DESCRIPTION Technical Field

The present invention relates to a process for preparing devulcanized rubber and to the devulcanized rubber prepared. It further relates to a process in which the devulcanized rubber prepared is re-processed, for example the devulcanized rubber may be used for preparing vulcanized rubber. Accordingly, the present invention also relates to a process of vulcanizing the devulcanized rubber and to the vulcanized rubber prepared.

Background art Vulcanized rubber products such as dipped vulcanized rubber products (e.g. latex products such as latex gloves) are difficult to recycle due to the chemical crosslinks in their structure.

The common method utilized in industry to recycle such products entails regrinding it to powder (micron size). The powder has limitations in term of its applications because it is still vulcanized, cannot flow and cannot be remoulded. Thus it is only used to replace some parts of virgin polymers in a product to reduce the overall cost of the product. It is normally blended with virgin polymers through the melt blending technique. The powder remains as solid particles during the blending.

Some chemical methods have been proposed to devulcanize rubber in the prior art which involve large usage of solvents (e.g. Saputra, R., et al., 2019, Journal of Environmental Chemical Engineering, 7(3), p.103151) and super critical fluids (e.g. Kojima, M., et al., 2005, Polymer, 46(7), pp.2016-2019). For example, in a research developed by Toyota, EPDM rubber was swelled in oil for 24 hrs before extrusion to devulcanize at a temperature of 3OO°C (e.g. Sutanto, P., et al., 2006, Chemical Engineering Science, 61(21), pp.7077-7086). These methods involve purification of recycled rubber, require high pressure and need a long preparation time. Thus adoption of these methods by industries is still at a low level. There is an ongoing need for an alternative process such as a process which does not require the usage of any solvent or which can be carried out at room temperature and/or pressure. In addition, there is an ongoing need for a devulcanization process which may provide devulcanized rubber suitable for replacing virgin rubber.

Summary of the Invention

A first aspect of the invention provides a process for preparing devulcanized rubber, comprising: treating vulcanized rubber with at least a C ₄ -C ₂ 8 fatty acid, a plasticizer and an oleoresin.

In some embodiments of the first aspect, the vulcanized rubber is dipped vulcanized rubber (e.g. dipped latex vulcanized rubber). In some embodiments, the vulcanized rubber is dipped vulcanized rubber obtained from gloves, condoms or balloons. Preferably, the dipped vulcanized rubber is dipped vulcanized rubber gloves.

Typically rubber dipping is a process in which rubber products (e.g thin walled rubber products) are produced by immersing a former into rubber and withdrawing the former in such a way to leave a rubber deposit on the former, the formation of the product is then completed for example by drying and vulcanization. Rubber dipping is a common method for the preparation of dipped rubber products such as gloves, condoms and balloons.

In some embodiments of the first aspect, the vulcanized rubber is a waste product. The process of the present invention may be applied to waste vulcanized rubber which may include used rubber products and those in crushed/shredded form and vulcanized rubber scraps that occur during rubber moulding.

In some embodiment of the first aspect, the vulcanized rubber is selected from the group consisting of natural rubber, chloroprene, nitrile butadiene, styrenebutadiene rubber, polybutadiene, EPDM (ethylene propylene diene monomer) and mixtures thereof. In some embodiments, the vulcanized rubber is nitrile butadiene rubber. In some embodiments of the first aspect, the vulcanized rubber comprises at least to wt% nitrile butadiene rubber based on the total weight of the vulcanized rubber. In some embodiments, the vulcanized rubber comprises 10-60 wt% nitrile butadiene rubber based on the total weight of the vulcanized rubber.

Vulcanized rubber typically denotes rubber comprising sulfur bonds (such as -S-, -S-S-, and -S-S-S-) (which may be called cross-links) between carbon chains of the rubber. Unvulcanized new rubber typically denotes rubber which has not been vulcanized, sometimes also called virgin rubber.

Devulanized rubber typically denotes rubber which was a vulcanized rubber but which has been treated to remove at least some of the sulfur bonds between the carbon chains of the rubber. It is not typically necessary for the devulcanization process to sever all of the sulfur bonds in the vulcanized rubber. Typically the devulcanization process severs the sulfur bonds partly to such an extent that the devulcanized rubber can be compounded or moulded like unvulcanized rubber. Hence, a vulcanized rubber product obtained by compounding and/or moulding the devulcanized rubber prepared by the process of the first aspect of the present invention may have similar rubber characteristics as that of a compounded and/or moulded rubber product processed from virgin unvulcanized rubber.

