Structure and Properties of Chitosan/Hydroxypropyl Methyl Cellulose Packaging Film

Abstract: A degradable packaging film was prepared by blending chitosan (CS) and hydroxypropylmethylcellulose (HPMC) solutions. The structure of the blend film was characterized by infrared spectroscopy, X-ray diffraction and atomic force microscopy, and the compatibility of the two blends was analyzed. The changes in tensile strength and elongation at break were analyzed by mechanical property tests. The results show that: when the volume fraction of HPMC in the blend film is 40%, the tensile strength of the blend film is basically unchanged, and the elongation at break is about 3 times higher than that of the pure CS film; the volume fraction of HPMC in the blend film is ≥ 40% , HPMC played a toughening effect on the CS film.

Key words:chitosan; hydroxypropyl methylcellulose; structure; mechanical properties

0.Preface

In the field of packaging, products such as lunch boxes, packaging bags and disposable garbage bags that use petroleum and other resources as raw materials, with the increase in people's demand for them in daily life, plastic waste has become a major public hazard that pollutes cities and oceans , The "white pollution" problem caused by these discarded packaging materials has become a hot spot of social concern, and it is urgent to seek new degradable materials to replace ordinary plastic packaging materials.

Chitosan is a natural polymer obtained by hydrolyzing chitin under alkaline conditions to partially deacetylate it. It is the only alkaline polysaccharide in nature and has many unique properties. It is non-toxic, has good film-forming properties, and can be completely degraded. It is considered to be a very potential coating material. The toughness of chitosan as a packaging film is too low, and some researchers have done research on improving its toughness. Srinivasa P C et al studied polyvinyl alcohol/chitosan blend film, its toughness is about 1 times higher than that of pure chitosan film. Zhang Ruping prepared polyvinyl alcohol and chitosan blend film, modified chitosan film, the toughness increased by about 1 times. Ding Minghui et al. added a suitable proportion of high molecular weight polyethylene glycol to chitosan, and the toughness of the film was increased by about 1 times. However, both polyvinyl alcohol and high molecular weight polyethylene glycol are synthetic polymers that are soluble in water but cannot be completely degraded. xu Y x et al. prepared a fully degradable film by blending various starches and chitosan, but the toughness of the film was only increased by about 0.5 times.

Hydroxypropylmethylcellulose (HPMC) is a natural cellulose derivative. It has good dispersibility, film-forming property, and excellent solubility in organic solvents. Since there is a hydroxypropyl group on the HPMC macromolecule, and the hydroxypropyl group is a short flexible branched chain, the hydroxyl group on the hydroxypropyl group can form a hydrogen bond with the oxygen atom on the furan ring or glycoside group of the chitosan macromolecule, replacing the The hydroxyl groups on the chitosan main chain form hydrogen bonds with these oxygen atoms, so the addition of HPMC can expand the macromolecular gap in the film, increase the movement capacity of the macromolecular chain, and improve the toughness of the chitosan film.

Luo Kun et al. blended HPMC with chitosan solution, indicating that the two can form a partially compatible system, but only studied the blending mechanism.

In this paper, HPMC was used to modify chitosan, and the effect of the blending ratio of chitosan and HPMC on the structure and mechanical properties of the blended membrane was discussed.

1. Experimental part

1.1 Experimental materials

Chitosan (CS): The degree of deacetylation is 84.39%, the viscosity is 149 mPa·s, the water content is 6.81%, and the ash content is 0.98%. Hydroxypropyl methyl cellulose (HPMC): the content of methoxyl group is 28%~30%, the content of hydroxypropyl group is 7%~12%, and the viscosity is 80 000 mPa·s.

1.2 Sample preparation

Dissolve CS powder in 0.5% acetic acid solution, dissolve and filter, then slowly add HPMC powder into CS solution under stirring condition. Mix according to the ratio of w(CS):w(HPMC) (mass ratio) 100:0, 80:20, 60:40, 50:50, 40:60, 20:80, 0:100. Under the condition of the same content of 1%, the substances are fully dissolved and mixed, filtered and defoamed, then the mixed solution is cast into a petri dish, and finally dried at a constant temperature at a set temperature to make a thickness of 25~ A 40 μm film is used for later use.

