WO2012158015A1

WO2012158015A1 - Method of quantitative measurement of mechanical stability time (mst) of latex suspensions and the apparatus for use in the method

Info

Publication number: WO2012158015A1
Application number: PCT/MY2011/000050
Authority: WO
Inventors: Alias Bin OTHMAN; Mohamad Khairul Akmal Bin AMRAN; Mohd Nizam Bin MANSOR
Original assignee: Lembaga Getah Malaysia
Priority date: 2011-05-19
Filing date: 2011-05-19
Publication date: 2012-11-22
Also published as: GB201318212D0; WO2012158015A9; CN102893148B; GB2503619B; DE112011105263T5; GB2503619A; CN102893148A

Abstract

A method for the quantitative measurement of mechanical stability time (MST) of a latex suspension comprises the steps of providing a load force measuring apparatus for automatic quantitative measurement of MST of the suspension; agitating the suspension at sufficient speed so as to cause changes in the physical properties of the suspension; measuring and monitoring the changes in physical properties of the suspension by way of the load force values detected and transmitted to a control means; and automatically calculating the MST of the suspension by normal distribution analysis of the collected load force value data. An apparatus for use in the method comprises a vessel (20) for containing the suspension; an agitator (10), the agitator provided to be submerged in the suspension in use and capable of agitating the suspension at sufficient speed so as to cause changes in the physical properties of the suspension; a rotatable base (30) for holding the vessel, the vessel being removably coupled to said base; and a connector (50) operatively connecting the rotatable base to a sensor (60). The sensor is capable of detecting and transmitting the load force values resulting from agitation of the suspension to a control means. The control means automatically calculates the MST of the suspension by normal distribution analysis of the collected load force value data.

Description

METHOD OF QUANTITATIVE MEASUREMENT OF

MECHANICAL STABILITY TIME (MST) OF LATEX SUSPENSIONS

AND THE APPARATUS FOR USE IN THE METHOD

This invention relates to a method of measuring physical properties of latex suspensions.

More particularly, this invention is related to a method of quantitative measurement of the mechanical stability time (MST) of latex suspensions and the apparatus for use in the method.

DESCRIPTION OF THE PRIOR ART

Mechanical stability is defined as the ability of a colloidal suspension to withstand the colloidal destabilization effects of mechanical forces such as shearing and agitation. The mechanical stability of colloidal lattices is a property of great industrial importance.

For latex, its mechanical stability has implications for its pumping, transportation and processing in that the latex must have sufficient mechanical stability to withstand shearing forces that arise during handling and processing without suffering colloidal destabilization.

Similarly for paints, plasties and other colloidal suspensions, the mechanical stability of these suspensions has implications in its application method (e.g. spray dispersion for paints), flow ability, molding time (e.g. for plastics) etc.

Currently, the MST of colloidal suspensions cannot be assessed quantitatively. Only qualitative MST tests are available at the moment and there is an element of subjectivity in these prior tests. The standard tests for determination of MST of natural rubber latex are those prescribed in tests ISO 35 and ASTM D-1076. Both standards prescribe determination of MST by manual qualitative methods by using the palm-of-the-hand method. The ISO 35 standard provides for an alternative qualitative test by using the dispersibility-in-water method.

In the "palm-of-the-hand" method, a clean glass rod is dipped into a test bottle in order to remove a drop of latex. Each drop of latex is gently spread on the palm of the hand. This is repeated at intervals of 15 seconds. The MST or end point of the sample is determined by first appearance of flocculum. The MST for the latex sample is expressed as the number of seconds that lapsed from the start of the test to the end point.

In the "dispersibility-in-water" method, a pointed rod is used to pick up a small drop of latex in the test bottle. The drop of latex is then immediately dispersed in a water-containing petri dish. The latex droplet will either disperse or flocculate. If the drop of latex flocculates, the latex has reached its coagulated condition. The MST is expressed as the time lapsed from the start of the test to the first appearance of floccules.

As can be appreciated, both the above standard tests for qualitative measurement of MST of latex are highly manual and prone to human error. Although a trained laboratory technician may be able to replicate his results satisfactorily, the issue of reproducibility for both the above standard tests still remains and is of great concern.

