Flexible polyurethane foams synthesized with palm oil-based bio-polyols obtained with the use of different oxirane ring opener

Industrial Crops & Products 115 (2018) 69–77

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Flexible polyurethane foams synthesized with palm oil-based bio-polyols obtained with the use of different oxirane ring opener

T

⁎

Aleksander Prociak, Elżbieta Malewska , Maria Kurańska, Szymon Bąk, Paulina Budny Cracow University of Technology, Department of Chemistry and Technology of Polymers, Cracow, Poland

A R T I C L E I N F O

A B S T R A C T

Keywords: Flexible polyurethane foam Palm oil Bio-polyol Oxirane ring opener Cell structure Mechanical properties

The synthesis of flexible polyurethane foams with different content of various palm oil-based polyols (10–25 wt. %.) and the reference sample based on a petrochemical polyol were performed. The bio-polyols were synthesized with the use of different oxirane ring opener (water and diethylene glycol). Two different bio-polyols with hydroxyl values 102 and 128 mgKOH/g were used. It was observed that the more the bio-polyols used, the hardness and hysteresis of the modified foams have higher value. The addition of both bio-polyols results in an increasing the support factor and a reduction of the resilience value up to 25%. The use of the bio-polyols results in unification of the cellular structure and increasing of closed cell content. The foams after fatigue tests have very good properties and could be applied by the furniture industry, taking into account especially their support factor in the range of 1.7–3.2 and compression set below 1.7%.

1. Introduction Polyurethanes (PURs) were first synthesized in 1937. (PURs) are classified as polymeric materials, which are produced in a polyaddition reaction of multifunctional isocyanates with polyols. PUR materials may be obtained in the form of a solid or foamed products. Currently, PURs are widely used in industry and daily life due to their universal properties and relatively easy processing. Areas of polyurethanes application are still developing. PURs most often are used in the furniture, automotive, footwear, construction and refrigeration industry (Szycher, 1999; Woods, 1990). There are multiple applications in which they appear as foamed materials. These types of materials may be in the form of flexible, viscoelastic, semi-rigid and rigid foams (Szycher, 1999; Woods, 1990; Gandhi et al., 2015; Prociak et al., 2014). Nowadays, economy and ecology determine the interest of polymeric products. Due to the specific properties and economical aspects, more and more petroleum polyols used in the synthesis of PURs are replaced with bio-polyols. Some of bio-polyols are received from vegetable oils such as palm oil, linseed oil, sunflower oil, rapeseed oil or castor oil. Polyols derived from lignin or suberin are also another group of bio-polyols. The harmful effect on the environment of petrochemical polyols can be reduced by replacing them with hydroxyl derivatives of raw materials obtained from renewable resources. From an economical point of view plant derived materials can be cheap and easily available (Gandhi et al., 2015; Ibrahim et al., 2015; Orgilés-Calpena et al., 2014;

⁎

Quirino et al., 2015; Xie et al., 2014; Cordeiro et al., 1999; Nadji et al., 2005; Cateto et al., 2008). Vegetable oils are triglycerides of fatty acids. Mostly, these compounds, do not have in their structure groups which are able to react with isocyanates. Therefore their modification is necessary in order to apply them in PUR systems. The aim of such modification is to convert oils preparation of bio-polyols from vegetable oils the following are mostly described in the literature epoxidation and oxirane ring opening, hydroformylation and reduction of aldehyde groups, transesterification, hydrogenation and ozonolysis, and nucleophilic substitution (Dworakowska et al., 2012; Kurańska et al., 2015, 2016; Lumcharoen and Saravari, 2014; Prociak, 2008; Prociak et al., 2015). The application of various methods for the synthesis of bio-polyols from vegetable oils results in different properties of obtained hydroxyl derivatives, such as hydroxyl value (OHV), dynamic viscosity and average molecular weight. The bio-polyols prepared by epoxidation and oxirane ring opening with the monohydric alcohols are characterized by the presence of secondary hydroxyl groups only, of which reactivity with an isocyanate group is less than the reactivity of primary groups (Prociak et al., 2014). On the other hand the application, as the epoxide ring opening agent of a such substance like a compound having two hydroxyl groups allows to synthesis bio-polyols with both primary and secondary hydroxyl groups. The synthesis method affects the OHV, which depends also on the type of vegetable oil that was used as a raw material. Bio-polyols may contain in their structure hydroxyl groups