In some embodiments of the first aspect, the devulcanized rubber prepared has less than about 20% (e.g. less than about 15%, less than about 10%, less than about 5%, or close to o) of the sulfur bonds remaining after the devulcanization process e.g. as determined through crosslink density measurement.

In some embodiments of the first aspect, the devulcanized rubber prepared has a Mooney Viscosity [ML(I+4), ioo°C] of 29-120. In some embodiments, the devulcanized rubber prepared has a Mooney Viscosity [ML(I+4), ioo°C] of 40-80. In some embodiments, the devulcanized rubber prepared has a Mooney Viscosity [ML(I+4), ioo°C] of 29-40. A Mooney Viscosity value may be determined according to ASTM 01646-193. In some embodiments of the first aspect, the devulcanized rubber prepared has a MH value (highest torque value) of to dMm or less. In some embodiments, the devulcanized rubber prepared has a MH value (highest torque value) of 5 dMm or less. In some embodiments of the first aspect, the devulcanized rubber prepared has a MH value (highest torque value) of 1 dMm or less.

In some embodiments of the first aspect, the devulcanized rubber prepared has a MH value (highest torque value) of 5-10 dNm. An MH value may be determined at temperature 150 °C using moving die rheometer model MDR2000 according to ASTM 027053 method.

As used herein a ‘C4-C28 fatty acid’ refers to an acyclic aliphatic monocarboxylic acid with a chain of 4 to 28 carbon atoms, which may be saturated or unsaturated, and which may be branched or unbranched.

In some embodiments of the first aspect, the C4-C28 fatty acid is unbranched.

In some embodiments of the first aspect, the C4-C28 fatty acid is a C13-C21 fatty acid. In some embodiments, the C4-C28 fatty acid is a C15-C21 fatty acid. In some embodiments, the C4-C28 fatty acid is a C16-C20 fatty acid. In some embodiments, the C4-C28 fatty acid is a C18 fatty acid.

In some embodiments of the first aspect, the C4-C28 fatty acid is a C13-C21 fatty acid selected from the group consisting of tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, nonadecanoic acid, eicosanoic acid, heneicosanoic acid, myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linolelaidic acid, a-linolenic acid, arachidonic, eicosapentaenoic acid and mixtures thereof. In some embodiments, the C ₄ -C ₂ 8 fatty acid is octadecanoic acid.

In some embodiments of the first aspect, the C4-C28 fatty acid is an acid of formula: CH ₃ (CH ₂ ) _X COOH wherein x is 2-26. In some embodiments, the C4-C28 fatty acid is a C13-C21 fatty acid of formula: CH ₃ (CH ₂ ) _X COOH wherein x is 11-19. In some embodiments, the C4-C28 fatty acid is a C16-C20 fatty acid of formula: CH ₃ (CH ₂ ) _X COOH wherein x is 14-18.

In some embodiments of the first aspect, the C ₄ -C ₂ s fatty acid is saturated. In some embodiments, the C ₄ -C ₂ s fatty acid is a saturated Ci ₃ -C _2i fatty acid optionally selected from the group consisting of tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, nonadecanoic acid, eicosanoic acid, heneicosanoic acid and mixtures thereof. In some embodiments the C ₄ -C ₂ s fatty acid is octadecanoic acid.

In some embodiments the first aspect, the C ₄ -C ₂ s fatty acid is stearic acid.

Stearic acid may also be called by its equivalent IUPAC name which is octadecanoic acid.

In some embodiments of the first aspect, the C ₄ -C ₂ s fatty acid is added in an amount of 0.5-35 wt% based on the total weight of the process composition. In some embodiments, the C ₄ -C ₂ s fatty acid is added in an amount of 10-20 wt% based on the total weight of the process composition.

As used herein the ‘total weight of the process composition’ refers the total weight of the vulcanized rubber component and any treatment components. For example if the vulcanized rubber component was only treated with a C ₄ -C ₂ s fatty acid, a plasticizer and an oleoresin, then the total weight of the process composition in that case would be the sum of the weight of those four components.

In some embodiments of the first aspect, the C ₄ -C ₂ s fatty acid is added in an amount of 1-40 pphr. In some embodiments, the C ₄ -C ₂ s fatty acid is added in an amount of 5-30 pphr. In some embodiments, the C ₄ -C ₂ s fatty acid is added in an amount of 10-25 pphr. In some embodiments, the C ₄ -C ₂ s fatty acid is added in an amount of 10-15 pphr.

