TECHNICAL FIELD

This disclosure relates to a method for producing plastic products from waste plastics and resulting polymeric mixtures.

BACKGROUND

Products made from or incorporating plastic are used in almost any work place or home environment. Generally, the plastics that are used to create these products are formed from virgin plastic materials. That is, the plastics are produced from petroleum and are not made from existing plastic materials. Once the products have outlived their useful lives, they are generally sent to waste disposal or a recycling plant.

Recycling plastic has a variety of benefits over creating virgin plastic from petroleum. Generally, less energy is required to manufacture an article from recycled plastic materials derived from post-consumer and post-industrial waste materials and plastic scrap (collectively referred to in this specification as "waste plastic material"), than from the comparable virgin plastic. Recycling plastic materials obviates the need for disposing of the plastic materials or product. Further, less of the earth's limited resources, such as petroleum and polymers, are used to form virgin plastic materials.

When plastic materials are sent to be recycled, the feed streams rich in one or more plastic materials may be separated into multiple product and byproduct streams. Generally, the recycling processes can be applied to a variety of plastics-rich streams derived from post- industrial and post-consumer sources. These streams may include, for example, plastics from office automation equipment (printers, computers, copiers, etc.), white goods (refrigerators, washing machines, etc.), consumer electronics (televisions, video cassette recorders, stereos, etc.), small domestic appliances (coffee makers, electric kettles, rice cookers, etc.), automotive shredder residue (ASR, the mixed materials remaining after most of the metals have been sorted from shredded automobiles and other metal-rich products "shredded" by metal recyclers), electronics shredder residue (ESR, the mixed materials remaining after most of the metals have been sorted from electronics "shredded" by metal recyclers), packaging waste, household waste, building waste and industrial molding and extrusion scrap.

Different types of plastic parts are often processed into shredded plastic -rich streams. The variety of parts can vary from a single type of part from a single manufacturer up to multiple families of part types. Many variations exist, depending on at least the nature of the shredding operation. Plastics from more than one source of durable goods may be included in the mix of materials fed to a plastics recycling plant. This means that a very broad range of plastics may be included in the feed mixture. Some of the prevalent polymer types in the waste plastic materials derived from the recycling of end-of-life durable goods are acrylonitrile- butadiene-styrene (ABS), high impact polystyrene (HIPS), polypropylene (PP), polyethylene (PE), polycarbonate (PC), and blends of PC with ABS (PC/ABS), polyamides (PA), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyether ether ketone (PEEK) , polysulfone (PSU), polyoxymethylene (POM) and others. In some cases, the polymer pieces contain flame retardants or fillers.

Mixtures of recycled plastic materials can also contain rubber, wood, thermosets and other non-plastic materials.

In order to create product streams suitable for the widest range of applications, it is desirable to purify the flakes such that they contain almost entirely one type of plastic and almost no non-plastic materials. Methods for separating the plastic flakes into streams that are suitable for re-use are described in U.S. Patent No. 7,802,685 (which is hereby incorporated by reference) and in U.S. Publication Application No. US-2014-0231557A1 (which is hereby incorporated by reference).

The products described in U.S. Publication Application No. US-2014-0231557A1 are typically much higher in specific gravity than 1.0, and most are higher in specific gravity than 1.1. At these high densities, there is a wide variety of plastics and the end product mixture may contain a number of contaminant plastics.

In the following, we describe a method for removing formaldehyde from these plastics mixtures by using an appropriate family of additives.

SUMMARY

This application provides methods for producing products low in formaldehyde content from mixtures of plastic flakes recovered from durable goods.

In some aspects, methods for producing a melt compounded plastic product provided herein can include adding one or more aminotriazines to a plurality of plastic flakes to produce a flake mixture and compounding the mixture in an extruder to produce a compounded mixture. In some cases, methods provided herein can include one or more processes of determining an amount of POM, PVC, or a combination thereof in the plurality of plasitc flakes. In some cases, methods provided herein can include one or more processes of determining an amount of the one or more aminotriazines to add to the plurality of plastic flakes based on the amount of POM, PVC, or a combination thereof. In some cases, a molar ratio of the amount of the one or more aminotrizines to the amount of POM is between 1 :6 and 1 : 1. In some cases, the plurality of plastic flake can include plastic flakes selected from the group consisting of PA6, PA66, PC, PC/ABS, PBT, PET, PSU, and combinations thereof. In some cases, the mixture includes at least 98 weight percent of PC/ABS, ABS, PC, or a combination thereof. In some cases, methods provided herein can include one or more processes of recovering the plurality of plastic flakes from a mixture of plastics and other materials from shredded electronics, automobiles, or a combination thereof

The one or more aminotriazines can include any suitable aminotriazine. In some cases, the one or more aminotrazines can include benzoguanamine, caprinoguanamine, acetoguanamine, melamine, or a combination thereof. In some cases the one or more aminotriazines can be added to the mixture of plastic flakes as a masterbatch after first being incorporated into a plastic carrier resin.