Corresponding author at: Cracow University of Technology, Department of Chemistry and Technology of Polymers, ul. Warszawska 24, 31-155 Cracow, Poland. E-mail address: [email protected] (E. Malewska).

https://doi.org/10.1016/j.indcrop.2018.02.008 Received 4 May 2017; Received in revised form 28 January 2018; Accepted 3 February 2018 0926-6690/ © 2018 Elsevier B.V. All rights reserved.

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of the partial replacement of petrochemical polyols with the bio-polyol based on palm oil on FPURF properties. Based on those results, it was found that the apparent density of foams contained the bio-polyol based on palm oil was higher comparing to the reference foam. Moreover, it turned out that the mechanical properties of the modified materials were improved. The foams with the addition of 15% by weight of the bio-polyol had almost twice the tensile strength and three times the compressive stress at 40% strain in comparison to the petrochemical reference foams. The foams resilience had a tendency to increase with an increased addition of the bio-polyol. The analysis of the results showed that with the increased concentration of palm bio-polyol, the foam cellular structure was more homogenous (Pawlik and Prociak, 2012). Dworakowska et al. (2012) have synthesized FPURF with the addition of bio-polyols based on rapeseed oil. They used two bio-polyols, one with an OHV of 196 mgKOH/g and the second having an OHV of 114 mgKOH/g. The results showed that the addition of such bio-based raw materials affects the foam cell structure, namely, it promotes the formation of a homogeneous cellular structure and decreases the average cross-section surface of cells (Dworakowska et al., 2012). The foams containing rapeseed oil-based polyols characterized by greater compressive strength, but tensile strength and elongation at break were characterized by smaller values. The rebound resilience test showed that the samples containing the bio-polyols were less resilient. It was also observed that the compressive strength tends to increase with the increased content of the bio-polyol, while the tensile strength in this case is reduced. Furthermore, the results showed that the mechanical properties vary depending on the kind of the bio-polyol. The foam modified with the bio-polyol having a higher OHV was characterized by a higher compressive strength but lower tensile strength, lower elongation at break and lower resilience than the sample with the bio-polyol having a lower OHV (Dworakowska et al., 2012). Gu et al. (2012) have synthesized FPURF using bio-polyols based on the soybean oil. Those studies have shown that the foams based on petrochemical polyols were characterized by lower apparent densities

located inside the main hydrocarbon chain. Such groups are characterized by a low reactivity. Primary hydroxyl group present at the end of hydrocarbon chains has the greatest ability to react, so the synthesis method of epoxidation and the epoxide ring opening results in a typically derived bio-polyols having a lower reactivity than polyols obtained using other techniques such as: ozonolysis, hydroformylation or ethoxylation because of the presence of secondary hydroxyl groups in the bio-polyol structure (Zhang and Kessler, 2015). The solution for the increased viscosity problem of bio-polyols derived from vegetable oils and synthesized by epoxidation and the opening of oxirane rings is to find a suitable epoxy group opening agent. The reduction of the biopolyol viscosity is possible by the introduction of long chain components at the stage of oxirane rings opening stage. Chain branchs can cause problems in the formation of crystalline structures at low temperatures (Salimon et al., 2011). Compounds containing in its structure active hydrogen atom are used in the process of epoxide ring opening as nucleophilic agents. In the synthesis of bio-polyols the amine groups can be also used. Therefore, the type of bio-polyol depends on the selection of the epoxy ring opening agent (Nohra et al., 2013). By the application of water, mono- or polyhydric alcohols in the bio-polyols synthesis, hydroxyl derivatives with different characteristic can be obtained. Moreover, by applying an aliphatic amine, bio-polyols with amine functional groups can also be obtained (Patent PL 206376 B1). Fig. 1a–c illustrate examples, a two-stage process of the bio-polyols synthesis (Lumcharoen and Saravari, 2014). The need, to replace petrochemical polyols with renewable raw materials, has prompted scientists to investigate the effect of biopolyols addition to the composition of flexible polyurethane foams (FPURF) on their properties. It was found that natural based raw materials change both physical and chemical properties of FPURF and such modifications most often result in a more ordered cellular structure of the foams modified with bio-polyols comparing to reference materials (Dworakowska et al., 2012; Pawlik et al., 2009; Pawlik and Prociak, 2012). Pawlik and Prociak (2012) have conducted a study of the influence

