Oenothera biennis seed oil as an alternative raw material for production of bio-polyol for rigid polyurethane-polyisocyanurate foams

Industrial Crops & Products 126 (2018) 208–217

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Oenothera biennis seed oil as an alternative raw material for production of bio-polyol for rigid polyurethane-polyisocyanurate foams

T

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Joanna Paciorek-Sadowska, Marcin Borowicz , Bogusław Czupryński, Ewa Tomaszewska, Joanna Liszkowska Department of Chemistry and Technology of Polyurethanes, Technical Institute, Faculty of Mathematics, Physics and Technical Science, Kazimierz Wielki University, J. K. Chodkiewicza Street 30, 85-064 Bydgoszcz, Poland

A R T I C LE I N FO

A B S T R A C T

Keywords: Oenothera biennisseed oil Polyurethane-polyisocyanurate foam 2.2′-mercaptodiethanol Bio-polyol Foam properties

The aim of this article is to discuss a process of obtaining a new bio-polyol based on an oil from Oenothera biennis seeds and 2,2′-mercaptodiethanol (2,2′-MDE) and its use for rigid polyurethane-polyisocyanurate (PUR-PIR) foams. The synthesis of the polyol was carried out with a two-step method. Firstly, the double bonds of unsaturated fatty acid residues were oxidized and subsequently the epoxide rings were opened by 2,2′-MDE. The properties of the obtained bio-polyol were examined for its use as a raw material for rigid polyurethane-polyisocyanurate foams, i.e. hydroxyl value, acid value, density, viscosity, pH, water content. Spectroscopic studies (FTIR, 1H NMR and 13C NMR) were also performed. Aforementioned studies confirmed the assumed chemical structure of the new polyol. The formulations of rigid foams containing from 0 to 0.3 mass equivalents of the new bio-polyol were arranged on the basis of obtained results. A significant impact of the new bio-polyol on functional properties of foams was noted: apparent density, compressive strength, brittleness, absorbability, water absorption and flammability. Modified foams had better functional properties than the reference foam.

1. Introduction “At the current level of civilization, sustainable development is possible, it’s a development in which the demands of the present generation can be met without diminishing the opportunities of future generations to satisfy them” (Gerwin, 2008). The quote from the WCED report from 1987 contains the principle of sustainable development. The doctrine presupposes a balance between three factors: economy, environment and society. It is necessary for running the economy in a way that does not impend environmental resources (Bukowski, 2009). This approach, in relation to polyurethane materials, can be found at the end of the 20th century. The basic environmental problem resulted from the production of foamed materials was the use of CFCs (chlorofluorocarbons). These compounds significantly damaged the Earth’s ozone layer. Also raw materials being used as of yet were obtained mainly from the processing of fossil raw materials (Prociak, 2008a). A number of works raises the issue of the use of natural raw materials as substitutes for the production of polyurethane (PU) materials. Random direction is a replacement of petrochemical withdrawal of compounds that are toxic for the environment polyols by bio-polyols

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made from vegetable raw materials. Current trends are determined by the restrictions of law regulations related to, for example, withdrawal of compounds, which are toxic for the environment (Chemistry and Business, 2011). Vegetable oils is an extensive class of plant raw materials used in production of polyol components. Those oils are obtained by the process of pressing oil plant seeds. The obtained crude oil is additively subjected to filtration process in order to separate solid seed residues (Bartuzi, 2012). Significant increase in these commodities has been noted in recent years. The reason is their pro-ecological character and an alternative to shrinking reserves of crude oil and gas. The production of vegetable oils on an industrial scale is strictly determined by the geographical location and agricultural production in this area. In Europe, the most popular oils are: rapeseed and sunflower; in Asia: palm and coconut; in North America: soybean (Prociak, 2008b; Prociak et al., 2014). In terms of chemical structure, oil raw materials are a mixture of mono-, di- and triglycerides of unsaturated fatty acids (eg linoleic, linolenic, oleic) and small extent of saturated fatty acids (stearic, palmitic). Unfortunately, most of vegetable oils do not have any functional group able to react with an isocyanate raw material. Therefore, they are not appropriate for using as a polyol raw material

Corresponding author. E-mail address: [email protected] (M. Borowicz).

https://doi.org/10.1016/j.indcrop.2018.10.019 Received 27 April 2018; Received in revised form 5 October 2018; Accepted 6 October 2018 0926-6690/ © 2018 Elsevier B.V. All rights reserved.