Pphr (parts per hundred parts rubber) is defined as parts by weight of an ingredient per 100 parts by weight of rubber. In some embodiments of the first aspect, the plasticizer is selected from the group consisting of phthalate esters, polyesters, citrate esters, bio-based plasticizers, terephthalate esters, carboxylic acid esters, epoxidized esters, paraffinic oils and mixtures thereof. In some embodiments, the plasticizer is selected from the group consisting of adipate esters, azelate esters, citrate esters, benzoate esters, dibenzoate esters, phthalate esters, terephthalate esters, sebacate esters, glutarate esters, trimellitate esters, bio-based plasticizers and mixtures thereof. In some embodiments, the plasticizer is selected from the group consisting of adipate esters, azelate esters, citrate esters, benzoate esters, dibenzoate esters, phthalate esters, terephthalate esters, sebacate esters, glutarate esters, trimellitate esters and mixtures thereof. In some embodiments, the plasticizer is selected from the group consisting of adipate esters, azelate esters, citrate esters, benzoate esters, dibenzoate esters, phthalate esters, terephthalate esters, sebacate esters, trimellitate esters and mixtures thereof. In some embodiments, the plasticizer is selected from the group consisting of adipate esters, azelate esters, citrate esters, benzoate esters, phthalate esters, terephthalate esters, sebacate esters and mixtures thereof. In some embodiments, the plasticizer is selected from the group consisting of phthalate esters, terephthalate esters and mixtures thereof. In some embodiments, the plasticizer is a phthalate ester.

In some embodiments of the first aspect, the plasticizer is a phthalate ester. In some embodiments the plasticizer is a phthalate ester selected from the group consisting of dimethyl phthalate, diethyl phthalate, diallyl phthalate, di-n-propyl phthalate, di-n-butyl phthalate diisobutyl phthalate, butyl cyclohexyl phthalate, di- n-pentyl phthalate, dicyclohexyl phthalate, butyl benzyl phthalate, di-n-hexyl phthalate, diisohexyl phthalate, diisoheptyl phthalate, butyl decyl phthalate, dibutoxy ethyl phthalate, di(2-ethylhexyl) phthalate, di(n-octyl) phthalate, diisooctyl phthalate, n-octyl n-decyl phthalate, diisononyl phthalate, di(2-propylheptyl) phthalate, diisodecyl phthalate, diundecyl phthalate, diisoundecyl phthalate, ditridecyl phthalate, diisotridecyl phthalate and mixtures thereof.

In some embodiments of the first aspect, the plasticizer is a polyester. In some embodiments, the plasticizer is a di-ester. In some embodiments, the plasticizer is an ester selected from the group consisting of adipate esters, sebacate esters, terephthalate esters, dibenzoate esters, glutarate esters, azelates esters, phthalate esters, other specialty blends and mixtures thereof. In some embodiments, the plasticizer is an ester selected from the group consisting of adipate esters, sebacate esters, terephthalate esters, dibenzoate esters, glutarate esters, azelate esters, phthalate esters and mixtures thereof.

In some embodiments of the first aspect, the plasticizer is a citrate ester. In some embodiments, the plasticizer is a citrate ester selected from the group consisting of triethyl citrate, acetyl triethyl citrate, tributyl citrate, acetyl tributyl citrate, trioctyl citrate, acetyl trioctyl citrate, trihexyl citrate, acetyl trihexyl citrate, butyryl trihexyl citrate, trimethyl citrate and mixtures thereof.

In some embodiments of the first aspect, the plasticizer is a bio-based plasticizer. In some embodiments, the plasticizer is a bio-based plasticizer selected from the group consisting of acetylated monoglycerides, methyl ricinoleate, epoxidized soybean oil, epoxidized vegetable oils and mixtures thereof.

In some embodiments of the first aspect, the plasticizer is a terephthalate ester. In some embodiments, the plasticizer is dioctyl terephthalate. In some embodiments of the first aspect, the plasticizer is a carboxylic acid ester.

In some embodiments of the first aspect, the plasticizer is added in an amount of 0.5- 50 wt% based on the total weight of the process composition. In some embodiments, the plasticizer is present in an amount of 10-50 wt% based on the total weight of the process composition.