Fig. 1. a) The oxidation reaction of palm oil with hydrogen peroxide, b) the oxirane ring opening reaction of epoxidized palm oil by diethylene glycol (DEG), c) the oxirane ring opening reaction of epoxidized palm oil by water (Lumcharoen and Saravari, 2014).

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than the foams modified with bio-polyols. It was also noted that the foams modified with the soy-based bio-polyol having a higher OHV had a higher apparent density than the sample with the bio-polyol having a lower OHV. The bio-foams based on oil derivatives compared with the foams based on non-renewable raw materials had a more ordered structure and more closed cell content (Gu et al., 2012). Comparing the sample based on petrochemical oils with vegetable oil based ones, it is clear that depending on the type of applied bio-polyol, the foams mechanical properties can be improved or impaired. The maximum elongation for both foams containing bio-polyols were lower than the value assigned to the respective reference foam (Gu et al., 2012). Malewska et al. (2015) have synthesized FPURF using rapeseed oil based bio-polyol in the range of 13–22 wt.% in polyol premixes. It was found that, the bio-polyol addition influences on the cell structure of modified foams because it gives an effect similar to surfactants, what results in smaller cell sizes. Additionally, it was observed that the mechanical properties of prepared foams depend on the concentration of rapeseed oil-based polyol. The introduction of such bio-polyol to PUR formulation reduced hardness and resilience of final foams. What is more, the foams modified with the rapeseed oil-based polyol had higher value of support factor in comparison to the reference foam (Malewska et al., 2015). The studies on using bio-polyols from rapeseed, palm and soybean oils show that it is possible to partially substitute petrochemical polyols. The addition of bio-polyols influences especially on the mechanical properties of the obtained products. It appears that in some cases, the bio-based raw materials have improved compression strength and tensile strength of FPURF. Bio-polyols also affect the foams apparent density and their cell structure (Dworakowska et al., 2012; Gu et al., 2012; Malewska et al., 2015; Pawlik et al., 2009; Pawlik and Prociak, 2012). The aim of this work as the synthesis of FPURF and the evaluation of selected properties of foams containing two type of bio-polyols based on palm oil, which were synthesized using two different agents at the oxirane ring opening stage. The scope of work included also the synthesis of reference material, and samples containing various amounts (10–25%) of the bio-polyols derived from palm oil. The cellular structure of foams was analyzed and following properties such as apparent density, resilience, support factor, hysteresis loops and hardness were determined.

Table 1 Characteristic of used polyols. Polyol symbol

F3600

P102

P128

OHV [mg KOH/g] AVa[mg KOH/g] Water content [% mas.] Viscosity [mPa s] Number average molecular weight [g/mol] Functionality State at 20 °C Producer

48 < 0.1 0.10 580b 3600 3.0 Liquid PCC Rokita

102 9.0 0.11 2319c 3657 3.0 Solid CUTd

128 2.4 0.18 323c 5884 2.8 Solid CUTd

a b c d

Acid value. At 25 °C. At 50 °C. Cracow University of Technology.

