Open-cell rigid polyurethane bio-foams based on modified used cooking oil

Journal Pre-proof Open-cell rigid polyurethane bio-foams based on modified used cooking oil

Maria Kurańska, Krzysztof Polaczek, Monika Auguścik-Królikowska, Aleksander Prociak, Joanna Ryszkowska PII:

S0032-3861(20)30009-4

DOI:

https://doi.org/10.1016/j.polymer.2020.122164

Reference:

JPOL 122164

To appear in:

Polymer

Received Date:

29 September 2019

Accepted Date:

04 January 2020

Please cite this article as: Maria Kurańska, Krzysztof Polaczek, Monika Auguścik-Królikowska, Aleksander Prociak, Joanna Ryszkowska, Open-cell rigid polyurethane bio-foams based on modified used cooking oil, Polymer (2020), https://doi.org/10.1016/j.polymer.2020.122164

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Journal Pre-proof PU_ref PU_P1_20 PU_P1_60 PU_P1_100

28.94mm/s; 32s

30

Velocity, mm/s

25 20

13.22mm/s; 43s

15

13.90; 50s 10

8.82mm/s; 61s

5 0 20

40

60

80

100

120

140

Time of foaming, s

P1 P2

Compressive strength at 10% of deformation, kPa

60 50 40 30 20 10 0 O

2O

4O

6O

Content of P1 or P2, %

8O

1OO

Journal Pre-proof Open-cell rigid polyurethane bio-foams based on modified used cooking oil Maria Kurańska, Krzysztof Polaczek, Monika Auguścik-Królikowska, Aleksander Prociak, Joanna Ryszkowska, Cracow University of Technology, Department of Chemistry and Technology of Polymers, Warszawska 24, 31-155, Cracow, Poland Warsaw University of Technology, Faculty of Materials Science and Engineering, Wołoska 141, 02-507, Warsaw, Poland Abstract In the present work, we report on rigid polyurethane foams based on modified used cooking oil. The bio-polyols with different hydroxyl values and viscosities as well as number average molecular weights from municipal waste were obtained by epoxidation and ring-opening reaction with diethylene glycol. The bio-polyols were used to prepare open-cell polyurethane foams for applications in construction industry. It was noticed that the structures of the biopolyols do not have a significant effect on the reactivity of the resultant polyurethane systems. The apparent densities of the final foams were comparable and in the range of 12–17 kg/m3. Beneficial effects of both the bio-polyols on the cellular structures as well as on the mechanical properties and thermal conductivity of the modified foams were observed, especially when a petrochemical polyol was replaced with 40-60 wt.% of the bio-polyols. Keywords: cleaner production of bio-polyols, open-cell foams, polyurethanes 1. Introduction The commercially available polyurethane foams are usually made from petroleum-based polyether or polyester polyols and polyisocyanates, in the presence of blowing agents, surfactants and catalysts (Marcovich et al., 2017). In recent years, an increase of the interest in the application of natural raw materials for the preparation of different groups of polymers has been observed (Andrzejewski et al., 2019; Barczewski et al., 2019a, 2019b; Formela et al., 2018)). In 2014, the production of different polymers using renewable raw materials was 1.7 million tones, and an increase to 7.8 million tones is expected by 2019 (Ryszkowska et al., 2018). In the case of polyurethanes, one of the main components – polyols - can be also obtained from renewable resources (Kurańska et al., 2017; Parcheta and Datta, 2018; Prociak et al.,

