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Co-production of thermoplastic composites with solid residue from enzymatic hydrolysis of recycled paper sludge
Accepted Manuscript Co-production of thermoplastic composites with solid residue from enzymatic hydrolysis of recycled paper sludge
Pedro Henrique Gonzalez de Cademartori, Francine Ceccon Claro, Nelson Potenciano Marinho, Patrícia Raquel Silva Zanoni, Washington Luiz Esteves Magalhães PII:
S0959-6526(17)31178-2
DOI:
10.1016/j.jclepro.2017.06.009
Reference:
JCLP 9759
To appear in:
Journal of Cleaner Production
Received Date:
18 May 2016
Revised Date:
05 April 2017
Accepted Date:
03 June 2017
Please cite this article as: Pedro Henrique Gonzalez de Cademartori, Francine Ceccon Claro, Nelson Potenciano Marinho, Patrícia Raquel Silva Zanoni, Washington Luiz Esteves Magalhães, Co-production of thermoplastic composites with solid residue from enzymatic hydrolysis of recycled paper sludge, Journal of Cleaner Production (2017), doi: 10.1016/j.jclepro.2017.06.009
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Wordcount: 4149
Co-production of thermoplastic composites with solid residue from enzymatic hydrolysis of recycled paper sludge
Pedro Henrique Gonzalez de Cademartori a, Francine Ceccon Claro b, Nelson Potenciano Marinho a, Patrícia Raquel Silva Zanoni c, Washington Luiz Esteves Magalhães b,c*
a
Centro de Ciências Florestais e da Madeira (PPGEF), Universidade Federal
do Paraná, 900, Av. Lothário Meissner, ZIP Code: 80210-170, Curitiba, SC, Brazil. [email protected]; [email protected]
b Programa
Integrado em Engenharia e Ciência dos Materiais (PIPE), Centro
Politécnico, Universidade Federal do Paraná, PO Box: 19011, ZIP Code: 81531-990, Curitiba, Brazil. [email protected]
c
Embrapa Florestas, Estrada da Ribeira, Km 111 – P.O Box: 319, ZIP Code:
83411-000, Colombo, Brazil, [email protected]; [email protected]
*Corresponding author: Dr. Washington Luiz Esteves Magalhães – [email protected] – Phone: +554136755712; Fax: +554136755601
ABSTRACT
ACCEPTED MANUSCRIPT The aim of this study is to enhance the use of waste agro-industrial byproducts and to address the environmental concerns by a novel method of co-production of thermoplastic composites with a solid residue constituting biorefinery. Accordingly, the reuse of 10-30 wt. % solid residues (SRH) from the enzymatic hydrolysis of recycled paper sludge (PS) in the production of thermoplastic composites with polypropylene (PP) was investigated. Thermal properties, water absorption, tensile strength and morphology of the prepared composites were evaluated. Higher thermal stability, rougher and wetter surface, and characteristics of a brittle material were observed in PP-SRH composites in comparison to the pristine PS-PP composites and the neat PP. The water absorption increased with increasing amount of SRH, but in lower proportion compared to other common raw materials used in the preparation of composites. Use of SRH resulted in similar or better properties compared to the composites made with the unhydrolyzed paper sludge, suggesting that SRH has potential for recycling and utilization as filler in the development of thermoplastic composites.
Keywords: paper mill sludge; solid residue; resource efficiency; thermal stability; wettability.
1 INTRODUCTION
Brazil is one of the main producers of pulp and paper. In 2015, Brazilian industries produced a total of 17.4 and 10.4 million metric tons of pulp and paper, respectively, of which 61% of paper production were recycled (IBÁ -
ACCEPTED MANUSCRIPT Brazilian Tree Industry, 2016). This large production resulted in a large generation of solid wastes, such as green liquor dregs, lime slaker grits, lime mud and wastewater treatment sludge (CANMET, 2005). Wastewater treatment sludge represents around 40-50 kg of dry material per metric ton of paper produced and its disposal costs up to 60% of the total cost of wastewater treatment (Bajpai, 2015; Mahmood and Elliott, 2006; Son et al., 2004). Thus, the recycling of paper sludge is still a challenge, for which a solution can bring economic and environmental benefits to the pulp and paper industry. Paper sludge (PS) is mainly composed of short cellulose fibers and inorganic materials, which makes this residue a good alternative for commercial applications (Biswas et al., 2008). The PS contains 25 to 75% carbohydrates (Shul and Pearton, 2000). Usually, the PS is incinerated or subjected to land spreading or landfilling. However, the high moisture and ash content of the PS limits the process of incineration. Furthermore, the disposal of PS in landfills creates environmental and economic problems, since it can cause excessive accumulation of acid or infiltration of organic materials into the soil due to the anaerobic digestion (Chen et al., 2014; Jeffries and Schartman, 1999; Rossel, 2007). This led to further studies reporting different applications for wastewater treatment sludge, especially regarding composite production (Hamzeh et al., 2011; Soucy et al., 2014), application on soil (CANMET, 2005), isolation of cellulose nanofibers (Mahmood and Elliott, 2006), incorporation into clay bricks formulation (Cusidó et al., 2015), partial cement replacement in concrete formulation (Wong et al., 2015) and conversion to bioethanol (Atikler et al., 2006; Schroeder et al., 2017).
