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Corn distiller’s dried grains with solubles (DDGS) - A value added functional material for wood composites
Industrial Crops & Products 139 (2019) 111525
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Corn distiller’s dried grains with solubles (DDGS) - A value added functional material for wood composites
T
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Joshua D. Liawa, Dilpreet S. Bajwaa, , Jamileh Shojaeiarania, Sreekala G. Bajwab a b
Department of Mechanical Engineering, North Dakota State University, Fargo, ND, 58108, United States Montana Agricultural Experiment Station, Montana State University, Bozeman, MT, 59717, United States
A R T I C LE I N FO
A B S T R A C T
Keywords: Distiller’s dried grains with solubles Particleboard Chemical treatment Physical and mechanical properties Sodium hydroxide Acetic acid
Corn distiller’s dried grains with solubles (DDGS) is widely marketed as a livestock feed due to its high protein content of 34%, fat content of 10%, and low cost of 8–13 cents per kilogram. In recent years, DDGS has been used as a multifunctional filler in synthetic resin bonded wood particleboards to improve their physical and mechanical properties where the adhesive properties of DDGS is derived from its hydrophobic zein proteins. The objective of this research was to evaluate if the high value proteins derived from sodium hydroxide and acetic acid treated DDGS can be functionalized as a natural binder in wood particleboard manufacturing by eliminating the use of harmful formaldehyde resins. Several formulations of particleboard were hot pressed using various concentrations of acid and alkali treatments, DDGS filler contents of 10, 25 and 50 wt.%, and DDGS particle sizes of 120 and 250 μm. ASTM D1037-12 standard was adapted to evaluate the particleboard properties. Superior flexural strengths of particleboards occurred at press temperature of 190°C. The acetic acid treated particleboards at higher DDGS concentrations exhibited better water resistance properties. Test results showed that the mean internal bond strengths exceeded the minimum requirement of ANSI A208.1–2009. FTIR results showed that the decoupling of proteins was achieved by acid or alkali treatment. These positive outcomes suggest that DDGS has strong potential to act as a natural adhesive for manufacturing medium-density particleboards.
1. Introduction Particleboard has evolved into a highly engineered product that can be used in housing floor application and industrial used for making furniture, cabinets, tables, and countertops (Puettmann et al., 2013). The ANSI A208.1–2009 standard states that particleboard is primary composed of cellulosic materials in the form of particles that are bonded together with a bonding system and may contain additives (ANSI A208.1-2009, 2009). The history of particleboard manufacturing goes back to the 1950s when manufacturers started utilizing industrial wood residues produced during the production of lumber and plywood (Puettmann et al., 2013). Later on, the field continued to grow and the projections of global wood-based panel market size is forecasted to reach $174.55 billion by 2025 (Wood Based Panel Market Size and Share, 2018). The growth in wood consumption has led to a high worldwide deforestation rate that can cause negative impacts on our environment (Zheng et al., 2007). To reduce wood dependency, it is crucial to replace wood with new lignocellulosic materials. Petroleum-based resins such as phenol formaldehyde, urea formaldehyde, and melamine fortified urea formaldehyde have been the
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conventional binders used in engineered wood products (Hemmilä et al., 2017). However, the carcinogenic nature of formaldehyde emissions and the regulations put in place by regulatory bodies like the California Air Resources Board (CARB) have driven manufacturers to research new ways to limit the usage of formaldehyde. Potential alternatives could come in the form of binders derived from renewable resource materials, such as soy flour and corn (BuildingNetwork, 2008; Sundquist and Bajwa, 2016). Corn residue, a biofuel alternative to petroleum, has become a leading candidate feedstock for lignocellulosic ethanol production (Villamil et al., 2015). A commonly used method in the U.S. for cornethanol production is the dry-grind process, also referred to as dry milling, with an annual production capacity of 14.7 billion gallons; the traits of this processing technique include low capital and energy investment costs (Tanneru and Steele, 2015). Corn ethanol production can generate roughly 0.33 kg each of ethanol, DDGS, and carbon dioxide by utilizing 1 kg of corn (Cheesbrough et al., 2008). The advantage of utilizing DDGS is its low cost of 8–13 cents per kilogram, which makes it cheaper than starch, wood fibers, and soy flour (Li and Susan Sun, 2011). The main components of DDGS are about 34%
Corresponding author at: North Dakota State University, 111 Dolve Hall, Fargo, ND, 58108, United States E-mail address: [email protected] (D.S. Bajwa).
https://doi.org/10.1016/j.indcrop.2019.111525 Received 2 February 2019; Received in revised form 26 June 2019; Accepted 28 June 2019 Available online 19 July 2019 0926-6690/ © 2019 Elsevier B.V. All rights reserved.
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proteins, 10% fat, and 39% fibers (Bajwa et al., 2015), where the adhesive properties of DDGS can be derived from its hydrophobic zein protein (Li and Susan Sun, 2011). This study emphasized the importance of zein protein because zein is the main protein found in both corn and DDGS (Xu et al., 2007). In order to utilize the adhesive effect of protein for bonding and solubilization, the native protein should be denatured to expose more polar groups (Rowell, 2012). Denaturation involves breaking down the existing hydrogen, secondary, and tertiary bonds so that the protein can form hydrogen bonds with wood surface (Rowell, 2012). Some of the most widely used methods to denature proteins were to expose to heat, acids, bases, and organic solvents (Kumar et al., 2002). Acid induced protein unfolding occurs between pH 2 and pH 5 and base induced involves pH 10 or higher (Konermann, 2012). For DDGS in particular, a previous patent indicated that an adhesive derived by hydrolyzing the particles with an aqueous sodium hydroxide solution produced a lap shear strength of 848 kPa (Mohanty et al., 2010). A recent study reported that when DDGS was added at 5 wt.% along with melamine urea formaldehyde resin at 10 wt.%, and wax at 10 wt. % into particleboard, it resulted in an increase in mechanical and physical properties of the particleboard. In this case, the proteins of the DDGS were dissociated and reacted with the melamine urea formaldehyde resin, which improved the mechanical properties, whereas the results also indicated that the improvement in moisture resistance was attributed to the fat component of the DDGS (Sundquist and Bajwa, 2016). However, it was unclear if DDGS can be functionalized with sodium hydroxide treatment or acetic acid treatment to manufacture formaldehyde free particleboard. Thus, this study investigated the performance of natural binder derived from sodium hydroxide treated and acetic acid treated DDGS particles. The results were compared with the minimum requirements of ANSI A208.1–2009 standard widely followed by particleboard industry.
Table 2 Particle size distribution of DDGS. U.S. Standard Sieve No. and Micron Equivalent
DDGS content, % (120 μm screen size)
DDGS content, % (250 μm screen size)
No. 60 (250 μm) No. 80 (180 μm) No. 100 (150 μm) Pan (< 150 μm)
0.3–1.2 6.2–17.7 2.9–12.2 73.8–87.3
7.4–8.7 19.1–23.0 12.4–13.1 56.6–59.6
DDGS – Distiller’s dried grains with solubles.
2.2. Design of experiment The experiment was divided into two different phases. The first phase of the experiment determined the effect of both temperature and chemical concentration on the mechanical properties of the particleboards. A screen size of 250 μm and a DDGS loading concentration of 50 wt.% were used to manufacture particleboards throughout the first phase. The final phase comprised of twelve formulations, 2 particle sizes × 3 DDGS loading concentrations × 2 chemical treatments. The hot-press platen temperature was set at 190℃. For each of these formulations, two boards were manufactured for testing. The second phase of the experiment was conducted to determine the effect of screen size and DDGS loading concentration on the physical and mechanical properties of the particleboards. This experiment was done using two different screen sizes (120 and 250 μm) and three different DDGS loading concentrations of 10, 25, and 50 wt%. A total of twelve formulations comprised of 2 particle sizes × 3 DDGS loading concentrations × 2 chemical treatments were designed. For each of these twelve different formulations, four boards were manufactured per formulation. Moreover, the control samples were prepared differently using combination of pine wood flour and 12 wt% phenol formaldehyde resin. Four boards were manufactured for the control sample. 2.3. Panel processing
2. Materials and methods To minimize the formation of aggregates, different DDGS loading concentrations at 10, 25, and 50 wt.% were dispersed in the pine wood flour matrices of 90, 75, 50 wt.%, respectively, by hand mixing the dried particles. The chemical solvents were prepared by dissolving concentrated acetic acid or sodium hydroxide in water to achieve the desired concentration. The chemical treatment process was initiated by hand mixing the desired concentration of chemical to both DDGS and pine wood flour particles at a ratio of 2:8. The treated particles were blended, mixed, and agitated for seven minutes in a twin shell dry blender (Patterson-Kelly Company, East Stroudsburg, PA, USA) to obtain uniform mixing. The control samples were manufactured by using a Vaper HVLP Spray Gun (Renton, WA, USA) to spray a Cement Mixer Model 998,252 (Northern Industrial Tools, Burnsville, MN, USA) with 12 wt% phenol formaldehyde resin. The wood particles and DDGS blends were then pressed into medium density particleboards using a Carver Hot Press Model 4122 (Carver Inc, Wabash, IN, USA). A pressure of 3.80 MPa was applied for the first phase of the experiment, and for the second phase 4.65 MPa was applied. The total press time was 12 min and the applied pressure was released every 4 min to reduce built up pressure by volatiles. The dimensions of each medium density particleboard were 305 mm (length) ×153 mm (width) ×6 mm (nominal thickness) with target density 720 kg/m3.
