Study on the application of hydroxypropylmethylcellulose in dry-applied tobacco leaf adhesive

Abstract: In order to study the application value of hydroxypropyl methylcellulose (HPMC) in dry-laid tobacco sheet, it was tested with three common adhesives 【guar gum, konjac gum and sodium carboxymethylcellulose (CMC)】 For comparison, the aqueous solution viscosity test of different adhesive systems, the film Fourier transform infrared spectrum test, the 350 ℃ low temperature pyrolysis analysis of the adhesive and the corresponding thin film and the tensile strength test of the corresponding thin film. The results show that: 1wt% HPMC aqueous solution 10 min It is soluble and can adjust the viscosity of the coating solution during the processing of tobacco sheets; after HPMC is compounded with the other three adhesives, there are physical cross-linking effects such as hydrogen bonds, which improves the longitudinal tensile strength of the dry-process tobacco sheets prepared by the corresponding adhesives Intensity, all>0. 5 kN/ m; 1wt% HPMC used in the preparation of dry-process tobacco sheet pyrolysis products contained low levels of toxic and irritating substances, which were 1. 83% and 5. 31%, respectively. The dry-process tobacco sheet has better comprehensive properties and has better application value.

Key words:hydroxypropyl methylcellulose; viscosity; thermal properties; dry-laid tobacco sheet; longitudinal tensile strength

At present, the global tobacco industry has entered an era of innovation. Heat-not-Burn (HnB) cigarettes have the characteristics of low temperature (about 350°C) non-combustion, satisfying the sensory experience of smokers, and low harmful components in smoke. Dry-process tobacco sheet is one of the new types of reconstituted tobacco. It is characterized by the use of dry-process airflow forming technology. It is mainly composed of substrates, tobacco powder, adhesives, smokers and spices. Fabricated, dried and calendered. Its product has a loose and porous structure, which leads to the defect of poor tensile strength. Adhesive is an important part in the preparation process of dry-process tobacco sheet, its function is to bond tobacco powder and other components together, and improve the tensile strength of the sheet to a certain extent.

Hydroxypropylmethylcellulose (HPMC) has excellent solubility in water, good film-forming properties, thickening properties, adhesion properties, and water retention properties. The prepared film material has good flexibility and mechanical properties, which can prolong the shelf life of food . In addition, compared with the single-component colloid, the compound glue will produce a synergistic effect, improve the mechanical strength of the product, and also improve the quality of processed food.

In order to investigate the application value of HPMC in dry-process tobacco sheets, three kinds of adhesives, guar gum, konjac gum and sodium carboxymethylcellulose (CMC), were selected in this study, and different dry-process tobacco sheets were prepared to compare with HPMC. , specifically researched the viscosity change rule of HPMC in the single/combined system of water/glycerol/propylene glycol solution, and carried out thermal cracking test by pyrolysis gas chromatography-mass spectrometry (Py-GC/MS), and studied the The change law of longitudinal tensile strength aims to provide new ideas for the adhesive part of the new tobacco sheet.

1. Experimental part

1.1 Materials

HPMC, 28-30% methoxyl, 7-12% hydroxypropyl, KIMA CHEMICAL CO., LTD; food grade guar gum, Henan Unisite Food Co., Ltd.; food grade konjac gum, Xinxin Biotechnology Co., Ltd. ; CMC, smoke powder (500 mesh) and dry-laid sheet substrate were provided by China Tobacco Hubei Company; glycerin (glycerol), 99%, Anhui Zesheng Technology Co., Ltd.; 1,2-, propylene glycol, 99%, SA En Chemical Technology Co., Ltd.; deionized water, self-made.

1.2 Equipment and instruments

BSA223S electronic balance (sensitivity 0.001 g, Sartorius Scientific Instruments (Beijing) Co., Ltd.); NDJ-8S digital viscometer (Deka Precision Measuring Instrument (Shenzhen) Co., Ltd.); IRPrestige-21 Fourier Infrared spectrometer (FTIR, Shimadzu Corporation, Japan); EGA/PY-3030D cracker (Frontier Corporation, Japan); pq2010 gas chromatography/mass spectrometer (GC/MS, Tsushima Corporation, Japan); SC-50N tension Testing machine (Shensei Company).

1.3 Method

1.3.1 Preparation of different systems of adhesive solutions and adhesive films

(1) Preparation of one-component adhesive aqueous solution: Weigh 2.5 g of HPMC into a container, add 250 g of deionized water, stir until the adhesive raw materials are completely dissolved, and obtain an aqueous solution of HPMC one-component adhesive. The same method was used to prepare single-component guar gum, konjac gum and CMC aqueous solutions.

