(APMP) Effluent and - American Chemical Society

Article pubs.acs.org/IECR

Grafted Copolymerization Modification of Hemicellulose Directly in the Alkaline Peroxide Mechanical Pulping (APMP) Effluent and Its Surface Sizing Effects on Corrugated Paper Liying Dong,* Huiren Hu, Shuo Yang, and Fei Cheng Tianjin University of Science and Technology, 13th Street, Binhai, Tianjin 300222, People’s Republic of China S Supporting Information *

ABSTRACT: In this work, the graft copolymerization of acrylamide (AM) and methacryloyloxy ethyl trimethyl ammonium chloride (DMC) with the hemicellulose in the alkaline peroxide mechanical pulping (APMP) effluent was investigated using the Fenton agent (FeSO4/H2O2) as an initiator. The effects of the reaction conditions on the characteristics of the graft copolymers were studied. On the basis of the graft copolymer characterization, the optimum conditions were as follows: total active ingredient concentration 31%, reactive temperature 50 °C, amount of the initiator 0.4%, ratio of H2O2 to FeSO4 1:1, molar ratio of DMC to AM 1.5:20 and optimum percentages of C, G, GE, and viscosity are 65%, 246%, 98%, and 5020 cP, respectively. Structure elucidation of the graft copolymer was obtained by 1H NMR spectroscopy and FT-IR. Gel-permeation chromatography (GPC) was employed to determine the molecular mass and molecular mass distribution of hemicellulose and graft copolymer. The thermal degradation properties of hemicellulose and the graft copolymers were measured by thermo gravimetric analysis (TGA). The graft copolymer was subsequently used as a corrugated paper surface sizing agent, which can significantly improve the physical strength and water resistance of corrugated paper. effluent.9,10 Xylan is the main hemicellulose in hardwood, which is a polysaccharide. Some researchers have synthesized graft copolymers using xylan.11,12 However, there have been no studies focused on grafting vinyl monomers with hemicellulose directly using APMP effluent and for further applications, which contains hemicellulose (53% based on the dry weight of APMP effluent), lignin (13% based on the dry weight of APMP effluent), organic acids and inorganic salts. In this work, first, the qualitative and quantitative determination of the compositions in the APMP effluent was done. Then the graft copolymerization of acrylamide (AM) and methacryloyloxy ethyl trimethyl ammonium chloride (DMC) was investigated with the hemicellulose, which directly used APMP effluent, rather than using hemicellulose that was isolated from APMP effluent. The main reason was that the high cost of precipitation hemicellulose from APMP effluent by ethanol did not apply to industrial production. The graft copolymer was subsequently used as a corrugated paper surface sizing agent. The graft copolymer has the potential to be a new type of surface sizing agent. This method allows for the reduction of wastewater emissions from paper mills as well as provides a new method for the utilization of biomass resources in APMP effluent. Corrugated paper used as packaging material must exhibit good physical strength as well as liquid water or moist air resistance, which is typically achieved by sizing treatment during paper manufacture. Sizing includes internal sizing and surface sizing. The internal sizing agents are often reactive substances, such as alkyl ketene dimer (AKD),13−15 alkenyl

