Chitosan-Based Reagents Endow Recycled Paper Fibers with

Article pubs.acs.org/IECR

Chitosan-Based Reagents Endow Recycled Paper Fibers with Remarkable Physical and Antimicrobial Properties Abdus Salam,† Lucian A Lucia,*,†,‡,§ and Hasan Jameel† †

Department of Forest Biomaterials, North Carolina State University, Raleigh, North Carolina 27695-8005, United States Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States, § State Key Laboratory of Pulp & Paper Science and Technology, Qilu University of Technology, Jinan City 250353, P. R. China ‡

ABSTRACT: The aim of the current work was to develop and study a paper additive system that endows recycled paper fibers with strong mechanical and antimicrobial properties. Five different types of modifying agents including succinic acid, carboxymethyladipic acid, butanetetracarboxylic acid, ethylenediaminetetraacetic acid, and diethylenetriaminepentaacetic acid (DTPA) were reacted with soy flour. Approximately 2% modified soy flour additive by mass relative to a old corrugated container (OCC) pulp slurry was mixed before generating a two-dimensional hand sheet for physical testing. DTPA-modified soy-flour-treated OCC pulp displayed better tensile relative to the results from the use of other modifying agents. Soy flour was treated with different DTPA concentrations, times, temperatures, and pH values to determine the optimal modification reaction conditions. Afterward, the DTPA− soy flour was complexed with chitosan to decrease the biodecomposition of soy protein, improve its incorporation into an OCC matrix, and increase interfiber bonding. The optimal conditions were found to be 20% DTPA, 120 °C, 3 h, and pH 10. Last, a low dosage of DTPA−soy flour/chitosan−OCC pulp was found to kill ∼95% of tested bacteria.

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INTRODUCTION

Selection of the Modification Agent. Approximately 5 g of the modifying agent [succinic acid, carboxymethyladipic acid, butanetetracarboxylic acid, ethylenediaminetetraacetic acid, or diethylenetriaminepentaacetic acid (DTPA)] was dissolved in 20 mL of deionized (DI) water in a 50 mL Petri dish. A total of ∼1 g of sodium hypophosphite (SHP) was then added to each modifying agent Petri solution. Soy flour (5 g) was combined with each modifying agent solution and vigorously mixed with a glass rod. The mixture was placed in an air oven at 130 °C for 4 h. The reaction products were washed with DI water and filtered several times to remove unreacted materials. The product obtained was modified soy flour, which was air-dried at 50 °C in an air oven overnight. The modified soy flour was complexed with chitosan using a known procedure that was previously described.9 Briefly, 1 g of chitosan was dissolved in 50 mL of a 1.5% acetic acid solution. Modified soy flour (1 g) was dissolved in 50 mL of water and added to 50 mL of chitosan solution in a 250 mL round-bottomed flask. The reaction mixture was stirred with a magnetic stirrer at 80 °C for 90 min.10 Approximately 2% modified soy flour additive by

Chemical modification of polysaccharides has been widely studied for the production of anionic, cationic, and amphoteric materials applied in paper, textiles, and food. Their modifications have typically been done by a classic Fisher esterification employing acetic anhydride, octenylsuccinic anhydride, citric acid, sodium monochloroacetate, fatty acid, epichlorohydrin, pentafluorobenzyl chloride, or fatty acid chlorides, among others.1−5 Etherification is also a common reaction especially for starch by using vinyl monomers for the production of hydrophobic starch in textile applications.6 Amphoteric starch has negatively and positively charged functional groups prepared with (3-chloro-2-hydroxypropyl)trimethylammonium chloride and sodium tripolyphosphate.7 Cationic starch has generally been prepared by reaction with (3-chloro-2-hydroxypropyl)amine.8 For the present research, selection of the modifying agent, optimal reaction conditions, and antimicrobial activity was pursued. Modifiers such as succinic acid, carboxymethyladipic acid, butanetetracarboxylic acid, ethylenediaminetetraacetic acid, and diethylenetriaminepentaacetic acid were reacted with soy flour in the presence of sodium hypophosphite and complexed with chitosan. A fixed amount of each modified soy flour additive was mixed in the pulp slurry to generate hand sheets. © XXXX American Chemical Society

