Preparation and Characterization of Flexible Polyurethane Foams

from Palm Oil-Based Polyol

Duangphon Lumcharoen1,a, Onusa Saravari1,b

1Department of Materials Science, Faculty of Science, Chulalongkorn University,

Bangkok 10330 Thailand

adl.duangphon@gmail.com, bsonusa@chula.ac.th

Keywords: Flexible Polyurethane Foam, Palm Oil, Polyol, Transesterification

Abstract. Flexible polyurethane (PU) foams were prepared by replacing commercial petroleum-

based polyether polyol with palm oil-based polyol up to 50 wt%. Palm oil was converted to polyol

by transesterification reaction with glycerol using calcium oxide as a catalyst. PU foams were then

prepared from reaction between mixtures of palm oil-based polyol and petrochemical polyols with

toluene diisocyanate (TDI) using water as blowing agent. The morphology and physical-mechanical

properties including apparent density, indentation hardness, compressive deflection coefficient or

support factor, tensile strength, and tear strength of the prepared foams were characterized and

compared to those of reference foam prepared using only conventional petrochemical polyols.

Scanning electron microscopy (SEM) indicated that the cellular structures of all the prepared foams

were semi-open and the cell size decreased with higher amount of palm oil-based polyol. The

apparent densities and the compressive deflection coefficient of the PU foams increased with the

increasing amount of palm oil-based polyol, while the indentation hardness showed the opposite

tendency. Furthermore, the obtained foam modified with palm oil-based polyol of 20 wt% were

found to have the highest tensile and tear strengths.

Introduction

Flexible polyurethane (PU) foams are used in several applications, mainly in cushioning industries

because of their availability in wide ranges of load-bearing properties and resiliency [1]. By the

proper choice of reactants, PU products can be made with variety of properties. One of the

important raw materials in PU flexible foam is polyol, mostly derived from petroleum which is a

non-renewable resource. Vegetable oil-based polyols can be potential substitutes for petrochemical

polyols due to their sustainability. Moreover, vegetable oil-based polyols are considered to be

environmentally friendly materials. Vegetable oil-based polyols with variable hydroxyl number can

be synthesized using different methods [2-6]. These bio-based polyols have been used as raw

materials for producing various PU products, for example, PU adhesives [2], rigid foams [3], semi-

rigid foams [4], and flexible foams [5-6]. Das and co-workers fabricated two series of flexible PU

foams by substituting petroleum-based polyol with increasing amount of soy-based polyol (SBP)

having different hydroxyl numbers and their results showed that the morphology and mechanical

properties of the foams were affected significantly by the foam fabrication method and SBP

hydroxyl numbers [5]. Pawlik and Prociak prepared flexible PU foam by substituting a part of

petrochemical polyether polyol with palm oil polyol and they found that the modifications of PU

formulation with palm oil polyol allow improving selected physical-mechanical properties of final

products [6]. In this study, palm oil, the cheapest oil in Thailand, was converted into polyol by

transesterification with glycerol. The PU foams were then prepared by substituting a portion of

petrochemical polyol with the obtained palm oil-based polyol. The molecular weight and the

hydroxyl number of the palm oil-based polyol were determined. The morphology and properties of

the prepared foams were examined and compared to properties of reference foam prepared from

conventional petrochemical polyol.

Advanced Materials Research Vol. 911 (2014) pp 352-356 Online: 2014-03-24© (2014) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.911.352

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Experimental

Materials. Palm olein oil with an acid value of 0.57, an iodine value of 60.41 and a specific gravity

of 0.9202 was obtained from Lam Soon (Thailand) Public Co. Ltd. AR grade glycerol, calcium

oxide, and ethanol were purchased from TTK Science (Bangkok, Thailand). TDI 80/20

(commercial grade), TDI 65/35 (commercial grade), commercial polyether polyols (ACTOLLR-00

and VORANOL 2070), catalysts (TEGOAMIN-L33 and DABCO T9) and surfactants (Niax

Silicone L638 and TEGOSTAB B 8244) were supplied by Bangkok Foam Co. Ltd. All materials

were used without further purification.

Synthesis of palm oil-based polyol. 400 g of palm olein oil was placed in a 1000 mL four-necked

round-bottom flask equipped with a mechanical stirrer, a thermometer, a condenser, a water

separator, and nitrogen gas inlet. The palm oil was heated to 150OC with stirring at 550 rpm under

nitrogen atmosphere and 44.16 g of glycerol was added. The mixture was then heated to 200OC

followed by the addition of 0.3 g of calcium oxide. The temperature was raised to 245OC and the

mixture was maintained at this temperature until one part of sample completely dissolved in three

parts of ethanol. The obtained product was cooled to room temperature under nitrogen atmosphere.