Journal Pre-proof 2017a). Natural oils, such as rapeseed, soybean, palm oil, after proper chemical modifications are valuable chemicals for the synthesis of porous polyurethane materials (PaciorekSadowska et al., 2018; Prociak et al., 2017b). Unfortunately, most of the vegetable oils can be classified as first generation of bio-based raw materials. This means that the synthesis of polyols based on edible oils is competing with the production of food (Kirpluks et al., 2016). Used cooking oil, as municipal waste, can solve this problem and can be modified into a reactive component by using the same method as for typical natural oils. More and more researches also concern various modifications of other wastes such as lignin (Ahvazi et al., 2017; Gómez-Fernández et al., 2018), glycerine from biodiesel production (Hejna et al., 2018), PET as well as tall oil (Mizera et al., 2018). Modified wastes are often used to obtain rigid polyurethane foams for heat insulating applications. Rigid polyurethane foams are mostly characterized by a closed cell structure. However, in recent years an increase of the interest in open-cell rigid and semi-rigid polyurethane foams has been observed. Polyurethane foams with an open cell structure are permeable to moisture, have a lower apparent density and as a consequence are cheaper. Nevertheless, their thermal conductivity is higher in comparison to closed-cell foams. The values of thermal conductivity of closed-cell polyurethane foams based on bio-polyols are in the range 22.0-24.5 mW/m·K (Kirpluks et al., 2018; Prociak et al., 2018). Meanwhile, in the case of polyurethane foams with open cells the thermal conductivity has values of ca. 38-40 mW/m·K, whereas the compressive strength is ca. 10 kPa. A low value of the compressive strength is associated with the foam apparent density which is in the range of 7-14 kg/m3. Open-cell polyurethane foams can be applied in the attics of buildings due to a low water vapour diffusion resistance factor (Kurańska et al., 2020). Such properties cause that this type of foams gains more and more popularity. Taking into account the aspect of environmental protection it is necessary to develop open-cell polyurethane foams based on bio-polyols. Zhang et al. (2019) analyzed the influence bio-based polyols derived from the liquefaction of peanut shells under different post-processing conditions. The apparent density of foams was in the range of 75–90 kg·m3.The foams exhibited a uniform cell structure with a high opencell rate and satisfactory compressive strength > 200 KPa. The authors suggest that such materials can be applied as floral foams. However, for thermal insulation applications a different type of bio-foams has to be developed. In the literature, the influence of biocomponents on open-cell polyurethane foams with a low density (<15 kg/m3) is not described. This paper shows that municipal waste can be used in chemical synthesis in order to obtain products which can be characterized by the same or even better properties. In this work

Journal Pre-proof we aim to examine the impact of two bio-polyols from municipal waste with different chemical structures and physical properties on the foaming processes, cellular structures, mechanical and thermal properties as well as dimensional stability of open-cell polyurethane foams. 2. Experimental 2.1. Materials Bio-based polyols were synthesized from used cooking oil using a two-step method, developed at Cracow University of Technology, of double bond epoxidation and oxirane ring opening with diethylene glycol. The epoxidation process was carried out at 60◦C using a peracetic acid generated in situ by the reaction of hydrogen peroxide (H2O2) with an acetic acid (Bene et al., 2019). Two hydroxylation processes of epoxidized used cooking oil were performed using different acid catalysts (Kurańska et al., 2019). The application of two types of catalysts - tetrafluoroboric acid and sulfuric acid - allowed obtaining two bio-polyols with different properties, bio-polyol P1 and P2, respectively (Table 1). The influence of the catalyst type on ring-opening reactions has been described in more detail in our other work (Kurańska et al., 2019). Table 1. Characterization of bio-polyols. Acid Symbo l

Hydroxyl

value,

value,

mgKOH/g

mgKOH/g

Content of water, %wt.

Number Viscosity 25oC,

average molecular Dispersity Functionality

mPa·s

weight, g/mol

P1

139.6

3.5

0.22

3275

1163

2.80

2.89

P2

159.2

5.6

0.14

961

833

2.90

2.36

A petrochemical polyether polyol with a hydroxyl value of 440 mgKOH/g was supplied by PCC Rokita SA. Polymeric methylene diphenyldiisocyanate (Ongronat 2100) containing 31.5 wt.% of free isocyanate groups was supplied by Borschodchem. Catalysts of foaming (dimethylaminoethoxyethanol) and gelling (dibutyltin dilaurate) processes as well as surfactant were provided by Evonik. Carbon dioxide generated in the reaction of water with isocyanate groups acting foaming reaction as a chemical blowing agent. The content of each component and the isocyanate index are shown in Table 2.

