Effects of Substituents and Molecular Weight on Surface Properties of Nonionic Cellulose Ether

According to Washburn’s impregnation theory (Penetration Theory) and van Oss-Good-Chaudhury’s combination theory (Combining Theory) and the application of columnar wick technology (Column Wicking Technique), several non-ionic cellulose ethers, such as methyl cellulose The surface properties of cellulose, hydroxypropyl cellulose and hydroxypropyl methylcellulose were tested. Due to the different substituents, degrees of substitution and molecular weights of these cellulose ethers, their surface energies and their components are significantly different. The data shows that the Lewis base of non-ionic cellulose ether is larger than the Lewis acid, and the main component of the surface free energy is the Lifshitz-van der Waals force. The surface energy of hydroxypropyl and its composition are greater than that of hydroxymethyl. Under the premise of the same substituent and degree of substitution, the surface free energy of hydroxypropyl cellulose is proportional to the molecular weight; while the surface free energy of hydroxypropyl methylcellulose is proportional to the degree of substitution and inversely proportional to the molecular weight. The experiment also found that the surface energy of the substituent hydroxypropyl and hydroxypropylmethyl in the non-ionic cellulose ether seems to be greater than the surface energy of cellulose, and the experiment proves that the surface energy of the tested cellulose and its composition The data are consistent with the literature.

Key words: nonionic cellulose ethers; substituents and degrees of substitution; molecular weight; surface properties; wick technology

Cellulose ether is a large category of cellulose derivatives, which can be divided into anionic, cationic and nonionic ethers according to the chemical structure of their ether substituents. Cellulose ether is also one of the earliest products researched and produced in polymer chemistry. So far, cellulose ether has been widely used in medicine, hygiene, cosmetics and food industry.

Although cellulose ethers, such as hydroxymethylcellulose, hydroxypropylcellulose and hydroxypropylmethylcellulose, have been produced industrially and many of their properties have been studied, their surface energy, acid Alkali-reactive properties have not been reported so far. Since most of these products are used in a liquid environment, and the surface characteristics, especially the acid-base reaction characteristics, are likely to affect their use, it is very necessary to study and understand the surface chemical characteristics of this commercial cellulose ether .

Considering that the samples of cellulose derivatives are very easy to change with the change of preparation conditions, this paper uses commercial products as samples to characterize their surface energy, and based on this, the influence of substituents and molecular weights of such products on the surface properties is studied.

1. Experimental part

1.1 Raw materials

The non-ionic cellulose ether used in the experiment is the product of KIMA CHEMICAL CO.,LTD,. The samples were not subjected to any treatment before testing.

Considering that cellulose derivatives are made of cellulose, the two structures are close, and the surface properties of cellulose have been reported in the literature, so this paper uses cellulose as the standard sample. The cellulose sample used was code-named C8002 and was purchased from KIMA, CN. The sample was not subjected to any treatment during the test.

The reagents used in the experiment are: ethane, diiodomethane, deionized water, formamide, toluene, chloroform. All liquids were analytically pure products except water which was commercially available.

1.2 Experimental method

In this experiment, the column wicking technique was adopted, and a section (about 10 cm) of a standard pipette with an inner diameter of 3 mm was cut as the column tube. Put 200 mg of powdered sample into the column tube each time, then shake it to make it even and place it vertically on the bottom of the glass container with an inner diameter of about 3 cm, so that the liquid can be adsorbed spontaneously. Weigh 1 mL of the liquid to be tested and put it into a glass container, and record the immersion time t and immersion distance X at the same time. All experiments were performed at room temperature (25±1°C). Each data is the average of three replicate experiments.

1.3 Calculation of experimental data

The theoretical basis for the application of column wicking technique to test the surface energy of powder materials is the Washburn impregnation equation (Washburn penetration equation).

1.3.1 Determination of the capillary effective radius Reff of the measured sample

When applying the Washburn immersion formula, the condition for achieving complete wetting is cos=1. This means that when a liquid is selected to immerse into a solid to achieve a fully wet condition, we can calculate the capillary effective radius Reff of the measured sample by testing the immersion distance and time according to a special case of the Washburn immersion formula.

1.3.2 Lifshitz-van der Waals force calculation for the measured sample

According to van Oss-Chaudhury-Good’s combining rules, the relationship between the reactions between liquids and solids.

