D3575-14. The panels produced by this method withstood a higher deflection force with less variability between samples, again indicating improved fusion of the foam particles in the molded articles produced by this method compared to molded articles produced as described in U.S. Patent No. 10,688,698. Furthermore, the difference between the two is statistically significant as indicated by a p-value of less than 0.05. [Table 1]

[0040] Example 2: Comparison with previous molding process for 1.5 inch panels Molded articles were produced as described herein and compared to molded articles produced by the method described in U.S. Patent No. 10,688,698 to Lifoam Industries LLC. In this example, the mold was vented during steam introduction. All tested molded articles were formed from poly(lactic acid). All tested molded articles were 9 inches (229 mm) x 9 inches (229 mm) x 1.5 inches (38 mm). Molded articles produced as described herein were molded on a Kurtz Ersa Corporation K68 HP5 Top-Line molding machine, available from Kurtz Ersa Corporation, Kreuzwertheim, Germany. The molding machine was modified with custom software to allow simultaneous venting during steam introduction and foam particle introduction.

[0041] The panels were tested 96 hours after production. The panels were conditioned at 73°F (23°C) for 24 hours at 50% relative humidity and then analyzed using the cut test described herein. The results of the cut test are shown in FIG. 3. FIG. 3 shows the inside of a molded article 302 produced by the method described in U.S. Pat. No. 10,688,698 and the inside of a molded article 304 produced by the method described herein with simultaneous aeration during steam introduction and particle introduction. The molded foam particles 306 are distinguishable from adjacent particles. As a result of the cut test, some foam particles are removed, leaving voids 308, indicating the degree of fusion between the foam particles. FIG. 3 shows that the degree of fusion of the molded article 304 produced by the method described herein is qualitatively improved over the molded article 302 produced by the method described in U.S. Pat. No. 10,688,698.

[0042] 4 is a graph showing the deflection force of 1.5 inch (38 mm) panels produced in this example as measured by ASTM D3575-14. Panels produced by this method withstand higher deflection forces with less variability between samples, again indicating improved fusion of foam particles in molded articles produced by this method compared to molded articles produced as described in U.S. Pat. No. 10,688,698. Furthermore, the difference between the two is statistically significant as indicated by a p-value of about 0.05.

[0043] Example 3: Comparison of previous molding process with EPS process Molded articles were produced as described herein and compared to molded articles produced by the method described in U.S. Patent No. 10,688,698 to Lifoam Industries LLC and molded articles produced using a conventional EPS process. The molded articles produced using the method described herein and U.S. Patent No. 10,688,698 were formed from poly(lactic acid), whereas the conventional EPS process used expandable polystyrene. All molded articles tested were in the form of an 8 inch (203 mm) by 6 inch (152 mm) by 10 inch (254 mm) open box with a sidewall thickness of 1.5 inch (38 mm). Each of the five walls of the open box was cut to obtain a 2 inch (51 mm) by 2 inch (51 mm) sample, yielding a total of 48 specimens from each of the molded articles. Molded articles produced as described herein were molded on a Kurtz Ersa Corporation K68 HP5 Top-Line molding machine, available from Kurtz Ersa Corporation, Kreuzwertheim, Germany. The molding machine was modified with custom software to allow simultaneous venting during the introduction of steam and foam particles.

[0044] FIG. 5 is a graph showing the deflection force of a 1.5 inch (38 mm) panel produced in this example as measured by ASTM D3575-14. The panels produced by this method withstood a higher deflection force with less variability between samples compared to the molded article produced as described in U.S. Pat. No. 10,688,698. Furthermore, the difference between the two is statistically significant as indicated by a p-value of less than 0.05. The panels produced by this method withstood a lower deflection force than the conventional EPS process, however, the panels produced by this method are biodegradable since they were formed from poly(lactic acid). This reduced deflection force was accompanied by less variability between samples and represented a more uniform fusion throughout the molded article.

