WO2020197503A1

WO2020197503A1 - Flame retardant ground rubber elastomeric composites

Info

Publication number: WO2020197503A1
Application number: PCT/SG2020/050171
Authority: WO
Inventors: Shengqin WANG; Yew Wei Leong
Original assignee: Agency For Science, Technology And Research
Priority date: 2019-03-28
Filing date: 2020-03-26
Publication date: 2020-10-01

Abstract

A flame retardant polymer composite is provided herein, comprising a thermoset binder such as a polyurethane binder, incorporated with a melamine-modified ammonium polyphosphate, wherein the thermoset binder comprises more than one isocyanate groups, wherein one or more of the isocyanate groups each forms a urea linkage with the melamine- modified ammonium polyphosphate, and elastomer particles such as ground rubber particles bound together by the thermoset binder. Its method of producing includes providing a dispersion comprising a melamine-modified ammonium polyphosphate and a thermoset binder, wherein the thermoset binder comprises more than one isocyanate groups, mixing the dispersion, elastomer particles, and water, to form a mixture, wherein the elastomer particles are encapsulated with the thermoset binder in the mixture, and curing the mixture to have one or more of the isocyanate groups each forming a urea linkage with the melamine-modified ammonium polyphosphate, thereby producing the flame retardant polymer composite.

Description

FLAME RETARDANT GROUND RUBBER ELASTOMERIC COMPOSITES

Cross-Reference to Related Application

[0001] This application claims the benefit of priority of Singapore Patent Application No. 10201902804R, filed 28 March 2019, the content of it being hereby incorporated by reference in its entirety for all purposes.

Technical Field

[0002] The present disclosure relates to a flame retardant polymer composite and its method of making.

Background

[0003] For environmental and economic reasons, there has been interest in recycling rubber. There may be about one billion worn out tires discarded around the world annually. Since rubbers tend to be crosslinked, they cannot be recycled using the same melting-molding process for recycling thermoplastics. Two practices were then established for recycling tire rubbers.

[0004] The first may be based on a devulcanisation process in which the three- dimensional network of rubber gets dissociated to linear polymer chains, which can be re-crosslinked. In this process, the S-C or S-S bonds of the crosslinked rubber may be selectively broken by mechanical and chemical means at temperatures of about 200°C. Meanwhile, the C-C bonds should be unaffected or less affected for retaining the rubber’s original mechanical properties once revulcanised. A key advantage of the devulcanised rubber may be its low cost, which may be about 1/4 to 1/3 of the original rubber. However, due to inevitable breaking of some C-C bonds during the treatment process, the recycled rubber may have shorter chain length, rendering a performance lower than what original natural rubber may exhibit. Furthermore, the devulcanisation process is likely energy consuming and releases air pollutants. As such, recycling of rubber via the devulcanisation process may be undesirable.

[0005] The second way for recycling rubber may be based on crumbing of rubber and use of ground rubber particles. This may avoid the use and/or release of volatile chemicals, rendering the second way more environmental friendly than the first. Furthermore, many grinding methods have been developed by the industry and various ground rubbers with well-controlled particle sizes down to 200 mesh may be commercially available. Retaining the resilient property of rubber, the ground rubbers may be used in many areas such as construction, land filling, producing concrete, asphalt or wood based composites. Among these applications, one important use of the ground rubber may be its combination with a polymer binder to make elastomeric composites for products like playground mats, running tracks, welcome mats, speed bumps, railroad crossing pads, carpet pads, etc. Owing to its high reactivity, polyurethane (PU) based binder may be used most.

[0006] For mixing with a PU binder, the process may include having a mixture of ground rubber and PU binder molded and cured. The rubber/binder composite may be cured via a“hot-cure” process, which requires elevated temperatures, or a“cold-cure” process, i.e. at ambient temperatures. Hot-cure processes may be performed under elevated pressures in manufacturing of small or medium sized products such as welcome mats, speed bumps, and the like. Cold-cure processes may be performed at ambient temperatures and pressures, and used when an on-site cure is needed, e.g. for playground surfaces or running tracks. The ground rubber/binder composite in a hot- cure process typically cures in minutes while the composite in a cold-cure process may take days to fully cure.

[0007] The ground rubber/binder composite may have good resilience and shock- resistant properties. In recent years, its application has expanded from conventional outdoor uses as mentioned above, to uses in building and construction, such as in anti ricochet ballistic protection panels or sound barriers. For these indoor applications, there happens to be a concern on flammability of the ground rubber/binder composite, as both the rubber and PU binder may be highly flammable. The composite is therefore required by law to be flame retardant for it to be potentially used indoors and in buildings. Improving flame retardant property of the ground rubber/binder composite thus became important in the industry.

[0008] Incorporating flame retardant additives may be a common strategy in the formulation of flame retardant polymer composites. However, for the ground rubber/PU binder composite, enhancement of flame retardant property tends to be challenging because the composite may contain 70 weight percent (wt%) to 90 wt% of flammable rubber particles. In composites containing a flame retardant filler, the filler may be dispersed in the PU phase that is bonded with rubber particles. Various flame retardant fillers have since been developed and PU composites having enhanced flame retardant property were formulated. In such conventional composites, as PU was the host polymer matrix and forms bulk of the composite, mechanical properties of PU may be a factor of consideration apart from its flame retardant property. However, the addition of flame retardant additives may compromise the mechanical property of PU.

[0009] Even in cases where PU is used as a binder, unreactive flame retardant fillers introduced into a polymer may adversely affect the binding properties of the binder. In other words, presence of unreactive fillers in a polymer resin may decrease binding strength of a binder.