bio-polyols. It was due to their different reactivity comparing to the petrochemical polyol. Isocyanate index (INCO) of all FPURF systems was 1.0. Firstly, components such as polyols, catalysts, water and surfactant were weighed and mixed together in a polypropylene cup for 30 s. Palm oil based bio-polyols were heated to 60 °C before adding to the petrochemical polyol, due to the fact that they are solids at room temperature. Secondly, an appropriate amount of isocyanate was added to the polyol pre-mixture and vigorously stirred at 1 200 rpm for 10s. The reaction mixture was poured into a mold (120 × 120 × 100 mm3). A free growth of the foams was carried out in a vertical direction. The synthesized foams were seasoned at 70 °C for 1 h. After 24 h from the synthesis, the foams were cut into the samples, accordingly to the applied ISO standards to measure their properties. Cellular structure of prepared porous materials was evaluated using SEM images. The foams were cut into sample in a vertical and horizontal direction in relation to the rise direction. To evaluate high, width and average cross-section area of cells, each photography was analyzed using the Aphelion™ image analysis software. The anisotropy index (I) was calculated as a ratio of cell height (h) to cell width (w). The apparent density of foam samples was measured according to EN ISO 845:2006 standard. Mechanical properties analysis were carried out after 24 h and 3 months from the foams synthesis, as well as after the fatigue test. Compressive strength was measured using Zwick Z005 TH Allround-Line according to the PN-EN ISO 3386-1:1997 standard. Each sample was compressed four times to 75% of its initial height. Between the successive measurements, 5 min intervals were introduced in order to allow the sample to return to its initial dimensions. The program recorded values of compressive stress during loading and unloading of samples. The hysteresis loop diagrams of compressive stress are based on those results. Hysteresis, support factor, compressive stress value at 75% deformation and stress-strain characteristic for 40% compression (hardness) were determined. The support factor and hysteresis were calculated using the following formulas (1) and (2) respectively (Malewska et al., 2015):

2. Experimental section FPURF were synthesized with the use of polyol mixtures of: Rokopol F3600 – glycerine-based copolymer block-statistic on ethylene oxide and propylene oxide, P102 – palm oil based bio-polyol synthesized by the epoxidation of unsaturated bonds in palm oil chains and the oxirane rings opening by water, P128 − palm oil based bio-polyol synthesized by the epoxidation of unsaturated bonds present in palm oil chains and the oxirane rings opening by diethylene glycol (DEG). A detailed description of the palm oil bio-polyols obtaining process has been described in our earlier publications (Marcovich et al., 2017). The characteristic of the polyols used in the synthesis of FPURF is shown in Table 1. Moreover, in the foam formulations the following components were used: Toluene diisocyanate (TDI) supplied by Ciech Pianki S.A., catalysts (Dabco T-9, Dabco BLV) produced by Air Products, surfactant (Niax L-618) produced by Momentive Performance Materials and carbon dioxide (blowing agent), that was generated in the reaction of an isocyanate component with water. All foams were prepared at room temperature using the one-shot method. The formulations used to prepare FPURF (reference and modified with bio-polyols) are shown in Table 2. The reference foam was synthesized with the use only the petrochemical polyol. In order to obtain foamed materials with proper quality and physical and mechanical properties it was necessary to change the amounts of catalysts, in the formulations modified with the

Support factor =

F65% F25%

(1)

where: F65%is the stress at 65% deformation [kPa], F25%is the stress at 25% deformation [kPa].

Hysteresis =

Wload − Wunload Wload

(2)

where: Wload is the work during the loading of a sample [J], Wunload is the work during the unloading of a sample [J]. Moreover, fatigue tests were carried out in order to measure the stability of foams mechanical parameters after 20 000 cycles of deformations. Samples were compressed by 50% of their initial height, 71

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Table 2 Formulations of synthesized foams. Component [g]

Foam symbol

Polyol F3600 Bio-polyol P102 Bio-polyol P128 Catalyst DABCO T-9 Catalyst DABCO BLV Silicone oil NIAX L-618 Water Isocyanate TDI

