materials Article
Preparation and Characterization of Soybean Oil-Based Polyurethanes for Digital Doming Applications Vincenzo Pantone 1 , Amelita Grazia Laurenza 2 , Cosimo Annese 3 , Roberto Comparelli 4 ID , Francesco Fracassi 2 , Paola Fini 4 , Angelo Nacci 2,3 , Antonella Russo 1 , Caterina Fusco 3, * and Lucia D’Accolti 2,3, * ID 1 2 3 4
*
Greenswitch s.r.l., 71013 Ferrandina (MT), Italy;
[email protected] (V.P.);
[email protected] (A.R.) Dipartimento di Chimica, Università di Bari “A. Moro”, Via Orabona 4, 70126 Bari, Italy;
[email protected] (A.G.L.);
[email protected] (F.F.);
[email protected] (A.N.) ICCOM-CNR, SS Bari, Via Orabona 4, 70126 Bari, Italy;
[email protected] IPCF-CNR, SS Bari, Via E. Orabona 4, 70125 Bari, Italy;
[email protected] (R.C.);
[email protected] (P.F.) Correspondence:
[email protected] (C.F.);
[email protected] (L.D.); Tel.: +39-080-544-2068 (C.F. & L.D.)
Received: 18 June 2017; Accepted: 21 July 2017; Published: 25 July 2017
Abstract: Polyurethane-resin doming is currently one of the fastest growing markets in the field of industrial graphics and product identification. Semi-rigid bio-based polyurethanes were prepared deriving from soybean oil as a valuable alternative to fossil materials for digital doming and applied to digital mosaic technology. Bio-resins produced can favorably compete with the analogous fossil polymers, giving high-quality surface coatings (ascertained by SEM analyses). In addition, polyurethane synthesis was accomplished by using a mercury- and tin-free catalyst (the commercially available zinc derivative K22) bringing significant benefits in terms of cost efficiency and eco-sustainability. Keywords: catalysis; soybean oil; bio-based polyurethane; doming application
1. Introduction Since 1937, pioneering works regarding to the polyurethanes (PU) [1] show that these polymers can be obtained with different properties ranging from rigid glasses to flexible foams, and used as elastomers, adhesives, coatings, resins, and so on [2–5]. Polyurethane linkages are usually obtained through the reaction of polyols with isocyanates, using hazardous Lewis acids as catalysts (e.g., mercury-compounds) and/or toxic bases (e.g., tertiary amines) [6–8]. Over recent years, the Hg compounds have suffered from severe restrictions by the European Chemical Agency (ECHA), while the derivatives of Sn (IV) are still admitted although equally toxic [9]. A special application of PU is digital doming, a process which adds value to any shape or size of non-porous material by coating the surface with a thick layer of resin (up to 5 mm) having a dome shape, which is due to the high surface tension of the liquid polymer during solidification. This technique, which gives to the surface a three-dimensional effect, is used for a variety of applications, such as key chains, stickers and nameplates. Polyurethane-resin doming is currently one of the fastest growing markets in the field of industrial graphics and product identification, as PU resins are very durable, tough long-lasting polymers that cannot be easily scratched or dented. In addition, a good-quality resin does not yellow when exposed to UV and presents no health and safety issues both in production and final application of the cured domed object [10]. Materials 2017, 10, 848; doi:10.3390/ma10080848
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An example of digital doming ofPVC PVCtiles tilescovered covered with polyurethane coating An example of digital domingisisthe thepreparation preparation of with polyurethane coating Materials 2017, 10, x FOR PEER REVIEW 2 of 14 for decoration the decoration of walls (Figure1). 1). usefuluseful for the of walls (Figure An example of digital doming is the preparation of PVC tiles covered with polyurethane coating useful for the decoration of walls (Figure 1).
Figure 1. Example MosaicoDigitale Digitale® (Pepe Italy)) tile tile prepared with with Figure 1. Example of ofMosaico (Pepe && CO, CO,Gravina, Gravina,BA,BA, Italy)) prepared polyurethane (PU_MD) deriving from fossil Domes polyol: (a) Deposition of Tile on PVC; (b) section polyurethane (PU_MD) deriving from fossil Domes polyol: (a) Deposition of Tile on PVC; (b) section of piece of tile: The “mosaico digitale” technology uses three components: (i) the resin, from which ® (Pepe of piece of tile: “mosaico digitale” technology uses threeGravina, components: (i) thetile resin, from which Figure 1. The Example of Mosaico Digitale & CO, BA, Italy)) prepared with the the dome or lens is formed, (ii) the dispensing equipment, that receives the resin from dedicated (PU_MD) deriving from fossil Domes polyol: (a) Deposition of from Tile on PVC; (b) section dome polyurethane or lens is formed, (ii) the dispensing equipment, that receives the resin dedicated containers containers and draws it on the support surface and (iii) a support, in this case a PVC foil, that receives of piece of tile: The “mosaico digitale” technology usesinthree (i) thethat resin, from which and draws it on the support surface and (iii) a support, this components: case a PVC foil, receives the resin the resin during the “pour time”. or time”. lens is formed, (ii) the dispensing equipment, that receives the resin from dedicated duringthe thedome “pour ®
containers and draws it on the support surface and (iii) a support, in this case a PVC foil, that receives
Most of the worldwide market plastics derive from fossil fuels such as oil, coal and natural gas, the resin during the “pour time”. accounting about 7% market of world consumption these resources. Considering theand continuous Most of thefor worldwide plastics derive of from fossil fuels such as oil, coal natural gas, depletion of fossil raw materials, the oil price fluctuations and environmental problems (e.g., nonaccountingMost for of about 7% of world consumption these resources. continuous the worldwide market plastics deriveoffrom fossil fuels such Considering as oil, coal andthe natural gas, recyclable toxic wastes, CO 2 emissions and climate change), in the last decade a wide-ranging depletion of fossil raw materials, theconsumption oil price fluctuations and environmental accounting for about 7% of world of these resources. Considering theproblems continuous(e.g., research started on the production of “bio-based” polymeric materials coming directly or indirectly depletion of fossil raw materials, the oil price and environmental problems (e.g., nonnon-recyclable toxic wastes, CO2 emissions andfluctuations climate change), in the last decade a wide-ranging from renewable raw materials such as starch, cellulose, sugars, lignin, etc. [11,12]. recyclable toxic wastes, CO 2 emissions and climate change), in the last decade a wide-ranging research started on the production of “bio-based” polymeric materials coming directly or indirectly In this context, vegetable oils, such as castor, linseed, and soybean oils, have been regarded as a research started on the production of “bio-based” polymeric materials coming directly or indirectly from convenient renewable raw materials suchfor asdeveloping starch, cellulose, sugars, lignin, etc. [11,12]. renewable feedstock bio-plastics [13–17]. from renewable raw materials such as starch, cellulose, sugars, lignin, etc. [11,12]. In this context, oils, such as castor, linseed, and oils, beenour regarded Our twenty vegetable years’ experience in green chemistry [18–23] hassoybean convinced us have to extend studies as a In this context, vegetable oils, such as castor, linseed, and soybean oils, have been regarded as a convenient renewable feedstock for developing bio-plastics [13–17]. to the synthesis of bio-polyurethanes [24]. In fact, in our recent work we just reported an efficient, convenient renewable feedstock for developing bio-plastics [13–17]. cost-effective, and environmentally safer conversion soybeanhas oil convinced (SO) into soy-based PU, using as Our twenty years’ experience in green chemistryof[18–23] us to extend our studies Our twenty years’ experience in green chemistry [18–23] has convinced us to extend our studies catalyst the molybdenum(VI) dichloride dioxide (MoCl 2 O 2 ) for one-pot synthesis starting from the to theto synthesis of bio-polyurethanes [24]. recentwork workwe we just reported an efficient, the synthesis of bio-polyurethanes [24].InInfact, fact, in in our our recent just reported an efficient, epoxidizedand oil (ESO) and with 2,6-tolyl-diisocyanate (TDI). (Figureoil 2).(SO) into soy-based PU, using as cost-effective, environmentally safer conversion of soybean cost-effective, and environmentally safer conversion of soybean oil (SO) into soy-based PU, using as catalyst the molybdenum(VI) dichloride dioxide forone-pot one-potsynthesis synthesis starting from catalyst the molybdenum(VI) dichloride dioxide(MoCl (MoCl 2O22))for starting from the the OCH O 2 3 O O O Bio-Polyol epoxidized oil (ESO) with 2,6-tolyl-diisocyanate (TDI). (Figure 2). epoxidized oil (ESO) andand with 2,6-tolyl-diisocyanate (Figure O N2). 7 O (TDI). 7 fragment OCH O
