Green Epoxy Resin System Based on Lignin and Tung Oil and Its

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A green epoxy resin system based on lignin and tung oil and its application in epoxy asphalt Junna Xin, Mei Li, Ran Li, Michael P. Wolcott, and Jinwen Zhang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b00256 • Publication Date (Web): 05 Apr 2016 Downloaded from http://pubs.acs.org on April 11, 2016

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ACS Sustainable Chemistry & Engineering

A green epoxy resin system based on lignin and tung oil and its application in epoxy asphalt

＊

Junna Xin,1 Mei Li,1,2 Ran Li,1 Michael P. Wolcott,1 Jinwen Zhang1

1

School of Mechanical and Materials Engineering,

Composite Materials and Engineering Center, Washington State University,

PO Box 641806, Pullman, WA 99164, USA 2

Institute of Chemical Industry of Forestry Products, CAF,

No. 16, Suojinwucun, Nanjing 210042, P.R. China

* To whom correspondence should be addressed. Tel.: 509-335-8723; Fax: 509-335-5077; Email: [email protected]

ACS Paragon Plus Environment


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Abstract In this work, lignin-based epoxy was synthesized by reacting epichlorohydrin (ECH) and partially depolymerized lignin (PDL) and then used for modification of asphalt. The Diels-Alder adduct of methyl esters of eleostearic acid and maleic anhydride (ME-MA) was synthesized and used as a biobased curing agent. The structure of PDL-epoxy was characterized by FTIR and 31P NMR. Non-isothermal curing kinetics and thermal properties of the cured epoxy resins were studied by differential scanning analysis (DSC), dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA), respectively. Curing behaviors of PDL-epoxy and a commercial epoxy DER332 were compared. Effects of epoxy content on rheological properties of the modified asphalt binder were studied using a parallel plate rheometer. Results show that the elastic behavior of asphalt binder at elevated temperatures was improved with increase in epoxy content.

Keywords: lignin; lignin-based epoxy; green epoxy resin; epoxy asphalt;


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Introduction Lignin abundantly exists in woody and other lignocellulosic biomass. Lignin is biologically synthesized from three monolignol units, namely coumaryl, synapyl and coniferyl alcohols, which are connected by ether bonds to form a complex branched polymer. The phenolic and alcohol hydroxyls present in lignin make it an attractive reactive ingredient to be incorporated into thermosetting resins [1-6]. As a result, uses of lignin as feedstock for synthesis of epoxy monomers and as a reactive additive have received a lot of investigation. The preparation methods for lignin-based epoxy resins generally falls in three categories: (a) blending lignin with general epoxy resin directly [7-10]; (b) modifying lignin derivatives such as Kraft lignin by glycidylation directly [11, 12]; and (c) modifying lignin derivatives to improve its reactivity followed by glycidylation [13-15]. However, the highly branched molecular structure makes its hydroxyls less accessible for derivatization and the resulting lignin derivatives immiscible in the resin system, giving poor end-use performance. In view of the characteristic structure of lignin, partial destruction of its bulky structure releases more hydroxyl groups for reactions and increases its miscibility or compatibility with other ingredients in the thermoset system. In our recent studies, we demonstrated that Kraft lignin and enzymolysis lignin were partially depolymerized under base catalysis in super critical methanol or over Raney Ni under mild conditions [16, 17]. The partial depolymerized lignin (PDL) exhibited increased solubility in organic solvent and increased hydroxyl content from both phenolic and aliphatic hydroxyl groups.