ACCEPTED MANUSCRIPT Production of ethanol from recycled PS involves the enzymatic hydrolysis of carbohydrates into monosaccharides, which can be subsequently fermented to alcohol with the aid of microorganisms (Schroeder et al., 2017). Since this bioprocess focuses on the use of the organic fraction, the remaining material is enriched with inorganic matter from the papermaking process, such as calcium carbonate (CaCO3), silicon and aluminum compounds. From a biorefinery point of view, this solid residue (SRH) also requires an application to maximize the use of resources, and to reduce or avoid waste disposal. Among many fillers used into thermoplastic composites – e.g. carbon fibers, graphite, cellulose fibers, wood, cotton, sisal and starch - (Xanthos, 2010), the incorporation of inorganic fillers such as CaCO3, kaolin and talc into these composites is commonly applied in the plastics industry. These inorganic fillers help to reduce the costs and to improve properties like rigidity, hardness and strength (Khunová et al., 1999; Leong et al., 2004). Therefore, this study investigated the reuse of SRH from enzymatic hydrolysis of PS – rich in inorganic materials - as filler source for the preparation of thermoplastic composites. If successful, the use of a waste material instead of a virgin raw material would result in positive environmental, economic and social impacts for both composites and pulp and paper sectors. The objectives of this study were 1) to investigate the role of different SRH proportions in the preparation of thermoplastic composites; 2) to compare the potential of SRH in relation to raw PS regarding thermal properties, water absorption, tensile strength and morphology of polypropylene composites.
2 MATERIAL AND METHODS
ACCEPTED MANUSCRIPT
The design of this study was based on the scheme illustrated in Figure 1. Enzymatic hydrolysis was performed and ethanol production using paper mill sludge was previously published by Schroeder et al. (2017). In this study, the solid residue from enzymatic hydrolysis was recovered and used for thermoplastic composite production as follow:
Please, insert Fig. 1. here
2.1 Raw material
The PS was provided by a recycled paper mill located in the state of Santa Catarina, Southern Brazil. It was collected from the wastewater treatment plant during the paper recycling process. The moisture and ash contents of PS were 71% (wet basis) and 57.7% (dry basis), respectively. PS has 33.5% carbohydrates, 27.5% glucan, 5.7% xylan, 7,4% acid insoluble lignin and 3.5% extractives. Calcium (76.86%), Aluminum (11.26%) and Silicon (10.71%) represented the basic composition of the ash content (Schroeder et al., 2017).
2.2 Enzymatic hydrolysis of paper sludge
The PS was hydrolyzed using an enzyme complex containing cellulase, β-glucosidase and hemicellulase (6%, enzyme weight / carbohydrate weight) in a sodium acetate buffer (pH 4.4). The hydrolysis step was performed in a shaker at 43°C, 250 rpm for 72 h. Then, the sample was vacuum filtered,
ACCEPTED MANUSCRIPT resulting in a solution of carbohydrates and in the SRH with a high quantity of inorganic compounds. The carbohydrate solution was destined to ethanol production as reported by Schroeder et al. (2017). The SRH was used to produce the thermoplastic composites. Ash content of SRH was 66% and the content of insoluble ash in hydrochloric acid was 29%.
2.3 Preparation of thermoplastic composites
The thermoplastic composites were prepared by compression molding method in a matrix of polypropylene (PP) H103 supplied by Braskem (Brazil). The polymer has a density of 0.905 g cm-3 and a melt flow rate of 40 g min-1. SRH and PP were mixed in a high-speed thermo-kinetic mixer at 3500 rpm at 120-130°C. Subsequently, the SRH/PP mixture was molded (120 x 120 x 3 mm) in an electrically heated hydraulic press at 175°C for 10 minutes, with a pressure of 40 MPa. The hydraulic press was then cooled to 30°C while pressure was maintained. The composites were kept in a climatic chamber (20°C of temperature and 65% of relative humidity) to reach constant mass. Three proportions of SRH were investigated: 10, 20 and 30 (wt%). Furthermore, composites with 30% of PS (nonhydrolyzed) were prepared. No additives and coupling agents were used in the preparation of the composites. Since SRH contains 66% of ash (mainly calcium, aluminum and silicon), the proportions tested in this study (10 - 30% SRH) correspond to about 7 to 20% of inorganic fraction in the final material, which are usual proportions for PP composites.
ACCEPTED MANUSCRIPT 2.4 Characterization of thermoplastic composites
The effect of SRH and PS incorporation was chemically analyzed by ATR-IR microscopy (HYPERION Series, Bruker Corporation) from an attenuated total reflectance (ATR) objective. The equipment was set to a resolution of 4 cm-1 for 32 scans in the spectral range of 600 to 4000 cm-1. The representation of the final spectra was determined by the average of three spectra in distinct points of each sample. Changes in morphology were investigated by Scanning Electron Microscopy (SEM, Tescan Vega3). Highresolution images were recorded at 1000x and 5000x at 15kV in low-vacuum. Thermogravimetric analyses (TGA) were performed in a TG-DTA/DSC equipment (Setsys Evolution, Setaram Instrumentation), with a temperature range of 30-600°C at a constant heating rate of 10°C min-1 under argon atmosphere. Differential scanning calorimetry (DSC) was performed in a TGDTA/DSC equipment (Setsys Evolution, Setaram Instrumentation) to determine the temperature of crystallization (Tc) and the melting temperature (Tm) of the composites. Tc was determined by heating the sample up to 180°C, keeping this temperature for 5 minutes, and then cooling down to 30°C. Tm was determined by heating the sample up to 600°C at a constant heating rate of 10°C min-1 under argon atmosphere. The degree of crystallization (Xc) was determined according to the method proposed by Amash and Zugenmaier (2000). Tensile strength and modulus of elasticity (MOE) were determined through the ASTM D638-14 method in a universal machine (EMIC, Brazil). The samples were prepared according to Type I requirements. Five replicates were
ACCEPTED MANUSCRIPT used for each treatment. The speed applied in the tests was 5 mm min-1 with a load cell of 2 metric tons. Surface wettability of the composites was investigated in a goniometer (Krüss DSA25) by the sessile drop contact angle technique. Three droplets (5 μl) of deionized water (surface tension of 72.80 mN m-1) were deposited onto the surface of the composites. Apparent contact angle (CA) was measured after 5 s of droplet deposition. Water absorption (WA) kinetics were determined as a function of time (24, 96, 216 and 600 h). Apparent contact angle, water absorption and tensile strength were evaluated by analysis of variance (ANOVA) at 95% of confidence level. When the null hypothesis (p < 0.05) was rejected, the average values were compared using Tukey Test at 95% confidence level.