O
7
[O]
O O7 OO 7 O 7 O SO O 7 O
O
7
7
O
O
7
7
O
OO
4
[O] 7
O O
7
O
CH3OH 7
7 7
7
O
OH OCH3 OCH3
7
ESO
cat. 4
7
O 7
CH3OH cat. 4
7
4
SO
O
O OO
O
O
7
O
O
ESO
Figure 2. Scheme of general
O O O O
7
7 7
O
R N
3
7
diiisocyanate
cat. O N
O O
Bio-Polyol fragment
OBio-Polyol
7 OH fragment OCH 7 HN R3 R N O HO OH N OCHO 3 7 H OCH diiisocyanate Bio-Polyol 3 O OCH3 O Intermolecular 4 7 fragment urethane linkage cat. 7 O O 7 OH O O OCH 3 OH 7 HN R soy-based PU N O soy-based HO polyol OCH3 H O OCH3 Intermolecular 4 7 urethane linkage OH O OCH3 soy-based PU synthesis of polyol soy-based PU. soy-based
O
Considering the results obtained, decided to extend our findings Figure 2. Scheme we of general synthesis of soy-based PU. to the digital doming Figure 2. Scheme of general synthesis of soy-based PU. technique, for which, to the best of our knowledge, only a few recent studies relate to the chemicalphysical properties of these resins petroleum-based [25–28], while no examples on the use of bioConsidering the the results obtained, ourfindings findingsto to digital doming Considering results obtained,we wedecided decided to to extend extend our thethe digital doming based PU resins have been reported until now. technique, which,totothe the best knowledge, only aonly few recent relate to the relate chemicaltechnique, for for which, bestofofourour knowledge, a fewstudies recent studies to the Investigations were carried out addressing two main issues: (i) the search for suitable ecophysical properties of these resins petroleum-based [25–28], while no examples on the use of biochemical-physical properties of these resins petroleum-based [25–28], while no examples on the friendly polymerization catalysts, based mainly on Zn(II) and Sn (IV) derivatives, for producing based PU resins have been reported until now. use ofmercury-free bio-based PU resins have been(ii) reported now. polyurethanes; and finding until new soy-based PU resin formulations for preparing Investigations were carried out addressing two main issues: (i) the search for suitable ecoInvestigations were carried out addressing main issues: (i) the search for suitable eco-friendly digital doming coatings of PVC tiles alternativetwo to the petrochemical ones. friendly polymerization catalysts, based mainly on Zn(II) and Sn (IV) derivatives, for producing polymerization mainly on Zn(II) (IV) derivatives, producing mercury-free All newcatalysts, materialsbased were characterized with and DSCSn and SEM techniquesfor to assess their chemical mercury-free polyurethanes; and (ii) finding new soy-based PU resin formulations for preparing and morphological properties. Thesoy-based surface hydrophilicity or hydrophobicity has been determined polyurethanes; and (ii) finding new PU resin formulations for preparing digital doming digital doming coatings of PVC tiles alternative to the petrochemical ones. using the contact angle [29,30]. coatings ofAll PVC tiles alternative the petrochemical new materials were to characterized with DSCones. and SEM techniques to assess their chemical All new materials were characterized with DSC and SEM to assess theirdetermined chemical and and morphological properties. The surface hydrophilicity or techniques hydrophobicity has been morphological properties. The surface hydrophilicity or hydrophobicity has been determined using using the contact angle [29,30].
the contact angle [29,30].
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2. Results and Discussion Investigations started with the preparation and characterization of a petrochemical polyurethane coming from the commercially available polyoland Domes Resin HGFP40702 (20 g, containing 2.Investigations Results and Discussion started with the model preparation characterization of a petrochemical the catalyst) and coming Isophorone diisocyanate prepolymer (IPDI prep.) (20.5Resin g), according to(20 a known polyurethane from the commercially model polyol Domes HGFP40702 g, Investigations started with the available preparation and characterization of a petrochemical containing the catalyst) and Isophorone diisocyanate prepolymer (IPDI prep.) (20.5 g), according to formulation already used industrially for the preparation of decorating mosaics (Figure 1). polyurethane coming from the commercially available model polyol Domes Resin HGFP40702 (20 g, a known already used industrially the preparation mosaics (Figure 1). toin The thusformulation obtained polyurethane (labeleddiisocyanate asfor PU_MD) started of to decorating cure 60(20.5 ming), and finished containing the catalyst) and Isophorone prepolymer (IPDIafter prep.) according The thus obtained polyurethane (labeled as PU_MD) started to cure after 60 min and finished 12 h. Theawetting contact angle (WCA), crucial parameter for domingofapplication being correlated known formulation already usedaindustrially for the preparation decorating mosaics (Figure 1).to in 12 h.tension, Thethus wetting contact angle a crucial doming application being ◦ indicating The obtained polyurethane as PU_MD) startedfortosurface cure after 60 min finishedof the surface was evaluated to be(WCA), 77(labeled aparameter hydrophilic [29]. DSCand analyses correlated to the surface tension, was evaluated to be 77° indicating a hydrophilic surface [29]. DSC ◦ C, suggesting 12 h. The wetting contact angle (WCA), crucial parameter for application being PU_MD in showed a glass transition temperatures Tg a= 59 thatdoming polyurethane sample is a analyses of PU_MD showed atension, glass transition temperatures Tgindicating = 59 °C, suggesting that polyurethane 3 correlated to the surface was evaluated to be 77° a hydrophilic surface [29]. DSC glass at room temperature. The density value was found to be 1.01 kg/dm . sample is a glass at roomshowed temperature. densitytemperatures value was found to be kg/dm3.that polyurethane analyses of PU_MD a glassThe transition Tg = 59 °C,1.01 suggesting Surface morphology, ascertained by SEM analyses, showed that the PU_MD possesses a Surface morphology, ascertained by SEM analyses, showed that the PU_MD a 3. sample is a glass at room temperature. The density value was found to be 1.01 kg/dmpossesses homogeneous surface that theuniform uniform covering ofpiece the piece of the tile3a). (Figure 3a). Some homogeneous surface thatallows allows the of the of the tile Some cracks Surface morphology, ascertained bycovering SEM analyses, showed that(Figure the PU_MD possesses a cracks can be observed in higher magnification image (Figure 3b). can be observed in higher magnification image (Figure 3b). homogeneous surface that allows the uniform covering of the piece of the tile (Figure 3a). Some cracks can be observed in higher magnification image (Figure 3b).
