Influence of Palm Oil-Based Polyol on the Properties of Flexible Polyurethane Foams
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- Pawlik, H. & Prociak, A. J Polym Environ (2012) 20: 438. doi:10.1007/s10924-011-0393-2
This paper describes the effect of the modification of polyurethane system with palm oil-based polyol on the cell structure and physical–mechanical properties of polyurethane foams. Flexible polyurethane foams were prepared by substituting a part of petrochemical polyether-polyol with the palm oil polyol. Selected physical–mechanical properties of these foams were examined and compared to the properties of reference foam. The properties such as apparent density, tensile strength, elongation at break, resilience, compressive stress and thermal stability were analyzed. It was found that the modifications of polyurethane formulation with palm oil polyol allow to improve selected properties of final products.
KeywordsRenewable raw materialsPalm oil-based polyolPolyurethane flexible foamsPhysical–mechanical properties
Polyurethanes (PUR) are one of the most versatile polymeric materials. They can be used as foams, elastomers, coatings, adhesives and sealants due to the wide range of their properties. Flexible and rigid foams have the largest market of PUR products .
All PUR products relies on petroleum oil as the feedstock for their major raw materials: polyols and isocyanates. The rising prices of petrochemical raw materials and decreasing deposits of petroleum resources cause the increasing of the interest in the applications of biodegradable and renewable polymeric materials .
Developing bio-renewable feedstock from vegetable oils for PUR manufacturing becomes highly desirable for both economic and environmental reasons. The derivatives of vegetable oils exhibit capacity for biological degradation . Moreover, life cycle assessment of vegetable oil polyols shows environmental benefits like reduction in the demand of fossil resources and formation of very low greenhouse gas emission . Therefore, the hydroxylated derivatives of vegetable oils are interesting and alternative replacements for petrochemical polyols in the synthesis of PUR materials [5–9].
Hydroxyl groups in polyol components are required in order to react with isocyanate and to form urethane bonds. Most of vegetable oils do not contains hydroxyl groups. Prior to their use for polyurethanes preparation they must be converted into a polyol by chemical modification.
Nowadays, several methods for conversion of vegetable oils into polyols are known. All of them are based on chemical modification of ester groups or double bonds in unsaturated chains of fatty acids. The most common conversion methods are direct oxidation , ozonolysis , epoxidation followed by ring opening , hydroformylation , and transesterification . Each of them has advantages and disadvantages . Various types of vegetable oils differ in the composition of saturated and unsaturated fatty acids . The diversity in unsaturation degree allows the synthesis of oil polyols with variable hydroxyl number .
Polyols applied in flexible foams should have low hydroxyl values (generally LOH < 100 mg KOH/g) and/or high molecular weights (generally Mn between 3,000 and 6,000 g/mol) to decrease cross-linking density and to improve elasticity of final products. Palm oil is a readily available renewable agricultural raw material, which can be used for the synthesis of polyols suitable for the preparation of flexible or semi-rigid PUR foams [16, 17]. Analysis of the content of unsaturated bonds in various oils confirmed that palm oil is a convenient raw material for the synthesis of the polyols with low and medium content of hydroxyl groups . Low content of unsaturated bonds (LI = 50–55) in palm oils allows to obtain (using the epoxidation method followed by ring opening) the products with hydroxyl numbers lower than 200 mg KOH/g and very low content of unreacted double bonds . Additionally, palm oil is the cheapest among the ones currently produced vegetable oils and had the largest contribution of the total production in 2010. Palm and palm kernel oils production was recorded at 53.6 million tonnes, which represents ca. 37% of the global vegetable oil market .
Palm oil-based polyols can be synthesized using different methods. The examples of palm oil applications in the synthesis of polyols for the preparation of rigid polyurethane foams can be found in literature. Such polyols are usually obtained by transesterification with the use of various agents such as diethanolamine (DEA) [19, 20].