3 RESULTS AND DISCUSSION
ATR-IR microscopy analyses were performed on the composites filled with SRH and PS to obtain their chemical information (Figure 2). The addition of SRH and PS in a PP matrix resulted in peaks related to hemicelluloses and cellulose. A peak at 1105 cm-1 referred to the OH association in hemicelluloses and cellulose (Yang et al., 2007), and a peak at 1367 cm-1 indicates the in-plane CH bending in cellulose and hemicelluloses (Fan et al., 2012), as well as in the PP matrix. The presence of inorganic compounds from the additives used in the pulp and paper process is shown by the peaks at 875 cm-1 and 1456 cm-1, which prove the presence of CaCO3 in different phases (Luo et al., 2013; Ni and
ACCEPTED MANUSCRIPT Ratner, 2008) of the composites’ structure. Note that the intensity of the peak at 875 cm-1 tends to increase as a function of the proportion of SRH or PS.
Please, insert Fig. 2. here
The effect of the proportions of SRH and PS in the composites was also evaluated by SEM (Figure 3). The addition of SRH and PS resulted in a rough surface. The presence of these materials is more pronounced in the 30% SRH proportion (Figures 3D and 3I), especially due to the formation of agglomerates on the composites’ surface. Cellulose fibers can be visualized in the morphology of 70%PP-30%PS (Figures 3E and 3J). Nevertheless, in general, both SRH and PS are dispersed throughout the entire surface, which may indicate the existence of some adhesion between the PP matrix and these fillers.
Please, insert Fig. 3. here
Thermograms (TG) (Figure 4A) illustrate an increase in the onset temperature with the addition of both PS and SRH, especially the latter. Among the composites, neat PP presented the lowest onset temperature (251°C), which proves that the increase of the thermal stability of the composites is related to the insertion of either PS or SRH. Use of 30% of PS (nonhydrolyzed material) resulted in a lower onset temperature than the use of SRH. This suggests a significant influence of high inorganic compound quantities,
ACCEPTED MANUSCRIPT especially for the composites filled with SRH. After 600°C, PS and SRH presented significant degradation at 720-740°C due to the thermal degradation of CaCO3 (Figure 4B).
Please, insert Fig. 4. here
Both PS and SRH showed thermal degradation at 305-360°C due to the presence of residual hemicelluloses and cellulose (Table 1). This degradation was more pronounced in PS, since this raw material was not hydrolyzed. The highest presence of residual carbohydrate in PS was significant to impairs the increase of the thermal stability of composites.
Please, insert Table 1 here
Table 2 summarizes the results for temperature of crystallyzation (Tc), melting temperature (Tm), heat of crystallization (ΔHf) and degree of crystallization (Xc) determined from the DSC curves (Figure 5). The use of PS and SRH as fillers/reinforcement for PP composites resulted in no significant changes in Tm, which means no influence of waste proportion in the crystal thickness (Dikobe and Luyt, 2007) of PP. The same behavior was reported for PP composites filled with mate-tea waste and eucalypt particles (Mattos et al., 2014) and for PP/heart-of-peach palm sheath composite (Magalhães et al., 2013).
Please, insert Table 2 here
ACCEPTED MANUSCRIPT
The action of PS and SRH as nucleating agents for PP crystallization is illustrated by the increase of Tc. The lowest proportion of SRH (10%) is sufficient to increase Tc in 5.18% (6.24°C). Among the proportions of PS and SRH, no significant changes were observed for Tc. Xc and ΔHf decreased with the addition of SRH. However, Xc increased with increasing SRH proportion, which denotes both PS and SRH act as a nucleation agent. PS was also reported as a nucleation agent in PP and ethylene propylene diene composites by Ismail and Bakar (2006).
Please, insert Fig. 5. here
Tensile strength decreased significantly with an increase of SRH proportion (Figure 6A). Adding both SRH and PS to a PP matrix resulted in a decrease of plasticity, which implies in a more brittle composite (Figure 6C). The reduction of tensile strength was significant from 20% SRH proportion, in which the decrease was up to 30%. These tensile strength values were in conformity with the requirements of the ASTM D7032 standard (24-27 MPa). On the other hand, the changes in the MOE were not significant (Figure 6B). The average values of MOE corroborated with the results observed by (Soucy et al. (2014)). The mechanical properties of composites filled with inorganic compounds depend on a good dispersion of these minerals (Thenepalli et al., 2015). Since CaCO3 is the most abundant inorganic compound in SRH, the agglomeration illustrated in Figure 3 may have influenced the tensile strength and modulus of elasticity. Furthermore, the lowest values of tensile strength
ACCEPTED MANUSCRIPT were verified for higher filler contents. This corroborated with previous studies with CaCO3/PP composites (Biswas et al., 2008; Thio et al., 2002). Atikler et al. (2006) attributed the decrease of tensile strength with the increase of filler loading in HDPE/CaCO3 composites to the presence of cracks around filler particles caused by stress concentrations.
Please, insert Fig. 6. here
Neat PP presented the highest apparent CA (Figure 7 A), since PP presents low surface energy due to the absence of polar groups and chemical inertness (Chashmejahanbin et al., 2014). The addition of both PS and SRH resulted in a significant increase of surface wettability. The lowest apparent CA was found for 70%PP – 30%SRH, 18.5% lower than apparent CA for neat PP.
Please, insert Fig. 7. here
The hydrophilic behavior of composites filled with SRH and PS was confirmed by WA kinetics (Figure 7B). The WA of thermoplastic composites increased with increasing the time of immersion, especially for higher proportions of SRH. After 600 h of immersion, the WA of neat PP increased around 2 times, while the WA of SRH and PS composites increased 2.3 to 4.3 times. Increases of both wettability and WA of the composites were expected, since PS presents a high quantity of carbohydrates from the recycling paper process, and SRH still contains unhydrolyzed hemicelluloses and cellulose.