In some embodiments of the first aspect, the plasticizer is added in an amount of 1-50 pphr. In some embodiment, the plasticizer is added in an amount of 5-35 pphr. In some embodiment, the plasticizer is added in an amount of 10-15 pphr.

In some embodiments of the first aspect, the oleoresin is a plant oleoresin. In some embodiments, the oleoresin is obtained from cedar, fir, juniper, pine, redwood, spruce, yew, larch and mixtures thereof. In some embodiments of the first aspect, the oleoresin is obtained from fruit, leaf, bark and trunk of various plants. In some embodiments, the oleoresin is obtained the trunk of a plant selected from the group consisting of cedar, fir, juniper, pine, redwood, spruce, yew, larch and mixtures thereof.

In some embodiments of the first aspect, the oleoresin is extracted from a plant. Examples of the method of extraction could include maceration, ultrasound assisted extraction, chemical extraction, supercritical extraction and distillation.

Oleoresins are known in the prior art, for example Copaiba oleoresin is described in Leandro et al., Molecules 2012, 17, pp 3866-3889 and the oleoresin of Zingiber officinale is described in Singh et al., Food and Chemical Toxicology, 2008, 46, pp 3295-3302.

In some embodiments of the first aspect, the oleoresin comprises compounds selected from the group consisting of ct-Thujene, a -Pinene, P-Pinene, Myrcene, a- Phellandrene, p-Mentha-i(7),8-diene, p-Cymene, 1,8-Cineole, Terpinolene, a- Cubebene, Eugenol, -Caryophyllene, Aromadendrene, o-Amorphene, Germacrene-D, Bicyclogermacrene, 8-Cadinene, Spathulenol, 8-Cadinene, Sabinene, y-Terpinene, Terpinen-4-ol, 8-Elemene, Viridiflorol, Methoxyeugenol, Isospathulenol, Neophytadiene, Docosane, Nonacosane, Z- cinnamaldhyde, Vitamin-E, E-cinnamaldhyde, ct-Copaene, o-Amorphene, 8- Cadinene, Terpinen-4-ol, -Caryophyllene, Coumarin, a-Muurolene, P- Bisabolene, Cadina-1(2), 4-diene, Ortho-methoxy cinnamadehyde, Cubenol, 1- Heptadecene, i-Nonadecene and mixtures thereof. In some embodiments of the first aspect, at least 10, 20, 30, 40, 50, 60, 70, 80, 90 or 95 wt% of the oleoresin is comprised of compounds selected from the group consisting of a-Thujene, a -Pinene, P-Pinene, Myrcene, a-Phellandrene, p- Mentha-i(7),8-diene, p-Cymene, 1,8-Cineole, Terpinolene, a-Cubebene, Eugenol, P-Caryophyllene, Aromadendrene, a-Amorphene, Germacrene-D, Bicyclogermacrene, 8-Cadinene, Spathulenol, 8-Cadinene, Sabinene, y- Terpinene, Terpinen-4-ol, 8-Elemene, Viridiflorol, Methoxy-eugenol, Isospathulenol, Neophytadiene, Docosane, Nonacosane, Z-cinnamaldhyde, Vitamin-E, E-cinnamaldhyde, ct-Copaene, a-Amorphene, 8-Cadinene, Terpinen- 4-0I, P-Caryophyllene, Coumarin, a-Muurolene, P-Bisabolene, Cadina-1(2), 4- diene, Ortho-methoxy cinnamadehyde, Cubenol, i-Heptadecene, i-Nonadecene and mixtures thereof, based on the total weight of the oleoresin. In some embodiments of the first aspect, the oleoresin consists of compounds selected from the group consisting of ct-Thujene, a -Pinene, P-Pinene, Myrcene, a- Phellandrene, p-Mentha-i(7),8-diene, p-Cymene, 1,8-Cineole, Terpinolene, a- Cubebene, Eugenol, -Caryophyllene, Aromadendrene, o-Amorphene, Germacrene-D, Bicyclogermacrene, 8-Cadinene, Spathulenol, 8-Cadinene, Sabinene, y-Terpinene, Terpinen-4-ol, 8-Elemene, Viridiflorol, Methoxyeugenol, Isospathulenol, Neophytadiene, Docosane, Nonacosane, Z- cinnamaldhyde, Vitamin-E, E-cinnamaldhyde, ct-Copaene, o-Amorphene, 8- Cadinene, Terpinen-4-ol, -Caryophyllene, Coumarin, a-Muurolene, - Bisabolene, Cadina-1(2), 4-diene, Ortho-methoxy cinnamadehyde, Cubenol, 1- Heptadecene, i-Nonadecene and mixtures thereof.