Figure 3. SEM microphotographsofofPU_MD PU_MD at at different (a)(a) 13 Kx andand (b) 180 Figure 3. SEM microphotographs differentmagnification: magnification: 13 Kx (b) Kx. 180 Kx. Figure 3. SEM microphotographs of PU_MD at different magnification: (a) 13 Kx and (b) 180 Kx.
Analysis of IR spectra of PU_MD after 12 h revealed the presence of functional groups characteristic Analysis of IR in spectra of PU_MD afterband 12 hat revealed the of functional of polyurethane, particular stretching 3400–3350 cm−1presence and C=O stretching band groups at Analysis of IR spectra ofNH PU_MD after 12 h revealed the presence of functional groups characteristic − 1 −1 −1 characteristic of polyurethane, in particular NH stretching band at 3400–3350 cm and C=O stretching 1683ofcm . The absence of the stretching band of isocyanate group at 2300–2250 cm ensures the −1 polyurethane, in particular NH stretching band at 3400–3350 cm and C=O stretching band at −1 . The absence −1 ensures polymerization. (Figure 4). bandcomplete at 1683 the stretching band isocyanate group at 2300–2250 −1. The absence 1683 cm cm ofofthe stretching band of of isocyanate group at 2300–2250 cm−1cm ensures the
the complete polymerization. (Figure complete polymerization. (Figure4).4).
Figure 4. IR spectrum of PU_MD.
FigureFigure 4. IR 4. spectrum of PU_MD. IR spectrum of PU_MD.
With the aim of preparing the analogous bio-based PU possessing physic-chemical and morphological properties like those of PU_MD, we attempted to replace the fossil polyol Domes
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With the aim of preparing the analogous bio-based PU possessing physic-chemical and
Resin HGFP40702 with the bio-polyol coming from methanolysis of ESO. This choice was based on the morphological properties like those of PU_MD, we attempted to replace the fossil polyol Domes similarity the physical of the two compounds, specifically onbased the values of Resin of HGFP40702 withand thechemical bio-polyolproperties coming from methanolysis of ESO. This choice was on viscosity, density and thephysical hydroxyl number (~3.5 of -OH per molecule). the similarity of the andgroup chemical properties thegroups two compounds, specifically on the In firstofinstance, fossil polyol was completely replaced withgroups its bio-based counterpart, the values viscosity,the density and the hydroxyl group number (~3.5 -OH per molecule). In first instance, theout fossil polyol replaced its bio-based counterpart, the 1:1.1 formulations were carried using 20 was g ofcompletely Bio-Polyol, 10.3 g with of IPDI prepolymer (OH:NCO formulations were carried out using 20 g of Bio-Polyol, 10.3 g of IPDI prepolymer (OH:NCO 1:1.1 molar ratio) and variable loadings (from 0.2% to 0.5% w/w) of DABCO T-12 (dibutyltin dilaurate molara ratio) andwhich variable loadingsto(from 0.2% to 0.5% w/w) DABCObond T-12 (dibutyltin dilaurate[6,8]. DBTDL), catalyst is known efficiently promote theof urethane forming reactions DBTDL), a catalyst which is known to efficiently promote the urethane bond forming reactions Under these conditions, polymerization time at room temperature was the same as that of[6,8]. PU_MD Under these conditions, polymerization time at room temperature was the same as that of (12 h), but the Bio-PU product (labeled as BioPU_100) proved to be rubbery at room temperature, with PU_MD (12 h), but the Bio-PU product (labeled as BioPU_100) proved to be rubbery at room Tg = 9 ◦ C, WCA = 71◦ and the density value of 1.22 kg/dm3 . temperature, with Tg = 9 °C, WCA = 71° and the density value of 1.22 kg/dm3. SEMSEM micrographs showed inthe thesurface surface morphology, evidenced by the micrographs showeda asignificant significant change change in morphology, evidenced by the formation of agglomerates, which impede formation of a homogeneous surface (Figure 5). formation of agglomerates, which impede formation of a homogeneous surface (Figure 5).
Figure 5. SEM microphotographs of BioPU_100 at different magnifications: (a) 10 Kx; (b) 180 Kx. Figure 5. SEM microphotographs of BioPU_100 at different magnifications: (a) 10 Kx; (b) 180 Kx.
To solve the problems of low Tg value (rubbery properties) and the poor surface homogeneity
To solve the problems of low (rubbery and thefragment, poor surface homogeneity of BioPU_100, most probably dueTgtovalue the flexible alkylproperties) chains of bio-polyol we decided to re-formulate by adding to the polyol aalkyl petrochemical that fragment, would produce a PU to of BioPU_100, most probably duebio-based to the flexible chains of fraction bio-polyol we decided with more to PU_MD. Indeed, according to international statements re-formulate bysimilar addingproperties to the bio-based polyol a petrochemical fraction thatstandards would produce a PUa with polymer can be labeled as “bio-based” if its “bio-carbon percentage” is at least 20–50% more similar properties to PU_MD. Indeed, according to international standards statements a (see polymer experimental [31]. if its “bio-carbon percentage” is at least 20–50% (see experimental can be labeled assection) “bio-based” section) [31]. 2.1. Selection of Fossil Polyol
Withofthe aimPolyol of selecting the appropriate fossil polyol to be mixed with the analogous bio-based 2.1. Selection Fossil
one, we carried out a screening among several homo-dispersed commercial polyols (Alcupol)
With the aim of selecting the appropriate polyolResin to beHGFP40702 mixed with the analogous bio-based displaying physic-chemical properties similarfossil to Domes (experimental section). one, Selection we carried out was a screening homo-dispersed commercial polyols (Alcupol) of polyol performedamong based onseveral the properties of polyurethanes obtained by formulation displaying physic-chemical properties similar to Domes with IPDI prepolymer, using DABCO-T12 as catalyst (TableResin 1). HGFP40702 (experimental section). Selection Results of polyol wasscreening performed based on the that properties of polyurethanes by formulation of the clearly evidenced all polyurethanes producedobtained were hydrophilic, as by WCA falling inasthe range 71°–83°. with demonstrated IPDI prepolymer, usingvalues DABCO-T12 catalyst (Table 1).As expected, Tg values were strictly dependent hydroxyl number the starting polyols, with the highestproduced values for Alcupol C5710 Results of on thethescreening clearly of evidenced that all polyurethanes were hydrophilic, (50 °C) and Alcupol R3810 (45 °C), that are also the most similar values to those of PU_MD (Table 1, ◦ ◦ as demonstrated by WCA values falling in the range 71 –83 . As expected, Tg values were strictly runs 2–3). dependent on the hydroxyl number of the starting polyols, with the highest values for Alcupol C5710 For this reason, and due to the similarity of density values, the two reagents Alcupol C5710 and (50 ◦ C) and Alcupol R3810 (45 ◦ C), that are also the most similar values to those of PU_MD (Table 1, R3810 immediately appeared as the most suitable fossil polyol counterpart for preparing Bio-PU for runs doming 2–3). applications. The final choice was based on the WCA value of the two polyurethane products For this reason, and71°) dueand to the similarity of(WCA density values, twotoreagents Alcupol C5710 and PU_5710/T12 (WCA PU_R3810/T12 79°) much the closer that of model PU_MD R3810 immediately appeared as the most suitable fossil polyol counterpart for preparing Bio-PU for doming applications. The final choice was based on the WCA value of the two polyurethane products PU_5710/T12 (WCA 71◦ ) and PU_R3810/T12 (WCA 79◦ ) much closer to that of model PU_MD (WCA
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fossil polyol used for the successive formulations.