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Lignin and lignin derivatives have found some applications in asphalt products. Cationic surfactants derived from lignin are used to prepare asphalt emulsion which has many advantages over the traditional hot and cutback asphalts in terms of energy savings, reduction of pollution, ease of use and improved adhesion [18]. Because lignin and asphalt both contain aromatic rings joined by alkyl chains in their chemical structures, use of lignin as an extender in asphalt has been suggested [19]. Because the asphalt binder is always subjected to wide temperature variation from season to season and great stress from heavy truck traffic, it is likely to crack in the cold winter and lose its cohesive strength in the hot summer months. In order to improve the temperature-resistance properties of asphalt, one approach is to modify the asphalt binder with the incorporation of epoxy resin which can greatly improve performance of the asphalt binder especially at higher temperatures. Current epoxies used for asphalt modification are all petroleum based and mostly bisphenol A (BPA) type epoxy resins. For example, Yu et al. and Cong et al. [20, 21] investigated the modification of asphalt by mixing styrene-butadiene-styrene copolymer and epoxy resin made from diglycidyl ether of bisphenol A and a commercial curing agent. BPA type epoxies are generally expensive and are also susceptible to chemical estrogen, there is a great interest in developing alternative epoxies. In this work, we studied the modification of asphalt binder using lignin-derived epoxy. To the best of our knowledge, there is only one report in the literature on the modification of asphalt by enzymatic hydrolysis lignin (EHL)-derived epoxy [22]. The results showed that the EHL epoxy shifted the softening point to a higher temperature and improved the aging resistance of asphalts.


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Still, the authors in that paper used EHL-derived epoxy in combination with a bisphenol A type epoxy to modify the asphalt. In contrast, we employed a lignin-derived epoxy alone for modification of asphalt in this study. Furthermore, a biobased anhydride which was the Diels-Alder adduct produced from addition of maleic anhydride and methyl ester of eleostearic acid (a major tung oil fatty acid) [23, 24] was used as the curing agent. As shown in our previous work, the partially depolymerized lignin (PDL) has good solubility in organic solvents and its hydroxyl groups are more accessible for modification. Therefore, the enzymatic hydrolysis lignin used for this work was partially depolymerized, and then the resulting PDL was then converted to a lignin-based epoxy monomer by reacting it directly with epichlorohydrin. Asphalt was formulated with PDL-epoxy monomer and tung oil fatty acid-derived curing agent in different proportions. The effects of epoxy resin content on the performance of epoxy asphalt mixture were evaluated. Experimental Materials The lignin was isolated from a residue of enzymatic hydrolysis of Douglas fir provided by Catchlight Energy LLC (Seattle, WA). The enzymatic hydrolysis method of Douglas fir woody biomass can be found in a previous report [25] and it was also briefly described in Supporting Information. The received residue was purified following the Klason method using 4% H2SO4 in an autoclave for 1 h at 120 ºC. 2-Chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane

(TMDP)


(Aldrich),

chromium


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acetylacetonate (Acros), epichlorohydrin (99%, Acros organics), sodium hydroxide (98.7%, J.T.Braker), benzyltriethylammonium chloride (97%, Aldrich), dimethylsulfoxide (99.9%, Fisher), tetrahydrofuran (99.9%, Fisher), ethyl ether (99+%, Fisher) and PG 64-28 asphalt with a specific gravity 1.03 at 15 °C (Western States Asphalt, Inc.) were used as received. The biobased curing agent ME-MA was prepared following the method described in our previous study [23] and its structure is shown in scheme 1. Preparation of partially depolymerized enzymolysis lignin (PDL) PDL was prepared by mild hydrogenolysis according to our previous report [16], and the general procedure is as follows. Enzymolysis lignin (7.5 g), Raney Ni 0.975 g (dry weight) and 3% NaOH in dioxane/H2O (500 mL) were charged to a 2 L Parr reactor. The reactor was pressurized with H2 to 2.0 MPa at room temperature and then the reaction was performed at 180 °C. The reaction was performed for 3.5 h under overhead mechanical stirring. After the reactor was cooled to room temperature, the upper mixture was filtered and the residue was washed by fresh water for several times by using a magnet absorbed the Raney Ni to the bottom of the reactor. Raney Ni catalyst was recovered. All the filtrates were combined.

After the filtrate was

adjusted to pH = 7.0 with 1N HCl, the product was precipitated and collected by centrifugation. The product was obtained after freeze-drying. The characterization results of molecular weight, hydroxyl value and FTIR of PDL are summarized in Supporting Information. Preparation of epoxy monomers from PDL The PDL based-epoxy was prepared by reacting epichlorohydrin (ECH) and PDL. Scheme 1


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shows the synthesis route of PDL-epoxy. In brief, after PDL (5 g), epichlorohydrin (30 g), benzyltriethylammonium chloride (75 mg) and dimethylsulfoxide (50 g) were charged to a flask, the temperature was raised to 70 °C (or 117 °C) and the reaction was continued for 3 h. After the reaction mixture was cooled to 60 °C, 1.23 g sodium hydroxide was charged. The mixture was stirred at 60 °C for 4 h. The crude product was washed with ethyl ether twice and then washed by deionized water twice. The products were dried by freeze-drying, receiving 4.33 g and 5.02 g, from the reactions at 70 and 117 °C, respectively. Thereafter, these two PDL-epoxies are referred as PDL-epoxy-70 °C PDL-epoxy-117 °C.