The chemical structure of the product was analyzed by Fourier transform infrared spectroscopy

(FTIR spectrophotometer; Perkin Elmer Spectrum One FTIR). The hydroxyl number was

determined based on ASTM D 4274-05 Method C. The molecular weight was characterized by gel

permeation chromatography (GPC; Waters E600) using tetrahydrofuran (THF) as a solvent.

Preparation of polyurethane foams. The foam formulations used in this study are given in Table 1.

The PU foams were prepared by substituting petrochemical polyol with palm oil-based polyol of

10-50 wt%, while reference foam (TP-STD) was produced using only petrochemical polyols. The

amount of each component was based on 100 parts by weight of total polyol and TDI amounts were

calculated at an isocyanate index of 85. Each PU foam was prepared by mixing all ingredients,

except TDI, at 2500 rpm under ambient condition for 30 s. This pre-mixture was then cooled to

20OC, after which, TDI component that kept at 20

OC was added and the mixture was stirred for 5 s

at 2500 rpm. The mixture was poured into an open mold and allowed to rise freely. The obtained

foams were allowed to cure for 72 h under ambient condition before cutting into test specimens.

Table 1 Formulation of flexible polyurethane foams

Components Parts by weight

TP-STD TP-10 TP-20 TP-30 TP-40 TP-50

ACTOLLR-00 50 50 50 50 50 50

VORANOL 2070 50 40 30 20 10 0

Palm oil-based polyol 0 10 20 30 40 50

TDI 65/35* 21.5 20.86 20.21 19.56 18.92 18.26

TDI 80/20* 21.5 20.86 20.21 19.56 18.92 18.26

Niax Silicone L638 0.3 0.3 0.3 0.3 0.3 0.3

TEGOSTAB B 8244 0.3 0.3 0.3 0.3 0.3 0.3

TEGOAMIN-L33 0.4 0.4 0.4 0.4 0.4 0.4

DABCO T9 0.04 0.04 0.04 0.04 0.04 0.04 * Parts of TDI were calculated at an isocyanate index of 85.

Characterization of flexible polyurethane foams. The morphology of the foams was studied

using a scanning electron microscope (JEOL JSM-5410LV) at the accelerated voltage of 15 kV.

The physical-mechanical properties of foams were determined following the appropriate standards;

the apparent density according to ISO 845:2006 (E), the tensile strength according to ISO

1798:2008, the tear strength according to ISO 8067:2008 (E) and the indentation hardness

according to ISO 2439:2008 (E).

Advanced Materials Research Vol. 911 353

Results and discussion

Characterization of palm oil-based polyol. The chemical structure of palm oil-based polyol was

analyzed using a FTIR technique. The FTIR spectra of palm oil-based polyol and palm oil are

shown in Fig. 1. The palm oil-based polyol shows a broad peak corresponding to OH-stretching at

wavenumbers around 3400 cm-1

. Furthermore, the obtained palm oil-based polyol part was

completely soluble in ethanol. The results indicated that the transesterification reaction transformed

the palm oil into polyol. The obtained palm oil-based polyol was a pale yellowish wax-like

compound at room temperature and it had a hydroxyl number of 140 mg KOH/g. GPC analysis

showed that this polyol had the number average molecular weight of 967 g/mol. Compared with the

prepared polyol, the replaced petrochemical polyol (VORANOL 2070) has lower molecular weight

(700 g/mol), higher hydroxyl number (238 mg KOH/g), and lower viscosity (245 mPa s). In

addition, the functionality (f) of palm oil based-polyol is lower (f = 2.41) than that of the replaced

polyol (f = 2.97).

Characterization of flexible polyurethane foams. This research was carried out to study the effect

of palm oil-based polyol concentration on physical-mechanical properties and cellular structure of

flexible PU foams. The foams were prepared by substituting the conventional petrochemical polyol

(VORANOL 2070) with palm oil-based polyol of 10, 20, 30, 40, and 50 wt% without changing the

concentrations of other ingredients except TDI amount which was calculated at an isocyanate index

of 85. It was found that all the prepared PU foams, except the one that contained palm oil-based

polyol of 50 wt%, were prosperously obtained. Hence, the morphology and properties of the foam

modified with palm oil-based polyol of 50 wt% were not evaluated.