Table 1. Screening of commercial polyols a . Table 1. Screening of commercial polyols a.
Run 1 2 3 4 5 6
Run
Polyol
Polyol
n. OH IPDI Prep Mn M n. OH IPDI (g/mol) n (mgKOH/g) (g)
Domes
1
Domes Resin Resin Alcupol C5710 Alcupol 2 Alcupol R3810 C5710 Alcupol R2510 Alcupol 3 Alcupol R1610 R3810 Alcupol C3531 Alcupol
(g/mol)
(mgKOH/g) Prep (g)
-
398
20.5
670
240
14.6
290 290 440 670 440 1050 4800
4
398 565 565 380 240 380 155 35
20.5 33.6 33.6 22.2 14.6 22.2 9.3 2.1
PU Products
Tg b
WCA c
(°) PU Products (°C) Tg b (◦ C) PU_MD
59
77
PU_R2510/T12
2
78
PU_C3531/T12
−62
83
PU_MD 59 PU_C5710/T12 50 PU_C5710/T12 50 71 PU_R3810/T12 45 PU_R2510/T12 2 PU_R3810/T12 45 79 PU_R1610/T12 −27 PU_C3531/T12 −62
c 3) d (kg/dm WCA d ◦ ( ) (kg/dm3 )
1.01
77 71 1.06 79 78 1.06 79 83
1.12
1.01 1.06 1.06 1.12 1.49 1.38
R2510 Formulation conditions: Polyol (20 g) and catalyst (0.5% w/w respect to polyol) mechanically stirred for 60 s were Alcupol b Estimated added with (as reported, ratio) and stirred PU_R1610/T12 5 IPDI prepolymer 1050 155OH:NCO 1:1.1 9.3 molar −27for further 79 2 min;1.49 R1610 error in the range of ±2–8; c Estimated error in the range of ±2. a
Alcupol C3531
6
4800
35
2.1
1.38
2.2. Catalyst and Loading conditions: SelectionPolyol (20 g) and catalyst (0.5% w/w respect to polyol) mechanically stirred Formulation a
for 60 s were added with IPDI prepolymer (as reported, OH:NCO 1:1.1 molar ratio) and stirred for
Petrochemical Alcupol wasofchosen also for selecting suitable catalyst for the errorR3810 in the range ±2–8; c Estimated error in the rangethe of ±2. further 2polyol min; b Estimated synthesis of our PUs. It is well known that organo-mercuric compounds are generally used as catalysts 2.2. Catalyst and Loading Selection in polyurethanes production, mainly in non-foaming applications where little or no blowing reaction Petrochemical polyol Alcupolof R3810 was chosen also for selecting the suitable theled to the are required [32]. However, toxicity mercury derivatives and other heavy catalyst metalsfor has synthesis of our PUs. It is well known that organo-mercuric compounds are generally used as development of alternative catalysts. catalysts in polyurethanes production, mainly in non-foaming applications where little or no blowing For our purposes, we [32]. chose organometallic compounds of Sn less toxic reaction are required However, toxicity of mercury derivatives andand otherZn, heavy metals hasthan led Hg and widely used asdevelopment catalysts inof the polyurethane to the alternative catalysts. industry. Selection was based on the evaluation of the For our purposes,reaction we chosebetween organometallic compounds Sn IPDI and Zn, less toxic than Hg and that this cure time of polymerization Alcupol R3810 of and prepolymer, assuming widely used as catalysts in the polyurethane industry. Selection was based on the evaluation of the time should not exceed the twelve hours required for the complete polymerization of PU_MD. cure time of polymerization reaction between Alcupol R3810 and IPDI prepolymer, assuming that Investigations werenot also extended to hours the catalyst whichpolymerization was evaluated by means of a set this time should exceed the twelve requiredloading, for the complete of PU_MD. of experiments carried out by varying the amount of almost all the catalysts in the range Investigations were also extended to the catalyst loading, which was evaluated by means of a 0.15–10% set of experiments carried out by varying the amount of almost all the catalysts in the range 0.15–10% w/w respect to polyol (Figure 6). respect polyol (Figure 6). Fromw/w results intoFigure 6 emerged that tin based compounds are the most active catalysts, with DABCO-T12 as the most efficient one. However, although the zinc derivative Borchi® Kat 22 displays an activity 20 times lower than DABCO-T12, the former can be suggested as more suitable catalyst due to its much lower toxicity according to the ECHA [9]. 2.3. Selection of Diisocyanate The preliminary screening aimed at selecting the best set of reactants (polyols and catalyst) was extended also to search for the best diisocyanate. IPDI prepolymers are widely used for the synthesis of rigid polyurethanes, due to the presence of cyclohexane ring, but they can also be replaced with more flexible linear aliphatic diisocyanates such as 1,6-Hexamethylene diisocyanate (HMDI) and Dicyclohexylmethane-4,40 -diisocyanate (H12MDI) (Table 2) [29,33].
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Figure 6. Cure times of PU production for some commercial Sn and Zn catalysts. Formulation Figure 6. Cure times of PU production for some commercial Sn and Zn catalysts. Formulation conditions: 20 g of Alcupol R3810, 22.2 g of IPDI prepolymer, temperature 25 °C.◦Catalysts: T12 = conditions: 20 g of Alcupol R3810, 22.2 g of IPDI prepolymer, temperature 25 C.® Catalysts: T12 = dibutyltin dilaurate (DBTDL) [DABCO T-12]; K22 = Zinc Bis(2-ethylhexanoate) [Borchi Kat 22]; T120 dibutyltin dilaurate (DBTDL) [DABCO T-12]; K22 = Zinc Bis(2-ethylhexanoate) [Borchi® Kat 22]; T120 = Dibutyl-bis(dodecylthio) stannane [T120]; UL21 = O,O′-bis(2-ethylhexyl)-(nonyl(octyl)stannanediyl) = Dibutyl-bis(dodecylthio) stannane [T120]; UL21 = O,O0 -bis(2-ethylhexyl)-(nonyl(octyl)stannanediyl) bis(carbonothioate) [UL21]. bis(carbonothioate) [UL21].
From results in Figure 6 emerged that tin based compounds are the most active catalysts, with ® Kat 22 a . Table 2. Diisocyanate in Polyurethane with R3810/Borchi DABCO-T12 as the most Effect efficient one. However,preparation although the zincAlcupol derivative Borchi® Kat 22 displays an activity 20 times lower than DABCO-T12, the former can be suggested as more suitable catalyst due to its muchDiisocyanate lower toxicity according to the ECHA [9]. ◦ b Run Product WCA (◦ ) c d (kg/dm3 ) Tg ( C) (g) 2.3. Selection of Diisocyanate 1 pure IPDI (17) PU_3810/K22/IPDI 68 79 1.11 2 preliminary H12MDI (19.7) aimed PU_3810/K22/H12MDI 77 1.06 was The screening at selecting the best 65 set of reactants (polyols and catalyst) 3 HMDI (12.6) PU_3810/K22/HMDI 19 72 extended also to search for the best diisocyanate. IPDI prepolymers are widely used for the 0.77 synthesis a Formulation conditions: Alcupol R3810 (20 g), diisocyanate (1:1.1 OH/NCO), Borchi® Kat 22 (2 g, 10% w/w of rigid polyurethanes, due to the presence of cyclohexane ring, but they can also be replaced with b Estimated error in the range of ±2–8; c Estimated error in the range of ±2. respect to polyol), cure time = 12 h;diisocyanates more flexible linear aliphatic such as 1,6-Hexamethylene diisocyanate (HMDI) and Dicyclohexylmethane-4,4′-diisocyanate (H12MDI) (Table 2) [29,33]. We tested these reactants togetherwith with pure pure IPDI, thethe influence of their skeleton We tested bothboth these reactants together IPDI,evaluating evaluating influence of their skeleton on the properties of the tile, with special attention to Tg and WCA values. on the properties of the tile, with special attention to Tg and WCA values.