Scheme 1. Synthesis route of lignin-epoxy and epoxy asphalt. Preparation of epoxy samples and epoxy modified asphalt In all formulations of the epoxy samples, epoxy and curing agent were maintained in a 1:0.88 weight ratio. 2-ethyl-1-4-methylimidazole was used as a catalyst and added at 1.0 wt% on the basis of the total weight of curing agent and epoxy. The ingredients were mixed at 70 °C to form a homogeneous mixture, and then the mixture was transferred into an aluminum mold with the



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dimensions of the cavities being 30 mm × 18 mm × 5 mm. Curing was performed at 150 °C for 2 h and then at 200 °C for 1 h. The cured samples were carefully removed from the mold and used for study of thermal properties. For the preparation of epoxy modified asphalt, neat asphalt was first heated at 90 ± 5 °C in an oven for 30 min. The premixed PDL-epoxy/ME-MA with 1 wt% catalyst was then combined with the neat asphalt at different concentrations, i.e., 7.5 wt%, 15 wt% and 22.5 wt% respectively. The samples were cured at 150 °C for 2 h and then 200 °C for 1 h. The resulting epoxy asphalt samples were used for the rheological test. Curing kinetics Curing kinetics for each of the above epoxy samples was studied by differential scanning calorimetry (DSC) on a 2920 MDSC (TA Instruments) instrument. After the formulated epoxy sample (~ 5 -10 mg) was sealed in a 40-µL aluminum crucible, the curing behavior was evaluated immediately by the non-isothermal DSC experiment. For each sample, the non-isothermal DSC scan was repeated twice and the average value of the results was used. The temperature was scanned from 35 to 250 °C at heating rates of 5, 10, 15 and 20 °C/min, respectively. The activation energy (Ea) of curing is calculated using the Ozawa method using the following equation:

Ea =

−R ∆ ln(φ ) 1.052 ∆ 1/ Tp

(

)

(1)

where φ is the heating scan rate, Tp the peak temperature of the DSC exothermic thermogram, and R the universal gas constant with the value of 8.314 J mol-1·K-1.


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Characterization FTIR spectra were recorded using a Nexus 670 spectrometer. The sample was scanned from 400 to 4,000 cm-1 with a resolution of 4 cm-1 for 32 times. The hydroxyl values of PDL and PDL-epoxy monomers were determined using 31P NMR. The 31

P NMR spectra were obtained on a Bruker 300 NMR spectrometer following a method in the

literature [26]. First, approximately 25.0 mg of lignin compound and an excessive amount of 2-chloro-4,4,5,5,-tetramethyl-1,2,3-dioxaphospholane (TMDP) were dissolved in a mixture solvent of pyridine/CDCl3 (1.6:1 v/v). Chromium acetylacetonate was used as a relaxation agent and cyclohexanol as the internal standard. The 31P NMR spectra were acquired using an inverse gated decoupling pulse sequence, 90° pulse angle, and 25 s pulse delay. Chemical shifts were calibrated by referring to the peak signal at δ 145.1 ppm for the internal standard of cyclohexanol. Thermogravimetric analysis (TGA) was performed on a SDT Q600 TGA instrument (TA Instruments). Each sample was scanned from 30 to 600 °C at a heating rate of 10 °C/min-1 under a nitrogen atmosphere. Rheological properties of neat asphalt and epoxy asphalt were measured using a Discovery HR-2 rheometer (TA instruments). A parallel plate geometry with a diameter of 25 mm and a gap set at 500 mm was used. Temperature sweep test was performed from 30 to 100 °C at a heating rate of 2 °C/min and a frequency of 10 rad/s. Frequency sweep test from 0.1 to 100 rad/s was also performed for each sample at 60 °C. For both experiments, the strain was set at 1.0%.



