US-12624131-B2 - Methods for producing polyisoprene latex dispersions

US12624131B2US 12624131 B2US12624131 B2US 12624131B2US-12624131-B2

Abstract

In various embodiments, methods for producing aqueous polyisoprene latex from natural cis-1,4-polyisoprene are described. The natural cis-1,4-polyisoprene may be sourced from guayule scrubs. In various embodiments, the method comprises extracting guayule plant material to form a miscella, fractionating the miscella to a preliminary cement, diluting the preliminary cement to a cement for dispersing, dispersing the cement in an aqueous surfactant mixture under high shear to produce an emulsion, and de-solventizing the emulsion to produce an aqueous latex dispersion. The rubber solids level can then be adjusted by centrifugation and dilution in water to produce a final aqueous cis-1,4-polyisoprene latex.

Inventors

Robert W. White
Michael R. Hartzell
Mark N. DeDecker
Jason K. KWAN

Assignees

BRIDGESTONE CORPORATION

Dates

Publication Date: 20260512
Application Date: 20210614

Claims (7)

1 . A method for producing a polyisoprene latex dispersion, the method comprising: (i) extracting guayule plant material in a solvent to produce a miscella; (ii) fractionating the miscella to obtain a preliminary cement; (iii) diluting the preliminary cement with a mixture of polar and non-polar hydrocarbon solvent to produce a rubber cement for dispersing, where the rubber cement includes from about 5 wt % to about 10 wt % natural cis-1,4-polyisoprene rubber; (iv) circulating water and a surfactant through a circulation system including a continuously stirred tank in fluid communication with a circulation loop including an inline high-shear mixing device, where the water and surfactant mix to form an aqueous surfactant mixture; (v) maintaining the continuously stirred tank at steady state conditions; (vi) dispersing the rubber cement into the aqueous surfactant mixture circulating through the circulation system to produce a biphasic latex emulsion, where said step of dispersing is controlled to introduce the rubber cement at a weight ratio of rubber cement to water and surfactant within the aqueous surfactant mixture of from about 1:200 to about 1:5 to thereby form the biphasic latex emulsion; (vii) homogenizing the biphasic latex emulsion within inline high-shear mixing device while the biphasic latex emulsion circulates through the circulation system; (viii) removing a portion of the biphasic latex emulsion from the circulation system; and (ix) removing organic solvent from the biphasic latex emulsion removed in said step of removing a portion of the biphasic latex emulsion to thereby form a latex wherein the natural cis-1-4, polyisoprene is dispersed within water, and where the method yields less than 10% rubber loss.
2 . The method of claim 1 , further comprising adjusting rubber solids in the polyisoprene latex dispersion to produce a polyisoprene latex having a target percent rubber solids level of from about 40 wt % to about 70 wt %, based on the total weight of the aqueous polyisoprene latex, the adjusting comprising at least one sequence of: (i) centrifuging the aqueous latex dispersion to produce two layers, a top layer comprising a high rubber solids and a bottom water layer; (ii) separating the two layers; and (iii) diluting the top high rubber solids layer with water to the target percent rubber solids level.
3 . A method for producing a polyisoprene latex dispersion, the method comprising: (i) providing a circulation system including a continuously stirred tank in fluid communication with a circulation loop including an inline high-shear mixing device; (ii) circulating a fluid through the circulation system, where the fluid includes water and a surfactant; (iii) maintaining the continuously stirred tank at steady state conditions; (iv) introducing a rubber cement to the fluid circulating through the circulation system, where the rubber cement includes from about 5 wt % to about 10 wt % natural cis-1,4-polyisoprene rubber dissolved in a mixture of polar and non-polar hydrocarbon solvent, where said step of introducing is controlled to introduce the rubber cement at a weight ratio of rubber cement to water and surfactant within the fluid of from about 1:200 to about 1:5 to thereby form a biphasic mixture; (v) homogenizing the biphasic mixture within the inline high-shear mixing device while the biphasic mixture circulates through the circulation system; (vi) removing a portion of the fluid from the circulation system; and (vii) desolventizing the fluid removed from the circulation system to thereby form a latex wherein the natural cis-1-4,polyisoprene rubber is dispersed within water.
4 . The method of claim 3 , where the surfactant is defined by the formula R—CO 2 M, wherein R represents a linear or branched alkyl or alkenyl group having between about 8 and 24 carbons and M represents an alkali metal or ammonium or alkyl- or dialkyl- or trialkyl-ammonium or alkanol-ammonium cation.
5 . The method of claim 4 , where M represents sodium or potassium.
6 . The method of claim 4 , where R is a linear alkyl group.
7 . The method of claim 4 , where the surfactant is potassium laurate.

