Cellular natural rubber articles

Abstract

1. A method for forming a natural rubber-chemical blowing agent composite, the method comprising: (a) providing a natural rubber cement; (b) introducing a blowing agent into the natural rubber cement to form a solvent-based mixture comprising natural rubber and the blowing agent; and (c) desolventizing the solvent-based mixture to form the natural rubber-chemical blowing agent composite.

Description

[Technical field]

[0001] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to cellular natural rubber articles characterized by advantageous physical properties and methods for making the cellular articles by using solution mixing techniques. Certain embodiments use guayule cis-1,4-polyisoprene. [Background technology]

[0002] Foam products have been prepared by using rubber polymers, whereupon the polymer composition is foamed. This can be accomplished by using chemical or physical foaming agents to create voids or cells within the composition. The foamed composition is cured by cross-linking the rubber polymer, thereby fixing the foam cells in place. Summary of the Invention

[0003] One or more embodiments of the present invention provide a method for forming a natural rubber-chemical blowing agent composite that includes: (a) providing a natural rubber cement; (b) introducing a blowing agent to the natural rubber cement to form a solvent-based mixture including natural rubber and the blowing agent; and (c) desolventizing the solvent-based mixture to form the natural rubber-chemical blowing agent composite.

[0004] Yet another embodiment of the present invention provides a method for forming a foam rubber article comprising: (i) providing a natural rubber-chemical blowing agent composite prepared by a process comprising: (ia) providing a natural rubber cement; (ib) introducing a blowing agent into the natural rubber cement to form a solvent-based mixture comprising natural rubber and the blowing agent; and (ic) desolventizing the solvent-based mixture to form a natural rubber-chemical blowing agent composite; (ii) introducing a curative into the composite to form a foamable vulcanizable composition; (iii) forming a profile from the foamable vulcanizable composition; and (iv) heating the profile to a temperature sufficient to decompose the chemical blowing agent and vulcanize the rubber. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0005] An embodiment of the present invention is based, at least in part, on the discovery of a cellular natural rubber article prepared by a method that includes blending a chemical blowing agent with a natural rubber cement. The cement, which includes a solvent-based mixture of a natural rubber polymer and a chemical blowing agent, is then desolventized to form a natural rubber-chemical blowing agent composite. A rubber curative can then be introduced into the composite to form a vulcanizable composition that can be cured to form a cellular natural rubber article. It has been unexpectedly discovered that by introducing the chemical blowing agent into the natural rubber cement, the chemical blowing agent is more uniformly dispersed in the natural rubber. This dispersion then provides several benefits, including smaller, more uniformly dispersed air bubbles, improving mechanical properties.

[0006] Accordingly, an embodiment of the present invention provides a method that includes (i) providing a natural rubber cement, (ii) introducing a chemical blowing agent to the cement to form a solvent-based mixture, and (iii) desolventizing the mixture to form a natural rubber-chemical blowing agent composite.

[0007] Supply of rubber cement As noted above, a natural rubber cement is provided. The cement includes a polymer obtained from a natural rubber source, the polymer dissolved or otherwise mixed in an organic solvent. The polymer is included in the solid portion of the cement. The solid portion may include dissolved solids and suspended or dispersed solids. As discussed in more detail below, the solid portion of the cement may also include other components that may be added to the cement, such as chemical blowing agents.

[0008] Natural rubber Several sources of natural rubber are known and can be used in carrying out the present invention. For example, natural rubber, in the form of cis-1,4-polyisoprene, is found in the latex of various trees, shrubs and plants, such as Hevea brasiliensis (i.e., the Amazon rubber tree), Castilla elastica (i.e., the Panama rubber tree), various Landophia vines (L. kirkii, L. heudelotis and L. owariensis), various dandelions (i.e., plants of the Taraxacum species), and Parthenium argentatum (guayule shrub). It has been discovered that natural rubber from guayule, which can be referred to as guayule rubber, can form cellular articles that are particularly advantageous when carrying out the present invention, and therefore the description of the present invention can be made with reference to guayule rubber. Based on this description, one skilled in the art can extend the teachings of the present invention to other types of natural rubber. As those skilled in the art will appreciate, the polymer obtained from guayule (Parthenium argentatu) is cis-1,4-polyisoprene, which may be referred to as guayule polymer, guayule polyisoprene, or guayule rubber.

[0009] In one or more embodiments, the guayule polymer (i.e., cis-1,4-polyisoprene) has a number average molecular weight (M) greater than 150 kg / mol, in other embodiments greater than 200 kg / mol, and in other embodiments greater than 225 kg / mol. n In one or more embodiments, the guayule polymer may be characterized by a number average molecular weight (M) of from about 150 to about 500 kg / mol, in other embodiments from about 200 to about 450 kg / mol, and in other embodiments from about 225 to about 400 kg / mol. n In these or other embodiments, the guayule polymer may have a weight average molecular weight (M) greater than 800 kg / mol, in other embodiments greater than 900 kg / mol, and in other embodiments greater than 950 kg / mol. wIn one or more embodiments, the guayule polymer may have a weight average molecular weight (M) of from about 800 to about 3000 kg / mol, from about 900 to about 2000 kg / mol in other embodiments, and from about 950 to about 1500 kg / mol in other embodiments. w In one or more embodiments, the guayule polymer may have a molecular weight distribution (M) of less than 7, in other embodiments less than 6, in yet other embodiments less than 5.5, and in still yet other embodiments less than 5. w / M n In one or more embodiments, the guayule polymer may have a molecular weight distribution of from about 3 to about 7, in other embodiments from about 4 to about 6, and in other embodiments from about 4.5 to about 5. The polymer molecular weight (M w and M n ) can be determined by gel permeation chromatography (GPC) using THF as the solvent and polystyrene standards.

[0010] solvent In one or more embodiments, the guayule cement is 5 ~C 10 Straight chain hydrocarbons, C 5 ~C 10 Branched chain hydrocarbons, C 5 ~C 10 Cyclic hydrocarbons, C 6 ~C 10 The solvents include generally non-polar hydrocarbon solvents that may be selected from aromatic hydrocarbons, and mixtures thereof. In various embodiments, combinations of solvents, including those that provide azeotropes, may be used.

[0011] Specific examples of hydrocarbon solvents include pentane isomers, such as n-pentane, isopentane, neopentane, and mixtures thereof, and hexane isomers, such as n-hexane, isohexane, 3-methylpentane, 2,3-dimethylbutane, neohexane, cyclohexane, and mixtures thereof. Other useful examples include C 6 ~C 10Aromatic hydrocarbons include, for example, benzene, toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, mesitylene, 2-ethyltoluene, 3-ethyltoluene, 4-ethyltoluene, and mixtures thereof.

[0012] In one or more embodiments, the guayule cement comprises a mixture of a non-polar hydrocarbon solvent and a polar organic solvent. Useful polar organic solvents include acetone, C 1 ~C 4 Alcohol, C. 2 ~C 4 diols, and mixtures thereof. In a particular embodiment, the solvent is a mixture of acetone and hexane. In another particular embodiment, the solvent is a mixture of acetone and isohexane. In yet another particular embodiment, the solvent is a mixture of isohexane, cyclohexane, and acetone.

