Universidade Federal de Santa Maria
Ci. e nat., Santa Maria, V. 41, e44, 2019
DOI: http://dx.doi.org/10.5902/2179460X39155
Received: 20/07/2019 Accepted: 28/08/2019
Chemestry
Epoxidized corn oil polyol-based composites polyurethane flexible foams, preparation, and characterization
Simone A. SilvaI
Luiz P. RamosII,
Ronilson V. BarbosaIII,
Sônia F. ZawadzkiIV
I Laboratório de Materiais Poliméricos, Department of Chemistry, Federal University of Parana, Curitiba, Brazil- simoneadriane@yahoo.com.br
II Centro de Pesquisa em Química Aplicada, Department of Chemistry, Federal University of Parana, Curitiba, Brazil- luiz.ramos@ufpr.br
IIILaboratório de Materiais Poliméricos, Department of Chemistry, Federal University of Parana, Curitiba, Brazil – ronilson@ufpr.br
IV Laboratório de Materiais Poliméricos, Department of Chemistry, Federal University of Parana, Curitiba, Brazil - zawadzki@ufpr.br
Abstract
Corn oil is a renewable resource useful for the preparation of polyols used in syntheses of polyurethane. The goal was to synthesize composites flexible foams from corn oil polyol obtained by epoxidation and 4,4’ – methylenebis (phenyl isocyanate) and evaluate their properties. It was used as filler inorganic clay (from up 2 to 5% of silica fume, montmorillonite, and bauxite). The samples were analyzed by DSC, TG, compressive properties and SEM analyses. On DSC analysis was observed the negative temperature of the glass transition for all the samples, and thermally stable up to 200°C. The composites flexible foams showed weakly resistance in the compressive strength and SEM test the specimens exhibited opened cells.
Keywords: Corn oil, Flexible foam polyurethane, Composites
1 Introduction
Vegetable oils are promising alternatives to petrochemicals for production of polymers and vegetable-based polyol. They are composed by triglycerides, i.e. a glyceride in which the glycerol is esterified with fatty acids. The most common chain lengths in these fatty acids have 18 or 20 carbon atoms, which can be either saturated or unsaturated. The major components of the corn oil are oleic, linoleic, and linolenic acid (ZHANG and MADBOULY 2016; RATHORE, NEWALKAR, and BADONI 2016; MIAO et al. 2014; FERRER, BABB, and RYAN 2008; KOTWAL et al. 2009; SINHA RAY and BOUSMINA 2005). Due to the hydrophobic nature of the triacylglycerols (TAG), the produced polymers have some excellent chemical and physical properties such as enhanced hydrolytic and thermal stability (CAMPANELLA and BALTANÁS 2006; REZENDE et al. 2005). However, most vegetable oil-based polyols currently utilized to produce polymers need some chemical modification. Several synthesis pathways have been successfully developed to prepare vegetable oil derivatives, such as, the epoxidation reaction, which is generally performed using organic peracids (usually peracetic acid) prepared in situ via the attack on a carboxylic acid with H2O2, in aqueous solution (HAZMI et al. 2013; JIANG et al. 2012; TAKEICHI, KANO, and AGAG 2005; SUN et al. 2011; CHUA, XU, and GUO 2012; SOUZA et al. 2012).
Polyurethane is based on the reaction between organic isocyanates and polyols, a class of polymers that shows versatile properties and it can be used as flexible or rigid foams, adhesives, elastomers, fibers, etc (ZHANG and MADBOULY 2016; BUTRUK et al. 2013; SONNENSCHEIN and WENDT 2013; CINELLI, ANGUILLESI, and LAZZERI 2013; SHARMA and KUNDU 2008; MUKHOPAHYAY, NORONHA, and SURAISHKUMAR 2007; BELGACEM and GANDINI 2008).
Flexible foams can be used as filters impregnated or not of the fillers for trapping heavy metals. The use of sorption processes in the treatment of wastewater containing heavy metals has been quite attractive, especially when compared to other methods, such as electrodialysis, reserve osmosis, ultrafiltration or adsorption employing bioadsorbents (SEMENZATO et al. 2009; ANJANEYULU, MARAYYA, and RAO 1993).
The goal of this work was to synthesize and evaluate the properties of flexible polyurethane foams which were based on epoxy-hydroxyl ester corn oil polyol (ECO) and 4,4’ – methylenebis (phenyl isocyanate) (MDI). It was also prepared PU foams composites with inorganic clays (silica fume, montmorillonite, and bauxite). The characterization of the polymers systems was done using morphological, thermal and mechanical studies.