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Results and Discussion Synthesis and Characterization of PDL-epoxy PDL-epoxy was synthesized by the traditional glycidylation method through the reaction of PDL and epichlorohydrin (ECH) (Scheme 1), and the reaction was performed at 70 or 117 °C. As shown in supporting information, PDL obtained from partial hydrogenolysis of enzymolysis lignin displayed narrow molecular weight distribution and enhanced hydroxyl value (Table S1 and S2). These properties will be beneficial to improve efficiency of glycidylation reaction of PDL. Initially, ECH was used as both reactant and solvent like in the usual glycidylation reaction. However, PDL was not soluble in ECH and the resulting products were hard to dissolve in usual organic solvents. Because the product obtained this way was insoluble in the mixed DCl3/pyridine solvent, analysis of the functionality by

31

P NMR could not be performed. The

lack of an effective solvent also makes it difficult to analyze the epoxy value of these products by the titration method in solutions. This result suggests that glycidylation of PDL without a suitable solvent is of low reaction efficiency. According to our previous study [16], PDL shows a good solubility in DMSO. When DMSO was used as a co-solvent in the glycidylation, PDL-epoxies were synthesized with yields of 86.6% at 70 °C and 100% at 117 °C, respectively. This result suggests that high temperature is beneficial to complete the glycidylation reaction. The obtained PDL-epoxies exhibited good solubility in the mixture solvent (CDCl3/pyridine). Therefore, DMSO was used as a co-solvent in the rest experiments for the preparation of the PDL-epoxy samples.


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FTIR characterization of PDL and PDL-epoxies Figure 1 shows the FTIR spectra of PDL and PDL-epoxies. All samples exhibited a broad absorption of -OH at 3470 cm–1, a absorption band of C-H at 2930 cm–1, a absorption peak for carbonyl at 1700 cm–1, two peaks for benzene ring vibrations at 1600 cm–1 and 1506 cm–1, and a C-H deformations band of asymmetric methyl and methylene appeared at 1460~1470 cm–1. Specifically, an absorption peak at 908 cm-1 attributed to the oxirane ring was noted in the spectra of both PDL-epoxies. These results suggest that PDL was successfully glycidylized to form PDL-epoxies.

Figure 1. The FTIR spectra of PDLPDL-epoxies synthesized at 70 °C and 117 °C. Determination of hydroxyl values of PDL and PDL epoxies by 31P NMR Figure 2 shows the 31P NMR spectra of the PDLand the two PDL-epoxies. There are three types



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of hydroxyl groups in these samples, aliphatic, aromatic and carboxylic. The hydroxyl value for each type of hydroxyls was determined by comparing the corresponding peak area to that of the internal standard. The results of different hydroxyl values for these samples aresummarized in Table 1. By comparing the spectra of the original PDL and PDL-epoxies (Figure 2), it is noted that the signal in the region of 136.6-144.7 ppm attributed to the phenolic hydroxyls in PDL-epoxies appeared very weak in the PDL-epoxy prepared at 70 °C and almost disappeared in PDL-epoxy prepared at 117 °C. The signal in the range of 133.6-136.6 ppm that was attributed to the carboxylic acid hydroxyls disappeared in the spectra of both PDL-epoxies. Conversely, the peak at 145.5-150.0 ppm for the aliphatic hydroxyls turned strong in PDL-epoxies. As shown in Table 1, the hydroxyl value of phenolic OH decreased from 3.7 mmol/g for PDL to 1.7 mmol/g and ~ 0 mmol/g for PDL-epoxies synthesized at 70 and 117 °C, respectively. This result suggests that the aromatic hydroxyl groups were completely reacted with ECH at the reaction temperature of 117 °C. The signals for carboxylic acid hydroxyls were not seen in the spectra of both PDL-epoxies (hydroxyl value ~ 0 mmol/g), indicating that the carboxylic acid group has high reactivity in reacting with ECH even at 70 °C. However, the aliphatic OH value exhibited an increase from 0.7 mmol/g of the original PDL to 2.4 mmol/g and 2.7 mmol/g for PDL-epoxies prepared at 70 and 117 °C, respectively. There are a few possible reasons accountable for this increase. Glycidylation is a two-step process (Scheme 1), the ring opening of the epoxide of ECH to form chlorohydrin and subsequent dehydrochloration. If somehow the second step is incomplete, an aliphatic hydroxyl group is also left in the product. During glycidylation reaction, the phenolic OH group may also react with the previously introduced epoxy ring, resulting in the