[0013] In one or more embodiments where the solvent is a mixture of polar and non-polar solvents, the mixture may comprise less than 50% by weight, in other embodiments less than 40% by weight, in other embodiments less than 30% by weight, and in other embodiments less than 20% by weight of polar solvent, with the remainder comprising non-polar solvent. In one or more embodiments, the mixture may comprise from about 1% to about 50% by weight, in other embodiments from about 10% to about 45% by weight, and in other embodiments from about 20% to about 40% by weight of polar solvent, with the remainder comprising non-polar solvent.

[0014] Cement Properties In one or more embodiments, the solid portion of the guayule cement comprises greater than 85 wt.%, in other embodiments greater than 90 wt.%, and in other embodiments greater than 95 wt.%, cis-1,4-polyisoprene, based on the total weight of the solid portion of the cement. In one or more embodiments, the solid portion of the cement comprises from about 85 to about 99 wt.%, in other embodiments from about 90 to about 98 wt.%, and in other embodiments from about 95 to about 97 wt.%, cis-1,4-polyisoprene, based on the total weight of the solid portion of the cement.

[0015] In one or more embodiments, the guayule cement has a solids concentration of less than 12 wt%, in other embodiments less than 10 wt%, in other embodiments less than 9 wt%, and in other embodiments less than 8 wt%, based on the total weight of the cement. In these or other embodiments, the guayule cement has a solids concentration of greater than 4 wt%, in other embodiments greater than 5 wt%, and in other embodiments greater than 6 wt%, based on the total weight of the cement. In one or more embodiments, the guayule cement has a solids concentration of about 4 to about 12 wt%, in other embodiments about 4 to about 10 wt%, in other embodiments about 5 to about 9 wt%, and in other embodiments about 6 to about 8 wt%, based on the total weight of the cement.

[0016] In one or more embodiments, the solid portion of the guayule cement may include other constituent materials found in the guayule and materials optionally added to the cement prior to the addition of the particulate filler.

[0017] In one or more embodiments, an additional component in the solid portion of the cement derived from guayule includes guayule resin. As those skilled in the art will appreciate, guayule resin generally refers to non-polyisoprene low molecular weight compounds that generally have a molecular weight of less than about 3000 g / mol. Examples of compounds in the resin include, but are not limited to, monoterpenes, triterpenes (argentatins A, B and C), sesquiterpene compounds (guayulins A and B) and fatty acids (as free fatty acids, monoglycerides, diglycerides, triglycerides, or combinations thereof). Additionally, the solid portion of the cement may include low molecular weight polyisoprene polymers and oligomers.

[0018] In one or more embodiments, the solids of the guayule cement may be characterized by a relatively low content of guayule resin. For example, the solids of the guayule cement may comprise less than 7% by weight, in other embodiments less than 6% by weight, and in other embodiments less than 5% by weight of guayule resin or low molecular weight polyisoprene, based on the total weight of the solids of the cement. In one or more embodiments, the solids of the cement comprise from about 0.5 to about 7% by weight, in other embodiments from about 1 to about 6% by weight, and in other embodiments from about 2 to about 4% by weight of guayule resin or low molecular weight polyisoprene, based on the total weight of the solids of the cement. In one or more embodiments, the weight ratio of guayule resin to low molecular weight polyisoprene may be from about 0.5:1 to about 1.5:1, in other embodiments from about 0.7:1 to about 1.3:1, and in other embodiments from about 0.9:1 to about 1.1:1.

[0019] In one or more embodiments, the solid portion of the guayule cement may include solids added to the cement prior to the addition of the particulate filler. In one or more embodiments, the solid portion of the cement may include an anti-degradant, such as an antioxidant and an antiozonant. Examples of useful anti-degradants include N,N' disubstituted p-phenylenediamines, such as N-1,3-dimethylbutyl-N'phenyl-p-phenylenediamine (6PPD), N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (77PD), N-phenyl-N-isopropyl-p-phenylenediamine (IPPD) and N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (HPPD). Other examples of antidegradants include acetone diphenylamine condensation products (Alchem ​​BL), 2,4-trimethyl-1,2-dihydroquinoline (Alchem ​​TMQ), octylated diphenylamine (Alchem ​​ODPA), and 2,6-di-t-butyl-4-methylphenol (BHT).

[0020] When present, the solid portion of the cement may comprise less than 1 wt. %, in other embodiments less than 0.5 wt. %, and in other embodiments less than 0.3 wt. %, of the antidegradant, based on the total weight of the solid portion. In one or more embodiments, the solid portion comprises from about 0.05 to about 1 wt. %, in other embodiments from about 0.07 to about 0.5 wt. %, and in other embodiments from about 0.1 to about 0.3 wt. %, of the antidegradant, based on the total weight of the solid portion.

[0021] Obtaining Guayule Polymer According to an embodiment of the invention, the method of the invention includes obtaining a guayule polymer from a guayule plant. In one or more embodiments, the process may include providing a guayule plant material, mechanically breaking down the plant material, extracting organic material from the broken down plant material to form a miscella, and fractionating the miscella to provide a cement or a swollen polymer mass. The swollen polymer mass or cement can then be diluted to provide a cement having a desired solids content.

[0022] In one or more embodiments, the step of disrupting the guayule plants may include mechanically bursting the stems, for example, by chopping, grinding, and / or macerating the dried guayule stems. In one or more embodiments, the stems may contain less than about 15% by weight, or in other embodiments less than 10% by weight of leaves. In these or other embodiments, the dried guayule stems include those containing less than 25% by weight, or in other embodiments about 5 to about 20% by weight of moisture.

[0023] In one or more embodiments, the step of extracting organic material from the crushed plant material includes combining the crushed plant material with a solvent adapted to dissolve the organic matter of the crushed plant. In one or more embodiments, the solvent includes a mixture of a hydrocarbon solvent (non-polar) and a polar organic solvent (e.g., 30% acetone and 70% hexane by weight). One of skill in the art can readily select an appropriate amount of the solvent mixture to combine with the crushed plant material. For example, it may be common to add sufficient solvent to provide a weight ratio of solvent to bagasse of about 2:1 to about 4:1. The organic material dissolved in the solvent mixture is called miscella, which is then separated from the residual woody tissue, bagasse. Separation of the miscella and bagasse can be accomplished by using one or more known techniques, including multi-stage extraction techniques and / or countercurrent extraction techniques.

[0024] Once the miscella has been substantially separated from the bagasse, it is subjected to a fractionation process to, among other things, separate those materials that are soluble in polar solvents (e.g., resins) from those components that are soluble in non-polar solvents (e.g., cis-1,4-polyisoprene). In one or more embodiments, the fractionation process involves the use of multi-stage countercurrent fractionation with simultaneous addition of a polar solvent (e.g., acetone) countercurrent to the miscella flow. Countercurrent fractionation and the production of swollen rubber chunks are described, for example, in W.W. Schloman Jr., et al., "Processing Guayule for Latex and Bulk Rubber," Industrial Crops and Products, 22, 41-47 (2005).

[0025] In one or more embodiments, the miscella can be diluted with additional acetone to precipitate the cis-1,4-polyisoprene in the form of a swollen rubber mass. The swollen rubber mass can then be diluted with additional hydrocarbon solvent or a mixture of at least one hydrocarbon solvent and at least one polar organic solvent to produce a cement having a desired solids content.

[0026] Introducing chemical foaming agents into cement As described above, once the desired guayule cement is fed into the process, a chemical blowing agent is introduced into the cement to form a solvent-based mixture of natural rubber and chemical blowing agent. In certain embodiments, additional materials are introduced into the cement prior to desolventization. The cement can be mixed by using conventional techniques for mixing the solution during and after the introduction of the chemical blowing agent. In certain embodiments, the reinforcing filler and optionally additional components of the vulcanizable composition are introduced into the cement along with the chemical blowing agent, thereby forming a solution masterbatch.