[0010] There is thus a need to provide for a solution that addresses one or more of the limitations mentioned above. The solution should at least provide for a flame retardant polymer composite that includes a thermoset binder having enhanced binding strength with an elastomer (e.g. rubber), without compromising the flame retardant property. The flame retardant polymer composite may be an elastomeric thermoset for use in building and construction.

Summary

[0011] In a first aspect, there is provided for a flame retardant polymer composite comprising:

a thermoset binder incorporated with a melamine-modified ammonium polyphosphate, wherein the thermoset binder comprises more than one isocyanate groups, wherein one or more of the isocyanate groups each forms a urea linkage with the melamine-modified ammonium polyphosphate; and

elastomer particles bound together by the thermoset binder.

[0012] In another aspect, there is provided for a method of producing the flame retardant polymer composite described according to various embodiments of the first aspect, the method comprising:

providing a dispersion comprising a melamine-modified ammonium polyphosphate and a thermoset binder, wherein the thermoset binder comprises more than one isocyanate groups; mixing the dispersion, elastomer particles, and water, to form a mixture, wherein the elastomer particles are encapsulated with the thermoset binder in the mixture; and curing the mixture to have one or more of the isocyanate groups each forming a urea linkage with the melamine-modified ammonium polyphosphate, thereby producing the flame retardant polymer composite.

Brief Description of the Drawings

[0013] The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present disclosure are described with reference to the following drawings, in which:

[0014] FIG. 1A shows the chemical structure of a melamine-modified ammonium polyphosphate. The melamine-modified ammonium polyphosphate is herein abbreviated as APP. The APP is suitable as a flame retardant filler for use in a polyurethane (PU) binder composite m may be an integer ranging from 70 to 90 and n may be an integer ranging from 30 to 10, respectively. Said differently and as a non limiting example, m and n may be integers that add up to a sum of at least 100, wherein m:n has a ratio ranging from 9: 1 to 7:3.

[0015] FIG. IB shows a scheme for reacting APP and a polymer binder having multiple isocyanate groups (-NCO) to produce the present flame retardant binder, which has flame retardant property with improved binding strength, for use in making a flame retardant ground rubber composite m and n have already been defined above. The APP serves as a highly effective intumescent flame retardant, is reactive to isocyanate at high temperatures, and is compatible with, e.g. a PU binder.

[0016] FIG. 1C shows a flow diagram for producing, as an example, the present flame retardant ground rubber composite. A flame retardant PU binder can be produced based on the scheme shown in FIG. IB, by mixing APP and a PU binder at room temperature (e.g. 20°C to 35°C). The flame retardant PU binder is mixed and molded with water and recycled ground rubber at 5 MPa, 120°C for 10 mins to form the flame retardant ground rubber composite.

[0017] FIG. 2A shows the formulations and properties of present ground rubber/PU composites compared to comparative ground rubber/PU composites having silane- modified ammonium polyphosphate. The weight of compositions are normalized based on 100 g rubber.

[0018] FIG. 2B shows the results of a present flame retardant ground rubber composite and a control subjected to a fire test conducted according to British Standard BS 476.

Detailed Description

[0019] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practised.

[0020] Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments. Features that are described in the context of an embodiment may correspondingly be applicable to the other embodiments, even if not explicitly described in these other embodiments. Furthermore, additions and/or combinations and/or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0021] The present disclosure relates to a flame retardant polymer composite. The flame retardant polymer composite may be a flame retardant elastomeric composite, as it may comprise an elastomer. The elastomer herein refers to a polymer with rubber- like elasticity as defined according to the IUPAC (International Union of Pure and Applied Chemistry). Examples of which include, but are not limited to, natural rubbers, styrene-butadiene block copolymers, polyisoprene, polybutadiene, ethylene propylene rubber, ethylene propylene diene rubber, silicone, fluoroelastomers, polyurethane, and nitrile rubbers.

[0022] The elastomer may be comprised of ground elastomers. This means that the elastomer may already be grinded into particles, for example, from recycling of an elastomer, to form into particles. A non-limting example of ground elastomers may be ground rubber. Said differently, the elastomer may be a recycled elastomer. An elastomer existing in the form of particles or flakes is herein referred to as elastomer particles.

[0023] The elastomer particles may be bound together by a flame retardant thermoset binder. A thermoset herein refers to a polymer that hardens when cured from its liquid form. The curing may be triggered or induced by moisture, oxygen, heat or electromagnetic radiation (e.g. ultraviolet), that is, to generate chemical reactions that lead to crosslinking between polymer chains, forming a polymer network therein. A cured thermoset is not remoldable and may degrade if heated again. A thermoset is distinguished from a thermoplastic in that thermoplastics may be softened or melted upon heating so that it is able to flow and therefore become moldable again. Once the desired shape is obtained, the thermoplastic can be cooled to solidify. The melting and solidification process is repeatable for thermoplastics by controlling the temperature. This is made possible as there is no crosslinking between the polymer chains. In other words, a thermoset solidifies by forming permanent crosslinks between the polymer chains from the curing process while thermoplastics solidify simply by cooling that reduces the mobility of polymer chains without any crosslinking reactions. This difference between a thermoset and a thermoplastic means that thermoset may be more thermally stable as it may withstand higher temperatures without loss of structural integrity, and have higher strength, rendering thermosets more advantageous for use as permanent components in building materials. Non-limiting examples of thermoset may include thermoset polyurethane, polyurea, polyepoxides, polycyanurates, melamine resin.

