WEN Cheng-Rong WANG Li-Xi WANG Zhi-Jing WU Chun-Hu LIU Y-Nn HE Ming-Xing PENG Shu-Hui PANG Jie② (College of Food Siene, Fujin Agriulture nd Forestry University, Fuzhou 350002, Chin) (Gungzhou City Polytehni, Gungzhou 510405, Chin) (Fuqing Testing Institute of Qulity nd Mesurement, Fuqing 350300, Chin)

1 INTRODUCTION

Konjac glucomannan (KGM) is one of the natural polysaccharides that glucose and mannose at the molar ratio of 1:1.6–1.7 are connected via α-1,4 glycosidic bonds[1]. There are branched chains at the C-3 positions of some glyco residues and they are connected via β-1,3 glycosidic bonds[2]. KGM is famous for its good healthy value. It can prevent colon cancer, breast cancer and a variety of common chronic diseases of intestines and stomach digestive system. In addition, KGM also has excellent absorbent thickening, gelling, film forming and biocompatibility[3]. However, pure KGM film has such problems as long film-forming time, low film strength, poor antibiotic capacity, great hygroscopicity and so on, which limited its application in some degree[4-6].

In order to improve the KGM film performance and expand its application in some areas, the researchers mainly conducted chemical physical modifications for KGM[7-8], and some properties of KGM were improved, but it also caused a chemical reagent residue and brought about hidden safety trouble. Physical modification can settle the safety issues in some degree. Plasma technology is a favorable cold physical surface processing tool[9].Owing to its advantages such as simple and clean process, easy operation, and so on, the technology has been widely applied in the field of biological materials as it does not change the nature of the substrate

Therefore, the ion beam injection machine was used to inject nitrogen ions into the KGM film in this paper, and FT-IR, laser Raman spectra and so on were utilized to analyze the chemical state and film behavioral changes of the KGM film before and after treatment. It is expected to provide theoretical basis for the application of plasma treatment technique in KGM and other macromolecules.

2 MATERIALS AND EXPERIMENT

2.1 Materials

Konjac refined powder was produced by Yunnan Zhaotong San’ai Konnjaku Products Co., Ltd.; other reagents were analytically pure.

2.2 Methods

2.2.1 Preparation of the KGM films

3 g of konjac powder was added to 300 mL of pure water which had already been heated up to 60 ℃. After that, it underwent water bath heating at 60 ℃ and stirred for 10 min. Then the film solution was poured into the 30cm × 30cm glass flat plate,kept standstill and swelled for 3 h, and placed into a drying oven to be dried at 60 ℃ for forming the film.In use, the film was cut into circular film with a diameter of 10 cm.

2.2.2 Ion injection

The ion beam injection machine was utilized to inject nitrogen ions into the KGM circular film. The ion beam energy was 25 KeV. Pulse radiation was used with the pulse time to be 15 s and pulse interval of 10 s. The ion dosage was 4000 units, and the unit ion density was 2.6×1013ions·cm-2. In this paper, the test and analysis for KGM films were only conducted at the dose of 4000 units.

2.2.3 Infrared spectroscopy analysis

Proper amount of powder was scraped from the KGM film sample. After fine grinding, the sample was prepared with kbr pellet technique. Air was used as reference, Vector 33 Fourier infrared spectrometer was used for scanning, and the scanning wavelength ranged from 4000 to 400 cm-1.

2.2.4 Laser Raman spectroscopy analysis

RM2000 micro laser Raman spectrometer was used. Determination conditions: Laser He-He; wavelength: λ = 633 nm; sample point power: 2–5 mw;exposure time: 10 s.

2.2.5 X-ray diffraction analysis

X-ray diffraction source diffractometer D/MAXRB was used for determination. Determination conditions: target type: Cu target; filter plate: graphite monochromator; tube voltage: 40 kV; tube current:200 mA; incident wavelength: 1.5418 ?; divergence slit and scattering slit: 1o; recipient slit: 0.3 mm;scanning speed: 5 °/min; step width: 2θ = 0.02°;scanning range: 3–70°; temperature: 25 ℃.

2.2.6 Determination of the film mechanical properties

Physical property meter was used for determination[10].

2.2.7 Determination of water vapor permeability (WVP)

Cup simulation method was used for determination[10].

3 RESULTS AND DISCUSSION

3.1 Infrared spectroscopy analysis of the KGM film

Figs. 1 and 2 show the FT-IR spectra of KGM film before and after plasma treatment, respectively.For the KGM film there were absorption peaks at 2891 cm-1(C–H stretching vibration absorption peak), 1730 cm-1(C=O group absorption peak of acetyl), 1424 cm-1(=CH2absorption peak) and 1383 cm-1(=CH2absorption peak) and 1155 cm-1(C–O absorption peak), as shown in Fig. 1. For the KGM film after plasma treatment, there was one C=O absorption peak at 1641 cm-1, indicating that plasma treatment did not affect the acetyl of KGM molecule.There were special absorption peaks at 896 and 810 cm-1, suggesting that the C–N bond may be introduced into the KGM molecule. For the absorption peaks at 2887 cm-1(C–H stretching vibration absorption peak), 1731 cm-1(C=O group absorption peak of acetyl), 1424 cm-1(=CH2absorption peak),1383 cm-1(=CH2absorption peak) and 1155 cm-1(C–O absorption peak), the wave crest increased in some degree, revealing that the content of these groups increased (Fig. 2). The absorption peaks between 3100 and 3500 cm-1were strengthened probably because the plasma treatment made KGM O–H group increase or N–H group appear.

