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Studies on newly developed urethane modified polyetheramide coatings from Albizia benth oil.

Introduction

The production of vegetable oil based polymeric materials with excelent physical and chemical properties has drawn large attention in recent times (Alam, 2004: Ahmad, 2005: Shabeer, 2005: F.Li, 2000). Introduction of hydroxyl groups at the position of double bonds of triglycerides opens the whole area of applications. Castor oil is the only natural source of an 18 carbon hydroxylated fatty acid with one double bond. The functionalities of most other vegetable oil depends largely on the modification carried out at the reactive sites. Reacting oil based diols with suitable monomers for example produces polyetheramides. This polymeric material had been reported to contain carbon carbon and ether linkages which confer good chemical resistance in particular against alkalis along with excellent adhesion and flexibility (LI, 2001: Ahmed, 2003) as well as good anticorrosive properties(Alam, 2004). Modification of polyetheramide with urethane will further confer on the final product (urethane modified polyetheramide) an improved thermal stability with good adhesion, excellent abrasion resistance, high toughness and good out door service as well as good water and acid resistance (Aigbodion, 2001: Ahmad, 2001).

Literature review reveals very few works reported on newly developed oil based polyetheramide (Alam, 2004: Ahmad, 2002: H Y Wei, 2002). The use of underutilized seed oil like Albizia benth oil as a cheap source of supply of renewable resources that may be used for production of enviromentally friendlier resin had been reported earlier (Akintayo and Adebowale, 2004). Albizia benth, a native of tropical Africa, Asia and Northern Australia is a fast growing nitrogen fixing heavy shade tree that is only used for reforestation and firewood. The high yield seed oil ca 40% is used only for curing leprosy and there is no reported work on the development of Albizia benth oil polyetheramide resin. This work thus seek to study the synthesis of polyetheramide produced by condensation polymerization of N- N- bis (2--hydroxyethyl) Albizia benth oil fatty amide [HEABOA] with Bisphenol--A. The product is modified with urethane linkage resulting from the addition reaction of free hydroxyl groups of HEABOA and isocyanate moiety of toluene 2,4--di isocyanate (TDI). The polyetheramide and its modified derivatives were characterized by FT-IR, 'H NMR and 13C NMR. The physicochemical and film coating properities were also carried out.

Experimental

(1) Collection of samples

Albizia benth seeds were collected from nearby farms and bushes in Ado-Ekiti, Nigeria. The seeds were milled on a C&N Junior laboratory mill size 5 (Christy and Norris Limited Engineers, Chemlsford, England).

(2) Extraction and refining of Oil.

Albizia benth oil (ABO) were extracted using n-hexane in a Soxhlet apparatus and solvent was removed on a rotavapour. The crude oil were refined by agitating with 18M NaOH (1:30g/g) for 15min. The resultant mixture was then heated to 75-80[degrees]C to break the soap stock and neutral oil separated by centrifugation.

(3a) Synthesis of Albizia benth oil fatty amide

0.32 mol of diethanolamine and 0.007mol of sodium methoxide were mixed in a four necked round bottom flask fitted with an electrical stirrer, thermometer and condenser and contents heated to 110[degrees]C while stirring. ABO (0,1mol) was then added dropwisely over a period of 60min. Progress of the reaction was monitored by TLC. On completion the reaction product was dissolved in diethyl ether, washed with 15% NaCl and dried over [Na.sub.2]S[O.sub.4]. The ethereal layer was filtered and evaporated in a vacuum evaporator to obtain the bis(2- hydroxyethyl) Albizia benth oil fatty amide (HEABOA)

(3b) Synthesis of Albizia benth Oil Polyetheramide (ABOPEtA)

Bis(2-hydroxyethyl) Albizia benth fatty amide (HEABOA) was first prepared as described above. Now 0.10mol of HEABOA and 0.07mol bisphenol were dissolved in 100ml of a mixture of xylene and butanone(1:1v/v) as solvent with dil.[H.sub.2]S[O.sub.4] as a catalyst in a four necked round bottom flask equipped with Dean stark, [N.sub.2] inlet, thermometer and stirrer. The reaction mixture was heated to 180[degrees]C and allowed to reflux. Progress of reaction was monitored by TLC and hydroxyl value.