Description

This application is a National-Stage application of PCT/US2021/037282 filed on Jun. 14, 2021, which claims the benefit of U.S. Provisional Application Ser. No. 63/038,883 filed on Jun. 14, 2020, and U.S. Provisional Application Ser. No. 63/112,128 filed on Nov. 10, 2020, which are incorporated herein by reference. FIELD OF THE INVENTION The present disclosure generally relates to polyisoprene latex and in particular to methods of preparing latex dispersions from natural polyisoprene. BACKGROUND Natural rubber provides products having remarkable resilience, heat resistance and tensile strength. For at least these reasons, tires may be produced from natural rubber rather than synthetic rubber. Out of the four possible isomers of polyisoprene, natural rubber is entirely cis-1,4-polyisoprene. Pure polymer chains of cis-1,4-polyisoprene form aligned polymer chains, resulting in these remarkable properties. Polyisoprene latex dispersions are useful in the manufacture of dipped products such as wetsuits, condoms, gloves, catheters, angioplasty balloons; to make medical devices or laboratory equipment; for making adhesives for medical and cosmetics uses; as well as in coatings, including those useful for tire applications. The dip molding process in particular relies on using rubber latex dispersions having certain physical and chemical properties to allow for optimization of variables in the process, e.g., dwell time in the latex, leach dip conditions, curing and finishing. In spite of the long history of natural polyisoprene rubber and latex dispersions comprising cis-1,4-polyisoprene, various industries would benefit from having reliable sources of stable polyisoprene latex dispersions having optimized polymer chain distributions, color, viscosity, and weight percent solids. What is still lacking is a latex process that provides a cis-1,4-polyisoprene latex dispersion having properties optimized for dip-molding. SUMMARY In accordance with various embodiments of the present disclosure, a process for producing cis-1,4-polyisoprene latex dispersions is described. In various embodiments, the cis-1,4-polyisoprene latex dispersions produced by the methods herein comprise hypoallergenic semi-synthetic guayule latex. In various embodiments of the present disclosure, a method of producing a cis-1,4-polyisoprene latex dispersion is described. The method is characterized by the steps of dispersing a cis-1,4-polyisoprene rubber cement of a particular weight percent solids into an aqueous surfactant mixture to produce an emulsion, followed by de-solventization of the emulsion to produce an aqueous latex dispersion. In various embodiments, the cement comprises cis-1,4-polyisoprene rubber dissolved in at least one organic solvent. In various embodiments, the de-solventization comprising removing the at least one organic solvent from the emulsion to produce the polyisoprene latex dispersion. The resulting latex dispersion may then be subjected to weight percent solids adjustment, such as by subjecting the latex dispersion obtained by de-solventization to at least one round of centrifugation into phases, phase separation, and dilution of the high solids phase, to adjust solids level to a final targeted weight percent solids. In various embodiments, a method for producing an aqueous polyisoprene latex comprises: dispersing a cement comprising cis-1,4-polyisoprene rubber dissolved in an organic solvent into an aqueous surfactant mixture to produce a latex emulsion, where said dispersing takes place at a shear rate of greater than 20,000 rad/sec; and removing the at least one organic solvent from the latex emulsion to produce the aqueous polyisoprene latex. In various embodiments, a method for producing an aqueous polyisoprene latex comprises: extracting guayule plant material with a solvent to obtain a preliminary cement comprising cis-1,4-polyisoprene rubber dissolved in the at least one organic solvent; diluting the preliminary cement with at least one organic solvent to produce a cement; dispersing the cement into an aqueous surfactant mixture to produce a latex emulsion; de-solventizing the latex emulsion to produce an aqueous polyisoprene latex dispersion; and adjusting a weight percent solids level of the aqueous latex dispersion to produce the aqueous polyisoprene latex. In various embodiments, a method for producing an aqueous polyisoprene latex comprises: extracting guayule plant material with at least one organic solvent to obtain a miscella; fractionating the miscella to obtain a preliminary cement comprising cis-1,4-polyisoprene rubber in the at least one organic solvent; diluting the preliminary cement with at least one organic solvent to produce a cement; dispersing the cement into an aqueous surfactant mixture to produce a latex emulsion; de-solventizing the latex emulsion to produce an aqueous polyisoprene latex dispersion; and adjusting a weight percent solids level of the aqueous latex dispersion to produce the a