The scanning electron microscope (SEM) can be used to observe the morphology of foams and

the SEM micrographs of the prepared foams are displayed in Fig. 2. All foams have semi-open cell

structure and the cells are mostly spherical in shape. The reference foam prepared using only

petrochemical polyols has more blow holes and a larger cell size than those of the foams containing

palm oil-based polyol. Meanwhile, as the concentration of palm oil-based polyol increased up to 20

wt%, the foams show a smaller cell size as well as more uniform in cellular structure. This may be

the effect of higher viscosity of palm oil-based polyol compared to the viscosity of the replaced

petrochemical polyol or due to the presence of palm oil-based polyol which can act as an additional

surfactant [6]. However, increasing palm oil-based polyol up to 30 and 40 wt%, the foam cells tend

to be less uniform.

Fig. 1 FTIR spectra of palm oil (a), and palm oil-based polyol (b)

354 Key Engineering Materials - Development and Application

Fig. 2 SEM micrographs of flexible PU foams: (a) TP-STD, (b) TP-10, (c) TP-20, (d) TP-30, and

(e) TP-40

The physical-mechanical properties of the prepared PU foams are presented in Table 2. The PU

foams containing palm oil-based polyol exhibit higher apparent densities than that of reference

foam. Besides, the apparent density of the foam increased as the concentration of palm oil-based

polyol increased and is in the range of 49.22-53.18 kg/m3. This may be the effect from the

decreased cells size with the increasing content of palm oil-based polyol, i.e., the increase in

thickness of cell wall or polymer matrix in same volume [7]. The results can also be related to

higher viscosity of palm oil-based polyol compared with that of substituted polyol, VORANOL

2070 [6].

The indentation hardness is a measure of the load-bearing properties of flexible foams for use in

cushioning applications [8]. It is the total force required to produce a specified indentation of a

sample under the standard conditions. High densities generally result in improved load-bearing

properties [9].The support factor or SAG factor or compressive deflection coefficient is the ratio of

65% indentation force deflection (IFD) to the 25% IFD. This factor can be used to indicate the

cushioning quality; higher support factors indicate better cushioning quality [9]. The data in Table

2 shows that both the 25% and 65% indentation hardness decrease with the increasing content of

palm oil-based polyol. Nevertheless, the support factors of all foams containing palm oil-based

polyol were higher than that of reference foam indicating better cushioning quality. Moreover, the

support factor increased as the amount of palm oil-based polyol increased. This may be due to

higher densities of foams when more palm oil-based polyol was added. It can also be related to

lower cross-linking density caused by lower functionality and hydroxyl number of palm oil-based

polyol.

Both the tensile and tear strengths of the PU foams modified with 20 wt% of palm-oil based

polyol were higher than those of reference foam as shown in Table 2. This result may be the effect

from different type of polyol, i.e., palm oil-based polyol is a polyester polyol while the replaced

petrochemical polyol is a polyether polyol. Normally, polyester-based flexible foams combine high

levels of tensile properties [8]. It also may be due to the more uniformity in cell structure of foam

containing palm oil-based polyol of 20 wt% (Fig. 2). On the other hand, with the amount of palm

oil-based polyol of 40 wt%, the tensile and tear strengths of PU foams decreased significantly,

which probably due to the decrease in cross-linking density.

a b c

d e

Advanced Materials Research Vol. 911 355

Table 2 Properties of flexible polyurethane foams

Properties TP-STD TP-10 TP-20 TP-30 TP-40

Density (kg/m3) 49.22 50.47 51.04 51.63 53.18

25% Indentation hardness (kPa) 3.08 2.73 2.80 1.92 1.66

65% Indentation hardness (kPa) 5.92 5.33 5.64 4.23 4.17

Support factor 1.92 1.95 2.01 2.20 2.51

Tensile strength (kPa) 96.851 95.707 105.33 94.143 50.199

Tear strength (N/cm) 6.28 6.03 6.96 5.50 2.63

Conclusions

The results showed that polyol derived from palm oil by transesterification with glycerol can be

used as a replacement for conventional petrochemical polyol to produce flexible PU foams.

Substituting palm oil-based polyol resulted in smaller cell size, higher apparent density, lower

indentation hardness, and higher support factor of PU foams. In the case of the foam containing

palm oil-based polyol of 20 wt%, the tensile strength significantly increased in comparison with

reference foam.

Acknowledgments

The authors appreciatively acknowledge Inoac (Thailand) Co. Ltd. for financial support. The

authors also gratefully acknowledge Department of Materials Science, Faculty of Science,

Chulalongkorn University for instrument support and Bangkok Foam Co. Ltd. for material and

instrumental support.

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