(3c) Synthesis of Urethanated Albizia benth Oil Polyetheramide (UABOPEtA)

Albizia benth Oil Polyetheramide (ABOPEtA) prepared as described above was mixed with toluene 2-4-diisocyanate in the ratios 9:1; 8:2; and 7:3 wt% in a mixture of xylene and butanone (1:1 v/v) in a four necked flask under [N.sub.2] atmosphere and continuous stirring and at 120[degrees]C. The reaction was monitored by TLC and hydroxyl value determination.

(4) Characterisation

Samples were characterised by spectroscopic techniques such as FT-IR, 1H NMR and [sup.13]C NMR. FTIR spectra were recorded on Tensor 27 FTIR-H1026302 (Bruker Optik, GmBh, Germany) and [sup.1]H and [sup.13]C--NMR spectra obtained on a Bruker Avance--400 (Bruker Instruments, Inc. Karlsruhe, Germany) Fourier transform spectrometer operating at 400.6 MHz. The gated decoupling pulse sequence was used with the following parameters, number of scans, 256; acquisition time, 1.366s; pulse width 10.3[micro]s. Free induction decay FID was transformed and zero filled to 300K to give digital resolution of 2Hz/point. Thermal analysis was carried out by DSC [822.sup.e] (Mettler Toledo GmBH, Giessen, Germany). Hydroxyl value (HV), Iodine value (IV), saponification value (SV) and refractive index (RI) were determined according to standard procedures (DFG, 1994).

(5) Evaluation of coating characteristics

Samples were thinned in toluene to a brushable consistency. The solutions prepared were applied by brush on clean mild steel panels of 15cmx 15cm for evaluating drying time, tin panels of the size 15x15cm for flexibility and adhesion, scratch hardness and impact resistance and glass panels of the size 15x15cm for water, alkali and solvent resistance. All coated panels were air dried for 48hr and sides protected by dipping them into molten wax before carrying out the above tests. The film characteristics were determined according to Indian standard specifications (Indian Standard specification, 1964:Indian Standard specification, 1981)

Results and Discussion

Schemes 1, 2 and 3 shows the reactions schemes for the synthensis of Hydroxylethyl Albizia benth oil amide [HEABOA] , Albizia benth oil Polyetheramide (ABOPEtA) and Urethaned Albizia benth oil Polyetheramide (UABOPEtA) respectively.

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The fatty amide were obtained by the reaction of diethnolamine with Albizia benth seed oil. HEABOA obtained was reacted with bisphenol-A to form polyetheramide (ABOPEtA) with free hydroxyl groups. Reactions of the ABOPEtA with toluene 2,4 diisocyanate at ratios 9:1, 8:2 and 7:3 yielded different urethane modified polyetheramide resin (UABOPEtA). The structural features of HEABOA, ABOPEtA and UABOPEtA were confirmed using FTIR, [sup.1]H NMR, [sup.13]C NMR spectral analysis.