2.1. Materials Pine wood flour of 2020-grade was obtained from American Wood Fibers (Wausau, WI, USA). The average particle size of the wood flour was determined to be 425 μm. DDGS was supplied by Blue Flint Ethanol plant (Underwood, ND, USA). The moisture content of wood flour and DDGS were 8% and 7%, respectively. Both the sodium hydroxide (NaOH) pellets with ≥ 90% NaOH concentration and reagent grade glacial acetic acid were obtained from MilliporeSigma (Burlington, MA, USA), whereas the distilled water was obtained from Department of Chemistry and Biochemistry at North Dakota State University (Fargo, ND, USA). Control samples were manufactured using phenol formaldehyde (Hexion Inc., Columbus, OH, USA) with 25–50% by weight of phenol-formaldehyde polymer sodium salt. The raw DDGS material was first grinded and screened using 120 microns and 250 microns screens in a Retsch Rotor Beater mill 300 (Newtown, PA, USA). The particle size distributions of the wood flour and grinded DDGS particles are shown in Tables 1 and 2, respectively.
Table 1 Particle size distribution of wood flour. U.S. Standard Sieve No. and Micron Equivalent
Wood flour content, %
2.4. Composition analysis
No. 20 (850 μm) No. 40 (425 μm) No. 60 (250 μm) Pan (< 250 μm)
<1 68–74 23–27 2-4
Composition analysis was performed on untreated DDGS particles, 12.8 M acetic acid treated DDGS particles, and 8.0 M sodium hydroxide treated DDGS particles that were milled with screen size of 250 μm to determine the nitrogen, crude protein, neutral detergent fiber (NDF), 2
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acid detergent fiber (ADF), lignin, and crude fat contents. The neutral detergent fiber (NDF) represents the amount of cellulose, hemicellulose, and lignin and the acid detergent fiber (ADF) represents the amount of lignin and cellulose. The content of hemicellulose was determined by taking the difference between the NDF and ADF. The amount of cellulose was determined by subtracting the lignin from the ADF. The tests were performed by the Department of Animal Sciences laboratory at North Dakota State University (Fargo, ND). The Association of Analytical Community’s (AOAC) method was followed for crude protein (2001.11), both fiber and lignin (973.18), and crude fat (920.39) tests, and the ANKOM method was used for NDF and ADF analyses.
Table 3 Composition analysis of treated and untreated DDGS.
2.5. Thermogravimetric analysis
DDGS – Distiller’s dried grains with solubles.
Thermogravimetric analysis (TGA) was performed to analyze the degradation temperature and the rate of degradation of the untreated DDGS particles, 12.8 M acetic acid treated DDGS particles, and 8.0 M sodium hydroxide treated DDGS particles. These DDGS particles were milled with screen size of 250 μm. The chemically treated samples were oven dried at 30 ℃ for more than 48 h to remove moisture from the samples prior to test. The analysis was conducted using a TA Q500 TGA (TA Instruments, New Castle, DE, USA) with a temperature ranged from 25℃ to 400℃ at a ramp rate of 10℃ min−1. Nitrogen gas was used at flow rate of 60 ml min−1.
DDGS compared with untreated DDGS, while the protein and fat contents in 12.8 M acetic acid treated DDGS were not noticeably different. In comparison to the untreated DDGS, both acid and alkali treated DDGS displayed lower percentages of NDF and ADF. The lower percentage of NDF is attributed to the degradation of cellulose, hemicellulose, and lignin, and the lower percentage of ADF is attributed to the degradation of lignin and cellulose. A recent study verified that 0.1 M sodium hydroxide treatment led to solubilization of DDGS fiber, which resulted in loss of protein, starch, hemicellulose, lignin, and fat contents in the DDGS (Pandey, 2018).
2.6. Differential scanning calorimetry
Column1
DDGS, untreated
DDGS, sodium hydroxide
DDGS, acetic acid
Nitrogen (%) Crude protein (%) NDF (%) ADF (%) Cellulose (%) Hemicellulose (%) Lignin (%) Crude fat (%)
5.30 33.15 45.29 15.32 13.26 29.97 2.06 8.71
4.63 28.91 25.49 9.65 9.00 15.84 0.65 4.33
5.38 33.62 41.85 14.87 12.82 26.98 2.05 8.13
3.2. Thermogravimetric analysis
Differential scanning calorimetry (DSC) was performed to analyze the melting peak and glass transition temperature of the untreated DDGS particles, 12.8 M acetic acid treated DDGS particles, and 8.0 M sodium hydroxide treated DDGS particles. These DDGS particles were milled with screen size of 250 μm. The chemically treated samples were oven dried at 30℃ for more than 48 h. The analysis was conducted using a TA Q1000 DSC (TA Instruments, New Castle, DE, USA) with a temperature range from -20℃ to 190℃ at ramp rate of 10℃ min−1. Nitrogen gas was used to purge the sample at a rate of 50 ml min−1.
The curves in Fig. 1 shows the percent change of weight and the first derivative of the percent change of weight of the sample when it is heated. In this study, the local maxima of the first derivative curves occur between 100 °C and 200 °C, which relates to the initial degradation of DDGS components. These DDGS components include hemicellulose, cellulose, residual starch, fat, lignin, and protein components (Morey et al., 2009). Between 250 °C and 350 °C of the first derivative curves, all samples display their mass decomposition of major components of DDGS, and this range is similar to a previous study (Sundquist and Bajwa, 2016). These major components include protein, hemicellulose, cellulose, and lignin (Bergman et al., 2005; Sundquist and Bajwa, 2016). Both acid treated and untreated DDGS particles exhibit higher degradation rate compared with alkali treated. This trend relates to a previous study which explained that better stability is achieved at lower protein content in DDGS (Reddy et al., 2011). The aforementioned results from the composition analysis indicate that alkali treated DDGS has a protein content of 28.91%, which is noticeably lower than both untreated DDGS and acid treated DDGS of 33.15% and 33.62%, respectively. Additionally, the percent change of weight curves shows that beyond 200℃, all the samples displayed weight loss of more than 90% due to thermal degradation. Thus, the processing temperature cannot be too high or too long or else there may be adverse effects on the composite such as decrease in mechanical properties.
2.7. Fourier transform infrared spectroscopy Fourier Transform Infrared Spectroscopy (FTIR) was performed to determine the difference in functionality of untreated DDGS particles, 12.8 M acetic acid treated DDGS particles, and 8.0 M sodium hydroxide treated DDGS particles. These DDGS particles were milled with screen size of 250 μm. The chemically treated samples were oven dried at 30℃ for more than 48 h. All of the samples were mixed with KBr and pressed using a mini-pellet press (Specac Limited, UK) at 2 tonnes to form discshaped specimens. The analysis was conducted using a Thermo Scientific Nicolet 8700 FTIR spectrometer (Thermo Fisher, Waltman, MA, USA). 2.8. Statistical analysis Statistical analysis software Minitab 18 (Minitab Inc., State College, PA, USA) was used to conduct one-way ANOVA to determine the significant factors affecting the physical and mechanical properties of the boards, with a criterion of 95% confidence interval (α = 0.05). Tukey’s multiple comparison test was used to determine whether the means were significantly different.
3.3. Differential scanning calorimetry Fig. 2 illustrates the DSC curves of untreated, alkali-treated, and acid treated DDGS. A previous study showed that the occurrence of glass transition temperatures for the unmodified DDGS, reduced fat DDGS, and de-waxed DDGS were between 20℃ to 50℃ (Ganesan and Rosentrater, 2006). In this study, untreated, alkali treated, acid treated DDGS displayed glass transition temperatures of 53.50 °C, 60.05 °C, and 63.93 °C, respectively. The higher glass transition temperatures and melting peaks of treated DDGS compared with untreated DDGS may be attributed to the degradation of fat and protein contents. The aforementioned results of the composition analysis show that the fat contents of untreated DDGS, sodium hydroxide treated DDGS, acetic acid treated
3. Results and discussion 3.1. Composition analysis Composition analysis was performed to determine the nutrient contents in DDGS. Table 3 shows that alkali treated DDGS at 8.0 M degraded and solubilized both the protein and fat components in the 3
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Fig. 1. Thermogravimetric analysis results of treated and untreated DDGS.
intensities of protein amide I and II may be attributed to the denaturing of protein caused by the weak acid and alkali treatments. 3.5. Relationship between temperature and mechanical properties of particleboards The samples were hot-pressed at 170°C, 180°C, and 190°C, as shown in Fig. 4. A similar study reported that superior flexural strength at 185°C was attributed to the plasticization of the DDGS (Tisserat et al., 2018). Moreover, the plasticization occurred when the samples had a smooth tactile feel on their surface, which mimicked a wood composite manufactured with a thermoset or thermoplastic resin (Tisserat et al., 2018). In this study, the flexural properties of the particleboards pressed at 190°C were superior to those pressed at 170°C and 180°C, which can be attributed to the highest plasticization of the DDGS while limited plasticization occurred at 180°C and below. The flexural strength results were below the minimum requirements of the ANSI A208.1–2009 standard. The highest internal bond strength for 12.8 M acetic acid and 2.0 M sodium hydroxide were attained at 180℃ and 190℃, respectively, as shown in Fig. 5. The decrease in internal bond strength of acetic acid treatment at 190℃ may be due to the brittleness of DDGS proteins and degradation of the DDGS. However, no clear trend is visible based on increasing or decreasing the temperature of sodium hydroxide treated DDGS. This is likely due to the lower number of press temperatures that were tested. The internal bond strength results met the minimum requirements of the ANSI A208.1–2009 standard.