ACCEPTED MANUSCRIPT This suggests a hydrophilic character, as reported by Soucy et al. (2014). Furthermore, PS and SRH contain calcium from the CaCO3 used as additive in the paper making process (Schroeder et al., 2017), which also has a hydrophilic character (Zhang et al., 2010) and may contribute to the increase of both wettability and water absorption of the composites. Nevertheless, even with the addition of PS and SRH, the WA of all composites was lower than the WA verified in other studies. The lowest WA of PP composites filled with mate-tea waste and eucalypt particles found by Mattos et al. (2014) was 4.42% after 24 h. Higher results were also found for hemp fiber-reinforced unsaturated polyester composites (Dhakal et al., 2007), for short flax fiber bundle/PP composites (Arbelaiz et al., 2005) and for PP composites containing wood flour, rice hulls or bagasse fibers (Tajvidi and Takemura, 2010). This suggests both PS and SRH as good alternatives to manufacturing composite materials with interesting water repellence in comparison to other natural and/or waste fillers. Furthermore, lower moisture/water quantities in the composites contribute to the reduction of microbiological activity and weathering.
4 CONCLUSIONS Incorporation of the solid residue from enzymatic hydrolysis of paper mill sludge into polypropylene is proposed to improve the biorefinery scenario of pulp and paper industries, enabling coproduction of biofuels and materials. The results revealed the increase of thermal stability and the decrease of crystallinity after the incorporation of solid residue from enzymatic hydrolysis. The composites filled with SRH and PS became more brittle, with a rougher surface,
ACCEPTED MANUSCRIPT and both wettability and water absorption increased. However, this increase was lower than reported by other studies for different lignocellulosic filler sources. In general, incorporation of both 20% and 30% proportions of solid residue resulted in similar thermal, physical and mechanical properties of composites filled with 30% paper mill sludge. Thus, the results proved the potential of solid residue from enzymatic hydrolysis of recycled paper sludge as a filler for thermoplastic composite manufacturing.
5 ACKNOWLEDGMENTS
The authors thank the National Council for Scientific and Technological Development (CNPq) and Embrapa Florestas for supporting this work. The authors are grateful to Ms. Bia Carneiro for the English language support.
6 REFERENCES
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ACCEPTED MANUSCRIPT Ni, M., Ratner, B.D., 2008. Differentiating calcium carbonate polymorphs by surface analysis techniques—an XPS and TOF-SIMS study. Surface and Interface Analysis 40, 1356-1361. Rossel, T.N., 2007. Plasma modification of carbon black surface: From reactor design to final application. Universitat Ramon Liull, Barcelona. Schroeder, B.G., Zanoni, P.R.S., Magalhães, W.L.E., Hansel, F.A., Tavares, L.B.B., 2017. Evaluation of biotechnological processes to obtain ethanol from recycled paper sludge. Journal of Material Cycles and Waste Management, 110. Shul, R.J., Pearton, S.J., 2000. Handbook of Advanced Plasma Proceessing Techniques. Springer-Verlag Berlin Heidelberg, New York. Son, J., Yang, H.-S., Kim, H.-J., 2004. Physico-mechanical Properties of Paper Sludge-Thermoplastic Polymer Composites. Journal of Thermoplastic Composite Materials 17, 509-522. Soucy, J., Koubaa, A., Migneault, S., Riedl, B., 2014. The potential of paper mill sludge for wood–plastic composites. Industrial Crops and Products 54, 248-256. Tajvidi, M., Takemura, A., 2010. Recycled Natural Fiber Polypropylene Composites: Water Absorption/Desorption Kinetics and Dimensional Stability. J Polym Environ 18, 500-509. Thenepalli, T., Jun, A.Y., Han, C., Ramakrishna, C., Ahn, J.W., 2015. A strategy of precipitated calcium carbonate (CaCO3) fillers for enhancing the mechanical properties of polypropylene polymers. Korean Journal of Chemical Engineering 32, 1009-1022. Thio, Y.S., Argon, A.S., Cohen, R.E., Weinberg, M., 2002. Toughening of isotactic polypropylene with CaCO3 particles. Polymer 43, 3661-3674. Wong, H.S., Barakat, R., Alhilali, A., Saleh, M., Cheeseman, C.R., 2015. Hydrophobic concrete using waste paper sludge ash. Cement and Concrete Research 70, 9-20. Xanthos, M., 2010. Functional Fillers for Plastics, 2nd ed. John Wiley & Sons, Hoboken. Yang, H., Yan, R., Chen, H., Lee, D.H., Zheng, C., 2007. Characteristics of hemicellulose, cellulose and lignin pyrolysis. Fuel 86, 1781-1788. Zhang, J., Guo, J., Li, T., Li, X., 2010. Chemical Surface Modification of Calcium Carbonate Particles by Maleic Anhydride Grafting Polyethylene Wax. International Journal of Green Nanotechnology: Physics and Chemistry 1, P65P71.
ACCEPTED MANUSCRIPT Figure captions
Fig. 1. Design of the study. Dotted line represents the arrangement of this study. Fig. 2. ATR-IR spectra of composites filled with SRH and PS (A). Zoom at 1800-600 cm-1 (B). Fig. 3. SEM morphology of neat PP (A-B), 90%PP – 10%SRH (C-D), 80%PP – 20%SRH (E-F), 70%PP – 30%SRH (G-H) and 70%PP – 30%PS (I-J). Magnification: 1000x (50 µm bar scale) at the top and 5000x (10 µm bar sale) at the bottom. Fig. 4. Thermograms of neat PP and the composites (A), SRH and PS (B) and their respective derivatives. Fig. 5. DSC curves for crystallization temperature (A) and melting temperature (B) of neat PP and their composites filled with SRH and PS. Fig. 6. Tensile strength (A), modulus of elasticity (B) and general pattern of force versus deformation curves (C) for neat PP and PP composites filled with SRH and PS. Fig. 7. Wettability (A) and kinetics of water absorption (B) for neat PP and PP composites filled with SRH and PS.