2 Experimental Procedures
2.1 Materials
Refined corn oil (i.e., degummed, neutralized, bleached and deodorized), provided by Corn Products Brasil was used as received. Ethanol (99,5%), sodium bisulfite (90%), potassium hydroxide (85%), purchased from Biotec, formic acid (acs, 85%), hydrogen peroxide (30 wt%), cyclopentane (99%), diethylene glycol (99%), hydrogen peroxide (30%), were purchased from Vetec, polyethylene glycol MM= 400, silicon oil, glycerol (99,5%) were purchased from Synth. Polymeric diisocyanate 4,4’ – methylenebis (phenyl isocyanate), (90%) was purchased from Arinos. Tin octanoate purchased from Evonik and pentametthyletilenetriamine (PMDETA, 99%) purchased from Sigma- Aldrich. All the chemicals were used as received.
2.2 Synthesis of the epoxy-hydroxyl corn oil polyol (ECOP)
To the corn oil (CO) a solution of formic acid and hydrogen peroxide (molar ratio:1 mol of double bonds: 3 mol of formic acid) was added. The 30% hydrogen peroxide was added dropwise (molar ratio: 1 mol of double bonds: 1.5 moles of hydrogen peroxide v/v) at room temperature for 30 minutes under mechanical stirring. After the complete addition, the mixture was heated to 65 °C for 2h, and then the reaction the organic phase in solvent dichloromethane was collected, washed with solution 10% sodium bisulfite then dried in sodium sulfate, and the solvent was removed under reduced pressure (MONTEAVARO et al. 2005). The polyol obtained was characterized by Fourier transform infrared (FTIR) spectroscopy using a Biorad, model Excalibur Series, nuclear magnetic resonance (NMR), 1H and 13C the spectra were acquired in CDCl3, 0.1% TMS, at room temperature on Bruker DPX 200 NMR spectrometer. The acid (ASTM D664), iodine (AOCS (Cd 1-25), and hydroxyl (ASTM D 1957-86) values determined. The data are the previous paper of Souza (2012) (SOUZA et al. 2012).
2.3 Compositions of flexible PU foams based on epoxy-hydroxyl corn oil polyol (ECO) and inorganic clays
The flexible polyurethane foams were obtained using the one-shot method, and the polymerization was conducted directly on a suitable vessel. The foams were made employing the considering range of polyols PEG 400: ECO: 11:9 and 13:7 v/v (mL), Table 1. All components: crosslinking agent (GLY) or chain extender (DEG), expansion agent (water), inorganic clays (bauxite, montmorillonite and fumed silica), surfactant (silicon) were added stoichiometrically in relation to the polyol. For the formulations of these foams, it was used a mixture of catalysts, tin octanoate, and N, N, N’, N’’, N’’ – pentamethylenetriamine (PMDETA), finally, 4,4’ – methylenebis (phenyl isocyanate) (MDI) was added. The polymeric blend remained in the mold for 24 hours for complete cure. After this period, the flexible foams were cut and analyzed. Eight formulations were chosen according to the visual morphological aspect. The pure foams and their composites were submitted to the thermal tests using the differential scanning calorimetry (DSC) – Netzsch 200F3 DSC, and Thermogravimetric analysis (TG) – Toledo TGA/ SDTA techniques and scanning electronic microscopy (SEM).
2.4 Differential scanning calorimetry (DSC)
The specimens were subjected to the following temperature programming in an inert atmosphere (50 mL.min-1): 1) cooling to – 100 °C; 2) heating at 100 °C; 3) isotherm for two minutes; 4) cooling to – 100 °C; 5) heating at 100 °C. It was considered the data generated from the second heating ramp. The experiments of the polyol and composites flexible foams were in a Netzsch, calorimeter DSC 200F3 Maia model.
2.5 Thermogravimetric analysis (TG)
Selected samples were subjected to the thermal degradation in an oxidizing atmosphere under a heating flow of 10 °C.min-1, from room temperature to 600ºC. The experiments of the composites foams were done in a Mettler Toledo TGA/SDTA851 model.
2.6 Compressive mechanical method- ASTM D 3574 – 95 Test C
The mechanical properties of the flexible foams were measured an Instron universal testing machine (model 4467) adapted to the ASTM D 3574 – 95 Test C standards. Samples were prepared in cylindrical specimens of (60 mm x 50mm). The cross-head speed was 4 mm.min-1, with a load cell of 100 kgf. The load was applied until the foam was compressed to approximately 30% of its original thickness. The strengths of three identical specimens per specimen were tested and the results averaged.
2.7 Scanning electron microscopy (SEM)
The small fragments of approximately (30 mm x 10mm) of the polyurethane foam specimens were dipped in liquid nitrogen for 10 minutes. They were fractured and fixed on the specific metallic support and coated with gold. The metalized specimens were visualized by scanning electron microscope – Baltec, SD005 Sputter Coater model and photographed by electronic microscope Jeol, JSM- 6360V model to evaluate the morphology of the flexible foams.