Fig. 2. Differential scanning calorimetry results of untreated and treated DDGS particles.
DDGS are 8.71%, 4.33%, and 8.13%, respectively. The higher glass transition temperatures of chemically treated DDGS were possibly due to lower fat content, and this is supported by a previous study where the glass transition temperature of defatted DDGS was 54 °C and untreated DDGS was 49.4 °C (Tisserat et al., 2018). Moreover, the untreated DDGS, alkali treated, and acid treated DDGS have melting peaks at 110.59 °C, 122.38 °C, and 125.04 °C, respectively. These melting peaks fell within the initial degradation range from the TGA, between 100℃ and 200℃, and these melting peaks possibly indicate both the denaturation temperatures of proteins and degradation temperatures of DDGS components. Thus, the higher melting temperatures of treated DDGS could possibly mean that chemically treated DDGS samples have been denatured to potentially act as a natural binder.
3.6. Relationship between chemical concentration and mechanical properties of particleboards
3.4. Fourier transform infrared spectroscopy (FTIR) All spectra displayed characteristics of −OH and –NH stretching, and those are represented by the broad peaks in the 3500-3200 cm−1 region, as shown in Fig. 3. Moreover, the peaks in the 2950-2500 cm−1 region indicate the −CH stretching. The FTIR results of these absorption trends are in agreement with a similar study, where the stretching vibrations of −OH and –NH are from carbohydrates and protein and −CH is from lipids (Muniyasamy et al., 2013). The peaks in the 15001000 cm−1 region represent the CHO bond of carbohydrates (Yu et al., 2011). The peaks in the region of 1700-1500 cm−1 region represent the protein amide I and II (Azarfar et al., 2013), whereas the peaks in the 1700-1800 cm−1 region represent the –C = O stretching. Moreover, the peaks in the 600-700 cm−1 region show the P–S and P]S stretching (Tisserat et al., 2018). The –C = O and P–S/P]S stretching are identified as lignin and protein, respectively (Tisserat et al., 2018). Overall, the peaks in this 1700-1600 cm−1 show weaker peak intensities for treated DDGS compared with untreated DDGS. The weaker peak
Fig. 6. depicts the effect of chemical concentration on the flexural strength of particleboards. Suitable chemical modification of DDGS is important because the protective structure of hemicellulose and lignin hinders the cellulose from hydrolysis (Zhang, 2013). Weak acid modification led to the hydrolysis of hemicellulose and resulted in increasing porosity of the lignocellulosic biomass, whereas alkaline treatment led to the removal of lignin (Harmsen et al., 2010). The highest flexural strength was achieved with 2.0 M sodium hydroxide and 12.8 M acetic acid, as shown in Fig. 6; these chemical concentrations may lead to better penetration of chemical into the composite and may also enhance the binding properties of DDGS particles with wood flour. The flexural strength results were below the minimum requirements of the ANSI A208.1–2009 standard. The internal bond strengths of particleboards increased with increasing concentration of sodium, hydroxide, as shown in Fig. 7, where 4
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Fig. 3. FTIR spectrum of (a) untreated DDGS particles, (b) sodium hydroxide treated DDGS particles, and (c) acetic acid treated DDGS particles.
8.0 M sodium hydroxide treated DDGS displayed a relatively high internal bond strength. The high internal bond strength may be attributed to the greater hydrolysis of DDGS proteins with the increase of sodium hydroxide concentration. In weak acid condition, the highest internal bond strength was achieved with 11.0 M acetic acid treatment; this may be attributed to the increase in chemical acidity from 8.0 M to 11.0 M that enhanced the internal bond strength because of better penetration of weak acid into the composite (Iswanto et al., 2018). Fig. 7 shows that the internal bond strengths have met the minimum requirement of ANSI A208.1–2009 standard.
The lower internal bond strength, flexural strength, and screw withdrawal force may be attributed to the DDGS aggregates, where visible aggregates formed at the higher DDGS concentrations of 25 wt. % and 50 wt.% for sodium hydroxide treatment and 50 wt.% for acetic acid treatment. Moreover, protein aggregation may have also resulted in weak correlation between DDGS loading concentration and internal bond strength with r2 coefficient of determination values of 0.12 and 0.70 for DDGS screen sizes of 120 μm (Eq. (1)) and 250 μm (Eq. (2)), respectively. The r2 coefficient of determination value for smaller DDGS particles is noticeably lower because smaller particles may have higher potential to agglomerate compared with larger particles.
3.7. Relationship between DDGS particle size and loading concentration on the mechanical and physical properties
Internal bond strength (120 μm) = 0.0059 × DDGS loading concentration
The internal bond strength results (Table 4) show that incorporation of DDGS treated with acid or alkali in wood composite reduced the internal bond strength, except for the 12.8 M acetic acid treatment with 250 μm sized DDGS and at higher concentrations, which exhibited improved strength compared with the control samples. Tukey’s multiple comparison tests indicated that the acetic acid-treated DDGS with 250 μm sized DDGS at 10 wt% filler concentration was significantly different, while other samples were statistically equivalent to the control samples. Similarly, the flexural strengths of all treated particleboards were lower than the control but not significantly different from one another, except for 8.0 M sodium hydroxide treated DDGS with 250 μm particle size at 50 wt% filler concentration, which was both lower and statistically different than the control. By contrast, the screw withdrawal resistance for all samples were significantly lower compared with the control.
Internal bond strength (250 μm) = 0.0224 × DDGS loading concentration
+ 0.6573
+ 0.221
(1)
(2)
DDGS particle size did not significantly influence the internal bond or flexural strengths of the particleboards. All particleboards met the ANSI A208.1–2009 standard for internal bond strength, but displayed inferiority in flexural strength. The lower flexural strength of the acetic acid and sodium hydroxide treated samples might be attributed to the brittle nature of the DDGS protein. Some articles reported that zein protein, the primary protein in DDGS, forms brittle films with poor flexibility, making them unsuitable for many applications (Lawton, 2002; Shi et al., 2010). All the mechanical properties of the boards displayed inconsistent standard deviations, which can be attributed to variations in density throughout every board. To quantify these variations, the density across
Fig. 4. Relationship between temperature and flexural strength of particleboards manufactured using acid and alkali treated DDGS. The error bars denote standard deviations of samples and means with the same letter are not significantly different. 5
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Fig. 5. Relationship between temperature and internal bond strength of particleboards manufactured using acid and alkali treated DDGS. The error bars denote standard deviations of samples and means with the same letter are not significantly different.
Fig. 6. Relationship between chemical concentrations and flexural strengths of particleboards manufactured using acid and alkali treated DDGS. The error bars denote standard deviations of samples and means with the same letter are not significantly different.
Fig. 7. Relationship between chemical concentrations and internal bond strengths of particleboards manufactured using acid and alkali treated DDGS. The error bars denote standard deviations of samples and means with the same letter are not significantly different.
3.8. Relationship of chemical treatments and moisture resistance of particleboards
three boards were measured, as shown in Fig. 8, and the samples that were closer to the center of the board were 23.2% denser compared with the edges, as shown in Fig. 9. These density variations likely have an effect on the mechanical properties of the sample, since it has been shown that higher density particleboard have better internal bond strength and flexural properties (Istek and Siradag, 2013). Note that for the boards manufactured in this study, individual sections of a particleboard may not meet the medium-density requirement, but the mean densities of the entire board fell within the range of 640–800 kg/m3 as prescribed by ANSI A208.1–2009.
