Synthesis and characterization of monofunctional benzoxazine from cardanol - Cao Xuan Viet

Journal of Science and Technology 55 (1B) (2017) 160–168 SYNTHESIS AND CHARACTERIZATION OF MONOFUNCTIONAL BENZOXAZINE FROM CARDANOL Cao Xuan Viet1, *, Nguyen Hoang Trinh1, Du Ngoc Uy Lan2, Tsutomu Takeichi3 1Department of Polymer Materials, Faculty of Materials Technology, HCMUT–VNUHCM 268 Ly Thuong Kiet Street, Ward 14, District 10, Ho Chi Minh City, Vietnam 2School of Material Engineering, Kompleks Pusat Pengajian UniMAP, Taman Muhibbah, University Malaysia Perlis, 02600 Jejawi, Arau, Perlis, Malaysia 3Department of Environmental and Life Sciences, Toyohashi University of Technology, Tempaku–cho, 1–1 Hibarigaoka, Tempaku, Toyohashi, Aichi, 441–8580, Japan *Email: caoxuanviet@hcmut.edu.vn Received: 30 December 2016; Accepted for publication: 3 March 2017 ABSTRACT A novel thermoplastic polybenzoxazine was synthesized based on agrochemical renewable cardanol–a by–product of cashew nut shell liquid (CNSL). A solventless synthesis of monofunctional benzoxazine monomer based on cardanol, aniline and paraformaldehyde was carried out. The liquid benzoxazine monomer was characterized by 1HNMR and FTIR spectroscopy. Curing characteristics at different temperatures were studied and monitored by differential scanning calorimeter (DSC). The appearance of two exothermic peaks associated with reaction of double bonds of the aliphatic side–chain and ring opening polymerization of benzoxazine. High thermal stability of the polymer sample was confirmed by thermogravimetric analysis (TGA). Keywords: benzoxazine, cardanol, cashew nut shell liquid, ring–opening polymerization. 1. INTRODUCTION Polybenzoxazines (PBzs) appeared as attractive candidates over traditional phenolic polymers due to their superior properties. These include higher thermal stability, char yield, superior modulus properties, low water absorption, near zero volumetric shrinkage, and no release of byproducts during its thermal ring–opening polymerization. Another advantages of this polymer is the versatile molecular design flexibility of its monomer. Generally, benzoxazine can be readily synthesized from a phenolic compound, a primary amine ad aldehydes [1, 2]. In recent years, the development of monomers and polymers starting from renewable resources has received significant consideration due to the increasing prices of petro–chemical products associated with growing environmental concerns. Renewable resources, generally known as biomass, refer to any material having recent biological origin, including plant ma ma syn Ca by an ch fle pro as com ver He an FT po 2.1 pro mm par (97 car Ch Wa Re Kin Ac Hy No terials, agri terials, card thesis purp rdanol is a m –product ab d Vietnam. C ain (C15H31–n Compared xibility due cessability. reactive dilu posites, ad Even thou y little resea rein, we wo d paraforma IR spectrosc lymer will b . Materials All reagen cured from Hg. The aformaldehy %) and so ried out in o aracteristic ter Content ( lative Density ematic Visco id Number (m droxyl Value n–volatile Co Cao cultural cro anol is con oses due to ajor consti undantly ava ardanol is a , n = 0, 1, 2, to conven to the int In addition, ent or blen hesives, and gh benzoxa rch reported uld like to r ldehyde by s opy. The cu e described h ts and solv Son Chau C characterist de (95 %) dium sulfat ven–dried fl Tab by vol/mass) at 25 °C (g/c sity at 25 °C g KOH/g) (mg KOH/g) ntent (by mas Xuan Viet, ps, and ev sidered as its unique tuent of the ilable in ma monohydro 3) at the me Figure 1. M tional phen ernal plasti monofuncti ded with oth paints [4, 5] zines have on synthesi eport a mon olventless m ring behavi ere. 2. MAT ents were us o., Ltd (Vie ics of card were purcha e (99 %) w ask. le 1. Characte (%) m3) (mm2/s) s) (%) Nguyen Hoa en animal an importa structural f cashew nut ny parts of xyl phenol o ta position ( olecular stru olic resins, cization of onal benzox er neat resi . been extens s and charac ofunctional ethod. The or of benzo ERIALS AN ed as receiv t Nam). Car anol is gi sed from M ere obtaine ristics of car ng Trinh, Du manure. Am nt starting eatures, abu shell liquid the