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formations of an ether linkage and an aliphatic OH group. After all, the 31P NMR result proves that PDL-based epoxies were effectively prepared by the conventional method and higher reaction temperature promoted the conversion of more hydroxyl groups to epoxy monomers. In the following preparation of epoxy resin, PDL-epoxy-117 °C was used for the study of curing behavior and its thermal properties.

Figure 2.

31

P NMR spectra of PDL and PDL epoxies

Table 1. Hydroxyl values of PDL and PDL-epoxies determined by 31P NMR Hydroxyl value (mmol/g) Total Aliphatic

Aromatic

Carboxylic



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PDL-epoxy-117 °C

2.7

0

0

2.7

PDL-epoxy-70 °C

2.4

1.7

0

4.1

PDL

0.7

3.7

0.3

4.7

Curing behaviors and thermal stability Figure 3 (a-d) shows the comparison of DSC curing thermograms for PDL-epoxies and commercial DER332 at different heating rates. The curing of PDL-epoxy exhibited a much broader exothermic peak than the curing of DER 332. This result was because PDL-epoxy has a much more complicated chemical structure in which the epoxies groups likely differ in reactivity. In contrast, the two epoxy groups in DER 332 have the same reactivity toward reacting with the curing agent. The peak exothermic temperature (Tp) typically moved to higher temperature with heating rate (ϕ). The plots of 1/(Tp) versus ln(ϕ) gives a straight line (Figure 3). The curing temperature at an infinitely slow heating rate (referred as zero heating rate) is achieved by extrapolating the results and is customarily considered as a reference for selecting an isothermal curing temperature. The calculated Tp at the zero heating rate for PDL-epoxy/ME-MA was 129.9 °C which was slightly lower that that (134.4 °C) for DER332/ME-MA (Table 2). On the other hand, the curing of PDL-epoxy/ME-MA exhibited an activation energy of curing (Ea) of 87.7 KJ/mol. This value was significantly higher than that for the curing of DER332/ME-MA (68.3 KJ/mol). Therefore, PDL-epoxy displayed lower reactivity in curing with ME-MA than DER332. This was probably because PDL-epoxy is a solid powder which would require more


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energy to enable the curing process.

Figure 3. Comparison of the non-isothermal curing of the PDL-epoxy and DER 332 at different heating rates (a, b) and the plots of 1/(Tp) vs. ln(φ ) (c, d).



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Table 2. DSC non-isothermal curing results and thermal properties of the cured epoxies Char Tp

Ea

Tg

ve (x10

3

T5%

T10%

Epoxy

yield at a

(°C)

a

(KJ/mol) (°C)

3

b

mol/mm ) (°C)

b

(°C)

585 °C PDL-epoxy/ 129.9

87.7

94.3

3.02

272.3 311.1

34.7 %

DER332c/ME-MA 134.4

68.3

36.1

0.46

219.8 289.9

6.43 %

ME-MA

a

Determined from DMA experiments, b T5% and T10%: temperatures of 5% and 10% weight loss

incurred during TGA experiments.

Dynamic mechanical analysis (DMA) In Figure 4, the DMA spectra show the changes of storage modulus (E′) and damping (tan δ) with temperature for ME-MA cured PDL-epoxy and DER332. The peak temperatures of the tan δ were taken as the glass transition temperatures (Tgs) of the cured resins. The crosslinking density (Ve) of the cured epoxy resins is calculated using the following equation based on the theory of rubber elasticity:


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where E is the elastic modulus of the cured epoxy in its rubbery state, R is the gas constant and T is the absolute temperature. Because the determination of E for the thermoset materials in rubbery state is a time-consuming experiment, it is an acceptable mechanism to use the E′ at a temperature at least 50 °C above its Tg as an approximation of E in the equation. At room temperature, the E′ for the cured PDL-epoxy was higher than that for the cured DER332. This result was because the bulky aromatic structure of lignin skeleton in the PDL-epoxy was more rigid than the structure of bisphenol A in DER332, therefore resulting in the cured resin with higher stiffness at room temperature. In Table 2, the cured PDL-epoxy exhibited much higher Tg and Ve than the cured DER332 resin. Therefore, the more rigid segments in PDL and higher crosslinking density led to a higher Tg for the cured epoxy resin.