In some embodiments of the first aspect, the oleoresin is added in an amount of 0.5-25 wt% based on the total weight of the process composition. In some embodiments, the oleoresin is added in an amount of 5-10 wt% based on the total weight of the process composition.

In some embodiments of the first aspect, the oleoresin is added in an amount of 1-30 pphr. In some embodiments, the oleoresin is added in an amount of 1-25 pphr. In some embodiments, the oleoresin is added in an amount of 1-9 pphr. In some embodiments, the oleoresin is added in an amount of 5-9 pphr.

In some embodiments of the first aspect, the oleoresin is added in an amount of 25 pphr or less. In some embodiments, the oleoresin is added in an amount of 20 pphr or less. In some embodiments, the oleoresin is added in an amount of 15 pphr or less. In some embodiments, the oleoresin is added in an amount of 12 pphr or less. In some embodiments, the oleoresin is added in an amount of 10 pphr or less. In some embodiments, the oleoresin is added in an amount of 9 pphr or less. In some embodiments, the oleoresin is added in an amount of 8 pphr or less.

In some embodiments of the first aspect, the process is performed at a temperature of less than 200 °C, or less than 150 °C, or less than too °C, or less than 50 °C or less than 40 °C. In some embodiments, the process is performed at a temperature of less than 30 o In some embodiments of the first aspect, the process is performed at room temperature. As used herein ‘room temperature’ may refer to a temperature of 15-25 °C. This provides several advantages over use of elevated temperature. Firstly, special apparatus to maintain the process at an elevated temperature is not required, making a process at room temperature more economical and energy efficient. Secondly, reaction at room temperature is less dangerous than at the elevated temperature of the prior art, meaning a process at room temperature is safer. Finally, a process at room temperature is more amenable to scale up for commercial quantities.

In some embodiments of the first aspect, the process is performed at atmospheric pressure. This provides several advantages over use of elevated pressure. Firstly, special apparatus to maintain the process at an elevated pressure is not required, making a process at atmospheric pressure more economical and energy efficient. Secondly, reaction at atmospheric pressure is less dangerous than at the increased pressures of the prior art, meaning a process at atmospheric pressure is safer. Finally, a process at atmospheric pressure is more amenable to scale up for commercial quantities. In some embodiments of the first aspect, the process has a treatment time of 5 hours or less, or 4 hours of less, or 3 hours of less or 2 hours or less. In some embodiments, the process as a treatment time of 1 hour or less. In some embodiments, the process as a treatment time of 30 minutes or less. In some embodiments of the first aspect, the vulcanized rubber maybe broken up, e.g. shredded, prior to the treatment.

In some embodiments of the first aspect, a shearing force is applied to the vulcanized rubber prior to the treatment. In some embodiments, a shearing force is applied to the vulcanized rubber using a two roll mill prior to the treatment.

In some embodiments of the first aspect, the vulcanized rubber is treated with the oleoresin prior to the treatment with the C4-C28 fatty acid and the plasticizer. In some embodiments of the first aspect, the process comprises treating vulcanized rubber with at least a C4-C28 fatty acid, a plasticizer, an oleoresin and vulcanized unsaturated vegetable oil. In some embodiments, the vulcanized rubber is treated with the C ₄ -C ₂ 8 fatty acid, a plasticizer and an oleoresin prior to the treatment with the vulcanized unsaturated vegetable oil. In some embodiments, the vulcanized unsaturated vegetable oil is added in an amount of 5 pphr or more. In some embodiments, the vulcanized unsaturated vegetable oil is added in an amount of to pphr or more. In some embodiments, the vulcanized unsaturated vegetable oil is added in an amount of 15 pphr or more.

In some embodiments of the first aspect, the process comprises treating vulcanized rubber with at least a C4-C28 fatty acid, a plasticizer and an oleoresin, and then treating with vulcanized unsaturated vegetable oil. In some embodiments, the vulcanized unsaturated vegetable oil is added in an amount of 5 pphr or more. In some embodiments, the vulcanized unsaturated vegetable oil is added in an amount of 10 pphr or more. In some embodiments, the vulcanized unsaturated vegetable oil is added in an amount of 15 pphr or more.