1. INTRODUCTION In recent years, many new APMP and P-RC APMP lines (preconditioning followed by refiner chemical treatment alkaline peroxide mechanical pulping lines) have been installed in China, and a large amount of APMP effluent has been produced. Currently, there are two different processes for treating the APMP effluent. In some pulp mills abroad, the APMP effluent is combined with the chemical pulping effluent in an existing chemical recovery system, which greatly reduces pollution and emission. The hemicellulose, which is produced annually as a byproduct of the pulping and papermaking process, is burned with a lower heat of combustion compared to lignin, which wastes biomass resources. The most widely employed approach for treating APMP effluent is the threestage flocculation−biological−flocculation process, which can effectively treat the APMP effluent, but its capital investment and operating cost are high.1 Directly discharging effluent causes environmental pollution and results in the waste of biomass materials. The utilization of a biomass feedstock (hemicellulose) in pulping effluent ingredients has recently drawn considerable attention. However, the hemicelluloses that are isolated from pulping effluent have a low molecular weight, which inhibits their direct application.2 Various chemical modifications of hemicellulose have been reported in the literature, including esterification, etherification, methacrylation, and graft copolymerization.3−8 These methods are the most commonly applied modification methods for polysaccharides. Graft polymerization is an effective way to overcome the disadvantages of hemicellulose and to tailor properties for specific end uses. Most graft copolymers are formed by radical polymerization. A considerable number of free radical grafting methods have been reported for the grafting of vinyl monomers onto hemicellulose, which are isolated from the pulping © 2014 American Chemical Society

Received: Revised: Accepted: Published: 6221

January 7, 2014 March 7, 2014 March 7, 2014 March 7, 2014 dx.doi.org/10.1021/ie4044423 | Ind. Eng. Chem. Res. 2014, 53, 6221−6229

Industrial & Engineering Chemistry Research

Article

Figure 1. Scheme for analysis of compositions in the APMP effluent.

succinic anhydride (ASA),16 rosin,17 which can form covalent bonds with the hydroxyl groups in cellulose.18,19 In contrast, surface sizing agents are nonreactive substances that are supposed to have both hydrophilic and hydrophobic end groups. After sizing, surface sizing agents can form a continuous film and cover the paper cellulose resulting in a water-repellent paper surface. For decades, starch has been the most common surface sizing agent. However, recent attention has been focused on the fact that starch is also part of the food supply chain. Therefore, abundant nonfood natural polymers, such as hemicellulose, have great potential for material applications. In this work, the graft copolymer was added to Al2(SO4)3 to replace part of the starch that was used as the corrugated paper surface sizing agent. The sized papers exhibited improved physical strength and water resistance compared to starch.

chromatography combined with mass spectrometry (GS/MS). The scheme for analysis of compositions of the APMP effluent was outlined in Figure 1. 2.2.2. Synthesis of Graft Copolymer. The desired amount of APMP effluent (240 mL: the content of hemicellulose was 6.75%) was introduced into a 500 mL three-necked roundbottom flask. Chelating agents (N,N′-methylenebisacrylamide) (0.033g:0.03% based on the mass of active ingredient in the reaction system), FeSO4, AM (2.5−4.1 mol/L) and DMC (0.25−0.41 mol/L) were sequentially added with constant stirring. Then, the mixture was stirred for an additional 10 min and the pH adjusted with 6 M NaOH or 6 M H2SO4. The reaction system was deoxygenated under a nitrogen atmosphere for 20 min prior to the reaction. Next, the H2O2 initiator was diluted in a certain amount of distilled water (40 mL). Upon reaching the desired temperature, the reaction was initiated by dropwise addition of the H2O2 solution, which was added with a peristaltic pump over a certain period of time. After adding the initiator, the reaction was allowed to continue at a stirring rate of 60 rpm for 4 h until the reaction was complete. 2.3. Graft Copolymer Characterization. The apparent viscosity is proportional to the graft copolymer average molecular weight. The apparent viscosity determination of the graft copolymer was determined by a rotating viscometer at 50 °C with a stirring rate of 100 rpm. The graft copolymerization process was accompanied by homopolymerization. The mixture that contained the homopolymer and graft copolymer was precipitated and washed repeatedly with an excess of 95% ethanol. Because the dissolution properties of graft copolymer and homopolymer were different, the homopolymer was extracted with acetone using a Soxhlet extractor. Then, the solid mass was dried in a