[0027] As those skilled in the art will appreciate, a chemical blowing agent is a compound that undergoes decomposition upon an external stimulant to form a gaseous compound. For example, useful chemical blowing agents include compounds that decompose upon heating to release one or more gases, such as, but not limited to, carbon dioxide, carbon monoxide, nitrogen gas, and ammonia.

[0028] Exemplary chemical blowing agents include azodicarbonamide (ADCA), azodiisobutyronitrile, benzenesulfonhydrazide, 4,4-oxybenzenesulfonyl-semicarbazide, p-toluenesulfonylsemicarbazide, barium azodicarboxylate, N,N'-dimethyl-N,N'-dinitrosoterephthalamide, and trihydrazinotriazine.

[0029] As one of ordinary skill in the art will appreciate, the chemical foaming agent may be in the form of solid particles when introduced into the cement. In one or more embodiments, the chemical foaming agent particles may have a median particle size (D50) of about 0.5 to about 30 μm, in other embodiments about 0.9 to about 20 μm, and in other embodiments about 1.0 to about 10 μm. In these or other embodiments, the chemical foaming agent is in solid particle form having a median particle size of less than 25 μm, in other embodiments less than 15 μm, and in other embodiments less than 8 μm. In these or other embodiments, the chemical foaming agent is a solid characterized by a D90 particle size of less than 30 μm, in other embodiments less than 20 μm, and in other embodiments less than 10 μm.

[0030] In one or more embodiments, the chemical blowing agent may be characterized by a decomposition temperature. For purposes of this description, decomposition temperature refers to the temperature at which 25% by weight of the compound is decomposed. In one or more embodiments, the chemical blowing agent used in the practice of the invention has a decomposition temperature of about 175 to about 200°C, in other embodiments about 180 to about 198°C, and in other embodiments about 185 to about 195°C. In these or other embodiments, the chemical blowing agent is characterized by a decomposition temperature of greater than 160°C, in other embodiments greater than 170°C, and in other embodiments greater than 180°C.

[0031] Several techniques can be used to introduce the chemical foaming agent into the guayule cement. In one or more embodiments, the chemical foaming agent is introduced directly into the cement in the form of dry solid particles. For example, the cement may be contained in a conventional stirred tank reactor, and the chemical foaming agent can be added directly to the cement in the form of dry solid particles from the headspace of the reactor.

[0032] In other embodiments, the chemical blowing agent particles are premixed with the carrier before being introduced into the cement. In one or more embodiments, the chemical blowing agent particles are dispersed in a solvent to form a solution or dispersion, which may be referred to as a blowing agent-solvent mixture, and the blowing agent-solvent mixture is introduced into the cement. For example, if the cement is contained in a conventional stirred tank reactor, the blowing agent-solvent mixture may be introduced into the cement through the head space of the reactor, or in other embodiments, the mixture may be injected into the cement by an inlet located below the liquid level of the reactor or through a conduit extending into the liquid level of the reactor.

[0033] In embodiments in which a blowing agent-solvent mixture is formed, the blowing agent-solvent mixture may be characterized by a blowing agent solids content (i.e., the weight of blowing agent relative to the total weight of the mixture, the remainder including the weight of the solvent) of less than 15 wt%, in other embodiments less than 12 wt%, and in other embodiments less than 10 wt%, based on the total weight of the mixture. In these or other embodiments, the mixture may include from about 3 to about 15 wt%, in other embodiments from about 4 to about 12 wt%, and in other embodiments from about 5 to about 10 wt% blowing agent, based on the total weight of the mixture.

[0034] When a blowing agent-solvent mixture is formed, the solvent used to make the mixture may include a hydrocarbon solvent, such as those described above for guayule cement, hi other embodiments, the solvent may include a blend of a hydrocarbon solvent and a polar organic solvent (e.g., 30% by weight acetone and 70% by weight hexane).

[0035] Properties of solvent-based mixtures In one or more embodiments, the solvent-based mixture (i.e., the blowing agent and rubber cement) may be characterized by the weight of the blowing agent relative to the weight of the polymer. In one or more embodiments, the solvent-based mixture includes less than 35 parts by weight, in other embodiments less than 25 parts by weight, and in other embodiments less than 20 parts by weight of the blowing agent per 100 parts by weight of the polymer. In these or other embodiments, the solvent-based mixture includes more than 1 part by weight, in other embodiments more than 5 parts by weight, and in other embodiments more than 7 parts by weight of the blowing agent per 100 parts by weight of the polymer. In one or more embodiments, the solvent-based mixture includes from about 1 to about 35 parts by weight, in other embodiments from about 3 to about 20 parts by weight, and in other embodiments from about 5 to about 15 parts by weight of the blowing agent per 100 parts by weight of the polymer.

[0036] Filler Particles As noted above, in one or more embodiments, filler particles may be added to the cement (i.e., in addition to the foaming agent). These filler particles may include reinforcing fillers. As one skilled in the art will appreciate, the reinforcing filler particles include carbon black filler particles. According to embodiments of the invention, the carbon black is added in an amount sufficient to provide the desired weight ratio of carbon black to guayule rubber.

[0037] Carbon Black In one or more embodiments, useful carbon blacks include furnace blacks, channel blacks, and lamp blacks. More specific examples of carbon blacks include super abrasion furnace blacks, medium super abrasion furnace blacks, high abrasion furnace blacks, high speed extrusion furnace blacks, fine furnace blacks, semi-reinforced furnace blacks, medium processing channel blacks, hard processing channel blacks, conductive channel blacks, and acetylene blacks.

[0038] In one or more embodiments, the carbon black used in preparing the solution masterbatch is 100 ml 2 / g, in other embodiments 115m 2 / g, and in other embodiments, 130 m 2 In these or other embodiments, the carbon black may have a surface area of ​​from about 100 to about 200 m / g. 2 / g, and in other embodiments, from about 115 to about 175 m 2 / g, and in other embodiments, from about 130 to about 150 m 2 For purposes herein, unless otherwise specified, carbon black surface area values ​​are reported as N2 surface area as determined by ASTM D-6556-19a.

[0039] In one or more embodiments, the carbon black combined with the guayule cement is not pelletized. In one or more embodiments, the carbon black added to the guayule cement is characterized by a median particle size (i.e., D50) of less than 65 nm, in other embodiments less than 60 nm, and in other embodiments less than 55 nm. In these or other embodiments, the carbon black is characterized by a median particle size of greater than 35 nm, in other embodiments greater than 40, and in other embodiments greater than 45 nm. In one or more embodiments, the carbon black has a median particle size of about 35 to about 65 nm, in other embodiments about 40 to about 60 nm, and in other embodiments about 45 to about 55 nm.

[0040] In embodiments in which a filler is incorporated into the rubber cement, the solvent-based mixture may be characterized by the weight of the filler (e.g., carbon black) relative to the weight of the polymer. In one or more embodiments, the solvent-based mixture includes less than 75 parts by weight, in other embodiments less than 65 parts by weight, and in other embodiments less than 55 parts by weight of the filler per 100 parts by weight of the polymer. In these or other embodiments, the solvent-based mixture includes more than 10 parts by weight, in other embodiments more than 25 parts by weight, and in other embodiments more than 35 parts by weight of the filler per 100 parts by weight of the polymer. In one or more embodiments, the solvent-based mixture includes from about 10 to about 75 parts by weight, in other embodiments from about 25 to about 65 parts by weight, and in other embodiments from about 35 to about 55 parts by weight of the filler per 100 parts by weight of the polymer.