The polyol from palm oil can be obtained also using the method, which involves the epoxidation of double bonds followed by oxirane ring opening by various agents. In the last few years, several works have been aimed at the use of such polyols for the preparation of flexible foams [21, 22]. These polyols have a hydroxyl number in the range 70–130 mg KOH/g . Using the glycols in the second step of this method it is possible to obtain palm oil-based polyols with primary and secondary hydroxyl groups. Another advantage of this method is the use of whole molecules of triglycerides in the preparation of polyol, thereby the resulting products are characterized by a high content of renewable raw materials. The content of hydroxyl groups in the oil polyols can be designed by choosing appropriate conditions of the epoxidation reaction . The application of different alcohols as ring-opening agents and chain extenders allows affecting the content of soft segments in PUR foams .
In this work, flexible foams were prepared by replacing up to 15% of conventional petrochemical polyether polyol with palm oil polyol. The influence of such modification on the selected physical–mechanical properties of final products is discussed.
palm oil-based polyol prepared on laboratory scale in Cracow University of Technology
Rokopol G-1000, polyether polyol (PCC Rokita S.A.)
Alfapol M-111, polyether polyol (ALFA Systems Sp. z o.o. Brzeg Dolny)
Alfapol T-501, polyester polyol (ALFA Systems Sp. z o.o. Brzeg Dolny)
TDI, toluene diisocyanate (80:20 wt% mixture of 2,4- and 2,6-isomers, ZACHEM S.A.)
DABCO T-9, tin catalyst (Air Products and Chemicals, Inc.)
DMCHA, amine catalyst (Texaco Chemical Deutschland, GmbH)
DABCO BL-11, amine catalyst (Air Products and Chemicals, Inc.)
Niax Silicone L-627, surfactant (Momentive Performance Materials)
Three commercially available petrochemical polyols: Alfapol M-111, T-501 and Rokopol G-1000 were selected for the preparation of reference flexible foams. These polyols were chosen in order to obtain flexible polyurethane foams (PURFs) with low resilience properties.
Characterization of polyols
Palm oil polyol
Number average molecular weight (Mn), g/mol
Hydroxyl number, mg KOH/g
Water content, wt%
Viscosity at 25 °C, mPa s
650 in 75 °C
Toluene diisocyanate (TDI) with NCO content 46 wt% was used as the isocyanate component for the preparation of PUR system. Water was applied as a chemical blowing agent. Gelling (DABCO T-9, DMCHA) and blowing (DABCO BL-11) catalysts and silicone-based surfactant (Niax Silicone L-627) were added to formulation in order to prepare foams with an open cellular structure.
Flexible polyurethane foams formulations
M-111, T 501, G1000
The prepared foams were conditioned at 22 °C and 50% relative humidity for 24 h. After that they were cut to specimens for testing of physical and mechanical properties.
Selected physical–mechanical properties of PURFs were measured according to the appropriate standards; the apparent density PN-EN ISO 845:2000; the compression value at 40% strain (CV40) PN-EN ISO 3386-1:2000, tensile strength and elongation at break PN-EN ISO 1798:2001. The cellular structure images of PURFs were taken using an optical microscope with a video track (PZO Warszawa). Foam slices were cut after freezing the foam samples in liquid nitrogen. Aphelion™ software was applied to analyze the images of foam structures. Cell size (height and width) was determined, and then cross-section surface and cell anisotropy were calculated on the base of more than 300 cells. Anisotropy coefficient was calculated dividing the height by the width of the cell. The content of closed cells was determined according to PN-ISO 4590. Thermogravimetric analysis (TGA) was carried out by TG Netzsch thermogravimetric analyzer (TG 209) at the heating rate of 10 °C/min in the air atmosphere from 20 to 600 °C. The resilience of foams was investigated by ball rebound test according to PN-EN ISO 8307:2007. The test was carried out by dropping 3.18 mm diameter steel ball on a specimen from the fixed height (0.5 m) and determining the rebound height. Soft-segment (SS) glass transition temperatures were determined using dynamic mechanical analysis (TA Instruments—DMA Q800). Foam disks 12.5 mm (diameter) × 10 mm (thickness) were tested in sinusoidal oscillation mode between two parallel plates. Storage modulus (G’) was recorded at the frequency of 1 Hz in the range of temperatures from −100 to 200 °C. The temperature ramp rate was 3 °C/min.