Table 5 shows the 2 h and 24 h percent mass and volume change of the particleboards immersed in water bath at room temperature (21℃). The composites manufactured from 8 M sodium hydroxide treated DDGS were not considered for analysis because the samples fell apart after being removed from the water. The most probable cause of this failure was that the sodium hydroxide degraded the fat and protein contents of the filler; this is also reflected in the composition analysis which showed lower fat and protein contents from sodium hydroxide 6
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Table 4 Mechanical properties of the particleboards. Chemical Type
phenol formaldehyde 12.8 M acetic acid
8.0 M NaOH
DDGS (%)
0 10 10 25 25 50 50 10 10 25 25 50 50
DDGS Particle Size
Average Property
0 120 250 120 250 120 250 120 250 120 250 120 250
Internal Bond (MPa)
Flexural Strength (MPa)
Screw Withdrawal (N)
1.06abϮ ± 0.102 0.81abc ± 0.132 0.33c ± 0.175 0.65bc ± 0.358 0.96ab ± 0.202 1.01ab ± 0.286 1.28a ± 0.310 0.78abc ± 0.080 0.70bc ± 0.125 0.98ab ± 0.032 0.80abc ± 0.210 0.63bc ± 0.342 0.66bc ± 0.167
6.72a ± 0.917 5.45ab ± 1.714 3.36ab ± 0.991 5.48ab ± 1.685 5.20ab ± 2.597 3.64ab ± 1.974 5.56ab ± 1.927 5.84ab ± 1.903 5.84ab ± 0.960 5.14ab ± 1.151 5.38ab ± 1.056 3.90ab ± 0.867 2.40b ± 1.086
794.35a ± 72.616 397.51bcd ± 87.157 281.87de ± 99.750 454.47b ± 53.220 308.92cde ± 43.725 315.55bcde ± 25.460 354.82bcde ± 58.960 446.33bc ± 41.978 409.78bcd ± 36.590 343.37bcde ± 58.254 403.24bcd ± 36.799 290.43de ± 40.056 224.49e ± 26.233
DDGS – Distiller’s dried grains with solubles. Ϯ Means with the same letter in superscript are not significantly different at 95% confidence interval; means are derived from four different replicates.
Fig. 9. Density of particleboards across the vertical component of the particleboard, where the standard deviations of samples are denoted by the error bars and the position of individual sections are represented by the data labels.
(4)) are 0.62 and 0.39, respectively. The low r2 values may be due to the DDGS agglomerates.
% Change in mass (120 μm) = −1.0112 × DDGS loading concentration + 101.88
(3)
% Change in mass (250 μm) = −0.7293 × DDGS loading concentration + 115.28
(4)
4. Conclusions
Fig. 8. Cut out patterns to study the variation of density across the vertical component of the particleboard where the individual sections are represented by numbers.
In this study, the influence of acid or alkali treated DDGS proteins as a functional filler in wood particleboards was evaluated. The physicomechanical testing of the particleboards were conducted following ASTM D1037-12 protocol and the test results were compared with ANSI A208.1–2009 performance standard. The flexural strength of particleboards pressed at 190 °C were superior to those pressed at lower temperatures, which can be attributed to higher levels of plasticization. The internal bond strength results of acetic acid treated DDGS showed an increasing trend in bond strength with higher DDGS concentration. Furthermore, the FTIR results indicate that the lower peak intensity of acid or alkali treated DDGS may be due to the denaturing of DDGS proteins, which helped DDGS proteins to act as a natural adhesive in order to bind with the pine wood flour in particleboard manufacturing. However, particleboards containing higher DDGS concentrations for both 8.0 M sodium hydroxide and 12.8 M acetic acid treatments exhibited lower mechanical properties in screw withdrawal resistance and flexural strength, likely due to DDGS aggregates. Additionally, it was
treatment of 4.33% and 28.91%, respectively, compared with the fat and protein contents of the acetic acid treatment of 8.13% and 33.62%, respectively. Generally, higher DDGS contents exhibited a smaller change in mass and volume during the water absorption test, which is corroborated both by the higher fat and protein contents of the acetic acid treatment in this study and a recent study (Sundquist and Bajwa, 2016). Another related study showed that higher DDGS concentrations of 50% and 75% displayed less water absorption and thickness swelling compared with lower DDGS concentrations of 10, 15, and 25% (Tisserat et al., 2018). This effect is likely because of the hydrophobic zein protein that may mostly improve the moisture resistance properties of the particleboards. The r2 coefficient of determination of the percentage change in mass of samples with screen sizes of 120 μm (Eq. (3)) and 250 μm (Eq. 7
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Table 5 Physical properties of the particleboards. Chemical Type
DDGS (%)
DDGS Particle Size
Volume (%) 2h
phenol formaldehyde 12.88 M acetic acid
0 10 10 25 25 50 50
0 120 250 120 250 120 250
Mass (%) 24 h
abϮ
42.33 ± 2.44 42.86ab ± 5.14 51.43a ± 5.68 27.34cd ± 3.94 37.18bc ± 4.13 15.32e ± 5.26 22.18de ± 3.40
2h b
45.82 ± 2.73 50.19ab ± 5.66 58.58a ± 6.27 32.65cd ± 6.01 43.21bc ± 4.59 23.21d ± 3.09 31.84cd ± 5.32
24 h ab
86.71 ± 11.77 87.11ab ± 11.97 99.67a ± 11.48 56.34bc ± 13.50 83.99ab ± 10.83 37.14c ± 22.06 67.77abc ± 24.29
95.66ab ± 9.33 96.54ab ± 11.05 110.13a ± 13.85 68.96bc ± 14.15 93.61ab ± 11.15 54.18c ± 15.60 80.10abc ± 23.63
DDGS – Distiller’s dried grains with solubles. Ϯ Means with the same letter in superscript are not significantly different at 95% confidence interval; means are derived from four different replicates.
observed that 8.0 M sodium hydroxide treatment was detrimental to the particleboard’s physical properties, due to the reduction in fat and protein contents of the DDGS compared with the 12.8 M acetic acid treatment. The reason that the 8.0 M sodium hydroxide treated DDGS formulations failed is currently unclear, and investigating the feasibility of lowering the sodium hydroxide concentration may reveal why the proteins and fat in DDGS were reduced and degraded. Despite these shortcomings, the high internal bond strength of the samples and decoupling of DDGS proteins demonstrate that acid or alkali treated DDGS fillers carry potential to replace harmful synthetic resins with chemically functionalized DDGS fillers in many wood composite products.
plastics based on soy protein products. Ind. Crops Prod. 16, 155–172. https://doi. org/10.1016/S0926-6690(02)00007-9. Lawton, J.W., 2002. Zein: a history of processing and use. Cereal Chem. 79, 1–18. https:// doi.org/10.1094/CCHEM.2002.79.1.1. Li, Y., Susan Sun, X., 2011. Mechanical and thermal properties of biocomposites from poly (lactic acid) and DDGS. J. Appl. Polym. Sci. 121, 589–597. https://doi.org/10.1002/ app.33681. Mohanty, A.K., Wu, Q., Singh, A., 2010. Bioadhesive from distillers’ dried grains with solubles (DDGS) and the methods of making those. US patent no. 7,837,779. Date issued: 23 November. Morey, R.V., Hatfield, D.L., Sears, R., Haak, D., Tiffany, D.G., Kaliyan, N., 2009. Fuel properties of biomass feed streams at ethanol plants. Appl. Eng. Agric. 25, 57–64. https://doi.org/10.13031/2013.25421. Muniyasamy, S., Reddy, M.M., Misra, M., Mohanty, A., 2013. Biodegradable green composites from bioethanol co-product and poly (butylene adipate-co-terephthalate). Ind. Crops Prod. 43, 812–819. https://doi.org/10.1016/j.indcrop.2012.08.031. Pandey, P., 2018. Hull Fiber from DDGS and Corn Grain as Alternative Fillers in Polymer Composites With High Density Polyethylene (PhD Thesis). North Dakota State University. Puettmann, M., Oneil, E., Wilson, J., 2013. Cradle to Gate Life Cycle Assessment of US Particleboard Production. A report by the Consortium for Research on Renewable Industrial Materials, USA. Reddy, N., Hu, C., Yan, K., Yang, Y., 2011. Acetylation of corn distillers dried grains. Appl. Energy 88, 1664–1670. https://doi.org/10.1016/j.apenergy.2010.12.019. Rowell, R.M., 2012. Handbook of Wood Chemistry and Wood Composites. CRC press, Boca Raton, FL. Shi, K., Huang, Y., Yu, H., Lee, T.-C., Huang, Q., 2010. Reducing the brittleness of zein films through chemical modification. J. Agric. Food Chem. 59, 56–61. https://doi. org/10.1021/jf103164r. Sundquist, D.J., Bajwa, D.S., 2016. Dried distillers grains with solubles as a multifunctional filler in low density wood particleboards. Ind. Crops Prod. 89, 21–28. https://doi.org/10.1016/j.indcrop.2016.04.071. Tanneru, S.K., Steele, P.H., 2015. Liquefaction of dried distiller’s grains with solubles (DDGS) followed by hydroprocessing to produce liquid hydrocarbons. Fuel 150, 512–518. https://doi.org/10.1016/j.fuel.2015.01.105. Tisserat, B.H., Hwang, H., Vaughn, S.F., Berhow, M.A., Petersen, S.C., Joshee, N., Vaidya, B.N., Harry-O’Kuru, R., 2018. Fiberboard created using the natural adhesive properties of distillers dried grains with solubles. BioResources 13, 2678–2701. Villamil, M.B., Little, J., Nafziger, E.D., 2015. Corn residue, tillage, and nitrogen rate effects on soil properties. Soil Till. Res. 151, 61–66. https://doi.org/10.1016/j.still. 2015.03.005. Wood based panel market size, share & trends analysis report by Product, 2018. 2018 2025 (Market Research Report). Grand View Research, San Francisco, CA. Xu, W., Reddy, N., Yang, Y., 2007. An acidic method of zein extraction from DDGS. J. Agric. Food Chem. 55, 6279–6284. https://doi.org/10.1021/jf0633239. Yu, P., Damiran, D., Azarfar, A., Niu, Z., 2011. Detecting molecular features of spectra mainly associated with structural and non-structural carbohydrates in co-products from bioethanol production using DRIFT with uni-and multivariate molecular spectral analyses. Int. J. Mol. Sci. 12, 1921–1935. https://doi.org/10.3390/ ijms12031921. Zhang, W., 2013. Analysis of Properties to Distillers Dried Grains With Solubles (DDGS) and Using Destoner and Low Moisture Anhydrous Ammonia (LMAA) to Utilize DDGS (Master Thesis). Iowa State University. Zheng, Y., Pan, Z., Zhang, R., Jenkins, B.M., Blunk, S., 2007. Particleboard quality characteristics of saline jose tall wheatgrass and chemical treatment effect. Bioresour. Technol. 98, 1304–1310. https://doi.org/10.1016/j.biortech.2006.04.036.