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phosphorus and sulfur containing polyol to obtaining polyurethane foams. The presence of flame retardant elements has significantly reduced the self-extinguish time and weight loss after combustion. The authors showed that the improvement of fire resistance was caused by the formation of a protective layer on the foam surface resulting from the decomposition of phosphorus compounds (Bhoyate et al., 2018). Bio-polyol based on rapeseed oil has gained a significant value in recent years. It is used to obtain all types of PU foams, elastomers and adhesives (Prociak, 2008a, b). Prociak et al. developed and patented methods for obtaining polyols based on rapeseed oil for synthesis of rigid and flexible PU foams. They consisted of epoxidation reaction of double bonds of fatty acids and opening of epoxy rings with diethylene glycol (Pielichowski et al., 2010a, b). During the research, they used the obtained bio-polyol raw material in a mixture with petrochemical raw material. Foams based on bio-polyol were characterized by higher content of closed cells and lower thermal conductivity (Prociak, 2008a,b; Rojek and Prociak, 2012). Prociak et al. also analyzed the influence of the chemical structure of bio-polyols from rapeseed oil on the foaming process of RPUF. They showed that the method of synthesis of bio-polyol raw material, which affects the reactivity of polyurethane systems, has a significant influence on the chemical structure. Polyols obtained by the transesterification method are more reactive than those obtained by the method of opening the epoxide ring. In addition, the introduction of the amino group into the molecule significantly increases the reactivity of the bio-polyol (Prociak et al., 2018). Kurańska et al. did research on the replacement of petrochemical polyol for a biopolyol based on rapeseed oil. The works pertained to the production of rigid polyurethane and polyurethane-polyisocyanurate (PUR-PIR) foams. Obtained materials had similar properties (such as: thermal conductivity coefficient, water absorption, closed cell contents) like unmodified foams (Kurańska and Prociak, 2014; Prociak et al., 2017; Kurańska and Prociak, 2016). Kirpluks et al. conducted research on obtaining of highly reactive bio-polyols from rapeseed oil for the synthesis of RPUF intended for thermal insulation. For this purpose, they used two methods of synthesis: ring opening of the appropriate epoxidized oil and transesterification of glyceryl backbone with different polyfunctional alcohols. The obtained bio-polyols were characterized by high functionality and reactivity. RPUF obtained on the basis of them had a low thermal conductivity coefficient and a high content of closed cells (Kirpluks et al., 2018). The article raises the issue of the research on obtaining a new biopolyol based on Oenothera biennis seed oil and 2,2′-mercaptodiethanol (2,2′-MDE) and its use to produce rigid polyurethane-polyisocyanurate foams.

without proper processing. However, the literature also reports on using of these raw materials as natural, non-reactive additives to PU foams. For example, the using of a small amount of linseed oil in the PU system has extended technological times and improved mechanical properties such as compressive strength (Członka et al., 2018). Oenothera biennis, also called evening-primrose, is a plant, that comes from North America. It was brought to Europe as an ornamental plant in the 17th century. Currently, this plant has spread to all continents in except Antarctica (Fleischhauer et al., 2013). Its advantage is that it blooms even in adverse climatic conditions and on poorly fertilized areas. It is grown commercially in over 30 countries around the world, mainly in Canada, the United States and China (Eskin, 2008). Although the whole plant is edible, the oil obtained from its seeds is the most important. Oenothera biennis oil is obtained in industry, as a result of cold pressing of seeds or solvent extraction with n - hexane. The largest producer of evening primrose oil is China. Over 90% of the world production of this raw material is obtained there (Eskin, 2008). Oenothera biennis seed oil is characterized by a high content of polyunsaturated fatty acids. First of all, it is one of the few natural sources of gamma-linolenic acid (GLA) (Ghasemnezhad and Honermeier, 2007, 2008). Polyunsaturated fatty acids contained in Oenothera biennis oil have antioxidant and anti-inflammatory effects. Therefore, it is used primarily in the food industry as a dietary supplement, that supports the treatment of such diseases as hypertension, allergy, psoriasis or cancer (Barre, 2001; Białek and Rutkowska, 2015), also in the cosmetics industry, as an ingredient of soaps and body lotions (Muggli, 2007). In comparison with the most popular oils, such as rapeseed, soybean, linseed, palm etc., the content of unsaturated fatty acids in this oil is much higher (over 90% of all fatty acids) (Paciorek-Sadowska et al., 2018). In fact, Oenothera biennis oil is a future raw material for the oleochemical industry, including for the production of bio-polyols for the synthesis of PU materials. The most popular methods for the synthesis of bio-polyols based on vegetable oils include: transesterification of fatty acid triglycerides with glycerol or triethanolamine (Veronese et al., 2011; Badri, 2012; Fridrihsone-Girone and Stirna, 2014), epoxidation of double bonds with opening of epoxide rings by diols (Noreen et al., 2016; Garrison et al., 2014), hydroformylation using synthesis gas (Guo et al., 2000; Petrović et al., 2010; Vanbesien et al., 2013), the addition of halogen or hydrogen halide to unsaturated double bonds in the reaction with secondary amine (Garrett and Du, 2010, 2014). Apart from the methods of obtaining polyols from vegetable oils, there are many other technologies based on these methods and their combinations. The choice of synthesis method depends on: scale of production, the type of final products, its usage and the availability of oil raw materials (Prociak et al., 2014). Noteworthy research on using bio-polyols based on soybean oil was conducted by Miao et al. The authors used soy polyols obtained from two methods (transesterification of triglycerides to monoglycerides and the opening of oxirane rings of epoxidized soybean oil) for the production of various PU materials. On the basis of first polyol raw material, they obtained PU elastomer characterized by very good mechanical properties and high cellular biocompatibility. The last parameter has particular importance in biomedical applications, eg in production of bio-implants. The second polyol was used to obtain oilbased materials with "shape memory". The research results proved that use of soybean bio-polyol improves the performance and creates new applications for this material, for example in biomedical engineering (Miao et al., 2012, 2013a; Miao et al., 2013b). Veronese et al. used a mixture of petrochemical and soybean polyol, synthesized in transesterification of hydroxylated oil with triethanolamine, in production of rigid polyurethane foams (RPUF). Obtained bio-based foams had better mechanical properties than their counterparts obtained from petrochemical raw materials (Veronese et al., 2011). Bhoyate et al. used biopolyols based on soybean, castor and orange peel oils in a mixture with