Spectral Analysis of HEABOA

Fig. 1 presents the FTIR spectrum of HEABOA. The broad band at 3400 [cm.sup.-1] showed the characteristic absorption band for alcoholic OH group. C[H.sub.2] assymetric and symmetric stretching peaks appear at 2925 [cm.sup.-1] and 2854 [cm.sup.-1] respectively. Band at 1621 [cm.sup.-1] represent the stretching vibration of C=O of amide. The C-N stretching peak is 1049cm-1 while the C[H.sub.2] bending is at 1466 [cm.sup.-1]. The 1H NMR spectrum, Fig 2 of HEABOA shows characteristic peaks at 5 0.88- 0.9 ppm (terminal C[H.sub.3]), [delta] = 2.04 -2.06ppm (C[H.sub.2] - C=), [delta] 2.37 -2.41ppm (C[H.sub.2] -C = N), [delta] 1.27ppm (C[H.sub.2]), [delta] 2.76-2.79ppm (=CC[H.sub.2]C=), C[H.sub.2] attached to amide nitrogen is at [delta] 3.46-3.57ppm while C[H.sub.2]-OH occurs at [delta] =3.78-3.84 ppm and alcoholic OH is at [delta] = 5.34 -5.38ppm. The [sup.13]C presented in Fig 3 further confirms the structure of HEABOA by the presence of the signals at [delta] 26-33ppm (various - C[H.sub.2]), 50-52ppm (C[H.sub.2]CO), 66.2ppm (-C[H.sub.2]N-), 128-130ppm (olefinic protons of fatty amide)

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Spectral Analysis of ABOPEtA

The formation of ABOPEtA is supported by the presence of the following characteristic peaks in the infrared spectra as presented in Fig 1; C-O-C for aryl alkyl ether at 1247-1177[cm.sup.-1] and 1081[cm.sup.-1] for asymmetrical and symmemtrical stretching respectively. The C H.sub.2] asymmetrical strecthing band at 2854[cm.sup.-1] and symmetrical streching at 2925[cm.sup.-1] are charactertistic of -C[H.sub.2] fatty amide chains. Bands observed at 3011[cm.sup.-1] is for the -C-H stretching of unsaturation in the chain. The terminal hydroxyl group is reflected by the broad band at 3308[cm.sup.-1] (with reduced intensity when compared to HEOA). C=O stretching of amide is observed at 1612cm-1 while the -CN- stretching occurs at 1464[cm.sup.-1]. The absorption bands appearing at 904-743[cm.sup.-1] are due to the group vibrational frequencies of C-H for both aromatic rings of bisphenol-A and (C[H.sub.2])n when n is more than four.

The [sup.1]H NMR of ABOPEtA (Fig 4) gives characteristic peaks at [delta] 1.28ppm and [delta] 6.73-7.17ppm for gem dimethyl protons and for aromatic ring proton of bisphenol-A respectively. The appearance of peaks at [delta] 4.08 -4.2 ppm corresponding to -C[H.sub.2] linked with -O- aromatic confirms the formation of ether in the reaction of HEOA with bisphenol A. The -C[H.sub.3] and C[H.sub.2] for terminal and internal fatty amide chains were conspicously observed at [delta] 0.91 and [delta] 1.29-1.31ppm respectively. While the -C[H.sub.2] linked with the olefinic double bond is at [delta] 2.03-2.08ppm, characteristic peaks for -C[H.sub.2] attached to amide nitrogen and that of amide carbonyl were both present at [delta]3.87 -3.8ppm and [delta] 2.4-2.29 ppm respectively. Peaks at [delta]=3.58-3.51 and [delta] =5.38-5.36ppm are all characteristic peaks for C[H.sub.2] attached to the hydroxyl and olefinic protons respectively. The presence of these peaks confirm that the reaction between HEOA with bisphenol-A produced ABOPEtA. The product is further confirmed by [sup.13]C NMR (Fig 5) that shows peaks at [delta] 29.5-29.7ppm of -C[H.sub.2] and [delta] 42ppm for quaternary carbon of bisphenol A, while that of aromatic carbon of bisphenol is obsrerved at [delta]= 128.5ppm to 126.5ppm and [delta] 15.1ppm. The -C[H.sub.2] peak of HEOA attached to bisphenol A through ethyl linkages is at [delta]= 20 - 61.29ppm. The olefinic carbon of fatty amide chain appear as peak at [delta] 138.1 - 133ppm.