2. EXPERIMENTAL SECTION 2.1. Materials. The APMP effluent in this study (pH = 7.12, concentration 14.5%) was poplar APMP pulping effluent supplied by a paper mill in the Shandong province in China. The corrugated paper and starch were supplied by a paper group in Tianjin, China. Hydrogen peroxide (H2O2, 30%) and the other chemicals used in this study were analytical reagents obtained from Tianjin Kermel Chemical Reagent Development Center in China. 2.2. Methods. 2.2.1. Qualitative and Quantitative Determination of Compositions in the APMP Effluent. The solid content of APMP effluent was determined according to the TAPPI standard. The contents of hemicellulose and lignin were determined by gravimetric method. Extractives were separated according to the previously reported literature.20 The identification of the extractives was performed using gas 6222

dx.doi.org/10.1021/ie4044423 | Ind. Eng. Chem. Res. 2014, 53, 6221−6229


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vacuum oven at 50 °C for 24 h. The final dry product was used for subsequent analysis. The grafting percentage (G), the grafting efficiency (GE), and the monomer conversion (C) were calculated using the following equation:

3. RESULTS AND DISCUSSION 3.1. Qualitative and Quantitative Determination of Compositions in the APMP Effluent. In the process of APMP pulping, many substances are dissolved, such as carbohydrates, lignin, as well as lipophilic extractives. In order to directly utilize hemicellulose in APMP effluent as a feedstock for production of higher value added products, it is essential to assess the chemical composition of the APMP effluents. The results showed that the solids content of the APMP effluent was 14.5%; 6.75% and 2.92% hemicellulose and lignin were isolated from APMP effluent, respectively. The others were lipophilic extractives and inorganic compounds. The chemical compounds identified of extractives were by GC/MS. The GC/MS chromatograms of the extractives are presented in Figure 2 and Supporting Information, SI, Tables S1 and S2.

G = (W2 − W0)/W0 × 100% GE = (W2 − W0)/(W1 − W0) × 100%

C = (W1 − Wm)/Wm × 100%

where W0 is the initial weight of the hemicellulose in the APMP effluent, W1 is the weight of the graft copolymer before the extraction, W2 is the weight of the graft copolymer after the extraction, and Wm is the weight of the AM and DMC monomers in the graft copolymerization reaction. The charge density of the graft copolymer was measured with a concentration of 10−5g/g in distilled water aqueous solution at room temperature using a Muteck PCD-03 charge analyzer. 2.4. Surface Sizing of Corrugated Paper and Sizing Performance. The surface sizing agent in the presence of 10% graft copolymer along with starch (70%) and Al2(SO4)3 (20%) was used to size the corrugated paper (100 g/m2). The concentration of sizing agent was 8%. The sizing was performed using a laboratory coater on the surface of the corrugated paper with a size press pickup of 6 g/m2 at the temperature of 65 °C. The sized paper sheets were dried with a dryer at 118−127 °C. The physical strength properties of the corrugated paper were determined according to TAPPI standard methods (50% RH, 23 °C). The water resistance was measured using a Cobb tester, which was used to represent the amount of water absorbed by the paper after bearing water with a height of 10 mm for 60 s at room temperature. 2.5. Graft Copolymers Verification. 2.5.1. Fourier-Transformed Infrared Spectroscopy (FT-IR) Analysis. The FT-IR spectra was recorded with a FTIR-650 scanning from 4000 to 400 cm−1 with a resolution of 2 cm−1 using KBr pellets at room temperature. 2.5.2. Nuclear Magnetic Resonance (1H NMR) Analysis. 1H NMR spectra was obtained from a Bruker DRX600 spectrometer operating at 400 MHz. The spectra was recorded at 25 °C. Chemical shifts (δ in ppm) were expressed relative to the resonance of Me4Si (TMS; δ = 0). Samples for 1H NMR analysis were prepared by dissolving 40 mg graft copolymer in 0.6 mL D2O.22 2.5.3. Thermogravimetric Analysis. The thermal degradation properties of hemicellulose and the graft copolymers were measured by thermogravimetric analysis (TGA). The sample was heated from room temperature to 800 °C at a heating rate of 20 °Cmin−1 in nitrogen (99.999%) gas at a flow rate of 30 mL/min. 2.5.4. Molecular Mass and Distribution of Molecular Weight Analysis. The molecular mass and molecular mass distribution of hemicellulose and graft copolymer were determined using gel-permeation chromatography (GPCMALS, Wyatt Technology Corporation) using dual detectors (Wyatt-DAWN HELEOS-II and Wyatt-Optilab rex).23 Hemicellulose and graft copolymer were dissolved in 0.1 M NaNO3 and 0.02% NaN3, at pH 9. The mobile phase was 0.1 M NaNO3 and 0.02% NaN3 (PH9) at a flow rate of 0.5 mL/min . The analysis was performed at the temperature 40 °C ..

