Indicator for indicating polymer degradation and product life thereof, and indicating method thereof

Abstract

The present invention relates to an indicator for indicating polymer degradation and its product life, comprising: a dye and a developer, the dye exhibiting a predetermined visual indication when the dye is combined with the developer, and the dye exhibiting a different visual indication when the developer is removed from the dye. The invention also relates to a self-degradation indicating polymer and a method for indicating degradation of the polymer.

Description

Technical Field

[0001] The invention relates to an indicator for indicating polymer degradation and a self-degrading indicating polymer, and also relates to a polymer degradation indicating method. Background Art

[0002] Polymers degrade when exposed to heat, light, chemicals, mechanical energy, etc. Polymer degradation usually results in changes in its chemical or physical properties, such as molecular weight, tensile strength, color, shape, etc., and may mean that the polymer is no longer able to perform its intended purpose. These changes in properties are often referred to as "aging".

[0003] Any degree of degradation may affect the properties of the polymer and may not necessarily be perceptible to humans, especially at an early stage. An expiry date may be provided after which the polymer will be considered unsafe to use. However, the rate of degradation may be affected by various environmental factors. Unexpected acceleration of degradation may result in exceptions to the normal degradation process. The expiry date may not correspond to expectations.

[0004] Some polymer degradation / aging can be identified by eye or bare hand through natural changes in the polymer, such as yellowing, discoloration, brittleness, cracking, chalking, breaking, or hardening. The problem is that these naturally occurring changes depend on various environmental factors. In the absence of certain environmental factors, these changes may not occur even if the polymer degrades and becomes unsafe. On the other hand, premature discoloration due to exposure to certain environmental factors (such as sunlight) may result in an inaccurate indication of the polymer's degradation state. Therefore, relying solely on naturally occurring changes to identify polymer degradation / aging may be unreliable and, therefore, undesirable. Summary of the invention

[0005] A first aspect of the present invention provides an indicator for indicating polymer degradation, comprising: a dye and a developer, wherein when the dye is bound to the developer, the dye presents a predetermined visual indication, and when the developer is removed from the dye, the developer presents a different visual indication.

[0006] Optionally, the developer comprises a hydrogen bond donor.

[0007] Preferably, the hydrogen bond donor includes a boric acid-based compound, a phenol-based compound, a silica-based oxide, or an alumina-based compound.

[0008] Preferably, the boronic acid-based compound is phenylboronic acid.

[0009] Optionally, the dye comprises crystal violet lactone which can be converted from a spiropyran form to a merocyanine form by binding to a developer.

[0010] Optionally, the merocyanine form of crystal violet lactone presents a visual blue indication as the predetermined visual indication.The dye may be bound to the developer in a default state such that the visual blue indication is most prominent in the default state.

[0011] Optionally, the presence of the degradable polymer disrupts the bond between the dye and the developer, causing the dye to change to a spiropyran form, thereby removing the visible blue indication.

[0012] Optionally, the chromogenic agent is capable of forming a more stable bond / interaction with the degradable polymer / residues formed during the degradation process than with the dye.

[0013] Optionally, the degradable polymer comprises an oxo-degradable polymer.

[0014] Optionally, the spiropyran form of the dye is more stable than the merocyanine form without the developer.

[0015] Optionally, the dye is a leuco dye.

[0016] A second aspect of the present invention provides a self-degrading indicating polymer, comprising: a degradable polymer and the above-mentioned indicator, wherein the indicator comprises a dye and a developer, wherein the dye is combined with the developer to form a first visual indication. The dye and the developer may be the same as those in the first aspect. The first visual indication may be blue. Visual indications of other colors are also possible, such as black and / or green.

[0017] Optionally, the degradable polymer degrades by oxo-degradation to form an oxo-degraded polymer. The oxo-degraded polymer may be capable of interacting with a developer to form a second visual indication. The second visual indication may be colorless.

[0018] Optionally, the interaction between the oxo-degraded polymer and the developer weakens or destroys the bond between the dye and the developer.

[0019] Optionally, the oxo-degraded polymer consists of hydroxyl and carbonyl moieties containing oligomer / degraded residues. The hydroxyl groups are preferably located on tertiary carbons of the monomers.