world, r a phenolic Figure 1) [3 cture of card cardanol ba the long c azine with l n for variou ively studied terization of benzoxazine monomer w xazine mono D METHO ed from com danol was d ven in Ta erck. Chloro d from Sigm danol used in Tes ASTM ASTM ASTM ASTM ASTM ASTM Ngoc Uy La ong these material bio ndant availa (CNSL) wh particularly lipid having ]. anol. sed polyme hain, which ow viscosity s applicatio in recent y benzoxazin prepared fr as character mer and the DS mercial sup istilled at 23 ble 1. Ani form (99 % a–Alrdrich this study. t Method D 95–13e1 D 4052–11 D 445–12 D 664–11a D 1957–86 D 1353–13 n, Tsutomu renewable –based ben bility and l ich is an ag in ASEAN a long hyd r may imp provides can be fur ns such as s ears, there es from Vie om cardano ized by 1HN rmal stabili pliers. Card 0–240 °C u line (99.5 ), sodium h . All reactio V 0 5 1 Takeichi 161 resource zoxazine ow cost. ricultural countries rocarbon rove the a better ther used tructural has been tnam [6]. l, aniline MR and ty of the anol was nder 2–4 %) and ydroxide ns were alues 0.1 .9363 1.47 0.8 84.8 99.5 Synthesis and characterization of monofunctional benzoxazine from cardanol 162 2.2 Synthesis of cardanol based benzoxazine monomer (C–Bz) Cardanol based benzoxazine was synthesized by a method adopted from earlier report [7]. Cardanol (10 g, 0.033 mol) was heated to 50 °C in a 100 mL three–necked round flask equipped with magnetic stirrer and thermometer. Then paraformaldehyde (1.98 g, 0.066 mol) and aniline (3 mL, 0.033 mol) were added drop wise under vacuum environment. The temperature was gradually raised to 80 °C and kept at this temperature for 5 h. The starting of reaction indicated by evolution of water and the color changing. The reaction color changed from yellow to orange or maroon. The reaction mixture was then cooled at room temperature and dissolved in chloroform. The product was washed three times with 2 N NaOH followed by washing with distilled water in a separating funnel. The organic phase was dried over sodium sulphate (Na2SO4) and filtered to give a red oil. The solvent was removed under reduced pressure and then dried at 60 °C for 12 h under vacuum to obtain the final product which is monomer benzoxazine with a yield of 73 %. 2.3 Polymerization of cardanol based benzoxazines To prepare samples for thermal characterization, benzoxazine CA–a monomer was dropped on the separate aluminum plates, put in an oven and heated simultaneously at different temperatures (160 °C, 180 °C, 220 °C) for 2 h. 2.4 Measurements 2.4.1. Structural characterization Fourier transform infrared (FTIR) spectra of the samples were recorded on a Bruker Tensor37 spectrophotometer with a resolution from 4000–400 cm–1 in the absorbance and transmittance modes. The test was done at Institute of Chemical Technology, Vietnam Academy of Science and Technology (VAST), Ho Chi Minh City. 1H (500 MHz) nuclear magnetic resonance (NMR) spectra were obtained using a Bruker Avance AM500 FT–NMR spectrometer with Fourier transform and CDCl3 as solvent. The chemical shift is given relative to tetra methyl silane (TMS). The NMR measurements and analysis were performed at Center for Applied Spectroscopy, Institute of Chemistry, Vietnam Academy of Science and Technology (VAST), Hanoi. High Performance Liquid Chromatography (HPLC) analysis of cardanol was done on Agilent 1200 Series coupled to MS detector, micrOTOF–QII Bruker (Agilent, USA) at Central Laboratory for Analysis, University of Science–VNUHCM. A column (C18, 150 mm × 4 mm, 5 µm) was used and the mobile phase was acetonitrile/water/acetic acid (80:20:1) at a flow rate of 1.80 mL/min. Absorbance was monitored at 280 nm. 2.4.2. Thermal characterization Differential scanning calorimetric (DSC) studies were carried out on a Mettler Toledo thermal analyzer using N2 as a purge gas, heated from room temperature to 300 °C at scanning rate of 10 °C/min. Cao Xuan Viet, Nguyen Hoang Trinh, Du Ngoc Uy Lan, Tsutomu Takeichi 163 The thermal stability of polymer was studied by thermogravimetric analysis (TGA) using a TGA Q500 instrument. The thermograms were obtained at a temperature rate of 10 °C/min from 25 °C to 800 °C under nitrogen environment. DSC and TGA measurements were carried out at Central Laboratory for Analysis, University of Science–VNUHCM. 