Waterborne polyurethane dispersions synthesized from jatropha oil

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Waterborne polyurethane dispersions synthesized from jatropha oil Sariah Saalah a,b,∗ , Luqman Chuah Abdullah a,c , Min Min Aung c,e , Mek Zah Salleh d , Dayang Radiah Awang Biak a , Mahiran Basri e , Emiliana Rose Jusoh c a

Department of Chemical and Environmental Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia Chemical Engineering Department, Faculty of Engineering, Universiti Malaysia Sabah, Jalan UMS, 88400 Kota Kinabalu, Sabah, Malaysia Institute of Tropical Forestry and Forest Products, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia d Radiation Processing Technology Division, Malaysian Nuclear Agency, 43000 Kajang, Selangor, Malaysia e Department of Chemistry, Faculty of Science and Technology, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia b c

a r t i c l e

i n f o

Article history: Received 25 August 2014 Received in revised form 17 October 2014 Accepted 24 October 2014 Available online xxx Keywords: Jatropha oil Polyurethane dispersion Renewable polyol Waterborne coating

a b s t r a c t A series of waterborne polyurethane dispersions derived from jatropha oil-based polyol (JOL) with different OH numbers ranging from 138 to 217 mgKOH/g, were successfully prepared. Jatropha oil-based polyols were synthesized by epoxidation and oxirane ring opening using methanol. The JOLs produced were then used to prepare jatropha oil based waterborne polyurethane (JPU) dispersions by reaction with isophrene diisocyanate (IPDI). Dimethylol propionic acid (DMPA) was used as an internal emulsifier to enable the dispersion of polyurethane in water. The influence of the OH number, DMPA content and hard segment content on the stability of the wet JPU dispersions, as well as the physical, mechanical and thermal properties of the dry JPU films were investigated. The results reveal that with increasing OH number, the DMPA content and hard segment content significantly decrease the particle size from 1.1 ␮m to 53 nm, indicating increasing stability of the dispersions. JPU films exhibit the stress–strain behavior of an elastomeric polymer with a Young’s modulus ranging from 1 to 28 MPa, a tensile strength of 1.8 to 4.0 MPa and elongation at break ranging from 85 to 325%. The polyurethane dispersions synthesized in this work possess good pendulum hardness, water repellence and thermal stability with promising application as a binder for wood and decorative coatings. © 2014 Elsevier B.V. All rights reserved.

1. Introduction Many of the commercial polyurethane adhesives and coatings are known to contain a significant amount of organic solvents and some also contain volatile isocyanate which is harmful to human health as well as the environment. Increasing concern on this issue has pressured the urethane industry to move toward water based systems. Waterborne polyurethane (PU) dispersion is a recent class of binder that is easily diluted with water and air-dried, stoved or crosslinked to produce volatile organic component (VOC) compliant coatings (Athawale and Nimbalkar, 2011). As with their solvent based counterparts, waterborne PU dispersions find application mainly in the ink, surface coating and adhesive industries. Polymers derived from waterborne PU dispersions exhibit an excellent combination of physical properties such as high tensile and tear

∗ Corresponding author at: Department of Chemical and Environmental Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia. Tel.: +60 3 89466288. E-mail address: s [email protected] (S. Saalah).

strength, high elasticity, a range of hardness, excellent abrasion resistance, good resistance to chemicals and good low temperature stability (Davies and Some, 1990). Waterborne PU dispersions can be prepared by adding water to a segmented polyurethane ionomer containing a very small amount of solvent as a diluent agent. Ionomers which contain hydrophilic groups are incorporated into the side chain or backbone of the polymer to enable dispersibility of water-insoluble polyurethane. The ionomer could be an anionic or cationic type but an anionic type such as dimethylol propionic acid (DMPA) is commonly used. The DMPA acts as an emulsifier to provide dispersion stability for longer storage of the waterborne PU dispersion. The hydrophilicity of ionic groups in the DMPA is reported to improve the mechanical properties, but tends to make the dispersion film more sensitive to water and chemicals (Bullermann et al., 2013). Therefore, the amount of DMPA should be controlled to be as low as possible in the polyurethane prepolymer. Currently, most waterborne PU dispersions are derived from petroleum based polyol which is non-renewable. As consumers are becoming more aware of environmental issues, they are changing their preference toward bio-based products. In addition, people