In some embodiments of the first aspect, the devulcanized rubber prepared is not separated from the C4-C28 fatty acid, plasticizer and oleoresin. In some embodiments of the first aspect, the devulcanized rubber prepared is used in the process of the third aspect without further purification.

In some embodiments of the first aspect, a shearing force is applied during the process. In some embodiments, the shearing force is applied using a two roll mill.

A second aspect of the invention provides devulcanized rubber prepared/preparable by the process of any embodiment of the first aspect of the invention. A third aspect of the invention provides a process of preparing vulcanized rubber comprising: treating the devulcanized rubber prepared according to the process of the first aspect of the invention or the devulcanized rubber according to the second aspect of the invention, with a treatment mixture comprising at least a vulcanization ingredient. Once the devulcanized rubber is prepared it may be further processed to form vulcanized rubber with and without fillers. The vulcanized rubber prepared may be for use in applications such as o-rings, floor mats, boots and oil seals. This devulcanized rubber may be a cheaper option compared to virgin rubber in these applications and may solve environmental issues related to disposal of vulcanized rubber.

In some embodiments of the third aspect, the vulcanization ingredient is sulfur. In some embodiments of the third aspect, the treatment mixture further comprises a filler. In some embodiments, the filler is selected from the group consisting of calcium carbonate, silica, carbon black and mixtures thereof. In some embodiments, the filler is selected from the group consisting of calcium carbonate, silica and mixtures thereof. In some embodiments the filler is calcium carbonate.

In some embodiments of the third aspect, the treatment mixture further comprises an activator. In some embodiments, the activator is zinc oxide. In some embodiments of the third aspect, the treatment mixture further comprises an accelerator. In some embodiments, the accelerator is selected from benzothiazyl disulphide, tetramethylthiuram disulphide and mixtures thereof.

In some embodiments of the third aspect, the treatment mixture further comprises a lubricant. In some embodiments, the lubricant is stearic acid.

In some embodiments of the third aspect, the process is performed at a temperature of less than 200 °C, or less than 150 °C, or less than too °C, or less than 50 °C or less than 40 °C. In some embodiments, the process is performed at a temperature of less than 30 °C. In some embodiments, the process is performed at room temperature. As used herein ‘room temperature’ may refer to a temperature of 15-25 °C.

In some embodiments of the third aspect, the process is performed at atmospheric pressure. In some embodiments of the third aspect, the process has a treatment time of 5 hours or less, or 4 hours of less, or 3 hours of less or 2 hours or less. In some embodiments, the process as a treatment time of 1 hour or less. In some embodiments, the process as a treatment time of 30 minutes or less.

In some embodiments of the third aspect, a shearing force is applied during the process. In some embodiments, the shearing force is applied using a two roll mill. In some embodiments, the vulcanized rubber prepared has a Mooney Viscosity [ML(I+4), IOO°C] of 29-120. In some embodiments, the vulcanized rubber prepared has a Mooney Viscosity [ML(I+4), ioo°C] of 40-80.

A fourth aspect of the invention provides vulcanized rubber prepared/ preparable by the process of any embodiment of the third aspect of the invention.

For the avoidance of doubt, insofar as is practicable any embodiment of a given aspect of the present invention may occur in combination with any other embodiment of the same aspect of the present invention. In addition, insofar as is practicable it is to be understood that any preferred or optional embodiment of any aspect of the present invention should also be considered as a preferred or optional embodiment of any other aspect of the present invention. For example, embodiments of the first aspect related to the devulcanized rubber prepared will also relate to the devulcanized rubber of the second aspect. For example, embodiments of the third aspect related to the vulcanized rubber prepared will also relate to the vulcanized rubber of the fourth aspect.

Example 1 Stage 1 - Devuclanization

In Stage 1, a dipped latex rubber product such as rejected nitrile butadiene rubber (NBR) gloves with nitrile butadiene content 18-50 wt% were used for the devulcanization process. A combination of stearic acid in solid form, plasticizer and an oleoresin were used as devulcanization ingredients. Method:

Devulcanization was carried out based on the formulations listed in Table i.

Table 1: Devulcanization of gloves

The amount of plasticizer, stearic acid and oleoresin was varied in examples 1-5. The process was carried out under shearing in a counter rotating two roll mill for 20 minutes, without any pre-treatment at room temperature and pressure. First the NBR gloves were dumped into the two roll mill and shredded to smaller pieces. This step was followed by mixing the shredded gloves with oleoresin in the same two roll mill. Once formation of continuous sheet was observed, plasticizer and stearic acid were added to the two roll mill. After 20 minutes, the sheet was removed from the two roll mill.