Further, both the standard tests require sampling of the latex at 15-second intervals until MST end point is reached. Besides being laborious and time consuming, these tests results in exposure of the laboratory technician to hazardous chemical fumes of the preservatives typically used in latex suspensions e.g. ammonia in natural rubber latex. As mentioned above, MST is a physical property of great industrial and commercial importance in the processing and use of latex suspensions. Hence, there is a need to efficiently and accurately measure MST of such suspensions quantitatively.

This invention thus aims to alleviate some or all of the problems of the prior art.

SUMMARY OF THE INVENTION

In accordance with an aspect of the invention, there is provided a method for the quantitative measurement of mechanical stability time (MST) of a latex suspension.

The method comprises the steps of:

(i) providing a load force measuring apparatus for automatic quantitative measurement of MST of the suspension, the apparatus comprising an agitator, a sensor for detecting and transmitting load force values to a control means;

(ii) submerging the agitator in the suspension, and agitating the suspension with the agitator at sufficient speed so as to cause changes in the physical properties of the suspension;

(iii) measuring and monitoring the changes in physical properties of the suspension by way of the load force values detected and transmitted to the control means by the sensor; and

(iv) automatically calculating the MST of the suspension by normal distribution analysis of the collected load force value data.

In an embodiment, the agitation of step (ii) may be conducted at a speed of between about 12,000 rpm to about 16,000 rpm. The agitation of step (ii) may preferably be conducted at a speed of about 14,000 rpm.

In another embodiment, step (ii) may further comprise the control means maintaining the agitator at an optimal agitation speed to achieve change in the In a further embodiment, calculation of the MST of the suspension in step (iv) may be by normal distribution analysis at 95% confidence interval.

In a further embodiment, calculation of the MST of the suspension in step (iv) may be by normal distribution analysis at 68% confidence interval.

According to an embodiment, the latex suspension may comprise natural rubber latex.

The method of this invention may further comprise preparing the latex suspension by diluting a latex concentrate with a suitable diluent such as ammonia, prior to step (i). The diluted latex suspension prepared prior to step (i) may have a total solid content of about 55%.

The method may further comprise warming the diluted latex suspension to a temperature of about 36 to 37°C, prior to step (i). According to another embodiment, the latex suspension may comprise synthetic rubber.

In accordance with another aspect of the invention, an apparatus for automatic quantitative measurement of mechanical stability time (MST) of a latex suspension is provided.

The apparatus comprises a vessel for containing the suspension; an agitator, the agitator provided to be submerged in the suspension in use and capable of agitating the suspension at sufficient speed so as to cause changes in the physical properties of the suspension; a rotatable base for holding the vessel, the vessel being removably coupled to said base; and a connector operatively connecting the rotatable base to a sensor. The sensor is capable of detecting and transmitting the load force values resulting from agitation of the suspension to a control means. The In use, agitation of the suspension by the agitator causes displacement of the vessel, displacement of said vessel in turn causes rotation of said base to which said vessel is coupled, rotation of the base is detected by the sensor through the connector and transmitted to the control means which automatically calculates the MST of the suspension by normal distribution analysis of the collected load force value data.

In an embodiment, the vessel may comprise a flat-bottom container having a smooth inner surface. The vessel may be substantially cylindrical.

In another embodiment, the vessel may be provided with coupling lugs and the base may be provided with corresponding openings to receive the lugs so as to enable the vessel to be removably coupled with the base, in use.

In a further embodiment, the agitator may be capable of agitating the suspension at a speed of between about 12,000 rpm to about 16,000 rpm. The agitator may preferably be capable of agitating the suspension at a speed of about 14,000 rpm. In yet another embodiment, the agitator may comprise a shaft coupled to a power source at the proximal end and having an agitator disk at the distal end. The agitator shaft may have a tapering configuration from its proximal to its distal ends.

According to an embodiment, the apparatus may further comprise a holder attached at the bottom of the base by way of a shaft, the holder and base arranged concentrically about the shaft, and the holder housing a bearing arrangement so as to enable rotational movement of the base, in use.

The connector may be removably attached to the base shaft. According to a further embodiment, the connector may comprise an attachment portion for removable attachment to the base shaft, and an abutment portion engaged with the attachment portion and contactable with the sensor, in use. The In another embodiment, the sensor may comprise a force sensor. In another embodiment, the sensor may comprise a torque sensor.

In a further embodiment, the control means may comprise a hardware component and a software component. The control means may be operatively connected to the agitator and, depending on a preset speed setting, is capable of maintaining the agitator at an optimal agitation speed, in use.