Acknowledgment The funding for this research was provided by North Dakota Corn Council. References ANSI A208.1-2009, 2009. Particleboard. National Composite Association, Leesburg, VA. Azarfar, A., Jonker, A., Yu, P., 2013. Protein structures among bio-ethanol co-products and its relationships with ruminal and intestinal availability of protein in dairy cattle. Int. J. Mol. Sci. 14, 16802–16816. https://doi.org/10.3390/ijms140816802. Bajwa, D.S., Otte, J., Sundquist, D., 2015. Functionalized distiller’s dried grains with solubles for improving impact properties of polylactic acid. J. Biobased. Mater. Bio. 9, 182–187. https://doi.org/10.1166/jbmb.2015.1511. Bergman, P.C., Boersma, A., Zwart, R., Kiel, J., 2005. Torrefaction for biomass co-firing in existing coal-fired power stations. Energy Cent. Neth. Rep No ECN-C-05-013. https:// www.researchgate.net/profile/Robin_Zwart/publication/204978559_Torrefaction_ for_Biomass_Co-Firing_in_Existing_Coal-Fired_Power_Stations/links/ 09e41511c9aaf0e1c7000000.pdf. BuildingNetwork, H., 2008. Alternative resin binders for particleboard, medium density fiberboard (MDF), and wheatboard. Health Build. Network (May), 1–6. Cheesbrough, V., Rosentrater, K.A., Visser, J., 2008. Properties of distillers grains composites: a preliminary investigation. J. Polym. Environ. 16, 40–50. https://doi.org/ 10.1007/s10924-008-0083-x. Ganesan, V., Rosentrater, K.A., 2006. Characterization of DDGS using differential scanning calorimetry. ASABE/CSBE North Central Intersectional Meeting. Harmsen, P., Huijgen, W., Bermudez, L., Bakker, R., 2010. Literature Review of Physical and Chemical Pretreatment Processes for Lignocellulosic Biomass. Wageningen URFood & Biobased Research. Hemmilä, V., Adamopoulos, S., Karlsson, O., Kumar, A., 2017. Development of sustainable bio-adhesives for engineered wood panels – a Review. RSC Adv. 7, 38604–38630. https://doi.org/10.1039/C7RA06598A. Istek, A., Siradag, H., 2013. The effect of density on particleboard properties. International Caucasian Forestry Symposium. pp. 932–938. Iswanto, A.H., Hermanto, S., Sucipto, T., 2018. The effect of particle immersing in acetic acid solution on dimensional stability and strength properties of particleboard. IOP Conference Series: Earth and Environmental Science. Konermann, L., 2012. Protein Unfolding and Denaturants. Wiley Online Libraryhttps:// doi.org/10.1002/9780470015902.a0003004.pub2. Kumar, R., Choudhary, V., Mishra, S., Varma, I., Mattiason, B., 2002. Adhesives and
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Corn distiller’s dried grains with solubles (DDGS) - A value added functional material for wood composites
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Joshua D. Liawa, Dilpreet S. Bajwaa, , Jamileh Shojaeiarania, Sreekala G. Bajwab a b
Department of Mechanical Engineering, North Dakota State University, Fargo, ND, 58108, United States Montana Agricultural Experiment Station, Montana State University, Bozeman, MT, 59717, United States
A R T I C LE I N FO
A B S T R A C T
Keywords: Distiller’s dried grains with solubles Particleboard Chemical treatment Physical and mechanical properties Sodium hydroxide Acetic acid
Corn distiller’s dried grains with solubles (DDGS) is widely marketed as a livestock feed due to its high protein content of 34%, fat content of 10%, and low cost of 8–13 cents per kilogram. In recent years, DDGS has been used as a multifunctional filler in synthetic resin bonded wood particleboards to improve their physical and mechanical properties where the adhesive properties of DDGS is derived from its hydrophobic zein proteins. The objective of this research was to evaluate if the high value proteins derived from sodium hydroxide and acetic acid treated DDGS can be functionalized as a natural binder in wood particleboard manufacturing by eliminating the use of harmful formaldehyde resins. Several formulations of particleboard were hot pressed using various concentrations of acid and alkali treatments, DDGS filler contents of 10, 25 and 50 wt.%, and DDGS particle sizes of 120 and 250 μm. ASTM D1037-12 standard was adapted to evaluate the particleboard properties. Superior flexural strengths of particleboards occurred at press temperature of 190°C. The acetic acid treated particleboards at higher DDGS concentrations exhibited better water resistance properties. Test results showed that the mean internal bond strengths exceeded the minimum requirement of ANSI A208.1–2009. FTIR results showed that the decoupling of proteins was achieved by acid or alkali treatment. These positive outcomes suggest that DDGS has strong potential to act as a natural adhesive for manufacturing medium-density particleboards.
1. Introduction Particleboard has evolved into a highly engineered product that can be used in housing floor application and industrial used for making furniture, cabinets, tables, and countertops (Puettmann et al., 2013). The ANSI A208.1–2009 standard states that particleboard is primary composed of cellulosic materials in the form of particles that are bonded together with a bonding system and may contain additives (ANSI A208.1-2009, 2009). The history of particleboard manufacturing goes back to the 1950s when manufacturers started utilizing industrial wood residues produced during the production of lumber and plywood (Puettmann et al., 2013). Later on, the field continued to grow and the projections of global wood-based panel market size is forecasted to reach $174.55 billion by 2025 (Wood Based Panel Market Size and Share, 2018). The growth in wood consumption has led to a high worldwide deforestation rate that can cause negative impacts on our environment (Zheng et al., 2007). To reduce wood dependency, it is crucial to replace wood with new lignocellulosic materials. Petroleum-based resins such as phenol formaldehyde, urea formaldehyde, and melamine fortified urea formaldehyde have been the
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conventional binders used in engineered wood products (Hemmilä et al., 2017). However, the carcinogenic nature of formaldehyde emissions and the regulations put in place by regulatory bodies like the California Air Resources Board (CARB) have driven manufacturers to research new ways to limit the usage of formaldehyde. Potential alternatives could come in the form of binders derived from renewable resource materials, such as soy flour and corn (BuildingNetwork, 2008; Sundquist and Bajwa, 2016). Corn residue, a biofuel alternative to petroleum, has become a leading candidate feedstock for lignocellulosic ethanol production (Villamil et al., 2015). A commonly used method in the U.S. for cornethanol production is the dry-grind process, also referred to as dry milling, with an annual production capacity of 14.7 billion gallons; the traits of this processing technique include low capital and energy investment costs (Tanneru and Steele, 2015). Corn ethanol production can generate roughly 0.33 kg each of ethanol, DDGS, and carbon dioxide by utilizing 1 kg of corn (Cheesbrough et al., 2008). The advantage of utilizing DDGS is its low cost of 8–13 cents per kilogram, which makes it cheaper than starch, wood fibers, and soy flour (Li and Susan Sun, 2011). The main components of DDGS are about 34%
Corresponding author at: North Dakota State University, 111 Dolve Hall, Fargo, ND, 58108, United States E-mail address: [email protected] (D.S. Bajwa).
https://doi.org/10.1016/j.indcrop.2019.111525 Received 2 February 2019; Received in revised form 26 June 2019; Accepted 28 June 2019 Available online 19 July 2019 0926-6690/ © 2019 Elsevier B.V. All rights reserved.