Journal Pre-proof Table 2. Formulations of foams. Component

PU_ref

PU_P1_20 or PU_P2_20

PU_P1_40 or PU_P2_40

PU_P1_60 or PU_P2_60

PU_P1_80 or PU_P2_80

PU_P1_100 or PU_P2_100

Polyether polyol

100

80

60

40

20

0

Bio-polyol P1 or P2

0

20

40

60

80

100

Gel catalyst

1.0

1.0

1.0

1.0

1.0

1.0

Blow catalyst

2.0

2.0

2.0

2.0

2.0

2.0

Non-hydrolysable polysiloxane polyether copolymer

5.0

5.0

5.0

5.0

5.0

5.0

Water

15.0

15.0

15.0

14.9

14.9

14.8

Isocyanate index

1.0

1.0

1.0

1.0

1.0

1.0

2.2. Characterization of bio-polyol The hydroxyl value and water content of the used cooking oil-based bio-polyol obtained were determined according to the standards PN-93/C-89052/03 and PN-81/C-04959, respectively. Gel Permation Chromatography (GPC) measurements were performed using a Knauer chromatograph equipped with a Plgel MIXED-E column and refractometric detector. Tetrahydrofuran was used as eluent at 0.8 mL/min flow rate. Calibration was performed using the poly(methyl acrylate) standards. The number-average functionalities of the polyols were calculated basing on the hydroxyl values and experimentally determined number-average molecular weight (M. Kurańska and Prociak, 2016). 𝑓𝑛 =

𝑀𝑛 ∙ 𝑂𝐻𝑣 56110

(1)

Where: fn—number-average functionality, Mn - number-average molecular weight and OHv hydroxyl value of polyol The viscosity was determined using a rotational rheometer HAAKE MARS III (Thermo Scientific) at 25oC. The control rate mode was used in the plate-plate arrangement with the plates having a diameter of 20 mm and rotation speeds of 100 cycles/min. 2.3. Preparation of samples PUR foams with different contents of bio-polyol P1 or P2 were prepared using a onestep method from a two-component (A and B) system. The polyols, amine catalyst, surfactant and water were mechanically stirred for 15s to ensure their complete homogenization. After that the proper amount of isocyanate (component B) was added to the polyol premix (component A) to obtain the molar ratio NCO/OH groups = 1:1. Next, the system was

Journal Pre-proof mechanically mixed for 5s and poured into an open mould. The obtained samples were seasoned at room temperature for 24h. The samples were coded as PU_PX_Y were X means the type of bio-polyol and Y is the amount of the bio-polyol in the polyol premix (per hundred polyol). 2.4. Characterization of foaming process and foam properties The foaming process was analyzed using the foam qualification system FOAMAT (Format Messtechnik GmbH) which allows determining characteristic parameters during the process such as dielectric polarization, temperature and growth velocities. Temperature was measured with a use of thin thermocouples. Rise pressure was measured using a Foam Pressure Measurement device. Dielectric polarization was measured using a Curing Monitor Device (CMD), which gives an insight into the electrochemical processes occurring during a foam formation. Dielectric polarization reflects the conversion degree of functional groups during a polyurethane formation. The morphology of cells was analyzed using a scanning electron microscope (HITACHI TM3000) as well as optical microscopes and the software Aphelion was used for image analysis. Foam samples of 1x1x1 cm before observation were covered with gold with palladium using a Polaron SC7640 duster. The sputtering process was carried out for 90 s at a current of 10 mA. Observations were carried out at an accelerating voltage of 15 keV. Additionally, the closed cell content in the foams was measured according to the ISO 4590 standard. The apparent density of the composites was determined according to PN-EN ISO 845. Measurements were carried out on five samples of each foam. The samples were measured and weighed to an accuracy of 0.01 mm and 0.01 g, respectively. The thermal conductivity coefficients were determined using a Laser Comp Heat Flow Instrument Fox 200 and foam samples with dimensions of 5 cm × 20 cm × 20 cm. Measurements were carried out on three samples of each foam. The measurements were made at an average temperature of 10oC (temperature of cold plate 0oC and warm plate 20oC). The compressive strength was determined for samples with dimensions of 5 cm × 5 cm × 5 cm according to PN-EN 826. The compressive force was applied at a speed of 2 mm/s, axially in the perpendicular direction to a square surface. The compressive stress was calculated at 10% deformation. The mechanical properties of the foams were evaluated in two directions, parallel (Ϭz) and perpendicular (Ϭx) to the foam rise direction.