Figure 4. Dynamic mechanical properties of DER332 and PDL-epoxy cured with ME-MA.

Thermogravimetric analysis (TGA)



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Figure 5 illustrates the changes of weight loss with temperature during the TGA experiment for the cured resins. The temperatures at 5% (T5%) and 10% weight loss (T10%) incurred and char yield at 585 °C are summarized in Table 2. These two cured resins showed very similar weight loss behaviors in the initial stage. PDL-epoxy/ME-MA showed higher T5% and T10% values than DER332/ME-MA. Compared to DER332/ME-MA, PDL-epoxy/ME-MA gave a higher char yield at 585 °C. These results indicate that PDL-epoxy is comparable to the epoxy resins derived from bisphenol A on thermal stability.

Figure 5. Comparison of thermal stability of cured PDL-epoxy and DER 332 resins. Modification of asphalt by the lignin-derived epoxy and commercial epoxy The pavement performance of asphalt binders can be assessed by their rheological properties under dynamic shear test conditions using a parallel plate rheometer. The traffic conditions can


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be correlated to the frequencies used in the dynamic shear testing. Frequencies between 10-1 and 102 rad/s are used to simulate the normal vehicle traffic on the pavement [21]. The complex shear modulus (G*) is related to the material strength, while the storage shear modulus and loss shear modulus represent the elastic and viscous responses of the material during the shearing process.

Figure 6. Effects of epoxy resin content on the rheological properties of asphalts modified by PDL-epoxy and DER332, respectively. (a) G*/sin vs. temperature at 10 rad/s. At 60 ºC, effects of frequency on the loss modulus (b), storage modulus (c), and complex modulus (e) of neat asphalt



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and epoxy asphalts.

Figure 6 (a) shows the changes of rutting parameter (G*/ sinδ) with temperature for different PDL-epoxy asphalt compositions. According to the Strategic Highway Research Program (SHRP) tests, the temperature at which G*/sinδ is equal to 1 KPa is defined as the maximum temperature for an asphalt binder to provide effective function in the pavement. As shown in Figure 6 (a), addition of epoxy as a modifier enhanced the maximum temperature. The neat asphalt exhibited a maximum temperature of ~73 ºC. In contrast, the modified asphalt binders containing 7.5%, 15% and 22.5% PDL-epoxy displayed maximum temperatures of 81 ºC, 85 ºC, and 100 ºC, respectively. This result indicates that PDL-epoxy asphalt binders would provide higher rutting resistance than the neat asphalt binder. The maximum temperature of the 7.5% PDL-epoxy modified asphalt was lower than that of the 7.5% DER332 modified asphalt, which was almost the same as the maximum temperature of the 15% PDL-epoxy asphalt. When the epoxy content was increased to 22.5%, the maximum temperature of the PDL-epoxy asphalt blend was a litter higher than that of the DER 332 asphalt blend. At a 22.5% loading, the superior modification effect of PDL-epoxy over DER332 is probably because the performance of the PDL-epoxy modified asphalt is influenced by two factors, the Tg of the cured epoxy network and its dispersion in the asphalt binder. It is believed that the solid PDL-epoxy was not dispersed as homogenously as the liquid DER 332. Therefore, at lower concentrations, the better dispersed DER 332 manifested higher reinforcing effect than PDL-epoxy. However, because PDL-epoxy