2. Materials and methods 2.1. Raw materials Crude oil from Oenothera biennis seeds was used for synthesis of the new bio-polyol in a two-step method, as a light yellow liquid with a density of 0.890 g/cm3 and viscosity 170 mPa·s, produced by local oil mill Olejarnia Kołodziejewo (Poland). The iodine value (IV) was 0.658 mol I2/100 g of fat, acid value (AV) was 5.320 mg KOH/g and the content of unsaturated fatty acids was 92.7% of all fatty acids in the oil. The fatty acid profile of Oenothera biennis oil was showed in Table 1. Oxidation system was applied in the beginning of the synthesis: 99.5% acetic acid (prod. by Chempur, Poland) and 30% solution of hydrogen peroxide (prod. by Chempur, Poland). 96% sulfuric acid (prod. by POCh, Poland) was used as catalyst for the reaction. Anhydrous magnesium sulfate (prod. by Chempur, Poland) was used for purified epoxidized Oenothera biennis oil drying. 98% 2,2′-mercaptodiethanol p.a. (prod. by Sigma-Aldrich, USA) was applied in order to open the epoxy rings and sulfuric acid, as reaction catalyst (as above). Anhydrous calcium chloride (prod. by POCh, Poland) was used to neutralize the catalyst and to remove water. 209

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sulfuric acid produced in situ peracetic acid, which oxidized double bonds in oil to epoxy groups (Fig. 1a). The reaction lasted for 3 h. During synthesis epoxy value of mixture was determined. Then the system was cooled and left for 24 h for separation oil phase and aqueous phase. The oil phase was washed with distilled water for removing residual acetic acid and catalyst. The remaining water was removed by anhydrous magnesium sulfate. In the purified intermediate product (epoxidized oil, EOB) an epoxy value was determined to select the right amount of epoxy ring opening agent. The EV was 0.266 mol/100 g of fat. Afterwards, epoxidized oil (EOB), 98% 2,2′-mercaptodiethanol (MDE) and 96% sulfuric acid were loaded into reactor equipped with a reflux condenser, thermometer and mechanical stirrer. The molar ratio of reactants (in relation to content of epoxy rings in epoxidized oil) was 1:1:0.01 for EOB:MDE:SA. Whole mixture was heated to 120 °C with continuous stirring. Second step of synthesis was carried out for 4 h to open all epoxide rings (Fig. 1b). The obtained bio-polyol (PW1) was neutralized with solid anhydrous calcium chloride, after the synthesis. In order to reduce the water content, the product was distilled under vacuum. The properties of the new bio-polyol based on Oenothera biennis oil were determined. Subsequently, reaction product was used for the synthesis of rigid polyurethane-polyisocyanurate foams.

Table 1 Fatty acid profile. Fatty acid

Content (%)

Number of unsaturated bonds

Palmitic acid Palmitoleic acid Stearic acid Oleic acid Vaccenic acid Linoleic acid Arachidic acid Trans-octadecatric acid Cis-11-eicosenoic acid α-Linolenic acid Behenic acid Erucic acid Other

5.32 0.08 1.55 14.19 1.50 67.15 0.30 7.32 1.56 0.73 0.13 0.16 < 0.01

0 1 0 1 1 2 0 3 1 3 0 1 –

Bio-polyol based on Oenothera biennis oil and polyol Rokopol RF551 - sorbitol oxyalkylation product, hydroxyl value HV = 420 mg KOH/g (prod. by ZCh PCC Rokita SA, Poland) was used for synthesis of rigid PUR-PIR foams. Purocyn B, a technical polyisocyanate (prod. by Purinova Ltd., Poland) was used as the isocyanate raw material. The main component was 4,4′-diphenylmethane diisocyanate. The content of NCO groups was equal 31%. The catalytic system for synthesis of rigid PUR-PIR foams was made from anhydrous potassium acetate (prod. by Chempur, Poland) used in 33% solution in diethylene glycol (prod. by Chempur, Poland) and DABCO - 1,4-diazabicyclo[2,2,2]octane (prod. by Alfa Aesar, USA) used also in 33% solution in diethylene glycol. Silicone L-6900 - polysiloxanepolyoxyalkylene surfactant (prod. by Witco, Sweden) was a foam structure stabilizer. Solkane HFC 365/227 - a mixture of 1,1,1,3,3pentafluorobutane and 1,1,1,2,3,3,3-heptafluoropropane in a mass ratio of 87:13 (prod. by Solvay, Belgium) was a blowing agent. Antiblaze TCMP - trichloro-2-methylethyl phosphate (prod. by Albright and Wilson, UK) was flame retardant.