EXPERIMENTAL SECTION

Received: February 26, 2016 Revised: June 16, 2016 Accepted: June 16, 2016

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DOI: 10.1021/acs.iecr.6b00776 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Article

Industrial & Engineering Chemistry Research

30 to 200 °C followed by isothermal heating at 200 °C for 15 min.15

mass relative to a OCC pulp-based slurry was thoroughly mixed before generation of a two-dimensional hand sheet for testing. Optimization of the Synthesis Conditions. Modification of soy flour was carried out in a 50 mL Petri dish with 10−50% DTPA and 5% SHP based on the weight of DTPA, pH 8−12, 100−140 °C, 1−5 h, and a soy flour−liquor ratio of 1:10. At the end of the reaction, the DTPA−soy protein flour product was washed with distilled water and dried.11 Thereupon, the DTPA−soy protein flour was complexed with chitosan at a solid-to-solid ratio of 1:1.12 Approximately 2% DTPA−soy flour/chitosan by mass relative to a OCC pulp-based slurry was mixed before generation of a two-dimensional hand sheet for testing. Optimization of the Complexation Reaction of Chitosan/Modified Soy Flour Additive. The complexation reaction was carried out in a 100 mL beaker with a 10:90− 50:50 chitosan/modified soy flour ratio at 40−90 °C for 0.5− 2.5 h. After the reaction, ∼2% DTPA−soy flour/chitosan by mass relative to a OCC pulp-based slurry was mixed before generation of a two-dimensional hand sheet for testing.10 Optimization of the Additive Dosage and pH. The hand sheet was prepared at varying DTPA−soy flour/chitosan additive concentrations, e.g., 0.5, 1, 1.5, and 2% based on the weight of an OD OCC pulp at pH 7. The tensile strength additive-treated OCC pulp sheet was tested to find the optimum additive dosage. Similarly, the additive-treated OCC pulp sheet was prepared at pH 3, 4, 5, 6, 7, and 8, separately, and the optimal pH was selected based on the highest tensile strength. Antimicrobial Activity of the Modified Soy Flour/ Chitosan System. The antimicrobial activities of both modified soy flour/chitosan and modified soy flour/chitosan additive-treated OCC pulp hand sheets were tested according to standard antimicrobial test method AATCC 147.13 A microbial suspension of bacteria (Escherichia coli and Staphylococcus aureus) was inoculated into the peptone liquid. After incubation in an air bath shaker (37.8 °C, 130 rpm) for 12 h, the culture broth was diluted. The peptone culture plates were prepared with mixtures of the microbial suspension and soy flour, modified soy flour/chitosan additive, or additive-treated OCC pulp sheet. A blank without a modified soy flour/chitosan additive or pulp sheet was also prepared for comparison. All the plates were incubated at 37.8 °C for 24 h. Last, the plates were taken out and the inhibition rate was calculated. The inhibition rate is defined as X=

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RESULTS AND DISCUSSION It was observed from Figure 1 that the DTPA-modified soyflour-treated OCC pulp exhibited a better tensile index relative

Figure 1. Effect of different types of modified soy flour on the mechanical properties of the pulp furnishings.

to the other modifying agents. The tensile properties of the modifiers are in the order DTPA > ethylenediaminetetraacetic acid > butanetetracarboxylic acid > carboxymethyladipic acid > succinic acid. It is observed from Figures 2−5 that the tensile index of DTPA−soy flour/chitosan additive-treated OCC pulp sheets

⎛ A − B⎞ ⎜ ⎟ × 100% ⎝ A ⎠

Figure 2. Effect of the DTPA concentration on the tensile indices of an additive-treated pulp sheet.