Aminotriazines can react with formaldehyde when the mixture is compounded in the extruder. The extruder used in methods provided herein can uses a variety of methods to remove additional formaldehyde and/or formaldehyde reaction products from the compounded mixture. In some cases, methods provided herein can include vacuum venting the compounded mixture. In some cases, methods provided herein can include melt filtrating the compounded mixture.

In some aspects, a recovered polymeric mixture provided herein can include at least 98 weight percent of PC/ABS, ABS, or PC, or a combination thereof and a reaction product of an aminotriazine and formaldehyde. In some cases, the recovered polymeric mixture is a compounded mixture. In some cases, the reaction product is present in an amount of at least 0.1 weight percent. In some cases, the recovered polymeric mixture is recovered from a mixture of plastics and other materials from stredded electronics, automobiles, or a combination thereof.

DETAILED DESCRIPTION

Methods for creating plastics that are low in formaldehyde from plastic mixtures recovered from durable-goods waste streams are provided herein. A recycling plant for the recovery of plastics from durable goods typically includes a number of process steps. For example, U.S. Patent No. 7,802,685 describes various sequences of various process steps for the removal of non-plastics and the separation of the various plastic types from streams containing mixtures of plastics from durable goods. The methods, systems, and devices provided herein can be used in sequence with or in substitution for the various process steps described in U.S. Patent No. 7,802,685, which is hereby incorporated by reference. These sequences of processes apply to both streams derived from durable goods and to streams of packaging materials, bottles or other mixtures rich in plastics.

The recycling plant described in U.S. Patent No. 7,802,685 primarily focuses on the recovery of ABS, HIPS and PP. In addition, some compositions of these recovered plastics are described in U.S. Patent No. 7,884,140. While these plastics are typically the most prevalent in streams of durable goods, the recovery of some of the other plastics can be of value. Strategies to recover these other plastics and the compositional requirements for the plastic products are described in U.S. Publciation Application No. US-2014-0231557-A1.

The plastics targeted for recovery in U.S. Publication Application No. US-2014- 0231557-A1 include those plastics higher in specific gravity than 1.10, as methods to recover the lower density plastics are covered in U.S. Patent No. 7,802,685. The targeted plastics therefore include PPE/HIPS (1.06-1.12), PA6 (1.14), PA66 (1.14), PMMA (1.18), PC (1.20- 1.22), PC/ABS (1.12-1.20) , ABS-FR (1.15 or 1.18-1.23), HIPS-FR (1.07-1.12 or 1.14-1.17), PVC (1.3-1.4), PEEK (1.32), PSU (1.23-1.36), POM (1.4), PBT (1.3), PC/PBT (1.2-1.3), PET (1.18) and PET/ABS (1.12).

Product mixtures rich in the plastics listed above may also contain small amounts of both POM and PVC. POM can degrade at high melt temperatures (typically greater than 250°C) such as those required for the melt processing of many of the listed polymers. In the absence of moisture, such degradation can result in the formation of methanediol.

PVC also degrades and gives off HC1 at these high melt temperatures. The HC1 can then catalyze the hydrolytic degradation of POM homopolymers or copolymers that may be present in the mixture. This hydrolytic degradation of POM results in the formation of formaldehyde, which is undesirable due to its negative effects on human health and because high levels can result in bubble formation on the product. Such degradation can occur even at concentrations of POM and PVC below 100 ppm.

In addition to the human health issues, the presence of methanediol and HC1 is problematic because these can also catalyze the hydrolytic degradation of some of the condensation polymers listed previously. Polymers including Polyamide 6 (PA6), Polyamide 66 (PA66), Polycarbonate (PC), Polycarbonate/Acrylonitrile-Butadiene-Styrene Blend (PC/ABS), Polyethyleneeterephthalate (PET), Polybutyleneterephthalate (PBT), and Polysulfone (PSU) are particularly susceptible.