2.3. Examining the properties of bio-polyol 2.3.1. Analytical tests Physicochemical, analytical and spectroscopic tests were performed on the new bio-polyol. It was aimed to determine its suitability for the synthesis of rigid PUR-PIR foams. The hydroxyl value (HV) was determined in accordance with Purinova Ltd. standards - WT/06/07/ PURINOVA, the acid value (AV) was determined in accordance with PN-EN ISO 660, the iodine value (IV) was determined in accordance with PN-EN ISO 3961:2013-10, the epoxy value (EV) was determined in accordance with PN-EN ISO 3001:1999. The viscosity of the bio-polyol was determined using a Fungilab digital rheometer at 20 °C (293 K). The measurements were carried out using a standard spindle (DIN-87) working with the bushing (ULA-DIN-87). Maintaining a constant temperature of measurement was provided by thermostat connected to the water jacket of the sleeve. Density was measured at 25 °C (298 K) in an adiabatic pycnometer in accordance with PN-EN 92/C-04504. The water content was determined by the Carl-Fisher method using a nonpyridine reagent under the trade name Titraqual in accordance with PN-81/C-04959. The pH value was measured using a Hanna Instruments microprocessor laboratory pH-meter (ORP/ISO/°C) with

2.2. Synthesis of new bio-polyol Crude Oenothera biennis oil (OB), 99.5% acetic acid (AC) and 96% sulfuric acid (SA) were loaded into reactor equipped with reflux condenser, thermometer, dropping funnel and mechanical stirrer. The mixture was heated to 40 °C with continuous stirring (700 rpm) and was gradually loaded with 30% hydrogen peroxide. The molar ratio of the reactants (in relation to content of double bonds in oil) was 1:1:1:0.02 for OB:AC:HP:SA. The mixture was heated to 60 °C, after addition of oxidizing agent. Hydrogen peroxide and acetic acid in the presence of

Fig. 1. Reactions of bio-polyol synthesis: a) Epoxidation reaction of Oenothera biennis oil; b) Epoxide rings opening reaction by 2,2′-mercaptodiethanol. 210

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Obtained polyurethane materials were thermostated after removal from the form for 4 h at 120 °C.

RS 22 C connector. The average molecular weight of the bio-polyol was determined by Gel Permeation Chromatography (GPC) using a Knauer chromatograph. The apparatus was equipped with thermostated columns and a refractometer detector. The measurements were made on the basis of calibration, using polystyrene standards in the range of molecular weights from 162 to 25,500 g/mol.

2.5. Assessing the properties of rigid PUR-PIR bio-foams 2.5.1. Foaming process The foaming process was analyzed by electronic stopwatch to determine the characteristic foaming times in accordance with ASTM D7487 13e1: cream time - from the start of mixing components A and B until fine bubbles begin to appear; free rise time- from the start of mixing the components A and B until the foam stops expanding; string gel time- from the start of mixing the components A and B until long strings of tacky material can be pulled away from foam surface when the surface is touched by tongue depressor; tack free time- from the start of mixing components A and B until the foam surface can be touched by tongue depressor without sticking (ASTM Standard, 2008).

2.3.2. Spectroscopy tests The bio-polyol was tested in IR spectroscopy using Brücker Vector spectrophotometer by KBr technique from 400 to 4000 cm−1 range and in nuclear magnetic resonance spectroscopy 1H NMR and 13C NMR using a Brücker NMR Ascend III spectrometer with a frequency of 400 MHz, in deuterated chloroform. 2.3.3. Thermal properties of synthesized polyol Analysis of the differential scanning calorimetry (DSC) of Oenothera biennis bio-polyol was carried out using TA Instruments DSC Q200 apparatus in atmosphere of inert gas - nitrogen. Temperature of measurement was from 20 °C to 400 °C.

2.5.2. Selected properties of new bio-based foams New polyurethane materials have been tested for: apparent density in accordance with ISO 845–1988, compressive strength measured in the direction of foam growth, on a universal strength machine Instron 5544 in accordance with PN-93/C-89071 (ISO 844), brittleness in accordance with ASTM C-421-61, absorbability and water absorption in accordance with DIN 53433.

2.4. Preparation of PUR-PIR foams Formulation of rigid PUR-PIR foams with bio-polyol based on plant oil (PW1) in early stages required an experimental investigations to determine the optimal composition of additive agents (catalysts, surfactant, flame retardant and blowing agent). The hydroxyl value was basis for determining the amount of polyol raw materials. These values allowed to calculate the mass equivalent (Eq) of the polyol and biopolyol. The addition of isocyanate raw material was selected in consideration of equivalent (Eq) ratio of NCO to OH groups in the reaction mixture. For rigid PUR-PIR foams, this ratio is 3:1. It is necessary for reaction between NCO and OH groups to produce a urethane bond and trimerization reaction of three NCO groups to produce an isocyanurate ring. The sum of mass equivalents of petrochemical polyol and biopolyol was always 1. The content of additive agents in percentage by mass to sum of polyol and polyisocyanate masses, i.e. urethane bond catalyst (1% wt.), isocyanate trimerization catalyst (2.5% wt.), physical blowing agent (10% wt.), flame retardant (17% wt.) and surfactant (1.7% wt.). Foams were obtained in a laboratory scale using the one-stage method, from the two-component system - A and B (Table 2). Component A was obtained as a result of mixing appropriate amounts of polyols, catalysts, surfactant, blowing agent and flame retardant. Component B was Purocyn B. Components A and B were mixed for 10 s with a mechanical stirrer (1800 rpm) in a suitable mass ratio. Mixture was poured into a cuboidal form with internal dimensions of 25 × 25 × 30 cm, where the growth of foam proceeded freely. Four types of foams were obtained: PW1.0 - foam without bio-polyol and PW1.1-P1.3 - foams with increasing equivalent content of biopolyol from 0.1 to 0.3 (difference by 0.1 eq), at the cost of petrochemical polyol. The synthesis of PUR-PIR foams was repeated twice.