where A and B are the number of colonies on the plates before and after inhibition. Characterization. Fourier Tranform Infrared (FT-IR) Analyses. IR spectra of all modified soy flour samples were recorded on a PerkinElmer FT-IR spectrophotometer.14 Thermogravimetric Analysis (TGA). TGA was determined in this study with a TGA Q500 analyzer. A nitrogen atmosphere was used at a temperature range and heating rate of 30−600 and 5 °C/min, respectively, followed by isothermal heating at 600 °C.15 Differential Scanning Calorimetry (DSC). A DSC Q100 differential scanning calorimeter with a Hermetic pan (T090127) was used to determine the thermal behavior. Samples were subjected to a 2 °C/min temperature ramp from

increased at levels up to 20% DTPA, 3 h, 120 °C, and relatively pH-independent, after which the increases plateaued. Thus, 20% DTPA, 3 h, 120 °C, and pH 10 were therefore selected as the optimal conditions. Figure 6 demonstrates that the tensile index increases with increased chitosan addition up to 30% within DTPA−soy flour and then decreases. Figures 7 and 8 illustrate optimization of the complexation reaction time and temperature, which were obtained at 1.5 h and 80 °C, respectively. In Figure 9, the tensile index of an OCC pulp sheet increased with increasing additive concentration up to 1.5% and then decreased. It is also observed from Figure 10 that the tensile index of an additive-treated pulp sheet decreased with the pH B


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Figure 6. Effect of chitosan addition into modified soy flour on the tensile indices of pulp furnishings (complexation reaction time = 1 h, 80 °C).

Figure 3. Effect of time on the tensile indices of an additive-treated pulp sheet..

Figure 4. Effect of temperature on the tensile indices of an additive treated pulp sheet.

Figure 7. Effect of the complexation reaction time of a chitosan/ modified soy flour additive on the tensile indices of pulp furnishings (complexation reaction temperature = 80 °C; chitosan/modified soy flour ratio = 30:70).

Figure 5. Effect of pH on the tensile indices of an additive-treated pulp sheet. Figure 8. Effect of the complexation reaction temperature of a chitosan/modified soy flour additive on the tensile indices of pulp furnishings (complexation reaction time = 1.5 h; chitosan/modified soy flour ratio = 30:70).

up to 6 and then increased. On the basis of the tensile properties and efficiency considerations, the optimum additive dosage and pH were 1.5% and 4 and 8, respectively. However, the drainage was tested and found to increase to ∼18%, in which the additive retention was found to be 65%. Decomposition of modified and unmodified soy flour additives was studied under open-air conditions for about 2 years. The unmodified soy flour additive began decomposing within 24 h, as evidenced by foul odors. This was not observed for the modified soy flour additive sample. In addition, 0.1% modified soy flour additive was added to 1 kg of a soy protein flour solution, and decomposition was observed for 6 months, over which time no foul odors were observed. The antimicrobial activities of both modified and unmodified soy

flour and modified soy flour/chitosan additive-treated recycle pulp hand sheets were monitored according to the standard antimicrobial test method AATCC 147. A microbial suspension of bacteria (E. coli) was used, which in Figure 11 demonstrated that the bacteria colonies significantly increased when unmodified soy protein flour was added. Similar results were found for unmodified corn starch. The soy flour has metabolic proteins that highly encourage bacterial growth. However, no bacterial colonies were observed when modified soy flour/ chitosan was added (Figure 11). The modified soy flour/ C


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OCC pulp sheet did not show any antimicrobial activity. However, the modified soy flour/chitosan-treated OCC pulp sheet killed ∼95% of the bacteria. The bacteria killing rate was not 100%, likely because of the very low amount of additive incorporated. Characterization of Modified Soy Flour and Modified Soy Flour/Chitosan Additive. FT-IR Spectra. The FT-IR spectra of soy flour (A), soy flour−DTPA (B), and soy flour− DTPA/chitosan (C) are shown in Figure 12. The spectrum of

Figure 9. Effect of the additive dosage percentage on the tensile indices of an additive-treated pulp sheet.