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in industry are constantly looking for alternatives as the price of fossil oil is typically increasing. Recently, the synthesis of waterborne PU dispersions derived from vegetable oil such as soybean oil, castor oil, rapeseed oil and linseed oil have been reported (Chang and Lu, 2012, 2013; Lu and Larock, 2008; Ni et al., 2010). However, to the best of our knowledge, no research has been reported concerning jatropha oil regarding its promising properties to produce waterborne dispersions. In Malaysia, jatropha become one of the most important crop after palm oil and rubber, mainly planted for biodiesel production. BATC Development Berhad was actively engaged in jatropha plantation and bio-fuel industry since 2007. Up to 2011, about 600,000 acres planted areas, 3.3 million areas landbanks and more than 300 nurseries and collection centers were reported in Malaysia (Bionas, 2011). Jatropha oil (JO) which is extracted from the seeds of the jatropha fruit is a promising candidate for chemical purposes as it contains 78.9% unsaturated fatty acids, mainly of oleic acids (43.1%) and linoleic acid (34.4%) (Sarin et al., 2007). This high degree of unsaturation provides a broad alternative for chemical modification to produce polymers with various properties. Furthermore, it is an advantageous to use jatropha oil because it is a non-edible oil and thus its usage will reduce the consumption of edible oils for chemical purposes (Rios et al., 2013). Previous researches have revealed the potential of producing alkyd resin (Boruah et al., 2012), polyurethane coatings (Sugita et al., 2012), polyurethane adhesive (Aung et al., 2014) and polyurethane elastomer (Hazmi et al., 2013) from jatropha oil. In this research, an attempt is made to produce a waterborne PU dispersion using a jatropha oil-based polyol. The aim of this study is to investigate the effect of the polyol OH number, DMPA content and hard segment content on the stability of the wet jatropha oil-based polyurethane (JPU) dispersion and the physical, mechanical and thermal properties of the dry JPU films. The stability of the dispersion was investigated by particle size analysis, pH and viscosity measurement. On the other hand, the physical properties of the JPU films were determined by pendulum hardness and water contact angle analysis. Tensile test and thermogravimetric analysis (TGA) were used to determine the mechanical and thermal properties of the JPU films. These properties will have an influence on the practical design of products as the PU dispersion can be used as a standalone coating or as a binder in wood and decorative coatings.

ratio of the oil double bond to formic acid and hydrogen peroxide was 1:0.6:1.7. The reaction temperature was then increased and maintain at 60 ◦ C. The reaction was quenched after a prescribed time by cooling the reaction mixture to room temperature. The mixture was then transferred to a 500 mL separating funnel to allow phase separation. The aqueous phase was removed, and the oil layer was washed successfully with distilled water to remove the remaining acid. The oil layer was then dried using magnesium sulphate. Four samples of EJO were prepared by varying the reaction time. 2.3. Preparation of jatropha oil-based polyols (JOL) by the oxirane ring opening method The reactions were carried out in a four neck flask, as mentioned in Section 2.2. A calculated amount of methanol and water was charged into the flask followed by adding sulphuric acid and heating to 64 ◦ C, and then added with EJO. The reaction was kept at 64 ◦ C for 30 min, and sodium bicarbonate was added to quench the reactions. After being cooled to room temperature, the deposit was discarded. Methanol and water were removed by vacuum distillation at 60 ◦ C for 30 min, followed by 80 ◦ C for 10 min. The resulted clear golden yellow polyol was analyzed for OH number according to ASTM D4274-99 (Test Method C-Reflux Phtalation). By using the same hydroxylation procedure for different EJO, a series of jatropha oil based polyols (JOL) with different OH numbers were prepared and coded as JOL 138, JOL 161, JOL 188 and JOL 217. The numbers represent the OH number of the polyol in mgKOH/g. 2.4. Preparation of jatropha oil-based polyurethane (JPU) dispersion

Crude jatropha oil was supplied by BATC Development Berhad, Kuala Lumpur, Malaysia. The hydrogen peroxide 30% and methanol were supplied by Merck, Germany. Isophrene diisocyanate (IPDI), dimethylol propionic acid (DMPA), n-methyl pyrollidone (NMP), 2-hydroxyethyl methacrylate (HEMA), phtalic anhydride and dibutyltin dilaurate (DBTDL) were purchased from Sigma–Aldrich. Ethyl methyl ketone (MEK), triethylamine (TEA), formic acid, magnesium sulphate anhydrous, pyridine, and sodium hydroxide were supplied by Systerm. All chemicals were reagent grade, and were used as received.