[0024] The thermo set used herein as the thermo set binder may have more than one isocyanate (-NCO) groups, and thus named herein as a polyisocyanate binder, wherein the prefix“poly” with respect to the term“polyisocyanate” refers to a compound having a plurality of isocyanate groups. Each of the isocyanate groups may react with a hydrogen present on the surface of an elastomeric particle, binding the elastomer particles together. The isocyanate groups may also formed a three-dimensional network when the thermoset is cured in presence of water.

[0025] The thermoset binder includes a flame retardant additive (i.e. flame retardant filler) that not only imparts a flame retardant property to the flame retardant polymer composite, but also improves binding between the elastomer particles and between the elastomer particles and flame retardant additive. This is because the flame retardant additive improves binding strength of the binder. The flame retardant additive contains melamine-modified ammonium polyphosphate. The melamine-modified ammonium polyphosphate contains one or more amine groups, wherein each of the amine groups may form a urea linkage with an isocyanate group of the thermoset. This translates to binding of the flame retardant additive to the elastomer particles, as the urea linkage binds the flame retardant additive to the thermoset and the isocyanate in turn binds the thermoset to the elastomer particles. The incorporation of melamine-modified ammonium polyphosphate, as the flame retardant additive, advantageously intensifies the network in the thermoset in that interfaces formed between the flame retardant additive and the thermoset are strongly bound. Moreover, bonding of the melamine- modified ammonium polyphosphate to the isocyanate groups of the thermoset does not compromise bonding between the isocyanates of the thermoset and the elastomer (e.g. rubber particles) as the thermoset may have multiple isocyanate groups sufficient for forming the various linkages.

[0026] On the other hand, in conventional flame retardant composites, flame retardant additives that do not react with the binder tend to be used. Said differently, an elastomer may be simply mixed with the flame retardant additive and binder, where no binding reactions occur to improve the binding strength of the binder. While such unreactive flame retardant additives are conventionally used to impart flame retardant property, the binding strength of the binder gets compromised.

[0027] Details of various embodiments of the present flame retardant polymer composite, its methods of producing, and advantages associated with the various embodiments are now described below.

[0028] In the present disclosure, there is provided for a flame retardant polymer composite comprising a thermoset binder incorporated with a melamine-modified ammonium polyphosphate, wherein the thermoset binder comprises more than one isocyanate groups, wherein one or more of the isocyanate groups each forms a urea linkage with the melamine-modified ammonium polyphosphate, and elastomer particles bound together by the thermoset binder.

[0029] Advantageously, the melamine-modified ammonium polyphosphate not only imparts the flame retardant property to the present composite, but also increases binding strength of the thermoset binder. The melamine-modified ammonium polyphosphate is able to retard flames by releasing inert gas such as nitrogen and ammonia into the flames and form a protective charred layer on the substrate. The substrate, if burning, gets cut off from heat and oxygen, to be doused. The substrate, if not yet caught with flames, gets prevented from catching fire. The melamine-modified ammonium polyphosphate contains one or more amine groups that may react with an isocyanate group of the thermoset used as the binder to form a urea linkage. The melamine-modified ammonium polyphosphate intensifies the network of the thermoset, thereby increasing its binding strength. This is advantageous over conventional flame retardant fillers that may decrease binding strength of the thermoset binder when mixed.

[0030] In various embodiments, the melamine-modified ammonium polyphosphate may have a polymerization degree of at least 100, at least 500, at least 1000, at least 1500, etc. A polymerization degree of at least 100 means the melamine-modified ammonium polyphosphate can have 100 or more monomeric units of ammonium phosphate forming the melamine-modified ammonium polyphosphate. A polymerization degree of at least 100 renders the melamine-modified ammonium polyphosphate less hydrophilic and less water-soluble, and hence more compatible with hydrophobic thermoset polymers and elastomers. The degree of polymerization may also render the present flame retardant polymer resistant to degradation by water and moisture, so that the flame retardant polymer does not get damage by water used to extinguish fire.

[0031] In various embodiments, the melamine-modified ammonium polyphosphate may have a melamine content of 10 mol% to 30 mol%, 20 mol% to 30 mol%, or 10 mol% to 20 mol%, with respect to phosphates present in the melamine-modified ammonium polyphosphate. If the melamine content gets higher than 30 mol%, more of the isocyanate groups in the thermoset may get bound to the melamine-modified ammonium polyphosphate, which may lead to lower binding strength between the binder and the elastomer. This is advantageous for applications that do not require the higher binding strength of the present composite.

[0032] The melamine-modified ammonium polyphosphate may be represented by a formula of: [0033] wherein m and n are integers which may add up to a sum of at least 100, at least 500, at least 1000, at least 1500, etc., and wherein m:n may have or may be present in a ratio ranging from 9: 1 to 7:3. For instance, where the degree of polymerization is 500, m may be 450 or 350 while n may be 50 or 150, respectively, such that m:n remains a ratio of 9: 1 to 7:3. If n gets higher than 3, this means the melamine content gets higher than 30 mol%, and more of the isocyanate groups in the thermoset may get bound to the melamine-modified ammonium polyphosphate, which may lead to lower binding strength between the binder and the elastomer. This is advantageous for applications that do not require the higher binding strength of the present composite.

[0034] The flame retardant additive, melamine-modified ammonium polyphosphate, is mixed with the thermoset to form the thermoset binder. As already mentioned above, the thermoset, i.e. the binder component may have more than one isocyanate groups which can be reacted with an amine group of the melamine-modified ammonium polyphosphate. The isocyanate group can also react with a hydrogen on the elastomer particle’s surface and cured to form a three-dimensional network in the presence of water. In other words, the thermoset binds to both the flame retardant additive and elastomer particles.

