WO2016030908A1

WO2016030908A1 - A method for coagulation of rubber latex

Info

Publication number: WO2016030908A1
Application number: PCT/IN2015/000018
Authority: WO
Inventors: Srimanta Ray; Saptarshi GUPTA; Raja SAHA
Original assignee: Individual
Current assignee: Individual
Priority date: 2014-08-28
Filing date: 2015-01-14
Publication date: 2016-03-03
Anticipated expiration: 2017-02-28

Abstract

The present invention deals with an alternate method of rubber latex coagulation that can be used to produce rubber for rubber goods from stabilized or un-stabilized rubber latex, having quality at par with the commercial rubber in an environmentally benign, less chemical intensive and economic way. The presented route can be used to coagulate rubber in a controlled fashion directly on desired forms for various rubber goods using electrostatic charge generated from renewable and non-renewable power source. The invention presents a systematic study to define the control variables and governing relationship of the control parameters with respect to rubber coagulation/mass of rubber coagulated as shown in (A) of Figure 5 (B). The applied potential, coulomb transport rate (current), time, ionic strength (salt concentration in latex) and rubber content of the latex are the variables/process parameter defined to control rubber coagulation for rubber latex with dry rubber content between less than 4% to greater than 24% as shown in (B) of Figure 7.

Description

A METHOD FOR COAGULATION OF RUBBER LATEX

Field of the invention;

The present invention relates to a method for coagulation of rubber latex . The invention illustrates a n a lternate route of rubber latex coagulation for processing of rubber latex . The a lternative route presented in this invention can be used to produce rubber for rubber goods which is at par with the acceptable commercial quality in a n environmentally benign, less chemical intensive a nd economic way . The presented alternative route can be used to coag ulate rubber directly on desired forms for various rubber goods in an eco-friendly approach . The present invention defines the control va riables .

Background and prior art of the invention:

Rubber latex is a stable dispersion of colloida l polymeric rubber particles in a solvent system . The stability of colloida l latex is particularly important for preservation and processing requi rement.

Accordingly the rubber latex are often sta bi lized by adding chemical agents. But, an important criterion for further processing of latex is to produce coagulation on demand and therefore rubber latex a re su bsequently desta bilized by adding further chemical agents. The chemical stabilization and subsequent destabil ization has huge environmental footprint and requires thorough treatment of process effluent.

The conventional route of latex processing widely used in the industry and in various commercial applications is chemical intensive and therefore has huge environmental footprint. Also in the conventional chemical coagulation the coagulation and recovery of rubber is largely uncontrolled. References to be made to patent US2366460 (1945) and US2424648 (1947) by Goodrich Co B F that reports a method of coagulating dispersions and method for continuously transforming a dispersion of a rubbery material into sheets.

Another reference may be made to US2487263 (1949) by US Rubber Co. on coagulation of synthetic rubber lattices, also latex coagulation technique US3024223 (1962) reported by Phillips Petroleum Co.

Also another reference may be made to a process for multi-step coagulation of rubber lattices, described in US 3079360 (1963) from Copolymer Rubber and Chem. Corp.

Yet another reference may be made to US6294061 (2001) reporting process and apparatus for electro-coagulate treatment of industrial waste water by Kaspar Electroplating Corporation.

Still another reference may be made to US8460520 (2013) electrochemical system and method for the treatment of water and wastewater from David Rigby.

Further another reference may be made to CA2200143 (1998) electro-coagulation printing ink bynormand Lepine, Adrien Castegnier, Elcorsy Technology Inc. In view of the above cited art, the inventors of the present inventions have come up with a method for coagulation of rubber latex, which obviates the drawbacks of the reported prior art.

Objectives of the present invention:

The main objective of the present invention is to provide an alternate route of rubber latex coagulation for processing of rubber latex. The alternative route presented in this invention can be used to produce rubber for rubber goods which is at par with the acceptable commercial quality in an environmentally benign, less chemical intensive and economic way. The presented alternative route can be used to coagulate rubber directly on desired forms for various rubber goods in an eco- friendly approach. The present invention defines the control variables.

The present alternative route can be used to coagulate rubber directly on desired forms for various rubber goods in an eco- friendly approach. The present invention illustrates an alternate route of latex processing that is environmentally benign and less chemical intensive. The alternative latex processing route of this invention claims to have the advantage of controlled coagulation and rubber recovery. The present invention provides a method to recover significant portion of rubber of equivalent quality from stabilized colloidal latex at comparable cost with respect to the conventional chemical route. The modulation of the key operational parameters of the alternative processing route presented in this invention, provide a control on the coagulation and extent of the recovery of the rubber from the rubber latex, which is very useful in various latex processing processes, industrial applications and in manufacturing processes of different commercial rubber goods.