Figure 12. FT-IR spectra of soy flour (A), soy flour−DTPA (B), and soy flour−DTPA/chitosan (C). The prominent 1748 cm−1 band derives from the ester carbonyl stretch (after DTPA linking).

soy flour shows a prominent peak at 1715 cm−1, which can be attributed to a carboxyl group from the soy protein. Not surprisingly, when the soy flour reacts with DTPA, an additional peak is observed at 1748 cm−1, and after further complexation with chitosan, signature peaks appeared at 1748 and 1664 cm−1, which are attributable to the ester carbonyl and amide of chitosan, respectively. Amide bands appeared because the soy flour−DTPA derivatives undergo complexation with chitosan followed by amidation from drying of the sample to >105 °C. This latter result implicates linking the soy flour− DTPA to chitosan by a coupling reaction between the amino groups of chitosan and the carboxylic groups of the soy flour− DTPA derivatives. Thermal Analysis. The thermal behavior of the soy flour derivatives is shown in Table 1. For several of the samples, a weight loss at ∼100 °C was attributable to water evaporation.14

Figure 10. Effect of pH on the tensile indices of an additive-treated OCC pulp sheet.

chitosan plays a significant role in killing the bacteria. The mechanism is likely attributable to an interaction between positively charged substrate molecules (the chitosan amino residues) and negatively charged microbial cell membranes.16 Once the columbic interaction occurs, there is a tendency for a flocculation event that disrupts the vital physiological activities of the microbes. In general, chitosan dissolves under acidic conditions to obtain positive charges that play a crucial role in preventing microbial digestion of soy flour and subsequent foul odor generation. It is also observed from Figure 11 that the

Figure 11. Antimicrobial activity of unmodified and modified soy flour/chitosan and modified soy flour/chitosan additive-treated OCC pulp sheets. D



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ACKNOWLEDGMENTS We are indebted to Georgia-Pacific, LLC, for the original 258 funding (Project ID No. 558678) that allowed portions of this work to be completed. We are especially grateful for the support and insight of Dr. Gary Boettcher, Dr. Rajesh Garg, and Dr. Aric Bacon provided for completion of this work. Finally, we acknowledge The Laboratory of Soft Materials & Green Chemistry for the infrastructure necessary to execute the experiments.

Table 1. Thermal Analysis of Soy Flour and Derivatives sample DTPA soy flour soy flour− DTPA soy flour− DTPA/ chitosan chitosan

TGA maximum (DTG) degradation temperature (°C)

residual char at 600 °C (%)

DSC endothermic peak (°C)