2.5.3. Flammability tests Three flammability tests were performed on the new PUR-PIR foams: Bütler's combustion test (vertical test) in accordance with ASTM D3014-73; horizontal combustion test in accordance with PN-78 C05012 and limited oxygen index (LOI) using Concept Equipment apparatus in accordance with ASTM D 2863-1970. 2.5.4. Foams structure Microstructure of cell structure was analyzed by scanning electron microscope (SEM) HITACHI SU8010 (Hitachi High-Technologies Co., Japan). The studies were performed at the accelerating voltage of 30 kV, with the working distance of 10 mm and magnification of 150x. 3. Results and discussion 3.1. Properties of new bio-polyol 3.1.1. Analytical tests and efficiency As a result of two-step synthesis, an orange, homogeneous biopolyol with a delicate, sulfuric smell, similar to pure 2,2′-mercaptodiethanol was obtained. Its density was equal 1.01 g/cm3, viscosity 1500 mPa·s, pH 7 and water content 0.3% wt. The remaining analytical results was necessary to calculate the reaction efficiency and to prepare a formulation of rigid PUR-PIR foams (Table 3). Epoxidation reaction’s efficiency of Oenothera biennis oil (1 st step) is defined by equation (1).

E1 = Table 2 Formulation of rigid PUR-PIR foams with bio-polyol. Foam symbol Component A Rokopol RF551 (g) PW1 (g) Silicone L-6900 (g) DABCO (g) Catalyst 12 (g) Antiblaze TCMP (g) Solkane HFC365/227 (g) Component B Purocyn B (g)

PW1.0

PW1.1

PW1.2

PW1.3

66.80 0.00 4.59 2.70 6.75 45.90 32.40

60.12 18.33 4.79 2.82 7.04 47.88 33.80

53.44 36.65 4.99 2.93 7.33 49.86 35.19

46.76 54.98 5.18 3.05 7.62 51.84 36.59

203.2

203.2

203.2

203.2

IVS−IVE ∙100% IVS

(1)

Where: E1 - epoxidation efficiency, IVS - iodine value of Oenothera biennis oil, IVE - iodine value of epoxidized oil. The reaction efficiency was 41.95%. Table 3 Analytical results of bio-polyol.

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Parameter

Bio-polyol PW1

IV (mol I2/100 g of fat) EV (mol/100 g of fat) AV (mg KOH/g) HV (mg KOH/g)

0.382 0.000 0.716 153.050

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ester group, vibrations in 3010 cm−1 (stretching) belonged to the CH unsaturated bonds, vibrations in 2950 cm−1 (stretching) and 1465 cm−1 (deformational) belonged to CH bond of the −CH2- group and in 2925 cm−1 (stretching) and 1380 cm−1 (deformational) to CH bond of the −CH3 group. Furthermore, the stretching vibration of the C]C unsaturated bond was in 1650 cm−1 and the pendulum vibrations of the CH2 group in 725 cm−1. The IR spectrum of the bio-polyol also showed high band intensity at 3450 cm−1, indicating the presence of OH bonds of the hydroxyl groups (Hakim et al., 2011, Septevani et al., 2015). Bio-polyol analysis in nuclear magnetic resonance spectroscopy 1H NMR (Fig. 3) and 13C NMR (Fig. 4) confirmed the presence of characteristic groups of these compounds, resulting from its expected chemical structure. 1 H NMR spectrum analysis (Fig. 3) showed characteristic chemical shifts for: 5.35 ppm protons of olefin groups of fatty acids eCH]CHe; 5.25 ppm methane protons of glyceryl CH2eCHeCH2-; 4.12–4.28 ppm methylene protons of glyceryl eCH2eCHeCH2-; 3.70-3.80 ppm protons of hydroxyl groups at the end of the chain -OH; 3.42-3.50 ppm protons of αeCH2 groups to the hydroxyl group eCH2−OH; 2.70–2.80 ppm protons of α−CH2 groups to the sulfide group eCH2eSeCH2; 2.29–2.32 ppm protons of the α−CH2 group to the carbonyl group eCH2eCO-; 2.10–2.25 ppm protons of hydroxyl groups inside the chain -OH; 1.60 ppm protons of the βeCH2 group to the carbonyl group eCH2−CH2eCOe; 1.25–1.40 ppm protons of CH2 groups in the fatty acid chain; 0.86–0.88 ppm protons of ending groups eCH3. 13 C NMR spectrum analysis (Fig. 4) showed characteristic chemical shifts for: 172.80–173.25 ppm carbons of carbonyl groups > C]O; 127.10–132.30 ppm carbons of olefin group of fatty acids eCH]CHe; 73.86 ppm carbons of α−CH groups linked to a hydroxyl group within the chain > CHeOH; 68.90 ppm methane carbons of glyceryl eCH2eCHeCH2-; 62.10 ppm methylene carbons of glyceryl eCH2eCHCH2-; 33.00 ppm carbons of α−CH2 groups to olefin group eCH]CHeCH2-; 31.90 ppm carbons of α−CH2 groups to the carbonyl group eCH2eOOCeCH2-; 27.20–29.80 ppm carbons of CH2 groups in the fatty acid chain; 22.70 ppm carbons of penultimate groups eCH2eCH3; 14.30 ppm carbons of ending groups eCH3 (Zhan et al., 2008; Zhang et al., 2014). FTIR, 1H NMR and 13C NMR spectroscopic analyses confirmed the assumed chemical structure of the synthesized bio-polyol.