In an embodiment, the latex suspension may comprise natural rubber latex.

In another embodiment, the latex suspension may comprise synthetic rubber.

It is an object of the invention to seek to mitigate the disadvantages of the prior art, and to provide an efficient and accurate method for measurement of MST of latex suspensions and the apparatus used in such a method.

Advantageously, the method and apparatus of this invention provides for an automated quantitative measurement of MST of latex suspensions that minimizes the need for manual input during the test i.e. occurrence of human error is correspondingly minimized and the results obtained is more accurate, consistent and reproducible.

Further, the method and apparatus of this invention also reduces the duration of the test and does away with the need to obtain samples of the latex suspensions at predetermined time intervals during the test (e.g. sampling at 15-second intervals for qualitative latex MST testing). This aids in preventing exposure of the laboratory technician to hazardous chemical fumes present in preservatives commonly used for such suspensions. Additionally, the apparatus of this invention also enables automatic maintenance of the optimal agitator speed throughout the duration of the test. This further aids in enhancing the accuracy of the test results.

BRIEF DESCRIPTION OF THE DRAWINGS This invention will now be further described by way of non-limitative examples, with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of the apparatus for automatic quantitative measurement of mechanical stability time ( ST) of a latex suspension according to an embodiment of this invention.

Figure 2 is a front view of the base, holder and connector of the apparatus of Figure 1. Figure 3 is a front view of an alternative configuration of the base, holder and connector of the apparatus of this invention.

Figure 4 are perspective views of the configuration of Figure 2. Figure 5 are perspective views of the configuration of Figure 3.

Figure 6 is a plan view of the base, holder and connector of Figure 2 with the abutment portion of the connector in contact with the sensor. Figure 7 is a diagrammatic representation of the transmittal of load force from the rotatable base to the sensor (control means) via the connector for the configuration of Figure 2. Figure 9 is a control graph for normal distribution analysis calculation of the MST of a latex suspension.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A method for the quantitative measurement of mechanical stability time (MST) of a latex suspension and the apparatus for use in the method are provided as follows.

Method for quantitative measurement of MST

A method for the quantitative measurement of mechanical stability time (MST) of a latex suspension according to the present invention, generally involves four main steps, namely, providing a load force measuring apparatus, agitating the suspension, measuring and monitoring the changes in physical properties of the suspension, and calculating the MST of the suspension.

A load force measuring apparatus for measurement of MST of a latex suspension according to a method of this invention is provided. The apparatus enables automatic quantitative determination of MST and mainly comprises an agitator 10, a sensor 60 and a control means. Further details of the load force measuring apparatus are provided in the following portions of this description.

Preparation of latex suspension test sample Preparation of a test sample of the latex suspension is dependent on the particular type of suspension being tested. Generally, methods of sample preparation for qualitative testing of such suspensions are prescribed in the ISO as well as ASTM standards. For example, as mentioned earlier, the standard tests for determination of MST of to about 55% total solid content and subsequently warmed to a temperature of between about 36°C to 37°C. The diluted and warmed latex sample is then preferably strained through a stainless steel sieve, prior to testing.

The standard tests for determination of MST of synthetic rubber are prescribed in ISO 2006 and ASTM D1417-90.

Agitating the suspension

The agitator 10 is provided to be submerged in the suspension in use, and is capable of agitating the suspension at sufficient speed so as to cause changes in the physical properties of the suspension e.g. flocculation. It is preferable that the agitator 10 is maintained at optimal agitation speed for achieving changes in the physical properties of the suspension. The optimal agitation speed is very much dependent on the suspension tested since interaction between particles differs from colloid to colloid e.g. van der Walls force, entropic force, steric force, electrostatic interaction etc.

When the method of this invention is used to quantitatively measure MST of natural rubber latex, it is preferred that the latex suspension is agitated at a speed of between about 12,000 rpm to about 16,000 rpm. It is particularly preferred that the latex suspension is agitated at a speed of 14,000 rpm.

Measuring and monitoring the changes in physical properties of the suspension

As the latex suspension is agitated, the agitator 10 will impart translational kinetic energy to the latex particles. This leads to physical deformation of the latex lattices ultimately resulting in flocculation. The load force within the agitated suspension increases as the particles flocculate.

