Article pubs.acs.org/IECR
Properties of Bio-based Epoxy Resins from Rosin with Different Flexible Chains Lianli Deng,† Chengyong Ha,‡ Chunning Sun,‡,§ Baowen Zhou,‡,§ Jing Yu,∇ Minmin Shen,*,‡ and Jianqiang Mo‡,§ †
School of Chemical Engineering, Guizhou Institute of Technology, Guiyang 550003, Guizhou, People’s Republic of China Laboratory of Cellulose and Lignocellulosics Chemistry, Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou 510650, Guangdong, People’s Republic of China § University of Chinese Academy of Sciences, Beijing 100039, Beijing, People’s Republic of China ∇ Department of Chemistry, Tangshan Normal University, Tangshan 063000, Hebei, People’s Republic of China ‡
ABSTRACT: Triglycidyl ester FPAE and glycidyl ethers FPEG1, FPEG2, and FPEG3, listed in order of increasing flexible chain amounts, were obtained from rosin and characterized by 1H nuclear mangetic resonance (1H NMR) and Fourier transform infrared (FTIR) spectroscopy. The effects of a harder dose on cured resin properties were studied by determining the tensile strength and water absorption. The results indicated that the optimum harder dose of the FPEG system was higher than the stoichiometric ratio. The effects of flexible chains on cured resin properties were studied by tensile strength characterization, differential scanning calorimetry, thermogravimetric analysis, water absorption, and acetone absorption. The results showed that the cured resin FPAE1C exhibited the best thermal properties, water resistance, and acetone resistance. FPAEC did not display the best tensile properties, because of its brittleness, but the tensile strength was improved by introducing the flexible chain. Moreover, FPAE, FPEG1, and FPEG2 displayed tensile strength similar to that of petrochemical E44, and FPAE exhibited a high glass-transition temperature (Tg), compared to E44.
1. INTRODUCTION Rosin is the second-largest natural product. Rosin has three constituents: rosin acid, neutral substance, and aliphatic acid, of which rosin acid is the main component, accounting for 85%− 90% of the material. The characteristic fused-ring structure of rosin acids is similar in rigidity to some petroleum-based cycloaliphatic or aromatic compounds, making rosin and its derivatives potential substitutes for current compounds in polymers. As a result, rosin has received increasing attention as a raw material for the preparation of some new polymers with specific chemical structures and valuable properties.1−17 In recent years, increasing efforts have been made to synthesize bio-based epoxy resins from rosin and its derivatives. Rosinbased epoxy resins are comprised of a rosin-based curing agent and a rosin-based epoxy prepolymer. Rosin-based curing agents based on maleopimaric acid were prepared by Liu et al. Commercial curing agents were also used in their studies for comparison. The results suggest the great potential of rosinbased curing agents to replace some of the current curing agents.18,19 The fused ring of rosin confers a higher glass transition temperature (Tg) of the material. However, rosin also reduces the mechanical properties, because of its brittleness. To overcome this disadvantage, flexible chain segments were incorporated into rosin-based curing agents.20 On the other hand, some reports have raised concerns about rosin-based epoxy prepolymers. Rosin-based epoxy resins from rosin ketone, condensed rosin acid-formaldehyde resins, and maleopimaric acid were studied.21−24 The results demonstrate that the fused ring of rosin acid confers a high Tg value and good thermal stability to the resulting material, and they © 2013 American Chemical Society
suggest that high-performance thermosetting resins can be developed from rosin acid.23,24 Nevertheless, the brittleness of rosin acid imparts adverse effects to the resulting material. Therefore, flexible chains should be introduced to enhance toughness. Flexible siloxane was incorporated into rosin-based epoxy resins.25 However, the relationship between flexible chains and the mechanical properties was not provided. Ethylene glycol diglycidyl ether (EGDE) has been widely used in epoxy resin preparation. As shown in Scheme 2 (presented later in this work), the structure of EGDE is a mixture (n = 0−2), similar to a diglycidyl ether of bisphenol A (DGEBA). EGDE does not contain a rigid ring in its structure. Therefore, it can be used as a flexible segment in epoxy resin preparation. Moreover, its hydroxyl groups improve the mechanical strength of the material. In this paper, triglycidyl ester FPAE was obtained by reacting fumaropimaric acid (FPA) with epichlorohydrin (EC). Glycidyl ether FPEG prepolymers were prepared from the reaction between FPA and EGDE. The amounts of flexible chains increased in the order of FPEG1, to FPEG2, to FPEG3. The properties of the novel rosin-based epoxy resin were studied. Commercial epoxy resin was also used for comparison. The results suggest that the biobased resin has great potential to replace some of the petroleum resin. Moreover, this study Received: Revised: Accepted: Published: 13233
February 17, 2013 August 19, 2013 August 22, 2013 August 22, 2013 dx.doi.org/10.1021/ie4005223 | Ind. Eng. Chem. Res. 2013, 52, 13233−13240
Industrial & Engineering Chemistry Research
Article
Scheme 1. Preparation of FPAE
provides the first report on the relationship between flexible chains and the properties for rosin-based resins.