[0035] The binder may be thermoset polymer containing at least two free isocyanate groups on each end of a polymer chain, wherein the polymer may have a molecular weight ranging from 1000 to 10,000 g/mol. The thermoset polymer may initially be in a liquid form having a viscosity of 100 to 1000 mPa-s. The thermoset polymer used herein gains binding strength and flame retardant property when mixed with the melamine-modified ammonium polyphosphate.

[0036] In various embodiments, the thermoset binder may comprise or may consist of thermoset polyurethane, which is interchangeably termed herein as polyurethane. In various embodiments, the thermoset binder or the polyurethane may comprise diphenylmethane diisocyanate-based polyurethane or toluene diisocyanate-based polyurethane. That is to say, the polyurethane is formed based on diphenylmethane diisocyanate or toluene diisocyanate. As already mentioned above, the present thermoset binder may be termed a polyisocyanate binder as it contains multiple isocyanate groups. While a polyisocyanate may be made by reacting an OH-containing (e.g. polyester or polyether) polyol with diisocyanate molecules, forming a urethane linkage adjacent to each of the isocyanate groups, such urethane linkages may not be necessary for the present polyisocyanate binder to be used herein. In other words, it is the presence of multiple isocyanate groups in the thermoset that aids in increase of the binding strength of the thermoset binder.

[0037] The thermoset binder, comprising the thermoset and melamine-modified ammonium polyphosphate, may be mixed with the elastomer. The thermoset binder may comprise 5 to 30, 10 to 30, 15 to 30, 20 to 30, or 25 to 30, parts by weight of the flame retardant polymer composite, and the elastomer particles may comprise 100 parts by weight of the flame retardant polymer composite. As the elastomer forms bulk of the flame retardant polymer composite of the present disclosure, the present flame retardant polymer composite may be interchangeably termed herein as a flame retardant elastomer composite.

[0038] The elastomer may be in the form of particles, i.e. elastomer particles. Non limiting examples of elastomer particles may include those of natural rubbers, styrene- butadiene block copolymers, polyisoprene, polybutadiene, ethylene propylene rubber, ethylene propylene diene rubber, silicone, fluoroelastomers, polyurethane, and nitrile rubbers.

[0039] In various embodiments, the elastomer particles may comprise ground rubber particles. The ground rubber particles may comprise two types of ground rubber particles having different shapes, e.g. one being a shredded rubber particle and the other a granular rubber particles. The granular rubber particle and shredded rubber particle may have an aspect ratio of 1 to 1.5 and more than 1.5, respectively. The term“aspect ratio” herein refers to a ratio of a longest dimension (e.g. length) and a shortest dimension (e.g. width) of the elastomer particle. In certain instances, the elastomer particles or ground rubber particles may have an average diameter or cross-sectional width of at least 1 mm. In other words, the elastomer particles may be spherical or non- spherical.

[0040] The flame retardant polymer composite of the present disclosure further comprises water. The water acts as a curing agent of the thermoset to crosslink the polyisocyanate binder. The water may be present in a range of 1 to 10 parts by weight of the flame retardant polymer composite. The water may be in the form of liquid water, water vapour, or steam.

[0041] The present disclosure also provides for a method of producing the flame retardant polymer composite as described in various embodiments of the first aspect of the present disclosure. Embodiments and advantages described for the flame retardant polymer composite of the first aspect can be analogously valid for the present method as described herein, and vice versa. As the various embodiments and advantages have already been described above, they shall not be iterated for brevity.

[0042] The present method may comprise providing a dispersion comprising a melamine-modified ammonium polyphosphate and a thermoset binder, wherein the thermoset binder comprises more than one isocyanate groups, mixing the dispersion, elastomer particles, and water, to form a mixture, wherein the elastomer particles are encapsulated with the thermoset binder in the mixture, and curing the mixture to have one or more of the isocyanate groups each forming a urea linkage with the melamine- modified ammonium polyphosphate, thereby producing the flame retardant polymer composite. The mixture may be a moist substance (e.g. a wet solid) due to presence of water, albeit at a significantly lower amount compared to the higher amounts of thermoset binder and elastomer particles.

[0043] In various embodiments, providing the dispersion may comprise mixing the melamine-modified ammonium polyphosphate and the thermoset binder. Advantageously, by contacting the melamine-modified ammonium polyphosphate with the thermoset binder first, efficient crosslinking can take place without interference of other components. Homogenity of the melamine-modified ammonium polyphosphate may also be better if the melamine-modified ammonium polyphosphate if first mixed with the thermoset binder.

[0044] As already described above, the melamine-modified ammonium polyphosphate may have a polymerization degree of at least 100. The melamine-modified ammonium polyphosphate may have a melamine content of, for example, 10 mol% to 30 mol% with respect to phosphates present in the melamine-modified ammonium polyphosphate. The melamine-modified ammonium polyphosphate may be represented by a formula of:

[0045] wherein m and n are integers which may add up to a sum of at least 100, and wherein m:n may have a ratio ranging from 9: 1 to 7:3.

[0046] As already described above, the thermoset binder may comprise or may consist of polyurethane. The thermoset binder or polyurethane may be or may comprise diphenylmethane diisocyanate-based polyurethane or toluene diisocyanate-based polyurethane.