Figure 2. Chromatogram of MTBE extractives.

GC/MS results (Figure 2) shows that APMP effluent contained a large number of extractives. Sixty compounds had been identified and classified in a single chromatogram. The low-molecular-weight hydroxy acid content was up to 32.5% of the total extractives. Meanwhile, extractives also contained comparable lignans, and the lignan content was 18%. Utilizing extraction with methl tert-butyl ether (MTBE), both lipophilic and phenolic low-molecular-mass components were extracted in high yield by MTBE.21 These latter components were classified into fatty acids, sterols, and glycerides. Fatty acids were shown to be the main group of lipophilic extractives followed by sterols and glycerides. The amouts of fatty acids and sterols were relatively high in wood plants because most of these compounds exist in esterified form. Sterol esters are formed by sterols and fatty acids. The common saturated fatty acids [Myristic acid (C14:0), hexadecanoic acid (C16:0), and docosanoic acid (C22:0)] and the unsaturated fatty acids [9octadecenoic acid (C18: 1) and 9,12-octadecadienoic acid (C18: 2)] were found in the APMP effluent. Hexadecanoic acid (C16: 0) and 9,12-octadecadienoic acid (C18: 2) were the most dominant. Sterols were found to be the second main group, dominated by sitosterol and stigmastanol. Others include campesterol in lesser amouts, and fatty alcohols (1dodecanol and 1-octadecanol) were found in relatively small amounts. 3.2. Graft Copolymers Verification. From the above analysis results, the compositions of APMP effluent are very complex. Hemicellulose are the main organic ingredients in the APMP effluent. The goal of our present investigation was to 6223



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since hemicellulose usually has a strong affinity for water. The 1405 cm−1 absorption represents the −CH2− streching vibration. The absorptions at 1081, 1052, 860, 620, and 545 cm−1 corresponded to the glycosidic linkage C−O−C bending vibration. The graft copolymer infrared spectra contained new peaks in addition to the characteristic absorption peaks of hemicellulose. The Graft copolymers peak at 1658 cm−1 was attributed to the CO stretching vibration in CONH2 (AM) and −COOCH2−. The peak at 1413 cm−1 was attributed to the methylene bending in −CH2−N+ (CH3)− (DMC). The peaks at 1114 and 617 cm−1 were attributed to C−O−C asymmetric stretching in −COOCH2− (DMC). The peak at 958 cm−1 was attributed to the peaks of the quaternary ammonium salts. The spectrum of the characteristic group observed on the graft copolymer confirmed that AM and DMC had grafted onto the hemicellulose. 3.2.2. 1H NMR Spectrum of the Graft Copolymer. The structural features hemicellulose and graft copolymer were analyzed by employing 1H NMR experiments. 1H NMR spectrum of hemicellulose and graft copolymer are presented in Figures 4 and 5. A strong signal at 4.779 ppm was attributed to the residual solvent (HDO). Comparing Figures 4 and 5, the signals within the range of 3.3−5.5 ppm were assigned to the proton spectrum of hemicellulose.22 The anomeric H signals were found in the spectral region of 4.521−5.417 ppm22 and the ring proton region (3.474−4.521 ppm). The signals at 3.474, 3.649, 3.779, 3.794, and 4.068 ppm were attributed to H2, H-3, H-4, H-5eq, H-5ax, of D-Xylp, respectively. Concerning the arabinofuranose (Araf) units, which were decorated at the C-2 and C-3 position of Xylp,23 the signals of H-1, H-2, H-3, H-4, H-5ax, and H-5eq appeared at 5.417, 3.998, 4.14, 4.278, 3.779, and 3.667 ppm.24 Moreover, the weak signals at 5.276, 3.72, 3.208, 3.474 ppm were characteristic respectively of H-1, H-3, H-4, and OCH3 of 4-O-methyl-D-glucuronic acid, which attached to the (1−4)-D-Xylp at position of C-2.25 Several