[0041] Direct desolvation According to an embodiment of the present invention, the solvent-based mixture (including the blowing agent and polymer dispersed, dissolved, or suspended in the solvent) is directly desolventized, which refers to a process in which the solvent is separated from the solid portion of the mixture (i.e., separated from the polymer and blowing agent) to form a composition that is substantially a solid composite of polymer and blowing agent (i.e., a natural rubber-chemical blowing agent composite). This can be distinguished from indirect desolventization methods such as steam desolventization, in which water is added to drive off the solvent, thereby producing a composition including water, polymer, and blowing agent.

[0042] Direct desolventization techniques, as well as equipment for carrying out these methods, are generally known in the art. For example, the temperature of the solvent-based mixture can be raised or maintained at a temperature sufficient to volatilize the solvent. Also, the pressure can be reduced within the vessel in which the desolventization takes place, which aids in the volatilization of the solvent. Additionally, the solvent-based mixture can be agitated, which can further aid in the removal of the solvent from the mixture. In one embodiment, a combination of heating, reduced pressure, and agitation can be used.

[0043] In one embodiment, the temperature of the solvent-based mixture, along with the pressure of the environment in which the mixture is devolatilized (i.e., within the desolvation vessel), is adjusted to facilitate devolatilization. For example, the desolvation step may be carried out at a temperature of greater than 35° C., in other embodiments greater than 37° C., in other embodiments greater than 40° C., in other embodiments greater than 50° C., in other embodiments greater than 75° C., in other embodiments greater than 100° C., in other embodiments greater than 110° C., and in other embodiments greater than 120° C., under a pressure of about −5 to about −30 mmHg. In one or more embodiments, the desolvation step is carried out at a temperature of about 35 to about 160° C., in other embodiments greater than 37 to about 140° C., and in other embodiments greater than 40 to about 130° C., under a pressure of about −5 to about −30 mmHg.

[0044] Various techniques can be used to agitate and / or impart shear to the solvent-based mixture during desolventization. As one of ordinary skill in the art will appreciate, agitation can expose greater surface area, thereby facilitating the release of solvent.

[0045] In one embodiment, desolvation can be achieved by using a drum dryer. In another embodiment, desolvation can be achieved by using a devolatilizer. The devolatilizer can include a devolatilizer extruder, which typically includes a screw device that can be heated by an external heating jacket. These extruders are known in the art and can include single and twin screw extruders.

[0046] Alternatively, the devolatilizer can include an extruder-like device that includes a shaft to which paddles are attached. These extruder-like devices can include a single shaft or multiple shafts. The shaft can be axial to the length of the device and the flow of the solvent-based mixture through the device / container. The composition (i.e., the solvent-based mixture) can be passed through the device by using a pump, which rotates the shaft, thereby allowing the paddles to agitate the composition, thereby aiding in the generation of the solvent. The paddles can be angled to aid in the movement of the composition through the devolatilizer, but the movement of the composition through the devolatilizer can be facilitated by a pump that can direct the composition into the devolatilizer, and can optionally be further assisted by an extruder that can be attached in line or at the end of the devolatilizer (i.e., the extruder helps pull the composition through the devolatilizer).

[0047] The devolatilizer may further include a backmixing vessel. Typically, these backmixing vessels include a single shaft containing blades that can be used to vigorously mix and thicken the composition (i.e., the solvent-based mixture).

[0048] In certain embodiments, a combination of various devolatilizers can be used to achieve the desired results. These combinations can also include the use of an extruder. In one example, a single-shaft "extruder-like" devolatilizer (e.g., one that includes a paddle) can be used with a twin-screw extruder. In this example, the solvent-based mixture first enters the "extruder-like" devolatilizer and then the twin-screw extruder. The twin-screw extruder advantageously assists in drawing the composition through the devolatilizer. The paddles of the devolatilizer can be adjusted to meet delivery needs.

[0049] In another example, a twin-screw "extruder-like" devolatilizer can be used. In some embodiments, the paddles on each shaft may be aligned to interdigitate with one another as they rotate. The rotation of the shafts can occur in the same or opposite directions.

[0050] In yet another example, the backmix volatilization vessel can be followed by a twin screw extruder, which can be followed by a twin screw extruder-like devolatilization vessel, which can be followed by a twin screw extruder.

[0051] Devolatilization equipment is known in the art and is commercially available. For example, devolatilizers can be obtained from LIST (Switzerland), Coperion Werner & Phleiderer, or NFM Welding Engineers, Inc. (Ohio). Exemplary equipment available from LIST includes the DISCOTHERM™, a single-screw "extruder-like" devolatilizer that includes various mixing / kneading bars or paddles, the CRP™, a twin-screw "extruder-like" devolatilizer, where the shafts are interrelated, and the ORP™, a twin-screw devolatilizer, where the shafts rotate in opposite directions.

[0052] As discussed above, desolventization of the solvent-based mixture results in a natural rubber-chemical blowing agent composite that can be used to form a foamable vulcanizable composition.

[0053] Foamable vulcanizable composition According to the present invention, the natural rubber-chemical blowing agent composite, which may also be referred to as a rubber-chemical blowing agent solid mixture prepared as described above, is used in the preparation of a foamable vulcanizable composition that can be foamed and cured. In addition to the natural rubber and chemical blowing agent, the vulcanizable composition may also contain other components, such as, but not limited to, synthetic elastomeric polymers, non-guayule natural rubber, reinforcing fillers, plasticizers, and curing agents. Specific examples of these components include, but are not limited to, carbon black, silica, fillers, oils, resins, waxes, metal carboxylates, curing agents and curing aids, anti-aging agents, and metal oxides.

[0054] Exemplary elastomeric polymers useful in the practice of the present invention (i.e., included within the vulcanizable composition) may be referred to as rubber polymers or vulcanizable polymers and include polydienes and polydiene copolymers. Specific examples of these polymers include, but are not limited to, polybutadiene, poly(styrene-co-butadiene), polyisoprene, poly(styrene-co-isoprene), and their functionalized derivatives. Other polymers that may be included in the polymer sample include neoprene, poly(ethylene-co-propylene), poly(styrene-co-butadiene), poly(ethylene-co-propylene-co-diene), polysulfide rubber, acrylic rubber, urethane rubber, silicone rubber, epichlorohydrin rubber, syndiotactic polybutadiene, and mixtures thereof or with polydienes and polydiene copolymers. These elastomers can have a myriad of macromolecular structures, such as linear, branched, and star structures. These elastomers may also contain one or more functional units, which typically contain heteroatoms, attached to the backbone of the polymer.

[0055] In one or more embodiments, useful carbon blacks include furnace blacks, channel blacks, and lamp blacks. More specific examples of carbon blacks include super abrasion furnace blacks, medium super abrasion furnace blacks, high abrasion furnace blacks, high speed extrusion furnace blacks, fine furnace blacks, semi-reinforced furnace blacks, medium processing channel blacks, hard processing channel blacks, conductive channel blacks, and acetylene blacks.