3 Results and Discussion
The polyurethane foams prepared just one corn oil-based polyol (ECOP) showed a rigid foam aspect, as described in the literature (CARDOSO, NETO, and VECCHIA 2012). This fact is due to the high polyol hydroxyl value. For this reason, the foams showed an undesired performance.
Therefore, they were prepared with new formulations using a mixture of the polyols: ECO polyol and petrochemical polyol (polyethylene glycol – PEG 400 HV = 145.47 g KOH.100 g-1) with these they were obtained flexible foams, the compositions showed in Table 1.
Table 1 – Compositions of the flexible foam PEG 400/ ECO and clays (silica fume (SI), bauxite (BAUX), and montmorillonite (MMT)
Foam |
Polyol |
MDI |
DEG1 |
GLY2 |
Inorganic Clay |
|
|
|
PEG 400 (mL) |
ECOP (mL) |
(mL) |
(mL) |
(g) |
(%) |
|
PUE |
13 |
7 |
10 |
0.5 |
--- |
0 |
|
PUF |
11 |
9 |
10 |
--- |
0.6 |
0 |
|
PUSI |
13 |
7 |
10 |
0.5 |
--- |
2 |
|
PUSI |
11 |
9 |
10 |
--- |
0.6 |
2 |
|
PUBAUX |
13 |
7 |
10 |
0.5 |
--- |
5 |
|
PUBAUX |
11 |
9 |
10 |
--- |
0.6 |
5 |
|
PUMMT |
13 |
7 |
10 |
0.5 |
--- |
5 |
|
PUMMT |
13 |
7 |
10 |
--- |
0.6 |
5 |
For all formulations, secondary reagents were quantified in H2O (0.4 mL), silicon (0.36g) catalyst system: tin octanoate (2 drops) and PMDETA (2 drops). 1 – DEG – diethylene glycol – chain extender; 2 – GLY – glycerol – crosslinking agent.
3.1 Differential scanning calorimetric
The ECOP showed two melting temperature Tm = – 6.6 and 7.3°C (Table 2), can be attributed to the complexity and diversity of the chemical structure of corn oil (SONNENSCHEIN and WENDT 2013). Figure 1 shows the curves obtained by DSC for samples. It was observed the foams with a higher crosslinking degree have bigger glass transition temperature (Tg) than lesser crosslinking degree foams, the ratio 11: 9 (PEG/ECOP, respectively) polyols provides a high crosslinking bond in the PU foams. Unfilled foams have lower Tg then filled foams, this behavior can be explained by the good interaction inorganic clay between polymeric matrix, resulting in rising glass transition temperature of PU materials. Despite the range of the glass transition temperature for all the samples, it is negative. This fact should be explained due to the presence of with different moieties of saturated fatty acids of different chain lengths not removed previously, beyond, pendants chains of the polyol (secondary hydroxyl), they work as plasticizers (CORCIONE and MAFFEZZOLI 2009; FASINA et al. 2008; MANO and MENDES 2004; WIRPSZA 1993).
Table 2 – Glass transition temperature (Tg) and melting temperature (Tm) values to foams and ECO polyol determined by differential scanning calorimetry.
|
Samples |
Tg (°C) |
Tm (°C) |
|
ECOP |
--- |
- 6.6 e 7.3 |
|
PUE (PEG/ECOP /DEG) |
-18.5 |
--- |
|
PUF (PEG/ECOP/GLY) |
-15.3 |
--- |
|
PUSI (PEG/ECOP/ DEG/ SI 2%) |
-7.9 |
--- |
|
PUSI (PEG/ECOP/GLY/ SI 2%) |
-5.8 |
--- |
|
PUBAUX (PEG/ECOP/DEG/ BAUX 5%) |
-6.9 |
--- |
|
PUBAUX (PEG/ECOP/GLY/ BAUX 5%) |
-3.0 |
--- |
|
PUMM (PEG/ECOP/DEG/ MMT 5%) |
-10.2 |
--- |
|
PUMMT (PEG/ECOP/GLY/ MMT 5%) |
-8.1 |
--- |
Figure 1 – Differential scanning calorimetry of the PEG/ECOP filled and unfilled PU foams
.