[FIGURE 1 OMITTED]

Spectral Analysis of UABOPEtA

Reactions between ABOPEtA with TDI forming urethane modified polyetheramide [UABOPEtA] is suggested by reduction both in intensity and broadness of the band of residual hydroxyl group at 3322.75[cm.sup.-1] presented in Fig 1. The appearance of band at 1710[cm.sup.-1] is characteristic of carbonyl of urethane linkage while the aromatic band for TDI is at 743 [cm.sup.-1.]

The 1H NMR (Fig 6) further confirms the structure as shown in scheme 3 with characteristic peaks of -C[H.sub.2] attached to urethane linkage at [delta] 2.68ppm - 2.67ppm, -C[H.sub.3] of TDI at [delta] 2.29ppm while aromatic protons appeared at [delta] 7.28-7.26ppm. The observed peak for -NH of urethane is at 5 7.3ppm. The disappearance of peaks at [delta] 3.5 - 3.8ppm corressponding to the C[H.sub.2] attached to amide and hydroxyl is an evidence that during the reaction between free -OH group of ABOPEtA and -NCO groups of TDI, -C[H.sub.2] were consumed and the reduction in peak [delta]=5.38- 5.36ppm signified consumption of olefinic proton while residual -OH peak appears at [delta] 5.5ppm.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

Carbon 13-NMR (Fig 7) spectra reveals the appearance of -C[H.sub.3] peaks for TDI at [delta]= 22.9ppm while that for internal -C[H.sub.2] of fatty amine chain appears at [delta] 31.4 - 27.6.ppm.

The -C[H.sub.2] attached to double bond and to amide carbonyl occur at 5 26.0ppm and [delta] 32.3 -31.9ppm respectively. Peak for quartenary carbon of bisphenol is still at [delta] 42.0ppm but dissapearance of peaks at 62.09 - 50.8ppm

Differential Scanning Calometric Analysis

The DSC thermograms of the ABOPEtA and UABOPEtA is shown in Fig 4. For ABOPEtA, curing starts at 210[degrees]C and ends at 250[degrees]C. Thermosetting of the resin starts after this event. The broadness of the peak shows the non-homogeneity of the sample. For UABOPEtA, curing starts at around 160[degrees]C and extend to 180[degrees]C. The presence of urethane linkages encourages curing at lower temperatures leading to configurational changes in the polymeric chains. Such enhancement of curing by urethane bonds has been earlier reported by Alam et.al (2004). Glass transition (Tg) of ABOPEtA was -20.56[degrees]C while the Tg of UABOPEtA occurred at 18.66[degrees]C. The increase in Tg on urethanation can be attributed to the stiffening due to the appended aromatic moieties of TDI and the intramolecular hydrogen bonding among the urethane groups.

[FIGURE 8 OMITTED]

Physicochemical characteristics

Table 1 presenting the physicochemical characteristics reveals that a decrease in hydroxy value (HV) and iodine value (IV) in the order HEABOA, ABOPEtA, UABOPEtA-10, UABOPEtA-15, UABOPEtA-20, UABOPEtA-30. The sharp decrease in HV on going from HEABOA to ABOPEtA is due to the reaction of some hydroxyl moeities of HEABOA with Bisphenol-A to form ABOPEtA while the same decrease observed for IV may be related to the increase in molar mass of ABOPEtA compared with HEABOA. Further slight decrease in HV observed with gradual loading of TDI may also be explained to be due to reaction of hydroxyl groups on the the ABOPEtA with the -NCO of TDI to form UABOPEtA. This reaction further leads to increase in molar mass of the polymer and this accounts for the further decrease in IV also observed on gradual loading of TDI.

The increase in specific gravity and refractive index from HEABOA, ABOPEtA, UABOPEtA-10, UABOPEtA-15, UABOPEtA-20, UABOPEtA-30 correlates with increase in molar mass of the system in that order.