ACCEPTED MANUSCRIPT Highlights 1) Recycled paper sludge was hydrolyzed and investigated for thermoplastic composites production. 2) SRH/PP composite presented higher thermal stability than PS/PP and neat PP composites. 3) Addition of PS or SRH increased the roughness, wettability and brittle of the composites. 4) SRH presented potential as a filler for thermoplastic composite manufacturing.
ACCEPTED MANUSCRIPT Table 1. Thermal characteristics of neat PP, SRH, PS and their composites. Onset
Mass loss at
Residual mass
temperature (°C)
360°C (%)
at 600°C (%)
Neat PP
251
9.73
0
90%PP – 10%SRH
405
0.24
13.07
80%PP – 20% SRH
400
0.64
17.68
70%PP - 30%SRH
401
0.10
17.18
70%PP - 30%PS
329
1.75
27.16
100% SRH
170
18.62
65.87
100% PS
228
28.14
55.98
Sample
ACCEPTED MANUSCRIPT Table 2. Thermal properties of neat PP, SRH and PS and their composites. Sample
Tc (°C)
Tm (°C)
ΔHf (J/g)
Xc (%)
Neat PP
114.27
165.52
76.89
40.46
90%PP – 10%SRH
120.51
165.52
51.21
29.94
80%PP – 20% SRH
120.61
164.26
49.34
32.45
70%PP - 30%SRH
120.56
163.81
49.85
37.47
70%PP - 30%PS
121.41
163.64
48.11
36.17
Tc = temperature of crystallyzation; Tm = melting temperature; ΔHf = heat of crystallization; Xc = degree of crystallization.
Pedro Henrique Gonzalez de Cademartori, Francine Ceccon Claro, Nelson Potenciano Marinho, Patrícia Raquel Silva Zanoni, Washington Luiz Esteves Magalhães PII:
S0959-6526(17)31178-2
DOI:
10.1016/j.jclepro.2017.06.009
Reference:
JCLP 9759
To appear in:
Journal of Cleaner Production
Received Date:
18 May 2016
Revised Date:
05 April 2017
Accepted Date:
03 June 2017
Please cite this article as: Pedro Henrique Gonzalez de Cademartori, Francine Ceccon Claro, Nelson Potenciano Marinho, Patrícia Raquel Silva Zanoni, Washington Luiz Esteves Magalhães, Co-production of thermoplastic composites with solid residue from enzymatic hydrolysis of recycled paper sludge, Journal of Cleaner Production (2017), doi: 10.1016/j.jclepro.2017.06.009
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Wordcount: 4149
Co-production of thermoplastic composites with solid residue from enzymatic hydrolysis of recycled paper sludge
Pedro Henrique Gonzalez de Cademartori a, Francine Ceccon Claro b, Nelson Potenciano Marinho a, Patrícia Raquel Silva Zanoni c, Washington Luiz Esteves Magalhães b,c*
a
Centro de Ciências Florestais e da Madeira (PPGEF), Universidade Federal
do Paraná, 900, Av. Lothário Meissner, ZIP Code: 80210-170, Curitiba, SC, Brazil. [email protected]; [email protected]
b Programa
Integrado em Engenharia e Ciência dos Materiais (PIPE), Centro
Politécnico, Universidade Federal do Paraná, PO Box: 19011, ZIP Code: 81531-990, Curitiba, Brazil. [email protected]
c
Embrapa Florestas, Estrada da Ribeira, Km 111 – P.O Box: 319, ZIP Code:
83411-000, Colombo, Brazil, [email protected]; [email protected]
*Corresponding author: Dr. Washington Luiz Esteves Magalhães – [email protected] – Phone: +554136755712; Fax: +554136755601
ABSTRACT
ACCEPTED MANUSCRIPT The aim of this study is to enhance the use of waste agro-industrial byproducts and to address the environmental concerns by a novel method of co-production of thermoplastic composites with a solid residue constituting biorefinery. Accordingly, the reuse of 10-30 wt. % solid residues (SRH) from the enzymatic hydrolysis of recycled paper sludge (PS) in the production of thermoplastic composites with polypropylene (PP) was investigated. Thermal properties, water absorption, tensile strength and morphology of the prepared composites were evaluated. Higher thermal stability, rougher and wetter surface, and characteristics of a brittle material were observed in PP-SRH composites in comparison to the pristine PS-PP composites and the neat PP. The water absorption increased with increasing amount of SRH, but in lower proportion compared to other common raw materials used in the preparation of composites. Use of SRH resulted in similar or better properties compared to the composites made with the unhydrolyzed paper sludge, suggesting that SRH has potential for recycling and utilization as filler in the development of thermoplastic composites.
Keywords: paper mill sludge; solid residue; resource efficiency; thermal stability; wettability.
1 INTRODUCTION
Brazil is one of the main producers of pulp and paper. In 2015, Brazilian industries produced a total of 17.4 and 10.4 million metric tons of pulp and paper, respectively, of which 61% of paper production were recycled (IBÁ -
ACCEPTED MANUSCRIPT Brazilian Tree Industry, 2016). This large production resulted in a large generation of solid wastes, such as green liquor dregs, lime slaker grits, lime mud and wastewater treatment sludge (CANMET, 2005). Wastewater treatment sludge represents around 40-50 kg of dry material per metric ton of paper produced and its disposal costs up to 60% of the total cost of wastewater treatment (Bajpai, 2015; Mahmood and Elliott, 2006; Son et al., 2004). Thus, the recycling of paper sludge is still a challenge, for which a solution can bring economic and environmental benefits to the pulp and paper industry. Paper sludge (PS) is mainly composed of short cellulose fibers and inorganic materials, which makes this residue a good alternative for commercial applications (Biswas et al., 2008). The PS contains 25 to 75% carbohydrates (Shul and Pearton, 2000). Usually, the PS is incinerated or subjected to land spreading or landfilling. However, the high moisture and ash content of the PS limits the process of incineration. Furthermore, the disposal of PS in landfills creates environmental and economic problems, since it can cause excessive accumulation of acid or infiltration of organic materials into the soil due to the anaerobic digestion (Chen et al., 2014; Jeffries and Schartman, 1999; Rossel, 2007). This led to further studies reporting different applications for wastewater treatment sludge, especially regarding composite production (Hamzeh et al., 2011; Soucy et al., 2014), application on soil (CANMET, 2005), isolation of cellulose nanofibers (Mahmood and Elliott, 2006), incorporation into clay bricks formulation (Cusidó et al., 2015), partial cement replacement in concrete formulation (Wong et al., 2015) and conversion to bioethanol (Atikler et al., 2006; Schroeder et al., 2017).
