Abstract: The determination of the properties of polymer solution and the determination of polymer molecular weight by viscosity method.
FIRST. The purpose of the experiment
1, determining the relative molecular weight of polyacrylamide;
2, master the use of Ubbelohde viscometer polymer molecular weight determination of the basic principles
SECOND. The experimental principle
The molecular weight is one of the basic parameters that characterize the properties of the compound. However, the molecular weight of the polymer is different and varies widely, usually between 103～107. Therefore, the molecular weight of the polymer is usually the average molecular weight. There are many methods for determining the high molecular weight. For the linear polymers, the range of the methods is shown in Table 3.1.
Table 3.1 Determination of high molecular weight response analysis method
Analysis method
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High molecular weight(Mr)
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End-based analysis
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<3×104
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Boiling point elevation, freezing point depression, isothermal distillation
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<3×104
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Osmotic pressure
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104～106
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Light scattering
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104～107
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Ultra - centrifugal sedimentation and diffusion
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104～107
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Viscosity method
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104～107
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The viscosity method is simple, easy to operate, has a very good experimental accuracy, but the viscosity method is not the absolute method of measuring the molecular weight, because the method used in the intrinsic viscosity and molecular weight empirical equation is to use other methods to determine. High Different materials, different solvents, molecular weight range is different, we must use a different empirical formula.
The viscosity of the polymer in the dilute solution mainly reflects the presence of internal friction in the flow of the liquid. The viscosity η of the polymer solution represents the comprehensive performance of the friction between the solvent molecule and the solvent molecule, between the polymer and the polymer, and between the polymer and the solvent molecule, which is generally much larger than the pure solvent viscosity η0 The The physical meaning of the pure solvent viscosity η0 is the viscosity exhibited by the internal friction between the solvent molecule and the solvent molecule. Relative to the pure solvent, the solution viscosity increase in the fraction, known as the increase in viscosity ηsp, that is,
1)
Where η r is called relative viscosity and its physical meaning is the ratio of solution viscosity to pure solvent viscosity. Ηr is also the behavior of the entire solution, ηsp means that the internal friction between the solvent molecules has been subtracted. For polymer solutions, the increasing viscosity ηsp tends to increase with the increase of the concentration C of the solution. For ease of comparison, the viscosity increase per unit density, ηsp / C, is referred to as the reduced viscosity.
In order to further eliminate the internal friction effect between the polymer molecules, it is necessary to dilute the solution concentration infinitely so that each polymer molecule is far away from each other and its mutual interference is negligible. At this time the solution shows the viscosity behavior of the polymer molecules and solvent molecules can reflect the internal friction between. Thus, theoretically defined ultimate viscosity is called the intrinsic viscosity, denoted by [η].
In the case of infinite dilution, the intrinsic viscosity [η] can be expressed by the following expression
(2)
Therefore, we have [η] there are two ways: one is ηSP / C on the C mapping, extrapolated to C → 0 intercept value; the other is lnηr / C on the C mapping, but also outside Push to the intercept value of C → 0, as shown in Figure 3.1, the two lines should be combined, which can also check the reliability of the experiment. In general, the expression of the two straight lines is in the following form:
(3)
Figure 3.1 extrapolation method [η]
If the molecular weight of the polymer molecules is larger, the greater the contact surface between the solvent and the solvent, the greater the friction, and the greater the intrinsic viscosity. The empirical relationship between the intrinsic viscosity [h] and the molecular weight is:
(4)
Where M is the relative average molecular weight; K is the proportionality constant; and α is the empirical parameter related to the molecular shape. K and α values and temperature, polymer, solvent properties, but also the size of the molecular weight. K value is affected by the temperature more obvious, and α value depends mainly on the polymer group at a certain temperature, the degree of relaxation in a solvent, its value between 0.5 to 1. The values of K and α can be determined by other absolute methods, such as osmotic pressure, light scattering, etc. [η] can Set be determined from the viscosity method.
Determination of viscosity methods are capillary method, drum method and drop ball method. In the determination of the intrinsic viscosity of polymer molecules, the capillary out of the viscosity of the method is most convenient. If the liquid in the capillary viscometer, due to gravity outflow, can be calculated by formula (5) viscosity.
(5)
Where η is the viscosity of the liquid; ρ is the density of the liquid; L is the length of the capillary; r is the radius of the capillary; t is the elapsed time; h is the average liquid column height flowing through the capillary liquid; V is the flow through the capillary Of the liquid volume; m for the capillary end of the correction parameters (usually r / L "1, you can take m = 1).
For a specified viscometer, (5) can be written as follows
(6)
Where, B <1, when the outflow of time t in about 2min (greater than 100s), the item (also known as kinetic correction items) can be omitted. (C & lt; 1 x 10-2 g cm-3), the density of the solution and the density of the solvent are approximately equal, so that ηr can be written as:
(7)
Where t is the elution time of the solution and t0 is the elution time of the pure solvent. Therefore, ηr is obtained from Equation 7 by the elution time of the solvent and the solution in the capillary, and [η] is obtained from Fig.