280.3 310.2 300.3

25.1 23.4 27.2

217.5 188.6 199.2

293.8

29.0

200.5

290.0

26.0

268.4

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REFERENCES

(1) Bhosale, R.; Singhal, R. Process optimization for the synthesis of octenyl succinyl derivative of waxy corn and amaranth starches. Carbohydr. Polym. 2006, 66, 521−527. (2) Tukomane, T.; Varavinit, S. Influence of octenyl succinate rice starch on rheological properties of gelatinized rice starch before and after retrogradation. Starch/Stärke 2008, 60, 298−304. (3) Chi, H.; Xu, K.; Xue, D.; Song, C.; Zhang, W.; Wang, P. Synthesis of dodecenyl succinic anhydride (DDSA) corn starch. Food Res. Int. 2007, 40, 232−238. (4) Aburto, J.; Alric, I.; Borredon, E. Preparation of long-chain esters of starch using fatty acid chlorides in the absence of an organic solvent. Starch/Stärke 1999, 51, 132−135. (5) Fang, J. M.; Fowler, P. A.; Tomkinson, J.; Hill, C. A. S. The preparation and characterisation of a series of chemically modified potato starches. Carbohydr. Polym. 2002, 47, 245−252. (6) Bayazeed, A.; Farag, S.; Shaarawy, S.; Hebeish, A. Chemical modification of starch via etherification with methyl methacrylate. Starch/Stärke 1998, 50, 89−93. (7) Youquan, Z.; Zhangfa, T.; Bengshan, Z. Preparation of phosphate amphoteric starch in simultaneous process and its application. Chem. J. Internet 2003, 5, 34−40. (8) Khalil, M.; Farag, S.; Hashem, A. Preparation and characterization of some cationic starches. Starch-Starke 1993, 45, 226−231. (9) Wing, R. E. Starch citrate: preparation and ion exchange properties. Starch-Starke 1996, 48, 275−279. (10) Salam, A.; Pawlak, J.J; Venditti, A. R.; El-tahlawy, K. Synthesis and characterization of starch citrate-chitosan foam with superior water and saline absorbance properties. Biomacromolecules 2010, 11, 1453− 1459. (11) Salam, A.; Pawlak, J.J; Venditti, A. R.; El-tahlawy, K. Incorporation of carboxyl group into hemicelluloses for improved absorbency. Cellulose 2011, 18, 1033−1041. (12) Salam, A.; Lucia, A. L.; Jameel, H. A Novel cellulose nanocrystals-based approach to improve the mechanical properties of recycled paper. ACS Sustainable Chem. Eng. 2013, 1, 1584−1592. (13) AATCC test method 147. (14) Salam, A.; Pawlak, J.J; Venditti, A. R.; El-tahlawy, K. Crosslinked hemicellulose citrate-chitosan aerogel foams. Carbohydr. Polym. 2011, 84, 1221−1229. (15) Alonso, D.; Gimeno, M.; Olayo, R.; Vázquez-Torres, H.; Sepúlveda-Sánchez, D. J.; Shirai, K. Cross-linking chitosan into UVIrradiated Cellulose Fibers for the Preparation of AntimicrobialFinished Textiles. Carbohydr. Polym. 2009, 77, 536−543. (16) Zheng, L.-Y.; Zhu, J.-F. Study on antimicrobial activity of chitosan with different molecular weights. Carbohydr. Polym. 2003, 54, 527−530.

However, a weight loss at >100 °C was likely caused by thermal decomposition of the soy flour and its derivatives.10 DTPA had a single sharp decomposition peak at 280.3 °C, whereas the soy flour had a single weight loss peak at 310.2 °C; however, all derivatives of soy flour displayed a decrease in the maximum weight loss temperature and a significantly higher residual mass after heating to 600 °C. The latter result is likely due to the soy flour surface-modifying agents having a lower decomposition temperature and the materials derived from esterification possessing a lower temperature of degradation.15 The thermal behavior obtained from DSC analysis of the soy flour derivatives is shown in Table 1. DTPA displays a very sharp endothermic peak at 217.5 °C, whereas for the soy flour, an endothermic peak was observed at 188.6 °C. The endothermic peak increased for the reaction products, as illustrated in Table 1. The increase in the magnitude of the endothermic peak may originate from changes in the chemical composition from increased hydrogen bonding and plasticization as well as an increase in the molecular organization from esterification.14

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CONCLUSIONS Five different types of modified soy flour additives were mixed with pulp slurries to generate pulp hand sheets. DTPAmodified soy-flour-additive-treated OCC pulp sheets exhibited better tensile versus other modifying agents. Four variables including the agent concentration, time, temperature, and pH were considered, and it was determined that, from an efficiency perspective, 20% DTPA, 3 h, 120 °C, and pH 10 were the optimal parameters for its manufacture. The complexation reaction conditions (chitosan percentage, time, and temperature) between chitosan and DTPA−soy flour were optimized. The optimal chitosan addition percentage, time, and temperature were 30%, 1.5 h, and 80 °C, respectively. On the basis of tensile, the optimum additive dosage and pH were 1.5% and 4 and 8, respectively. The drainage ability increased 18%, and the additive retention was found to be 65%. It was shown that DTPA−soy flour/chitosan killed 100% bacteria, but DTPA− soy flour/chitosan-treated OCC pulp killed ∼95% of the bacteria.

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AUTHOR INFORMATION

Corresponding Author

*Tel: +1 919 515 7707. Fax: +1 919 515 6302. E-mail: lalucia@ ncsu.edu. Notes

The authors declare no competing financial interest. E


Chitosan-Based Reagents Endow Recycled Paper Fibers with

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