[0056] In one or more embodiments, examples of suitable silica fillers include precipitated amorphous silica, wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), fumed silica, calcium silicate, aluminum silicate, calcium aluminum silicate, magnesium silicate, and the like.

[0057] In one or more embodiments, the surface area of ​​the silica, as measured by the BET method, is from about 32 to about 400 m. 2 / g(32m 2 / g~400m 2 / g), and may be about 100m 2 / g~about 300m 2 / g(100m 2 / g~300m 2 / g), and about 150m 2 / g ~ approx. 220m 2 / g(150m 2 / g~220m 2 / g). In one or more embodiments, the pH of the silica may be characterized as about 5.5 to about 7, or slightly above 7, or in other embodiments, about 5.5 to about 6.8. Some commercially available silica fillers that can be used include, but are not limited to, those sold under the trade name Hi-Sil, such as 190, 210, 215, 233, and 243 by PPG Industries, as well as those available from Degussa Corporation (e.g., VN2, VN3), Rhone Poulenc (e.g., Zeosil™ 1165 MP), and JM Huber Corporation.

[0058] In one or more embodiments, a silica coupling agent is included in the vulcanizable composition. As those skilled in the art will appreciate, these compounds contain hydrolyzable silicon moieties (often called silanes) and moieties that can react with the vulcanizable polymer.

[0059] Suitable silica coupling agents include, for example, those containing groups such as alkylalkoxy, mercapto, blocked mercapto, sulfide-containing (e.g., monosulfide-based alkoxy-containing, disulfide-based alkoxy-containing, tetrasulfide-based alkoxy-containing), amino, vinyl, epoxy, and combinations thereof. In certain embodiments, the silica coupling agent may be added to the rubber composition in the form of a pretreated silica. The pretreated silica is pre-surface treated with a silane before being added to the rubber composition.

[0060] Non-limiting examples of alkylalkoxysilanes suitable for use in certain embodiments of the fourth embodiment disclosed herein include octyltriethoxysilane, octyltrimethoxysilane, trimethylethoxysilane, cyclohexyltriethoxysilane, isobutyltriethoxy-silane, ethyltrimethoxysilane, cyclohexyl-tributoxysilane, dimethyldiethoxysilane, methyltriethoxysilane, propyltriethoxysilane, hexyltriethoxysilane, heptyltriethoxysilane, nonyltriethoxysilane, decyltriethoxysilane, ethyl ... Examples of suitable silanes include, but are not limited to, silane, dodecyltriethoxysilane, tetradecyltriethoxysilane, octadecyltriethoxysilane, methyloctyldiethoxysilane, dimethyldimethoxysilane, methyltrimethoxysilane, propyltrimethoxysilane, hexyltrimethoxysilane, heptyltrimethoxysilane, nonyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, tetradecyltrimethoxysilane, octadecyl-trimethoxysilane, methyloctyldimethoxysilane, and mixtures thereof.

[0061] Non-limiting examples of bis(trialkoxysilylorgano) polysulfides suitable for use in certain exemplary embodiments of the fourth embodiment disclosed herein include bis(trialkoxysilylorgano) disulfides and bis(trialkoxysilylorgano) tetrasulfides. Specific non-limiting examples of bis(trialkoxysilylorgano) disulfides suitable for use in certain exemplary embodiments of the fourth embodiment disclosed herein include 3,3'-bis(triethoxysilylpropyl) disulfide, 3,3'-bis(trimethoxysilylpropyl) disulfide, 3,3'-bis(tributoxysilylpropyl) disulfide, 3,3'-bis(tri-t-butoxysilylpropyl) disulfide, 3,3'-bis(trihexoxysilylpropyl) disulfide, 2,2' 3,3'-bis(dimethylmethoxysilylethyl) disulfide, 3,3'-bis(diphenylcyclohexoxysilylpropyl) disulfide, 3,3'-bis(ethyl-di-sec-butoxysilylpropyl) disulfide, 3,3'-bis(propyldiethoxysilylpropyl) disulfide, 12,12'-bis(triisopropoxysilylpropyl) disulfide, 3,3'-bis(dimethoxyphenylsilyl-2-methylpropyl) disulfide, and mixtures thereof. Non-limiting examples of bis(trialkoxysilylorgano)tetrasulfide silica coupling agents suitable for use in certain embodiments of the fourth embodiment disclosed herein include, but are not limited to, bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropyl-benzothiazole tetrasulfide, 3-triethoxysilylpropyl benzothiazole tetrasulfide, and mixtures thereof.Bis(3-triethoxysilylpropyl) tetrasulfide is sold under the trade name Si 69 by Evonik Degussa Corporation.

[0062] Non-limiting examples of mercaptosilanes suitable for use in certain embodiments of the fourth embodiment disclosed herein include, but are not limited to, 1-mercaptomethyltriethoxysilane, 2-mercaptoethyltriethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldiethoxysilane, 2-mercaptoethyltripropoxysilane, 18-mercaptooctadecyldiethoxychlorosilane, and mixtures thereof.