All the devulcanized samples (1-5) was compounded with 5 pphr ZnO, 1.5 pphr benzothiazyl disulfide (MBTS), 1.0 pphr tetramethylthiuram disulfide (TMTD), 2.0 pphr sulfur and stearic acid 2 pphr. The compounding was carried out to determine the Mooney Viscosity and ability to crosslink again the devulcanized NBR through rheological tests (Table 2). The formulation with best process ability was used in Stage 2.

Table 2: Rheological data and mechanical properties of product from Stage 1.

ML: Stiffness of uncured compound at a given temperature ts 2: Time when the stiffness of the sample increases 2 units above ML value, scorch time (actual curing starts)

MH: The highest torque recorded in the graph ts 90: The time which 90% of MH value is recorded

CRI: Cure rate index

%EB: % elongation at break M100: Modulus at 100% elongation

M300: Modulus at 300% elongation

Stage 2 - Compounding

Vulcanization ingredients which included a combination of sulfur based crosslinker, activators, accelerator and/or lubricant were used in the compounding process. Ground calcium carbonate (GCC), silica and carbon black grade N330 were used as fillers in this study. Method:

The devulcanized rubber product obtained using formulation No. 3 from Stage 1 was chosen for compounding to produce composites using fillers such as silica, calcium carbonate and carbon black in Table 3. Formulation No. 3 was preferred based on the process ability of product from Stage 1 and the cost effectiveness of the formulation.

The blending can be done using any shearing mixing equipment such as two roll mill or extruder. In this study a two roll mill was used. The devulcanized rubber was dumped into the two roll mill, followed by ZnO, benzothiazyl disulfide (MBTS), tetramethylthiuram disulfide (TMTD), stearic acid and/or fillers. Once formation of homogenous compound was observed, sulfur was added lastly to the two roll mill to reduce pre-mature vulcanization.

Table 3: Formulation for stage 2 preparation:

The products were then pressed in a hot press moulding machine to prepare samples for mechanical testing. Table 4: Rheological data and mechanical properties of product from Stage 2.

Results from Table 4 shows that products using calcium carbonate or silica filler show better scorch safety with scorch time above 2 minutes than those using carbon black.

Composites B, C, F, G and H has standard medium Vc(ML 1+4 @100 °C): from 40 up to 80, while composites with calcium carbonate, D and E exhibit low viscosity Vc(ML 1+4 @100 °C): from 29 up to 40. A large increase in tensile properties could also be observed for all the composites compared to product A.

Testing and Characterization Mooney viscosity of the devulcanized rubber and compounded rubber from Stage i and Stage 2 respectively, was measured using Mosanto Mooney Viscometer Model # L87865. The measurement was carried out using large rotor, 1 minute of pre-heating time and 4 minutes of shearing time at chamber temperature of too °C.

The cure characteristic of the devulcanized rubber and compounded samples from Stage 1 and 2 respectively, were determined at temperature 150 °C using moving die rheometer model MDR2000 according to ASTM 027053 method. The cure time obtained from the rheological test was used for compression molding and crosslinking of the compounded samples in Stage 2. The products from Stage 2 were molded using

GT-7014-H Hydraulic Molding Hot Press at temperature 150 °C into sheets with 1 mm thickness.

Tensile test on the products were carried out using INSTRON Universal Testing Machine in accordance to ASTM D412 method.

Example 2

A formulation was prepared with the aim of increasing the process ability and storage ability of the de-crosslinked dipped latex product.

The formulation is as shown in Table 5.

The blending can be done using any shearing mixing equipment such as two roll mill or extruder. In this study a two roll mill was used. The devulcanized rubber from Formulation 3 (see table 1 from example 1) was dumped into the two roll mill, followed by vulcanized unsaturated vegetable oil. Mooney viscosity of the Y and Z compound was determined as shown in Table 6.

Table 5: Formulation with vulcanized unsaturated vegetable oil

Table 6: Mooney Viscosity of the formulation with vulcanized unsaturated vegetable oil Analysis:

Addition of vulcanized unsaturated vegetable oil reduces the Mooney Viscosity of the product which will increase the ease of processing and flexibility of the de-crosslinked rubber.