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proteins, 10% fat, and 39% fibers (Bajwa et al., 2015), where the adhesive properties of DDGS can be derived from its hydrophobic zein protein (Li and Susan Sun, 2011). This study emphasized the importance of zein protein because zein is the main protein found in both corn and DDGS (Xu et al., 2007). In order to utilize the adhesive effect of protein for bonding and solubilization, the native protein should be denatured to expose more polar groups (Rowell, 2012). Denaturation involves breaking down the existing hydrogen, secondary, and tertiary bonds so that the protein can form hydrogen bonds with wood surface (Rowell, 2012). Some of the most widely used methods to denature proteins were to expose to heat, acids, bases, and organic solvents (Kumar et al., 2002). Acid induced protein unfolding occurs between pH 2 and pH 5 and base induced involves pH 10 or higher (Konermann, 2012). For DDGS in particular, a previous patent indicated that an adhesive derived by hydrolyzing the particles with an aqueous sodium hydroxide solution produced a lap shear strength of 848 kPa (Mohanty et al., 2010). A recent study reported that when DDGS was added at 5 wt.% along with melamine urea formaldehyde resin at 10 wt.%, and wax at 10 wt. % into particleboard, it resulted in an increase in mechanical and physical properties of the particleboard. In this case, the proteins of the DDGS were dissociated and reacted with the melamine urea formaldehyde resin, which improved the mechanical properties, whereas the results also indicated that the improvement in moisture resistance was attributed to the fat component of the DDGS (Sundquist and Bajwa, 2016). However, it was unclear if DDGS can be functionalized with sodium hydroxide treatment or acetic acid treatment to manufacture formaldehyde free particleboard. Thus, this study investigated the performance of natural binder derived from sodium hydroxide treated and acetic acid treated DDGS particles. The results were compared with the minimum requirements of ANSI A208.1–2009 standard widely followed by particleboard industry.
Table 2 Particle size distribution of DDGS. U.S. Standard Sieve No. and Micron Equivalent
DDGS content, % (120 μm screen size)
DDGS content, % (250 μm screen size)
No. 60 (250 μm) No. 80 (180 μm) No. 100 (150 μm) Pan (< 150 μm)
0.3–1.2 6.2–17.7 2.9–12.2 73.8–87.3
7.4–8.7 19.1–23.0 12.4–13.1 56.6–59.6
DDGS – Distiller’s dried grains with solubles.
2.2. Design of experiment The experiment was divided into two different phases. The first phase of the experiment determined the effect of both temperature and chemical concentration on the mechanical properties of the particleboards. A screen size of 250 μm and a DDGS loading concentration of 50 wt.% were used to manufacture particleboards throughout the first phase. The final phase comprised of twelve formulations, 2 particle sizes × 3 DDGS loading concentrations × 2 chemical treatments. The hot-press platen temperature was set at 190℃. For each of these formulations, two boards were manufactured for testing. The second phase of the experiment was conducted to determine the effect of screen size and DDGS loading concentration on the physical and mechanical properties of the particleboards. This experiment was done using two different screen sizes (120 and 250 μm) and three different DDGS loading concentrations of 10, 25, and 50 wt%. A total of twelve formulations comprised of 2 particle sizes × 3 DDGS loading concentrations × 2 chemical treatments were designed. For each of these twelve different formulations, four boards were manufactured per formulation. Moreover, the control samples were prepared differently using combination of pine wood flour and 12 wt% phenol formaldehyde resin. Four boards were manufactured for the control sample. 2.3. Panel processing
2. Materials and methods To minimize the formation of aggregates, different DDGS loading concentrations at 10, 25, and 50 wt.% were dispersed in the pine wood flour matrices of 90, 75, 50 wt.%, respectively, by hand mixing the dried particles. The chemical solvents were prepared by dissolving concentrated acetic acid or sodium hydroxide in water to achieve the desired concentration. The chemical treatment process was initiated by hand mixing the desired concentration of chemical to both DDGS and pine wood flour particles at a ratio of 2:8. The treated particles were blended, mixed, and agitated for seven minutes in a twin shell dry blender (Patterson-Kelly Company, East Stroudsburg, PA, USA) to obtain uniform mixing. The control samples were manufactured by using a Vaper HVLP Spray Gun (Renton, WA, USA) to spray a Cement Mixer Model 998,252 (Northern Industrial Tools, Burnsville, MN, USA) with 12 wt% phenol formaldehyde resin. The wood particles and DDGS blends were then pressed into medium density particleboards using a Carver Hot Press Model 4122 (Carver Inc, Wabash, IN, USA). A pressure of 3.80 MPa was applied for the first phase of the experiment, and for the second phase 4.65 MPa was applied. The total press time was 12 min and the applied pressure was released every 4 min to reduce built up pressure by volatiles. The dimensions of each medium density particleboard were 305 mm (length) ×153 mm (width) ×6 mm (nominal thickness) with target density 720 kg/m3.
2.1. Materials Pine wood flour of 2020-grade was obtained from American Wood Fibers (Wausau, WI, USA). The average particle size of the wood flour was determined to be 425 μm. DDGS was supplied by Blue Flint Ethanol plant (Underwood, ND, USA). The moisture content of wood flour and DDGS were 8% and 7%, respectively. Both the sodium hydroxide (NaOH) pellets with ≥ 90% NaOH concentration and reagent grade glacial acetic acid were obtained from MilliporeSigma (Burlington, MA, USA), whereas the distilled water was obtained from Department of Chemistry and Biochemistry at North Dakota State University (Fargo, ND, USA). Control samples were manufactured using phenol formaldehyde (Hexion Inc., Columbus, OH, USA) with 25–50% by weight of phenol-formaldehyde polymer sodium salt. The raw DDGS material was first grinded and screened using 120 microns and 250 microns screens in a Retsch Rotor Beater mill 300 (Newtown, PA, USA). The particle size distributions of the wood flour and grinded DDGS particles are shown in Tables 1 and 2, respectively.
Table 1 Particle size distribution of wood flour. U.S. Standard Sieve No. and Micron Equivalent
Wood flour content, %
2.4. Composition analysis
No. 20 (850 μm) No. 40 (425 μm) No. 60 (250 μm) Pan (< 250 μm)
<1 68–74 23–27 2-4
Composition analysis was performed on untreated DDGS particles, 12.8 M acetic acid treated DDGS particles, and 8.0 M sodium hydroxide treated DDGS particles that were milled with screen size of 250 μm to determine the nitrogen, crude protein, neutral detergent fiber (NDF), 2
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acid detergent fiber (ADF), lignin, and crude fat contents. The neutral detergent fiber (NDF) represents the amount of cellulose, hemicellulose, and lignin and the acid detergent fiber (ADF) represents the amount of lignin and cellulose. The content of hemicellulose was determined by taking the difference between the NDF and ADF. The amount of cellulose was determined by subtracting the lignin from the ADF. The tests were performed by the Department of Animal Sciences laboratory at North Dakota State University (Fargo, ND). The Association of Analytical Community’s (AOAC) method was followed for crude protein (2001.11), both fiber and lignin (973.18), and crude fat (920.39) tests, and the ANKOM method was used for NDF and ADF analyses.
Table 3 Composition analysis of treated and untreated DDGS.
2.5. Thermogravimetric analysis
DDGS – Distiller’s dried grains with solubles.
Thermogravimetric analysis (TGA) was performed to analyze the degradation temperature and the rate of degradation of the untreated DDGS particles, 12.8 M acetic acid treated DDGS particles, and 8.0 M sodium hydroxide treated DDGS particles. These DDGS particles were milled with screen size of 250 μm. The chemically treated samples were oven dried at 30 ℃ for more than 48 h to remove moisture from the samples prior to test. The analysis was conducted using a TA Q500 TGA (TA Instruments, New Castle, DE, USA) with a temperature ranged from 25℃ to 400℃ at a ramp rate of 10℃ min−1. Nitrogen gas was used at flow rate of 60 ml min−1.
DDGS compared with untreated DDGS, while the protein and fat contents in 12.8 M acetic acid treated DDGS were not noticeably different. In comparison to the untreated DDGS, both acid and alkali treated DDGS displayed lower percentages of NDF and ADF. The lower percentage of NDF is attributed to the degradation of cellulose, hemicellulose, and lignin, and the lower percentage of ADF is attributed to the degradation of lignin and cellulose. A recent study verified that 0.1 M sodium hydroxide treatment led to solubilization of DDGS fiber, which resulted in loss of protein, starch, hemicellulose, lignin, and fat contents in the DDGS (Pandey, 2018).
2.6. Differential scanning calorimetry
Column1
DDGS, untreated
DDGS, sodium hydroxide
DDGS, acetic acid
Nitrogen (%) Crude protein (%) NDF (%) ADF (%) Cellulose (%) Hemicellulose (%) Lignin (%) Crude fat (%)
5.30 33.15 45.29 15.32 13.26 29.97 2.06 8.71
4.63 28.91 25.49 9.65 9.00 15.84 0.65 4.33
5.38 33.62 41.85 14.87 12.82 26.98 2.05 8.13
3.2. Thermogravimetric analysis
Differential scanning calorimetry (DSC) was performed to analyze the melting peak and glass transition temperature of the untreated DDGS particles, 12.8 M acetic acid treated DDGS particles, and 8.0 M sodium hydroxide treated DDGS particles. These DDGS particles were milled with screen size of 250 μm. The chemically treated samples were oven dried at 30℃ for more than 48 h. The analysis was conducted using a TA Q1000 DSC (TA Instruments, New Castle, DE, USA) with a temperature range from -20℃ to 190℃ at ramp rate of 10℃ min−1. Nitrogen gas was used to purge the sample at a rate of 50 ml min−1.