[0063] Non-limiting examples of blocked mercaptosilanes suitable for use in certain embodiments of the fourth embodiment disclosed herein include, but are not limited to, those described in U.S. Pat. Nos. 6,127,468, 6,204,339, 6,528,673, 6,635,700, 6,649,684, and 6,683,135, the disclosures of which are incorporated herein by reference. Representative examples of blocked mercaptosilanes for use herein in certain exemplary embodiments disclosed herein include 2-triethoxysilyl-1-ethylthioacetate, 2-trimethoxysilyl-1-ethylthioacetate, 2-(methyldimethoxysilyl)-1-ethylthioacetate, 3-trimethoxysilyl-1-propylthioacetate, triethoxysilylmethyl-thioacetate, trimethoxysilylmethylthioacetate, triisopropoxysilylmethylthioacetate, methyldiethoxysilylmethylthioacetate, methyldimethoxysilylmethylthioacetate, methyldiisopropoxysilylmethylthioacetate, dimethylethoxysilylmethylthioacetate, dimethylmethoxysilylmethylthioacetate, dimethylisopropoxysilylmethylthioacetate, 2-triisopropoxy ... 2-(methyldiethoxysilyl)-1-ethylthioacetate, 2-(methyldiisopropoxysilyl)-1-ethylthioacetate, 2-(dimethylethoxysilyl-1-ethylthioacetate, 2-(dimethylmethoxysilyl)-1-ethylthioacetate, 2-(dimethylisopropoxysilyl)-1-ethylthioacetate, 3-triethoxysilyl-1-propylthioacetate, 3-triisopropoxysilyl-1-propylthio acetate, 3-methyldiethoxysilyl-1-propyl-thioacetate, 3-methyldimethoxysilyl-1-propylthioacetate, 3-methyldiisopropoxysilyl-1-propylthioacetate, 1-(2-triethoxysilyl-1-ethyl)-4-thioacetylcyclohexane, 1-(2-triethoxysilyl-1-ethyl)-3-thioacetylcyclohexane, 2-triethoxysilyl-5-thioacetylnorbornene,2-triethoxysilyl-4-thioacetylnorbornene, 2-(2-triethoxysilyl-1-ethyl)-5-thioacetylnorbornene, 2-(2-triethoxy-silyl-1-ethyl)-4-thioacetylnorbornene, 1-(1-oxo-2-thia-5-triethoxysilylphenyl)benzoic acid, 6-triethoxysilyl-1-hexylthioacetate, 1-triethoxysilyl-5-hexylthioacetate, 8-triethoxysilyl-1-octylthioacetate, 1-triethoxysilyl-7-octylthioacetate, 6-triethoxysilyl 1-Triethoxysilyl-1-hexylthioacetate, 1-triethoxysilyl-5-octylthioacetate, 8-trimethoxysilyl-1-octylthioacetate, 1-trimethoxysilyl-7-octylthioacetate, 10-triethoxysilyl-1-decylthioacetate, 1-triethoxysilyl-9-decylthioacetate, 1-triethoxysilyl-2-butylthioacetate, 1-triethoxysilyl-3-butylthioacetate, 1-triethoxysilyl-3-methyl-2-butylthioacetate, 1-triethoxysilyl-3-methyl-3- Butyl thioacetate, 3-trimethoxysilyl-1-propyl thiooctanoate, 3-triethoxysilyl-1-propyl-1-propyl thiopalmitate, 3-triethoxysilyl-1-propyl thiooctanoate, 3-triethoxysilyl-1-propyl thiobenzoate, 3-triethoxysilyl-1-propyl thio-2-ethylhexanoate, 3-methyldiacetoxysilyl-1-propyl thioacetate, 3-triacetoxysilyl-1-propyl thioacetate, 2-methyldiacetoxysilyl-1-ethyl thioacetate, 2-triacetoxysilyl-1-ethyl thioacetate, Triacetoxysilyl-1-ethylthioacetate, 1-methyldiacetoxysilyl-1-ethylthioacetate, 1-triacetoxysilyl-1-ethyl-thioacetate, tris-(3-triethoxysilyl-1-propyl)trithiophosphate, bis-(3-triethoxysilyl-1-propyl)methyldithiophosphonate, bis-(3-triethoxysilyl-1-propyl)ethyldithiophosphonate, 3-triethoxysilyl-1-propyldimethylthiophosphinate, 3-triethoxysilyl-1-propyldiethylthiophosphinate,Tris-(3-triethoxysilyl-1-propyl)tetrathiophosphate, bis-(3-triethoxysilyl-1-propyl)methyl trithiophosphonate, bis-(3-triethoxysilyl-1-propyl)ethyl trithiophosphonate, 3-triethoxysilyl-1-propyl dimethyl dithiophosphinate, 3-triethoxysilyl-1-propyl diethyl dithiophosphinate, tris-(3-methyldimethoxysilyl-1-propyl)trithiophosphate, bis-(3-methyldimethoxysilyl-1-propyl)-methyl dithiophosphonate, bis-(3-methyldimethoxysilyl-1-propyl)-ethyl dithiophosphonate, 3-methyldimethoxysilyl-1-propyl dimethyl thiophosphinate, 3-methyldimethoxysilyl-1-propyl diethyl thiophosphinate, 3-triethoxysilyl-1-propyl methyl thiosulfate, 3-triethoxysilyl-1-propyl methane thiosulfonate, 3-triethoxysilyl-1-propyl ethane thiosulfonate, 3-triethoxysilyl-1-propyl benzene thiosulfonate, 3-triethoxysilyl-1-propyl toluene thiosulfonate, 3-triethoxysilyl-1-propyl naphthalene thiosulfonate, 3-triethoxysilyl-1-propyl xylylene thiosulfonate, triethoxysilylmethyl methyl thiosulfate, triethoxysilylmethyl methane thiosulfonate, triethoxysilylmethyl ethane thiosulfonate, triethoxysilylmethyl benzene thiosulfonate, triethoxysilylmethyl toluene thiosulfonate, triethoxysilylmethyl naphthalene thiosulfonate, triethoxysilylmethyl xylylene thiosulfonate, etc. Mixtures of various blocked mercaptosilanes can be used. Further examples of blocked mercaptosilanes suitable for use in certain exemplary embodiments are those sold under the trade name NXT Silane (3-octanoylthio-1-propyltriethoxysilane) by Momentive Performance Materials Inc.

[0064] In one or more embodiments, the plasticizer includes oils and solid resins. Useful oils or spreading agents that may be used include, but are not limited to, aromatic oils, paraffinic oils, naphthenic oils, vegetable oils (other than castor oil), low PCA oils (such as MES, TDAE, and SRAE), and heavy naphthenic oils. Suitable low PCA oils also include oils of various plant origins, such as those obtained from vegetables, nuts, and seeds. Non-limiting examples include, but are not limited to, soybean oil, sunflower oil, safflower oil, corn oil, linseed oil, cottonseed oil, rapeseed oil, cashew oil, sesame oil, camellia oil, jojoba oil, macadamia nut oil, coconut oil, and palm oil. As is commonly understood in the art, oil refers to a compound that has a relatively low viscosity compared to other components of the vulcanizable composition, such as resins. In one or more embodiments, the resin may be a solid having a Tg greater than about 20° C. and may include, but is not limited to, hydrocarbon resins such as cycloaliphatic resins, aliphatic resins, aromatic resins, terpene resins, and combinations thereof. Useful resins include styrene-alkylene block copolymers, thermoplastic resins, such as C 5 Resin, C 5 ~C 9 Resin, C 9 Examples of resins that can be used include, but are not limited to, terpene-based resins, terpene aromatic compound-based resins, rosin-based resins, dicyclopentadiene resins, alkylphenol-based resins, and partially hydrogenated resins thereof.

[0065] In one or more embodiments, the vulcanizable composition of the present invention includes a cure system. The cure system includes a curing agent, which may also be referred to as a crosslinking agent, a rubber curing agent, or a vulcanizing agent. The curing agent is a compound such as those described in Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 20, pgs. 365-468, (3 rdEd.1982), especially Vulcanization Agents and Auxiliary Materials, pgs.390-402, and AYCoran, Vulcanization, Encyclopedia of Polymer Science and Engineering, (2 nd Ed. 1989), which are incorporated herein by reference. In one or more embodiments, useful curing systems include sulfur or sulfur-based crosslinkers, organic peroxide-based crosslinkers, inorganic crosslinkers, polyamine crosslinkers, resin crosslinkers, oxime-based and nitrosamine-based crosslinkers, and the like. Examples of suitable sulfur crosslinkers include "rubber manufacturer's" soluble sulfur, sulfur donating vulcanizing agents such as amine disulfides, polymeric polysulfides, or sulfur olefin adducts, and insoluble polymeric sulfur. In other embodiments, the crosslinker includes sulfur and / or sulfur-containing compounds. In other embodiments, the crosslinker excludes sulfur and / or sulfur-containing compounds. The vulcanizing agents may be used alone or in combination.

[0066] Other ingredients typically used in rubber compounding may also be added to the rubber composition, including accelerators, accelerator activators, additive plasticizers, waxes, anti-char agents, processing aids, zinc oxide, tackifying resins, toughening or curing resins, fatty acids (e.g., stearic acid), deflocculants, and antidegradants (e.g., antioxidants and antiozonants).

[0067] Ingredient amount The vulcanizable composition can be characterized by the total polymer content (i.e., the polymer introduced via the polymer-blowing agent aggregate and the polymer elastomer added to the vulcanizable composition). In one or more embodiments, the vulcanizable composition comprises a polymer content (e.g., elastomer) of greater than 20 wt%, in other embodiments greater than 30 wt%, and in other embodiments greater than 40 wt%, based on the total weight of the vulcanizable composition. In these or other embodiments, the vulcanizable composition comprises a polymer content (e.g., elastomer) of less than 80 wt%, in other embodiments less than 70 wt%, and in other embodiments less than 60 wt%, based on the total weight of the vulcanizable composition. In one or more embodiments, the vulcanizable composition comprises a polymer content (e.g., elastomer) of about 20 to about 80 wt%, in other embodiments about 30 to about 70 wt%, and in other embodiments about 40 to about 60 wt%, based on the total weight of the polymer content (e.g., elastomer) of the vulcanizable composition.