investigate whether grafted copolymerization modification of hemicellulose could be performed directly in APMP effluent, rather than using extracted hemicellulose. The characterization of the graft copolymer gave us the answers. 3.2.1. FT-IR Characterization of Graft Copolymer. The chemical structures of hemicellulose and graft copolymer were characterized by FT-IR. Figure 3 shows the infrared spectra of the unmodified hemicellulose extracted from the APMP effluent and the graft copolymer.

Figure 3. FT-IR spectra of hemicellulose and the graft copolymer.

The original absorptions of hemicellulose at 3415, 2829, 1637, 1405, 1081, 1052, 860, 620, and 545 cm−1 were indicative of hemicellulose. The signals at 3415 and 2829 cm−1 were assigned to the stretching −OH and −CH, respectively. The absorption at 1637 cm−1 was attributed to the absorbed water,

Figure 4. 1H NMR spectrum of hemicellulose. 6224



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Figure 5. 1H NMR spectrum of the graft copolymer.

characteristic peaks were due to the addition of different monomers. The protons in the methenyl (−CH2−(1), −CH− (2))connected to amide group in AM were evidenced by the peaks at 1.665 and 1.782 ppm(1), and 2.220 and 2.349 ppm(2), respectively. The protons in the methyl (−CH3 (6)) group connected to the ammonium group in DMC could be found at 3.208−3.251 ppm26 (6). The protons (−CH3(3), −CH2−(4), −CH2−(5)) in DMC were exhibited at 1.169, 1.204, and 1.286 ppm (3), 4.424 ppm (4), and 3.684 ppm (5), respectively, which confirmed the successful graft of AM and DMC onto hemicellulose . 3.2.3. TG Analysis. The thermal behavior of the hemicellulose and graft copolymer was distinguished by the TG analysis. TG and differential thermo-gravimetric (DTG) curves are shown in Figure 6. The TG thermogram and DTG curve of hemicellulose indicated that there were three weight loss stages. The first

decomposition step was recorded from room temperature to 144 °C with a 7% weight loss, which was attributed to the evaporation of absorbed moisture. Almost no chemical reactions occurred. The second degradation step occurred in the range of 144−338 °C with a maximum decomposition temperature peak at 248 °C, and the mass loss was approximately 36.5%, which was due to the pyrolysis of hemicellulose. The final degradation stage was detected in the range of 338−611 °C with a 25.1% weight loss due to the formation and evaporation of some volatile compounds. In comparison to hemicellulose, three weight loss stages were observed below 800 °C . The first decomposition step in the range of 168−273 °C with a 14.5% weight loss was primarily due to degradation of hemicellulose, partially due to degradation of the lateral chain in the graft copolymers. The second degradation step in the range of 273−456 °C, which exhibited a 39.2% weight loss, was primarily due to the degradation of the lateral chain in graft copolymers. The graft copolymers product exhibited a new decomposition peak at 323 °C, which was due to the degradation of the polyacrylamide side chain. The third degradation step of the graft copolymer in the range of 456−757 °C was due to the decomposition of hemicellulose and the coking process, which supported the success of grafting AM and DMC onto hemicellulose (polyacrylamide exhibits no degradation above this temperature). By chemical modification of hemicellulose, the thermal resistance properties can be increased. 2.2.4. Molecular Weight and Molecular Weight Distribution Analysis. In order to investigate the difference of molecular weight between hemicellulose and graft copolymer, molecular weight and molecular weight distribution were analyzed by gel-permeation chromatography (GPC). The GPC results are shown in Figures 7 and 8, SI Tables S3 and S4. As seen in Figure 7, the number average molecular mass (Mn) and weight average molecular mass (Mw) of hemicellulose were 1383 and 6117 g/mol, respectively, which were lower than those of natural hemicellulose. Their polydispersity, defined by

