Solidification of a natural rubber latex by polyquaternary polymers

Abstract

The present invention relates to a solidification process of the natural rubber latex by means of polyquaternary polymers. The process of the present invention has the advantage to not require the addition of acids and/or salts, with an evident saving in terms of cost for the reagents. Furthermore, in such a way neither the neutralization step of the rubber nor the treatment of the processing water before their disposal are required. The process of the present invention is suitable both for the continuous and batchwise embodiment, with evident advantages as far as its industrial application is concerned.

Claims

1. A process for solidification of a natural rubber latex comprising: a) contacting the natural rubber latex, said natural rubber latex having a pH between 7.2 and 13 with a polyquaternary polymer, obtaining a suspension of solid natural rubber particles in a liquid phase comprising a latex serum; and b) separating the solid natural rubber particles from the liquid phase of the suspension, wherein the process does not require a pH adjustment of the natural rubber latex before it is in contact with said polyquarternary polymer.

2. The process according to claim 1, wherein the process carried out batchwise.

3. The process according to claim 1, wherein the contacting a) comprises a first phase in which substantially all the natural rubber latex to be processed is fed to a mixing area and a second phase in which the polyquaternary polymer is fed to said mixing area.

4. The process according to claim 3, wherein said polyquaternary polymer is fed to said mixing area under stirring in a time ranging from 0.5 to 60 minutes.

5. The process according to claim 1, wherein the suspension of solid natural rubber particles obtained in the contacting a) is maintained under stirring for a time ranging from 0.5 to 120 minutes before passing to the separating b).

6. The process according to claim 1, wherein the process is carried out continuously.

7. The process according to claim 1, wherein the contacting a) is carried out by co-feeding both the natural rubber latex and the polyquaternary polymer to a mixing area.

8. The process according to claim 1, wherein the natural rubber latex is obtained from guayule type plants.

9. The process according to claim 1, wherein the natural rubber latex comprises at least one stabilizer and/or at least one preservative.

10. The process according to claim 1, wherein the polyquaternary polymer is the copolymer dimethylamine-epichlorohydrin.

11. The process according to claim 1, wherein said polyquaternary polymer is fed to the first mixing area in the contacting a) in the form of an aqueous solution.

12. The process according to claim 1, wherein the total quantity of said polyquaternary polymer used in the contacting a) is ranging from 0.25 phr to 5 phr.

13. The process according to claim 1, wherein the contacting a) is carried out at a temperature ranging from 0.5′C to 50′C.

14. The process according to claim 1, wherein the separation of the solid natural rubber particles from the liquid phase of the suspension of the separating b) is carried out b filtration of said suspension.

15. The process according to claim 1, wherein the separation of the solid natural rubber particles from the liquid phase of the suspension of the separating b) is effected by decanting or siphoning.

16. The process according to claim 1, which comprises an optional washing of the solid natural rubber particles with water.

Description

EXAMPLE 1 (SOLIDIFICATION TEST OF A NATURAL RUBBER LATEX OF GUAYULE WITH A POLYQUATERNARY POLYMER)

(1) Into a container of 500 mL containing 50 g of natural rubber latex of guayule with 52% of solid and having a pH value of about 12, 190 mL of a solution consisting of 0.25 g of dimethylamine-epichlorohydrin copolymer (commercially available under the commercial name Prodefloc® or Floquat® FL 2250) in 190 ml of water were added.

(2) The obtained mixture was maintained at the temperature of 25° C. for about 1 minute, by mixing with a magnetic stirrer set at 200 rpm.

(3) In this conditions, the latex coagulation and the formation of a suspension of solid natural rubber particles in latex serum was observed.

(4) Particles were separated without any difficulty from the suspension obtained by filtration with a filter of 325 meshes (44 μm) net.

(5) The characterization of the obtained solid natural rubber particles provided results which were in line with the international standards (for example, ASTM D2227-96—reapproved in 2015), confirming the effectiveness of the process in order to obtain the natural rubber having excellent mechanical properties and workability.

EXAMPLE 2 (SOLIDIFICATION TEST OF A NATURAL RUBBER LATEX OF GUAYULE WITH A POLYQUATERNARY POLYMER)

(6) Into a container of 500 mL containing 90 g of natural rubber latex of guayule with 41% of solid and having a pH value of about 12, 200 mL of a solution consisting of 0.5 g of dimethylamine-epichlorohydrin copolymer (commercially available under the commercial name Prodefloc® or Floquat® FL 2250) in 200 ml of water were added.

(7) The obtained mixture was maintained at the temperature of 25° C. for about 1 minute, by mixing with a magnetic stirrer set at 200 rpm.

(8) In this conditions, the latex coagulation and the formation of a suspension of solid natural rubber particles was observed. The suspension of solid natural rubber particles in latex serum was then poured in a 10 L container, containing 8 L of water.

(9) The aqueous suspension thus obtained was maintained under stirring for about 2 minutes, then particles were separated from the suspension by filtration with a filter of 325 meshes (44 μm) net.

(10) The characterization of the obtained solid natural rubber particles provided results which were in line with the international standards (for example, ASTM D2227-96—reapproved in 2015), confirming the effectiveness of the process in order to obtain the natural rubber having excellent mechanical properties and workability.