The curves in Fig. 1 shows the percent change of weight and the first derivative of the percent change of weight of the sample when it is heated. In this study, the local maxima of the first derivative curves occur between 100 °C and 200 °C, which relates to the initial degradation of DDGS components. These DDGS components include hemicellulose, cellulose, residual starch, fat, lignin, and protein components (Morey et al., 2009). Between 250 °C and 350 °C of the first derivative curves, all samples display their mass decomposition of major components of DDGS, and this range is similar to a previous study (Sundquist and Bajwa, 2016). These major components include protein, hemicellulose, cellulose, and lignin (Bergman et al., 2005; Sundquist and Bajwa, 2016). Both acid treated and untreated DDGS particles exhibit higher degradation rate compared with alkali treated. This trend relates to a previous study which explained that better stability is achieved at lower protein content in DDGS (Reddy et al., 2011). The aforementioned results from the composition analysis indicate that alkali treated DDGS has a protein content of 28.91%, which is noticeably lower than both untreated DDGS and acid treated DDGS of 33.15% and 33.62%, respectively. Additionally, the percent change of weight curves shows that beyond 200℃, all the samples displayed weight loss of more than 90% due to thermal degradation. Thus, the processing temperature cannot be too high or too long or else there may be adverse effects on the composite such as decrease in mechanical properties.
2.7. Fourier transform infrared spectroscopy Fourier Transform Infrared Spectroscopy (FTIR) was performed to determine the difference in functionality of untreated DDGS particles, 12.8 M acetic acid treated DDGS particles, and 8.0 M sodium hydroxide treated DDGS particles. These DDGS particles were milled with screen size of 250 μm. The chemically treated samples were oven dried at 30℃ for more than 48 h. All of the samples were mixed with KBr and pressed using a mini-pellet press (Specac Limited, UK) at 2 tonnes to form discshaped specimens. The analysis was conducted using a Thermo Scientific Nicolet 8700 FTIR spectrometer (Thermo Fisher, Waltman, MA, USA). 2.8. Statistical analysis Statistical analysis software Minitab 18 (Minitab Inc., State College, PA, USA) was used to conduct one-way ANOVA to determine the significant factors affecting the physical and mechanical properties of the boards, with a criterion of 95% confidence interval (α = 0.05). Tukey’s multiple comparison test was used to determine whether the means were significantly different.
3.3. Differential scanning calorimetry Fig. 2 illustrates the DSC curves of untreated, alkali-treated, and acid treated DDGS. A previous study showed that the occurrence of glass transition temperatures for the unmodified DDGS, reduced fat DDGS, and de-waxed DDGS were between 20℃ to 50℃ (Ganesan and Rosentrater, 2006). In this study, untreated, alkali treated, acid treated DDGS displayed glass transition temperatures of 53.50 °C, 60.05 °C, and 63.93 °C, respectively. The higher glass transition temperatures and melting peaks of treated DDGS compared with untreated DDGS may be attributed to the degradation of fat and protein contents. The aforementioned results of the composition analysis show that the fat contents of untreated DDGS, sodium hydroxide treated DDGS, acetic acid treated
3. Results and discussion 3.1. Composition analysis Composition analysis was performed to determine the nutrient contents in DDGS. Table 3 shows that alkali treated DDGS at 8.0 M degraded and solubilized both the protein and fat components in the 3
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Fig. 1. Thermogravimetric analysis results of treated and untreated DDGS.
intensities of protein amide I and II may be attributed to the denaturing of protein caused by the weak acid and alkali treatments. 3.5. Relationship between temperature and mechanical properties of particleboards The samples were hot-pressed at 170°C, 180°C, and 190°C, as shown in Fig. 4. A similar study reported that superior flexural strength at 185°C was attributed to the plasticization of the DDGS (Tisserat et al., 2018). Moreover, the plasticization occurred when the samples had a smooth tactile feel on their surface, which mimicked a wood composite manufactured with a thermoset or thermoplastic resin (Tisserat et al., 2018). In this study, the flexural properties of the particleboards pressed at 190°C were superior to those pressed at 170°C and 180°C, which can be attributed to the highest plasticization of the DDGS while limited plasticization occurred at 180°C and below. The flexural strength results were below the minimum requirements of the ANSI A208.1–2009 standard. The highest internal bond strength for 12.8 M acetic acid and 2.0 M sodium hydroxide were attained at 180℃ and 190℃, respectively, as shown in Fig. 5. The decrease in internal bond strength of acetic acid treatment at 190℃ may be due to the brittleness of DDGS proteins and degradation of the DDGS. However, no clear trend is visible based on increasing or decreasing the temperature of sodium hydroxide treated DDGS. This is likely due to the lower number of press temperatures that were tested. The internal bond strength results met the minimum requirements of the ANSI A208.1–2009 standard.
Fig. 2. Differential scanning calorimetry results of untreated and treated DDGS particles.
DDGS are 8.71%, 4.33%, and 8.13%, respectively. The higher glass transition temperatures of chemically treated DDGS were possibly due to lower fat content, and this is supported by a previous study where the glass transition temperature of defatted DDGS was 54 °C and untreated DDGS was 49.4 °C (Tisserat et al., 2018). Moreover, the untreated DDGS, alkali treated, and acid treated DDGS have melting peaks at 110.59 °C, 122.38 °C, and 125.04 °C, respectively. These melting peaks fell within the initial degradation range from the TGA, between 100℃ and 200℃, and these melting peaks possibly indicate both the denaturation temperatures of proteins and degradation temperatures of DDGS components. Thus, the higher melting temperatures of treated DDGS could possibly mean that chemically treated DDGS samples have been denatured to potentially act as a natural binder.
3.6. Relationship between chemical concentration and mechanical properties of particleboards
3.4. Fourier transform infrared spectroscopy (FTIR) All spectra displayed characteristics of −OH and –NH stretching, and those are represented by the broad peaks in the 3500-3200 cm−1 region, as shown in Fig. 3. Moreover, the peaks in the 2950-2500 cm−1 region indicate the −CH stretching. The FTIR results of these absorption trends are in agreement with a similar study, where the stretching vibrations of −OH and –NH are from carbohydrates and protein and −CH is from lipids (Muniyasamy et al., 2013). The peaks in the 15001000 cm−1 region represent the CHO bond of carbohydrates (Yu et al., 2011). The peaks in the region of 1700-1500 cm−1 region represent the protein amide I and II (Azarfar et al., 2013), whereas the peaks in the 1700-1800 cm−1 region represent the –C = O stretching. Moreover, the peaks in the 600-700 cm−1 region show the P–S and P]S stretching (Tisserat et al., 2018). The –C = O and P–S/P]S stretching are identified as lignin and protein, respectively (Tisserat et al., 2018). Overall, the peaks in this 1700-1600 cm−1 show weaker peak intensities for treated DDGS compared with untreated DDGS. The weaker peak
Fig. 6. depicts the effect of chemical concentration on the flexural strength of particleboards. Suitable chemical modification of DDGS is important because the protective structure of hemicellulose and lignin hinders the cellulose from hydrolysis (Zhang, 2013). Weak acid modification led to the hydrolysis of hemicellulose and resulted in increasing porosity of the lignocellulosic biomass, whereas alkaline treatment led to the removal of lignin (Harmsen et al., 2010). The highest flexural strength was achieved with 2.0 M sodium hydroxide and 12.8 M acetic acid, as shown in Fig. 6; these chemical concentrations may lead to better penetration of chemical into the composite and may also enhance the binding properties of DDGS particles with wood flour. The flexural strength results were below the minimum requirements of the ANSI A208.1–2009 standard. The internal bond strengths of particleboards increased with increasing concentration of sodium, hydroxide, as shown in Fig. 7, where 4
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Fig. 3. FTIR spectrum of (a) untreated DDGS particles, (b) sodium hydroxide treated DDGS particles, and (c) acetic acid treated DDGS particles.
8.0 M sodium hydroxide treated DDGS displayed a relatively high internal bond strength. The high internal bond strength may be attributed to the greater hydrolysis of DDGS proteins with the increase of sodium hydroxide concentration. In weak acid condition, the highest internal bond strength was achieved with 11.0 M acetic acid treatment; this may be attributed to the increase in chemical acidity from 8.0 M to 11.0 M that enhanced the internal bond strength because of better penetration of weak acid into the composite (Iswanto et al., 2018). Fig. 7 shows that the internal bond strengths have met the minimum requirement of ANSI A208.1–2009 standard.
The lower internal bond strength, flexural strength, and screw withdrawal force may be attributed to the DDGS aggregates, where visible aggregates formed at the higher DDGS concentrations of 25 wt. % and 50 wt.% for sodium hydroxide treatment and 50 wt.% for acetic acid treatment. Moreover, protein aggregation may have also resulted in weak correlation between DDGS loading concentration and internal bond strength with r2 coefficient of determination values of 0.12 and 0.70 for DDGS screen sizes of 120 μm (Eq. (1)) and 250 μm (Eq. (2)), respectively. The r2 coefficient of determination value for smaller DDGS particles is noticeably lower because smaller particles may have higher potential to agglomerate compared with larger particles.