Coating Properties

The ABOPEtA and the urethaned modified samples were applied on 15cm X 15cm steel panels and kept in vertical positions. The results presented in table 2 show that while the ABOPEtA were non-drying, the urethaned modified ABOPEtA were air drying and the drying time decreased with increase in TDI loading. While the UABOPEtA-10 took 1.5h to become dry to touch and 12h to hard dry, UABOPEtA-30 took onlz 30min to surface dry and 1h to hard dry.

The scratch hardness was estimated by estimating the pencil hardness of the films. The hardness was expressed in terms of the designation of the hardest pencil that failed to scratch the films. The results presented in table 2 also revealed that scratch hardness improved with increased loading of TDI.

Table 2 also revealed that the impact resistance (1kg load) and bend test (1/8 inch-mandrel) were passed by the UABOPEtA-10, UABOPEtA-15, UABOPEtA-20 while the UABOPEtA-30 failed. These properties may be correlated to the polar groups present in the samples. Outstanding flexibility (1/8 inch mandrel) is conferred by the polar urethane and ether linkages as well as the fatty amide chains. These also lead to good adhering coatings which have improved impact resistance. The -NH groups of urethane linkages form hydrogen bonds with the substrate and with carbonyl oxygen atoms of the poletheramide( ) leading to enhanced scratch hardness, impact resistance and flexibility behaiviour. However, UABOPEtA-30 failed these physico- chemical properties. At UABOPEtA-30, it is likely that the additional isocynate is liable to give too much cross linking, Also the presence of Bisphenol groups along with the aromatic ring of TDI (at 30wt of loading and above) introduce rigidity in the polymer resin leading to a deterioration of the above properties.

Chemical Resistance

The thinned solutions of the resins were applied on a 15cm X 15cm glass panels and each set was immersed separately in distilled water, xylene, 2% solution of each of HCl and NaOH and 3.5% solution of NaCl. The panels were taken out of the solutions at regular intervals of time, washed in fresh running water, dried for an hour and film examined for visible change. The results presented in table 3 indicate that urethanation of ABOPEtA led to greatly improved chemical resistance

Conclusion

A new urethaned modified polyetheramide resin was developed using Albizia benth oil , a sustainable resource. The resin was airdrying with improved scratch hardness and better flexibilty and showed better chemical resistance which may be attributed to the combination of properties of bisphenol-A, ether and urethane. The resin also cured at lower temperature. All these reveal the new resin as a good candidate for preparing ambient cured anticorrosive coating.

Acknowledgement

This work was funded by the International Foundation for Science (IFS) in conjuction with the Organisation for the Prohibition of Chemical Weapons (OPCW), Grant No F\4588-1 to Akintayo C.O. We also appreciate the provision of some facilities by Prof Thomas Ziegler of the Institute of Organische Chemie, Universitat Tubingen, Tubingen, Germany.

References

Aigbodion, A.I., C.K.S. pillai, I.O. Bakare, L.E. Yahaya, 2001. Ind . J Chem Technology, 8:378

Akintayo, C.O., K.O. Adebowale, 2004. Prog Org Coat., 50: 133.

Akintayo, C.O., K.O. Adebowale, 2004. Prog Org Coat., 50: 207

Alam, M., E. Sharmin., S.M. Ashraf, S. Ahmad, 2004 Prog Org Coat., 50: 224.

Ahmad, S., S.M. Ashraf, E. Sharmin, M. Nazir, M. Alam, 2005. Prog Org. Coat., 52: 85.

Ahmed, S., S.M. Ashraf, F. Naqvi, S.Y.adav, A. Hasnat, 2003. Prog Org Coat., 47: 95.

Ahmad, S., S.M. Ashraf, F. Naqvi, S.Y.adav, A. Hasnat, 2001. J, Polymer. Mater., 18: 53.

Ahmad, S., S.M. Ashraf, E. Sharin, F. Naqvi, S. Yadav, A. Hasnat, 2002. Prog Cryst. Growth, 45: 83.