(2) Preparation of HPMC composite adhesive aqueous solution: Weigh 1.25 g of guar gum and 1.25 g of HPMC in the same container, add 250 g of deionized water at 40 °C, and stir until the adhesive raw materials are completely dissolved to obtain HPMC/ Aqueous solution of guar gum compound adhesive. Follow the same steps to prepare HPMC/konjac gum and HPMC/CMC compound adhesive aqueous solution respectively.

(3) Preparation of HPMC composite adhesive glycerin/1,2-propanediol blended aqueous solution: Weigh 1 g guar gum and 1 g HPMC respectively in 5 different containers, add 200 g deionized water at 40°C, and stir until The adhesive raw materials were dissolved to obtain the HPMC/guar gum composite adhesive aqueous solution. Add glycerin and 1,2-propanediol with a mass ratio of 40:0, 28:12, 20:20, 12:28 and 0:40 to the aqueous solution, and stir until the blended solution is evenly mixed to obtain HPMC/guar Glue Compound Adhesive Glycerin/1,2-Propanediol Aqueous Solution. Follow the same procedure to prepare HPMC/konjac gum and HPMC/CMC composite adhesive glycerin/1,2-propanediol aqueous solution.

(4) Preparation of adhesive film: Prepare an aqueous adhesive solution according to the above method, weigh 50 g of the adhesive solution in a petri dish, put it in an oven at 80°C for 8 h, remove it from the mold, and obtain an adhesive film.

1. 3. 2 Preparation of dry-process tobacco sheet

Prepare 101 g of an adhesive aqueous solution with a mass ratio of adhesive to water of 1:100 according to the above-mentioned steps for preparing an aqueous adhesive solution; weigh 79 g of smoke powder, add 150 g of deionized water, and stir until there is no smoke powder in the slurry to obtain smoke powder. powder slurry; add 12 g glycerin, 8 g 1,2-propanediol and an aqueous adhesive solution to the smoke powder slurry, and mechanically stir until the blend is evenly mixed to obtain a coating liquid; spray the coating liquid onto the positive side of the substrate several times. On the reverse side, the substrates used in the preparation of thin film samples with different adhesive formulations are all produced in the same batch according to the enterprise standard, and the tensile strength of the substrate itself is consistent, and then dried (sprayed once and dried once, 4 times in total), and finally obtained Dried tobacco sheet samples.

1. 3. 3 Viscosity test of adhesive solution

Use an oven to stabilize the temperature of the solution at 30°C, select the rotor of the viscometer, and turn the lifting knob

Make the rotor until the engraved line on the rotor is flush with the liquid surface, adjust the instrument level, set the parameters for testing, after the value is stable, the opening angle value is between 15% and 85%, and the viscosity of the adhesive aqueous solution at 30°C is obtained.

1.3.4 Fourier transform infrared spectroscopy (FTIR) test

The adhesive film adopts total infrared transmission, the resolution is 4 cm-1, the test range is 650-4000 cm-1, and the number of scans is 32 times.

1. 3. 5 Pyrolysis test

Weigh 0.1 mg of sample into the cracker, the initial temperature is 50°C, heated to 350°C, the heating rate is 10°C/ms, and kept for 25 s. Helium at a flow rate of 70 mL/min was selected as the carrier gas of the cracked product, and then transferred to GC/MS analysis. A HR-35MS chromatographic column (30 m×250 μm×0. 25 μm) was used. The scanning range of the mass spectrum is 20~400 m/z, the scanning rate is 500 Da/s, and the spectral library NIST-14 is searched.

1. 3. 6 Tobacco sheet tensile strength test

The test method of tensile strength refers to the standard GB/T 12914-2008 Determination of tensile strength of paper and cardboard. The sample is a rectangular sample with a length of 200 mm and a width of 15 mm, and the tensile rate is 20 mm/min.

2. Results and Discussion

2.1 Dissolution properties of HPMC and its compound adhesive

Prepare each adhesive aqueous solution according to the above operation, and dissolve it by adding water into the container containing the adhesive, and observe the dissolution characteristics of the adhesive powder raw material.

It can be seen that under the same dissolution conditions, the HPMC/konjac gum equal-volume compound and single-component konjac gum have the shortest dissolution time, and the HPMC/CMC equal-volume compound and single-component CMC have the longest dissolution time. It shows that the complete dissolution time of the compound adhesive is mainly determined by the components with a long dissolution time.