ACCEPTED MANUSCRIPT Production of ethanol from recycled PS involves the enzymatic hydrolysis of carbohydrates into monosaccharides, which can be subsequently fermented to alcohol with the aid of microorganisms (Schroeder et al., 2017). Since this bioprocess focuses on the use of the organic fraction, the remaining material is enriched with inorganic matter from the papermaking process, such as calcium carbonate (CaCO3), silicon and aluminum compounds. From a biorefinery point of view, this solid residue (SRH) also requires an application to maximize the use of resources, and to reduce or avoid waste disposal. Among many fillers used into thermoplastic composites – e.g. carbon fibers, graphite, cellulose fibers, wood, cotton, sisal and starch - (Xanthos, 2010), the incorporation of inorganic fillers such as CaCO3, kaolin and talc into these composites is commonly applied in the plastics industry. These inorganic fillers help to reduce the costs and to improve properties like rigidity, hardness and strength (Khunová et al., 1999; Leong et al., 2004). Therefore, this study investigated the reuse of SRH from enzymatic hydrolysis of PS – rich in inorganic materials - as filler source for the preparation of thermoplastic composites. If successful, the use of a waste material instead of a virgin raw material would result in positive environmental, economic and social impacts for both composites and pulp and paper sectors. The objectives of this study were 1) to investigate the role of different SRH proportions in the preparation of thermoplastic composites; 2) to compare the potential of SRH in relation to raw PS regarding thermal properties, water absorption, tensile strength and morphology of polypropylene composites.
2 MATERIAL AND METHODS
ACCEPTED MANUSCRIPT
The design of this study was based on the scheme illustrated in Figure 1. Enzymatic hydrolysis was performed and ethanol production using paper mill sludge was previously published by Schroeder et al. (2017). In this study, the solid residue from enzymatic hydrolysis was recovered and used for thermoplastic composite production as follow:
Please, insert Fig. 1. here
2.1 Raw material
The PS was provided by a recycled paper mill located in the state of Santa Catarina, Southern Brazil. It was collected from the wastewater treatment plant during the paper recycling process. The moisture and ash contents of PS were 71% (wet basis) and 57.7% (dry basis), respectively. PS has 33.5% carbohydrates, 27.5% glucan, 5.7% xylan, 7,4% acid insoluble lignin and 3.5% extractives. Calcium (76.86%), Aluminum (11.26%) and Silicon (10.71%) represented the basic composition of the ash content (Schroeder et al., 2017).
2.2 Enzymatic hydrolysis of paper sludge
The PS was hydrolyzed using an enzyme complex containing cellulase, β-glucosidase and hemicellulase (6%, enzyme weight / carbohydrate weight) in a sodium acetate buffer (pH 4.4). The hydrolysis step was performed in a shaker at 43°C, 250 rpm for 72 h. Then, the sample was vacuum filtered,
ACCEPTED MANUSCRIPT resulting in a solution of carbohydrates and in the SRH with a high quantity of inorganic compounds. The carbohydrate solution was destined to ethanol production as reported by Schroeder et al. (2017). The SRH was used to produce the thermoplastic composites. Ash content of SRH was 66% and the content of insoluble ash in hydrochloric acid was 29%.
2.3 Preparation of thermoplastic composites
The thermoplastic composites were prepared by compression molding method in a matrix of polypropylene (PP) H103 supplied by Braskem (Brazil). The polymer has a density of 0.905 g cm-3 and a melt flow rate of 40 g min-1. SRH and PP were mixed in a high-speed thermo-kinetic mixer at 3500 rpm at 120-130°C. Subsequently, the SRH/PP mixture was molded (120 x 120 x 3 mm) in an electrically heated hydraulic press at 175°C for 10 minutes, with a pressure of 40 MPa. The hydraulic press was then cooled to 30°C while pressure was maintained. The composites were kept in a climatic chamber (20°C of temperature and 65% of relative humidity) to reach constant mass. Three proportions of SRH were investigated: 10, 20 and 30 (wt%). Furthermore, composites with 30% of PS (nonhydrolyzed) were prepared. No additives and coupling agents were used in the preparation of the composites. Since SRH contains 66% of ash (mainly calcium, aluminum and silicon), the proportions tested in this study (10 - 30% SRH) correspond to about 7 to 20% of inorganic fraction in the final material, which are usual proportions for PP composites.