[0047] In various embodiments, mixing the dispersion, elastomer particles, and water, may comprise mixing the thermoset binder in an amount of 5 to 30 parts by weight of the flame retardant polymer composite with the elastomer particles in amount of 100 parts by weight of the flame retardant polymer composite.

[0048] The present method involves curing the mixture, which may comprise heating the mixture in a mold at a temperature ranging from 80°C to 160°C under a pressure ranging from 1 to 10 MPa for 5 mins to 15 mins. For example, the curing may be carried out at 120°C under 5 MPa for 10 mins. This curing step renders reaction between the amine groups of the melamine and the isocyanate groups of the thermoset so as to increase binding strength of the thermoset binder. The reaction between an amine of the melamine and an isocyanate group occurs at elevated temperatures, unlike for an aliphatic amine which an isocyanate group may easily react with. In the melamine molecule, the N atom of the amine group is conjugated to the N-H six-membered ring structure such that it significantly reduces the reactivity of such amines with the isocyanate. [0049] As already described above, the elastomer particles may comprise ground rubber particles and/or have an average diameter of at least 1 mm.

[0050] The word“substantially” does not exclude“completely” e.g. a composition which is“substantially free” from Y may be completely free from Y. Where necessary, the word“substantially” may be omitted from the definition of the invention.

[0051] In the context of various embodiments, the articles“a”,“an” and“the” as used with regard to a feature or element include a reference to one or more of the features or elements.

[0052] In the context of various embodiments, the term“about” or“approximately” as applied to a numeric value encompasses the exact value and a reasonable variance.

[0053] As used herein, the term“and/or” includes any and all combinations of one or more of the associated listed items.

[0054] Unless specified otherwise, the terms "comprising" and "comprise", and grammatical variants thereof, are intended to represent "open" or "inclusive" language such that they include recited elements but also permit inclusion of additional, unrecited elements.

Examples

[0055] The present disclosure relates to a flame retardant polymer composite, and a method of producing the flame retardant polymer composite. The flame retardant polymer composite may be a flame retardant elastomeric composite. The flame retardant elastomeric composite may include a ground vulcanized rubber, a polyurethane binder, a melamine-modified ammonium polyphosphate, and water. The flame retardant elastomeric composite, which may be a cured rubber, may have high flexibility, high strength, without compromising flame retardant property, rendering the flame retardant elastomeric composite applicable for use in shock resistant mats, liners, or anti-ricochet pads in building and construction.

[0056] The use of melamine-modified ammonium polyphosphate for improving the flame retardant property of, for example, polyurethane, and also enhancing the polyurethane’s binding strength with rubber. Conventionally, ammonium polyphosphate tends to be used as a flame retardant additive in thermoplastics, but not in thermosets, such as polyurethane. That is to say, flame retardant polyurethanes were conventionally incorporated with unmodified and hydrophilic ammonium polyphosphates. The present APP, in contrast to unmodified and hydrophilic ammonium polyphosphates, improves binding strength of, e.g. polyurethane, to an elastomer, e.g. rubber, without compromising any flame retardant property.

[0057] The present flame retardant elastomeric composite and its method of making are described in further details, by way of non-limiting examples, as set forth below.

[0058] Example 1A: Present Flame Retardant Elastomeric Composite

[0059] As already mentioned above, the present disclosure provides for formulation of an elastomeric composite. The elastomeric composite may include a thermoset. The thermoset may be polyurethane. The elastomeric composite has improved flame retardant property over unmodified polyurethane and enhanced binding strength between a binder and the elastomer, for example, a modified polyurethane binder and rubber. The rubber may be rubber particles. As a non-limiting example, a elastomeric composite of the present disclosure can include (i) a polyurethane resin, which can be a diphenylmethane diisocyanate -based or a toluene diisocyanate-based polyurethane, and (ii) a flame-retardant filler, which can be melamine-modified ammonium polyphosphate (APP) whose chemical structure is shown in FIG. 1A. The melamine- modified ammonium polyphosphate can have, but is not limited to, a polymerization degree of at least 100 and a melamine content of 10-30 mol% relative to the phosphate units.

[0060] The present melamine-modified ammonium polyphosphate is a highly effective intumescent flame retardant for polymers. Containing N and P atoms, the melamine- modified ammonium polyphosphate can retard flames by releasing inert gas such as nitrogen and ammonia into the flames and form a protective charred layer on the substrate. The substrate, if burning, gets cut off from heat and oxygen, to be doused. The substrate, if not yet caught with flames, gets prevented from catching fire.

[0061] The present melamine-modified ammonium polyphosphate is advantageous over pristine ammonium polyphosphate that is hydrophilic and not compatible with polyurethane, which is hydrophobic. The hydrophobic polyurethane, usable herein as a component of the present thermoset binder, may comprise an isocyanate-terminated polyether or an isocyanate-terminated polyester. [0062] In the present disclosure, use of ammonium polyphosphate specifically modified by melamine has at least two advantages. First, it enhances compatibility with various thermosets, such as polyurethane. Second, it enhances binding strength of the thermoset with the elastomer. For instance, the melamine-modified ammonium polyphosphate incorporated into polyurethane binds stronger to rubber. This is because the amine groups of melamine-modified ammonium polyphosphate can react with the isocyanate groups of a polyurethane even without water, and incorporation of the melamine-modified ammonium polyphosphate intensifies the PU network, thereby enhancing its binding strength.

[0063] In comparison, ammonium polyphosphate modified with groups that are not reactive or do not easily react, e.g. alkyl groups, may compromise the binding strength of a PU thermoset binder.