From data in Table 2 clearly emerged that all polyurethanes produced were hydrophilic in nature, Table 2. Diisocyanate Effect in Polyurethane preparation with Alcupol R3810/Borchi® Kat 22 a. ◦ ◦ as demonstrated by WCA values falling in the range 72 –79 . In addition, the highest Tg values were b 3) Diisocyanate (g) Product and pureTg (°C) (Table WCA (°) c 1–2), d (kg/dm observed Run for PUs coming from diisocyanate H12MDI IPDI 3, runs while the one PU_3810/K22/IPDI 1 pure IPDI (17) 68 79 1.11 deriving from HMDI was a rubber at room temperature (Table 2, run 3). PU_3810/K22/H12MDI 2 H12MDI (19.7) 65 77 1.06 0 -diisocyanate The polyurethane coming from Dicyclohexylmethane-4,4 (H12MDI) was PU_3810/K22/HMDI 3 HMDI (12.6) 19 72 0.77 chosen for the subsequent formulations, due to its physical proprieties in accordance with those ofg,the model a Formulation ® conditions: Alcupol R3810 (20 g), diisocyanate (1:1.1 OH/NCO), Borchi Kat 22 (2 b c polyurethane PU_MD because haserror been recently for coating in the range ofused ±2–8;successfully Estimated error 10% w/w respect and to polyol), cure this time diisocyanate = 12 h; Estimated in the range of ±2. application [29]. SEM analyses pointed out the good coating quality of the produced polyurethane (PU_3810/K22/H12MDI) evidenced the homogeneous surface (Figure 7). were hydrophilic in From data in Table 2 clearlyby emerged that all polyurethanes produced nature, as demonstrated by WCA values falling in the range 72°–79°. In addition, the highest Tg values were observed for PUs coming from diisocyanate H12MDI and pure IPDI (Table 3, runs 1–2), while the one deriving from HMDI was a rubber at room temperature (Table 2, run 3).
2.4. Formulations of Bio-Based Polyurethane With the whole set of selected reactants in hand (soy-based polyol, fossil Alcupol R3810, diisocyanate H12MDI, and catalysts K22), we searched for the best formulation of Bio-based polyurethane for doming applications, by mixing in several ratios the soy-based Bio-polyol and its fossil counterpart (Alcupol R3810) [33,34]. Based on International standards statements for labeling a product as “bio-based” (it must be Materials 2017, 10, 848 composed of at least 20–50% of carbon atoms from renewable sources) [31], we produced a series of polyurethanes (namely BIOPU_%C) possessing the bio-component percentage in the range of 11–31% (Table 3). Table 3. Formulation of soy-based BIOPU_%C from PU_3810/K22/H12MDI a .
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Table 3. Formulation of soy-based BIOPU_%C from PU_3810/K22/H12MDI a.
O O
OCH3 7
O
7 OH OCH3
Bio-Polyol fragment
OCH3 7
OH
7 7 OH HO OCH3 O 4 7 O OCH3 OH O
+
O
+
HO R OH
O
fossil polyol (Alcupol3810)
R' N
O
O O HN R' O R NH O Intermolecular
diisocyanate (H12MDI)
urethane linkage
soy-based PU
soy-based Bio-polyol Polyols Mixture g PolyolsAlcupol Mixture g BioPolyol Alcupol R3810 20.2 Bio-Polyol 4 R3810 9.6 4 20.2 4 9.2 6 8 9.6 4 8
fossil-Polyol fragment
O
cat. K22 (10%)
N
Diisocyanate
Diisocyanate H12MDI (g) H12MDI (g) 19.8 10.2
Kat-22 (g) Kat-22 (g) (10% w/w)
(10% w/w) 2.42 1.36 2.42 1.52 1.68 1.36 PhHg 1.52 decanoate
19.8 10.4 11.3 10.2
Domes resinPEER REVIEW IPDI prep Materials x FOR 9.2 2017, 10, 6 10.4
% of %b of Bio-C
Bio-C b
11 19 25 31 0
11 19 25
Bio-PU Bio-PU Products
Products
Tg c WCA d (°C)Tg c (◦ C) (°)
BIOPU_11 BIOPU_19 BIOPU_11 BIOPU_25 BIOPU_31 BIOPU_19
73 62 49 48
PU_MD e
59
BIOPU_25
90 75
d (kg/dm d ) d WCA ◦ (kg/dm3 ) ( ) 3
1.06 1.05
73 76
90 1.06
1.06
62 82
1.08 75
1.05
77
1.01
49
76
b Determined according to Equation (1) Formulation according to procedure in 1.68 experimental sections; 8 8 11.3 31 BIOPU_31 48 82 c Estimated error in the range of ±2–8; d Estimated error in the range of ±2; e For in Section 3.4;coming The polyurethane from Dicyclohexylmethane-4,4′-diisocyanate (H12MDI) PhHg e preparation of PU_MD experimental section. 0 PU_MD 59 77 Domes resin IPDI see prep a
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was chosen 1.01 for the subsequent formulations, due to its physical proprieties in accordance with those of the model decanoate apolyurethane b Determined PU_MD because this diisocyanate been recently usedtosuccessfully for coating Formulation according to and procedure in experimental sections;has according Equation (1) in Section 3.4; c Estimated error in the range of ±2–8; d Estimated error in the range of ±2; e For preparation of PU_MD see application [29]. SEM analyses pointed out the good coating quality of the produced polyurethane experimental section. (PU_3810/K22/H12MDI) evidenced by the homogeneous surface (Figure 7).
Figure 7. SEM microphotographs of PU_3810/K22/H12MDI at different magnifications: (a) 10 Kx; Figure 7. SEM microphotographs of PU_3810/K22/H12MDI at different magnifications: (a) 10 Kx; (b) (b) 180 Kx. 180 Kx.