THIRD. Equipment and drugs
instrument:
1 set of thermostat
Uber Luther viscometer 1 Set
Pipette (10mL) 2 Set
Pipette (5mL) 1 Set
Stopwatch 1 Set
Wash ear ball 1 Set
Capacity bottle (50mL) 1
Cone flask (100mL) 2
Beaker (50mL) 1
Screw clip 1 Set
Rubber tube (about 5cm long) 2 root
drug:
Polyacrylamide analysis was formulated in a pure (0.03-0.06 g) / 100 ml solution
NaCl solution was prepared (1 mol / L and 2 mol / L) solution
FOURTH. the experimental steps
The experiment with the Uberlouer viscometer, also known as gas bearing hanging cylinder type viscometer. Its greatest advantage is that it can be diluted in the viscometer to save a lot of operating procedures, its structure shown in Figure 3.2.
(1) first wash the viscometer with a wash, and then tap water, distilled water were washed several times, each time should pay attention to repeatedly wash the capillary part of the wash after the dry spare.
(2) adjust the temperature of the bath to (30.0 ± 0.1) ℃, in the viscometer B and C tube are put on the rubber tube, and then put it vertically into the thermostat, so that the water completely immersed G ball.
(3) (3) Determination of solution elution time
10 mL of the known concentration of the polyacrylamide solution and 10 mL of the NaCl solution (2 mol / L) were pipetted into the viscometer from the tube A, and the solution was mixed with the rinse ball at the C tube to mix the solution and the concentration For the C1, constant temperature 10min, for determination. The measurement method is as follows:
The C tube with a clip clamped so that it is not ventilated, in the B tube with the ear ball solution from the F ball by the D ball, capillary, E ball to the middle of the ball G, the solution to the clip, so C tube through the atmosphere, The solution is back into the F ball, so that the liquid above the capillary floating. The liquid drops above the capillary, when the liquid flow through the a scale, immediately press the stop table to start taking time, when the liquid level dropped to b scale, and then press the table, measured scale a, b between the liquid flow through the capillary Time required. Repeat this operation at least three times, the difference between them is not greater than 0.3s, take the average of three times t1.
Then, the solution was diluted with 5 mL, 5 mL, 10 mL, 15 mL NaCl solution (1 mol / L), and the solution concentration was C2, C3, C4 and C5 respectively. Capillary time t2, t3, t4, t5. It should be noted that each time after adding NaCl solution, to be fully mixed evenly, and pumping viscometer E ball and G ball, so that the concentration of the solution inside the viscose equal.
(4) Determination of solvent elution time
Wash the viscometer with distilled water, especially the capillary section of the viscometer. Washed with NaCl 1 to 2 times, and then about 10 mL of 1 mol / L NaCl solution was added from tube A. The elution time of the solvent was measured by the same method.
After the experiment, the viscometer must be washed with distilled water.
FIFTH. Data processing
(1) The measured experimental data and calculation results are entered in the following table.
The original solution concentration C0 (g · cm-3) constant temperature ℃
C(g·cm-3)
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t1/s
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t2/s
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t3/s
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t平均/s
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ηr
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lnηr
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ηSP
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ηSP/C
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lnηr/C
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C1
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C2
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C3
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C4
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C5
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(2) as ηSP / C-C and lnηr / C-C of FIG, and extrapolated to intercept determined by the C → 0 [η].
(3) Substituting [η] into equation (4) to calculate the relative molecular weight of polyacrylamide.
It is known that the polyacrylamide is related to the aqueous solution of 1 mol / L NaCl at 30 ° C
K = 3.75 x 10-2 dm3 · kg-1, a = 0.66
SIXTH.Note
(1) The viscometer must be clean and the floc can not be moved into the viscometer if it is in the polymer solution.
(2) the dilution of this solution is carried out directly in the viscometer, so every time you add a solvent to dilute must be mixed evenly, and pumping E ball and G ball.
(3) the temperature of the incubator during the experiment to be constant, the solution can be measured after each dilution temperature.
(4) Viscometer to be placed vertically. Do not vibrate viscometer during the experiment.
SEVENTH, polyacrylamide profile
Polyacrylamide (Polyacryamide, referred to as PAM). Is the acrylamide (acrylamide, referred to as AM, the formula CH2 = CHCONH2) and its derivatives homopolymers and copolymers collectively. Industrial polymers containing more than 50% of the AM monomer are known as polyacrylamide. Polyacrylamide (PAM) is a linear water-soluble polymer, water-soluble polymer compounds is one of the most widely used varieties. PAM can be used as effective flocculant, thickener, paper enhancer and liquid drag reducing agent, widely used in water treatment, paper, oil, coal, mining, geology, textile, construction and other industrial sectors. Low molecular weight polyacrylamide as a dispersant; medium molecular weight polyacrylamide as a paper reinforcing agent.
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