Journal Pre-proof Thermogravimetric analysis was carried out using a TA Instruments TGA Q500 device. The samples used for the tests had a mass of 10 ± 1 mg. The samples placed on platinum dishes were heated under a nitrogen atmosphere from room temperature to a temperature of 700 ° C at a rate of 10 °C/min. The results were analyzed in TA Instruments Universal Analysis 2000 version 4.7A. The dimensional stability was calculated using the formula according to the PN-92/C89083 standard and the marking system is shown in Fig. 5. The dimensional stability of RPU foams was measured after 24h of keeping samples at +70oC as well as at -25oC. a b c

Fig. 1. Marking system of sample dimensions.

3. Results and discussion The PUR foams were prepared using different contents of bio-polyol P1 or P2 - in the polyol premix. The bio-polyols were characterized by a small difference in the hydroxyl value and a larger difference in the viscosity (Table 1). The viscosity of polyol P1 was ca. 3 times higher than the viscosity of P2. From the application point of view, it is interesting to evaluate the influence of such bio-components on useful properties in building construction. The foaming process is a significant step in the production of cellular materials. Due to the use of bio-polyols with different physical and chemical properties it was necessary to analyze the influence of these components on the foaming process. The analysis was done for the systems with the same contents of the catalyst and different contents of the bio-polyols P1 or P2. Fig. 2 shows the changes in the reactivity of the reference PUR system as well as the ones modified with polyol P1 (Fig. 2a) and P2 (Fig. 2b). a.

b.

Journal Pre-proof

Dielectric polaryzation

700 600 500 400 300 200

PU_ref PU_P2_20 PU_P2_60 PU_P2_100

800 700

Dielectric polaryzation

PU_ref PU_P1_20 PU_P1_60 PU_P1_100

800

600 500 400 300 200 100

100

0

0 0

100

200

300

400

500

600

0

100

200

Time of foaming, s

c. 180

PU_ref PU_P1_20 PU_P1_60 PU_P1_100

180 160 o

140 120 100 80 60

191oC; 137s

200

Temperature, C

o

Temperature, C

160

500

600

PU_ref PU_P2_20 PU_P2_60 PU_P2_100

183oC; 165s 172oC; 174s 164oC; 182s

140 120 100 80 60

40

40

20

20 0

0 0

50

100

150

200

250

300

350

400

450

500

550

0

600

50

100

150

200

250

300

350

400

450

500

550

600

Time of foaming, s

Time of foaming, s

e.

f. PU_ref PU_P1_20 PU_P1_60 PU_P1_100

28.94mm/s; 32s

30

20

13.22mm/s; 43s

15

13.90; 50s 10

8.82mm/s; 61s

25 20

16.91mm/s; 38s 15

11.30; 44s 10

5

5

0

0

20

40

60

80

100

Time of foaming, s

120

140

PU_ref PU_P2_20 PU_P2_60 PU_P2_100

28.94mm/s; 32s

30

Velocity, mm/s

25

Velocity, mm/s

400

d. 191oC; 137s 185oC; 165s 175oC; 162s 169oC; 175s

200

300

Time of foaming, s

8.05mm/s; 60s

20

40

60

80

100

120

140

Time of foaming, s

Fig. 2. Influence of two types of bio-polyols P1 and P2 and their contents on dielectric polarization (a, b), temperature (c, d) and growth velocities (e, f) of reaction mixtures. Independently of the type of bio-polyol, a reduction of the reaction rate was confirmed by a slower decrease of the dielectric polarization of the systems modified with the biopolyols. The dielectric polarization decreased as the reactions progressed. This effect was caused by the presence of secondary hydroxyl groups in the structure of the bio-polyol, characterized by lower reactivity comparing with primary hydroxyl groups contained in the