Summary of the present invention:

The present invention illustrates an alternate route of latex processing that is environmentally benign and less chemical intensive. The present invention uses static charge to destabilize stable colloidal system of rubber latex in a controlled fashion and thereby shows an alternative route of latex processing useful for industrial applications. The alternative route of latex processing presented in this invention claims to recover significant portion of colloidal rubber from stabilized latex at comparable cost with respect to the conventional chemical route. The recovered rubber by electrostatic coagulation is claimed to be of equivalent quality as that produced from conventional latex processing route. The applied potential, time, ionic strength of the latex and rubber content of the colloidal latex are the key operational variables of the alternative latex processing route presented in this invention. The modulation of the key operational parameters provides a control on the coagulation and extent of the recovery of the rubber from the rubber latex. Hence, the alternative latex processing route of this invention claims to have the advantage of controlled coagulation and rubber recovery in contrast to the chemical coagulation where the coagulation and recovery is largely uncontrolled.

Accordingly, the present invention provides a method of coagulation of rubber, under controlled parameters, comprises the steps of destabilizing the colloidal rubber latex within an electrochemical cell using electrostatic charge for producing rubber or rubber goods having quality at par with the commercial rubber.

In an embodiment of the present invention, the controlling parameters include but not limited to the applied potential, coulomb transfer rate (current), time, ionic strength of latex (salt concentration in latex) and dry rubber content of colloidal latex. In another embodiment of the present invention, the governing relationship of the controlling variables with the extent of coagulation of rubber is established.

In yet another embodiment of the present invention, the rubber latex used is in raw state/ unstabilized/ unfortified OR fortified/ stabilized by chemical agents/ stabilizer/ anticoagulants without addition of chemicals, using electrostatic charge in a less hazardous and less polluting route (with respect to conventional chemical route).

In still another embodiment of the present invention, the electrostatic charge being applied by controlling electrical parameters with no moving parts, generated from renewable and non-renewable power source capable of generating a potential field between 0 - 50^' V for application in industry, more particularly for micro-small and medium scale sector/enterprises, and remotely located household applications. In yet another embodiment of the present invention, the said method further comprises the steps of recovering at least up to 70% colloidal rubber from stabilized or un-stabilized latex in controlled condition, bypassing the conventional chemical route, in an economic way with cost that is comparable to the conventional chemical route. Further in another embodiment of the present invention, the potential applied is in the range of 0 - 30V, such that the amount of coagulation increases with increase in applied potential.

In still another embodiment of the present invention, the time through which current passes through the experimental liquid, is in the range of 0 - 20 minutes, thus the amount of coagulation increases with increase in time.

In yet another embodiment of the present invention, the dry rubber content, preferably in the range of 1 - 25%, increases the availability of rubber particles near the electrodes, thus increasing coagulation of rubber.

In still another embodiment of the present invention, the said method is used to coagulate rubber directly on desired forms for various rubber goods in an eco-friendly approach. Brief description of the drawings: Figure 1 illustrates the schematic of the experimental setup and the electrochemical cell. The electro-coagulation (EC) experimental setup is shown in Figure 1. The setup consists of a regulated DC Power supply (A) connected with the electrodes (B) through the insulating copper wire (C). The electrodes (B) are then dipped into the container (D), which is filled by the experimental liquid (E).

Figure 2 illustrates the variation of applied potential with coagulated rubber for 15 % DRC for 5 min.

Figure 3 illustrates the variation of applied potential and time on coagulation of rubber for (A) 24.5% DRC, (B) 17.5% DRC, (C) 10.5% DRC and (D) 3.5% DRC.

Figure 4 illustrates the variation of ionic strength (salt concentration), current with coagulated rubber for 24.5% DRC at 5 V for 5 min.

Figure 5 illustrates (A) Comparative study of kinetics of coagulation of rubber at 5V for different DRC and (B) The effect of different applied potential on kinetics of coagulation of rubber at different DRC

Figure 6 illustrates mass change of electrode with time for electrostatic coagulation of rubber. Figure 7 illustrates mass balance on total DRC recovered with nominal DRC for different DRC %.