[0064] The melamine content in the melamine-modified ammonium polyphosphate can range from 10-30 mol% with respect to the phosphate units. If the melamine content gets higher than 30 mol%, more of the isocyanate groups in, for example, a polyurethane, may get bound to the melamine-modified ammonium polyphosphate, which may lead to elastomeric composites having lower binding strength between the binder and the elastomer. This is advantageous for applications that do not require the enhanced binding strength of the present elastomeric composite.

[0065] As another non-limiting example, the present flame retardant elastomeric composite may be a ground rubber composite formulated using the flame retardant PU binder, the ground rubber composite comprising (i) a ground rubber 100 parts by weight of the ground rubber composite, wherein the ground rubber may be recycled rubber, wherein the rubber may constitute two types of rubber particles each type having different shapes, wherein the rubber may be a combination of shredded and granular rubber particles in 100 parts by weight of the ground rubber composite, (ii) a polyurethane resin present in a range of 5 to 30 parts by weight of the ground rubber composite, wherein the polyurethane resin may be a diphenylmethane diisocyanate- based or a toluene diisocyanate -based polyurethane, (iii) a melamine-modified ammonium polyphosphate present in a range of 5 to 30 parts by weight of the ground rubber composite, whererin the melamine-modified ammonium polyphosphate. May have a polymerization degree of at least 100 and a melamine content of 10-30 mol% relative to the phosphate units, and (iv) water as a catalyst for curing of PU, wherein the water may be present in a range of 1 to 10 parts by weight of the ground rubber composite.

[0066] Example IB: General Formulation of Present Flame Retardant Elastomeric Composite

[0067] A non-limiting example of the present method of producing the flame retardant elastomeric composite, which may be the ground rubber composite, is discussed herein. The method may include the steps of (i) mixing a melamine-modified ammonium polyphosphate with the polyurethane binder under mechanical stirring till a fine dispersion is obtained, (ii) mixing a ground rubber, the dispersion and water, under mechanical stirring until a homogenous mixture (i.e. a moist substance) is obtained, wherein the surfaces of the ground rubber gets uniformly covered with the polyurethane binder, (iii) curing the mixture with a hot press under a temperature ranging from 80 to 160°C (e.g. 120°C) at a pressure ranging from 1 to 10 MPa (e.g. 5 MPa) for about 10 mins.

[0068] Example 2A: Present Flame Retardant Elastomeric Composite Sample 1

[0069] 30 g melamine-modified ammonium polyphosphate (APP-0M, crystalline type II, particle size of 16 pm, polymerization degree > 1500 and melamine content of about 20 mol% relative to phosphate units, from Sanwa Flame Retardant Technology Ltd, China) was mixed with 70 g PU resin (from Miroad Rubber Industries Sdn Bhd, Malaysia) under mechanical stirring at 500 rpm for 10 mins. The APP/PU binder was obtained, wherein the APP was present at 30 wt%.

[0070] 60 g ground rubber containing 45 g shred rubber (4 mesh, from Miroad Rubber Industries Sdn Bhd, Malaysia) and 15 g granular rubber (1-3 mm, from Miroad Rubber Industries Sdn Bhd, Malaysia), 12.9 g of the APP/PU binder and 3 g water was mixed using mechanical stirring. The mixing was completed when a homogenous mixture (i.e. a moist substance) was obtained and surfaces of the ground rubber were uniformly covered with PU.

[0071] The mixture was cured with a metal mold of 100 mm x 100 mm x 3 mm using a hot press under a temperature of 120°C and pressure of 5 MPa for about 10 mins.

[0072] Example 2B: Present Flame Retardant Elastomeric Composite Sample 2 [0073] 40 g melamine-modified ammonium polyphosphate (APP-0M, crystalline type II, particle size of 16 pm, polymerization degree > 1500 and melamine content of about 20 mol% relative to phosphate units, from Sanwa Flame Retardant Technology Ltd, China) was mixed with 60 g PU resin (from Miroad Rubber Industries Sdn Bhd, Malaysia) under mechanical stirring at 500 rpm for 10 mins. The APP/PU binder was obtained, wherein the APP was present at 40 wt%.

[0074] 60 g ground rubbers containing 45 g shred rubber (4 mesh, from Miroad Rubber Industries Sdn Bhd, Malaysia) and 15 g granular rubber (1-3 mm, from Miroad Rubber Industries Sdn Bhd, Malaysia), 15 g of the APP/PU binder and 3 g water was mixed using mechanical stirring. The mixing was completed when a homogenous mixture (i.e. a moist substance) was obtained and surfaces of the ground rubber were uniformly covered with PU.

[0075] The mixture was cured with a metal mold of 100 mm x 100 mm x 3 mm using a hot press under a temperature of 120°C and pressure of 5 MPa for about 10 mins.

[0076] Example 2C: Present Flame Retardant Elastomeric Composite Sample 3

[0077] 50 g melamine-modified ammonium polyphosphate (APP-0M, crystalline type II, particle size of 16 pm, polymerization degree > 1500 and melamine content of about 20 mol% relative to phosphate units, from Sanwa Flame Retardant Technology Ltd, China) was mixed with 50 g PU resin (from Miroad Rubber Industries Sdn Bhd, Malaysia) under mechanical stirring at 500 rpm for 10 mins. The APP/PU binder was obtained, wherein the APP was present at 50 wt%.