3. RESULTS AND DISCUSSION 3.1. Structural characterization of cardanol based benzoxazine Cardanol is a monophenol compound with a C15 unsaturated side chain at the m–position. Cardanol used in this work is a mixture of monoene (15 %), diene (15 %) and triene (47 %), and unidentified product (the rest, not isolated) as determined by HPLC (Figure 2). The material was used for benzoxazine synthesis without any further purification since we would like to ensure the viability of large scale commercial applications. Figure 2. HPLC chromatogram of cardanol (peak at retention time 4.7, 6.5 and 10.7 minutes are due to cardanol triene, diene, and monoene component). According to Tyman et al. cardanol that has unsaturated triene bonds is easily polymerized, while the unsaturated binding of monoene and diene are more stable [7]. The content of unsaturated triene of the cardanol in this study was 47 % and higher than that of the cardanol used in other works which is always below 39 % [8, 9], indicating that the carbon chains in this cardanol are readily available for polymerization/oligomerization by thermal. A monomer was obtained under solvent free conditions from cardanol, paraformaldehyde and aniline in molar ratio of 1:2:1 as shown on Figure 3. Sy 16 spe Bz str ban 30 str ph hy ab cm ab see ben ch bo we 2.0 nthesis and 4 The struc ctra of pure shows sign etching of A d at 1498 c 08 cm–1 and etching of C enolic OH o droxyl grou sorption ban –1, respectiv sence of unr F The 1H N n that the zoxazine ri ain of carda nded methyl re observed 5 and 2.80 p characteriza Figure 3. ture of the m cardanol an ificant absor r–O–C grou m–1 due to tr the bands a H2 of oxazin f cardanol a p of cardan ds of aniline ely), NH b eacted anilin igure 4. FTIR MR spectra 1H NMR sp ng, but also nol. The tw ene protons as multiplet pm, are attr tion of mono Synthetic sch onomer wa d C–Bz mon ption bands p at 1241 a i–substituted t 2924 and 2 e ring as we round 3344 ol to oxaz due to the a ending (161 e in the C–B spectra of ca gave further ectrum of t chemical sh o signals at (Ar–CH2–N in position a ibuted to the functional b eme of cardan s confirmed omer is disp of the benzo nd 1031 cm benzene rin 852 cm–1 ar ll as aliphat cm–1 is abs ine ring. M symmetric a 9 cm–1), an z monomer rdanol and ca support to he C–Bz p ifts that bel 4.58 ppm –, and –O– t 6.63–7.26 long alkyl c enzoxazine ol based benz by FTIR a layed in Fig xazine due –1, respectiv g. C–H stre e attributed ic side chain ent, suggesti oreover, th nd symmetr d C–N stre [9, 10]. rdanol based C–Bz chemi resents not ong to the a (a) and 5.3 CH2–N–) re ppm. The p hain of card from cardano oxazine (C–B nd 1H NMR ure 4. The F to the asymm ely. The sp tching of be to the asymm of cardanol ng a comple e absence ic NH stretc tching (128 benzoxazine cal structure only the sp romatic sign ppm (b) co spectively. T eaks observe anol [2, 9]. l z). spectroscop TIR spectru etric and sy ectrum also nzene ring a etric and sy . The band d te conversi of the char hing (3442 1 cm–1) con (C–Bz). (Figure 5). ecific signa als and the rrespond to he aromatic d at 0.90, 1 y. FTIR m of C– mmetric shows a ppears at mmetric ue to the on of the acteristic and 3360 firm the It can be ls of the aliphatic nitrogen protons .29, 1.55, 3.2 ex tem cur ben F S Figure 5 . Thermal c Figure 6 othermic tra perature of ve. The cu zoxazines a igure 6. DSC ample C–Bz M160 M180 M220 Cao . 1H NMR sp haracteriza displays the nsition obser exothermic ring charac fter heating thermogram Table 2. Summ To (oC) 126.4 129.1 158.7 148.4 Xuan Viet, ectra of carda tion of card DSC therm ved was cha peak (Tp) a teristics (To at different t s of cardanol ary of value Peak 1 Tp (oC) 145.6 179.8 180.3 193.9 Nguyen Hoa nol and carda anol based ograms of racterized b nd heat of c , Tp and ∆ emperatures based benzox s of the DSC ∆H (J.g–1) 17.6 14.3 6.4 20.8 ng Trinh, Du nol based ben benzoxazin the C–Bz y determini uring reacti H) of C–Bz are summar azines at diff thermograms To (oC 258.5 248.9 244. – Ngoc Uy La zoxazine mo e monomer a ng onset cur on (∆H) from monomer ized in Tabl erent polymer of the benzox Pe ) Tp (oC 273. 