Figure 8 illustrates comparative FTIR for Electro-coagulated rubber and Rubber Standard Sheet (RSS4). The FTIR spectra of Electro- Coagulated (EC) Rubber and Commercial Rubber Standard Sheet (RSS4) confirm that the quality of both the rubber is very much comparable. The quality of EC rubber is close to RSS4 rubber sheet of demand in the commercial market.

Detailed description of the invention:

The present invention uses static charge to destabilize stable or chemically stabilized colloidal system of rubber latex in a controlled fashion. The efficacy of this innovative technique in destabilizing chemically fortified rubber latex (but not limited to preserved field latex (PFL)) has been assessed at varying level of the applied potential, time, ionic strength and rubber content of the latex. The amount of rubber coagulated increases with the increase in applied potential. Increased applied potential generates higher number of counter-ions with respect to negatively charged rubber particles in chemically fortified rubber latex and results in production of higher amount of coagulated rubber. The amount of coagulated rubber also increases with the increase in time. The dry rubber content in latex (DRC) has a very high impact on the coagulation of rubber. As the DRC increases the availability of the rubber particles near the electrode increases which results in higher coagulation of rubber.

Electrical conductance of the system depends on the ionic strength. The ionic strength of the solution is varied by adding different concentration of salt. Increased ionic strength increases the electrical conductance in the system, leading to increased coagulation of rubber.

Cost analysis of the experimental process is conducted by calculating the cost of production of electro coagulated rubber comparing the same with the cost of production of chemically coagulated rubber. For chemical coagulation the calculated cost of production per kilogram of rubber is found out to be about Rs. 50 - 100. The cost of electro coagulated rubber is also found out to be Rs 56.00 per kilogram for electro-coagulation process with 70 % efficiency.

The present invention describes a method for developing a process of coagulation of raw state/ unstabilized OR fortified/stabilized rubber latex using electrostatic charge generated from renewable and non-renewable power source capable of generating a potential field between 0 - 50 V for application in industry, preferably useful for micro-small and medium scale sector/enterprises and remotely located household applications.

The present invention develops a process to destabilize colloidal system of rubber latex which is in raw state/ unstabilized/ unfortified OR fortified/stabilized by chemical agents/stabilizer/anticoagulants without addition of chemicals, using electrostatic charge.

The present invention can be used to produce rubber for rubber goods which is at par with the acceptable commercial quality of rubber.

The present invention describes a process of coagulation of rubber latex that is less chemical intensive and therefore more environmentally benign/eco-friendly, less hazardous and less pollution load with respect to the conventional chemical route.

The present invention further describes a process, which can be used to coagulate rubber directly on desired forms for various rubber goods in an eco-friendly approach.

The present invention also describes a process, where a colloidal system of rubber latex can be destabilized in a controlled fashion. The controlled coagulation of rubber is expected to be very useful in various latex processing processes, industrial applications and in manufacturing processes of different commercial rubber goods.

The present invention defines the control variables for coagulation of rubber latex and also claims of defining the governing relationship of the control variables with the extent of coagulation of rubber. The present inventions claims of establishing the relationship for applied potential, coulomb transport rate (current), time, ionic strength (salt concentration in latex) and rubber content of the latex with mass of coagulated rubber.

The present invention further describes to develop a process of coagulating of colloidal rubber from stabilized latex at comparable cost with respect to the conventional chemical route. The present invention recovers significant portion of rubber of quality equivalent to commercial rubber from stabilized colloidal latex with dry rubber content varying from less than 4% to greater than 24%.

The present invention aims to develop a process of coagulating colloidal rubber from stabilized latex that is controlled electrically in a set-up with no moving parts, thus requiring less maintenance. The following examples are given by the way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention.

Example 1

Two electrodes of effective cross sectional area of 0.003 m² were prepared from the galvanized iron (GI) sheet of 0.00131 m nominal thickness. The electrodes were connected using standard 8AWG insulated copper wire. The separation distance between electrodes was maintained constant at 0.015 m throughout the experimentation. Cathode and anode are connected with the negative and positive terminal of the DC power supply. The prepared experimental solution is stirred and the electrodes are then dipped in the solution. The applied potential was varied between 0- 32 V. The electric potential is applied for the current to pass through the experimental liquid for the required time (0-20 min) resulting in coagulation of rubber.