The method of this invention advantageously allows for these changes in load force A sensor 60 is provided for detecting these changing (increasing) load force values and transmitting the same to a control means. The sensor 60 detects the load force values and converts the same into electrical signals for transmittance to the control means. Any type of load sensor (load cell) may be used in the method of this invention e.g. a force sensor or a torque sensor. It is preferred that a force sensor is used. Calculating the MST of the suspension

A control means for storing the load force value data collected by the sensor 60 and calculating the MST of the suspension is provided. The control means converts the electrical signal received from the sensor 60 into digital data that is stored.

At the conclusion of the test, the control means automatically analyzes the stored load force value data and calculates MST of the latex suspension by way of normal distribution analysis (graph plot of force (N) against time (s)). Generally, 68%, 95% and 99.7% of the test values in a normal distribution analysis lie within one, two or three standard deviations (σ), respectively, away from the mean. These values are shown in Figure 9.

Whether MST (end point) of the suspension is calculated by normal distribution analysis at 68%, 95% or 99.7% confidence interval (interpolation between time- force lines at respective confidence intervals) very much depends on user requirements.

For example, for natural rubber latex, analysis at 99.7% confidence interval is not relevant since the MST obtained exceeds that of MST obtained by prescribed standard manual methods. Theoretically, as is known in the art, coagulation of latex is expected to take place sooner than can be detected by sight. Hence, MST obtained for latex at 99.7% confidence interval is not reliable. Analysis at either 68% or 95% confidence interval would be more appropriate when obtaining MST (end point) of latex. For testing purposes, it is preferable that normal distribution analysis be done at 95% confidence interval to determine latex MST as such analysis will provide the most accurate MST result (MST 1 minute earlier than that obtained via manual methods) in comparison with analysis at 68%.

However, it may be preferable that analysis is done at 68% confidence interval to obtain latex MST for research purposes since additional technical information about the physical properties of the latex sample may be obtained e.g. earlier coagulation possible.

Apparatus for quantitative measurement of MST Figures 1 to 7 show an apparatus of this invention for use in the method of quantitative measurement of MST according to this invention.

The apparatus of this invention allows for automatic quantitative measurement of MST of a latex suspension and mainly comprises a vessel 20, an agitator 10, a rotatable base 30, a connector 50, a sensor 60 and a control means.

The test vessel 20 for containing the latex suspension to be tested is preferably a flat-bottom container having a smooth inner surface. Most preferably, the vessel 20 is substantially cylindrical.

Preferably, the vessel 20 is cylindrical with a diameter of about 57.8 mm (± 1 mm) and a height of 127 mm. The thickness of the vessel wall is preferably about 2.3 mm. In a preferred embodiment, the vessel 20 has a plurality of coupling lugs 21 equally distributed about the outer circumference of its bottom. Most preferably, a pair of coupling lugs 21 is provided. These lugs 21 enable the vessel to be removably of load force (arising from agitation of the suspension) to the sensor 60 and control means (through the rotatable base 30 and connector 50).

An agitator 10 is provided to be submerged in the suspension in use and comprises a shaft coupled to a power source (not shown) at its proximal end and provided with an agitator disk (not shown) at its distal end.

The agitator shaft is preferably of a tapering configuration toward its distal end (enhances the structural strength of the agitator 10). Most preferably, the shaft is of approximately 6.3 mm in diameter at its distal end.

The agitator disk comprises a polished stainless steel disk having a centrally disposed threaded stud for attachment to the proximal end of the agitator shaft. Most preferably, the disk is 20.83 ± 0.03 mm in diameter and 1.57 ± 0.05 mm in thickness.

The agitator 10 must be capable of agitating the suspension at sufficient speed so as to cause changes in the physical properties of the suspension. Preferably, a high- speed agitator capable of maintaining an agitation speed of between about 12,000 to 16,000 rpm for the duration of the test is used.

The configuration comprising the rotatable base 30, holder 40 and connector 50, is provided to be vertically movable in use so that it can be conveniently lowered and raised to the desired height in relation to the position of the agitator 10 i.e. to ensure that the agitator disk is submerged to the desired depth within the latex suspension for the duration of the test.