Figure 6. TGA and DTG curves for hemicellulose and the graft copolymer. 6225



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Figure 7. Molecular weight distribution curves of hemicellulose.

Figure 8. Molecular weight distribution curves of the graft copolymer.

the ratio Mw/Mn, was 4.43, which showed a relatively high polydispersity index, inplying a chemical and structural heterogeneity. Compared with hemicellulose, the number average molecular mass (Mn) and weight average molecular mass (Mw) of graft copolymer were higher than those of hemicellulose, which were 191 400 and 221 000 g/mol, Their polydispersity value was 1.155, which was under 1.4, and a rather small value for a polymer, which implied that the graft copolymer was more homogeneous and had better application performance.26 3.3. Influence of Reaction Conditions on Hemicellulose Graft Copolymer Characterization. According to radical polymerization theory, selection of initiator systems for graft copolymerization reactions is critical for achieving a high degree of grafting and directly relates to the initiation temperature and the amount of initiator in the polymerization system. In this study, several common initiators, including ceric

ammonium nitrate, FeSO4/H2O2, ammonium persulphate, sodium hydrogen sulphite, and ammonium persulphate were studied. Because of the complexity of the APMP effluent, only FeSO4/H2O2 was capable of initiating grafting. The effects of the reaction conditions on the grafting percentage (G), grafting efficiency (GE), the percentage monomer of conversion (C), and the apparent viscosity were studied. The results are shown in SI Figures S1−S11. 3.3.1. Effect of the Total Active Ingredient Concentration. The total active ingredient concentration varied from 27 to 38% by changing the AM and DMC monomer concentrations. The graft copolymer C, GE, and G decreased as the total active ingredient concentration increased. However, the viscosity of the grafting copolymer increased as the total active ingredient concentration increased, and then, the viscosity decreased. The decrease in C, GE, and G as the total active ingredient concentration increased could be attributed to a higher 6226



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Table 1. Effect of the Graft Copolymer on the Physical Properties and the Water Resistance of Corrugated Papera paper

tensile index (N·m·g )

tensile index increased ratio (%)

1 2 3

34.8 51.25 57.9

47 66

a

−1

ring crush index (N·m·g )

ring crush index increased ratio (%)

4.49 6.27 7.57

40 69

−1

burst index (kpa·m2·g )

burst index increased ratio (%)

Cobb value (g·m−2)

1.08 1.42 1.69

31 56

127.1 77.2 27.6

−1

1, original paper; 2, starch + 20%Al2(SO4)3; 3, starch + 20%Al2(SO4)3 + 10% Graft copolymer.

3.3.5. Ratio of DMC/AM. The DMC/AM ratio varied from 1:20 to 3:20. The DMC/AM ratio was the key parameter affecting both the properties of the graft copolymer and the cost of the product. The DMC/AM ratio also determined the cationic degree of the graft copolymer. The graft copolymer C, GE, G, viscosity, and cationic degree gradually increased as the DMC/AM ratio increased. When the DMC/AM ratio was 1.5:20, the graft copolymer, which is typically electronegative, became electropositive (0.002 mmol/g).