Efficiency of epoxide rings opening reaction (2nd step) was defined by equation (2).

E2 =

EVS−EVE ∙100% EVS

(2)

Where: E2 - epoxide rings opening reaction efficiency, EVS - epoxy value of epoxidized Oenothera biennis oil, EVE - epoxy value of bio-polyol. The reaction efficiency was 100%. That is to say that the thiodiglycol molecule has been attached to all epoxide rings (Marcovich et al., 2017; Ji et al., 2015). The hydroxyl value (HV) of the bio-polyol based on Oenothera biennis oil was 153.05 mg KOH/g (Table 3). This value is lower, than the theoretical hydroxyl value (tHV) would suggest - 244.25 mg KOH/g. In fact, that a homogeneous product was obtained as a result of the synthesis and the reaction efficiency of the epoxide ring opening (E2) was 100%, the incomplete reaction between 2,2′-mercaptodiethanol and epoxidized oil was excluded. The reasons for the low hydroxyl value were the oligomerization of the bio-polyol molecules and the esterification of hydroxyl groups with free fatty acids or other compounds in the unrefined oil. Decrease of free fatty acid content in the bio-polyol is visible after the decrease of acid value from 5.320 (unrefined oil) to 0.716 mg KOH/g (Ionescu, 2016; Petrović, 2008). Despite the lower hydroxyl number, the bio-polyol obtained is acceptable by industry standards. The average molecular weight of the bio-polyol determined by GPC was 1562 g/mol. This value is higher, than the molecular weight of the petrochemical polyol - Rokopol RF-551, which was equal 600 g/mol. The high molecular weight was caused by the side reaction of the oligomerization of bio-polyol molecules (Dworakowska et al., 2012). Functionality of bio-polyol was calculated:

f=

Mn ∙HV 56100

(3)

Where: f – functionality of bio-polyol based on Oenothera biennis oil, Mn – average molecular weight of bio-polyol, HV – hydroxyl value of biopolyol. Functionality of the oil-based bio-polyol was 4.26, while the functionality of the petrochemical polyol (Rokopol RF-551) was 4.5. 3.1.2. Spectroscopy tests Analysis of bio-polyol based on Oenothera biennis oil in infrared spectroscopy (Fig. 2) showed that there were bonds characteristic for the structure of fatty acid glycerides. Vibrations in 1740, 1240, 1160 and 1099 cm−1 (stretching) belonged to the C]O and C–O bonds of the

3.1.3. Thermal properties of synthesized polyol Analysis of DSC curve of bio-polyol PW1 showed the presence of

Fig. 2. IR spectra of new bio-polyol. 212

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Fig. 3. 1H NMR spectra of new bio-polyol.

Fig. 4.

13

C NMR spectra of new bio-polyol.

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Fig. 5. DSC curve of new bio-polyol.

influence on reactivity. In the case of Rokopol RF-551, hydroxyl groups are located on the ends of the polyether chains, while in the bio-polyol based on oil from Oenothera biennis, these groups are both at the end of the 2.2′-MDE substituted chain and inside of chain fatty acid residues (Fig. 1). This distribution of the hydroxyl groups was confirmed by 1H NMR analysis (Fig. 3). The presence of secondary OH groups inside the fatty acid chain, beside the thiodiglycol chain, inhibits the reaction with the NCO group of the polyisocyanate and significantly affects the difference in polyurethane crosslinking density (Ionescu, 2016).

three extremes (P1-P3, Fig. 5). Its corresponded to transition of various energetic characters. The first transition (P1) was endothermic. It was related to vaporization of water, contained in bio-polyol (0.5% by mass) and low-boiling substances derived from crude oil, and degradation of other trace substances (i.e. vitamins). Transition occurring in polyols, after exceeding 150 °C, are most often associated with their temperature degradation. As a result of heat supply (endothermic effect), complex molecules are broken up into small-molecule products (Liszkowska, 2016; Pillai et al., 2016). P2 and P3 peaks showed exothermic character. That is to say that the chemical changes generated heat during the process of warming. The positive energy effect resulted from coupling reaction of thioalcohol chains with double bonds (C]C). The reaction products were mainly sulfides of fatty acids and aliphatic thioglycol (Colak et al., 2016; Desroches et al., 2011). This phenomenon did not occur when the polyol did not contain sulfur atoms in its structure (Zieleniewska et al., 2014). It was possible that in the area of peaks P2 and P3 was a degradation of bio-polyol. However, the endothermic effect of this process could be masked by the strongly exothermic reaction between the thioglycol chain and free double bonds.