2.4. Formulations of Bio-Based Polyurethane
2.4. Formulations of Bio-Based Polyurethane
With the whole set of selected reactants in hand (soy-based polyol, fossil Alcupol R3810,
With the whole set of selected hand (soy-based fossilofAlcupol R3810, diisocyanate H12MDI, and catalystsreactants K22), weinsearched for the bestpolyol, formulation Bio-based polyurethane for doming by mixing in several for ratios thebest soy-based Bio-polyol its diisocyanate H12MDI, and applications, catalysts K22), we searched the formulation ofand Bio-based fossil counterpart (Alcupol R3810) [33,34]. polyurethane for doming applications, by mixing in several ratios the soy-based Bio-polyol and Based on International standards statements for labeling a product as “bio-based” (it must be its fossil counterpart (Alcupol R3810) [33,34]. composed of at least 20–50% of carbon atoms from renewable sources) [31], we produced a series of Based on International standards statements for labeling a product as “bio-based” (it must be polyurethanes (namely BIOPU_%C) possessing the bio-component percentage in the range of composed of at least 20–50% of carbon atoms from renewable sources) [31], we produced a series of 11–31% (Table 3). polyurethanes (namely BIOPU_%C) possessing the bio-component percentage in the range of 11–31% (Table 3). Table 3. Formulation of soy-based BIOPU_%C from PU_3810/K22/H12MDI a. From data reported in Table 3 emerged that all bio-polyurethane products possess physical O OCH3 Bio-Polyol properties (Tg, WCA and density values) much closer to those of the model (totally fossil) PU_MD. 7 O OCH3 7 fragment OH The curing time was also checked by IR spectroscopy. The very low intensity 7 of the stretching OH O OCH3−1 fossil-Polyol O cat. K22 band at 2274 cm , due to isocyanate group, indicates that for the several Bio-PU investigated the N O (10%) + + fragment HO R OH R' 7 O 7 was almost complete in the expected time of 12 h (Figure 8). O curing process O N O O OH HO
OCH3 O 4 7 O OCH3 OH
fossil polyol (Alcupol3810)
diisocyanate (H12MDI)
HN R' NH
Intermolecular urethane linkage
soy-based PU
soy-based Bio-polyol Polyols Mixture g Alcupol BioR3810 Polyol 20.2 4 9.6 4
O R O
Diisocyanate H12MDI (g)
Kat-22 (g) (10% w/w)
% of Bio-C b
Bio-PU Products
Tg c (°C)
WCA d (°)
d (kg/dm3)
19.8 10.2
2.42 1.36
11 19
BIOPU_11 BIOPU_19
73 62
90 75
1.06 1.05
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From data reported in Table 3 emerged that all bio-polyurethane products possess physical properties (Tg,reported WCA and much to those of the model (totally fossil)physical PU_MD. From data in density Table 3values) emerged thatcloser all bio-polyurethane products possess The curing time was also checked by IR spectroscopy. The very low intensity of the stretching properties (Tg, WCA and density values) much closer to those of the model (totally fossil) PU_MD. −1 due to isocyanate group, indicates that for the several Bio-PU investigated the atcuring 2274 Materialsband 2017, 848 cm The10, time, was also checked by IR spectroscopy. The very low intensity of the stretching8 of 14 curing process was almost completegroup, in the expected h (Figure −1 band at 2274 cm , due to isocyanate indicatestime that of for12the several8). Bio-PU investigated the curing process was almost complete in the expected time of 12 h (Figure 8).
Figure IR analysis of Bio-polyurethanesafter after 12 12 h. Figure 8. IR8.analysis of Bio-polyurethanes h. Figure 8. IR analysis of Bio-polyurethanes after 12 h.
To verify that no change in transparency or clarity of PU has occurred after addition of the soyTobased verifypolyol that no change in transparency or clarity of PU has occurred after addition we change compared the UV-visible polyurethanes BIOPU_25 and To verify that no in transparency or clarity spectra of PU hasofoccurred after addition of the soyof the PU_3810/K22/H12MDI soy-based polyol we compared the UV-visible spectra of polyurethanes BIOPU_25 and in the range of 200–800 nm. As shown in Figure 9, both polymers display very based polyol we compared the UV-visible spectra of polyurethanes BIOPU_25 and PU_3810/K22/H12MDI in the range of 200–800 nm. As shown in Figure 9, polymers displayin very similar absorption spectra a weak signalnm. in the UVin (centered 289both nm) and nodisplay absorption PU_3810/K22/H12MDI in thewith range of 200–800 Asnear shown Figure 9,atboth polymers very similar absorption spectra with a weak signal in the near UV (centered at 289 nm) and no absorption the visible region (Figure 9). similar absorption spectra with a weak signal in the near UV (centered at 289 nm) and no absorption in
in thethe visible 9). visibleregion region (Figure (Figure 9).
Figure 9. UV spectra for PU_3810/K22/H12MDI (a) and BIOPU_25 (b). Figure 9. UV spectra for PU_3810/K22/H12MDI (a)(a) and BIOPU_25 (b). (b). Figure 9. UV spectra for PU_3810/K22/H12MDI and BIOPU_25 Interestingly, SEM analyses revealed that BIOPU_25, a bio-polyurethane that can be surely labeled as “bio-based”, displays a superior quality of surface morphology respect to PU_MD. In fact, Interestingly, SEM analyses revealed that BIOPU_25, a bio-polyurethane that can be surely besides the homogeneous coating that allows uniform covering of the piece of the tile (Figure it Interestingly, SEM analyses revealed that BIOPU_25, a bio-polyurethane that can be surely labeled labeled as “bio-based”, displays a superior quality of surface morphology respect to PU_MD. In 10a), fact, also displays, in contrast to PU_MD (Figure 3b), the absence of cracks as can be observed in the higher as “bio-based”, displays a superior of surface respect tothe PU_MD. In fact, besides the homogeneous coatingquality that allows uniformmorphology covering of the piece of tile (Figure 10a),besides it magnification image oftoFigure 10b. also displays, in contrast PU_MD (Figure 3b), the absence of cracks as can be observed in the higher
the homogeneous coating that allows uniform covering of the piece of the tile (Figure 10a), it also magnification image of Figure 10b. displays, in contrast to PU_MD (Figure 3b), the absence of cracks as can be observed in the higher magnification image of Figure 10b. This different morphology can be due to the foaming process caused by atmosphere moisture at the bond surface of polyurethane. This phenomenon, known also as “surface crazing”, produces deep cracks and splits through the polymer, with the depth of cracking increasing with greater extension [35]. This occurrence can be directly connected with the hydrophilic properties of the reacting mixture, and particularly with those of the starting polyol. Therefore, it is expected that the more hydrophilic fossil polyether polyol composing PU_MD gives rise to surface crazing in a greater extent respect to the bio-polyol of BIOPU_25 bearing the more lipophilic aliphatic long chains of soybean oil.
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Figure 10. SEM microphotographs of BIOPU_25 at different magnifications: (a) 20 Kx; (b) 180 Kx.
Figure 10. SEM microphotographs of BIOPU_25 at different magnifications: (a) 20 Kx; (b) 180 Kx.
This different morphology can be due to the foaming process caused by atmosphere moisture at
3. Experimental the bond surface of polyurethane. This phenomenon, known also as “surface crazing”, produces deep cracks and splits through the polymer, with the depth of cracking increasing with greater extension [35].
