DE2612253B2 - Vulcanometer for determining the course of vulcanization of rubber and its mixtures - Google Patents

Description

Recording of the crosslinking isotherm y = f (t) \ determination of y ₀ and joo

Determination of corresponding value pairs:

yuh; y ₂ , t ₂ ; ymt ";

Formation of value pairs:

The application of
'8 "Γ

versus time t gives approximately that in FIG. 3 curves shown.
For η = 1, straight lines with a slope are obtained

25th

The invention relates to a Vulkameter for determining the course of vulcanization of rubber and its mixtures for registering and graphing the crosslinking isotherms and one with the torque transducer electrically connected to the torque measuring amplifier and a downstream of this electronic peak storage device and one connected to the latter electronic recorder.

The reaction kinetic evaluation of the crosslinking isotherms measured with such a Vulkameter and graphically represented in the form of a so-called envelope curve according to DIN 53 529, Sheets 1 and 2, is used to determine the rate constant "k", the order "n" and the activation energy "£ _a ".

The theoretical bases for this are as follows: If the deflection "7" (curve Y in Fig. 2) of the vulcanized parameter is proportional to the shear modulus "G" on the sample and if there is also a linear relationship (as demonstrated below) between " G «and the network density, then the law of time can be written in its general form as follows:

dy / dt =

- y) n

(1)

50

The crosslinking isotherm of the 1st order results in general from:

y =

(yoo-yo) 0 -e ~ * «- '<»), (2)

55

wherein:

60

yo = basic deflection for uncrosslinked samples, y ₀₀ = final deflection at t = 00,
ti = induction time (from inserting the sample to the start of the crosslinking reaction).

Two methods are known for evaluating such isotherms. First, the conventional method: this classic evaluation method (1) to determine the order "n" and the speed-In 10 "

According to Arrhenius, the activation energy F _a can be determined from the temperature dependence of Ar (DIN 53 529 Part 2, Vulkametrie, Chapter 33.8. Determination of the activation energy A ...):

k = k ₀₀ e -

RT '

In the event that ηφ \ one obtains curved curves as can be seen in FIG. According to DIN 53 529 and "Kautschuk und Gummi, Kunststoffe, 18.1965" the order can be determined by a trial and error procedure, in that if η is greater than 1, a rectification according to the 2nd order is attempted. This is done according to

-l \

JOo-W

η - 1 (4)

the left side of this expression is plotted against t. If straight lines result, then n = 2 and A: can be taken from the slope. In the case of concave curvature, η is less than 2, and a rectification with 1 less than η less than 2, i.e. with π = 1.5, should be attempted.

For this very cumbersome evaluation method, the true final value yoo must always be known in order to be able to form the differences between yoo-y and yoo-yo. An error in the determination of yoo leads to incorrect values of k and n in this measuring method, even if the increase in crosslinking density was correctly represented at the beginning of the curve.

Such systematic errors in kinetic measurements with the Vulkameter have been investigated and thoroughly analyzed (rubber and rubber, plastics, 23,1970,406).

The second known method is the difference method. In the event that the true final value yoo of a crosslinking reaction of the first order is not accessible (reversion, thermal postcrosslinking, measurement times that are too long, etc.), a method for the evaluation mentioned was taken up (Kautschuk und Gummi, Kunststoffe, 23, 1970, 609; Guggenheim, Prue:

Physicochemical Calculations, Amsterdam 1955, 542). With this "difference method" the differences between equidistant measured values y ( _{t +} A,) - y ( _t ß '- * ° ^as ^ ) are formed from the crosslinking isotherm y = f (t) and plotted logarithmically as a function of time, as shown explicitly could result from this plot for / 7 = 1 straight line of the slope

Ic
j ^ -jQ (rubber and rubber, plastics, 24, 1971,

10). ,O

Unfortunately, this evaluation method, too, requires a relatively large number of pairs of values for sufficient accuracy requires, so time-consuming that it has not found its way into industrial practice.

The invention is based on the object of having a Vulkameter of the type mentioned at the beginning to create simple means by which instead of the known manual reaction kinetic evaluation, now a direct, d. H. an "on-line" registration of the previously discussed interested parties Parameter is enabled.

According to the invention this is achieved in that the peak value storage device with a per se known electronic differentiating device and this with an electronic one known per se Logarithmizing device are connected, the differentiating device and the log device also electronically connected to the recorder and all Signals can be processed by means of known, correspondingly interposed electronic components are.