[0020] Optionally, the oxo-degradable polymer comprises a carbonyl group.

[0021] Optionally, the degradable polymer comprises a polyolefin, such as polypropylene, polyethylene or polystyrene.

[0022] A third aspect of the present invention provides a method for indicating polymer degradation, the method comprising: mixing an indicator and a polymer, the indicator comprising a dye and a developer, the dye being able to present a predetermined visual indication when combined with the developer, and presenting a different visual indication when the developer is removed from the dye, for example in the presence of a degradable polymer that disrupts the bond between the dye and the developer.

[0023] A fourth aspect of the present invention provides a polymer composite comprising a polymer and a material comprising a dye and a developer. The polymer may comprise a polyolefin, such as polypropylene. The material may be an indicator in any of the first, second and third aspects. The amount of the dye and developer depends on the degradable polymer.

[0024] Preferably, specific amounts of dyes and colorants can be used to indicate specific degradation events occurring in the degradable polymer.

[0025] The present invention has the following beneficial effects:

[0026] The indicator for indicating polymer degradation of the present invention can grasp the product cycle stage of the degradable plastic through color changes.

[0027] Other features and aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.Any feature described herein with respect to one aspect or embodiment may be combined with any other feature described herein with respect to any other aspect or embodiment, as appropriate. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0029] Figure 1 The working principle of the present invention is shown;

[0030] Figure 2 shows a visual indication of the degradation process of the inventive polymer sample 107 at 70°C and 80°C;

[0031] Figure 3 Shows Figure 2 Changes in tensile strength of polymer sample 107 during degradation at 70 °C and 80 °C. DETAILED DESCRIPTION

[0032] Before explaining any embodiment of the present invention in detail, it should be understood that the application of the present invention is not limited to the details of construction and arrangement of parts described in the following description or shown in the following drawings. The present invention can have other embodiments and can be practiced or implemented in various ways. In addition, it should be understood that the words and terms used herein are for descriptive purposes and should not be regarded as limiting. Degree terms such as "substantially" or "approximately" are understood by ordinary technicians to refer to a reasonable range outside a given value, for example, the general tolerances associated with the manufacture, assembly, testing and use of the described embodiments.

[0033] In one embodiment, an indicator is provided for indicating the degradation of a degradable polymer, such as a polyolefin (e.g., polypropylene (PP), polyethylene (PE), polystyrene (PS), or other polymers containing only C and H). The polymer may be a polymer in a plastic product, which may or may not contain polymers other than polyolefins. The indicator may be introduced into the polymer to make a final product, or may be added to the polymer in a degradation test as needed. In a preferred embodiment, the indicator is added to the polymer during the manufacturing process of the polymer or plastic product to form a polymer composite. For example, the indicator may be mixed (e.g., blended) with the polymer in a molten form, during which the indicator undergoes a reaction and a change in state, thereby providing an indication of degradation. The polymer composite may contain about 0.1 wt% to about 10 wt%, about 0.3 wt% to about 5 wt%, or about 0.4 wt% to about 1 wt% of the indicator relative to the polymer in the polymer composite.

[0034] Preferably, the indicator is a visual indicator that gives a visual indication when the polymer has / has begun to degrade. As used herein, "visual indication" refers to a phenomenon that can be visually observed by the naked eye or optical equipment (such as a microscope), and preferably does not require additional assistance, such as additional chemicals. Visual indications may include, but are not limited to, color changes, size changes, and the presence / absence of features (such as bubbles). Preferably, complete visual indications (i.e., the end point of any visible changes) occur before and throughout the degradation of polymer functionality. In addition to or in lieu of visual indications, indicators may also provide other forms of indications, such as odor indications that indicate polymer degradation.

[0035] As used herein, "degradation" refers to the process by which a polymer is subjected to one or more environmental factors, thereby causing chain depolymerization, random scission, or reaction of substituents, breaking the polymer into smaller molecules and ultimately possibly decomposing. The one or more environmental factors may include, but are not limited to, heat, light, chemicals, or any other applied force.

[0036] The indicator can be used to indicate the entire process of degradation from a newly manufactured polymer to a state where it begins to degrade, and finally to a state where the tensile strength of the polymer is significantly reduced and makes it unsuitable for use. Alternatively, the indicator can be used to indicate certain parts or stages of the above process.

[0037] In one embodiment, the indicator is a visual indicator, and the visual indicator includes a dye and a developer. As used herein, a "dye" refers to a coloring material that imparts color to a substrate chemically bonded thereto. A "developer" refers to a material that interacts with a coloring material to produce a specific visual indication. This interaction may be reversible. The molar ratio of the dye to the developer in the indicator can be from about 0.1 to about 2, from about 0.3 to about 1.5, or from about 0.5 to about 1. The molar ratio of the dye to the developer is preferably 1:1.

[0038] When the dye is bound to the developer in a molar ratio of 1: 1, the dye can present a first predetermined visual indication, and when the developer is removed from the dye, a second different visual indication can be presented. For example, the dye can be a colorless dye that changes reversibly or irreversibly between two chemical forms to give different visual indications. For example, the dye can change from one color to another, or from colorless to colored, and / or vice versa. The developer can include a heat source, a light source, a pH source, a reducing agent, or an oxidant responsible for the conversion between two chemical forms. Preferably, the developer can be a hydrogen bond (hydrogen bond) donor, such as a boric acid-based compound, and in an embodiment of the present invention, the developer is phenylboronic acid (PBA). It is believed that boric acid provides a safer option compared to traditional developers (such as bisphenol A and its derivatives), and bisphenol A and its derivatives are widely banned due to their toxicity.

[0039] The above-mentioned indicator includes a dye and a developer, which can be used in a method for indicating polymer degradation. The method includes mixing the indicator and the polymer, for example, by melting the polymer, and then mixing the dye and the developer into the molten polymer. The molar ratio of the dye to the developer in the indicator can be about 0.1 to about 2, about 0.3 to about 1.5, or about 0.5 to about 1. Relative to the polymer in the polymer composite, the resulting polymer composite can contain about 0.1wt% to about 10wt%, about 0.3wt% to about 5wt% or about 0.4wt% to about 1wt% of the indicator, preferably 0.5wt%. As described above, when the dye is bound to the developer, the dye can present a predetermined visual indication, and when the developer is removed from the dye, for example, in the presence of a degradable polymer that destroys the bond between the dye and the developer, a different visual indication can be presented, which will be discussed later.

[0040] In a preferred embodiment, the dye comprises crystal violet lactone (CVL), which is variable between a spiro (e.g., spiropyran) form and a merocyanine form when it reacts with a developer. Scheme 1 schematically shows the reaction between an indicator (including a dye and a developer) and a polymer. CVL is more stable in the spiropyran form than in the merocyanine form without a developer. When a developer (i.e., a hydrogen bond donor HX) is added, CVL binds to the developer and is converted into a merocyanine form that strongly absorbs visible light, thereby producing a strong color. In one embodiment of the present invention, in a default state, the CVL is in a merocyanine form by interacting or binding with a developer. Before the polymer degrades, the dye presents a visual blue indication as a predetermined visual indication. This visual blue indication may be the most significant, for example, the strongest, in a default state. When the polymer begins to degrade to form a degraded polymer, the degraded polymer may interfere with the binding of the dye and the developer, or interact with the developer, thereby destroying the binding between the dye and the developer. This results in the dye being converted back to the spiropyran form. As used herein, "degradable polymer" refers to a polymer that breaks down to form smaller molecules during degradation or after complete degradation, and thus also includes any such smaller molecules.

[0041]

[0042] In the presence of degraded polymer (for example oxo-degraded polymer), at least some dyes and developer no longer rest on the default state." oxo-degraded polymer " refers to or is undergoing oxidation process (i.e. oxo-degradation) to form a polymer of smaller molecules, therefore also includes any such small molecule. The degraded polymer destroys the combination between the dye and the developer, and makes the dye become the spiropyran form, thereby removing the visible blue indication. In the oxo-degradation process, some polymer fragments containing hydroxyl, carbonyl may be formed. They can be used as decolorizing agents, destroy or weaken the interaction between CVL and PBA, to induce the coloring change that for example indicates the end of polymer life.