Factors such as the content, distribution and powder characteristics of the hydrophilic groups in the polysaccharide molecular structure will significantly affect its dissolution process. The dispersibility of HPMC and konjac gum powder is better, and the hydrophilic groups are mostly distributed on the surface of the rubber powder, and when the rubber powder meets water, it quickly absorbs water and swells, so the dissolution time is shorter; The distribution of hydrophilic groups on the surface is relatively small, so during the dissolution process, the outermost layer of the hard-to-disperse rubber powder group absorbs water after contacting with water.

A large amount of water is absorbed to form a rubber block with a large amount of rubber powder inside, which prevents water molecules from entering the inside of the rubber block, thus requiring a lot of dissolution time. Compared with the other 3 adhesives, HPMC has the advantage of fast dissolution.

2.2 Viscosity comparison of aqueous solutions of different HPMC systems

2. 2. 1 Viscosity comparison between HPMC and other one-component adhesives and compound aqueous solutions

From the viscosity diagrams of the single-component adhesives and HPMC compounded adhesive solutions, the mass ratio of adhesive to water is 1 ∶ 100, the ratio of compounded adhesive is 1 ∶ 1, and the test temperature is 30°C. From largest to smallest, they are guar gum, konjac gum, HPMC and CMC. Among them, the viscosity value of guar gum aqueous solution reached 13218 mPa·S, while the viscosity value of CMC aqueous solution was only 1108 mPa·S; under the same adhesive content, compared with the single-component adhesive aqueous solution, guar gum and konjac After compounding glue and HPMC, the viscosity of the blended aqueous solution decreased significantly compared with the viscosity of the single-component aqueous solution; and after compounding CMC and HPMC, the viscosity of the blended aqueous solution increased slightly compared with the viscosity of the single-component aqueous solution.

The hydroxyl group on the main chain of CMC is relatively the least, the intermolecular interaction is small, and the viscosity of the aqueous solution is relatively minimum; the hydroxyl group on the molecular chain of HPMC is relatively more, the hydrogen bond between the molecules is stronger, and the viscosity of the aqueous solution is moderate; while guar gum is similar to konjac gum, The long main chain contains a large number of hydrophilic groups, and the intramolecular hydrogen bonds and different molecular chains are entangled, resulting in a higher viscosity of the aqueous solution; after HPMC is compounded with guar gum, konjac gum and CMC, the intermolecular force is changed, making the compound The viscosity of the solution changes.

The addition of HPMC changed the distribution of other adhesive molecules in the solution and the intermolecular force, thus changing the viscosity of the adhesive aqueous solution. Therefore, HPMC can play a role in adjusting the viscosity of the coating liquid during the processing of tobacco sheets.

2.2.2 Viscosity comparison of glycerin/1,2-propanediol aqueous solution compounded by HPMC and other adhesives

Glycerin and 1,2-propanediol are the main tobacco sheet atomizers (smoke agents), so use a viscometer to test the viscosity of HPMC and the adhesive glycerin/1,2-propanediol aqueous solution compounded with other adhesives. The viscosity of the aqueous solution, where the mass ratio of adhesive to water is 1:100, and the test temperature is 30°C.

It can be seen that the addition of glycerol or 1,2-propanediol will affect the viscosity of HPMC and its compound system aqueous solution. Among them, the viscosity of single-component HPMC, HPMC and konjac gum, and the compound aqueous solution of HPMC and CMC did not change much after the addition of glycerin and 1,2-propylene glycol; The viscosity of the compound glue of guar gum and HPMC decreased slightly, and the addition of pure 1,2-propanediol greatly increased the viscosity.

Both glycerin and 1,2-propanediol have hydroxyl groups on the molecules, which will form hydrogen bonds with some groups on the adhesive molecule, and the addition of 1,2-propanediol may make the HPMC/guar gum compound solution form a dispersed The local single-phase region makes the viscosity of the compound adhesive solution rise sharply.

In addition, the hydroxyl density of glycerol molecules is greater than that of 1,2-propanediol, and the intermolecular forces are stronger. The macroscopic manifestation is that the viscosity of glycerin is higher. After adding glycerol alone, its own intermolecular force was strong, and no new intermolecular force was formed with HPMC molecules or guar gum molecules. On the contrary, the addition of glycerol destroyed the original molecular chain entanglement and hydrogen bond between the two adhesives, making the long molecular chains of HPMC and guar gum change from the original cross-entangled state to the stretched state, resulting in a decrease in the viscosity of the system. .

Therefore, after compounding different adhesive aqueous solutions, and after adding glycerin, 1,2-propanediol or the mixture of the two again, the solution viscosity will change. But the effect on different formulations is also different, which is related to the compatibility between the molecules of each component in the blend solution.