3.1. Materials Methodscan be directly connected with the hydrophilic properties of the reacting This and occurrence mixture, and particularly those ofdilaurate the starting polyol. Therefore, it is expected that the more Polymerization catalystswith dibutyltin (DBTDL, DABCO T-12), dibutyl-bis(dodecylthio) hydrophilic fossil polyether polyol composing PU_MD gives rise to surface crazing in a (UL21) greater and 0 stannane (T120), O,O -bis(2-ethylhexyl)-(nonyl(octyl)stannanediyl) bis(carbonothioate) extent respect to the bio-polyol of ®BIOPU_25 bearing the more lipophilic aliphatic long chains of Zinc bis (2-ethylhexanoate) (Borchi Kat 22) were supplied from Borchers GmbH (Langenfeld, soybean oil. Germany), Evonik Degussa Italia (Pandino, CR, ITALT) and Momentive Performance Materials Inc (Waterford, NY, USA). 3. Experimental Petrochemical polyether polyols alcupol (Table 4) were supplied by S.p.A. (Rho, MI, Italy) (each 3.1.as Materials and Methods polyol possessing n. OH/molecule = 3). Domes resin HGFP40702 was a of them a homo-dispersed mixture ofPolymerization polyether polyols withdibutyltin differentdilaurate chain length containing phenylmercury neodecanoate catalysts (DBTDL, DABCOalso T-12), dibutyl-bis(dodecylthio) (0.3–0.8% w/w) having the following properties: OH/molecule = 3, n. OH (mgKOH/g) 398,and density stannane (T120), O,O′-bis(2-ethylhexyl)-(nonyl(octyl)stannanediyl) bis(carbonothioate) (UL21) 3 ® Zinc bis (2-ethylhexanoate) Kat 22) were Borchers GmbHdiisocyanate (Langenfeld, and 1.04 (kg/dm ), viscosity 550 cP:(Borchi IPDI prepolymer (a supplied mixture from of pure isophorone Germany), Evonik Degussa Italia (Pandino, CR, ITALT) (Ferrandina, and Momentive Performance domes resin). Both were a gift by Greenswitch Industry Matera, Italy). Materials Inc (Waterford, NY, USA). Petrochemical polyether polyols alcupol (Tablepolyols 4) wereEigenmann supplied by (Rho, MI, Italy) (each Table 4. Petrochemical polyether & S.p.A. Veronelli. of them as a homo-dispersed polyol possessing n. OH/molecule = 3). Domes resin HGFP40702 was a mixture of polyether different chain length containing also phenylmercury 3) Commercial Name polyols n. OHwith (mgKOH/g) Viscosity (cP) Density (kg/dm neodecanoate (0.3–0.8% w/w) having the following properties: OH/molecule = 3, n. OH (mgKOH/g) Alcupol C5710 570 1.05 700 398, density 1.04 (kg/dm3), viscosity 550 cP: IPDI prepolymer (a mixture of pure isophorone Alcupol R3810 380 1.03 350 diisocyanate and domes resin). Both were a gift by Greenswitch Industry (Ferrandina, Matera, Italy). Alcupol R2510 250 1.02 260 Alcupol R1610 160 1.02 250 & Veronelli. Alcupol C3531Table 4. Petrochemical 35 polyether polyols Eigenmann 1.05 800 Alcupol C2831 Name 1.06 (kg/dm3) 1100(cP) Commercial n.28OH (mgKOH/g) Density Viscosity Alcupol C5710 570 1.05 700 Alcupol R3810 380 1.03 350 1,6-hexamethylene diisocyanate (HDI), pure isophorone diisocyanate (IPDI), dicyclohexylmethaneAlcupol R2510 250 1.02 260 0 4,4 -diisocyanate (H12MDI) were purchase from oil (SO) was procured from the local Alcupol R1610 160 Evonik. Soybean 1.02 250 C3531 35 1.05 of 130 g I2 /100 800 g). Epoxidation market and used Alcupol without any further purification (iodine number Alcupol 28 using HBF were 1.06carried out following 1100 of Soybean oil (SBO) andC2831 Methanolysis of ESO the literature 4
procedure [24]. Chemical properties of ESO were reported: number of oxirane oxygen 6.3 g O/100 g; 1,6-hexamethylene diisocyanate (HDI), pure isophorone diisocyanate (IPDI), dicyclohexylmethanenumber of epoxy groups 4 for molecule; number of Iodine 1.5 g I2 /100 g, number of double 4,4′-diisocyanate (H12MDI) were purchase from Evonik. Soybean oil (SO) was procured from the local bonds/molecule 0.05without and Mnany (g/mol) market and used further943.807. purification (iodine number of 130 g I2/100 g). Epoxidation of Chemical Bio-polyolofare the following: colorless Mn (g/mol) 1054.207: carried liquid, out following the literature Soybean oilproperties (SBO) and of Methanolysis ESO using HBF4 were average number ofChemical bio-carbon 56.232ofcorresponding to 674.840 average of carbon procedure [24]. properties ESO were reported: numberg/mol, of oxirane oxygennumber 6.3 g O/100 g; deriving from methanol 3.45 corresponding to 41.437 g/mol of carbon, spectral data in agreement with literature [24]. Density (kg/dm3 ) 1.00176, viscosity (cP) 4550, n. OH (mg KOH/g) 191, n. OH/molecule 3.45. The NMR spectra were in agreement with literature [24].
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3.2. Characterization Techniques NMR spectra were recorded on an Agilent Technologies 500 MHz spectrometer (Agilent Company, Santa Clara, CA, USA); the 1 H-NMR spectra (500 MHz) were referenced to residual isotopic impurity of CDCl3 (7.26 ppm). A Viscometer Cannon-Fenske reverse flows YNT instrument (CANNON Instrument Company® , State College, PA, USA) was used to determine the viscosity using the standard method [36] The determination of density was carried out with the pycnometer method [37] Iodine number was determined with EN ISO 661 method, [38] oxirane number (ON) was determined with ASTM D 1652 method [39] and hydroxyl number values was determined with ASTM D4274 method [40] for all pre-polymers [24]. DSC analyses were performed on a Q200 TA Instruments apparatus (TA Instruments, New Castle, DE, USA). Experiments were carried out using the temperature range from −80 ◦ C to 120 ◦ C with a heating rate of 10 ◦ C/min, under N2 gas at a flow rate of 30 mL/min [24]. The FE-SEM analyses were conducted with a Zeiss Sigma Field-emission scanning electron microscope instrument (Zeiss International, Oberkochen, Germany) operating at 5 kV and equipped with in-lens secondary electron detector. Samples were mounted onto stainless steel sample holders by double-sided carbon tape and gold sputtered prior to analysis. Water Contact Angle (WCA) measurements were carried out by means of a CAM200 digital goniometer (KSV Instruments, Biolin Scientific SE-426 77, Västra Frölunda, Sweden) equipped with a BASLER A60f camera (KSV Instruments, Biolin Scientific SE-426 77, Västra Frölunda, Sweden). WCA values were determined using the sessile drop method with a double distilled water droplet of 1 µL (five measurements for each sample). In this case, the liquid is water, thus if a contact angle is greater than 90◦ , the solid surface is called “hydrophobic surface”, if the contact angle is less than 90◦ the surface is called “hydrophilic surface”. Infrared absorption spectra of PU_MD and all BIO_PU were acquired in the range 375–4000 cm−1 with a resolution of 4 cm−1 , using a vacuum Bruker Vertex 70v Fourier transform infrared (FTIR) spectrometer (Buker, Milan, Italy). Spectra were collected in attenuate total reflectance (ATR) mode utilizing an ATR module (Bruker Platinum ATR) equipped with a single reflection diamond ATR crystal (refractive index of 2.4). UV-Vis absorption spectra were recorded with a UV-Vis-near IR Cary 5 Varian spectrophotometer (Agilent Technologies, Inc., Santa Clara, CA, USA) equipped with a coating support. 3.3. Digital Doming Polyurethane Synthesis Polyol (20 g) and catalyst (0.15–10% w/w respect to polyol) were mechanically stirred for 60 s to ensure their complete homogenization. After that, diisocyanate (or IPDI prepolymer) (OH: NCO 1:1.1 molar ratio) was added to the mixture and mechanically stirred for 2 min into a plastic container (pour time) [24]. Alternatively, reaction was performed by using a volumetric precision low-pressure doser consisting of two cylindrical reservoirs containing polyols and diisocyanate. After degassing, reactants are pumped into a static mixer and then deposited on the PVC layer through a nozzle (Figure 11). The gel times at room temperature for each compound were 4–12 min, while the polymerization time was 12 h.
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Figure 11. Volumetric precision low pressure doser.
Figure 11. Volumetric precision low pressure doser.