REF

10 P102

15 P102

20 P102

25 P102

10 P128

15 P128

20 P128

25 P128

100 – – 0.18 0.28 1.0 4.2 49.3

90 10 – 0.11 0.53 1.0 4.2 50.1

85 15 – 0.11 0.53 1.0 4.2 50.5

80 20 – 0.11 0.53 1.0 4.2 51.0

75 25 – 0.11 0.53 1.0 4.2 51.6

90 – 10 0.20 0.53 1.0 4.2 50.6

85 – 15 0.20 0.53 1.0 4.2 51.3

80 – 20 0.20 0.53 1.0 4.2 51.9

75 – 25 0.20 0.53 1.0 4.2 52.6

reference foam. In addition, it was observed that the usage of P102 biopolyol causes greater changes in the cell size of modified FPPUR than P128 bio-polyol. The foams containing P102 bio-polyol have a lower number of cells per area unit, which have a larger average size than in the case of the foams containing P128 polyol. The initial viscosity of bio-polyols used to prepare PUR foams is one of the most important factors, which influence on the cellular structure of the resultant foams. A high viscosity of polyols may cause problems when mixing the PUR ingredients and affected the generation and distribution of the cells formed by the blowing agent (Dong et al., 2015; Luo et al., 2013). The average width and height of the cells in the compared foams change proportionally to the increase of cell area, therefore the anisotropy index is similar for all foams in a particular test direction. Anisotropy index of the cells examined in the perpendicular cross-section to the foam rise direction oscillate around a value of 1, which means that the cells are approximately spherical in shape (Fig. 2a). However, in the case of cells analyzed on a cross-section parallel to the foam rise direction, their anisotropy index increases from value of the of 1.02 for the reference foam to the value between 1.2 and 1.4 for the foams modified with the both bio-polyols (Fig. 2b). This phenomenon is often described as cell elongation in the direction of foam rise (Malewska et al., 2015). Increasing anisotropy of cells in foams modified with the bio-polyols in comparison to the reference foam may be caused by a higher concentration of a blowing catalyst, which might cause a more rapid rise of the modified foams. SEM images of the obtained foams are shown in Fig. 2a and b. These images reveal less defects of windows in the foams obtained with a higher content of both bio-polyols. It means that these foam have more closed cells structure. The similar effect has been noticed also in other works, concerning PUR foams modified with bio-polyols and it can be explained by an action of bio-polyols similar for surfactants decreasing

with a frequency of 0.5 Hz. Then after 1 h of relaxation time, compression test was performed in the same manner as before the fatigue test. The compression set of the foams was measured after 20 000 compression cycles and calculated using the following formula (3):

Compression set =

(h 0 − h20000) ·100% h0

(3)

where: h0 is high of foam sample before fatigue test, h20000 is high of foam sample after 20 000 compression cycles. Foam resilience was determined according to the ball rebound test (EN ISO 8307:2007standard), measured parallel to the foam rise direction. 3. Results and discussion The cellular structure of FPPUR has generally significant influence on their physical-mechanical properties. Therefore, it is important to evaluate cellular structure of compared foams. The number, size and surface of cells cross-section were determined on the basis of converted SEM images. An adjustment of an original SEM image of PUR foam to be analyzed was made with using the Aphelion software. The results of the cellular structure analysis are presented in Table 3. Our studies showed that the addition of both bio-polyols increases the average cell cross-section area, as well as cell high and width in the relation to these parameters for the cells in the reference foam. Increasing the cell size corresponds to a reduction in their number per 1 mm2. However, it was not observed that the amount of used biopolyols affected the size of the cells. Their sizes fluctuate irrespective of the amount of used bio-polyols, however are greater than the respective values characterizing the Table 3 Foams cell structure characterization. Perpendicular surface to the rise direction

Cell number Cell cross-section surface. mm2 Cell height. mm Cell width. mm Anisotropy index

REF

10P102

15P102

20P102

25P102

10P128

15P128

20P128

25P128

33 0.17 0.45 0.44 1.02

18 0.25 0.56 0.55 1.02

25 0.20 0.47 0.47 1.00

27 0.19 0.45 0.48 0.94

16 0.33 0.60 0.59 1.02

25 0.20 0.48 0.50 0.96

28 0.19 0.46 0.47 0.98

22 0.23 0.55 0.52 1.06

29 0.20 0.51 0.49 1.04

REF

10P102

15P102

20P102

25P102

10P128

15P128

20P128

25P128

35 0.18 0.45 0.44 1.02

18 0.25 0.64 0.44 1.45

25 0.23 0.55 0.44 1.25

18 0.26 0.61 0.48 1.27

13 0.23 0.51 0.43 1.19

25 0.23 0.60 0.45 1.33

23 0.21 0.58 0.47 1.23

17 0.26 0.60 0.47 1.28

21 0.23 0.58 0.42 1.38

Parallel surface to the rise direction

Cells number Cell cross-section surface. mm2 Cell height. mm Cell width. mm Anisotropy index