The JOL and DMPA (dissolved in NMP) were added to a fournecked flask equipped with a mechanical stirrer, nitrogen inlet, condenser, and thermometer. The mixture was heated to 70–80 ◦ C and stirred for 30 min to obtain a homogeneous mixture. IPDI was then added dropwise for 30 min followed by adding a few drops of dibutyltn dilaurate as a catalyst. MEK was added batch by batch to reduce the viscosity of the system. After an additional 3 h of reaction, HEMA was added until the NCO peak at 2270 cm−1 of Fourier transform infrared (FTIR) spectra disappeared, showing that all the diisocyanate had been consumed. The reactants were then cooled to 40 ◦ C and neutralized by adding TEA (1.2 equiv. per DMPA), followed by dispersion at high speed with distilled water to produce the JPU dispersions with a solid content of ∼25 wt.% after removal of the MEK under vacuum. The reaction scheme for this method is shown in Fig. 1. The formulation for waterborne JPU dispersion is shown in Table 1. The “JPU 138” designation indicates that the OH number of the polyol used for the JPU preparation is 138 mgKOH/g. For all formulation, the molar ratio between the polyol (JOL), IPDI, DMPA and HEMA was fixed which led to JPUs with an increase in the hard segment and DMPA content. The corresponding JPU films were obtained by casting the JPU dispersions into a Teflon mold, and drying at room temperature for 7 days, followed by drying in a vacuum oven at 60 ◦ C for 12 h. The JPU films were stored in a desiccator at room temperature.

2.2. Preparation of epoxidized jatropha oil (EJO)

2.5. Characterization

The reactions were carried out in a 1000 mL four neck flask equipped with a mechanical stirrer, condenser, a thermometer sensor and an isobaric funnel. The reaction temperature was controlled by placing the flask in a water bath. Jatropha oil (200 g) and formic acid were poured into the flask and heated to 40 ◦ C, before adding hydrogen peroxide dropwise over a period of 30 min. The molar

The attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra were recorded on a Perkin-Elmer Spectrum 2000 spectrometer which collects mid-infrared scattered radiation using a single-beam improved Michelson interferometer. The spectra were recorded in the range of 4000–500 cm−1 with a nominal resolution of 4 cm−1 .

2. Materials and methods 2.1. Materials

Please cite this article in press as: Saalah, S., et al., Waterborne polyurethane dispersions synthesized from jatropha oil. Ind. Crops Prod. (2014), http://dx.doi.org/10.1016/j.indcrop.2014.10.046

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O O

OH

OH

H3C

OCH3

OCH3

O O

3

+

CH3

CH3

CH3

HO H2C

+

O C N

OH

O CH2

OH

+

H2C

COOH

N C O

IPDI

O

C

CH3

DMPA

HEMA

O

JOL

DBTDL ( catalyst )

O H3CO

O

O

O

O

OCH3

O O

OH

O

N H

O

H N

O O

O

O

N H

O

O

CH2

CH3

O

OH

O

O

H N

OCH3 CH2 CH3

O

CH2

CH3

N

TEA

CH2 CH3

O O

O H3CO

O

O

O

O

OCH3

O O

N H

O

H N

O O

O COO

OCH3

O

N H

O

H N

O O

O

CH2

CH3

NH

O

O O

Water

Jatropha oil-based waterborne PU (JPU) dispersion Fig. 1. Reaction scheme for synthesis of waterborne polyurethane dispersions.