3.2.2. Selected properties of new bio-based foams An important parameter of rigid PUR-PIR foams was apparent density. It was influenced indirectly on compressive strength in the direction of foam growth and brittleness. The increase in content of new polyol raw material resulted in decrease of the apparent density from 50.19 kg/m3 for the reference foam to 37.35 kg/m3 for the foam with 0.3 equivalent of bio-polyol. Addition into polyurethane, a component containing long, linear chains caused a decrease in the packing degree of polymer macromolecules. It meant that fatty acid residues had flexible segments with low or non-cross-linking potential. This phenomenon also had an influence on the compressive strength of rigid foams. With the increase in amount of flexible segments and the decrease in apparent density, this parameter was decreased from 201.38 kPa (PW1.0) to 183.23 kPa (PW1.3). Despite decrease in compressive strength, the value of this parameter is at a satisfactory level. Decrease in stiffness was another consequence of decreasing the packing degree. This reliance influenced on lower brittleness of obtained rigid PUR-PIR foams. When the bio-polyol based on Oenothera biennis oil was using, a significant decrease of this parameter was noted (from 40.17% for the PW1.0 foam to 17.04% for the PW1.3 foam). Important application parameters of the porous materials are absorbability and water absorption. The first one was the percentage amount of water in the material, immediately after removal from immersion. The second one was the percentage amount of water that stayed inside the foams. In both cases, decrease in value of this parameter was noted. This decrease was mainly caused by the addition of hydrophobic groups derived from vegetable oil into the macromolecule of polyurethane.

3.2. Properties of rigid PUR-PIR bio-foams 3.2.1. Foaming process The influence of bio-polyol on processing times, was measured during the production of new PUR-PIR bio-foams in accordance with ASTM D7487 13e1. Its showed a tendency to elongation (Table 4). After using bio-polyol, increase was noticed in: cream, free rise, string gel and tack free times. This suggested that the new bio-polyol based on Oenothera biennis had a lower reactivity than the petrochemical polyol. This is confirmed by the lower hydroxyl value and functionality of the vegetable oil-based polyol. The type of hydroxyl also has a significant Table 4 Processing times of PUR-PIR foams with bio-polyol. Foam symbol

PW1.0

PW1.1

PW1.2

PW1.3

Cream time (s) Free rise time (s) String gel time (s) Tack free time (s)

6 34 16 26

7 48 17 27

9 48 19 31

9 49 20 31

3.2.3. Flammability tests High flammability is an important quality of porous polyurethane 214

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Table 5 Performance properties of PUR-PIR foams with bio-polyol. Parameter 3

Apparent density (kg/m ) Compressive strength (kPa) Brittleness (%) Absorbability (%) Water absorption (%)

PW1.0

PW1.1

PW1.2

PW1.3

50.19 ± 1.22 201.38 ± 4.01 40.17 ± 2.03 39.03 ± 1.26 7.23 ± 0.41

38.07 ± 0.83 177.45 ± 3.26 30.44 ± 1.23 15.13 ± 0.79 0.64 ± 0.09

37.74 ± 0.68 178.69 ± 4.56 23.11 ± 1.86 11.38 ± 0.84 0.57 ± 0.10

37.35 ± 0.72 183.23 ± 3.71 17.04 ± 0.89 7.77 ± 0.36 0.53 ± 0.07

Table 6 Flammability tests of PUR-PIR foams with bio-polyol. Parameter

PW1.0

PW1.1

PW1.2

PW1.3

Combustion residue (%) Limited Oxygen Index(%vol. of O2) Horizontal combustion test

90.38 ± 0.65 23.1 ± 0.1 self-extinguishing

94.83 ± 0.41 23.4 ± 0.1

95.53 ± 0.72 23.7 ± 0.1

96.65 ± 0.33 24.0 ± 0.2

materials. Rigid PUR-PIR foams have an isocyanurate ring in their structure, and are characterized by lower flammability than PUR foams. However, due to the strict fire safety requirements, they must contain flame retardants (Li et al., 2013; Paciorek-Sadowska et al., 2010, 2015). Flammability tests of new polyurethane materials: Bütler’s combustion test, the horizontal combustion test and the limited oxygen index (Table 6) showed that the increased content of bio-polyol based on Oenothera biennis oil influenced on the fire resistance of these materials. The combustion residue increases respectively from 90.38% for PW1.0 to 96.65% for PW1.3, and the limited oxygen index from 23.1% to 24.0%. The horizontal combustion test rated all of these materials as non-smoking after withdrawal of the source of fire. Results of flammability showed that the increasing of bio-polyol content in foam formulation significantly affected the flame retardation of rigid PUR-PIR foams. The reason of this phenomenon was a presence of sulfur atoms in its molecule. This element was categorized into group of flame retardant. Abovementioned result demonstrated, that the new bio-polyol is also an internal flame retardant. A slight influence on the improvement in fire resistance could result from the fact, that with the increase of bio-polyol content, the amount of the added flame retardant (Antiblaze TMCP) was also increased.

3.2.4. Foams structure Abdel Hakim et al. conducted research on the using of bio-polyol based on sugar-cane bagasse. Rigid polyurethane foams containing 30% of plant-based polyol had irregular surface and cell shapes (Abdel Hakim et al., 2011). In case of using polyols based on vegetable oils for the production of rigid polyurethane and polyurethane-polyisocyanurate foams, relevant influence on the shape and size of the foam cells was observed. The use of mixtures of petrochemical polyol and soybean based polyol resulted in obtaining materials with larger cells than materials without the participation of bio-polyols (Zhang and Kessler, 2015). As a result, the using of mixture a bio-polyol based on castor oil and raw glycerol with petrochemical polyol exerted a positive influence on the cellular structure of rigid PUR-PIR foams. Decrease in average cell size from 372 to 275 μm and an increase in content of closed cells were noted. (Hejna et al., 2017). The structure of cells was analyzed with regard to foam without Oenothera biennis oil-based bio-polyol (PW1.0 - Fig. 6a) and foam with the highest content of it (PW1.3 - Fig. 6b). Based on micrographs it was ascertained that the increase in bio-polyol content caused an increase in cell size and its wall thickness. The average cell size of reference foam was 275 ± 16 μm, while foams with 0.3 Eq of bio-polyol 408 ± 31 μm. The average cell wall thickness were 21 ± 3 μm for PW1.0 and 47 ± 5 μm for PW1.3. Despite the increase in cell size, their shape remained regular. The average amount of cells per volume unit were 24 cell/mm2 for the reference foam and 10 cell/mm2 for the foam