[0043] In a preferred embodiment, the developer includes electrophilic sites, and the degradable polymer serves as a nucleophilic agent to attack electrophilic sites. The developer may be able to form a more stable combination with dye than with the degradable polymer. For example, the degraded polymer may include a hydroxyl-containing polymer chain, for example, each monomer of the degradable polymer may include at least one hydroxyl (for example, formula I), or the degraded polymer may include a carbonyl (for example, formula II, wherein R is any substituted or unsubstituted alkyl or aryl), for competing with dye and combining with developer. For example, the hydroxyl may be located on the tertiary carbon of the monomer, thereby forming a large amount of 1,3-diol groups in the polymer chain, for combining with developer. Additionally or alternatively, the structural change of the degraded polymer may hinder (for example, destroy or weaken) the interaction between the dye and the developer. The nucleophilic attack of the oxygen atom of the degradable polymer to the boron atom of the developer may cause the formation of the adduct of the developer and the degradable polymer, thereby weakening or destroying the interaction or bonding between CVL and PBA.

[0044]

[0045] Due to the lack of enough degradable polymers to compete with dyes, some dyes become spiropyran forms during degradation, while the remaining dye remains as merocyanine forms. Therefore, in this state, visible blue indications are still visible, but not as strong as in the default state. In other words, the blue indication disappears gradually during degradation. As degradation proceeds, all dyes can become pyran forms, and the blue indication can be removed completely, i.e., the dye can become colorless. In an embodiment where the polymer is colorless, this color change from blue to colorless can also be observed. Along with degradation, polymer composites (including dyes) may turn yellow. Depending on the type of degradation, the color change of polymer composites may be different. For example, in the absence of oxygen degradation, incomplete decolorization will occur, and the polymer composite will become colorless from blue, and will not become yellow.

[0046] Scheme 2 shows a preferred embodiment, wherein the polymer is PP, the oxo-degraded polymer contains 1,3-diol groups, and the developer is PBA. The "BO" click reaction between the degraded polymer and the developer destroys the interaction between the dye and the developer, inactivates the merocyanine form, and promotes conversion to the spiropyran form, resulting in decolorization of the dye, see Figure 1 .

[0047] Two polymer composite samples containing CVL and PBA were prepared by melting the polymer PP and mixing the two reagents (i.e., CVL and phenylboronic acid in a ratio of 1:1 and 0.5 wt% relative to the polymer) into the molten PP. One of the two samples ( Figure 2 The bottom row) has a pro-oxidant masterbatch added (4 wt% relative to the polymer content) to accelerate degradation, especially oxo-degradation, while the other ( Figure 2 The top row of the table has no data, which serves as the control group. Figure 2 As shown, a gradual fading phenomenon was observed for both composite materials. In particular, the sample without pro-oxidant changed from blue to light blue, while the sample with pro-oxidant changed from blue to light blue and finally to colorless. It was also observed that the edges of the discolored (colorless) areas of the samples with pro-oxidant turned yellow. This is a natural change produced by degradation in the presence of UV radiation and oxygen in the air. This is not an accurate indication of the end of the product's life, as its occurrence depends on other naturally occurring factors. As mentioned above, premature fading may occur when the product is exposed to more than usual amounts of UV radiation and oxygen. In contrast, no significant changes were observed in the control group.

[0048] Thermal aging tests were also carried out on three polymer composite samples to investigate the effect of the indicator. Figure 3 As shown. In this example, two substantially identical polymer composite samples 97 and 98 (the weight ratio of the two is 1:1) are prepared by melting a polymer including low-density polyethylene (LDPE) and PP, and then blending a CVL indicator (0.5wt% relative to the polymer content) and a pro-oxidant masterbatch (4wt% relative to the polymer content) into the polymer through a tandem extrusion process. Sample 97 is a single-layer polymer composite with 0.5wt% CVL indicator and 4wt% pro-oxidant masterbatch. Sample 98 is a sandwich polymer composite, with a middle layer of 0.5wt% CVL indicator and 4wt% pro-oxidant masterbatch, and a top layer and a bottom layer of PP (polypropylene). The pro-oxidant masterbatch is PP (polypropylene) or PE (polyethylene). The indicator includes CVL and PBA in a weight ratio of 1:1. A third polymer composite sample 100 is prepared similarly, but without any pro-oxidant. In other words, the second polymer composite sample serves as a control group. The three samples are then cut and treated in a 70°C oven and an 80°C oven for 16 days. The color and tensile strength / functional properties of the samples are recorded at specific time intervals until a sharp drop in tensile strength / functionality is observed. Figure 3 As shown, functional degradation of samples 97 and 98 occurred after day 7. These results also show complete discoloration of samples 97 and 98 from blue to colorless to yellow at 80°C on day 7, and a simultaneous dramatic drop in tensile strength / functional performance.