The particle size of the polyurethane dispersions was measured by a Zetasizer Nano-S (Malvern Instruments). Approximately 0.1 mL of the polyurethane dispersion was diluted with 3 ml distilled water and measured at 25 ◦ C. The Zetasizer Nano ZS was also applied for zeta potential measurements using electrophoresis principle. The viscosity of the polyurethane dispersion was determined according to ASTM D4878-03 using a Brookfield Viscometer (RV DV-II+ Pro) with spindle number 40. The measurement was conducted at temperature 25 ◦ C. The pendulum hardness was determined according to ASTM D4366-82. The JPU dispersions were applied on a glass plate with a

wet film thickness of 120 ␮m using a hand bar coater. After 72 h of drying at room temperature the pendulum hardness was measured using a Byk pendulum hardness tester. The mechanical properties of the dispersion cast films were analyzed using a tensile tester (Strograph R1 Toyoseiki), according to ASTM D638-03 Type V specifications. The crosshead speed was 10 mm/min with 1 kN load cell. The stress and strain measurements data were analyzed for Young’s modulus, tensile strength, and elongation at break. The values were reported as the average of a minimum of five measurements for each sample. The measurement was carried out at room temperature and 50% relative humidity.

Table 1 The formulation of jatropha oil-based polyurethane (JPU) dispersions. Sample designation

JPU 138 JPU 161 JPU 188 JPU 217 a

JOL OH number

Molar ratio

(mg KOH/g)

JOL (OH)

DMPA (OH)

HEMA (OH)

IPDI (NCO)

138 161 188 217

1 1 1 1

0.38 0.38 0.38 0.38

0.2 0.2 0.2 0.2

1.25 1.25 1.25 1.25

DMPA (wt.%)

HSa (wt.%)

4.1 4.6 4.9 5.4

34.2 38.0 40.6 45.0

Hard segment content [HS = Mass (IPDI + DMPA + HEMA + TEA)/Mass (Polyol + DMPA + IPDI + HEMA + TEA)].

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Fig. 2. FTIR spectra of jatropha oil-based polyol (JOL) and polyurethane (JPU) film.

3. Results and discussion 3.1. FTIR analysis The IR spectra of jatropha oil-based polyol and water-borne polyurethane (JPU) films are shown in Fig. 2. It can be seen that the broad absorbance at 3454 cm−1 in the polyol shifted to 3334 cm−1 in the JPU implying that the OH group was converted to a hydrogen bonded NH group. There is no peak at 2270 cm−1 indicating that the isocyanate group ( NCO) had fully reacted. In addition, the absorption band corresponding to C O of urethane linkage (hydrogen bonded) of the PU components can be observed at 1710 cm−1 while the absorption bands at 2923 cm−1 , 2853 cm−1 and 1461 cm−1 correspond to the C H stretching of the CH2 and CH3 groups. It is also worth mentioning that there was a minimum side reaction to form urea as no absorption band of the carbonyl group (C O) at a range of 1645–1635 cm−1 was observed.

3.2. Particle size of the JPU dispersions Particle size and zeta potential analysis are important methods to predict the stability of the dispersion. A stable dispersion is generally recognized by a smaller particle size and high absolute value of the zeta potential. The results (Table 2) indicate a significant reduction in particle size from 1167 to 53.3 nm when the OH number increases from 138 to 217 mgKOH/g. The particle size distribution of the JPU188 dispersion is shown in Fig. 3. One particle distribution peak was observed at 164 nm and the

polydispersity index (PDI) of 0.219 indicated that the dispersion exhibited a homogeneous composition. According to Table 1, when the OH number of the polyol increases, the amount of diisocyanate and DMPA also increases to maintain a constant molar ratio between the NCO and OH groups. However, increasing the amount of IPDI and DMPA in the PU formulation results in a higher hard segment content as well as DMPA content. As shown in Fig. 4, as the amount of hard segment increases in the PU formulation, the particle size decreases due to the decrease in the soft segment content, which is more hydrophobic as it is derived from vegetable oil. The ionic stabilization of the dispersion particles by an ionomer is well documented. Generally, the hydrophobic component forms the core of the particles while the ions are on the surface which creates an electrochemical double layer consisting of COO− from the DMPA and counter ions of NH(Et3 )+ from the neutralization with TEA (Bullermann et al., 2013). The particle size reduction as a result of increasing the DMPA content is clearly shown in Fig. 5. The decreasing trend of particle size as the OH number increases is due to a combination of high hard segment content and a sufficient amount of DMPA in the JPU formulation. The results are supported by the Zeta potential data suggesting that JPU dispersions synthesized from JOL with a high OH number are more stable, which is indicated by a high absolute value for the zeta potential. From the point of view of colloidal