3.7. Relationship between DDGS particle size and loading concentration on the mechanical and physical properties
Internal bond strength (120 μm) = 0.0059 × DDGS loading concentration
The internal bond strength results (Table 4) show that incorporation of DDGS treated with acid or alkali in wood composite reduced the internal bond strength, except for the 12.8 M acetic acid treatment with 250 μm sized DDGS and at higher concentrations, which exhibited improved strength compared with the control samples. Tukey’s multiple comparison tests indicated that the acetic acid-treated DDGS with 250 μm sized DDGS at 10 wt% filler concentration was significantly different, while other samples were statistically equivalent to the control samples. Similarly, the flexural strengths of all treated particleboards were lower than the control but not significantly different from one another, except for 8.0 M sodium hydroxide treated DDGS with 250 μm particle size at 50 wt% filler concentration, which was both lower and statistically different than the control. By contrast, the screw withdrawal resistance for all samples were significantly lower compared with the control.
Internal bond strength (250 μm) = 0.0224 × DDGS loading concentration
+ 0.6573
+ 0.221
(1)
(2)
DDGS particle size did not significantly influence the internal bond or flexural strengths of the particleboards. All particleboards met the ANSI A208.1–2009 standard for internal bond strength, but displayed inferiority in flexural strength. The lower flexural strength of the acetic acid and sodium hydroxide treated samples might be attributed to the brittle nature of the DDGS protein. Some articles reported that zein protein, the primary protein in DDGS, forms brittle films with poor flexibility, making them unsuitable for many applications (Lawton, 2002; Shi et al., 2010). All the mechanical properties of the boards displayed inconsistent standard deviations, which can be attributed to variations in density throughout every board. To quantify these variations, the density across
Fig. 4. Relationship between temperature and flexural strength of particleboards manufactured using acid and alkali treated DDGS. The error bars denote standard deviations of samples and means with the same letter are not significantly different. 5
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Fig. 5. Relationship between temperature and internal bond strength of particleboards manufactured using acid and alkali treated DDGS. The error bars denote standard deviations of samples and means with the same letter are not significantly different.
Fig. 6. Relationship between chemical concentrations and flexural strengths of particleboards manufactured using acid and alkali treated DDGS. The error bars denote standard deviations of samples and means with the same letter are not significantly different.
Fig. 7. Relationship between chemical concentrations and internal bond strengths of particleboards manufactured using acid and alkali treated DDGS. The error bars denote standard deviations of samples and means with the same letter are not significantly different.
3.8. Relationship of chemical treatments and moisture resistance of particleboards
three boards were measured, as shown in Fig. 8, and the samples that were closer to the center of the board were 23.2% denser compared with the edges, as shown in Fig. 9. These density variations likely have an effect on the mechanical properties of the sample, since it has been shown that higher density particleboard have better internal bond strength and flexural properties (Istek and Siradag, 2013). Note that for the boards manufactured in this study, individual sections of a particleboard may not meet the medium-density requirement, but the mean densities of the entire board fell within the range of 640–800 kg/m3 as prescribed by ANSI A208.1–2009.
Table 5 shows the 2 h and 24 h percent mass and volume change of the particleboards immersed in water bath at room temperature (21℃). The composites manufactured from 8 M sodium hydroxide treated DDGS were not considered for analysis because the samples fell apart after being removed from the water. The most probable cause of this failure was that the sodium hydroxide degraded the fat and protein contents of the filler; this is also reflected in the composition analysis which showed lower fat and protein contents from sodium hydroxide 6
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Table 4 Mechanical properties of the particleboards. Chemical Type
phenol formaldehyde 12.8 M acetic acid
8.0 M NaOH
DDGS (%)
0 10 10 25 25 50 50 10 10 25 25 50 50
DDGS Particle Size
Average Property
0 120 250 120 250 120 250 120 250 120 250 120 250
Internal Bond (MPa)
Flexural Strength (MPa)
Screw Withdrawal (N)
1.06abϮ ± 0.102 0.81abc ± 0.132 0.33c ± 0.175 0.65bc ± 0.358 0.96ab ± 0.202 1.01ab ± 0.286 1.28a ± 0.310 0.78abc ± 0.080 0.70bc ± 0.125 0.98ab ± 0.032 0.80abc ± 0.210 0.63bc ± 0.342 0.66bc ± 0.167
6.72a ± 0.917 5.45ab ± 1.714 3.36ab ± 0.991 5.48ab ± 1.685 5.20ab ± 2.597 3.64ab ± 1.974 5.56ab ± 1.927 5.84ab ± 1.903 5.84ab ± 0.960 5.14ab ± 1.151 5.38ab ± 1.056 3.90ab ± 0.867 2.40b ± 1.086
794.35a ± 72.616 397.51bcd ± 87.157 281.87de ± 99.750 454.47b ± 53.220 308.92cde ± 43.725 315.55bcde ± 25.460 354.82bcde ± 58.960 446.33bc ± 41.978 409.78bcd ± 36.590 343.37bcde ± 58.254 403.24bcd ± 36.799 290.43de ± 40.056 224.49e ± 26.233
DDGS – Distiller’s dried grains with solubles. Ϯ Means with the same letter in superscript are not significantly different at 95% confidence interval; means are derived from four different replicates.
Fig. 9. Density of particleboards across the vertical component of the particleboard, where the standard deviations of samples are denoted by the error bars and the position of individual sections are represented by the data labels.
(4)) are 0.62 and 0.39, respectively. The low r2 values may be due to the DDGS agglomerates.
% Change in mass (120 μm) = −1.0112 × DDGS loading concentration + 101.88
(3)
% Change in mass (250 μm) = −0.7293 × DDGS loading concentration + 115.28
(4)
4. Conclusions
Fig. 8. Cut out patterns to study the variation of density across the vertical component of the particleboard where the individual sections are represented by numbers.
In this study, the influence of acid or alkali treated DDGS proteins as a functional filler in wood particleboards was evaluated. The physicomechanical testing of the particleboards were conducted following ASTM D1037-12 protocol and the test results were compared with ANSI A208.1–2009 performance standard. The flexural strength of particleboards pressed at 190 °C were superior to those pressed at lower temperatures, which can be attributed to higher levels of plasticization. The internal bond strength results of acetic acid treated DDGS showed an increasing trend in bond strength with higher DDGS concentration. Furthermore, the FTIR results indicate that the lower peak intensity of acid or alkali treated DDGS may be due to the denaturing of DDGS proteins, which helped DDGS proteins to act as a natural adhesive in order to bind with the pine wood flour in particleboard manufacturing. However, particleboards containing higher DDGS concentrations for both 8.0 M sodium hydroxide and 12.8 M acetic acid treatments exhibited lower mechanical properties in screw withdrawal resistance and flexural strength, likely due to DDGS aggregates. Additionally, it was
treatment of 4.33% and 28.91%, respectively, compared with the fat and protein contents of the acetic acid treatment of 8.13% and 33.62%, respectively. Generally, higher DDGS contents exhibited a smaller change in mass and volume during the water absorption test, which is corroborated both by the higher fat and protein contents of the acetic acid treatment in this study and a recent study (Sundquist and Bajwa, 2016). Another related study showed that higher DDGS concentrations of 50% and 75% displayed less water absorption and thickness swelling compared with lower DDGS concentrations of 10, 15, and 25% (Tisserat et al., 2018). This effect is likely because of the hydrophobic zein protein that may mostly improve the moisture resistance properties of the particleboards. The r2 coefficient of determination of the percentage change in mass of samples with screen sizes of 120 μm (Eq. (3)) and 250 μm (Eq. 7
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Table 5 Physical properties of the particleboards. Chemical Type
DDGS (%)
DDGS Particle Size
Volume (%) 2h
phenol formaldehyde 12.88 M acetic acid
0 10 10 25 25 50 50
0 120 250 120 250 120 250
Mass (%) 24 h
abϮ
42.33 ± 2.44 42.86ab ± 5.14 51.43a ± 5.68 27.34cd ± 3.94 37.18bc ± 4.13 15.32e ± 5.26 22.18de ± 3.40
2h b
45.82 ± 2.73 50.19ab ± 5.66 58.58a ± 6.27 32.65cd ± 6.01 43.21bc ± 4.59 23.21d ± 3.09 31.84cd ± 5.32
24 h ab
86.71 ± 11.77 87.11ab ± 11.97 99.67a ± 11.48 56.34bc ± 13.50 83.99ab ± 10.83 37.14c ± 22.06 67.77abc ± 24.29
95.66ab ± 9.33 96.54ab ± 11.05 110.13a ± 13.85 68.96bc ± 14.15 93.61ab ± 11.15 54.18c ± 15.60 80.10abc ± 23.63
DDGS – Distiller’s dried grains with solubles. Ϯ Means with the same letter in superscript are not significantly different at 95% confidence interval; means are derived from four different replicates.
observed that 8.0 M sodium hydroxide treatment was detrimental to the particleboard’s physical properties, due to the reduction in fat and protein contents of the DDGS compared with the 12.8 M acetic acid treatment. The reason that the 8.0 M sodium hydroxide treated DDGS formulations failed is currently unclear, and investigating the feasibility of lowering the sodium hydroxide concentration may reveal why the proteins and fat in DDGS were reduced and degraded. Despite these shortcomings, the high internal bond strength of the samples and decoupling of DDGS proteins demonstrate that acid or alkali treated DDGS fillers carry potential to replace harmful synthetic resins with chemically functionalized DDGS fillers in many wood composite products.
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