The rotatable base 30 comprises a holding portion 32 and a shaft 33 disposed perpendicular to the holding portion 32. The holding portion 32 of the base 30 may be in any suitable shape to receive the test vessel 20. Preferably, the base holding portion 32 is provided with a plurality of circumferential openings 31 about its walls. The holder 40 comprises a support portion 41 attachable at the bottom of the holding portion 32 of the rotatable base 30 and a housing portion 42 that encases a bearing arrangement 43 which enables rotational movement of the base 30, in use. The holder 40 and the base 30 are arranged concentrically about the shaft 33 of the base 30 i.e. the holder bearing arrangement 43 encases the base shaft 33. The bearing arrangement 43 aids in ensuring the concentric alignment of the holder 40 and the base 30. Together with the coupling lugs 21 (vessel 20) and corresponding openings 31 (base 30), the bearings 43 also enables the vessel 20 to be in concentric alignment with the holder 40 and the base 30. This aids in more efficient translation of load force resulting from agitation of the suspension to the sensor 60.

An exemplary configuration of the holder 40 is shown in Figures 2 to 7. It is envisioned that the holder 40 may have any configuration suitable to perform its function as above described.

The connector 50 is attached to the shaft 32 of the base 30 (holder 40). Preferably, the connector 50 is removably attachable adjacent the proximal end of the shaft 32. The connector 50 is disposed such that it is contactable with the sensor 60 when the apparatus is in use. It can be said that the connector 50 provides the physical connection between the rotational movement of the base 30 (via shaft 32) and the sensor 60, in use i.e. the connector 50 enables the resulting load force from agitation of the suspension (within the vessel 20 coupled to the base 30) to be transmitted to the sensor 60.

The connector 50 comprises an attachment portion 51 for removable attachment to the base shaft 32, and an abutment portion 52 engaged with the attachment portion 51. The abutment portion 52 is contactable with the sensor 60, in use. The connector 50 may be provided in one molded piece, as shown in Figures 2, 4, 6 and 7. The abutment portion 52 of the connector 50 shown in these Figures has a serpentine configuration. Alternatively, the attachment portion 51 and the abutment portion 52 of the connector 50 may be separately provided, as seen in Figures 3 and 5. In this embodiment, the attachment portion 51 has a ring-like shape with a threaded opening disposed along its horizontal axis and the abutment portion 52 comprises a threaded stub that is received through the threaded opening of the attachment ring. An end of the threaded stub is contactable with the sensor 60, in use. As with the holder 40, it is envisioned that the connector 50 may have any configuration suitable to perform its function.

The sensor 60 is provided to detect the changing load force values and transmit the same to the control means. The sensor 60 detects the load force values resulting from agitation of the suspension (conveyed via the base 30, holder 40, connector 50) and converts the same into electrical signals prior to transmitting it to the control means.

It is envisioned that any type of load sensor (load cell) be used in the apparatus of this invention e.g. a force sensor or a torque sensor. A force sensor is preferred over a torque sensor as it has been observed to have greater sensitivity i.e. more accurate results.

In a preferred embodiment, a force sensor capable having a maximum load force value of 10N is used. Alternatively, a torque sensor having a maximum load force value of lONm may be used.

The control means (Data Acquisition System (DAS)) comprises a hardware component (data acquisition hardware (DAQ)) and a software component. The DAQ hardware may be in the form of any DAQ hardware capable of functioning as an Analog to Digital Converter. The software component may be any software suitable to be used for the purposes of MST testing and is preferably provided with security features to avoid plagiarism. This security feature functions in a similar manner to typical software protection dongles.

The DAS converts the electrical signal received from the sensor 60 to a digital signal. The software picks up the digital signal via serial communication between the computer and the DAQ and translates the digital signal to a readable unit. The data is displayed in real time and also stored for further analysis.

Upon conclusion of the test (preset duration of time), the software automatically analyzes the data by normal distribution analysis and determines the MST (end point) of the latex suspension, as described above.

Advantageously, the DAS is operatively connected to the agitator 10. Depending on a preset speed setting, the DAS is capable of monitoring the speed of the agitator 10 and maintaining the agitator at an optimal agitation speed in use e.g. for a latex suspension sample, the agitator 10 can be maintained at 14,000 rpm throughout the duration of the test.

In use, agitation of the suspension in the test vessel 20 causes physical deformation of the latex lattices (translational kinetic energy imparted to the latex particles by agitator 10) and ultimately, flocculation. The load force within the agitated suspension increases as the particles flocculate. Agitation of the suspension also results in displacement of the vessel 20. As the vessel 20 is coupled to the base 30 in use, displacement of the vessel 20 causes rotation of the base 30 (holder 40). Rotational movement of the base 30 (holder 40) is transmitted via the connector 50 to the sensor 60 which emits an electrical signal read by the Data Acquisition System (DAS).