While it is possible to remove POM and PVC from most of the plastics by additional sorting steps (e.g. density, electrostatic separations or others), these sorting steps add to the costs of recovering the plastics and may result in lost yield.

In order to reduce the amount of formaldehyde released into the product or into the atmosphere, and to avoid the catalytic degradation of condensation polymers, it is possible to add chemical ingredients that react with or react with the formaldehyde or HCl produced in the melt.

Molecular sieves are capable of absorbing small molecules such as formaldehyde. An example of a commercially available molecular sieve is Abscents™ (available from UOP LLC, Des Plaines, IL).

Chemicals such as aminotriazines also are suitable for eliminating formaldehyde because of their reactivity with formaldehyde. It is well known that melamine, the most well known representative of the aminotriazines, reacts with formaldehyde to produce melamine- formaldehyde resins under the influence of acids at moderate enhanced temperature (100 - 150°C) in aqueous solutions to impregnate or glue papers and wood panels. The mechanism for this reaction is shown in equation (1) below.

The reactivity of the remaining amino functions increases with each substitution of one proton by formaldehyde. The product if the above reaction is therefore more reactive than melamine alone.

The resulting products of equation (1) can degrade at high temperatures or over time to emit some amounts of formaldehyde, but the levels emitted are much reduced compared with the products in the absence of the triazine additives.

In the polymer melt streams of the present invention, reactions such as that shown above would need to occur at temperatures of 250°C or greater. Example 1 shows that such reactions indeed occur. We might expect melamine to react with the engineering plastic, with the melamine inserting itself along the chain to create two smaller polymer chains. Such a reactions is shown in equation (2), where the polymer is polycarbonate (PC) and Rl and R2 are polymeric segments consistent with the structure of PC. Such reactions might occur in PC and PC/ABS, though similar reactions might occur in other condensation polymers such as PA6, PA66, PET,

PBT or PSU.

Reactions such as that shown in equation (2) would result in dramatic losses in the molecular weight of the polymer, and therefore would reduce the viscosity and possibly the mechanical properties as well. It therefore is of interest to select aminotriazines with substituents that might reduce the reactivity such that the side reaction shown by equation (2) is less likely to occur.

The polymeric products containing the aminotriazine group shown in equation (2) can also, in some instances, react with up to two additional polymers such that it is possible to create a three armed star polymer and eventually could result in crosslinking when there is a sufficient level of melamine present. Star and crosslinked polymers would have some effect on the rheology and mechanical properties of the polymer.

We expect that substituting one of the amino functions of the melamine with a bulky substituent might reduce the reactivity of the other two amino functions with respect to the polymer, while at the same time retaining the desired reactivity with formaldehyde. Equation (3) shows the preferred reaction where Ru is a bulky substituent in place of one of the amino groups.

(3) A further question regarding the diaminotriazine with the bulky Ru group is whether such compounds can participate in side reactions similar to those shown in equation (2). We would expect these reactions to be slightly slower than for melamine because of the steric hindrance if the Ru functional group, though such reactions still may occur as shown by equation (4). Equation (4) is the same reaction as equation (2), though we note that it is not likely for the molecule to react further to form a three armed star polymer or cross-linked network.

The Ru group can be any functionalisation, preferably with bulky groups as phenyl, alkyl, naphtyl, biphenyl, polyphenyl, oligomers and polymers, though non-bulky groups like hydrogen are also possible. Of the various sterically preferred Ru groups, electron acceptors such as as phenyl and carbonyl are preferred.

Commercially available Aminotriazines suitable for removing formaldehyde from extruded melt streams are benzoguanamine, caprinoguanamine, acetoguanamine or melamine.

Melamine provides three amino functions and should therefore provide the full reactivity for formaldehyde and for acids. Melamine may also be able to react into condensation polymers by splitting them into two parts, and can potentially produce a three armed star polymer.

Acetoguanamine (shown in Fig. 1) provides two amino functions. Due to the small and electronically neutral methylene group substituting one amino function, the reactivity of the remaining two amino functions should be suitable for formaldehyde and for acids.

Caprinoguanamine (shown in Fig. 2) provides two amino functions. Due to the large group substituting one amino function, the reactivity of the remaining two amino functions should be reduced and should show a preference for the formation of linear chains.