Results and Discussion
The investigations were carried out to determine the influence of the different content of the palm oil polyol in PUR formulation on the mechanical properties of flexible foams. The attempts to replace the possibly large part of petrochemical polyol with the palm oil polyol without other changes the formulation were undertaken. Porous materials containing 5, 10, and 15 wt% of palm oil polyol in the polyol premix (component A) were successfully obtained. In the case of foams, that contained palm oil-based polyol in an amount exceeding 15 wt% shrinkage effects were observed. Therefore, those materials were not evaluated. It was found that significant changes in the foam formulation are required in order to obtain foams with higher content of palm oil polyol. Making changes in such foam formulation is necessary due to different structure and nature of palm oil-based and petrochemical polyols. In order to eliminate unfavorable effects as shrinkage the correction of the foam formulation, including quantities of used catalysts and surfactants, have to be made, however, such modification excludes the direct comparison of such materials.
The investigated foams slightly differed in apparent density, therefore their mechanical properties could be directly compared. It was found that the increase of palm oil polyol content in the formulation causes higher compressive stress values of the modified foams. The compressive stress values (measured in both directions, parallel and perpendicular to the foam rise) of the foams modified with palm oil polyol were higher than that of the reference foam. The content increase of palm oil polyol up to 15 wt% in the polyol premix caused the higher (almost three times) the compressive stress at 40% in comparison to reference foam (Fig. 2).
The resilience is extremely important in the case of the specific type of flexible foams, so called viscoelastic foams, that characterized by higher energy absorption. The resilience is affected by the morphology of foam, specifically by the ratio between soft and hard segments. The ratio of soft and hard segments, their distribution and separation in the polyurethane matrix significantly affects viscoelastic properties of final products . These characteristics are reflected in the tan δ values and ball rebound results .
The properties of foams considerably depend on the raw materials, especially polyols which are used in PUR formulations. Various chemical groups such as urethane, urea, allophanate and others, are identified in PUR materials. The range of thermal decomposition of PUR foams is strongly influenced by the physical characteristics of the polyurethane matrix, mainly, internal crosslinking, hydrogen bonds and the inner crystalline structure . The thermal decomposition of polyurethane matrix occurs in the random places by one or more of the following three mechanisms: depolymerisation (dissociation to the isocyanate and polyol precursors), dissociation (to a primary amine, an olefin and CO2) and elimination of CO2 leading to the replacement of the urethane bond by secondary amine groups .
Temperatures (°C) at which weight loss reached the specified levels
Selected parameters of the cellular structure of flexible polyurethane foams
Average values of parameters of the cells
Cell cross-section surface, mm2
Cell height, mm
Cell width, mm
The presented results confirmed that polyol synthesized using palm oil can be successfully applied for modification of flexible polyurethane foams. The modifications of polyurethane formulations with palm oil polyol allowed improvement of selected properties of flexible polyurethane foams.
The replacement of petrochemical polyol with palm oil polyol up to 15 wt% in the polyol premix resulted in more uniform cell size, increased apparent density and considerable improvement of compressive stress. Increase of the content of palm oil polyol strongly affects on the tensile strength of the flexible polyurethane foams. In the case of the foam modified with 15 wt% of palm oil polyol, the considerable increase (even 80%) of tensile strength is possible in comparison to the reference foam, while the value of elongation at break may be kept on similar level.
The foams modified with palm oil polyol up to 15 wt% only slightly change the ability of energy absorption. The resilience increases from 11.3% for reference foam to 13.8% for the foams modified with 15 wt% of palm oil polyol. The modification of polyurethane systems using palm oil polyol also slightly decreases the Tg value of the foams from −35 °C for reference foam to −42 °C for the foam modified with 15 wt% of palm oil polyol.
The presence of palm oil-based polyol in the foam structure allows to decrease the rate of weight loss during the thermal decomposition.
Research were co-financed from means of European Regional Developed Fund and from means of State Budget as a part of Operational Programme Innovative Economy for 2007–2013 Contract no UDA-OP-IE.01.03.01-00-092/08-00, Annexe to the contract no UDA-OP IE.01.03.01-00-092/08-01 from 15 September, 2009, Annexe no UDA-OP IE.01.03.01-00-092/08-02 from 26 April, 2010 “New eco-friendly polymer composites with renewable sources” realized as a part of Measure 1.3 OP IE, Sub-measure 1.3.1.
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