The function and advantages of the Vulkameter designed according to the invention and working with it are described in more detail below with reference to the drawing:

With the in F i g. 1, the combination of known electronic components shown for the first time has made it possible for the first time to take the parameters or functions determined during the test of the vulcanization behavior directly from the recorder diagram, ie from the three recorded curves. These recorded three curves already represent the results of the electronically performed arithmetic operations or the results of the electronic processing and evaluation of the known recorded networking isotherm y = f (t) .

Simultaneously with the torque measurement and the recording of the crosslinking isotherms y = f (t) , the temporal course of the crosslinking speed y "= f (t) and the logarithmic crosslinking isotherm log X = / (^ are also recorded on the recorder the rate constant »it«, the order »/ 7« and the activation energy »£""can be read off or determined immediately (see Fig. 2 \

The above-mentioned problem could possibly also be solved by digitizing the y - f (t) curve and storing the values in a downstream computer; however, this would mean a great deal of expenditure on electronic components.

The Vulkameter designed according to the invention, however, makes it possible without the determination of yoo as well as without Memory and calculator to solve the above problem.

The decisive step here is the differentiation of the y = f (t) curve, i.e. the following transformation:

This expression tends towards 0 for larger values of t , but otherwise contains the same information about k and t as equation 2. This expression is then logarithmized:

In / = In (yoo-yo) + In A - fc (/ - i, ·) (6)

from it

Ig y ' = const. -

In 10

t.

A recording of Ig y ' as a function of t thus again yields straight lines of the slope

In IO '

Both operations, differentiation and logarithmization, are carried out electronically simultaneously with the recording of the crosslinking isotherm y = f (t). The following, shown in FIG. Register 2 curves shown:

f (t) = crosslinking isotherm.
f (t) = cross-linking speed as a function of time.
f (t) - logarithmic crosslinking isother

me.

The Vulkameter designed according to the invention also has the following advantages: for crosslinking processes of the first order, the rate constant k can be taken directly from the \ gy '= f (t) diagram without any further plotting or conversion. For this purpose, the apparatus only needs to be calibrated once. The calibration can be dispensed with when determining Ea. As usual, it is sufficient to plot the ratio of the slopes proportional to the ^ values according to Arrhenius.

The evaluation of crosslinking processes with ηψ 1 has so far been quite difficult, since η had to be determined by repeated, step-by-step rectification attempts (rubber and rubber, plastics, 18,11) 65,138).

With the Vulkameter designed according to the invention, however, η and thus k for πφ \ can be determined very easily, η is defined by equation 1; logarithmized it results:

Ig / = Ig fc + n \ g (y _oo -y).

- dy, y = - ^ - = (yoo- yo)

(5)

Deceptive can thus corresponding values of Y '(Yoo-y) doppellogarithmisch against each other, we obtain a straight line n of the pitch. With a known η then the Vernetzungsisothermen for the determination of k, easy to rectify Equation 4 (see FIG. F ig. 3).

Practical use of the Vulkameter designed according to the invention: In the characterization of Accelerator systems have so far served as an expression of the

Type 7 = -. τ is the reciprocal of the for one

Conversion of 5-90% of the final value y <x> required time as a measure of the crosslinking speed.

However, the volcanic meter designed according to the invention now makes it possible, instead of this mean value «; -

to directly register the exact temporal course of the crosslinking rate during the entire crosslinking reaction. This enables the optimization of accelerator systems, e.g. B. finding the fastest combination is made much easier. The time course of the crosslinking speed y '= f (t), which is registered here “on-line”, is characteristic of every mixture.

Especially in the area of the increase in the crosslinking isotherm, the curve y '= f (t) shows small changes in the crosslinking system much more sensitively than the y = f (t) curve itself Mixtures are a particularly valuable addition to the usual volcanic curve y = f (t).

For this purpose 2 sheets of drawings

Claims (1)

Claim: Vulcanometer for determining the course of vulcanization of rubber and its mixtures for Registration and graphical representation of the crosslinking isotherms with one with the torque transducer electrically connected torque measuring amplifier and a downstream one electronic peak storage device and one with the latter connected electronic recorder, characterized in that the peak value storage device with an electronic differentiating device known per se and this with an electronic logarithmizing device known per se are connected, the differentiating device and the logarithmic device also electronically connected to the recorder and all signals by means of known, accordingly interconnected electronic components can be processed. contant »λ« has already been described in detail (Kautschuk und Gummi, Kunststoffe, 18, 1965, 138). It consists of the following procedural steps: