Study on Viscosity Test Method of High Viscosity Hydroxypropyl Methyl Cellulose

Abstract: Using the domestic NDJ-1 rotational viscometer and the American Brooktield (LVDV-I+) viscometer, the viscosity test method of hydroxypropyl methylcellulose with a viscosity greater than 105mPa·s was studied, and the comparative viscosity test was carried out. The results show that for HPMC with 2% K solution viscosity less than 105mPa·s, the 1#, 2#, 3# and bell rotors of the NDJ-1 rotational viscometer correspond to the 61#, 62#, 63# of the Brookfield viscometer respectively , 64# rotor. The test results are consistent when the rotational speed is the same. For HPMC with a viscosity of 2% aqueous solution greater than 105 mPa s, it is necessary to obtain the viscosity of 2% aqueous solution through the conversion coefficient of 1% aqueous solution viscosity when testing with NDJ-1 rotational viscometer. (LVDV-I+) viscometer test, due to the wide test range, can get more accurate viscosity value, more suitable for practical operation and application.

Key words:hydroxypropyl methylcellulose; Brookfield viscometer; viscosity

Hydroxypropyl methylcellulose (HPMC) is a kind of non-ionic cellulose mixed ether with excellent performance. It has good dispersion, emulsification, thickening, bonding, water retention and gel retention properties. It can also be dissolved in ethanol and acetone below 70%. HPMC can be widely used as film coating, slow-release agent and binder of pharmaceutical preparations, and can also be widely used in petrochemical, building materials, ceramics, textiles, food, daily chemical, In industrial fields such as synthetic resin, medicine, paint and electronics.

The main chemical reaction for preparing HPMC is divided into two steps: the reaction of cellulose with aqueous alkali solution to form alkali cellulose; the etherification reaction of alkali cellulose with two etherifying agents, methyl chloride and propylene oxide. In the process of HPMC production, due to the different origins of raw cotton, each refined cotton manufacturer has different treatment methods for cotton linters, and each cellulose ether enterprise uses processes such as alkalization, etherification, neutralization and washing in the production of HPMC. There are also differences in conditions, resulting in differences in the properties of the HPMC produced and variations in the viscosity ratio coefficient between 2% and 1% aqueous solutions.

At present, domestic common NDJ. Type 1 rotational viscometer measures the viscosity of HPMC aqueous solution at 20°C. NDJ-1 rotational viscometer has 4 kinds of rotors (1#, 2#, 3#, 4#) and 4 kinds of rotation speeds (6, 12, 30, 60 r/min), the measuring range is 10~1X 10 mPa·s. The rotational viscometer produced by American Brookfield Company is the world standard for viscosity measurement. The LVDV-I+ viscometer adopts liquid crystal display, and the display information includes viscosity, torque, rotor and speed. There are 4 types of rotors (61#, 62#, 63#, 64#) and 18 speeds (0.3, 0.6, 1.5, 3. 6, 12, 30, 60, 0.5, 1.0, 2.0, 2.5, 4.0, 5.0, 10, 20, 50, 100 t/min), measuring range 10~2X 10 mPa·s. In addition, the Shanghai Institute of Geosciences Instruments newly developed the NDJ-8S digital rotational viscometer in 2007, with 4 types of rotors (1#, 2#, 3#, 4#) And 8 speeds (0.3, 0.6, 1.5, 3, 6, 12, 30, 60 r/min), the measurement range is 10~2X 106 mPa·s, the domestic awareness of this model is still low.

Since there is no national standard for the testing of various indicators of HPMC in China, the NDJ-1 rotational viscometer is commonly used to test the viscosity of HPMC aqueous solution, and its range is only 1X 10% mPa s. HPMC can't measure its precise viscosity value, while Brookfield viscometer is commonly used in the world to test the viscosity of aqueous solution of cellulose ether products. In order to make domestic HPMC products better in line with international standards, to increase the export volume of domestic HPMC products, and to provide reference for the determination of viscosity in the revision of HPMC national standards in the future, this paper uses NDJ-1 rotational viscometer and LVDV-I+ Brookfield viscosity meter Taking "KIMA" brand HPMC as the experimental object, a viscosity comparison experiment was carried out to investigate the difference of the viscosity test of HPMC under the two viscometers, and it was proposed to use the Brookfield viscometer test and the NDJ-1 type rotational viscometer to estimate the HPMC viscosity. A method with a viscosity greater than 10 mPa·s.

1. Experiment

1.1 Main equipment and instruments

NDJ-1 rotational viscometer, Shanghai Precision Scientific Instrument Co., Ltd.

LVDV-I+ Brookfield Viscometer, Brookfield Company, USA.

Constant temperature water bath, temperature 20±0.2°C; thermometer, temperature range 0-50°C, accuracy 0.1°C.

1.2 Materials and reagents

"KIMA'' brand HPMC; deionized or distilled water.

1.3 Test steps

Weigh 2.4 g (prepared test solution with a mass fraction of 1%) or 4.8 g (prepared with a mass fraction of 2% test solution) sample dried at 105±2°C for 2 h, accurate to 1 mg. Add hot water at 80---90°C to the beaker, swell for 5-10 minutes, then put it into cold water (or ice water) at 0---5°C, stir well to make it dissolve, add water to dilute to a mass fraction of 1 % or 2% solution. Put the beaker in a constant temperature water bath at 20+0.2°C for 1 hour, take it out, stir it by hand for 10 s, measure its viscosity with a NDJ-1 rotary viscometer and a LVDV-I+ Brookfield viscometer, and take the reading after the rotor rotates for 1 min.

1.4 Calculation of results

2. Results and Analysis

2.1 Comparison of HPMC viscosity test between NDJ-1 type rotational viscometer and LVDV-I+ type Brookfield viscometer

Select a 2% aqueous solution with a viscosity less than 105 mPa. 10 batches of low-, medium-, and high-viscosity HPMC samples were tested at 20°C with NDJ-1 rotational viscometer (installed with protective frame) and LVDV-I+ Brookfield viscometer (installed with protective frame) respectively. aqueous solution viscosity.

From the experimental data, it can be known that for HPMC with a 2% aqueous solution viscosity less than 10 mPa s, the 1#, 2#, 3#, and 4# rotors of the NDJ-1 rotational viscometer correspond to the LVDV-I+ Brookfield viscometer respectively. The 61#, 62#, 63#, 64# rotors have the same test results when the speed is the same, so when the viscosity of HPMC 2% aqueous solution is less than 105 mPa s, the NDJ-1 rotary viscometer can completely replace the LVDV -Brookfield Viscometer Type I+.

2.2 The method of measuring the viscosity of HPMC greater than 10 mPa s by NDJ-1 rotational viscometer

The maximum measuring range of the NDJ-1 rotational viscometer is 1X 100000 mPa s, and the precise viscosity of HPMC products with a viscosity greater than 100000 mPa s cannot be measured, and can only be roughly known through coefficient conversion. Firstly, 3~5 batches of HPMC products with 2% viscosity less than 100000 mPa s were extracted, and the viscosity ratio coefficient between 2% and 1% aqueous solution was calculated within a certain time interval (such as 1 month), and then the average value was calculated as For the viscosity coefficient during this period, multiply this coefficient by the viscosity of HPMC 1% aqueous solution greater than 100000mPa·s to obtain the viscosity of 2% aqueous solution.

The theoretical basis for adopting this method is that within a certain period of time, the refined cotton used by each cellulose ether enterprise to produce HPMC is basically the same manufacturer, the cotton origin is the same, and the production process of each enterprise is stable within a certain period of time, so the production The viscosity ratio coefficient between 2% and 1% aqueous solutions of HPMC products does not change much, so the viscosity of HPMC 2% aqueous solutions greater than 100000 mPa·s can be roughly estimated by the viscosity of 1% aqueous solutions.

2.3 LVDV-I+ type Brookfield viscometer test is greater than 100000 mPa. s HPMC Viscosity Method

LVDV-I+ type Brookfield viscometer maximum range is 2×1000000 mPa. s, for HPMC products greater than 100,000 mPa·s, the precise viscosity of its 2% aqueous solution can be tested.

3. Conclusion

1) For HPMC with a 2% aqueous solution viscosity less than 100,000 mPa·S, the 1#, 2#, 3#, and 4# rotors of the NDJ-1 rotational viscometer correspond to the 61#, 62 rotors of the LVDV-I+ Brookfield viscometer, respectively. #, 63#, and 64# rotors have the same test results at the same speed, so when the viscosity of HPMC 2% aqueous solution is less than 100,000 mPa·s, the NDJ-1 rotational viscometer can completely replace the LVDV-I+ Brookfield viscometer .

2) For HPMC with 2% aqueous solution viscosity greater than 100000 mPa·s, NDJ-1 rotational viscometer can roughly estimate greater than 100000 mPa according to the viscosity ratio coefficient between HPMC 2% and 1%o aqueous solution within a certain period of time. s HPMC 2% aqueous solution viscosity, but this method is only applicable to cellulose ether production enterprises, and it is not convenient for analysis and detection of downstream enterprises.

3) For HPMC whose 2% aqueous solution viscosity is greater than 105 mPa-s, the LVDV-I+ Brookfield viscometer can test its precise viscosity, which is more conducive to the analysis and detection of cellulose ether production enterprises and downstream enterprises. In addition, because the Brookfield viscometer is an imported model, the price is relatively expensive. The domestic NDJ-8S digital rotational viscometer has the same measurement range as the LVDV-I+ Brookfield viscometer, and the price is relatively cheap. Whether it can be replaced in the future still needs to be determined. Relevant analytical tests and comparative data.