monomer concentration leading to multiple radical sites. A certain concentration range (27−31%) was favorable for the formation and extension of the graft chain. However, a further increase in the monomer concentration stimulated the formation of the AM homopolymer and small chains grafted onto the hemicellulose, which was evident from the decrease in the viscosity of the graft copolymer at higher concentrations. 3.3.2. Effect of Reaction Temperature. The temperature of the graft copolymerization reaction varied from 30 to 70 °C. The graft copolymer C, GE, G, and viscosity increased up to a temperature of 50 °C and then decreased, which is most likely due to the increased diffusion rate of the monomer and the decomposition rate of H2O2 as the temperature increased. Nevertheless, a higher temperature reduced the effectiveness of the initiator due to a shorter half-life resulting in graft copolymerization with poor selectivity leading to the formation of more homopolymers and an accelerated termination process. 3.3.3. Effect of the Amount of Initiator. The amount of the initiator varied from 0.1% to 0.5%. The graft copolymer C, GE, G, and viscosity increased as the amount of the initiator increased. The highest increase rate of C, GE, G, and viscosity was obtained with 0.4% of initiator. Beyond this point, the graft copolymer formation decreased slightly. When the amount of initiator was 0.1%, G was 0%, and there was no significant change in the viscosity in the reaction medium, indicating that the grafting reaction did not occur. The initial increase in the C, GE, G, and viscosity as the amount of initiator increased was due to the formation of a larger amount of radicals and more active grafting sites, which was beneficial to the graft copolymerization.9 A further increase in the initiator amount resulted in an increase in the termination reactions and chain transfer rate due to an increased number of free radicals. Furthermore, the homopolymer formation at a higher initiator concentration competed with the grafting reaction for the available monomers, leading to a decrease in C, GE, G, and viscosity. 3.3.4. Effect of the Molar Ratio of H2O2/FeSO4. The molar ratio of H2O2/FeSO4 varied from 10:30 to 10:6. The graft copolymer C, GE, and G increased as the molar ratio of H2O2 /FeSO4 increased and then decreased. The maximum percentages of C, GE, G, and viscosity were obtained when the molar ratio of H2O2/FeSO4 was 1:1. This result may be due to the property of the redox initiator used in the grafting reactions. The ratio of H2O2/Fe2+ plays an essential role in controlling the graft polymerization initiation by the Fenton reagent because the hydroxyl radical that was formed by the reduction of hydrogen peroxide by a ferrous ion initiated the homopolymerization of the AM monomers and created radicals at different sites on the hemicellulose molecule resulting in the production of graft copolymers. However, an excess amount of ferrous ion could inhibit free radical polymerization, resulting in decreasing percentages of C, GE, G, and viscosity. However, a low dose of ferrous ion affected the activity of the initiator.

4. EFFECTS OF THE GRAFT COPOLYMER SURFACE SIZING ON THE PHYSICAL PROPERTIES AND WATER RESISTANCE OF CORRUGATED PAPER The purpose of the paper surface sizing is to improve the paper’s resistance to both liquid water and moist air, as well as improve the physical properties of the paper. The main components of the APMP effluent are hemicellulose, lignin, and organic acids, which are all hydrophilic. The direct graft copolymerization of vinyl monomers (AM and DMC) with hemicellulose using APMP effluent cannot change its hydrophilicity. Therefore, certain amounts of Al2(SO4)3 (20%) were added to the graft copolymer surface sizing agent, which results in a clear improvement in the water resistance. The Al2(SO4)3 addition results in adsorbed aluminum compounds that form cationic sites on pulp fibers after surface sizing. Then, the anionic trash with anionic charges from the APMP effluent were adsorbed onto the cationic sites of the pulp fibers reducing the impact of the wet-end white water after waste paper recycling. The effect of 10% dosages of graft copolymer along with starch (70%) and Al2(SO4)3 (20%) on the physical properties of the corrugated paper and the water resistance properties are shown in Table 1. The rate of increase of the tensile index, ring crush index, and burst index were 19%, 29%, and 25%, compared to those of paper sized with starch, respectively. The Cobb value was 27.6 g/m2. The physical properties of the paper significantly improved. These results were attributed to the role of the hydroxyl group (−OH and −NH2) and the covalent bonds formed between the cellulose and the graft copolymer sizing agent, which was beneficial to the physical strength of the corrugated paper. 4. CONCLUSIONS (1) In this study, the graft copolymers were directly synthesized using APMP effluent with AM and DMC. The optimum synthesis conditions of the graft copolymerization were as follows: total active ingredient concentration 31%, reaction temperature 50 °C, amount of initiator 0.4%, ratio of H2O2/FeSO4 1:1, molar ratio of DMC/AM 1.5:20. The optimum G, GE, C, and viscosity were 65%, 246%, 98%, and 5020 cP, respectively. (2) The graft copolymer dosage (10%) combined with starch (70%) and Al2(SO4)3 (20%) can increase the tensile 6227