273. 8 266. – n, Tsutomu nomer (C–Bz nd its polym ing tempera the area u and cardan e 2. ization tempe azines. ak 2 ) ∆H 8 1 6 8 4 Takeichi 165 ). er. The ture (To), nder the ol based ratures. (J.g–1) 21.2 86.1 6.7 – Synthesis and characterization of monofunctional benzoxazine from cardanol 166 Typically, the thermogram of C–Bz reveals two exotherm peaks. The lower exotherm peak may be due to the reaction took place through unsaturation of side chain, both from internal double bond (monoene, diene) and vinyl bond (triene). This reaction could lead to the increase in viscosity of the benzoxazine monomer [3]. According to Rodrigues et al. cardanol could be thermal oligomerized at 140 °C and the dimer was the main oligomer formed. The two possible dimerization reactions are presented in Figure 7: (I) obtained from internal double bond loss, taking the monoene as example, and (II) from vinyl loss in triene. It can be seen that decrease in ∆H values of this process was not significant because the oligomerization was slow [11]. Interestingly, this phenomenon was not observed from other reports [8, 9]. Figure 7. Dimerisation reaction of cardanol from: (I) internal double bond loss (monoene) and (II) vinyl loss in triene. Figure 8. Polymerization of cardanol based benzoxazine. It is well known that the opening of oxazine ring occurred at very high temperature (൒ 200 °C), thus the peak observed at 273 °C is attributed to the polymerization temperature of the cardanol based benzoxazine. The opening of the oxazine ring at higher temperature indicates a greater stability of the ring, due to increased strength of C–O bond [1, 2]. In this case, cardanol– based benzoxazine exhibits higher curing temperature than traditional benzoxazines because of their unique molecular structure. As expected, a progressive decrease in To and Tp values with increasing polymerization temperature was found. It was also observed that the polymerization was completed at 220 °C. The increase in ∆H value of peak 1 for this sample implies that the rea 8 i DT sta tha Th Th we an oc mo sol spe C– com the Ac Re ction of lon llustrates the Thermal s G trace is s bility. From t the cured ere are four e degradatio ight loss (72 d of the M curred at the In this nofunctiona ventless me ctroscopy. D Bz also inv pared to th rmal stabilit knowledgeme search Grant Cao g alkyl side thermal rin tability of c hown in Fig the TGA cu sample have –stage weig n at first sta %) could b annich bridg temperature Figure 9. T paper we l benzoxazi thod. The SC results olved in th e conventio y. nts. The auth for Alumni (C Xuan Viet, chain may b g–opening p ured benzox ure 9. Card rve, there w nearly zero ht loss proc ge could be e attributed t es in the p above 500 GA thermogr 4. described t ne monome monomer s indicates th e curing p nal benzoxa ors would lik RA). Nguyen Hoa e competed olymerizatio azines (M22 anol based b as no weigh moisture c esses caused related to th o the degrad olymer. Fin °C [12]. ams of cardan CONCLU he success r from card tructure we at the long a rocess and zines. The p e to thank A ng Trinh, Du with the ring n of C–Bz m 0) was stud enzoxazines loss observ ontent or lo by the deg e decomposi ation of the ally, the d ol based ben SIONS full synthe anol, a by–p re confirme lkyl chain s lead to hig olymer is fl UN/SEED N Ngoc Uy La –opening po onomer. ied by TGA possess rel ed below 20 w molecular radation of ng of pheno side chain o egradation o zoxazine poly sis and ch roduct of c d by the F ubstituent at her polyme exible and s et for their fin n, Tsutomu lymerizatio . A typical T atively good 0 °C which weight com molecule st lic moiety. T f the cardano f the arom mer. aracterizatio ashew indus TIR and 1 the meta po rization tem hows a good ancial suppo Takeichi 167 n. Figure GA and thermal indicates pounds. ructures. he main l moiety atic ring n of a try by a H NMR sition in perature thermal rt through Synthesis and characterization of monofunctional benzoxazine from cardanol 168 REFERENCES 1. 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