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has a more bulky and rigid structure than DER 332 as discussed above, the cured PDL-epoxy resin exhibits a much higher Tg than the cured DER332. As a consequence, when the epoxy content was increased from 15% to 22.5%, the high Tg of PDL-epoxy resin compensates the effect of its poor dispersion in asphalt and can still greatly improve maximum temperature of rutting-resistance when added at a certain level. Figures 6 (b) and 6 (c) show the storage and loss moduli for neat asphalt and PDL-epoxy asphalt binders at 60 ºC. The storage and loss modulus of PDL-epoxy and DER 332 modified asphalts were higher than the neat asphalt and increased with epoxy content. Similar to the intendancy of G*/sinδ, the storage and loss moduli of PDL-epoxy modified asphalt were lower than that of DER 332 modified asphalts at low epoxy contents but similar at higher epoxy content. This result suggests that PDL-epoxy resin can impart similar viscoelastic behaviors to asphalt compared to the commercial DER332. The effect of epoxy resin content on complex modulus (G*) at 60 ºC for each binder can be seen in Figure 6 (d). PDL-epoxy asphalts exhibited higher G* than the neat asphalt binder in the whole frequency range studied, G* increased continuously with epoxy resin contents. Also, the PDL-epoxy asphalt displayed similar G* as the DER 332 epoxy asphalt at 22.5% epoxy content. This result further illustrates that PDL-epoxy will be a potential epoxy modifier for asphalt in place of bisphenol A type epoxy.

Conclusions



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In this work, lignin was successfully converted to epoxy compounds and the lignin-derived epoxy was demonstrated to offer comparable performance as the commercial bisphenol A type epoxy in modifying asphalt. Preparation of Lignin-derived epoxy can be effectively performed by reacting epichlorohydrin (ECH) and partially depolymerized lignin (PDL) at 117 °C, resulting in a relatively high yield of the PDL-epoxy product. The thermal and mechanical properties of the PDL-epoxy cured with a Tung oil derived anhydride curing agent (ME-MA) are comparable to that of the bisphenol A type epoxy DER332 cured with the same curing agent. For modification of asphalt, compared to the DER332, the PDL-epoxy asphalt similarly exhibited significant improvement on the viscoelastic performance, especially at elevated temperatures. This study sets up a framework for the modification of asphalt using lignin-derived epoxy, and the results suggest lignin-derived epoxy is promising in epoxy asphalt application.

Supporting Information: preparation of enzymolysis lignin, molecular weight distribution (MWD) of PDL, characterization of depolymerized lignins.

Acknowledgements This work, as part of the Northwest Advanced Renewables Alliance (NARA), was funded by the Agriculture and Food Research Initiative Competitive Grant no. 2011-68005-30416 from the USDA National Institute of Food and Agriculture. The authors also thank the Institute of Chemical Industry of Forestry Products, CAF, China for supporting Mei Li’s visiting study at WSU.


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References ‐ based epoxy resins. [1] Hofmann K., Glasser W. Engineering plastics from lignin, 23. Network formation of lignin

Macromolecular Chemistry and Physics. 1994;195:65-80. [2] Sun G., Sun H., Liu Y., Zhao B., Zhu N., Hu K. Comparative study on the curing kinetics and mechanism of a lignin-based-epoxy/anhydride resin system. Polymer. 2007;48:330-7. [3] Yin Q. F., Di M. W. Preparation and mechanical properties of lignin/epoxy resin composites.