DFG, 1994. German Society for fat science, German Standard Methods for the Analysis of fats and other Lipids. Wissenschaftliche Verlagsgesellschaft mbH, Stuttgart, Germany.

Indian Standard specification, 1964. (IS), 101: 38.

Indian Standard specifications, 1981. (IS), 158(8): 9.

Li, F., D.W. Marks, R.C. Larock and J.U Otaigbe, 2000 Polymer., 41: 7925.

LI, F., M.V. Hanson, R.C. Larock, 2001. Polymer., 42: 1567.

Shabeer, A., A. Garg, S. Sundararaman, K. Chandrashekhara, V. Flanigan and S. Kapila, 2005. J.Appl. Polym Sci., 98: 1772.

Wei, H.Y., W.F. Shi, K.M. Nie, X.F. Shen, 2002. Polymer., 43: 1969.

Akintayo Cecilia O and Akintayo Emmanuel T.

Chemistry Department, University of Ado-Ekiti, P.M.B 5363, Ado-Ekiti, Ekiti State, Nigeria

Corresponding Author: Akintayo Cecilia O and Akintayo Emmanuel T, Chemistry Department, University of AdoEkiti, P.M.B 5363, Ado-Ekiti, Ekiti State, Nigeria

Email: temitopeakintayo@yahoo.com
Table 1: Physico-Chemical characteristics of HEABOA,
ABOPEtA and various UABOPEtA

              Hydroxyl    Iodine          Specific      Refractive
              value       value           gravity       Index
              (mgKOH/g)   (mg Iodine/g)   (g\ml 250C)   (250C)

ABO           0.30        104.50          0.915         1.4725
HEABOA        10.52       85.50           0.925         1.4850
ABOPEtA       5.25        40.05           0.935         1.5225
UABOPEtA-10   4.05        35.24           0.938         1.5240
UABOPEtA-15   3.90        32.15           0.942         1.5245
UABOPEtA-20   3.35        28.26           0.948         1.5252
UABOPEtA-30   2.90        22.50           0.951         1.5275

Table 2: Physico-mechanical performance of ABOPEtA
and various UABOPEtA

              Scratch       Impact            Surface
              hardness      Resistance        Drying
              (Pencil       (1Kg              Time(hr)
              brand)        load)

ABOPEtA       6B            Fail              Non- Drying
UABOPEtA-10   4B            Pass              1.5
UABOPEtA-15   2B            Pass              1.0
UABOPEtA-20   2H            Pass              0.5
UABOPEtA-30   3H            Fail              0.5

              Hard Drying   Flexibility and
              Time(hr)      Adhesion
                            (1/8 inch
                            mandrel)

ABOPEtA       Non-Drying    Fail
UABOPEtA-10   12            Pass
UABOPEtA-15   6             Pass
UABOPEtA-20   4             Pass
UABOPEtA-30   1             Pass

Table 3: Chemical resistance performance of
ABOPEtA and various UABOPEtA

                                         Alkali
              Water        Xylene        Resistance
              Resistance   Resistance    (2% NaOH)

ABOPEtA       e            f             e
UABOPEtA-10   c            b             e
UABOPEtA-15   b            a             c
UABOPEtA-20   b            a             b
UABOPEtA-30   b            a             b

              Acid         Salt
              Resistance   Resistance
              (2% Hcl)     (3.5% NaCl)

ABOPEtA       e            e
UABOPEtA-10   d            c
UABOPEtA-15   c            b
UABOPEtA-20   b            b
UABOPEtA-30   b            b

a--not affected

b--slight loss of gloss

c--loss of gloss

d--slight blistering

e--blistering

f--film completely removed
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Title Annotation:Original Article
Author:Akintayo, Cecilia O.; Akintayo, Emmanuel T.
Publication:Advances in Natural and Applied Sciences
Article Type:Report
Geographic Code:6NIGR
Date:May 1, 2010
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