ACCEPTED MANUSCRIPT 2.4 Characterization of thermoplastic composites
The effect of SRH and PS incorporation was chemically analyzed by ATR-IR microscopy (HYPERION Series, Bruker Corporation) from an attenuated total reflectance (ATR) objective. The equipment was set to a resolution of 4 cm-1 for 32 scans in the spectral range of 600 to 4000 cm-1. The representation of the final spectra was determined by the average of three spectra in distinct points of each sample. Changes in morphology were investigated by Scanning Electron Microscopy (SEM, Tescan Vega3). Highresolution images were recorded at 1000x and 5000x at 15kV in low-vacuum. Thermogravimetric analyses (TGA) were performed in a TG-DTA/DSC equipment (Setsys Evolution, Setaram Instrumentation), with a temperature range of 30-600°C at a constant heating rate of 10°C min-1 under argon atmosphere. Differential scanning calorimetry (DSC) was performed in a TGDTA/DSC equipment (Setsys Evolution, Setaram Instrumentation) to determine the temperature of crystallization (Tc) and the melting temperature (Tm) of the composites. Tc was determined by heating the sample up to 180°C, keeping this temperature for 5 minutes, and then cooling down to 30°C. Tm was determined by heating the sample up to 600°C at a constant heating rate of 10°C min-1 under argon atmosphere. The degree of crystallization (Xc) was determined according to the method proposed by Amash and Zugenmaier (2000). Tensile strength and modulus of elasticity (MOE) were determined through the ASTM D638-14 method in a universal machine (EMIC, Brazil). The samples were prepared according to Type I requirements. Five replicates were
ACCEPTED MANUSCRIPT used for each treatment. The speed applied in the tests was 5 mm min-1 with a load cell of 2 metric tons. Surface wettability of the composites was investigated in a goniometer (Krüss DSA25) by the sessile drop contact angle technique. Three droplets (5 μl) of deionized water (surface tension of 72.80 mN m-1) were deposited onto the surface of the composites. Apparent contact angle (CA) was measured after 5 s of droplet deposition. Water absorption (WA) kinetics were determined as a function of time (24, 96, 216 and 600 h). Apparent contact angle, water absorption and tensile strength were evaluated by analysis of variance (ANOVA) at 95% of confidence level. When the null hypothesis (p < 0.05) was rejected, the average values were compared using Tukey Test at 95% confidence level.
3 RESULTS AND DISCUSSION
ATR-IR microscopy analyses were performed on the composites filled with SRH and PS to obtain their chemical information (Figure 2). The addition of SRH and PS in a PP matrix resulted in peaks related to hemicelluloses and cellulose. A peak at 1105 cm-1 referred to the OH association in hemicelluloses and cellulose (Yang et al., 2007), and a peak at 1367 cm-1 indicates the in-plane CH bending in cellulose and hemicelluloses (Fan et al., 2012), as well as in the PP matrix. The presence of inorganic compounds from the additives used in the pulp and paper process is shown by the peaks at 875 cm-1 and 1456 cm-1, which prove the presence of CaCO3 in different phases (Luo et al., 2013; Ni and
ACCEPTED MANUSCRIPT Ratner, 2008) of the composites’ structure. Note that the intensity of the peak at 875 cm-1 tends to increase as a function of the proportion of SRH or PS.
Please, insert Fig. 2. here
The effect of the proportions of SRH and PS in the composites was also evaluated by SEM (Figure 3). The addition of SRH and PS resulted in a rough surface. The presence of these materials is more pronounced in the 30% SRH proportion (Figures 3D and 3I), especially due to the formation of agglomerates on the composites’ surface. Cellulose fibers can be visualized in the morphology of 70%PP-30%PS (Figures 3E and 3J). Nevertheless, in general, both SRH and PS are dispersed throughout the entire surface, which may indicate the existence of some adhesion between the PP matrix and these fillers.
Please, insert Fig. 3. here
Thermograms (TG) (Figure 4A) illustrate an increase in the onset temperature with the addition of both PS and SRH, especially the latter. Among the composites, neat PP presented the lowest onset temperature (251°C), which proves that the increase of the thermal stability of the composites is related to the insertion of either PS or SRH. Use of 30% of PS (nonhydrolyzed material) resulted in a lower onset temperature than the use of SRH. This suggests a significant influence of high inorganic compound quantities,
ACCEPTED MANUSCRIPT especially for the composites filled with SRH. After 600°C, PS and SRH presented significant degradation at 720-740°C due to the thermal degradation of CaCO3 (Figure 4B).
Please, insert Fig. 4. here
Both PS and SRH showed thermal degradation at 305-360°C due to the presence of residual hemicelluloses and cellulose (Table 1). This degradation was more pronounced in PS, since this raw material was not hydrolyzed. The highest presence of residual carbohydrate in PS was significant to impairs the increase of the thermal stability of composites.
Please, insert Table 1 here
Table 2 summarizes the results for temperature of crystallyzation (Tc), melting temperature (Tm), heat of crystallization (ΔHf) and degree of crystallization (Xc) determined from the DSC curves (Figure 5). The use of PS and SRH as fillers/reinforcement for PP composites resulted in no significant changes in Tm, which means no influence of waste proportion in the crystal thickness (Dikobe and Luyt, 2007) of PP. The same behavior was reported for PP composites filled with mate-tea waste and eucalypt particles (Mattos et al., 2014) and for PP/heart-of-peach palm sheath composite (Magalhães et al., 2013).
Please, insert Table 2 here
ACCEPTED MANUSCRIPT
The action of PS and SRH as nucleating agents for PP crystallization is illustrated by the increase of Tc. The lowest proportion of SRH (10%) is sufficient to increase Tc in 5.18% (6.24°C). Among the proportions of PS and SRH, no significant changes were observed for Tc. Xc and ΔHf decreased with the addition of SRH. However, Xc increased with increasing SRH proportion, which denotes both PS and SRH act as a nucleation agent. PS was also reported as a nucleation agent in PP and ethylene propylene diene composites by Ismail and Bakar (2006).
Please, insert Fig. 5. here
Tensile strength decreased significantly with an increase of SRH proportion (Figure 6A). Adding both SRH and PS to a PP matrix resulted in a decrease of plasticity, which implies in a more brittle composite (Figure 6C). The reduction of tensile strength was significant from 20% SRH proportion, in which the decrease was up to 30%. These tensile strength values were in conformity with the requirements of the ASTM D7032 standard (24-27 MPa). On the other hand, the changes in the MOE were not significant (Figure 6B). The average values of MOE corroborated with the results observed by (Soucy et al. (2014)). The mechanical properties of composites filled with inorganic compounds depend on a good dispersion of these minerals (Thenepalli et al., 2015). Since CaCO3 is the most abundant inorganic compound in SRH, the agglomeration illustrated in Figure 3 may have influenced the tensile strength and modulus of elasticity. Furthermore, the lowest values of tensile strength
ACCEPTED MANUSCRIPT were verified for higher filler contents. This corroborated with previous studies with CaCO3/PP composites (Biswas et al., 2008; Thio et al., 2002). Atikler et al. (2006) attributed the decrease of tensile strength with the increase of filler loading in HDPE/CaCO3 composites to the presence of cracks around filler particles caused by stress concentrations.