EXAMPLE 3 (SOLIDIFICATION TEST OF A NATURAL RUBBER LATEX OF HEVEA BRASILIENSIS WITH A POLYQUATERNARY POLYMER)

(11) Into a container of 500 mL containing 45 g of natural rubber latex of Hevea brasiliensis with 60% of solid and having a pH value of about 9.5, 100 mL of a solution consisting of 0.17 g of dimethylamine-epichlorohydrin copolymer (commercially available under the commercial name Prodefloc® or Floquat® FL 2250) in 100 ml of water were added.

(12) The obtained mixture was maintained at the temperature of 25° C. for about 1 minute, by mixing with a magnetic stirrer set at 200 rpm.

(13) In this conditions, the latex coagulation and the formation of a suspension of solid natural rubber particles in latex serum was observed. The suspension of solid natural rubber particles in latex serum was then poured in a 10 L container containing 4 L of water.

(14) The aqueous suspension thus obtained was maintained under stirring for about 2 minutes, then particles were separated from the suspension by filtration with a filter of 325 meshes (44 μm) net.

(15) The characterization of the obtained solid natural rubber particles provided results which were in line with the International Standards (for example, ASTM D2227-96—reapproved in 2015), confirming the effectiveness of the process in order to obtain the natural rubber having excellent mechanical properties and workability.

EXAMPLE 4 (SOLIDIFICATION TEST IN CONTINUOUS OF A NATURAL RUBBER LATEX OF GUAYULE WITH A POLYQUATERNARY POLYMER)

(16) A natural rubber latex of guayule with 46% of solid and having a pH value of about 12 and a 0.25% w/v solution of dimethylamine-epichlorohydrin copolymer (commercially available under the commercial name Prodefloc® or Floquat® FL 2250) in water were fed, through two peristaltic pumps at rates of 170 mL/min and 180 mL/min respectively, in a screw 20 cm long and having a diameter of 4 cm, arranged along an inclined position with a slope of 30° and maintained in rotation at the rate of 10 rotations per minute. The suspension of solid natural rubber obtained was transferred in continuous from the screw in a vessel containing 5 L of water at the temperature of 25° C. and maintained under slow stirring by mechanical stirrer. The natural rubber solidified in the form of particles which are well separated and the formation of sticky macrocoagula is not observed. Through flotation, the above-mentioned solid natural rubber particles accumulated in the higher portion of the vessel which was full of water and they overflew through an overflow structure, being then held by a sieve with a net of 325 meshes arranged in correspondence of the overflow structure itself. The determination of the amount of residual rubber in the coagulation serum, collected at the screw outlet, provided values close to zero, thus confirming that the process of coagulation is substantially a quantitative process. The characterization of the natural rubber of the obtained solid particles provided results which are in line with the International standards (for example, ASTM D2227-96—reapproved in 2015) and confirmed the effectiveness of the process carried out in continuous in order to obtain natural rubber having excellent mechanical and workability properties.

COMPARATIVE EXAMPLE 5 (SOLIDIFICATION TEST OF A NATURAL RUBBER LATEX OF GUAYULE WITH SULPHURIC ACID 20% BY WEIGHT)

(17) 3 mL of sulfuric acid 20% by weight are added into a container of 500 mL containing 50 g of natural rubber latex of guayule with 40% of solid and having a pH value of about 12.

(18) The obtained mixture was maintained at the temperature of 25° C. for about 1 minute, by mixing with a magnetic stirrer set at 200 rpm.

(19) In this conditions, the latex coagulation is observed. However, the solid natural rubber aggregates in a sticky macrocoagulum, which incorporates a quote of the latex serum and it is hardly separable from the latter.

(20) Such macrocoagulum, in view of the particular sticking showed, was able to block the stirring system, with the consequence to make particularly difficult the subsequent processing.

COMPARATIVE EXAMPLE 6 (SOLIDIFICATION TEST OF A NATURAL RUBBER LATEX OF GUAYULE WITH CACL.SUB.2.)

(21) 30 g of CaCl.sub.2.2H.sub.2O are added into a container of 500 mL containing 50 g of natural rubber latex of guayule with 40% of solid and having a pH value of about 12.

(22) The obtained mixture was maintained at the temperature of 25° C. for about 1 minute, by mixing with a magnetic stirrer set at 200 rpm.

(23) The latex coagulation is observed that, however, also in this case goes up to the formation of a sticky macrocoagulum. Also in this case, the macrocoagulum, in view of the particular sticking showed, was able to block the stirring system, with the consequence to make particularly difficult the subsequent processing.

COMPARATIVE EXAMPLE 7 (SOLIDIFICATION TEST OF A STYRENE-BUTADIENE SYNTHETIC RUBBER LATEX WITH A POLYQUATERNARY POLYMER, WITHOUT PH ADJUSTMENT)

(24) 200 mL of a solution constituted by 0.5 g of dimethylamine-epichlorohydrin copolymer (commercially available under the commercial name Prodefloc® or Floquat® FL 2250) in 200 ml of water are added into a container of 500 mL containing 100 g of styrene-butadiene synthetic rubber with 30% of solid and having a pH of about 10 (prepared as described, for example, in U.S. Pat. No. 2,680,111).

(25) The obtained mixture was maintained at the temperature of 25° C. for about 1 minute, by mixing with a magnetic stirrer set at 200 rpm.

(26) In this conditions, the latex coagulation is not observed.

(27) As described in U.S. Pat. No. 4,001,486, it is important to note that the preventive pH adjustment to values included in the range of 1.5-7.0 is necessary to obtain the coagulation of the synthetic rubber latex.

(28) Finally, it is to be intended that further modifications and variations can be made to the described and illustrated process, without coming out from the scope of protection of the appended claims.