72

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apparent density

hardness at 65% aŌer 24 hours hardness at 65% aŌer faƟque test

30

10

25

8

20

6

15

4

10

0 REF

10 P102

15 P102

20 P102

Hardness at 65% [kPa]

12

Apparent density [kg/m 3]

35

hardness aŌer 3 months

hardness aŌer faƟque test

apparent density

20 0.4 15 10

5

5

0

0

b

30

10

25

hysteresis aŌer 24 hours

20 0.4

15 10

2

5

5

0

0

20 P128

d

25 P128

0.6

25

4

15 P128

25 P102

hardness at 65% aŌer 3 months

6

10 P128

20 P102

hardness at 65% aŌer faƟque test

20

REF

15 P102

hardness at 65% aŌer 24 hours

8

0

0.0 10 P102

30

Hardness at 65% [kPa]

35

12

0.2

REF

40

14

c

0.6

25

25 P102

hardness aŌer 24 hours

hardness at 65% aŌer 3 months hysteresis aŌer 24 hours

30

40

14

2

Hardness at 40% [kPa]

a

Hysteresis

hardness aŌer 3 months

hardness aŌer faƟque test

15 10

Hysteresis

hardness aŌer 24 hours

Apparent density [kg/m3]

Hardness at 40% [kPa]

Fig. 2. SEM images of (A) REF, (B) 10P102, (C) 15P102, (D) 20P102, (E) 25P102, (F) 10P128, (G) 15P128, (H) 20P128, (I) 25P128 at cross-section perpendicular surface to the foam rise direction, (J) REF, (K) 10P102, (L) 15P102, (M) 20P102, (N) 25P102, (P) 10P128, (R) 15P128, (S) 20P128, (T) 25P128 at cross-section parallel surface to the foam rise direction.

0.2

0.0 REF

10 P128

15 P128

20 P128

25 P128

Fig. 3. Hardness at 40% deformation and apparent density of foams modified with the bio-polyols P102 (a) and P128 (b) and hardness at 65% deformation and hysteresis of foams modified with P102 (c) and P128 (d).

polyols is usually slightly higher (by ca. 10%) than in the case of reference foams obtained using petrochemical polyols (Dworakowska et al., 2012; Gu et al., 2012; Malewska et al., 2016a; Michałowski and Prociak, 2015; Pawlik and Prociak, 2012; Rojak and Prociak, 2012; Zhang and Kessler, 2015). The effect noticed for the foams modified

surface tension during the foaming process of PURs (Pawlik and Prociak, 2012; Prociak et al., 2017). The addition of the palm oil-based bio-polyol increases the apparent density and hardness at 40% deformation of studied foams (Fig. 3a, b). The apparent density of foams modified with vegetable oil based bio-

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REF 10P102 15P102 20P102 25P102

70 60

60 Hardness [kPa]

50

REF 10P128 15P128 20P128 25P128

70

a

40 30

50 40 30

20

20

10

10

0

b

0

0

15

30

45

60

75

0

15

DeformaƟon [%] REF 10P102 15P102 20P102 25P102

60 50

45

60

REF

70

c

75

d

10P128 60

15P128 20P128

50 Hardness [kPa]

70

30

DeformaƟon [%]

40 30

25P128

40 30

20

20

10

10 0

0 0

15

30

45

60

0

75

15

30

45

60

75

Fig. 4. The hysteresis loops of the REF and foams modified with different content of P102 (a) and P128 (b) bio-polyols after 3 months from synthesis and P102 (c) and P128 (d) biopolyols after fatigue test of 20 000 compressions.