[0078] 60 g ground rubbers containing 45 g shred rubber (4 mesh, from Miroad Rubber Industries Sdn Bhd, Malaysia) and 15 g granular rubber (1-3 mm, from Miroad Rubber Industries Sdn Bhd, Malaysia), 18 g of the APP/PU binder and 3 g water was mixed using mechanical stirring. The mixing was completed when a homogenous mixture (i.e. a moist substance) was obtained and surfaces of the ground rubber were uniformly covered with PU.

[0079] The mixture was cured with a metal mold of 100 mm x 100 mm x 3 mm using a hot press under a temperature of 120°C and pressure of 5 MPa for about 10 mins.

[0080] Example 3: Control

[0081] 60 g ground rubbers containing 45 g shred rubber (4 mesh, from Miroad Rubber Industries Sdn Bhd, Malaysia) and 15 g granular rubber (1-3 mm, from Miroad Rubber Industries Sdn Bhd, Malaysia), 9 g PU resin and 3 g water was mixed using mechanical stirring. The mixing was completed when a homogenous mixture (i.e. a moist substance) was obtained and surfaces of the ground rubber were uniformly covered with PU.

[0082] The mixture was cured with a metal mold of 100 mm x 100 mm x 3 mm using a hot press under a temperature of 120°C and pressure of 5 MPa for about 10 mins.

[0083] Comparative Example 1

[0084] 30 g silane-modified ammonium polyphosphate (APP-0S, crystalline type II, hydrophobic, particle size of 16 pm, polymerization degree > 1500, from Sanwa Flame Retardant Technology Ltd, China) was mixed with 70 g PU resin (from Miroad Rubber Industries Sdn Bhd, Malaysia) under mechanical stirring at 500 rpm for 10 mins. The silane-modified ammonium polyphosphate/PU binder was obtained, wherein the silane- modified ammonium polyphosphate was present at 30 wt%.

[0085] 60 g ground rubbers containing 45 g shred rubber (4 mesh, from Miroad Rubber Industries Sdn Bhd, Malaysia) and 15 g granular rubber (1-3 mm, from Miroad Rubber Industries Sdn Bhd, Malaysia), 12.9 g of the binder and 3 g water was mixed using mechanical stirring. The mixing was completed when a homogenous mixture (i.e. a moist substance) was obtained and surfaces of the ground rubber were uniformly covered with PU.

[0086] The mixture was cured with a metal mold of 100 mm x 100 mm x 3 mm using a hot press under a temperature of 120°C and pressure of 5 MPa for about 10 mins.

[0087] Comparative Example 2

[0088] 40 g silane-modified ammonium polyphosphate (APP-0S, crystalline type II, hydrophobic, particle size of 16 pm, polymerization degree > 1500, from Sanwa Flame Retardant Technology Ltd, China) was mixed with 60 g PU resin (from Miroad Rubber Industries Sdn Bhd, Malaysia) under mechanical stirring at 500 rpm for 10 mins. The silane-modified ammonium polyphosphate/PU binder was obtained, wherein the silane- modified ammonium polyphosphate was present at 40 wt%.

[0089] 60 g ground rubbers containing 45 g shred rubber (4 mesh, from Miroad Rubber Industries Sdn Bhd, Malaysia) and 15 g granular rubber (1-3 mm, from Miroad Rubber Industries Sdn Bhd, Malaysia), 15 g of the binder and 3 g water was mixed using mechanical stirring. The mixing was completed when a homogenous mixture (i.e. a moist substance) was obtained and surfaces of the ground rubber were uniformly covered with PU.

[0090] The mixture was cured with a metal mold of 100 mm x 100 mm x 3 mm using a hot press under a temperature of 120°C and pressure of 5 MPa for about 10 mins.

[0091] Comparative Example 3

[0092] 50 g silane-modified ammonium polyphosphate (APP-0S, crystalline type II, hydrophobic, particle size of 16 pm, polymerization degree > 1500, from Sanwa Flame Retardant Technology Ltd, China) was mixed with 50 g PU resin (from Miroad Rubber Industries Sdn Bhd, Malaysia) under mechanical stirring at 500 rpm for 10 mins. The silane-modified ammonium polyphosphate/PU binder was obtained, wherein the silane- modified ammonium polyphosphate was present at 50 wt%.

[0093] 60 g ground rubbers containing 45 g shred rubber (4 mesh, from Miroad Rubber Industries Sdn Bhd, Malaysia) and 15 g granular rubber (1-3 mm, from Miroad Rubber Industries Sdn Bhd, Malaysia), 18 g of the binder and 3 g water was mixed using mechanical stirring. The mixing was completed when a homogenous mixture (i.e. a moist substance) was obtained and surfaces of the ground rubber were uniformly covered with PU.

[0094] The mixture was cured with a metal mold of 100 mm x 100 mm x 3 mm using a hot press under a temperature of 120°C and pressure of 5 MPa for about 10 mins.

[0095] Example 4: Characterization and Results

[0096] The tensile strength and ultimate elongation of the present flame retardant composite samples were measured following the standard of ASTM D412 using Instron 5569 Table Tester.

[0097] The flame retardant property was evaluated with specimens having a size of 3 mm x 10 mm x 50 mm. The specimen was mounted along its long axis vertical. A blue flame was applied to the lower edge of the specimen for 5 seconds and removed. If the specimen did not ignite, 5 seconds was added into the burning time for a fresh specimen of the same sample in the following test. The process was repeated until the specimen started and continued to bum after the removal of the flame. The ignition time that is a characteristic indicator for the flammability of the present flame retardant composite was recorded. [0098] A rigorous fire test following British Standard BS 476: Part 7 titled with“Fire Tests on Building Materials and Structures - Method of Test to Determine The Classification of The Surface Spread of Flame of Products” was conducted.