[0049] The above embodiments provide an indicator that does not simply rely on naturally occurring changes (such as yellowing), ie, an artificial indicator, thereby improving the reliability and accuracy of polymer degradation determination.

[0050] The indicator is able to visually indicate the process of plastic degradation / aging and can therefore be used to monitor progress and shelf life predictions. For example, when a product turns yellow, the end of the product's life can be predicted. As another example, a color comparison chart showing the colors corresponding to each stage of degradation (e.g., day, week, month, etc.) can be used with the CVL indicator to make better and more accurate predictions. In one embodiment of the present invention, the color of the CVL indicator and polyolefin changes from blue to light blue, then yellow, and then colorless. This change is gradual over the entire useful life of the polymer.

[0051] Those skilled in the art will appreciate that, without departing from the spirit or scope of the present invention as described broadly, the present invention can be carried out many changes and / or modifications as shown in the specific embodiments.For example, except those developer and leuco dye that can be colored by acid triggering, developer and leuco dye also can be used as indicator.In addition, if in addition to leuco dye, another color additive is added to the polymer, then indicator can work in a similar manner as described above.That is to say, this indicator can still provide visual indication, or alternatively or additionally, provide other forms of indication.For example, if in addition to blue leuco dye, red dye is also added, then polymer may be purple in the initial state, and becomes red after polymer degradation, when blue leuco dye becomes colorless.Therefore, described embodiment of the present invention should be considered to be illustrative in all aspects, rather than restrictive.

Claims

1. An indicator for indicating polymer degradation, characterized in that: include: A dye and a developer, the dye presenting a predetermined visual indication when bound to the developer and presenting a different visual indication when the developer is removed from the dye.

2. The indicator according to claim 1, characterized in that The developer includes a hydrogen bond donor.

3. The indicator according to claim 2, characterized in that The hydrogen bond donor includes a boric acid-based compound, a phenol-based compound, a silica-based oxide, or an alumina-based compound.

4. The indicator according to claim 3, characterized in that The boronic acid-based compound is phenylboronic acid.

5. The indicator according to any one of claims 1 to 4, characterized in that The dye comprises crystal violet lactone, which is converted from a spiropyran form to a merocyanine form by binding to the developer; the merocyanine form of the crystal violet lactone presents a visual blue indication as the predetermined visual indication.

6. The indicator according to claim 5, characterized in that The presence of degraded polymer disrupts the bond between the dye and the developer, causing the dye to change to the spiropyran form, thereby removing the visible blue indication.

7. The indicator according to any one of claims 1 to 6, characterized in that The dye is a leuco dye.

8. A self-degrading indicating polymer, characterized in that: include: Degradable polymers, The indicator according to any one of claims 1 to 7, The dye is combined with the developer to form a first visual indication.

9. The self-degradable indicating polymer of claim 8, wherein the first visual indication is blue; the degradable polymer degrades by oxo-degradation to form an oxo-degradable polymer; the oxo-degradable polymer is capable of interacting with the developer to form a second visual indication; the second visual indication is colorless; the interaction between the oxo-degradable polymer and the developer weakens or breaks the bond between the dye and the developer; the degradable polymer comprises a polyolefin.

10. The self-degrading indicating polymer according to claim 9, characterized in that: The degradable polymer includes polypropylene, polyethylene or polystyrene; the amount of dye and color developer depends on the degradable polymer; a specific amount of dye and color developer can be used to indicate a specific degradation event occurring in the degradable polymer.

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