As the suspension flocculates, the load force value transmitted to the sensor 60 EXAMPLE

The following .Example illustrates the various aspects of the method of this invention. This Example does not limit the invention, the scope of which is set out in the appended claims.

Comparison of MST values obtained using the method of this invention versus the manual palm-of-the-hand method

A test to compare the MST values obtained by using the method of this invention and the manual palm-of-the-hand method was conducted by Lembaga Getah Malaysia in 2011. Two latex samples were tested, firstly a high ammonia (HA) sample, and secondly, a low ammonia (LATZ) sample.

The samples for both test methods (that of this invention as well as the manual method) were prepared according to the standards prescribed by ISO 35 and ASTM D-1076.

Approximately 80. Og of latex concentrate was diluted with ammonia solution to about 55% total solids and subsequently warmed to a temperature of about 36°C to 37°C. The diluted and warmed latex was immediately strained through a stainless steel sieve into the test vessel.

Agitation (by stirring) of the latex sample was conducted at a speed of 14,000 rpm until the MST end point was reached.

The MST end point can be obtained via norma! distribution analysis using Figure 9 (control graph) as described on the following page. Figure 9 is a control graph used for analyzing the change in the physical properties of the latex samples over time. The central line of the graph represents the average, the upper line represents the upper control limit (UCL) and the lower line represents the lower control limit (LCL). By comparing the data obtained in relation to these limits, conclusion as to whether variations obtained are consistent (in control) or unpredictable (out of control, affected by assignable causes of variation) may be drawn.

The formulae used for calculation of CL, UCL and LCL are as provided below:

Center line = Average

Upper control limit = Average + (lo standard deviation)

Lower control limit = Average - (1σ standard deviation)

Upper control limit = Average + (2o standard deviation)

Lower control limit = Average - (2σ standard deviation)

Upper control limit = Average + (3σ standard deviation)

Lower control limit = Average - (3σ standard deviation)

lo represents 68% confidence interval

2σ represents 95% confidence interval

3o represents 99.7% confidence interval According to the Western Electric rules for statistical process control, conclusions may be drawn that a particular process is out of control if either

1. One point plot is outside the 3σ control limit.

2. Two out of three consecutive point plots beyond the 2σ limit

3. Four out of five consecutive point plots at a distance of 1σ or beyond from the center line

4. Eight consecutive point plots on one side of the center line.

Table 3 shows the value for standard

deviation, average for center line, upper control limit and lower control limit of the control graph of Figure 9.

With reference to the control graph of Figure 9, it can be concluded that the process is "out of control" at the point beginning 1190s because there are 2 out of 3 consecutive point plots at a distance of 2σ from the center line.

The MST (end point) obtained by the palm-of-the-hand method is 1209s.

The test process is repeated five times to obtain correlation variance. The test results are provided in Table 1 and Table 2 on the following page.

Table 1 shows the results of MST determination of a sample of high ammonia latex (preserved with 0.7% ammonia).

Table 2 shows the results of MST determination of a sample of low ammonia (LATZ) latex (preserved with 0.2% ammonia).

As will be readily apparent to those skilled in the art, the present invention may easily be produced in other specific forms without departing from its scope or essential characteristics. The present embodiments are, therefore, to be considered as merely illustrative and not restrictive, the scope of the invention being indicated by the claim rather than the foregoing description, and all changes therefore are intended to be embraced therein.

Claims

A method for the quantitative measurement of mechanical stability time (MST) of a latex suspension, said method comprising the steps of:

(i) providing a load force measuring apparatus for automatic quantitative measurement of MST of the suspension, said apparatus comprising an agitator (10), a sensor (50) for detecting and transmitting load force values to a control means;

(ii) submerging said agitator (10) in the suspension, and agitating the suspension with said agitator at sufficient speed so as to cause changes in the physical properties of the suspension;

(iii) measuring and monitoring the changes in physical properties of the suspension by way of the load force values detected and transmitted to said control means by said sensor (50); and

The method as claimed in claim 1 wherein the agitation of step (ii) is conducted at a speed of between about 12,000 rpm to about 16,000 rpm.

The method as claimed in claim 2 wherein the agitation of step (ii) is conducted at a speed of about 14,000 rpm.