Fig. 1. FT-IR spectra of the KGM film

Fig. 2. FT-IR spectra of the KGM film after plasma treatment

3.2 Raman spectra analysis of KGM film

To further understand the information on molecular vibration, based on the FT-IR spectra, Raman spectra analysis was introduced to analyze the KGM film samples before and after treatment in this paper

The C–H stretching vibration of KGM film without plasma treatment appeared at 2900 cm-1,C–O–C 1118 cm-1and 1090 cm-1. C–O–C stretching vibration was observed at 905 cm-1(Fig. 3).However, it shows in Fig. 4 that some vibrations of the KGM carbon skeleton slightly changed after plasma treatment. The main changes were reflected at the following positions: compared with pure KGM, the C–H vibration appeared at 2900 cm-1, but the strength was significantly improved, and the C–O–C vibration appearing at 1118 cm-1clearly showed the gradual decrease tendency (Fig. 4).Plasma treatment resulted in KGM degradation,molecular weight reduction and hydrogen bond number increase. In sum, plasma treatment caused KGM degradation, and the molecular weight decreased and the number of hydrogen bonds increased, and further it may reduce the film moisture absorbance and the film WVP.

Fig. 3. Raman spectra of the KGM film

Fig. 4. Raman spectra of the KGM film after plasma treatment

3.3 X-ray diffraction analysis of KGM film

According to Figs. 5 and 6, X-ray diffraction pattern of pure KGM consisted of dispersion diffraction characteristic and a few spike diffraction characteristics. Around 2θ = 19.02o, there was one relatively obvious crystalline peak (Fig. 5). Therefore, it could hold that KGM has generally disordered and partially ordered structure. That is to say, KGM is one amorphous substance in general and is amorphous powder, but there are microcrystalline structures in some positions. This was consistent with the viewpoint that KGM was amorphous powder consisting of radial micelle given by Ogwa et al.[11]. For the KGM film after plasma treatment,the X-diffraction curve figure did not change significantly, but there was one absorption peak at 31.27o (Fig. 6), indicating that the amorphous state of KGM was changed after radiation treatment, but the ordered arrangement increased and crystalline region was raised.

Fig. 5. X-ray diffraction of the KGM film

Fig. 6. X-ray diffraction of the KGM film after plasma treatment

3.4 Film mechanical properties analysis

The tensile strength (bσ) and breaking elongation(bε) of KGM film before and after plasma treatment were determined, and the results are shown in Fig. 7, where A represents the tensile strength, and B is the breaking elongation. For the KGM film after treatment, the tensile strength was increased,breaking elongation was reduced (Fig. 7), and film mechanical properties were improved in some degree. Existing cracks reduced the material strength.With the corrasion effect of plasma treatment, it could eliminate microcracks in the KGM film surface, achieve strain in surface microstructure,decrease the focal points of stress and improve the stored strain energy. In addition, the impact by highenergy particle would release internal stress inside the film and enhance the tensile strength.

3.5 Water vapor permeability (WVP) analysis

Fig. 8 shows the WVP of KGM film with and without treatment. According to the data of WVP of KGM film before and after treatment, the WVP value of treated KGM film decreased compared with KGM (Fig. 8), which means it is more difficult for the water molecules to go through the film, and thus the film can better prevent the moisture loss of fruits and vegetables. It is well known that water vapor passes the macromolecule film mainly via free volume and micro pores among the macromolecular chains as well as the gap caused by thermal vibration of the macromolecular segments. After plasma treatment, THE KGM crystalline region increased and THE WVP rate decreased[10,13].

Fig. 7. Change of the tensile strength and breaking elongation rate

Fig. 8. WVP of the KGM films with different treatments

4 CONCLUSION

KGM has fine film-forming property, but it also has such problems as long film-forming time, low film strength, poor antibiotic capacity, high hygroscopicity, high air permeability, and so on, and these problems are related to the KGM structural stability. Therefore, the physical and chemical methods were introduced to modify KGM, and then the spatial structure changed, which led to the film properties to change. Plasma treatment is one physical cold treatment technique emerging in recent years. Presently, there is no study on the effect of plasma treatment on the KGM film structure yet. In this study, ion beam injection machine was used to inject nitrogen ions into the KGM film. Compared with pure KGM film, the KGM film thus formed had improved the mechanical properties and reduced WVP, which was related to the KGM film structural change. Nitrogen groups appeared on the KGM strand after treatment, so the properties of KGM film were improved. Part of the molecular chain fractured,and the number of hydrogen bonds increased, the molecule remained amorphous non-crystalline state,but the crystalline regions were increased, indicating the plasma treatment could improve the KGM film properties. It is significant to further discuss the KGM film structural change with plasma modification.

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