Effect of Plasticizers on Properties of Rice Straw Fiber Film

Chen Hong-rui, Chen Hai-tao, Liu Shuang, Dun Guo-qiang, and Zhang Ying

College of Engineering, Northeast Agricultural University, Harbin 150030, China

Effect of Plasticizers on Properties of Rice Straw Fiber Film

Chen Hong-rui, Chen Hai-tao*, Liu Shuang, Dun Guo-qiang, and Zhang Ying

College of Engineering, Northeast Agricultural University, Harbin 150030, China

In order to improve the properties of rice straw fiber film, one factor contrast test method was employed. Plasticizer type was chosen as input variable, dry tension strength and elongation, wet tension strength and elongation, bursting strength and tearing strength were chosen as indexes. The results showed that there were significant differences among the means of dry tension strength, dry elongation and bursting strength of different plasticizers; there were not significant differences among the means of wet tension strength, wet elongation and tearing strength of different plasticizers; for dry tension strength and elongation, glycerol had a significant difference with sorbitol and PEG, no significant difference was observed between sorbitol and PEG, dry tension strength added glycerol had been reduced 6.8% compared with that added sorbitol, reduced 9.5% compared with that added PEG; elongation had been improved 6.1% and 9.4%, respectively; for bursting strength, sorbitol had a significant difference with glycerol and PEG, no significant difference was observed between glycerol and PEG; bursting strength added glycerol and added PEG had been improved 6.9% and 5.6%, respectively compared with that of the added sorbitol. The results provided a theoretical reference for further improving the straw fiber film manufacturing process.

rice straw, film, plasticizer, comparative test

Introduction

In the latest years, with the wide use of mulching film, the problems existed are also emerging. Most of the films used currently are made of synthetic polymers, such as polyethylene and polyvinyl chloride (PVC), which can not be degraded themselves. Mass of plastic piece residual in the soil lead to the destruction of soil structure, and cause great difficulties to plowing and sowing (Zhou and Zhu, 2002; Han and Chen, 2008; Lu et al., 2007). To solve the problem generated by plastic film, researches on biodegradable films attract great attention. Microbes in the oil can decompose films that use plant fiber as material. Products of these decomposed films can be used as organic fertilizer which will increase oil fertility (Yang and Chen, 2010; Chu and Shi, 2007; Sun et al., 2000).

Plant fiber film has a definite strength without adding any adhesives because of its own fiber strength, fiber bonding strength and the arrangement of the fibers. But unplasticized plant fiber films exist a rapid evaporation of water at the amorphous region and the crystalline region during the process of dryness. Cellulose macromolecule draws closer gradually under the effects of hydrogen bond and the Van Edward force, hydrogen bonds form directly by cellulose molecules increase, intermolecular force enhances greatly andactivation energy needed for macromolecule increases at the same time. Thus, lead to the difficulties of deformation (Tan, 2001). So unplasticized plant fiber film appears as a property of inflexibility, such as crisping, hard and easy to tear. In order to solve the problems, a plasticizing measure was often carried out, such as adding some low molecular alcohol compounds which can produce hydrogen bonding force with OH groups on cellulose macromolecule to permeate into the inside of a film. That is hanging up numbers of low molecular alcohol compounds on molecular chain can enlarge the distance between chains, weaken hydrogen bonding force of OH groups on macromolecular chain, and improve the relative sliding motion of the chains among macromolecules (Tan, 2001; Zhang, 2007).

In order to search for the effects of plasticizer on properties of straw fiber film, screen out the optimum plasticizer for making rice straw fiber film and provide theory reference for the manufacturing process of straw fiber film, an experimental research on plasticization of rice straw fiber film with the method of adding plasticizer was carried out.

Materials and Methods

Materials

Dongnong 425 rice straw was provided by Northeast Agricultural University, Harbin, China; KP wood fiber; glycerol (AR) was purchased from Jizhun Chemical Reagent Co., Ltd. (Tianjin, China); Sorbitol (biochemical reagent) was purchased from Bodi Chemical Reagent Co., Ltd. (Tianjin, China); PEG was purchased from Guangfu Science and Technolory Chemical Reagent Co., Ltd. (Tianjin, China); and wet strength agent was provided by Xinxing Chemical Plant (Mudanjiang, China).