15

10 Volume (%)

The contact angle between a water drop and the surface of the sample was measured using a contact-angle meter (FACE, Japan). The drop of water was mounted on the surface of the films using a microsyringe and the contact angle was measured. A high value of contact angle indicates a good hydrophobic nature of the coating, while a low value indicates that the water wets the surface. The angle measurements were done in triplicate on different parts of the films. Thermogravimetric analysis (TGA) was performed using a TGA/SDTA851e, Mettler Toledo, Switzerland. The films were heated from 25 to 600 ◦ C at a rate of 10 ◦ C/min under a nitrogen atmosphere.

5

0 0.1

1

10 100 Parcle diameter (nm)

1000

10000

Fig. 3. Particle size distribution of JPU 188 dispersion.

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60

Konig Hardness (s)

50 40 30 20 10 0 JPU 161

JPU 188

JPU 217

Fig. 6. Pendulum hardness of JPU films. Fig. 4. Effect of soft segment content on particle size of a JPU dispersion.

Generally, greater transparency of a dispersion indicates a greater amount of DMPA in the formulation and consequently the dispersion is more hydrophilic. In the present study, all JPU samples were physically dried after evaporation of water except for JPU 138, which formed a soft and tacky surface. This may due to insufficient amount of hard segment content which is responsible for the dry film formation of the PU dispersion.

1400

Particle size (d, nm)

1200 1000 800 600 400

3.4. Pendulum hardness of JPU films

200

The pendulum hardness of jatropha oil-based waterborne polyurethane films is reported in Fig. 6. The hardness of the polyurethane increased as a high OH number for the polyol was used in the PU formulation. This is due to the high functionality of the polyol to incorporate a greater amount of diisocyanate as a hard segment component, thus contributing to a higher crosslinking density of the polyurethane. The results are higher than those for a waterborne polyurethane wood coating derived from rapeseed oil fatty acid methyl ester, hardened by the addition of polyisocyanate with a hardness in the range of 17–27 s (Philipp and Eschig, 2012). It is interesting to note that the JPU films were produced solely by evaporation of water and without any additional curing or chemical crosslinking agent. The hardness of JPU 217 was comparable to a linseed oil based coating, with a reported hardness of 46 s, air dried by slow oxidation polymerization in the presence of metal drier (Chang and Lu, 2012). The hardness of the PU dispersions could be improved by introducing chemical crosslinking structure by radiation curing such as electron beam and ultraviolet (Chang and Lu, 2012).

0 4

4.2

4.4

4.6 4.8 5 DMPA content (wt%)

5.2

5.4

5.6

Fig. 5. Effect of DMPA content on particle size of a JPU dispersion.

stability, the ideal particle size for polymer dispersions should be around 100 nm and below (Tielemans et al., 2006). However, the intended application is another aspect to be considered as relatively larger particles are preferred in surface coatings for rapid drying, while smaller sizes are desirable when the deep penetration of the dispersion into a substrate is essential (Asif et al., 2005). 3.3. Characteristics of the JPU dispersions The solid content, viscosity, pH, acid value and color of the JPU dispersions are reported in Table 2. All samples show a relatively low viscosity in the range 7–80.4 mPa s at a solid content of 24.2–26.9 wt.%. The viscosity information is very important in deciding a suitable application method of dispersion on a substrate. A lower viscosity is generally required for spray and brush application. The reported pH of 7.0 is in the range of the pH of commercially available polyurethane dispersions. All samples had the same pH even though the acidity value varied from 4.80 to 8.60 mgKOH/g. In terms of appearance, the JPU dispersions were milky white to yellowish in color and turned to transparent and glossy films as they dried. Similar observations were reported by Ni et al. (2010) for waterborne PU dispersions derived from soy bean oil, while Lu and Larock (2008) obtained clear and slightly blue dispersions.