3.4. Bio-PU Synthesis and Determination of Bio-Carbon Percentage
3.4. Bio-PU Synthesis and Determination of Bio-Carbon Percentage
Procedure for the synthesis of Bio-PU was the same as that of the fossil resin, but in this case
polyolic reactant wassynthesis preliminarily prepared by mixing the proper of fossil polyol (Alcupol) Procedure for the of Bio-PU was the same as thatamounts of the fossil resin, but in this case andreactant soy-based Bio-polyol and stirring them until obtaining homogeneous mixture. polyolic was preliminarily prepared by mixing the aproper amounts of fossil polyol (Alcupol) A typical calculation determining the bio-carbon of Bio-PU, considering the and soy-based Bio-polyol andfor stirring them until obtaining apercentage homogeneous mixture. several polymer components, is carried out according to Equation (1): A typical calculation for determining the bio-carbon percentage of Bio-PU, considering the several g/mol polymer to674.840 Equation (1): % components, is g carried out according g g g g (1)
674.840
mol
41.437
mol
144.128
mol
180.160
mol
192.171
mol
n Bp × 674.840 g/mol
component (soy-based polyol, Mn 1054.207 gg/mol, (1) where %C n=Bp is the molesg number of Bio-polyol g g g (n Bp × 674.840 mol ) +(nmet × 41.437 mol ) +(n Fp × 144.128 mol ) + (n NCO × 180.160 mol ) +(ncat × 192.171 mol ) average number of bio-carbon 56.232, corresponding to 674.840 g/mol), nmet is the moles number of methanol (basedof Bio-polyol on hydroxyl number (soy-based of 191 mgKOH/g, equivalent to where nBp is thecomponent moles number component polyol, Mn 1054.207 g/mol, 3.45 -OH/molecule and thus to 3.45 -OCH 3/molecule, corresponding to 41.437 g/mol of carbon), nFp is average number of bio-carbon 56.232, corresponding to 674.840 g/mol), nmet is the moles number of the moles number of fossil polyol component (Alcupol R3810, MF C12H44O9, MW 440.3 g/mol, methanol component (based on hydroxyl number of 191 mgKOH/g, equivalent to 3.45 -OH/molecule corresponding to 144.128 g/mol of carbon), nNCO is the moles number of diisocyanate component and thus to 3.45 -OCH3 /molecule, corresponding to 41.437 g/mol of carbon), nFp is the moles (H12MDI dicyclohexylmethane-4,4′-diisocyanate, MF C15H22N2O2, MW 262.17 g/mol, corresponding number of fossil polyol component R3810, MFofCcatalyst g/mol, 12 H44 Ocomponent 9 , MW 440.3 to 180.160 g/mol of carbon) and ncat(Alcupol is the moles number (K22, MF Ccorresponding 16H30O4Zn, to 144.128 g/mol of carbon), n is the moles number of diisocyanate component (H12MDI NCO MW 350.14 g/mol, corresponding to 192.171 g/mol of carbon).
dicyclohexylmethane-4,40 -diisocyanate, MF C15 H22 N2 O2 , MW 262.17 g/mol, corresponding to 4. Conclusions 180.160 g/mol of carbon) and ncat is the moles number of catalyst component (K22, MF C16 H30 O4 Zn, MW 350.14 corresponding to 192.171 g/mol offrom carbon). Ang/mol, innovative bio-based polyurethane deriving soybean oil has been developed and for the first time applied to digital doming using mosaico digitale® technology. Results of this work
4. Conclusions demonstrate that these bio-based polyurethanes can favorably compete with analogous fossil
polymers in doming applications, and openderiving the way to the substitution petrochemical materials An innovative bio-based polyurethane from soybean oilofhas been developed and for widely used in the field of decorations, such as those shown in Figure 12 depicting an example of ® the first time applied to digital doming using mosaico digitale technology. Results of this work tiles commercially using resin and the synthesized bio-based polyurethane. demonstrate that these bio-based polyurethanes can favorably compete with analogous fossil polymers Results of this work also allowed the two following advances: (i) the efficient synthesis of in doming applications, open the way to the on substitution petrochemical widely mercuryand tin-freeand bio-polyurethanes based a clean andofeco-friendly Zinc materials catalyst (K22) and used in the(ii) field decorations, such as showndigital in Figure 12 depicting an PU_MD, example by of measuring tiles commercially theof fully characterization of those commercial doming tiles of fossil for usingthe resin the polyurethane. firstand time insynthesized the literaturebio-based the physic-chemical properties (Tg, WCA and density) and surface morphology. All thesealso improvements that this new formulation soy-based polyurethanes, Results of this work allowed theindicate two following advances: (i) theofefficient synthesis of mercurywhich has no precedent in the literature, brings significant benefits in catalyst terms of (K22) cost efficiency and tin-free bio-polyurethanes based on a clean and eco-friendly Zinc and (ii) and the fully eco-sustainability and has a good potential for tiles industrial applications. characterization of commercial digital doming of fossil PU_MD, by measuring for the first time in the literature the physic-chemical properties (Tg, WCA and density) and surface morphology. All these improvements indicate that this new formulation of soy-based polyurethanes, which has no precedent in the literature, brings significant benefits in terms of cost efficiency and eco-sustainability and has a good potential for industrial applications.
Materials 2017, 10, 848 Materials 2017, 10, 848
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Figure 12. Comparison of tile obtained with domes resin (PU_MD) and BIOPU_25 (picture kindly
Figure 12. Comparison of tile obtained with domes resin (PU_MD) and BIOPU_25 (picture kindly provided by Greenswitch Company, IT). provided by Greenswitch Company, IT). Acknowledgments: This research was supported by: Regione Puglia MIUR PON Ricerca e Competitività 20072013 Avviso 254/Ric. del 18/05/2011, Project PONa3 00369 “Laboratorio SISTEMA”, Project PON03PE_00004_1, Acknowledgments: This research was supported by: Regione Puglia MIUR PON Ricerca e Competitività 20072013 “MAIND” MAteriali eco-innovativi e tecnologie avanzate per l’INDustria Manifatturiera e delle costruzioni. Avviso 254/Ric. del 18/05/2011, Project PONa3 00369 “Laboratorio SISTEMA”, Project PON03PE_00004_1, Thanks to Salvatore Pepe for fund “PIANI di SVILUPPO INDUSTRIALI attraverso PACCHETTI INTEGRATI di “MAIND” MAteriali eco-innovativi e tecnologie avanzate per l’INDustria Manifatturiera e delle costruzioni. AGEVOLAZIONE (PIA) Basilicata progetto 227179”. Thanks to Salvatore Pepe forRegione fund “PIANI dicodice SVILUPPO INDUSTRIALI attraverso PACCHETTI INTEGRATI di
AGEVOLAZIONE (PIA) Regione codicethe progetto 227179”. Author Contributions: V.P. andBasilicata A.R. performed preparation of tile, C.A., C.F. and A.N. performed the study onContributions: metal catalysis, A.G.L. andA.R. L.D.performed performed the and of preparation analyzedthe thestudy Author V.P. and the synthesis preparation tile, C.A.,the C.F.precursors, and A.N.P.F. performed DSCcatalysis, R.C. performed SEM and UV analysis; performed WCA and IR analysis, L.D. and conceived on metal A.G.L.the and L.D. performed theF.F. synthesis andthe preparation the precursors, P.F.C.F. analyzed the DSC and designed experiments and wroteF.F. the performed paper. R.C. performed thethe SEM and UV analysis; the WCA and IR analysis, L.D. and C.F. conceived and designed the experiments and wrote the paper. Conflicts of Interest: The authors declare no conflict of interest.
Conflicts of Interest: The authors declare no conflict of interest. References
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