[0068] In one or more embodiments, the vulcanizable composition includes a filler such as carbon black or silica. In one or more embodiments, the vulcanizable composition includes more than 10 parts by weight (pbw), in other embodiments more than 35 pbw, and in other embodiments more than 55 pbw of filler (e.g., carbon black and / or silica) per 100 parts by weight of rubber (phr). In these or other embodiments, the vulcanizable composition includes less than 140 pbw, in other embodiments less than 95 pbw, and in other embodiments less than 75 pbw of filler in phr. In one or more embodiments, the vulcanizate includes from about 10 to about 200 pbw, in other embodiments from about 10 to about 140 pbw, in other embodiments from about 35 to about 95 pbw, in other embodiments from about 40 to about 130 pbw, in other embodiments from about 50 to about 120 pbw, and in other embodiments from about 55 to about 75 pbw of filler (e.g., carbon black and / or silica) in phr. Carbon black and silica may be used together in a weight ratio of silica to carbon black of from about 0.1:1 to about 30:1, in other embodiments from about 0.5 to about 20:1, and in other embodiments from about 1:1 to about 10:1.

[0069] In one or more embodiments in which silica is used as a filler, the vulcanizable composition may include a silica coupling agent. In one or more embodiments, the vulcanizable composition may generally include greater than 1 pbw, in other embodiments greater than 2, and in other embodiments greater than 3 pbw, of the silica coupling agent in phr. In these or other embodiments, the vulcanizable composition may generally include less than 40 pbw, in other embodiments less than 20, and in other embodiments less than 10 pbw, of the silica coupling agent in phr. In one or more embodiments, the vulcanizable composition includes from about 1 to about 40 pbw, in other embodiments from about 2 to about 20 pbw, in other embodiments from about 2.5 to about 15 pbw, and in other embodiments from about 3 to about 10 pbw, of the silica coupling agent in phr.

[0070] In these or other embodiments, the amount of silica coupling agent may be defined relative to the weight of the silica. In one or more embodiments, the amount of silica coupling agent introduced to the silica (either in situ or pre-reacted) is from about 1 to about 25 pbw, in other embodiments from about 2 to about 20 pbw, and in other embodiments from about 3 to about 15 pbw of silica coupling agent per 100 parts by weight of silica.

[0071] The vulcanizable composition may generally include more than 5 pbw of plasticizer (e.g., oils and solid resins) in phr, in other embodiments more than 10, and in other embodiments more than 20 pbw. In these or other embodiments, the vulcanizable composition may generally include less than 80 pbw of plasticizer in phr, in other embodiments less than 70, and in other embodiments less than 60 pbw. In one or more embodiments, the vulcanizable composition may generally include from about 5 to about 80 pbw of plasticizer in phr, in other embodiments from about 10 to about 70, and in other embodiments from about 20 to about 60 pbw of plasticizer. In further embodiments, the vulcanizable composition may include less than 15 pbw, alternatively less than 10 pbw, or less than 5 pbw of liquid plasticizer. In certain embodiments, the vulcanizable composition is free of liquid plasticizer. In other embodiments, the vulcanizable composition may include at least 20 pbw of resin, at least 25 pbw of resin, or at least 30 pbw of resin.

[0072] One of ordinary skill in the art would be able to readily select the amount of vulcanizing agent to achieve the desired level of cure. In certain embodiments, sulfur is used as a curing agent. In one or more embodiments, the vulcanizable composition may comprise greater than 0.5 pbw sulfur in phr, greater than 1 in other embodiments, and greater than 2 pbw sulfur in other embodiments. In these or other embodiments, the vulcanizable composition may generally comprise less than 10 pbw sulfur in phr, less than 7 pbw sulfur in other embodiments, and less than 5 pbw sulfur in other embodiments. In one or more embodiments, the vulcanizable composition may generally comprise from about 0.5 to about 10 pbw sulfur in phr, from about 1 to about 6 in other embodiments, and from about 2 to about 4 pbw sulfur in other embodiments.

[0073] Preparation of Foamable Vulcanizable Composition The foamable vulcanizable composition can be prepared using conventional mixing techniques. For example, the components of the vulcanizable composition can be introduced into a mixing device and mixed in the solid state. The foamable vulcanizable composition can then be formed into a green vulcanizate and then subjected to conditions that result in foaming and vulcanization (i.e., curing or crosslinking) of the polymer network.

[0074] For example, all the components of the vulcanizable composition can be mixed in standard mixing equipment such as Banbury or Brabender mixers, extruders, kneaders and two-roll mills. In one or more embodiments, this may include a multi-stage mixing procedure in which the components are introduced and / or mixed in two or more stages. For example, in the first stage (often referred to as the masterbatch mixing stage), the natural rubber-chemical blowing agent of the present invention is mixed together with any additional fillers and any optional components. In one or more embodiments, if a silica coupling agent is used, the silica coupling agent may also be added during one or more masterbatch stages. Generally speaking, the masterbatch mixing process involves adding the components and performing mixing conditions with energy (e.g., temperature and shear) that exceeds the energy that would scorch the composition in the presence of the curative. Similarly, the remill mixing stage is performed with the same or similar energy, except that no components are added during the remill mixing stage. It is believed that the energy imparted to the vulcanizable composition during the masterbatch or remill mixing is sufficient to disperse the fillers and cause hydrolysis and subsequent condensation of the hydrolyzable groups. For example, during one or more of these mixing steps, it is believed that the hydrolyzable groups of the silica functionalizing agent hydrolyze and then bond to the silica particles via a condensation reaction.To this end, in one or more embodiments, the master batch or remill mixing can be carried out in the presence of a catalyst that helps promote the reaction between the hydrolyzable groups and the silica.These catalysts are generally known in the art and include, but are not limited to, strong bases, such as alkali metal alkoxides, for example sodium or potassium alkoxides, guanidines such as triphenylguanidine, diphenylguanidine, di-o-tolylguanidine, N,N,N',N'-tetramethylguanidine, and hindered amine bases such as 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene, tertiary amine catalysts such as N,N-dimethylcyclohexylamine, triethylenediamine, triethylamine, quaternary ammonium bases such as tetrabutylammonium hydroxide, and bisaminoethers such as bis(dimethylaminoethyl)ether.

[0075] Thus, the masterbatch and remill mixing is done in the absence of a curing agent and proceeds at a temperature where curing would otherwise occur if the curing agent was present. For example, the mixing can be done at a temperature greater than 120°C, in other embodiments greater than 130°C, in other embodiments greater than 140°C, and in other embodiments greater than 150°C. It will also be understood that the mixing steps (e.g., the masterbatch and remill mixing steps) are done at a temperature below the decomposition temperature of the chemical blowing agent. For example, the mixing is done at a maximum temperature (i.e., the maximum temperature achieved by the composition) less than 175°C, in other embodiments less than 170°C, and in other embodiments less than 165°C.