1.3.3 Calculation of Lewis acid-base force of the measured samples

In general, the acid-base properties of solids are estimated from data impregnated with water and formamide. But in this article, we found that there is no problem when using this pair of polar liquids to measure cellulose, but in the test of cellulose ether, because the immersion height of the polar solution system of water/formamide in cellulose ether is too low, making time recording very difficult. Therefore, the toluene/chloroform solution system introduced by Chibowsk was selected. According to Chibowski, a toluene/chloroform polar solution system is also an option. This is because these two liquids have very special acidity and alkalinity, for example, toluene has no Lewis acidity, and chloroform has no Lewis alkalinity. In order to get the data obtained by the toluene/chloroform solution system closer to the recommended polar solution system of water/formamide, we use these two polar liquid systems to test cellulose at the same time, and then get the corresponding expansion or contraction coefficients before applying The data obtained by impregnating cellulose ether with toluene/chloroform are close to the conclusions obtained for the water/formamide system. Since cellulose ethers are derived from cellulose and there is a very similar structure between the two, this estimation method may be valid.

1.3.4 Calculation of total surface free energy

2. Results and Discussion

2.1 Cellulose standard

Since our test results on cellulose standard samples found that these data are in good agreement with those reported in the literature, it is reasonable to believe that the test results on cellulose ethers should also be considered.

2.2 Test results and discussion of cellulose ether

During the test of cellulose ether, it is very difficult to record the immersion distance and time due to the very low immersion height of water and formamide. Therefore, this paper chooses the toluene/chloroform solution system as an alternative solution, and estimates the Lewis acidity of cellulose ether based on the test results of water/formamide and toluene/chloroform on cellulose and the proportional relationship between the two solution systems. and alkaline power.

Taking cellulose as a standard sample, a series of acid-base characteristics of cellulose ethers are given. Since the result of impregnating cellulose ether with toluene/chloroform is directly tested, it is convincing.

This means that the type and molecular weight of the substituents affect the acid-base properties of cellulose ether, and the relationship between the two substituents, hydroxypropyl and hydroxypropylmethyl, on the acid-base properties of cellulose ether and the molecular weight completely opposite. But it could also be related to the fact that MPs are mixed substituents.

Since the substituents of MO43 and K8913 are different and have the same molecular weight, for example, the substituent of the former is hydroxymethyl and the substituent of the latter is hydroxypropyl, but the molecular weight of both is 100,000, so it also means that the premise of the same molecular weight Under the circumstances, the S+ and S- of the hydroxymethyl group may be smaller than the hydroxypropyl group. But the degree of substitution is also possible, because the degree of substitution of K8913 is about 3.00, while that of MO43 is only 1.90.

Since the degree of substitution and substituents of K8913 and K9113 are the same but only the molecular weight is different, the comparison between the two shows that the S+ of hydroxypropyl cellulose decreases with the increase of molecular weight, but S- increases on the contrary. .

From the summary of the test results of the surface energy of all cellulose ethers and their components, it can be seen that whether it is cellulose or cellulose ether, the main component of their surface energy is the Lifshitz-van der Waals force, accounting for about 98%~99%. Moreover, the Lifshitz-van der Waals forces of these nonionic cellulose ethers (except MO43) are also mostly greater than those of cellulose, which indicates that the etherification process of cellulose is also a process of increasing Lifshitz-van der Waals forces. And these increases lead to the surface energy of cellulose ether being greater than that of cellulose. This phenomenon is very interesting because these cellulose ethers are commonly used in the production of surfactants. But the data is noteworthy, not only because the data about the reference standard sample tested in this experiment is extremely consistent with the value reported in the literature, the data about the reference standard sample is extremely consistent with the value reported in the literature, for example: all these cellulose The SAB of ethers is significantly smaller than that of cellulose, and this is due to their very large Lewis bases. Under the premise of the same substituent and degree of substitution, the surface free energy of hydroxypropyl cellulose is proportional to the molecular weight; while the surface free energy of hydroxypropyl methylcellulose is proportional to the degree of substitution and inversely proportional to the molecular weight.

In addition, because cellulose ethers have larger SLW than cellulose, but we already know that their dispersibility is better than cellulose, so it can be preliminarily considered that the main component of SLW constituting nonionic cellulose ethers should be the London force.

3. Conclusion

Studies have shown that the type of substituent, degree of substitution and molecular weight have a great influence on the surface energy and composition of non-ionic cellulose ether. And this effect seems to have the following regularity:

(1) S+ of non-ionic cellulose ether is smaller than S-.

(2) The surface energy of nonionic cellulose ether is dominated by Lifshitz-van der Waals force.

(3) Molecular weight and substituents have an effect on the surface energy of non-ionic cellulose ethers, but it mainly depends on the type of substituents.

(4) Under the premise of the same substituent and degree of substitution, the surface free energy of hydroxypropyl cellulose is proportional to the molecular weight; while the surface free energy of hydroxypropyl methylcellulose is proportional to the degree of substitution and inversely proportional to the molecular weight.

(5) The etherification process of cellulose is a process in which the Lifshitz-van der Waals force increases, and it is also a process in which Lewis acidity decreases and Lewis alkalinity increases.