[0099] Samples made using 50 g melamine-modified ammonium polyphosphate (see sample 3 in example 2C) and a control were tested in TLTV SLID PSB.

[00100] The formulations and properties of the present flame retardant composites are summarized in FIG. 2A. With the incorporation of melamine-modified ammonium polyphosphate, the tensile strength and flame retardant property of a flame retardant composite made and described according to the present disclosure were both enhanced.

[00101] In comparison, for samples incorporated with ammonium polyphosphate modified by silane, the flame retardant composites exhibited an enhanced flame retardant property but their tensile strength decreased.

[00102] The BS 476: Part 7 test results are exhibited in FIG. 2B. While the control (unmodified flame retardant composite) is within Class 4 according to BS 476, the composite filled with melamine-modified ammonium polyphosphate is a Class 3 material, enabling its wide applications in building and construction, for example, for use as shock-resistant finishes to wall, column, beam and ceiling, and anti-ricochet pads in sprinkler-protected buildings. The Class 3 flame retardant composites can be used as finish materials in sprinkler-protected institutional buildings according to the Singapore Civil Defence Force (SCDF) Fire Code.

[00103] Example 5: Commercial and Potential Applications

[00104] In summary, the present disclosure includes a method of improving flame retardant property of polyurethane and concurrently enhancing binding strength thereof. The present disclosure also includes a formulation for ground rubber elastomeric composite with high mechanical strength and good flame retardant property.

[00105] The present flame retardant polymer composite and its method of making are industrially scalable and cost effective. Applications in which the present flame retardant polymer composite can be used include, but are not limited to, anti-ricochet ballistic protection panels, sound barriers, and shock-absorbing mat.

[00106] While the invention has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.

Claims

1. A flame retardant polymer composite comprising:

elastomer particles bound together by the thermoset binder.

2. The flame retardant polymer composite of claim 1, wherein the melamine- modified ammonium polyphosphate has a polymerization degree of at least 100.

3. The flame retardant polymer composite of claim 1 or 2, wherein the melamine- modified ammonium polyphosphate has a melamine content of 10 mol% to 30 mol% with respect to phosphates present in the melamine-modified ammonium polyphosphate.

4. The flame retardant polymer composite of any one of claims 1 to 3, wherein the melamine-modified ammonium polyphosphate is represented by a formula of:

wherein m and n are integers which add up to a sum of at least 100; and wherein m:n has a ratio ranging from 9:1 to 7:3.

5. The flame retardant polymer composite of any one of claims 1 to 4, wherein the thermoset binder comprises polyurethane.

6. The flame retardant polymer composite of any one of claims 1 to 5, wherein the thermoset binder comprises diphenylmethane diisocyanate-based polyurethane or toluene diisocyanate -based polyurethane.

7. The flame retardant polymer composite of any one of claims 1 to 6, wherein the elastomer particles comprise ground rubber particles.

8. The flame retardant polymer composite of any one of claims 1 to 7, wherein the elastomer particles have an average diameter of at least 1 mm.

9. The flame retardant polymer composite of any one of claims 1 to 8, wherein: the thermoset binder comprises 5 to 30 parts by weight of the flame retardant polymer composite; and

the elastomer particles comprise 100 parts by weight of the flame retardant polymer composite.

10. The flame retardant polymer composite of any one of claims 1 to 9, further comprising water.

11. A method of producing the flame retardant polymer composite of any one of claims 1 to 10, the method comprising:

providing a dispersion comprising a melamine-modified ammonium polyphosphate and a thermoset binder, wherein the thermoset binder comprises more than one isocyanate groups;

mixing the dispersion, elastomer particles, and water, to form a mixture, wherein the elastomer particles are encapsulated with the thermoset binder in the mixture; and

curing the mixture to have one or more of the isocyanate groups each forming a urea linkage with the melamine-modified ammonium polyphosphate, thereby producing the flame retardant polymer composite.

12. The method of claim 11 , wherein providing the dispersion comprises mixing the melamine-modified ammonium polyphosphate and the thermoset binder.

13. The method of claim 11 or 12, wherein the melamine-modified ammonium polyphosphate has a polymerization degree of at least 100.

14. The method of any one of claims 11 to 13, wherein the melamine-modified ammonium polyphosphate has a melamine content of 10 mol% to 30 mol% with respect to phosphates present in the melamine-modified ammonium polyphosphate.

15. The method of any one of claims 11 to 14, wherein the melamine-modified ammonium polyphosphate is represented by a formula of:

wherein m and n are integers which add up to a sum of at least 100; and wherein m:n has a ratio ranging from 9: 1 to 7:3.

16. The method of any one of claims 11 to 15, wherein the thermo set binder comprises polyurethane.

17. The method of any one of claims 11 to 16, wherein the thermo set binder comprises diphenylmethane diisocyanate-based polyurethane or toluene diisocyanate- based polyurethane.

18. The method of any one of claims 11 to 17, wherein mixing the dispersion, elastomer particles, and water, comprises mixing the thermoset binder in an amount of 5 to 30 parts by weight of the flame retardant polymer composite with the elastomer particles in amount of 100 parts by weight of the flame retardant polymer composite.

19. The method of any one of claims 11 to 18, wherein curing the mixture comprises heating the mixture in a mold at a temperature ranging from 80°C to 160°C under a pressure ranging from 1 to 10 MPa for 5 mins to 15 mins.

20. The method of any one of claims 11 to 19, wherein the elastomer particles comprise ground rubber particles and/or have an average diameter of at least 1 mm.