2007). It the case of studied foams it was also noted that the small increase of the apparent density was followed by a significant increase of the hardness in the case of materials containing the bio-polyol P102. For example, for the 25P102 formulation, the hardness of the respective foam increased ca. 63.4% comparing to the 20P102 foam, while the apparent density of the 25P102 foam is higher only ca.3.5 kg/m3 (11.4%). In contrast, the foam containing P128 bio-polyol was characterized by a proportional increase of both hardness and apparent density. The hardness of the 25P128 foam increased ca. 8.3% comparing to the 20P102 foam, while the apparent density of the 25P102 foam is higher for 8.3%. The hardness values of the material obtained with the P128 bio-polyol may be less than for P102 foams due to differences in chemical structure and functionality of the applied biopolyols. The foams modified with bio-polyols can have a lower hardness due to the plasticization effect of dangling hydrocarbon chains in the structure of bio-polyols (Malewska et al., 2016b). However, the OHV and functionality of used bio-polyols have also an important influence on the foam hardness (Michałowski and Prociak, 2015; Prociak et al., 2012). In the case of the PUR systems modified with the bio-polyols P102 and P128, their high OHV caused the increase of necessary isocyanate amount and affected the hardness of the both types of modified foams. Higher hardness values were noticed in the case of the foams modified with the P102 bio-polyol. The use of 25 wt.% of this bio-

Table 4 Foams hysteresis values and compression set. Sample

REF 10 P102 15 P102 20 P102 25 P102 10 P128 15 P128 20 P128 25 P128

Hysteresis

Compression set [%]

After 24 h

After 3 months

After fatigue test

0.45 0.51 0.56 0.59 0.65 0.53 0.56 0.59 0.61

0.45 0.53 0.61 0.66 0.66 0.56 0.57 0.60 0.65

0.44 0.54 0.57 0.60 0.65 0.54 0.55 0.59 0.63

± ± ± ± ± ± ± ± ±

0.01 0.00 0.01 0.00 0.01 0.01 0.02 0.00 0.01

± ± ± ± ± ± ± ± ±

0.01 0.05 0.03 0.05 0.01 0.02 0.01 0.01 0.02

± ± ± ± ± ± ± ± ±

0.01 0.04 0.02 0.01 0.01 0.01 0.01 0.01 0.01

0.06 0.45 0.65 0.39 0.24 1.22 1.69 1.51 0.27

± ± ± ± ± ± ± ± ±

0.07 0.18 0.45 0.30 0.16 0.18 0.53 0.25 0.02

with bio-polyols can be probably related to most often higher viscosity of bio-polyols (even 7 times) comparing to the viscosity of the replaced petrochemical polyols (Pawlik and Prociak, 2012; Rojek and Prociak, 2012). Moreover, increasing the hardness of the foams is also generally observed with increasing content of bio-polyols in PUR system (Aremu et al., 2015; Das et al., 2009; Dworakowska et al., 2012; Malewska et al., 2016a,b; Michałowski and Prociak, 2015; Pawlik and Prociak, 2012; Prociak et al., 2012; Rojek and Prociak, 2012; Zhang et al., 74

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support factor aŌer 24 hours

support factor aŌer 3 months

support factor aŌer faƟgue test

resillience aŌer 24 hours

a

resilience aŌer faƟgue test 7.0

45 40

6.0

Support factor

30

4.0

25

3.0

20

Resilence [%]

35 5.0

15

2.0

10 1.0

5

0.0

0 REF

10 P102

15 P102

25 P102

b

support factor aŌer 3 months resillience aŌer 24 hours

7.0

45

6.0

40 35

5.0

30

4.0

25

3.0

20 15

2.0

Resilence [%]

Support factor

support factor aŌer 24 hours support factor aŌer faƟgue test resilience aŌer faƟgue test

20 P102

10

1.0

5

0.0

0 REF

10 P128

15 P128

20 P128

25 P128

Fig. 5. Support factor and resilience of foams modified with P102 (a) and P128 (b) bio-polyols.