Benzoguanamine (shown in Fig. 3) provides two amino functions. Due to the large and negative benzyl group substituting one amino function, the reactivity of the remaining two amino functions should be reduced and should show a preference for the formation of linear chains. Aminotriazines can additionally be able to act as bases and scavenge HCl (as arising from degrading PVC) before it can catalyze the degradation of POM.

In some cases, processes provided herein can optimize the concentration of the aminotriazines added to polymers. In some cases, a sufficient amount of aminotriazines can be added to capture HCl or formaldehyde, but not be so much as to lead to the chain scission reactions shown in equations (2) and (3), as such reactions can result in reductions in the molecular weight and reduced mechanical properties.

In some cases, a molar ratio of aminotriazines to POM is between 1 :6 and 1 : 1 in processes provided herein. In some cases, melamine can be used at 1/6 of the formaldehyde molarity to function as a formaldehyde scavanger. In some cases, higher concentrations of melamine can increase the reactivity of the side reactions including chain scission and eventual crosslinking. Such reactions can be undesirable as they can reduce the mechanical properties of the polymer. In some cases, functionalized diaminotriazines can be used at higher concentrations as they are less likely to cause chain scission in the polymers. In some cases, the molar ratio of the resulting diol for transesterification and linear cross-linking to formaldehyde can be 1 :2 (see 2-fold saturation of Aminofunctions in Example 1).

In some cases, aminotriazines can be limited to a molar ratio of 1 : 1 to avoid chain scission due to unreacted Aminotriazines.

The problem of trace amounts of POM and PVC is most problematic in condensation polymers such as PA6, PA66, PBT, PET, PSU, PC and PC/ABS products. These products contain residual moisture because they are hydrophilic, and they are also typically processed at high temperatures in order to melt the polymer (in the case of PA6 or PA66) or in order to efficiently process the melt (in the case of PC or PC/ABS).

In addition to the use of aminotriazines to reduce the level of formaldehyde and HCl in the system, the compounding step can in some cases include adequate de-gassing to remove formaldehyde and other volatile and semi-volatile species.

The following example shows how aminotriazines may be used to reduce levels of formaldehyde in PC/ABS products.

Example 1 : Compounding aminotriazines with a PC/ABS flake mixture containing POM and PVC as impurtities

A mixture of PC/ABS flake recovered from shredded waste electronics was compounded in a twin screw extruder at a melt temperature of 265°C. The extruder included both atmospheric and vacuum de-gassing stages. The flakes were dried overnight prior to extrusion. The flake mixture contained POM and PVC impurities at levels of approximately 500 ppm each. We would expect the extrusion process to degrade the PVC and POM at these temperatures, resulting in the emission of formaldehyde vapor and the acid catalyzed degradation of the PC in the PC/ABS.

We compounded the PC/ABS flake mixture without additives and with various levels of aminotriazines including melamine, acetoguanamine, caprinoguanamine and benzoguanamine.

Table 1.1 summarizes the compositions and results for the compounded PC/ABS samples.

Table 1.1 : Emissions and properties of PC/ABS compounds with added aminotriazines

Formaldehyde emissions are ranked on a scale of 0 to 2, with 0 being "no noticeable emissions" and 2 being "strong emissions". We note that all of the aminotriazines function to reduce the formaldehyde emissions, with formaldehyde proving the biggest effect due to its greater reactivity.

The melt flow rate (MFR) measured following ISO 1 133 at 240°C with a load of 5 kg is related to the viscosity of the molten polymer with higher values of the MFR corresponding to lower values of the viscosity. Since the viscosity increases strongly with the molecular weight, higher values of the MFR would suggest that the polymer has been degraded. We note that samples with 0.1% caprinoguanamine or benzoguanamine have the lowest MFRs that are similar to (or slightly less than) the PC/ABS without additives. This suggests that these additives are best at maintaining the molecular weight.

We note that all of the samples with 3% added aminotriazine have higher values for the MFR, which suggests that the chain scission reactions become important as the concentration of the additive increases.

The un-notched izod impact strengths (measured according to ISO 180-leU) are related to the toughness of the polymer, which in turn should be related to the molecular weight. We note that samples with 0.1% caprinoguanamine or benzoguanamine have slightly higher impact strengths than the PC/ABS material without additive. The sample with 0.1% acetoguanamine has a much reduced impact strength, and the sample with 0.1% melamine has almost no remaining impact strength. All samples with 3% added aminotriazines have almost no remaining impact strength.