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index, ring crush index, and burst index by 19%, 29%, and 25%, compared to those of paper sized with starch, respectively. The Cobb value was 27.6 g/m2. (3) The structure elucidation of the graft copolymer by 1H NMR spectroscopy and FT-IR had confirmed that AM and DMC had been grafted onto the hemicellulose. (4) The graft copolymer has the potential to be a new type of surface sizing agent. In addition, this method for APMP effluent utilization is conductive to reducing paper mill wastewater emissions as well as providing a new method for biomass resource utilization.

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ASSOCIATED CONTENT

S Supporting Information *

The effect of the total active ingredient concentration on C, GE, and G (Figure S1); The effect of temperature on C, GE, and G (Figure S2); the effect of the amount of initiator on C, GE, and G (Figure S3); the effect of the H2O2/FeSO4 molar ratio on C, GE, and G (Figure S4); the effect of the DMC/AM molar ratio on C, GE, and G (Figure S5); the effect of the total active ingredient concentration on the viscosity (Figure S6); the effect of temperature on viscosity (Figure S7); the effect of the amount of initiator on the viscosity (Figure S8); the effect of the H2O2/FeSO4 molar ratio on the viscosity (Figure S9); the effect of the DMC/AM molar ratio on the viscosity (Figure S10); The effect of the DMC/AM molar ratio on the charge density of the graft copolymer (Figure S11); main compositions and relative amounts of MTBE extractives (Table S1); main compositions and relative amounts of lipophilic extractives (Table S2); molecular weight and molecular weight distribution of hemicellulose (Table S3); molecular weight and molecular weight distribution of the graft copolymer (Table S4). This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Tel: +86 18631613698. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors would like to acknowledge the financial support from the Scientific and Technological Supporting Program of the Ministry of Science and Technology of China (Grant No. 2011BAC11B04), and the Tianjin R&D Innovation System and Facility Development Program (Grant No.10SYSYJC28000).

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REFERENCES

(1) Liu, T.; He, Z.; Hu, H.; Ni, Y. Treatment of APMP Pulping Effluent Based on Aerobic Fermentation with Aspergillus Niger and Post-Coagulation/Flocculation. Bioresour. Technol. 2011, 102, 4712. (2) Ye, D. Z.; Jiang, X. C.; Xia, C.; Liu, L.; Zhang, X. Graft Polymers of Eucalyptus Lignosulfonate Calcium with Acrylic Acid: Synthesis and Characterization. Carbohydr. Polym. 2012, 89, 876. (3) Wan, X.; Li, Y.; Wang, X.; Chen, S.; Gu, X. Synthesis of Cationic Guar Gum-Graft-Polyacrylamide at Low Temperature and Its Flocculating Properties. Eur. Polym. J. 2007, 43, 3655. (4) Thakur, V. K.; Thakur, M. K.; Gupta, R. K. Graft Copolymers from Cellulose: Synthesis, Characterization and Evaluation. Carbohydr. Polym. 2013, 97, 18. 6228



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