Example 2

The ions from passing current through rubber latex neutralize the charge of the rubber particle and hence destabilize the colloidal system initiate coagulation. The cathode remains as such, rubber doesn't get deposited on it, but the rubber particles get coagulated and deposited on the anode. The best effective condition for electro coagulation of rubber could be obtained with applied potential of 15V for 15 minutes for which no less 70% of the rubber was recovered from the chemically stabilized rubber latex (but not limited to PFL) with 17.5 % DRC. Increase in coagulation time increases the amount of coagulated rubber. Nonetheless, as the layer of deposited rubber increases beyond a threshold thickness for a specific applied potential the extent of coagulation is significantly reduced due to hindered the ion transport from the electrode surface through rubber layer

Example 3

Coagulated rubber is deposited on the wall of the anode. On the other hand the amount of rubber coagulated is directly dependent on the effective cross-sectional area. Since the rubber deposited on the wall of the anode, the shape of the rubber coagulated will be the shape of the anode. So any type of shape of coagulated rubber can be prepared depending on the requirement. Probably the process can be more effective if the rubber coagulated by electrocoagulation for a short interval of time is dipped into acidic solution for a specific time and the process is repeated until proper coagulation rubber thickness is obtained .

Advantages of the present invention:

1. The electro-coagulation technique for rubber recovery from latex requires simple equipment, involves easy operation, avoids uses of chemicals, is environmentally benign with less pollution load.

2. The electro-coagulation technique for rubber recovery from latex is capable of removing the smallest colloidal particles, because the applied electric field sets them in faster motion, thereby facilitate the coagulation and allow enhanced recovery of colloidal particle even from dilute rubber latex. 3. The electro-coagulation technique for rubber recovery from latex is controlled electrically does not involve any moving parts, thus requiring less maintenance.

4. The electro-coagulation technique for rubber recovery from latex can be conveniently used in rural areas where electricity is not available, since a solar panel attached to the unit may be sufficient to carry out the process.

5. The electro-coagulation technique for rubber recovery from latex allows easy control of the coagulation process through modulation of the process variables including (but not limited to) applied potential, coulomb transport rate (current), time, ionic strength (salt concentration in latex) and rubber content of the latex.

6. The electro-coagulation technique for rubber recovery from latex can be used to coagulate rubber directly on desired forms for various rubber goods in an eco-friendly approach

Claims

I claim:

1. A method of coagulation of rubber, under controlled parameters comprising the steps of destabilizing the colloidal rubber latex in an electrochemical cell using electrostatic charge for producing rubber or rubber goods having quality at par with the commercial rubber.

2. A method as claimed in claim 1, wherein the controlling parameters include but not limited to the applied potential, coulomb transfer rate (current), time, ionic strength of latex (salt concentration in latex) and dry rubber content of colloidal latex.

3. A method as claimed in claim 1, wherein a governing relationship of the controlling variables with the extent of coagulation of rubber being established

4. A method as claimed in claim 1, wherein the rubber latex used being is in raw state/ un-stabilized/ unfortified OR fortified/ stabilized by chemical agents/ stabilizer/ anticoagulants and is coagulated without addition of chemicals, using only electrostatic charge in a less hazardous and less polluting route (with respect to conventional chemical route).

5. A method as claimed in claim 1, wherein the electrostatic charge being applied by controlling electrical parameters with no moving parts, generated from renewable and non-renewable power source capable of generating a potential field between 0 - 50 V for application in industry, more particularly for micro-small and medium scale sector/enterprises, and remotely located household applications.

6. A method as claimed in claim 1, wherein the said method further comprising the steps of recovering at least up to 70% colloidal rubber from stabilized or un-stabilized latex in controlled condition, bypassing the conventional chemical route, in an economic way with cost that is comparable to the conventional chemical route.

7. A method as claimed in claim 2, wherein rubber the applied potential varying from 0 up to, but not limited to 30V, wherein the amount of coagulated rubber increasing with increase in applied potential.

8. A method as claimed in claim 2, wherein the time through which current passes through the experimental liquid, varying in the range of 0 minute up to, but not limited to 20 minutes, wherein the amount of coagulation increasing with increase in time.

9. A method as claimed in claim 4, wherein the dry rubber content, being preferably varying in the range of 1% to 25%, wherein coagulation of rubber increasing with increase in dry rubber content in latex.

10. A method as claimed in claim 1, wherein the said method being capable of being used to coagulate rubber directly on desired forms for manufacturing various rubber goods in an eco-friendly approach.