The volume fraction of HPMC corresponding to the mass ratio of CS and HPMC 100:0, 80:20, 60:40, 50:50, 40:60, 20:80, 0:100 is 0, 15%, 30%, respectively , 40%, 50%, 70% and 100%.

1.3 Structural Observation and Characterization

1.3.1 Infrared Absorption Spectroscopy (FTIR) Analysis

The infrared absorption spectrum of the blend film was measured in ATR mode with a Nicolet 5700 Fourier infrared spectrometer produced by American Thermoelectric Company. The scanning range is 500-4 000 cm-1, the number of scans is 32, and the interval of data points is 1928 cm-1. After the sample film was dried at 50 °C for 24 h, infrared spectroscopy was carried out.

1.3.2 Wide-angle X-ray Diffraction (XRD) Determination

ARL XTRA type X-ray diffractometer produced by Thermo ARL Company of Switzerland was used for determination. The X-ray source was a nickel-filtered Cu-ka wire (40 kV, 40 mA). Scan angles from 5° to 55°. The scanning speed is 6°/min.

1.3.3 Atomic force microscope (AFM) observation

The XE-100E atomic force microscope produced by Korean PSIA company was used to measure in non-contact mode to observe the phase structure of the film surface.

1.4 Mechanical property test

The AGI type universal material testing machine produced by Shimadzu Corporation of Japan was used to test the tensile strength and elongation at break of the film. Preparation before the test: select a uniform, clean, and flawless sample, cut it into a rectangle with a width of 10 mm, a clamp distance of 50 mm, and a tensile rate of 100 mm/rain, and the rest shall be carried out according to the standard.

2. Results and Discussion

2.1 Structure of CS and HPMC blend membrane

Theoretically speaking, both CS and HPMC molecules have hydrogen bonds, and HPMC and CS can be blended to form a "partially compatible" system. The kinetic process of further phase separation in this system is quite slow. Therefore, it can be A blend film with stable structure and performance is obtained.

2.1.1 Infrared absorption spectrum analysis of CS and HPMC blend film

The absorption bands of pure CS films between 3 100 and 3 400 cm-1 are the result of the stretching vibrations of one OH bond and one NH bond overlapping at the same place. The absorption bands around 1 630, 1 538 cm-1 and 1 338 cm-1 belong to the amide I, II and III bands, respectively, and the bands near 1 630 and 1 338 cm-1 are relatively weak, indicating that the chitosan used in this paper The content of acetamide in the sugar is less, which is consistent with the fact that the deacetylation degree of chitosan is 84.39%. The bending vibration of the N—H bond in NH2 overlaps with amide II near 1 538 cm-1, and the peak at 1 538 cm-1 is stronger, indicating that there are a large number of amino groups in the CS film. Around 895cm-1 is the characteristic peak of p-configuration glycosidic bond. This is consistent with the presence of p-configuration glycosidic bonds in CS used here.

The absorption band around 3 418 cm -1 of pure HPMC film is caused by the stretching vibration of O-H bond. The absorption peaks at 1 454, 1 373, 1 315 cm-1 and 945 cm-1 are assigned to the asymmetric, symmetric deformation vibration, in-plane and out-of-plane bending vibration of CH3, respectively. These peaks of the methyl group are weak, which is consistent with the content of CH3 in the HPMC used in this paper is 28%-30%.

CS was modified with HPMC. With the addition of HPMC, the absorption band in the high wave region of the blend film gradually narrows and moves to high wave. When the volume fraction of HPMC is 40%, the absorption peak is around 3 442 cm-1, which is higher than that of pure HPMC peak. With further addition of HPMC, the absorption peak moves to a lower wave, which is lower than that of pure HPMC, and the peak intensity becomes lower. It shows that with the addition of HPMC, the hydrogen bond force between the two polymer molecules is enhanced. When the volume fraction of HPMC is 40%, the hydrogen bond force is the strongest, and when it is greater than 40%, the hydrogen bond force is weakened. This is because HPMC contains a large number of hydroxyl groups, and excess HPMC tends to form intramolecular hydrogen bonds of HPMC, thus weakening the intermolecular hydrogen bond force between CS and HPMC. Around 1 150 cm-1 is the characteristic absorption peak of the one-OH hydroxyl group on C3, which almost disappears in the blend, indicating that almost all the one-OH group on C3 forms intramolecular or intermolecular oxygen bonds.