The viscosity of the coating liquid has a great influence on the coating quality of the reconstituted tobacco leaves, and adjusting the viscosity of the coating liquid by appropriate means can effectively improve the quality of the reconstituted tobacco leaves. Therefore, changing the viscosity of the coating solution by adding HPMC, glycerol or 1,2-propanediol may improve the quality of the corresponding prepared tobacco sheets.

2.3 Infrared spectroscopy analysis of HPMC and its thin films

Infrared analysis was carried out on the HPMC single-component film and its composite film with other three adhesives. The specific infrared light and the characteristic peak at 3741 cm-1 correspond to the stretching vibration of -OH, and the broad absorption band around 3392 cm-1 It is the stretching vibration of crystal water in the film. The characteristic peak at 2916 cm-1 is related to the variable-angle stretching vibration of CH3, CH2 and CH. The characteristic peak at 1648 cm-1 is caused by the carbonyl in the cellulose glucose unit. The characteristic peak at 1 is the shear vibration of C-O-C. In the spectrogram of HPMC and CMC composite film, the characteristic peak at 1608 cm-1 has an obvious blue shift compared with that of HPMC film, which is caused by the hydrogen bond formed between the two. In addition, there is a difference in peak intensity between the compound adhesive film spectrum and the HPMC spectrum at 1041 cm-1, which indicates that there is a certain physical cross-linking between HPMC and the other three adhesives.

Therefore, HPMC and the other three adhesives have physical crosslinking effects such as intramolecular and intermolecular hydrogen bonds and molecular chain entanglement in the composite film. Hydrogen bonding and cross-linking can reconstruct the network structure of adhesive molecules, improve the mechanical properties of the film, and further improve the mechanical strength of the corresponding tobacco sheet.

2.4 Longitudinal tensile strength test and analysis of dry-processed thin slices prepared by HPMC

Dry-laid tobacco sheets with different adhesive formulations were prepared according to the preparation process of dry-laid tobacco sheets. The aqueous solution of adhesive was composed of: adhesive: water = 1 ∶ 100, the ratio of each adhesive in the compound adhesive was 1 ∶ 1, and the weight of the sheet was controlled at 200 g. / m²

(±20), and the longitudinal tensile strength of the prepared sheet was tested by a tensile testing machine.

It can be seen from the results that after compounding HPMC with the other three adhesives, the longitudinal tensile strength of the corresponding dry-laid tobacco sheet has been improved to a certain extent. After compounding with guar gum, konjac gum and CMC, compared with single Component HPMC, sheet tensile strength increased by 2%, 12% and 16%, respectively, and the strength value> 0. 5 kN/m. This corresponds to the results of infrared analysis, indicating that after HPMC is compounded with the other three adhesives, the interaction between the adhesives improves the tensile strength of the corresponding dry-processed tobacco sheet.

2.5 Analysis of thermal cracking products of HPMC and its preparation of dry-process tobacco sheet

In order to further explore whether HPMC can be applied in dry-processed tobacco sheet, the pyrolysis products of HPMC at low temperature (350°C) were quantitatively analyzed by pyrolysis gas chromatography-mass spectrometry (Py-GC/MS).

According to the analysis results of Py-GC/MS, there are 61 kinds of thermal cracking products in HPMC, accounting for 93.04% of the total cracking products, corresponding to the preparation of dry-process tobacco sheet, there are 143 kinds of thermal cracking products, accounting for 90.33% of the total cracking products. %.

The analysis found that the thermal cracking products of HPMC at 350 °C include acids, esters, alcohols, amines, ketones, aldehydes and ethers, etc., accounting for 53.74% of the total cracking products, of which the content of aldehydes is the highest, reaching 16%. . 94%; The pyrolysis products of dry-process tobacco sheet prepared by HPMC at 350°C include acids, esters, alcohols, amines, ketones, aldehydes, ethers, alkenes and hydrocarbons, etc., accounting for 50. 73% of the total pyrolysis products. %, among which the content of alkenes is the highest, reaching 14.83%.

In addition, the thermal cracking products were summarized, from the aroma-generating substances, irritating and toxic substances and their relative contents in HPMC and its corresponding dry-laid tobacco sheets. In the product, there are no identical substances in the irritating substances, the contents are 3.82% and 7.96% respectively; there are no identical parts in the toxic substances, the contents are 5.31% and 1.83% respectively. Therefore, the relative content of pyrolysis products of HPMC in the corresponding pyrolysis products of dry-process tobacco sheet is very small.