Journal Pre-proof petrochemical polyol. The modification of the reference system with the bio-components had also an effect on the temperature of the reaction mixture (Fig. 2 c,d). The maximum temperature of the reference system during the foaming process was 191oC. The replacement of the petrochemical polyol with the bio-polyols led to a decrease of this parameter to 164oC for the system with 100 php of bio-polyol P2. It was observed that the systems with bio-polyol P1 were characterized by slightly higher temperatures during the foaming processes. The values of the temperatures are much higher than those described in the literature. In our earlier work we observed that systems with 70 and 100 php of biopolyols had maximum temperatures of 150 and 140oC, respectively (Kurańska and Prociak, 2016). In the case of the reference system, this parameter was ca. 170oC. The effect of higher maximum temperatures of the systems dedicated to the preparation of open-cell foams can be associated with a high amount of water used as a blowing agent in order to obtain low density porous materials. High temperatures during foaming processes have also been observed for formulations modified with bio-polyols based on amines (Prociak et al., 2018). The decrease of the reactivity is also connected to the growth velocity of the PUR system (Fig. 2 e, f). The higher the content of the bio-polyol, the lower the growth velocity of the reaction mixture. A slightly higher growth velocity was observed for formulation PU_P1_100 and it corresponds to the maximum of the temperature during the foaming process in comparison to PU_P2_100. Based on the analysis of the foaming processes it can be concluded that formulations PU_ P1_60 and PU_ P1_100 had slightly higher reactivity than PU_ P2_60 and PU_ P2_100. This phenomenon can be associated with the higher functionality of bio-polyol P1. However, the differences in the characteristic parameters of the foaming processes are not significant despite the very different characteristics of bio-polyols P1 and P2. The foaming process has a decisive influence on the cellular structure of foamed materials. Moreover, Hongyu Fan et al. (2013) observed that the viscosity of used bio-polyol was high which led to reduced coalescence among bubbles, consequently decreasing the cell size. The cellular structure determines both the thermal insulation properties as well as mechanical properties of porous materials. In our case, the modification of the reference system with the bio-polyols regardless of their type caused a reduction of the size of the foam cells (Fig. 3). However, an effect of the bio-polyol on the foam thermal conductivity is observed for the materials in which a petrochemical polyol was replaced with the bio-polyols in an amount of more than 60 wt,% (Table 3). In the case of the foams with a low apparent

Journal Pre-proof density (ca. 15-17 kg/m3), this effect is especially important because the polyurethane matrix constitutes only ca. 1.5% of the porous material. The modification of the reference system by replacing only 20% of the petrochemical polyol with bio-polyol P1 produced a finely pored structure. In the case of the material modified with bio-polyol P2, beneficial changes in the cellular structures of the foams were observed after replacing 60% of the petrochemical polyol with bio-polyol P2. It can be an effect of higher reactivity of PU_P2_20 and disturbing the balance between the foaming and gelling reactions. The modified open-cell PUR foams were characterized by lower apparent densities of ca. 15% compared to the reference material (PU_ref). From the economic point of view, it is one of the advantages of bio-foams, because such systems are more efficient (Table 3). The more favourable cellular structure of the modified material had an influence on the coefficient of thermal conductivity. A reduction of this parameter for the foams modified with 20php of both bio-polyols P1 and P2 was ca. 17% compared to the reference foam (Table 3) and it is directly associated with the cellular structures and lower apparent densities of the modified materials. Although the coefficient of thermal conductivity and, associated with it, heat transfer coefficient of the open-cell foams are slightly higher than for the closedcell foams, these bio-materials can still provide excellent thermal insulating and air barrier properties. The porous materials obtained in our experiment were characterized by an open cell structure because the content of closed cells was below 5%. Such materials are more permeable to moisture than closed-cell foams.