washed with acetic acid. Purification was continued by washing with hot water to remove unreacted FA. Purified FPA was a white powder. The yield was 107 g (35%, relative to the weight of the reactants). 1 H NMR (CD3Cl, δ ppm): 12.83 (s, 3H), 5.40 (s, 1H), 2.90−2.85 (d, 2H), 2.59 (s, 1H), 2.39−2.36 (m, 1H), 1.78− 1.24 (m, 13H), 1.20 (s, 3H), 1.00−0.98 (d, 6H), 0.58 (s, 3H). FT-IR (cm−1): 795, 850, 926, 944, 1010, 1086, 1140, 1279, 1234, 1388, 1465, 690, 1780, 1844, 2860, 2942, 3500−3100. Acid value: Theoretical: 402 mg KOH g−1; Found: 400 mg KOH g−1. 2.3. Preparation of Epoxy Resins. 2.3.1. FPAE, Triglycidyl Ester from FPA (Scheme 1). A 250-mL four-neck roundbottomed flask, equipped with a reflux condenser, a mechanical stirrer, a thermometer, and a N2 inlet, was charged with FPA (30 g, 0.073 mol), EC (122 g, 1.32 mol), and triethylamine (0.15 g (0.1 wt % on the basis of the total weight of FPA and EC)). The acidity of the system was monitored by titration with KOH ethanol solution. The temperature of the system was maintained at 110 °C until the acid number was 100
0.47 (0.51d)
>100
0.19 (0.23d)
a The cure reactions were conducted at 110 °C for 2 h and at 160 °C for 3 h. bN1 = n(MeHHPA):n(epoxy group). cN2 = n(epoxy group):n(carboxy group). dCalculated value.
remove EC in a vacuum oven, and the yellow transparent and stringy liquid was obtained. 1 H NMR (CD3Cl, δ ppm): 5.35 (1H), 4.3−4.5 (3H), 3.9− 4.0 (2H), 3.70−3.72 (1H), 3.11−3.32 (3H), 2.78−2.87 (5H), 2.55−2.70 (4H), 2.40−2.42 (1H), 2.18−2.3 (1H), 1.78−1.24 (13H), 1.15 (3H), 1.08−0.98 (6H), 0.59 (3H); FT-IR (cm−1): 466, 620, 721, 759, 849, 908, 1020, 1071, 1103, 1173, 1249, 1384, 1453, 1730, 2869, 2954, 3446. 2.3.2. FPEG, Glycidyl Ether of Ethylene Glycol Diglycidyl Ether Modified Fumaropimaric Acid (Scheme 2). A 250-mL four-neck round-bottomed flask, equipped with a reflux condenser, a mechanical stirrer, a thermometer, and a N2 inlet, was charged with FPA, EGDE, and triethylamine (0.1 wt %, based on the total weight of EGDE and FPA). The acidity of the system was monitored by titration with KOH ethanol solution. The temperature of the system was maintained at 110 °C until the acid number was