Equipment and instrument

D200 type of the straw fiber extruder, manufactured by Northeast Agricultural University; electronic scale, Haikang Electronic Instrument Factory (Shanghai, China); ZT-400 Valli beater, Zhongtong Test Equipment Co., Ltd. (Shanxi, China); JA5003B electronic balance, Tianmei Science and Technolory Instrument Co., Ltd. (Shanghai, China); ZTG-100 pulp degree test machine, ZCX-A paper sheet forming device, ZL-300 pendulum paper tension strength test machine, ZDNP-1 paper bursting strength test machine, and ZSED-1000 paper tearing strength test machine, Yueming Small Test Machine Co., Ltd (Changchun, China).

Methods

One factor contrast test method was carried out with plasticizer type as the input variable, dry and wet tension strength, elongation, bursting strength and tearing strength of the rice straw fiber film as indexes. According to references and results of the previous tests, three plasticizers were chosen as followings, glycerol, sorbitol and PEG. Test data is shown in Table 1. Concentration of every plasticizer was 3%, additive amount of the wet strength agent and rosin were 1.6% and 0.4%, respectively, and additive amount of the alumina was 4.5 times as rosin (Lv et al., 2012).

Procedure

1) Cut Dongnong 425 rice straw harvested in autumn of 2013 into 10 cm, soaked in normal atmospheric temperature for 12 h. Then, used D200 straw fiber preparation machine to produce coarse fiber.

2) Beated rice straw fiber film and KP pulp board to 45 SR referring to QB/T3702-1999.

3) Mixed the two kind pulps together with the additive amount of rice straw fiber 70% and KP pulp 70%, calculated the additive amount of every additive and then stirred the mixing pulp as added additives into it (Cheng et al., 2009).

4) Referring to QB/T3703-1999, used the well stirred pulp to make film samples with the ration of 80 g ? m-2. Then, put the film samples on drying machine for 2 min, sprayed different plasticizer liquor on the surface of the film samples as they had not been dried completely. Exposed them under normalatmospheric temperature for 1 min and then to the bead machine to be pressured for 3 min to make fibers combine more closely. Again, put film samples on the drying machine to be dried completely.

5) Referred GB/T453 to measure the dry, wet tension strength and elongation of the film sample, referred GB/T454 to measure bursting strength, and referred GB/T455 to measure tearing strength. Every experiment was taken for five times. Used Design-Expert software to make statistical analyses of the data.

Results and Discussion

Results of the experiment are shown in Table 1.

Table 1 Test factors and data

Analyses of variance

Results of ANOVA are shown in Table 2.

For the given significant level of 0.1, the value of Prob＞F less than 0.1 indicated that factor had a significant difference on the indexes; and the value of Prob＞F more than 0.1 indicated that factor had no significant difference on the indexes.

Table 2 Analyses of variance

Therefore, from Table 2, we could conclude that there were significant differences among the means of dry tension strength, dry elongation and bursting strength of different plasticizers; there were not significant differences among the means of the wet tension strength, wet elongation and tearing strength of different plasticizers.

Effect of different plasticizers on dry tension strength and elongation

Results of multiple comparisons are shown in Tables 3 and 4.

Table 3 Multiple comparisons of different plasticizer effects on dry tension strength