3.5. Tensile properties of JPU films Fig. 7 shows the stress–strain curves of JPU films, demonstrating an elastomeric behavior of the films. Tensile properties of the JPU films are given in Table 3. The tensile strength and Young’s modulus increased and the elongation at break decreased with increasing OH number of the polyol. This is related to an increasing functionality of the polyol with increasing OH number, and increasing hard segment content to provide more crosslinking sites for the formation of hydrogen bonding in the hard segment chain.

Table 2 Some properties of the JPU dispersion with different OH numbers. Sample

pH

Acid value (mg KOH/g)

Solid content (wt.%)

Viscosity (mPa s)

Color

Average particle size (d nm)

Zeta potential (MV)

JPU 138 JPU 161 JPU 188 JPU 217

7.0 7.0 7.0 7.0

8.63 4.80 7.93 6.23

24.8 24.2 26.9 26.5

30.0 7.3 80.4 78.2

Milky white Milky white Milky white Yellowish

1167.0 670.4 165.9 53.3

−46.37 −46.7 −68.23 −66.4

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100.00 JPU 217

JPU 217 10

JPU 188

80.00

JPU 188

JPU 161

JPU 161

Weight (%)

Stress (MPa)

8 6 4

60.00

40.00

20.00

2 0.00 0.00

0 100

0

200 Strain (mm/mm)

300

100.00

200.00

300.00 400.00 Temperature (°C)

500.00

600.00

400 Fig. 9. TGA curves of JPU films.

Fig. 7. Stress–strain curve of JPU films. Table 3 Tensile properties of JPU films. Sample

Young’s Modulus (Mpa)

Tensile Strength (Mpa)

Elongation at break (%)

JPU 161 JPU 188 JPU 217

1.0 ± 0.3 8.7 ± 0.7 27.9 ± 2.5

2.4 ± 0.5 1.8 ± 0.0 4.0 ± 0.2

325.1 ± 46.8 145.5 ± 5.3 84.9 ± 4.0

Increasing crosslinking density in the polyurethane reduces the mobility of chain segments, hence provides better resistance to externally applied extension forces which leads to higher tensile strength and lower elongation at break (Hwang et al., 2011). The increase in hard segment content also suppresses the soft segmenthard segment phase separation, and results in decreased elongation (Lee and Kim, 1995). 3.6. Water contact angle of JPU films The hydrophilicity of the JPU films was evaluated by measuring the contact angle formed between the surface of the cast film and a drop of distilled water. The results obtained are shown in Fig. 8. A remarkable difference in contact angle between compositions with different hard segment contents can be observed. The contact angle increased significantly from 66◦ for sample JPU 188 which included 34.2% hard segment content to 90◦ for sample JPU

100

Contact angle (degree)

90

80

JPU 161 JPU 188

70

JPU 217

60

50

40 0

2

4

6 Time (min)

8

10

Fig. 8. Water contact angle of JPU films as a function of time.

12

217 which included 45.0% hard segment content. This was based on the contact angle data taken one minute after the water drop was mounted on the surface of the samples. A contact angle of 90◦ or more indicates a nonwetting surface (Pathak et al., 2009). Therefore, the increased contact angle represents a lower level of wetting of the coating films by water. It is worth noting that JPU 217 demonstrated a hydrophobic character even though the DMPA content is the highest (Table 1). This reveals that the hydrophobicity of the dry films is mainly governed by the high hard segment content, and the increase in ionic content does not significantly increase the hydrophilicity. The results are comparable with PU coatings derived from other vegetable oils such canola oil, sunflower oil, and camelina oil based PU (Kong et al., 2013) and also petroleum based PU dispersions (Negim et al., 2011). 3.7. Thermal properties of JPU films Investigation into the thermal degradation of polymers is important to determine the proper conditions for manipulation and processing, and for obtaining high-performance products that are stable and free of undesirable by-products (Asif et al., 2005). The TGA curves for the JPU films prepared using polyol with different OH numbers are shown in Fig. 9, and the thermal parameters are summarized in Table 4. The TG curves are similar for all samples, and two thermal degradation stages can be observed. The onset of first degradation can be observed from 286.69 to 296.38 ◦ C and peak temperatures (the maximum rate of mass loss) from 313.92 to 321.6 ◦ C. This stage involves a loss of 28–37% of the sample mass, which represents the decomposition of the urethane linkage and the formation of isocyanates, alcohols, primary amines, ´ secondary amines, olefins, and carbon dioxide (Javni and Petrovic, 2000). Stage II exhibited similar onset temperatures from 361.18 to 399.2 ◦ C and similar peak temperatures from 392.26 to 401.38 ◦ C, with a 60–68% loss of sample mass due to dissociation of the soft segment. Among all JPU films, JPU 161 demonstrated the highest thermal stability with a low mass loss in the first stage degradation. This is related to the low amount of urethane bond due to the low OH number of polyol used for the synthesis of JPU. It is well known that the urethane bond is weak at a decomposition temperature of less than 300 ◦ C. However, there is an increasing trend for the peak temperature as the OH number of the polyol increased which indicated that higher crosslinking occurred in the films to compensate with a high OH functionality. Based on these results, it can be concluded that the waterborne PU films derived from jatropha oil have good heat resistance. These thermal properties of JPU are comparable to those of waterborne PU derived from soybean oil (Lu