Advanced

Materials Research: Trans Tech Publ; 2012; 482-484:1959-62. [4] Cateto C. A., Barreiro M. F., Rodrigues A. E., Belgacem M. N. Optimization study of lignin oxypropylation in view of the preparation of polyurethane rigid foams. Industrial & Engineering Chemistry Research. 2009;48:2583-9. [5] Li Y., Ragauskas A. J. Kraft lignin-based rigid polyurethane foam. Journal of Wood Chemistry and Technology. 2012;32:210-24. [6] Li Y., Ragauskas A. J. Ethanol organosolv lignin-based rigid polyurethane foam reinforced with cellulose nanowhiskers. Rsc Advances. 2012;2:3347-51. [7] Feldman D., Banu D., Natansohn A., Wang J. Structure–properties relations of thermally cured epoxy–lignin polyblends. Journal of applied polymer science. 1991;42:1537-50. [8] Wang J., Banu D., Feldman D. Epoxy-lignin polyblends: effects of various components on adhesive properties. Journal of adhesion science and technology. 1992;6:587-98. [9] Feldman D., Banu D., Luchian C., Wang J. Epoxy–lignin polyblends: Correlation between polymer interaction and curing temperature. Journal of applied polymer science. 1991;42:1307-18. [10] Simionescu C. I., Rusan V., Macoveanu M. M., Cazacu G., Lipsa R., Vasile C., et al. Special Issue Microphenomena in Advanced Composites Lignin/epoxy composites. Composites science and technology. 1993;48:317-23. [11] Simionescu C. I., Cazacu G., Macoveanu M. M. Lignin-epoxy resins. II. Physical and chemical characterization. Cellulose chemistry and technology. 1987;21:525-34. [12] D'Alelio G. F. Polymerizable lignin derivatives. 1976; US3984363. [13] Simionescu C., Rusan V., Turta K., Bobcova S., Macoveanu M., Cazacu G., et al. Synthesis and characterization of some iron-lignosulfonate-based lignin-epoxy resins. Cellulose chemistry and technology. 1993;27:627-44. [14] Hofmann K., Glasser W. G. Engineering plastics from lignin. 21.1 Synthesis and properties of epoxidized lignin-poly (Propylene oxide) copolymers. Journal of wood chemistry and technology. 1993;13:73-95. [15] Zhao B., Chen G., Liu Y., Hu K., Wu R. Synthesis of lignin base epoxy resin and its characterization. Journal of materials science letters. 2001;20:859-62. [16] Xin J., Zhang P., Wolcott M. P., Zhang X., Zhang J. Partial depolymerization of enzymolysis lignin via mild hydrogenolysis over Raney Nickel. Bioresource technology. 2014;155:422-6. [17] Qin J., Woloctt M. P., Zhang J. Use of polycarboxylic acid derived from partially depolymerized lignin as a curing agent for epoxy application. ACS Sustainable Chemistry & Engineering. 2013;2:188-93. [18] Liu Z., Zong L., Zhao L., Xie X. Preparation and storage stability of asphalt emulsions made from modified lignin cationic asphalt emulsifiers. Applied mechanics and materials. 2013;357-360:781-5. [19] Sundstrom D. W., Klei H. E., Daubenspeck T. H. Use of byproduct lignins as extenders in asphalt. Industrial & Engineering Chemistry Product Research and Deelopment. 1983;22:496-500.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 25

[20] Yu J., Cong P., Wu S. Laboratory investigation of the properties of asphalt modified with epoxy resin. Journal of applied polymer science. 2009;113:3557-63. [21] Cong P., Yu J., Chen S. Effects of epoxy resin contents on the rheological properties of epoxy-asphalt blends. Journal of applied polymer science. 2010;118:3678-84. [22] Xie Y., Lü Q. F., Jin Y. Q., Cheng X. S. Enzymatic hydrolysis lignin epoxy resin modified asphalt.

Advanced

Materials Research. 2011;239-242:3346-9. [23] Huang K., Zhang P., Zhang J., Li S., Li M., Xia J., et al. Preparation of biobased epoxies using tung oil fatty acid-derived C21 diacid and C22 triacid and study of epoxy properties. Green Chemistry. 2013;15:2466-75. [24] Xin J., Zhang P., Huang K., Zhang J. Developing vegetable oil-based high performance thermosetting resins. In Soy-Based Chemicals and Materials; Chapter 13, ACS Symposium Series: Washington DC, 2014;299-313. [25] Gao J., Anderson D., Levie B. Saccharification of recalcitrant biomass and integration options for lignocellulosic sugars from Catchlight Energy's sugar process (CLE Sugar). Biotechnolgy for Biofuels. 2013;6:10. [26] Pu Y., Cao S., Ragauskas A. J. Application of quantitative 31P NMR in biomass lignin and biofuel precursors characterization. Energy & Environmental Science. 2011;4:3154-66.


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For Table of Contents Use Only A green epoxy resin system based on lignin and tung oil and its application in epoxy asphalt Junna Xin, Mei Li, Ran Li, Michael P. Wolcott, Jinwen Zhang

A green epoxy resin based on lignin was synthesized and applied for preparation of bio-epoxy asphalt with good performance.


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