Other characteristic peaks possessed by the pure component polymers appeared in their blended films, and the intensity of these peaks in the blended films varied with the proportion of blended polymers.

2.1.2 XRD analysis of CS and HPMC blend film

Pure CS film has 4 diffraction peaks (8.7°, 11.8°, 18.6° and 23.30), and pure HPMC at 32.6°. There is a sharp diffraction peak nearby. After the two are blended, 32.6. Nearby peaks disappeared, and other peaks were clearly attenuated. With the increase of HPMC, 23.3. , 8.7. The nearby peaks disappear one by one, and the Mantou peak appears. When HPMC increased to 80%, the other two peaks also disappeared, only one peak of steamed bread. Mantou peak is the peak of amorphous material. It shows that the addition of HPMC destroys the arrangement of CS molecular chains, and the crystallinity of the blend film decreases, which shows that HPMC and CS have a certain phase tile effect in the crystal region.

2.1.3 AFM characterization of CS and HPMC co-t film

Since the principle of the AFM phase diagram is based on the difference in material hardness and friction, it can eliminate the influence of surface roughness, and at the same time avoid the false phase of the surface topography plan due to macroscopic unevenness, and truly reflect the material composition structure. Light colors represent hard phases and dark colors represent soft phases. The CS film contains a large number of hard phase particles represented by white, while the HPMC contains a small amount of large particles. With the addition of HPMC, it can be seen that the hard phase particles coalesce non-uniformly and disperse again. Irregular small pieces are aggregated due to collisions, and larger particles appear. The hard phase particles are not all on the same plane, that is, most of the dispersed phase particles shown in the image are not at their largest cross section, so the particle size shown in the figure cannot truly reflect the size of the hard phase. But on the whole, the particle size distribution tends to be uniform. When the volume fraction of HPMC is 70%, the hard phase particles almost disappear, indicating that there is an interaction between CS and HPMC.

2.2 Tensile properties of CS and HPMC blend films

The performance of the blended membrane is affected by many factors, including the performance and proportion of each component, the morphology of the blended membrane, and the interface combination of the two-phase system.

The elongation at break and tensile strength of the pure CS film are about 4.4%, 75.7 MP, respectively, and that of the pure HPMC film are 13.0%, 71.5 MP, respectively. The two are calculated according to the series formula proposed by Nielsen. The elongation at break and tensile strength of the blend film as a function of composition.

The addition of HPMC has a significant effect on the properties of the blend membrane. It can be seen from the solid line that when the volume fraction of HPMC is 40%, both the tensile strength and the elongation at break have peaks. This is because a small amount of crystallites in the film act as physical cross-linking points to increase the tensile strength of the film; the microcrystals in the film also play a toughening effect, increasing the elongation at break of the film. When the HPMC composition is in the range of about 40% to 70%, the tensile strength and elongation at break of the sample both exceed the calculated values, that is, the effect of strengthening and toughening is achieved. There are two reasons: first, the compatibility of the two is good. From the previous FTIR analysis, it can be seen that the hydrogen bond force between HPMC and CS molecular chains of equal mass is relatively large, making the interface bonding relatively good. Too little HPMC, which forms hydrogen bonds with CS is unsaturated; too much HPMC, excess HPMC tends to form intramolecular hydrogen bonds of HPMC, thus weakening the intermolecular hydrogen bond force between CS and HPMC; the second is the crystallization of the blend film The degree is small, almost becoming amorphous.

3. Conclusion

Infrared analysis showed that CS and HPMC solutions were blended to form a film, and CS and HPMC were partially compatible through hydrogen bonding. XRD analysis and AFM phase diagram observation showed that HPMC was used to modify CS, and the crystallinity of the blend film decreased, which indicated that HPMC and CS had certain interactions in the crystal region. Using HPMC to modify CS, the tensile strength of the blended film is basically unchanged, and the elongation at break can be increased by about 3 times compared with the pure chitosan film, that is, the toughness is greatly improved.