Journal Pre-proof

2 mm

2 mm

2 mm

2 mm

2 mm

2 mm

2 mm

2 mm

2 mm

2 mm

2 mm

Fig. 3. Cellular structure of the reference and modified foams. Fig. 4 presents the mechanical properties of the open-cell PUR foams. Compared to the reference foam, the compressive strength of the modified foams (measured in parallel direction to foam rise) has increased by 47, 56, 77, 79 and 68% for the foams modified with 20, 40, 60, 80 and 100% bio-polyol P1, respectively.

Table 3. Selected properties of the reference and modified open-cell PUR foams.

Journal Pre-proof

Coefficient of Symbol

Apparent density,

thermal

kg/m3

conductivity,

Heat transfer

Content of

coefficient,

closed cells, %

W/m2·K

mW/m·K PU_ref

16.28±0.31

45.76 ± 0.66

0.93 ± 0.02

<5

PU_P1_20

13.61±0.27

38.05 ± 0.65

0.75 ± 0.03

<5

PU_P2_20

13.65±0.43

38.11 ± 0.58

0.74 ± 0.00

<5

PU_P1_40

13.33±0.13

38.45 ± 0.57

0.75 ± 0.00

<5

PU_P2_40

13.35±0.12

39.20 ± 0.70

0.77 ± 0.03

<5

PU_P1_60

13.50±0.35

39.65 ± 0.57

0.78 ± 0.03

<5

PU_P2_60

13.45±0.46

39.40 ± 0.14

0.76 ± 0.01

<5

PU_P1_80

12.71±0.19

40.25 ± 0.65

0.79 ± 0.00

<5

PU_P2_80

13.24±0.08

41.15 ± 0.45

0.83 ± 0.06

<5

PU_P1_100

13.16±0.45

39.09 ± 0.45

0.76 ± 0.01

<5

PU_P2_100

13.65±0.67

40.34 ± 0.04

0.80 ± 0.01

<5

Compressive strength at 10% of deformation, kPa

50 40 30 20 10 0

a

O

2O

4O

6O

Content of P1 or P2, %

8O

1OO

P1 P2

60

Compressive strength at 10% of deformation, kPa

P1 P2

60

50 40 30 20 10 0

b

O

2O

4O

6O

8O

1OO

Content of P1 or P2, %

Fig. 4. Compressive strength of modified materials measured in two directions: parallel (a) and perpendicular (b) to the foam rise direction. In the case of the materials modified with both bio-polyols P1 and P2 the values of the compressive strength measured parallel to the foam rise direction are generally higher than those measured for the reference material. However, more beneficial for the foams based on the bio-polyol P1 were observed. Materials PU_P1_60 and PU_P2_60 were characterized by

Journal Pre-proof one of the highest values of compressive strength and it was independent of the type of biopolyols. It was observed that the compressive strength measured in a perpendicular direction did not depend on the type of bio-polyol. The content of bio-polyols up to 40 php in the polyol premix did not have an influence on the compressive strength of the modified foams. Increasing the content of bio-polyol P1 and P2 in the polyol premix above 40 php caused worsening of the mechanical properties slightly, however the dimensional stability measured at 70 and -25oC of those materials were satisfactory. The changes in each dimension did not exceed 0.6% regardless of the temperature applied (70 or – 25oC) of conditioning for 24 h (Table 4). Table 4. Dimensional stability of the foams measured at 70oC and -25oC. Symbol