Fig. 6. a) Micrograph of PW1.0 foam. (b) Micrograph of PW1.3 foam.

with bio-polyol. The main reason of changes in foam structure was the presence of long linear molecules (from fatty acid glycerides) in bio-polyol. The high elasticity of the polyol segments and the low cross-linking of the bio-polyol (low hydroxyl value) allowed to greater migration of the 215

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blowing agent. Consequently, the obtaining foams had larger cell diameters and thicker cell walls. It affected inter alia the decrease of apparent density, compressive strength and brittleness (Table 5).

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4. Conclusions A new bio-polyol based on Oenothera biennis seed oil was obtained in a two-step method of epoxidation of double bonds and opening epoxy rings with 2,2′-mercaptodiethanol (Pat Appl. PL422888). It was characterized by hydroxyl value of 153.05 mg KOH/g, acid value of 0.716 mg KOH/g and water content of 0.3% wt. Bio-polyol was used as raw material for the synthesis of rigid PUR-PIR foams from 0 to 0.3 mass equivalents in a mixture with a polyol based sorbitol propoxylate. Selected properties of these materials were extensively examined. The conducted research has shown that foams based on bio-polyol have a lower apparent density, compressive strength and brittleness. The presence of sulfur in polyol macromolecule significantly reduced the flammability of these materials. These properties are important for building engineering, e.g. as interior of sandwich panels or as industrial thermal insulation materials. The price of the finished product is also important. The using of an bio-polyol based on Oenothera biennis oil and 2,2′-mercaptodiethanol in mixture with petrochemical polyol allows to reduce the using of expensive fire retardants. The production costs of this bio-polyol are similar to the production costs of polyol based on sorbitol propoxylate. What in the economic balance-sheet gives a reduction in the price of the obtained polyurethane material. The using of oil from Oenothera biennis as an alternative raw material for the synthesis of bio-polyols offers great opportunities. Appropriate choice of the qualitative and quantitative composition of reaction mixture allows to obtain various products, that may be used in various industries, for example in building engineering, automotive, footwear, textile or furniture industries. Besides using of bio-polyols based on vegetable oils for the synthesis of PUR materials is in line with the principle of sustainable development. It enables the partial replacement of petrochemical polyols. Flame retardancy of these compounds is a compelling issue, that can lead to a reduction in use of expensive and environmentally toxic flame retardants. Acknowledgenents This research did not receive any grant from funding agencies in public, commercial, or non-profit sectors. We would like to express our gratitude the company Purinova Ltd. from Bydgoszcz for the compressive strength test. References Abdel Hakim, A.A., Nassar, M., Emam, A., Sultan, M., 2011. Preparation and characterization of rigid polyurethane foam prepared from sugar-cane bagasse polyol. Mater. Chem. Phys. 129, 301–307. https://doi.org/10.1016/j.matchemphys.2011.04.008. ASTM Standard D7487 – 13e1, 2008 (2016). Standard Practice for Polyurethane Raw Materials: Polyurethane Foam Cup Test. ASTM International, West Conshohocken, PA. https://doi.org/10.1520/D7487-13E01. Badri, K.H., 2012. Biobased polyurethane from palm kernel oil-based polyol. In: Zafar, F., Sharmin, E. (Eds.), Polyurethane. Tech Open, pp. 447–470. https://doi.org/10.5772/ 47966. Barre, D.E., 2001. Potential of evening primrose, borage, black currant, and fungal oils in human health. Ann. Nutr. Metab. 45, 47–57. https://doi.org/10.1159/000046706. Bartuzi, K., 2012. Vegetable oils, characteristics and production technology. J NutriLife 9. Bhoyate, S., Ionescu, M., Kahol, P.K., Gupta, R.K., 2018. Sustainable flame-retardant polyurethanes using renewable resources. Ind Crops Prod. 123, 480–488. https://doi. org/10.1016/j.indcrop.2018.07.025. Białek, M., Rutkowska, J., 2015. The importance of γ-linolenic acid in the prevention and treatment. Postep. Hig. Med. Dosw 69, 892–904. Bukowski, Z., 2009. Sustainable Development in the Law System. TNOIK Dom Organiztora, Toruń in polish. Chemistry and Business, 2011. Perspectives of the Global Bioplastics Market. (accessed 1 February 2018). http://www.chemiaibiznes.com.pl/wydanie/chemia-i-biznes/nr-52011. Colak, B., Da Silva, J.C.S., Soares, T.A., Gautrot, J.E., 2016. Impact of the molecular environment on thiol-ene coupling for biofunctionalization and conjugation.

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