The method as claimed in any one of the preceding claims wherein step (ii) further comprising the control means maintaining the agitator (10) at an optimal agitation speed to achieve change in the physical properties of the suspension.

The method as claimed in any one of the preceding claims wherein calculation of the MST of the suspension in step (iv) is by normal distribution analysis at 95% confidence interval. The method as claimed in any one of claims 1 to 4 wherein calculation of the MST of the suspension in step (iv) is by normal distribution analysis at 68% confidence interval.

The method as claimed in any one of the preceding claims wherein the suspension comprises natural rubber latex.

The method as claimed in claim 7 further comprising preparing the latex suspension by diluting a latex concentrate with a suitable diluent such as ammonia, prior to step (i).

The method as claimed in claim 8 wherein the diluted latex suspension prepared prior to step (i) has a total solid content of about 55%.

The method as claimed in claim 8 or claim 9 further comprising warming the diluted latex suspension to a temperature of about 36 to 37°C, prior to step (<)^■

The method as claimed in any one of claims 1 to 6 wherein the suspension comprises synthetic rubber.

An apparatus for automatic quantitative measurement of mechanical stability time (MST) of a latex suspension, said apparatus comprising:

a vessel (20) for containing the suspension;

an agitator (10), said agitator provided to be submerged in the suspension in use and capable of agitating the suspension at sufficient speed so as to cause changes in the physical properties of the suspension;

a rotatable base (30) for holding said vessel (20), the vessel being removably coupled to said base; and

a connector (50) operatively connecting said rotatable base (30) to a sensor (60); said control means capable of calculating the MST of the suspension;

whereby, in use, agitation of the suspension by said agitator (10) causes displacement of said vessel (20), displacement of said vessel in turn causes rotation of said base (30) to which said vessel is coupled, rotation of said base is detected by said sensor (60) through said connector (50) and transmitted to said control means which automatically calculates the MST of the suspension by normal distribution analysis of the collected load force value data.

The apparatus as claimed in claim 12 wherein said vessel (20) comprises a flat-bottom container having a smooth inner surface.

The apparatus as claimed in claim 12 or claim 13 wherein said vessel (20) is substantially cylindrical.

The apparatus as claimed in any one of claims 12 to 14 wherein said vessel (20) is provided with coupling lugs (21) and said base (30) is provided with corresponding openings (31) to receive said lugs so as to enable said vessel to be removably coupled with said base, in use.

The apparatus as claimed in any one of claims 12 to 15 wherein said agitator (10) is capable of agitating the suspension at a speed of between about 12,000 rpm to about 16,000 rpm.

The apparatus as claimed in claim 16 wherein said agitator (10) is capable of agitating the suspension at a speed of about 14,000 rpm.

18. The apparatus as claimed in any one of claims 12 to 17 wherein said agitator (10) comprises a shaft coupled to a power source at the proximal end and having an agitator disk at the distal end.

20. The apparatus as claimed in any one of claims 12 to 19 further comprising a holder (40) attached at the bottom of said base (30) by way of a shaft (33), said holder and base arranged concentrically about said shaft, and said holder housing a bearing arrangement (43) so as to enable rotational movement of said base, in use.

21. The apparatus as claimed in claim 20 wherein said connector (50) is removably attached to said base shaft (33).

22. The apparatus as claimed in any one of claims 12 to 21 wherein said connector (50) comprises an attachment portion (51) for removable attachment to said base shaft (33), and an abutment portion (52) engaged with said attachment portion and contactable with said sensor (60), in use.

23. The apparatus as claimed in claim 22 wherein said connector (50) is provided in one molded piece. 24. The apparatus as claimed in claim 22 or claim 23 wherein said abutment portion (52) has a serpentine configuration.

25. The apparatus as claimed in any one of claims 12 to 24 wherein said sensor (60) comprises a force sensor.

26. The apparatus as claimed in any one of claims 12 to 24 wherein said sensor (60) comprises a torque sensor.

27. The apparatus as claimed in any one of claims 12 to 26 wherein said control means comprises a hardware component and a software component.

28. The apparatus as claimed in claim 27 wherein said control means is operatively connected to said agitator (10) and, depending on a preset speed The apparatus as claimed in any one of claims 12 to 28 wherein the suspension comprises natural rubber latex.

The apparatus as claimed in any one of claims 12 to 28 wherein the suspension comprises synthetic rubber.