Fig. 6. SEM images of 10P102 before (a) and after (b) fatigue tests.

caused by a further cross-linking of the material during its seasoning because not all the functional groups have been reacted in the first 24 h after foams preparation. In general, the reaction of isocyanate groups with secondary hydroxyl groups or moisture from the air can take place a few days after the foam synthesis causing the additional hardening of the material. It was observed that 3 months of seasoning for the materials modified with the bio-polyols resulted in an increase of their hardness especially at 65% deformation (Fig. 3c, d). In contrast, in the case of the

polyol in the polyol premix caused the increase of hardness by two times comparing to the reference foam, however the difference of apparent density of these foams was only ca. 17%. It was observed that for 3 months foam seasoning resulted in an overall increase of hardness at 40% deformation in the case of materials modified with the P102 bio-polyol. After 3 months, the hardness increased up to 14% for the sample 20P102. Foams modified with P128 bio-polyol had similar or slightly lower hardness comparing to the values measured for the reference foam. The hardness increase vs. time is 75

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It was observed that the more the bio-polyol was used, the hardness and hysteresis had higher values. The addition of both bio-polyols resulted in a beneficial increase of the support factor and a reduction of resilience value for the modified foams. The materials after fatigue tests have still very good such properties as resilience, hardness and support factor which can be interesting for potential users of flexible polyurethane bio-foams in furniture applications.

reference foams, the hardness at 65% strain had decreased by 12% after 3 months. Regardless of the type of foams, their fatigue tests resulted in an overall decrease of hardness in the whole test range. In the case of materials modified with the P128 bio-polyol hardness changes after fatigue test did not exceed 6% of difference in relation to the hardness measured after aging by 3 months. In contrast, the foams modified with the P102 bio-polyol were characterized by the changes of hardness at 65% of deformation up to 9%. The hysteresis loops determine the ability of foamed materials for energy absorbing. The use of the bio-polyols in the synthesis of PUR foams resulted in an increase of the hysteresis values when compared to the reference foam. (Fig. 4a, b). Hysteresis changes are analogous to the changes of hardness of compared foams. The higher content of the biopolyols was used, the foam hysteresis was higher. In addition, the seasoning of foams for 3 months has caused an overall increase of the hysteresis values, excluding the reference foams (Table 4). The PUR foam samples subjected to the fatigue test of 20 000 x compressions in order to determine the influence of the palm oil-based polyols on the foams dimensional stability (Fig. 4c, d). It was observed that the hardness of samples did not changed significantly after such test. It means that the introduction of the bio-polyols into FPURF did not influence significantly the foams dimensional stability as in the case of the reference foam. Furthermore, another analysis was conducted in order to determine the rebound resilience. The addition of bio-polyols based on palm oil has reduced the resilience of the modified foams (Dworakowska et al., 2012; Malewska et al., 2015; Michałowski and Prociak, 2015; Prociak et al., 2012; Srihaum et al., 2016). A trend of resilience decreasing with an increasing content of both bio-polyols in the foams was noticed (Fig. 5). Inverse relationship observed Pawlik and Prociak (2012), the analysis of those results concluded that the higher resilience was associated with the increased concentration of palm bio-polyols in PUR formulations. A similar trend of the support factor increasing as an effect of the bio-polyols content in the investigated PUR formulation was noticed (Fig. 4c, d). In the case of the foams modified with the P102 bio-polyol, the highest increase (47%) of support factor was noticed for the foam 25P102 comparing to the reference foam. Foams seasoning for 3 months resulted in an increase of their support factor value in every case. Such phenomenon is very beneficial, because the value of the support factor has increased to the value of 3. Materials characterized by the support factor with such value are considered to be comfortable. Higher changes of the support factor after foam aging was observed for the materials modified with the bio-polyols based on palm oil than for the reference material. The higher content of the bio-polyols was used the increase of the support factor was more beneficial. It can be observed that the foams based on petrochemical polyols are more resilient. Comparing different materials synthesized with the palm oil-based polyols, the highest resilience was noticed for the foams with the P128 (Fig. 4d). The seasoning of foams and fatigue tests did not result in any significant changes in the resilience of all studied materials. After the fatigue test, the foams hysteresis did not change significantly. Similar effect after multiple compressions was observed before in another research concerning the FPURF modified with rapeseed oil-based polyol (Malewska et al., 2016b). The cell structure of foams after the fatigue tests also did not change significantly. The cellular structure comparison of the material before and after 20,000 compression cycles is shown in Fig. 6. However, the cell structure after fatigue test (Fig. 6b) is less regular and some defects distinctly visible.

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