[0045] Example 4: Comparison of Cycle Time, Steam Time, and ΔT with the EPS Process The method described herein was implemented to determine the advantages in total cycle time, steaming time, and ΔT compared to a standard EPS process. The results are shown in Table 2. [Table 2]

[0046] As shown in Table 2, the disclosed method is nearly 40 seconds faster than the conventional EPS process, requiring a lower ΔT, corresponding to less steam time and less energy consumption. By introducing steam during foam particle introduction, the required direct steam can be reduced from about 13 seconds to about 1 or 2 seconds. It is also noteworthy that there is no use of cooling water in the new process. Although conventional molding processes typically prevent the introduction of steam during foam particle introduction, motivated by a desire to prevent wasted steam, it was unexpectedly discovered that the total cycle time and steam time can be dramatically reduced, despite the possibility of wasting steam by introducing steam during particle packing.

[0047] Although the present disclosure has been described with reference to a number of embodiments, it will be understood by those skilled in the art that the present disclosure is not limited to such embodiments. Rather, the present disclosure can be modified to incorporate any number of variations, alterations, substitutions, or equivalent arrangements not described herein, but which are commensurate with the spirit and scope of the present disclosure. Unless otherwise expressly stated or understood within the context in which it is used, conditional language used herein, such as "can," "could," "may," or "might," is generally intended to convey that a particular embodiment includes certain features, elements, or functional capabilities, while not including other embodiments. Furthermore, although various embodiments of the present disclosure have been described, it should be understood that aspects of the present disclosure may include only some of the described embodiments. Thus, the present disclosure is not to be deemed limited by the foregoing description, but is limited only by the appended claims.

Claims

1. 1. A method of making a molded foam article, comprising: (i) wetting and heating foam particles introduced into a mold for articles in which the foam particles are not fused; and then (ii) applying a negative pressure cycle, during which the foam particles expand and fuse together to form the article; and then (iii) removing the molded foam article from the mold.

2. 10. The method of claim 1, wherein step (i) comprises introducing steam into the mold simultaneously with introducing foam particles into the mold.

3. The method of claim 1 , wherein step (ii) comprises injecting steam into the mold.

4. 10. The method of claim 1, wherein step (i) further comprises applying a slight vacuum cycle to the mold simultaneously with the introduction of the foam particles and the steam.

5. 2. The method of claim 1, wherein step (i) comprises: (a) introducing the foam particles into the mold; and then (b) introducing steam into the mold while venting the mold, the venting being effective to prevent the foam particles from expanding or collapsing.

6. Steam heats the mold to a first temperature and then After filling with the foam particles, the mold is cooled to a second temperature during the negative pressure cycle; The method of claim 1, wherein the first temperature is 5 to 25° C. higher than the second temperature.

7. 7. The method of claim 6, wherein the first temperature is 10°C, 15°C, or 20°C higher than the second temperature.

8. The method of claim 1 , wherein the molded foam article has a thickness in at least one dimension of from about 0.3 inches to about 12 inches.

9. 10. The method of claim 8, wherein the method is effective to obtain a molded article having greater flexural strength, as measured by ASTM C203, than foam articles molded using conventional processes.

10. 10. The method of claim 1, wherein the method is effective to obtain a molded article having a greater deflection force, as measured by ASTM D3575-14, than foam articles molded using conventional processes.

11. 10. The method of claim 1, wherein the method is effective to obtain a molded article having greater fusion uniformity than foam articles molded using conventional processes.

12. The method of claim 1 , wherein the molded article has a deflection variability of less than 8%.

13. 10. The method of claim 1 having a total molding time that is at least 50% shorter than the total molding time of conventional expandable polystyrene molding processes.

14. The method of claim 1 , wherein steam is introduced into the mold at an angle effective to agitate the foam particles within the mold.

15. The method of claim 1 , wherein cooling water is not used to cool the mold.

16. 10. The method of claim 1, wherein the foam particles comprise a homopolymer, graft polymer, or copolymer of poly(butylene succinate), poly(ethylene terephthalate), poly(lactic acid), poly(poly(hydroxybutyrate), poly(butylene terephthalate), poly(caprolactone), poly(butylene adipate terephthalate), poly(hydroxyalkonate), or blends thereof.

17. (i) wetting and heating the foam particles introduced into a mold for an article in which the foam particles are not fused; and then (ii) applying a negative pressure cycle during which the foam particles expand and fuse together to form the article; and then (iii) removing the molded foam article from said mold.

18. 20. The molded article of claim 17, wherein the foam particles comprise poly(lactic acid) and the molded article is in the form of a panel, edge protector, box, lid, or other molded shape.

19. 20. The molded article of claim 18, wherein the other panel has a thickness of from about 1.5 inches to about 12 inches.

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