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Table 4 The thermal properties of JPU films produced from polyol with different OH numbers. Sample

T1on (◦ C)

T1max (◦ C)

*w1 (%)

T2on (◦ C)

T2max (◦ C)

*w2 (%)

Residue at 600 ◦ C (%)

JPU 161 JPU 188 JPU 217

286.69 290.80 296.38

313.92 319.86 321.60

28.00 34.70 37.20

361.18 361.32 399.20

393.12 392.26 401.38

68.28 61.90 60.70

3.69 3.13 2.18

*w, mass loss (%).

and Larock, 2008; Ni et al., 2010) and petroleum based UV curable PU-acrylate (Xu et al., 2012). 4. Conclusions Environmentally friendly waterborne polyurethane dispersions have been synthesized from jatropha oil-based polyols and IPDI. Dispersions with a wide range of particle size from 53 nm to 1.1 ␮m were obtained, and the trend demonstrated increasing JPU dispersion stability as the OH number, hard segment content and DMPA content increased. Physically dried, tack free JPU films with pendulum hardness ranging from 20 to 50 s were obtained by the evaporation of water, which indicated good film formation. Water contact angle analysis demonstrated that the hydrophobic character of the surface of the films is mainly related to the hard segment content. The resulting JPU coating films for all formulations demonstrated good thermal stability with a minimum onset of degradation temperature at 286 ◦ C. On the other hand, the films exhibited elastomeric polymer behavior with a Young’s modulus ranging from 1 to 28 MPa, a tensile strength of 1.8 to 4.0 MPa and elongation at break ranging from 85 to 325%. The polyurethane dispersion synthesized in this work possesses good properties with promising application as a binder for wood and decorative coatings. Acknowledgements The authors gratefully acknowledge the Ministry of Higher Educations Malaysia for the financial support provided for this work. The authors would also like to thank the Malaysian Nuclear Agency for the use of their facilities and instruments. References Athawale, V.D., Nimbalkar, R.V., 2011. Waterborne coatings based on renewable oil resources: an overview. J. Am. Oil Chem. Soc. 88 (2), 159–185. Davies, W., Some, 1990. Property aspects of aqueous polyurethane ionomer dispersions. In: Kansa, D.R. (Ed.), Additives for Water-Based Coatings. The Royal Society of Chemistry, Cambridge, pp. 181–209. Bullermann, J., Friebel, S., Salthammer, T., Spohnholz, R., 2013. Novel polyurethane dispersions based on renewable raw materials – stability studies by variations of DMPA content and degree of neutralisation. Prog. Org. Coatings 76 (4), 609–615. Chang, C., Lu, K., 2013. Linseed-oil-based waterborne UV/air dual-cured wood coatings. Prog. Org. Coatings 76 (7–8), 1024–1031.

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Please cite this article in press as: Saalah, S., et al., Waterborne polyurethane dispersions synthesized from jatropha oil. Ind. Crops Prod. (2014), http://dx.doi.org/10.1016/j.indcrop.2014.10.046