Please, insert Fig. 6. here
Neat PP presented the highest apparent CA (Figure 7 A), since PP presents low surface energy due to the absence of polar groups and chemical inertness (Chashmejahanbin et al., 2014). The addition of both PS and SRH resulted in a significant increase of surface wettability. The lowest apparent CA was found for 70%PP – 30%SRH, 18.5% lower than apparent CA for neat PP.
Please, insert Fig. 7. here
The hydrophilic behavior of composites filled with SRH and PS was confirmed by WA kinetics (Figure 7B). The WA of thermoplastic composites increased with increasing the time of immersion, especially for higher proportions of SRH. After 600 h of immersion, the WA of neat PP increased around 2 times, while the WA of SRH and PS composites increased 2.3 to 4.3 times. Increases of both wettability and WA of the composites were expected, since PS presents a high quantity of carbohydrates from the recycling paper process, and SRH still contains unhydrolyzed hemicelluloses and cellulose.
ACCEPTED MANUSCRIPT This suggests a hydrophilic character, as reported by Soucy et al. (2014). Furthermore, PS and SRH contain calcium from the CaCO3 used as additive in the paper making process (Schroeder et al., 2017), which also has a hydrophilic character (Zhang et al., 2010) and may contribute to the increase of both wettability and water absorption of the composites. Nevertheless, even with the addition of PS and SRH, the WA of all composites was lower than the WA verified in other studies. The lowest WA of PP composites filled with mate-tea waste and eucalypt particles found by Mattos et al. (2014) was 4.42% after 24 h. Higher results were also found for hemp fiber-reinforced unsaturated polyester composites (Dhakal et al., 2007), for short flax fiber bundle/PP composites (Arbelaiz et al., 2005) and for PP composites containing wood flour, rice hulls or bagasse fibers (Tajvidi and Takemura, 2010). This suggests both PS and SRH as good alternatives to manufacturing composite materials with interesting water repellence in comparison to other natural and/or waste fillers. Furthermore, lower moisture/water quantities in the composites contribute to the reduction of microbiological activity and weathering.
4 CONCLUSIONS Incorporation of the solid residue from enzymatic hydrolysis of paper mill sludge into polypropylene is proposed to improve the biorefinery scenario of pulp and paper industries, enabling coproduction of biofuels and materials. The results revealed the increase of thermal stability and the decrease of crystallinity after the incorporation of solid residue from enzymatic hydrolysis. The composites filled with SRH and PS became more brittle, with a rougher surface,
ACCEPTED MANUSCRIPT and both wettability and water absorption increased. However, this increase was lower than reported by other studies for different lignocellulosic filler sources. In general, incorporation of both 20% and 30% proportions of solid residue resulted in similar thermal, physical and mechanical properties of composites filled with 30% paper mill sludge. Thus, the results proved the potential of solid residue from enzymatic hydrolysis of recycled paper sludge as a filler for thermoplastic composite manufacturing.
5 ACKNOWLEDGMENTS
The authors thank the National Council for Scientific and Technological Development (CNPq) and Embrapa Florestas for supporting this work. The authors are grateful to Ms. Bia Carneiro for the English language support.
6 REFERENCES
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ACCEPTED MANUSCRIPT Figure captions
Fig. 1. Design of the study. Dotted line represents the arrangement of this study. Fig. 2. ATR-IR spectra of composites filled with SRH and PS (A). Zoom at 1800-600 cm-1 (B). Fig. 3. SEM morphology of neat PP (A-B), 90%PP – 10%SRH (C-D), 80%PP – 20%SRH (E-F), 70%PP – 30%SRH (G-H) and 70%PP – 30%PS (I-J). Magnification: 1000x (50 µm bar scale) at the top and 5000x (10 µm bar sale) at the bottom. Fig. 4. Thermograms of neat PP and the composites (A), SRH and PS (B) and their respective derivatives. Fig. 5. DSC curves for crystallization temperature (A) and melting temperature (B) of neat PP and their composites filled with SRH and PS. Fig. 6. Tensile strength (A), modulus of elasticity (B) and general pattern of force versus deformation curves (C) for neat PP and PP composites filled with SRH and PS. Fig. 7. Wettability (A) and kinetics of water absorption (B) for neat PP and PP composites filled with SRH and PS.
ACCEPTED MANUSCRIPT Highlights 1) Recycled paper sludge was hydrolyzed and investigated for thermoplastic composites production. 2) SRH/PP composite presented higher thermal stability than PS/PP and neat PP composites. 3) Addition of PS or SRH increased the roughness, wettability and brittle of the composites. 4) SRH presented potential as a filler for thermoplastic composite manufacturing.
ACCEPTED MANUSCRIPT Table 1. Thermal characteristics of neat PP, SRH, PS and their composites. Onset
Mass loss at
Residual mass
temperature (°C)
360°C (%)
at 600°C (%)
Neat PP
251
9.73
0
90%PP – 10%SRH
405
0.24
13.07
80%PP – 20% SRH
400
0.64
17.68
70%PP - 30%SRH
401
0.10
17.18
70%PP - 30%PS
329
1.75
27.16
100% SRH
170
18.62
65.87
100% PS
228
28.14
55.98
Sample
ACCEPTED MANUSCRIPT Table 2. Thermal properties of neat PP, SRH and PS and their composites. Sample
Tc (°C)
Tm (°C)
ΔHf (J/g)
Xc (%)
Neat PP
114.27
165.52
76.89
40.46
90%PP – 10%SRH
120.51
165.52
51.21
29.94
80%PP – 20% SRH
120.61
164.26
49.34
32.45
70%PP - 30%SRH
120.56
163.81
49.85
37.47
70%PP - 30%PS
121.41
163.64
48.11
36.17
Tc = temperature of crystallyzation; Tm = melting temperature; ΔHf = heat of crystallization; Xc = degree of crystallization.