Table 4 Multiple comparisons of different plasticizer effects on elongation

As shown in Tables 3 and 4, for dry tension strength and elongation, glycerol had a significant difference with sorbitol and PEG, no significant difference was observed between sorbitol and PEG at the significant level of 0.1. As shown in Table 1, the order of the dry tension strength of the rice straw fiber film added with 3% different plasticizers was PEG＞sorbitol＞glycerol, and the order of elongation was glycerol＞sorbitol＞PEG. From the multiple comparison results, glycerol had a significant difference with sorbitol and PEG, dry tension strength added glycerol had been reduced 6.8% compared with that added sorbitol, reduced 9.5% compared with that added PEG; elongation had been improved 6.1% and 9.4%, respectively. It was because small molecular alcohols inserted into the chains of the plant film, enlarged the distance of the molecules and finally weakened the force of the plant fiber molecules. The main factors against plasticization were gravitation and crystalline of the polymer molecule chains, so plasticization could be improved by decreasing the gravitation of the molecule chains or reducing the crystalline of the polymer molecule chains. Thus, rice straw fiber film appeared as the decrease of the tension strength and the increase of the elongation on a macro level (Yu, 1990; Han et al., 2011; Chen et al., 2013). At the same time, glycerol was tribasic alcohol, sorbitol was hexabasic alcohol, while PEG was polymer. Cellulose was polymer of the multi hydroxyl glucose, three-dimensional regular high polymer connected by anhydrous glucose residues through β1, 4 glucosidic bond. The motion resistance of it was hydrogen bond in and between molecules. Glycerol was the smallest molecule of these three which could insert into molecule chains more easily compared with the other two (Shi and He, 2004; Zhan and Zhao, 2009; Zeng and Wu, 2006). To further improve the plasticization of the rice straw fiber film on the premise of the tension strength, according to the mean results, only the film added with 3% PEG whose dry tension strength larger than 30 N couldmeet the mechanical performance for laying field. The elongation of it was 1.6%, enhanced 0.35% compared to that not be plasticized. So PEG was given priority as the optimum plasticizer of rice straw fiber film. If the film demanded a higher plasticization and considering economical efficiency, glycerol was the optimum plasticizer of the rice straw fiber film, elongation of the film enhanced 0.5% compared with that not be plasticized.

Effect of different plasticizers on wet tension strength and elongation

As shown in Table 1, the order of the wet tension strength of the rice straw fiber film added with 3% different plasticizers was PEG＞sorbitol＞glycerol, and the order of elongation was glycerol＞sorbitol＞PEG. From the analyses of variance, no significant difference was observed between wet tension strength and elongation of different plasticizers. It might be that water molecules inserted into cellulose molecule chains in place of the plasticizer molecules in wet condition that made the effect of plasticizers was not so significant as in dry condition (Jin, 2009; Wang et al., 2013; Sun et al., 2010; Gong et al., 2008).

Effect of different plasticizers on bursting strength and tearing strength

Results of multiple comparisons are shown in Table 5.

Table 5 Multiple comparisons of different plasticizer effects on bursting strength

As shown in Table 5, for bursting strength, sorbitol had a significant difference with glycerol and PEG, no significant difference was observed between glycerol and PEG, at the significant level of 0.1.

Addition of plasticizers reduced the brittleness of rice straw fiber film, gave it a certain tenacity and strength, and improved the bursting strength of it. As shown in Table 1, the order of the bursting strength of the rice straw fiber film added with 3% different plasticizers was glycerol＞sorbitol＞PEG, bursting strength added glycerol and PEG had been increased 6.9% and 5.6%, respectively compared with that added sorbitol. Combined with the results of the multiple comparisons, no significant difference was observed between glycerol and PEG on bursting strength. For tearing strength, no significant difference was observed among different plasticizers. If considering bursting strength, both glycerol and PEG could be chosen as plasticizers. But the price of glycerol was the lowest of these three, so glycerol was the optimum plasticizer of rice straw fiber film from the economic point of view.

Conclusions

There were significant differences among the means of the dry tension strength, dry elongation and bursting strength of the different plasticizers; there were not significant differences among the means of the wet tension strength, wet elongation and tearing strength of different plasticizers; for dry tension strength and elongation, glycerol had a significant difference with sorbitol and PEG, no significant difference was observed between sorbitol and PEG, dry tension strength added glycerol had been reduced 6.8% compared with that added sorbitol, reduced 9.5% compared with that added PEG; elongation had been improved 6.1% and 9.4%, respectively; forbursting strength, sorbitol had a significant difference with glycerol and PEG, no significant difference was observed between glycerol and PEG; bursting strength added glycerol and PEG had been improved 6.9% and 5.6%, respectively compared with that added sorbitol.

On the present basis of the rice straw fiber film manufacturing process, adding 3% PEG to film could enhance elongation and bursting strength by 0.35 and 16%, respectively, as tension strength could also meet the mechanical performance for laying field at the same time. Properties of the film was promoted further.

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1006-8104(2014)-04-0067-06

Received 10 October 2014

Supported by the Fund of Science and Technology Research Project of the 12th Five-year Plan (2012BAD32B02-5)

Chen Hong-rui (1990-), female, Master, engaged in the research of biomass material technology. E-mail: 429267765@qq.com

* Corresponding author. Chen Hai-tao, professor, supervisor of Ph. D student, engaged in the research of biomass material technology and agricultural mechanization engineering. E-mail: htchen@neau. edu. cn