a, %

b, %

c, %

70oC

-25oC

70oC

-25oC

70oC

-25oC

0

0

-0.04

0.01

-0.03

0

PU_P1_20

-0.06

0.02

-0.02

0.02

-0.25

-0.05

PU_P2_20

-0.09

0.02

-0.07

0.04

-0.46

0.05

PU_P1_40

0.01

-0.03

-0.05

0.04

-0.08

0.04

PU_P2_40

-0.06

0.01

-0.08

0.02

-0.25

-0.02

PU_P1_60

0.01

0

0.18

-0.18

-0.06

0.09

PU_P2_60

-0.08

0.02

-0.24

0.02

-0.59

0.05

PU_P1_80

-0.12

-0.04

-0.10

0.16

0.02

0.03

PU_P2_80

-0.17

-0.03

-0.18

0.02

-0.15

-0.01

PU_P1_100

-0.09

0.01

0.16

-0.08

0.28

-0.18

PU_P2_100

-0.21

0.03

-0.13

0.02

-0.36

0.04

PU_ref

The thermal stability of PUR foams is important from the scientific and technological points of view. In order to evaluate the behaviour of PU-ref and the bio-foams, TGA and DTG tests were conducted under a nitrogen atmosphere. The TGA and DTG curves of the materials are presented in Fig. 5. The summarized results of the thermogravimetric analysis of the materials are listed in Table 5. Table 5. Thermal properties of open-cell rigid polyurethane foams

Journal Pre-proof Symbol

T5%, °C

Tmax1, °C

Tmax2, °C

Residue at 800°C, %

PU_ref

280

332

490

15

PU_P1_20

266

330

488

15

PU_P2_20

270

330

483

14

PU_P1_40

268

322

488

18

PU_P2_40

271

329

481

16

PU_P1_60

270

328

483

15

PU_P2_60

266

330

482

13

PU_P1_80

268

323

480

14

PU_P2_80

264

323

478

11

PU_P1_100

266

313

478

12

PU_P2_100

262

313

471

14

Tmax1 - the maximum degradation rate temperature of the first step; Tmax2 - the maximum degradation rate temperature of the second step; T5% - the temperature corresponding to a mass loss of 5%.

1.0

2.0

0.8

40

0.6 0.4

20

0.4

40

o

0.6 60

Deriv. weight, %/ C, %

1.0

80

Weight loss, %

1.4 1.2

60

0.8

1.6

o

Weight loss, %

80

PU_P1_100 PU_P2_100

100

1.8

Deriv. weight, %/ C, %

PU_ref PU_P2_20 PU_P2_40 PU_P2_60 PU_P2_80 PU_P2_100

100

0.2

20

0.2 0.0

0 100

200

300

400

500 o

Temperature, C

600

700

800

0 100

200

300

400

500

0.0 600

o

Temperature, C

Fig. 5. TGA and DTG curves of bio-foams: a. reference and modified with bio-polyol P2 , b. modified with bio-polyols P1 and P2 in amount 100 php. The temperature at the beginning of thermal degradation T5% was the highest for the reference sample (280°C). Replacing the petrochemical polyol with either the P1 or P2 biopolyols reduced T5%. This changes were in the range of 262-271°C. The lowest value of this temperature was observed for the materials with a 100% bio-polyol content. This indicates that these materials are more susceptible to thermal degradation. The beginning of thermal

Journal Pre-proof degradation takes place mainly in rigid segments. This proves that the application of used cooking oil-based polyol caused changes in the structure of these segments in the final foams. The thermal degradation process of rigid polyurethane foams takes place in two stages. The lowest temperature Tmax1 and Tmax2 of the maximum degradation rate was exhibited by the foams with the highest content of the used cooking oil-based polyols. The first degradation stage (313-332°C) is related to the degradation processes of urethane and urea bonds in rigid segments (Levchik and Weil, 2004; Szycher, 2012). The second stage of degradation is related to the decomposition of fragments such as esters or more strongly bonded fragments associated with the polyol and probably to the degradation of the remaining carbonaceous materials from the previous step (Lin et al., 2009). In the thermograms of the foams with the highest content of the bio-polyols, the peak corresponding to the distribution of bonds in the soft phase of the foams begins to be visible. Conclusions Main problem associated with application waste in synthesis components for plastic is repeatability of waste. Used cooking oil can be characterized by differences in iodine value due to side reactions during frying process. Iodine value determine hydroxyl value of biopolyols. The hydroxyl values of bio-polyols used to preparation open cell polyurethane foams were 140 and 159 mgKOH/g. Significant differences were in the case of viscosities of biopolyols - 3275 and 961 mPa·s. It was concluded that differences in hydroxyl value and viscosity didn’t affect on reactivity of polyurethane systems, nevertheless on content of biopolyol. The compressive strength of PU_P1_60 and PU_P2_60 measured in parallel direction has increased by ca. 80% respect to reference material. In this case effect of different properties of bio-polyols was not observed. Modification of reference system with bio-polyols caused lower temperature at the beginning of thermal degradation. However, for application point of view such thermal stability it is satisfactory. The most important conclusion from these studies is, despite the significant difference in the properties of the components for synthesis, the properties of open cell polyurethane foams are comparable. The results confirm that the differences in the properties of the iodine number which determines the hydroxyl number are of no importance in the case of material properties. Acknowledgements