[0076] Once the masterbatch is prepared, the vulcanizing agents may be introduced and mixed into the masterbatch in a final mix stage, which is typically carried out at a relatively low temperature to reduce the possibility of premature timing of vulcanization. For example, the mixing may be carried out at a temperature below 120° C., in other embodiments below 110° C., and in other embodiments below 100° C. An additional mix stage, sometimes called a remill, may also be employed between the masterbatch mix stage and the final mix stage.

[0077] It should be understood that in one or more embodiments, regardless of the mixing technique and temperature profile used, the mixing temperature, including the temperature at which the foamable vulcanizable composition reaches a peak temperature during mixing, should remain below the decomposition temperature of the chemical blowing agent.

[0078] Preparation of foamed vulcanizates The foamable vulcanizable composition is then fabricated into a desired shape, which may be called a profile, which may include extruding the desired profile, or in other embodiments, which may include placing the vulcanizable composition into a desired mold.

[0079] In one or more embodiments, the vulcanizates are prepared by subjecting the foamable vulcanizable composition to conditions that decompose the chemical blowing agent, thereby foaming the composition, and then vulcanizing or otherwise hardening the rubber within the composition. In one or more embodiments, the steps of decomposing the chemical blowing agent and vulcanizing the rubber are performed simultaneously. In other words, decomposition and vulcanization can occur simultaneously by heating the foamable vulcanizable composition to a threshold temperature. In other embodiments, decomposition of the chemical blowing agent can occur first, followed by vulcanization. In yet other embodiments, the chemical blowing agent is partially decomposed, and then vulcanization occurs.

[0080] In one or more embodiments, the profile is heated to decompose the chemical blowing agent and vulcanize the rubber. In one or more embodiments, the profile is heated to a temperature of about 175 to about 215° C., in other embodiments about 180 to about 210° C., and in other embodiments about 185 to about 205° C. In one or more embodiments, the profile is heated for a time to decompose at least 40% by weight of the chemical blowing agent. In one or more embodiments, the profile is maintained at the desired temperature for at least 5 minutes, in other embodiments at least 7 minutes, and in other embodiments at least 9 minutes. In these or other embodiments, the profile is maintained at the desired temperature for about 5 to about 15 minutes, or in other embodiments about 7 to about 12 minutes. [Industrial Applicability]

[0081] As described above, the foamable vulcanizable composition of the present invention can be cured to prepare various tire components. In one or more embodiments, these components include pneumatic tire components such as, but not limited to, tire treads, tire sidewalls, belt skims, innerliners, ply skims, and bead apexes. These tire components can be included in various vehicle tires, including passenger tires, truck and bus tires, and off-the-road tires.

[0082] In one or more embodiments, the foamed articles produced by the practice of the present invention may be characterized by a low density compared to a solid of the same profile. As one of ordinary skill in the art will appreciate, this density can be calculated by measuring the mass (i.e., weight) and volume of the foamed article. In one or more embodiments, the foamed article has a density of less than 1000 kg / m 3 in other embodiments, 900 kg / m 3 and in other embodiments less than 800 kg / m 3 In these or other embodiments, the foamed article has a density of from about 500 to about 900, from about 550 to about 850 in other embodiments, and from about 600 to about 800 kg / m 3 has a density of

[0083] experiment Two vulcanizable compositions were prepared by using the formulations provided in Table I below. Both samples used guayule rubber (GR) obtained from guayule rubber cement and dried, but sample 1 included cement mixed in accordance with the present invention and a chemical blowing agent introduced into solution. Sample 2, the control, was prepared using the same drying and compounding conditions without the addition of a chemical blowing agent (CBA).

[0084] The chemical foaming agent was azodicarbonamide, characterized by an average particle size of 5 μm and a decomposition temperature of 202-204 °C. For sample 1, 12.5 phr of CBA was first dispersed in 930 mL of GR cement with continuous stirring at 12,000 rpm for 20 min at room temperature. The GR cement contained 7% GR with a weight average molecular weight of about 900 kg / mol, and the ratio of hexane:acetone in the cement was 80:20. Both solutions were drum dried at 150 °C to remove the solvent, and then the dried polymer of each sample was mixed with the other ingredients in a 65 g Brabender mixer at 100 °C for 3 min at 60 rpm. The compositions were then sheeted and cut into 3 x 3 x 0.075 in. samples for compression molding. The samples were compression molded at 200 °C for 10 min under 8.2 MPa pressure to cure and foam.

[0085] [Table 1]

[0086] The cured samples were analyzed for tensile properties and the test results are shown in Table II below. Sample 1 foam had a strength of 974.5 kg / m 3 Compared to the solid profile of sample 2, which has a density of 697.7 kg / m 3 The density was 1.01 μm.

[0087] [Table 2]

[0088] The foam of Sample 1 exhibits improved tensile modulus, stress and toughness compared to solid GR. The improved tensile performance of the GR-foam is expected to be due to the enhanced strain-induced crystallization resulting from the unique porous structure.

[0089] Various modifications and alterations that do not depart from the scope and spirit of the present invention will be apparent to those skilled in the art. This invention is not to be duly limited to the illustrative embodiments set forth herein.

Claims

1. 1. A method for forming a natural rubber-chemical blowing agent composite, comprising: (a) providing a natural rubber cement; (b) introducing a blowing agent into the natural rubber cement to form a solvent-based mixture comprising the natural rubber and the blowing agent; (c) desolventizing said solvent-based mixture to form a natural rubber-chemical blowing agent composite.

2. 10. The method of claim 1, wherein the natural rubber cement is guayule cement.

3. 3. The method of claim 1, wherein the guayule cement comprises less than 12% by weight of polymer.

4. The method according to any one of claims 1 to 3, wherein the chemical blowing agent has a decomposition temperature above 160°C.

5. The method of any one of claims 1 to 4, wherein the chemical blowing agent is in the form of microparticles having a median particle size of about 0.5 to about 30 μm.

6. 6. The method of any one of claims 1 to 5, wherein the chemical blowing agent is dispersed in a carrier solvent prior to the step of introducing the chemical blowing agent into the guayule cement.

7. The method of any one of claims 1 to 6, wherein the desolventizing step comprises a direct desolventization technique.

8. The method of any one of claims 1 to 7, wherein the step of desolvating comprises flashing off the solvent from the solvent-based mixture.

9. 9. The method according to any one of claims 1 to 8, wherein the guayule cement comprises a solid portion comprising cis-1,4-polyisoprene obtained from guayule.

10. 10. The method according to any one of claims 1 to 9, wherein the guayule cement comprises a solid portion comprising a resin obtained from guayule.

11. 11. The method of any one of claims 1 to 10, wherein the solid portion of the guayule cement comprises greater than 85% by weight of cis-1,4-polyisoprene derived from guayule.

12. 12. The method of any one of claims 1 to 11, wherein the solid portion of the guayule cement comprises from about 0.5 to about 7 weight percent guayule resin or low molecular weight polyisoprene.

13. The method of any one of claims 1 to 12, wherein the guayule cement comprises a hydrocarbon solvent.

14. The method of any one of claims 1 to 13, wherein the guayule cement comprises a hydrocarbon solvent and a polar organic solvent.

15. 1. A method for forming a foam rubber article, comprising: (a) providing a natural rubber-chemical blowing agent composite according to claim 1; (b) introducing a curative into the composite to form a foamable vulcanizable composition; (c) forming a profile from the foamable vulcanizable composition; and (d) heating the profile to a temperature sufficient to decompose the chemical blowing agent and vulcanize the rubber.

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