3.2 Thermogravimetric analysis (TG)
The TG curves of filled and unfilled PU foams (Figure 2) shows degradation temperatures are summarized in Table 3. Foams based on vegetable polyol, which has secondary hydroxyl groups can exhibit until three steps of degradation. The first step refers to the breakdown of the urethane linkages, and the second and third steps are related to the decomposition of the polyol carbon chain (CORCIONE and MAFFEZZOLI 2009; NARINE et al. 2007). PU samples with a crosslinking agent (GLY) and bigger polyol ratio (11: 9) displayed higher initial temperatures of degradation compared to the polyurethane-based in diethylene glycol (DEG) as chain extender, indicating the higher thermal stability as a result of crosslinking. Increasing the filler content, the thermal stability increased suggesting a good filler-matrix interaction. These results are an agreement to the DSC data for BAUX and MMT fillers contributed to the higher thermal stability of the foam, and this may be due to better distribution and larger amount filler (%) than silica fume in the polymer. The silica fume was difficult to homogenize in the chemical reagents mix because it has very low density and bulky.
Figure 2 – Thermogravimetric curves obtained under the oxidizing atmosphere of the PEG/ECOP filled and unfilled PU foams.
Table 3 – Values obtained of the thermogravimetric analyses (TG) for PU flexible foams-based on corn oil polyol
|
Samples |
T1* |
T2* |
T3* |
|
PUE (PEG/ECOP/DEG) |
292 |
--- |
522 |
|
PUF (PEG/ECOP/GLY) |
305 |
406 |
523 |
|
PUSI (PEG/ECOP/DEG/SI 2%) |
297 |
--- |
516 |
|
PUSI (PEG/ECOP/GLY/SI 2%) |
302 |
403 |
543 |
|
PUBAUX (PEG/ECOP/DEG/ BAUX 5%) |
283 |
--- |
484 |
|
PUBAUX (PEG/ECOP/GLY/BAUX 5%) |
295 |
--- |
502 |
|
PUMMT (PEG/ECOP/DEG/MMT 5%) |
292 |
--- |
482 |
|
PUMMT (PEG/ECOP/GLY/MMT 5%) |
308 |
387 |
510 |
3.3 Compressive mechanical method- ASTM D 3574 – 95 Test C
Figure 3 displays compressive strength- strain curves for the PU specimens based on epoxy-hydroxyl corn oil polyol, all the foams showed low strength to compression. The inorganic clays did not contribute to upgrading the performance of the flexible foams, comparing with the unfilled foams on resistance to compressive strength. The better strength is the PUE (PEG/ECOP/DEG). All foams behave as hard rubber (KANDANARACHCHI, GUO, and PETROVIC 2002).
Figure 3 – Compressive strength versus strain of PEG/ECOP filled and unfilled PU foams
3.4 Scanning electronic microscopy (SEM)
SEM micrographs of the cross-section of PU foams, based on PUE (Figure 4 (a) PEG/ECOP /DEG) showed irregular shape, size, closed cells, and the surface of the walls showed slightly rough. The composites flexible foams presented regularity of opened and closed pores (Figure 4 (b) PEG/ECOP/DEG/Si 2%) and it was not observed filler grains in the outer walls of the cell. It was noticed that increasing the filler content caused a deformity in the cells of the PUBAUX (Figure 4 (c) PEG/ECOP/DEG/BAUX 5%) and PUMMT (Figure 4 (d) PEG/ECOP/GLY/MMT 5%). The literature report regularity of the cells, different from the obtained epoxidized corn oil polyol in these PU flexible foams (JI et al. 2015).
Figure 4 – SEM micrographs of PU foams: (a) PUE (PEG/ECOP/DEG), (b) PU/SI (PEG/ECOP/DEG/Si 2%), (c) PU/BAUX (PEG/ECOP/DEG/BAUX 5%) and (d) PU/MMT (PEG/ECOP/GLY/MMT 5%)
4 Conclusion
The epoxidation is an efficient methodology to obtain polyols of the vegetable oils, as epoxidized corn oil (ECOP) synthesized in this work. Due to high hydroxyl value, consequently higher crosslinking degree, it was not possible to obtain flexible foams. Therefore, it was necessary to add petrochemical polyol, for efficient achievement of flexible foams. The filled specimens and that ones with higher crosslinking degree showed glass transition temperatures slightly higher than unfilled specimens and with the lower crosslinking degree. The thermogravimetric analysis showed an improvement on the thermal resistance of the most reticulated foams and for foams with most filler content. Results of DSC and TG suggested good compatibility between inorganic clays- polyurethane matrix and the bigger ECO content. Flexible foams showed low strength to compression, the incorporation of inorganic clays did not contribute to upgrading the performance of the flexible foams. The SEM exhibited a rough surface on composites, and the increase the filler content caused deformation in the cells.
Acknowledgments
This work was supported by research grants from CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico), Corn products Brasil, Laboratório de materiais poliméricos- Lamap, Centro de Pesquisa em Química Aplicada – Cepesq, TG analysis, Laboratório de análises de minerais e rochas – Lamir, SEM analysis, Centro de miscroscopia óptica – UFPR and mechanical analysis- Lactec.
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