Journal Pre-proof The authors gratefully acknowledge the support for this work by a research grant from the National Center for Research and Development in Poland under the Lider Program, contract no. LIDER/28/0167/L-8/16/NCBR/2017. The authors are grateful to BorsodChem Zrt. company, the member of Wanhua Chemical Group, for supplying isocyanates. References Ahvazi, B., Wojciechowicz, O., Xu, P., Ngo, T.-D., Hawari, J., 2017. Formation of LignoPolyols: Fact or Fiction. BioResources 12, 6629–6655. https://doi.org/10.15376/biores.12.3.6629-6655 Andrzejewski, J., Szostak, M., Barczewski, M., Łuczak, P., 2019. Cork-wood hybrid filler system for polypropylene and poly(lactic acid) based injection molded composites. Structure evaluation and mechanical performance. Compos. Part B Eng. 163, 655–668. https://doi.org/10.1016/j.compositesb.2018.12.109 Barczewski, M., Andrzejewski, J., Matykiewicz, D., Krygier, A., Klozinski, A., 2019a. Influence of accelerated weathering on mechanical and thermomechanical properties of poly(lactic acid) composites with natural waste filler. Polimery 64, 119–126. https://doi.org/10.14314/polimery.2019.2.5 Barczewski, M., Sałasińska, K., Szulc, J., 2019b. Application of sunflower husk, hazelnut shell and walnut shell as waste agricultural fillers for epoxy-based composites: A study into mechanical behavior related to structural and rheological properties. Polym. Test. 75, 1–11. https://doi.org/10.1016/j.polymertesting.2019.01.017 Bene, H., Prociak, A., Trhlíkov, O., Walterov, Z., 2019. Investigation of epoxidation of used cooking oils with homogeneous and heterogeneous catalysts Maria Kura n b , Wioletta Stochli n 236. https://doi.org/10.1016/j.jclepro.2019.117615 Fan, H., Tekeei, A., Suppes, G.J., Hsieh, F., 2013. Rigid polyurethane foams made from high viscosity soy‐polyols. J. Appl. Polym. Scien. 127, 1623-1629. https://doi.org/10.1002/app.37508 Formela, K., Zedler, L., Hejna, A., Tercjak, A., 2018. Reactive extrusion of bio-based polymer blends and composites – Current trends and future developments. Express Polym. Lett. 12, 24–57. https://doi.org/10.3144/expresspolymlett.2018.4 Gómez-Fernández, S., Günther, M., Schartel, B., Corcuera, M.A., Eceiza, A., 2018. Impact of the combined use of layered double hydroxides, lignin and phosphorous polyol on the fire behavior of flexible polyurethane foams. Ind. Crops Prod. 125, 346–359.

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Declaration of interests x The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

The authors gratefully acknowledge the support for this work by a research grant from the National Center for Research and Development in Poland under the Lider Program, contract no. LIDER/28/0167/L-8/16/NCBR/2017.

Journal Pre-proof The use of vegetable oils in a "double way". Open-cell polyurethane foams based on modified used cooking oil.

Beneficial effects of bio-polyols on the cellular structures. Different properties of bio-polyols not affect on properties of open cell foams.